EPA/600/R-02/020
April 2002
Stabilization and Testing of Mercury
Containing Wastes: Borden Sludge
by
Paul Bishop, Renee A. Rauche, Linda A. Rieser,
Makram T. Suidan, and Jian Zhang
Department of Civil and Environmental Engineering
University of Cincinnati
Cincinnati, Ohio 45221-0071
Contract No. 68-C7-0057
Task Order #10
Task Order Manager
Paul Randall
Land Remediation and Pollution Control Division
National Risk Management Research Laboratory
Cincinnati, Ohio 45268
National Risk Management Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
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Notice
The U.S. Environmental Protection Agency through its Office of Research and Development funded and
managed the research described here under Contract No. 68-C7-0057, Task Order #10, to the University of
Cincinnati. It has been subjected to the U.S. EPA's peer and administrative review and has been approved for
publication as an EPA document. Mention of trade names or commercial products does not constitute an
endorsement or recommendation for use.
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Foreword
The U.S. Environmental Protection Agency is charged by Congress with protecting the Nation' s land, air, and
water resources. Under a mandate of national environmental laws, the Agency strives to formulate and
implement actions leading to a compatible balance between human activities and the ability of natural systems
to support and nurture life. To meet this mandate, EPA's research program is providing data and technical
support for solving environmental problems today and building a science knowledge base necessary to manage
our ecological resources wisely, understand how pollutants affect our health, and prevent or reduce
environmental risks in the future.
The National Risk Management Research Laboratory is the Agency's center for investigation of technological
and management approaches for preventing and reducing risks from pollution that threatens human health and
the environment. The focus of the Laboratory's research program is on methods and their cost-effectiveness
forprevention and control of pollution to air, land, water, and subsurface resources; protection of water quality
in public water systems; remediation of contaminated sites, sediments and ground water; prevention and control
of indoor air pollution; and restoration of ecosystem s.NRMRL collaborates with both public and private sec tor
partners to foster technologies that reduce the cost of compliance and to anticipate emerging problems.
NRMRL's research provides solutions to environmental problems by: developing and promoting technologies
that protect and improve the environment; advancing scientific and engineering information to support
regulatory and policy decisions; and providing the technical support and information transfer to ensure
implementation of environmental regulations and strategies at the national, state, and community levels.
This publication has been produced as part of the Laboratory's strategic long-term research plan. It is published
and made available by EPA's Office of Research and Development to assist the user community and to link
researchers with their clients.
E. Timothy Oppelt, Director
National Risk Management Research Laboratory
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Abstract
This report details the stability assessment of a mercury containing sulfide treatment sludge. Information
contained in this report will consist of background data submitted by the generator, landfill data supplied by
EPA and characterization and leaching studies conducted by UC and contract laboratories.
Borden Chemicals and Plastics (BCP) provided background data for the time period June 1997 through
November 1998. Included in the data summary are total mercury, reactive sulfide, Toxicity Characterization
Leaching Procedure (TCLP) and pH information relating to their sulfide treated sludge.
BCP' s sulfide sludge is currently being disposed in a subtitle C landfill located in Carlyss, Louisiana. Data on
the leachate from the landfill was provided by EPA - OSW.
Samples obtained by UC and EPA personnel at the BCP plant on November 19, 1998 were characterized by
UC and two contract laboratories for thermogravimetric analysis, total mercury content, pH, acidity and cation
exchange capacity, etc. Leaching tests and analytical work performed by UC and their contract laboratories
included the toxicity characteristic leaching procedure (TCLP), solid stability in water, leaching atconstantpH
values, and acidity.
Preliminary point estimates of measured mercury concentrations in the generated leachates indicate that the
mercuric sulfide complex is very strong in low pH environments; however, higher pH conditions may result in
mercury mobilization to the aqueous phase.
This report was submitted by the University of Cincinnati (UC) in fulfillment of Contract No. 68-C7-Q057
under the sponsorship of the United States Environmental Protection Agency (EPA). This report covers a
period from October 1998 through March 1999; laboratory work was completed as of March 1999.
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Table of Contents
Foreword iii
Abstract iv
1.0 Background 1
1.1 Waste Characterization 1
1.1.1 Data Quality Discussion 2
1.2 Landfill Data 3
2.0 Characterization of BCP Sulfide Sludge 4
2.1 Thermogravimetric Analysis 5
2.1.1 Background 5
2.1.2 Method 5
2.1.3 Results 5
2.1.4 Data Quality Discussion 6
3.0 Leachability of Sulfide Stabilized Sludge 7
3.1 Solid Stability in Water 7
3.1.1 Introduction 7
3.1.2 Procedure 7
3.1.3 Results 7
3.1.4 Data Quality Discussion 8
3.2 Acidity 8
3.2.1 Introduction 8
3.2.3 Procedure 8
3.2.3 Results 8
3.2.4 Data Quality Discussion 9
3.3 Toxicity Characteristic Leaching Procedure (TCLP) 9
3.3.1 Introduction 9
3.3.2 Procedure 9
3.3.3 Results 10
3.3.4 Data Quality Discussion 10
3.4 Constant pH Leaching Test 10
3.4.1 Introduction 10
3.4.2 Procedure 10
3.4.3 Results 11
3.4.4 Data Quality Discussion 11
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Table of Contents, Cont.d
4.0 Conclusions 12
4.1 Background Data 12
4.2 Landfill Data 12
4.3 Characterization 12
4.4 Leaching Tests 12
4.5 Data Quality Discussion 14
4.5.1 Background Data 14
4.5.2 Landfill Data 15
4.5.3 Characterization Data 15
4.5.4 Thermo gravimetric Analysis 16
4.5.5 Solid Stability in Water 16
4.5.6 Acidity 16
4.5.7 Toxicity Characteristic Leaching Procedure 16
4.5.8 Constant pH Based Leaching Test 18
Appendicies*
A Operation Procedure for Treatment of BCP Waste
B Analytical Data Produced by BCP
C Thermogravimetric Data
D Acidity Titration Curves
•D Available from Paul Randall, Task Order Manager, U.S. EPA, at randall.paul(5jepa.gov or by calling
513 569-7673.
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List of Tables and Illustrations
1.1 Borden Background Data Summary 2
1.2 Landfill Leaching Data 3
2.1 Chemical Characterization of BCP Sludge 4
2.2 Physical Characterization of BCP Sludge 5
3.1 Solid Stability in Water Results 7
3.2 Acidity Results 8
3.3 TCLP Results 10
3.4 Constant pH Leaching Test Results 11
4.1 Laboratory QC Data for GCALI Total Mercury and TCLP Result 14D
4.2 Laboratory QC Data for EEI Total Mercury Result 15
4.3 Laboratory QC Data for EEI Total Mercury and TCLP Result 17D
4.4 Laboratory QC Data for EEI Total Mercury Results 19
List of Figures
3.1 Acidity vs. Sample Solid 9
4.1 Bisulfide Species as Function ofpH 13
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1.0 Background
The Borden Chemicals and Plastics plant (BCP) is located in Geismar, Louisiana. The
company produces, among other chemicals, vinyl chloride. The vinyl chloride synthesis employs a
mercuric chloride catalyst in the process. At intervals, the catalyst is changed resulting in some
spillage. A diked concrete pad under the process area catches these spills along with any process
leakage etc. The pad is washed with water. The water collected, along with any rain water that falls
over the process area, is diverted into two 10,000 gallon tanks. The tank contents are adjusted to a pH
between 3.5 and 5, treated with sodium sulfide, and dewatered with diatomaceous earth, added as a
filtering aid. The resulting filter cake, which is the subject of this study, is loaded into thirty-cubic-
yard steel roll-off boxes. When full, the contents are transported to the subtitle C landfill located in
Carlyss, Louisiana.
1.1 Waste Characterization
The background BCP (Table 1.1) data provide a range of TCLP values from 0.0120 mg/L to
0.6540 mg/L, with two samples below the detection limit. Of eight TCLP values provided, five are
below the TCLP regulatory limit of 0.2 mg/L mercury. Three pH values are provided. The values
reported are 9.43, 1.31 and 5.32. These values indicate a highly variable and not well controlled
treatment process. (Complete data are provided in Appendix A, available from Paul Randall, see
Table of Contents.)
According to the treatment procedure supplied by BCP, the optimum pH range for this
process before addition of sodium sulfide, is 3.5 to 5.0. The sulfide used in this process should act as
a base. Thus, it is unknown why the pH of the waste after sulfide treatment could be as low as 1.3.
On the only other two sampling days for which pH values were supplied, the pH (5.32 and 9.43) was
higher than the maximum allowable pH (5.0).
The analytical data provided by BCP indicate that there is a significant amount of reactive
sulfide remaining in the samples after treatment. The samples with higher reactive sulfide
concentrations produced the lowest TCLP mercury concentrations. The two samples with high
reactive sulfide concentrations had TCLP values that were acceptable, while the sample with the
lowest reactive sulfide concentration failed the TCLP test. Unfortunately, no pH or reactive sulfide
concentrations were provided with the other TCLP results, so direct correlations can not be made. It
is surprising, though, that one waste containing 40.0 mg/kg reactive sulfide did not bind up the
mercury enough to prevent leaching in the TCLP test.
Based on these results, it appears that it is possible for the Borden company to produce waste
forms that will pass the TCLP test. The characteristics of the treated sludge are highly variable and
indicate the need for additional process quality control.
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1.1.1 Data Quality Discussion
The background data presented came from several sources and are considered secondary data
by EPA Order 5360.1 CHG 1, July 1998. Some QA information is available for the Gulf Coast
Analytical Laboratories data (see Appendix A, Table of Contents) and a summary of this information
is presented in Section 4.5. No QA information was available for the SAIC data.
Table 1.1: Borden Background Data Summary
Sample Date
10/27/97
10/27/97
10/27/97
10/27/97
02/13/98
02/13/98
02/13/98
05/15/98
05/15/98
05/15/98
11/11/98
11/11/98
11/11/98
11/20/98
06/04/97
06/04/97
06/04/97
06/04/97
Test Date
10/31/97
10/31/97
10/31/97
10/31/97
02/16/98
02/17/98
02/20/98
05/19/98
05/19/98
05/26/98
11/13/98
11/13/98
11/14/98
11/23/98
06/14/97
06/11/97
Type of Analysis
Total Hg
TCLP Hg
Total Hg
TCLP Hg
pH Extract
Reactivity Sulfide
TCLP Hg
pH Extract
Reactivity Sulfide
TCLP Hg
pH Extract
Reactivity Sulfide
TCLP Hg
TCLP Hg
Total Hg
TCLP Hg
Total Hg
TCLP Hg
Results
2.27 mg/kg
<0.0002mg/L
21.4 mg/kg
<0.0002mg/L
9.43
165 mg/kg
0.0160mg/L
1.31
120 mg/kg
0.0120 mg/L
5.32
40.0 mg/kg
0.3520 mg/L
0.0422 mg/L
2 1,1 00 mg/kg
0.2600 mg/L
17, 700 mg/kg
0.6540mg/L
Sample Designation
97102900091
97102900091
97102900101
97102900101
98021301041
98021301041
98021301041
98051800941
98051800941
98051800941
98111101241
98111101241
98111101241
98112000321
BGO62
BGO62
BGO63
BGO63
(1) Provided by BCP-analysis by Gulf Coast Analytical Laboratories Inc., 7979 GSRI Ave., Baton Rouge, LA.
(2) Provided by EPA-analysis by SAIC
(3) Provided by EPA-analysis by Gulf Coast Analytical Laboratories INC.
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1.2 Landfill Data
Data supplied by EPA-OSW on the landfill leachate from cells containing the BCP sludge
are listed in Table 1.2.
Table 1.2 Landfill Leaching Data
Cell '
5
6
14
Mercury (jig/L)
ND2
0.94
0.57
PH3
—
9.51 (average)
—
(l)Cell - the isolated location within the landfill of the stored waste
(2)ND - No data on detection limit value was supplied
(3) Supplied by EPA-OSW
The data in Table 1.2 indicate that the mercury concentration in landfill leachate generated in
the vicinity of the Borden waste is highly variable, ranging from 0.94 jig/L to non-detectable. These
are actual leachate concentrations before dilution with groundwater, and the values can not be
compared directly to TCLP values. TCLP leachate concentrations are based on a leachate/waste ratio
of 20:1 (w/w) and TCLP leachate concentrations for this landfill material may be much lower than
those actually observed for in situ leachate. Typically, voids occupied by leachant in a TCLP test are
an order of magnitude greater than that recorded for in situ samples, meaning that there may be much
more leachant in the TCLP test than in the field, per unit volume of waste. Therefore, the TCLP
concentration could be lower. Consequently, these landfill samples may pass the TCLP test, even
though their field leachate concentrations may be higher than the TCLP limit.
1.2.1 Data Quality Discussion
The data presented in Table 1.2 supplied by EPA-OSW, were defined as secondary data by
EPA Order 5360.1 CHG 1, July 1998. No QC information is available. No detection limit value is
available. No information is available on the generation of leachate. Only a single pH value was
provided and was labeled as an average. Insufficient detail is available to assess the secondary data.
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2.0
Characterization of BCP Sulfide Sludge
On November 19, 1998, 12 two-liter samples of dewatered sludge were collected from BCP
at the Geismar, Louisiana plant by UC and EPA personnel. The samples were obtained by random
collection from a full thirty-cubic-yard transport container labeled 4279-30 LCHCWM. Before mixing
6 of the 2 L bottles were sampled for TCLP to assess variability of the waste. To obtain a
representative sample, 6 of the partially full 2L bottles were mixed in a five-gallon container for 24
hours prior to sampling. Only one sample was analyzed for total Hg from the homogenized mixture,
consequently no statement can be made concerning the effectiveness of the homogenization process.
The following characterization data (Tables 2.1 and 2.2) were generated for this waste:
Table 2.1 Chemical Characterization of BCP Sludge*
Chemical Parameter
Total Mercury
Calcium
Magnesium
Sodium
Potassium
Hydrogen
pH
pH
Redox Potential @ 22 C
Redox Potential @ 22 C
Acidity
Cation Exchange Capacity
Concentration
8,100mg/kg
300 mg/kg
30 mg/kg
660 mg/kg
29 mg/kg
89 mg/kg
3.1
3.8
+393
+420
7.07 mg CaCO3 per g of sample
13.6 meq/lOOg
Method of Analysis
SW-846-7470A14
Extraction with Ammonium acetate2
Extraction with Ammonium acetate2
Extraction with Ammonium acetate2
Extraction with Ammonium acetate2
Measuring pH in Adams Evans Buffer Soln.
pH electrode2
pH electrode3
Redox electrode with Ag/AgCl2 used as
reference2
Redox electrode with Ag/AgCl2 used as
reference3
Standard Methods3
Summation of Cations (SSSA)2
*A11 values are point estimates.
(1) Analysis performed by Environmental Enterprises Incorporated, Cincinnati, Ohio
(2) Analysis performed by Agvise Laboratories, Northwood, North Dakota - No QA/QC data available
(3) Analysis performed by University of Cincinnati, Cincinnati, Ohio
(4) See section 4.5.3 for data quality analysis
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Table 2.2 Physical Characterization of BCP Sludge
Physical Parameter
0.5 - 2mm
0.002 - 0.5mm
0.0002-0.002mm
Moisture at 1/3 bar
Organic Matter
Bulk Density (disturbed)
Weight Percent
14.5
74.8
10.7
50.7
43
0.35 gm/cc
Method of Analysis
Pipette Method
Pipette Method
Pipette Method
Gravimetric loss upon drying
Furnace Method
Weight Ratios
* All values are point estimates
2,1 Thermogravimetric Analysis (TGA)
2.1.1 Background
Thermogravimetry measures the weight change in a specimen as a function of temperature
and time. The mode of Thermo gravimetry used for this study is known as dynamic thermogravimetry,
in which different specimen types are heated in an environment whose temperature is changing in a
pre-determined manner at a linear rate. The resulting mass-change verus temperature curve provides
information concerning the thermal stability and composition of the specimen.
2.1.2 Method
Thermo gravimetric analysis was run on two 100 mg samples of BCP sulfide treated sludge.
Samples were warmed with dry nitrogen gas to 50°C for about 10 minutes. A small amount of the
sample was lost (probably moisture) during this initial warming in an inert medium. Following this,
the heating program was initiated at a constant heating rate of 10°C/min until a temperature of 1000°C
was reached. The thermal curves and derivative thermal curves were recorded for each sample by the
data acquisition unit of the instrument. (These curves are provided in Appendix B, see Table of
Contents.)
2.1.3 Results
The TGA data, generated in duplicate, show four basic inflection points at 167°C, 252°C,
331°C, and 425°C. The initial weight loss between room temperature and 167°C is largely due to loss
of moisture. These data indicate a thermally stable waste form. Heat generated in processing or long
term storage is unlikely to affect long term stability of the waste.
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Between 167°C and 425°C, organic constituents are decomposing rapidly, affecting changes
in the waste form. The inflection point at 252°C is most likely the loss of sulfur from the system. The
cause of the 331°C inflection point is unknown at this time. Above 450°C little change occurs.
2.1.4 Data Quality Discussion
Plans for conducting thermogravimetric analyses were not included in the EPA approved
Quality Assurance Project Plan.
The thermogravimetric analyzer was calibrated according to the procedures outlined in the
Perkin-Elmer manual. Initial calibration was performed on September 9, 1997. There were three
calibration procedures performed, two for temperature and one for weight. The temperature
calibration involved a furnace calibration and a two point standard curie temperature calibration. The
furnace calibration performs a nine point temperature calibration between lower and upper
temperature (100 C to 1350 C) limits. The thermocouple temperature is matched to the furnace
temperature when the calibration is complete. The two point standard curie temperature calibration
was performed using Nickel (magnetic transition temperature 354 C) and Hisat-50 (magnetic
transition temperature 1000 C) magnetic standards to perform the curie point temperature calibration.
The weight calibration was performed using a 100 milligram class M calibration standard
provided by Perkin-Elmer. Once these calibrations were completed, the results were permanently
stored in the computer and incorporated into all runs. Recalibration is necessary only if the
equipment is moved, computer software is reinstalled or a new gas supply is used.
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3.0 Leachability of Sulfide Stabilized Sludge
3.1 Solid Stability in Water
3.1.1 Introduction
This test varies the liquid/solid mass ratio during leaching to study the effect of the aqueous
contaminant concentration on the diffusion of contaminants from the waste form. If the amount of
contaminant released from the waste form decreases as the liquid/solid ratio decreases, then the
contaminant concentration in the leachate may be great enough to reduce the concentration gradient
between the waste form and the leachate and impede its diffusion from the waste.
3.1.2 Procedure
Samples collected on November 19, 1998 from BCP were dried at room temperature for 24
hours in an exhaust hood/1' Four tests were run using 10, 20, 50 and 100 grams of waste. Each solid
sample was placed in a 2 liter Nalgene HDPE bottle and then filled with 2 liters of deionized water
corresponding to 5, 10, 25 and 50 g of waste per liter, as reported in Table 3.1. The bottles were
capped and tumbled for 18 hours and then each leachate sample was filtered through a 0.45jim filter
and placed in a sample container. Each leachate sample was acidified to a pH of less than 2 with
HNO3 and stored at 4°C until analyzed within the 28 day holding-time requirement. Mercury
concentrations were measured by cold vapor atomic absorption spectroscopy (CVAAS).
3.1.3 Results
As shown in Table 3.1, mercury present in the leachate did not increase with greater volumes
of leachant. Mercury released from Sample 1 was less than the reported detection limit of 0.001
mg/L. In terms of total mercury leached from the waste, the other three samples released similar
amounts of mercury. Consequently, it is likely that mercury concentration gradients between the waste
form and the leachant do not control leaching rates.
Table 3.1 Solid Stability in Water Results1
Liquid/Solid Mass Ratio
Waste (g/L)/Mercury (mg)
Mercury in Leachate(mg/L)
Total Mercury Leached (%)
Sample 1
200:1
5/40.5
< 0.00100
—
Sample 2
100:1
10/81.0
0.00100
0.00120
Sample 3
40:1
25/203
0.00116
0.00054
Sample 4
20:1
50/405
0.00304
0.00074
(1) Mercury analysis performed by Environmental Enterprises Incorporated, Cincinnati, Ohio
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(1) Samples were dried in an exhaust hood rather than by oven drying as required by the QAPP. The
modification was made to avoid heating of the wastes to the point where mobility of contaminants
could be increased
3.1.4 Data Quality Discussion
The solid stability-in-water test provides only single point indicators as leachates were
measured at a single time point (18 hours). There is no information on whether the interval was
sufficient to establish mercuric equilibrium between solid and solution phases. Section 4.5.5 provides
the data quality analysis for Solid Stability in Water Results.
3.2 Acidity
3.2.1 Introduction
Acidity is related to the capacity of a material to react with a strong base. An acidity titration
was run on each leachate produced from the solid-stability-in-water tests to assess the acid-generating
capacity of the waste. Each sample was titrated with a strong base to an end point pH of 9 to obtain a
smooth titration curve. Construction of the titration curve identifies the inflection points and thus
determines the buffering capacity of the leachate.
3.2.2 Procedure
A known volume of leachate (40 mL) from the solid-stability-in-water test was placed in a
breaker and a 0.1N sodium hydroxide titrant was added to the sample in incremental amounts until the
acidity end point was obtained. The amount of sodium hydroxide required to neutralize the acidity of
the sample is expressed as equivalent milligrams (mg) of CaCO3 relative to a liter (L) of leachate and
normalized to a gram (g) of the waste. An Orion electrode was used to measure the pH.
3.2.3 Results
The titration curves are shown in Appendix C (see Table of Contents). The resulting acidity
for each sample is shown in Table 3.2, and Figure 3.1 shows measured acidity in the leachate versus
mass of the waste.
Table 3.2 Acidity Results1
Liquid/Solid Ratio (w/w)
Acidity (as mg CaCO3/L)
Normalized (mg CaCO3/g)
20:1
753.8
15.08
40:1
397.5
15.90
100:1
206.3
20.63
200:1
103.8
20.76
(1) Analysis performed by University of Cincinnati, Cincinnati, Ohio
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Figure 3.1 Acidity vs. Sample Solid
soo
700 H
o
O 500 -
'op 400 -
^ 300 -
'$ 200 -
100 -
0
0
= 7.Q727x + 47.041
R2 = 0.9979
20
40
60
Sample (g)
80
100
120
The values were normalized to sample weight in order to compare them on a per gram of sample
basis. Results suggest that the sample has some buffering capacity in low pH ranges, dropping off above
pH 6. The low buffer capacity of the waste may explain the wide variation in pH values reported both for
the waste and for the landfill leachate.
3.2.4 Data Quality Discussion
Data generated in acidity analyses consist of single point estimates. Section 4.5.6 provides the
data quality analysis for the Acidity data.
3.3 Toxicity Characteristic Leaching Procedure (TCLP)
3.3.1 Introduction
This test attempts to determine the potential mobility of contaminants in an acetic acid solution
that is intended to serve as simulated leachate under landfill conditions.
3.3.2 Procedure
Prior to performing the TCLP analysis, an initial pH measurement of the waste must be made to
determine the appropriate pH of the extraction fluid (4.93 or 2.88) that must be used in the test. The pH of
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the BCP waste was 3.8, which is well below pH 5, thus the TCLP method dictates that the extraction fluid
corresponding to a pH of 4.93 must be used.
A total of 100 grams of dried waste were added to a 2 liter container with 2 liters of extraction
fluid to yield essentially no head space in the container. The containers were sealed and then rotated end-
over-end for 18 hours. Each leachate sample was then filtered through a 0.70 Jim filter and placed in a
sample container. The leachate samples were acidified to a pH of less than 2 with HNO3 and stored at 4°C
until analyzed within the 28 day holding-time requirement. Mercury concentrations were measured by
CVAAS.
3.3.3 Results
Table 3.3 summarizes the analytical results for the TCLP test of the material obtained from BCP
on November 19, 1998 prior to mixing. TCLP results fall in a range of values from 0.00247 mg/L to
0.06555 mg/L, all well below the regulatory limit (0.2 mg/L). The sample pH was within the acceptable
range for waste treatment. It appears that the mercury in this sample was well stabilized.
Table 3.3 TCLP Results1
Sample
TCLP (mg/L)
Total Mercury (mg/kg)
TCLP Limit
0.2
1
0.00247
8,870
2
0.00879
8,020
3
0.04100
4,830
4
0.06555
3,890
5
0.00498
4,290
6
0.041672
3,330
(1) Mercury analysis performed by Environmental Enterprises Incorporated, Cincinnati, Ohio
(2) The datum represents an undiluted result that exceeds the highest calibration standard (0.04000 mg/L).
3.3.4 Data Quality Discussion
Section 4.5.7 provides the data quality analysis for TCLP data.
3.4 Constant pH Leaching Test
3.4.1 Introduction
Constant pH leaching tests are a means to determine the effect pH has on mobilizing
contaminants found in waste samples. The basic premise of this test is to leach samples in a constant pH
solution, adjusting the sample pH to the set point as necessary.
3.4.2 Procedure
Constant leaching tests were run at pH values of 2, 4, 6, 8, and 10, using 500 ml ofdeionized
water and 25 grams of dried solid to produced a liquid/solid mass ratio of 20:1. A duplicate test was run at
a pH value of 8. The samples were stirred using stirring bars on stir plates throughout the experiment. The
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pH was maintained at the initial value for a 24 hour period, with samples being extracted for analysis at 2,
10 and 24 hours. Each sample was filtered through a 0.7 Jim glassfiber filter, acidified to a pH of less than
2 with HNO3 and stored at 4°C until analyzed within the 28 day holding-time requirement. Mercury
concentrations were measured by C VAAS.
3.4.3 Results
Table 3.4 summarizes the reported mercury concentrations for each distinct pH test carried out.
As can be seen, leachate mercury concentrations were well below regulatory limits in all samples when the
leachant pH was 6.0 or lower. With higher pH leachants, the leachate mercury concentrations dramatically
increased. At pH 10, the highest amount of mercury was leached. At a pH of 2, a steady-state condition
may have been reached between 10 and 24 hours, as the mercury concentrations for these time intervals
are within 15 percent of each other. At pH 4 and 6, mercury concentrations fluctuated between the 10 and
24 hour leaching times, but remained within the same order of magnitude. For other pH values, it is hard to
tell if a steady-state condition was reached because mercury concentrations continued to increase through
the entire time interval. A longer testing period is recommended for future research. All test blanks except
those for a pH of 8 are below the reported detection limit of 0.00100 mg/L. Even for the blanks at pH 8,
there is no significant bias, given the comparatively high mercury concentrations reported for the leachate
samples.
Table 3.4 Constant pH Leaching Test Results1
2hr
10 hr
24 hr
Blank
Leachate Mercury, mg/L
pH 2
0.01090
0.01480
0.01310
< 0.00100
pH 4
0.00634
0.00616
0.00274
< 0.00100
pH 6
0.00218
0.00286
0.00582
< 0.00100
pH8(l)
< 0.00100
0.02060
0.11600
0.00274
pH 8 (2)2
missing
0.01350
0.40600
0.00106
pH 10
0.17400
0.37200
1.63000
< 0.00100
(1) Mercury analysis performed by Environmental Enterprises Incorporated, Cincinnati, Ohio
(2) Test duplicate.
3.4.4 Data Quality Discussion
Section 4.5.8 provides the data quality analysis for Constant pH Leaching Test results.
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4.0 Conclusions
4,1 Background Data
Background data supplied by BCP and EPA indicate that it is possible for BCP to produce waste
forms that will pass TCLP; however, process quality control needs improvement (data quality analysis,
Section 4.5.1).
4.2 Landfill Data
BCP waste landfill samples were highly variable, with leachate mercury concentrations ranging
from 0.94 jig/L to non-detectable (data quality analysis, Section 4.5.2).
4.3 Characterization
A thorough physical and chemical characterization of the BCP waste sample proved useful
throughout the testing process. Compositional data was used for background information (data quality
analysis, Section 4.5.3).
4.4 Leaching Tests
The preliminary tests generated single point estimates. Therefore, the following discussion is
intended to provide preliminary observations only. Preliminary observations should be qualified based on
the QA/QC data quality discussions provided in 4.5.5 (Solid Stability in Water), 4.5.6 (Acidity), 4.5.7
(TCLP) and 4.5.8 (Constant pH Leaching).
Based on solid-stability-in-water tests, it is likely that mercury concentration gradients between
the waste form and the leachant do not control leaching rates. A total of six TCLP tests were performed.
Mercury concentrations ranged from 0.00247 mg/L to 0.06555 mg/L, all well below the regulatory limit
(0.2 mg/L). Acidity testing indicates a small amount of buffering capacity in low pH regions and very
little above pH 6. Constant pH leaching revealed mercury concentrations below 0.025 mg/L in all samples
where the pH of the sample was 6.0 or lower. With higher pH leachants, soluble mercury concentrations
dramatically increased.
These results may be explained using thermodynamic data for mercuric sulfide. Mercuric sulfide
(HgS) is very insoluble in water, with a solubility product, Ksp, of 1Q"52 (Bard, 1966)1. However, the
solubility of HgS in water can be increased measurably by association with various hydrogen sulfide
species to form a number of mercuric-hydrogen-sulfide ions that enhance the solubility of HgS in water
(Clever et al, 1985)2. These associations can lead to the formation of HgS-2H2S°, Hg(HS)3", HgS-2HS",
Bard, A.J., Chemical Equilibrium, Harper and Row, Publishers, New York, 1966.
-12-
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and HgS22". HgS-2H2S° is the dominant water soluble form at pH values less than 6.2, while Hg(HS)3" is
the most soluble form between the pH values of 6.2 and 7. HgS-2HS" is the most soluble mercuric sulfide
association between the pH of 7 and 8.3, and HgS2 " is the most soluble form of mercuric sulfide above a
pH of 8.3. In fact, the solubility of HgS22" increases linearly with the hydroxyl ion concentration for pH
values over 8.3. Figure 4.1 presents a detailed distribution of the various bisulfide species as a function of
pH (Clever etal, 1985).
Figure 4.12
E
o
-5.OO
6.OO -
-TOO -
-a.och
-9.OQ
-IQOO
-LOO
- -200
10.0
Clever, H.L., S.A. Johnson, and M .E. Derrick, "The Solubility of Mercury and Some Sparingly Soluble
Mercury Salts in Water and Aqueous Electrolyte Solutions," J. Phys. Chem. Ref. Data, Vol. 14, No.3,
1985.
-13-
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The above discussion and Figure 4.1 serve to illustrate the effect of pH on the solubility of Hg(II)
in water. Furthermore, the figure illustrates the importance of maintaining a pH less than 6 for
precipitation of HgS in order to minimize the mobilization of mercury into the aqueous phase.
4.5 Data Quality Discussion
Unprocessed analytical data generated by EEI are provided in Appendix D, see Table of
Contents.
4.5.1 Background Data
The background data presented are considered secondary data by EPA Order 5360.1 CHG 1, July
1998. Some QA information is available for the Gulf Coast Analytical Laboratories data (Table 4.1).
However, no QA information was available for the SAIC data.
The limited QC data for Gulf Coast Analytical Laboratory Inc. (GCALI) show results for the
laboratory control standard (LCS) and an occasional spike sample (Table 4.1). There is no information on
initial calibration/blank and continuing calibration/blank or laboratory duplicates. All LCS samples meet
the QC criterion of ±15 percent of the true value, with the exception of the 10/27/87 TCLP sample.
Table 4.1 Laboratory QC Data for GCALI Total Mercury and TCLP Result
Sample ID
True
VOfL
Found
\Ug/L
Percent
Recovery
EPD
%
Dilution
Factor
Reported Re suit
M-g/L
TCLP Re suits
LCS 10/27/97
Spike 10/27/97
LCS 02/13/98
LCS 05/15/98
LCS 11/14/98
LCS 11/23/98
5.00
5.00
5.00
5.00
5.00
5.00
4.20
4.50
4.95
4.90
4.57
4.40
84.0
90.0
99.0
98.0
91.4
88.0
nr
nr
nr
nr
nr
nr
nr
nr
nr
nr
nr
nr
nr
nr
nr
nr
nr
nr
Total Mercury Results
LCS 10/27/97
Spike 10/27/97
5.00
5.00
4.70
4.95
94.0
99.0
nr
nr
nr
nr
nr
nr
nr = not reported
-14-
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4.5.2 Landfill Data
The data presented in Table 1.2, are defined as secondary data by EPA Order 5360.1 CHG 1, July
1998. No QC information is available. No detection limit value is available. No information is available
on the generation of leachate. Only a single pH value was provided and labeled as an average. Insufficient
detail is available to assess these secondary data.
4.5.3 Characterization Data
Twelve samples of BCP sludge were collected by UC and EPA on November 19, 1998 and
composited prior to sending off a sample to Environmental Enterprises Inc. (EEI) for total mercury
analysis. Table 4.2 summarizes the laboratory QC data for the single mercury result reported in Table 2.1.
The calibration curve was established using mercury standards of 0.50, 2.00, 5.00, 10.00 and 40.00 Jig/L,
with a corresponding correlation coefficient of 0.9993. Initial and continuing calibration standards and
blanks were within the control limits. The mercury recovery on the LCS was below the lower limit of 85
percent, and the RPD for the sample and duplicate exceeds the limit of 25 percent. Data pertaining to a
laboratory spike were absent.
Table 4.2 Laboratory QC Data for EEI Total Mercury Result
Sample ID
True
M-S/L
Found
M€^
Percent
Recovery
RPD
%
Dilution
Factor
Reported Result
LLg/kg
Work Order 99-02-413: T otal Mercury Results
ICV
CCV1
CCV2
CCV3
LCS
ICB
CCB1
CCB2
CCB3
01A
OlA-du plicate
5.00
5.00
5.00
5.00
3,300
<0.50
<0.50
<0.50
<0.50
—
—
4.78
4.64
4.58
4.58
2,764
<0.5Q
<0.5Q
<0.5Q
<0.50
9.24
6.96
95.6
92.8
91.6
91.6
83.8
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
28.2
—
—
—
—
—
—
—
—
—
1,000,000
1,000,000
—
—
—
—
—
—
—
—
—
9,240,000
6,960,000
A sample spike was not performed.
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4.5.4 Thermo gravimetric Analysis
Plans for conducting thermogravimetric analyses were not included in the EPA approved Quality
Assurance Project Plan. Calibration information is provided in Section 2.1.4.
4.5.5 Solid Stability in Water
Prior to use, the pH meter was calibrated using a two-point calibration with certified calibration
standards, pH 4 and pH 10. The calibration efficiency, defined as the measured value divided by the
known value, is 1.0097, which is in the range of 1.05 to 0.95 from the QAPP. The experimental blank was
run with other samples, but not sent out for Hg analysis. For Hg analysis, these samples were grouped with
samples from the constant pH leaching test. Therefore, QC results of this grouping are presented in Section
4.5.7.
4.5.6 Acidity
Prior to the titration, the pH meter was calibrated using a two-point calibration with certified
calibration standards, pH 4 and pH 10. The calibration efficiency has a value of 1.02 and is in the range of
1.05 to 0.95, per the QAPP.
4.5. 7 Toxicity Characteristic Leaching Procedure
TCLP was performed on six separate grab BCP sludge samples. The pH meter calibration
efficiency is 0.98, and is in the range of 1.05 to 0.95, per the QAPP. Mercury concentration of the method
blank is <0.50 jig/L.
Table 4.3 summarizes the laboratory QC data for the total mercury in the solid and TCLP results
reported in Table 3.3. The calibration curve was established using mercury standards of 0.50, 2.00, 5.00,
10.00 and 40.00 jig/L, with a corresponding correlation coefficient of 0.9993 for total mercury results and
0.9997 for TCLP results. Initial and continuing calibration standards and blank-16-s were within the
control limits, as was the LCS. The RPD for the TCLP sample and duplicate exceeds the limit of 25
percent. Data pertaining to a laboratory spike were absent.
-16-
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Table 4.3 Laboratory QC Data for EEI Total Mercury and TCLP Result
Sample ID
True
Hg
-------
4.5.8 Constant pH Based Leaching Test
Prior to titration, the pH meter was calibrated using a two-point calibration with certified calibra-
tion standards, pH 4 and pH 10. All calibration efficiencies are in the range of 1.05 to 0.95 from the
QAPP.
A test duplicate was run for pH 8. The sample collected at 2 hours for the duplicate run was not
analyzed. The RPDs for 10 hours and 24 hours are 42% and 111% respectively, which reflects the
variability in homogeneity of the BCP sludge.
Hg concentrations for all experimental blanks are <1.00 jig/L, except for pH 8 runs. The
experimental blanks forpH 8 have Hg concentration of 2.74 jig/L and 1.06 Jig/L (test duplicates), which
indicates very low contamination.
Table 4.4 summarizes the laboratory QC data for the total mercury and TCLP results reported in
Tables 3.1 and 3.4. The calibration curve was established using mercury standards of 0.50, 2.00, 5.00,
10.00 and 40.00 jig/L, with a corresponding correlation coefficient of 0.9996 for Work Order 99-03-404
and 0.9997 for the other work orders. Initial and continuing calibration standards and blanks were within
the control limits, as was the LCS. There were no RPD or spike results reported for Work Order 99-03-
404. The sample and duplicate for the remaining work orders contained mercury below the detection limit
of 0.50 jig/L, and no RPD value was calculated. Results for the spike are within control limits.
-18-
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Table 4.4 Laboratory QC Data for EEI Total Mercury Results
Sample ID
True
H-8/L
Found
[ig/L
Percent
Recovery
RPD
%
Dilution
Factor
Reported Result
M-g/L
Work Order 99 03-404
ICV
CCV1
CCV2
CCV3
CCV4
LCS
ICB
CCB1
CCB2
CCB3
CCB4
5.00
5.00
5.00
5.00
5.00
10.00
<0.50
<0.50
<0.50
<0.50
<0.50
5. Id
4.95
4.78
4.84
4.64
9.82
<0.50
<0.50
<0.50
<0.50
<0.50
103
99.0
95.6
96.8
92.8
98.2
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
Work Orders 99 03 494 & 99-03-556
ICV
CCV1
CCV2
CCV3
CCV4
LCS
ICB
CCB1
CCB2
CCB3
CCB4
03A
03 A -duplicate
03A-spike
5.00
5.00
5.00
5.00
5.00
10.00
<0.50
<0.5Q
<0.50
<0.50
<0.5Q
—
—
5.00
4.92
4.84
4.89
4.82
4.55
9.15
<0.50
<0.50
<0.50
<0.50
<0.50
<0.50
<0.50
5.10
98.4
96.8
97.8
96.4
91.0
91.5
—
—
—
—
—
—
—
102
—
—
—
—
—
—
—
—
—
—
—
NC
NC
—
—
—
—
—
—
—
—
—
—
—
—
2
2
—
—
—
—
—
—
—
—
—
—
—
—
<1.00
<1.00
—
A sample duplicate and spike are not available for samples associated with Work Order 99-03-404.
NC - not calculated because sample and duplicate are below the detection limit.
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