-------
The accuracy of the method was measured by the percent recovery of the
spiked and unspiked sample concentration as calculated by the following equation:
% Recovery = 100 x (Cm/Csrm)
where Cm = measured concentration of standard reference material (srm)
Csrm = actual concentration of srm
i
According to the Quality Assurance Objectives outlined in the quality assurance
project plan, the accuracy of the matrix spike samples is to be 80 fc> 120 percent of
the actual value. All but two samples were outside of this limit for accuracy. The
completeness of the matrix spike and matrix spike duplicate samples were calculated
by the following equations:
C= 100-
where
C = percent completeness i
V = number of measurements judged valid
T = total number of measurements - i
The completeness was determined to be 96.7 percent which is well within the 90
percent completeness specified for this study. The most likely reason the two
samples were outside of the limit for accuracy was the error in the matrix spike
addition.
* . ' /
Method blanks were also analyzed with each batch of samples to determine
the amount of target analyte in the blank samples. Table 4-2 presents the method
blank data obtained through the analysis of the lead, sodium, and iron samples.
4-5
-------
TABLE 4-2. METHOD BLANK ANALYSES BY ATOMIC ABSORPTION
Analyte
Lead
Sodium
1
Iron
analysis
8/2/93
8/3/93
8/11/93
8/17/93
8/19/93
8/24/93
9/1/93
9/13/93
8/7/93
8/11/93
8/16/93
8/19/93
8/31/93
8/24/93
9/1/93
.«*•• • i^siv, N*VHH*CTIUallUII
(mg/L)
NDa
ND
ND
ND !
ND '
ND ;
ND
ND ,
ND
ND i
2
ND
ND ;
ND
ND
a Nondetectable. ;
All but one of the method blanks were below the method detection limit of 1 mg/L for
lead, sodium, and iron.
4.3 MASS BALANCES
Mass balances were performed on lead and sodium in all 24 bench-scale
electromembrane experiments. The percent closure of the mass balance also
indicates the reliability of the atomic absorption data and the procedures used to
perform the experiments. Table 4-3 presents the mass balance closures for lead.
The lead mass balances were calculated by the following formula: !
Mi = I (C x V) + Mc
where
M, = Mass of lead used in test solution g
Z(C x V) = (CL x VJ + (CS1 x VS1) + (CS2 x VS2) +
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= Volume of liquid in cathode chamber, L !
= Concentration of sample 1, 2..., g/L
VS1, VS2... = Volume of sample 1, 2..., L
Mc = Mass of lead deposited on cathode, g
Seven of the 24 electromembrane experiment lead mass balance results were
outside of the quality control range of 80 to 120 percent established in the quality
assurance project plan; five of the seven experiments were only slightly outside of
this range. The percent mass balance closure was outside of the quality control
range by more than 5 percent for Runs 4 and 15. The closures were below 100
percent indicating that either the initial quantity of lead was measured low, or the
outputs (quantity of lead in the samples, the lead deposited on the cathode, and the
final quantity of lead in the cathode) were measured too high. Because the initial
quantity of lead is known and is approximately equivalent to 0.8 percent lead solution
for Runs 4 and 15, it was assumed that the quantity of lead in the outputs was
measured too high. Thus, the percent lead removal may be lower than originally
reported. ''
The mass balance for sodium was calculated for each electromembrane
experiment by the following formula:
/ *MA
where: : . . . i
i - - - • . - - - j
Mj = percent mass balance closure for sodium, %
AMc = difference in initial and final mass of sodium in the cathode chamber
9 . ; • '
AMa = difference in initial and final mass of sodium in the anode chamber, g
The percent closure of the mass balance was calculated by first determining the
amount of sodium lost from the anode chamber. This calculation was!made by
subtracting the sum of the final mass of sodium in the anode chamber solution and
the total mass of sodium in t^e samples collected at various intervals during the tests,
from the initial mass of sodium in the anode chamber solution. The difference in the
amount of sodium is the amount transferred to the cathode chamber. The amount of
4-1.2
-------
sodium received by the cathode chamber was calculated in the same manner. Table
4-4 presents tfcejsodium mass balance data determined from the 24 electro-
membrane tests. All but five of the mass balances were outside of |the 80 to 120
percent quality control range. Based on the precision and accuracy! da*a presented in
Table 4-1, the method of sodium analysis appears to be adequate. However, the
sample matrix appears to pose some difficulties in analyzing sodiuni as indicated by
the mass balance data. Because the material balance closures for sodium were
outside of the quality control limits, the data does not appear to be useful for
comparison of sodium concentrations. ',
4.4 DUPLICATE TESTS
Several tests were performed with the same test parameters to determine if
the test results could be duplicated. The following tests are duplicates:
Run
No.
1
2
5
7
8
9
23
24
: Current:
Chelating Target lead con- Density,
Agent centration, % ma/cm2
Na4EDTA
Na4EDTA
DTPA
DTPA
DTPA
DTPA
DTPA (Ionics
membrane)
DTPA (Ionics
membrane)
0.8
0.8
0.8
0.8
4
4
0.8
0.8
25
25
25 j
25
25
25
15
15 :
i
The percent lead removal rates in Runs 1 and 2 were 99.4 and 98.0, respectively.
The quantities of lead deposited on the cathode were 27.6 and 26.6 grams in Runs 1
and 2, respectively. Other parameters measured during the electromembrane tests
(e.g., temperature of the anode and cathode chambers, pH of the anode and cathode
chambers) were similar for the two tests. Current efficiencies after a' 180-minute
4-13
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reaction period were 35 and 36.6 percent in Runs 1 and 2, respectively. Therefore,
the tests with tefra~sodium EDTA show good replication.
The percent lead removals in Runs 5 and 7 were 85.8 and 58.0 percent,
respectively. These percentages are quite different; however, the percentage of lead
removal after 150 minutes was 66.8 percent in Run 7, which is a higher percentage
than for 180 minutes. Therefore, it is assumed that the analysis of the last lead
sample (180 minutes) was below what the actual lead concentration should have
been. The actual lead removal should be approximately 77 percent for the 180-
minute sample in Run 7. The amount of lead deposited on the cathode was similar:
34.9 grams as deposited in Run 5, and 31.1 grams as deposited in Run 7. All other
data (e.g., pH of anode and cathode chamber, temperature of anode and cathode
chamber) were similar in both tests. Current efficiencies for Runs 5 and 7 were 32
and 23.5, respectively. Therefore, the runs show good replication.
In Runs 8 and 9, the percent lead removals were 33.8 and 40.2 percent,
respectively after a 3-hour reaction period. The amount of lead deposited on the
cathode was 67.5 grams in Run 8 and 36.2 grams in Run 9. The experimental data
from Table 3-2 shows that the anode and cathode chamber temperatures, and anode
and cathode chamber pH levels were very similar for the two tests. 4urrent effici-
encies in Runs 8 and 9 were 66.1 and 64.4 (after 210 minutes) percent, respectively.
In Runs 23 and 24, the percent lead removals were 28.1 and 47.3 percent,
respectively, after a 3-hour reaction period. The quantities of lead deposited on the
cathode was 18.4 grams in Run 23 and 15.2 grams in Run 24. The initial quantity of
lead in the cathode chamber was 32.0 and 30.3 grams for Runs 23 and 24, respec-
tively. According to the experimental data presented in Table 3-2, th§ anode and
cathode chamber pH levels were similar, the anode chamber temperatures were
similar, but the change in cathode chamber temperature was higher for Run 24
(8.4°C) than for Run 23 (4.9°C). The current efficiencies for Runs 23!and 24 were
19.7 and 28.5 (after 3 hours) percent, respectively. Based on the data for Runs 23
and 24, the results are comparable.
Based on the comparisons of the duplicate tests, it appears thajt better replica-
tion of results occurred for the tests conduced with 0.8 percent lead solutions than for
i. 4-19
-------
4 percent lead solutions. Only a selected number of conditions were duplicated
Other test conditions such as use of cadmium electrodes and use of the Ionics; '
membrane were performed with a minimum number of tests in order to approximate
the percent lead recoveries under these conditions. Further testing would need to be
performed ,f these parameters were to be selected for pilot- or full-scale application. ;
4.5 Impact on Quality
^ The bench-scale treatability program was designed as a screening study to
identify effects of various experimental parameters. Conclusions have been made in
the report based on trends that are intuitively apparent from the data These
conclusions are not interpreted in light of analytical and field QC samples that were
analyzed in conjunction with the field samples. The results from the; bench-scale
treatability program provide, useful conclusions regarding the effects iof various
parameters investigated in this study, but may not be compared directly to results
obtained outside of this study.
The following subsection presents a discussion of certain parameters that were
outs.de of the limits specified in the quality objectives and how this impacts the
results of this study. !
4.5.1 oH '• !
• i
The data quality objectives for this study were to adjust the initial lead-chelate
solution pH levels to ± 0.5 PH unit of the prescribed experimental ph! level. For Runs
2, 4, 5, 7, 17, 19, 20, and 21, the pH level of the starting lead-chelate solution was
greater than ±0.5 pH unit from the experimental pH. In Runs 2, 4, 5J 7 and 17 the
solutions were made with 0.8 percent lead. :
Runs 19, 20, and 21 were conducted with 1.5 percent iron in the 4 percent
starting lead solutions. While the lead/iron-chelate solution was being mixed the iron
was oxidized to Fe+3 and sulfuric acid was generated, which decreased the solution
pH to below PH level 7. According to Tables 3-3 and 3-4, almost all of the lead was
chelated in the solutions for Runs 19, 20, and 21. Therefore, there appears to be no
appreciable impact to the results of these tests due to the low starting solution pH
levels. ,
4-20
-------
4.5.2 Lead Removal
In Runs TOT11, 12, 13, 15, 16, 18, 21, 22, and 23, the lead concentration in
the initial cathode sample was lower than in subsequent samples. Therefore, either
the subsequent sample analyses were high or the initial quantity of lead in the
cathode chamber should have been greater. If the initial quantity of ilead was higher
than actually measured, then the percent lead removal should have been higher than
reported. This may be the case for Runs 11, 12, and 23 where more than one
subsequent sample contained more lead than the initial cathode chamber sample.
The percent lead removal from Run 11 was used to compare ihe lead removal
rates for 0.8 and 4 percent lead solutions of DTPA, and for 15 and 2^ ma/cm2 tests
with 4 percent lead solutions. Based on the data presented in Table!3-3, the initial
lead solution concentration is assumed to be 42,650 mg/L By extrapolation, the lead
solution concentration for 180 minutes plating time was calculated to be 36,300 mg/L.
Using these new lead solution concentrations, it is estimated that the! percent lesid
removal was 14.9 percent after a 3-hour plating time. Because this new percent lead
removal is lower than the original percent removal of 35.5 percent, the conclusions
for Run 11 are correct.
Based on the data presented in Table 3-3, the initial lead solution concentra-
tion in the cathode chamber is assumed to be 46,000 mg/L, which would yield an
overall percent lead removalof 21.7. The percent lead removal fromiRun 12 was
used to compare the lead removal for 1) 4 percent lead solutions of EDTA and DTPA,
2) lead and cadmium electrodes, and 3) lead and lead/iron chelate solutions. In all
three cases, the 21.7 percent lead removal is still lower than the lead'removals of the
other runs compared to Run 12, Therefore, it is assumed that the conclusions for
Run 12 are correct.
The percent lead removal from Run 23 was compared to Runs;4 and 24 to
determine if the type of membrane affects lead removal. Based on the data
presented in Table 3-3, the initial lead solution concentration for Run ?3 is assumed
to be 8583.3 mg/L, which yields a 33.0 percent lead removal. Because the new
percent lead removal for Run 23 is still less than that of Runs 4 and 2^4, the
conclusion for Run 23 is correct. '
4-21
-------
SECTION 5.0
CONCLUSIONS AND RECOMMENDATIONS
The purpose of this study was to examine the ability of an innovative
electromembrane process (which uses a cation-transfer membrane separating the
anode and cathode chambers in an electrolytic cell) to recover lead from a synthetic
lead solution. The synthetic lead solution was used to simulate a soil washing
solution (obtained after chelation) from a typical battery reclamation site. Process
parameters that were studied included the following: type of chelating agent, type of
membrane, current density, lead concentration, and reaction time. The bench-scale
treatability program was designed as a screening study and was notj intended to
€>nable development of rigorous conclusions regarding the various experimental
parameters. Thus, no quantitative criteria were established to determine significant
differences between or among runs. The conclusions that have been made in the
report are those that are intuitively apparent from different sets of data. Certain
conclusions are not fully supported by all the data collected for the report.
Preliminary jar tests performed in this study determined that lead dioxide and
elemental lead could not be chelated by any of the chelating agents studied (di-
sodium EDTA, tetra-sodium EDTA, and DTPA), but lead sulfate and basic lead
carbonate could be completely chelated by all three chelating agents!. The optimal
chelating-agent-to-lead molar ratios were determined to be 1:1 for diTSodium EDTA,
1:1.5 for tetra-sodium EDTA, and 1:2 for DTPA. !
A comparison of the tests using di-sodium EDTA and tetra-sodium EDTA under
the same conditions showed that both forms of EDTA produced approximately the
same lead recovery. Based on the treatability study data, there appears to be no
advantage to using one sodium form of EDTA over the other. The use of DTPA as
the chelating agent resulted in lower lead recoveries based on data Using a solution
containing 0.8 percent initial lead concentration and higher lead recoveries for the
solutions containing 4 percent initial lead concentration. Because the test with 4
I ~
5-1 i '
-------
percent lead concentration tetra-sodium EDTA solution and 25 ma/cm2 current
density (Run 1£X appeared to have a lower-than-expected lead recovery, it is
uncertain whether DTPA is superior. Additional tests with actual soil and a cost
analysis should be performed to compare the capabilities and cost-effectiveness of
EEDTA and DTPA for removing lead from soil.
i > |
' • i
The data from the regenerated chelating agent solution tests showed that the
regenerated chelating agent solutions resulted in lead removals comparable to those
from the original solutions.
A comparison of the data obtained in the tests performed using initial target
lead concentrations of 0.8 and 4 percent showed that a higher percentage of lead
was recovered in the 0.8 percent lead solution test, but the amount of lead recovered
was greater in the 4 percent lead solution test. One possible reason the lead
removal percentages were not higher in the electromembrane tests conducted with 4
percent lead-chelate was the limited surface area of the cathode. The cathode
appeared to be "saturated" with lead, and therefore the lead may have been inhibited
from plating onto the cathode and thus remained in the solution. It is suggested that
future tests be run to investigate how surface area and shape of the electrode affect
lead recovery. This data also indicates that the use of a higher percentage lead
solution results in more lead recovery and higher current efficiencies.
A comparison of the tests conducted with 15 and 25 ma/cm2 current densities
showed that the lead recovery rates and current efficiencies were higher for the 25
ma/cm2 current density tests. |
Lead recovery efficiencies of the Nafion® and Ionics membranes were com-
pared to determine if the type of membrane used had any effect on lead recovery.
Based on the data from the tests in the 0.8 and 4 percent lead solutions, it appears
that there is no difference in lead recovery for both the Nafion® and Ionics mem-
branes. A cost analysis would need to be performed to determine which membrane is
more cost-effective. ;
The tests with lead and cadmium electrodes were compared using DTPA
solutions as well as tetra-sodium EDTA solutions. In tests conducted with tetra-
5-2
-------
sodium EDTA, the cadmium electrodes were definitely superior to the lead electrodes
with respect tojeid recovery rates. However, the initial lead concentration for the
test with 4 percent lead concentration EDTA solution, 25 ma/cm2 current density, and
lead electrodes (Run 12) was in question because the lead concentration was higher
in subsequent samples. The tests with DTPA solutions, however, did not reveal a
significant increase in lead recovery when using the cadmium electrodes. A cost
analysis should be performed to determine if the lower cost of cadmium outweighs
the benefit of lead product purity. With the lead electrodes, it was anticipated that the
entire electrode would be smelted instead of scraping the lead from the cathode. The
use of cadmium as the cathode requires a comparison of the cost of iscraping the
lead from the cathode versus the saleable product produced from the lead deposited
onto the cadmium electrode.
" , !
In the tests conducted with 1.5 percent iron, a slightly higher lead recovery was
observed in the solutions containing iron.
In future testing, it is recommended that actual lead-contaminated soil be used
in the study to determine if exclusive lead chelation is possible and to! determine the
degree to which other metals in the soil are chelated. Various types of soils ranging
from clay to sandy should be tested to determine the effect of particle: size on separa-
tion of soil and chelating agent solution. Previous soil washing tests have shown that
a colloid of soil and chelating agent may form which can carry-over to; the
electromembrane process and plug the membrane.
In this study, the chelating agent solutions were regenerated once; however, it
is unknown whether there is a limit to regeneration that will produce an unusable
chelating agent solution. Multiple regenerations of the chelating agent should be
investigated, especially with soil, to determine the extent of regeneration of the
chelating agent ;
5-3
-------
3.
4.
5.
6.
8.
9.
10.
SECTIONS
REFERENCES
on' lnC' CERCLA BDAT Standard Analytical Reference Matrix
(SARM) Preparation and Results of Physical Soils Washing Experiments U S
Environmental Protection Agency. 1987. '
PEI Associates, Inc. Innovative Electromembrane Process for Recovery of Lead
from Contaminated Soils. Project conducted under a grant from the National
Science Foundation, Grant No. ISI-8560730. July 1986.
Vendor literature from Hampshire Chemicals Company, 1993.
Vendor literature from DuPont orr Nafion® membranes. 1992.
Vendor literature from Ionics on CR 67 membranes. 1992.
Kirk-Othmer's Encyclopedia of Chemical Technology, Volume 5. John Wilev &
Sons. New York, New York. 1981. pp. 339-362.
Ringbom, A. Complexation in Analytical Chemistry: A Guide for the Critical
Selection of Analytical Methods Based on Complexation Reactions. Interscience
Publishers. 1963. :
Krishnamurthy, S. Extraction and Recovery of Lead Species from Soil Environ-
mental Progress/Volume 11, No. 4. November 1992. pp. 256-260.
Bureau of Mines, Assessment of Current Treatment Techniques at Superfund
Battery Sites. Presented at the Air & Waste Management Association Con-
ference. February 7, 1990.
U.S. Environmental Protection Agency. Test Methods for Evaluating Solid
Waste. Third Edition, SW-846. Office of Solid Waste and Emergency Re-
sponse, Washington, D.C. November 1986.
Personal conversation with Mr. Peter Carbett of Hampshire Chemicals Company
July 23, 1993. ,
6-1
-------
APPENDIX A
SOLUTION PREPARATION METHOD
FOR THE ELECTROMEMBRANE TESTS
A-1
-------
Jar Tests ,
The lead solutions containing di-sodium EDTA, tetra-sodium EDTA, and DTPA
were prepared by adding deionized water, chelating agent, and lead; to a 250 ml
beaker. The contents of the beaker were stirred using a magnetic stirrer. While the
solutions were being stirred, the,solution pHs were adjusted to a philevel of 9 with
sulfuric acid for the tetra-sodiumi and DTPA solutions, and to a pH level of 5 with
sodium hydroxide for the di-sodiLm EDTA solutions. The solutions were allowed to
mix for one hour after pH adjustment. The tetra-sodium EDTA and DTPA cheating
sigents were commercial solutions purchased from the Hampshire Chemical
Company. The tetra-sodium EDTA solution was a mixture of approximately 38
percent by weight chelating agent and the remaining 62 percent by weight was water,
trisodium nitrilotriaeetic acid (<2(percent) and sodium hydroxide (1 to; 2 percent). Di-
sodium EDTA was, supplied as a solid containing 10 percent water, the DTPA
solution was a mixture of 40.1 percent chelating agent, and the remaining 5%9 s
percent by weight was water, trijsodium nitriloacetic acid, and sodium hydroxide, fhe
following presents the quantities of lead, water, and chelating agent solutio^ us€tf lo
prepare the 4 percent by weight lead Jar test solutions. i
i
Molar ratio (chetating agentlead)
Di-sodium EDTA
1:1
Lead sulfate, g , 8.1
Basic lead carbonate, g
Di-sodium EDTA» g
Deionized water, ml
Tetra-sodium EDTA
Lead Fsulfate. g ^
Basic lead carbonate, g
Di-sclium EDTA, g
Deionized- water, ml
DTPA
Lead sulfate, g
Basic lead carbonate, g ;
Di-sodium EDTA, g
Deionized water, ml
6.3
13.t
180
8.1
6.3
26.9
153.1
8.1
6.3
33.8
146.2
1.5:1
8.1
6.3
19,8
tsb
i
8.1
6.3
40.4
139.6
8.1
6.3 !
50.7!
129.3
2:1
8 1
V* 1
6 3
WiiJ
26.1
180
/
i
8 1
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6 3
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53 8
^*J * W
126r.2
8 1
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6 3
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675
^f 9 *\J
112.5
A-2
-------
Bench-Scale Tests
• *•* ~-
The 0.8 and 4 percent by weight lead solutions were prepared by adding the
chelating agent, water, and lead to a 4-liter flask. The contents were stirred using a
magnetic stirrer. While the solutions were being stirred, the solution IpHs were
adjusted to the experimental pH with sulfuric acid for tetra-sodium EPTA and DTPA
solutions, and with sodium hydroxide for di-sodium EDTA solutions. I The lead chelate
solutions were allowed to mix for one hour to complete the lead chelation. The
solutions were prepared with the following quantities of lead, chelatirjg agent, and
water.
0.8 percent lead 4 percent lead
Di-sodium EDTA i
Lead sulfate, g 35.0
Basic lead carbonate, g 26.8 -
Di-sodium EDTA, g 56.0 i - • 5
Deionized water, ml 4,000 - *
(1:1 Di-sodium EDTA-to-lead molar . • 'I
ratio)
Tetra-sodium EDTA*
Lead sulfate, g 35.0 179.8
Basic lead carbonate, g 26.8 137.4
Tetra-sodium EDTA, ml 173.1 \ . 888.5
Deionized water, ml 3,826.9 ! 3,111.5
(1.5:1 Tetra-sodium EDTA-to-lead : .
molar ratio)
DTPA
Lead sulfate, g 35.0 ! 179.8
Basic lead carbonate, g 26.8 137.4
DTPA, ml ^ 289.5 1,485.9
Deionized water, ml , 3,710.5 2,514.1
(2: llDTPA-to-lead molar ratio) ;
For the solutions prepared with 1.5 percent by weight iron, 298.7 grams ferrous
sulfate (FeSO4»7H2O) was added to the lead solution prior to pH adjustment.
A-3
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