EPA-670/2-73-053-0
August 1973
Environmental Protection Technology Series
RECOMMENDED METHODS OF
REDUCTION, NEUTRALIZATION, RECOVERY OR
DISPOSAL OF HAZARDOUS WASTE
Volume XV Research and Development Plans
Office of Research and Development
U.S. Environmental Protection Agency
Washington. D.C. 20460
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EPA-670/2-73-053-0
August 1973
RECOMMENDED METHODS OF
REDUCTION, NEUTRALIZATION, RECOVERY
OR DISPOSAL OF HAZARDOUS WASTE
Volume XV. Research and Development Plans
By
R. S. Ottinger, J. L. Blumenthal, D. F. Dal Porto
G. I. Gruber, M. J. Santy, and C. C. Shih
TRW Systems Group
One Space Park
Redondo Beach, California 90278
Contract No. 68-03-0089
Program Element No. 1D2311
Project Officers
Norbert B. Schomaker
Henry Johnson
Solid and Hazardous Waste Research Laboratory
National Environmental Research Center
Cincinnati, Ohio 45268
Prepared for
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
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REVIEW NOTICE
The Solid Waste Research Laboratory of the National Environmental
Research Center - Cincinnati, U.S. Environmental Protection Agency has
reviewed this report and approved its publication. Approval does not
signify that the contents necessarily reflect the views and policies of
this Laboratory or of the U.S. Environmental Protection Agency, nor does
mention of trade names of commercial products constitute endorsement or
recommendation for use.
The text of this report is reproduced by the National Environmental
Research Center - Cincinnati in the form received from the Grantee; new
•
preliminary pages and new page numbers have been supplied.
ii
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FOREWORD
Man and his environment must be protected from the adverse
effects of pesticides, radiation, noise and other forms of pollu-
tion, and the unwise management of solid waste. Efforts to protect
the environment require a focus that recognizes the interplay between
the components of our physical environment—air, water, and land.
The National Environmental Research Centers provide this multidisci-
plinary focus through programs engaged in:
• studies on the effects of environmental
contaminants on man and the biosphere, and
• a search for ways to prevent contamination
and to recycle valuable resources.
Under Section 212 of Public Law 91-512, the Resource Recovery
Act of 1970, the U.S. Environmental Protection Agency is charged
with preparing a comprehensive report and plan for the creation of
a system of National Disposal Sites for the storage and disposal of
hazardous wastes. The overall program is being directed jointly by
the Solid and Hazardous Waste Research Laboratory, Office of Research
and Development, National Environmental Research Center, Cincinnati,
and the Office of Solid Waste Management Programs, Office of Hazard-
ous Materials Control. Section 212 mandates, in part, that recom-
mended methods of reduction, neutralization, recovery, or disposal
of the materials be determined. This determination effort has been
completed and prepared into this 16-volume study. The 16 volumes
consist of profile reports summarizing the definition of adequate
waste management and evaluation of waste management practices for
over 500 hazardous materials. In addition to summarizing the defini-
tion and evaluation efforts, these reports also serve to designate a
material as a candidate for a National Disposal Site, if the material
meets criteria based on quantity, degree of hazard, and difficulty of
disposal. Those materials which are hazardous but not designated as
candidates for National Disposal Sites, are then designated as candi-
dates for the industrial or municipal disposal sites.
A. W. Breidenbach, Ph.D., Director
National Environmental Research Center
Cincinnati, Ohio
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This volume of the final report presents more detailed information for
some of the projects proposed and summarized in Chapter 6 of Volume I. This
volume contains two types of project descriptions: (1) where TRW has had
previous experience with a similar project, or (2) where proof-of-principle
experimentation has been performed by TRW. Of the projects described herein,
proof-of-principle experimentation has been performed for the cementation
processes, both inorganic and organic, for the sulfur sequestering, for
arsenic removal from soil, and for the recovery of alumina from clay and
sulfur oxide scrubbing wastes. The project descriptions are intended to
provide further background and technical rationale for the use of the pro-
posed approaches summarized in Volume I.
iv
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TABLE OF CONTENTS
VOLUME XV
RESEARCH AND DEVELOPMENT PLANS
Page
Characterization of Incineration Parameters for the Safe Disposal
of Pesticides 1
New Chemical Concepts for Utilization of Waste Pesticides 9
Introduction - Development of Low Cost Cementation Approaches to
Passification of Heavy Metal Sludges and Solids 21
Stabilization of Nondegradable Toxic Wastes by Inorganic
Cementation 23
Development of Low Cost Organic Cementation Approaches for
Stabilizing Heavy Metal Containing Solid Wastes 43
Decontamination of Soils and Silts by Gaseous Extraction 53
Isolation of Mercury and Other Hazardous Heavy Metals from Dilute
Waste Streams 83
A New Process for the Economic Utilization of the Solid Waste
Effluent from Limestone Slurry Wet Scrubber Systems 105
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CHARACTERIZATION OF INCINERATION PARAMETERS
FOR THE SAFE DISPOSAL OF PESTICIDES
1. Introduction
The disposal of pesticide wastes and containers contaminated by
pesticide residues is one of the serious environmental problems that
has caused growing concern in recent years. Large stocks of surplus
pesticide wastes have been accumulated as a result of the cancellation
of registrations, the degradation of pesticides from either long-term
or improper storage conditions, and the cleaning of empty pesticide
containers by rinsing. Conventional means of disposal such as deep-well
injection and sanitary landfill without prior detoxification have been
deemed inadequate because of potential pollution to land and water. At
the present time, TRW has determined that controlled incineration at
high temperatures followed by efficiency scrubbing of the furnace gas
effluent is the only satisfactory method for the disposal of bulk quan-
tities of organic and metallo-organic pesticide chemicals in concentrated
form. -
It is recognized that a number of the incinerators currently 1n use
for the disposal of industrial and municipal wastes are readily adaptable
to the disposal of pesticide wastes. On the other hand, information on
the combustion characteristics of pesticides is limited so that at present
it is not possible to identify those existing incinerator installations
that could.be safely used for the disposal of pesticide wastes. In its
investigation under the current contract, TRW has concluded that very
little practical experimental data relating to the incineration of pesti-
cides has been determined. In order to fill this gap in the techno-
logical base for pesticide disposal, TRW recommends a program to provide
the necessary pesticide incineration data by pilot scale testing and to
utilize these data for the certification of specific incinerator instal-
lations for pesticide disposal. To achieve these objectives in a short
\
period of time, the recommended study is subdivided into the following
tasks:
(1) Characterization of pesticide incineration to the degree
necessary for incinerator selection.
1
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(2) Development of qualification procedures for incinerators
suitable for pesticide disposal.
(3) Identification and testing of incinerator installations
throughout the country for safe pesticide disposal.
The approach which TRW proposes is detailed in the following para-
graphs.
2. Technical Plan
Characterization of Pesticide Incineration
Determination of Test Parameters. The operational characteristics of
currently available incinerator systems would be reviewed and selections
made of the nominal ranges of combustion temperature, residence time, and
excess air requirements that will be investigated in pilot scale pesticide
incineration. The consideration of turbulence will be limited to the
assurance that in all cases the turbulence attained in the pilot work will
be at least as good as that achievable in the best commercially available
incineration units. This approach would serve not, only to limit the
variable ranges to be examined, but also to ensure that the information
generated in the pilot study would be applicable to state-of-the-art
equipment.
Incinerator-Scrubber Design and Installation. A pilot scale inciner-
ator would be designed and fabricated. The incinerator would be designed
to allow for variable changes over the ranges of interest. It would be
instrumented to monitor all variables of importance including effluent
pollutant levels. Sampling points would be located along the furnace
length so that the effects of residence time could be determined by chem-
ical analysis of the collected samples. It is currently expected that the
incinerator furnace design would be similar to that currently employed by
TRW for testing injector designs and operating conditions to minimize oxides
of nitrogen emissions. The fuel/air injection system would be designed to
provide the capability for combusting mixtures over a wide fuel-to-air ratio
-------
including those with excess nitrogen and excess oxygen. Special consider-
ation would be taken in the design to ensure mixing of the fuel and air prior
to ignition, and to ensure simulation of a high turbulence commercial in-
cinerator.
A scrubber system would be designed and installed to protect
operating personnel and equipment as well as ensure against atmospheric
pollution. The scrubber system effluents would be monitored to ensure
that acceptable emission levels are maintained. The exact configuration
of the scrubber system is of secondary importance to the objectives of
the program since the amount of pesticide fed to the incinerator would be
regulated to ensure that pollutant loadings (HC1, HF, SO , NO , PoOr,
X A £ 0
COClp) in the incinerator effluent were consistent with those currently
being efficiently abated with state-of-the-art scrubbing equipment.
Development of Analytical Procedures. The proper evaluation of the
incinerator and scrubber system for the safe disposal of pesticides
requires the careful sampling and analysis of the feed pesticides,
solvent, and auxiliary fuel, the intake air, combustion products along
the incineration path, the scrubber liquor, and the stack effluent.
In general, the feed gases and liquids would only have to be measured
periodically to ensure that the composition of each input component
remains relatively constant, whereas the incinerator and scrubber
effluents would be closely monitored.
Analysis of the gas samples would be accomplished by the application
of both gas chromatography and mass spectrometry. Gas chromatography with
electron capture detection would be employed to determine the constituents
of the gas samples quantitatively and a mass spectrometer would be used
from time to time to qualitatively identify each constituent.
Pesticides and solvent residues and other organic intermediates
present in the aqueous scrubber liquor would be extracted with appropriate
organic solvents such as hexane, isooctane, and kerosene. Liquid
chromatography with UV detectors would be utilized for the quantitative
3
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analysis of the extracted samples, and the liquid fraction collected from
the liquid chromatograph detector effluent would be subsequently analyzed
in a mass spectrometer for the identification of the chemical species
present.
Development of Data Reduction Analysis Program. Data reduction
models based on elemental and mass balances would be formulated and pro-
grammed for the on-line computer to convert the test data into a useful
form. The test information required as input to the program would include
the flow rates and chemical composition of the pesticide-solvent, secondary
fuel and air fed to the incinerator, the temperature, pressure and gas
chromatograph counts for each chemical component in the collected samples
along the furnace length and at the stack, and the liquid chromatograph
counts for each chemical component in the scrubber liquor. Output infor-
mation from the program would include the percent of pesticide destroyed
and the composition of the effluent gas as functions of residence time
and incineration temperature, as well as estimates on the amount of ash
obtained.
Selection of Representative Pesticides. Key pesticides representative
of the major pesticide families would be selected based on the following
criteria: production volume, volume in storage awaiting disposal, toxicity,
persistence in the environment., and chemical classification. The latter
consideration would also take into account the possible release of harmful
combustion products such as hydrogen chloride, hydrogen sulfide8 sulfur
dioxide, nitrogen and phosphorus oxides. For the pesticides selecteds
both the reagent grade and the common commercial formulations would be
employed in the testing.
Selection of Solvents and Secondary Fuel. Solvents Would be selected
and purchased for use as a carrier and/or a diluent for the candidate pes-
ticides when the form of the pesticide so requires. The primary considera-
tions in selecting the appropriate solvents would be the hazardous proper-
ties of the individual solvents, the solvent cost per unit weight of pes-
ticide dissolved, as well as the additional use of the solvent as a fuel.
-------
If necessary, a secondary fuel would be selected for use in the incinerator
as both a heat source and a hydrogen.source to ensure that any halogen
gases formed during combustion are converted to hydrogen ha!ides. Elimina-
tion of the halogen gases will facilitate more efficient scrubbing of the
incinerator effluent as the hydrogen halides are more readily soluble in
both aqueous and alkaline solutions.
Selection of Test Conditions and Running of Tests. Test conditions
selected would be primarily based on operating conditions found in state-
of-the-art incineration technology. Within those operating limits,
temperature is the main variable of concern. Higher temperatures lead
to the complete combustion of pesticide wastes, but at the samectime also
favor the formation of halogen gases and nitrogen oxides. On the other
hand, too low a temperature results in the release of unreacted pesticides
to the atmosphere. To bracket the optimum teroerature range for the com-
bustion of a pesticide waste, the upper temperature limit would be deter-
mined by examination of the equilibrium combustion product distribution
predicted by computerized equilibrium calculations such as the TRW
Chemical Analysis Program, whereas the lower temperature limit would be
provided by the knowledge that complete combustion of pesticides is
usually not obtained below 1,300 F even at very long residence times.
For each pesticide under investigation, a matrix of tests would be
performed by varying the combustion mixture of pesticide, solvent, air
nitrogen and fuel. Each series of tests would be planned by analyzing
the results from previous test runs to ensure that the additional
information obtained will always provide useful data points.
Analysis and Presentation of Test Results. Results from the
incinerator test runs would be carefully analyzed so that the effects
of temperature, residence time, air-to-fuel ratio and type of solvent
on the combustion products can each be individually assessed to allow
for the determination of the optimum operating conditions for the safe
disposal of pesticide wastes.
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Development of Qualification Procedures
Determination of Applicable Types of Incinerators. The operational
characteristics of the various classes of incinerators would be evaluated
to determine which types are applicable to pesticide incineration. The
operational characteristics would be determined through contacts with
manufacturers and users, as well as a review of current literature
including the incineration process reports presented in Volume III.
Determination of Applicable Pesticide and Pesticide Incinerator
Product Monitors and/or Analytical Procedures. Applicability of monitoring
and analytical instrumentation for full scale pesticide incinerator testing
would be determined by the following factors: mobility, precision and
accuracy within an acceptable range of error, and ease of operation and
maintenance.
Selection of Test Pesticides. The original selection criteria for
pesticides employed in pilot scale testing and the test results for these
pesticides would be reviewed. Five to ten pesticides requiring more
severe operating conditions to attain complete combustion would be selected
for testing in the full scale incinerator installations.
Specification of Solvents and Mix Compositions. Based on the results
of pilot scale testing, solvent types and solvent/pesticide active ingre-
dient ratios that would bring about the desirable combustion characteris-
tics would be specified.
Recommendation of Effluent Standards. Criteria for permissible levels
in public water supplies and in air have already been established for a
number of pesticides and related chemical species. For the other pesti-
cides suitable for disposal by incineration, effluent standards would be
recommended based on published toxicity data such as the ACGIH TLV's
and the 48-hour TL for marine organisms. The provisional recommendation
developed as a part of the current program, could be used as the effluent
standards where other data are not available.
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Specification of Operating Ranges. The major factors affecting the
incinerator operation are control of temperature, degree of turbulence,
and residence time. However, turbulence is difficult to characterize and
only the temperature and residence time ranges required to obtain complete
combustion of the pesticides would be specified, based on pilot scale test
results. As discussed previously, the full scale incinerators normally
do not have turbulence characteristics as good as the pilot scale unit
used in testing„ and hence only those incinerator installations that
could meet the temperature and time specifications would be considered
for certification testing,
Identification and Certification Testing
of Incineration Installations
Survey Manufacturers to Appraise Applicability of Specific Models.
The major manufacturers of incineration units would be contacted to deter-
mine the applicability of specific units to pesticide incineration. Primary
concern would be placed on assuring that proper operational conditions, as
determined in the pilot study, can be maintained in the various specific
units. A further effort would be made to obtain information which will
lead to the generation of a list of owners and/or operators of the specific
types of incinerators of interest.
Survey of Organizations Possessing Incinerators. The organizations
known to possess and/or operate incinerators which can serve as waste
pesticide destructors would be contacted to determine their willingness
to be tested, certified and utilized as waste pesticide disposal units.
This information would lead to the generation of a list of companies and
facilities willing to operate as disposers, as well as any conditions or
limitations which those companies feel must be satisfied.
Verification Testing and Issuance of Certifications. Verification
tests would be performed including sampling and analysis of waste effluents
Results of the verification tests along with recommendations would be sub-
mitted to EPA for final approval and the issuance of certifications.
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3. Program Implementation
It is anticipated that the recommended program could be accomplished
within a time frame of 12 months at a cost of approximately $250,000.
when the optional task of verification testing and issuance of certifica-
tions is not included. The manpower required has been estimated to be
7,000 hours of engineering and 3,500 hours of technical support.
8
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NEW CHEMICAL CONCEPTS FOR
UTILIZATION OF WASTE PESTICIDES
1. Introduction
The objective of the recommended program "Characterization of Inciner-
ation Parameters for the Safe Disposal of Pesticides" is to solve the near
term problem of pesticide waste disposal. To obtain more in-depth informa-
tion on the combustion characteristics of pesticide incineration, the
effects of combustible pesticide containers on pesticide incineration, and
the possibility of recovering marketable products from the high temperature
reactions of pesticides with various reagents, TRW proposes an analytical
investigation aimed at: (1) developing thermochemical and kinetic models of
the behavior of a broad range of representative pesticides in high tempera-
ture combustion and/or coreactant environments; (2) identifying waste
pesticide/coreactant products of potential commercial value; and (3) pro-
viding preliminary engineering and economic evaluation of processing
approaches for waste pesticide utilization. The coreactants would be
selected on the basis of cost, availability, and reactivity with the
selected pesticides. Since increasing volumes of pesticides are now
packaged in plastic containers and containers with plastic liners, the co-
reactants selected will necessarily include the three most common plastics;
polyethylene, polystyrene, and polyvinyl chloride. The knowledge of waste
plastics utilization systems acquired from previous investigations such as
the TRW study "New Chemical Concepts for Utilization of Waste Plastics"
(HEW Bureau of Solid Waste Management Contract PH 86-68-206) could thus be
used to provide a strong base for the proposed program.
Specifically, TRW recommends a two-part theoretical study program on
five representative volume pesticides from the five major pesticide
families: DDT (chlorinated hydrocarbons), aldrin (cyclodienes), carbaryl
(carbamates), parathion (phosphorus based), and 2,4-D-acid (herbicide).
The first task of the program is to determine the equilibrium reaction
9
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product distributions of the selected pesticide/coreactant systems under a
wide range of mixture ratio, temperature, and pressure conditions utilizing
an equilibrium calculation program. The results of the thermochemical equi-
librium analysis will be examined for commercially attractive end products
and potentially harmful pollutants, and would be used to identify the thermo-
chemically feasible reaction paths. The second task of the proposed program
is to develop reaction kinetic models suitable for the description of time-
dependent behavior of various reactions occurring in pesticide/coreactant
systems of interest. The mathematical models would be formulated into
computer programs and applied to simulate actual operating conditions. The
data generated from the technical analysis would be used to perform pre-
liminary design and economic analysis of chosen chemical processes and pro-
vide information on the economic feasibility of waste pesticide and pesticide
container utilization methods.
Assuming that safe, economically attractive waste pesticide/coreactant
products and processing conditions can be identified, two possible types of
reactor hardware systems are currently envisioned. The first system would
involve a relatively small, mobile processing unit which could be moved
directly to a location of storage of waste pesticides, process those pesti-
cides and then move on to the next storage site. The second approach would
involve processing waste pesticides as an intermediate feed along with a
continuous feed of waste plastics in a large fixed location plant.
2. Technical Plan
Five volume pesticides representative of the major familes of pesticides
will be investigated in the program. These are:
10
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(1)
(2)
(3)
(4)
(5)
Cl
-C-NH-CH
Cl
DDT
ALDRIN
CARBARYL
PARATHION
2,4-D
The primary effort in the program will involve technical and economic
evaluation of the chemical interactions of these five pesticides with
selected coreactants. This study will involve two interrelated tasks as
shown in the project flow diagram (Figure 1) and described below:
Therrnochemical Equilibrium Analysis
The objectives of this task are twofold:
(1) To determine the equilibrium product distribution of waste
pesticide/coreactant reactions and identify the potential
pollutants and marketable products.
11
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THERMOCHEMICAL
EQUILIBRIUM ANALYSIS
REACTION
KINETIC ANALYSIS
\
Selected Pesticides
and Reactants
Phase I
Thermochemical
Analysis
ollutio
Economi c
Criteria
X
Thermochemically Feasibl
Reaction Paths
1
\
Selected Reaction
Paths
Chemical Kinetic
Model
\
\
Economic
Data
7
\
Chemical Kinetic
Analysis
Kinetlcally Feasible
Systems
Economic Description
Laboratory Criteria
Final
Report
Figure 1. Project Flow Diagram
12
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(2) To determine the thermodynamically feasible reaction
paths from pesticide/coreactant reactions to desirable
intermediate and/or end products.
The equilibrium product distribution as a function of a broad range
of temperature, pressure,, and initial reactant composition will be computed
rapidly and inexpensively using a computerized equilibrium calculation pro-
gram such as the TRW developed Chemical Analysis Program. The TRW program
is capable of describing systems containing gases, pure liquids, pure
solids, and solutions, and simultaneously considering up to 200 gaseous
products, together with 50 condensed species. Chemical reagents to react
with the five representative pesticides will include air (combustion),
steam, polyethylene*, polystyrene*, polyvinyl chloride*, and others to be
selected on the basis of cost, availability and reactivity with the pesti-
cides. As an example, the equilibrium product distributions resulting
from the thermal decomposition and combustion of each of the five pesticide
systems at atmospheric pressure and three temperatures, 1,200 C, 800 C,
500 C have been computed. The numerical results are summarized in the
appendix. It is interesting to note that very similar product distributions
occur in approximately the same temperature and fuel/air mixture ratio
range in the combustion of waste plastics. Thus reactor equipment designed
for the partial or total combustion of plastic materials with recovery of
products such as HC1 would also appear to be suitable for the disposal of
plastic pesticide containers.
The thermochemical data base utilized in this example analysis has not
been expanded beyond those species required for the waste plastics analysis
even though it is clear that the base will require some expansion. Decom-
position species determined in the Foster D. Snell, Mississippi State, and
Oregon State studies, including the pesticides themselves, which are not
currently considered will be added to the data file along with others
which appear feasible. Literature information, where available, will be
used to prepare the necessary enthalpy and entropy data. Estimation
techniques will be used where data are not available.
* Utilization of plastic containers contaminated by pesticide wastes.
13
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The second part of this task involves the application of the thermo-
chemical equilibrium program to determine the thermodynamically feasible
reaction paths, i.e., whether or not certain intermediate reaction steps
are likely to occur thermodynamically. This will be done simply by re-
running the equilibrium program after deletion of all major equilibrium
product species found in the previous run. For example, the DDT thermal
decomposition system predicted methane, hydrogen, hydrogen chloride/and
graphite as the principal equilibrium products. The first stage of the
reaction path analysis will eliminate these species from consideration and
perhaps find ethylene, acetylene, methyl chloride, and chlorine to be the
next most feasible intermediates. Subsequent deletions will lead to iden-
tification of still higher (and probably more valuable) intermediates and
a complete description of the possible reaction paths to the thermodynami-
cally stable end products. The resulting information from the reaction
path analysis will be used to scope reaction of intermediates and mechanisms
for the reaction kinetic model.
Reaction Kinetic Analysis
The second task of the theoretical study will employ mathematical
models to describe the time-dependent behavior of pesticide/coreactant
reaction systems,, Emphasis of the analysis will be placed on the quanti-
tative characterization of reaction products as a function of time and
temperature, and the identification of reaction systems leading to the
development of economically attractive waste pesticide and pesticide
container utilization processes.
The first part of this task will be mathematical modeling of the
chemical kinetics of selected pesticide/coreactant reactions in the form
of systems of differential equations. Information from the Thermochemical
Equilibrium Analysis and the literature will be used to define the reaction
intermediates and the decomposition mechanism yielding the identified final
products. The reaction rate parameters will be taken from the literature,
or estimated by theoretical-empirical techniques when data are not
available.
14
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The second part of the Reaction Kinetic Analysis will involve the
application of the reaction kinetic models to determine the effects of
temperature, pressure, and residence time variation on the product distri-
bution in a kinetically controlled environment. The information obtained
will be used in the preliminary design of chemical reactors and processing
systems capable of attaining desirable end products.
Finally, the processing concepts for utilization of waste pesticides
and pesticide containers will be assessed in terms of their economic
potential. The results of the analyses will indicate the direction for
future laboratory research on waste pesticides.
3. Program Implementation
It is anticipated that the proposed program could be accomplished
within a time frame of 10 to 12 months at a cost of approximately $150,000.
4. Appendix A - Equilibrium Product Distribution
The equilibrium product distribution for the thermal decomposition and
air combustion of five selected pesticides as a function of temperature and
initial composition* (weight percent pesticides in the reacting system) are
presented in this appendix (Tables 1-5). The data format used in the tables
_v
is an exponential form, i.e., X.XX-Y is equivalent to X.XX 10 . Mole
fractions less than 10 are indicated by - .
*
The case of 100 weight percent pesticide is equivalent to thermal
decomposition in an inert atmosphere.
15
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TABLE 1
EQUILIBRIUM COMPOSITION OF DDT/AIR SYSTEM*
(1 ATM PRESSURE) MOLE FRACTION, GAS PHASE
wt. •%
Pesti- Temp- CH
cide 4
100 1200
800
500
70 1200
800
500
50 1200
800
500
20 1200
800
500
C 2.331-4
C 3.617-3
C 6.596-2
C 1.000-4
C 1.541-3
C 2.372-2
C
C 6.191-4
C 8.854-3
C
C
C
CO
—
-
1.205-1
1.148-1
1.143-2
2.039-1
1.924-1
1.790-2
, -
- •
-
1
3
5
8
1
1
1
CO,
"•
-
-
.880-3
.275-2
-
.280-3
.033-2
.040-1
.044-1
.055-1
H2 f
2.853-1
2.795-1
1.726-1
1.867-1
1.824-1 2.
1.035-1 5.
1.185-1
1.156-1 2.
6.325-2 5.
5.
6.
8.
—
-
-
736-3
733-2
-
907.3
486-2
514-2
129-2
321-2
^^•••H
7.
7.
7.
4.
4.
5.
2.
2.
3.
1.
1.
7.
HC1
.144-1
169-1
614-1
678-1
706-1
210-1
969-1
995-1
397-1
236-1
123-1
096-2
Condensed
Phase Graphite
HCN N2 Mol/lOOG Feed
—
-
2.673-4 2.
2.
2.
2.771-4 3.
3.
4.
6.
6.
6.
•
246-1
260-1
502-1
802-1
837-1
351-1
656-1
688-1
757-1
1.706
1.696
1.522
0.840
0.851
1.039
0.119
0.147
0.517
-
-
-
* . _v
The data format used is an exponential form, i.e., X.XX-Y is equivalent to X.XX 10 .
+ -4
Mole fractions less than 10 are indicated by -.
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TABLE 2
EQUILIBRIUM COMPOSITION OF PARATHION/AIR SYSTEM (1 ATM PRESSURE) MOLE FRACTION, GAS PHASE*f*
wt. %
Pesti-
cide. Temo.
100 1200 C
800 C
500 C
70 1200 C
800 C
500 C
50 1200 C
800 C
500 C
20 1 200 C
800 C
500 C
CHA
6.584-4
1.224-2
1.460-1
3.384-4
5.736-3
6.884-2
1.795-4
2.854-3
3.465-2
-
-
5.524-3
CO
3.784-1
2.812-1
1.983-2
3.693-1
2.937-1
2.170-2
3.632-1
3.020-1
2.319-2
8.885-2
6.655-2
2.581-2
COo
1.229-4
1.129-2
9.855-2
1.171-4
1.230-2
1.181-1
1.132-4
1.301-2
1.347-1
1.109-1
1.342-1
1.669-1
Ho
4.795-1
5.142-1
2.568-1
3.438-1
3.520-1
1.764-1
2.504-1
2.483-1
1.251-1
3.222-2
4.287-2
4.996-2
3.834-4
1.890-2
2.467-1
2.683-4
1.351-2
1.854-1
1.921-4
9.799-3
1.405-1
9.896-2
7.917-2
6.245-2
HCN h
1.572-4 5.
9.
1.
3.417-4 3.
6.
8.
3.700-4 2.
.4.
5.
9.
1.
2.
I0S
140-2
095-2
322-1
538-2
082-2
288-2
424-2
195-2
545-2
140-3
913-2
017-2
No
3.025-2
4.631-2
6.622-2
1.993-1
2.446.1
3.254-1
3.208-1
3.695-1
4.719-1
6.484-1
6.521-1
6.637-1
Condensed
Phase Graphite
P*0t Mol/100 G Feed
2.
3.
1.
2.
1.
1.
5.
5.
5.
316-2
314-2
-
564-2
081-2
-
092-2
395-2
013-3
042-3
132-3
1.693
2.298
2.748
0.740
1.199
1.800
0.105
0.461
1.123
-
-
0.022
Small amounts of CS2> COS, ?2, P4, and S2 are also present at 1,200 C.
fThe data format used is an exponential form, i.e., X.XX-Y is equivalent to X.XX 10"Y.
Mole fractions less than 10 are indicated by -.
-------
TABLE 3
EQUILIBRIUM COMPOSITION OF ALDRIN/AIR SYSTEM (1 ATM PRESSURE) MOLE FRACTION, GAS PHASE*1"
. wt. %
P^~ Temp,
cide K
100 1200
800
500
70 1 200
800
500
50 1200
800
500
20 1200
800
500
C
C
C
C
C
C
C
C
C
C
C
C
CH4
9.222-4
2.256-2
1
2.730-4 1
4.302-3 1
2
2
1.262-3 2
5
5
1.260-4 2
CO
-
.573.1
.502-1
.572-2
.396-1
.259-1
.129-2
.878-2
.619-2
.579-2
co2
-
-
3.220-3
6.191-2
-
7.280-3
1.136-1
1.450-1
1.476-1
1.667-1
H
1.428-1
1.411-1
1.010-1
7.831-2
7.679-2
4.409-2
4.468-2
4.371-2
2.388-2
2.403-3
4.986-3
7.545-3
HO
-
-
1.508-3
3.357-2
-
1.291-3
2.463-2
1.459-2
1.200-2
9.426-3
8.
8.
8.
4.
4.
5.
2.
2.
3.
1.
1.
1.
HC1
572-1
579-1
765-1
708-1
731-1
178-1
688-1
711-1
063-1
019-1
019-1
034-1
Condensed
Phase Graphite
HCN N2 Mol/100 G Feed
-
1.978-4 2.
2.
3.
1.844-4 4.
4.
5.
6.
6.
6.
933-1
948-1
226-1
467-1
506-1
090-1
773-1
773.1
871-1
3.288
3.286
3.246
1.991
2.003
2.202
0.911
0.937
1.279
-
-
0.045
"'The data format used is an exponential form, i.e., X.XX-Y is equivalent to X.XX 10 .
tMole fractions less than 10 are indicated by -.
-------
TABLE 4
EQUILIBRIUM COMPOSITION OF 2.4D/AIR SYSTEM (1 ATM PRESSURE) MOLE FRACTION, GAS PHASE
*t
wt. %
Pesti-
cide TemP- CHA
100 1200
800
500
70 1 200
800
500
50 1200
800
500
20 1200
800
500
C
C
C
C
C
C
C
C
C
C
C
C
2.329-4
3.522-3
4.171-2
1.002-4
1.520-3
1.832-2
-
6.167-4
7.594-3
-
-
1.045-3
CO
4.283-1
3.883-1
2.812-2
4.010-1
3.661-1
2.772-2
3.820-1
3.508-1
2.762-2
7.792-2
7.012-2
2.771-2
1
2
1
1
1
1
1
1
1
1
1
1
co?
.574-4
.151-2
.982-1
.380-4
.912-2
.925-1
.253-4
.756-2
.911-1
.560-1
.638-1
.924-1
H
2.852-1
2.758-1
1.373-1
1.870-1
1.812-1
9.099-2
1.189-1
1.154-1
5.858-2
8.168-3
1.656-2
2.173-2
H.20
2.580-4
1.400-2
1.870-1
1.585-4
8.671-3
1.222-1
1.000-4
5.292-3
7.836-2
4.322-2
3.543-2
2.916-2
HC1
2.859-1
2.967-1
4.077-1
1.875-1
1.930-1
2.499-1
1.192-1
1.220-1
1.522-1
5.198-2
5.199-2
5.300-2
OOm«-_£^^irefllMMB^MBB^H^«^«
HCN . N
-
-
-
2.671-4 2.
2,
2.
2.772-4 3.
3.
4.
6.
6.
6.
•WO^^VMMVBM^NMM^B^MMMHBi^HHVM
Condensed
Phase Graphite
2 Mol/100 G Feed
238-1
304-1
983-1
794-1
883-1
845-1
621-1
621-1
750-1
2.575
2.667
3.297
1.472
1.558
2.213
0.554
0.633
1.293
-
-
0.056
Y
The data format used is an exponential form, i.e., X.XX-Y is equivalent to X.XX 10.
Mole fractions less than 10 are indicated by -.
-------
TABLE 5
EQUILIBRIUM COMPOSITION OF CARBARYL/AIR SYSTEM (1 ATM PRESSURE) MOLE FRACTION, GAS PHASE*1"
wt. %
100 1200 C
800 C
500 C
70 1 200 C
800 C
° 500 C
50 1200 C
800 C
500 C
20 1200 C
800 C
500 C
CH
1.346-3
2.016-2
2.433-1
6.378-4
9.584-3
1.158-1
3.185-4
4.807-3
5.887-2
-
2.285-4
9.531-3
2.
2.
1.
2.
2.
1.
3.
2.
2.
2.
2.
2.
CO
500-1
274-1
562-2
808-1
565-1
850-2
008-1
758-1
075-2
778-1
682-1
473-2
7
6
9
8
1
1
2
3
1
co2
-
.380-3
.118-2
-
.387-3
.582-2
-
.086-2
.079-1
.229-2
.180-2
.533-1
H2
6.855-1
6.599-1
3.316-1
4.720-1
4.550-1
2.288-1
3.335-1
3.222-1
1.631-1
1.148-1
1.237-1
6.562-2
HO
3.620-4
1.961-2
2.509-1
2.800-4
1.525-2
2.051-1
2.119-4
1.162-2
1.639-1
2.269-2
1.343-2
7.862-2
HCN
2.701-4 6.
6.
9.
4.446-4 2.
2.
3.
4.552-4 3.
3.
4.
5.
5.
6.
Condensed
Phase Graphite
N Mol/100 G Feed
247-2
542-2
711-2
458-1
542-1
451-1
647-1
746-1
853-1
624-1
627-1
682-1
4.
4.
5.
3.
3.
3.
1.
1.
2.
0.
965
995
145
036
098
542
750
822
406
-
-
565
* _v
The data format used is an exponential form, i.e., X.XX-Y is equivalent to X.XX 10 .
t -4
Mole fractions less than 10 are indicated by -.
-------
DEVELOPMENT OF LOW COST CEMENTATION APPROACHES
TO PASSIFICATION OF HEAVY METAL SLUDGES AND SOLIDS
The following two research plans describe two different approaches to
the stabilization of heavy metal wastes prior to ultimate disposal. The
first plan concentrates on agglomerating and solidifying waste sludges with
low cost inorganic cements. The second plan involves incorporating a very
high loading >90 percent of dry, heavy metal waste into a polymeric matrix.
The initial condition of the waste material (sludge or dry solid for example)
is likely to determine the most cost effective approach for any particular
waste stream.
-------
STABILIZATION OF NONDEGRADABLE TOXIC WASTES
BY INORGANIC CEMENTATION
1. Problem Background
Sludges from industrial processing, mineral ore processing, backwash
from granular media filters, metallurgical processes, petroleum refining,
treatment of municipal sewages, etc., very often contain toxic metal com-
pounds, such as arsenic, mercury, lead, selenium, beryllium, cadmium, zinc,
chromium, etc. These hazardous heavy metal compounds represent a danger
of reentering into the environment and must be made inert to dispersion
before ultimate disposal of the sludge solids. Hazardous sludge solids
should be properly inactivated to make them physically and chemically re-
sistant to the action of environmental conditions and properly disposed of
in landfills, oceans, backfill mines, otherwise they may reappear in the
ecology, e.g. water, air, soil, plants, etc., after a relatively short
time. Conversion into a safe and stable form or state from which dissipa-
tion into the ecology either does not occur at all or is negligible should
precede disposal. The problem of establishing the admissible limits of
rate of dissipation for numerous toxic metals and metal compounds is still
an open question. As a baseline for evaluating stabilization techniques it
is recommended that the rate of dissipation of hazardous metals from their
natural ores and at natural conditions (i.e. conditions before any mining
operations) be considered the maximum allowable dispersion rate. The prob-
lem of safe disposal of hazardous metals and/or their compounds contained
in sludges, slurries, solid wates, etc. consists of finding economical
method(s) of bringing them into a passive form or passive state or embedding
into a passive impermeable matrix.
2. Recommended Technical Approach
It is assumed that the toxic solids subject to stabilization and
ultimate disposal do not present any current or future commercial interest
-------
for recovery and recycling of the metals or their compounds. Technological
processes for stabilization of hazardous solids from sludges, slurries,
wastes, tailings, etc., must meet certain requirements. The most important
are:
(1) the processes must be effective, i.e. the stabilized toxic
solids may not reenter into the ecology at a rate greater
than the admissible limit;
(2) the process must be economical, its cost will burden the
main product(s) responsible for the generation of the
sludge or solid wastes; and
(3) Economical considerations impose restrictions of using
only the lowest cost materials and reagents and the
simplest operations and equipment in processing.
Several processes have been suggested for stabilization of toxic metals
and/or their compounds in sludges, slurries, solid wastes, etc., such as
1 2
caging, encapsulation, complexing, compacting, chelating and cementation*. '
The latter, i.e. cementation shows considerable promise of assuring satis-
factory performance combined with potentially low cost. Stabilization of
the toxic solids from sludges and wastes by inorganic cementation involves
blending and overlaying the sludge solids after proper preparation with
cementitious materials or cement forming raw materials. Setting and
hardening of the entire mix follows with a resulting "sludge-concrete".
The intended procedure partially resembles cementation or stabilization of
soil ' and partially resembles building concretes with the compacted sludge
or solid waste replacing, respectively, the soil or sand/rock aggregates.
Either inorganic or organic bonding agents or their combinations may be
applied.
*Cementation is taken to include both inorganic and polymeric cements.
This research work concentrates primarily on inorganic cements while
the one which follows involves polymeric cements.
Preparation of the solids for cementation from sludges, slurries,
and wastes is discussed in the section titled "Technical Problems
in Cementation of the Sludges."
-------
Inorganic cements meant for application in the stabilization of
sludges are materials which, when mixed with water, form plastic and viscous
pastes with bonding properties which set and harden in air or under water.
Lime, plaster of pan's, port!and cement, and calcium aluminate cements
belong to this category. Cement forming mixtures are composed of materials
which separately may or may not exhibit cementitious properties, but they
mutually react with formation of compounds which will set and harden.
Examples of such mixtures are lime-clay, lime-pozzolan, calcium aluminate-
calcium sulfate, etc.
Bituminous materials, coal tar, coal pitch and asphalts may be
attractive as bonding materials for sludge conglomerates both from the
point of view of performance as well as cost. The deleterious effect of
soil bacteria and fungi may be overcome by incorporating fungitoxic and
bacteriatoxic agents. This precaution may be of particular importance if
the "sludge-concrete" has to be disposed of in moist and warm sites.
The set, hardened and eventually cured "sludge-concrete" blocks,
when removed from wooden rectangle molds are expected to possess sufficient
strength for further handling and transportation to the ultimate disposal
site. They may or may not exhibit sufficient resistance to land or sea
water leaching or to erosion. In the latter case additional surface
coating and/or surface hardening may be necessary. Spraying of cemented
blocks with metal fluorosilicates (Mg, Zn) may harden the surfaces and
increase the resistance to erosion and leaching, and impregnating or
coating with bitumens, paraffins, or resins may increase the resistance
to Teachability.
Economic reasons dictate that the formation of the "sludge-concrete"
must be achieved with no more cement than usually used in normal
concretes or in cemented soils.
A cement/sludge ratio (on a dry weight base) in excess of 1:5 will
probably be prohibitive costwise. While the requirements regarding leach-
ability and erosion resistance are high, the strength requirements are
-------
limited to about 1/10 of the strength of usual concrete compositions,,
Compressive strength of the "sludge-concrete" of the order of 500 psi will
probably be adequate for transportation. The low strength requirements of
"sludge-concretes" opens the possibility of substituting for the well-
established commercial cements (e.g., Portland cement) inferior quality
but potentially lower cost cementitious mixtures.
Figure 1 presents a tentative flow diagram of a few alternate
procedures for cementation of sludges.
3. Technical Problems in Cementation of Sludges
Characteristics of the Sludges. Sludges have to be distinguished
from slurries. Slurries are liquids having sufficient suspended solids
to be a distinct phase. The solids in slurries are usually granular or
crystalline, but sometimes may be amorphous. Sludges are thick viscous
mixtures of solids and liquids, in appearance they resemble a single phase
and generally have little, if any, free liquid. These semi-liquid wastes
have a total solids concentration of at least 2,500 ppm. They are obtained
from waste water containing impurities by processes, such as liquid-solid
separation (e.g., sedimentation, clarification), a chemical reaction, e.g.
coagulation, or a biological process. Often they are jelly-like and
colloidal with a gray, black, brown or other color. Usually sludges can be
made to flow, can be pumped, and exhibit thixotropic properties. In most
cases they are too liquid for transportation by a conveyor or shovel.
Sludges vary in moisture content from 99 percent, which is typical for
alum sludges from water treatment plants, to perhaps 40 to 50 percent which
is typical for chemical plant sludges, clay products, evaporated black
liquor wastes in pulp and paper mills. The characteristics of a sludge
depend on the quantity and type of suspended and dissolved materials.
Sludges contain water in at least four different ways:
(1) chemically combined water, such as the water of hydration;
(2) colloidally held or "bound" water;
-------
Partial dewatering by
sedimentation
Sludge
I
Chemical treatment
(if necessary)
Adding flocculent
and binder
Filtration or
centrifuging
Slaking quicklime
Crushing of filter
cake
i Adding pozzolan or
other siliceous mat'l
Physical or chemical
consolidation of sludge
conglomerate
Compacting by
vibration
Screening
Blending with
inorganic cement
Prolonged curing
Surface hardening
Pre-impregnation or
coating
Blending with hot
tar or asphalt
i
Hardening
Disposal^.
Figure 1. Stabilization of hazardous sludges by cementation
-------
(3) physically trapped or confined water (such as inside
living cell walls or in hollow fibers);
(4) water of dilution or entrained water.
Most sludges are aqueous, but there are also sludges based on alcohols,
ethers, or other liquids that are used in chemical processing. Sludges
are difficult to dewater, transport, or keep from emitting odors. Treatment
of sludges depends on their settleability, filterability, pH, turbility,
biodegradability,. odor, etc.
Preparation of the Sludge for Inorganic Cementation. The preparation
of the sludge for cementation may include the following operations:
(1) Total removal or at least maximal reduction of toxic
ions from surrounding solution.
(2) If necessary or practical converting the sludge solids
into compounds having minimum solubility and which do not
interfere in setting or hardening of the applied cement.
(3) Dewatering of the sludge.
(4) Consolidation of the sludge solids into a conglomerate
suitable for cementation.
Removal or maximum reduction of the concentration of toxic ions in solution
surrounding the sludge aims at achieving practically toxic-ion-free solution
after subsequent total or partial dewatering of the sludge. This may be
achieved by adding an excess of the precipitating ions at selected pH and
temperature. The latter being controlled because the solubility product
is pH and temperature dependent. For example, if calcium arsenate is the
.0
toxic component of the sludge, the concentration of AsO, ions may be
++
reduced by an excess of Ca ions, and if HgS is the toxic compound, an
excess of S~~ ions will be necessary.
Conversion of sludge toxic solids into other compounds may be
necessary in two cases: if the solubility of the toxic compound is too
high and if following the separation of solids the remaining solution still
contains an excessive amount of toxic ions which cannot be otherwise econom-
ically removed; of if the toxic solid is harmful for setting or curing of
the "sludge concrete" (see additives to cement in the next paragraph).
28
-------
For example, cadmium and zinc hydroxides are known to inhibit setting
of cements. Converting these solids into silicates (ZnSiO- or Zn0SiO, and
24
CdSi03 or Cd2$i04) with Si03 or Si04 anions respectively (addition of
water glass) or into fluorosilicates ZnSiFg and CdSiFg may solve the
problem.
Dewatering of the sludge. Most sludges contain more water than may be
needed in cement-sludge-conglomerate-water mixtures in making "sludge con-
crete". Apart from this, it is doubtful if chemically or colloidally-
bound water from sludges may be useful for hydration of hydraulic cements.
The removal of unwanted kinds and excess of water may be economically
achieved by flocculating the sludge solid particles with either inorganic
or organic flocculents or mixtures of both, followed by sedimentation,
vacuum filtration, or centrifuging. Flocculents which may contribute to
the consolidation of the sludge solids and act as binders should be pre-
ferred. Among flocculents and binders worthy of consideration are: limes,
alums, veegum (hydrated magnesium silicates), clays, acrylamides,- stearine
and sterates, gum arabic, polyvinyl alochol, lignosulfonates and others.
Acrylamide base commercial flocculents have been claimed effective in con-
centrations of approximately 0.2 Ib per ton of solid (cost of the floccu-
lent is about $1.00 per pound). In sludges with "moderately bonded"
colloidal water adequate dewatering may be achieved by gravity thickening
with the addition of inert weighting additives (e.g. soils, fly ash, etc.).
The use of quicklime (CaO) instead of hydrated lime (Ca(OH)2) may help in
the destruction of the colloidal texture of the sludge.
Gentle vibration may ease the separation of solids from liquids and
improve the performance of the thickening operation.
The sludge cakes from vacuum filtration or centrifuging will be broken
into pieces to pass 1/4 in. mesh sieve but be retained by 200 mesh sieve.
They may have or may not have enough coherence and rigidity for use as an
aggregate in the formation of the "sludge-concrete". Sludge conglomerates
too loose for cementation may need additional consolidation for achieving
the necessary coherence and rigidity. This can be done by sludge rolling,
29
-------
an operation simulating the powder rolling used in powder metallurgy. By
this operation the particles are consolidated into a coherent mass of defi-
nite size and shape. In the sludge rolling, the sludge conveyed either
horizontally or vertically through a set of steel rolls, may be compacted
in the roll gap and will emerge as a sheet. In the rolling operation com-
paction occurs essentially only in one direction since very little pressure
is transmitted sideways. The strength of the roll-compacted sludge will
depend on its characteristics, kind and amount of the binder added in the
dewatering operation and it will be the limiting factor for both the thick-
ness and width of the sheet. Roll size, gap, speed, and rate of the sludge
feed are the major factors to be controlled.
The roll-compacted sludge sheet can be broken into pieces (minus
1/4 in. mesh, plus 200 mesh) for use as an aggregate. Also, it may be
cut into rectangular pieces. These pieces piled up to a certain height,
one on another, may be subsequently covered on the outside with a layer
of a soil-cement concrete, 0.5 to 2.0 in. thick (2 in. at the bottom and
Oo5 in. on the sides). Brush or spray impregnation of the surface pores
of the soil cement concrete with bitumen or paraffin will render the block
resistant to leaching and ready for disposal.
An alternate procedure may involve bonding the rectangular pieces
together with a lime-sand (ratio 1: 3) or lime-port!and cement-sand (ratio
1:1:6) mortar.
Some improvement of coherence of sludge conglomerates obtained from
filtration may be expected also by rinsing them alternately with lime
emulsions and solution of magnesiums and zinc fluorosilicate.
Cements for Cementation of Sludges. The following criteria will
govern the selection of the cements or cementitious mixtures for
stabilization of toxic sludges:
(1) site of ultimate disposal (land or ocean dumping);
30
-------
(2) cement performance, particularly its compatibility with
the sludge aggregate chemicals;
(3) local availability;
(4) cost per weight or volume unit of the stabilized sludge.
The role of cements in,the "sludge-concrete" is the same as in normal
concretes (i.e. sand-rock-cement); namely, to create a cementitious matrix
which embeds the compacted sludge conglomerates. The applicability of well
established commercial cements, such as Portland cement, lime and plaster
of pan's for bonding sludge conglomerates must be considered first.
Commercial Cements„ The outstanding performance of Portland cement
in concrete construction is well known. Pricewise: (about l<£/lb) it is one
of the lowest cost products of the kind on the market. What is important
for its application in the "sludge-concrete" is consideration of the extent
to which the presence of different inorganic or organic compounds in the
sludge conglomerate and mixing waters may be deleterious for setting and
curing. Harmful substances that may be present in conglomerates include
organic impurities, silt, clay, coal, lignite and certain lightweight and
soft particles. Organic impurities may delay setting and hardening of con-
crete,, Small percentages of certain organic impurities such as sugar may
actually prevent the setting of Portland cement for several days. Other
organic impurities such as peat, humus, and organic loom may not be as
serious but should be avoided,, Materials finer than those passing the
No.200 sieve, especially silt and clay, may be present as dust or may form
a coating on the aggregate particles. Even thin coatings of silt or clay
on gravel particles may be harmful because they may weaken the bond between
the cement paste and the aggregate particles. The same may apply to certain
inorganic salts either dispersed from poorly consolidated sludge conglome-
rates or present in the mixing water due to leaching. Salts of manganese,
tin, zinc, copper and lead are active,, Other salts that are potential
retarders include sodium borate, sodium phosphate, sodium iodate, sodium
sulfide and others.
31
-------
In normal concretes, cement paste (cement plus water plus air)
ordinarily constitutes 25 to 40 percent of the total volume of concrete
(7 to 15 percent by volume of cement). Probably the same amount by volume
may be needed for "sludge-concretes".
Plaster of pan's is used as a cementing agent in gypsum concrete which
consists of calcined gypsum, Inorganic aggregate such as perlite (siliceous
volcanic glass), vermiculite (micaceous mineral) or sand and wood chips
or shavings. The applicability of plaster of pan's or other calcined
gypsum products without additives for cementing sludge conglomerates
is an open question. Pure plaster of paris sets (initial hardening) in
about 30 minutes but impurities and age of the plaster may introduce con-
siderable variations. Set can be advanced by the use of accelerators such
as small quantities of hardened plaster, zinc sulfate, potassium sulfate,
common salt, alum or sodium carbonate. Retarders are borax, tartaric acid,
citric acid, acetic acid and certain organic substances; ordinary glue dis-
solved in the mixing water is one of the most widely used retarders0
Among the precautions applicable to the use of plaster of paris is:
avoidance of dry-outs, and freezing prior to hardening. The plaster must
be permitted to hydrate before drying out, otherwise it will be strength-
less and chalky. As soon as the plaster has had a few hours to harden,
however, it should be dried out by ventilation or the circulation of warm
air. Drying temperatures below 100 C will not harm the plaster.
By impregnating plaster of paris with resins (phenol- or urea-
formaldehyde) either before or after casting, the strength may be increased.
making the plaster suitable for cementing of sludge conglomerates. At the
cost of $3.50 to 4.00/ton the plaster of paris is attractive. The price of
urea-formaldehyde resin, if prepared on the spot from urea and formaldehyde,
may be below 6<£/lb. Generally, 1 to 10 percent of resin is added to the
plaster. Addition of 5 percent resin would raise the cost of plaster to
about $9/ton.
32
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Lime is a general term covering the various chemical and physical
forms of quicklime, hydrated lime and hydraulic lime. The lime products
of building construction are mainly mixtures of hydrated lime with sand
to form mortars, stuccos, plasters, sand-lime brick and silica-lime brick.
Hydrated lime is often blended with gypsum plaster and is also used as a
workability or plasticizing agent in concrete.
For bonding sludge conglomerates lime putty alone or a mixture of lime
putty with Portland cement may be useful. Lime putty is prepared from
quick-lime (CaO) by slaking with more water than required for forming
hydrate ±Ca(OH)2l and aging. The approximate volumetric proportion of lime
to sludge conglomerate may be similar to lime/sand in mortars; namely, 1:3.
If Portland cement is added the proportions may be:
Lime: portland cement: conglomerate = 1:1:6
or 2:1:9
The amount of water should be kept at the minimum required for workability;
excess water weakens the product and increases drying shrinkage. Lime will
not harden under water unless it contains impurities such as clay or silica.
The rate of hardening of pure lime depends upon the rate of annexation of
carbon dioxide from the atmosphere. Dolomitic limes also may be used for
stabilization of soils.
The cost of lime depends upon the cost of limestone (calcium carbonate,
about $1.00 to 1.50/ton) and the cost of calcination and slaking.
Coal tars and pitches, as well as asphalts, have been successfully used
4
in concrete paving and stabilization of soils for many years. For stabili-
zation of soils the amount used varies from 4 to 10 percent depending upon
the gradation and composition or the soils. Protection from the action of
bacterias is important. Pricewise, they are attractive: the price of
asphalt cement is about $20/ton.
33
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Low Cost Cementing Materials for Stabilization of Sludges. A mixture
of lime with siliceous materials such as silica^ clay or soil reacts slowly
with the formation of calcium silicates having bonded properties. The fol-
lowing procedure may be envisaged for stabilization of sludges; a non-
airslaked quicklime is added to a partially dewatered sludge containing 10
to 30 percent water in a wooden mold, slaked with one part of the remaining
water and allowed to age to form a lime putty (contaminated with the sludge
solids) under cover of plastic for prevention of the access of COp from air.
Graded soil (in the range of particle size -4 and +200 mesh) or clay is
added (the optimum ratio of lime to soil to be determined) and the entire
content of the mold thoroughly blended. Compacting of the mold content may
be achieved by vibration.
Setting and hardening may take several days. Some heating with steam,
if applicable, would accelerate setting and hardening. The hardened block
may be expected to require a coating for prevention of leaching of
hazardous sludge components.
Undersintered cements of composition similar to Portland cement but
calcined at much lower temperatures exhibit hydraulic properties also; but
with prolonged setting time and inferior strength properties. Such cements
may be prepared by mixing limestone with clay or shale and burning at a
temperature range of 850 to 950 C (portland cement requires firing of the
order of 1600 C). The lower heat treatment will reduce the price of the
cement.
Sulfoaluminate cements are of interest for bonding sludge con-
glomerates in regions abundant in low grade ferruginous bauxites (e.g.
Oregon) or high alumina clays, or where waste tailings from alumina pro-
duction are disposed of and may be available as a raw material. Calcium
sulfoaluminate cement may be obtained by burning a batch composed approx-
imately by weight of 1/2 gypsum, 1/4 aluminous .mineral (tailings, bauxite,
clay) and 1/4 chalk at about 800 C. The resulting product, a mixture of
calcium aluminate sulfates exhibits hydraulic properties and hardens with
water into the compound SCaO-Al^O^'SCaSO^-SlHpO which should form a matrix
for incorporating sludge solids.
34
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Pozzolaniotype cements are of interest in regions such as
California, where pozzolanic-type materials such as volcanic tocks,
diatomaceous earths etc,,, are abundant. ASTM C219 defines a pozzolanic
as a siliceous or siliceous and aluminous material, which in itself pos-
sesses little or no cementitious value but will, in finely divided forms
and in the presence of moisture, chemically react with calcium hydroxide
at ordinary temperatures to form compounds possessing cementitious pro-
perties. A number of natural materials such as diatomaceous earth,
opaline cherts and shales, tuffs and pumicites and some artificial
materials such as fly ash are used as pozzolans0 The use of pozzolans
as cement replacements can substantially reduce the early strength of
concrete, especially during the first 28 days. Because of the slow
pozzolanic action, prolonged continuous wet curing and favorable curing
temperatures must be provided.
Flyash is sometimes used as a pozzolanic admixture. Pozzolans may
be mixed with port!and cement to reduce its cost.
Low Cost Coatings. The "sludge-concrete", formed from sludge solids
compacted into conglomerates and inorganic cements or cementitious bonding
agents, may be expected to have fairly low surface erosion resistance and
perhaps exhibit higher Teachability of the hazardous sludge elements than
desired. Optimization of the water/cement ratio, or optimization of con-
glomerate gradation cannot result in a water-tight, sludge-concrete unless
the aggregate is water impermeable, and this may not be expected from
sludge conglomerates. These deficiencies of the "sludge-concrete" must be
remedied prior to its final disposal. A promising method for surface
finishing of the "sludge-concrete" includes two stages:
(1) surface hardening with fluorosilicates;
(2) filling the pores or covering the surface with a water
impermeable or water repellant coating.
Well established processes of hardening concrete surfaces with fluoro-
silicate solutions seems suitable for the sludge-concrete also. If Portland
35
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cement or an excess of calcium hydroxide was used as cements the surface
may be directly coated with the fluorosilicate solution. Hydrolysis of
the portland cement components, tri- and di-calcium silicates, will pro-
vide the necessary calcium hydroxide. Otherwise the surface of the
sludge-concrete must be first impregnated with an emulsion of calcium
hydroxide (approximately 2 Ib of hydrated lime per gallon of water). The
surface is then treated with a solution of magnesium and zinc fluorosilicate
having the approximate composition:
Water 1 gallon
Zinc fluorosilicate 0.5 Ib
Magnesium fluorosilicate 2.0 Ib
Wetting agent 0.1 percent of the solution
The following reactions will occur:
g + 3Ca(OH)2 *-2CaF2 + ZnF2 + CaSiOg + 3H20
g + 3Ca(OH)2 »-CaF2 + MgF2 + CaSi03 + 3H20
Formation of insoluble fluorides and silicates impart to the surface
outstanding hardness and abrasion resistance. The procedure is relatively
inexpensive: 1 gallon of solution (estimated cost below 40<£) may suffice
for three coatings of two (1 cubic meter) blocks of the sludge-concrete.
A simple and efficient filling of the remaining pores of the sludge-
concrete after its surface hardening may be achieved with the application
of high-melting paraffin. The surface of the concrete will be heated with
hot air and molten paraffin brushed into the pores. The method has been
claimed as efficient for preventing capillary penetration of water. If
the concrete contains large cracks of openings, they must first be filled
with a cement grout. The amount of paraffin per 1 cubic meter of the
sludge-concrete will depend upon its porosity, and probably will vary
from 1 to 4 Ib. The current price of paraffin is about 6<£/lb.
Bituminous paints, portland cement paints, coal tar epoxy coatings
present an alternate solution for preventing leaching of hazardous
36
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elements from the sludge-concrete. Asphalt or coal tar coating may be
applied either cold or hot. Two coats are generally applied, a thin
priming coat to ensure bond and a thicker finishing coat. The thickness
of each coat is below 1 mm.
Black varnish consists of soft pitch fluxed back to brushing or
spraying consistency mixed with coal tar naphtha. It has been used for
protection of industrial steel work and as antifouling marine paint.
Portland cement paints are a composition of either pure portland
cement or portland cement with hydrated lime (up to 25%) and water re-
pellant agent such as calcium or aluminum stearate (about 1%). They
o
reduce the water permeability of concretes and are commercially available.
Coal tar or pitch/epoxy and coal tar/polyurethane coatings are
p
superior in quality but higher in price. These pitch/resin coatings
consist of soft pitch, and epoxy or polyurethane resin, a suitable
hardener, a mineral filter, and a volatile aromatic solvent. These
components are mixed to give two parts: one containing the resin and
the other the hardener (curing agent). Usually, 3 parts of tar and filler
are used for 1 part of resin. A curing agent is used in an amount of 5 to
10 percent of the total weight. In spite of the relatively high price of
the epoxy or urethane resins, the method may be still economical because
of the low thickness of the required coatings (0.4 to 1.0 mm).
4. Recommended Program
The recommended program encompasses two phases. In the first phase
investigations will be performed to establish the feasibility of several
alternative operations involved in the cementation of heavy metal sludges or
slurries with the use of inorganic or mineral cementing materials. These studies
will be performed on a simulated sludge containing about 50 percent water
and 45 percent solids, such as lead arsenate, cadmium sulfide and mercury
sulfide, and about 5 percent colloidal clay. The sludge will be either
-------
partially or totally dewatered*.
Inorganic cement e.g. portland cement or cementitious materials (e.g.
lime and pozzolan) will be mixed with partially dewatered sludge and the mix-
ture placed in a plastic or wooden molding for setting and hardening.
In a second approach, the totally dewatered sludge will be consolidated
into conglomerate. After crushing and grading, the conglomerate will be blended
with cement and water and allowed to set and harden in a plastic or wooden mold,
The time of setting and hardening will be determined for different cementitious
materials.
The set and hardened specimens will be subjected to the following
testing:
(1) leaching resistance in ocean water
(2) leaching resistance in water saturated with C02, 02 and
containing 3 percent HLS (simulation of aggressive
ground waters)
(3) compression strength
(4) erosion resistance to water streams.
Specimens will be suspended in a flow of water of certain linear velocity.
Their weight will be determined as a function of time.
The feasibility studies on inorganic cementation of heavy metal sludges
will include:
(1) Investigation of practical application of partial or total
dewatering of sludges by sedimentation, filtration and/or
coagulation;
(2) feasibility studies of forming sludge conglomerate, by either
physical or chemical methods, suitable for concentration.
Filter cakes obtained from vacuum or pressure filtration with
or without addition of binders and roll pressed compacts will
be tested as aggregates. The possibility of increasing the
hardness of soft filter cakes by treatment with fluorosilicate
solution will be investigated;
*The term "total dewatering" means removal of the fluid water, but not
necessarily the entire content of H^O, particularly not the water
which may add to cohesion or plasticity of the solid.
38
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(3) investigation of the applicability of tars or asphalts
for cementing;
(4) investigation of the applicability of Portland cement
for cementation;
(5) investigation of the applicability of plaster of pan's/
urea formaldehyde mixture for cementation;
(6) investigation of the feasibility of slaking quickline
with sludge waters;
(7) investigation of the applicability of pozzolanic cements;
(8) investigation of the feasibility of surface hardening of
"sludge-concretes" with fluorosilicate solutions;
(9) investigation of the feasibility of impregnation of
"sludge-concrete" pore with paraffin or black varnish;
(10) investigation of the feasibility of coating and bituminous
pai nts;
(11) technical and economic assessment of the above approaches
and selection of the most promising for demonstration
testing.
In Phase II of the program there will be a demonstration of upscaling
of the most promising methods for cementation of sludges. A few hazardous
industrial sludges in amounts of about 50 to 100 gallons each will be used
for this purpose. A Detailed Economic and Technical Assessment of the best
stabilization techniques will be performed.
It is estimated that Phase I of the program will take one year and
Phase II six months. The complete two-phase 18 months program is estimated
to cost about $150,000. Table 1 presents the proposed schedule.
39
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TABLE 1.
PROPOSED SCHEDULE FOR TWO-PHASE PROGRAM
• — -
PHASE I
1 J
Applicability of lime base mortars for cementation of sludge conglomerates
OQ ng o ., u go concrc
/ rU" ."9 °r P^ "_*___
PHASE II
. .
pjC3 ing °
Month
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18,
A
A
__- .. A
A
A
_A
A
A
A
A
A
A
A
A
/\
A
A
A
AA AAAAAAAAAA
A
A
A
A A A A A A
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REFERENCES
1. Burk, M. Stabilization of heavy metals in sludges, slurries, solid
waste, before ultimate disposal. TRW No. 4742.2.72-010. Jan. 13, 1973.
2 p.
2. Lubowitz, H. Chemical passivation of heavy metal wastes for ultimate
disposal. Proposed laboratory effort concerning passivation of heavy
metal wastes. TRW No. 4742.3.72-145. Oct. 23, 1972. 6 p.
3. Soil-cement laboratory handbook. Skokie, Illinois, Portland Cement
Association, 1959. 62 p.
4. Soils manual for design of asphalt pavement structures. 2d ed. The
Asphalt Institute, 1964.
5. Design and control of concrete mixtures, llth ed. Engineering Bulletin.
Skokie, Illinois, Portland Cement Association, 1968.
6. E. I. du Pont de Nemours & Company, Inc. British patent. 519,078(1940)
C. A. 35_ 8243(5). 1941.
7. Effect of various substances on concrete and protective treatment, where
required. Bulletin No. 3. Skokie, Illinois, Portland Cement Association,
Dec. 1968.
8. Kirk-Othmer encyclopedia of chemical technology. 22 v. and suppl.
New York, Interscience Publishers, 1963-1971.
41
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DEVELOPMENT OF LOW COST ORGANIC CEMENTATION APPROACHES
FOR STABILIZING HEAVY METAL CONTAINING SOLID WASTES
In the preceding research plan inorganic cements are recommended for
agglomerating and stabilizing heavy metal containing sludges prior to ulti-
mate disposal in either a landfill or ocean burial environment. The in-
organic cementation approach is attractive for waste materials containing
significant water, since the wastes can be agglomerated and solidified
without the need for separating the bulk of the water from the solids. On
the other hand, the waste loading of these "sludge concretes" is expected
to approach only 60 to 70 percent. There are many heavy metal containing
wastes which are essentially dry (e.g., powders from bag houses, or re-
sidual arsenical pesticide wastes) for which it is felt can be more
effectively stabilized at a much higher waste loading with organic cemen-
tation and coating procdures. This research plan addresses itself to the
alternative approach of utilizing organic cements and coatings with an
objective of obtaining stabilized agglomerates with a waste solids loading
of greater than 90 percent.
Cementing and Coating Criteria
The primary technical considerations are:
(1) Initial resistance of the passified wastes to dispersion
into the environment by the chemical and physical forces
of nature.
(2) Long term resistance of the passified wastes to aging
processes, these being bacteriological, chemical, and
physical.
The stability of freshly passified wastes with respect to dispersion
into the ecology will depend mainly upon the resistance of the wastes to
diffusion through the agglomerate cement and coating, and the resistance
of the coated agglomerates to counter diffusion of aqueous media. Such
diffusion will be affected by the conditions of the final disposal environ-
ment.
43
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The passified heavy metal contaminants must resist dispersion into the
environment not only initially but for a long period of time as well. Con-
sequentially, bacteriological action is an important consideration when
agglomerated wastes are placed in the earth for final disposal. Although
underground, radiation resistance should also be estimated because of possi-
ble radiation degradation in preparation, transportation, and handling.
The laboratory effort therefore must establish the effects of bacteriological,
radiative, and chemical degradative forces as well as those of the leaching
action of natural water.
Selection of Materials for Cementing and Coating
Materials selected for passivation of dry heavy metal containing wastes
must satisfy the criteria previously given. In addition, they must be
inherently low in cost. Cost is minimized, of course, when the selected
organic cementation and coating materials are capable of yielding products
having a high percentage loading content of metal contaminants.
Equal consideration must be given to ease of processing the passified
products. It is desirable that siinple equipment be employed, and that pro-
cessing be uncomplicated so that a detailed procedure for passivation is not
necessary.
In the light of the performance and cost criteria, materials for
cementing and coating dry heavy metal wastes were selected mainly from among
organic resins, particularly the olefinic resins. Polyolefins are hydro-
phobic and they resist bacteriological degradation. They can be made re-
sistant to intense ultraviolet radiation, and they can be chemically cross-
linked, a property that contributes to products meeting high chemical
resistance standards. In addition, they are relatively low cost, stemming
from the petrochemical industry; and commercial resins, in the main, are
recognized to be nonhazardous. Furthermore, polyolefins readily wet solidus
material due to their low surface tension and hydrophobic properties. Thus
a small amount of resin can be suitable for effectively cementing a large
quantity of metal contaminants and subsequent coating of the agglomerated
formations.
44
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The proof-of-principle experimentation utilized polybutadiene oligomers
and powdered polyethylene for formation of heavy metal waste containing pro-
ducts. These resins were selected after careful consideration of commercial
polyolefins in the light of the objectives of this work. Although polyolefins
such as pitch, tar, and polyethylene have been employed for this purpose by
other workers, the use of polybutadiene oligomers and powdered polyethylene,
is believed to provide significant advantages in carrying out heavy metal
passivation. The oligomers required here can be prepared at low cost from
butadiene, and waste polyethylene.
Let us first consider polybutadiene oligomers. These resins have
moderate molecular weights and are commercially available. Furthermore,
they may be obtained with terminal, chemically functional groups, (hydroxyl
and carboxyl groups). Being hydrocarbon in nature and of moderate molecular
weight, the resins are capable of being blended with large amounts of
solidus material. Utilizing the terminal functional groups, the molecular
weight of these materials may be increased markedly by chemical coreactants.
Desirable high molecular resins are thus fashioned in the presence of the
solidus filler. This advantage negates the task of blending filler into
high molecular weight resin, a difficult task due to the high viscosity of
such materials.
The resulting agglomerates obtained through the above procedure may be
tailored to exhibit the desired stiffness. For this purpose, the pendant
unsaturation of the resin can be utilized as well as its terminal groups.
Employing peroxides and/or polyfunctional chemical coreactants, the stiff-
ness of the agglomerated contaminants is tailored to satisfy the technique
of coating and the requirements of long-term disposal.
Powdered polyethylene is employed in powder coating the agglomerated
contaminants. The solventless technique of powder coating is presently
gaining increased importance in material coating operations due to recent
governmental legislation restricting the venting of solvents into the atmo-
sphere. At the present time, many resins are being offered commercially
45
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in response to this need in powder coating. In our opinion polyethylene
best satisfies cost and performance criteria and therefore is potentially
the material best suited for sealing agglomerates of heavy metal con-
taminants.
The purpose of the two-step operation consisting of cementing and coat-
ing as described above is the preparation of passified waste products con-
taining waste loadings significantly greater than previously realized. The
methods employed previously in the disposal of low level radioactive waste
consisted of simply blending the contaminants into resins. Products con-
taining more than 40 percent by weight of solid waste were difficult to
obtain with previously attempted techniques due to the high viscosity of
such systems. Furthermore, these products often exhibited uncoated con-
taminants on their surfaces which could be dispersed into the environment
by water leaching. It was anticipated that the above described two-step
operation (thermoset cement plus thermoplastic coat) could at least double
the solids loading and would eliminate the problem of uncoated surfaces.
Proof of Principle Experimentation
In order to assure the formation of ultimate disposal products which
resist leaching, it is prudent to tailor the heavy metal wastes to exhibit
the least inherent solubility in water. In the framework of cost limita-
tions, this operation is definitely desirable, and in practice this proce-
dure will be invoked. For the purpose of testing cementing and coating
materials, however, such testing is more meaningful when results are
obtained with respect to very water soluble materials. Therefore, the
resins for use in heavy metal passivation were evaluated using highly
soluble sodium chloride as the "simulated" waste. Techniques were developed
for preparing very integral stable products with a high solids loading
(Figure 1). The products contain a core consisting of salts (NaCl) re-
siding in a matrix of thermoset polybutadiene. The exterior coating material
is polyethylene which results from the fusion of powdered polyethylene on
to the core.
46
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Figure 1. Sodium chloride filled test specimen.
-------
The dimensions of the cylindrical products were 3-1/4 x 3-1/2 inches.
This size was found to be convenient for handling and testing in the
laboratory effort. In practice, larger blocks, about 36 x 36 x 36 in.
square can be readily produced.
The above constitutes a description of the preferred products, as
they resulted from a study of resins and techniques systematically screened
in proof-of-principle experimentation. For reasons given previously poly-
olefinic resins were the preferred materials at the onset of the program.
the resins yielding the most satisfactory products stemmed from polybutadiene
oligomers with carboxyl terminal groups, whose microstructure contained un-
saturation of which approximately 85 to 90 percent was of the pendant,
vinyl configuration.
Epoxides were employed for the purpose of significantly increasing the
molecular weight of the oligomers in the presence of the salt waste simulant.
These epoxides represented about 10 percent by weight of the composition
of the resinous matrix of the core and stem from diglycidyl ethers of
phenol A. These materials represent the preponderance of the low cost
commercial epoxides. Low cost peroxides were also employed to the extent of 1
percent of the composition for the purpose of stiffening the core composi-
tion in order to render it dimensionally stable for use in the subsequent
operation of fusing powdered polyethylene onto the core.
With respect to deciphering the preferred techniques, the roles of the
polyolefinic resins employed was interchanged with respect to their
functioning as core and/or coating materials. Polybutadiene was found to
be ineffective as a coating material because upon thermosetting the con-
comitant shrinkage occurring caused flows upon the surface. These flows
lead to improperly sealed cores. When powdered polyethylene was fused with
salt in order to form the core, it was found that this arrangement did not
properly seal the salt, and when additional polyethylene was employed in
order to form a coated core, the core arrangement was not dimensionally
stable under the temperatures of fusion, consequently salt penetrated to
the surface of the product.
48
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One question stemming from the program of deciphering the preferred
technique was whether polyethylene could be coated onto a core consisting
of salt and a thermoplastic resin having a melting point greater than poly-
ethylene. This approach was ruled out on three counts because: (1) the
thermoplastic resins having greater heat resistance are not low cost, (2)
the desirable high filler content products are not readily obtained due to
the viscous nature of these thermoplastic materials, and (3) the core
materials stemming from salt-powder resin fusion did not yield salt
effectively coated by resin, especially so when fashioning high salt content
arrangements. As a consequence of the latter phenomenon, the resins employed
for coating the core must adhere to salt as well as resin in order to
effectively seal the core. Due to the markedly dissimilar chemical nature
of salt and resin, adherence did not occur, thereby a flow was formed
which lead to the del ami nation of the coating. In contrast, the fluid poly-
butadiene oligomers yielded a resin coated salt e/en at high salt content.
The salt is entrapped into the resinous matrix and consequently, provides
a more effective base for sealing of the core.
Products were prepared using the preferred technique of thermosetting
core and thermoplastic coating containing sodium carbonate and sodium
chloride up to 87 percent by weight. The resistance to weight change
of these products subjected to the leaching action of aqueous 0.1 HC1 was
observed over a period of thirteen days. The products were weighed after
periodic removal from the solution, patted dry with paper towels, and
allowed to air dry. The stability of the products as indicated by~reten-
tion of weight was found to be excellent. No significant weight change
was found with many of the samples after the leaching tests.
Recommended Research and Development. It is recommended that a Phase I
Program consisting of four tasks be initiated:
Task I Preparation of molds designed for fashioning
agglomerate and fusing powdered resin into
6 x 6 x 6 in. cubes of material.
49
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Task II Preparation of 6 x 6 x 6 in. coated samples
containing a water soluble salt content of
90 percent by weight.
Task III Long term testing of the products in aqueous
leaching media.
Task IV Economic assessment
In Task I simple 6 x 6 x 6 in. rectilinear molds will be designed and
fabricated. Emphasis will be placed on designing low-cost molds which are
readily scaleable to larger sizes (e.g. 18 x 18 x 18 in.). It is believed
that a rectilinear configuration is more desirable than a cylindrical con-
figuration since rectilinear blocks represent a more effective utilization
of space in the ultimate disposal environment.
The Task II effort will involve the development of optimized mixing,
casting and coating techniques for stabilizing both soluble and insoluble
waste constituents. Olefinic oligomers with appropriate additives will be
utilized as cementing materials and both commercial and waste polyethylene
will be evaluated as block coatings. The objective is to obtain sealed
agglomerate blocks containing greater than 90 percent solids loading. Uti-
lizing the optimized techniques a number of 6 x 6 x 6 in. blocks will be
prepared for laboratory leaching studies (Task III).
The Task III laboratory leaching studies will consist of a systematic
exposure of the test blocks to simulated landfill and ocean burial environ-
ments. Landfill experiments will be conducted in outdoor test bins where
the air-soil-water environment is controlled and modeled to simulate a
typical California Class I landfill. Ocean burial experiments will be con-
ducted in tanks through which sea-water is circulated and typical marine
life is maintained. The landfill and ocean simulated environments will be
regularly sampled to determine the extent to which hazardous waste consti-
tuents are leached from the test blocks. Testing will continue for at
least 12 months after which the test block specimens will be removed and
completely analyzed (destructively) to determine their stability.
50
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The fourth program task will consist of a detailed analysis of the costs
associated with stabilizing and disposing of heavy metal containing wastes
by the organic cementation process. Comparison will be made of the costs
and effectiveness of the polymeric bonding approach with alternative methods
of preparing material for ultimate disposal (e.g. inorganic cementation,
sealed vaults, etc.) and a cost benefit analysis prepared.
It is estimated that this Phase I Program can ba completed in 18 months
at a cost of about $150,000. Test specimens would be prepared in the first
four to six months and tested in simulated ultimate disposal environments
over the next 12 to 14 months.
51
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DECONTAMINATION OF SOILS AND SILTS BY GASEOUS EXTRACTION
1. Problem Background
The fate of chemicals in soils is a subject of current national
interest due to their role in environmental pollution. Agricultural
pesticides have been singled out for special consideration since large
quantities are being dispersed on major agricultural soils. As a con-
sequence, soils represent a vast reservoir, receiving pesticides applied
either intentionally or accidentally.
A second serious source of soil contamination, limited to certain
regions but nevertheless very dangerous, resulted from manufacture and
demilitarization of poisonous chemicals by the U. S. Army units. The
exact amount of contaminated soils is hard to estimate. In the Rocky
Mountain Arsenal—Basin A only—there are 1.3 million tons of soil con-
taminated with arsenic oxides, arsenic chloride, mercury halides and other
inorganic chemicals. Many of the pesticides, specifically those contain-
ing heavy metals such as arsenic or mercury, exhibit a tendency to convert
into inorganic compounds and assumulate0
Residual hazardous heavy metal compounds present problems from an
agricultural and environmental standpoint. Many plants exhibit the ca-
pacity to absorb and convert them into food and fiber products. Pesticide
residues have damaged crops, found their way into air and water, and con-
sequently, have affected marine life and animal life. In some cases,
pesticides have accumulated in the lower organisms and are magnified in
concentration through food chains. Among the hazardous components present
in the soil as contaminants, arsenic, mercury, and their compounds pose
a particularly serious problem.
53
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2. Hazards from Arsenic and Mercury Compounds in the Soil
Inorganic arsenicals such as arsenic trioxide A$203, arsenic pent-
oxide ASpO,-, sodium hydrogen arsenate ^HAsO., sodium arsenite (NaAsOp or
Na-jAsOg), dipotassium hydrogen arsenate I^HAsO^, lead arsenate Pb3(AsO^)2»
lead hydrogen arsenate PbHAsO^, and pan's green, 3Cu(As02)2'Cu(C2H302)2, as
well as organic arsenicals such as disodium methane arsonate, DSMA,
CH3AsO(ONa)2 and cacodylic acid (CH3)2AsO(OH), have been used as insecti-
cides, herbicides, and soil sterilants for many years. Whereas the average
arsenic content of the soil is below 5 ppm, arsenic concentration several
hundred times this amount has accumulated in certain soils. Disposal
of arsenic containing chemicals by the U.S. Army has resulted in waste
lagoons with soil contamination by arsenic about 40 to 50 ppm. Arsenic
chemicals converted into arsenate or arsenite salts may exist either as
water soluble or water insoluble compounds. The water soluble compounds
are the most toxic to plants and mammals. The insoluble materials such
as iron arsenate (FeAsO^), aluminum arsenate (AlAsO^) or calcium arsenate
are less phytotoxic.
Plants vary in their tolerance for arsenic. The least tolerant plants
include peaches and apricots among the fruits; barley, wheat, peas, and
beans among the field crops; and alfalfa, clovers, vetch and Sudan grass
among the forages.
Arsenic toxicity is evidenced by slow, stunted growth and late maturity
of plants. Shot-hole and marginal scorch occur on the leaves of the more
sensitive fruits, notably peach and apricot. Legumes tend to die in the
seedling stage, following the appearance of small spots of dead tissue
scattered over the leaves. Grain crops turn yellow and die back from the
tips of the leaves. Arsenic-poisoned corn seems to suffer from too little
moisture. Arsenites seem to be more troublesome than arsenates.
Mercury oxide HgO and chlorides (Hg2Cl2 and HgCl2) and the organic
mercurials including methyl, ethyl, phenyl mercury derivatives, for example
PMA (phenyl mercury acetate CgH5HgOCOCH3) are being used as seed disinfectants,
54
-------
for weed control, and as pesticides and germicides. Mercuric chloride has
been applied to seeds both in the dry state and.in solution. Mercurous
chloride is less toxic to living organisms than mercuric chloride. Mercuric
oxide HgO is relatively insoluble in water; it has been used for disinfecting
white and sweet potato seed. Ethyl mercuric chloride is used as a fungicide.
It sublimes easily. Ethyl mercuric phosphate C2H5HgPO., is water soluble
and is used as a component of seed disinfectants. Bactericidal and fungi -
cidal compositions of mercurials may be either liquid or solid. Solid
compositions are compounded by blending the active mercurial ingredient
with finely divided solids such as attapulgite clays, diatomaceous earth,
synthetic fine silica, or flours derived from walnut shell, redwood, soy-
bean, cotton seed, etc.
Mercurials undergo translocation in plants and animals; that is, a
mercurial sprayed on a plant leaf or placed on seed will find its way to
roots, the stalk and even the grain. Seed treated with mercury compounds
bears grain containing considerably more mercury than untreated seed.
Mercury from soil can be converted by bacteria to highly toxic methyl-
mercury compounds which find their way through the food chains to mammals.
Mercury being an element cannot be detoxified in the same sense as
many of the toxic but non-persistent pesticides which decompose in air
and sunlight. Mercury and its compounds may be displaced from soil into
river beds and become more hazardous due to possible methylation processes.
The application of mercurous and mercuric compounds to soils could also
result in the release of mercury vapor. The soil factors which would
increase the rate of conversion of mercury salts to metallic mercury in-
clude greater moisture, organic matter content, pH, and temperature. Be-
cause of the high toxicity of this element and its components, the maximum
concentration for mercury in soils should not exceed the ppb level. The
accumulation of mercury through disposal of mercurial chemicals by the
U.S. Army in certain soils is of the order of 40 to 50 ppm or higher, i.e.,
it exceeds several throusand times the allowable limit.
55
-------
3. Soil as the Carrier of Arsenic and Mercury Contaminants
Soil is one of the most complex materials. The natural body is com-
posed of minerals, disintegrated and decomposed rocks, and minerals mixed
with organic matter in all stages of decay. Air and water are usually
considered soil components along with the microflora.
Two main groups of minerals are found in the soil. In the primary
group are those minerals that have persisted in the soil more or less
unchanged from the original rock. Feldspars usually dominate the primary
silicate minerals. Quartz dominates the resistant oxide groups with such
oxides as zircon (ZrOp-SiCL), ilmenite (FeO'TiO^), gibbsite A^O-^XHpO
and hematite Fe203'XH20 being present in greater or lesser amounts. These
minerals most often are found with particle size diameter of more than 2
microns and they make up the silt, sand and gravel of the soils. The
minerals of the second groups have been changed by weathering and are
referred to as secondary minerals. The most important of this group are
the clay minerals which are present in various amounts. The secondary
minerals are usually less than 2 microns in diameter.
The organic matter represents an accumulation of partially decayed
and partially resynthesized plant and animal residues. The content is
usually small—only about 3 to 5 percent by weight in the case of a
representative mineral topsoil. It may reveal any stage of decomposition.
It is generally divided into two groups: (1) the original organic tissue
and its products of partial decomposition and (2) the more lignified
protein complex, the humus. Usually, humus is brown or black in color,
and colloidal in nature. Humus has a capacity to attract and hold water,
gases, and ions. The adsorptive capacity of humus greatly exceeds that
of any clay even that of montmorillonite. Humus is not a specific compound.
Its adsorption capacity is attributed to the presence of carboxylic (-COOH)
and phenolic (-OH) groups attached to a central unit of a humus colloid
-------
(composed mostly of C and H atoms). Thereby the phenolic hydroxyl groups
are connected to aromatic rings while the carbonylic groups are bonded to
other carbon atoms in the central unit. The charge on humus colloids is
pH-dependent.
Chemicals in the soils are subject to many complicated processes which
generally may be divided into three classes:
(1) Physical Processes: Vaporization; leaching or movement by
capillary water into the soil profile;
photodecomposition; physical adsorption
into various soil colloids.
(2) Biological Processes: Metabolism by soil microorganisms and
root uptake, absorption by plant.
(3) Chemical Processes: Processes not mediated by the microflora
of the soil.
At the soil surface, volatilization and photo-decomposition are important.
Biological and chemical processes gain in importance after the chemicals
move beneath the soil surface.
Among many processes and reactions occurring in and/or with the
participation of the soil component, adsorption is one of the most important
in the governing of the behavior of the metallic components within the soil.
Physical adsorption means concentration at the soil surface or inside the
capillary texture of organic and inorganic matter. Chemical absorption (by
plants) means exclusion from the soil surface. Adsorption directly or
indirectly influences the movement of hazardous contaminants, plant uptake,
microbiological and chemical decomposition and volatilization. Components
strongly adsorbed by soil components are not readily moved by water passing
into and within the soil. When present at the soil surface, they are more
susceptible to photodegradation and volatilization.
57
-------
Soil organic matter usually is the component most highly correlated
with adsorption, and retention against leaching. The second major soil
components affecting adsorption are the crystalline layer silicate clays
such as montmorillonite and vermiculite because of their high cation
exchange capacities (80-150 meq/100 gram of soil) and hiqh surface areas
p
(600-800 M /g). Other clay minerals such as 11 lite, kaolinite, halloysite,
etc., and oxides and hydroxides of iron and aluminum may contribute to
adsorption also. Fe- and Al- oxides and hydroxides develop a pH-dependent
positive charge and may have high surface areas. Soils rich in Fe and Al
content have high anion adsorption capacities.
In many soils, significant quantities of noncrystalline colloidal
matter are found. Part of the iron and aluminum hydrous oxides, as well
as part of silica, in some soils is amorphous. The most important amor-
phous matter in soils in allophane, a poorly defined combination of silica
and alumina. Its composition approximates the formula AlpO-j • 2Si02 • H^O.
Allophane exhibits highly pH dependent ion exchange, capacity, both cationic
and anionic.
The cationic exchange capacity of different soil components may be
roughly illustrated by the following numbers:
Humus 200 milliequivalent/100 gram of soil
Vermiculite 150 milliequivalent/100 gram of soil
Montmorillonite 100 milliequivalent/100 gram of soil
Hydrous mica 30 mi Hi equivalent/100 gram of soil
Kaolinite 8 milliequivalent/100 gram of soil
Hydrous oxides 4 mi Hi equivalent/100 gram of soil
The power of the soil particles to bind both cations and anions makes
it an amphoteric adsorbent. In general, the soils' particles carry a net
negative charge which can be directly demonstrated by electrophoresis.
This charge arises in two ways: By isomorphous ion substitution and by
ionization of hydroxyl groups attached to silicon of broken tetrahedron
planes: Si-OH + H20 -> SiO~ + H30+. Negative charges also originate from
humus (-COOH, -OH) and phosphoric and silicic acids which constitute more or
58
-------
less an integral part of the clay particle surface. The adsorption of
arsenic and mercury compounds by soil components complicates their removal.
The amphoteric character of soil as adsorbent enables adsorption of arsenic
++ 3-
as cation (As for example in AsCK) or anion (arsenate As(h " or arsenite
As033").
Lateritic soils (soils rich in Al and Fe) and H- and Ca- soils
(resulting from cation exchange of H or Ca cations, respectively,)
exhibit enhanced capacity for adsorbing arsenate ions. The presence of
iron oxide Fe^Ck and high pH (alkaline reaction) seem to favor conversion
t. O
of arsenite ions into arsenate ions. Adsorbed arsenate ions can be partially
replaced by phosphate or citrate ions. High arsenate adsorption generally
involves a decrease in arsenite adsorption. The adsorbed arsenate ions are
strongly fixed to the soil.
The chemical behavior of arsenic in soils resembles that of phosphorus.
Both elements may be fixed in the surface soils if sufficient iron, aluminum
or calcium compounds are available for reaction. They may act as antagonists
toward each other. A high level of phosphate in nutrient solutions contain-
ing arsenic causes less arsenic to accumulate in plants because of antag-
onistic action. However, in soils, increasing the level of phosphate
enhances arsenic uptake, because phosphate replaces arsenate from aluminum
arsenate, becoming itself insoluble and making the arsenate soluble.
No direct information could be found about the sorption of the mercury
component by the soil adsorbents. Both ionic and molecular adsorption may
occur with the participation of both humus and mineral adsorbents. Sorption
^ J A.^
of mercury as Hg2 or Hg in exchange for common exchangeable cations
usually present in soils such as Ca , Mg , H , K , Na and NH« may be
expected. The extent of this adsorption can be expected to depend on the
soil texture, its composition, pH, etc. Several indirect indications on
the adsorption of mercury compounds by an adsorbent functionally similar
to that found in the soil support this view. Diatomite filters (opal-like
siliceous residue SiCL • nH^O of one-celled organisms) have been claimed
to reduce mercury content in certain industrial wastes from 5 ppm to 0.5 ppm.
59
-------
Some activated carbons were found efficient for the removal of mercury
components. Synthetic carboxylic acid cation exchange resins are known
to effectively adsorb mercury cations.
Mercury compounds located in the soil become even more dangerous if
they reach the water table. Formation of highly toxic and soluble organic
derivatives (such as MeHg or Me2Hg) due to the action of microorganisms is
highly probable. The toxicity of the latter compounds far exceeds the
toxicity of elemental mercury and the inorganic mercury compounds.
4. Removal of Arsenic and Mercury by Gaseous Extraction
The removal of arsenic, mercury and their compounds from the soils
presents a real technological challenge to a process engineer. The dif-
ficulties are manifold. The most essential are:
(1) Complex character of the soil as substrate for the contaminants
and chemical, physico-chemical and biological interaction of
the contaminants with the soil.
(2) Reduction of trace concentration of the contaminants in a
multicomponent and reactive material (soil) requires ap-
plication of highly selective reagents and processes.
(3) Huge tonnage of the treated soil and its relatively low
market value (about $l/ton plus transportation cost, if
any) limits the process engineer to application of the
least expensive reagents, simplest operations and simplest
equipment. Otherwise, the cost of decontamination may be
excessive.
(4) Retain fertility.
The gas extraction process for the decontamination of soils from
mercury and arsenic promises to overcome the above difficulties.
-------
Description of the Process. The essence of the process is conversion
of arsenic and mercury and all their compounds into volatile chlorides
(arsenic trichloride, AsCK, and HgClp) by fluidized bed reaction between
dry soil and a gas mixture composed of hydrogen chloride, hydrogen and
small amounts of chlorine. This gas mixture may or may not be diluted by
a neutral gas carrier such as nitrogen or nitrogen enriched air. Thermo-
dynamic calculations (see next paragraph) show that the presence of
chlorine is not necessary for converting either mercury or arsenic into
respective chlorides. Its addition to the reactant gas mixture is dic-
tated by the desire of facilitating the process, especially improving the
kinetics of the reactions, and also converting the titanium values of the
soil into volatile titanium tetrachloride.* Methyl alcohol or methyl
chloride vapor in the amount of about 1 percent to 2 percent may be added
to the reactant gas mixture also as reaction catalyst. Treatment of the
soil with proper composition of the reactant gas mixtures will not affect any
of the mineral components of the soil except titanium (which is desirable),
and iron oxides. Formation of the hardly volatile ferric or ferrous chlo-
rides (in the operation temperatures) would be disadvantageous to the process
because of consumption of chlorine values and accumulation of chlorine in
the soil. Fortunately, however, iron chlorides may be readily converted
back to iron oxides and phosgene; the latter compound being a saleable
by-product of the process. The organic matter of the soil is not expected
to react chemically with the reactant gas mixture to any considerable ex-
tent unless, for some unusual reasons, it contains a lot of compounds with
double bonds. Polysaccharides (cellulose, hemicellulose, starch, pectic
substances) and lignins exhibit a sufficient degree of chemical resistance
to most chemicals. On the other hand, physical adsorption of the gas mix-
ture reactants on the soil will occur, particularly at low temperatures, but
desorption will follow at a later stage of processing with the expulsion
of volatile chlorides from the soil by heat at vacuum.
*Titanium usually is present in the soils in the amount from 0.2 to
1.0 percent. It seems to be neither useful nor detrimental to the fertility
of the soils.
61
-------
Soil pulverized to minus 200 mesh screened and dried* (Figure 1 and
Figure 2) is brought into contact in a fluidized bed reactor with a gas
mixture of the following approximate composition:
Nitrogen 40 to 70 percent
Hydrogen chloride 20 to 50 percent
Hydrogen 4 to 12 percent
Chlorine 0 to 8 percent
Methyl alcohol 0 to 2 percent
Safety reasons require that the total nitrogen and hydrogen chloride be
not less than 70 percent. One or two fluidized bed reactors may be needed.
Thermodynamic calculations show that the desired reactions are feasible.
at room temperature, but no satisfactory rate of reactions is expected
below 100 C. If the soil/gas reaction is carried out at moderate temper-
atures and pressures above 1 atm the reaction products HgCl2, FeCl2 and
Fed., will remain in the soil, and the very volatile AsCl3 and TiCl^ (as
well as water vapor from chemical reaction) will be entrapped by the
gas mixture. The volatile components may be separated from the gas
mixture by cooling to ambient temperature. The gas mixture, after ad-
justing its composition and drying, is recirculated to the fluidized bed
reactor. The comparatively less volatile reaction product HgClp may be
expelled from the soil by heating under vacuum at about 250 to 300 C. It
may be recovered together with traces of FeCl- in a cold trap. Most of the
iron chlorides will, however, remain in the soil. Heating of the soil
under vacuum also will result in partial decomposition and carbonization
of the organic matter. After expulsion of mercuric chloride, hot air is
admitted to the soil (Figure 2). In this condition, the following reactions
will occur.
FeCl9 + C + 09 >• FeO + COC1-
C. 4. £ i
(The carbon, C, comes from carbonization of organic matter)
2FeCl3 + 3C + 302 »• Fe203 + 3COC12
*The optimal sequence of operations as well as the optimum particle
size and optimum reaction temperatures must be found experimentally.
For thermodynamics of the^p reactions, see next chapter.
62
-------
CO
CONTAMINATED SOIL
PULVERIZING
SCREENING
N,,
HCI
STARTUP AND COMPENSATION
FOR LOSSES
*
DRYING
FLUIDIZED BED
REACTION
EXPULSIC
VOLATIL
AND AsC
1
)N OF
ES HgCI2
>3
1
RECIRCULATING
GAS MIXTURE
1
l
\
CONDENSATION
OF VOLATILES
Figure 1. Tentative simplified flowsheet for decontamination of soils by gaseous extraction.
-------
HCI SC
TO ELEC
1
1HOT AIR
N,
REMOVAL OF OXYGEN
FROM AIR ON
Cu OR Fe
HjO ICuO
L
O2 (NO I
>IUTION
:TROLYSIS
-
REDUCTION OF
CuO TO Cu WITH
HYDROGEN
JSE)
ELECTROLYSIS OF HjO
CONDENSATION OF
AiClj, TiCI4 AND H2O
•
HOT WATER
HYDROLYSIS
OF AsCI-j AND TiCI4
FILTRAT
TiO2 X
[
ON OF
HjO AND
XHjO
i
DRYING
EXPULSION OF
As2 Oj FROM TiOj
260°C UNDER VACUUM
CONDENSATION
OF As2 O3
VAPORS
1
H,
HCI
GAS MIXTURE
N2+ HCI •>• SMALL AMTS
OF H2,.CI2 ,
i
CH-OH
GAS MIXTURE
DRYING
RECIRCULATING
GAS MIXTURE
Ti
O«b
MIXTURE
HgCI2
AIR ANC
CONDENSATION
HgCI2
PREHEATING
FLUIDIZED BED
REACTION
EXPULS
HgCI2 L
VACUU
SOIL
DECHLORIN
SOIL AND
OF PHOSG
) PHOSGENE
ION OF
JNDER
M
- CI2
H2 [_
CONTAM-
INATED
SOIL
r HOT AIR
JATIONOF
FORMATION
NE
ADSORPTION OF
PHOSGENE ON
CHARCOAL
r
DESORPTION
DECONTAMI
SOIL
DRY HYDROGEN
CHLORIDE
ELECTROLYSIS
OF HCI SOLUTION
H20
DRYING
'
SCREENING
t OVERSIZ
PULVERIZING
^JATED CONTAM NA:
SOIL
1
COCIj
0, Hgdj
Figure 2. Flow diagram. Decontamination of soil by gaseous extraction
of arsenic, mercury and excess chlorine.
64
-------
The iron oxides will remain in the soil and phosgene will be entrained by
air from which it can be quantitatively removed by adsorption with charcoal.
Condensed arsenic and titanium chlorides may be hydrolyzed by hot water
at ratios not less than 20 moles of H20 per mole AsCl3- The following
reactions will occur:
"AsCl
Boiling the solution and stripping it of HC1 will shift the reactions to
the right. After filtration the filtrate containing HC1 solution is sent
to electrolysis and the solid residue is dried and calcined at normal or
reduced pressure for expelling As203, which is volatile, from Ti02, which
is not. At normal pressure, heating up to 450 C may be required. At
10mm Hg pressure, it is necessary to heat only to about 260 C. The gas
extraction method of soil decontamination promises a number of advantages:
(1) the method is simple, fast and efficient;
(2) it requires little basic equipment (fluidized bed column
and condenser) ;
(3) the process may be continuous;
(4) the decontamination units may be mobile for on-site
operations;
(5) only moderate temperatures applied;
(6) recycling of the gas mixture limits the actual use of
reactive gases to negligible amounts;
(7) no filtration or settling needed;
(8) the process is inexpensive; and
(9) in favorable conditions, the process presents the commercial
option of extracting titanium values from the soil and
producing the by-product. phosgene. (Figure 2).
-------
A mobile unit for decontamination of the soil by gaseous extraction
in a fluidized bed may be mounted on a truck (Figure 3).
Physico-Chemical Aspects of the Process
The process takes advantage of the high volotility of several
compounds and the considerable reactivity of arsenic and mercury compounds
with hydrogen chloride and chlorine.
The volatilities of arsenic trichloride9 titanium tetrachloride,
mercury and mercury chloride are high (Table 1).
The calculated free energies of several reactions between the soil
contaminants and the HCl-hL-C^-gas mixture are negative (Table 2),
The negative free energies of reactions (Table 2) imply that no free
chlorine is needed in the reacting gas mixture for converting As and Hg
compounds into their chlorides.
The calculated free energies of reaction of all mineral soil
components with HC1-H,, gas mixture, except iron oxides, are positive.
Addition of chlorine to the gas mixture changes the sign of the free
energies at certain concentrations (Table 3).
Except for iron oxides no soil component, i.e., clay minerals, silica,
alumina, etc., will be converted into chloride unless free chlorine is
present in the gas mixture. Titanium compounds (ilmenite or dioxide)
require lower concentration of free chlorine in the gas mixture
HC1 + H? + Cl? for forming titanium tetrachloride, than other soil
components for forming respective chlorides (Table 3). Because of its
high volatility in practice much lower concentrations of chlorine may
suffice to get TiCl, in the gas phase. Ferrous and/or ferric chlorides
may be expected among the reaction products. Reconversion of these
chlorides back into their oxides may be expected to proceed easily with
the formation of phosgene, provided enough reducing carbonaceous matter
is present in the purified soil (Table 4)0
66
-------
Figure 3. Pictorial representation of truck mounted system
-------
TABLE 1
VAPOR PRESSURE OF SEVERAL COMPOUNDS OF INTEREST
FOR THE SOIL DECONTAMINATION PROCESS
Compound
As
AsCl3
As2°3
AlClg
FeCl2
Fed 3
Hg
HgCl2
TiCl4
H2°
M.P. C
814
-18
312.8
192.4
304
-38.9
277
-30
0
1 mm
372
-11.4
212.5
100.0
194.0
126.2
136.2
-13.9
-17
(ice)
Temperature in C at wh.ich the
indicated pressure is reached
10mm 40mm 100mm 400mm
437
23.5
259.7
123.8
700
235.5
184.0
180.2
21.3
11.3
483
50.0
299.2
139.9
779
256.8
228.8
212.5
48.4
34.1
518
7009
33205
152.0
842
272.5
261.7
23700
71.0
51.6
579
109.7
412.2
171.6
961
298.0
323.0
275.5
112.7
82.9
760mm
Hg
610
130.4
457.2
180.2
1026:
319.0
357.0
304.0
136.0
100
68
-------
TABLE 2
CALCULATED CHANGES OF FREE ENERGY OF REACTIONS BETWEEN
SOIL CONTAMINANTS AND HC1 + C12 + H? GAS MIXTURE
#
la
Ib
le
Id
le
If
2a
2b
3a
3b
4a
4b
5a
5b
6a
6b
6c
6d
6e
6f
Reaction
As203 + 3H2 + 3C12 = 2AsCl3 -f 3H20(g)
. As203 + 6HC1 = 2AsCl3 + 3H20(g)
As203 + 3H2 = 2As + 3H20(g)
2As + 3C12 = 2AsCl3
As,0c + 5H, + 3C1, = 2AsCl, + 5H,0(g)
c. D c. c. o c.
As205 + 2H2 + 6HC1 = 2AsCl3 + 5H20(g)
PbHAs04 + 7/2H2 + 5/2Cl2 = PbCl2 + AsCl3 + 4H20(g)
PbHAs04 + H2 + 5HC1 = PbCl2 + AsCl3 + 4H20(g)
CaHAs04'H20 + 7/2H2 + 5/2Cl2 = CaCl2 + AsCl3 + 4H20(g)
CaHAsO.'H.O + H... + 5HC1 = CaCl, + AsCU + 4H,0(g)
*T C. £. C. J C
Ca3(As04)2 + 8H2 + 6C12 = 3CaCl2 + 2AsCl3 + 8H20(g)
Ca3(As04)2 + 2H2 + 12HC1 = 3CaCl2 + 2AsCl3 + 8H20(g)
Ba3(As04)2 + 8H2 + 6C12 = 3BaCl2 + 2AsCl3 + 8H20(g)
Ba3(As04)2 + 2H2 + 12HC1 = 3BaCl2 + 2AsCl3 + 8H20(g)
Hg + C12 = HgCl2
HgCl2 + H2 = Hg + 2HC1
HgO +. H2 = Hg + H20
HgS04 + H2 = H2S04 + Hg
HgS04 + 2HC1 = HgCl2 + H2$04
HgS04 + H2 + C12 = HgCl2 + H2S04
. a , Remarks
-163.1
-26.3
-26.1
-137.0
-225.4
-88.6
No data available
-158
-44
-391*
-117*
-415* Calculation was made
,41* for comparison
-42.2
-3.4
-40.6
-23*
-20*
-65*
* The free energy of formation of Ca or Ba arsenates have been assumed to be equal to 009 of the enthalpy
(AF = 0.9 AH)
-------
TABLE 3
CALCULATED CHANGES OF FREE ENERGY OF REACTIONS BETWEEN THE
SOIL COMPONENTS AND HC1
+ H2 + C12 GAS MIXTURE
1
7a
7b
8a
8b
9a
9b
lOa
lOb
lOc
lOd
lla
lib
12a
12b
12c
12d
Reaction
S102 + 2C12 + 2H2 = S1C14 + 2H20(g)
S102 + 4HC1 = SiCl4 + 2H20(g)
A1203 + 3C12 + 3H2 = ZA1C13 + 3H20(g)
A1203 + 6HC1 = 2A1C13 + 3H20
Clay minerals (kaoHnlte or halloyslte):
(2S102)'A1203*2H20 + 7H2 + 7C12 « 2S1C14 + 2A1C13 + 9H
(2S102)'A1203*2H20 + 14HC1 <= 2S1C14 + 2A1C13 + 9H20
Fe,0, + 3C1, + 3H9 = 2FeCl, + 3H90(g)
t J C b i? &
Fe203 + 6HC1 => 2FeCl3 + 3H20(g)
Fe203 + 3H2 + 2C12 = 2FeCl2 + 3H20(g)
Fe70, + 4HC1 + H, = 2FeCl, + 3H90(g)
C. J c c. C
T102 + 2C12 + 2H2 • T1C14(1) + 2H20(g)
T102 + 4HC1 = T1Cl4/1j + 2H20(g)
Mineral llmenite:
FeT10, + 7/2C1, + 3H, = Fed, + T1Cl.m + 3H,0
0 b c w > \ 1 / ^-
FeTIO, + 6HC1 + 1/2C1, = FeCl- + TICl. + 3H90
J £. J *r &
FeT10, + 3C1? + 3H9 « FeCl, + T1C1. + 3H,0
J i c Z 42
FeT10, + 6HC1 = Fe C10 + T1C1. + 3H00
AF at RT % concentration of C12 1n
kcal HC1 + Cl, + H,' mixture for AF^O'
i 2
-53.3
+37.9 17'°
-91.5
+45.3 16.5
2° ~185' 21 4
+134.
-145.7
-8.9 0
-131.1
-39.9 0
-66.6
+24.6 12'7
-127.5
+9.3 11.5
-120.2
+16.6 6.3
-------
TABLE 4
CALCULATED CHANGES OF FREE ENERGY - FORMATION
OF PHOSGENE FROM IRON CHLORIDES
Mo.
Reaction
Free energy change in kcal at temp.
RT 400 K 500 K
13a
13b
2FeCl
3C
3COC1
Fed 2 + C + 02 = FeO + COC12
169.4
-36.4
177.7
-36.8
-171.8
-37.1
-------
Laboratory Feasibility Study
In an experimental setup for the laboratory feasibility study of the
soil purification process by gaseous extraction of the contaminants, the
gas mixture from a gas manifold passed through a drying tower filled with
drierite, into the fluidized bed reactors and then into the condenser
(Figure 4). The fluidized bed reactor was heated by wrapping the glass^
column with a heating tape. Temperature was controlled by a C/A thermo-
couple connected to a power controlling thermostating unit. The experi-
mental fluidized bed reactor processed 30 grams of soil (Figure 5).
The laboratory setup was calibrated at ambient and elevated temperature for
the necessary gas flow for a given gas distributor and volume expansion of
the soil sample. Studies were performed on agricultural soils contaminated
with arsenic and Rocky Mountain Arsenal soil contaminated with arsenic and
mercury. The reactive gases HC1, Hp and C12 were diluted with nitrogen.
The concentration of the gas mixture and temperature were among the variables
of the process subject to experimentation.
Stainless steel mesh, filter glass paper and glass frits, coarse,
medium and fine, have been tried as gas distributors and specimen support
in the fluidized bed column,, Fritted glass, size fine (pore size 4 to 6
microns) performed satisfactorily and was used in all feasibility
experiments.
In the calibration of the experimental unit the pressure drop across
the gas distributor, or across the gas distributor and the layer of the spe-
cimen on it was correlated with the different gas flows at ambient temperature
and at 150 C (Table 5)0 The expansion of the soil layer due to the gas flow
was recorded at room temperature,. The soil was not visible during operation
at elevated temperature because the glass tube was wrapped with the heating
tape. In most experiments, the decontamination of the soil was performed in
two stageso In the first stage9 the soil was contacted with the gas mixture.
In the second stage, soil was heated under vacuum for thorough expulsion of
the volatile contaminants0
72
-------
GAS MANIFOLD
FLOWMETERS
CJ
TOTAL
HEATING
TAPE
Q Q O Q Q
DRYING
TOWER
(DRIERITE)
DIMENSION IN MM
40
CONDENSER
GAS
OUTLET
(OR TO VACUUM
IN THE SECOND
STAGE OF OPERATION)
Figure 4. Laboratory set-up for decontamination of soils by gas extraction
-------
Figure 5. Laboratory fluidized bed reactor system.
74
-------
TABLE 5
CALIBRATION OF THE LABORATORY SETUP FOR DECONTAMINATION
OF SOILS BY GASEOUS EXTRACTION
Pressure dron across glass frit*, no soil sample
Gas Flow (nitrogen) Pressure Dron, mm Hg
ml/min RT 150 C
200
400
600
800
Pressure dron across glass frit* and 30g samole of soil
(-200 mesh)
Gas Flow Pressure Dron, mm Hg Height of
ml/min RT 150 C soil at RT, mm
14
28
40
56
19
39
62
80
0
200
400
600
800
0
16
29
42
57
0
21
41
65
90
41
50
50
52
70-110
*Glass frit D 32 mm, thickness 2 mm, porosity:
fine (4-6 microns)
75
-------
Preliminary feasibility studies of soil decontamination by gaseous
extraction have been restricted to removal of arsenic and mercury from
the soils. No attempts have been made as yet to demonstrate the
feasibility of extracting commercial by-products„
The best result achieved up-to-date was removal of more than 99
percent of mercurys down to a level of 0,2 ppm and removal of about
70 percent of arsenic down to the level below 14 p.pm (Table 6)0
Classification of Soils by Gas Elutriatidn0 The fine clay and humus
particles of the soil exhibit much higher retention capacity for mercury
and arsenic contaminants than do the coarser soil components. This leads
to an idea of separation of the contaminated soil into two fractions,
according to a certain size. The fraction finer than the selected size
might contain only negligible amounts of the contaminants,. Only the finer
fraction of the soil would necessitate decontamination0 In result, the
amount of soil subject to decontamination procedure could be considerably
reduced.
The correctness of this concept was checked by separation of a sample
of the Army soil (3000 grams) into two fractions by gas elutriation method.
Calculations based on the Stoke's law showed that using an 18 mm tube and
an air or nitrogen gas flow 20 cu0ft/hours a separation could be achieved
along an approximate particle size 44 microns, corresponding to 325 mesh
sieve. Separation experiments showed enrichment of finer fraction in As
and Hg content (Table 7)0 The departure of closure from 100 percent at
least partially may be attributed to losses of As and Hg during blowing of
the soil with gas0 The coarser fraction contains less contaminants than
the original soils but too much for setting aside its decontamination
processing,, It is clear that the cut-off particle size should be much
higher than 44 microns9 probably between 100 and 200 microns. Separation
of particles of the latter sizes by air elutriation is impractical„
Further studies on this line might be performed using mechanical
screening.
-------
TABLE 6
FEASIBILITY STUDIES ON DECONTAMINATION OF SOILS BY GASEOUS EXTRACTION
4~>
c
QJ
E
l»
OJ
Q.
X
LU
1
2
3
4
5
6
7
8
9
10
n
12
14
15
16
17
18
19
20
Soil Sample
Source of Soil
Agriculture
Soil
Etzkorn
Rocky Mountain
Soil from
Army Arsenal
Basin A
'article
Size
Mesh
-200
-200
-200
-200
-200
-200
-200
-200
-200
-200
-200
-200
-200
-200
-200
-200
-200
-200
-200
Gas Mixture
Flow
ml /mi n
560
560
560
560
432
666
600
-
666
700
_
666
(660
1660
666
666
666
666
666
666
N
T
71.4
61.4
66.4
61.4
50.0
67.6
100
-
67.6
40.0
_
67.6
76.6
51.5
67.6
66.6
65.6
51.6
52.0
50.0
HC1
%
28.6
28.6
28.6
28.6
37.1
24.0
-
-
24.0
40.0
„
24.0
48.5
24.0
24.0
24.0
43.c
48.0
48.0
H2
r
-
10.0
_
5.0
12.9
8.4
-
-
8.4
20.0
_
8.4
24.0
8.4
8.4
8.4
8.4
-
Cl
% i
_
-
5.0
5.0.
-
-
-
-
-
-
_
.
.
-
-
-
-
-
2.0
CH,C1
%J
_
-
_
-
-
-
-
-
-
-
_
.
_
-
1.0
2.0
-
-
Extraction
Temperature
C
150
150
150
150
200
200
200
-
250
250
.
300
/300
j 300
200
250
250
250
250
250
Time
hrs
1/2
1/2
1/2
1/2
1/2
1/2
1/2
-
1/2
1/2
_
1/2
fl/6
1/3
1/2
1/2
1/2
1/2
1/2
1/2
Evacuation
Temperature
C
_
-
.
-
-
200
-
200
250
250
300
300
(300
300
300
300
300
300
300
Time
hrs
_.
-
_
-
-
1/2
-
1/2
1/2
1/2
1/2
1/2
fl/2
i
1/2
1/2
1/2
1/2
1/2
1/2
Concentration of Arsenic
(ppm)
Before
385
385
385
385
385
40
40
40
40
40
40
40
40
40
40
46
46
46
46
After
335
260
358
356
190
26
40
32
16.5
18
39
26
26.7
28
23.7
15.6
14.9
20.6
13.7
%
Removed
13.0
32.5
7.0
7.5
50.7
35.0
0
20.0
58.7
55.0
2.5
35.0
33.3
30.0
40.7
67.0
67.6
44.8
70.3
Concentration of
Mercury (ppm)
Before
_
-
-
-
-
39
39
39
39
39
39
39
39
39
39
59
59
59
59
After
_
-
-
-
-
6.
23.
26.
0.8
1.2
1.2
0.4
0.6
1.2
0.2
0.8
0.2
0.2
%
Removed
.
-
.
-
-
84.5
41.0
33.3
98.0
97.0
97.0
99.0
98.5
97.0
99.8
98.5
99.8
99.8
-------
TABLE 7
SEPARATION OF ARMY SOIL BY NITROGEN ELUTRIATION
Total . H
wt % As Hg
Soil as received 100 40 ppm 37 ppm
Fraction +44 microns 73.3 12 ppm 16 ppm
Fraction -44 microns 26.7 44 ppm 53 ppm
Closure *, % — 52 70
*Contaminants found in both fraction as percentage of their
respective amounts in the soil before elutriation.
78
-------
5. Technical Plan
Classification and Selective Grinding. When the soil is separated into
two fractions according to particle size, the finer fraction is enriched and
the coarser fraction impoverished in the content of mercury and arsenic con-
taminants. Classification according to a pre-set particle size and selective
grinding for diminuting the arsenic and mercury compounds, but not the rock
particles, may allow reducing the tonnage of the soil subject to gaseous
extraction. Soil will be first divided into two classes using certain mesh
size, for example, 100 (corresponding particle size 149 microns). This
fraction will contain coarse and hard rocky particles. If the +100 mesh
fraction will contain only negligible amounts of Hg and As, it will be re-
turned to the soil without decontamination. However, if the amount of Hg
and As will be excessive, this fraction will be ground selectively and
classified again. The finer fraction of the sol"! (in the example -100 mesh)
combined with the undersize fraction from grinding, will be decontaminated.
This portion of the proposed study will aim at optimizing the cut-off
of the particle for classification and the method of selective grinding.
The latter will include search for a proper hardness grinding medium and
time of grinding.
Optimization of Process Variables. These studies will include finding
optimum conditions for the decontamination process. The following variables
will be studied in detail:
(1) Gas composition
(2) Temperature
(3) Time
(4) Effect of particle size
(5) Effect of moisture in the soil
(6) Effect of compounds with methyl group
such as methanol or methyl chloride on
the volatilization of mercury and arsenic
compounds.
79
-------
The gas extraction method carries the option ^of producing saleable
by-products. It'is possible to recover practically all mercury from the
mercury contaminants, extract titania from the soil and convert it into
commercial titanium oxide pigment and also to produce some amounts of
phosgene. The feasibility study of the "commercial" version of the decon-
tamination process may be studied also. It will include optimal conditions
for simultaneous conversion of arsenic, mercury and titanium compounds into
their volatile chloride, as well as the reaction of formation of phosgene
by reaction of iron chlorides with hot air and carbonaceous organic matter
from the soil.
Upscaling the Process and Conversion to Continuous Operation. After
completion of laboratory optimization studies, the process will be evaluated
in detail from a technological and economical point of view. Detailed flow
diagram, material and energy balances will be worked out. Upscaling the
process in the laboratory for decontamination of 5 Ib of soil per hour will
be combined with recirculating of the reacting gases and conversion of the
process into a continuous or semi continuous operation.
6. Implementation of the Program
Implementation of the program, divided into specific tasks, is pre-
sented on the following page (Table 8).
SO
-------
TABLE 8
PROGRAM IMPLEMENTATION
Classification
Month
56 7
10 11 12
OS
Selective Grinding
Optimization
Gas Composition
Temperature
Time
Particle Size for Fluidization
Water Content
Effect of Methyl Group
Commercial Version
Effect of Gas Composition and
Temperature on the Yield of
T1C1.
Optimum Conditions for Formation
of Phosgene
Evaluation Studies
Technological
Flow Sheet
Material Balance
Thermal Balance
Economical Evaluation
-------
7. Manpower Requirement
The activity outlined in the previous sections is anticipated to require
two man years of technical effort over a one year period. The estimated cost
is $100,000. If the results of the laboratory efforts justify further work,
a Phase II pilot scale program at the four man years, $200,000 level should
be funded. This would be followed by a demonstration program requiring ap-
proximately $500,000.
'82
-------
ISOLATION OF MERCURY AND OTHER HAZARDOUS.
HEAVY METALS FROM DILUTE WASTE STREAMS
1. Introduction
Governmental legislation restricting the amount of hazardous waste
industry may discharge into the environment presents a singular challenge
to technology; that is to provide the means whereby industry may be re-
sponsive to such legislation on the one hand, and on the other hand,
minimize the cost of the products it manufactures.
The cost restriction disallows many of the techniques and processes
relative to hazardous waste isolation and passivation developed to date.
Low cost processes are required, particularly in respect to heavy metal
contaminants. These contaminants .stem for the most part from industrial
operations which yield relatively inexpensive products such as power,
plated materials, insecticides, herbicides, etc. No significant increase
is allowable in the price of such products.
It is the purpose of this section to present efficient, low cost
vehicles for isolating heavy metals from aqueous waste streams. The heavy
metal isolation technology is formulated with the view of providing processes
potentially lower in cost than those processes comprising the present tech-
nology. Furthermore, the technology is designed to specifically remove
hazardous heavy metals from aqueous waste streams while minimizing inter-
action with other stream components.
This section shows sulfur and its polymeric compounds as the preferred
vehicles for isolating heavy metals from water. Selected sulfur compositions
are described and the pertinent technical literature is reviewed with respect
to showing the chemical versatility of these compositions. The selected
sulfur compositions are related to various isolation techniques. Experimental
work at TRW Systems showed how sulfur compositions could be tailored to
83
-------
increase the effectiveness of heavy metal isolation from water by filtration
and by extraction. The recommended future work is designed to yield addi-
tional sulfur compositions for use as efficient, low cost vehicles in
isolating metal contaminants.
2. Technical Approach
The isolation of contaminants and their passivation (discussed else-
where in this volume) is the key to the decontamination of heavy metal
containing aqueous streams. Ideally, mercury and other hazardous heavy
metals in aqueous waste streams should be isolated in as pure a form as
possible since the low amount of material gives lowest cost in the process
selected for their passivation prior to ultimate disposal. However, re-
duction of the contaminant to the minimal quantity may lead to increased
isolation costs; therefore, tradeoff may be required to minimize overall
disposal costs. A major factor in the cost analysis is the cost of the
materials used to separate the heavy metal.
Sulfur and its polymeric compounds are proposed as key materials for
separation of heavy metal contaminants from water because they are very
low in cost and chemically versatile. Their potential ability to reduce
heavy metal contaminants in aqueous streams to extremely low concentrations
is particularly important. Furthermore, the costs of these materials is
expected to decrease in the future since the products of desulfurization of
coal, oil and other fuels are sulfur compounds. As fossil fuel desulfurization
becomes more practical the compounds will be produced in increasing amounts.
. Sulfur and its polymeric compounds can be used to separate heavy metals
such as mercury, arsenic, chromium, lead, selenium, cadmium, and beryllium
from a dilute aqueous environment. This separation can be carried out by
employing one of three isolation operations: (1) flocculation, (2) ion
exchange, or (3) extraction.
The technical approach is designed to designate or tailor sulfur and
its polymeric compounds for each of the three isolation techniques. With
84
-------
these operations in hand, one can address the method deemed appropriate
for decontamination in light of the chemical and physical make-up of the
aqueous stream under consideration, thus providing general applicability.
Sulfur and its Polymeric Compounds. The classes of composition of
sulfur recommended for study are sulfhydryls and polymeric sulfurs bearing
chemically functional groups. Some of the sulfhydryls are designed to
bear acidic functional groups in addition to mercaptan groups. Certain
sulfur compositions bear either weak or strong acid groups, the former
being carboxylic and the latter being sulphonic. Others bear negatively
charged sulfur with sodium counter!ons. The role of the polymeric sulfur,
in addition to its inherent ability to sequester heavy metals in aqueous
streams, is to fashion metal complexes that are applicable to the selected
isolation operation. Thus in flocculation, for example, the size of the
insoluble suspensoids fashioned upon formatior, of metal complexes is
tailored by polymeric sulfur to make flocculation efficient. In extraction,
polymeric sulfur renders the metal complexes soluble in non-polar solvents.
And in ion exchange, it disperses the functional groups so that maximum
contact is effected with the aqueous environment.
Sulfhydryl Compounds with S Moieties. Fanelli showed that upon
passing of hydrogen sulfide (H2$) through molten sulfur at 160 to 390 C
the viscosity of the melt is reduced by as much as one thousandfold. In
this case H2S acts as chain stopper as follows:
H2S + Sx + HS - Sx-1 - SH (1)
In reaction 1, the mercaptan groups (-SH) which render heavy metals highly
water insoluble are bound by low cost sulfur atoms. Here H2$, a gas which
also readily precipitates heavy metals from aqueous solution, is chemically
"fixed" by sulfur. The resulting non-gaseous compounds are applied to
aqueous streams more conveniently than the hazardous gas, H^S. Furthermore,
tailoring the sulfhydryl compounds by varying their molecular weights pro-
vides a means whereby the precipitant may be designed for most effective
flocculation.
85
-------
Other reactions valuable in providing materials for the flocculation
operation are the reactions of sulfur with aqueous sodium hydroxide at
•}
100 C which yield sodium polysulphides as follows:
NaOH , Nas SNa (2)
A X"* £
Reaction 2 products may be employed as such as precipitants for heavy
metals, or they may be "cracked" by heating at pressures of 10 to 15 mm-
Hg to yield a mixture containing \{£^ H2S3' anc* ^3^4' ' tnese latter
compounds containing the desirable mercaptan groups.
Of particular interest in this study are the sulfane monosulphonic
acids.
0
II
HS-S -S-OH
x B
0
Sulphane Monosulphonic Acid
The sulfonic acid group is hydrophilic in contrast to the sulfane
portion of the molecule which is hydrophobic. Such materials form stable
dispersions in water; and the small size of the dispersoids, approximately
colloidal dimensions, makes a large area of material available for inter-
action with metal contaminants. Dispersions may also be formed through
utilization of alkaline metal salts of sulphane monosulphonic acids.
Sulphane monosulphonic acids provide the mercaptan groups for reaction
with metal contaminants in an aqueous environment. Particularly important,
in our opinion, are the high sulfur containing compounds since the mer-
captan groups stemming from higher molecular weight compounds of reaction
1 are not as readily available for interaction because these compounds tend
to be increasingly hydrophobic with increasing molecular weights. Furtner-
more, the strong acidic nature of these sulphane monosulphonic acids allows
stable dispersions in acidic as well as basic aqueous waste streams.
86
-------
A ready method for the preparation of sulphane monosulphonic acids
was given by Schmidt. Treating sulphanes (such as those prepared by
reaction 1) at low temperatures in ether with sulfur trioxide yields
sulphane monosulphonic acids as follows:
HS - Sx_1 - SH + S03 -> HS - Sx - S03H (3)
Another source of sulphanes for reaction with sulfur trioxide as shown in
reaction 3 are the aforementioned "cracking" reactions of sodium poly-
sulphides.
Polymeric Sulfur as Electron Donors. The salts of many heavy metals
form additional compounds with electron donor molecules, and polymeric
sulfurs are strong electron donors. Such n iterials provide .an advantage
in heavy metal decontaminantion processes, heavy metals are more readily
separated chemically from sulfur compounds without mercaptan groups than
from those containing such groups. Furthermore, when required, they offer
the potential of isolating contaminant metals without affecting noncon-
taminant ones such as calcium. Polymeric sulfurs fashion insoluble
complexes with heavy metals in the presence of alkaline earth metals and
leave the latter unprecipitated due to the absence of sulfhydryl compositions,
•v
Of particular interest is polymeric sulfur containing the carboxyl
group and sulphonic acid group because these groups facilitate the formation
of dispersions in water. Carboxyl containing sulphanes are realized through
the interaction of free radicals with elemental sulfur at 112 C ' as fol-
lows:
HOOC-RNpR-COOH + Sv -*• HOOC-R-S -R-COOH + S -R-COOH (4)
C. X A A
The free radicals are intermediate products of reaction 4 produced as
follows:
HOOC-RN2R-COOH -»• -R COOH + NZ t (5)
87
-------
The free radicals formed in reaction 5 react with elemental sulfur to give
the products shown in reaction 4.
Sulphane disulphonic acids are prepared as follows:
0
8
S0
50% Aqueous
-V
Acetic Acid
0
II §
HO-S-S -S-OH
tl
0
0
(6)
Thus by employing reactions 4 and 6 polymeric sulfur bearing weak and
strong acid groups are realized. By these means it is possible to tailor
dispersions and precipitants relative to the isolation operation.
The heavy metal sequestering power of polymeric sulfur is exemplified
by the reaction between Hg++ ions and HOOCH2CH2SXCH2CH2COOH to yield
[OOCCH2CH2SxCH2CH2COOHg]n, which in turn forms an intramolecular chelate
idealized as follows:
CH,
CH;
|x-rCH2"CH2'
S—CH2,
CH,
Such compounds render heavy metals amenable to isolation from aqueous
waste streams by either extraction or flocculation operations because:
(1) their covalent character promotes solubility in organic solvents,
and (2) their precipitants are hydrophobic which promotes separation
from aqueous environments.
The electron donor portion of sulfur which contains carboxyl or
sulfonic acid groups resides in the sulfur atoms. Mercury chloride, for
example, is known to complex with thio ethers to yield compounds of the
following type:
88
-------
R
Cl S CH,
cr s—CH
2
F1peculation Operation. Flocculation is an isolation operation
wherein insoluble contaminants suspended in a liquid matrix are made to
consolidate and settle. The decontaminated liquid is siphoned off. This
operation is widely employed in municipal and industrial water clarification
processes. With suitable, cheap materials for rendering soluble heavy
metals amenable for flocculation, this operation is an attractive means
for the decontamination of aqueous waste streams containing heavy metals.
To provide information about mercury untaining suspensoids amenable
to flocculation, the proof-of-principle experimental studies carried out
at TRW included an investigation of degree of heavy metal consolidation
effected employing sulfur compositions as a function of several reaction
variables. The objective was the formation of large particles containing
mercury with a very low concentration of the contaminant reamining in the
aqueous environment. Large particles are desired in order to effect ef-
ficient flocculation.
Sulfhydryl Ion Exchange Materials. Ion exchange materials cause the
isolation of chemical species by the release of expendible ones. Such
materials' are effective in decontamination of heavy metal containing
aqueous waste streams, involving the expenditure of non-hazardous metals
for hazardous ones. In this respect ion exchange resins are well known,
and in a recent work silicon alloys were employed in place of resins for
g
the removal of heavy metals from water and brine.
TRW proposes modified sulfur and its polymeric compounds as ion ex-
change resins for decontamination of aqueous streams containing heavy
metals. Sulfhydryl ion exchange materials may be prepared by the
89
-------
addition of hydrogen sulfide to polyunsaturated olefinic resins. Such
additions are facilitated by catalysts, among which are clay, metallic
11 12
sulfides, and sulfur. Of particular interest in our study are materials
stemming from the addition of hydrogen sulfide to polybutadienes in the
presence of sulfur. The ion exchange materials fashioned will contain a
varied multiplicity of alkyl mercapto, polysulfomercapto and sulphane
groups that have unusual affinity, as described previously, for heavy
metals in aqueous solution. In addition, these materials can be fashioned
as low density foams having dimensional integrity, offering maximum exposure
of functional groups to an aqueous environment and capability for mechanical
withdrawal from that environment.
Extraction Operation. For extraction, heavy metal complexes are formed
by the heavy metal contaminants with selected sulfur compounds. Such com-
plexes may be soluble in water or insoluble; they are, however, designed for
maximum solubility in organic liquids such as benzene, toluene, xylene,
kerosine, etc. This solubility in organic liquids which are nonmiscible
with water permits the extraction of heavy metal contaminants from an
aqueous matrix by organic liquids.
Mercaptans were selected for TRW proof-of-principle experiments as
the model compounds with which the extraction operation may be carried out.
The reaction of a mercaptan or thiophenol with aqueous solutions of salts
of heavy metals gives highly insoluble mercaptides. The insoluble compounds
of mercury, lead, zinc, and copper have been previously synthesized and
13
studied. The reaction of a heavy metal salt, e.g., lead, salt, with a
mercaptan occurs as follows:
2RSH + (CH3COO)2 Pb + Pb(SR)2 + 2CH3COOH . (7)
The heavy metal mercaptides produced in reaction 7 are highly insoluble in
water due to the covalent nature of the heavy metal-sulfur bond and the
alkyl groups, R. The latter can be tailored to further promote the insol-
ubility of these compounds in aqueous matrices. Fortunately, the above
parameters causing water insolubility on the other hand, are those which
90
-------
promote, on the other hand, dissolution in organic liquids. Tailoring the
extent of solubility of these compounds in organic liquids may be carried
out by varying the nature of the R groups.
Although the TRW proof-of-principle experimental study included in-
vestigation of the above process employing R groups of alkyl compositions,
the final objective is to replace alkyl compositions with $x ones. Tailoring
of S groups to make extraction operations possible will follow experimental
A
observations concerning extractability of heavy metal alkyl mercaptans by
non-polar solvents in an aqueous environment.
3. Proof-of-Principie Experimentation
One objective of this study was to determine whether S anions are
A
employable in reducing the mercury content of aqueous waste streams to
values less than 10 ppb. Although heavy mete,! sulfides are known to be
generally very nonsoluble in water, this knowledge is at best only in-
dicative of the sequestering power of S ions. The determination of the
A
solubility of heavy metal sulfides per se does not indicate whether these
compounds readily consolidate in an aqueous matrix in a manner amenable to
isolation operations. In the absence of such compound consolidation,
isolation operations, such as filtration and flocculation, cannot be carried
out efficiently. In other words, sequestered heavy metals must be tailored
to the isolation operation employed in order to realize effective decontam-
ination. In the proof-of-principle studies filtration through filter paper
was investigated to simulate flocculation operation.
Mercury Flocculation Study. Sv ions were employed in the precipitation
' " "'" " ' J ™ '"• —' A
of mercury from aqueous solutions of mercuric chloride (HgCl2) at .001M
(201 ppm Hg) and .01M (2010 ppm Hg). The precipitants were formed by mixing
with sodium polysulfide solutions to yield mixtures of pH 8. Precipitations
were also carried out in the presence of ammonium chloride. The resulting
cloudy, grey mixtures were filtered through Whatman Filter Paper No. 42.
The aqueous effluents were mixed with a stannous chloride solution, a re-
ducing solution for mercury cations, producing elemental mercury whose
concentration was determined by fTameless Atomic Absorption Technique.
91
-------
Table 1 gives the results of these determinations in respect to the above
procedure.
No apparent mercury appears in the aqueous effluents (Table 1), how-
ever, examination of the filter papers showed essentially no retention of
solidus matter from mixtures resulting from the .001M solutions. These
observations indicated that mercury indeed existed in the aqueous effluents
but in a state non-reducible by the stannous chloride solutions explaining
the essential absence of mercury indicated by absorption analysis. In order
to render the aqueous effluents amenable to analysis by Atomic Absorption
they were treated with permanganate solution producing mercury cations.
These effluents were then reduced by stannous chloride.
The initial concentration of mercuric chloride solutions was found to
determine whether the resulting precipitants consolidated sufficiently to
be effectively isolated by the filter paper employed (Table 2). The more
effective decontamination was obtained through precipitation of the more
concentrated solution, i.e., 2010 ppm Hg. Furthermore, the results (Table
2 combined with those of Table 1) show that essentially all the precipitated
mercury which persists in the aqueous effluent does not exist in the cationic
state.
Observations of color and/or particles in the aqueous effluents in-
dicated that extraneous dissolved and dispersed matter existed in the
aqueous effluents. Combining these observations and the results (Table 1
and 2) leads to the conclusion that both the dissolved matter and the dis-
persed matter within the water contained mercury9 and that the mercury
existed in a chemical complex bearing a negative charge. This conclusion
explains the non-consolidation of the dispersed mercury, and its non-
formation of elemental mercury upon treatment with reducing solution.
Nonfilterable mercury in aqueous effluents from S precipitation,
}\
therefore, was postulated to exist as negative charge complexes in the
physical state of dissolution and dispersion. Since the charge stabilized
the dispersion of mercury in the aqueous matrix, neutralization of this
-------
TABLE 1
MERCURY CATIONS REMAINING IN WATER FOLLOWING
PRECIPITATION BY VARIOUS POLYSULFUR ANIONS
Concentration of Hg in Aqueous Effluent, ppm
^X. Precipitating
N. Anion*
Hg N.
Concen. N.
in Water, >.
Dom N.
201
2010
201f
2010*
S1.2 S1.3 S1.4 S1.5
<.01§ <.01 <.01 <.01
<.01 <.01 <.01. .04
.01 <.01 .04 <.01
<.01 .01 .01 <.01
*Postulated composition stemming from the amount of elemental sulfur
dissolved in caustic yielding sodium polysulfide solution.
Residing in the presence of 0.001 M NH4C1.
^Residing in the presence of 0.01 M NH4C1.
An absolute value below the analytical sensitivity of fTameless
atomic absorption.
93
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TABLE 2
MERCURY DECONTAMINATION EFFECTIVENESS OF VARIOUS POLYSULFUR ANIONS
IN RESPECT TO INITIAL CONCENTRATION OF CONTAMINANT
Concentration of Hg in Aqueous Effluent, ppm
>v Preci pi tati ng
x. Anion*
Hg N.
Concen. N.
in Water, >v
pom ^v
201
2010
201 f
2010^
S1.2 S1.3 S1.4
166 - 55
6 - 3.2
>108 150
- 1.0 1.0
*Postulated composition stemming from the amount of elemental sulfur
dissolved in caustic yielding sodium polysulfide solution.
fResiding in the presence of 0.001 M NH4C1
^Residing in the presence of 0.01 M NH^Cl,
94
-------
charge should effect additional mercury consolidation. Consequently, poly-
valent cations stemming from low cost compounds were screened. In this
particular case, calcium chloride was found to be an efficient consolidating
agent for nonfilterable mercury.
The above described procedure was found to be very effective (Table 3).
These results upon comparison of the results in Table 2 show that further
decontamination was carried out by neutralization of the negative charge
complexes. It was accomplished, essentially, by more effective consoli-
dation of the dispersed mercury in the aqueous effluents. The formation
of particles can be observed visually. Figure 1 provides a photographic
rendition of the phenomena yielding results given in Table 2 and 3.
By allowing the consolidation of dispersed mercury by calcium chloride
to occur in the presence of dispersed matter Nt :har-C-19-14, in the aqueous
matrix, very effective decontamination was realized (Table 4). Employing
the S=1 4 ppt. ions, (the value of 1.4 obtained adding elemental sulfur to
Na2S) the resulting aqueous effluent is estimated to contain less than
10 ppb of mercury. Nuchar-C-190-14 was found to also separate mercury from
water, however, even with extensive treatment, the mercury content of the
water did not fall to a value less than 0.56 ppm.
Mercury Extraction Study. A further objective of the proof-of-
principle study was determination of the chemical compositions containing
sulfur which facilitate separation of mercury from water by the extraction
operation. The materials employed in producing mercury complexes which are
extractable from water by organic liquids were commercia.lly available mer-
captans from Industrial Chemicals Division, Pennsalt Chemical Corporation.
«
Selected for investigation in this study were three materials:
(1) n-butyl mercaptan
(2) n-octyl mercaptan
CH3 CH2 CH2 CH2 CH2 CH2 CH2 CH2 SH
95
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TABLE 3
DECONTAMINATION EFFECT OF CALCIUM IONS
Concentration of Hg in Aqueous Effluent, ppm
Precipitating
Anion*
Hg
Concen.
in Water,
ppm
201 2.40 0.32
*Postulated composition stemming from the amount of elemental sulfur
dissolved in caustic yielding sodium polysulflde solution.
96
-------
(£>
Aqueous solution
of 201 ppm Hg
Dispersion fashioned with
sodium polysulfide
Coagulation resulting
from calcium chloride
Figure 1. Nature of dispersion of mercury in water with sequential addition of sulfur
anions and calcium cations.
-------
TABLE 4
DECONTAMINATION EFFECT OF CALCIUM IONS
IN THE PRESENCE OF CALCIUM BLACK
Concentration of Hg in Aqueous Effluent, ppm
Precipitating
Anlsn*
Hg
Concen.
in Water,
ppm
201 .01 <.01
*Postulated composition stemming from the amount of elemental sulfur
dissolved in caustic yielding sodium polysulflde solution.
98
-------
(3) n-amyl mercaptan
CH3 CH2 CH2 CH2 CH2 SH
The organic liquids used to extract the metal complexes can be renewed
by distillation, cooled to precipitate the complexs or extracted of the
heavy metal by an aqueous acidic solution as follows:
Hg(SR)2 + HC1 + 2RSH + HgCl2
In the last method the metal is released from the complex and dissolves into
the aqueous phase. The sulfur bearing moiety of the complex remains within
the organic liquid, and it is active for further heavy metal isolation.
About 20 cc of .001M mercury acetate solutions (201 ppm Hg) were
treated with the above mercaptans, and extractions of the resulting pre-
cipitants dispersed in the aqueous environment were carried out with an
equal volume of toluene. The mixture was hand shaken, allowed to settle
in a separatory funnel, and the bottom aqueous layer was drawn off.
Visual observation of the aqueous effluents showed that sparkling clear
water was obtained when n-butyl mercaptan was employed. Neither of the
other two mercaptans, n-octyl mercaptan and n-amyl mercaptan produce a clear
product. Analysis of the aqueous phase of the n-butyl mercaptan system
demonstration that mercury concentration was reduced to a value of .01 ppm.
The above method was repeated employing mercury chloride in place
of mercury acetate to determine whether the method was equally effective
for heavy metal salts of strong acids as it was for those of weak acid.
It was found that the method was equally effective in both cases.
Conclusions from Proof-of-Principle Experimentation. The experimental
work at TRW leads to certain conclusions concerning the sequestering of
heavy metal contaminants in dilute aqueous waste streams. As observed by
other workers, sulfide anions per se were found to be not capable of re-
ducing the mercury content of water to very low values, I.e., 10 ppb. It
99
-------
is postulated that this is due to the drift to basicity which the aqueous
solution undergoes upon addition of alkaline metal sulfides to water in
amounts sufficient to realize stoichiometric equivalence vis-a-vis heavy
metal contaminants. At this point, the contaminants are incorporated into
negative charge complexes. In contrast to the cationic state of the con-
taminants, these complexes remain dispersed in water in the presence of
additional sulfide ions.
The extent of cationic mercury in the water converted into negative
charge complexes was found to depend upon the initial concentration of the
contaminant in the aqueous matrix. The more concentrated solutions were
found to yield precipitates of larger size, and these larger particles were
more resistant to dispersion by a basic aqueous matrix. Consequentlys
significantly higher conversion of cationic contaminants into negative
charge complexes occur in the more dilute solutions. Indeed as Table 2
shows concerning the 201 ppm Hg solution, practically all of the mercury
was converted, whereas for the 2010 ppm Hg the extent of conversion was nil.
Notwithstanding the more efficient separation of mercury from increasingly
concentrated aqueous solutions, water was not decontaminated to the extent
that it was free (less than 10 ppb) of heavy metal.
A significant conclusion of the TRW proof-of-principle experimentation
is that the efficiency of coagulating the negative charge complexes through
the use of polyvalent cations depends upon the amount of sulfur in the com-
plex. This conclusion will be instrumental for defining future work in the
sequestering of heavy metal contaminants in dilute aqueous streams. Specif-
ically, it suggests a study providing detailed definition of sulfur
compositions and polyvalent cations which, on the one hand, will aggregate
heavy metal contaminants in dilute aqueous solutions into large insoluble
particles, such particles being amenable to ready isolation. The aqueous
stream, on the other hand, is left free of heavy metal contamination.
The TRW proof-of-principle experimentation showed that the extraction
of mercury in water by organic liquids is more effective when the lower
molecular weight alkyl mercaptans are employed. This is believed due to
the greater miscibility in water of the lower molecular weight mercaptans.
-------
Despite greater hydrophilicity of the lower molecular weight compounds the
resulting mercapto-mercury complexes were extracted easily by organic
liquids. This result leads to the conclusion that the preparations of
Finelli, HS-Sv ,-SH and those preparations stemming from the "cracking"
5 6
of sodium polysulphides ' .are polymeric sulfur compositions potentially
valuable for use in extraction of heavy metals from water by non-polar liquids
because in these preparations, polymeric sulfurs are obtained in the low
molecular weight range.
4. Recommended Future Work
»
The proof-of-principle studies, including review of literature concerning
sulfur chemistry applicable to sequestering heavy metals in an aqueous en-
vironment, and the experimental work provided information showing the validity
of the concept of employing polymeric sulfur for efficient heavy metal sep-
aration from water. The objective of further work is to define the chemical
parameters and the reaction variables for polymeric sulfur, aqueous heavy
metal systems important to three isolation operations; flocculation, 1on
exchange, and extraction. Realization of this objective will provide the
means for tailoring the reaction systems specifically to the purification
of a great variety of heavy metal containing aqueous effluents. The purpose
of the proposed effort is to reduce the heavy metal content of aqueous
waste streams to a value less than 10 ppb at low cost.
TRW recommends that work in the immediate future consists of three
tasks each concentrating on a class of sulfur system providing properties
necessary to the three separation operations.
Task I concentrates on the polymeric system containing both mercaptan
groups and a negative charge. The proposed effort is a continuation of the
work previously described. Its objective is to define and produce chemical
systems stemming from polymeric sulfur compositions and attendant chemical
compositions which make flocculation and extraction operations effective
in separating heavy metals from water. The chemical systems will be des-
ignated to meet the requirements of present flocculation operations employed
commercially.
101
-------
Task II involves the investigation of additional polymeric sulfur
compositions (mercapto and acidic groups containing polymeric sulfur) in
a manner analogous to Task I. Its objective is the definition and prepara-
tion of chemical systems containing polymeric sulfur which sequesters heavy
metals in water under conditions not conducive to the utilization of Task I
materials, such as strongly acidic aqueous streams. The acidic groups of
materials to be studied are limited to the sulphonic acid and carboxylic
acid types.
Task III is the synthesis of materials positioning the chemical groups
of Task I and Task II onto a carrier in an arrangement capable of being
submerged and withdrawn from water. These materials can function as ion
exchange resins providing an alternative operation to flocculation and
liquid-liquid extraction. One of the objectives of this task is the prepa-
ration of ion exchange resins which are lighter than water, dimensionally
stable foams having a high surface area. With such materials a solid-liquid
extraction operation may be feasible in contrast to the liquid-liquid
extraction utilized in TRW's proof-of-principle experimentation. In batch
operation the heavy metal contaminated water would agitate with the foamed
ion exchange resins which would float to the surface and be removed by
skimming. The collection of the resin can be readily carried out by
methods now employed in cleaning oil slicks from the surface of water.
5. Manpower and Schedule Requirements
It is estimated that the recommended three-task program of laboratory
research can be completed within a time frame of 12 to 18 months at a cost
of $150,000 to $200,000. Successful laboratory demonstration of polysulfide
materials would be followed by bench-scale and pilot plant evaluations of
the best sequestering materials with actual waste streams.
102
-------
of the sulfanes, ^So, H?S3, HoSA and ^SK. Zeitschrift fuel Anorganische
/*! (_ . .„ J *^^ • __ ™ «l_ _•_ ^^^• 1 T O TOO T /•^P'V1" ' "" ••!-•• i..>««. - «r.......
REFERENCES
1. Panelli, R. Solubility of hydrogen sulfide in sulfur. Industrial and
Engineering Chemistry. 41:2,031-2,033, 1949.
2. Arntson, R. H., F. W. Dickson, and G. Tunell. Systems S-NapO-I^O and
S-H20; application to the mode of origin of natural alkaline poly-
sulfide and thiosulfate solutions. American Journal of Science.
258:547-582, 1960.
3. Feher, F. and G. Winkhaus. Chemistry of sulfur. XXXI. The preparation of
the sul fanes 1^5, H2Sg, HoSy, and ^Sg. Zeitsch
Chemie and Allgemeine Chemie. 288:123-130, 1956.
4. Feher, F., W. Laue, and G. Winkhaus. Chemistry of sulfur. XXX. Preparation
of the sulfanes, ^Sg, ^3, ^$4 and HpSg. Zeit
Chemie und Allgemeine Chemie. 288:113^22, 1956.
5. Schmidt, M. Acids of sulfur. II. A new class of sulfur acids. Zeitschrift
fuer Anorganische und Allgemeine Chemie. 289:158-174, 1957.
6. Tinyakova, E. I., B. A. Dolgoplosk, and M. P. Tikhomolova. Reactions of
free radicals in solutions. III. Reactions of free radicals with sulfur.
Zhurnal Obshchei Khimii. 25:1,387-1,394, 1955.
7. Schoberl, A., and A. Wagner. Methoden der organichen Chemie. v. 9.
(Ed. Houben-Weyl) Thieme, Stuttgart, 1955. p. 88-92.
8. Barbieri, R., and M. Bruno. The mechanism of the reaction H^S + S02 and
the formation of higher polythionic acids. Recerca Scientifica.
30:211-221, I960.
9. McKaveney, J. P., W. P. Fassinger, and D. A. Stivers. Removal of heavy
metals from water and brine using silicon alloys. Environmental
Science and Technology. 6(13):1,109-1,113, Dec. 1972.
10. Reuter, R., and F. L. Gaus. Production of mercaptans. Patent No.
2,101,096. Dec. 1937.
11. Williams, E. C., and C. C. Allen. Production of valuable products from
unsaturated compounds and hydrogen sulfide. Patent No. 2,052,268.
Aug. 1936.
12. Jones, S. 0., and E. E. Reid. Addition of sulfur, hydrogen sulfide,
mercaptans to unsaturated hydrocarbons. Journal of the American
Chemical Society. 60:2,452, 1938.
13. Wertheim, E. Derivatives for the identification of mercaptans.
Journal of the American Chemical Society. 51:3,661, 1929.
-------
A NEW PROCESS FOR
THE ECONOMIC UTILIZATION OF THE SOLID WASTE EFFLUENT
FROM LIMESTONE SLURRY WET SCRUBBER SYSTEMS
1. Problem Background
Over 60 billion Ib of sulfur oxides are emitted yearly into the
atmosphere in the United States and of this total, 60 percent of the
oxides of sulfur come from coal fired power plants. At the present time
limestone slurry wet scrubbing systems for removing sulfur oxides from
power plant stack gases have advanced to major pilot plant and full scale
demonstration stages. Although these systems are promising for controlling
the power plant sulfur oxide air pollution problem they, in turn, also have
the potential of creating a major solid waste pollution problem. Namely,
for a typical 1,000 MW wet scrubbed power plant, some 1,300 tons/day of
calcium sulfate-calcium sulfite-fly ash solid waste are produced.
A second problem, seemingly unrelated to sulfur oxide pollution,
Involves the current dependence of the U.S. alumina (A1203) and aluminum
industries on the importation of foreign ores. Over 85 percent of the
ores (e.g., bauxite) used in the U.S. production of alumina (and ultimately
aluminum) are currently imported and hence are subject to the political
influences of foreign countries. Extraction of alumina from abundant low
grade domestic ores such as clay (A^O^Si^^HgO) have been extensively
evaluated at the bench-scale and pilot plant level. However, at the pres-
ent time these processes (such as the Bureau of Mines lime-soda sinter
process) fall just short of being economically competitive with the Bayer
processing of imported bauxite.
2. Recommended Problem Solution
TRW has recently conceived a processing scheme which addresses itself
to the solution of both the above described problems. Namely, the calcium
105
-------
(or magnesium) containing waste from the sulfur oxide wet scrubbing system
can be economically utilized in the extraction of alumina from low grade
domestic ores (clay). The process also produces cement (calcium silicates)
and sulfur. This processing scheme results in the total utilization of
the wet scrubber solid waste effluent, further, the sale of the products is
expected to pay the processing costs.
A simplified process flow diagram and rough material balance (Figure 1)
have been prepared for a system designed to operate on the solid effluent
from a wet scrubbed, 1,000 MW, coal burning power plant which produces
300 tons per day of sulfur as either calcium sulfate or calcium sulfite.
Thirteen hundred tons per day of CaSO, or equivalent together with 640 tons
per day of clay (As203'2Si02'2H20), 25 tons per day of makeup sodium car-
bonate and 225 tons per day of recycle sodium carbonate are fed to a rotary
kiln where the reactants are heated in a reducing combustion environment
at 1,000 to 1,250 C. The sulfur present in the feed is converted to H2S
which is fed together with the combustion gases to a Glaus type of sulfur
recovery unit or possibly a TRW S-100 sulfur recovery unit. Primary re-
actions in the kiln result in the formation of soluble sodium aluminate
(Na20-Al203) and insoluble dicalcium silicate (Si02'2CaO) thus providing
the means for separating the alumina from the silica portion of the clay.
The sintered product from the kiln is leached with a dilute solution
of sodium carbonate which dissolves the sodium aluminate and leaves the
dicalcium silicate as an insoluble residue. The dicalcium silicate is
filtered and used as a primary raw material in the manufacture of cement.
Carbon dioxide is bubbled through the sodium aluminate solution resulting
in the precipitation of aluminum hydroxide and the regeneration of the
sodium carbonate. The aluminum hydroxide is filtered and calcined to the
final alumina product. The sodium carbonate is recycled to the kiln.
Based on current raw material and product prices and assuming that
calcium sulfate is free to the process; $3,210.00/day of raw materials
result in $14,020.00/day of saleable products.* Therefore, rather
*Taking no credit for sulfur and only $l/ton for dicalcium silicate.
106
-------
substantial operating and capital costs can be tolerated and still result
in a net positive cash flow for the process.
3. Recommendations
The basic chemistry depicted (Figure 1) is well established. However
the applicability of the chemistry to the new processing scheme (Figure 1)
and to actual scrubber effluent material has not yet been demonstrated.
It is therefore recommended that a Phase I program of bench-scale labor-
atory investigation and preliminary engineering design be initiated in
order to determine the technical and economic potential of this recommended
process. The initial program phase would be aimed at:
(1) determining probable ranges of operating conditions for
each of the major processing steps (reduction, calcination,
leaching, separation);
(2) determining (with actual scrubber effluent) probable yields
and purity of products;
(3) developing a preliminary process design including material
and energy balances;
(4) estimating capital and operating costs and determining
the economic viability of the process.
It is estimated that the Phase I feasibility study described above can
be completed within 12 months at a cost of about $150K.
107
-------
8
00
BASIS: o 1000 MW WET SCRUBBED COAL BURNING POWER PLANT
o 3%S IN THE COAL
o ~ 300 TONS/DAY REMOVED FROM STACK
o 1300 TONS/DAY CaSO4 OR EQUIVALENT FORMED
o 90% YIELD OF ALUMINA
o 10% LOSS OF SODIUM CARBONATE
320 T/DAY H2S
FROM POWER PLANT FED TO SULFUR
WET SCRUBBER RESIDUE RECOVERY UNIT
r^n .._ „„ „
OR EQUIVALENT REDUCTION AND CALCINATION
4CaS04*No2«VA,203.2S!02.2H20
^•"4 + "'" " ' ~°" + REDUCING COMBUS1 ION GAStb NujO Alj O3
CLAY, AI203 -25102-2^0 •* "°2° ' AI2°3 + 2 S!°2 ' (2CaO) 390 T/DAY
615T/DAY * +4H2S + (,OMBUSIIONGASbS SiOj • 2 CaO
Na co . fc inno-i9yir n.-jioinHB R?OT/bAY &
u?«,5 RESIDENCE TIME
25 T/DAY
SODIUM CARBONATE, Na2 CO.
CLAUS PLANT
OR OTHER
RECOVERY
PROCESS
-A
SULFUR
PRODUCT
300 T/DAY
LEACHING AND SEPARATION
o SEPARATE No2O • AI2C
SiOj • 2 CaO BY LEAC
ALUMINATE WITH Ntaj
SOLUTION— FILTER AN
THE RESIDUAL SiO2 • 2
o PRECIPFTATE ALUMINU
FROM THE LEACH BY C
WITH CO2, FILTER AN
o CALCINE THE ALUMIN
TO ALUMINA
o RECYCLE SODIUM CAM
RECYCLE 225T/DAY
RAW MATERIAL AND PRODUCT SUMMARY
RAW MATERIALS COST/DAY PRODUCTS
>3 FROM
HINGTHE
D DRY
CoO
W HYDROXIDE
ARBONATION
DDRY
JM HYDROXIDE
JONATE
A'
ALUMINA
PRODUCT
220 T/DAY .
-A
L\
DICALCIUM
SILICATE
PRODUCT
820 T/DAY
CEMENT PLANT
VALUE/DAY
RAW MATERIALS COST/DAY
1.
2.
3.
CaSO41300 T/DAY FREE TO PROCESS $ 0.00
CLAY, 615 T/DAY AT J4.00A $ 2460.00
SODIUM CARBONATE, 25 T/DAY J 750.00
AT t in OOA
PRODUQS
1.
2.
3.
ALUMINA, 220 T/DAY AT $ 60A
DiCALCIUM SILICATE, 820 T/DAY
AT JlAON
SULFUR 300 f/DAY, NO VALUE
VALUE/DAY
$
$
$
13,200.00
820.00
0.00
$3210.00
14,020.00
Figure 1. Recommended processing scheme.
-------
BIBLIOGRAPHIC DATA
SHEET
1. Report No.
EPA-670/2-73-053-0
3. Recipient's Accession No.
,. Title and Subtitle
Recommended Methods of Reduction, Neutralization, Recovery, or
Disposal of Hazardous Waste.
Volume XV, Research and Development Plans
5. Report Date
Issuing date - Aug. 1973
6.
7. Authors) R. S. Ottinger, J. L. Blumenthal, D. F. Dal Porto,
G. I. Gruber, M. J. Santy, and C. C. Shih
8- Performing Organization Rept.
N°'21485-6013-RU-OO
9. Performing Organization Name and Address
TRW Systems Group, One Space Park
Redondo Beach, California 90278
10. Project/Task/Work Unit No.
11. Contract/Grant No.
68-03-0089
12. Sponsoring Organization Name and Address
National Environmental Research Center
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
13. Type of Report & Period
Covered
Final
14.
15. Supplementary Notes
Volume XV of 16 volumes.
16. Abstracts
This volume presents more detailed information for some of the projects proposed and
summarized in Chapter 6 of Volume I. The projects described herein include cementation
processes, both inorganic and organic, sulfur sequestering, arsenic removal from soil,
recovery of alumina from clay and sulfur oxide scrubbing wastes, characterization of
incineration parameters for the safe disposal of pesticides, new chemical concepts for
utilization of waste pesticides, and isolation of mercury and other heavy metals from
dilute waste streams.
17. Key Words and Document Analysis. 17a. Descriptors
Research and Development
Sulfur Sequestering
Arsenic Removal
Recovery of Alumina
Pesticides
Mercury
Heavy Metals
17b. Idemifiers/Open-Ended Terms
I7c. COSATI Field/Group 06F; 06T; 07B; 07C;-Q7E; 13B; 13H; 19A; 19B
18. Availability Statement
Release to public.
- 109 -
19.. Security Class (This
Report)
UNr.l.ASSIFIF.O
20. Security Class (This
Page
'UNCLASSIFIED
21- No. of Pages
115
22. Price
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