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PORTLAND CEMENTASSOCIATION
Guide to Improving theEffectiveness of Cement-BasedStabilization/Solidification
Guide to Improving theEffectiveness of Cement-BasedStabilization/Solidification
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EB211
PCA Serial No. 2075
Guide to Improving the Effectiveness ofCement-BasedStabilization/Solidification
This engineering bulletin was authored by: Jesse R. ConnerConner Technologies214 Field Club Rd.Pittsburgh, PA 15238USA(412) 963-6358
Edited by:Charles M. Wilk, Program Manager, Waste Management,andNatalie C. Holz, Editorial/Administrative AssistantPublic Works Department,Portland Cement Association
Published by:Portland Cement Association5420 Old Orchard Rd.Skokie, IL 60077-1083USA(847) 966-6200
© 1997 Portland Cement AssociationAll rights reserved. No part of this publication may bereproduced in any form without permission in writingfrom the publisher, except by a reviewer who wishes toquote brief passages in a review written for inclusion ina magazine or newspaper.
Printed in the United States of America
This publication is intended SOLELY for use by PROFESSIONALPERSONNEL who are competent to evaluate the significance andlimitations of the information provided herein, and who will accepttotal responsibility for the application of this information. ThePortland Cement Association DISCLAIMS any and allRESPONSIBILITY and LIABILITY for the accuracy of and theapplication of the information contained in this publication to thefull extent permitted by law.
Caution: Contact with wet (unhardened) concrete, mortar,cement, or cement mixtures can cause SKIN IRRITATION,SEVERE CHEMICAL BURNS, or SERIOUS EYE DAMAGE.Wear waterproof gloves, a long-sleeved shirt, full-length trou-sers, and proper eye protection when working with thesematerials. If you have to stand in wet concrete, use waterproofboots that are high enough to keep concrete from flowing intothem. Wash wet concrete, mortar, cement, or cement mixturesfrom your skin immediately. Flush eyes with clean waterimmediately after contact. Indirect contact through clothingcan be as serious as direct contact, so promptly rinse out wetconcrete, mortar, cement, or cement mixtures from clothing.Seek immediate medical attention if you have persistent orsevere discomfort.
Cover photo courtesy of Geo-Con, Inc.
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PCA EB211
Guide to Improving theEffectiveness of Cement-Based
Stabilization/Solidificationby Jesse R. Conner
© Portland Cement Association 1997ISBN 0-89312-176-2
51
PCA EB211
Contents
I. INTRODUCTION ................................................................................................................. 1
II. PROBLEMS IN SOLIDIFICATION AND PHYSICAL PROPERTYDEVELOPMENT ................................................................................................................. 3
Setting Problems ............................................................................................................................. 3Compressive Strength Development Problems ......................................................................... 6Permeability Development Problems ......................................................................................... 7Durability Problems ....................................................................................................................... 7
III. PROBLEMS IN TARGET CONSTITUENT STABILIZATION- CHEMICAL PROPERTIES ...............................................................................................7
Metals ............................................................................................................................................... 8Organics ......................................................................................................................................... 12Organo-Metallics .......................................................................................................................... 14Soluble Salts .................................................................................................................................. 14
IV. ADDITIVES USED IN CEMENT-BASED STABILIZATION/SOLIDIFICATION ...............................................................................................................15
Metal Stabilization ....................................................................................................................... 15Immobilization of Organic Constituents .................................................................................. 20Processing and Anti-Inhibition Aids ......................................................................................... 21
V. PHYSICAL/CHEMICAL TECHNIQUES USED IN CEMENT-BASEDSTABILIZATION/SOLIDIFICATION ................................................................................ 22
Anti-Inhibition Aids..................................................................................................................... 22Physical Property Development ................................................................................................ 22Processing Aids ............................................................................................................................ 22Mixing Techniques ....................................................................................................................... 23
VI. REFERENCES ...................................................................................................................24
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PCA EB211
Guide to Improving theEffectiveness of Cement-Based
Stabilization/Solidificationby Jesse R. Conner
counter problems in solidification caused by the wasteitself. The purpose of this Guide is to explain theseadditives and techniques, the problems encounteredin S/S that may require their use, and how they areapplied in treatment operations. The Guide is in-tended to be a practical tool. It is not a discussion ofmechanisms and theory.
There are a number of standard types of portlandcement, categorized as ASTM Types I through V, withsub-types within some of these. While there has beensome investigation of the efficacy of using differentcement types in S/S, experience to date indicates thatthis is not a common practice, and there is often littledifference between the types for S/S work. Generally,Type I is used because it is readily available every-where and is often the least expensive. However, incertain geographical areas, Type II or other types maybe more available and/or cheaper, and therefore morepractical.
The American Society for Testing and Materials(ASTM) Designation C 150, Standard Specification forPortland Cement, provides for eight types of portlandcement as follows:
Type I normalType IA normal, air-entrainingType II moderate sulfate resistanceType IIA moderate sulfate resistance, air-
entrainingType III high early strengthType IIIA high early strength, air-entrainingType IV low heat of hydrationType V high sulfate resistance
© Portland Cement Association 1997
I. INTRODUCTION
Stabilization/solidification (S/S) is a very effectivetool in the treatment of various wastes, hazardous andnon-hazardous. These wastes are commonly gener-ated in ongoing commercial and industrial opera-tions, and are also encountered in remedial activitiesat old dump sites and other contaminated media.They are usually concentrated residuals from air orwater pollution control processes, direct processstreams, or contaminated media such as soil. Gener-ally, wastes selected for S/S have already been con-centrated to the maximum extent that is economicallyfeasible, and S/S technology is used to prepare thewaste for final land disposal. Such preparation re-quires transforming the waste into a physically ac-ceptable, mechanically stable form, and convertingtoxic constituents into minimally mobile species.
The United States Environmental ProtectionAgency (EPA) considers S/S an established treatmenttechnology (USEPA, 1995). For remediation (cleanup)sites, 29 percent of source control Records of Decision(RODs) signed from 1982 through 1994 in EPA'sSuperfund program include S/S as part of the selectedremedy (USEPA, 1995). This makes S/S the mostfrequently selected technology for treating the sourceof contamination. In the treatment of industrial haz-ardous wastes, the EPA has identified S/S as BestDemonstrated Available Technology (BDAT) for 57Resource Conservation & Recovery Act (RCRA) listedwastes (USEPA, 1993).
Portland cement* alone accomplishes these objec-tives to a high degree in many instances, but somesituations (because of the waste itself, the disposalscenario, and/or the regulatory requirements) requirethe use of additives or physical/chemical techniquesto provide improved properties in the waste form or to
ISBN 0-89312-176-2
* In this Guide, the term “cement” will refer to Type I PortlandCement, unless otherwise stated.
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Guide to Improving the Effectiveness of Cement-Based Stabilization/Solidification
The use of cement in S/S has different require-ments than its common use in concrete and mortars —for example:
• S/S has much lower strength requirements thanconcrete - normally less than 100 psi vs thou-sands of psi;
• Fast set and high early strength are usually notrequired, and may not be desirable, in S/S;
• Long term physical durability - resistance to freeze/thaw and wet/dry cycling, and immersion in water- are not normally important, although they maybe required in some specifications;
• Physical properties, in general, usually are lessimportant in S/S work than are the system'sability to immobilize hazardous constituents inthe waste;
• Concrete chemistry is complex. The chemistryof waste-cement systems is even more so, due tothe very complex nature of most wastes.Many additives have been tried out in cement-
based S/S processes. A listing of the most important,most commonly encountered additive types is givenin Table 1 (pp 28-32). Many of these have been usedcommercially or at pilot scale; some have only beentested in the laboratory. There are also a number ofproprietary additives and formulations available com-mercially, but these are generally based on the genericcategories listed here. For this reason, and because thecomposition of the proprietary products is usually notgiven, these products are not discussed as such unlessno generic equivalent is available. In addition toadditives, various physical/chemical techniques arealso used for similar purposes. Table 2 lists thesetechniques.
The problems encountered in S/S can be broadlyclassified into solidification problems, i.e., obtainingthe required physical properties in the resultant wasteform; and stabilization problems, i.e., adequately im-mobilizing the waste constituents. To more effec-tively discuss the subject, this Guide is organized inthe following manner:1. Problems in Solidification and Physical Prop-
erty Development:Setting ProblemsCompressive Strength Development ProblemsPermeability Development ProblemsDurability ProblemsThe challenges described here are those of devel-
opment of physical properties in the solidified wasteform, and the term solidification is used to describe theprocess. Table 3 (pp 33-37) lists the additives andtechniques that are most important in solidification,or have been proven for this use in actual applications.Other possible solutions to these problems are dis-cussed and referenced in the text.2. Problems in Target Constituent Stabilization -
Chemical Properties:MetalsOrganicsOrgano-MetallicsSoluble SaltsThe challenges described here are those of devel-
opment of chemical properties, i.e., immobilization ofcertain species, in the stabilized waste form, and theterm stabilization is used to describe the process. Tables7 and 9 (pp 38-39, 43-44) list the more importantadditives and techniques used in stabilization, or thosethat have been proven for this use in actual applica-tions. Other possible solutions to these problems are
TECHNIQUE EFFECT RELATIVECOST
Aeration: Alteration of biological status; removal ofinterfering volatiles
Low
Temperature Control: Acceleration of reaction rate to counter retardingeffect; improvement of leaching characteristics
Low
Viscosity/PumpabilityAlteration:
Important for some applications where pumping oftreated waste before curing is necessary
Low to Moderate
Humidity Control: Prevention of excessive drying during curing LowDewatering: Removal of excess free water Low to ModerateAir Entrainment: Addition of air into the structure to provide better
freeze/thaw durabilityLow
Mixing Type and Degree:Ex-Situ Prevent over-mixing, assure adequate mixing LowIn-Situ Necessary for proper slurry-grout formulation Low to Moderate
Table 2. Physical/Chemical Techniques Used in Cement-based S/S
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discussed and referenced in the text.3. Additives Used in Cement-based Stabilization/
Solidification:Metal StabilizationImmobilization of Organic ConstituentsProcessing and Anti-Inhibition AidsAdditives of commercial importance are dis-
cussed individually, or by chemical type, in moredetail.4. Physical/Chemical Techniques Used in
Cement-based Stabilization/Solidification:Anti-Inhibition AidsPhysical Property DevelopmentProcessing AidsMixing TechniquesVarious physical/chemical techniques other than
the use of additives are discussed in more detail.A great deal of attention has been paid to “interfer-
ence mechanisms” in cement-based systems. Consider-able experimental work was done for the EPA at the U.S.Army Corps of Engineers Waterways Experiment Sta-tion (WES) on the causes, effects, and cures for thisproblem (United States Environmental ProtectionAgency, 1982; U.S. Army Corps of Engineers Water-ways Experiment Station, 1990; Battelle Columbus,1993). Conner (1990) describes the various additivesused in S/S and summarizes the chemical factors thataffect solidification. Other individual investigators andsummaries (Coté, 1986; Eaton et al., 1987; El-Korchi etal., 1990; Spence, 1992) have contributed to the knowl-edge base on this subject, and the reader is referred tothese sources for further detailed information.
II. PROBLEMS IN SOLIDIFICATIONAND PHYSICAL PROPERTYDEVELOPMENT
There are many factors which retard, inhibit andaccelerate the setting and curing of S/S systems.Some also affect the final strength, permeability andother physical properties of the fully cured S/S prod-uct. Others affect chemical properties, which will bediscussed in Section III, Problems in Target Constitu-ent Stabilization - Chemical Properties. Many of thecompounds, materials and factors which are known tohave such solidification effects were described byConner (1990), Battelle Columbus (1993), U.S. ArmyEngineer Waterways Experiment Station (1990), U.S.Army Engineer Waterways Experiment Station (1990),and Eaton et al. (1987); some are general knowledge inthe field of cement technology (Portland Cement As-sociation, 1979).
The effects are many and varied, but in spite of ourknowledge about them, these effects are not simple to
predict and sort out from knowledge of the composi-tion of the waste, even when that infomation is avail-able. Most often, a number of species are present in thewaste, sometimes with opposing effects. The samespecies may have opposite effects depending on con-centration. This latter phenomenon has been foundwith calcium chloride, calcium sulfates, sodium hy-droxide, sodium silicate, lead, copper and tin salts,amines and hexachlorobenzene. For example, ionexchange can inhibit or retard S/S reactions by remov-ing calcium from solution, preventing it from enteringinto the necessary cementitious reactions (Conner,1990). It can also accelerate the process by removinginterfering metal ions from solution. Which occursmay depend on the selectivity of the ion exchangematerial. Other examples are metals that may retardand inhibit the reactions by substituting for calcium inthe cementitious matrix, which may explain the effectof magnesium in dolomitic lime and lime products.Certain substances are natural or synthetic complexingagents which remove calcium from availability in thesetting and curing reactions. On the other hand,alcohols, amides and specific surfactants can aid inwetting solids and dispersing fine particulates and oilwhich interfere with reactions by coating the reactingsurfaces. Flocculants can also serve this purpose.Some of these materials and techniques are discussedin sections IV and V.
Specific problems and solutions which have beenused are discussed below. They are also summarizedand tabulated in Table 3.
Setting Problems
Will not set. Waste form remains non-solid even aftercuring for up to 28 days.Cause:
Fine particulates coating cement particles, pre-venting or slowing reaction: silt (Kitsugi, 1976)(Kitsuge and Kozeki, 1976), clay (Kitsugi, 1976)(Kitsuge and Kozeki, 1976), colloidal matter(Kitsugi, 1976) (Kitsuge and Kozeki, 1976)
Possible Solution:Use surface active agents: wetting agents(amides, alcohols), dispersants (carboxylic ac-ids, carbonyls, sulfonates), flocculants (amines,iron salts, magnesium salts, silica) to removeand coagulate fine particulates
Cause:Anaerobic conditions
Possible Solution:1. Aerate2. Add oxidizer3. Add lime, soluble silicate (Conner, 1990)
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Guide to Improving the Effectiveness of Cement-Based Stabilization/Solidification
(Conner, 1974) (USEPA, 1982)4. Add biocide — commercial products are
availableCause:
Calcium removers in the waste: phosphatesPossible Solution:
Replace lost calcium
Sets, but does not harden. Waste form undergoes aninitial set, but does not harden further even aftercuring for up to 28 days.Cause:
Fine particulates coating cement particles, pre-venting or slowing reaction: silt (Kitsugi, 1976)(Kitsuge and Kozeki, 1976), clay (Kitsugi, 1976)(Kitsuge and Kozeki, 1976), colloidal matter(Kitsugi, 1976) (Kitsuge and Kozeki, 1976)
Possible Solution:Use surface active agents: wetting agents(amides, alcohols), dispersants (carboxylic ac-ids, carbonyls, sulfonates), flocculants (amines,iron salts, magnesium salts, silica) to removeand coagulate fine particulates
Cause:Anaerobic conditions
Possible Solution:1. Aerate2. Add oxidizer3. Add lime, soluble silicate (Conner, 1990)
(Conner, 1974) (USEPA, 1982)4. Add biocide — commercial products are
availableCause:
Calcium removers in the waste: phosphates,glucose
Possible Solution:Replace lost calcium
Set is retarded. Waste form set and hardening areretarded, but both take place more or less normallyafter curing for up to 28 days. Set retardation may lastfor a week or more.Cause:
Fine particulates coating cement particles, pre-venting or slowing reaction: silt (Kitsugi, 1976)(Kitsuge and Kozeki, 1976), clay (Kitsugi, 1976)(Kitsuge and Kozeki, 1976), colloidal matter(Kitsugi, 1976) (Kitsuge and Kozeki, 1976)
Possible Solution:Use surface active agents: wetting agents(amides, alcohols), dispersants (carboxylic ac-ids, carbonyls, sulfonates), flocculants (amines,iron salts, magnesium salts, silica) to removeand coagulate fine particulates
Cause:Presence of sugar, sugar derivatives (PortlandCement Association, 1979) (Kitsugi, 1976)(Kitsuge and Kozeki, 1976)
Possible Solution:1. Add more sugar - 0.2%; an optimum level of
sugar may be difficult to achieve. (PortlandCement Association, 1979)
2. Add a sorbent: clay, flyash, diatomaceousearth, carbon
3. Chemical oxidation with potassium perman-ganate, sodium persulfate, calcium orsodium hypochlorite
Cause:Presence of phosphates (Kitsugi, 1976) (Kitsugeand Kozeki, 1976)
Possible Solution:Add calcium ion in excess (cement kiln dust,hydrated lime)
Cause:Presence of sulfur (Battelle Columbus, 1993)
Possible Solution:None established
Cause:Presence of bicarbonates of sodium and potas-sium (Portland Cement Association, 1979)
Possible Solution:Pretreat with acidic material to decompose bi-carbonate
Cause:Presence of other chemical interference -inorganics, general (U.S. Army Engineer Water-ways Experiment Station, 1990) (Battelle Co-lumbus, 1993) (Cullinane et al., 1986) (Cullinaneet al., 1987); presence of certain inorganic salts(Cullinane et al., 1986) (Cullinane et al., 1987):salts of magnesium (Battelle Columbus, 1993),tin (Battelle Columbus, 1993), zinc (Battelle Co-lumbus, 1993) (ASTM, 1985) (Cullinane et al.,1987), arsenic (El-Korchi, 1990), chromium (El-Korchi, 1990), cadmium (El-Korchi, 1990), cop-per (Battelle Columbus, 1993) (Cullinane et al.,1987) and lead (Battelle Columbus, 1993) (El-Korchi, 1990) (Cullinane et al., 1987), sodiumiodate (Battelle Columbus, 1993), sodium phos-phate (Battelle Columbus, 1993), sodium arsen-ate (Battelle Columbus, 1993), sodium borate(Battelle Columbus, 1993), sodium sulfide(Battelle Columbus, 1993), sodium hydroxide(Cullinane et al., 1987), sodium sulfite (Cullinaneet al., 1987)
Possible Solution:Add sulfates (Kitsugi, 1976) (Harada et al., 1977),
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PCA EB211
soluble silicates (Conner, 1990) (Conner, 1974)(USEPA, 1982), aluminates (Kitsuge and Kozeki,1976) (Harada et al., 1977), phosphates (Carlson,1987), hydroxylated organic acids (Bonnel andHevanee, 1972), glycols (U.S. Patent 3,642,503)(Harada et al., 1977), amines (Harada et al.,1977), iron compounds (for sulfides, tin lead,arsenates) (Conner, 1990) (Electric Power Re-search Institute, 1996), ASTM set accelerators(U.S. Army Engineer Waterways ExperimentStation, 1990), other organics.
Cause:Presence of other chemical interference - chelat-ing agents (Battelle Columbus, 1993) (U.S. ArmyEngineer Waterways Experiment Station, 1990):ethylenediaminetetracetic acid (EDTA),nitrilotriacetic acid (NTA), lignins, tannins, glu-cose, starch
Possible Solution:See possible solutions above under inorganics
Cause:Presence of other chemical interference - organ-ics, general: oil, grease, tars, resins, carbohy-drates, phenol, trichloroethylene,hexachlorobenzene, coal, lignite, general organ-ics (Cullinane et al., 1987) (El-Korchi, 1990)(Eaton, 1987) (Cullinane et al., 1986) (BattelleColumbus, 1993) (U.S. Army Engineer Water-ways Experiment Station, 1990)
Possible Solution:1. Add sorbent (cement kiln dust, clays, lime,
limestone, flyash, carbon)2. Evaporate VOCs3. Chemical oxidation with hydrogen
peroxide, potassium permanganate, sodiumpersulfate, calcium or sodium hypochlorite
4. See also possible solutions above underinorganics
Cause:Mild anaerobic conditions
Possible Solution:1. Aerate2. Add oxidizer3. Add lime, soluble silicate (Conner, 1990)
(Conner, 1974) (USEPA, 1982)4. Add biocide — commercial products are
availableCause:
Insufficient cure time
Possible Solution:Cure longer
Cause:General retardation of set
Possible Solution:Add calcium chloride (<2%) (Blake, 1975), so-dium silicate (Conner, 1990) (Conner, 1974), lime(Conner, 1990)
Supernatent liquid on surface, or softer surface layer,after setting. Large differences in specific gravitybetween the waste and the reagent result in a tendencytoward phase separation. Most reagents used in S/Shave particle specific gravities much larger than thewaste density as a whole: >2.0 versus 1.0 to 1.5 in mostsystems. Although reagent particle size is generallysmall, it is not usually sufficient to make up for thisdifference, and some settling will occur unless viscos-ity is sufficient to prevent phase separation until theinitial setting reaction can physically immobilize allcomponents in place. Alternatively, sufficient reagentcan be added to quickly take up all the free water, or aviscosity-increasing agent can be added. Rheologicalagents which accomplish the latter technique are avail-able, but add significantly to the cost of the process andsometimes can interfere with the reactions which mustsubsequently take place for proper curing. Gellantssuch as soluble silicates do this by causing an almostimmediate thickening or gelling reaction between freecalcium ion from the cement and the silicate, creatingan elastic silica gel which does not interfere withcement or pozzolanic reactions.Cause:
Set is too slowPossible Solution:
Add set accelerator: calcium chloride (<2%)(Blake, 1975) (U.S. Army Engineer WaterwaysExperiment Station, 1990); sulfates, soluble sili-cates (Conner, 1990) (Conner, 1974), aluminates(Kitsuge and Kozeki, 1976) (Harada et al., 1977),hydroxylated organic acids (Bonnel andHevanee, 1972), or glycols (U.S. Patent 3,642,503)(Harada et al., 1977); amines (Harada et al.,1977); other organics
Cause:Water content is too high
Possible Solution:1. Dewater. Decant water; filter raw waste2. Add sorbent3. Add bulking agent4. Add low-cost, reactive bulking agent:
cement kiln dust, flyash, blast furnace slag(Chudo et al., 1981)
Cause:Viscosity of system is too low
Possible Solution:Increase viscosity of system, using gelling agentor sorbent: soluble silicates, flyash, clay (dried or
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Guide to Improving the Effectiveness of Cement-Based Stabilization/Solidification
expanded), organic sorbents (wood chips, corncob, etc.)
Sets too rapidly for satisfactory processing. Somewastes contain, or act as, cement setting accelerators,causing the set to be so rapid that the cement cannot beuniformly mixed into the waste in the desired treat-ment scheme, or the waste cannot be handled asrequired after mixing. The former problem is espe-cially important in ex-situ batch mixing, and in somein-situ processes.Cause:
Presence of accelerating agents: sulfates; solublesilicates, aluminates, phosphates; hydroxylatedorganic acids, glycols, other organics; ion ex-change material
Possible Solution:1. Use a proprietary, concrete set retarder2. Add zinc, copper or lead oxide/hydroxide;
calcium chloride (>4%); magnesium andtin salts; phosphates, chlorides, sugars(Metcalf and Ellers, 1980), clays
3. Lignosulfonic acid salts and derivatives,hydroxylated carboxylic acids, polyhydroxycompounds (ASTM C494, Types A and B)(U.S. Army Engineer Waterways Experi-ment Station, 1990)
Cause:Presence of carbonates and bicarbonates of so-dium and potassium (Portland Cement Associa-tion, 1979)
Possible Solution:Decompose or neutralize with acid or acidicadditive
Cause:Presence of sugar at high level (0.2% or more)(Portland Cement Association, 1979)
Possible Solution:1. Add a retarder (see above)2. Chemical oxidation with hydrogen
peroxide, potassium permanganate, sodiumpersulfate, calcium or sodium hypochlorite
Compressive Strength DevelopmentProblems
Insufficient unconfined compressive strength. Thefinal waste form has insufficient unconfined compres-sive strength (ASTM D-2166, D-1633) for the intendeddisposal scenario, even after full curing.Cause:
Insufficient cement to develop desired strength
Possible Solution:Use more cement
Cause:Presence of salts of manganese, tin, zinc(Cullinane et al., 1987), copper (Cullinane et al.,1987) and lead (Portland Cement Association,1979) (Cullinane et al., 1987)
Possible Solution:Add sulfates (Kitsugi, 1976) (Harada et al., 1977),soluble silicates (Conner, 1990) (Conner, 1974),aluminates (Kitsuge and Kozeki, 1976) (Harada etal., 1977), phosphates (Carlson, 1987), hydroxy-lated organic acids (Bonnel and Hevanee, 1972),glycols (U.S. Patent 3,642,503) (Harada et al., 1977),amines (Harada et al., 1977), other organics.
Cause:Presence of sodium sulfide (Portland CementAssociation, 1979), sodium sulfite (Cullinane etal., 1987) and sodium hydroxide (high concen-trations) (Cullinane et al., 1987)
Possible Solution:1. Chemical oxidation with hydrogen
peroxide, potassium permanganate, sodiumpersulfate, calcium or sodium hypochlorite
2. Neutralization (sodium hydroxide)3. Add iron salts: ferrous sulfate to immobilize
sulfide ionCause:
Presence of sugar (Portland Cement Associa-tion, 1979)
Possible Solution:Chemical oxidation with hydrogenperoxide, potassium permanganate, sodiumpersulfate, calcium or sodium hypochlorite
Cause:Presence of algae (Portland Cement Associa-tion, 1979)
Possible Solution:1. Add sorbent (clays, limestone, flyash,
carbon)2. Chemical oxidation with hydrogen
peroxide, potassium permanganate, sodiumpersulfate, calcium or sodium hypochlorite
3. Add lime4. Add a biocide — commercial products are
availableCause:
Anaerobic conditionsPossible Solution:
1. Aerate2. Add oxidizer3. Add lime, soluble silicate (Conner, 1990)
(Conner, 1974) (USEPA, 1982)4. Add biocide — commercial products are
available
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Cause:Presence of oils (Portland Cement Association,1979) and grease (Cullinane et al., 1987)
Possible Solution:1. Add sorbent: bentonite (Gilliam and Wiles,
1996, p. 584), limestone, flyash (Gilliam andWiles, 1996, p. 584), carbon
2. Evaporate VOCs3. Chemical oxidation with hydrogen
peroxide, potassium permanganate, sodiumpersulfate, calcium or sodium hypochlorite
4. Add quicklime (CaO)5. Add phosphorus pentoxide and a stearate
(Takashita, 1979)Cause:
Water content is too highPossible Solution:
Dewater, use a water reducing agent (ASTM C-494 Types A, D, F and G) if applicable (U.S. ArmyEngineer Waterways Experiment Station, 1990)
Permeability Development Problems
High Permeability. Permeability of the final wasteform is too high (SW846, Method 9100).Cause:
Incomplete curing of waste formPossible Solution:
Cure for at least 28 days before testingCause:
Insufficient cement to develop the require ma-trix
Possible Solution:Use more cement
Cause:Waste has natural high permeability
Possible Solution:1. Add bentonite clay (Conner, 1990)2. Add hydrophobizing agent (Conner, 1986)3. Add a stearate (Portland Cement Associa-
tion, 1974)(Takashita, 1979)4. Add a pore filling and/or hydrophobic
organic polymer compatible with cement5. Develop better microstructure with flyash
((Gilliam and Wiles, 1996, p. 251), slag(Gilliam and Wiles, 1996, p. 251), silica fume(Gilliam and Wiles, 1996, p. 135)
Durability Problems
Poor durability, stability, or strength. Final wasteform has poor freeze-thaw or wet-dry durability
(ASTM D-4842-90, D-4843-88), poor immersion stabil-ity (10 CFR 61, Regulatory Guide, May 1983), or poorstrength (see Compressive Strength DevelopmentProblems Sections above).Cause:
Insufficient cementPossible Solution:
Add more cementCause:
Poor microstructurePossible Solution:
1. Add flyash ((Gilliam and Wiles, 1996,p. 251), slag (Gilliam and Wiles, 1996,p. 251), silica fume (Gilliam and Wiles, 1996,p. 135), etc. to improve microstructure
2. Air entrainment (U.S. Army EngineerWaterways Experiment Station, 1990)
Cause:Excessive porosity, due to non-optimum watercontent
Possible Solution:1. Modify water content by addition or
removal2. Add bulking agent or water absorber3. Add a pore filling and/or hydrophobic
organic polymer compatible with cement4. Add wood resins, proteinaceous materials,
synthetic detergents (ASTM C-260) (U.S.Army Engineer Waterways ExperimentStation, 1990)
Cause:Presence of large amounts of soluble salts: sul-fates, nitrates, chlorides
Possible Solution:For treatment of waste in saline or brackishenvironments, as near a coast, some projectshave specified Type II or Type V sulfate resistantcements
III. PROBLEMS IN TARGETCONSTITUENT STABILIZATION -CHEMICAL PROPERTIES
In contrast to solidification, there is only one basicproblem in stabilization — the degree of immobiliza-tion of the target constituents of concern: metals,organics, organo-metallics, and salts. In most cases,these are entities that are hazardous to human healthand the environment. The solutions to the problem,however, depend on the particular inorganic or or-ganic compound of interest. Therefore, discussion ofadditive use in stabilization is organized along thelines of particular chemical species.
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Guide to Improving the Effectiveness of Cement-Based Stabilization/Solidification
Metals
The stabilization of metals in hazardous wastes hasbeen done at remedial operations and at fixed treat-ment sites in the U.S. for more than 20 years. Manyprivate companies have been running stabilizationoperations for metals at RCRA Treatment, Storageand Disposal Facilities (TSDFs) for decades, treatingliterally thousands of different waste streams. Gov-ernment and private research and testing laboratorieshave done tens of thousands of treatability studies todevelop formulations for all RCRA metals, as well asfor the more recent constituents of concern: copper,nickel, zinc, antimony, beryllium, and vanadium.
Table 4 is a list of metals which are regulated byfederal or state agencies in the United States. These arethe metals of primary concern in stabilization technol-ogy, and are commonly referred to as the “toxic met-als” or “RCRA metals.” Those marked with an aster-isk are the Toxicity Characteristic (TC) metals forwhich EPA established required treatment levels us-ing the Toxicity Characteristic Leaching Procedure(TCLP) (USEPA, 1990). The other metals have beencontrolled under the Land Disposal Restrictions (LDRs)(USEPA, 1985), the Universal Treatment Standards(UTS) (USEPA, 1994), or state regulatory systems.
Table 5 lists many of the types of metal com-pounds that may be found in waste streams. Theasterisk denotes the more common species. Thislisting does not include anions containing the toxicmetals themselves, or individual organic complexes.
More is known about metal stabilization thanabout the stabilization, destruction and immobiliza-tion of any other hazardous constituent group en-countered in stabilization technology. The mobility ofthese metals in a landfill situation, as measured byleaching tests such as the TCLP, is greatly reduced inthe vast majority of treatment scenarios by simplestabilization with cement-based S/S systems, with orwithout additives or special techniques. Some metalsand metal species may require more complex formu-lations or pre-treatment. Species that have been en-countered in actual wastes are listed in Table 6. Inaddition, non-additive methods such as temperatureadjustment (Vejmelka et al., 1985) and control of free
water may be used. Most of these special situationsrequire either changing the valence state of the metal,or dealing with metal complexes. Methods for reduc-ing mobility of these species are discussed under thefollowing individual metal headings, and are summa-
Table 4. Toxic Metals
Antimony Lead* VanadiumArsenic* Mercury* ZincBarium* NickelBeryllium Selenium*Cadmium* Silver*Chromium Thallium * TC Metals
Table 5. Metal Species
Acetates Ferrocyanides Phosphates*Bromides Fluorides Silicates*Carbonates* Hydroxides* Sulfates*Chlorides * Iodides Sulfides*Citrates Nitrates* Organic ComplexesCyanides OxalatesFerricyanides Oxides
Table 6. Potential Problem Metal Species
Arsenic trisulfide - As2S3 Organo-mercury compoundsTrivalent arsenic Nickel cyanide
compounds -As+3 Organo-nickel compoundsOrgano-arsenic compounds Hexavalent seleniumHexavalent chromium and its compounds - Se+6
and its compound - Cr+3 Finely divided elementalMetallic lead metalsOrgano-lead compoundsMetallic mercury
rized and tabulated in Table 7 (pp 38-39); metals ormetal species that are adequately stabilized by cementalone, and do not require additives, are shaded in thetable. Table 8 (pp 40-42) provides a general summaryof actual, commercial additive utilization for variousmetals and metal species. It should be noted thatflyash or bedash is often used in commercial pro-cesses, especially at TSDFs, for a variety of reasonsother than metal stabilization, but it is difficult toseparate out the actual purpose in most cases. Addi-tives per se will be discussed in Section IV. Followingare brief discussions of the various metals of concern,and their stabilization treatment.
Antimony. Antimony may exhibit a valence of -3,+3,or +5, and is classified as a non-metal or metalloid; thetrivalent state exhibits metallic characteristics. It formsa number of inorganic and organic compounds, manyof complex structure. Until the LDRs, antimony com-pounds in wastes were hazardous only under Califor-nia regulations, with a reasonably high allowableleaching level. Very little information is available onstabilization methods (although leachate analyses of-ten include antimony) and problems with antimonystabilization were rarely, if ever, encountered. An
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internal study at Chemical Waste Management (Chemi-cal Waste Management, 1992) on K061 waste (ElectricArc Furnace Dust) and soil spiked with antimony chlo-ride showed that simple stabilization with cement pro-vided excellent reduction in mobility, with leachinglevels below 0.11 mg/l, the Level of Quantification(LOQ) for analysis. Higher cement content (up to mixratios of 1.0 at least) did not increase leachability, indi-cating that antimony is not sensitive to over-treatment.
Arsenic. Arsenic is also classified chemically as anonmetal or metalloid, although it is grouped with themetals for most environmental purposes. Its principalvalence states are +3, +5 and -3. The compounds ofarsenic listed below are those commonly found inwaste materials.
Arsenic trioxide, As2O3Cacodylic Acid and Sodium CacodylateMetal Arsenates
Ca3(AsO4)4PbHAsO4 - acid lead arsenatePb4(PbOH)•(AsO4)3
•H2O - basic lead arsenateCu(CuOH)AsO45ZnO•2AsO5
•4H2ONa2HAsO4MnHAsO4
Metal ArsenitesSodium arsenite, NaAsO2Copper acetoarsenite,
(CH3CO2)2Cu•3Cu(AsO2)O3, or Paris greenArsenic Sulfides
Arsenic trisulfide, As2S3Arsenic sulfide, As4S4Arsenic pentasulfide, As2S5
The oxide is amphoteric and thus is soluble in bothacids and bases. Arsenites are often present as com-plexes such as Scheele’s green, CuHAsO3, and copperacetoarsenite described previously. Arsenates derivedfrom the arsenic acids are oxidizing agents. Arsenicforms the three sulfides described above. The trisulfideis soluble only in bases. It is often encountered in wastefrom phosphoric acid manufacture where it is precipi-tated from strong acid solution. This property is anunusual one for metal sulfides, which are usually de-composed by acids, but are stable and have low solubil-ity in bases.
Normally, traditional chemical stabilization pro-cesses are able to immobilize arsenic in contaminatedsoils, incinerator ashes and other wastes to well belowregulatory requirements (Conner and Lear, 1992). Cer-tain arsenical species—arsenic trisulfide and organicarsenicals, primarily—are very difficult to stabilize byconventional, chemical means. One solution to thisproblem has been the use of alkaline oxidation, hydro-
lyzing the sulfide and oxidizing As+3 to As+5 withsubsequent precipitation as calcium arsenate, a rela-tively insoluble species (Conner, 1993a). Another is theuse of ferrous sulfate as an additive (Electric PowerResearch Institute, 1996). Young (1979) reported im-proved resistance to arsenic leaching by the addition ofcalcium and manganese chlorides, sulfates, and ac-etates. The organic arsenical problem is discussedbelow in the section on Organo-Metallic Compounds.
Barium. Barium is classed as an alkaline earth metal(Group IIA of the periodic table), along with calciumwhose chemical behavior it resembles. Its valence stateis +2. Barium is present in many waste streams, and isalso easily stabilized to well below RCRA levels. Bariumleaching is not a problem in any experience to date.Even with extremely high barium wastes, it is suffi-cient to add sodium sulfate or gypsum to any standardstabilization formulation to precipitate barium as thesulfate. Very often, even drinking water standards canbe achieved in the leachate.
Beryllium. Beryllium, along with thallium and zinc,appeared in the RCRA Listed Waste K061 LDRs. Itrarely has been analyzed for in other non-wastewaterhazardous wastes, so there is little data on its stabiliza-tion. In one study (Chemical Waste Management,1992), K061 waste and soil spiked with beryllium wereeasily stabilized to below LOQ (<0.01 mg/l) with ce-ment alone, with greater than three orders of magni-tude reduction in TCLP leachability. Higher cementcontent (up to mix ratios of 1.0 at least) did not increaseleachability, indicating that beryllium is not sensitiveto over-treatment.
Cadmium. Cadmium is a Group IIB element, with onlyone valence state for all practical purposes (+2). Cad-mium compounds present in wastes may include:
Cadmium Arsenides, Antimonides, and Phos-phides
Cadmium BoratesCadmium CarbonateCadmium ComplexesCadmium HalidesCadmium HydroxideCadmium NitrateCadmium OxideCadmium Selenide and TellurideCadmium SulfateCadmium SulfideCadmium TungstateUnlike zinc, the cadmium ion is not very amphot-
eric and its hydroxide, Cd(OH)2, has quite low solubil-ity in an alkaline medium. In view of the low solubility
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Guide to Improving the Effectiveness of Cement-Based Stabilization/Solidification
of most cadmium species in alkaline systems, and thenon-amphoteric nature of Cd, the primary treatmentmethod has been precipitation with nearly any alkali,including cement and lime. In the presence ofcomplexing agents, such as cyanide, the cadmium ionwill not precipitate (Weiner, 1967). It is then necessaryto destroy the cyanide complex, usually by alkalinechlorination, which precipitates the Cd as the hydrox-ide. Oxidation of cyanide by hydrogen peroxide is alsoreported to break the complex and precipitate CdO. Inmost cases, even the lowest LDR level can be met withstandard stabilization formulations, especially cement-based formulations. High pH caused by over treat-ment (excessive mix ratios) is not a problem withcadmium as it is with chromium and lead.
Chromium. Chromium belongs to Group VIB of theperiodic table. It has three valence states, +2, +3, and+6, but the latter two are the most common. Cr+6 isacidic, forming chromates (CrO4)
-2 and dichromates(Cr2O7)
-2, while the other valence states are basic. Themajor chromium compounds encountered in stabili-zation work are composed of Cr+3 and Cr+6 valencestates in the following compounds:
Pigments - lead chromate, chromium oxide greensChromium sulfateChromated copper arsenate (CCA)Chromium lignosulfonatesSodium or potassium dichromateChromic acidAmmonium dichromateChromic nitrateCr+6 compounds are usually reduced to the triva-
lent state and precipitated with bases. The resultantCr(OH)3 is the form in which the majority of chro-mium is encountered in stabilization treatment. Be-cause of its low solubility, fixation of chromium as thisspecies has not been a problem, even though chro-mium is nearly ubiquitous in waste streams. As longas chromium is speciated as Cr+3, stabilization of char-acteristic wastes to the Toxicity Characteristic level iseasy if the final leachate pH is maintained above 6.0. Inwastes, this generally requires cement mix ratios above0.2, or cement kiln dust above 0.5, the latter dependingheavily on the alkalinity of the dust.
The hexavalent form is encountered in a numberof wastes, either by mixing of untreated chromatesolutions with wastewater treatment sludge or be-cause it is intrinsic to the waste, as in some incineratorresidues and in wood-treating wastes. It is also amajor problem where soil has been contaminatedwith chromate or chromic acid solutions, a frequentsituation with old plating operations. The classicalway to manage Cr+6 has been a two-step process:
reduce the chromium to the trivalent state and thenprecipitate it as the hydroxide. However, especiallywhen the Cr+6 level is low, reducing agents such asferrous sulfate, sodium metabisulfite, or sodium hy-drosulfite may be added directly to the cement orcement kiln dust based stabilization system.
Chromium is amphoteric, and so exhibits mini-mum solubility at around pH 9, with increasing leach-ability at higher pH. However, empirical measure-ments in cement-based stabilization systems(Cote1986) have shown that leachability of Cr+3 compoundsdoes not increase substantially below pH 12+. There-fore, over-treatment is normally not a problem andhigh reductions in mobility of Cr+3 compounds can beachieved at almost any mix ratio.
Lead. Lead is a member of Group IVA of the periodictable. It has two valence states, +2 and +4, with the +2state being the most common. Pb+4 compounds areregarded as being covalent, while Pb+2 compounds areprimarily ionic. Lead is amphoteric and forms soluble,anionic plumbites and plumbates as well as bothcations. Lead compounds encountered in stabiliza-tion include:
HalidesOxidesSulfideSulfateNitrateAcetatesCarbonatesSilicatesOrganolead CompoundsIn lead stabilization, pH control is more impor-
tant than with most metals. Minimum lead leaching innearly all stabilization systems occurs when the pH ismaintained between about 8 and 10 in the leachate,but substantial reduction in leachability can be at-tained in most instances up to pH 12. In most wastes,lead is easily stabilized to the TC requirements, andleaching reductions of two or more orders of magni-tude are common in cement-based systems. Researchon stabilization of F006 and, especially, K061 wastes,has often focussed on lead, and as a result there arelarge data bases on lead stabilization. In some cases,remedial projects require the achievement of very lowlead levels, sometimes at the drinking water level.This may necessitate the use of additives such ascarbonates or sulfur compounds.
The use of calcium carbonate has become com-mon practice in treatability studies on lead-contami-nated soils and many other wastes. The function ofcarbonate is not clear. It may result in the formation oflead carbonate or basic lead carbonate
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[Pb3(CO3)2(OH)2], which are much less soluble thanlead hydroxide. It also buffers many systems to moremoderate pH, but simple buffering action does notexplain all of the effects of calcium carbonate. Be-cause they are inexpensive, cannot cause over-treat-ment, and are applicable to a very wide range of lead-contaminated wastes, cement-calcium carbonate for-mulations are often the best overall choice for lead-contaminated soil and debris treatment.
Mercury. Mercury salts exist in two valence states, +1and +2. Many mercury compounds are volatile; theyare also labile and easily decomposed by light, heat,and reducing agents, even weak reducing agentssuch as amines, aldehydes, and ketones. Because oftheir covalent nature and ability to form a variety oforganic complexes, mercury compounds have un-usually wide solubility. Compounds that may befound in wastes are:
Mercuric ChlorideMercuric OxideMercuric NitrateMercuric SulfateMercuric SulfideOrganomercury CompoundsMercury concentrations found in most wastes
are quite low, and substantial reduction in mercuryleachability is easily accomplished in most stabiliza-tion processes. Even at higher levels—100 mg/kg ormore—stabilization is very effective. If necessary,lower leachability—to the 0.01 mg/l level or below—can be attained by additions of inorganic or organicsulfides or elemental sulfur. The only area wherestabilization difficulty might be encountered is whereelemental mercury or organo-mercury compoundsare present, but this appears to be quite uncommon.
Nickel. Nickel is a Group VIII transition element,along with iron and cobalt. It forms compounds inwhich the nickel atom has the oxidation states of -1, 0,+1, +2, +3 and +4. The Ni+2 valence state, however,represents the majority of all nickel compounds.Nickel is not amphoteric, but the ease with which itforms coordination complexes at high pH gives it theappearance of being so. Ni(OH)2 has low watersolubility, which accounts for the adequate fixation ofnickel in most wastes by simple pH control. Nickelcompounds encountered in wastes include:
Nickel OxideNickel SulfateNickel NitrateNickel HalidesNickel CarbonateNickel Hydroxide
Nickel FluoroborateNickel CyanideNickel SulfamateNickel SulfideWhere proper pH control is exercised, there is
usually no difficulty in fixing nickel, but more recentLDR requirements sometimes are difficult to meetwithout additives. The simplest approach in thissituation is the addition of organo-sulfur compounds.The most common difficulties that are encounteredhave been caused by the presence of complexed nickel,either a cyanide complex or an organo-complex, espe-cially the latter (see organo-metallics below). Non-complexed nickel species do not appear to be sensitiveto over-treatment.
Selenium. Selenium is next to sulfur in group VIA,and between arsenic and bromine in period 4 of theperiodic table. It forms compounds, both inorganicand organic, similar to those of sulfur. Its valencestates are -2, 0, +4, and +6. The most importantcompounds of selenium are halides, oxides, oxyacids(H2SeO3 - selenious, and H2SeO4 - selenic), and se-lenides. Selenates, if known to be present at highlevels, would pose a potential leaching problem be-cause of their solubility. Possible treatment would beeither reduction to the selenite form, or precipitationwith strontium to produce the low solubility stron-tium selenate.
Rarely is selenium found in industrial wastes inappreciable amounts, and selenium leaching abovethe RCRA level of 1.0 mg/l, even from the untreatedwaste, is seldom encountered. In stabilization-treatedwastes, leaching is usually below detection limits,with substantial reductions in mobility. Selenium athigh levels or in some complex species that mightprove difficult to stabilize have not been reported inthe literature (Conner 1990). However, the selenateion appears to have been encountered in at least oneinstance (Conner, 1994). Ferrous sulfate, probably asa co-precipitant, is believed to be useful for selenates,and precipitation as strontium selenate has been pro-posed. In most instances, selenium stabilization withsimple cement or pozzolan systems appears to bestraightforward.
Silver. Silver is a noble metal with only one normalvalence state. Most of its compounds are relativelyinsoluble, especially the halides, cyanide, sulfide, andthiocyanate. Because of the value of silver, and theease with which most dissolved species can be pre-cipitated by chloride ion, fixation of silver in stabiliza-tion systems is rarely a problem since very little isnormally present. Leaching results are normally be-
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Guide to Improving the Effectiveness of Cement-Based Stabilization/Solidification
low regulatory levels. If wastes with high silver levelsare encountered, very low leachabilities can be at-tained by the simple expedient of adding chloride ion,either as sodium chloride or hydrochloric acid. Thishas been done at TSDFs.
Thallium. Thallium is a member of group IIIA of theperiodic table with boron, aluminum, gallium, andindium (Cote, 1986). Unlike the others, it exists in bothmonovalent and trivalent forms, with the former beinggenerally the most stable. It is used in alloys and inelectrical applications. Virtually nothing appears inthe literature on stabilization treatment or stabilizationof thallium. In the treatability study referenced previ-ously (Chemical Waste Management, 1992), K061 wasteand soil spiked with thallium were stabilized to lessthan 1.0 mg/l with cement alone, or nearly two ordersof magnitude reduction in TCLP leachability. Thehigher the cement content (up to mix ratios of 1.0 atleast) the lower the leachability. This indicates thatthallium is not sensitive to over-treatment.
Vanadium. In the treatability study referenced previ-ously (Chemical Waste Management, 1992), K061 wasteand soil spiked with vanadium were easily stabilizedto less than 0.1 mg/l with cement alone, or nearly threeorders of magnitude reduction in TCLP leachability.The higher the cement content (up to mix ratios of 1.0at least) the lower the leachability. This indicates thatvanadium is not sensitive to over-treatment.
Zinc. There is considerable data on zinc stabilization,all of it indicating the substantial reduction in leach-ability is achieved with simple pH control, usingsimple cement-based stabilization systems. Whilecomplexation with cyanide is common in electroplat-ing wastes, the data on treatment of electroplatingsludges and other wastes indicate no problems withstabilization of zinc in these residuals.
Finely Divided Elemental Metals. Particulate, el-emental metals may be divided into three categories.• Very finely divided metals are often pyrophoric,
and must be handled as D003 Reactive Waste.The usual way to de-activate these wastes wouldbe to react the metals to a higher valence state;care should be taken due to the possibility ofhydrogen gas formation, an explosion hazard.In this process, the metal could be speciated in arelatively insoluble form and may or may notrequire further special treatment.
• Non-reactive elemental metals with low solubil-ity in the TCLP test—beryllium, cadmium, chro-mium, nickel, silver, zinc—would likely pose no
difficulty stabilized or not stabilized.• Metals with higher solubility in the test—lead,
mercury and selenium —should experience sub-stantial reduction in leachability in stabilizeddebris because the metal, as it dissolves, reactswith the alkalinity in the cement or pozzolan toform low-solubility hydroxides.
Organics
Organic stabilization, although more recent than metalstabilization, has been shown in numerous studies(Conner, 1990) (Gilliam et al., 1986) (Caldwell et al.,1990) (Soundararajan et al., 1990) to be capable ofconsiderably reducing the mobility of organic constitu-ents. In 1990-1991, a massive study was conducted onthe stabilization of low-level organic contaminants insoils (Conner and Lear, 1991). It demonstrated that themobility of nearly all classes of organics could be sub-stantially reduced by the proper choice of additive, asmeasured either by the Toxicity Characteristic Leach-ing Procedure (TCLP) or by Total Waste Analysis(TWA). In view of the most recent regulatory stance onorganic stabilization, it is necessary in many cases toconduct both Total Constituent Analysis (TCA) andTCLP analyses on samples before and after stabiliza-tion to prove the effectiveness of the treatment.
Stabilization, with additives, can meet the presentTC standards for all TC-constituents (USEPA, 1990).S/S can also meet the Proposed Universal TreatmentStandards (UTS) (Federal Register, 1993)(USEPA, 1994)based on Total Constituent Analysis (TCA) for most ofthe 50 constituents tested in the Conner and Lear(1991) study. Reductions in TCLP leachability rangedfrom a minimum of 90% to better than 99%. Reduc-tions in TCA ranged up to 99.9%, with some reductionin all cases.
One surprising result of the above and other recentexperimental work (Spence et al., 1990) has been thefact that Volatile Organics (VOCs) are not necessarilylost by volatilization during S/S, as was previouslythought (Weitzman et al., 1987). TCA reduction levelssuggest that VOCs sorbed onto or associated with soilparticles may be less susceptible than expected to vola-tilization during stabilization, at least in these slowexotherm, cement-based systems under relatively staticair flow conditions. Some additives, such as rubberparticulate, have been shown in independent studies(Environmental Technologies Alternative, 1994) tosubstantially reduce the evaporation rate of VOCs sothat air pollution is minimized, and also reduce theflash point of the system, thus providing an additionalsafety factor in treatment and disposal. This property
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is expected to be of increasing importance as the new airpollution control requirements (USEPA, 1991) for treat-ment units come into effect.
Based on the work by Conner and Lear (1991), threeadditives –—activated carbon, organoclays, and a pro-prietary rubber particulate formulation — all are broadlyuseful with specific contaminants in specific test meth-ods, and none works best for all. Carbon is effectiveoverall for reduction in TCLP leachability but not forreduction in TCA. Particulate rubber is not as effectivein TCLP reduction, but is the only additive that wasbroadly useful for TCA reduction, especially for thelow-volatility compounds. Organo-clays are effectivewith specific contaminants.
In addition to these three additives, some othershave been found to have very narrow applicability forspecific situations. Tables 9 - 11 (pp 43-46) list a numberof organic compounds that have been stabilization-testedwith various additives (Gilliam et al., 1986) (Conner andLear, 1991) (Conner, 1995) (Conner et al., 1990) (Connerand Smith, 1993). Unless otherwise stated, the test workwas performed on natural soil spiked with the indicatedconcentrations of target organic compounds. The spikedsoil was stabilized with 20% cement alone, and with 20%cement plus a number of generic and proprietary addi-tives. In most cases, the additive was used at the 10%addition level because the total level of target constitu-ents approached the 10,000 mg/kg (1%) level. Thisresults in very expensive formulations. However, inpractice it is probable that much lower levels can be usedin most instances - most likely in the 1% to 5% range,which would result in additive costs of about $5 to $100per ton of waste treated.
All samples were subjected to both TCLP and TCAtesting. The tables give the best level achieved in TCLPand TCA testing, respectively, for each target com-pound, and the additive and addition ratio used toattain that level (in a few instances, designated by “none,”no addititive was required). Because of the uncertaintyat this time as to what the final regulatory stance will beregarding organics, it is difficult to state how useful S/Swould be in any given scenario. However, the achiev-able TCLP and TCA levels shown here should allow thereader to determine whether S/S may be effective in agiven waste/treatment/disposal situation once the re-quirements are established. Table 12 (page 47) summa-rizes reagent utilization, showing the most useful addi-tives for various organic groupings. In using thesetables, it is important to understand that, in addition tothe additive that gave the best result, other additivesusually also produced improved results for a givencombination of target constituent and test method. Inpractice, the actual selection of additive(s) must bedetermined by treatability testing with actual wastes.
Volatile organics (VOCs). Although there is no oneadmixture that produces the best results for all con-stituents or combination thereof, activated carbonworks best for TCLP reduction of VOCs overall(Conner and Lear, 1991). Although some volatiliza-tion undoubtedly takes place, comparison of the TCAand TCLP results shows that this is a minor effect inmost instances. Carbon has now been used success-fully in a number of specific remediation treatabilitystudies (Chemical Waste Management, 1994) (Siegristet al., 1992) (Morse and Dennis, 1994). Organo-clayshave also been used successfully in organic VOCstabilization. A modified rubber particulate, KAX-100™1, also worked well for VOC stabilization, espe-cially for TCA reduction. Table 9 lists the most effec-tive additives for the various organic compounds thathave been tested.
Semi-volatile organics (SVOCs). Conner and Lear(1991) showed that, for SVOCs, carbon produces thebest TCLP mobility reductions, but rubber particulate(Environmental Technologies Alternatives, Inc., 1994a)provides the best reductions in TCA (Conner andSmith, 1993). A mixture of carbon and rubber particu-late would seem to be way to go for SVOCs, depen-dent on what EPA finally does in the way of organicstabilization regulations. Rubber particulate is sur-face treated, finely ground tires or other rubber scrap,with particle sizes in the range of 10 to 60 mesh. It isgenerally less expensive than carbon, especially vir-gin carbon. Thus a mixture of the two would be costeffective. Table 10 lists the most effective additives forthe various semi-volatile organic compounds thathave been tested.
Mixtures of VOCs and SVOCs. This common situa-tion seems to be best handled by a mixture of carbonand rubber particulate, by a modified rubber particu-late (Environmental Technologies Alternatives, Inc.,1995), or by organo-clays for specific compounds. Thebest additive or combination of additives can be deter-mined by comparing the mixture of target compoundsto be treated with Tables 9 and 10.
Polychlorinated biphenyls (PCBs). PCBs are wellknown to be immobile in virtually any stabilizationsystem. There is considerable literature (Conner, 1990)showing the latter effect. Therefore, PCB stabilizationcan be effectively accomplished in simple cement-based systems.
1 KAX-50™ and KAX-100™ are proprietary rubber particu-late-based additives manufactured by EnvironmentalTechnology Associates, Inc., Port Clinton, OH.
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Guide to Improving the Effectiveness of Cement-Based Stabilization/Solidification
Pesticides, herbicides. Conner and Lear (1991) foundthat pesticides and herbicides are easily immobilizedleachability-wise with cement plus carbon formulations,and in many cases, by cement alone. TCA reductionsrange from 50% to greater than 99%. A general formula-tion here would again be a cement/carbon/rubber mix-ture; however, depending on the regulatory interpreta-tion of what test method constitutes “mobility reduc-tion” for organics, cement alone might be used in manycases. Table 11 lists the most effective additives for thevarious pesticides and herbicides that have been tested.
Organo-Metallics
Many industrial waste streams contain soluble metalcomplexes that are very difficult to treat because of theirstability. Simple complexes such as cyanides can bedestroyed by alkaline chlorination. More stable com-plexes such as citrates, EDTA chelates, and a widevariety of non-chelate organometallics may requirestrong oxidants such as potassium permanganate orpotassium persulfate, and possible use of elevated tem-perature. Other problems complicate the oxidativedestruction of complexes. If chromium is present it willbe oxidized to Cr+6 and must then be reduced beforeprecipitation. With either oxidizing or reducing agents,species other than the target compound may competefor the reagent; large additions of oxidizing agent maybe necessary and this becomes very expensive and timeconsuming. Therefore, a non-oxidative method forhandling complexed nickel is desirable. Recently, an-other approach was used with nickel chelates—sorp-tion on activated carbon. This reduced the leachabilityof nickel substantially and met the required regulatorylevel. Additional studies have shown that this tech-nique also works with chromium, and should workwith arsenic and cadmium. The sorbed organometalliccompounds may then be solidified using portland ce-ment. Table 7 lists the additives used for organo-metallic compounds.
Organo-arsenic compounds. The organic arsenicalsare of special interest in stabilization because they areoften found in wastes, especially in remediation work atold lagoons and other contaminated disposal sites.Arsenic combines readily with carbon to form a widevariety of compounds many of which are manufacturedand used commercially, but may also be formed aswaste products in manufacturing and during wastetreatment processes.
Organo-cadmium compounds. A number of organicligand complex systems involving cadmium are known:
acetic acid, dimethylglyoxime, EDTA, glycolic acid,methylamine, oxalic acid, pyridine, sulfamic acid, tar-taric acid, and thiourea. Dialkyl cadmium compoundsare used as polymerization catalysts in organic andpolymer synthesis, and as heat and light stabilizers inplastics. The major complex in use, however, is inor-ganic Cd(CN)4
-2, which is used in electroplating and istreated with alkaline chlorination.
Organo-lead compounds. Tetraethyllead (TEL), usedas an antiknock additive in gasoline until recently, isthe most important organo-lead compound from astabilization standpoint. While TEL has undoubtedlybeen present in various waste streams, there does notseem to have been a reported leachability problemtraceable to it. This may be due to its low solubility, orto low levels in the wastes.
Organo-nickel compounds. Organo-nickel complexesinclude salts such as acetate, formate, oxalate and stear-ate, and nickel chelates. Nickel acetate is found in metalfinishing operations such as aluminum anodizing andelectroplating. The fatty acid salts are used in dying ofsynthetic fibers. Various soluble chelates are formed,and these are the source of most of the problems en-countered in fixation of nickel. Organo-nickel com-plexes such as EDTA, citrate, and gluconate may re-quire high temperature oxidation with strong oxidiz-ing agents. Nickel cyanide complexes can be brokenwith alkaline chlorination, leaving a nickel species whichcan be stabilized to low leaching levels.
Organo-silver compounds. In cases where a stable,soluble silver complex is present in large amounts,several techniques are available. Magnesium sulfateand lime can be used to precipitate a mixed sulfate-oxide. Alkaline chlorination can be used to break thecomplex and precipitate silver chloride. Sulfides andhydrosulfites are also used to treat silver complexes.
Soluble Salts
Chlorides, nitrates, sulfates. While it is possible toinsolubilize these anions (e.g., silver for chloride, bariumfor sulfate, etc.), there is no practical way to do so withinthe realm of S/S processes. The best approach is toproduce a low permeability matrix, and/or one that ishydrophobic, to limit the diffusion of the solute out ofthe stabilized mass. However, this technique will notbe effective with crushed or ground material, as isdeliberately done in the TCLP test. Actual field leach-ing of stabilized masses should be much lower thanTCLP tests indicate, because of the monolith effect.
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Cyanides. This issue has been in dispute betweenindustry and EPA. As we understand it, the disputecenters around whether one-step alkaline chlorina-tion as presently used constitutes “destruction” inEPA’s meaning of the word, i.e., conversion to CO2and nitrogen. This also affects the use of calciumpolysulfide, which converts the cyanide to thiocyan-ate. EPA has said that stabilization is not permitted forcyanide treatment, and that these two processes mayconstitute stabilization, especially if they are used inconjunction with normal cement or pozzolan treat-ment. Therefore, while cyanide standards can be metwith additive-enhanced stabilization, the regulatorysituation is unclear at this time.
IV. ADDITIVES USED IN CEMENT-BASED STABILIZATION/SOLIDIFICATION
Many additives have been tried out in S/S processes,and a number are used commercially, especially atTSDFs. A summary of the most commonly encoun-tered additives and the characteristics of their use isgiven in Table 1. In this section, specific additives areunderlined for easier identification in the text. Refer-ences to the use and properties of many of theseadditives have been given in earlier sections; where noreference is given, refer to Conner (1990), BattelleColumbus (1993), U.S. Army Corps of Engineers Wa-terways Experiment Station (1990), and United StatesEnvironmental Protection Agency (1982). Stabiliza-tion additives can be categorized in three basic ways:metal stabilization; immobilization of organic con-stituents; processing and anti-inhibition aids.
Metal Stabilization
pH control and buffering. Acids, alkalies and salts,such as lime, caustic soda, and ferrous sulfate, can beused to control the pH of the system. Buffers such ascalcium carbonate and magnesium oxide are used tokeep it within the desired range after the leaching testis complete. Control of pH can also effect the removalof interfering substances from solution in certain cases,e.g., destruction of gels and film-formers.Lime
The most common alkali used in stabilization islime (either quicklime (CaO) or hydrated lime(Ca(OH)2)), because it is the most cost effectivein most instances. Lime also supplies additionalcalcium for cement reactions and may react withcertain interfering organics. Lime products may
be either high calcium or dolomitic. The lattercontains substantial amounts of MgO or Mg(OH)2in place of some of the calcium.
Sodium Hydroxide (NaOH)In addition to neutralizing acids and raising pH,NaOH may also solubilize silica for quicker reac-tions of the pozzolanic type. One problem withthe use of sodium alkalies is that the cementitiousreactions which serve to moderate high pH inthose systems (Cote, 1986) are counteracted bythe presence of sodium ion.
Magnesium Oxide (MgO)Acts as a pH control, buffering agent. MgO hasalso been found to be useful as an additive toportland cement solidification in the nuclear wastearea (Carlson, 1987).
Sodium Carbonate (Na2CO3)Also known as soda ash, Na2CO3 is much lessfrequently used than lime in S/S work, but issometimes present in raw wastes where it wasused for neutralization of wastewaters or otherprocess wastes. Sodium carbonate also may beused in lead stabilization, and as a buffer inachieving more precise pH control.
Sodium Bicarbonate (NaHCO3)Acts as an accelerator (Shinoki et al., 1980) as wellas a pH control, buffering agent.
Reduction. Reducing agents are used for the treatmentof hexavalent chromium (Cr+6). The most common areferrous sulfate (FeSO4•7H2O), sodium metabisulfite(Na2S2O)5 and sodium hydrosulfite (Na2S2O4). Withferrous sulfate, the additive is mixed in first with thesystem preferably at low pH, then the portland cementis added and mixed in. With sodium hydrosulfite, thereagents and additive can be added in any order.Ferrous Sulfate
Probably the most widely used metal reducingagent in the S/S field, primarily on wastes con-taining Cr+6. It is safe to use, inexpensive (asreducing agents go), and often produces addi-tional benefits by co-precipitating the toxic met-als. Its main drawbacks are large volume increaseand the requirement of low pH for acceptabletreatment times. The latter problem is especiallyacute in the case of wastes with high alkalinity,where very large quantities of acid may be re-quired for pH adjustment. Reduction with fer-rous sulfate is a three step process: 1) pH adjust-ment to <3, 2) addition of ferrous sulfate andmixing until reaction is complete, and 3) raisingpH to >7 with portland cement to precipitatemetal as the hydroxide or as a co-precipitate withferric and ferrous iron. The last step allows oxida-
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Guide to Improving the Effectiveness of Cement-Based Stabilization/Solidification
tion of ferrous iron to the Fe+3 valence state byoxygen in solution, and any residual reagentshould be destroyed. Reduction occurs over awider pH range, but at lower rates (Allied Chemi-cal Co., 1976)(Eary and Rai, 1988).
Sodium Metabisulfite/Sodium BisulfiteThese two additives react in the same way, sincemetabisulfite is the anhydrous form of bisulfite.The former is often used because it does not cakein storage. These reagents are effective reducingagents for Cr+6 and require much less acid andalkali than does ferrous sulfate, thereby generat-ing less sludge. While considerably more expen-sive than ferrous sulfate, which can often beobtained as a waste product, much less is used.The overall cost of bisulfite reduction is often lessthan that of ferrous sulfate. The principal objec-tion to the use of the bisulfites in S/S systems istheir tendency to generate sulfur oxides in vol-ume on contact with acids, a very serious prob-lem. The solids in waste residuals seem to in-crease the evolution of SO2, perhaps by a surfacecatalysis reaction. This is especially evident whentreating Cr+6 contaminated soils. Reduction ratedepends on pH (Allied Chemical Co., 1976).
Sodium HydrosulfiteThis additive is effective at the alkaline pH ofmany waste residuals, hence it normally doesnot require pH adjustment before addition. Also,it remains effective after addition of the usuallyhighly alkaline solidification reagents. This al-lows the addition of both types of reagent inrapid sequence, or even together. The majordrawback to the use of sodium hydrosulfite iscost; it is several times as expensive than themetabisulfate and more of it is required, al-though no acid is used. Nevertheless, where theCr+6 level in the waste is not too high, the addi-tional cost may be justified by simplification ofthe process (Allied Chemical Co., 1976).
Metallic IronIron filings have been tested successfully for usein reduction, but commercial use to date is notdocumented.
Other Reducing AgentsSulfides, sodium borohydride, reductive resins,and hydrazine have all been suggested for usein S/S, but have found little or no commercialapplication.
Oxidation. Oxidizing agents are used for severalpurposes: to increase the oxidation state of certainmetals such as arsenic (converting As+3 to As+5); todestroy soluble complexes such as organo-metal com-pounds (so that they can be precipitated as a less
soluble species), cyanides, hydrogen sulfide and phe-nol; to destroy interfering substances in the waste,such as algae; to alter the biological status of thesystem. There are many oxidizing agents which could,in principle, be used but most are impractical for onereason or another, usually cost. For As+3 oxidation andamenable cyanide destruction, a hypochlorite(Ca(OCl)2 or NaOCl) is normally used. For destruc-tion of organo-metal compounds, a more powerfuloxidant such as potassium permanganate (KMnO4) orammonium persulfate ((NH4)2S2O8) is used. Hydro-gen peroxide may be used for biological control. Majorproblems in the use of oxidants are non-specificityand competing constituents. If a waste contains bothnickel chelate and Cr+3 ion, oxidizing the chelate torelease nickel may also oxidize the chromium to Cr+6,which must subsequently be reduced again. This iscostly not only in the extra processing required, but inthe use of oxidizing agent where it is not needed orwanted. Organics such as oil and grease will competefor the oxidizing agent, making oxidation a very costlyprocedure if a selective agent cannot be found.Sodium or Calcium Hypochlorite
Hypochlorites are the most common oxidizingagents in S/S, having been used commerciallyprimarily for cyanide destruction and for triva-lent arsenic compounds (Conner, 1993a).
Potassium PermanganateA powerful oxidizing agent, potassium perman-ganate is used for destruction of certain organ-ics. Commercially, it has been used for phenoldestruction (Conner, 1990).
Ammonium/Sodium PersulfatePersulfates are effective in some instances wherepermanganates are not as effective. No com-mercial use has been documented.
Speciation, Re-Speciation. By far the most importantfixation mechanism for metals in S/S systems is chemi-cal precipitation as low-solubility species. All of thecement-based S/S processes and methods precipitatedissolved metals as hydroxides, silicates, or sulfides,and less frequently as carbonates, phosphates, or vari-ous complexes. However, few of these systems arereally as simple as they appear. Usually, a combina-tion of mechanisms is active and the products oftreatment are frequently not simple compounds.Equally important, the wastes being treated by S/Stechnology often are already speciated as relativelyinsoluble compounds in sludges, filter cakes, and soils.Carbonates
In certain cases, metal carbonates are less solublethan their corresponding hydroxides. In cementchemistry, the natural formation of carbonates
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from carbon dioxide from the air is termed “car-bonation” (Cote 1986). Patterson et al. (1977)found that the formation of hydroxide precipi-tates controlled the solubility of zinc and nickelover a range of pH values, but cadmium and leadsolubilities were controlled by carbonate precipi-tates in a narrower range. This is in keeping withthe results of treatability tests conducted by theauthor on lead-bearing wastes, using soluble and“insoluble” carbonates. One problem is that thecarbonates are decomposed at low pH, such asthat encountered in the TCLP test, if the pH of theleaching solution in contact with the solid actu-ally drops too low. If CO2 is evolved, the reactionis irreversible even if the final pH of the leachantis high, and the final speciation of the metal willbe as the hydroxide. This may explain the widelyvarying results reported (informally) by investi-gators testing carbonates, since the efficacy ofcarbonate precipitation would seem to be unusu-ally sensitive to test variables; the sample beingtested could either lose carbonate as CO2, or gainit in the same way from the atmosphere (air) inthe test container. The most common carbonateused in S/S is calcium carbonate (limestone oragricultural lime) because it is so inexpensive.While its solubility is low, calcium carbonate canprecipitate even less soluble carbonates such asthose of lead and barium. More soluble carbon-ates such as those of sodium or potassium may bemore effective, but are also more expensive.
Sulfur-Based AgentsOther than precipitation as hydroxides, sul-
fide precipitation of metals has probably been themost widely used method to remove metals fromwastewater. This method has been successfullyapplied in S/S treatment as well, especially forachieving regulatory limits for wastes containingmercury. Unlike water treatment, S/S treatmentrequires the use of cement, either concurrentlywith the sulfide treatment or afterwards, to pro-duce a stable product. Most metal sulfides are lesssoluble than the hydroxides at alkaline pH (ar-senic is an exception). Another interesting excep-tion in sulfide precipitation is that of chromium,which does not precipitate as the sulfide, but as thehydroxide. Therefore, chromium leaching will becontrolled by hydroxide precipitation, and henceby pH, at least in theory. Metal sulfide solubilitiesare not as sensitive to changes in pH. There arethree classes of sulfide precipitation reagents whichhave been investigated and used in S/S work:
Soluble inorganic sulfidesSodium sulfide (Na2S) and calcium polysulfide
(CaSx) are the primary examples of commercialuse of this class of sulfides in S/S. In some cases,the soluble sulfides will precipitate chromiumdirectly without pretreatment to reduce it to thetrivalent state, and sulfides are claimed to pre-cipitate complexed metals (Cherry, 1982). It isnecessary to maintain pH 8 or above to preventevolution of H2S. While excess sulfide ion isnecessary for the precipitation reaction, the ex-cess must be kept to a minimum so that freesulfide removal treatment is not required beforethe waste can be landfilled. The sulfide is addedbefore any of the solidification reagents, sincethe latter contain calcium, magnesium, iron andother metals which will compete for the solublesulfide. However, calcium sulfide, which haslimited solubility, may act as a sulfide buffer tomaintain a small excess available sulfide level inthe system, similar to the action of the alkalies inhydroxide precipitation.
“Insoluble” inorganic sulfidesOne answer to the problems encountered withuse of soluble sulfides is the use of very low-solubility species such as FeS or elemental sulfur.In the case of FeS, its solubility is about 0.0001mg/l in water. The former technology has beencommercialized as the Sulfex™ process (Knockeet al., 1977) (Feigenbaum, 1977). The advantageof this approach is that very little excess sulfideis present in the system at any time, so the prob-lem of H2S odor and toxicity is eliminated. Thecombination of elemental sulfur + alkali (Ader etal., 1989) has also been tested in S/S systems. Theprinciple here is that sulfide ion is generated as itis used up in metal-sulfide reactions, but only asmall amount of S-2 ion is present at any one time,thereby minimizing risk.
Organo-sulfur compoundsIn principle, organo-sulfur compounds may havecertain advantages over the inorganics. Severalinvestigators (Yagi and Matsunaga, 1976) (Yagi,1975) have found thiourea to be useful in reduc-ing mercury leaching from caustic-chlorine pro-duction wastes and other residues to very lowlevels, 0.0001 mg/l, in water. Nakaaki et al.(1975) lowered the mercury leachability of sea-bed sludge with a fixing agent containingpolydithiocarbamates and an iron or copper salt.Notably, all of these applications of organo-sul-fur compounds have been on mercury. This maybe due to the extremely low regulatory leachinglevels for mercury, or to the basic insolubility ofmercury sulfides, or both. Little has been re-ported on the use of these reagents for other
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Guide to Improving the Effectiveness of Cement-Based Stabilization/Solidification
metals in sludges and other waste residuals. Onevendor (Chemical Engineering, 1988) has a lineof organosulfur reagents for use in wastewatertreatment, and there are a number of other re-agents of this class offered on a proprietary basis.
SilicatesThe reactions of polyvalent metal salts in solu-tion with soluble silicates have been studiedextensively over many years (Conner, 1990).Nevertheless, the “insoluble” precipitates whichresult from such interactions are not usuallywell characterized, especially in the complexsystems representative of most wastes. Metalsilicates are non-stoichiometric compounds inwhich the metal is coordinated to silanol groups,SiOH, in an amorphous silica matrix. The reac-tions of soluble silicates in solution is best sum-marized by Vail (1952), who states, “The precipi-tates formed by the reaction of the salts of heavymetals with alkaline silicates in dilute solutionare not the result of the neat stoichiometric reac-tions describing the formation of crystalline sili-cates, but are the product of an interplay offorces which yield hydrous mixtures of varyingcomposition and water content.” In any case,metals in solution can be effectively precipitatedby soluble silicates, and the reaction productstend to be less sensitive to pH variations in theenvironment than are hydroxide species. How-ever, metals already in relatively insoluble formare generally not re-speciated by soluble sili-cates. Nevertheless, there is evidence that suchspecies can be re-speciated in situations wheresilicates are constantly being formed. Bishop(1988) postulated that the observed low leachingof metals in portland cement CFS systems wasdue to the association of the metals with silica,possible as silicates. Perhaps most interesting isa patent application (Conner and Rieber, 1992)which claims the continuous production ofsoluble silicates from biogenetic, amorphoussilica and alkali.
For S/S work, the soluble silicate is usedalong with portland cement and/or cement kilndust, normally with the cement or kiln dustbeing added first and mixed into the wastebefore the silicate is added. The cement pro-vides the physical properties required in thetreated waste, due both to the action of thecement itself, and to its release of calcium ion toreact with the excess silicate, forming a solidcalcium silicate gel. It also results in betteroverall chemical properties in the waste form,moderating the high pH conditions in the soluble
silicate itself and interacting with waste con-stituents in ways already discussed.
PhosphatesPhosphate chemistry is very complex and var-ied. Compounds containing monomeric PO4
3-
are called orthophosphates or simply phos-phates. The simple phosphate salts of the toxicmetals have low water solubility, although theyare soluble in acids. For lead immobilization,either phosphoric acid or a sodium phosphate isused. For most S/S work, the phosphate is usedalong with portland cement and/or cement kilndust, normally with the phosphate being addedfirst and mixed into the waste before the cementis added. As is the case with soluble silicates, thecement provides the physical properties requiredin the treated waste. While phosphate is some-times used alone where lead is the only constitu-ent of concern and where physical propertydevelopment is not required, the immobilizatonof other RCRA metals requires the properties ofcement.
Iron CompoundsThe removal of toxic metals from wastewaterwith systems which co-precipitate and/or floc-culate them with iron salts is well known andwidely used (Sittig, 1973) (Swallow et al., 1980).More recently, it has been used to reduce thesolubility of various toxic metals in hazardouswaste treatment (Pojasek, 1980). The ratio of Fe+2
to Fe+3 is important, with ratios of 1:1 to 1:2reported as yielding optimum results. Sano etal. (1975) attribute the removal of zinc and cad-mium to the formation of ferrite crystals whichcould subsequently be removed magnetically.The crystals capture the other metals in thelattice, or adsorb them on the surfaces. Thismechanism has not been confirmed by others,who ascribe the results obtained to co-precipita-tion followed by flocculation. Sols of hydrousmetal oxides are stabilized by the presence ofexcess ferric ion, but acquire a negative charge,destabilize and flocculate under alkaline condi-tions. As the system becomes alkaline, the fer-rous ion is also easily oxidized to ferric, andprecipitates as the hydroxide. These reactionsremove other metal ions from solution, reduc-ing their concentrations to levels below thoseobtained with simple hydroxide precipitation.Whatever the mechanism, the net effect is reduc-tion of leachability in many instances. In addi-tion to the iron species, co-precipitation withcalcium carbonate and other species has beenreported (Envir. Sci. Tech., 1982).
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Again, for S/S work, the iron compound isused along with portland cement and/or ce-ment kiln dust, normally with the iron salt beingadded at the same time as the cement. Whereferrous iron salts are used for electrochemicalreduction, the iron salt is normally added first,and the cement added after reduction is com-plete. The cement provides the physical proper-ties required in the treated waste, as well as thealkalinity and other properties of cement neces-sary for immobilization of RCRA metals.
XanthatesCellulose and starch xanthates have been usedfor the stabilization of a number of metals inwaste streams, especially cadmium, chromium,nickel, and mercury (Bricka and Hill, 1989). Themost widely publicized additive has been in-soluble starch xanthate (ISX) (Wing, 1975). ISXis produced by treating starch with crosslinkingagents, then xanthating it with CS2 in the pres-ence of an alkali metal base such as sodiumhydroxide. The resulting product is a particu-late solid. Since 1980, ISX has been a commer-cially available product with usage in the treat-ment of wastewaters from metal finishing andsimilar sources. ISX is also reported to act as areducing agent for Cr+6. Chromium is reducedto Cr+3 and removed by neutralization to pre-cipitate the hydroxide. It should be noted thatISX operates at low pH and the process is lesseffective as pH rises. Tests with selenium(Navickis, 1975) indicated that the metal afterimmobilization with ISX could not be extractedwith either high or low pH water, but chlorideion does cause some release of selenium. Starchxanthate fixes mercury better than cellulose xan-thate, but xanthates alone are not adequate forfixation of cadmium, chromium and nickel —cement also is required. The latter finding prob-ably demonstrates the necessity for pH controlin the alkaline range for adequate fixation ofcadmium, chromium, and nickel, a result that isnot surprising.
Insoluble SubstratesRather than precipitate metals from solution inthe usual sense—by formation of low-solubilityspecies from ions in solution—another approachis to react the metal with an active area or func-tional group on the surface of an insoluble sub-strate. Nelson (1980) used a treated leatherwaste to remove heavy metal ions, particularlylead and cadmium, from nitrate and acetatesolutions. Another process (Chemical Engineer-ing, 1979) uses modified casein to remove cad-
mium, chromium, copper, mercury, nickel, andzinc from wastewater. Chromium reportedlycan be removed as directly as Cr+6, without priorreduction, to levels below 1.0 ppm from streamscontaining up to 500 ppm Cr+6. The casein ismodified by treating with formaldehyde to forma cross-linked, insoluble product.
Inorganic ComplexationMany metals exist in ores and rocks as complexcrystalline structures. The curing of cement-based solidification systems may eventually re-sult in complexes such as those formed whenmetals are removed from solution by substitu-tion for calcium, aluminum, etc. in cement hy-dration products. Another example is the for-mation of ferrite crystals mentioned previously,if indeed these actually form in CFS systems.Both ferricyanide and ferrocyanide form low-solubility species with a number of metals.
Organic ComplexationMany organic compounds form low-solubilityspecies with certain metals (e.g., tartrates ofcadmium, lead, mercury(+1), and nickel). Un-fortunately, little information is available oneither the actual solubility numbers for metalorganic compound in aqueous solution or on theeffects of pH and other ions. Manahan andSmith (1973) report that humic acids formed inthe decay of vegetable matter immobilize metalions in sediments and soil.
MiscellaneousSodium sulfate (Na2SO4) and sodium chloride(NaCl), respectively, are used to immobilizesoluble barium and silver species. Young (1979)reported improved resistance to arsenic leach-ing by the addition of calcium and manganesechlorides, sulfates, and acetates. Onoda CementCo. (1976) used gypsum to produce an improvedproduct from S/S with cement. Chen (1978)reported improved leaching properties by usinga mixture of cement and vermiculite. Phospho-rus pentoxide and a stearate (Takashita, 1979)were used to treat oily sludges.
Co-precipitation and flocculation. Aggregation offine particles and film-formers into larger size flocsthat are removed from the reactive cement particlesurfaces can prevent the inhibition of cement settingand hardening. There are many organic surfactantsthat might be used for this purpose, and a few inor-ganic additives. Co-precipitation can be very useful inimmobilizing metal and organic compounds in a com-plex structure. It is difficult to separate the effects ofco-precipitation from those of sorption in systems
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Guide to Improving the Effectiveness of Cement-Based Stabilization/Solidification
where the sorbent is formed in-situ.Ferrous Sulfate
In addition to its use as a reducing agent, ferroussulfate is used as a co-precipitant and flocculat-ing additive, primarily in lead stabilization andespecially where mobile colloidal species arepresent. It can also be used for the same purposefor other metals such as arsenic, if necessary.
Organic Flocculants, SurfactantsThere is a large variety of organic surfactants thatcan be used to remove fine particulate matterfrom the surfaces of the reactive cement par-ticles, thereby preventing their inhibiting effect.Alcohols, amides, lignosulfonates (Kokusai, 1981)(Veda and Ito, 1977), and other specific surfac-tants can aid in wetting solids and dispersingfine particulates and oil which interfere withreactions by coating the reacting surfaces.Flocculants can also serve this purpose.
Other surface effects. Dispersion of oils, greases, andfine particulates away from reacting surfaces, and pre-cipitation of interfering substances have effects analo-gous to the use of flocculation on interfering particulatematter. Generally, a wide variety of commercial organicsurfactants can be used for this purpose.
Ion Exchange. Ion exchange can be either beneficial ordetrimental to cement-based S/S. It can inhibit orretard S/S reactions by removing calcium from solu-tion, preventing it from entering into the necessarycementitious reactions. It can also accelerate the pro-cess by removing interfering metal ions from solution.Which occurs may depend on the selectivity of the ionexchange material.
Substitution. Certain metals may retard and inhibitthe reactions by substituting for calcium in thecementitious matrix, which may explain the effect ofmagnesium in dolomitic lime products. Certain sub-stances are natural or synthetic complexing agentswhich remove calcium from availability in the settingand curing reactions. However, cement can also im-prove metal immobilization when the metals substi-tute for calcium in the hydrated cement matrix.
Sorption. Here, the term “sorption” is used to coveradsorption at surfaces, absorption into the interior ofsolid substrates, and chemisorption. Often, it is impos-sible to distinguish between these various effects inreal, complex systems, and in the practical sense, it doesnot matter anyway. An example of sorption of metalson active oxides is given by Posselt and Anderson(1968). They used hydrous manganese dioxide formed
in-situ by reduction of permanganate ion (Mn+7). Metalion sorption was rapid, with equilibrium attainedwithin minutes. Dzombak and Morel (1987) foundconsiderable data which show that metals adsorbstrongly to iron and aluminum oxides. Lagvankar etal. (1986) described an interesting process using ironfilings which are activated by the waste stream itself.Metal sorbents can be broken down into a number ofclasses or groupings:
Metal OxidesIron, manganese, aluminum, etc.
ClaysBentonite, montmorillonite, attapulgite,illite, kaolinite - all natural and modified.
Natural MaterialsPeat moss, natural zeolites, sawdust,vermiculite, sand, etc.
Synthetic MaterialsZeolites, flyash, cullite, activated alumina,organic polymers, etc.
Activated CarbonCement Hydrate PhasesChan et al. (1980) evaluated ten potential sorbents,
natural and synthetic, for their ability to remove avariety of pollutants from landfill leachate. They foundthat no single sorbent is effective in removing all pollut-ants, and some were not attenuated by any of thematerials tested (bottom and flyashes, vermiculite, il-lite, sand, activated carbon, kaolinite, natural zeolite,activated alumina, and cullite). As expected, activatedcarbon was most effective for organics, with illite alsobeing successful. Specific sorbents were effective onfluoride and cyanide, but not on chloride. Activatedalumina was moderately effective in removing nickel,but none of the other sorbents achieved any successwith this metal. None of the sorbents tested wereeffective for lead. Other investigators have found thatflyash, kaolin, and sawdust (Benson, 1980), and a cal-cined mixture of bentonite and flyash (Japan Kokai,1980) were effective in immobilizing a variety of metals.
Immobilization of Organic Constituents
Sorption. Sorbents are used for immobilization oforganics and organo-metallic compounds (arsenic,chromium, lead, and nickel). While many sorbentshave been tested, the most effective overall are acti-vated carbon, organo-clays, and rubber particulate.From a practical standpoint, a combination may be thebest single sorbent where a variety of organic constitu-ents of concern are present. Sorbents can also immo-bilize organo-metallic species, especially thosecomplexed forms which are otherwise difficult to
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precipitate. Sorbents can also be used for removal ofinterfering substances from reacting surfaces.Activated Carbon
One of the earliest mentions of the use of acti-vated carbon for immobilization of organics (pri-marily phenol) was by Chappell (1980). Sincethen, carbon has been used for this purpose in anumber of commercial projects (Lawson et al.,1996) and has been demonstrated in many treat-ability studies (Conner and Lear, 1991).
ClaysNatural clays are not very effective stabilizationagents for organics, less so than for metals.However, treated clays – the so-called organo-clays – are effective (Boyd and Mortland, 1987).These are natural clays that have been reactedwith various reagents, primarily quaternary am-monium compounds and derivatives, to renderthem organophillic on internal as well as exter-nal surfaces. The organophillic groups attachedto the clays attract and hold organic contami-nants in the waste. Organo-clays have beenused for this purpose in a number of commercialprojects (Lawson et al., 1996) and have beendemonstrated in many treatability studies(Conner and Lear, 1991).
Rubber ParticulatesThese are proprietary formulations (Environmen-tal Technologies Alternatives, Inc., 1994a) – KAX-50™ and KAX-100™–based on rubber particulatederived from ground scrap tires, and were report-edly specifically formulated for this purpose.KAX-50™ was most effective with semi-volatileorganics (Conner and Smith, 1993), while KAX-100 ™ worked best for mixtures of VOCs andSVOCs, as well as the pesticides/herbicides group.
Oxidation of unwanted species. Powerful oxidizingagents such as potassium permanganate and sodiumpersulfate are effective in destroying certain organiccontaminants in wastes. See “Oxidation” in the previ-ous section, Metal Stabilization, for more informationon these additives. However, there are a number ofdrawbacks to the use of oxidizers for this purpose. Theprimary problem is cost. Since these additives aregenerally non-selective in their action, all oxidizablespecies in the waste will compete for the additive;examples are oils, biological materials, vegetative mat-ter, metal species such as Cr+3 and many other commonwaste components. Thus, a very large excess of addi-tive may be required. Secondly, the oxidation processis exothermic and considerable heat is often generated,which will tend to vaporize VOCs rather than destroythem, and cause air pollution problems. Also, any
chromium in the waste will be oxidized to the Cr+6
valence state, and then require reduction so that it canbe stabilized. For these reasons, oxidation has beenlittle used for organic treatment, except in instanceswhere the constituent is easily oxidized and present atlow levels and there is little other oxidizable species inthe waste. One successful use has been for phenoldestruction in metal finishing wastes (Conner, 1990).
Processing and Anti-inhibition Aids
More and more, additives are being used in chemicalsystems for purposes other than stabilization. Ce-ment-based systems, especially, are sensitive to manywaste components discussed previously in their set-ting and strength development. Additives such aslime and sodium silicate are often used to counterthese inhibition effects. On the other hand, somewaste components cause premature setting and re-quire the use of set retarders commonly used in mak-ing concrete. The latter effect must also be controlledin some delivery systems, especially in in-situ S/S.Other processing aids are sometimes used: “water-reducing agents” or surfactants to lower viscosity, orclays and polymers to increase viscosity. This subjectis covered in some detail in Section II, and will only bediscussed briefly here.
Acceleration. There are many compounds that havebeen reported for their ability to accelerate the settingand/or hardening of cement. Many of these may beeffective also in cement-based S/S systems. Commonadditives and groups of additives, along with refer-ences to their use, are listed as follows:
Calcium Chloride (Kantro, 1975)Dispersants/Water Reducing Agents (Falcoux
et al., 1980)Magnesium Oxide (Kawasaki Steel Corp., 1980)Lime (Falcoux et al., 1980)Calcium Aluminate MineralsAmines (Wagner and Ellis, 1980)Organic Acids and Salts (Falcoux et al., 1980)
(Yamagisi et al., 1980) (Bonnel andHevanee, 1972)
Glycols and Related Compounds (Wagner andEllis, 1980)
Calcium Tetraformate (Berry, 1980)Asphalt Emulsion
Combined with cement, calcium aluminateminerals, and calcium sulfate(Higuchi, 1978)
Metal IonsMechanism unclear
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Guide to Improving the Effectiveness of Cement-Based Stabilization/Solidification
Cement Kiln DustSource of lime
Of all of these additives, calcium chloride, lime,cement kiln dust, sodium silicate (see below), and theproprietary concrete set retarders have been most usedin S/S technology.
Anti-Inhibition. These additives function in the samemanner as accelerators in many cases, and thus arebasically the same materials. However, some additivesnot normally used in concrete technology are used inS/S. An example of this is sodium silicate, which reactswith interfering metals and other waste componentsand also causes acceleration of initial set by very rap-idly forming a silicate gel.
Retardation. To date, most applications of set retardersin S/S systems have been with the proprietary setretarders commonly used in concrete ready-mix batchplants. These applications have been for in-situ S/Swhere the pumpable grout is made up first, and theninjected into the waste, requiring it to remain pumpablefor up to several hours before beginning to set. Otherretarders are:
Sugars and Derivatives(Metcalf and Ellers, 1980) (Industrial WaterEngineering, 1970)
Excessive Water Content. Excessive water in the wastecan result in supernatent liquid on the surface aftersetting and in low strength in the cured waste form.Additives used to counter these problems are of threetypes: accelerators to reduce set time; bulking agents orsorbents to reduce the free water; and gellants to in-crease viscosity of the system. Accelerators were dis-cussed in Section IV, gellants in Section II. Bulkingagents commonly used are listed below:
FlyashCement Kiln DustBlast Furnace Slag (Chudo et al., 1981)Corn Cob, Wood Chips, etc.
V. PHYSICAL/CHEMICAL TECHNIQUESUSED IN CEMENT-BASEDSTABILIZATION/SOLIDIFICATION
In addition to additives, other techniques are used inS/S to improve the properties of the product, to aid inprocessing, and to immobilize or destroy various con-stituents of concern.
Anti-Inhibition Aids
There are some physical, non-additive techniques thatcan be used to counter the effects of inhibiting materi-als in the waste.
Aeration. Aeration can serve several purposes: alter-ation of biological status of the waste, which mayprevent the formation of inhibiting film formers onthe surfaces of the cement binder; and removal ofinterfering VOCs.
Temperature Adjustment. This technique can be usedboth to improve the leaching characteristics of the wasteform produced by S/S (Vejmelka et al., 1985), and toaccelerate the reaction rate to counter retarding effects.
Physical Property Development
Humidity Control. Ambient humidity in the curingarea must be kept high if the product is to cure properly.Evaporation of water from the surface will inhibit orstop solidification, and perhaps some fixation reactionsin the surface layer. In the laboratory, samples arenormally cured at about 95% relative humidity to pre-vent this effect from masking the real solidificationreactions. In very hot and dry field conditions, espe-cially where the layer of curing S/S product is thin, itmay be necessary to keep the waste moistened as itcures, much as is done with concrete under the sameconditions.
Dewatering. Removal of excess water by physicalmeans is often less costly than the use of additives toabsorb the water.
Air Entrainment. This technique may be useful insome cases where maximum freeze/thaw resistanceis required. It generally employs additives to aid inentrainment of air. Air entrainment is not known tohave been deliberately applied in the field.
Processing Aids
Viscosity/Pumpability Alteration. Water reducingagents, flyash (Industrial Water Engineering, 1970),and natural clays (attapulgite and illite) (IndustrialWater Engineering, 1970) have been used to adjust theviscosity of grout formulations, especially for in-situS/S applications.
Elevated Temperature. S/S processes are chemical
23
PCA EB211
reactions and would be expected to follow the generalrules of such – that reaction rate usually increases withtemperature, perhaps according to the old rule-of-thumb that reaction rate doubles with each 10oC rise intemperature. S/S reaction rates do increase withtemperature, but there are limitations. Below freezingtemperatures can cause irreversible changes in thefinal product by breaking gel structures at a criticalstage, much as can happen with concrete. At very hightemperatures, release of steam can actually break upthe solid mass, and the loss of water can interfere withsubsequent curing reactions. This latter phenomenonis of concern in cement-based systems which are exo-thermic. Some additives also generate a large exothermand very rapidly. This must be considered whendesigning the mechanical aspects of the system. Also,the low heat transfer rate from a large mass of treatedwaste while curing can drive the internal temperatureto unacceptable levels, even though a laboratory testdid not indicate a potential problem. This, also, mustbe taken into consideration in the system design. Selfheating of the mass, however, is a valuable aid tocuring if it is kept under control and within limits. Tobe assured that cementitious reactions will start, thetemperature should be maintained above -3oC.
Mixing Techniques
Mixing is an important, sometimes critical, element ofany S/S process. While it seems obvious that thor-ough dispersion of the S/S reagents in the waste isimportant, it is also possible to over-mix certain sys-tems. Fluid wastes such as low-solids sludges areusually easiest to mix, while sticky sludges and filtercakes with the consistency of peanut butter are themost difficult. Soils, solid particulates, and granularmaterials fall in-between. Selection of a mixer is notonly determined by the physical characteristics of thewaste, however. Some wastes and some processes arequite sensitive to the energy input and shear rate of themixer. Use of a high-shear mixer with some wastesmay irreversibly alter their properties, causing phaseseparation. On the other hand, high-shear mixingmay be required to completely homogenize othermixtures—for example, to incorporate non-polar or-ganics in aqueous systems. High energy input mayhelp with some plastic, pseudoplastic, or thixotropicwastes by decreasing their viscosity temporarily, andby aiding in the reactions (Kitsugi, 1978) (Munster,1982). In rare cases, dilatent materials may literallysolidify in the mixer before reagents are even added.
Over-mixing, either by using the wrong mixer ormixing too long, interferes with the initial gel forma-
tion of cementitious S/S systems, causing delayed set,slow curing and even the loss of final physical proper-ties. An extreme example of this is seen in the use ofsoluble silicates, where it irreparably destroys thesilica gel structure, preventing the process from work-ing properly at all. Over-mixing can also go the otherway. Many a processor has had to dig out a mixerbecause the blend set up before it could be emptied.This usually happens in batch systems, but has alsobeen observed in continuous mixers when the mixer isstopped while full.
While it is widely assumed that very thoroughand intimate mixing is require to assure that reactionwill take place and fixation of hazardous constituentswill be complete, it is known that such mixing does nothappen with most in-situ techniques and still the endresult may be satisfactory. One investigation (Chemi-cal Waste Management, 1987) tentatively reached theconclusion that complete mixing at the microscopicscale is not always necessary in commercial S/S sys-tems. Other scientists have recently realized this asthey began to look at the microstructures of solidifiedwastes (Eaton et al., 1985). At this level, apparentlyunreacted waste conglomerates are evident, as areareas of unmixed reagent. The question now remains:At what size level can inhomogeneities exist and stillnot prevent the process from achieving its function?There is probably no single answer; it varies fromwaste to waste and process to process.
Ex-Situ Mixing. The choice of mixer is determined bythe rheological properties of the waste, the reagents tobe added (including how many and in what order), themode of operation (batch, continuous, or in-situ), thethrough-put rate, and the waste conveyance methods.For large volume operations with a continuous, rea-sonably consistent feed, continuous mixing usuallygives the best results at the lowest cost. For smallerprojects, and where the waste feed is very variable,batch mixing may be the only feasible method. Some-times the two are combined by accumulating a largebatch of waste and homogenizing it to provide a uni-form feed to a low through-put, continuous mixer untilthe batch is processed.
In-Situ Mixing. In-situ mixing is a special case untoitself. The equipment used is not generally thought ofas a mixer, but has some other primary function as, forexample, a backhoe, a drilling auger used for stabiliz-ing foundations, or a rock cutting head used in mining.More recently, specialized equipment has been appliedmore and more to this area, most of it being constructedby or for the S/S contractor himself. Several require-ments for state-of-the-art in-situ S/S that are peculiar to
24
Guide to Improving the Effectiveness of Cement-Based Stabilization/Solidification
in-situ work are deliberate retarding of the set to allowtime for handling, injection and mixing of a grout intothe waste, and the formulation of that grout.
VI. REFERENCES
Ader, M., Glod, E.F., and Fochtman, E.G .,U.S. Patent4,844,815, Jul. 4, 1989.
Allied Chemical Co., Treatment of Chromium WasteLiquors, New York, 1976.
American Society for Testing and Materials (ASTM),Temperature Effect On Concrete, Philadelphia, PA,1985, p.104.
Ashworth, R., “Some Investigations into the Use ofSugar as an Admixture to Concrete,” Proc. Inst.of Civil Engineering, London, 1965.
Battelle Columbus, Technical Resource Document So-lidification/Stabilization and Its Application to WasteMaterials 4-29 - 4-44, EPA/530/R-93/012, UnitedStates Environmental Protection Agency, RiskReduction Engineering Laboratory, Cincinnati,OH, Jun. 1993.
Benson, R.E. Jr., “Natural Fixing Materials for the Con-tainment of Heavy Metals in Landfills,” Proc. Mid-Atlantic Industrial Waste Conf., 1980, pp. 212-15.
Berry, D., U.S. Patent 4,191,584, Mar. 4, 1980.Bishop, P.L., “Leaching of Inorganic Hazardous Con-
stituents from Stabilized/Solidified HazardousWastes,” Hazardous Wastes & Hazardous Materi-als 5, No. 2, 1988, pp.129-43.
Blake, L.S., ed., Civil Engineer's Reference Book,Butterworths, London, 1975.
Bonnel, B. and Hevanee, C., U.S. Patent 3,656,985,Apr. 18, 1972.
Boyd, S.A. and Mortland, M.M., “Use of ModifiedClays for Absorption and Catalytic Destructionof Contaminants,” 13th Annual Research Sympo-sium at Cincinnati, U.S.EPA, Cincinnati, Jul. 1987.
Bricka, R.M. and Hill, D.O., “Metal Immobilization bySolidification of Hydroxide and Xanthate Slud-ges,” Environmental Aspects of Stabilization andSolidification of Hazardous and Radioactive Sludges,ASTM STP 1033, American Society for Testing andMaterials, Philadelphia, PA, 1989, pp. 257-272.
Caldwell, R.J., Cote, P.L., and Chao, C.C.,“Investi-gation of Solidification for the Immobilization ofTrace Organic Contaminants,” Hazardous Waste& Hazardous Materials 7, No. 3, pp. 273-282.
Carlson, J.E., “The Chemistry of Processing NuclearWaste with Portland Cement,” Chemical WasteManagement Stabilization Seminar, Jun. 4-5, 1987.
Chalasani, D., Cartledge,F.K., Eaton, H.C.,Tittlebaum, M.E., and Walsh, M.B., “The Effects
of Ethylene Glycol on a Cement-Based Solidifi-cation Process,” Hazardous Wastes & HazardousMaterials, 3, No. 2, 1986.
Chan, P.C., Liskowitz, J.W., Perna, A., and Trattner,R.,Evaluation of Sorbents for Industrial Sludge LeachateTreatment, EPA-600/2-80-052, U.S. EPA, Cincin-nati, 1980.
Chappell, C.L., U.S. Patent 4,230,568, Oct. 28, 1980.Chemical Engineering, May 2, 1979, pp. 83-4.Chemical Engineering, Feb. 15, 1988.Chemical Waste Management, Internal Study, 1987.Chemical Waste Management, Stabilization of Sb, Be,
Tl and V Using AA100, Geneva Research Center,Geneva, IL, 1992.
Chemical Waste Management, Private Communica-tion, 1994.
Chen, K.S., U.S. Patent 4,113,504, Sep. 12, 1978.Cherry, K.F., Plating Waste Treatment, Ann Arbor
Science Pub., Ann Arbor, MI, 1982.Chudo, A., Sugi, T., and Katsoka, K., U.S. Patent
4,266,980, May 12, 1981.Conner, J.R., U.S. Patent 3,837,872, Sep. 24, 1974.Conner, J.R., U. S. Patent 4,518,508, May 21, 1985.Conner, J.R., U.S. Patent 4,623,469, Nov. 18, 1986.Conner, J.R., U.S. Patent 4,600,514, Jul. 15, 1986a.Conner, J.R., U.S. Patent 5,078,795, Jan. 7, 1992.Conner, J., Chemical Fixation and Solidification of Haz-
ardous Wastes, Van Nostrand Reinhold, NewYork, NY, 1990, pp. 77-102, 298-304.
Conner, J.R. and Lear, P.R., “Immobilization of Low-Level Organic Compounds in HazardousWaste,” Proc. Air and Waste Management 84thAnnual Meeting, Vancouver, BC, 1991.
Conner, J.R. and Lear, P.L., Treatment of Landban-Varianced Arsenic Wastes at TSDFs, ChemicalWaste Management, Geneva, IL, 1992.
Conner, J.R. and Rieber, R.S., U.S. Patent 5,078,795,Jan. 7, 1992.
Conner, J.R., “Advanced Stabilization Methods forTreatment of Hazardous Wastes,” Conference onChemical-Physical Treatment of Industrial Wastes,Univ. of Brescia, Italy, Jun. 17-18, 1993a.
Conner, J.R., “Recent Findings on Immobilization ofOrganics as Measured by Total ConstituentAnalysis,” Waste Management 15, Nos. 5/6, 1995,pp.359-369.
Conner, J.R. and Smith, F.G., “Immobilization ofLow-level Hazardous Organics Using RecycledMaterials,” Third International Symposium on Sta-bilization/Solidification of Hazardous, Radioactive,and Mixed Wastes, Williamsburg, VA, Nov. 1-5,1993.
Conner, J.R., Private Communication, 1993.Conner, J.R., Li, A., and Cotton, S., “Stabilization of
25
PCA EB211
Hazardous Waste Landfill Leachate TreatmentResidue,” Journal of Hazardous Materials 24, 1990,pp.111-121.
Coté, P., Contaminant Leaching From Cement-Based WasteForms Under Acidic Conditions, PhD Thesis,McMaster Univ., Hamilton, ON, Canada, 1986.
Cullinane, J.M., Jr., Jones, L.W., and Malone, P.G.,Handbook for Stabilization/Solidification of Hazard-ous Waste, EPA/540/2-86/001, U.S. EPA, Cincin-nati, OH, 1986.
Cullinane, M.J., Bricka, R.M., and Francingues, Jr.,N.R.,“An Assessment of Materials That Interferewith Stabilization/Solidification Processes,” InProc. 13th Annual Research Symposium, U.S.EPA,Cincinnati, OH, 1987, pp. 64-71.
Dzombak, D.A. and Morel, F.M., “Development of aData Base for Modeling Adsorption of Inorganicson Iron and Aluminum Oxides,” EnvironmentalProgress 6, No. 2, 1987, pp. 133-7.
Eary, L.E. and Rai, D., “Chromate Removal fromAqueous Wastes by Chromium Reduction withFerrous Ion,” Environmental Science Technology22, No. 8, 1988, pp. 972-7.
Eaton, H.C., Walsh,M.B., Tittlebaum,M.E., Cartledge,F.K., and Chalasani, D., “Organic Interference ofSolidified/Stabilized Hazardous Wastes,” Envi-ronmental Monitoring and Assessment 9, 1987, pp.133-142.
Eaton, H.C., Walsh, M.B., Tittlebaum, M.E., Cartledge,F.K., and Chalasani, D., “Microscopic Character-ization of the Solidification/Stabilization of Or-ganic Hazardous Wastes,” Energy Sources andTechnology Conference and Exhibition, ASME Pa-per No. 85-Pet-4, 1985.
Electric Power Research Institute, In-SituSolidification/Stabilization of Arsenic Contaminated Soils - DraftReport, Palo Alto, CA, Apr. 1996.
El-Korchi, T., Melchinger, K., Kolvites, B., and Gress, D.,The Effect of Heavy Metals and Organic Solvents on theMicrostructure of Cement Stabilized Hazardous Waste,University of New Hampshire, 1990.
Environmental Science Technology 16, No. 12, 1982, 641a.Environmental Technologies Alternatives, Inc., Con-
trol of Air Emissions in Hazardous Waste Stabiliza-tion Operations, KAX-50™ Technical Bulletin TB-214, Port Clinton, OH, 1994.
Environmental Technologies Alternatives, Inc., Im-mobilization of Organics in Debris and Characteristic(D-code) Wastes, Technical Bulletin TB-234, PortClinton, OH, 1994a.
Environmental Technologies Alternatives, Inc., KAX100™ Technical Bulletin, Port Clinton, OH, 1995.
Falcoux, P., Filhol, R., and Communal, J., U.S. Patent4,238,236, Dec. 9, 1980.
Federal Register: 48(176), Sep. 14, 1993, pp. 48092-48204.Feigenbaum, H.N., “The Sulfex™ Process for Re-
moval of Heavy Metals in a Textile WasteStream,” Proc. Textile Wastewater Treatment andAir Pollution Control Conference, Jan. 1977.
Gilliam, T.M., Dole, L.R., and McDaniel, E.W.,“Waste Immobilization in Cement-BasedGrouts,” Hazardous and Industrial Solid WasteTesting and Disposal: Sixth Volume, ASTM STP933, American Society for Testing and Materi-als, Philadelphia, PA, 1986, pp. 295-307.
Gilliam, T.M. and Wiles, C.C., eds., Stabilization andSolidification of Hazardous, Radioactive, and MixedWastes, 3rd Volume, STP 1240, ASTM, WestConshohocken, PA, 1996.
Harada, Y., Itai, N., Uchikawa,H., Kato, H., Sato, K.,and Itoh, A., U.S. Patent 4,060,425, Nov. 29, 1977.
Higuchi, Y., Harada, Y., Nakagawa, K., Kawaguchi, I.,and Kasahara, Y., U. S. Patent 4,084,981, Apr. 18,1978.
Industrial Water Engineering, Oct. 1970.Japan Kokai 70/40,797, Oct. 20, 1980.Kantro, D.L., “Tricalcium Silicate Hydration in the
Presence of Various Salts,” ASTM Journal OfTesting and Evaluation, July, 1975.
Kawasaki Steel Corp., Japan Kokai 80,136,166, 1980.Kitsuge, K. and Kozeki, S., U.S. Patent 3,947,283,
Mar. 30, 1976.Kitsugi, K., U.S. Patent 3,947,284, Mar. 30, 1976.Kitsugi, K. and Shimoda, M., Japan Kokai 78 12,770,
Feb. 4, 1978.Knocke, W.R., Croy,L.P., and Kelley, R.T., An Evalu-
ation of the Solids Handling Characteristics of SludgeProduced by Two Metals’ PrecipitationTechniques, Virginia Polytechnic Institute,Blacksburg, VA, 1977.
Kokusai, G., Japan Kokai 81 53,796, May 13, 1981.Lagvankar, A., Mayenkar, K., and Pherson, P.A.,
“An Innovative Process for Removing HeavyMetals from Wastewater,” 59th Annual MeetingCentral States Water Pollution Control Association,May 14-16, 1986.
Lawson, M.A., Venn, J.G., Pugh, L.B., and Vallis, T.,Stabilization and Solidification of Hazardous, Radio-active, and Mixed Wastes, 3rd Volume, ASTMSTP 1240, West Conshohocken, PA, 1996.
Manahan, S.E. and Smith, M.J., “The Importance ofChelating Agents,” Water and Sewage Works, 1973,pp. 102-6.
Metcalf, A.S. and Ellers, L.H., U.S. Patent 4,210,455,Jul. 1, 1980.
Morse, J.G. and Dennis, D., “Assessment and Cleanupof Soils Using In Situ Stabilization at a Manufac-tured Gas Plant Site,” At 87th Annual Meeting &
26
Guide to Improving the Effectiveness of Cement-Based Stabilization/Solidification
Exhibition, AWMA, Cincinnati, Jun. 19-24, 1994.Munster, L., U.S. Patent 4,338,134, July 6, 1982.Nakaaki, O., Horie, Y., Idohara, M., and Shiraogi, J.,
Japan Kokai 75,99,962, Aug. 8, 1975.Navickis, L.L., Wing, R.E., and Bagley, E.B., “AISX
Reduces Selenium Count in Process Wastewa-ters,” Industrial Wastes, Jan./Feb. 1979, pp. 26-30.
Nelson, D.A., “Removal of Heavy Metal Ions fromAqueous Solution with Treated Leather,” Ameri-can Chemical Society, Houston, TX, 1980.
Onoda Cement Co., U.S. Patent 3,947,284, Mar. 30, 1976.Patterson, J.W., Allen, H.E., and Scala, J.J., “Carbonate
Precipitation from Heavy Metals Pollutants,” Jour-nal of the Water Pollution Control Federation 12,1977, pp. 2397-410.
Pojasek, R.B., Toxic and Hazardous Waste Disposal, Vol.1-4, Ann Arbor Science Pub., Ann Arbor, 1980.
Portland Cement Association, Portland Cements,Skokie, IL, 1974.
Portland Cement Association, Design and Control ofConcrete Mixtures, Skokie, IL, 1979.
Posselt, H.S. and Anderson, F.J., “Cation Sorption onColloidal Hydrous Manganese Dioxide,” Envi-ronmental Science Technology 2, 1968, pp. 1087-93.
Rosskopg, P.A., Linton, F.J., and Peppler, R.B., “Effectof Various Accelerating Chemical Admixtures onSetting and Strength Development of Concrete,”Journal of Testing and Evaluation 3, No. 4, 1975.
Sano, M., Sugano, I., and Okuda, T., Japan Kokai75,133,654, Oct. 23, 1975.
Shinoki, K., Katayame, T., and Yamaguchi, S., JapanKokai 80 44,355, Mar. 28, 1980.
Siegrist, R.L. et al., “In-situ Treatment of Clay Soils byPhysicochemical Processes Coupled with SoilMixing: Highlights of the X-231b Technology Dem-onstration,” At I&EC Special Symposium, ACS, At-lanta, GA, Sep. 21-23, 1992.
Sittig, M., Pollutant Removal Handbook, Noyes DataCorp., London, 1973.
Soundararajan, R., Barth, E.F., and Gibbons, J.J., “Us-ing an Organophilic Clay to Chemically StabilizeWaste Containing Organic Compounds,” Haz-ardous Materials Control, Jan./Feb. 1990.
Spence, R.D., Gilliam, T.M., Morgan, I.L., and Osborne,S.C., “Stabilization/Solidification of Wastes Con-taining Volatile Organic Compounds in Commer-cial Cementitious Waste Forms,” Presented at 2ndInternational Symposium on S/S of Hazardous, Radio-active and Mixed Wastes, Williamsburg, VA, May29-Jun. 1, 1990.
Spence, R., Chemistry and Microstructure of SolidifiedWaste Forms, Lewis Publishers, Ann Arbor, MI,1992.
Swallow, K.C., Hume, D.N., and Morel, F.M., “Sorp-
tion of Copper and Lead by Hydrous FerricOxide,” Environmental Science Technology 14,No. 11, 1980, pp. 1326-31.
Takashita, I., Japan Kokai 79,162,844, 1979.United States Environmental Protection Agency, Guide
to the Disposal of Chemically Stabilized and SolidifiedWaste, SW-872, Office of Solid Waste and Emer-gency Response, Washington, DC, Sep. 1982.
United States Environmental Protection Agency, Fed-eral Register 50, No. 105, May 31, 1985, pp. 23250.
United States Environmental Protection Agency,Cleaning Up the Nation’s Waste Sites: Markets andTechnology Trends, EPA 542-H-92-012, Washing-ton, DC, April, 1993.
United States Environmental Protection Agency, Fed-eral Register 55, No. 61, Mar. 29, 1990, pp. 11798-11877.
United States Environmental Protection Agency,Federal Register 56, No. 140, Jul. 22, 1991, pp.33490-33579.
United States Environmental Protection Agency,Technical Resource Document: Solidification/Stabi-lization and its Application to Waste Materials,EPA/530/R-93/012, Office of Research andDevelopment, Washington, DC, Jun. 1993.
United States Environmental Protection Agency,Land Disposal Restrictions Phase II — UniversalTreatment Standards, and Treatment Standards forOrganic Toxicity Characteristics Wastes and NewlyListed Wastes, Final Rule, 40 CFR 148, Sep. 1994,pp. 260-261, 264-266, 268, 271.
United States Environmental Protection Agency,Innovative Treatment Technologies: Annual StatusReport (Seventh Edition) Applications of New Tech-nologies at Hazardous Waste Sites, EPA-542-R-95-008, Office of Solid Waste and Emergency Re-sponse, Sep. 1995.
U.S. Army Corps of Engineers Waterways Experi-ment Station, U.S. Patent 3,642,503, InterferenceMechanisms in Waste Stabilization/Solidification Pro-cesses, EPA 600/2-89/067, United States Environ-mental Protection Agency, Risk Reduction Engi-neering Laboratory, Cincinnati, OH, Jan. 1990.
Vail, J.G., Soluble Silicates, Reinhold, New York, 1952.Veda, S. and Ito,M., Japan Kokai 77 38,468, Mar. 25,
1977.Vejmelka, P.R., Kosher, and Hauler, W., U.S. Patent
4,533,395, Aug. 6, 1985.Wagner, H.B. and Ellis, J.R., U.S. Patent 4,211,572,
Jul. 8, 1980.Walsh, M.B., Eaton, H.C., Tittlebaum, M.E.,
Cartledge, F.K., and Chalasani, D., “The Effect ofTwo Organic Compounds on a Portland Ce-ment-Based Stabilization Matrix,” Hazardous
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Wastes & Hazardous Materials 3, No. 1, 1986.Weiner, R.F., “Acute Problems in Effluent Treat-
ment,” Plating 54, 1967, pp. 1354-6.Weitzman, L., Hamel, L.E., and Cadmus, S.R., Vola-
tile Emissions From Stabilized Waste In HazardousLandfills, U.S.EPA Contract 68-02-3993, ResearchTriangle Park, Aug. 28, 1987.
Wing, R.E., “Corn Starch Compound Recovers Met-als from Water,” Industrial Wastes, Jan./Feb. 1975,pp. 26-7.
Yagi, T., Japan Kokai 75,105,541, Aug. 20, 1975.Yagi, T. and Matsunaga, S., Japan Kokai 76,123,775,
Oct. 28, 1976.Yamagisi, H., Sakamaki, S., Nakagawa, K., and
Sirasawa, M., U.S. Patent 4,190,454, Feb. 26, 1980.Young, J.F., “A Review of the Mechanisms of Set-
Retardation of Cement Pastes Containing Or-ganic Admixtures,” Cement and Concrete Research2, No. 4, 1972.
Young, D.A., U.S. Patent 4,142,912, Mar. 6, 1979.
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Guide to Improving the Effectiveness of Cement-Based Stabilization/Solidification
Additive Effect RelativeCost
pH Control andBuffering:
pH adjustment; removal of interferingsubstances from solution; destruction of gelsand film-formers
Lime - CaO or Ca(OH)2 Neutralizes acids, raises pH Low
Sodium hydroxide Neutralizes acids, raises pH Low
Sodium carbonate Neutralizes acids, raises pH Low
Sodium bicarbonate Buffer Low
Magnesium oxide Buffer Moderate
Ferrous sulfate Lowers pH, alkalinity Low
Sulfuric acid Lowers pH, alkalinity Low
Reduction: Alteration of valence state of metals
Ferrous sulfate Reducing agent in acid conditions Low
Sodium hydrosulfite Reducing agent in alkaline conditions Moderate
Sodium metabisulfite Reducing agent in acid conditions Low
Blast furnace slag Reducing agent Low
Metallic iron Reducing agent Low
Oxidation: Alteration of valence state of metals;destruction/conversion of interferingsubstances
Potassiumpermanganate
Powerful, non-selective oxidizing agent;alteration of biological status
High
Sodium or potassiumpersulfate
Powerful, non-selective oxidizing agent;alteration of biological status
High
Sodium or calciumhypochlorite
Non-selective oxidizing agent; alteration ofbiological status
High
Hydrogen peroxide Mild, non-selective oxidizing agent;alteration of biological status
Moderate
Speciation, Re-Speciation:
Alteration of the species of the constituentsof concern to fix metals and other ions
Carbonates With lead, forms carbonates, basiccarbonates
Low
Iron and aluminumcompounds
Various Low tomoderate
Table 1. Additives Used in Cement-based S/S
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Table 1. Additives Used in Cement-based S/S
Phosphoric acid andsalts
With lead, forms phosphate compounds thathave low solubility through a wide pH range
Low tomoderate
Sodium silicate Forms low-solubility, silicate species with avariety of metals in solution; anti-inhibitor
Low tomoderate
Sodium sulfide Forms metal sulfides, except with chromium Low
Calcium polysulfide Forms metal sulfides, except with chromium Low
Organic sulfurcompounds -thiocarbamates
Forms metal sulfides, except with chromium;safer than inorganic sulfides
Moderate
Sulfur + alkali Forms metal sulfides, except with chromium Low
Xanthates Form low-solubility starch or cellulosexanthate substrates with metals attached
Moderate
Sodium chloride Silver fixant Low
Sodium sulfate Barium fixant Low
Ferrous sulfate Removes sulfide ion from solution Low
Precipitation andFlocculation:
Aggregation of fine particles and film-formers; dispersion of oils and greases andfine particulates away from reactingsurfaces
Ferrous sulfate Co-precipitating agent Low
Proprietary organicflocculants, surfactants
Flocculants and dispersants Low tomoderate
Alcohols Wetting agent Low tomoderate
Amides Wetting agent Low tomoderate
Carboxylic acids Dispersants Moderate
Aldehydes and Ketones Dispersants Moderate
Sulfonates Dispersants Moderate
Amines Flocculants Moderate
Iron salts Flocculants Low
Magnesium salts Flocculants Low toModerate
Silica Flocculants Low
Additive Effect Relative Cost
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Guide to Improving the Effectiveness of Cement-Based Stabilization/Solidification
Table 1. Additives Used in Cement-based S/S
Additive Effect Relative Cost
Sorption, Bulking,StructuralModification:
Removal of interfering substances fromreacting surfaces; immobilization of organicspecies; free water reduction; viscositycontrol; improvement of microstructure
Activated carbon Sorbent for organics, especially VOCs,organo-metallics, and some metals
High
Organoclays Sorbent for organics High
Rubber particulate Sorbent for organics, especially SVOCs Moderate
Fly ash Sorbent for some metals and organics;pozzolanic reaction with alkalies; bulkingagent
Low
Rice hull ash Sorbent for organics, especially VOCs;reacts with alkalies to form soluble silicates
Moderate
Natural clays Sorbents for some metals; bulking agent;viscosity control
Low
Expanded minerals Sorbents for some metals; bulking agent Low tomoderate
Diatomaceous earth Sorbents for some metals; bulking agent Low tomoderate
Blast furnace slag Pozzolanic reaction with alkalies; bulkingagent; reducing agent; structuralmodification
Low
Silica fume Pozzolanic reaction with alkalies; bulkingagent; structural modification
Low
Wood chips Sorbent; bulking agent Low
Ground corn cob Sorbent; bulking agent Low
Cement kiln dust Pozzolanic bulking agent, as well asaccelerator in some cases
Low
Acceleration/Anti-Inhibition:
Counter the effects of set retarders in waste;accelerate the normal set time of cement-based systems
Calcium chloride Accelerates set Low
Calcium aluminate Accelerates set Low
Calcium sulfate Accelerates set Low
Glycols Accelerates set Moderate
31
PCA EB211
Table 1. Additives Used in Cement-based S/S
Additive Effect Relative Cost
Sugar Accelerates set Moderate
Amines Accelerates set Moderate
Organic acid salts Accelerates set Moderate
Lime Supplies additional calcium for reaction;reacts with certain interfering organics; anti-inhibitor; controls biological status
Low
Sodium silicate Reacts with interfering metals; anti-inhibitor;causes acceleration of initial set; fixesmetals
Low tomoderate
Iron compounds Counters effect of tin, lead arsenates,sulfides by reaction
Low
Triethanolamine Accelerates set Moderate
Calcium formate Accelerates set Moderate
Phosphates Accelerates set Low
Bentonite Sorbs oils, organics; anti-inhibitor Low
Cement kiln dust Accelerator in some cases Low
Retardation: Retardation of setting to allow for betterprocessing control
Sugar Retards of setting at low levels Low
Sugar derivatives Retards setting Moderate
Zinc hydroxide Retards setting Low
Copper hydroxide Retards setting Low
Lead hydroxide Retards setting Low
Calcium chloride >4% Retards setting Low
Magnesium salts Retards setting Low
Tin salts Retards setting Low
Phosphates Retards setting Low
Lignosulfonic acid saltsand derivatives
Retards setting Low toModerate
Hydroxy carboxylicacids
Retards setting Low toModerate
Polyhydroxycompounds
Retards setting Low toModerate
32
Guide to Improving the Effectiveness of Cement-Based Stabilization/Solidification
Table 1. Additives Used in Cement-based S/S
Additive Effect Relative Cost
Free Water Control: Control (usually reduction) of the free watercontent of the system
Slag Bulking agent; pozzolan Low
Flyash Bulking agent; pozzolan Low
Concrete waterreducing additives
Reduce water requirement whereapplicable
Low tomoderate
Cement kiln dust Bulking agent, pozzolan Low
Miscellaneous:
Biocides Counter biological activity Moderate
Organic polymers Fill pores, improve microstructure, improvedurability
Moderateto High
Air entrainmentadditives
Improve durability Low toModerate
Wood resins Improve durability Moderate
33
PCA EB211
Tab
le 3
. S
olid
ific
atio
n P
rob
lem
s
PR
OB
LE
MP
RO
BA
BLE
CA
US
E -
WA
ST
EC
HA
RA
CT
ER
IST
ICS
,IN
GR
ED
IEN
TS
AP
PR
OA
CH
TO
SO
LUT
ION
SP
EC
IFIC
AD
DIT
IVE
S O
RT
EC
HN
IQU
ES
US
ED
AD
DIT
ION
RA
TIO
RA
NG
E(w
eigh
t %)
CO
ST
RA
NG
E($
per
ton
of w
aste
trea
ted)
Will
not
set
1.
Fin
e pa
rtic
ulat
es:
silt,
clay
, co
lloid
al m
atte
r2.
A
naer
obic
con
ditio
ns3.
C
alci
um r
emov
ers
1.
Sur
face
act
ive
agen
ts:
wet
ting
agen
ts,
disp
ersa
nts,
flo
ccul
ants
2.
Aer
ate;
add
oxi
dize
r,lim
e, b
ioci
de3.
R
epla
ce lo
st c
alci
um
1.
Iron
sal
ts,
ferr
ous
sulfa
te,
mag
nesi
um s
alts
, si
lica,
as
phal
t em
ulsi
ons,
alc
ohol
sam
ides
, am
ines
, ca
rbox
ylic
acid
s, c
arbo
nyls
, su
lfona
tes
2.
Air,
oxy
gen,
lim
e,ca
lciu
m/s
odiu
m h
ypoc
hlor
ite,
prop
rieta
ry b
ioci
de3.
Li
me,
cal
cium
chl
orid
e,g
ypsu
m
1.
0.01
- 1
.02.
1
- 5
3.
1 -
10
1. <
1 -
202.
1
- 25
03.
1
-25
Set
s, b
ut d
oesn
’th
ard
en
1.
Fin
e pa
rtic
ulat
es:
silt,
clay
, co
lloid
al m
atte
r2.
A
naer
obic
con
ditio
ns
1.
Sur
face
act
ive
agen
ts:
wet
ting
agen
ts,
disp
ersa
nts,
flo
ccul
ants
2.
Aer
ate;
add
oxi
dize
r,l im
e, b
ioci
de3.
R
epla
ce lo
st c
alci
um
1.
Iron
sal
ts,
ferr
ous
sulfa
te,
mag
nesi
um s
alts
, si
l ica,
as
phal
t em
ulsi
ons,
alc
ohol
sam
ides
, am
ines
, ca
rbox
ylic
acid
s, c
arbo
nyls
, su
lfona
tes
2.
Air,
oxy
gen,
lim
e,ca
lciu
m/s
odiu
m h
ypoc
hlor
ite,
prop
rieta
ry b
ioci
de3.
Li
me,
cal
cium
chl
orid
e,g
ypsu
m
1.
0.01
- 1
.02.
1
- 5
3.
1 -
10
1. <
1 -
202.
1
- 25
03.
1
-25
34
Guide to Improving the Effectiveness of Cement-Based Stabilization/Solidification
Tab
le 3
. S
olid
ific
atio
n P
rob
lem
s (c
on
tin
ued
)
Set
is
reta
rded
1.
Fin
e pa
rtic
ulat
es:
silt,
clay
, co
lloid
al m
atte
r2.
S
ugar
3.
Pho
spha
tes
4.
Sul
fur
5.
Bic
arbo
nate
s of
sodi
um a
nd p
otas
sium
6.
Che
mic
alin
terf
eren
ce:
a.
Ino
rgan
ics:
met
alsa
lts,
sodi
um i
odat
e,so
dium
pho
spha
te,
sodi
um a
rsen
ate,
sodi
um b
orat
e, s
odiu
msu
lfide
b.
Che
latin
g ag
ents
c.
Org
anic
s7.
M
i ld a
naer
obic
cond
ition
s8.
In
suffi
cien
t cu
re t
ime
9.
Gen
eral
set
reta
rdat
ion
1.
Sur
face
act
ive
agen
ts:
wet
ting
agen
ts,
disp
ersa
nts,
flo
ccul
ants
2a.
Add
mor
e su
gar
-
0
.2%
2b.
Add
a s
orbe
nt3.
Add
cal
cium
ion
4.
Non
e es
tabl
ishe
d5.
U
se a
cidi
c m
ater
ial t
od
eco
mp
ose
6a,b
. A
dd a
n ac
cele
rato
ror
ant
i-inh
ibito
r6c
. A
dd a
sor
bent
,ox
idan
t, ac
cele
rato
r or
anti-
inhi
bito
r7.
A
erat
e; a
dd o
xidi
zer,
l ime,
bio
cide
8.
Cur
e lo
nger
9.
Add
a g
ener
alac
cele
rato
r C
alci
um c
hlor
ide
1.
Iron
sal
ts,
ferr
ous
sulfa
te,
mag
nesi
um s
alts
, si
lica,
as
phal
t em
ulsi
ons,
alc
ohol
sam
ides
, am
ines
, ca
rbox
ylic
acid
s, c
arbo
nyls
, su
lfona
tes
2a.
Sug
ar2b
. C
lay,
fly
ash,
diat
omac
eous
ear
th,
carb
on3.
Li
me,
gyp
sum
, ca
lciu
mch
lorid
e5.
A
cids
, fe
rrou
s su
lfate
6a,b
. S
ulfa
tes,
sol
uble
sil ic
ates
, al
umin
ates
,ph
osph
ates
, hy
drox
ylat
edor
gani
c ac
ids,
gly
cols
, am
ines
,iro
n co
mpo
unds
, A
ST
M s
etac
cele
rato
rs6c
. C
lay,
lim
e, li
mes
tone
,fly
ash,
car
bon;
hyd
roge
npe
roxi
de,
pota
ssiu
mpe
rman
gana
te,
sodi
umpe
rsul
fate
, ca
lciu
m/s
odiu
mhy
poch
lorit
e; a
lso
see
6a,b
ab
ove
7.
Air,
oxy
gen,
lim
e,ca
lciu
m/s
odiu
m h
ypoc
hlor
ite,
prop
rieta
ry b
ioci
de9.
C
alci
um c
hlor
ide,
sod
ium
silic
ate,
lim
e
1.
0.01
- 1
.02a
. >
0.2
2b.
.5 -
53.
1
- 5
5. 0
.1 -
10
6a,b
. 0.
01 -
56c
. 0.
1 -
107.
0.1
- 5
9.
1 -
5
1. <
1 -
202a
. <
1 -
202b
. 1
- 10
3.
1 -
55.
<1
- 5
6a,b
. 1
- 25
6c.
1 -
100
7.
2 -
109.
1
- 10
PR
OB
LE
MP
RO
BA
BLE
CA
US
E -
WA
ST
EC
HA
RA
CT
ER
IST
ICS
,IN
GR
ED
IEN
TS
AP
PR
OA
CH
TO
SO
LUT
ION
SP
EC
IFIC
AD
DIT
IVE
S O
RT
EC
HN
IQU
ES
US
ED
AD
DIT
ION
RA
TIO
RA
NG
E(w
eigh
t %)
CO
ST
RA
NG
E($
per
ton
of w
aste
trea
ted)
35
PCA EB211
Tab
le 3
. S
olid
ific
atio
n P
rob
lem
s (c
on
tin
ued
)
PR
OB
LE
MP
RO
BA
BLE
CA
US
E -
WA
ST
EC
HA
RA
CT
ER
IST
ICS
,IN
GR
ED
IEN
TS
AP
PR
OA
CH
TO
SO
LUT
ION
SP
EC
IFIC
AD
DIT
IVE
S O
RT
EC
HN
IQU
ES
US
ED
AD
DIT
ION
RA
TIO
RA
NG
E(w
eigh
t %)
CO
ST
RA
NG
E($
per
ton
of w
aste
trea
ted)
Su
pe
rna
ten
tliq
uid
on s
urfa
ceaf
ter
setti
ng(U
sual
ly d
ue t
ola
rge
part
icle
siz
ean
d/or
hig
hpa
rtic
le s
peci
ficgr
avity
in lo
wca
lciu
m/s
odiu
mhy
poch
lori
tevi
scos
itym
ed
ium
)
1.
Set
is t
oo s
low
2.
Wat
er c
onte
nt i
s to
ohi
gh3.
V
isco
sity
of
syst
em is
too
low
1.
Add
set
acc
eler
ator
or a
nti-i
nhib
itor:
2.
Dew
ater
or
sorb
wat
er3.
In
crea
se v
isco
sity
of
syst
em
1. S
ulfa
tes,
sol
uble
sili
cate
s,al
umin
ates
, ph
osph
ates
,hy
drox
ylat
ed o
rgan
ic a
cids
,gl
ycol
s, a
min
es,
iron
com
poun
ds,
AS
TM
set
acce
lera
tors
2.
Dec
ant
wat
er;
filte
r ra
ww
aste
; ad
d fly
ash,
cla
y, s
lag,
sil ic
a fu
me,
woo
d ch
ips,
grou
nd c
orn
cob,
diat
omac
eous
ear
th,
expa
nded
min
eral
s
3.
Gel
l ing
agen
t -
sodi
umsi
licat
e; s
orbe
nt -
see
(2)
ab
ove
1.
1-10
2.
5-50
3.
1-50
1.
2-20
2.
0-25
3.
0-25
Set
s to
o ra
pidl
yfo
r sa
tisfa
ctor
ypr
oces
sing
1.
Acc
eler
atin
g ag
ents
:su
lfate
s; s
olub
lesi
l icat
es,
alum
inat
es,
ph
osp
ha
tes;
hydr
oxyl
ated
org
anic
acid
s, g
lyco
ls,
othe
ror
gani
cs;
ion
exch
ange
mat
eria
l2.
C
arbo
nate
s an
dbi
carb
onat
es o
f so
dium
and
pota
ssiu
m3.
S
ugar
> 0
.2%
1.
Add
set
ret
arde
r2.
D
ecom
pose
or
neut
raliz
e w
ith a
cidi
cad
ditiv
e3a
. A
dd r
etar
der
3b.
Che
mic
al o
xida
tion
1.
Pro
prie
tary
, co
ncre
te s
etre
tard
er;
zinc
, co
pper
or
lead
oxid
e/hy
drox
ide;
cal
cium
chlo
ride
(>4%
0; m
agne
sium
and
tin s
alts
; ph
osph
ates
,cl
ays
2.
Fer
rous
sul
fate
, su
lfuric
aci
d3a
. S
ee (
1) a
bove
3b.
Hyd
roge
n pe
roxi
de,
calc
ium
/sod
ium
hyp
ochl
orite
,po
tass
ium
per
man
gana
te,
sodi
um p
ersu
lfate
1.
0.01
- 5
2.
1 -
103a
. 0
.01
- 5
3b.
1 -
10
1.
2 -
52.
<1
- 20
3a.
2 -
53b
. 5
- 2
50
36
Guide to Improving the Effectiveness of Cement-Based Stabilization/Solidification
PR
OB
LE
MP
RO
BA
BLE
CA
US
E -
WA
ST
EC
HA
RA
CT
ER
IST
ICS
,IN
GR
ED
IEN
TS
AP
PR
OA
CH
TO
SO
LUT
ION
SP
EC
IFIC
AD
DIT
IVE
S O
RT
EC
HN
IQU
ES
US
ED
AD
DIT
ION
RA
TIO
RA
NG
E(w
eigh
t %)
CO
ST
RA
NG
E($
per
ton
of w
aste
trea
ted)
Tab
le 3
. S
olid
ific
atio
n P
rob
lem
s (c
on
tin
ued
)
Insu
ffic
ient
un
con
fine
dco
mpr
essi
vest
reng
th (
AS
TM
D-2
166,
D-1
633)
1.
Che
mic
alin
terf
eren
ce:
met
al s
alts
,le
ad n
itrat
e, s
odiu
mio
date
, so
dium
phos
phat
e, s
odiu
mar
sena
te,
sodi
umbo
rate
, so
dium
sul
fide
2.
Sod
ium
sul
fide,
sodi
um s
ulfit
e, s
odiu
mhy
drox
ide
3.
Sug
ar4.
A
lgae
5.
Ana
erob
ic c
ondi
tions
6.
Oil
and
grea
se7.
P
heno
l8.
W
ater
con
tent
too
high
9.
Cem
ent
cont
ent
too
low
1. A
dd a
n ac
cele
rato
r or
anti-
inhi
bito
r2.
Ir
on s
alts
; ch
emic
alox
idat
ion;
aci
d3.
C
hem
ical
oxi
datio
n
4a.
Add
sor
bent
4b.
Che
mic
al o
xida
tion
4c.
Add
lim
e4d
. A
dd b
ioci
de5.
A
erat
e; a
dd o
xidi
zer,
l ime,
bio
cide
6a.
Che
mic
al o
xida
tion
6b.
Add
sor
bent
6c.
Add
che
mic
als
7.
Che
mic
al o
xida
tion
8a.
Dew
ater
or
sorb
wat
er9.
A
dd m
ore
cem
ent
1.
Sul
fate
s, s
olub
le s
ilica
tes,
alum
inat
es,
phos
phat
es,
hydr
oxyl
ated
org
anic
aci
ds,
glyc
ols,
am
ines
, iro
nco
mpo
unds
, A
ST
M s
etac
cele
rato
rs2a
. F
erro
us s
ulfa
te2b
. H
ydro
gen
pero
xide
,ca
lciu
m/s
odiu
m h
ypoc
hlor
ite3a
. H
ydro
gen
pero
xide
,po
tass
ium
per
man
gana
te,
sodi
um p
ersu
lfate
,ca
lciu
m/s
odiu
m h
ypoc
hlor
ite4a
. C
lays
, l im
esto
ne,
flyas
h4b
. S
ee (
3a)
5.
A
ir, o
xyge
n, li
me,
calc
ium
/sod
ium
hyp
ochl
orite
,pr
oprie
tary
bio
cide
6a.
See
(3a
)6b
. F
lyas
h, b
ento
nite
,l im
esto
ne6c
. Q
uick
l ime,
ste
arat
es7.
P
otas
sium
per
man
gana
te,
sodi
um p
ersu
lfate
8.
Dec
ant
wat
er;
filte
r ra
ww
aste
; ad
d fly
ash,
cla
y, s
lag,
sil ic
a fu
me,
woo
d ch
ips,
grou
nd c
orn
cob,
diat
omac
eous
ear
th,
expa
nded
min
eral
s
1.
1 -
102a
. 1
- 1
02b
. 1
- 1
03.
1
- 10
4a.
2 -
10
4b.
1 -
10
4c.
2 -
10
4d.
0.0
1 -
15.
1
- 10
6a.
1 -
10
6b.
2 -
10
6c.
2 -
10
7.
2 -
108.
5
- 50
1.
2 -
202a
. 2
- 2
02b
. 5
- 2
003.
5
- 25
0
4a.
1 -
54b
. 5
- 2
504c
. 2
- 1
04d
. <
1 -
205.
5
- 20
06a
. 5
- 2
506b
. 1
- 5
6c.
2 -
50
7.
5 -
250
8.
2 -
20
37
PCA EB211
Tab
le 3
. S
olid
ific
atio
n P
rob
lem
s (c
on
tin
ued
)
PR
OB
LE
MP
RO
BA
BLE
CA
US
E -
WA
ST
EC
HA
RA
CT
ER
IST
ICS
,IN
GR
ED
IEN
TS
AP
PR
OA
CH
TO
SO
LUT
ION
SP
EC
IFIC
AD
DIT
IVE
S O
RT
EC
HN
IQU
ES
US
ED
AD
DIT
ION
RA
TIO
RA
NG
E(w
eigh
t %)
CO
ST
RA
NG
E($
per
ton
of w
aste
trea
ted)
Pe
rme
ab
ility
to
oh
igh
(S
W8
46
,M
eth
od
91
00
)
1.
In
com
ple
te c
uri
ng
2.
In
suff
icie
nt
cem
en
t3
. H
igh
wa
ste
pe
rme
ab
ility
1.
Cu
re f
or
at
lea
st 2
8d
ays
2.
Use
mo
re c
em
en
t3
a.
Ad
d l
ow
pe
rme
ab
ility
ad
diti
ve3
b.
Ad
dh
ydro
ph
ob
izin
g a
ge
nt
3c.
F
ill p
ore
s w
ith w
ate
rre
sist
an
t m
ate
ria
l3
d.
De
velo
p b
ete
rm
icro
stru
ctu
re
2.
Po
rtla
nd
ce
me
nt
3a
. B
en
ton
ite c
lay
3b
. E
mu
lsifi
ed
asp
ha
lt,st
ea
rate
s3
c.
La
tex
or
oth
er
wa
ter-
com
pa
tible
po
lym
er
3d
. F
lya
sh,
bla
st f
urn
ace
sla
g,
silic
a f
um
e
3a
. 5
- 3
03
b.
1 -
53
c.
5 -
10
3a
. 5
- 3
03
b.
1 -
53
c.
50
- 1
00
Po
or
du
rab
il ity
(AS
TM
D-4
84
2-
90
, D
-48
43
-88
)
1.
In
suff
icie
nt
cem
en
t2
. P
oo
r m
icro
stru
ctu
re3
. E
xce
ssiv
e p
oro
sity
4.
La
rge
am
ou
nts
of
solu
ble
sa
lts s
ulfa
tes,
chlo
rid
es,
nitr
ate
s
1.
Ad
d m
ore
ce
me
nt
2a
. A
dd
fly
ash
, si
lica
fum
e2
b.
Air
en
tra
inm
en
t3
a.
Mo
dify
wa
ter
con
ten
t3
b.
Ad
d b
ulk
ing
ag
en
to
r w
ate
r a
bso
rbe
r3
c.
Ad
d p
ore
fill
ing
ag
en
t3
d.
Ad
dh
ydro
ph
ob
izin
g a
ge
nt
4.
No
ne
re
po
rte
d
1.
Po
rtla
nd
ce
me
nt
2a
. F
lya
sh,
silic
a f
um
e2
b.
Use
air
en
tra
inin
g a
ge
nt,
pro
cess
to
en
tra
in a
ir3
a.
De
can
t w
ate
r; f
ilte
r ra
ww
ast
e3
b.
Fly
ash
, cl
ay,
sla
g,
silic
afu
me
, w
oo
d c
hip
s, g
rou
nd
co
rnco
b,
dia
tom
ace
ou
s e
art
h,
exp
an
de
d m
ine
rals
3
c.
La
tex
or
oth
er
wa
ter-
com
pa
tible
po
lym
er
3d
.
Em
uls
ifie
d a
sph
alt,
ste
ara
tes
2a
. 5
- 2
52
b.
0.0
1 -
13
b.
5 -
25
3c.
5
- 1
03
d.
1 -
5
2a
. 2
- 2
02
b.
2 -
20
3b
. 2
- 1
03
c.
50
- 1
00
3d
. 1
- 5
38
Guide to Improving the Effectiveness of Cement-Based Stabilization/Solidification
Tab
le 7
. S
tab
iliza
tio
n o
f M
etal
s
Pro
blem
or
Tar
get
Con
stitu
ent
orS
peci
esA
ppro
ach
to S
olut
ion*
Spe
cific
Add
itive
s U
sed*
Add
ition
Rat
ioR
an
ge
(wei
ght %
)
Cos
t R
ange
($ p
er t
on o
fw
aste
trea
ted)
An
timo
ny
Ars
enic
tris
ulfid
e1.
O
xida
tion
to A
s+5 f
ollo
wed
by
2.
P
reci
pita
tion
with
cal
cium
1.
Cal
cium
/sod
ium
hyp
ochl
orite
or
pota
ssiu
m p
erm
anga
nate
2.
Lim
e
1.
1 -
202.
5
- 10
1.
20 -
400
2.
5 -
10
Ars
enic
com
plex
es
1.
Imm
obili
ze b
y so
rptio
n2.
D
estr
oy c
ompl
ex b
y ox
idat
ion
1.
Act
ivat
ed c
arbo
n2.
P
otas
sium
per
man
gana
te,
sodi
umpe
rsul
fate
1.
1 -
102.
5
- 10
1.
20 -
200
2.
100
- 20
0
Bar
ium
, so
lubl
eco
mp
ou
nd
sP
reci
pita
te a
s su
lfate
Cal
cium
sul
fate
(gy
psum
)1
- 5
1 -
5
Ber
yll iu
m
Cad
miu
m,
sim
ple
Rai
se p
HLi
me,
lim
esto
ne,
high
-fre
e-l im
e ce
men
tki
ln d
ust
5 -
105
- 10
Cad
miu
m c
yani
deD
estr
oy c
ompl
ex b
y al
kal in
eox
idat
ion
Cal
cium
/sod
ium
hyp
ochl
orite
or
hydr
ogen
per
oxid
e1
- 10
20 -
200
Chr
omiu
m,
sim
ple
Chr
omiu
m a
s C
r+6
Red
uce
to C
r+3
Fer
rous
sul
fate
, so
dium
bis
ulfit
e or
met
abis
ulfit
e, o
r so
dium
hyd
rosu
lfite
5 -
2010
- 1
20
Chr
omiu
mco
mpl
exes
Imm
obil i
ze b
y so
rptio
nA
ctiv
ated
car
bon
1 -
1020
- 2
00
Lead
, si
mpl
e1.
C
o-pr
ecip
itate
2.
Spe
ciat
e as
car
bona
te,
basi
cca
rbo
na
te3.
S
peci
ate
as s
ulfid
e
1.
Fer
rous
sul
fate
2.
Cal
cium
car
bona
te,
sodi
umca
rbo
na
te3.
S
odiu
m s
ulfid
e or
org
ano-
sulfu
rco
mp
ou
nd
s
1.
5 -
102.
5
- 20
3.
0.1
- 5
1.
10 -
20
2.
2 -
103.
2
- 40
Lead
, co
mpl
exed
1.
Imm
obil i
ze b
y so
rptio
n2.
D
estr
oy c
ompl
ex b
y ox
idat
ion
1.
Act
ivat
ed c
arbo
n2.
C
alci
um/s
odiu
m h
ypoc
hlor
ite,
pota
ssiu
m p
erm
anga
nate
, so
dium
pers
ulfa
te
1.
1 -
102.
5
- 10
1.
20 -
200
2.
100
- 20
0
Not
e:M
etal
s or
met
als
spec
ies
that
are
ade
quat
ely
stab
ilize
d by
cem
ent a
lone
are
sha
ded.
39
PCA EB211
Lead
, el
emen
tal
Incl
ude
a so
urce
of
carb
onat
e to
re-
spec
iate
lead
as
it di
ssol
ves
Cal
cium
car
bona
te,
sodi
um c
arbo
nate
5 -
202
- 10
Mer
cury
, si
mpl
eS
peci
ate
as s
ulfid
e1.
S
odiu
m s
ulfid
e or
org
ano-
sulfu
rco
mp
ou
nd
s2.
S
ulfu
r +
alk
ali
1.
0.1
- 5
2.
1 -
101.
2
- 40
2. <
1 -
5
Nic
kel,
sim
ple
Spe
ciat
e as
sul
fide
Sod
ium
sul
fide
or o
rgan
o-su
lfur
com
po
un
ds
0.1
- 5
2 -
40
Nic
kel c
yani
deD
estr
oy c
ompl
ex b
y al
kalin
eox
idat
ion
Cal
cium
/sod
ium
hyp
ochl
orite
or
hydr
ogen
per
oxid
e1
- 10
20 -
200
Nic
kel c
ompl
exes
1.
Imm
obil i
ze b
y so
rptio
n2.
D
estr
oy c
ompl
ex b
y ox
idat
ion
1.
Act
ivat
ed c
arbo
n2.
P
otas
sium
per
man
gana
te,
sodi
umpe
rsul
fate
1.
1 -
102.
5
- 10
1.
20 -
200
2.
100
- 20
0
Sel
eniu
m,
sim
ple
Sel
eniu
m,
sele
nate
Co-
prec
ipita
teF
erro
us s
ulfa
te1
- 5
2 -
10
Silv
er,
sim
ple
Silv
er,
high
leve
lP
reci
pita
te a
s ch
lorid
eS
odiu
m c
hlor
ide
0.1
- 1
<1
- 1
Tha
ll ium
Va
na
diu
m
Zin
c
Met
als,
ele
men
tal,
finel
y di
vide
dD
e-ac
tivat
e by
dis
solu
tion
ifpy
roph
oric
Aci
ds1
-10
<1
- 5
Tab
le 7
. S
tab
iliza
tio
n o
f M
etal
s (c
on
tin
ued
)
Pro
blem
or
Tar
get
Con
stitu
ent
orS
peci
esA
ppro
ach
to S
olut
ion*
Spe
cific
Add
itive
s U
sed*
Add
ition
Rat
ioR
an
ge
(wei
ght %
)
Cos
t R
ange
($ p
er t
on o
fw
aste
trea
ted)
*It
is a
ssum
ed th
at th
e tr
eatm
ent i
s be
ing
done
in th
e co
ntex
t of a
cem
ent-
base
d S/
S sy
stem
. Th
eref
ore,
mul
tiste
p tr
eatm
ent r
equi
ring
prec
ipita
tion
or s
peci
atio
n by
cem
ent i
n th
e la
st s
tep
is a
ssum
ed in
the
tabl
e an
d is
not
spe
lled
out.
40
Guide to Improving the Effectiveness of Cement-Based Stabilization/Solidification
Con
tam
inan
tA
dditi
ve U
sed
(X)
Fly
ash/
Bed
Ash
Hyd
rate
dLi
me
FeS
O4
CaC
O3
Na
2CO
3N
aCl
Na
2SO
4O
rgan
o-S
ulfu
rC
arbo
nC
a(O
Cl)
2/N
aOC
lK
MnO
4/(N
H4) 2
S2O
8
Na
2S2O
4N
a2S
/S
ulfu
r
Ant
imon
y
Ars
enic
- A
s+5,
conv
entio
nal
X
Ars
enic
- A
s+3X
XX
X
Ars
enic
-or
gano
-co
mpo
unds
XX
XX
Bar
ium
XX
Ber
yll iu
m
Cad
miu
mX
X
Chr
omiu
m -
Cr+3
,co
nven
tiona
l
X
Chr
omiu
m -
Cr+6
,he
xava
lent
XX
X
Chr
omiu
m -
com
plex
esX
Lead
-co
nven
tiona
lX
XX
XX
Lead
-or
gano
-co
mpo
unds
XX
X
Tab
le 8
. G
ener
al A
dd
itiv
e U
tiliz
atio
n L
ist,
Met
als
41
PCA EB211
Tab
le 8
. G
ener
al A
dd
itiv
e U
tiliz
atio
n L
ist,
Met
als
(co
nti
nu
ed)
Con
tam
inan
tA
dditi
ve U
sed
(X)
Flya
sh/
Bed
Ash
Hyd
rate
dLi
me
FeS
O4
CaC
O3
Na
2CO
3N
aCl
Na
2SO
4O
rgan
o-S
ulfu
rC
arbo
nC
a(O
Cl)
2/N
aOC
lK
MnO
4/(N
H4) 2
S2O
8
Na
2S2O
4N
a2S
/S
ulfu
r
Ati
Lead
-el
emen
tal
X
Mer
cury
-co
nven
tiona
lX
XX
Mer
cury
-or
gano
-co
mpo
unds
XX
Mer
cury
-el
emen
tal
X
Nic
kel -
conv
entio
nal
XX
Nic
kel -
cyan
ide
com
plex
es
XX
X
Nic
kel -
orga
no-
com
poun
ds
XX
X
Sel
eniu
m -
conv
entio
nal
X
Sel
eniu
m -
sele
nate
*X
Silv
erX
X
Tha
ll ium
42
Guide to Improving the Effectiveness of Cement-Based Stabilization/Solidification
Con
tam
inan
tA
dditi
ve U
sed
(X)
Fly
ash/
Bed
Ash
Hyd
rate
dLi
me
FeS
O4
CaC
O3
Na
2CO
3N
aCl
Na
2SO
4O
rgan
o-S
ulfu
rC
arbo
nC
a(O
Cl)
2/N
aOC
lK
MnO
4/(N
H4) 2
S2O
8
Na
2S2O
4N
a2S
/S
ulfu
r
Tab
le 8
. G
ener
al A
dd
itiv
e U
tiliz
atio
n L
ist,
Met
als
(co
nti
nu
ed)
*St
ront
ium
is r
epor
ted
to b
e us
eful
in s
tabi
lizat
ion
of s
elen
ate
ion
Va
na
diu
m
Zin
cX
43
PCA EB211
TA
RG
ET
CO
NS
TIT
UE
NT
UTS
LE
VE
L
TC
LP T
ES
TIN
G (
mg/
l)T
CA
TE
ST
ING
(m
g/kg
)
Un
-tr
ea
ted
Tre
ated
Add
itive
Add
ition
Rat
io(%
)
Un
-tr
ea
ted
Tre
ated
Add
itive
Add
ition
Rat
io(%
)
Ace
ton
e16
0
12
0.5
17
.25
KA
X-5
0™
10
918
<
20
0K
AX
-10
0™
10
Be
nze
ne
10
26
.5<
1.2
5C
arbo
n1
041
8
26
.4K
AX
-10
0™
10
2-B
utan
one
(Met
hyl
ethy
l ke
tone
)36
6
8.0
6.0
Car
bon
10
430
9
5.8
Car
bon
10
Car
bon
Dis
ulfid
e
4
.8*
5.0
<0
.25
***
10
83
<0
.25
Non
e-
Car
bon
Tet
rach
lorid
e6
1
8.0
<1
.25
Car
bon
10
429
1
4.5
KA
X-1
00
™1
0
Ch
loro
be
nze
ne
6
35
.5<
1.2
5C
arbo
n1
014
00
40
2C
arbo
n1
0
Chl
orof
orm
6
48
.5<
2.5
KA
X-
10
0™
10
431
9.
8K
AX
-10
0™
10
1,2-
Dic
hlor
oeth
ane
6
68
.5<
2.5
KA
X-
10
0™
10
654
<
0.2
5K
AX
-10
0™
10
1,1-
Dic
hlor
oeth
ylen
e6
-
--
-2
.24
<
0.2
5O
-cla
y1
0
Eth
yl A
ceta
te33
2
9.5
<0
.25
KA
X-5
0™
10
258
<
0.2
5**
10
Eth
yl B
enze
ne10
1
1.0
<2
.5**
**1
010
40
2.6
3C
arbo
n1
0
Met
hyle
ne C
hlor
ide
30
15
.0<
0.2
5K
AX
-50
™1
062
<
0.2
5K
AX
-10
0™
10
4-M
ethy
l-2-P
enta
none
(M
ethy
l is
obut
ylke
tone
)3
31
04
.5<
2.5
Car
bon
10
1030
6
10
KA
X-1
00
™1
0
Tet
rach
loro
ethy
lene
6
22
.0<
1.2
5C
arbo
n1
019
80
61
5K
AX
-10
0™
10
To
lue
ne
10
33
.5<
1.2
5C
arbo
n1
093
8
25
6K
AX
-10
0™
10
1,1
,1-T
richl
oroe
than
e6
3
4.5
<0
.25
KA
X-5
0™
10
550
<
0.2
5K
AX
-10
0™
10
Tric
hlor
oeth
ylen
e6
4
4.5
<1
.25
Car
bon
10
881
8
9.1
KA
X-1
00
™1
0
Tab
le 9
. S
tab
iliza
tio
n o
f V
ola
tile
Org
anic
s
44
Guide to Improving the Effectiveness of Cement-Based Stabilization/Solidification
TA
RG
ET
CO
NS
TIT
UE
NT
UTS
LE
VE
L
TC
LP T
ES
TIN
G (
mg/
l)T
CA
TE
ST
ING
(m
g/kg
)
Un
-tr
eate
dT
reat
edA
dditi
veA
dditi
onR
atio
(%)
Un
-tr
eate
dT
reat
edA
dditi
veA
dditi
onR
atio
(%)
Tab
le 9
. S
tab
iliza
tio
n o
f V
ola
tile
Org
anic
s (c
on
tin
ued
)
Tri
chlo
roflu
orom
etha
ne30
-
--
-0
.49
<
0.2
5N
one
-
1,1
,2-T
richl
oro
-1,2
,2-T
riflu
oroe
than
e30
-
--
-9.
1
<0
.25
***
10
Tot
al X
ylen
es30
1
1.0
<1
.25
Car
bon
10
1070
1
74
Car
bon
10
N-B
utan
ol2.
6
55
.03
1.4
KA
X-5
0™
10
3350
<
5K
AX
-10
0™
10
Cyc
loh
exa
no
ne
0
.75*
--
--
536
<
5K
AX
-10
0™
10
Iso-
But
yl A
lcoh
ol17
0
--
--
2100
<
5K
AX
-10
0™
10
Me
tha
no
l
0.75
*2
33
.05
0.4
Car
bon
10
2337
4
44
KA
X-1
00
™1
0
Not
e:
“O-c
lay”
= o
rgan
ocla
y
* =
TLC
P
**
= C
arbo
n, O
-cla
ys, o
r K
AX
-100
™
***
= O
-cla
y or
KA
X-1
00™
*
***
= C
arbo
n or
O-c
lays
45
PCA EB211
Tab
le 1
0. S
tab
iliza
tio
n o
f S
emi-
Vo
lati
le O
rgan
ics
TA
RG
ET
CO
NS
TIT
UE
NT
UT
SL
EV
EL
TC
LP T
ES
TIN
G (
mg/
l)T
CA
TE
ST
ING
(m
g/kg
)
Un-
tre
ate
dT
rea
ted
Ad
diti
veA
dd
itio
nR
atio
(%)
Un-
tre
ate
dT
rea
ted
Ad
diti
veA
dd
itio
nR
atio
(%
)
An
thra
cen
e3.
4
0.0
32
<0
.02
**1
054
4
6.9
KA
X-5
0™
10
Bis
(2-E
thyl
hexy
l) P
htha
late
28
0.5
2<
0.0
2K
AX
-50
™1
077
6
<0
.99
KA
X-5
0™
10
1,2-
Dic
hlor
oben
zene
6
2.1
<0
.02
Ca
rbo
n1
042
9
6.7
8K
AX
-50
™1
0
1,4-
Dic
hlor
oben
zene
6
1.8
6<
0.0
2C
arb
on
10
461
6
.03
KA
X-5
0™
10
2,4-
Din
itrot
olue
ne14
0
6.2
6<
0.0
2C
arb
on
10
438
<
0.9
9K
AX
-50
™1
0
He
xach
loro
be
nze
ne
10
--
--
440
6
.96
KA
X-5
0™
10
He
xach
loro
bu
tad
ien
e5.
6
0.1
4<
0.0
2*
10
620
1
0K
AX
-50
™1
0
He
xach
loro
eth
an
e30
0
.38
<0
.02
Ca
rbo
n1
038
1
6.4
6K
AX
-50
™1
0
4-M
ethy
l ph
enol
5.6
12
.2<
0.1
**1
0
Na
ph
tha
len
e5.
6
2.1
--
-58
4
6K
AX
-50
™1
0
Nitr
ob
en
zen
e14
1
1.6
0.0
5C
arb
on
10
372
3
.66
KA
X-5
0™
10
Pe
nta
chlo
rop
he
no
l7.
4
2.3
<0
.2**
*1
015
2
<1
.8*
10
Pyr
idin
e16
3
0.2
28
.2C
arb
on
10
1900
3
5.1
KA
X-5
0™
10
2,4,
5-T
rich
loro
phen
ol7.
4
8.2
<0
.5*
10
132
3
.37
Ca
rbo
n1
0
2,4,
6-T
rich
loro
phen
ol7.
4
13
.7<
0.1
K
AX
-50
™1
095
2
<0
.99
KA
X-5
0™
10
Not
e:
* =
Car
bon
or K
AX
-50™
/KA
X-1
00™
**
= C
arbo
n, O
-cla
ys, o
r K
AX
-100
™ *
** =
Car
bon
or O
-cla
ys
46
Guide to Improving the Effectiveness of Cement-Based Stabilization/Solidification
TA
RG
ET
CO
NS
TIT
UE
NT
UTS
LE
VE
L
TC
LP T
ES
TIN
G (
mg/
l)T
CA
TE
ST
ING
(m
g/kg
)
Un
-tr
ea
ted
Tre
ate
dA
dditi
veA
dditi
onR
atio
(%)
Un
-tr
ea
ted
Tre
ate
dA
dditi
veA
dditi
onR
atio
(%)
gam
ma-
BH
C (
Lind
ane)
0.0
66
1.5
<0
.2*
10
25
<5
.0K
AX
-1
00
™1
0
Hep
tach
lor
0.0
66
0.4
<0
.00
8**
10
16
35
4O
-cla
ys1
0
End
rin0
.13
0.3
<0
.02
**2.
60.
8C
arbo
n1
0
Met
hoxy
chlo
r0
.18
<1
0.
<0
.2**
10
1.1
0.2
8C
arbo
n1
0
Chl
orda
ne0
.26
<0
.03
<0
.03
***
10
52
5.6
Car
bon
10
To
xap
he
ne
2.6
<0
.5<
0.5
***
10
68
26
Car
bon
10
2,4-
Dic
hlor
ophe
noxy
acet
ic a
cid
10
<0
.1<
0.1
***
10
26
00
01
7K
AX
-1
00
™1
0
N
otes
:
“O-c
lay”
= o
rgan
ocla
y
*
= O
-cla
y or
KA
X-5
0™/K
AX
-100
™
** =
Car
bon
***
= C
arbo
n, O
-cla
y or
KA
X-5
0™//1
00™
Tab
le 1
1. S
tab
iliza
tio
n o
f P
esti
cid
es a
nd
Her
bic
ides
47
PCA EB211
Tab
le 1
2. G
ener
al A
dd
itiv
es U
tiliz
atio
n L
ist,
Org
anic
s
TA
RG
ET
CO
NS
TIT
UE
NT
CA
RB
ON
OR
GA
NO
-CLA
YR
UB
BE
RP
AR
TIC
ULA
TE
KA
X-5
0™
MO
DIF
IED
RU
BB
ER
PA
RT
ICU
LAT
EK
AX
-10
0™
TC
LPTC
AT
CLP
TCA
TC
LPTC
AT
CLP
TCA
VO
Cs
XX
XX
XX
X
Sem
i-VO
Cs
XX
XX
XX
XX
PC
Bs
NR
ND
NR
ND
NR
ND
NR
ND
Pes
ticid
es,
Her
bici
des
XX
XX
XX
XX
Org
ano-
met
all ic
sX
ND
ND
ND
XN
DX
ND
Pol
y N
ucle
ar A
rom
atic
s (P
NA
s)X
XX
XX
XX
Alc
ohol
sX
ND
ND
XX
NR
= N
ot R
equi
red
ND
= N
o D
ata
KEYWORDS: additives, cement, compressive strength, durability, fixation, heavy metals, immobilization,metals, organics, organo-metallics, permeability, portland cement, solidification, soluble salts, stabilization.
ABSTRACT: Portland cement-based stabilization/solidification (S/S) has been used to successfully treat a widevariety of wastes. Some situations (because of the waste itself, the disposal scenario, and/or the regulatoryrequirements) require the use of additives or physical/chemical techniques to improve the effectiveness ofcement-based S/S. The problems encountered in S/S can be broadly classified into solidification problems, i.e.obtaining the required physical properties in the treated waste, and stabilization problems, i.e. adequatelyimmobilizing the hazardous constituents of the waste. The Guide lists additives and techniques that can beapplied to specific solidification problems such as problems in development of set, compressive strength, andfree liquids. Also included are lists of additives and techniques that can be applied to immobilization of specifichazardous constituents such as lead, cadmium, and chromium, as well as classes of constituents such as volatileorganics, organo-metallics and soluble salts. The Guide lists a variety of generic additives for specific desiredstabilization/solidification effects, including those that can be used to control the pH of wastes; to reduce,oxidize, and co-precipitate constituents; and to accelerate or retard set.
This publication is intended SOLELY for use by PROFESSIONALPERSONNEL who are competent to evaluate the significance andlimitations of the information provided herein, and who will accepttotal responsibility for the application of this information. The PortlandCement Association DISCLAIMS any and all RESPONSIBILITY andLIABILITY for the accuracy of and the application of the informationcontained in this publication to the full extent permitted by law.
Portland Cement Association 5420 Old Orchard Road, Skokie, Illinois 60077-1083, (847) 966-6200, Fax (847) 966-9781
An organization of cement manufacturers to improve and extend the usesof portland cement and concrete through market development, engineer-ing, research, education and public affairs work.
Printed in U.S.A. EB211.01W