The Determination of Toxic Elements in Hazardous Liquid Waste using High
Resolution EDXRF Spectrometry
Andrew T. Ellis, Philip A. Russell and Ray James’
Oxford Instruments, Industrial Analysis Group
19-20 Nuffield Way, Abingdon, Oxon.
OX14 ITX, UK
1 Rechem International,
Gwent NP4 5DQ, Wales, U.K.
Abstract
The analysis of liquid hazardous waste (LHW) prior to disposal using high temperature incineration
or as an alternative fuel is required for process and regulatory control. The typical requirement of the
industry sector is rapid screening to support decisions on the most appropriate treatment of the waste.
This paper reports the use of high resolution EDXRF spectrometry for the analysis of halides and
toxic heavy elements using a new rapid technique incorporating an unique sample preparation
methodology. Calibrations are developed using traceable certified 1000 mg 1-T aqueous standards and
pure organic solvents. Samples are stabilised in an alumina matrix and measured against a suitable
calibration.
The benefits of this new technique are:
l
Ease of obtaining calibration standards
l
Removal of sample history - i.e. control of matrix effects
l
Minimisation of analyte loss during sample preparation
l
Wide range of matrix types measurable using a single calibration - e.g. clean solvents to turbid
sewage sludge
l
Accuracy of measurement - typically within 10% relative in the concentration range lo- 1OOmg kg1 with a precision better than 5% relative
l
Speed of analysis - for >20 elements typically ~15 minutes from receipt of sample.
Results presented in this paper show high resolution EDXRF to be ideally suited to the analysis of
LHW due to good heavy element detection in the atomic number range 30 - 82 (Zn - Pb). Detection
limits achieved using rapid screening EDXRF and the new alumina sample preparation technique are
in the range 3- 17 mg kg-1 for heavy elements and below the working calibration range for Cl, P, and
S. These limits satisfy typical requirements for process and regulatory control which are of
importance in the analytical range >O. 1 %m/m for P, S & Cl and >50 mg kg-1 for the heavier
elements.
Introduction
The analysis of waste for the purposes of disposal risk assessment features some unique difficulties
arising from the extremely wide range of matrices encountered. The types of elemental analytes and
relevant ranges of measured values selected for waste assessment usually reflect requirements of
environmental regulation and waste disposal licensing1 . The key purposes of these measurements
are:* To ensure compliance with regulatory requirements (e.g. for waste-derived fuels)
l
To enable appropriate selection of disposal strategy
l
To confirm the waste composition
l
To ensure appropriate process control where a treatment or incineration disposal option is selected.
Copyright (C) JCPDS-International Centre for Diffraction Data 1997
Copyright 0 JCPDS-International
Centre for Diffraction Data 1997
This document was presented at the Denver X-ray
Conference (DXC) on Applications of X-ray Analysis.
Sponsored by the International Centre for Diffraction Data (ICDD).
This document is provided by ICDD in cooperation with
the authors and presenters of the DXC for the express
purpose of educating the scientific community.
All copyrights for the document are retained by ICDD.
Usage is restricted for the purposes of education and
scientific research.
DXC Website
– www.dxcicdd.com
ICDD Website
- www.icdd.com
The target analytes can be considered to fall into three groups:* Process control / acid generating elements
l
Heavy metals
l
Toxic/volatile metals
Precision, Accuracy and Appropriate Analysis
The typical level of accuracy and precision achieved in the analysis of liquefied waste is generally
considered to be acceptable if better than 20% relative. The contribution from inter-element effects to
the accuracy of an analysis can be significant in LHWs. The use of matrix modification methods
reduces these inter-element or matrix effects and their accuracy needs typically to be ~5% to be of
value. The alumina method proposed in this paper relies on the principle of little or no inter-element
effects being present in the final specimen which is demonstrated by the linearity of the calibrations
for all elements studied. Dilution into the linear calibration ranges is used to maintain the
minimisation of matrix effects while still achieving appropriate detection limits for the elements of
interest for both process and regulatory control. The reduction of matrix effects enables calibrations
to be developed from pure element standards prepared in aqueous or organic solvent.
Table 1 identifies the main areas of potential error encountered
the analysis of LHWs.
in any analytical technique used for
Table l- Key sources of error in the analysis of liquid hazardous waste
sample
Analyte losses
one stage.
O-100%
N
No preparation/digestion stages
ensuring no analyte loss.
No preparation/digestion stages
preventing uncontrolled chemical
reactions.
XRF spectra simple. Alumina
normalises matrix effects and reduces
inter-element effects to <5%
Chemical Interferences
O-100%
N
Instrumental
Interferences
l-15%
Y
linearity over measured
range
O-25%
Y
Simple sample dilution after s/w out of
range warnings.
~Stability of calibrations
O-15%
Y
Very stable technique and measures a
static sample identical to calibration
stds.
I
Copyright (C) JCPDS-International Centre for Diffraction Data 1997
Copyright 0 JCPDS-International
Centre for Diffraction Data 1997
Existing methods of inorganic elemental analysis of LHW and their limitations are summarised
Table 2:
in
Table 2 - Summary of existing methods and limitations
7, 8
Halides, P, S,
trace metals
Digestion
+
9
6, IO, 12, 13.
14.15
Fusion,
total due to complexing of inorganic halides with
metal species; Oxidation prevents determination of
I.
Halide interference; Heating during preparation
causes loss of important analytes e.g. Pb, TI, Hg;
Particulates; Large cont. of alkali metals can cause
significant interference; Organic solvents
Halides interference; Particulates; Organic
solvents
Homogeneity; Loss of analytes in fusion or
digestion process
Fundamentals of the alumina method for XRF
All techniques used for the analysis of liquefied waste suffer from matrix variation but the mixing of
activated alumina with the sample minimises this effect in EDXRF analysis. A key feature of the
alumina method is the reduction, by dilution, of all samples to a common matrix form thereby largely
eliminating the sample history. The alumina method uses this principle of diluting a sample to a
common matrix form with the following additional benefits in respect to the analysis of LHW:
I. The alumina is activated and will stabilise highly volatile solvents, reducing losses that may
otherwise occur during preparation and measurement.
II. The diluting matrix, i.e. alumina, is significantly heavier in atomic number than the original
sample which reduces background in the XRF spectrum compared to that produced by a low Z
organic or aqueous solution. Matrix effects are also reduced substantially.
III The density of an alumina-mixed sample compared to the original liquid form of the sample helps
to ensure that the alumina sample is infinitely thick with respect to the K series fluorescence Xrays emitted from heavy elements such as Cd or Sb. This ensures calibrations for heavy elements
such as Cd are linear at trace concentrations.
IV Compared to a calibration based on liquids of varying density there is no need to carry out a ratio
(e.g. to Compton scatter) correction.
V. Mixing a sample with alumina ensures that liquid phases camrot separate prior to or during
analysis and that undissolved solids are correctly incorporated into the analysis.
VI.The sample used for analysis is safer to handle in the spectrometer, i.e. leakages cannot occur in
the sample support tihn due to small punctures or chemical attack during analysis.
VII.The sample mass used for analysis is relatively large (5g) compared to alternate techniques.
Copyright (C) JCPDS-International Centre for Diffraction Data 1997
Copyright 0 JCPDS-International
Centre for Diffraction Data 1997
Experimental
Sample preparation materials:
Calcined Ahm7ina (15OO”C)a.
50-6Oml wide mouth HDPE sample bottles.
A minimmn of two, I cm diameter stainless steel ball bearings.
Chemplexb or SpexC Industries 3 1.5mm X-ray sample cups.
4pm Prolened & 4~117Hostaphane sample support films.
Standard Solutions:
As, Cd, Cr, Cu, Fe, Hg, Ni, Pb, Sb, Se, Sn, Tl, V, Zn - 1000 mg 1-l pure analyte aqueous standard
solutions as used for Atomic absorption spectroscopy (AAS)a.
P - Triethyl phosphate, S - Dithioglycol, Cl - Trichlorobenzene
Br - 1-bromonaphthalene,
I- Iodobenzoic acida.
Low molecular weight polyethylene glycol (PEG 400)a.
Preparation Procedure for Standards and Samples
Weigh 15g +/- 0.01 g alumina into a 60ml wide mouth polyethylene bottle. Add 5g +/- 0.0 1g of
sample to the bottle. Place two 1cm diameter stainless steel ball bearings into the bottle. Seal the
bottle with the screw cap and shake it vigorously until the sample and alumina are completely mixed
(approximately 30 seconds). Tapping the bottle on a hard surface will aid the mixing process.
Transfer sufficient sample to fill a standard 3 1.5mm diameter vented sample cup fitted with a suitable
X-ray transmission film for the element lines being measured. Gently tap the cup on a flat surface
(analysis face down) to compact the sample and remove any air gaps. The sample is now ready for
analysis.
The analysis is carried out using a calibration based on the same alumina : sample ratio.
Calibration
Calibration standards were prepared gravimetrically by blending the pure element standards into a
suitable calibration suite as determined by the final analytical requirements. Two calibrations ‘Light
Elements and Halogens’ and ‘Toxic Elements’ were prepared to cover the following concentration
ranges:
Toxic Elements: all elements O-600 mg kg-I
Light Elements and Halogens: P, S, Cl 0.05-5%, Br O-l%, I O-0.2%
The instrument used was an Oxford Instruments ED2000 EDXRF spectrometer fitted with a silver
target X-ray tube. The instrument conditions are shown in Tables 3 and 4. Intensities were obtained
using the method of least squares peak fitting to library spectral6 using XpertEase software - an
Oxford Instruments proprietary EDXRF software package for Microsoft WindowsTM operating
systems. The calibrations were all straight lines with no need for any interelement corrections.
” Merck/BDH, Dorset, UK
‘)Chemplex Industries,Tuckahoe,
NY, USA.
’ Spex Industries, Edison, NJ., USA
” ProleneO is a trade name of Chemplex industries Inc, Tuckahoe, NY, USA.
’ IHostaphanO is a high purity, 4ym polyester film obtainable from Oxford Instruments,
Copyright (C) JCPDS-International Centre for Diffraction Data 1997
Copyright 0 JCPDS-International
Centre for Diffraction Data 1997
Abingdon,
Oxon, UK
Table 3 - Instrument
,:::.. .......
‘:
,..
.,.,.,.,.,.,
conditions for Toxic Elements
.v..:
........
.I.
.I
:ilil~~~d~~~~rr’;I;:;:~~<~~&j5j :ii::vol~~~~~~~~
..\../\.
..A.
. .
.
.
:.:.:.:
. . . . . . . :.:.:..
is:~~jrr~~~~~~
...........
~~~~~~~i~~~~~
.....
1
air
2
3
4
air
air
air
I5
35
4s
50
Table 4 - Instrument
1
2
3
He
He
He
1000
65
100
500
. . . . . . . . . ,...
.,.
,.,.,.,.,.,.,.,.,.
,. ,.
~~~~~~~~~~~~~~~~~~
. . ,.....
Thick Al
Thin Ag
Thick Ag
Thick Cu
,. ,.......
,...
,. ,. ,. ,.
.:
V - Fe
Ni-Br
Hg-Pb
Cd-I
...
,. ,.
,. ,.,.,.
.,
.~~~~~~~~~~~~~~~~~~
......./........................\:.:...:
.\\:.:.:.:.:
100
100
150
150
conditions for Light Elements and Halogens
1000
6.5
500
5
35
50
none
Thin Ag
Thick Cu
P-K
Br
I
150
50
50
Method validation
The use of reference standards for validating this method was not possible. as no liquid waste
standard reference material are available. Method validation was, therefore, based entirely upon
spiking real waste samples with known concentrations
of analytes. Three types of actual waste
solutions were selected from routine test samples taken at an incineration plant:
l
Clear solutions
l
Turbid solutions, i.e. containing significant solids not in suspension
l
Biphasal solutions, i.e. contained two distinctly immiscible liquid phases
Results
Calibration details and standard errors
Table 5 shows the 30 lower limit of detection (where appropriate)
Error):
Table 5 - Calibration
results
Copyright (C) JCPDS-International Centre for Diffraction Data 1997
Copyright 0 JCPDS-International
Centre for Diffraction Data 1997
and regression details (Standard
n/a - Not Applicable. These elements were calibrated at concentrations
respective detection limits.
Measurement times as per Tables 3 & 4 - instrument conditions.
significantly
higher than their
Accuracy and Matrix spike results
Errors shown in the following tables are taken from the results output of the instrument and are
nominally +/- 2 sigma 16. These represent the total error attributed to spectrum processing and
counting statistics. Details of the calculations used in the error calculations can be found in Reference
16.
Accuracy
Table 6 shows the results of the measurement of calibration
on given vs. calculated concentration for each element:
Table 6 - Accuracy measurement
standards. The % accuracy figure is based
results
Matrix / matrix spike recoveries
Tables 7, 8 & 9 for the toxic elements, and Tables 10, 11 & 12 for the Light elements and halogens
give results for the measurement of the spiked samples separated into the three matrix types.
Using Equcctivn I shown below, a recovery figure for each analyte in each matrix type was
determined. The results, referred to as a matrix spike/matrix spike duplicate (MS/MSD), are shown
below.
Equution 1
% MS/MSD recovery = ((C2 - (Dl x Cl)) I C3)
x 100
1
Dl
= dilution factor due to matrix spike addition = l- (spike mass) / (sample mass + spike)
Cl
c2
c3
= talc. cont. of matrix without spike
= talc. cont. of matrix + spike
= given cont. of matrix spike
Copyright (C) JCPDS-International Centre for Diffraction Data 1997
Copyright 0 JCPDS-International
Centre for Diffraction Data 1997
Toxic Elements
Table 7 - Toxic elements spiking results: Biphasal
Table 8 - Toxic elements spiking results: Single phase
:.:::...::.:.:..
C~~~~~~~~~c:i:iiiii:iliiiiiiiiiiiii~.:
::.,;;;J::
:..
........
.,.....,.
:. ..:....:.:
.... .j:....
:il;:::-iiiail~~i~~~~~‘ii’~~~~~~
..)>:.:...:.p~:
Ic
j;,j
. . ..I...............
.::
,..
,......
.....
..... ...
y
..........................................
........
.:
,...::..:.
:
..
............ ..
,.,.
,.,.:.:.:.:.:.:.:.:.:.~.~.~.~.~.~,,.~.~.~.~.~.~.~.~.~.~.~
,:,:,:
:::::::.:::::::.:.:.:::.:.:~:~:~:~:~:~:~:~:~
:::::::::::::::::::::::::::::::::::::::::::::
::::::::::::::::::::::::::::::::::::::::::::::.:.,
MS/MSD recoverv _.\,
(%I
110
I 114
I 109
I 104
I 10.5
error mg kg6
2
6
10
5
spike cow. mg kg-’
116.8
109.5
109
105.7
109.9
.,.,.,
,.,,. .,.,.,.,.
.,.
:.:.,:,.:::,:
:.
:,,,,,,,,
:,,.,.,y:,:,:,:,:,:,:,:,::,:,
::::::::::::.~~~~~~~~~~~~~~~~~~~.~
..,........,...,.,,,,., :::ls~:iliii:jnjiiiiiiiiiiiiiiiiiii
.,.
~~~
iiiii~iii#;rlll:i:I:i:::il’:‘:“:’:
iiii~~
‘..’;,.I
:.:..:j.
,.,.,,,,,,,.,,,,.,,.,.,.,,.,.,,.,.,
.A........
.\......\.........,.....
.......... ................................ ............
MS/MSD recoverv (%)
108
I 100
I 95
I 112
I 98
error mg kg-’
9
3
3
6 ’
9
soike cont. rng kg- ‘
105
45.5
55.5
54.6
97.0
ix,
Table 9 - Toxic elements spiking results: Turbid
Light elements & Halides
Table 10 - Light elements & halogens spiking results: Biphasal
spike cont. %m/m
Copyright (C) JCPDS-International Centre for Diffraction Data 1997
Copyright 0 JCPDS-International
Centre for Diffraction Data 1997
:.
:....:.
...
. .
:i~~:i~~~~~~~~~~~~~~~~~~
.,..
,..
.......................
90
I 108
5
4
105.3
103.8
‘.:.i~l:i:l’l’l’l’~~~~~~
77
10
96
I error *
Table 11 - Light elements & halogens spiking results: Single phase
lia:i~~~~~:tx-~~I;;i_:li::iii_:i:ii:i:i
‘:’
,.,., .,.,.,.,.,........... ....
,.,.,.,.,.
.......
MSiMSD recovery (%)
error %m/m
spike COIIC.%m/m
...... . . . . ... ,........
~,,::iii~~~~~~~~~~~~~~~~~~~~~~~~.~.~~~~::~~~::~
,.,,.,.,:,:,.,
,.,:,.,.,::.:..:.:........................
111.3
0.02
120
0.01
0.9156
0.926
. . . . . . . . ... ............ ....... .....,.,.,.,.
110
0.007
1.279
:i:ili:iiiiiiiiii:i’:‘i::ii:iii:iiiiiii:~
.,.,.,.,.
.,..,.,.,.,.,.,.
.,..,.,, ,‘, ;::: .‘.‘.:.:.:.:.:x.:x::.
95
0.0007
0.0599
100
0.0032
0.856
Table 12 - Light elements & halogens spiking results: turbid
~:..
.....
,.
ril:~~r~ir~j~~~~
:, :.:.:.:...:.....:.:.:.:.:.:.:.:.:...::~~
..:.::
.......... ..................... .. ,.
.:.:.:.:.:.:.:.:
.. .,..,.,.
MS/MSD recovery (%)
error %m/m
sDike cont. %m/m
Method
... .. .. ....... ....... ....... ... . ...................... .. ...
.,..,.,
,.
,.,
I:~~j)j:: ::‘.......:.
::i:Q~~~~~~~:~~~:,:,:~:~:~:-,?:‘iriarz~~~~~~~~~~~~~~
iiijjbii#i#s~~~~~~~:~:~:~~:
.,.,................
:.. ... .......... .
...,....A:...):.:
,,,,,,,,,,,,,,,,,,,,,
::::::::‘::::‘(~~~~::~~:::::~::::::::::::~:~~~:~.:.......
98
0.01
91
0.009
89
0.005
104
0.0006
100
0.0034
0.849
0.805
0.858
0.042
0.845
Reproducibility
A number of repeat analyses were made of a waste sample to demonstrate the reproducibility of the
sample preparation on the two calibrations, i.e. ‘toxic elements’ and ‘light elements and halogens’,
1. A single measurement from each of 10 repeat sample preparations was made for Cl content. A
repeat of this process was made on newly-prepared samples 48 hours later.
2. A single measurement from each of 10 repeat sample preparations was made for a waste sample
spiked with 54.3mg kg-l Cd.
A single Cl analysis of the waste sample prepared using the alumina technique and measured on an
Oxford XR400 EDXRF spectrometer, at a separate site and by a second operator, is shown in the last
column of Table 13.
Table 13 - Sample preparation
% R.S.D.
reproducibility
results
- % relative standard deviation
Discussion
The recovery
results show that all but 3, i.e. 93%, of the results from the toxic elements calibrations
lie within +/- 15% relative of the spiked value. 81% are within 10% relative. All the results from the
light elements and halogens calibration lie within +/- 15% relative of the spiked values. The majority
are within 10% relative.
During the running of these experiments
a number of possible areas of bias were observed. These
effects are summarised
as follows:
l
Under certain conditions
the prolene
film used for the analysis of the light elements and halogens
was seen to relax and become crinkled. This was found to be associated with samples containing
Copyright (C) JCPDS-International Centre for Diffraction Data 1997
Copyright 0 JCPDS-International
Centre for Diffraction Data 1997
high concentrations of certain chlorinated compounds. It is recommended that samples are
measured within 30 minutes of preparation. The toxic elements calibration uses Hostaphan film
and is not affected in the same way.
l
High concentrations of Br can affect the determination of Tl due to the fitting of the Tl L peaks in
the spectrum. The accuracy of measurement of Tl will depend on detector resolution and accuracy
of peak fitting routines used to determine the count-rate of individual elements in a spectrmn.
Conclusions
The alumina matrix modification technique provides a reliable, fast and robust method of sample
preparation prior to analysis by high resolution EDXRF spectrometry. The typical levels of accuracy
achieved for both major acid-producing elements and environmentally sensitive toxic trace elements
were within 15% relative using spiked real waste samples. Reproducibility of total measurement was
better than 2.5%. The wide element range, low power and non-destructive nature of EDXRF
spectrometry strongly lends itself to be the ideal instrument for LHW screening. The technique
outlined in this report has been shown to be fit-for-purpose by exhibiting: traceable analysis; relative
accuracy better than 20% and rapid analysis (<I 5 minutes) for the determination of elements in LHW.
The following matrix types are suitable for analysis using high resolution EDXRF spectrometry
the activated alumina method of sample preparation.
l
Industrial waste solvents
l
Sewage sludge
l
Liquefied waste fuels
l
Paints and inorganic pigments in liquid form
l
Electroplating solutions
l
Waste oils
with
A single calibration for the determination of light elements and halogens and a second one for the
determination of heavy trace elements can be used for most types of LHW samples. The simple
alumina sample preparation technique allows for rapid analysis, with total time, including sample
preparation, as follows:
Halogens and light elements determination typically <lSminutes
An additional 15 minutes for the heavy trace elements.
The alumina matrix modification technique described in this report is tailor-made for the
determination of most elements encountered in LHW, unlike alternative instrumental techniques
which must use some kind of aggressive (digestion) pre-treatment. This absence of pre-treatment
minimises unpredictable analyte losses, producing a high degree of analytical confidence.
The implementation of the alumina matrix technique can improve the reliability and accuracy of
results such that regulators and regulatory bodies could increase the number of elements determined
beyond the current minimum. The acceptance of the alumina technique coupled to high resolution
EDXRF spectrometry as an industry standard would ensure that a near total elemental analysis of all
LHW became possible. Currently a lack of appropriate available techniques and matrix difficulties
restricts the type and number of analyses carried out on any particular waste.
The method has been extensively used on one UK incineration site after the UK Environmental
Agency (EA) approved its use for the determination of Br.
Copyright (C) JCPDS-International Centre for Diffraction Data 1997
Copyright0 JCPDS-International Centre for Diffraction Data 1997
References
I. James R., Chemspec Europe 95 BACS Symposium
2. Marshall, J., Carroll, J., Crighton J. S., Barnard C. L. R., Journal Analytical Atomic Spectrometry,
l993,8,337R
3. Marshall, J., Carroll, J., Crighton J. S., Barnard C. L. R., Journal Analytical Atomic Spectrometry,
l994,9,319R
4. Marshall, J., Carroll, J., Crighton J. S., Journal Analytical Atomic Spectrometry, 1995, 10, 359R
5. McCrindle, R. I., Rademeyer. C. J., Journal Analytical Atomic Spectrometry, 1995, 10, 399
6. Lui et al, Guangpuxue Yu Guangpu Fenxi, 1992, 12, 83 (Chinese)
7. Vanhoe H., Goossens J., Moens L., Dams R., Journal Analytical Atomic Spectrometry, 1994,9,
177
8. Applied Zeeman Graphite Furnace Atomic Absorption Spectrometry Chem. Lab. Toxicol., eds.,
Minoia C., Caroli S., Pergamon , Oxford, 1992, 79
9. Tserovsky E., Arpadjam S., Koradjava I., Journal Analytical Atomic Spectrometry, 1993, 8, 85
1O.Peraniemi S., Vepsalainen J., Mustalahti H., Ahlgren M., Fresenius J. Anal. Chem. 1992, 344, 118.
I I .Meltsh B., Muenzberg I., Janssen A., LaborPraxis, April 1995, 19(4), 64, 67 German
12. West H., Cawley J., Wills R., Analyst, May 1995, 120, 1267
I 3. Lucke N ., Wehner B., Thi Hong Lan T., Kalla E., Acta Hydrochim., Hydrobio, 199 1, 19,275
German
14.Seiber J. R., Advances in X-ray Analysis, 1993,36, 155
15.ASTM D5839 method in press
lG.Statham, P., Analytical Chemistry,1977, 49, 2149
Acknowledgements
Our many thanks to Jeanette Gravel1 and David James for long hours preparing samples and
standards.
Copyright (C) JCPDS-International Centre for Diffraction Data 1997
Copyright 0 JCPDS-International
Centre for Diffraction Data 1997