POSIVA 2006-01
Effects of Salinity and High pH
on Crushed Rock and Bentonite
– Experimental Work and Modelling
Ulla Vuorinen
Jarmo Lehikoinen
Ari Luukkonen
Heini Ervanne
May 2006
POSIVA
FI-27160
OY
OLKILUOTO,
FINLAND
Phone (02) 8372 31 (nat.), (+358-2-) 8372 31 (int.)
Fax (02) 8372 3709 (nat.), (+358-2-) 8372 3709 (int.)
POSIVA 2006-01
Effects of Salinity and High pH
on Crushed Rock and Bentonite
– Experimental Work and Modelling
Ulla Vuorinen
Jarmo Lehikoinen
VTT Processes
Ari Luukkonen
VTT Building and Transport
Heini Ervanne
University of Helsinki, Department of Chemistry
May 2006
POSIVA
FI-27160
OY
OLKILUOTO,
FINLAND
Phone (02) 8372 31 (nat.), (+358-2-) 8372 31 (int.)
Fax (02) 8372 3709 (nat.), (+358-2-) 8372 3709 (int.)
ISBN 951-652-142-8
ISSN 1239-3096
The conclusions and viewpoints presented in the report are
those of author(s) and do not necessarily coincide
with those of Posiva.
Posiva-raportti – Posiva Report
Raportin tunnus – Report code
POSIVA 2006-01
Posiva Oy
FI-27160 OLKILUOTO, FINLAND
Puh. 02-8372 (31) – Int. Tel. +358 2 8372 (31)
Tekijä(t) – Author(s)
Julkaisuaika – Date
May 2006
Toimeksiantaja(t) – Commissioned by
Ulla Vuorinen, VTT Processes
Ari Luukkonen, VTT Building and Transport
Heini Ervanne, University of Helsinki,
Department of Chemistry
Jarmo Lehikoinen, VTT Processes
Posiva Oy
Nimeke – Title
EFFECTS OF SALINITY AND HIGH PH ON CRUSHED ROCK AND BENTONITE –
EXPERIMENTAL WORK AND MODELLING
Tiivistelmä – Abstract
In the research work presented here the results obtained in Finland in the three-year ECOCLAY II project are presented.
Two types of experiments were carried out; flow-through experiments, which simulated one suggested backfill concept for
the disposal tunnel of spent nuclear fuel consisting of compacted bentonite and crushed rock, and batch experiments
including sorption studies. Sorption was studied with two radionuclides, 45Ca and 22Na. Both types of experiments were
conducted in anaerobic CO2-free atmosphere. In both experiments the solid materials used were the same; MX-80 bentonite
and crushed crystalline rock powder from Olkiluoto disposal site in Finland. The solid materials were attacked by simple
simulated groundwater compositions; synthetic aqueous solutions covering fresh alkaline (pH=12.5), saline alkaline
(pH=12.5), and saline hyperalkaline (pH=13.5) conditions in order to simulate the effects of cement in the repository, but
also fresh (pH=8.8) and saline (pH=8.3) conditions were included for comparison purposes. Chemical changes were
analysed in the various solution phases and solid phases were characterised prior to and after the solution attacks (both
experiments included). The experimental results were bases in the modelling task containing both forward and inverse
modelling.
The flow-through experiment results showed clear increasing trends of the propagation of the attacking solutions in
bentonite in the case of saline and saline alkaline experiments. Trends in the pH value and/or the element concentrations
(Na, Ca, K, Mg, Si, SO4, Cl) of the out-flow solutions progressed with increasing experimental time reflecting the alteration
processes occurring in bentonite (e.g., cation exchange, dissolution). Only in the saline alkaline experiment the out-flow
solution pH showed an increasing trend with increasing experimental time (9.5 at completion), while in the other two
experiments constant pH levels were maintained (9.5 for fresh and 8 for saline experiment). In the saline alkaline
experiment the pH value in bentonite porewater was highest (around 11) at the in-flow interface and showed a steep
decreasing trend towards the out-flow interface (down around 8). Corresponding trends were seen in the exchangeable
cation (Na, Ca, K and Mg) capacities. Based on the results obtained it could be concluded that the alkaline attack had
affected the bentonite column to some extent throughout the entire column.
Sorption of 22Na was low on crushed rock (Kd 0.02-1.2˜10-3 m3/kg) and bentonite (Kd 0.65-2.1˜10-3 m3/kg). An exception
was the fresh alkaline experiment with bentonite (Kd 1.5-2.7˜10-2 m3/kg). High sorption of 45Ca on crushed rock was
measured only in the saline hyper alkaline experiment (Kd 0.81-9.1˜10-3 m3/kg), whereas very high sorption on bentonite
was observed (Kd 0.015-100 m3/kg) in all three alkaline experiments. Effect of the initial solution Na and Ca on sorption
was also studied. Only minor effects were observed.
Main mineral alterations of the solids were detected in the batch experiments. By alkaline attack Nax-montmorillonite was
partially altered to Nax-bedellite, and bentonite interactions with alkaline solutions produced CSH-phases (less in flowthrough experiments) structurally analogous to 14Å-tobermorite. In the flow-through experiments the saline attack
introduced smectite alteration towards Cax-montmorillonite and the fresh solution attack caused some purification within the
smectite layers.
The experimentally observed uptake of Na and Ca was adequately explained by the simple thermodynamic model developed
for montmorillonite, provided that Ca uptake occurred predominantly by precipitation of Ca-bearing mineral phases. In the
inverse modelling some problems were encountered, e.g., multiple independent sources and sinks for the same element
could not be handled and the inverse cation exchange calculations failed.
Avainsanat - Keywords
bentonite, crystalline rock, alkaline attack, alkaline plume, mineral alteration, sorption, modelling
ISBN
ISSN
ISBN 951-652-142-8
Sivumäärä – Number of pages
116
ISSN 1239-3096
Kieli – Language
English
Posiva-raportti – Posiva Report
Raportin tunnus – Report code
POSIVA 2006-01
Posiva Oy
FI-27160 OLKILUOTO, FINLAND
Puh. 02-8372 (31) – Int. Tel. +358 2 8372 (31)
Tekijä(t) – Author(s)
Julkaisuaika – Date
Toukokuu 2006
Toimeksiantaja(t) – Commissioned by
Ulla Vuorinen, VTT Processes
Ari Luukkonen, VTT Building and Transport
Heini Ervanne, University of Helsinki,
Department of Chemistry
Jarmo Lehikoinen, VTT Processes
Posiva Oy
Nimeke – Title
XXXXXXXX
XXXXX
Tiivistelmä – Abstract
Tässä raportissa esitetään EU:n viidenteen puiteohjelmaan sisältyneen kolmivuotisen ECOCLAY II projektin Suomen
tutkimusosuuden tulokset. Tutkimuksessa selvitettiin korkean pH:n vaikutusta bentoniitissa ja kivimurskeessa
kahdentyyppisillä kokeilla; virtauskokeet sylinterissä ja eräkokeet. Läpivirtaus(sylinteri)kokeilla simuloitiin yhtä
mahdollista käytetyn polttoineen loppusijoituskonseptia: kompaktoidun bentoniitin ja kalliomurskeen kontaktia tunnelissa.
Sorptiota tutkittiin eräkokeissa 45Ca:lla ja 22Na:lla. Kokeet tehtiin anaerobisissa hiilidioksidittomissa olosuhteissa..
Kummassakin kokeessa kiinteät aineet olivat samoja; MX-80 bentoniitti ja Olkiluodon kallioperän kivimurske. Kokeiden
simuloidut vedet kattoivat makean (pH=8,8), suolaisen (pH=8,3), makean alkalisen (pH=12,5), suolaisen alkalisen
(pH=12,5) sekä suolaisen hyperalkalisen (pH=13.5) olosuhteen. Liuosten ja bentoniitin huokosveden kemiallisia muutoksia
seurattiin kokeen aikana ja lopussa. Kummankin kokeen bentoniitti ja kivimurske karakterisoitiin ennen kokeita ja niiden
jälkeen. Kokeelliset tulokset olivat perustana mallinnustyölle, jossa sovellettiin sekä ennuste-, että käänteismallinnusta.
Läpivirtauskokeiden tuloksissa oli nähtävissä selviä kehityssuuntia suolaisen ja suolaisen alkalisen veden vaikuttaessa
bentoniittiin. Koeajan pidentyessä kehityssuunnat pH arvoissa ja/tai ulostulopuolen vesiliuosten alkuainepitoisuuksissa
(Na, Ca, K, Mg, Si, SO4, Cl) olivat selvästi eteneviä ilmentäen bentoniitissa tapahtuvia prosesseja (mm. kationinvaihto ja
liukeneminen). Ulosvirtausliuosten pH-avoissa vain suolaisen alkalisen veden kokeessa näkyi selvä kasvava trendi koeajan
pidentyessä (pH=9.5 kokeen lopussa), kun taas suolaisen ja makean veden kokeissa pH arvot säilyivät lähes vakiotasoilla
(8 ja 9.5 vastaavasti). Suolaisen alkalisen veden kokeessa bentoniitin huokosveden kokein arvo (11) mitattiin
sisäänvirtauspuolen rajapinnan näytteessä, jonka jälkeen pH trendi oli jyrkästi laskeva rajapinnan näytteissä saavuttaen
ulosvirtauspuolen näytteessä pH arvon 8. Vastaavanlaisia trendejä oli nähtävissä bentoniitin vaihtuvien kationien (Na, K,
Ca, Mg) tuloksissa. Koetulosten perusteella voitiin päätellä, että alkalisen liuoksen vaikutukset bentoniitissa olivat
nähtävissä jossain laajuudessa koko sylinterin pituudelta.
Eräkokeiden tulokset osoittivat, että 22Na:n sorptio kivimurskeeseen (Kd 0.02-1.2˜10-3 m3/kg) ja bentoniittiin (Kd 0.652.1˜10-3 m3/kg) oli matala muutoin paitsi bentoniitissa makean alkalisen veden kokeissa (Kd 1.5-2.7˜10-2 m3/kg). Korkea
arvo 45Ca:n sorptiolle kivimurskeeseen (Kd 0.81-9.1˜10-3 m3/kg) mitattiin ainoastaan suolaisen hyperalkalisen veden
kokeissa, kun taas sorptio bentoniittiin oli erittäin korkea kaikissa (Kd 0.015-100 m3/kg) kolmen alkalisen veden kokeissa.
Lähtövesien Na- ja Ca-pitoisuuksilla ei havaittu olevan suurempaa vaikutusta 22Na:n ja 45Ca:n sorptioon.
Pääasialliset mineraalimuutokset havaittiin eräkokeiden tuloksista. Alkalinen vesi aiheutti Nax-montmorilloniitin osittaisen
muuntumisen Nax-bedelliitiksi. Bentoniitin ja alkalisen veden vuorovaikutuksen seurauksena muodostui myös CSH-faaseja
(vähemmän läpivirtauskokeissa), jotka rakenteellisesti olivat analogisia 14Å-tobermoriitin kanssa. Läpivirtauskokeissa
suolainen vesi aiheutti smektiitin muuntumista Cax-montmorilloniitiksi, kun taas makean veden kokeissa smektiitti
kerrosten sisällä tapahtui tietynlaista puhdistumista.
Montmorilloniitille kehitettiin yksinkertainen termodynaaminen malli, jonka avulla kokeissa havaittu Na:n ja Ca:n sorptio
voitiin selittää riittävän hyvin, edellyttäen, että Ca:n sorptiota hallitsi Ca:a sisältävien mineraalien saostuminen. Käänteisen
mallinnuksen yhteydessä törmättiin joihinkin hankaluuksia, mm. yhdelle alkuaineelle ei voitu käyttää laskennassa
useampaa erillistä lähdettä tai nielua ja kationinvaihtolaskenta ei onnistunut oikein.
Avainsanat - Keywords
bentoniitti, kiteinen kallio, alkalinen pH, mineraalien muuntuminen, sorptio, mallinnus
ISBN
ISSN
ISBN 951-652-142-8
Sivumäärä – Number of pages
116
ISSN 1239-3096
Kieli – Language
Englanti
1
TABLE OF CONTENTS
Abstract
Tiivistelmä
PREFACE.......................................................................................................................3
1
INTRODUCTION ...................................................................................................5
2
SOLID MATERIALS AND SOLUTIONS ................................................................7
3
FLOW-THROUGH EXPERIMENTS ......................................................................9
3.1
3.2
3.3
3.4
4
Experimental ................................................................................................9
Model simulation ........................................................................................12
Results .......................................................................................................14
3.3.1 Out-flow solutions...........................................................................14
3.3.2 Exchangeable cations ....................................................................17
3.3.3 Bentonite porewater .......................................................................21
Main conclusions........................................................................................24
BATCH EXPERIMENTS .....................................................................................27
4.1
4.2
Experimental...............................................................................................27
Results .......................................................................................................29
4.2.1 Sorption and retention of radionuclides on solid phases................29
4.2.2 Effect of element concentration on sorption...................................32
4.2.3 Evolution of pH during experiment of crushed rock and bentonite
with water .......................................................................................33
4.2.4. Evolution of various elements during experiments of solid phase .34
4.3 Conclusions.................................................................................................38
5
SOLID PHASES ..................................................................................................39
5.1
5.2
6
MX-80 bentonite.........................................................................................39
5.1.1 Mineralogical summary of the bentonite alterations.......................40
Crushed rock material ................................................................................42
5.2.1 Mineralogical summary of the crushed rock alterations .................43
MODELLING .......................................................................................................45
6.1
6.2
Inverse modelling of bentonite batch experiments .....................................45
6.1.1 Fresh alkaline experiments ............................................................46
6.1.2 Saline alkaline experiments ...........................................................48
6.1.3 Saline hyperalkaline experiments ..................................................50
Inverse modelling of crushed rock batch experiments ...............................51
6.2.1 Fresh alkaline experiments ............................................................54
6.2.2 Saline alkaline experiments ...........................................................55
2
6.3
7
6.2.3 Saline hyperalkaline experiments ..................................................57
Forward modelling of batch experiments ...................................................58
6.3.1 Fresh alkaline experiment ..............................................................60
6.3.2 Saline alkaline experiment .............................................................61
6.3.3 Saline hyper-alkaline experiment ...................................................63
6.3.4 Conclusions....................................................................................64
SHORT SUMMARY AND MAIN CONCLUSIONS...............................................65
REFERENCES .............................................................................................................69
APPENDIX 1
RESULTS FROM FLOW-THROUGH TESTS ....................................73
APPENDIX 2
RESULTS FROM BATCH EXPERIMENTS ...................................... 79
APPENDIX 3
BENTONITE INTERPRETATIONS .................................................. 85
APPENDIX 4
CRUSHED ROCK INTERPRETATIONS...........................................103
APPENDIX 5
CHARACTERISTICS OF MX-80.......................................................115
3
PREFACE
The studies presented in this report were carried out under a cost-sharing contract with
the European Atomic Energy Community (EURATOM) (EC Contract nq FIKW-CT2000-00028 ECOCLAY II) within specific programme on sNuclear Energys (19982003), Key Action on Nuclear Fission, Area: sSafety of the Fuel Cycle Waste and
Spent Fuel Management and Disposals. The ECOCLAY II (Effects of Cement on Clay
Barrier Performance) project had 16 participants; ANDRA and BRGM from France,
SCK.CEN from Belgium, GRS from Germany, SERCO from United Kingdom,
ENRESA, UAM, IETcc, and CSIC EEZ from Spain, NAGRA, PSI, and UniBe from
Switzerland, SKB from Sweden, VTT, HU, and POSIVA from Finland.
The studies presented in this report were performed at VTT Processes, VTT Building
and Transport, and the University of Helsinki (HU), Department of Chemistry. In the
case of VTT the work was carried out on the cost-sharing contract between EC and
Posiva Oy.
A summary of the results can be found in the ECOCLAY II project final report
(ECOCLAY II: Effects of Cement on Clay Barrier Performance - Phase II. Final
Report.
EC
project
n°FIKW-CT-2000-200028;
Andra
report
n°CRPASCM040009.pdf.), whereas this report includes more details and some
additional results.
Aknowledgements
Ola Karnland from Clay Technology, Sweden, is thanked for providing us the MX-80
bentonite used in the studies and for the characterization of the initial material.
4
5
1
INTRODUCTION
Salinity of groundwater increases with depth in crystalline bedrock. At the depth of the
planned repository for disposal of spent nuclear fuel at Olkiluoto in Finland
groundwater is quite saline. In the present disposal concept compacted bentonite
surrounds the spent fuel canisters in the deposition holes in the bottom of the tunnels
excavated deep in the granitic bedrock. One option for filling of the tunnels is a mixture
of crushed rock and bentonite. However, in constructing the repository extensive
amounts of cements, e.g. concrete, shotcrete and grouting cement, are likely to be used
for various purposes and all the cement materials used can not be removed before
closure of the repository. It is known that cement materials will release high alkaline
solutions in contact with geological porewaters when degrading slowly in time and
causing evolving chemical disturbance in space. The anticipated effects of the released
alkaline solutions are e.g. dissolution of primary minerals and the precipitation of
secondary minerals as well as changes in retention properties of radionuclides.
When considering the safety of the repository, especially in respect of the
appropriateness of bentonite in contact with concrete, it is of extreme importance to be
able to assess the impact of the highly alkaline solutions on the system and the possible
alterations brought about in bentonite, as well as the consequential effects on the
anticipated processes occurring, e.g., sorption, diffusion, ionexchange, coprecipitation.
Modelling and assessing the processes occurring in the complicated system including
crystalline rock, cement, bentonite and groundwater is not a straightforward assignment,
however, studying simplified systems can facilitate both understanding and modelling
of the system.
In this study two types of experiments were chosen to be performed. In both
experiments the solid materials used were the same; MX-80 bentonite and crushed
crystalline rock powder from Olkiluoto site in Finland. Flow-through experiments were
performed at VTT (Technical Research Centre of Finland), and at the University of
Helsinki batch experiments including sorption studies. The effects of an alkaline
perturbation was simulated with different aqueous solutions in the experiments covering
fresh, saline, fresh alkaline, saline alkaline, and saline hyperalkaline conditions.
The experimental set-up in the flow-through system simulated one suggested backfill
concept for the tunnel consisting of compacted bentonite and crushed rock. The
conditions chosen to study simulated those anticipated deep in the granitic bedrock at
the final disposal site for spent nuclear fuel at Olkiluoto. The batch experiments aimed
at obtaining information on the possible alterations in bentonite and crystalline rock
caused by high pH of an alkaline plume and in addition to study the effect of salinity on
the retention of selected radionuclides (45Ca and 22Na) onto crushed rock and bentonite
before and after exposure to an alkaline perturbation under conditions relevant for saline
groundwaters encountered deep in crystalline bedrock. The solid materials were
characterized prior to and after the experiments in order to facilitate modelling of the
alterations caused by the attacking solutions.
6
The objective in this research was to obtain information on the hazardous alterations in
bentonite caused by high pH, but also alterations in the crystalline rock were of interest
as both these materials are prone to an alkaline attack in a repository containing
cementitious materials. In more detail the main objectives were;
- to study the possible alterations in bentonite and crushed rock powder (accessory
and neoformed minerals) brought about by saline alkaline water,
- to evaluate the spatial propagation of the alkaline plume in bentonite as detected
by chemical changes,
- to study the sorptive properties of bentonite and crushed rock powder in saline
alkaline solutions as compared to the unaltered materials,
- to examine the possible alterations at the interface of bentonite and crushed rock
powder
- to make a modelling simulation of the altered properties in bentonite and crushed
crystalline rock powder by the hyper-alkaline pore-water in moderately saline
conditions
- to use the results in mechanistic sorption modelling (HYDRAQL/CE) of the fresh
solution/clay system and to quantify the effect of increasing salinity on the extent
of sorption in the alkaline system
- to pursue qualitative interpretation of the sorption mechanisms involved
More detailed descriptions of the plans, setting up the experiments and preliminary
results can be found in a previous report (Vuorinen et al. 2003). In this report the
experimental part and results are presented first including conclusions. Thereafter
summaries on the characterisation of the solids are presented followed by the modelling
part. The appendices contain additional chemical data as well as the detailed
interpretations of the solids.
7
2
SOLID MATERIALS AND SOLUTIONS
The solid materials used in the two types of experiments (flow-through and batch) were
the same.
Bentonite:
MX-80, commercial Wyoming bentonite from American Colloid Co., was obtained
from Clay Technology (Sweden). Characterisation of the material was performed also
by Clay Technology, Ola Karnland (Appendix 5).
The following composition was calculated for the MX-80 bentonite
(Al 3.11 Fe3+0.38 Mg 0.51) (Si 7.86 Al 0.14) O20 (OH) 4 , Na 0.49 Ca 0.05 Mg 0.02 K 0.01
The analysed mineral assemblage included montmorillonite (83%), albite (7%), quartz
(5%), cristobalite (3%), gypsum (1%), muscovite (1%) and in addition grains of pyrite,
barite and iron hydroxides.
Additional information on the performance of this bentonite can be found in Andra
(2005).
Crushed rock powder:
Crushed-rock powder simulated the material to be excavated at Olkiluoto from the
planned repository tunnels and shafts. The collected rock material, mica gneiss, granite
pegmatite and tonalite, was crushed to rock powder with a maximum grain size of
approx. 1.5 mm. (details and characterisation in Ch. 5).
Synthetic solutions:
Solutions used in the experiments were synthetic ones simulating fresh and saline
groundwater compositions as well as alkaline high-pH compositions. In the batch
experiments all three solutions used were alkaline (Table 4-1), whereas in the flow
through experiments only one of the three solutions was alkaline (Table 3-1). This saline
alkaline solution (pH=12.5) had the same nominal composition in both experiments.
8
9
3
FLOW-THROUGH EXPERIMENTS
The experiments were run inside an anaerobic glove box (nitrogen atmosphere
CO2<0.1 ppm) in order to prevent interference of atmospheric CO2, especially on the
high pH solutions.
3.1
Experimental
The solid materials were used as received, without any pre-treatment.
The nominal compositions of the three different synthetic feed solutions used (fresh,
saline and saline alkaline) are shown in Table 3-1. The compositions were based on
hydrogeochemical equilibrium computations. All the feed solutions were prepared
inside the anaerobic glove-box using nitrogen-flushed MilliQ-water equilibrated with
the glove-box atmosphere at least for two weeks. After preparation of the feed solutions
they were let equilibrate still another two weeks before use.
Table 3-1.
The nominal composition of the simulated anoxic CO2-free waters.
+
Na
mol/L
2+
s
-
s
Cl
K
+
Mg
s
2+
s
s
SiO2
HCO3
SO4
Saline
Saline-Alkaline
(ALL-MR)
(OL-SS)
(OL-SA)
8.8
pH
Ca
Fresh
-
2-
Ionic
strengt
s
s
s
8.3
12.5
2.3·10
-3
0.215
0.428
0.13·10
-3
0.100
0.018
1.4·10
-3
0.414
0.462
0.10·10
-3
0.03·10
-3
0.03·10
-3
1.1·10
-3
0.10·10
-3
0.51
0.46
0.05
10
A schematic representation of the flow-through test system is shown in Figure 3-1.
sinter
crushed rock
(< 1.5 mm)
solution inlet
sinter
solution outlet
flow rate
2.5 mL/day
compactedbentonite
bentonite
compacted
(MX- 80)
sample collection
Figure 3-1. Schematic of the flow-through system. The cylinder and sinter material
was titanium and all tubings were plastic (HDPE). Compaction of bentonite was to a
density of 2.0g/cm3 at saturation.
Six identical cylinders were prepared for the tests. The cylinders were packed with
crushed rock powder (<1.5 mm) in one half of the cylinder and compacted bentonite in
the other half (more detailed description of the preparation of the cylinders is found in
Vuorinen et al. 2003). Both solid materials were characterized in the initial state and
after completing the experiments (Chapter 5). Each test cylinder was attacked by a slow
longitudinal flow of the feed solution. Both the solution inlet and outlet was assembled
in the crushed rock half of the cylinder, thus the slow feed solution flow passed through
crushed rock and only diffusion at the interface allowed interaction with compacted
bentonite. The flow-rate used (2.5 mL/day) was comparable to the anticipated flow
(1PL/min/cm2) in a deep repository. Controlling of the slow flow rate was managed by a
syringe pump (Figure 3-2). The out-flow solution was collected in small plastic bottles
(Nalgene), which were kept closed during collection, only a syringe needle was pierced
through the cap. After becoming filled the bottles were replaced with empty ones and
the filled ones were saved for further analysing. The tests were run with parallel
cylinders in two sets, and three cylinders in each set. The difference between the
cylinders in a set was the composition of the attacking feed solution.
11
Feed
solution
Sample
collection
Figure 3-2. The experimental arrangement inside the glove-box. The sample cylinders
were placed upright (on the right). The syringe pump with six syringes managed the low
flow (on the left).
The two sets of cylinders were prepared for two different experimental time periods,
about 1 year and 1.5 years. The difference in the experimental times was anticipated to
give information on the propagation of the alkaline plume in bentonite by changes in the
porewater, the distribution of exchangeable cations as well as alterations of the solid
phases. Additional results were obtained from analyses of the out-flow solutions.
After completing the flow-through tests the cyliders were opened and dismantled; the
first set of cylinders after about a year (360 d) and the other set after about 1.5 years
(560 d). Photographs of the opened cylinder ends (560 d) are shown in Appendix 1 (Fig.
A1-1). The saline (OL-SS) cylinder was very hard and the interface of bentonite and
crushed rock very distinctive. The fresh (ALL-MR) cylinder was rather soft, because
bentonite had partly swelled into the pore space of the crushed rock half. Swelling was
also seen around the edgings of the bentonite half, especially at the in-flow end. In the
saline alkaline (OL-SA) experiment the interface was slimy as well as the cylinder
edgings, indicating possible presence of new phases.
The solid materials were pressed out from the cylinders and sectioned according to
Figure 3-3. The samples obtained were coded along the flow direction starting with A at
the in-flow end. First the crushed rock was sectioned in three samples, A, B, and C
(width 4cm), and then the compacted bentonite in six slices, A, B,...., F (width 2cm) and
each slice (Fig. 3-3b) was further sectioned to smaller samples for porewater analyses
(slice A to PWAx, slice B to PWBx, ...., and slice F to PWFx) and with the same
principle samples to determination of the cationic distribution (KA). Furthermore, both
the crushed rock powder and bentonite samples were characterised and analysed for
mineral alterations (results in Chapter 5 and Appendices 3 and 4).
12
a)
b)
1 cm
A
B
1.5 cm
1 cm
PW A1
K A1R
PW A2
K A2R
C
AY
K A1L
1 cm
AY
A
B
C
D
E
F
K A2L
AY
AY
1 cm
AY
2 cm
Figure 3-3. a) Sectioning diagram of the flow-through cylinder solids. Upper part (A,
B, C) for crushed rock and lower part (A, B,...,F) for compacted bentonite. b) Further
sectioning of the bentonite slices; 1 denotes samples at the interface and 2 samples
below the interface samples, PWA for porewater samples in the first slice A and likewise
KA for cationic distribution samples.
Bentonite samples were subjected to analysis of cationic distribution (CEC) and
porewater, but porewater was analysed only in the case of the saline alkaline (OL-SA)
experiment except for one bentonite sample (PWA1) from each of the other two
experiments as well.
Because of the limited amount of bentonite available from the test cylinders no
complete sets of samples were available for the analyses performed but sets of samples
had to be selected.
Note! In most of the figures the sample coding shown is given just with A1, A2, B1,...,
F1, F2, due to the lack of space.
3.2
Model simulation
Simple model calculations of the flow-through experiments were performed to gain
information of the propagation of the alkaline plume in the cylinders. The plume and the
concomitant changes in the cation exchange chemistry of bentonite were investigated by
permeation of the calcium-bearing aqueous feed solutions (chemical compositions given
in Table 3-1) through the diffusion column. In the filter plates and crushed rock powder,
the transport of calcium was driven by advection and diffusion, while in compacted
bentonite, the fate of calcium was determined by the interplay of diffusion and
adsorption (cation exchange). For the adsorption equilibrium, a non-linear Langmuir
isotherm model was applied.
OL-SS
For this system, the Langmuir model parameters for strontium from Khan et al. (1995)
were applied for calcium adsorption in bentonite. The results of the simulation at 560 d
13
carried out using FEMLAB (COMSOL, 2002) are depicted in Figure 3-4. Comparison
of the model results with experimental findings (Table A1-1, Appendix 1) reveals a
good fit between the two without any adjustable parameters.
Max.0.576
0.575
0.57
0.565
0.56
0.555
flow
0.55
0.545
0.54
Min.0.538
Figure 3-4. Calculated exchangeable calcium (meq/g) in bentonite for the saline
OL-SS at 560 d.
Max.0.182
0.18
0.175
0.17
0.165
0.16
0.156
flow
0.15
0.145
0.14
0.136
0.13
Min. 0.129
Figure 3-5. Calculated exchangeable calcium (meq/g) in bentonite for the saline
alkaline OL-SA at 560 d.
14
OL-SA
For this system, an adequate fit between the model and experimental results was not
possible using the same set of model parameters as for OL-SS. Instead, a reduction of
adsorption model equilibrium constant by 70% was required to yield an acceptable fit
(Figure 3-5). Notice the different scales in Figures 3-4 and 3-5.
ALL-MR
From poor to extremely poor fits were obtained for this system with any set of model
parameters used. The reason for this was that the adsorption model was simply not
elaborate enough to reproduce the experimentally observed reduction in the
exchangeable calcium in the column (Table A1-1, Appendix 1).
General observations
Based on the modelling attempts for the three systems studied, we can say that the
predictive capability of this simple model is poor, because it lacks the mechanistic tools
to handle the complex problem of coupled transport and multi-species chemistry. In this
light, the apparently good fit of the model results to experimental results for OL-SS was
merely fortuitous.
3.3
Results
3.3.1
Out-flow solutions
The original plan was that one set of the test cylinders would run for about a year and
the other set for about two years. But due to the difficulties encountered in the beginning
of the experiments the longer period samples were ran only for about 1.5 years. Some
difficulties were also encountered first in getting the flow of the alkaline feed solution to
run through the installed syringe pump (infusion and withdrawal) system. It was not
noticed until after several weeks that the three-way valves in the syringe system worked
falsely with the alkaline feed solution. The pump did not conduct the flow into the
sample but let it back to the bottle with the solution for filling the syringes, even though,
when the three-way valves were manually tested by pressing the solutions with the
syringes everything seemed to work properly.
The trends of the pH values versus time passed are shown in Figure 3-6. It has to be
noted that the different behaviour of the ALL-MR duplicates in the initial stage was due
to the wrong assembly of 3/II cylinder; the flow was first entering the bentonite half
instead of the crushed rock powder half. This resulted in clogging of the sinter and
stopping of the flow. After considering and checking other alternatives for the clogging
the sample was opened and the wrong assembly confirmed. The sinters were thoroughly
cleaned in an ultrasonic bath and the sample was reassembled and the test was
continued. The pH trend in the fresh out-flow solution (ALL-MR) was first slightly
increasing and after reaching a pH value of about 9.5 remained around that value to the
end of the experiment. The pH values in the saline (OL-SS) out-flow solution gradually
15
decreased after an initial increase and quite quickly levelled off at a value of slightly
below the pH of the in-flow OL-SS (8.3). The pH values in the saline alkaline out-flow
solution quickly dropped about four pH units after which an increasing trend was
observed. At the end of the experiments the pH slowly reached a value of 9.5.
Alkalinity titrations of the out-flow samples (Table 3-2) were performed only at the
three points in time (Fig. 3-6) when also the out-flow solution analyses were performed.
In the saline alkaline case (OL-SA) alkalinity dropped from about 50 meq/L down to
about 1 meq/L showing only slight increase, up to around 2 meq/L, towards the end of
the experiment, whereas, in the saline (OL-SS) and fresh (ALL-MR) alkalinities
increased from the initial values of 0.03 meq/L and 1.1meq/L, respectively, up to about
0.32 meq/L and 3.3 meq/L, respectively. A slight decrease towards the end of the
experiment was observed in the values in the case of OL-SA while in ALL-MR the
alkalinity values stayed virtually the same throughout the experiment.
12.5
ALL-MR initial
11.5
ALL-MR 3/I
ALL-MR 3/II
10.5
pH
OL-SA initial
OL-SA 1/I
OL-SA 1/II
9.5
OL-SS initial
OL-SS 2/I
8.5
OL-SS 2/II
7.5
0
100
200
300
400
500
600
out-flow solutions analysed at
0.8 y 1.0y 1.5y
days
Figure 3-6. Measured pH values in the out-flow solutions versus time in days. Initial
pH values of the feed solutions are shown at zero on the y-axis. The stars depict the
points in time when samples were subjected to chemical analyses (results in Table 3-2).
The measured conductivity values versus the amount of solution passed through the
cylinders are shown in Figure 3-7.
In the case of the fresh ALL-MR cylinder the out-flow solution conductivity (Figure
3-7A) after an abrupt initial increase dropped quickly and continued to decrease
gradually towards the value of the feed solution. In the saline out-flow solutions the
changes were quite small; in the saline OL-SS the conductivity slightly increased in the
beginning, whereas in the saline alkaline OL-SA the conductivity quickly dropped, and
towards the end of the experiment a slightly declining trend was observed, approaching
the saline feed solution initial value (Figure 3-7B).
16
B)
A)
0.10
ALL-MR initial
ALL-MR I
ALL-MR II
0.09
conductivity [mS/m]
conductivity [mS/m]
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0.00
0
100 200 300 400 500 600 700 800 900 1000
mL
0.50
0.49
0.48
0.47
0.46
0.45
0.44
0.43
0.42
0.41
0.40
0.39
0.38
0.37
0.36
0.35
OL-SA initia
OL-SS initial
0
100
200
300
OL-SA II
OL-SS II
OL-SA I
OL-SS I
400
500
600
700
800
900 1000
mL
Figure 3-7. Trends of conductivity in the out-flow solutions. a) fresh ALL-MR
cylinders, b) saline OL-SS and saline alkaline OL-SA cylinders. Initial conductivity
values of the feed solutions are shown at zero on the y-axis. (Note the different y-axis
scales).
Samples of each out-flow solution were analysed so that changes in the concentrations
could be observed. The analytical results (meq/L) are presented in Table 3-2 and as
figures in Appendix 1 (Na, Ca and K in Figure A1-2 and Mg, Si and SO42- in Figure
A1-3). Two solution samples were analysed for the shorter test period (column A, 360d
cylinders) and three solution samples for the longer test period (column B, 560d
cylinders). Analyses were performed after 0.8 y (222d), at the end of the shorter period
experiment 1 y (368d), and at the end of the longer period experiment 1.5 y (560d).
Na showed a decreasing trend towards the initial feed solution value indicating decrease
in the release of Na. Only in the case of OL-SA (with high Na content) Na
concentrations remained rather even around the initial feed solution content indicating
minor occurrence of ion-exchange. Ca concentrations showed an increasing trend
towards the feed solution initial concentration in the saline (OL-SS) experiment
supporting gradual saturation of Ca exchange in the column. In the alkaline column
(OL-SA) and fresh column (ALL-MR) the analysed Ca concentrations remained below
the feed solution values, with a slightly decreasing trend and rather constant value,
respectively. Ca was retained in the two cylinders by ion exchange or some other
processes.
In the saline alkaline (OL-SA) and saline (OL-SS) experiments both K and Mg showed
decreasing trends. In both experiments K showed virtually the same concentrations
released, but in the case of Mg the concentrations in OL-SA were distinctly lower and
the decreasing trend steeper indicating possible retention (precipitation?) of Mg inside
the column. Also in the fresh (ALL-MR) out-flow solutions the Mg concentrations
showed a decreasing trend. The concentrations remained below the initial feed solution
value implying to possible retention of Mg in the column, as well. Al was also analysed,
17
but was below the detection limit (<1 mg/L) in the saline solutions but in the ALL-MR
out-flow solutions small amounts (0.052-0.08 meq/L) without a clear trend were
analysed.
In all three experiments the out-flow solution concentrations of SO42- decreased, and at
the end of the experiment the concentration in ALL-MR was still higher than in the
initial feed solution, hence indicating that the SO42- source was not exhausted during the
experiment. Increasing trends in all three experiments were seen in the concentrations of
Si. The highest amount was released in the case of ALL-MR, well above the initial feed
solution content, probably due to the higher pH in the out-flow solution throughout the
experiment (Fig. 3-6). The analysed Cl contents were somewhat higher than the feed
solution initial contents.
Table 3-2.
Analytical results of the out-flow solutions at three points in time
(222 d|0.8 y, 368 d|1 y and 560 d| 1.5 y). Both sets of cylinders A (360 d) and B
(560 d). Feed solution (OL-SA, OL-SS, ALL-MR) results are also given in red italics.
(- = not analysed)
pH
Sample
A
OL-SA
B
AlkTOT
Na+
Ca2+
Cl-
K+
Mg2+
Si(aq)
SO42-
meq/L
meq/L
meq/L
meq/L
meq/L
meq/L
meq/L
meq/L
A
12.5
B
A
51.7
B
A
B
422
34.9
A
B
A
B
A
B
A
B
A
B
400
-
-
-
-
-
-
-
-
222 d
8.6
8.7
0.66
0.80
405
405
17.5 17.5
451
448
2.81 2.81
4.77
4.77
0.90 1.05 8.95
8.74
368 d
9.1
9.3
1.95
0.83
405
409
14.0 14.0
451
440
2.25 2.23
2.14
2.06
1.08 1.07 6.45
6.04
0.99
409
11.0
378
1.25
2.91
0.028
213
210
412
560 d
OL-SS
8.3
1.84
-
-
0.50
-
-
-
-
-
-
219 d
8.1
8.1
0.32
0.30
309
309
110
110
415
426
2.81 2.81
12.34
12.34
0.84 0.83 5.20
5.20
368 d
8.2
8.2
0.30
0.20
261
265
155
155
406
417
2.33 2.40
12.34
12.34
1.13 1.07 3.12
3.12
1.66
9.87
1.41
2.50
560 d
0.27
ALL-MR
8.8
219 d
9.5
9.6
368 d
9.7
9.7
560 d
3.3.2
1.13
3.41
235
190
415
2.48
0.27
1.38
0.13
0.063
0.36
3.26
13.9 14.4 0.06 0.06 1.44
1.55
0.14 0.15
0.018
0.017
1.57 1.57 8.54
9.16
3.16
9.13 9.13 0.13 0.05 1.66
1.47
0.10 0.11
0.016
0.009
2.42 2.42 4.16
4.37
1.64
0.07
0.006
2.71
1.02
3.29
6.09
0.08
-
-
Exchangeable cations
In MX-80 bentonite Na-montomorillonite undergoes cation exchange; especially Na+ is
apt to become exchanged with Ca2+. The major exchangeable cations (Na+, Ca2+, K+,
Mg2+) of the bentonite samples were determined by extraction with NH4SCN in ethanol
(Müller-Vonmoos and Kahr 1983). In both the saline alkaline (OL-SA) and saline
(OL-SS) cases the total cation exchange capacity (CECTOT) values determined for the
various samples were higher (Table 3-3) than that determined for the initial MX-80,
0.72 [meq/g of bentonite]. The higher CECTOT value is due to Na in bentonite, which is
clearly shown in the CECTOT determinations of MX-80 bentonite (App. 5) changed into
18
Na-state compared with the initial MX-80 (on average CECTOT was 0.86 meq/g and
0.74 meq/g, respectively).
Table 3-3.
Measured total CEC values for bentonite samples from the three
different cylinder experiments and the initial MX-80.
attacking solution
OL-SA
OL-SS
ALL-MR
initial MX-80
CECTOT
[meq/g bentonite]
0.76 0.93
0.78 0.83
0.66 0.86
0.72
The CEC values measured for the individual exchangeable ions are given in Table A1-1
(Appendix1) and depicted in Figure 3-8 (Na and Ca) and Figure 3-9 (K and Mg). In the
saline alkaline case (OL-SA) a decreasing trend in CECTOT was observed along the
cylinder length towards the out-flow end, whereas in the saline case (OL-SS) the
increase was rather even throughout the cylinder length. In the fresh case (ALL-MR) the
CECTOT values showed unsystematic variations, lower or higher than the initial value of
MX-80. The trends can be seen in the sub-figures (Figure 3-8) of the individual
exchangeable cations, Na+ (upper row) and Ca2+(lower row), which are the main
contributors in the CECTOT value. In each sub-figure the initial value determined for
MX-80 is shown with a red bar on the left and in each sub-figure the darker bars are for
the shorter period experiments (1 y) and the lighter bars for the longer period
experiments (1.5 y). Each category number represents a bentonite sample along the
cylinder length (see Figure 3-3); in-flow end on the left and out-flow end on the right.
The cation exchange processes in bentonite replace Na+ with divalent cations. This is
clearly seen in the results of CECNa (decrease) and CECCa (increase) in the case of
OL-SS and ALL-MR experiments, whereas in the case of OL-SA the results are
different; an increase in CECNa and a slight increase in CECCa.(Fig. 3-8) when compared
with the initial MX-80 values. This can partly be explained by the about an order of
magnitude smaller amount of Ca in OL-SA and a higher amount Na (Table 3-1).
However, when comparing the Ca amount in OL-SA, about two orders of magnitude
higher, to that in ALL-MR the CECCa results obtained need additional insight to
possible processes occurring, possibly secondary phase formation.
Figure 3-9 shows the results for the other two exchangeable cations, K+ (upper row) and
Mg2+ (lower row). The changes in the ion exchange capacities are distinctly seen in both
the saline alkaline (OL-SA) and saline (OL-SS) experiments, especially in the case of
K+ and Mg2+. Both cations showed increasing values along the cylinder lengths from the
in-flow end towards the out-flow end, and furthermore, decreased capacities were
obtained for the longer period experiments indicating occurrence of further exchanges.
These results indicate that the exchange processes were not completed in the entire
column during the experimental time. In the fresh case (ALL-MR) no trend was seen as
all the K+ and Mg2+ values were somewhat randomly scattered, little higher or lower
than the initial values of MX-80..
[meq/g of bentonite]
9
1
2
3
4
5
6
7
8
10
0.0
0.0
0.0
6D2 E1
7
8
9
10
E2
F1
F2
0.1
0.1
0.1
1
2
3 C2
4
5
B1
B2
C1
D1
0.2
0.2
0.2
F1
8 F2
9
0.3
0.3
0.3
E1
F1
6
7
0.4
0.4
0.6
0.7
0.4
B2
C1
3
4 D1
5
Ca
0.5
0.6
0.7
0.0
0.5
A1
B1
1
2
Ca
9
0.5
0.6
0.7
8
0.0
0.0
7
0.1
0.1
0.1
6
0.2
0.2
0.2
5
0.3
0.3
0.3
4
0.4
0.4
0.4
3
0.5
0.5
0.5
2
0.6
0.8
0.6
Na
0.9
0.6
0.8
OL-SS
0.7
Na
0.9
0.7
1
OL-SA
0.7
0.8
0.9
19
2
3
4
5
6
7
8
9
10
Ca
11
Na
12
1 2
5 C2
6 D1
7 D2
8 E1
9 10
A1
A2 3B1 4B2 C1
E2 11
F1 12
F2
1
ALL-MR
Na MX-80
Ca / 560
Ca / 360
Ca MX-80
Na / 560
Na / 360
Figure 3-8. CEC values (meq/g fo bentonite) measured for the bentonite samples. The upper row of figures shows values for Na and the
lower row for Ca, whereas the leftmost figures are for the saline alkaline (OL-SA) solution, the middle ones for the saline (OL-SS) solution
and the rightmost figures for the fresh (ALL-MR) solution. The category markings refer to the analysed sample; A denotes the in-flow end
of the cylinder and F the out-flow end, 1 refers to samples from the interface and 2 to samples from below the interface ones. (see Figure
3-3)
[meq/g of bentonite]
[meq/g of bentonite]
9
1
2
3
4
5
6
7
8
10
0.00
0.00
0.01
0.00
1
2
3
4
5
B1
B2
C1 C2
D1 6D2 7E1 8E2 9F1 10
F2
0.01
0.01
0.02
F1 F2
8
9
0.02
0.02
F1
6E1 7
0.03
0.03
0.03
B2
C1
D1
3
4
5
0.04
0.04
0.04
0.06
0.07
0.05
0.06
Mg
0.05
A1
B1
1
2
Mg
0.07
0.003
0.004
0.05
0.06
0.07
9
0.000
8
0.000
7
0.000
6
0.001
5
0.001
4
0.002
0.002
3
0.001
0.003
0.003
2
0.002
0.004
0.004
0.005
0.006
0.005
0.007
0.008
0.005
K
0.009
0.006
0.008
OL-SS
0.006
K
0.009
0.007
1
OL-SA
0.007
0.008
0.009
20
2
3
4
5
6
7
8
9
Mg
10 11 12
K
1 A2
2 B1
3 B2
4 C1
5 C2
6 D1
7 D2
8 E1
9 E2
10 F1
11 F2
12
A1
1
ALL-MR
Mg / 560
Mg / 360
Mg MX-80
K / 560
K / 360
K MX-80
Figure 3-9. Measured CEC values (meq/g fo bentonite) in bentonite. The upper row of figures shows values for K and the lower row for
Mg, whereas the leftmost figures are for the saline alkaline (OL-SA) solution, the middle ones for the saline (OL-SS) solution and the
rightmost figures for the fresh (ALL-MR) solution. The category markings refer to the analysed sample; A denotes the in-flow end of the
cylinder and F the out-flow end, 1 refers to samples from the interface and 2 to samples from below the interface ones (Figure 3-3).
[meq/g of bentonite]
21
3.3.3
Bentonite porewater
Porewater was pressed from some samples chosen from the alkaline (OL-SA) cylinder.
The samples were chosen to represent the cylinder length both from the interface of
bentonite and crushed rock as well as further from the interface (See Fig. 3-3).
Additionally, for comparison purposes only one sample from each of the other two
cylinders (OL-SS and ALL-MR) could be included in the porewater studies. Both
samples were from the interface the first ones from the in-flow end (sample code
PWA1, see Fig. 3-3, Note! For reasons of clarity in the letters PW are left out from the
sample codes.) as they were expected to show the greatest alterations occurred in the
columns. A detailed description of the squeezing and analysing of bentonite pore water
can be found in Muurinen and Lehikoinen, 1999. Figure A1-4, (App.1) shows the
equipment used in porewater squeezing. All the analytical results of porewaters are
shown in Table A1-2, Appendix 1. The common trend in the analysed constituents
(alkalinity and pH excluded) was that with increased experimental time concentrations
in the porewater decreased in both the interface samples and samples further from the
interface.
The results of the porewater pH measurements are depicted in Figure 3-10. The first
four categories (red codes) show the pH values for the interface samples along the flow
direction. The following three categories (blue lining of bars and blue codes) show the
results for samples below the interface samples. The red (OL-SS) and black (ALL-MR)
bars on the right show the pH values of the samples from the corresponding cylinders
spatially corresponding to the first sample at the interface from the in-flow end. Clearly
increased pH values were seen only in the interface samples, especially in the 560d
experiment. The trend in the changes of pH was decreasing towards the out-flow end of
the cylinder. The highest pH values measured varied from about 11 down to around 9
but still all the values did not reach the value of the initial feed solution (12.5). In all the
other samples (both 360 d and 560 d) the pH value remained virtually the same, around
8. In the case of the saline (OL-SS) and fresh (ALL-MR) experiments the porewater pH
in the first sample at the interface from the in-flow end of the cylinder (the red and black
bar, respectively) showed pH values around 8 as well. In the case of OL-SS it was
slightly decreased (8.2) from the initial value of 8.3, whereas, in the case of ALL-MR
the pH value had decreased down to about 7.7 from the initial value of 8.8.
Both the main components, Na+, and Cl-, in the feed solution (OL-SA), showed similar
trends in the analysed porewater samples, Figure 3-11. As expected greater changes
occurred at the interface samples than in the samples further from the interface. The
concentrations of both ions were clearly lower than those in the feed solution and the
concentrations showed decreasing trends with increasing experimental time (darker vs.
lighter bars). The decrease in Na+ concentrations was greater than in Cl- concentrations,
also in the case of the saline (red bars, OL-SS) and fresh (ALL-MR) experiments (Table
A1-2, App.1 and Figures 3-11, -12 and -13).
22
12
10
OL-SS
ALL-MR
pH
8
360 d
6
560 d
4
2
0
1
A1
A1
2
3
4 A2
B1
D1 D1
F1 F1
B1
5 B2
A2
6D2
B2
7
A1
D2
8
A1
A1
9
A1
Figure 3-10. Measured pH-values in the bentonite porewater samples. Blue bars are
for the saline alkaline (OL-SA) experiment for both the 360 d and 560 d cylinders
indicated by the legend. The interface samples are shown in four first categories (red
codes) and the samples below these are shown in the next three categories (blue codes
and blue lining of bars). The red and black bars in the two rightmost categories are for
the saline (OL-SS) and fresh (ALL-MR) cylinders, respectively, the samples correspond
spatially to the first interface sample (light blue bar, 560d).
140
120
120
100
100
80
Cl [meq/L]
Na [meq/L]
Na
140
OL-SS
60
Cl
OL-SS
80
60
40
40
20
ALL-MR
20
ALL-MR
0
0
A1
1
A1
B12
B1
D1 3
D1
F1 4 A2
F1
5B2
A2
D2
6
B2
A17
D2
A1 8
A1
9
A1
A1
1
A1
B12
B1
D1 3 F1
D1
A2
4
F1
B2
5
A2
D2
6
B2
A1
7
D2
A1 8
A1
9
A1
Figure 3-11. Analytical results (meq/L) for Na and Cl in the porewater samples. The
interface samples are shown in four first categories (red codes) and the samples below
these are shown in the next three categories (blue codes and blue lining of bars). The
red and black bars in the two rightmost category are for the saline (OL-SS) and fresh
(ALL-MR) cylinders, respectively, the samples correspond spatially to the first interface
sample (lighter bar, 560d). The darker bars are for the 360d experiment and the lighter
ones for the 560d experiment.
Mg2+, K+, SO42- and Si(aq) all showed similar trends, Figure 3-12. After the shorter
experimental time (darker bars, 360d) increased concentrations were observed at the
interface along the flow direction also in the samples further from the interface. In the
case of Mg2+and K+ the concentrations were higher in the interface samples when the
opposite was true for SO42- and Si(aq). After completion of the experiments (lighter
bars, 560d) the concentrations of the constituents in the porewater had further decreased
so that no clear trends were seen.
23
Higher concentrations of K+, Mg2+ and SO42- in the porewater were seen in the saline
experiment (OL-SS) at completion (red bar) as compared with the corresponding results
in OL-SA experiment (lighter bar, category A1), only the Si(aq) concentration was
higher in the alkaline case, indicating greater dissolution of silicates supported by the
higher pH of the porewater (Fig. 3-10).
4
0.4
Mg
K
3
Mg [meq/L]
K [meq/L]
0.3
OL-SS
0.2
OL-SS
0.1
2
1
ALL-MR
ALL-MR
0.0
0
A1
1
A1
40
D1D1
3 F1
4 A2 A2
5B2
F1
6D2
B2
A1
7
D2
A1A1
8
9
A1
A1
1
A1
40
2-
SO4
B12 D1 3 F1
B1 D1
4 A2 A2
5B2
F1
D2
6
B2
A1
7
D2
A1 8
A1
9
A1
Si(aq)
35
30
30
25
25
Si [meql/L]
SO 4 [meq/L]
35
B1
2
B1
20
15
10
15
10
OL-SS
5
20
OL-SS
ALL-MR
5
ALL-MR
0
0
A1
1
A1
B1B1
2 D1 D1
3 F1
4 A2 A2
5B2
F1
D2
6
B2
A1
7
D2
A1A1
8
A1
1
A1
9
A1
B1
2 D1 D1
3 F1
B1
4 A2
F1
5B2
A2
D2
6
B2
A1
A1 A1
7
8
D2
9
A1
Figure 3-12. Analytical results (meq/L) for K+, Mg2+, SO42- and Si(aq) in the porewater
samples. Category codings and bar identities as given in Fig. 3-11.
OL-SS, 73 [m eq/L]
10
9
8
Ca [meq/L]
7
6
360 d
5
560 d
4
3
2
1
ALL-MR
0
A1A1
B1B1
1
2 D1
3 F1 F1
4A2
D1
B2
5
A2
D2
6
B2
A1
7
D2
A1A1
8
9
A1
Figure 3-13. Analytical results (meq/L) for Ca2+ in the porewater samples. Category
codings and bar identities as given in Fig. 3-11.
24
The trend of Ca2+ concentrations in porewater (Figure 3-13) after the shorter
experimental period (360d) were decreasing along the flow direction. Only the first
sample (A1) at the interface showed a clearly lower concentration. After completing
(560d) the experiments Ca2+ concentrations had dropped to a level around 2 meq/L in all
other samples except in the two first ones at the interface from the in-flow end. This
supports the results of higher CECCa measured for the corresponding samples (Figure
3-8). Similar results are seen in the case of OL-SS experiment; clearly decreased
concentration of Ca in the porewater and increased CECCa .
3.4
Main conclusions
In the interpretation of the results obtained a major lack of knowledge rose from missing
experiments; namely interaction of the three feed solutions with only the crushed rock
powder. Therefore the results can not be concluded to have occurred only due to
bentonite interactions, because the solutions interacting with bentonite had already
interacted with the crushed rock. The chemical results of the out-flow solutions were
prone to some alterations by the crushed rock powder, but the extent of the alterations is
presumed to be rather small. Some indications of the changes in the component
concentrations in the saline alkaline (OL-SA) experiment can be obtained from the
batch experiment using the same interacting solution (Table A2-8, App. 2). It has to be
kept in mind that in the batch experiment the interaction conditions between the phases
was quite different (continuous shaking vs. slow flow). The main changes seen in the
batch experiments in the long run to the initial solution in contact with crushed rock
powder were
x decrease in Na and Ca concentration
x increase in Cl concentration
x increased concentrations of Al, K and Si
x Mg concentrations were below detection limit (<0.1mg/L).
These results provide an explanation to the somewhat higher Cl concentrations obtained
in the flow-through experiments in the out-flow solutions compared to the initial feed
solution values (Table 3-2). However, there was also a distinct decrease in the Cl
content in the out-flow solution in the longer period experiment in the OL-SA case. The
reason to this decrease was most probably a reflection of increased interaction with
bentonite similarly as was seen in the batch experiments; decreasing Cl content with
increasing experimental time (Table A2-8, App. 2).
The Mg result above supports those obtained in the flow-through analyses. In the case
of exchangeable Mg the amount left in the OL-SA bentonite samples was less than in
the OL-SS samples (Fig. 3-9), but this was not reflected in the Mg contents in the outflow solutions (Fig. A1-3, App. 1) even if the pore water analysis showed depletion of
Mg (Fig. 3-12). Mg release from bentonite by ion-exchange increased with increasing
experimental time whereas decreasing trends of concentrations were seen in both the
out-flow solutions and the bentonite porewater as experimental time increased. This was
an indication that Mg remained to some extent inside the alkaline column and
participated in some kind of reactions (brucite precipitation?, co-precipitation?).
25
When comparing the results of Si contents in the bentonite porewater (Fig. 3-12) and the
out-flow solution samples(Fig. A1-3, App1.) Si was released more efficiently from the
fresh experiment (ALL-MR) column than from the saline alkaline (OL-SA) column
(Fig. A1-3, App. 1) despite of the higher pH (8.8 vs. 12.5) and even if higher pH should
increase dissolution of silicates. This may refer to the formation of CSH phases in the
OL-SA experiment, supported by the Ca behaviour;
x the decrease of Ca in porewater (Fig. 3-13),
x less increase in the exchangeable Ca (Fig. 3-8) compared with that in the ALL-MR
experiment, even if the initial Ca amount in the OL-SA feed solution was an order of
magnitude higher (Table 3-1) and
x the decreasing trend in the out-flow solutions of OL-SA (Table 3-2) with increasing
experimental time.
Also the observed sliminess at the interface of crushed rock and bentonite supported the
presence of new phases.
The simple saline feed solutions, OL-SA and OL-SS, did not initially contain K, Si or
SO4. The levels of K were quite similar both in the determined exchangeable cations
remaining in bentonite (Fig. 3-9), as well as the amounts entered into the out-flow
solutions (Fig.A1-2, App. 1) indicating that interactions with bentonite were well
reflected in the out-flow solution K+ composition. This was also true for SO4 and Si,
based on the pore water and out-flow solution results.
In both saline experiments (OL-SS and OL-SA) the measured cation exchange capacity
of bentonite (CECTOT) was higher than that determined for the initial MX-80 (Table 3-3)
This was attributed at least partly to the presence of Na-bentonite as shown by the
characterisation results of the initial MX-80 bentonite and MX-80 bentonite transformed
into Na form (0.74 vs. 0.86 meq/g).
The physical appearances of the three types of column experiments (Fig. A1-1, App. 1)
supported the known facts that salinity prevents swelling of bentonite whereas in contact
with fresh solution swelling occurs. The hardness of the saline (OL-SS) column gave
reason to suspect possible presence of a new phase (salt?) as well as the sliminess
observed in the saline alkaline column (OL-SA) (CSH phases?).
When considering the spatial propagation of the alkaline plume in bentonite some bias
to the observations may result from the edge influence; the flowing solution has had a
way to attack bentonite partly also along the cylinder edges as seen in the figure
depicting the opened cylinder ends. However, when possible the samples for bentonite
analyses (Fig.3-3) were selected so that the edge parts were excluded, but due to the
small amount of samples this was not entirely avoidable. Anyhow, it can be concluded
that the alkaline solution (OL-SA) affected bentonite throughout the entire column to
some extent at the interface and less further from the interface, indicated by
x the clear decreasing trend in the contents of exchangeable K and Mg with increasing
experimental time and a progressive trend along the flow path
x the pH values of the bentonite pore waters supported alkaline changes only near the
interface with a clear decreasing trend towards the cylinder end; the high pH value
(~11) at the in-flow end decreased down to around 8, the value at which pore water
seemed well buffered in samples further from the interface
26
x
concentrations of the other porewater constituents supported the anticipated plume
behaviour as well
The out-flow solution had reached a pH value around 9.5 by the end of the experiment
and showed an increasing trend. If the alkaline pH was to keep its trend the estimated
time needed for the out-flow solution pH value to reach a value around 11 would be
about 6 years and to reach the initial value of 12.5 would take about 10 years.
In the fresh and saline experiments the out-flow solution pH values levelled off at
around 9.5 and 8, respectively.
27
4
BATCH EXPERIMENTS
4.1
Experimental
The experiments were carried out in nitrogen atmosphere at ambient room temperature.
The nitrogen atmosphere was provided by an anaerobic glove-box or by a constant
nitrogen flow in a rotator. The oxygen and carbon dioxide concentrations in the
atmosphere of the glove-box were controlled.
Synthetic solutions
In the batch experiments all the synthetic solutions used were alkaline, and only one, the
saline alkaline solution (OL-SA), had the same nominal composition as in the flowthrough experiments.
Three types of synthetic alkaline solutions were prepared in CO2 free water (Table 4-1).
One of the solutions was fresh alkaline and the other two were saline alkaline solutions.
MilliQ-water was boiled and bubbled by nitrogen gas to remove the carbon dioxide
before preparing the solutions. The solutions were equilibrated for two weeks in the
glove-box and the pH values of the solutions were followed and adjusted if necessary.
The waters were filtered through 0.45 Pm filter (Acrodisc“, GHP) before the
experiments were started (Vuorinen and Snellman 1998). To confirm that the
preparation of the simulated solutions could be repeated accurately three batches of the
solutions were prepared, and the composition of the solutions was followed by
measuring the calcium content. The results were within the precision of AAS (flame)
(Table A2-1 in Appendix2).
Table 4-1. Nominal compositions of the synthetic alkaline solutions.
Synthetic water
pH
Ionic
strength
(mol/L)
Na
(mol/L)
Fresh alkaline
Saline alkaline (OL-SA)
Saline hyperalkaline
12.5
12.5
13.5
0.05
0.46
0.88
0.023
0.428
0.931
Ca
Cl
(mol/L)
(mol/L)
0.0095
0.018
0.0004
0.0014
0.462
0.413
When the chemical composition of the prepared solutions was analysed also minor
amounts of impurity elements were detected. Table A2-2 in Appendix 2 gives the
analytical results and calculated maximum amounts of impurities introduced from the
p.a. chemicals used in preparing the solutions. The content of silica found in all
solutions was higher than could have originated from the chemicals used. The most
probable origin of silica was the glassware used. However, the influence of the small
amounts of impurites on the results was insignificant.
28
Radionuclides
The radionuclides used in the sorption experiments were 45Ca (T1/2=163d) and 22Na
(T1/2=2.602a) from Amersham International, UK. The dilution of the tracer solutions
was done in the nitrogen glove box to 0.001 M HCl. The beta activity of 45Ca was
measured by LSC (Wallac Quantulus) and the activity of 22Na by gamma spectrometry
(Wallac Wizard) (ASTM 1995).
Both solid materials, MX-80 bentonite and the crushed Olkiluoto rock powder
(Characterised in Ch.4), were treated separately with the three synthetic solutions in the
glove-box. The sorption experiments were performed in batch mode in polypropylene
centrifuge tubes (ASTM 1993). The solid to solution ratio was 1:10. The amount of dry
crushed rock powder or bentonite (8 % moisture) weighed was 3.8 g to which 38 mL of
solution was added. Four parallel samples were prepared for each solution/solid pair and
for two radionuclides adding up to 48 samples altogether. An end-over-end rotator for
mixing samples in nitrogen atmosphere was constructed. During the experiment the
samples were continuously rotating to prevent sedimentation. A constant nitrogen flow
guaranteed that no carbon dioxide contamination occurred during the experiment. The
alteration times for both crushed rock powder and bentonite were 1 week, 1 month, 6
months and 1.5 years (6, 30, 180 and 540 days).
From one set of the samples the phases were separated at the end of the alteration time
by centrifugation/filtration. The centrifugation was performed at 7 500 G for 30 minutes
after which the solution was filtered through 0.45 Pm filter (Acrodisk“,GHP). From
one sample of the four in a set the pH was measured with a standard procedure (ASTM
1975) using a combination glass electrode (Radiometer, pHC2401). The solution was
analyzed for major components (Na, Ca, Mg, Al, Si, Fetot by ICP-AES, K, Cl by ICPMS and SO4 by ion chromatography (IC)). Electric conductivity (EC) in the solution
was measured by potentiometer. The solid phases were let to dry in nitrogen
atmosphere. The bulk composition of the solid phases were analyzed and the altered
phases were characterised (see Chapter 5).
The other set of samples was spiked with 45Ca or 22Na ((4-8)˜10-10 M and (2-4)˜10-9M
respectively). After 2 weeks contact time the phases were separated as described above
and the amount of sorption was determined.
Some samples with contact time of 6 months and 1.5 years were separated by
centrifugal filter devices with a cut-off of 5 000 D1 (Millipore Amicon Centricon® Plus20). The electric conductivity could not be measured from bentonite with fresh alkaline
samples filtered through 0.45µm, but from samples filtered through 5 000 D the
measurement succeeded.
1
D = Dalton | 1.5 nm
29
4.2
Results
4.2.1
Sorption and retention of radionuclides on solid phases
The results of sorption experiments with radioactive tracers are expressed as the mass
distribution ratio Kd-value. The mass distribution ratio, Kd, was calculated from formula
4-1:
Kd
where
(
Atracer Asample
Asample
Asample
Atracer
V
m
)u
V
m
(4-1)
= activity of the sample solution (Bq)
= activity of the spiking solution (Bq)
= volume of water in the sample (m3)
= mass of the solid in the sample (kg).
The average values of the parallel samples were calculated and the results from the
short-term experiment are collected in in Appendix 2 in Tables A2-3 and A2-4 for 22Na
and 45Ca, respectively. The standard deviation of the radioassay was 1 sigma for an
individual measurement. Table A2-5 (Appendix 2) shows the corresponding pH values.
The follow-up results of the pH values measured in the initial solutions during the
experiment are in Table A2-6 (Appendix 2). The chemical composition of the solutions
initially and after the experiment are presented in Tables A2-7, A2-8, A2-9 and A2-10
in Appendix 2.
Due to the colloidal formation especially in bentonite samples contacted with the fresh
alkaline solution these samples were ultrasentrifugated through 5000 D pore size. The
bentonite sample with saline alkaline water (OL-SA) was filtered through 0.45µm filter
and 5000 D. This did not cause any change in the measured sorption.
The sorption of 22Na on crushed rock was low in all solutions (Kd = (0.021.2)˜10-3 m3/kg), but on bentonite it was a little higher (Kd = (0.65-2.1)˜10-3 m3/kg) than
on crushed rock in the saline waters (Kd = (0.02-1.2)˜10-3 m3/kg). However, in the fresh
solution high sorption was observed (Kd = (1.5-2.7)˜10-2 m3/kg) on bentonite. In this
sample there was observed a strong formation of colloidal matter. The sorption was
highest for samples with shorter experimental time decreasing in samples with longer
time except in bentonite with fresh water. The sorption on these samples remained about
the same. The changes in mass distribution ratio for crushed rock and bentonite as a
function of experimental time are shown in Figures 4-1 and 4-2, respectively. The
evolution of mass distribution ratio Kd was about the same for crushed rock in all
waters. For the longest experimental time the sorption was too low to be detected in
crushed rock contact with fresh alkaline water.
30
0
2
Na
logKd(m /kg)
-1
logKd(m3/kg)
Ca
1
3
-2
-3
-4
0
-1
-2
-3
-4
-5
-5
0
200
400
600
0
200
Time(d)
400
600
Time (d)
Figure 4-1. The sorption of sodium (on the left) and calcium (on the right) on crushed
rock from fresh alkaline (Ɣ), saline alkaline (OL-SA) (Ŷ) and saline hyper alkaline (Ÿ)
water. (The solid curves do not imply any functional dependency of logKd on time.)
5
0
Ca
Na
3
logKd(m3/kg)
logKd(m3/kg)
-1
-2
-3
1
-1
-3
-4
-5
-5
0
200
400
Time (d)
600
0
200
400
600
Time (d)
Figure 4-2. The sorption of sodium (on the left) and calcium (on the right) on
bentonite from fresh alkaline (Ɣ), saline alkaline (OL-SA) (Ŷ) and saline hyper alkaline
(Ÿ) water. (The solid curves do not imply any functional dependency of logKd on time.)
31
0
Na
logKd(m /kg)
-2
3
3
logKd(m /kg)
-1
-3
-4
-5
0
200
400
2
1
0
-1
-2
-3
-4
-5
Ca
0
600
200
400
600
Time (d)
Time (d)
Figure 4-3. The sorption (Kd(m3/kg)) of sodium (on the left) and calcium (on the right)
on crushed rock from chemical analyses. Waters were fresh alkaline (Ɣ), saline
alkaline (OL-SA) (Ŷ), and saline hyper alkaline (Ÿ) water. (The solid curves do not
imply any functional dependency of logKd on time.)
1
0
-2
3
3
0
logKd(m /kg)
-1
logKd(m /kg)
Ca
Na
-3
-1
-2
-4
-3
-5
-4
0
200
400
Time (d)
600
0
200
400
600
Time (d)
Figure 4-4. The sorption (Kd(m3/kg)) of sodium (on the left) and calcium (on the right)
on bentonite from chemical analyses. Waters were fresh alkaline (Ɣ), saline alkaline
(OL-SA) (Ŷ), and saline hyper alkaline (Ÿ) water. (The solid curves do not imply any
functional dependency of logKd on time.)
The sorption of 45Ca on crushed rock was only somewhat higher than for sodium for the
fresh and saline alkaline waters for shorter experimental time (Kd (0.12-5.7)˜10-3 m3/kg)
(Fig. 4-1). Instead for the saline hyper alkaline water the sorption was high (Kd (0.819.1)˜10-1 m3/kg). The sorption increased on samples of crushed rock with longer
experimental time. On the bentonite samples there were observed a very high sorption
for all water types (Kd (0.015-100) m3/kg) (Fig. 4-2). On the bentonite samples of saline
alkaline water (OL-SA) there were observed high sorption, but the sorption varied
much. The evolution of mass distribution ratio Kd varied for different waters.
32
The sorption values calculated from chemical analyses were compared to those values
obtained from tracer experiments. The results from chemical analyses are shown in
Figures 4-3 and 4-4. For crushed rock in fresh water the sorption values from chemical
analyses of sodium are significantly higher than those from sorption studies. For (OLSA) and saline hyper alkaline waters there is a good correlation. For bentonite there is a
good correlation for sodium. For crushed rock in all waters again is a good correlation
found for calcium between the different analyses. For bentonite in all waters there is
good correlation for fresh water and saline alkaline water (OL-SA). The results from
chemical analyses for hyper alkaline water are smaller than those from tracer studies.
4.2.2
Effect of element concentration on sorption
Kd–values for natrium and potassium as a function of element concentration are shown
in Figures 4-5 and 4-6. The corresponding water composition (Tables A2-7...A2-9 in
Appendix 2) before adding the tracer was used (see section 4.2.4). In case of sodium
there was not observed any effect on crushed rock, but on bentonite there was a small
increase in Kd at the lower concentration. In case of calcium there was a small decrease
at first, but the difference between higher concentrations was small on crushed rock
(notice the log-scaling). In case of bentonite there was a clear decreasing effect of the
initial concentration. In studies of other alkaline-earth elements there have been seen the
dependence of initial element concentration on sorption (Kulmala and Hakanen 1995).
0
Ca
Na
-1
-3
logKd(m3/kg)
logKd(m3/kg)
-2
-4
-5
-2
-3
-4
-6
-5
0
0,2
0,4
0,6
0,8
Concentration (mol/l)
1
0
0,005
0,01
0,015
0,02
Concentration (mol/l)
Figure 4-5. Effect of initial element solution concentration on sorption on crushed
rock. Waters contact with solid material was fresh alkaline (pH 12.5) (Ɣ), saline
alkaline OL-SA (pH 12.5) (Ŷ) and saline hyper alkaline (pH 13) (Ÿ) water. The
experimental time was one week.
33
0
2
Na
logKd(m3/kg)
logKd(m3/kg)
-1
-2
-3
1
0
-1
-4
-2
-5
-3
0
0,2
0,4
0,6
0,8
Ca
0
1
0,002
0,004
0,006
0,008
Concentration (mol/l)
Concentration (mol/l)
Figure 4-6. Effect of initial element solution concentration on sorption on bentonite.
Waters contact with solid material was fresh alkaline (pH 12.5) (Ɣ), saline alkaline
OL-SA (pH 12.5) (Ŷ) and saline hyper alkaline (pH 13) (Ÿ) water. The experimental
time was one week.
4.2.3
Evolution of pH during experiment of crushed rock and bentonite with
water
The pH of samples did not change for the crushed rock samples with fresh and saline
alkaline (OL-SA) waters. There was observed a slight decrease for the saline hyper
alkaline water. The pH of bentonite samples decreased considerably in case of the fresh
and saline alkaline waters, but the pH for the saline hyper alkaline water was
maintained. The observed decrease in pH has earlier been in same type of studies
explained due to the dissociation of the dissolved silica (ECOCLAY 2000). In their
study at higher pH a decrease from 13.5 to 8.5 was observed, however, in our study this
kind of decrease was not seen. The pH of the initial waters was also measured during
the experiments. They maintained their pH. The evolution of pH is shown in Figure 4-7.
14
Rock
Bentonite
Water
pH
13
12
11
10
0
200
400
Time(d)
600 0
200
400
Time(d)
600 0
200
400
600
Time(d)
Figure 4-7. The evolution of pH in the fresh alkaline (Ɣ), saline alkaline OL-SA (Ŷ)
and saline hyper alkaline (Ÿ) waters in contact with crushed rock or bentonite and
without contact to mineral phases.
34
4.2.4
Evolution of various elements during experiments of solid phase
The chemical composition of the water in contact with crushed rock and bentonite was
followed. The evolution of sodium and calcium are shown in Figures 4-8 and 4-9 and
potassium, aluminium and silicon are shown together in Figures 4-10 and 4-11. After an
initial decrease the concentration of sodium increased back to the initial concentration
level in crushed rock with fresh alkaline water. On the other hand in bentonite sample
after an initial decrease an increase was observed, but then the concentration remained
clearly below the initial level. For saline alkaline (OL-SA) and saline hyper alkaline
waters only minor variation was observed. The alteration of crushed rock and bentonite
did not have a major effect on the sodium concentration of the waters, except in
bentonite with fresh alkaline water.
In the crushed rock sample a slow decrease in the calcium concentration was observed
for all waters. In bentonite with fresh alkaline water the same trend was observed. For
(OL-SA) and saline hyper alkaline waters, after an initial decrease a stable concentration
level was obtained. The increasing time for alteration of crushed rock and bentonite
decreased the total concentration of calcium in all waters.
Potassium, aluminium and silicon behaved similarly, the minerals containing these
elements were dissolving and introducing these elements to the solutions. For the
crushed rock sample there was observed an increase in the concentration of these
elements for all waters. After an initial increase in the concentration in the bentonite
sample a decrease for fresh alkaline water was obtained. In saline hyper alkaline water
more silicon was still dissolving.
In a former Ecoclay project the experimental conditions of pH 12.6 and pH 13.5 at
35 °C corresponds best the fresh alkaline water in our study (ECOCLAY 2000). The
amount of K ions in their solution decreased regularly with time over first 6 months,
indicating that a K-bearing phase was precipitating and/or those cations were exchanged
between solutions and clay minerals. This was not observed in our study. In their
experiments the concentrations of Al and Mg remained practically invariable throughout
the tests regardless the reaction time. The concentration of magnesium and iron
increased mostly in bentonite with fresh alkaline water in our study. After initial
increase the concentration dropped below the detection limit. In most other samples the
concentration was below the detection limit. The behaviour of iron was following that of
magnesium, except in crushed rock with saline hyper alkaline water there was a slight
increase in the concentration of iron with increasing contact time.
In bentonite samples the sulphate concentration of solution increased to a level of about
0.003 M for all waters. The sulphate originated from the impurity compounds in
bentonite mainly CaSO4 and less MgSO4 (Muurinen and Lehikoinen 1999). In crushed
rock the concentration of sulphate slightly increased for fresh alkaline water and for
other waters the concentration was below the detection limit or close to it. The chloride
concentration increased slightly in fresh water samples and only after 6 months in
bentonite was observed a greater increase. For saline alkaline (OL-SA) and saline hyper
alkaline waters there was observed variation. In bentonite with saline alkaline (OL-SA)
water there was after an initial increase a decrease back to the initial concentration level.
35
In crushed rock there was an initial drop followed by a small increase in the
concentration. In saline hyper alkaline water there was a slight increase after 6 month.
The electric conductivity was lowest both in crushed rock and bentonite samples when
the contact time of waters was longest.
0,1
1
10
0
200
Time (d)
400
Fresh alkaline
600
1
10
100
1000
0
400
Time (d)
200
Saline alkaline
600
0,01
0,1
1
10
100
1000
10000
0
400
Time (d)
200
600
Saline hyper alkaline
0,1
1
10
100
0
200
Time (d)
400
Fresh alkaline
600
1
10
100
1000
0
400
Time (d)
200
Saline alkaline
600
0,001
0,01
0,1
1
10
100
1000
10000
0
Time (d)
200
400
Saline hyper alkaline
600
Figure 4-9. Evolution of solutions (Na (Ŷ) and Ca (Ɣ) concentrations during experiments of bentonite rock with fresh alkaline (on the
right), saline alkaline OL-SA (in the middle) and saline hyper alkaline waters (on the right).
Concentration(mmol/l)
1000
Concentration(mmol/l)
Figure 4-8. Evolution of solutions (Na (Ŷ) and Ca (Ɣ) concentrations during experiments of crushed rock with fresh alkaline (on the left),
saline alkaline OL-SA (in the middle) and saline hyper alkaline waters (on the right).
Concentration(mmol/l)
100
Concentration(mmol/l)
36
Concentration(mmol/l)
Concentration(mmol/l)
0,001
0,01
0,1
1
0
400
Time (d)
200
600
Fresh alkaline
0,001
0,01
0,1
1
10
0
400
Time (d)
200
Saline alkaline
600
Concentration(mmol/l)
Concentration(mmol/l)
0,001
0,01
0,1
1
10
0
400
Time (d)
200
600
Saline hyper alkaline
0,001
0,01
0,1
1
10
0
400
Time (d)
200
Fresh alkaline
600
0,01
0,1
1
10
0
400
Time (d)
200
600
Saline alkaline
0,001
0,01
0,1
1
10
100
0
400
Time (d)
200
Saline hyper alkaline
600
Figure 4-11. Evolution of solutions (K (Ŷ), Al (Ÿ), Si (Ɣ) concentrations during experiments of bentonite with fresh alkaline (on the left),
saline alkaline OL-SA (in the middle) and saline hyper alkaline waters (on the right).
Concentration(mmol/l)
100
Concentration(mmol/l)
Figure 4-10. Evolution of solutions (K (Ŷ), Al (Ÿ), Si (Ɣ) concentrations during experiments of crushed rock with fresh alkaline (on the
right), saline alkaline OL-SA (in the middle) and saline hyper alkaline waters (on the right).
Concentration(mmol/l)
10
37
Concentration(mmol/l)
38
4.3
Conclusions
The sorption of 22Na on crushed rock was low for all synthetic waters (Kd
(0.02-1.2)˜10-3 m3/kg). The sorption on bentonite was a little higher (Kd (0.65-2.1)˜10-3
m3/kg), than for crushed rock for saline waters. However, for the fresh water a high
sorption was observed (Kd (1.5-2.7)˜10-2 m3/kg). The sorption was highest for samples
of shortest experimental time decreasing in samples of longer experimental time except
in bentonite with fresh water. The sorption on these samples remained about the same.
The evolution of mass distribution ratio Kd was about the same for crushed rock in all
waters. For the longest experimental time the sorption was too low to be detected in
crushed rock contact with fresh alkaline water.
The sorption of 45Ca on crushed rock was only somewhat higher than for sodium for the
fresh and saline alkaline (OL-SA) waters (Kd (0.12-5.7)˜10-3 m3/kg). Instead for the
saline hyper alkaline water the sorption was high (Kd (0.81-9.1)˜10-3 m3/kg). The
sorption increased on crushed rock with longer experimental time. On the bentonite
samples there were observed a very high sorption for all water types (Kd 0.015-100
m3/kg). The evolution of mass distribution ratio Kd varied for different waters.
The changes in the chemical composition of waters contact with crushed rock or
bentonite during the experiments was followed by analysing the major cations (Na, Ca,
K, Fe, Mg, Al, Si) and anions (Cl, SO4) at the beginning and at the end of all alteration
periods. The effect of the initial concentration for sodium and calcium to the sorption
was studied. In case of sodium there was not observed any effect on crushed rock, but
on bentonite there was a small increase in the Kd at the lower concentration. In case of
calcium there was observed a small increase in mass distribution ratio at the higher
concentration on crushed rock. In case of bentonite there was a decreasing effect of the
initial concentration. Furthermore the evolution of the pH of the solutions contact with
solid materials was followed. The pH did not change for the crushed rock samples for
fresh and saline alkaline (OL-SA) waters. There was a slight decrease observed for the
saline hyper alkaline water. The pH of bentonite samples decreased considerably in case
of the fresh and saline alkaline (OL-SA) waters, but the pH for the saline hyper alkaline
water was maintained.
39
5
SOLID PHASES
The initial and final solids received from the experiments were characterised in various
ways. The main target was to clarify how various phases react as a result of saline
alkaline or hyper alkaline attack. The studied solids, bentonite and crushed crystalline
rock, are anticipated components in the repository tunnel backfill, but only bentonite is
planned for usage as a buffer around the waste canisters. The essential remarks on initial
and final bentonite, and crushed rock are presented in the following. The more detailed
considerations and interpretations of the initial and final solid phases are presented in
Appendices 3 and 4.
5.1
MX-80 bentonite2
By comparing the published experimental results and the compiled
composition/property tables of the Wyoming MX-80 bentonite (e.g. Wieland et. al.
1994, Bruno et al. 1999, Muurinen and Lehikoinen 1999, Huertas et al. 2000, Bradbury
and Baeyens 2002) it is evident that the composition of MX-80 bentonite varies in a
moderate range. Table 5-1 represents the mineralogical variation in accordance with the
compilation of Bruno et al. (1999). Compared to the recent composition tabulations of
MX-80 bentonite by Bradbury and Baeyens (2002), Table 5-1 contains only minor
differences. Bradbury and Baeyens (2002) report smaller amount kaolinite and feldspar,
and more quartz than Bruno et al. (1999). They also indicate a trace of mica in bentonite
while Table 5-1 specifies this phase as illite. Interestingly, Bradbury and Baeyens
(2002) specify both calcite (0.7 wt%) and siderite (0.7 wt%) from MX-80. However,
Table 5-1 assumes that only the carbonate present in MX-80 bentonite is calcite (1.4
wt%).
The cation exchange capacity (CEC) for bentonite is around 787 meq/kg (Bradbury and
Baeyens, 2003). The initial cation occupancy within the exchange sites are presented in
Table 5-1. The specific surface area in MX-80 bentonite available for surface
complexation is around 31.5 m2/g (Wieland et al., 1994; Bradbury and Baeyens, 2002;
Wersin, 2003). In accordance with Wieland et al. (1994), the total BET surface area
(31.5 m2/g) comprises of basal planes of montmorillonite platelets (28.5 m2/g) and
platelet edges (3.0 m2/g).
The single sited surface complexation model presented in Table 5-1 is simplified. It
does not take into account the aspect that the basal planes and the clay platelet edges are
usually charged differently in surface complexation. Recently, Bradbury and Baeyens
(1997) introduced their detailed mechanistic surface complexation model for Namontmorillonite that considers three different surface sites available for complexation.
Of these sites, the significance of the strongly bound site ({SsOH) is negligible for most
studies. However, at moderate pH the two weak protolysis sites imitate rather well the
reality. For example at pH of 7, the first weak site ({Sw1OH) is negatively charged while
2
Note! At the time when this work was performed the results on the characterization of MX-80
performed by Clay Technology (App. 5) were not available.
40
the second weak site ({Sw2OH) is positively charged, but the total net charge of the
surface sites is negative.
According to Table 5-1 one gram of Volclay bentonite contains likely reactive calcite
(14.0 mg), and minor amounts of reactive gypsum (3.0 mg) and pyrite (3.0 mg).
Bentonite contains as well significant amounts of albite (76 mg) and quartz (110 mg)
that are potentially or likely reactive during the attack of alkaline solutions. The
abundant Na-montmorillonite (750 mg) is the major source for cation exchange, and
protonation/deprotonation properties of the MX-80 bentonite.
Table 5-1.
Estimated average mineral composition of the Wyoming MX-80 bentonite.
Mineral
Unit wt g/mol MX-80 ca. wt% a)
Montmorillonite
372
75.0
Illite
388
0.0-4.0
Kaolinite
258
1.0-7.0
Albite
262
5.0-9.0
Quartz
60
10.0
Gypsum
136
0.3
Pyrite
120
0.3
Calcite
100
1.4
b), c)
30
CH2O
c)
58
NaCl
d)
Cation occupancies in the exchange sites
2+
Ca
Mg2+
Na+
K+
e)
Surface site capacities
ŁSwOH
a)
e)
b)
c)
Estimate wt% Estimate mmol/g
75.0
2.02
4.0
0.10
Bruno et al. 1999, Pirhonen 1986, Bradbury and Baeyens 2002,
Wieland et al. 1994
5.1.1
7.6
11.0
0.3
0.3
1.4
0.4
0.29
1.83
0.02
0.03
0.14
0.13
0.001
0.03
0.02
0.67
0.01
0.03
d)
Bradbury and Baeyens 2003,
Mineralogical summary of the bentonite alterations
The detailed mineralogical studies of the bentonite alterations are presented in
Appendix 3. In the batch experiments (Table 5-2) the initial Nax-montmorillonite was
found to alter partially to Nax-beidellite. The degree of conversion is related to the
Na/Ca-ratio of initial solution and pH. The long-term (e.g. 540 days) hyperalkaline
attack produced smectite that gave good resemblance to crystallography of Naxbeidellite.
All batch experiments produced CSH-gel in the solid phase. In the case of solids with
relatively low CaO/SiO2 ratios (C/S < 1.0), the silicate degradation is considered to
produce a CSH-gel structurally analogous to 14Å-tobermorite (Savage et al. 2002,
Kirkpatrick et al. 1997). The gel precipitation was especially strong in the fresh alkaline
experiments. According to Hong and Glasser (1999, 2002) CSH-gel is a significant Nasink especially in the high Na-solute conditions. The other main cations were
considered to be released from the bentonite exchange sites. K is left to final water,
while Mg is assumed to adsorb or precipitate in the CSH-gel (cf. Taubald et al. 2000).
41
Table 5-2. Summary of the bentonite mineralogical observations interpreted from the
batch and flow-through cell experiments. + increase in final bentonite, – decrease in
final bentonite, () inferred but not observed.
Batch Experiments
Fresh Saline
Saline
Alkaline Alkaline Hyperalk.
(OL-SA)
Nax-Montmorillonite
Cax-Montmorillonite
Nax-Beidellite
Gypsum
Albite
Quartz
Halite
Calcite
CSH-gel (Tobermorite?)
NaX
KX
CaX2
MgX2
–
–
–
+
–
(–)
(–)
+
–
–
(–)
+
+
+
+
–
–
––
++
–
––
–
+
+
+
+
–
––
––
+
++
+
–
Flow-through Experiments
Fresh
Saline
Saline
Alkaline
(OL-SA)
–
+
–
–
–
+
+
+
–
––
+
++
+
–
–
(–)
+
+
+
+
–
–
–
In the batch experiments, the main sink for Ca was the CSH-gel and at a minor extent
calcite. Saline alkaline experiments (OL-SA) had highest Ca concentrations in the initial
water, and these were found to precipitate a little more calcite than the other
experiments. Especially in the hyperalkaline case quartz was partially, and albite was
almost completely dissolved. Saline batch experiments precipitated significantly halite
but this was a consequence of final drying of the experimented samples.
In the flow-through cylinder experiments (Table 5-2) the changes in smectite were
found to be diverse. The dilute near-neutral-pH fresh water injection seemed to result
some purification within the cell and within smectite interlayers. The constant releases
of Na+ and silica from the flow-through cell to the outflow water were indications of
this washing and purification. The near-neutral-pH saline water had a relatively low
Na/Ca-ratio. This resulted compositional change in smectite towards Caxmontmorillonite. Otherwise, the alteration effects in saline experiment were similar to
fresh water experiment. Gypsum dissolved and both experiments precipitated calcite.
Due to near-neutral conditions no silicate alteration or dissolution reactions were
expected to occur. This deduction was in concordance with the absence of CSH-gel in
these experiments. The final drying of the saline experiment samples resulted in
precipitation of halite.
The saline alkaline (OL-SA) water interaction within the flow-through cylinders
indicated comparable smectite alteration to the equivalent batch experiments (Table 52). The CSH-gel formed in the cylinders acted as a sink for Ca and silica. The nearneutral-pH experiments released Na while the alkaline experiment adsorbed Na into the
cylinder. Similarly, in the near-neutral-pH saline experiment Mg was left to final water
42
while in the saline alkaline experiment Mg was apparently absorbed by CSH-gel. In
concordance with earlier observations saline alkaline cylinders precipitated calcite (and
halite).
5.2
Crushed rock material
Crushed-rock of the backfill-pattern simulated the material to be excavated from the
planned repository tunnels and shafts. The excavated rock is planned to be crushed and
recycled back to the tunnels and shafts during the closure of the planned repository. In
the collection of the backfill-pattern rock samples the main rock types were weighted as
given in Table 5-3.
Table 5-3.
Weight-percentages of rock types in the crushed rock backfill-pattern.
Mica gneiss
Granite pegmatite
Tonalite
75
20
5
wt-%
wt-%
wt-%
This weighting was estimated to represent well the average Olkiluoto rock composition
in the planned repository volume and should represent relatively well the composition
of the whole Olkiluoto island. The collected rock material was crushed in two steps to
rock powder with a maximum grain size approx. 1.5 mm. In practice, this means that
the majority of the rock powder was more fine-grained than the maximum grain size.
The first crushing step was performed with a jaw crusher and the final powdering step
was carried out with a rotatory crusher.
Both the jaws and the rotatory cylinders have been analysed chemically. In the view of
the ECOCLAY II experiments, it is worth noting that the jaws and the cylinders may
have contaminate the samples with iron and manganese. Mainly the contamination
occurs if random splits break off from the jaws or the cylinders. However, the
occurrence of splits is usually minor and therefore the risk of contamination was not
considered high. Such splits are easily identified from the rock powder especially if the
powder is examined with a magnet. In our case such an examination was not performed.
Based on mineralogical analyses presented in Appendix 4, it is estimated that the
mineralogy of the initial mixture is approximately as presented in Table 5-4. The Kfeldspar in crushed rock was likely microcline, and according to the mineral analyses
the plagioclase feldspar was dominantly oligoclase. Most of the mafic minerals found
were relatively Fe rich (e.g. biotite, chlorite, and garnet), while some contained
significant amounts of Mg (cordierite). The crushed rock assemblage contained a small
amount of sulphides including pyrite, pyrrhotite, molybdenite and galena.
43
Table 5-4. Estimated initial mineral composition (in wt%) for the crushed rock used
in the experiments.
Mineral
Quartz
Oligoclase
Microcline
Biotite
Cordierite
Sillimanite
Muscovite/Sericite
Chlorite/Hornblende
Zircon
Epidote/Saussurite
Carbonate
Apatite
Garnet
Sulphides
5.2.1
Unit wt g/mol
Estimate wt%
Estimate mmol/g
60
266
277
456
614
162
398
619
183
469
100
482
489
120
23.2
19.2
17.1
21.1
8.5
5.4
2.9
1.4
0.3
0.3
0.1
0.1
0.0
0.3
3.87
0.72
0.62
0.46
0.14
0.33
0.07
0.02
0.02
0.01
0.01
0.002
0.001
0.02
Mineralogical summary of the crushed rock alterations
Microcline dissolution as a result of saline hyperalkaline attack seemed to be evident.
Both saline alkaline (OL-SA) and saline hyperalkaline experiments appeared to produce
sericite/illite during the experiments. This is likely a result of microcline alteration. In
the saline hyperalkaline experiments minute plagioclase dissolution was possible. In the
saline alkaline batch experiments (Table 5-5) the relatively high Ca-solute concentration
was suspected to promote production of epidote (i.e. saussurite), and possibly partial
dissolution of plagioclase. The high Na-solute concentrations in the saline experiments
possibly inhibited dissolution of Na-parts of plagioclase. The altered spectra of the
saline alkaline and saline hyperalkaline experiments indicated relatively well the partial
alteration of cordierite. The specification of possible hornblende reactions remained
uncertain due to apparently small mineral concentrations, and frequently overlapping
peaks in the diffraction patterns. However, it was assumed that further hydration of
hornblende was possible and produced more chlorite or chlorite-like minerals on the
reaction product side. This conversion would need Mg2+ that was produced, for
example, by decomposition of cordierite.
All crushed rock batches produced minute amounts of CSH-gel. As in the case of
bentonite experiments, it was judged that the gel-phase was analogous to the structurally
defect 14Å-tobermorite. CSH-gel is an effective sink for solute Ca and silica.
Furthermore, other experimental studies indicate that several other elements, like Na
and Al, are sorbed effectively into CSH-gel (Hong and Glasser 1999, 2002). As a
concluding remark, however, the overall mass-transfers in crushed rock batch
experiments were low.
44
In the flow-through experiments (Table 5-5) minimal changes in the crushed rock were
expected to occur. The reactivity of bentonite is much higher than that of crushed rock.
In the saline alkaline experiment, similar changes were assumed than in the saline
alkaline batch experiment. In the near-neutral-pH experiments the crushed silicates were
expected to be non-reactive. Small amounts of precipitated halite were observed from
the saline flow-through experiments. It was also assumed that the fresh surfaces of
crushed minerals were potential for Na adsorption.
Table 5-5. Summary of the crushed rock mineralogical observations interpreted from
the batch and flow-through cell experiments. + increase in final crushed rock,
- decrease in final crushed rock, () inferred but not observed.
Batch Experiments
Saline
Fresh
Saline
Alkaline Alkaline Hyperalk.
(OL-SA)
Cordierite
Hornblende
Chlorite
Microcline
Sericite/illite
Oligoclase
Saussurite
Halite
CSH-gel (Tobermorite?)
NaX
(–)
(+)
(–)
(+)
(–)
+
+
–
(–)
(+)
(–)
+
–
+
+
+
+
–
(–)
(+)
–
+
–
(+)
+
+
+
Flow-through Experiments
Fresh
Saline
+
+
+
Saline
Alkaline
(OL-SA)
–
(–)
(+)
(–)
+
–
+
+
+
+
45
6
MODELLING
6.1
Inverse modelling of bentonite batch experiments
In the following the fresh alkaline, saline alkaline (OL-SA) and saline hyperalkaline
batch experiments are considered in more detail. Before the inverse calculations, one
forward assumption was made to initial waters.
According to Bradbury & Baeyens (2002), MX-80 bentonite contains small amounts of
organic matter (ca. 0.4 wt%). Since mineralogical observations indicate precipitation of
calcite in all experiments, it was assumed that part of this organic carbon is dissolved in
the initial waters. During weighting and batch preparation, samples are contaminated
with air. Based on porosity of 0.65 (= Vvoid/Vtot), a density estimate of 1.2 g/cm3 of
loose 3.8g bentonite sample, and 0.2 atm partial pressure of O2 in air, it is assumed that
each sample is contaminated with approximately 0.5 mmol of O2. All contaminated O2
is consumed to organic carbon oxidation according to Equation (6-1).
CH2O + O2 = CO2 + H2O
(6-1)
Equation (6-1) indicates that 0.5 mmol of organic carbon is dissolved in the initial
waters that gives ca. 31 mg/l CO32- in the high pH conditions.
In accordance with mineralogical interpretations (cf. Ch. 5.1) it is assumed that all
experiments consume Nax-montmorillonite and produce Nax-beidellite. Based on the
LLNL thermodynamic database delivered with PHREEQC-2 (Parkhurst & Appelo
1999) a simplified form of the smectite conversion could be rewritten as follows:
Na0.33Mg0.33Al1.67Si4O10(OH)2 + 0.66Al3+ = Na0.33Al2.33Si3.67O10(OH)2 + 0.33Mg2+
Na-montmorillonite
Na-beidellite
(6-2)
+ 1.32H+ + 1.68H2O + 0.33H4SiO4
log K = -3.163
According to the equilibrium constant (Eq. 6-2) the thermodynamic equilibrium stays in
the near-neutral conditions eagerly on the left favouring the existence of Naxmontmorillonite. It is apparent that this conversion is not capable to produce enough
protons for pH drop witnessed in final water. However, the high pH conditions should
favour the product side of the equilibrium. Equation (6-2) indicates that there must be
an Al source in the system to make the balance function. Mineralogical studies indicate
that both Na-montmorillonite and albite decomposition can be the sources, and they
follow the thermodynamic equilibria:
Na0.33Mg0.33Al1.67Si4O10(OH)2 + 4H2O + 6H+ = 0.33Mg2+ + 0.33Na+ + 1.67Al3+
Na-montmorillonite
+ 4H4SiO4
log K = 2.484
(6-3)
NaAlSi3O8 + 4H+ + 4H2O = Al3+ + Na+ + 3H4SiO4
(6-4)
Albite
log K = 2.765
46
Both Equations (6-3) and (6-4) produce more Na in the system that goes to CSH-gel
sorption, smectite cation exchange, or it is left to final water. Practically in all
experiments, the produced Mg (cation exchange, mineral dissolution) must be sorbed in
the CSH-gel. Considering the pH drop in the experiments, the consumption of protons
in both Equations (6-3) and (6-4) do not promote the reactions presented. Therefore, the
main producer of protons must be found on the alteration product side of the systems.
According to e.g. Savage et al. (2002) and Kirkpatrick et al. (1997) solids with
relatively low CaO/SiO2 ratios (C/S < 1.0) degrade in high pH environments by
producing calcium-silicate hydrate phase (CSH-gel) analogous to structurally defect
14Å-tobermorite. Based on the LLNL database the formation of tobermorite occurs in
the following manner:
Ca5Si6H21O27.5
14Å-tobermorite
+ 10H+ = 5Ca2+ + 6H4SiO4 + 3.5H2O
(6-5)
log K = 63.845
Equation (6-5) indicates that if there is protons available CSH-gel is highly unstable.
However, in high pH conditions CSH-gel is the important producer of protons that are
consumed to the pH drop and degradation of Na-montmorillonite and albite. According
to Equation (6-5) the production of CSH consumes significantly Ca and silica. Silica is
produced in Equations (6-2), (6-3), and (6-4). According to mineralogical observations,
the dissolution of quartz occurs as well in the saline hyperalkaline experiments.
Consideration of Ca and silica in Equation (6-5) leads to following conclusion. The
availability of Ca affects significantly to which level the final pH drops. Higher amounts
of Ca lead to larger precipitation of CSH-gel, and drop of pH. Since the cation exchange
capacity is a limited source of Ca, the most significant factor, affecting to the final pH
reached, is the concentration of Ca in the initial water. In the view of Al mass balance, it
is worth to note that the only currently considered sink for Al is in the conversion of
Nax-montmorillonite to Nax-beidellite (Eq. 6-2). However, several studies (e.g. Hong
and Glasser 2002, Kalinichev and Kirkpatrick 2002) confirm that Al can be an essential
part of gel precipitated in the high pH systems.
6.1.1
Fresh alkaline experiments
The results of calculations with fresh alkaline experiments are presented in Table 6-1.
The mineralogical interpretations did not support dissolution of albite and quartz in the
experiments. Hence, these minerals have not been taken into account in the calculations.
The Na/Ca equivalent ratio in the initial water is around 3/1.
The studied cases (6, 30, 180, and 540 days) indicate strong fractionation of Na and Mg
into the exchange phase (Table 6-1) because there is no other sink for these elements.
This exchange leads to an unrealistic contribution of Ca from the exchange phase. The
total amount of exchange sites in the initial 3.8 g of bentonite is approximately 3.0
mmol, and at maximum, only about 0.1 mmol of Ca can be extracted from this source
(cf. Table 5-1). It seems evident that the bentonite exchange sites cannot receive all the
47
Na and Mg available but an alternative sink for these elements has to occur in the
experiment as well.
According to Hong & Glasser (1999), there should be Na-sorption into the CSH-gel.
However, sorption estimates into the CSH-gel contain several sources of uncertainties.
If the precipitated CSH has a CaO/SiO2 ratio about 0.85 (i.e. 14Å-tobermorite), then
based on distribution ratios, a Na-concentration around 50 mmol/L in solution would
indicate Na-sorption about 0.25 mmol/g into CSH (Hong & Glasser 1999). However, no
exact laboratory estimates are available of the amount of CSH-gel formed during the
experiments. There is only a visual approximation that the volume of "solid" phase is
over doubled with CSH-gel production in the fresh alkaline experiments. Nevertheless,
the sorption into gel is a potential sink for several cations.
The sources of Ca are limited into few in the calculations, but it is needed in the CSHgel formation. The almost only source of Ca is the initial solution. Although not taken
into account in the Nax-montmorillonite dissolution (cf. Eq. 6-3) the experimented
montmorillonite contains also traces of Ca (cf. App. 3, Ch. A3.1). It can be assumed as
well that if plagioclase is dissolved, it contains also traces of Ca, though named as
albite. Dissolution reactions of silicates are supported by high silica concentrations in
the final waters, and by Al-contaminants found in early final waters (see footnotes of
Table 6-1). Any further Ca is bound to originate from the cation exchange.
Unfortunately, the inverse calculations remain incomplete. The method cannot handle
multiple independent sources and sinks for same elements. Although, observations did
not support albite or quartz dissolution in the experiments, the dissolution of both seems
possible. Similarly, the CSH-gel is bound to be significant "non-stoichiometric" sink for
e.g. Na in the experiments (i.e. nothing has to come out as a return), but this cannot be
handled in the calculations.
48
Table 6-1. Initial and final water compositions (per 1kg water) from fresh-alkaline
batch experiments presented together with calculated mole-transfers for selected
mineral phases in 3.8g of MX-80 bentonite. pH-values were adjusted to achieve water
charge balance for initial and final waters. Inverse calculations assume 5% analytical
imprecision in elemental concentrations unless otherwise noted. Negative value
indicates a sink (to solid phase) and positive value a source (from solid phase).
Fresh Alkaline
pH
Al
C
Ca
Cl
K
Mg
Na
SO4
Si
Initial
0 days
12.5
mg/l
0.1
6.4
329
43
0.3
0.1
1 160
0.1
0.2
Halite
Gypsum
Nax-Montmorillonite
Nax-Beidellite
14Å-Tobermorite
Calcite
NaX
KX
CaX2
MgX2
CE (mmol/3.8g)
1)
2)
6.1.2
6 days
11.6
mg/l
1)
0.1
0.01
51
57
13
115
585
296
2070
30 days
11.5
mg/l
2)
0.1
0.01
24
48
8.7
55
682
334
1070
180 days
11.4
mg/l
0.1
0.01
4.2
72
8.2
0.1
737
365
453
540 days
11.2
mg/l
0.1
0.01
6.5
415
7.8
0.1
728
379
230
mmol/3.8g mmol/3.8g mmol/3.8g mmol/3.8g
0.02
0.00
0.03
0.40
0.12
0.13
0.14
0.15
3.93
2.51
1.71
1.63
-2.82
-1.80
-1.22
-1.17
-0.43
-0.33
-0.29
-0.32
-0.02
-0.02
-0.02
-0.02
-1.34
-1.03
-0.89
-1.27
0.01
0.01
0.01
0.01
1.78
1.25
1.00
1.17
-1.12
-0.74
-0.56
-0.54
3.57
2.51
2.02
2.34
Original value 680 mg/L - colloidal infiltration
Original value 260 mg/L - colloidal infiltration
Saline alkaline experiments
Calculation results for the saline alkaline (OL-SA) experiments are presented in Table
6-2. The results are quite similar compared to the fresh alkaline cases. A slightly smaller
amount of smectite goes through the montmorillonite–beidellite conversion, but
approximately same amount of CSH-gel is precipitated. The modelling does not assume
albite or quartz dissolution, though mineralogical studies indicated minor reactions. The
equivalent Na/Ca ratio in the initial water is about 10/1.
Similarly to the fresh alkaline cases, the inverse cation exchange calculations do not
succeed correctly. The major reason is the missing additional sink for Na as pointed out
49
in the fresh alkaline studies. Because of the lack of separate cation sorption into CSHgel, calculations recycle too high amounts of cations in the exchange sites that are
supposed to present the sites of montmorillonite only.
Table 6-2. Initial and final water compositions (per 1kg water) from saline-alkaline
(OL-SA) batch experiments presented together with calculated mole-transfers for
selected mineral phases in 3.8g of MX-80 bentonite. pH-values were adjusted to achieve
water charge balance for initial and final waters unless noted otherwise. Inverse
calculations assume 5% analytical imprecision in elemental concentrations unless
noted otherwise. Negative value indicates a sink (to solid phase) and positive value a
source (from solid phase).
Saline Alkaline (OL-SA)
pH
Al
C
Ca
Cl
K
Mg
Na
SO4
Si
Initial
0 days
12.5
mg/l
0.1
6.4
678
14 400
1.0
0.1
9 770
1.0
1.2
Halite
Gypsum
Nax-Montmorillonite
Nax-Beidellite
14Å-Tobermorite
Calcite
NaX
KX
CaX2
MgX2
CE (mmol/3.8g)
1)
2)
6 days
10.8
mg/l
0.4
0.01
166
16 400
46
0.1
2)
8 223
293
38
30 days
10.6
mg/l
0.1
0.01
158
2)
15 100
41
0.1
9 310
302
47
180 days
10.3
mg/l
0.1
1)
0.01
133
2)
14 650
42
0.1
9 633
325
59
540 days
10.2
mg/l
0.1
0.01
246
2)
14 300
21
0.1
9 017
317
44
mmol/3.8g mmol/3.8g mmol/3.8g mmol/3.8g
2.18
0.00
0.00
0.00
0.12
0.12
0.13
0.13
1.32
1.33
1.35
1.34
-0.94
-0.96
-0.97
-0.96
-0.29
-0.29
-0.30
-0.30
-0.02
-0.02
-0.02
-0.02
-0.90
-0.88
-0.82
-1.05
0.04
0.04
0.04
0.02
0.86
0.86
0.84
0.96
-0.43
-0.44
-0.45
-0.44
1.77
1.76
1.71
1.93
10% analytical imprecision accepted in the elemental concentration
During calculation the value were adjusted to achieve water charge balance
The sources of silica (needed for CSH-gel) are the Nax-montmorillonite/Nax-beidellite
conversion (Eq. 6-2) and the dissolution of Nax-montmorillonite (6-3). The other
potential sources of silica are omitted because of the computational limitations of the
inverse method. It is worth to note that the initial Ca-concentration in the saline alkaline
solution (Table 6-2) is double higher than in the initial fresh alkaline solution (Table
6-1). Consequently, the pH drop is larger in the final saline alkaline solutions than in the
final fresh alkaline solutions.
The Cl concentration in the final water, after the 6 days of experiment, must be brought
out separately (Table 6-1). The high 16 400 mg/L Cl-concentration leads to
50
considerable dissolution of halite from bentonite. However, Table 5-1 (in Ch. 5)
indicates that the 3.8 gram sample of bentonite should contain halite only about 0.004
mmol. The experimented final water composition may indicate significant heterogeneity
in halite distribution in bentonite (at "gram" scale) or it may point to some analytical
problems.
6.1.3
Saline hyperalkaline experiments
Results for the saline hyperalkaline experiments are presented in Table 6-3. The
mineralogical interpretations indicated that a major part of albite is dissolved in the
experiments and quartz dissolution is significant as well. Therefore, these reactions have
been taken into account in the calculations. In the calculations these additions have to be
made with the cost of fixing the smectite conversion (Eq. 6-2). The fixing is calculated
as follows. All albite (Eq. 6-4) is assumed to dissolve in the system (cf. Table 5-1, the
3.8 gram sample gives about 1.10 mmol albite). All Al produced is consumed to
smectite conversion. This means an alteration of 1.66 mmol Nax-montmorillonite to
Nax-beidellite (cf. Eq. 6-2), and no additional Nax-montmorillonite is dissolved. The
total initial reserve of Nax-montmorillonite is approximately 7.7 mmol (cf. Table 5-1).
Practically all Na produced in the albite dissolution is used to satisfy the Na
concentration levels in the final waters. Noteworthy, quartz dissolution in addition to
other silica sources is needed to satisfy the high silica levels in final waters.
The calculations assume that the cation exchange sites in bentonite can be emptied from
Ca, and all released Ca shall be consumed for CSH-gel. However, in the normal cases (6
and 30 days, Table 6-2) it turns out that the CSH precipitation reduces only the initial
solute Ca concentrations. The exchange sites are used for production of slightly elevated
K concentrations in the final waters. In real, it is likely that the high Na/Ca equivalent
ratio (1 000/1) extracts Ca from the exchange sites. In the 6- and 30-day cases, the
amount of produced gel is small compared to earlier modelling attempts. This is in a
loose concordance with the observation that the saline hyperalkaline experiments
produced perhaps the least amount of CSH-gel in the experiment series.
The calculations for 180- and 540-day experiments (Table 6-3) indicate abnormal
exchange of cations. In the view of the 180-days case, the problem is the high final
concentration of Cl. In order to meet the concentration the model dissolves significantly
halite (cf. Table 6-1), and this leads to too high Na concentrations. The excess of Na is
put to cation exchange, which results a pulse of Ca in the solution, and consequently
enhanced precipitation of CSH-gel. Considering the 540-day case, the final Na solute
concentration is so low that extensive amount of the initial Na has to be removed from
the solution with the cation exchange manipulation. Similarly to the earlier calculations,
the modelling cannot take into account an additional sink for Na. Inferred from the
study of Hong and Glasser (1999) the adsorption of Na into CSH-gel should be
significant with the initial Na concentrations of 790 mmol/L. With this high
concentration, small changes in gel precipitation may have large effects to final solution
composition.
As a final point, the current calculations assumed no dissolution of smectite. The
smectite conversion reaction used all Al contributed into solution. However, a recent
51
study of Hong and Glasser (2002) indicate that the availability of Al makes the
precipitation of CASH-gels possible.
Table 6-3. Initial and final water compositions (per 1kg water) from salinehyperalkaline batch experiments presented together with calculated mole-transfers for
selected mineral phases in 3.8g of MX-80 bentonite. pH-values were adjusted to achieve
water charge balance for initial and final waters. Inverse calculations assume 5%
analytical imprecision in elemental concentrations unless noted otherwise. Negative
value indicates a sink (to solid phase) and positive value a source (from solid phase)
Saline Hyperalkaline
pH
Al
C
Ca
Cl
K
Mg
Na
SO4
Si
Initial
0 days
13.5
mg/l
0.2
6.4
13
13 700
2.0
0.1
17 710
1.0
7.0
Halite
Quartz
Gypsum
Albite
Nax-Montmorillonite
Nax-Beidellite
14Å-Tobermorite
Calcite
NaX
KX
CaX2
MgX2
CE (mmol/3.8g)
1)
6.2
6 days
13.5
mg/l
0.2
0.01
0.3
13 900
38
0.1
18 480
304
981
30 days
13.4
mg/l
0.2
1)
0.01
0.5
14 300
27
0.2
18 740
321
1220
180 days
12.8
mg/l
0.3
1)
0.01
0.7
15 750
46
0.1
17 560
300
1970
540 days
12.9
mg/l
0.2
0.01
0.1
13 800
21
0.1
16 640
310
2350
mmol/3.8g mmol/3.8g mmol/3.8g mmol/3.8g
0.00
0.00
2.28
0.00
1.50
1.84
4.38
4.59
0.12
0.13
0.12
0.13
1.10
1.10
1.10
1.10
1.66
1.66
1.66
1.66
-1.66
-1.66
-1.66
-1.66
-0.02
-0.02
-0.27
-0.22
-0.02
-0.02
-0.02
-0.02
-0.04
-0.02
-2.53
-1.98
0.04
0.02
0.04
0.02
0.00
0.00
1.24
0.98
0.00
0.00
0.00
0.00
0.04
0.02
2.53
1.98
10% analytical imprecision accepted in the elemental concentration
Inverse modelling of crushed rock batch experiments
Among the potential reactions, occurring in crushed rock batch experiments, is the
consumption of microcline and possibly partial alteration to kaolinite or sericite/illite.
Based on the LLNL thermodynamic database delivered with PHREEQC-2 (Parkhurst &
Appelo 1999) the mineralogical conversions from microcline can be rewritten as
follows:
52
2KAlSi3O8 + 2H+ + 9H2O = Al2Si5O5(OH)4 + 2K+ + 4H4SiO4
Microcline
Kaolinite
(6-6)
log K = -7.99
3KAlSi3O8 + 2H+ + 3H2O = KAl3Si3O10(OH)2 + 2K+ + 6H4SiO4
Microcline
Muscovite/Sericite
(6-7)
log K = -14.4
The equilibrium constants (Eqs. 6-6 and 6-7) indicate that the thermodynamic
equilibrium stays eagerly on side of microcline. Moreover, in the highly alkaline
environment these reactions attempt to consume almost extinct protons. The equilibrium
presented in Equation (6-7) is likely conservative because it is based on the muscovite
half-reaction, while the more probable alteration product is the less crystalline
sericite/illite.
Considering plagioclase feldspar, the mineralogical evidences of oligoclase alteration
and breakdown are not distinct in most cases. The Ca-part (anorthite) of oligoclase
perhaps reacts partially in the hyperalkaline experiments leading to production of
saussurite. Equation (6-8) is a simplification of this alteration. The Ca-part in oligoclase
solid solution is approximated with anorthite, and the saussurite product is described
with clinozoisite.
3CaAl2Si2O8 + Ca2+ + 2H2O = 2CaAl3Si3O12(OH) + 2H+
(6-8)
Anorthite
Clinozoisite/Saussurite
log K = -6.78
The Ca-part of plagioclase solid solution is not a pure phase and the equilibrium
constant (Eq. 6-8) implies that reaction favours the stability of anorthite. Experimental
final waters indicate a distinct sink for Ca among the solids, and drop of pH during the
experiments. Due to inverse computational limitations, however, it was assumed that the
reaction (Eq. 6-8) is not among the dominant reactions in the present experiments.
The analytical results of final waters
systems. Furthermore, all experiments
Similarly, some long-lasting fresh
contribution into the final water. It
decomposes with reactions:
indicate that there is a source of Al3+ in the
indicate increase of K during the experiments.
alkaline experiments seem to indicate Na
is assumed that a part of feldspars simply
KAlSi3O8 + 4H+ + 4H2O = Al3+ + K+ + 3H4SiO4
Microcline
(6-9)
log K = -0.28
NaAlSi3O8 + 4H+ + 4H2O = Al3+ + Na+ + 3H4SiO4
Albite
(6-10)
log K = 2.76
Both reactions (Eqs. 6-9 and 6-10) consume protons and attempt to raise pH. According
to Equation (6-10), albite decomposition is not highly favoured in the high-pH and
high-Na conditions.
According to Ogiermann (2002), cordierite alteration (pinitisation) at low temperatures
produces poorly crystalline phases with high water content. He suggests that these
phases should be phyllosilicate mixtures containing e.g. smectites and
pyrophyllite/kaolinite. The following balance assumes that cordierite decomposes to
kaolinite:
53
Mg2Al4Si5O18:H2O + 4H+ + 3H2O = 2Al2Si2O5(OH)4 + 2Mg2+ + H4SiO4
Cordierite (hydrous)
Kaolinite
(6-11)
According to Ogiermann (2002), the actual resulting phyllosilicate mixtures are Cabearing. This indicates that the alteration of initially Ca-free cordierite may form a
partial sink for Ca during the experiments. However, due to limitations of inverse
modelling, it is currently assumed that the only true sink for Ca is the CSH-gel as in the
case of bentonite modelling (c.f. Ch. 6.1, Eq. 6-5).
There is a possibility that certain experiments may consume hornblende that leads to a
possibility of chlorite production, or some hydrated analogue of chlorite. The following
mass-balance between Mg-hornblende and Mg-chlorite can be assumed possible:
Ca2[Mg4Al][Si7Al]O22(OH)2 + Mg2+ + 2H+ + 2H2O = Mg5Al2Si3O10(OH)8 +
Mg-hornblende
Mg-chlorite
(6-12)
2Ca2+ + 4H4SiO4
Equation (6-12) is simplified. It does not include Fe3+ that usually occurs both in
hornblende and in chlorite substituting Al3+. Furthermore, in the Olkiluoto hornblende
Ca2+ is partially substituted with Na+ that, in turn, causes additional charge balancing
and more complexity in the rest of the crystal structure. Equation (6-12) needs dissolved
Mg in solution. Because initial waters do not contain Mg, it must be produced e.g. with
cordierite alteration. Because mineralogical studies did not indicate direct evidence of
hornblende alteration, hornblende is omitted in the following calculations, and the Mg
mass-balances have been handled with cordierite - kaolinite/brucite reactions.
Final water results of the experiments indicate a sink for Na among reactive solid
phases. In all initial water types, Na is the dominant cation. The following calculations
assume that Na binds eagerly to new surface edge sites of recently crushed rock, and it
is adsorbed into the precipitated CSH-gel as well. Otherwise, it is assumed that cation
exchange capacity within solid phases is minimal compared to bentonite studies, and are
omitted from the calculations. The separate Na-exchange site, simulating the surface
edge sites and CSH-gel, is arranged as follows.
Na+ + W- = NaW
H+ + W- = HW
(6-13)
Equations (6-13) mean that in calculations Na+ is exchanged with H+ from the edge
sites. The manipulation corresponds to the situation where equal amount of NaOH is
taken away from the reacting water. pH is lowered and Na+ balance is handled. This
approach were considered justified, because in the most cases pH values are
manipulated anyway during finding charge balances for waters utilised in the
calculations.
Most of the degradation reactions presented above depend heavily on the availability of
protons. The bentonite studies (Ch. 4) proved that the formation of CSH-gel, even at
small extent, is the probable engine in the systems. Contrary to the bentonite
experiments, reaction rates in the crushed rock experiments are slow. Overall, smaller
reactive surface areas hinder fast propagation of degradation reactions of silicates. This
54
means lower availability of dissolved silica for CSH-gel production, and this in turn
means lower rates for pH drop in the experimental systems.
6.2.1
Fresh alkaline experiments
The calculation results for fresh alkaline experiments are presented in Table 6-4. All
waters used in the calculations were charge balanced by adjusting pH values from the
measured ones. In all cases, however, adjustments were minor. In the calculations, the
most distinct and difficult feature is the abrupt drop of Na concentrations in the shortterm experiments. Na concentrations drop to 1/3 of its initial value in 6 days, though
there is rebound in the long-term samples. Three of the four experiments (Table 6-4)
indicate significant adsorption of Na in the solid phases. As indicated above (Eq. 6-13),
surface complexation has been assumed as principal Na binding process.
The calculations suggest that the dissolution amount of microcline should increase
gradually with time. Contemporaneously, an increasing amount of kaolinite is
precipitated. This reaction couple (Eq. 6-6) satisfies the gradual increase of K
concentrations in the final water as a function of time. However, Al concentrations grow
to high levels in the long-term final waters. Therefore, also a significant amount of
albite is dissolved in the modelling calculations. It is worth noting, however, that Al
concentrations (tabulated for long-term samples in Table 6-4) are beyond the solubility
limit of Al (e.g. Richardson and McSween 1989). At the pH of 12.5, the solubility limit
for Al is around 6.5 mg/L. The anomalous Al concentrations met in the samples are
likely partially results of infiltration of aluminous colloids into solutions during the
sample reparation.
The formation of CSH-gel (tobermorite) is coupled with the drop of Ca concentrations
in the final waters. The slow rate in the drop of Ca concentrations indicates that the gel
formation process is relatively slow in the crystalline rock experiments. This must be a
consequence of the slow reaction rates of silica producers (dissolution of feldspars), as
seen in the slow increase rate of K and silicon concentrations in the final waters.
The drop in pH should correlate with the formation of CSH-gel. However, this feature
cannot be verified in the current experiments. Apparently, the reaction amounts within
solids are too small to cause effective changes in the pH values.
55
Table 6-4. Initial and final water compositions (per 1kg water) from fresh alkaline
batch experiments presented together with calculated mole-transfers for selected
mineral phases in 3.8g of crushed rock. pH-values were adjusted to achieve water
charge balance for initial and final waters. Inverse calculations assume 5% analytical
imprecision in elemental concentrations. Negative value indicates a sink (to solid
phase) and positive value a source (from solid phase).
Fresh Alkaline
pH
Al
C
Ca
Cl
K
Mg
Na
SO4
Si
Initial
0 days
12.5
mg/l
0.1
0.01
329
43
0.30
0.1
1160
0.1
0.2
Halite
K-Feldspar
Sericite/illite
Albite
Cordierite
Kaolinite
14Å-Tobermorite
Brucite
NaW
HW
6.2.2
6 days
12.3
mg/l
4.3
0.01
296
56
11
0.1
385
0.3
1.8
30 days
12.4
mg/l
6.4
0.01
257
49.5
16.3
0.1
633
0.5
1.4
180 days
12.6
mg/l
39.5
0.01
9.2
47.1
53.4
0.1
1170
0.5
13.0
540 days
12.4
mg/l
27.5
0.01
15.0
39.1
55.6
0.1
706
0.5
12.0
mmol/3.8g mmol/3.8g mmol/3.8g mmol/3.8g
0.014
0.007
0.000
0.000
0.010
0.016
0.052
0.054
0.000
0.000
0.000
0.000
0.000
0.022
0.112
0.114
0.000
0.000
0.000
0.000
-0.002
-0.014
-0.054
-0.065
-0.004
-0.014
-0.061
-0.060
0.000
0.000
0.000
0.000
-1.293
-0.898
0.000
-0.862
1.293
0.898
0.000
0.862
Saline alkaline experiments
The results of saline alkaline (OL-SA) experiments are presented in Table 6-5. In
general, the results follow similar constraints as in the fresh alkaline experiments. The
saline alkaline results indicate, however, larger mass-transfers. Microcline dissolves
more eagerly. The precipitation of sericite/illite, instead of kaolinite, seems to explain
better K and silicon concentrations in final waters. The dissolution possibility of albite
is mostly omitted because the initial Na concentration levels are high. Therefore, albite
dissolution does not produce any Al in the final solutions.
In the short-term experiments, pH values of final waters were adjusted to reach the
charge balance for waters. However, for long-term experiments the charge balances
were found by adjusting Cl concentrations. The adjusted Cl concentrations for the 180days and 540-days final waters were 13 500 and 14 000 mg/L, respectively. The reasons
for these exceptions were obvious. In the case of the 180-days case, the pH would drop
56
to an unrealistically low level if the pH-related charge balancing is used. In the view of
the 540-days case, the final low Cl-concentration presented in Table 6-5 would require
relatively large precipitation of halite that is not a likely case in the crushed rock
experiments. The same reasoning should apply to the 30-days sample as well
(precipitates halite). However, in order to minimise the manipulations, this case has
been kept as original analysis indicates.
Compared to the fresh alkaline case (Table 6-4) the pH drop is more clear in the saline
alkaline experiments (Table 6-5). Correspondingly, the precipitation of CSH-gel is more
significant. The conclusion is similar to the bentonite studies. The availability of Ca in
the system affects significantly to the level where pH drops during the experiment. The
higher is the Ca concentration in the initial solution the larger amount of CSH-gel is
potentially able to precipitate. In the crushed rock case, however, the amount of
dissolved silica (available for CSH-gel) limits the pH drop rate. This becomes evident if
saline alkaline experiments with bentonite and crushed rock batches (Tables 6-2 and
6-5) are compared with each other.
Table 6-5. Initial and final water compositions (per 1kg water) from saline alkaline
(OL-SA) batch experiments presented together with calculated mole-transfers for
selected mineral phases in 3.8g of crushed rock. pH-values were adjusted to achieve
water charge balance for initial and final waters unless noted otherwise. Inverse
calculations assume 5% analytical imprecision in elemental concentrations. Negative
value indicates a sink (to solid phase) and positive value a source (from solid phase).
Saline Alkaline (OL-SA)
pH
Al
C
Ca
Cl
K
Mg
Na
SO4
Si
Initial
0 days
12.5
mg/l
0.1
0.01
678
14 400
1.0
0.1
9 770
1.0
1.2
6 days
12.4
mg/l
0.2
0.01
606
14 100
23.5
0.1
10 500
1.0
0.7
30 days
12.5
mg/l
0.6
0.01
392
12 400
31.1
0.1
9 430
1.0
0.8
180 days
12.2
mg/l
15.9
0.01
124
1)
16 700
82.3
0.1
8 810
1.0
5.0
540 days
12.1
mg/l
13.4
0.01
111
1)
10 500
75.4
0.1
9 110
2.2
6.7
mmol/3.8g mmol/3.8g mmol/3.8g mmol/3.8g
Halite
0.000
-2.241
0.000
0.000
K-Feldspar
0.022
0.087
0.278
0.285
Sericite/illite
0.000
-0.057
-0.197
-0.211
Albite
0.000
0.085
0.000
0.000
Cordierite
0.000
0.000
0.084
0.092
Kaolinite
-0.011
0.000
0.000
0.000
14Å-Tobermorite
-0.008
-0.058
-0.110
-0.112
Brucite
0.000
0.000
-0.168
-0.184
NaW
1.470
1.537
-0.201
-0.339
HW
-1.470
-1.537
0.201
0.339
1)
During calculation the value were adjusted to achieve water charge balance
57
Certain contradictions are evident while considering the Na and Cl concentrations in the
final solutions (Table 6-5). In the 6-days case, the high final concentration of Na
indicates a clear Na source but the Cl concentration precludes that the source could be
halite. In the 30-days experiment, the low final Cl concentration indicates ostensible
precipitation of halite, and consequently a Na source is needed. The Cl concentrations in
the later-date samples are manipulated, and then the direction of Na sorption is in
accordance with the earlier reasoning (Eq. 6-13). There is something abnormal in the
systems as pointed out as well in the saline-alkaline bentonite experiments (cf. Ch.
6.1.2)
As a final note, the Al solute concentrations in the 180-day and 540-day cases are too
high for waters with pH around ~12.2.
6.2.3
Saline hyperalkaline experiments
The results of calculations with saline hyperalkaline experiments are presented in Table
6-6. The calculations indicate small microcline dissolution and the amount gradually
increases with time. This is a consequence of gradual increase of K concentration in
final waters. At the same time, small amounts of kaolinite tend to precipitate into solid
phase. The degree of kaolinite precipitation depends largely on the simultaneous
availability of Al and silica during calculation. In the view of final water compositions,
it is worth noting that a large analytical imprecision (50%) has been assigned to all final
Al concentrations. This is in loose concordance with the fact that the Al solubility
should be around 7.0–10.0 mg/L at the pH levels around 12.6 – 12.9 (Richardson &
McSween 1989). In the 6-day case, a large imprecision (50%) has been assigned to
silicon concentration as well. The result for the 6-day case cannot be found unless the
silicon concentration is almost doubled (60 mg/L) and Al concentration is halved
(9.8 mg/L) during the inverse calculation.
In Table 6-6, the analytical results indicate again a strong relation between the
availability of Ca and pH drop. The Ca level in the initial hyperalkaline solution is
relatively low (Table 6-6). Consequently, the calculated models precipitate small
amounts of CSH-gel (tobermorite) during the experiments. Because the pH drops during
the experiments were small, no additional sources Ca (e.g. altering or dissolving
hornblende – cf. Eq. 6-12) were assumed in the calculations.
There are certain contradictions in the Na/Cl ratios in the long-term experiments. The
drop in Cl solute concentrations in the 180-day and 540-day cases indicates a sink for
Cl. Only halite precipitation can be assumed to act as such. However, such precipitation
is improbable without solution evaporation, and surpassing the solubility limit of halite.
At the same time, Na concentrations remain at an approximately constant level in all
waters indicating that no significant sink for Na is present. In the 540-day case, the
precipitation of halite leads to ostensible recycling of Na from the solid phase into
solution.
As a concluding remark, mass transfers within hyperalkaline experiments seem to be
smaller than in saline alkaline (OL-SA) experiments. Apparently, the high pH gives the
58
potential for a solution to be aggressive, but the availability of both Ca and silica in
solution really launches the CSH engine that feeds protons to other silicate reactions and
neutralises alkaline conditions.
Table 6-6. Initial and final water compositions (per 1kg water) from salinehyperalkaline batch experiments presented together with calculated mole-transfers for
selected mineral phases in 3.8g of crushed rock. pH-values were adjusted to achieve
water charge balance for initial and final waters. Inverse calculations assume 5%
analytical imprecision in elemental concentrations unless noted otherwise. Negative
value indicates a sink (to solid phase) and positive value a source (from solid phase).
Saline Hyperalkaline
pH
Al
C
Ca
Cl
K
Mg
Na
SO4
Si
1)
6.3
Initial
0 days
13.5
mg/l
0.2
0.01
12.8
13 700
2.0
0.1
17 700
1.0
7.0
6 days
13.5
mg/l
1)
19.0
0.01
3.6
13 700
36.4
0.1
18 900
1.0
1)
38.7
30 days
12.6
mg/l
1)
41.2
0.01
1.4
14 100
39.1
0.1
18 200
1.0
65.3
180 days
12.9
mg/l
1)
95.6
0.01
0.6
11 000
45.1
0.1
17 800
7.0
141
540 days
13.1
mg/l
1)
91.8
0.01
0.4
11 500
67.8
0.1
17 600
1.0
155
mmol/3.8g mmol/3.8g mmol/3.8g mmol/3.8g
Halite
0.000
0.000
-2.950
-2.464
K-Feldspar
0.034
0.035
0.043
0.070
Sericite/illite
0.000
0.000
0.000
0.000
Albite
0.000
0.000
0.000
0.000
Cordierite
0.000
0.000
0.014
0.000
Kaolinite
-0.010
-0.003
0.000
0.000
14Å-Tobermorite
-0.002
-0.002
-0.002
-0.002
Brucite
0.000
0.000
-0.029
0.000
NaW
0.000
0.000
0.000
2.343
HW
0.000
0.000
0.000
-2.343
50% analytical imprecision accepted in the elemental concentration
Forward modelling of batch experiments
The solid-to-solution ratio in the experiments was 1:10 (3.8 g of MX-80 in 38 ml of
solution). Three different aqueous solutions, the chemical compositions of which are
given in Table 6-7, were used. The characteristics of the thermodynamic model and of
MX-80 bentonite used for the calculations are listed in Table 6-8. Chemical inertness of
the montmorillonite component of MX-80 was assumed throughout. Furthermore, the
kaolinite and illite contained by MX-80 were deemed unreactive (Vuorinen et al.,
2003).
59
Table 6-7. Chemical compositions of the aqueous solutions (in mmol/L).
Component
Fresh alkaline
Na
Ca
Cl
pH
50.3
8.2
1.2
12.5
Saline alkaline
(OL-SA)
425.0
16.9
406.2
12.5
Saline hyperalkaline
770.3
0.3
386.4
13.5
Table 6-8. Parameters of the thermodynamic models used in the study (from Wersin
(2003) unless noted otherwise).
Parameter
Cation exchangea
logK
logK
logK
logK
CECb
Initial NaZb
Initial CaZ2b
Initial MgZ2b
Initial KZb
Surface complexationc
logK
logK
logK
logK
{!XOH}tot
{!YOH}tot
Surface area
Unit/reaction
Value
H+ + NaZ œ HX + Na+
K+ + NaZ œ KX + Na+
Ca2+ + 2NaZ œ CaX2 + 2Na+
Mg2+ + 2NaZ œ MgX2 + 2Na+
(meq/g)
(eq. fraction)
(eq. fraction)
(eq. fraction)
(eq. fraction)
0
0.60
0.41
0.34
0.687
0.756
0.165
0.065
0.014
!XOH + H+ œ !XOH2+
!XOH œ !XO– + H+
!YOH + H+ œ !YOH2+
!YOH œ !YO– + H+
(meq/g)
(meq/g)
(m2/g)
4.5
-7.9
6.0
-10.5
0.042
0.040
31.5
Dissolution/precipitation of minor solids
Calcite (CaCO3)
(wt%)
Gypsum (CaSO4·2H2O)
(wt%)
Quartz (SiO2)
(wt%)
Halite (NaCl)
(wt%)
d
Albite (NaAlSi3O8)
(wt%)
Microcline (KAlSi3O8)d
(wt%)
Anorthite (CaAl2Si2O8)d
(wt%)
a
According to the Gaines-Thomas convention.
b
This work.
c
According to the 2-pK diffuse layer model.
d
Calculated from Table 6.2 of Huertas et al. (2000).
1.4
0.405
10–15
0.0079
1.9
0.7
0.9
60
The modelling procedure was constrained by a condition that the equilibrium pH (at
540 d) is fixed at 11.2, 10.2 and 12.9 for the fresh alkaline, saline alkaline and saline
hyper-alkaline solutions, respectively. No adjustable parameters were applied in the
modelling.
The equilibrium constants for the silicate mineral reactions were taken from the EQ3/6
database, data0.alt.V8.R6 (Wolery, 1992). The calculations were carried out using the
Visual MINTEQ v. 2.15a software (Gustafsson, 2003). For cation-exchange
computations, the counter-ion accumulation option of Visual MINTEQ was used
(Dzombak and Hudson, 1995).
6.3.1
Fresh alkaline experiment
The calculated sorption of sodium and calcium on reacted MX-80 bentonite is compared
with experimental results in Table 6-9. The model predictions are separated into two
distinctly different contributions to sorption: the first (Ads.) from cation exchange and
the second (Prec.) from precipitation. The sum of these components should be taken as
the total sorption. For both sodium and calcium, the sorption is well explained by the
model. However, unlike for sodium, the bulk of calcium sorption occurs via
precipitation and not via cation-exchange. The cation occupancies on the cationexchange complex are presented in Table 6-10. It can be seen that the model
overestimates the cation-exchange of sodium but underestimates the exchange of other
major cations. The comparison is, however, somewhat hampered by the apparent
increase in the cation exchange capacity as a result of the overall reaction of the system
(see footnote of Table 6-10).
Table 6-9. Sorption of sodium and calcium on reacted MX-80 bentonite in the fresh
alkaline solution (in %).
Sorbate
Experimental
Model
Ads. Prec.
Na
59.5 ± 1.6
61.5 ± 0.3
59.1
1.6
Ca
99.9 ± 5.1
99.9 ± 3.3
5.3
94.6
Table 6-10. Cation occupancies on reacted MX-80 bentonite in the fresh alkaline
solution (in %).
Cation
Experimental
Model
Na
K
Ca
Mg
81.6
1.4
16.8
0.2
94.5
0.3
5.2
0.0
Note: The CEC increased from 0.687 meq/g to 0.816 meq/g.
61
The experimental and calculated equilibrium solution phase chemistries are compared in
Table 6-11. The most drastic differences pertain to the concentrations of major cations:
model underestimation for potassium and calcium by a factor of five and overestimation
for sodium by less than 40%.
Table 6-12 lists the equilibrium mineral phases in descending order in their abundances
(on a molal basis). Of the primary minor solids, gypsum, halite and anorthite were
found to dissolve completely. All the secondary minerals formed were silicates
(prehnite, gyrolite and celadonite). As such, these solid phases should be considered as
tentative ones, devoid of critical expert judgement or support from independent
mineralogical investigations, however.
Table 6-11. Solution phase equilibrium concentrations for the fresh alkaline solution
(in mmol/L).
Component
Experimental
Model
K
Cl
Ca
Na
SiO2(aq)
SO4
0.20
11.71
0.16
31.67
3.83
3.95
0.04
1.34
0.03
43.11
2.80
2.35
Table 6-12. Equilibrium mineral phases for the fresh alkaline solution.
Quartz (SiO2)a
Calcite (CaCO3)b
Prehnite (Ca2Al2Si3O10(OH)2)
Gyrolite (Ca2Si3O7(OH)2·1.5H2O)
Celadonite (KMgAlSi4O10(OH)2)
Albite (NaAlSi3O8)c
Microcline (KAlSi3O8)d
Dissolution by a 7%, b 6%, c 76% and d 66%.
6.3.2
Saline alkaline experiment
The sorption of sodium and calcium is fairly well explained by the model (Table 6-13).
Differences in the sorption component contributions stem from arguments similar to the
fresh alkaline system. This time, calculated cation occupancies on reacted MX-80 in
Table 6-14 are rather close to the experimental ones, with a slight overestimation for
sodium and underestimation for other major cations. This was the case despite the fact
that the increase in the CEC was more pronounced than with the fresh alkaline solution
62
(footnote of Table 6-14). The decrease in sorption with ionic strength for sodium (cf.
Tables 6-9 and 6-13) lends support to cation-exchange being the governing sorption
mechanism of sodium on reacted MX-80. No such dependence was found for calcium.
The equilibrium solution phase chemistries are seen to be very close to each other
(Table 6-15).
With regard to the mineral phase transformations, the only notable difference in
comparison to the fresh alkaline system is the disappearance of albite in Table 6-16.
Table 6-13. Sorption of sodium and calcium on reacted MX-80 bentonite in the saline
alkaline solution (in %).
Model
Sorbate
Experimental
Ads.
Prec.
Na
11.5 ± 1.0
9.91 ± 1.88
13.0
0.0
Ca
97.6 ± 4.9
97.6 ± 2.2
6.4
78.8
Table 6-14. Cation occupancies on reacted MX-80 bentonite in the saline alkaline
solution (in %).
Cation
Experimental
Model
Na
K
Ca
Mg
87.7
0.9
11.3
0.1
91.7
0.4
7.8
0.0
Note: The CEC increased from 0.687 meq/g to 0.856 meq/g.
Table 6-15. Solution phase equilibrium concentrations for the saline alkaline solution
(in mmol/L).
Component
Experimental
Model
K
Cl
Ca
Na
SiO2(aq)
SO4
0.52
403.35
6.14
392.22
0.73
3.30
0.49
406.31
6.22
421.43
0.39
2.35
63
Table 6-16. Equilibrium mineral phases for the saline alkaline solution.
Quartz (SiO2)a
Calcite (CaCO3)b
Prehnite (Ca2Al2Si3O10(OH)2)
Gyrolite (Ca2Si3O7(OH)2·1.5H2O)
Celadonite (KMgAlSi4O10(OH)2)
Microcline (KAlSi3O8)c
a
b
c
Dissolution by 2%, 1% and 88%.
6.3.3
Saline hyper-alkaline experiment
Tables 6-17 to 6-19 show an excellent match between experimental and model results
for sorption, cation occupancies (despite the doubling of the CEC – see footnote of
Table 6-18) and solution phase chemistry.
The most significant mineral transformations are the complete dissolution of the
primary minor solids and formation of a zeolite (analcime) and silicate phases (Table
6-20).
Table 6-17. Sorption of sodium and calcium on bentonite in the saline hyper-alkaline
solution (in %).
Sorbate
Experimental
Model
Ads. Prec.
Na
8.56 ± 0.49
9.29 ± 0.92
8.2
1.7
Ca
100 ± 2
100 ± 2
0.0
100.0
Table 6-18. Cation occupancies on reacted MX-80 in the saline hyper-alkaline solution
(in %).
Cation
Na
K
Ca
Mg
Experimental
99.5
0.3
0.2
0.0
Model
99.6
0.4
0.0
0.0
Note: The CEC increased from 0.687 meq/g to
1.395 meq/g.
64
Table 6-19. Solution phase equilibrium concentrations for the saline hyper-alkaline
solution (in mmol/L).
Component
K
Cl
Ca
Na
SiO2(aq)
SO4
Experimental
0.54
389.25
<0.002
723.80
39.05
3.23
Model
0.78
386.57
<0.002
747.57
125.48
2.35
Table 6-20. Equilibrium mineral phases for the saline hyper-alkaline solution.
Analcime (Na0.96Al0.96Si2.04O6·3H2O)
Gyrolite (Ca2Si3O7(OH)2·1.5H2O)
Celadonite (KMgAlSi4O10(OH)2)
6.3.4
Conclusions
A simple thermodynamic model developed for montmorillonite was applied to describe
the uptake of sodium and calcium on MX-80 bentonite reacted with a fresh alkaline,
saline alkaline and saline hyper-alkaline solution. The experimentally found decrease in
sorption with ionic strength for sodium indicated cation-exchange to be the governing
sorption mechanism of sodium on reacted MX-80. No such ionic strength dependence
was found for calcium, suggesting the uptake to occur by another mechanism. The
experimental findings were adequately explained by the model, provided that sorption
of calcium takes place predominantly by way of precipitation of calcium-bearing
mineral phases.
Of the minor solids contained by MX-80, quartz, calcite and microcline persisted in the
fresh and saline alkaline solutions. In the fresh solution, albite was predicted to co-exist,
too. In both of these alkaline solutions, the secondary minerals consisted of silicate
phases. The most drastic mineral transformations were predicted to be caused by a
change in chemical conditions from alkaline to hyper-alkaline. According to the model
results, the minor solid assemblage of bentonite was completely destroyed upon reacting
with the hyper-alkaline solution, which resulted in the formation of a zeolite and silicate
phases. At this point, the mineralogical interpretation of the secondary solid phases is
fraught with uncertainties, however.
65
7
SHORT SUMMARY AND MAIN CONCLUSIONS
The experiments performed produced a lot of samples, which all could not be
thoroughly analysed within the framework of this project. This was also reflected in the
interpretations of the results. More insight to the chemical changes occurred in the
experiments might have been gained also from additional modelling, e.g., with coupled
codes. Below a short summary of the experiments, results and main conclusions are
presented.
In the batch experiments the solids, bentonite and crushed rock powder, were treated in
separate batches with three different alkaline solutions (fresh alkaline, saline alkaline
and saline hyperalkaline, Table 4-1). The obtained results gave a better insight to the
alterations of the materials by alkaline attack than the flow-through experiments (Fig.
3-1) where both the crushed rock powder and bentonite were together interacting with
each test solution (fresh, saline and saline alkaline, Table 3-1) in a same experiment.
Besides, interaction of the solids with solutions was more vigorous in the batch
experiments (continuous shaking) than in the flow-through experiments and only one of
the test solutions in the two types of experiments was the same, namely the saline
alkaline solution (OL-SA) with a pH value of 12.5.
For assessing the alterations occurring in the batch experiments, after each experimental
time (6d, 30d, 180d and 540d) the solution and solid was separated by
centrifugation/filtration. The solutions were analysed for major components (Tables
A2-7, -8 and -9, App. 2) and the solids were characterised. The results gave basis for
modelling of the processes occurred, but also indications of the changes in the solution
chemistries brought about by either the crushed rock or bentonite, which results were
needed in the case of the saline alkaline solution (OL-SA) to succour interpreting some
of the solution results in the flow-through experiments.
In addition to the batch experiments for assessing the alterations in alkaline
environments, another two sets of batch experiments were performed in order to assess
sorption on crushed rock and bentonite. One set of samples was spiked with 45Ca and
the other set with 22Na. Sorption of these radionuclides was assessed on the altered
solids as well as the effect of element concentration on their sorption.
22
x The sorption of
Na on crushed rock was low in all cases studied (Kd
-3
3
(0.02-1.2)˜10 m /kg) (Fig. 4-1) and only a little higher on bentonite (Kd (0.652.1)˜10-3 m3/kg) in the saline alkaline cases, whereas, in the fresh alkaline
experiment high sorption on bentonite was observed (Kd (1.5-2.7)˜10-2 m3/kg) (Fig.
4-2).
45
22
x The sorption of Ca on crushed rock was only somewhat higher than for Na in the
fresh and saline alkaline cases (Kd (0.12-5.7)˜10-3 m3/kg) (Fig. 4-1), whereas in the
saline hyper alkaline experiment sorption was high (Kd (0.81-9.1)˜10-3 m3/kg). 45Ca
sorption on crushed rock increased with longer experimental time, whereas, on
bentonite it was very high in all three alkaline waters (Kd 0.015-100 m3/kg) (Fig.
4-2).
x No effect of the initial Na concentration in the solutions on sorption on crushed rock
was observed, but in the case of bentonite a small increase in the Kd values was
66
observed at the lower concentrations. In case of higher initial Ca concentration a
small increase in sorption on crushed rock was observed, but on bentonite a
decreasing effect of the initial concentration was seen.
In the flow-through experiments two sets of cylinders (three cylinders in each, one for
each feed solution) were included for two different experimental periods, 368d and
560d. The out-flow solutions were continuously collected in small vials and analysed
for major components at three points in time (222d, 368d and 560d) (Table 3-2). The
out-flow solution chemistry reflected changes brought about by both bentonite and
crushed rock and not only either one of the solids. In any case, based on the batch
experiment results, it was concluded that bentonite was the cause for major alterations
in the out-flow solution chemistries in addition to some presumptive processes
(formation of CSH-gel, retention of Mg). Additional information was gained from
determined exchangeable cation distributions in the bentonite samples and from the
analytical results on bentonite porewater (only from the saline alkaline experiment).
x All the results showed distinct trends either with progressing flow-path along the
cylinder interface and/or with increasing experimental time indicating propagation
of each solution attack. Greatest alterations were naturally seen in the saline alkaline
and saline experiments.
x It was concluded that the alkaline attack affected bentonite to some extent
throughout the experimental column. Major alterations were seen at the in-flow end
interface decreasing towards the out-flow end. After completing the experiments
(560d) the pH values of bentonite porewater had increased up to 11 at the in-flow
interface but were around 8 at the out-flow interface. While pH value of the outflow solution had increased to a value around 9.5. By the increasing trend in the outflow solution pH value it was roughly estimated that in order to reach the pH value
of the initial feed solution (12.5) in the out-flow solution the experiment would have
to run for about 10 years.
x Ca and Si behaviour in the analysed samples indicated formation of CSH-phases in
the alkaline case, and Mg was anticipated to participate in some kind of retention
processes inside the column.
x K, SO4 and Si results of the out-flow solutions reflected rather well the involvement
of bentonite in the alterations.
x Salinity prevented swelling of bentonite, as expected.
Characterisation of the alterations of the solid phases indicated that;
x In the batch experiments Nax-montmorillonite was partially altered to Nax-beidellite.
Bentonite interaction produced CSH-gel that was structurally analogous to 14Åtobermorite, and in the case of fresh alkaline experiment the gel production was
especially strong. Minute amounts of CSH-gel precipitated in all crushed rock
batches, as well, and it was judged to be analogous to the structurally defect 14Åtobermorite.
x In the experiments Mg became possibly adsorbed or precipitated in the CSH-gel
with some other elements (e.g. Na and Al).
x In the flow-through experiments the saline alkaline attack caused comparable
smectite alteration with that in the corresponding batch experiment, and the
presence of CSH-gel was confirmed as well. The fresh solution interaction resulted
67
x
x
x
x
in some purification within the smectite layers, whereas in the saline experiment
smectite alteration was towards Cax-montmorillonite.
Minor precipitation of calcite occurred in all bentonite experiments as well as
dissolution of gypsum.
The saline hyperalkaline attack on crushed rock evidently dissolved microcline
resulting in formation of sericite/illite, a likely alteration also seen in the saline
alkaline experiments. In addition partial alteration of cordierite was observed in both
the saline alkaline and hyperalkaline experiments.
Small amounts of precipitated halite with crushed rock were observed in both saline
flow through experiments.
The overall mass-transfers in crushed rock experiments were notably lower than in
the bentonite experiments, as expected. The fresh surfaces of crushed minerals were
assumed to be potential for Na adsorption.
The experimental results were bases in the modelling tasks included in the studies. Both
inverse and forward modelling of the batch experiments were performed.
Inverse modelling:
x In the case of fresh alkaline attack on bentonite the modelling result remained
incomplete. The method used could not handle multiple independent sources and
sinks for the same elements. Although, observations did not support albite or quartz
dissolution in the experiments, the dissolution of both seemed possible. Similarly,
the CSH-gel was bound to be a significant "non-stoichiometric" sink for e.g. Na in
the experiments (i.e. nothing has to come out as a return), but this could not be
handled in the calculations.
x Similar problems were encountered in calculations of the other two alkaline attacks.
However, in the saline hyperalkaline cases calculations assumed, in accordance with
observations, that all albite dissolved during the experiments. The inverse cation
exchange calculations did not succeed correctly for the lack of an additional sink for
Na.
x In the saline experiments high Cl concentrations brought about difficulties that
probably were related to post-experiment sample preparations. The reason to the Cl
anomalies in the final samples remained unclear.
Forward modelling:
x A simple thermodynamic model developed for montmorillonite was applied to
describe the uptake of Na and Ca. The experimental findings (decrease in Na uptake
with ionic strength, overall high uptake of Ca) were adequately explained by the
model, provided that sorption of calcium takes place predominantly by way of
precipitation of calcium-bearing mineral phases.
x According to model results of the minor solids contained by MX-80, quartz, calcite
and microcline persisted in the fresh and saline alkaline solutions while albite was
predicted to co-exist only in the fresh alkaline solution. In the case of hyper-alkaline
attack the minor solid assemblage of bentonite was completely destroyed, which
resulted in the formation of a zeolite and silicate phases. However, the mineralogical
interpretation of the secondary solid phases was fraught with uncertainties.
68
69
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72
73
APPENDIX 1
RESULTS FROM FLOW-THROUGH TESTS
Initial
B
B
B
B
Fresh (ALL-MR)
B
Saline (OL-SS)
B
in-flow ends
B
Saline alkaline (OL-SA)
out-flow ends
Figure A1-1 Photographs of the test cylinders. The uppermost one shows the cylinder
in the initial state before closing and starting of the experiments. Below are
photographs after opening of the longer time period cylinders. The bentonite half is
marked with a white B.
•
In the case of the fresh (ALL-MR) experiment the crushed rock part has
become softer as bentonite has swelled into the pore space.
• In the saline (OL-SS) experiment the entire column was very hard and the
interface clearly distinguishable when separating the halves from each
other.
• In the saline alkaline (OL-SA) experiment the interface of bentonite and
crushed rock appeared slimy as well as the edgings of the cylinder. This
could imply to formation of new phases.
74
Table A1-1
Results of cation exchange determinations (meq/100g of bentonite) for
both 360 d and 560 d cylinders.
Na
+
+
K
meq / 100g
Samp-
Ca
meq / 100 g
2+
Mg
meq / 100g
2+
CECTOT
meq / 100g
meq / 100 g
360 d
560 d
360 d
560 d
360 d
560 d
360 d
560 d
360 d
560 d
A1
73.0
75.1
0.30
0.25
18.1
13.5
0.13
0.10
91.5
88.9
B1
75.2
72.3
0.35
0.23
15.4
19.9
0.09
0.12
91.1
92.6
B2
72.5
70.8
0.45
0.32
9.0
8.4
0.23
0.14
82.2
79.6
C1
71.9
69.2
0.45
0.39
13.2
11.7
0.13
0.11
85.7
81.4
D1
68.8
70.0
0.50
0.44
13.6
11.9
0.39
0.15
83.2
82.4
E1
65.3
67.2
0.52
0.49
13.9
11.7
0.88
0.37
80.6
79.8
F1
62.2
65.7
0.55
0.47
14.0
12.0
1.31
0.57
78.0
78.7
F1
60.5
65.2
0.58
0.44
13.9
11.8
1.53
0.57
76.4
78.0
F2
61.6
65.2
0.57
0.47
14.1
12.1
1.97
0.68
78.2
78.5
B1
21.1
19.0
0.33
0.25
58.5
63.0
1.72
0.86
81.7
83.1
B2
20.6
19.3
0.34
0.29
57.5
61.5
2.13
1.32
80.5
82.4
C1
21.9
19.0
0.37
0.33
56.1
59.8
2.36
1.23
80.7
80.4
C2
21.4
18.3
0.44
0.30
55.5
60.6
2.72
1.41
80.0
80.6
D1
22.7
18.5
0.47
0.37
54.3
59.8
3.01
1.73
80.5
80.4
D2
21.8
19.5
0.46
0.35
53.0
59.7
3.30
1.87
78.6
81.4
E1
23.6
18.7
0.56
0.38
52.5
58.1
3.25
2.04
80.0
79.2
E2
22.6
19.4
0.53
0.38
51.3
59.6
3.51
2.31
77.9
81.7
F1
23.9
18.9
0.53
0.37
51.3
58.4
3.54
1.96
79.3
79.6
F2
24.4
19.2
0.52
0.39
52.4
58.0
4.00
2.49
81.3
80.1
A1
47.0
46.4
0.75
0.83
19.1
19.7
5.41
5.15
72.2
72.1
A2
48.2
43.3
0.80
0.79
19.2
17.6
5.34
4.55
73.6
66.2
B1
45.4
45.2
0.68
0.78
18.3
18.8
5.16
5.05
69.6
69.9
B2
45.7
55.8
0.70
0.90
18.5
23.3
5.25
6.14
70.2
86.1
C1
47.4
44.0
0.68
0.75
18.3
17.9
5.38
4.99
71.8
67.7
C2
48.5
40.3
0.72
0.67
18.7
17.1
5.40
4.31
73.3
62.3
D1
47.0
47.1
0.74
0.78
18.4
20.0
5.34
5.04
71.5
72.9
D2
53.4
50.0
0.80
0.80
21.0
20.3
5.95
4.93
81.1
76.1
E1
50.6
48.0
0.82
0.82
20.2
19.6
5.70
5.25
77.3
73.7
E2
47.0
48.0
0.77
0.80
18.9
20.4
5.31
5.33
72.0
74.5
F1
48.0
46.1
0.69
0.72
18.2
18.3
5.32
4.80
72.2
69.9
F2
47.9
48.5
0.70
0.81
18.6
19.4
5.52
5.19
72.7
73.9
le
OL-SA
OL-SS
ALL-MR
MX-80 initial
55.2
0.86
10.6
5.02
71.7
75
Table A1-2
Analysis results of the porewater samples (red and blue figures). The
nominal initial concentrations in the feed solutions (black figures) OL-SA, OL-SS and
ALL-MR are included as well.
(blank = no sample, < = below detection limit, but the detection limit is for
diluted samples, whereas the results were corrected with the dilution factors).
Sample
pH
Alk tot
Na
meq/L
meq/L
360d 560d 360d 560d 360d
A1
9.6
2+
meq/L
Cl
-
+
meq/L
2+
K
Si(aq)
Mg
meq/L
meq/L
meq/L
560d 360d 560d 360d 560d 360d 560d 360d 560d 360d
SO4
2-
meq/L
560d 360d 560d
462
18
428
12.5
OL-SA
Ca
+
10.8
2.6
4.7
107
86
3.1
1.4
100
75
0.14 0.05
11.6
5.9
0.2
<0.004 7.6
2.1
111
79
3.9
1.8
100
73
0.05 0.05
11.5
2.3
0.2
<0.004 9.2
3.4
90
0.09
<0.004
3.4
A2
8.1
7.8
1.7
0.9
B1
7.9
10.1
3.4
4.8
1.2
96
9.0
0.1
B2
8.0
8.0
5.2
2.2
96
75
2.7
1.7
78
69
0.12 0.07
24.2
2.9
0.3
D1
7.6
9.0
1.7
1.2
137
85
5.9
2.3
131
81
0.21 0.06
13.1
2.7
0.5
D2
7.8
8.0
2.4
1.4
111
75
2.6
1.8
86
70
0.18 0.06
29.7
2.9
0.5
0.2
F1
7.7
7.6
125
57
4.8
1.7
114
54
0.31 <0.03 13.9
3.7
1.7
0.3
OL-SS
8.3
A1
8.2
ALL-MR
8.8
A1
7.7
2.7
1.6
215
50
414
67
73
133
0.10
3.5
2.3
0.07
1.4
0.10
2.9
<0.02
0.3
0.01
18.2 5.6
<0.004 10.0 2.4
23.5 5.6
1.3
9.5
3.6
3.7
0.01
0.02
0.05
2.2
<0.004
0.9
small syringe for collectring
the pressed porewater
Figure A1-4 Equipment for squeezing porewater from bentonite samples. On the left;
the parts of sample holder, in the middle; the assembled sample holder, on the right; the
sample holder mounted to the pressing device.
[meq/L]
[meq/L]
0.0
0.8y
1
1
Ca
1.0y
2
2
1.5y
3
3
76
initial
4
4
0.0
0.1
0.2
0.0
0.3
0.5
1.0
1.5
2.0
2.5
3.0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
1
0.8y
1
1
K
2
1.0y
2
2
3
1.5y
3
3
4
initial
4
4
<= ALL-MR
<= OL-SS
<= OL-SA
Figure A1-2 Analysed Na, Ca, and K concentrations (meq/L) in the out-flow solutions measured at three points in time. If initially present in
the feed solution the element concentration is shown with a red bar on the right of the figure. The upper three diagrams are for saline
alkaline (OL-SA) solution, the middle three diagrams for saline (OL-SS) solution and the bottom three for fresh (ALL-MR) solution. Note!
Different y-scales.
0
0.5
2.0
2.5
3.0
3.5
4.0
0
4.5
50
100
150
200
250
300
350
400
0
450
5
4
initial
4
4
1.0
3
1.5y
3
3
1.5
2
1.0y
2
2
50
100
150
200
250
300
350
400
450
10
1
0.8y
1
1
Na
15
20
25
30
35
40
45
0
50
100
150
200
250
300
350
400
450
0
50
100
150
200
250
300
350
400
450
[meq/L]
[meq/L]
[meq/L]
[meq/L]
[meq/L]
[meq/L]
[meq/L]
0
5
10
15
0
5
10
15
1
0.8y
1
1
Mg
2
1.0y
2
2
3
1.5y
3
3
4
initial
4
4
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
1
1
1
0.8y
Si
2
1.0y
2
2
3
1.5y
3
3
77
4
initial
4
4
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
0.8y
SO4
1.0y
1.5y
initial
<= ALL-MR
<= OL-SS
<= OL-SA
Figure A1-3 Analysed Mg, Si, and SO4 concentrations (meq/L) in the out-flow solutions measured at three points in time. If initially present
in the feed solution the element concentration is shown with a red bar on the right of the figure. The upper three diagrams are for saline
alkaline (OL-SA) solution, the middle three diagrams for saline (OL-SS) solution and the bottom three for fresh (ALL-MR) solution. Note!
Different y-scales.
0.00
0.05
0.10
0.15
[meq/L]
[meq/L]
[meq/L]
[meq/L]
[meq/L]
[meq/L]
[meq/L]
[meq/L]
[meq/L]
78
79
APPENDIX 2
Table A2-1
RESULTS FROM BATCH EXPERIMENTS
Calcium content in the different batches of the synthetic solutions.
Water
Initial
(mol/L)
0.00954
Fresh alkaline
Saline alkaline
(OL-SA)
0.018
Saline hyperalkaline
0.00044
TableA2-2
Element
Fe
Si
Al
K
Mg
SO4
Measured
(mol/L)
0.00889
0.00957
0.00872
0.00895
0.0185
0.0176
0.0184
0.00031
0.00031
0.00036
Average
(mol/L)
0.00903±0.00037 (4,1%)
0.0182±0.0005 (2.7%)
0.00034± 0.00002 (6.5%)
The maximum amount of impurities in simulated waters introduced from
used p.a. chemicals.
MilliQ- Fresh alkaline
Saline alkaline (OL-SA) Saline hyper alkaline
water
Calculated Found Calculated
Found
Calculated Found
(mg/L)
(mg/L)
(mg/L) (mg/L)
(mg/L)
(mg/L)
(mg/L)
<0.03
<.,06
<1E-3
<0.01
<0.05
-
0.4
0.009
0.004
0.4
0.005
0.4
<0.03
0.24
<0.1
0.32
<0.1
0.11
0.05
0.02
0.01
3
0.2
0.2
<0.03
1.24
<0.1
<1
<0.1
<1
0.2
0.2
0.1
13
0.3
0.3
<0.03
6.97
<0.21
<2
<0.1
<1
80
22
Table A2-3
Na sorption percentages and mass distribution ratio on crushed rock
and bentonite for different waters. The results are average of parallel samples. Samples
marked with * are filtered through 5 000 D.
Material Rock
=>
Quantity Time
=>
(d)
6
Fresh
30
Alkaline
180
540
Saline
alkaline
(OL-SA)
6
30
180
540
Saline
hyper
alkaline
6
30
180
540
Bentonite
S
(%)
6.12 ±0.03
4.02 ±0.05
1.88 ±0.03
<0.2
<0.2*
10.4 ±0.5
4.22 ±0.01
0.89 ±0.01
2.4 ±2.4
2.2 ±2.2*
6.39 ±0.16
3.02 ±0.01
1.39 ±0.03
0.26 ±0.20
<0.2*
Kd
(m3/kg)
(6.52 ±0.03)10-4
(4.19 ±0.05)10-4
(1.92 ±0.03)10-4
<2 10-5
<2 10-5
(1.16 ±0.05)10-3
(4.41 ±0.01)10-4
(8.98 ±0.10)10-5
(2.5 ±2.5)10-4
(2.3 ±2.3)10-4
(6.83 ±0.17)10-4
(3.11 ±0.01)10-4
(1.40 ±0.03)10-4
(2.6 ±2.0)10-5
<2 10-5
Time
(d)
6
30
180
540
6
30
180
540
6
30
180
540
S
(%)
70.8 ±1.7
68.3 ±0.2
73.2 ±12.4*
59.5 ±1.6
61.5 ±0.3*
16.2 ±0.2
17.3 ±0.1
9.34 ±0.06
7.13 ±0.07*
11.5 ±1.0
9.91 ±1.88*
14.2 ±0.03
14.7 ±0.1
7.66 ±0.05
6.08 ±0.01*
8.56 ±0.49
9.29 ±0.92*
Kd
(m3/kg)
(2.43 ±0.06)10-2
(2.15 ±0.01)10-2
(2.73 ±0.46)10-2
(1.47 ±0.04)10-2
(1.60 ±0.01)10-2
(1.94 ±0.02)10-3
(2.09 ±0.01)10-3
(1.03 ±0.01)10-3
(7.68 ±0.08)10-4
(1.30 ±0.12)10-3
(1.10 ±0.21)10-3
(1.66 ±0.01)10-3
(1.72 ±0.01)10-3
(8.30 ±0.06)10-4
(6.47 ±0.02)10-4
(9.36 ±0.47)10-4
(1.02 ±0.10)10-3
81
Table A2-4 45Ca sorption percentages and mass distribution ratio on crushed rock
and bentonite for different waters. The results are average of parallel samples. Samples
marked with * are filtered through 5000 D.
Material Rock
=>
Quantity Time
=>
(d)
Fresh
6
alkaline
30
180
540
Saline
alkaline
(OL-SA)
6
30
180
540
Saline
hyper
alkaline
6
30
180
540
Bentonite
S
(%)
1.14 ±0.01
36.4 ±1.2
89.8 ±7.3
98.9 ±15.4
98.9 ±16.1*
11.2 ±0.1
14.1 ±0.2
49.0 ±6.6
99.9 ±6.2
99.9 ±5.6*
88.9 ±5.0
93.7 ±6.0
96.8 ±4.4
96.9 ±14.5
97.0 ±15.3*
Kd
(m3/kg)
(1.15±0.01)10-4
(5.72±0.20)10-3
(8.84±0.72)10-2
(9.16±1.42)10-1
(9.07±1.48)10-1
(1.27±0.01)10-3
(1.64±0.02)10-3
(9.60±1.30)10-3
(7.68 ±0.47)10-1
(7.13 ±0.40)10+0
(8.05 ±0.00)10-2
(1.49 ±0.10)10-1
(3.06 ±0.14)10-1
(3.10 ±0.05)10-1
(3.28 ±0.52)10-1
Time
(d)
6
30
180
540
6
30
180
540
6
30
180
540
S
(%)
94.4 ±0.0
94.4 ±15.7
99.5 ±10.3*
99.9 ±5.1
99.9 ±3.3*
59.4 ±1.5
99.6 ±1.0
68.6 ±0.4
68.0 ±0.3*
97.6 ±4.9
97.6 ±2.2*
99.9 ±1.0
99.8 ±3.0
99.8 ±1.4
99.8 ±1.8*
100 ±2
100 ±2*
Kd
(m3/kg)
(1.70 ±0.0)10-1
(1.67 ±0.28)10-1
(1.81 ±0.19)10+0
(1.43 ±0.07)10+1
(1.43 ±0.05)10+1
(1.46 ±0.04)10-2
(2.32 ±0.02)10+0
(2.18 ±0.01)10-2
(2.12 ±0.01)10-2
(4.02 ±0.20)10-1
(4.03 ±0.19)10-1
(7.68 ±0.08)10+0
(4.34 ±0.13)10+0
(4.54 ±0.01)10+0
(4.54 ±0.08)10+0
(100 ±2)10+0
(100 ±2)10+0
Table A2-5 Evolution of pH of waters in conctact with crushed rock and bentonite.
Material =>
Time (d) =>
Fresh alkaline
Saline alkaline
(OL-SA)
Saline hyper
alkaline
Rock
6
12.3
12.4
30
12.4
12.5
180
12.6
12.2
13.5
12.6
12.9
540
12.4
12.1
Bentonite
6
30
11.6
11.5
10.8
10.6
180
11.4
10.3
540
11.2
10.2
13.1
13.5
13.4
12.8
12.9
30
12.4
12.5
180
12.6
12.4
540
12.7
12.5
13.5
13.0
13.1
Table A2-6 Evolution of pH of synthetic waters.
Initial
Time (d) => 6
12.5
Fresh alkaline
12.5
Saline alkaline
(OL-SA)
13.5
Saline hyper
alkaline
30
12.5
12.6
180
12.5
12.5
540
12.5
12.5
Final
6
12.2
12.4
13.5
13.5
13.5
13.5
82
Table A2-7 Chemical composition of fresh alkaline water in contact with crushed rock
and bentonite.
Material =>
Time (d) =>
Element (mg/L)
Na
Ca
K
Mg
Al
Si
Fe
Cl
SO4
EC (mS/m)
Rock
6
30
180
385
296
11.0
<0.1
4.27
1.83
0.21
55.7
0.25
670
633
257
16.3
<0.1
6.36
1.41
<0.03
49.5
0.48
850
1172
9.19
53.4
<0.1
39.5
13.0
<0.03
47.1
0.46
570
540
Bentonite
6
30
180
540
706
15.0
55.6
<0.1
27.5
12.0
<0.03
391
517
310
585
51.0
12.8
115
679
2072
167
57.2
296
-
737
4.21
8.16
<0.1
<0.1
453
<0.03
71.7
365
178
728
6.46
7.84
<0.1
<0.1
230
<0.03
415
379
204
682
24.4
8.74
55.0
261
1067
73.5
47.7
334
-
Table A2-8
Chemical composition of saline alkaline (OL-SA) water in contact with
crushed rock and bentonite.
Material =>
Time (d) =>
Element (mg/L)
Na
Ca
K
Mg
Al
Si
Fe
Cl
SO4
EC (mS/m)
Rock
6
30
180
10490
606
23.5
<0.1
0.18
0.70
<0.03
14100
<1
4300
9434
392
31.1
<0.1
0.59
0.80
<0.03
12400
<1
4200
8808
124
82.3
<0.1
15.9
4.95
<0.03
16700
<1
2200
540
Bentonite
6
30
180
540
9107
111
75.4
<0.1
13.4
6.67
<0.03
16700
<1
3900
8223
166
45.7
0.1
0.36
38.0
0.06
16400
293
2000
9633
133
42.3
<0.1
<0.1
59.3
<0.03
14650
325
2175
9017
246
20.5
<0.1
<0.1
43.8
<0.03
14300
317
3200
9310
158
41.0
<0.1
<0.1
47.1
<0.03
15100
302
1900
83
Table A2-9
Chemical composition of saline hyper alkaline water in contact with
crushed rock and bentonite.
Material =>
Time (d) =>
Element (mg/L)
Na
Ca
K
Mg
Al
Si
Fe
Cl
SO4
EC (mS/m)
Table A2-10
Rock
6
30
180
18860
3.58
36.4
<0.1
19.0
38.7
0.58
13700
<1
11000
18160
1.41
39.1
<0.1
41.2
65.3
0.99
14100
<1
11000
17800
0.55
45.1
<0.1
95.9
141
0.5
11000
7.02
9900
540
Bentonite
6
30
180
540
17570
0.43
67.8
<0.1
91.8
155
0.49
11500
<1
6100
18480
0.25
38.4
<0.1
0.19
981
<0.03
13900
304
9200
17563
0.73
45.5
<0.1
0.28
1965
<0.03
15750
300
4750
16640
<0.1
21.0
<0.1
0.22
2346
0.08
13800
310
3900
18740
0.52
26.5
0.16
0.22
1215
<0.03
13300
321
5000
Chemical composition of original waters.
Solution => Fresh alkaline
Element (mg/L)
1157
Na
329
Ca
0.32
K
<0.1
Mg
<0.1
Al
0.24
Si
<0.03
Fe
42.6
Cl
0.11
SO4
1400
EC (mS/m)
Saline alkaline
(OL-SA)
9770
678
<1
<0.1
<0.1
1.24
<0.03
14400
<1
4500
Saline hyper alkaline
17710
12.8
<2
<0.1
0.21
6.97
<0.03
13700
<1
9800
84
85
APPENDIX 3
A3
BENTONITE INTERPRETATIONS
1
Smectite crystal chemistry
According to Deer et al. (1995), the chemical formula of the montmorillonite–beidellite
series can be expressed by the formula:
[ X (+x + y ) / 2 ] Al 2− y Mg y [ Si4− x Al x O10 ] (OH ) 2 *zH2O.
Interlayer
Octahedral
(A3-1)
Tetrahedral
The crystal structure is di-octahedral where octahedrally co-ordinated Al ions are
sandwiched with two inward pointing sheets of linked SiO4 tetrahedra. The tetrahedral
layers compose a pseudohexagonal network, while the central section can be regarded as
a layer of gibbsite, Al2(OH)6. However, in a gibbsite unit cell 2/3 of the apical OH have
been replaced with the apical oxygen atoms of SiO4 tetrahedra (cf. Fig. A3-1). The
series is classified so that for montmorillonite y > x and for beidellite y < x. The ideal
montmorillonite structure can be expressed as follows:
[ ( 12 Ca, Na ) 0.35 ] Al1.65 Mg 0.35 [ Si4.00 O10 ] (OH ) 2 *zH2O,
Interlayer
Octahedral
(A3-2)
Tetrahedral
while the ideal beidellite structure is more aluminous giving formula:
[ ( 12 Ca, Na ) 0.35 ] Al 2.00 [ Si3.65 Al 0.35 O10 ] (OH ) 2 *zH2O.
Interlayer
Octahedral
(A3-3)
Tetrahedral
According to Huertas et al. (2000) the principal smectite in the initial MX-80 bentonite
is Na-montmorillonite having the following composition:
[Na0.21Ca0.08K0.02]Al1.51Mg0.27Fe0.17Ti0.01[Si3.98Al0.02O10](OH)2
Figure A3-1
Structure of smectite. Modified from Grim (1962).
(A3-4)
86
A3
1.1
Bentonite IR spectra
The dried samples utilised in infrared (IR) spectral studies were prepared on glass
holders, and measurements were done at ambient relative humidity and temperature.
However, only HYRL samples were studied. A Perkin-Elmer 983G infrared
spectrophotometer was used for the analyses.
According to Van der Marel & Beutelspacher (1976) the IR characteristic bands for
montmorillonite are 3 624, 1 115, 1 038, 915, 878, 845, 796, 623, 522, and 467 cm-1.
All these lines originate from co-ordinated crystal lattice bonds mainly with cations Al,
(Mg, Fe) and Si, and anions O and OH. Most of the bands are readily identified from
Figures A3-2...A3-4, as well as, the general form of the illite-montmorillonite IR
spectrum. The adsorbed water forms two distinct bands in the illite montmorillonite
spectrum at 3 440 cm-1 and 1 630 cm-1. The more tightly bound crystal water gives a
slight band at 3 235 cm-1.
In addition to illite-montmorillonite identification the IR method is sensitive for certain
bentonite impurities. Especially kaolinite, calcite and quartz may be found with the IR
analysis even if they are absent in the X-ray diffraction spectrum. Kaolinite is most
easily identified with the bands 3 698, 3 668, and 752 cm-1. The significant
characteristic bands for calcite are at 1 422 cm-1 and 878 cm-1. Evidently, the 878 cm-1
band overlaps with the montmorillonite adsorption band originating from (Al,Fe)...OH
bond vibrations. According to Van der Marel & Beutelspacher (1976) quartz forms a
sharp doublet band at 798–778 cm-1. If the amount of quartz is very small this doublet is
decreased to a single band at 796–800 cm-1. According to Wilson (1987), tridymite
generates a single broad adsorption band at 792 cm-1. These bands overlap the
montmorillonite 796 cm-1 band that has been assigned for (Al,Mg)...OH bond vibrations
(Van der Marel & Beutelspacher, 1976). In the case of some other bentonite impurities,
the IR method is less sensitive than the X-ray method. These minerals include
cristobalite, mica, hematite and feldspars (Van der Marel & Beutelspacher, 1976).
In Figures A3-2...A3-4 only the H2O bands, identified impurity mineral bands, and
certain unique interatomic bond bands are denoted. It seems evident that in every series
the amount of adsorbed interlayer water increases in the samples, although the samples
have been dried before the mineralogical studies. In the all experiment series the
adsorption at 915 cm-1 seem to strengthen slightly suggesting an increase in the relative
amount of octahedral (Al,Al)...OH bonds in the altered bentonite samples. Similarly, the
adsorption band at 845 cm-1 is seems strengthened in the experimented samples
indicating that the relative amount of octahedral (Al,Mg)...OH bond vibrations have
been increased.
In the case of saline hyper-alkaline experiments (Fig. A3-4) the adsorption band at
878 cm-1 gives an indirect conclusion considering the montmorillonite alteration. There
is constantly calcite in the altered samples proved as well with the X-ray spectrum
analyses (Section A.3.3). Therefore, the disappearance of the band 878 cm-1 originating
from montmorillonite (Al,Fe)...OH bond vibrations indicates that the octahedral Fe has
been extracted away from montmorillonite during the experiments.
87
Deductions are scarce considering the other bond vibrations related to the experimented
smectites. Based on Equations A3-2 and A3-3, if changes in montmorillonite–beidellite
compositions occur further changes in characteristic bands could be expected.
Interpretation is not simple, however. According to Wilson (1987) beidellite has small
characteristic IR spectrum bands at 818 cm-1 and 770 cm-1. Unfortunately, neither of
these can be confirmed from Figure A3-4. Instead Figure A3-4 indicates that there is a
slight general decrease in IR transmission intensities in the wavenumber area 830–
700 cm-1.
As a conclusion on montmorillonite IR spectral studies, it seems that montmorillonite
looses Fe from its octahedral sites especially during saline hyperalkaline attack (cf. Eq.
A3-4). While Fe is extracted away from montmorillonite, Al seems to prefer to stay in
the lattice sites.
Considering the other bentonite minerals, it seems that kaolinite does not exist in the
samples studied. The initial bentonite sample indicates small amounts of calcite and
quartz as impurities. In every experiment series the amount of calcite increases as a
result of alkaline water interaction. This increase seems to be especially distinct in freshalkaline (Fig. A3-2) and saline alkaline (Fig. A3-3) experiments. In the case of saline
hyper-alkaline series (Fig. A3-4) it is evident that noticeable part of quartz reacts in the
hyper-alkaline attack and is extracted away from bentonite.
Figure A3-2 IR spectra for bentonite specimens altered in the fresh-alkaline batch
experiments. The uppermost reference is the initial MX-80 bentonite.
88
Figure A3-3 IR spectra for bentonite specimens altered in the saline-alkaline (OL-SA)
batch experiments. The uppermost reference is the initial MX-80 bentonite.
Figure A3-4 IR spectra for bentonite specimens altered in the saline hyper-alkaline
batch experiments. The uppermost reference is the initial MX-80 bentonite.
89
A3
2
Bentonite XRD spectra
No special pre-treatments were done for the bentonite samples. Both initial MX-80 and
final experimented bulk samples were dried and finely ground in a mortar at ambient
relative humidity and temperature. A Philips X'pert-MPD diffractometer with CuKα
radiation was used for the analyses. The scanned interval was in the 2Θ interval 2-70°
and the resolution was 0.02° with 0.5 s counting time. The samples were prepared on
glass holders and each sample were scanned four times. Between each run the samples
were re-blended to ensure the sample disorientation. The spectra presented in the
following are averages of four runs.
A3
2.1
Initial bentonite
Based on JCPDS (1997) diffraction database three montmorillonite patterns (Table
A3-1) were chosen for X-ray diffraction peak identification presented in Figure A3-5. In
general, the peaks of Nax-Mt resembles well the MX-80 montmorillonite. The peak
values 6.41Å, 4.51Å, 3.25Å and 1.50Å of the Nax-Mt can be readily identified from the
presented spectrum. The highest peak (12.9Å) of the Nax-Mt pattern resembles well the
measured peak at 12.7Å, although this smectite interlayer spacing is not only a function
of interlayer cations but adsorbed water as well (cf. Fig. A3-1). However, certain
montmorillonite diffraction peaks remain unexplained. The measured high d-value
26.3Å (Fig. A3-5) is an indication of interstratification of illite (mica) and
montmorillonite (smectite) layers, and it resembles with the peak value of a illitemontmorillonite pattern of JCPDS database (Table A3-1). Finally, the measured X-ray
spectrum (Fig. A3-5) contains a somewhat broaden peak at 3.18Å. It is not possible to
explain this with bentonite accessory minerals only, but it probably contains a
contribution from montmorillonite. The information from JCPDS (1997) database
indicates that the montmorillonite interlayers may contain also additional components
like Al(OH)2+-ions. The card 11-303 referred in Table A3-1 is the only montmorillonite
that has a peak value around 3.18Å.
Considering the accessory minerals, quartz is readily identified from the X-ray spectrum
(Fig. A3-5). Bentonite contains also albite, and apparently a slight amount of orthoclase.
Based on relative peak intensities albite seems to be partially disordered. The only peak
that can be assigned uniquely to orthoclase is 3.45Å, but the intensity is so small that the
determination remains uncertain. Based on the 7.59Å diffraction peak (Fig. A3-5) MX80 bentonite contains a small amount of gypsum.
90
Table A3-1 Characteristic diffraction patterns (JCPDS, 1997) used for the diffraction
peak identification of the initial MX-80 montmorillonite. Card numbers refer to the
database and acronyms to text and Figure A3-5. Diffraction data are given as
d-values (Å).
Chemical formula
Card No
Acronym used
Characteristic d-values (rel. intensity)
Nax(Al,Mg)2Si4O10(OH)2*zH2O
12-0204
Nax-Mt
K0.5Al2(Si,Al)4O10(OH)2*zH2O
07-0330
ill
(Al(OH)2)0.33Al2Si3.67Al0.33O10(O
H)2
11-303
Al(OH)2-Mt
12.9(1.0), 6.55(0.1), 4.51(0.7), 3.25(0.2),
2.58(0.2), 1.70(0.2), 1.50(0.4)
25.8(1.0), 12.4(0.8), 4.47(0.8), 2.56(0.5),
2.45(0.3), 1.49(0.5)
11.1(1.0), 3.17(0.4)
Figure A3-5 Diffraction pattern of the initial MX-80 bentonite. Acronyms Nax-Mt, ill,
Al(OH)2-Mt refer to Table A3-1. Otherwise the acronyms are: Qz = quartz, Ab = albite,
Kf = orthoclase, Gp = gypsum. Codes in superscript refer to relative peak intensities of
minerals and the numbers below the acronyms refer to d-values.
A3
2.2
Results from flow-through experiments
The results of bentonite from the flow-through cylinder experiments are summarised in
the following. The first set of experiments were decommissioned after an one year (360
days) operation and the second set after about 1.5 years (560 days). The solids received
from cylinders were divided in parts. Mineralogical samplings were made at three
91
locations of the cylinders. The locations of samplings are illustrated in the insets of
Figures A3-6...A3-8. It turns out that three different types of montmorillonite
compositions (JCPDS 1997) are needed to interpret the MX-80 montmorillonite
alteration results. The details of these montmorillonite patterns are presented in Table
A3-2. The presented patterns in Figures A3-6...A3-8 are concentrated on the 2Θ interval
of 10–30° where the most of changes tend to occur during the water-bentonite
interactions.
Table A3-2 Characteristic diffraction patterns (JCPDS, 1997) used for the diffraction
peak identification of the altered montmorillonite received from experiments. The card
numbers refer to the JCPDS database and acronyms to text and Figures A3-6...A3-11.
Diffraction data are given as d-values (Å).
Chemical formula
Card No
Acronym used
Characteristic d-values (rel. intensity)
Ca0.2(Al,Mg)2Si4O10(OH)2*4H2O
13-013
Cax-Mt
Na0.3Al2(Si,Al)4O10(OH)2*2H2O
43-0688
Nax-Bd
Al2O3·4SiO2·xH2O
03-0016
Mt
15.0(1.0), 5.01(0.6), 4.50(0.8), 3.02(0.6),
2.58(0.4), 1.50(0.5), 1.49(0.5)
12.4(1.0), 6.2(0.5), 4.48(0.8), 3.10(0.6),
2.57(0.3), 2.06(0.1), 1.69(0.1), 1.50(0.1)
14.0(1.0), 5.00(0.2), 4.41(1.0), 3.09(0.6),
2.51(0.8), 1.49(0.8)
Fresh water
Considering the complete 2Θ diffraction spectrum it can be concluded that no
significant changes occur outside the illustrated 10–30° region (Fig. A3-6). During the
first 360 days it seems that only minor changes occur in bentonite. Changes are mostly
related to slight drops in the peak intensities. Gypsum, however, is dissolved readily
from the cylinders and small calcite peaks emerge in the spectra.
After 560 days changes are more evident (Fig. A3-6). Nax-Mt peak at 6.41Å diminishes
and at the same time it seems that a slight anomaly is created at 5.01Å. Furthermore, the
significant montmorillonite peak at 3.18Å is moved towards lower d-values. A new
montmorillonite peak grows at 3.10Å. As a result of this peak movement the less
prominent albite and Nax-Mt peaks below the main 3.18Å peak become visible.
Similarly, it seems that the important montmorillonite peak at 4.47Å swifts to a slightly
lower d-value (~4.41Å). It seems that montmorillonite looses impurities (e.g. Al(OH)2,
cf. Fig. A3-5 and Table A3-1) from the smectite interlayer. Especially in the tail parts of
the cylinder, the diffraction spectrum of altered montmorillonite seem to fit best to a
purified montmorillonite structure (Mt, Table A3-2). The diffraction data of synthetic
Mt presented in Table A3-2 indicates peaks at 5.00Å, 4.41Å, and 3.09Å that fit to
altered spectra presented in Figure A3-6.
According to water analyses, the flow-through cylinder releases constantly Na into the
outflow water. At the same time the cylinder captures a little Ca from the inflow water.
The dissolving gypsum forms a small additional Ca source in the cylinder but at the
same time a small part of Ca available is consumed to calcite precipitation. It seems
evident that the major part of inflow Ca is captured into the cation exchange sites of
92
smectite, while a double amount of Na (in moles) is released into the outflow water.
However, this exchange is minor compared to the total cation exchange capacity, and
therefore, no Na/Ca conversion in the smectite structure is visible. Montmorillonite
likely exchange cations mostly in the head parts of the cylinder. However, for unknown
reason the washing effect considered above is most clearly visible in the tail parts of the
cylinder.
Considering the other minerals present in the experiment it seems that the nearly neutral
pH fresh water is not aggressive enough to attack against quartz or feldspars. However,
the water analyses indicate that Si concentrations in the outflow water, after 560 days,
are still quite notable. This Si release in the outflow water can be either colloidal or it
manifests gradual purification of montmorillonite interlayers.
Figure A3-6 Partial diffraction pattern of bentonite after interaction with fresh water (blue) compared with the initial bentonite pattern
(red). Acronyms Nax-Mt, ill, Al(OH)2-Mt refer to Table A3-1 and acronym Mt to Table A3-2. Otherwise the acronyms are: Qz = quartz, Ab
= albite, Kf = orthoclase. The numbers below the acronyms refer to d-values.
93
94
Saline water
The Na/Ca ratio in the saline inflow water is almost 1:1 while in the fresh and saline-alkaline cases
this ratio is around 10:1. Considering the diffraction patterns outside the 10–30° region presented in
Figure A3-7, one important change is evident in all altered samples. The main peak of Nax-Mt at
12.7Å (Fig. A3-5) moves towards higher d-values usually around 15.2Å. This is a sign of Ca
contamination in the smectite interlayer (Fig. A3-1). Similarly to fresh water case, peak intensities
in the altered samples tend to drop somewhat.
In the detailed view (Fig. A3-7) distinct changes occur as well. After 360 days the Nax-Mt peak
intensities at 6.41Å have diminished significantly in all sampling locations in the cylinder and a new
peak at 5.07Å has started to grow. After 560 days this evolution is distinct. The 3.18Å peak moves
in all altered samples to lower d-values. This peak movement and the gradual growth of the new
peak at 3.04Å develop logically. The changes are more prominent in the head parts of the cylinder
than in the tail parts, and the changes after 360 days are not so distinct as after 560 days. The
developed new anomalies are best explained with the Cax-Mt presented in Table A3-2. The results
indicate that Nax-Mt releases Na easily if cations with higher charge are available.
The water analyses indicate that the saline flow-through cylinder releases Na but catches eagerly Ca
from the inflow water. In fact at 560 days, about equal amount of Ca is captured as Na is released.
This is in conflict with the exchange stoichiometry (Eq. A3-2) since only half of the captured Ca can
be used for exchange. It is possible that continuos calcite precipitation occurs in the cylinder, though
this cannot be confirmed from Figure A3-7 due to peak superimposition. Gypsum dissolves readily
from the samples. Likely, the nearly neutral solution does not have enough potential to attack
against quartz or feldspars.
Saline-alkaline water
The inflow water has the same Cl concentration as saline water but its Na/Ca equivalent ratio is
similar to fresh water case, and its pH is high (12.5). The main Nax-Mt diffraction peak at 12.7Å (cf.
Fig. A3-5) does not change its position during the alkaline water attack indicating that apparently
very significant changes do not occur in the Na/Ca ratios within the smectite interlayer.
In the view of the 10-30° region presented in the Figure A3-8 there are, however, clear changes in
the diffraction patterns. The location of 6.41Å peak of Nax-Mt moves a little to the position of
6.22Å and its intensity seems to grow with time. Both in the 360-day-cylinder and in the 560-daycylinder there seems to be clear swift of the 3.18Å peak to the d-value of 3.12Å. As a result of this
swift the overlaid albite peaks become visible. It appears that both the detailed spectra presented in
Figure A3-8 and the complete diffraction spectra of altered samples fit well to the Na-beidellite
pattern of the JCPDS (1997) database (Table A3-2). This implies changes in the Nax-Mt intra-layer
structure. A significant part of octahedrally co-ordinated Mg and Fe -cations should be leached from
the smectite structure (Eq. A3-3). At the same time it seems that Si is leached more easily from the
tetrahedral sites than Al (Eq. A3-2). Apparently this kind of change is not possible without at least
partial break-up of Nax-Mt crystals before the conversion to Nax-Bd occurs.
The accessory mineral interpretations are similar to other experiments. Gypsum is dissolved and a
slight calcite precipitation is indicated by the altered diffraction patterns. The dissolution of quartz
or feldspars is hard to verify.
Figure A3-7 Partial diffraction pattern of bentonite after interaction with saline water (blue) compared with the initial bentonite pattern
(red). Acronyms Nax-Mt, ill, Al(OH)2-Mt refer to Table A3-1 and acronym Cax-Mt to Table A3-2. Otherwise the acronyms are: Qz =
quartz, Ab = albite, Kf = orthoclase. The numbers below the acronyms refer to d-values.
95
Figure A3-8 Partial diffraction pattern of bentonite after interaction with saline water (blue) compared with the initial bentonite pattern
(red). Acronyms Nax-Mt, ill, Al(OH)2-Mt refer to Table A3-1 and acronym Nax-Bd to Table A3-2. Otherwise the acronyms are: Qz =
quartz, Ab = albite, Kf = orthoclase. The numbers below the acronyms refer to d-values.
96
97
A3
2.3
Results from batch experiments
The batch experiments were carried out with three water types and several sets of
batches. The batches were decommissioned according to the time-schedule: 6, 30, 180,
and 540 days. The mineralogical results of the bentonite batches are summarised in the
following. All waters utilised in the experiments have a high pH. The initial fresh
alkaline water has the Na/Ca equivalent ratio of about 3, while saline-alkaline has about
10, and saline hyperalkaline has about 1000. It becomes evident that the Nax-Bd
diffraction pattern presented in Table A3-2 is essential in the alteration result
interpretations.
Fresh alkaline water
In the view of the complete 2Θ spectra (2–70°, cf. Fig. A3-5) two features are clear. The
smectite main peak at 12.7 Å stays at its original position, and as the water interaction
time increases a new peak starts to grow around 2.09Å. After 540 days this 2.09Å
diffraction peak is already quite distinct and it may be related both calcite and Nax-Bd.
There seem to be also small intensity drop at the albite 2.12Å peak (Fig. A3-5) possibly
indicating that some of albite has reacted during alkaline attack. Like in the flowthrough experiments cases the altered diffraction patterns confirm the dissolution of
gypsum.
The detailed spectrum (Fig. A3-9) indicates a few changes. The Nax-Mt peak at 6.41Å
moves a little towards a lower d-value. At the same time the intensity of this peak grows
higher. The significant montmorillonite peak at 3.18Å moves as well towards lower dvalues. After 540 days this peak has moved to 3.13Å. This value is difficult to assign
directly to any smectite reference pattern available. The possibilities are few, however.
The peak movements towards Nax-Bd peak positions (Table A3-9) point to structural
changes in the smectite. The not-exact-fit peak positions possibly indicate that the final
smectite contains Ca in its interlayer.
The final fresh water results seem to confirm the partial structural changes in the
smectite structure. In the short experiments (6 days, 30 days) there are significant
increases in concentrations of K, Fe, Mg, Al, and Si in the final water. Although, part of
Fe is likely contributed from the dissolved pyrite, it seems evident that some Namontmorillonite breaks up and Fe, Al, Si are released in the water. An another effective
process must be cation exchange that releases K, Mg, and Na(?) from the smectite
interlayers. The adsorbed Ca is consumed to strong CSH-gel precipitation and to calcite
crystallisation. Likely, the CSH-gel acts as a sink to Na as well. According to laboratory
observations the gel precipitation was especially strong in the case of fresh alkaline
experiments.
98
Figure A3-9 Partial diffraction pattern of bentonite after interaction with fresh alkaline
water (blue) compared with the initial bentonite pattern (red). Acronyms Nax-Mt, ill,
Al(OH)2-Mt refer to Table A3-1 and acronym Nax-Bd to Table A3-2. Otherwise the
acronyms are: Qz = quartz, Ab = albite, Kf = orthoclase. The numbers below the
acronyms refer to d-values.
Saline alkaline water
As in the case of fresh alkaline experiments, it is clear from the complete 2Θ spectra (2–
70°) that the smectite interlayer distance stays approximately at 12.7Å. Similarly, a new
small peak emerges and strengthens at d-value of 2.09Å. After 540 days, the complete
spectrum indicates several clearly identifiable calcite peaks. Apparently, calcite
precipitation is more stronger in the saline alkaline case than in the fresh alkaline case.
The indication of gypsum dissolution is clear in all studied spectra.
The partial diffraction spectra (Fig. A3-10) exhibit a time-dependent evolution around
the peak at 6.18Å. The intensity of the peak grows as the interaction time gets longer.
The smectite peak at 3.18Å moves to 3.12Å, and the smaller albite peaks emerge below
the moving smectite peak. Visually the 540-day-sample already exhibits relatively good
resemblance to Nax-Bd. The diffraction peaks at 4.03Å and 3.75Å hint to partial albite
dissolution reactions because the drop of the peak intensity (especially at 4.03Å) seem to
99
be larger than the drop of the background intensity. This interpretation is supported with
the slight peak intensity drop at 2.12Å (Fig. A3-5), outside the detailed spectra presented
in Figure A3-10.
The final saline alkaline water results indicate that bentonite batches release K, Si and
SO4, but retard Ca and Na. It appears that a significant part of captured Ca is bound to
precipitate as CSH-gel and at lesser extent calcite. The final saline alkaline waters
contain sulphate. Certainly, a major part of this sulphate originate from gypsum.
According to X-ray spectra, there is no direct evidence that also pyrite would dissolve
from bentonite. Apparently, pyrite concentrations are below the sensitivity of the study
method.
Figure A3-10 Partial diffraction pattern of bentonite after interaction with saline
alkaline water (blue) compared with the initial bentonite pattern (red). Acronyms NaxMt, ill, Al(OH)2-Mt refer to Table A3-1 and acronym Nax-Bd to Table A3-2. Otherwise
the acronyms are: Qz = quartz, Ab = albite, Kf = orthoclase. The numbers below the
acronyms refer to d-values.
100
Saline hyperalkaline water
Considering the complete diffraction spectra it can concluded that the 12.7Å peak holds
it location. As in the earlier batch cases 2.09Å peak grows as a function of time. In the
hyperalkaline cases it seems evident that smectite diffraction (Nax-Bd) have distinct
contribution to this d-value. The albite peak at 2.12Å seem to loose its intensity almost
completely. After 540 days the main peak of calcite is clearly visible (3.03Å, cf. Fig.
A3-11). However, the intensity of calcite peak seems somewhat smaller than in the
saline alkaline water experiments. Predictably, gypsum is dissolved.
The partial montmorillonite alteration seems evident in the saline hyperalkaline
experiments (Fig. A3-11). The peak 6.41Å moves to the d-value 6.18Å that fits well to
Nax-Bd pattern (Table A3-2). At the same time the peak intensity grows logically. The
peak at 3.18Å moves to 3.10Å that fits to Nax-Bd pattern. Peaks at 4.03Å, 3.18Å and
3.21Å related to albite are almost vanished after the 540 days of reaction time. Similarly,
intensities of the peaks 4.26Å and 3.34Å related to quartz are clearly diminished after
the 540 days of experiment time.
According to final water compositions of saline hyperalkaline experiments, the
bentonite batches release K and significantly Si. The amount of released Si grows as
function of reaction time, and likely this indicates break down of silicates. Diffraction
spectrum indicates dissolution of gypsum and precipitation of calcite. The adsorption of
Ca into smectite is likely not important because Na/Ca equivalent ratio is almost 1000 in
the initial input water. Therefore, the Ca-sink is probably CSH gel, detected with eye in
the laboratory, and calcite.
101
Figure A3-11 Partial diffraction pattern of bentonite after interaction with saline
hyperalkaline water (blue) compared with the initial bentonite pattern (red). Acronyms
Nax-Mt, ill, Al(OH)2-Mt refer to Table A3-1 and acronym Nax-Bd to Table A3-2.
Otherwise the acronyms are: Qz = quartz, Ab = albite, Kf = orthoclase. The numbers
below the acronyms refer to d-values.
102
103
APPENDIX 4
A4
1
CRUSHED ROCK INTERPRETATIONS
Initial rock material
The samples from boreholes OL-KR10 and OL-KR12 (from depth interval 460–500m)
were used for mineralogical studies and whole-rock analyses.
Microprobe analyses of minerals
The analysed mineralogical compositions of the selected minerals of the backfill-pattern
rock types are presented in Table A4-1. The quantitative mineralogical analyses of the
polished thin sections were carried out with the Cameca Camebax SX50 electronmicroprobe based at the Geological Survey of Finland, Espoo. For the wavelength
dispersive analyses (WDS) the accelerating voltage was 15 kV. The probe currents were
5, 10 and 5 nA for silicates, carbonates and apatite, respectively.
According to the WDS results (Table A4-1) K-feldspar contain only a small amount of
albite in micropertite and K-feldspar is likely low microcline in composition in all
backfill-pattern rock types (cf. Deer et al. 1995). The purest microcline may be found in
granite pegmatite. Plagioclase is mostly oligoclase in composition in all the rock types.
Based on the analysed averages and the standard deviations of plagioclase samples,
there are small, though significant, differences in the plagioclase compositions among
the rock types.
Biotite and chlorite are relatively iron-rich. In biotite and chlorite, the Fe-content
increases and Mg-content decreases among the rock types in the order: Mica gneiss,
granite pegmatite and tonalite gneiss. This order remains the same if the atomic
Fe/(Fe+Mg) ratios in biotite and chlorite are considered. Moreover, within each rock
type the Fe/(Fe+Mg) ratios in biotite (0.61–0.66) and chlorite (0.59–0.65) resemble
closely each other indicating an intimate relationship between the two in the alteration
processes. Muscovite exhibits a different behaviour. Its Fe and Mg contents diminish in
the order: mica gneiss, tonalite gneiss and granite pegmatite. The atomic Fe/(Fe+Mg)
ratios in muscovite are also distinctly lower (0.44–0.47) than in the case of biotite and
chlorite. In mica gneiss and tonalite gneiss the Fe atomic ratio seems to exhibit an
antipathetic relationship among the sheet silicates. While the Fe-ratio increases in biotite
and chlorite, it decreases in muscovite.
Table A4-1
(next page). Average compositions of the selected minerals in the
backfill-pattern rock types. All average concentrations (Ave) and standard deviations
(Stdev) are presented in weight-%. Mineral names have been abbreviated as follows: Kfs = alkali-feldspar, Plag = plagioclase, Bt = biotite, Mu = muscovite, Chl = chlorite,
Sill = sillimanite, Gra = garnet, Crd = cordierite, Ap = apatite, and Cc = carbonate.
The number following each mineral name abbreviation denotes the amount of chemical
analyses used in the component average and standard deviation calculations. In the
case of carbonate, the CO2 content is not analysed but calculated as difference to 100.
Mineral formulas calculated at the bottom are based on the fixed oxygen numbers,
except for apatite that is based on the fixed phosphorus number.
Granite Pegmatite
Mica Gneiss
104
SiO2
TiO2
Al2O3
Cr2O3
FeO
MnO
MgO
CaO
Na2O
K2O
BaO
SrO
NiO
F
Cl
Total
SiO2
TiO2
Al2O3
Cr2O3
FeO
ZnO
MnO
MgO
CaO
Na2O
K2O
BaO
SrO
NiO
SO3
F
Cl
CO2
Total
K-fs(1
Ave
64.16
0.03
18.32
0.02
0.04
0.01
0.00
0.04
1.05
15.13
0.36
0.04
0.01
0.04
0.01
99.26
24 Plag(4
Stdev
Ave
0.50 63.02
0.03
0.02
0.21 22.59
0.03
0.01
0.05
0.02
0.02
0.01
0.01
0.00
0.02
4.20
0.38
9.30
0.56
0.26
0.06
0.01
0.05
0.09
0.02
0.01
0.04
0.03
0.01
0.01
99.60
31 Bt(7
Stdev
Ave
0.34 34.80
0.04
3.29
0.31 19.08
0.02
0.09
0.03 20.43
0.02
0.05
0.01
7.45
0.19
0.03
0.22
0.09
0.07
9.49
0.02
0.04
0.08
0.05
0.02
0.04
0.03
0.52
0.01
0.01
95.45
47 Mu(10
Stdev
Ave
0.28 46.56
0.36
0.03
0.42 32.33
0.04
0.02
0.47
3.26
0.04
0.03
0.28
2.00
0.03
0.06
0.04
0.26
0.14
9.79
0.04
0.18
0.07
0.04
0.03
0.02
0.06
0.26
0.01
0.02
94.84
14 Chl(13
Stdev
Ave
1.18 30.22
0.06
0.13
2.38 23.78
0.03
0.04
2.08 22.82
0.03
0.09
1.36
8.77
0.05
0.30
0.29
0.03
0.46
0.47
0.20
0.00
0.04
0.05
0.02
0.04
0.11
0.22
0.03
0.02
87.01
6 Sill(16
Stdev
Ave
7.02 36.94
0.14
0.04
5.70 61.34
0.02
0.04
11.28
0.24
0.04
0.01
2.91
0.03
0.44
0.02
0.06
0.00
0.44
0.01
0.01
0.01
0.06
0.03
0.04
0.01
0.06
0.04
0.03
0.01
98.75
25 Crd(19
Stdev
Ave
0.36 48.20
0.05
0.03
0.49 31.99
0.04
0.02
0.10 10.13
0.02
0.16
0.04
7.04
0.02
0.02
0.00
0.18
0.01
0.01
0.02
0.01
0.05
0.03
0.01
0.01
0.03
0.10
0.01
0.01
97.92
24
Stdev
0.25
0.04
0.29
0.03
0.29
0.03
0.12
0.02
0.05
0.01
0.01
0.05
0.02
0.05
0.01
K-fs(2
Ave
64.37
0.03
18.27
0.01
0.02
21 Plag(5
Stdev
Ave
0.52 63.96
0.05
0.01
0.21 22.44
0.02
0.02
0.03
0.02
15 Bt(8
Stdev
Ave
0.41 34.84
0.03
2.65
0.36 19.96
0.02
0.02
0.02 22.67
4 Mu(11
Stdev
Ave
0.65 46.20
0.33
0.44
0.70 35.84
0.02
0.01
0.74
0.78
25 Chl(14
Stdev
Ave
0.72 24.31
0.49
0.11
1.06 21.05
0.02
0.02
0.31 30.98
18 Sill(17
Stdev
Ave
0.22 36.32
0.09
0.05
0.44 61.44
0.03
0.01
0.57
0.21
8 Cc(20
Stdev
Ave
0.43
0.04
0.72
0.02
0.07
0.04
0.02
0.01
0.35
0.02
0.01
0.03 55.37
0.00
0.00
0.05
0.08
0.03
0.02
0.08
0.04
0.01
0.01
0.02
0.05
0.00
0.00
0.00
44.04
100.00
7
Stdev
14 Ap(21
Stdev
Ave
0.15
0.04
0.03
0.13
0.02
42.21
0.48
0.20
0.50
0.18
0.19
0.02
0.04 54.24
0.00
0.01
0.00
0.09
0.05
0.02
0.06
4.12
0.01
0.02
-1.74
99.33
6
Stdev
0.04
0.01
0.00
0.04
0.71
15.77
0.05
0.05
0.01
0.02
0.01
0.02
0.11
0.18
0.03
0.06
0.02
0.01
0.00
3.64
9.46
0.20
0.02
0.07
0.02
0.02
0.01
0.35
0.21
0.08
0.03
0.07
0.02
0.13
6.76
0.06
0.08
8.10
0.01
0.02
0.00
0.07
0.10
0.05
0.04
1.01
0.01
0.04
0.00
0.01
0.36
0.05
0.32
10.59
0.03
0.04
0.01
0.02
0.18
0.12
0.13
0.56
0.03
0.04
0.02
0.17
10.27
0.04
0.01
0.05
0.01
0.04
0.02
0.03
0.39
0.03
0.03
0.06
0.02
0.06
0.02
0.00
0.01
0.03
0.00
0.04
0.03
0.05
0.01
0.04
0.01
0.03
0.01
0.05
0.01
0.04
0.01
0.55
0.02
0.05
0.01
0.12
0.00
0.05
0.01
0.28
0.01
0.04
0.01
0.06
0.00
99.40
Tonalite Gneiss
(3
K-fs
Ave
63.80
0.02
18.24
0.02
SiO2
TiO2
Al2O3
Cr2O3
P 2 O5
FeO
MnO
MgO
CaO
Na2O
K2O
BaO
SrO
NiO
F
Cl
-OŁF,Cl
Total
0.02
0.02
0.01
0.05
0.66
15.71
0.45
0.08
0.01
0.05
0.00
99.15
1)
2)
3)
4)
5)
6)
7)
8)
9)
10)
11)
12)
13)
14)
15)
16)
17)
18)
19)
20)
21)
99.92
(6
19 Plag
Stdev
Ave
0.39 62.65
0.03
0.03
0.10 22.91
0.03
0.01
0.03
0.02
0.01
0.03
0.20
0.22
0.09
0.09
0.02
0.03
0.01
0.02
0.01
0.01
4.59
9.01
0.23
0.01
0.13
0.01
0.05
0.00
99.67
95.86
(9
22 Bt
Stdev
Ave
0.60 34.18
0.03
3.20
0.26 17.64
0.01
0.02
0.03
0.02
0.01
0.30
0.21
0.11
0.02
0.07
0.02
0.04
0.01
23.48
0.13
6.63
0.02
0.02
9.58
0.04
0.02
0.01
0.59
0.02
95.55
94.79
87.37
(12
(15
24 Mu
Stdev
Ave
0.19 46.99
0.46
0.66
0.37 31.61
0.03
0.03
0.39
0.04
0.25
0.02
0.02
0.11
0.04
0.03
0.02
0.05
0.01
2.14
0.01
1.44
0.03
0.14
11.08
0.10
0.03
0.01
0.29
0.02
94.58
12 Chl
Stdev
Ave
0.44 25.01
0.39
0.19
0.65 19.02
0.03
0.02
0.34
0.01
0.23
0.04
0.05
0.26
0.06
0.04
0.02
0.06
0.01
32.02
0.25
9.57
0.08
0.00
0.11
0.01
0.06
0.01
0.28
0.01
98.27
9 Gra(18
Stdev
Ave
0.50 36.68
0.14
0.02
0.81 20.43
0.03
0.01
0.93
0.10
0.39
0.05
0.00
0.10
0.02
0.08
0.02
0.03
0.01
86.65
K0.90Na0.09Ca0.01(Al0.01Si0.99)AlSi2O8
K0.94Na0.06AlSi3O8
K0.93Na0.06Ca0.01(Al0.01Si0.99)AlSi2O8
Na0.80Ca0.19K0.01(Al0.19Si0.81)AlSi2O8
Na0.81Ca0.17K0.01(Al0.17Si0.83)AlSi2O8
Na0.78Ca0.21K0.01(Al0.20Si0.80)AlSi2O8
K0.93Na0.01(Fe1.32Mg0.86Al0.41Ti0.19)Al1.32Si2.68O10(OH,O,F)2
K0.80Na0.01(Fe1.45Mg0.77Al0.47Ti0.15Mn0.01)Al1.33Si2.67O10(OH,O,F)2
K0.96(Fe1.54Mg0.78Al0.31Ti0.19Mn0.01)Al1.32Si2.68O10(OH,O,F)2
K0.84Na0.03(Fe0.18Mg0.20Al1.73)Al0.85Si3.15O10(OH,O,F)2
K0.90Na0.04(Fe0.04Mg0.04Al1.90Ti0.02)Al0.92Si3.08O10(OH,O,F)2
K0.96Na0.02(Fe0.12Mg0.15Al1.72Ti0.03)Al0.81Si3.19O10(OH,O,F)2
K0.06Na0.01(Ca0.03Fe1.97Mg1.35Al2.05Ti0.01Mn0.01)Al0.88Si3.12O10(OH,O,F)8
K0.01(Fe2.85Mg1.68Al1.40Ti0.01Mn0.02)Al1.33Si2.67O10(OH,O,F)8
K0.02(Ca0.01Fe2.99Mg1.59Al1.29Ti0.02Mn0.02)Al1.21Si2.79O10(OH,O,F)8
(Al0.98Si0.01Fe0.01)AlSiO5
(Al0.99Fe0.01)AlSiO5
(Fe2.41Mg0.29Mn0.23Ca0.07)(Al0.98Fe0.02)2Si3O12
(Mg1.10Fe0.88Na0.04Mn0.01)(Si5.03Al3.94)O18*nH2O
Ca2.99Mn0.01CO3
(Ca4.88Mn0.01Fe0.01)(PO4)3(F,O,OH,Cl)
35.76
3.33
2.38
0.80
0.00
0.01
0.00
0.07
0.02
0.21
0.01
99.75
Alkali-feldspar
Plagioclase
Biotite
Muscovite
Chlorite
Other
0.05
0.02
0.24
0.02
0.49
0.00
0.10
0.03
0.02
0.01
0.03
0.00
0.01
0.41
0.39
0.07
0.04
0.02
0.30
0.03
0.07
0.01
105
The Camebax SX50 equipment was used also for qualitative and semi-quantitative
energy dispersive spectrometer (EDS) analyses. The EDS-analyses were used for
selected accessory mineral identifications in the rock types. Typically these minerals
were among those, which are opaque under polarising light microscopy. In the order of
number of the EDS-observations, mica gneiss contains pyrite, graphite, pyrrhotite and a
trace of molybdenite as opaque minerals. Similarly, granite pegmatite contains pyrite,
graphite and a trace of galena, and tonalite gneiss contains pyrite and pyrrhotite.
A few graphitic inclusions found in granite pegmatite were studied in a more detailed
scale and were analysed with the EDS-equipment. It turned out that the graphitic
inclusions in granite pegmatite frequently tend to contain traces of uranium silicates as
well.
Mineralogical composition of the backfill pattern
The calculated modal composition results from 14 rock type samples are presented in
Table A4-2. These calculations were performed with a counter-equipped polarising
microscope from the same polished thin section samples as utilised in the WDS
mineralogical analyses. By comparing Tables A4-1 and A4-2 it becomes evident that
from the counted and identified minerals of Table A4-2 only quartz, hornblende, zircon,
epidote/saussurite and opaque minerals have not been analysed quantitatively.
For the present purposes, quartz and zircon were considered essentially stoichiometric
compounds. The minor amounts of hornblende are easily mixed up with chlorite in the
optical microscopy. Possibly, for this reason hornblende was not found for WDSanalyses. However, XRD-analyses from the crushed rock powder (see below) suggest a
minor amount of ferroan magnesiohornblende in the backfill pattern. The
epidote/saussurite -group was practically impossible to analyse with the WDSequipment. In the studied samples, all the epidote/saussurite findings are a part of the
impure sub-microscopic crystalline alteration phase of plagioclase. Hence, the optically
identifiable epidote does not exist in the backfill-pattern crushed rock, and epidote has
been assigned in the group name simply because further calculations require a mineral
formula approximation for this phase as well. The identified opaque minerals (pyrite,
graphite, pyrrhotite, molybdenite, and galena) are assumed as stoichiometric compounds
in the current calculations.
106
Table A4-2
Modal compositions of the backfill-pattern rock types. All average
concentrations (Ave) and standard deviations (Stdev) are presented in volume-%.
Numbers abbreviated with N denote the amount of sample analyses used for mineral
amount average and standard deviation calculations. Each analysis is based on the
mineral identification of 2000 points from a studied thin section sample.
N
Quartz
Plagioclas e
K-fe lds par
B iotite
Chlorite /Hornbl.
M us c./Se ricite
Sillimanite
Cordie rite
Carbonate
Garne t
Apatite
Zircon
Epid./Saus s .
Pyrite
Pyrrhotite
Graphite
M olybde nite
Gale na
M ica Gne is s
Granite Pe gmatite
6
4
Ave (vol%) S t D e v
Ave (vol%) S t D e v
5 .8
4.8
20.6
37.0
6
.9
9.4
17.2
25.4
5 .4
10.2
16.3
25.4
3 .5
0.5
0.9
24.9
0
.7
0.5
1.1
2.2
0 .2
2.7
1.8
6.8
3 .1
0.4
5.8
1.0
4 .4
11.8
0.4
0.6
0.0
0.2
0.2
0.1
0.0
0.0
0.0
100.0
0 .1
0 .1
0 .1
0 .1
0.0
0.1
0.3
0.2
0.0
0 .1
0.2
0 .1
0 .0
0 .0
0.2
0 .1
0.0
100.0
0.0
Tonalite Gne is s
4
Ave (vol%) S t D e v
1.6
25.0
2
.0
39.3
0 .8
15.6
1.9
13.7
0
.7
0.9
0 .5
1.8
0.7
0.7
0.3
1.1
0.6
0.4
0 .6
0 .4
0 .1
0 .8
0 .2
0 .1
0 .0
100.0
There is a huge number of literature references available about diadogies, solid solutions
and impurities in sulphides (e.g. Ribbe 1974, Deer et al. 1995). Of the currently
identified sulphides, pyrite and pyrrhotite may contain trace amounts of Ni, Co, Cu, As,
Pb, Zn and Mn. Lead in galena may be substituted in small amounts with Sb, As, Bi, Ag,
Tl, Zn, Cd, Fe, Mn, and Cu. Molybdenite may contain Rh, Re, Ag, Au, and Se etc. as
impurities. However, practically all these metals are beyond the scope of the current
studies. Moreover, the concentrations of these metals are of no interest considering the
total elemental molalities of the crushed crystalline backfill-pattern.
The total opaque concentrations detected in the optical microscopy have been distributed
to the EDS-observed opaque minerals in Table A4-2. The tabulated opaque mineral
concentrations are weighted with the EDS-findings frequencies. The sums of the opaque
mineral concentrations within each rock type equal the microscopically detected totals.
1)
100.0
0.2
0.0
0.0
0.0
0.0
19.6
16.4
15.2
26.9
11.3
6.8
1.8
1.1
0.3
0.2
0.0
0.0
0.0
0.1
0.1
0.1
0.1
0.7
0.2
3.1
4.4
3.5
5.4
6.9
5.8
750.0
1.8
0.1
0.2
0.1
0.3
147.0
122.8
114.2
201.4
84.9
51.1
13.6
8.6
2.2
1.7
0.1
0.1
0.1
0.5
0.5
1.0
0.9
5.5
1.7
23.3
32.7
26.3
40.5
51.8
43.5
Stdev
100.0
0.1
0.2
0.3
1.2
7.2
2.5
0.1
0.3
0.6
0.0
36.7
25.2
24.7
1.0
0.0
0.1
0.1
0.0
0.4
0.2
0.1
0.5
2.7
0.4
0.5
10.2
9.4
4.8
200.0
0.2
0.3
0.6
2.5
14.4
4.9
0.3
0.6
1.2
0.1
73.4
50.4
49.4
1.9
0.1
0.2
0.1
0.1
0.8
0.4
0.1
0.9
5.5
0.8
0.9
20.3
18.8
9.7
100.0
0.8
0.9
1.1
0.6
1.9
0.9
0.5
1.1
24.2
38.1
14.8
15.0
0.1
0.2
0.6
0.4
0.8
0.1
0.7
0.5
1.9
0.8
2.0
1.6
50.0
0.4
0.5
0.6
0.3
0.9
0.5
0.2
0.5
12.1
19.0
7.4
7.5
Granite Pegmatite 200 g
Tonalite Gneiss 50 g
Ave (wt%) Stdev Grams Stdev Ave (wt%) Stdev Grams
Assumed epidote formula: Ca2(Al2.5Fe0.5)Si3O12(OH)
Carbonate
Apatite
Garnet
Pyrite
Pyrrhotite
Graphite
Molybdenite
Galena
Quartz
Oligoclase
Microcline
Biotite
Cordierite
Sillimanite
Musc./Sericite
Chlorite/Hornbl.
Zircon
Epid./Sauss.(1
Mica Gneiss 750 g
Ave (wt%) Stdev Grams
0.1
0.1
0.3
0.2
0.4
0.1
0.3
0.3
1.0
0.4
1.0
0.8
Stdev
1000.0
232.5
192.3
171.1
210.8
84.9
53.6
28.8
14.0
2.7
2.8
1.2
0.8
0.5
2.9
0.4
0.5
0.1
0.2
0.1
0.1
0.3
0.1
0.7
0.3
0.7
0.8
1.8
1.1
6.8
7.4
24.1
32.7
28.2
61.2
71.6
54.0
60.1
265.7
276.9
456.0
613.6
162.3
397.8
619.3
183.3
468.8
100.1
482.1
488.8
120.0
87.9
12.0
128.0
239.3
Crushed Rock 1000 g
Grams Stdev Unit wt
3.868
0.724
0.618
0.462
0.138
0.330
0.073
0.023
0.015
0.006
0.012
0.002
0.001
0.024
0.005
0.041
0.001
0.001
0.000
0.000
0.027
0.001
0.006
0.001
0.001
0.008
0.004
0.006
0.011
0.019
0.148
0.053
0.062
0.221
0.270
0.899
mmol/g
Ave Stdev
Table A4-3 Mineral compositions of the backfill-pattern rock types. For each rock-type the first two columns (Ave and Stdev) are
presented in weight-%. The volume-%'s (Table A4-2) have been recalculated to grams for each rock type assuming an amount of 1 kg of
crushed rock, and summed up in the columns "Crushed Rock". Unit formula weights (Unit wt) presented are based on Table A4-1 where
appropriate. Two final columns represent average molalities and standard deviations of minerals (mmol/g) in the crushed rock.
107
108
The modal compositions presented in Table A4-2 have to be converted to the weight-%
-based compositions for the further calculations. The densities of minerals required in
these conversions have been adapted from literature (Deer et al. 1995). Frequently,
mineral densities are on a mineral composition dependent range. Therefore, the
compositional information available from Table A4-1 has been utilised for the density
estimations, as well. The mineral compositions of the backfill-pattern rock types are
presented on the weight-% basis in Table A4-3.
In Table A4-3 two final columns give the molar average mineral composition and the
standard deviations for the prepared crushed rock backfill-pattern. The standard
deviations presented in Table A4-3 originate from the point counting method of mineral
amounts. The counting was carried out from relatively small thin section slabs. The
sources of variation are several, but in the current case the following are the main ones:
the rocks are heterogeneous by nature, and the abundance of large minerals is
exaggerated in relation to small minerals (that tend to be underrated).
According to Table A4-3, one gram of the crushed rock backfill-pattern contains
significant amounts of potentially reactive quartz (233 mg), biotite (211 mg), plagioclase
(192 mg), alkali-feldspar (171 mg) and cordierite (85 mg). A limited potentiality,
considering the reaction product side, can be expected from sericite (29 mg),
chlorite/hornblende (14 mg) and epidote/saussurite (2.8 mg). Of the minor minerals it is
likely that carbonate (1.2 mg), pyrite (2.9 mg) and pyrrhotite (0.4 mg) interact with the
hyper alkaline solution.
Of the major minerals sillimanite (54 mg) is expected to stay mostly inert in the alkaline
interaction experiments. Finally, of the minor minerals it is expected that zircon (2.7
mg), apatite (0.8 mg), garnet (0.5 mg) and graphite (0.5 mg) do not react in the
experiments.
A4
2
Final rock material
No special pre-treatments were done for the crushed rock samples. Both initial and final
experimented bulk samples were dried and finely ground in a mortar at ambient relative
humidity and temperature. A Philips X'pert-MPD diffractometer with CuKα radiation
was used for the analyses. The scanned interval was in the 2Θ interval 2-70° and the
resolution was 0.02° with 0.5 s counting time. The samples were prepared on glass
holders and each sample were scanned four times. Between each run the samples were
re-blended to ensure the sample disorientation. The spectra presented in the following
are averages of four runs.
The mechanical fluctuations of the X'pert goniometer were eliminated by calibrating the
horizontal axis of the spectra with two fixed well-known quartz d-values (i.e. 4.26Å and
1.541Å) with linear regressions. Furthermore, because temporal variations in the
induction voltage are possible, and because the presented diffraction patterns (Fig. A4-1)
were run at different times, the background levels of the patterns were calibrated to
equal levels. The diffracted intensity in three windows (2Θ values 6.00°–6.30°, 38.08°–
109
38.38°, and 62.30°–62.58°) were utilised for the background calibration, and
calculations were done with linear regressions against the vertical axis of the spectra.
Finally, the presented diffraction patterns were filtered with the moving average of three
neighbouring terms (the width of the moving window was 0.04°).
In spite of these calibration and smoothing treatments, the diffraction pattern
comparisons among crushed rock samples are subject to higher uncertainties that in the
case of bentonite. This is mainly because of coarser size of mineral grains in crushed
rock. Grain size increases uncertainties in two ways. "Coarse" grains mean less reactive
surface area for minerals, and thereby less and slower mass transfers between water and
minerals. During the sample preparation the mechanical distribution of "coarse" grains
cause as well random deviations from the ideal average. Finally, it has to be pointed out
that the backfill pattern is a mixture of three rock types. This means that more minerals
and more mineral compositions can expected from the mixture than from a single
crushed rock type. As a summary, the current diffraction pattern interpretations are
prone to ambiguities. However, certain conclusions can be drawn.
Partial diffraction patterns from the HYRL batch experiments are presented in Figure
A4-1. The characteristic patterns utilised in the peak identification are presented in
Table A4-4. As a general note, it seems that very little has happened in the fresh alkaline
experiments. Altered spectra from the saline alkaline and saline hyperalkaline indicate
more variation in the peak intensities. Possibly the high pH (12.5 in fresh alkaline) alone
is not enough to cause "fast" alteration of samples. The systems are catalysed if the ionic
strength of initial solution is higher, and it contains suitable solutes in addition to high
pH (e.g. Ca in saline alkaline experiment). On the other hand, it seems that if pH is high
enough (13.5 in saline hyperalkaline) alteration reactions are induced anyway.
110
Table A4-4
Characteristic diffraction patterns (JCPDS, 1997) used for the
diffraction peak identification of the crushed rock diffraction patterns. Card number
refer to the database and acronyms to text and Figure A4-1. Diffraction data are given
as d-values (Å).
Chemical formula
Card No
Ca2(Mg,Fe)5(Si.Al)8O22(OH)2
21-0149
Acronym
used
Hbl
Ca2(Al,Fe)Al2Si3O12(OH)
09-0438
Ep
Mg5Al(Si3Al)O10(OH)8
29-0853
Chl
(Na,Ca)Al(Al,Si)Si2O8
02-0532
Olg
NaAlSi3O8
09-0466
Ab
KAlSi3O8
01-0705
Mkl
SiO2
05-0490
Qtz
KAl2Si3AlO10(OH)2
07-0025
Mu
K(Mg,Fe)3(Al,Fe)Si3O10(OH,F)2
42-1437
Bt
(K,H3O)Al2Si3AlO10(OH)2
26-0911
ill
Mg2Al4Si5O18
13-0294
Crd
CaCO3
05-0586
Cc
ZrSiO4
02-0701
Zr
NaCl
01-0993
Ha
Fe1-xS
29-0726
Po
Characteristic d-values (rel. intensity)
8.51(0.6), 3.29(0.3), 3.14(1.0), 2.82(0.2),
2.72(0.4), 2.17(0.2)
7.98(0.1), 5.02(0.4), 4.00(0.4), 3.49(0.4),
2.90(1.0), 2.81(0.5), 2.68(0.6), 2.59(0.6),
2.40(0.7), 2.11(0.4)
7.16(1.0), 4.77(0.7), 3.58(0.6), 2.86(0.4),
2.01(0.2)
6.40(0.5), 4.07(0.8), 3.67(0.8), 3.47(0.6),
3.18(1.0), 2.90(0.6), 2.52(0.6), 2.43(0.5),
2.29(0.5), 2.10(0.6)
6.39(0.2), 4.03(0.2), 3.78(0.3), 3.68(0.2),
3.66(0.2), 3.20(1.0), 2.93(0.2)
4.28(0.4), 4.01(0.2), 3.85(0.2), 3.35(0.3),
3.25(1.0), 2.94(0.3), 2.16(0.3), 1.80(0.3)
4.26(0.4), 3.34(1.0), 2.46(0.1), 2.28(0.1),
1.82(0.3), 1.54(0.2), 1.38(0.1)
10.1(1.0), 4.49(0.9), 3.66(0.6), 3.36(0.9),
3.07(0.5), 2.58(0.5), 2.57(0.9)
10.1(1.0), 3.35(0.4), 2.63(0.3),2.45(0.2),
1.54(0.2)
10.0(0.9), 5.02(0.5), 4.48(0.2), 4.44(0.1),
3.46(0.1), 3.34(1.0), 2.99(0.2), 2.01(0.5)
8.52(0.9), 8.45(1.0), 4.09(0.5), 3.13(0.6),
3.04(0.7), 3.03(0.7), 3.01(0.6)
3.86(0.1), 3.03(1.0), 2.50(0.1), 2.29(0.2),
2.10(0.2), 1.91(0.2), 1.88(0.2)
3.30(0.5), 2.96(1.0), 2.54(0.7), 1.81(1.0),
1.55(1.0)
2.81(1.0), 1.99(0.8), 1.63(0.3), 1.26(0.3),
1.00(0.3)
2.99(0.4), 2.65(0.6), 2.07(1.0), 1.27(0.4)
111
Figure A4-1 Partial diffraction patterns of crushed rock after various interaction times
in the three batch experiment series. Acronyms refer to Table A4-4 and the numbers
below the acronyms refer to d-values. Acronyms and d-values printed in red are
considered in more detail in the text.
112
The clearest indications of mineral alteration can be found from the saline alkaline
experiment (Fig. A4-1). A new nebulous peak emerges into the altered spectra at d-value
of 7.80Å. This peak and indications elsewhere in the diffraction patterns (e.g. 4.02Å and
2.93Å in Fig. A4-1) suggest that the new mineral is epidote. In the normal weathering of
rocks epidote is found as a submicroscopic alteration product of Ca-containing
plagioclase. The reaction can be presented in a simplified form considering only the
anorthite component of the plagioclase solid solution:
3CaAl2Si2O8 + Ca2+ + 2H2O = 2CaAl3Si3O12(OH) + 2H+
Anorthite
(A4-1)
Clinozoisite/Saussurite
Equation (A4-1) indicates that the solute Ca should promote the reaction towards right.
At the same time reaction produces protons that are eagerly received by the highly
alkaline solution. The reaction seems likely, though its effects to oligoclase peaks are
difficult to verify from the saline alkaline experiments (Fig. A4-1).
Altered spectra of the saline alkaline and saline hyperalkaline experiments indicate
relatively well partial alteration of cordierite. The changes in peak intensities with dvalues of 8.52Å and 8.48Å in the both experimented series support this interpretation. In
the saline hyperalkaline experiment also peaks with d-values of 4.07Å and 3.04Å give
similar impression. The cordierite alteration at low temperatures is complex process, but
it seems that it eagerly produces poorly crystalline highly water containing phases
depending on the solution composition (Ogiermann 2002). However, the peak 4.07Å is
shared with oligoclase and is therefore ambiguous. Likely this peak indicates dissolution
of plagioclase as well in the hyperalkaline experiments. In the saline hyperalkaline
experiments, the reduction in the peak intensity at d-value of 6.46Å indicates relatively
clearly alteration of plagioclase.
The main peak of microcline (at 3.25Å) exhibit visible reduction of intensity especially
in the saline hyperalkaline experiments. Furthermore, the analysed final water results of
the experiments exhibit strong increases in dissolved K and Al in final waters. At the
same time, the prominent peak (at 10.0Å) that can be related to K-bearing sheet silicates
exhibits clear variation in intensity in both saline alkaline and saline hyperalkaline
experiments. It seems likely that microcline is both dissolved and altered to
sericite/illite, or to kaolinite.
The saline alkaline and saline hyperalkaline experiments also suggest that some
hornblende is possibly altered (i.e. d-value 8.58Å). Reactions with minor hornblende are
difficult to prove from the diffraction patterns because of the frequent peak overlap.
However, nor initial neither final waters of the experiments contain dissolved Mg,
though alteration of cordierite (and dissolution of hornblende?) produces Mg in the
solution. A possible way to get rid of dissolved Mg is further hydration of hornblende
e.g. with reaction:
Ca2[Mg4Al][Si7Al]O22(OH)2 + Mg2+ + 2H+ + 2H2O = Mg5Al2Si3O10(OH)8 +
Mg-hornblende
Mg-chlorite
2Ca2+ + 4H4SiO4
(A4-2)
113
Equation (A4-2) produces Ca in solution that is easily consumed e.g. to production of
CSH-gel or with reaction indicated in Equation (A4-1).
As a concluding remark, all solid material received from the experiments contained
small amounts of CSH-gel detected with eye in the laboratory. However, the amounts of
gel precipitate in the experiments were much smaller than in the bentonite batch
experiments.
114
115
APPENDIX 5
CHARACTERISTICS OF MX-80
MX-80 bentonite used in the studies was obtained from Clay Technology (Sweden)
Characterisation of the material was performed also by Clay Technology, (Ola
Karnland). Additional infromation on the performance of this bentonite can be found in
Andra (2005).
All MX-80 samples for characterization were picked from the same batch (Batch 200101-19) of commercial Wyoming bentonite from American Colloid Co.
ECO R1 represents the bulk reference material and ECO R1c represents the clay fraction
of the reference material. The last letter in sample ID represents different samples from
the reference material analyzed at different occasions during the ECOCLAY and other
projects. Table A5-1 gives the determined chemical compositions of the materials and
Table A5-2 the determined CEC values for individual ions as well as the total cation
exchange capacity (Cu-CEC).
Table A5-1. Results on ICP/AES analyses of MX-80 (LOI = loss on ignition).
Sample
ECO R1-A
ECO R1-B
ECO R1c-A
ECO R1c-B
%
SiO2 Al2O3
58.5 19.1
58.4 19.4
59.5 20.7
60.8 20.9
Fe2O3
3.81
3.68
3.69
3.79
MgO
2.39
2.32
2.62
2.69
CaO
1.42
1.32
0.94
0.84
Na2O
2.10
1.99
2.23
2.25
K2O
0.54
0.49
0.16
0.19
TiO2
0.16
0.16
0.14
0.14
P2O5 MnO Cr2O3
0.03 0.01 0.03
0.04 0.01 0.05
0.03 <0.01 0.00
0.04 0.00 0.00
CTOT
0.29
0.28
0.42
0.00
STOT
0.32
0.29
0.17
0.13
LOI
11.9
11.9
9.8
8.1
Sum
100.6
100.3
100.4
99.9
Table A5-2. The type of exchangeable cations was determined by NH4-CEC and the
Cation Exchange Capacity (CEC) with Cu-CEC.
NH4-CEC, meq/100g
Cu-CEC
ECO R1-A
ECO R1-B
ECO R1-C
ECO R1-D
ECO R1c-A
ECO R1c-B
ECO R1c-C
ECO R1c-D
ECO R1c-E
ECO-R1c-G
meq/100g
70
74
76
75
88
88
85
81
86
87
Ca
K
Mg
Na
Sum
11
11
15
1
1
2
4
5
6
54
53
57
71
71
80
The material was ion-exchanged into Na-state and the clay fraction was thereafter
determined to be 85% of the bulk material (dry mass in both cases).
116
XRD was used to identify the minerals in the material, and the same XRD scan results
were analyzed by use of Siroquant software in order to quantify the minerals (Table
A5-3). In addition, grains of pyrite (FeS2), barite (BaSO4) and iron hydroxides in
quantities less than 1%.
Table A5-3 The mineral composition of MX-80 from XRD analysis.
Albite
Cristobalite
Gypsum
Montmorillonite
Muscovite
Quartz
Mx-80
7
3
1
83
1
5
100
Mx-80c
2
96
2
100
The following composition was calculated based on the ICP/AES analyses of the clay
fraction, the CEC values of the clay fraction determined by the Cu-method, and the
cation distribution in the bulk material:
(Al 3.11 Fe3+0.38 Mg 0.51) (Si 7.86 Al 0.14) O20 (OH) 4 ,
Na 0.49 Ca 0.05 Mg 0.02 K 0.01