Clays and Clay Minerals, Vol. 27, No. 6, 411416, 1979.
E F F E C T OF IONIC S T R E N G T H AND ION PAIR FORMATION
ON THE ADSORPTION OF NICKEL BY KAOLINITE
SItAS V. MATTIGOD, A. S. GIBALI,1 AND A. L. PAGE
Department of Soil and Environmental Sciences
University of California, Riverside, California 92521
Abstract---Adsorption of Ni(II) by Ca- and Na-saturated kaolinites was studied in equilibrating solutions
with total Ni concentrations ranging from 118 to 946/xg/liter. Background electrolytes used in these :experiments were 0.005, 0,0l, 0.025, and 0.5 M Ca(NO3)~, 0.002 and 0.005 M CaSO4,0.0l and 0.1 M NaNO3,
and 0.005 and 0.05 M Na2SO4. Ion speciation in equilibrium solutions was calculated by the computer
program GEOCHEM. Computed Ni2+ concentrations and activities at equilibrium were correlated with
total Ni adsorbed by kaolinite. Increasing ionic strength resulted in decreasing Ni adsorption. Adsorption
of Ni was greater from solutions when NO3 was the dominant anion. Based on adsorption data in SO4
medium, the standard free energy of adsorption of Ni2* ion on kaolinite was computed to be -27 kJ/mole.
Key Words---Ion speciation, Ionic strength, Ion pair, Kaolinite, Nickel adsorption.
INTRODUCTION
Accumulation of excessive amounts of trace metals
such as nickel in soils amended with municipal and industrial wastes can have a toxic effect on soil organisms
and plants (Page, 1974; Dowdy et al., 1976; Walsh et
al., 1976). Similar problems can be induced by accidental spills of geothermal brines on agricultural lands
(Phelps and Anspaugh, 1976). Such concern has
prompted many studies of trace metal chemistry in soils
in order to understand, assess, and attenuate the risks
involved in sludge applications to agricultural lands.
In soil, Ni exists in various solid and solution forms.
In solution, Ni exists not only as the free aquo ion (Ni 2+)
but also as ion pairs and complexes with various inorganic and organic ligands. Reported concentrations of
nickel in the saturation extracts of some California soils
range from <0.01 to 0.09 ppm (Bradford et al., 1971).
However, in some soils treated with sewage sludge,
nickel concentrations in soil solutions may be as high
as 53 ppm (L. Lund, Department of Soil and Environmental Sciences, University of California, Riverside,
California 92521; personal communication). Ni in the
solid phase exists not only in various mineral forms but
also in exchangeable and specifically adsorbed forms.
Therefore, a thorough understanding of Ni chemistry
in soils should encompass a study of all possible phases
of this metal.
One of the important aspects of Ni interaction in soils
is its adsorption on mineral surfaces. Adsorption of Ni
on clay minerals has been studied by McLean (1966),
Kabata-Pendias (1968), Counts (1975), and Koppelman
and Dillard (1977); however, these studies were not
directed towards elucidating the effects of various factors such as ion-pair formation and ionic strength on the
adsorption of Ni. Therefore, the purpose of the present
study was to clarify the adsorption behavior of Ni on
1 Current address: Alfateh University, Libya.
Copyright (~) 1979, The Clay Minerals Society
4ll
kaolinite at solution concentrations encountered generally in uncontaminated soil solutions. Ni adsorption
by kaolinite with respect to changing ionic strength in
the presence of cations such as Ca ~+ and Na + and as
influenced by ion-pair formation with ligands NO3- and
SO~2- were also part of this study.
MATERIALS AND METHODS
Preparation o f kaolinite suspension
A sample of kaolinite from Birch Pit, Macon, Georgia
was obtained from Ward's Natural Science Establishment. The <2-/xm fraction of this material was collected by centrifugation. Part of this <2-/xm material in suspension was saturated with Ca by washing it three times
with 0.5 N Ca(NO3)~. Excess Ca was removed by successive washing with deionized water. Another part of
the <2-~m fraction was saturated with Na by three
washes with 1.0 N N a N Q solution. Successive washing with 0.005 N NaNO3 was used to remove excess
Na. These ion-saturated kaolinite suspensions were
stored in plastic bottles and were used in all the adsorption experiments. The weight of clay per unit volume of suspension in each case was determined after
drying four samples of suspension, each 10 ml in volume, for 48 hr at 100~ The oven-dry weights of
Ca-kaolinite and Na-kaolinite suspensions were determined to be 6.35 and 2.99 mg/mt, respectively. The
cation-exchange capacity of the Ca-kaolinite was
determined to be 11.7 -+ 0.8 meq/100 g by displacement
with ammonium acetate buffered at pH = 5.3.
Adsorption experiments
To study the adsorption of Ni by Ca-kaolinite, 1-ml
suspensions were placed in 50-ml plastic centrifuge
tubes. Solutions of Ni(NO3)2 from 118 to 946/~g/liter of
Ni were prepared in a series of 0.005, 0.01, 0.025, and
0.5 M Ca(NO3)2 solutions. Similar Ni(NQ),2 solutions
were prepared in 0.002 and 0.005 M CaSO4 solutions.
412
Mattigod, Gibali, and Page
Table 1.
Clays and Clay Minerals
Stability constants for aqueous species at 25~ under 1 atmosphere pressure.
Reaction
CO2(g) + HzO = H2COf
H § + HCO3 = HxCOf
H + + CO3z = HCO:(
H + + SO4x- = HSO4
H § + NO3 = H N O f
H § + OH = H 2 0
Ca x+ + CO3x = CaCO:fl
Ca x+ + HCO:~- = C a H C Q +
Ca x§ + SO4x = CaSO4 ~
Ca 2+ + OH = CaOH +
Ca 2+ + NO3 = CaNO3 +
Ca z+ + 2NO3 = Ca(NO:~)f
Na § + CO3~ = NaCO3
Na § + HCO3 = N a H C O f
Na + + SOa2 = NaSO42Na + + SO42 = Na~2SO4~
Na + + NO3 = N a N O f
Na § + OH = N a O H ~
Ni z+ + CO~z = N i C O f
Ni x+ + 2CO3x- = Ni(CO3)~2
Ni x+ + HCO3 = NiHCO3 +
Ni x§ + SO4x = NiSO4 ~
Ni z+ + 2SO42 = Ni(SO4)f
Ni x+ + HSO4 = NiHSO4 +
Ni x+ + NO3 = NiNO3 +
Ni x+ + OH = NiOH +
Ni x+ + 2OH = Ni(OH)x ~
Ni 2+ + 3OH- = Ni(OH):~Ni z+ + 4OH- = Ni(OH)4 z2Ni z+ + OH = Ni2OH 3+
4Ni 2+ + 4OH = Ni4(OH)44+
log K
Reference
-1,46 _+ 0.003
6,36 _+ 0.004
10.33 +_ 0.04
1.99 _+ 0.004
-1.43
14,00_+ 0.001
3,15 _+ 0.08
1.02 _+ 0.10
2.31 _+ 0.04
1.39 +_ 0.04
0.68
0.65
0.55
0.16 _+ 0.06
1.10 _+ 0.08
1.51
-0.60
-0.18
6.871
10.111
2.141
2.33
1.021
1.10l
0.40
4.14
9.00
12.00
12.00
3.30
28.26
Harned and Davis (1943)
Nakayama (1970)
Nakayama (1970)
Dunsmore and Nancollas (1964)
Helgeson (1967)
Olofsson and Hepler (1975)
Reardon and Langmuir (1974)
Jacobsen and Langmuir (1974)
Nakayama and Rasnick (1967)
Bell and George (1953)
Fedorov et al. (1974)
Fedorov et al. (1974)
Nakayama (1970, 1971)
Nakayama (1970, 1971)
Fisher and Fox (1975)
Lafon and Truesdell (1971)
Davies (1927)
Baes and Mesmer (1976)
Mattigod and Sposito (1977)
Mattigod and Sposito (1977)
Mattigod and Sposito (1977)
Nair and Nancollas (1959)
Mattigod and Sposito (1977)
Mattigod and Sposito (1977)
Fedorov et al. (1973)
Baes and Mesmer (1976)
Baes and Mesmer (1976)
Baes and Mesmer (1976)
Baes and Mesmer (1976)
Baes and Mesmer (1976)
Baes and Mesmer (1976)
1 Estimated.
Thirty-five milliliters o f each o f t h e s e solutions w e r e
equilibrated with the kaolinite s u s p e n s i o n s at r o o m
temperature (-25~
in an automatic wrist-action shaker for 5 hr. Preliminary studies had s h o w n that the ads o r p t i o n r e a c h e d a s t e a d y state well within a span o f 5
hr. A f t e r equilibration, the s u s p e n s i o n s w e r e centrifuged at - 2 0 , 0 0 0 g for 25 rain, and the p H o f the sup e r n a t a n t was m e a s u r e d . T h e Ni c o n c e n t r a t i o n in the
s u p e r n a t a n t was m e a s u r e d using a Perkin E l m e r flameless atomic a b s o r p t i o n s p e c t r o p h o t o m e t e r ( F A A S ) ,
m o d e l 403, e q u i p p e d with an H G A 2100 graphite furn a c e and a d e u t e r i u m b a c k g r o u n d c o r r e c t o r . To avoid
e l e c t r o l y t e i n t e r f e r e n c e s and, w h e r e n e c e s s a r y , to conc e n t r a t e Ni to levels g r e a t e r than the limits o f d e t e c t i o n ,
Ni was e x t r a c t e d f r o m equilibrium solutions using amm o n i u m pyrrolidine d i t h i o c a r b a m a t e - m e t h y l isobutyl
k e t o n e ( A P D C - M I B K ) . This p r o c e d u r e , d e v e l o p e d by
Sprague and Slavin (1964), m a y b e e m p l o y e d with a
n u m b e r o f h e a v y metals and c o n s i s t s o f adding a d r o p
o f 1.0 N HNO3 and 1 ml o f 5% solution o f A P D C to a
25 ml aliquot of the s u p e r n a t a n t and shaking it vigorously for a b o u t half a minute. N e x t , the aliquot is agitated for a n o t h e r minute after adding 5 ml o f M I B K . Ni
in the organic p h a s e was d e t e r m i n e d using an F A A S .
Similar series o f Ni a d s o r p t i o n e x p e r i m e n t s w e r e
c o n d u c t e d with N a - s a t u r a t e d kaolinite. Solutions o f
N i ( N Q ) 2 ranging f r o m 118 to 946/zg Ni/liter w e r e prep a r e d with 0.01 and 0.10 M N a N Q as the b a c k g r o u n d
e l e c t r o l y t e for one series o f e x p e r i m e n t s and with 0.005
and 0.05 M NaeSO4 solutions for a n o t h e r series o f experiments.
Calculation o f ion s p e c i a t i o n in solution
In t h e s e e x p e r i m e n t s , total Ni a d s o r b e d b y Ca- or Nakaolinite can b e calculated f r o m the d i f f e r e n c e b e t w e e n
Ni a d d e d and that r e c o v e r e d in the equilibrium solutions. But, it should be n o t e d that Ni in solution may
exist not only as Ni 2+, but also as ion pairs and c o m p l e x e s with various ligands. T h e r e f o r e , it is useful to
k n o w the Ni 2§ c o n c e n t r a t i o n in solution in o r d e r to correlate with o b s e r v e d a d s o r p t i o n o f Ni o n t o kaolinite.
The solution speciation o f metal ions in a multicomp o n e n t c h e m i c a l s y s t e m is a f u n c t i o n of various p a r a m eters such as the total c o n c e n t r a t i o n s o f various metals
and ligands, p H , t e m p e r a t u r e , and partial p r e s s u r e o f
various gases. T h e r e f o r e , calculations w e r e m a d e o f the
distribution o f various ion s p e c i e s using the c o m p u t e r
p r o g r a m G E O C H E M (Sposito and Mattigod, 1977).
Vol. 27, No. 6, 1979
Adsorption of nickel by kaolinite
413
Table 2. Computed distribution of aqueous species in equilibrium solution at 25~ under I atmosphere pressure.
Ca(NO,)~ medium
Ni
Ca
Total conc.
pCv
Free conc.
pCM~*
MNOs*
M(NO:02~
MOH +
MHCO~+
MCO~~
4.91
0.78
4.99
0.94
5.68
1.35
-2.29
9.92
8.57
9.24
6.29
9.64
9.29
CaSO4 medium
Ni
Ca
4.84
2.90
4.89
2.95
MSO4 ~
MNOs +
MOH*
MHCQ +
MCOs ~
5.80
3.86
9.12
6.88
9.56
--
8.87
8.03
9.19
--
All concentrations are in M indicated as negative logarithms. Only those species which are present in concentrations
greater than 10 10M are included in this table.
Critically evaluated experimental association constants
of various aqueous species were used in these calculations (Table 1). Association constanis were estimated
for aqueous species for which the experimental values
were not available (Mattigod and Sposito, 1977). In
these calculations only those aqueous species whose
existence has been experimentally confirmed were included. There is sufficient experimental evidence to
confirm the existence of complexes such as NiNO3 +,
N i H C O S , NiCO3 ~ NiHSO4 +, NiSO4 ~ N i O H +,
Ni(OH)2 ~ Ni(OH)~ , Ni(OH)42-, Ni~OH '~+, and
Ni4(Ott)44+ (Fedorov et al., 1973; Pitwell, 1967; Nair
and Nancollas, 1959; Baes and Mesmer, 1976). All the
above Ni species, as well as similar Ca and Na species,
were included in the calculations. Such a procedure is
an essential aspect of chemical equilibrium calculations
for multicomponent systems (Mattigod and Sposito,
1977). The partial pressure of carbon dioxide in all these
computations was fixed at 10-3.5 atmospheres. The activity coefficients were calculated by Davies' equation
(Davies, 1962). A typical result of a calculation of ion
speciation is indicated in Table 2. The results of these
calculations indicate that, under the experimental conditions, only soluble complexes of metal-nitrate and
metal-sulfate were significant. The N i N Q + species
constituted from 1% to 17% of the total Ni concentration in various solutions, whereas the NiSO4~ species
accounted for 6% to 38% of the total soluble Ni. The
calculations also indicate that supersaturated conditions with respect to solids, such as nickel hydroxide
and nickel carbonate, did not exist in any of the initial
or the equilibrium solutions.
RESULTS AND DISCUSSION
Effects of ionic strength
The effect of ionic strength on the adsorption of Ni
by Ca-kaolinite is shown in Figure I. All adsorption isotherms appear to be linear and those isotherms for ionic
strengths less than 0.37 M appear to be constant par-
tition type according to the classification system of
Giles et al. (1960). This type of isotherm is characterized by a constant partition of ions between solution
and the adsorbent up to the maximum possible adsorption, where an abrupt change to a horizontal plateau
occurs. The linearity of the isotherms indicates that the
number of sites for adsorption remains constant (Giles
et al., 1960). Apparently, adsorption maxima were not
reached for the range of Ni concentrations used in these
experiments.
Generally, these adsorption isotherms (Figure 1)
show that there is a corresponding decrease in Ni adsorption with increasing ionic strength [Ca(NO:0=, as the
background electrolyte]. For instance, for the same
equilibrium concentration of Ni 2+ in solution, Ni adsorption at an ionic strength of 0.37 M is roughly 40%
of that observed at an ionic strength of 0.005 M. Similar
decreases in Ni adsorption with increasing ionic
strength were observed in experiments with C a S Q ,
NaNO3, and NazSO4 as background electrolytes. This
phenomenon can be attributed to (1) increasing Ca z+
concentration (or Na + concentration) with increasing
ionic strength and therefore increasing competition for
the adsorption sites on the clay mineral, and (2) decreasing activity of Ni 2+ ion in solution due to increasing non-ideality of solution with ionic strength. This
non-ideality is due to increasing electrostatic interaction and resulting formation of N i N Q + and NiSO4~ ion
pairs. Since Ni adsorption is governed by its activity in
solution, decreased activity in solution means decreased adsorption on kaolinite.
Effect of exchangeable cations
To compare the Ni adsorption on kaolinite in competition with Ca and Na, free nickel (Ni z+) ion activities
in the equilibrium solution were plotted against total Ni
adsorbed in rag/mole of kaolinite (Figures 2, 3). In solution media with NO3- as the dominant anion, substantially more Ni was adsorbed on Na-kaolinite than
on Ca-kaolinite at comparable Ni z+ activities in solu-
414
Clays and Clay Minerals
Mattigod, Gibali, and Page
600
500
Co (NO5) 2 MEDIUM
i [ SLOPE]~NTERCEPT] r
0.005 58.504 o.~78
(/010 45.571 09978
0:024 36.425 0,9988
0370 3450l -40.04 09941
o
E
MED, M L SLOPE I'"TE"CEPTI r l
I : 0.005
I:0.010
~ :
Co(NO~2 73.779x106 -0.99011
CoSO4
10.488x106 2Z80.3 0.9018/
o c~ (N03)2
600
/o
500
/
0 024
400
C3
t,I
if21
400
O
LLI
rr 300
9
09
o 300
cO
200
o
Z
.!'z 200
A I'
/ O
/
o
O
O
JO
I00
CaSO4
MEDIUM 9
I00
O0
MEDIUM
2
4
t
6
~
8
it0
t
J
~
I
12
CNi2* (/..t.M)
Figure 1. Effect of increasing ionic strength on the adsorption of Ni on kaolinite with Ca(NO3)2 as the background electrolyte.
6 *
0
0
[
2.
,}
4
I
6
I
8
I
10xl0 -6
GNi 2.
Figure 2. Ni adsorption on Ca-kaolinite as a function of Ni2+
activity in Ca(NO3)z and CaSO4 media.
tion. Similar results were obtained in solution media in
which SO42- was the principal anion.
such as CuCI +, CuOH +, Cu-glycine+, ZnOH +, and
ZnCI+, can occur on clay minerals (Elgabaly and Jenny,
Effects of ion-pair formation
1943; Farrah and Pickering, 1976; Koppelman and DilThe principal effect of ion-pair formation is the re- lard, 1977; Papanicolaou and Nobeli, 1977). It has also
duced NF + concentration in the equilibrating solution. been established that neutral ion pairs and negatively
Therefore, a ligand which forms ion pairs of greater sta- charged complex species are not adsorbed to any meability with a given metal decreases the concentration of surable extent on kaolinite. These studies suggest that
free divalent metal to a greater degree than a ligand in the present experiments, Ni 2+ as well as NiNO3 + ion
which forms a weak ion pair. Reduction in metal ad- pair are the adsorbing species in the NO3 system,
sorption can, therefore, be related to the nature of ion whereas only Ni 2+ ion is the adsorbing species in the
pairs involving the dominant anion in a system. The SO4 system. Therefore, when the total Ni concentraSO42- ion forms neutral ion pairs with Ni 2§ Ion pairs tion is the same in the two systems, the concentration
involving NO3- and Ni z+ also exist. The association of adsorbing species in solution Will be higher in the
constants for NiSO4~ and N i N Q + are 102.33and 10~176 NO3 system than in the SO4 system, leading to greater
adsorption of Ni on kaolinite in the NO3 system.
respectively (Nair and Nancollas, 1959; Fedorov et al.,
1973). Therefore, SO42 is considerably more effective Free energies of adsorption
in reducing Ni z+ concentrations in comparison with
Since Ni 2+ ion is the only Ni species to be adsorbed
NO3- ion. This effect, in turn, should be reflected in a
on
kaolinite in the SO4 system, the free energy of addecreased Ni 2+ concentration (and activity) in solution
sorption
of this ion can be calculated as follows:
and hence a decreased Ni adsorption on kaolinite. The
A metal ion adsorbing onto a clay mineral can be repNi adsorption isotherms for Ca-kaolinite (Figures 2, 4)
show clearly that the adsorption of Ni is considerably resented by the half reaction
less for the SO42 system in comparison with the NO3
system. Similar comparisons also can be made for Ni
adsorption on Na-kaolinite (Figure 3).
The difference in adsorption of Ni on kaolinite between the NO3 and the SO4 system can also be examined in light of the ionic species of Ni present in equilibrium solutions. A number of studies indicated that
specific adsorption of ion pairs of transition metals,
M +m + m X - = MX,~
(1)
where M = metal ion or ion pair with charge m
X = the clay mineral
MX m = metal-clay complex.
Assuming that the actual activity of X - is unity and
the activity of the adsorbed metal ion to be equal to its
mole fraction (N) on the adsorbent (implying an ideal
Vol. 27, No. 6, 1979
Adsorption of nickel by kaolinite
o/~
700
415
on Ca-kaolinite. A d s o r p t i o n o f Ni is d e p r e s s e d to a
g r e a t e r d e g r e e w h e n SO42 is the d o m i n a n t a n i o n in solution instead o f NO3 . This difference in a d s o r p t i o n
c a n b e a t t r i b u t e d to h i g h e r c o n c e n t r a t i o n s of a d s o r b i n g
species (Ni 2+ a n d N i N Q +) p r e s e n t in NO3 m e d i a in
c o m p a r i s o n to SO4 m e d i a in w h i c h only Ni 2+ was the
a d s o r b i n g species.
~la NO 3 MEDIUM
600
500
ACKNOWLEDGMENT
E9
E
d:3
LLI
0:3
r'f
o
u3
d3
<:[
W e t h a n k Dr. G. S p o s i t o for c o n s t r u c t i v e comments.
300
REFERENCES
I-Z
200
MEDIUM I SLOPE I INTERCEPT I r I
Na NO 5 185.75x106
-0.9853
No2SO4 59.699x IO5 65.299
0.9704
I00
0 t
I
I
I
I
I
0
2
4
6
8
I0 x 106
C],Ni2*
Figure 3. N i adsorption on Na-kaolinite as a function of Ni z+
activity in NaNO3 and NazSO4 media.
m i x t u r e of solutes o n the a d s o r b e n t ) , the e q u i l i b r i u m
c o n s t a n t (K) for t h e r e a c t i o n c a n b e w r i t t e n as:
K = N/a
(2)
w h e r e N = a c t i v i t y of a d s o r b e d ion ( = m o l e fraction)
and
a --- ion activity in e q u i l i b r i u m solution.
Eq. (2) c a n b e w r i t t e n as:
N = Ka
(3)
By p l o t t i n g N as t h e d e p e n d e n t and a as t h e i n d e p e n d e n t v a r i a b l e , o n e c a n o b t a i n K f r o m t h e slope of
t h e line.
T h e s t a n d a r d free e n e r g y o f a d s o r p t i o n (AG~
for
a r e a c t i o n s u c h as Eq. (1) c a n t h e n be c o m p u t e d f r o m
the relationships:
AG~
= - R T In K
(4)
w h e r e R = gas c o n s t a n t (8.3147 • 10 -3 kJ/deg mole)
and
T = absolute temperature.
T h e c a l c u l a t e d aG%ds v a l u e for Ni z+ o n kaolinite was
- 27 kJ/mole.
CONCLUSIONS
I n c r e a s i n g ionic s t r e n g t h d e c r e a s e s Ni a d s o r p t i o n o n
kaolinite. M o r e Ni was a d s o r b e d on N a - k a o l i n i t e t h a n
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416
Mattigod, Gibali, and Page
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Pe3mme--I/I3yqaJlacb a~lcop6tlnn Ni(II) Kaoa14nnTaMn, nacbmlennblM14 Ca n Na, 8 paBuoBecublX
paCTBOpax C O61IlnM14 KOHtlenTpalIn~tM14 Ni, 143MeHnlOlii14M14Cn OT 118 ~Io 946 /zr/J114Tp. j],onoJIn14TeJlbm,lMn 3JleKTpOnnTaMn, ncnonb3yeMl,iMn a 3T14X 3Kcnep14MenTax 61,1n14 0,005, 0,01, 0,025; n 0,5 M
Ca(NO3)2; 0,002 n 0,005 M CaSO4; 0,01 n 0,1 M NaNO3; n 0,005 n 0,05 M NaSO 4. O6pa3oaanne
nonoa B paBnoBecm,~x pacTsopax onpeJIe~nnoc~, c nOMOllI~,ro KOMnbmTepnofi nporpaMMbl FEOXHM.
l-Iojlcq14TaHHble KOHIIeHTpallH14 14 aKTMBHOCTMNi 2+ npn paBHOBeCltn KoppeJ144poBa~tdCb C O6IUI4M KO31HqeCTBOM Ni, a~lcop6upoBann~,ru Kao.ln,n-I14TOM. YBe~nqnBatoma~cn Hoaaaa cr~J~a nbl3Ba.rla yMem,menne
ajlcop611nn Ni. Ajicopflmn Ni ~3 pacTBopoa 6bi.aa 6oJihule, KorjIa NO3 6y.~ rJlaBIfbIM artnonoM. Ha
ocnosann14 ~Ianub~x a~Icop6anH 8 cpeRe SO4, 6bI21a Bbiqi4cYienacTau~lapTna~l cBo6o]Ina~ 3ttepFillt a~Icop6unn nona Ni 2+ Kao)3nnnTo~, pashas - 2 7 K~/MOJn,.
Resiimee---Die Adsorption von Ni 2+ durch Ca- und Na-gesiittigte Kaolinite wurde in LSsungen nahe dem
Gleichgewicht untersucht, die Gesamt-Ni-Konzentrationen im Bereich yon 118 bis 946/Lg/liter batten. Als
Hilfselektrolyte wurden in diesen Experimenten verwendet: 0,005, 0,01, 0,025, und 0,5 M Ca(NO3)2,0,002
und 0,005 M CaSO4,0,01 und 0,1 M NaNO.3 sowie 0,005 und 0,05 M NazSO4. Die Verteilung der Ionenarten
in den GleichgewichtslSsungen wurde mit dem Computerprogramm GEOCHEM berechnet. Die berechneten Ni2+-Konzentrationen und -Aktivit~iten bei Gleichgewicht wurden mit dem Gesamt-Ni, das durch
Kaolinit adsorbiert war, korreliert. Eine zunehmende Ionenst~irke bewirkt eine abnehmende Ni-Adsorption. Die Ni-Adsorption aus den LSsungen war grSBer, wenn NO~ das vorherrschende Anion war. Aufgrund der Adsorptionsdaten bei SO42 -Medium wurde die Freie Energie der Ni2+-Adsorption an Kaolinit
mit -27 kJ/mol berechnet.
Resum6----L'adsorption de Ni(II) par des kaolinites satur6es de Ca et N a a 6t6 6tudi6e dans des solutions
6quilibrantes avec des concentrations totales de Ni s'6tendant de 118 ~t 946/xg/litre. Des 61ectrolytes de
fond utilis6es dans ces exp6riences 6taient 0,005, 0,01, 0,025, et 0,5 M Ca(NO:3)2; 0,002 et 0,005 M CaSO4;
0,01 et 0,1 M NaNO~; et 0,005 et 0,05 M Na,_,SO4. La sp6ciation d'ions dans les solutions d'6quilibre a 616
calcul6e par le programme d'ordinateur GEOCHEM. Les concentrations et activit6s de Ni z+ calcul6es h
l'6quilibre ont 6t6 apparent6es h Ni total adsorb6 par la kaolinite. La force ionique croissante a r6sult6 en
une adsorption d6croissante de Ni. Lorsque N Q 6tait l'anion dominant dans les solutions, l'adsorption de
Ni 6tait la plus 61ev6e. En se basant sur les donn6es d'adsorption dans un milieu SO4, on a calcul6 que
l'6nergie libre standard d'adsorption de l'ion Ni 2+ sur la kaolinite 6tait - 2 7 kJ/mole.