final report - records collections · laboratory (anl) conducted a competitive procurement of...

CHROMATE REDUCTION ANDHEAVY METAL FIXATION

IN SOIL

Final ReportContract No. 02112401 '

ByKlaus Schwitzgebel, Ph.D.

Sizemcre Technical Services, Inc.2011 Lamar Drive

Rcurrl Reck. Texas 78654(5*2) 255-1388

Prepared lor

Office of Research and Deveicorrsr.i Research arc Deve opre.'tTechnology Oeve'ccmsnt. CcC'C.nnr.cn C'f.ce

Envircnmental Res:orat.cr. ar:c xJJvTNrcT? .. Wast* M.irager-yrtWaste Mar.agemer: > XX -r- XW\ arc Tecn-s:csy Oev^-cc

U.S. Deaart.-rer: c! Energy /£•/ .-.v.;-.- \ \ Cn.caga F:c j C':'.e1COO incepencerce A^or^e fe/ | • ft"/", \Vl U.S. Dc-pa-mcr.: -• Er*Wacn.rgtcn. DC 2C535-C3S2 lil I i .| ]*} 93CO 5 Cass Avsnye

' ' * Arge-ie. !L €C~'-9

Research and OeveicpTient Program Ccarcioai-on O" ceChemical Tecr.r-cicgy D.v.o.cn. A.-gsnne National Lascfarsr/

9700 S ,CuSa A.erue. Argcr.ne. IL 5C-33-:e3runder pnme csnrrac: \V-3:-iC9-E:i3-3S :c the U S. Oepafime"' of F.-ef;y

June 1992

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DISCLAIMER'This report wa> prepared as an account of work sponsored by ah agency ofIhc United States Government. Neither the United States Government norany agency thereof, nor any of theiremployees. makes any warranty. e\prcv>or implied, or assumes an; legal liability ur responsibility tor the accaracy.completeness, or usefulness of any information, apparatus, product, oc pro-cess disclosed, or represents that its use \\ouldnot infringe privately t<wnedrights. Reference herein to any .specific commercial product, process, or\cr\ice by trade name, trademark, manufacturer, or otherwise, dres notnecessarily constitute or imply ilx endorsement, recommendaiiixj. orfavoring by the United States Government or any agency thereof. The\ie»sand opinions of authors expressed herein do not necessarily stale or reflectthose of the United States Government or any agency thereof.

Reproduced from the best available copy.

Available to DOE and DOE co/nractors from theOflke of Scientific and Technical Intbmuiion

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DOE/CH-9214Distribution Category:General. Miscellaneous, and ProgressRepom(UC )t)

DOE/CH—9214

°E93 °°2266Contract No. 02112401

CHROMATE REDUCTION ANDHEAVY METAL FIXATION

IN SOIL

ByKlaus ScrMfltzgebel, PUD.

Sizemore Technical Services, Inc.2011 Lamar Drive

Round Rock. Texas 78664(512)255-1983

Preparedfor : ;

Offica ol Research and DevelopmentTechnology Development. Environmental Restoration and Waste Management

U.S. Department of Energy1000 Independence AvenueWashington. DC 205854002

Research and Development Program Coordination OfficaWaste Management and Technology Development. Chicago Field Office

U.S. Department of Energy9800 S. Cass AvenueArgonne. IL 60439

Research and Development Program CoorrJnatica OfficeChemical Technology Division. Argonne National Laboratory

9700 S. Cass Avenue. Argonne. B. 60439-4837under prime contract W-3M09-Eng-33 to the U.S. Department ol Energy

MASTERDiSTnlBUT.ON CF THIS DOCUMENT IS UNLIMITED

PREFACE

Currently available technology is not adequate to assess environmental contamination atDepartment of Energy (DOE) sites, take permanent remedial action, and eliminate or minimizethe environmental impact of future operations. Technical resources to address these shortcomingsexist within the DOE community and the private sector, but the involvement of the private sectorin attaining permanent and cost-effective solutions has been limited.

During 1990, on behalf of DOE's Office of Technology Development, Argonne NationalLaboratory (ANL) conducted a competitive procurement of research and development projectsaddressing soil remediation, groundwater remediation, site characterization, and contaminantcontainment Fifteen contracts were negotiated in these areas.

This report documents work performed as pan of the Private Sector Research andDevelopment Program sponsored by the DOE's Office of Technology Development within theEnvironmental Restoration and Waste Management Program. The research and developmentwork described herein was conducted under contract to ANL.

On behalf of DOE and ANL, I wish to thank the performing contractor and especially thereport authors for their cooperation and their contribution to development of new processes forcharacterization and remediation of DOE's environmental problems. We anticipate that the R&Dinvestment described here will be repaid many-fold in the application of better, faster, safer, andcheaper technologies.

Details cf the procurement process and status reports for all 15 of the contractorsperforming under this program can be found in "Applied Research and Development PrivateSector Accomplishments - Interim Report" (Report No. DOE/CH-9216) by Nicholas J. Beskid,Jas S. Devgun, Mitchell D. Erickson and Margaret M. Zielke.

Mitchell D. EricksonContract Technical Representative

Research and DevelopmentProgram Coordination Office

Chemical Technology DivisionArgonne National Laboratory

Argonne, LL 60439-4837

fTABLE OF CONTENTS

Abstract...._..............._...................._..........._........._.................._.._,..._................. vii

Executive Summary.._..._......................._..............__.._............_._..._............._ vin

1.0 Introduction................._.................._.................._......_......_____................ 1

1.1 Chromate Reduction by Iron II in Neutral and Alkaline Medium.................... 11.2 Silica Gels.............................................__.„..............._................................ 21.3 Leaching Rate Minimization through Permeability and Solubility

Reduction.............................™...................._........_...._.._........................ 31.4 Technology Use and Environmental Considerations........................................ 4

2.0 Methodology and Approach......_.._..............................._..._.._......_.............. 5

2.1 Facilities and EquipmenL.........................._..............__..............._....._,. 5

2.2 Reagents and Supplies..................................................._................_........... 5

2.3 Experimental............._........................_....._._....___._................... 6

23.1 Soils _..................................__....__..._._................._ 623.2 Soil Treatment .........................._........._...._.._......................... 72.3.3 Column and Sequential Batch Experiments.................................... 823.4 Soil-Metal Isotherms for Single Metals__.___...._.......... 82.3.5 Metal Adsorption on Gels........................_.._...„_............„.......... 8

2.4 Data Reduction and Interpretation........_..._....__„__„.._......................... 9

2.4.1 Soil-Metal Isotherms...........__„_..„„.._....__........................... 92.4.2 Reduction of Column Effluent and Sequential Batch Data.............. 92.4.3 Hydraulic Conductivity.._................_...................................... 10

2.5 QA/QC__.._.................................._..................__.............................. 12

3.0 Results and Discussion..............................................................................——.......... 133.1 Soil Characterization.............................™—...........—..................................... 13

3.2 Soil-Metal Adsorption Isotherms_......_..........._....———........—.......... 15

Silica Gel Composition (Acid Gels; Zeolite Gels)___..—_......................— 183.4 Hydraulic Conductivity of Soil Treated with Silica Gels——........................ 19

3.5 Metal Protection by Acid Gels in the Absence of Soil..——............—........ 20

3.6 Iron II and Acid Gels: Fixation of Chromates (Exp. #1 - 126).......——....... 22

3.6.1 Summary................................——........—..—................——....... 23

iti

1

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3.7 Iron n and Acid Gels: Fixation of Chromates Plus Metals(Exp. #127 - 180).............................._.........._........................................... 27

3.7.1 Chromium.....;..................._.........................................„.........„...... 273.7.2 Lead..................................._............................................................. 283.7.3 Zinc...................................._.............._............................................. 283.7.4 Copper..............................._.............._........._................................. 283.7.5 Cadmium............................_................_........................................... 293.7.6 Nickel............................................................................................... 293.7.7 Summary.........................._............_............._............................. 30

3.8 Iron III. Acid Gels, Zeolite Gels: Fixation of Metals(Exp. #181 - 249)............................._.........._...............................™.....;... 32

3.8.1 Protection of Lead by Iron IIL Acid Gels, and Zeolite Type Gelsin the Absence, of Chromate.._.........._........_...............__...... 32

3.8.2 Protection of Zinc. Copper. Czdmium and Nickel by Iron III.Acid Gels, and Zeolite Gels in the Absence of Chromate.................... 32

3.9 Iron HI and Zeolite Gel 2-10: Fixation of Metals (Exp. #250-316)............... 35

3.9.1 Lead......................................_.........._........................................... 353.9 2 Zinc .......*.............._............_.........._._......_.............._...._. 363.9.3 CopperZZZZZ~ZZZ_ZZL"_ZZZZZZZZZZ!" 363.9.4 Cadmium.............................._..........._.._......_............._.......... 373.9.5 Nickel..................................._........................................................... 373.9.6 Summary: Treatment Effect of Iron plus Gel 2-10 (Zeolite Gel)........ 38

3.10 Column Behavior up to 1000 mi Effluent for Zinc. Cadmium, andNickel (Colorado Met 400; TCLP #1)_............__.............................._........ 45

3.11 Comparison of In Situ and Dried Gel Experiments _........................_........ 47

3.12 Sequential Batch Extractions..........—............—.......................................... 49

3.13 Combined Protection by Reduction of Soil Permeabilityand Chemical Fixation.....................—..........—...........—........................... 51

3.13.1 Protection by Flow Rate Reduction......—..........—........................... 513.13.2 Protection by Flow Rate Reduction and Chemical Fixation................. 523.13.3 Time Estimate to Elute 40 Pore Volumes from a Cube of 1 m*

under a Pressure Gradient of 1 cm/m —..—......................—........ 52

4.0 Technology Status......................................._.........._........._„.........„.„..__„....... 53

4.1 Soil Chemistry and Chemical Treatment Methods for Sludges and Wastes.... 53

42 Mechanical Soil Mixing...................—........————..—............——......... 564.3 la Sim Chromate Reduction............—............—.......................................... 57

5.0 Acknowledgements......................................—..........—........................................... 58

IV

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FIGURES

Figure 1 Polymerization Behavior of Silica.........™.........................™............................ 3

Figure 2 Determination of the Hydraulic Conductivity.................................................. 10

Figure 3 Adsorption of Nickel on Balcones Soil as aFunction of Time.............™..........................._................._._._._........... 15

Figure 4 Cd Adsorption Isotherms for Colorado. Balcones.and Round Rock Soils at pH = 7.3........™.......................™............................ 16

Figure 5 Gel Time of Sols Made from Sodium-Silica Solutionsand H2SO.4 as a Function of Concentration and pH...._................................. 18

Figure 6 Cr Concentration in Column Effluents Before andAfter Soil Treatments...................™.......™........................._.......................... 26

Figure 7 Comparison of Pb Concentration in Column EffluentsUsing Acid and Zeolite Gels..............................._...,_...™............................ 34

Figure 8 Pb Protection by 6600 pprn Fe III and Gel 2-10......™.......™............................ 40

Figure 9 Zn Protection by 6600 ppm Fe in and Gel 2-10..™.........._........................... 41

Figure 10 Cu Protection by 6600 ppm Fe HI and Gel 2-10._..____........_.......... 42

Figure 11 Cd Protection by 6600 ppm Fe HI and Gel 2-10...............—.......................... 43

Figure 12 Ni Protection by 6600 pprn Fe III and Gel 2-10.............................................. 44

Figure 13 Leaching Results for Zn. Ni and Cd in Colorado Soil.—...............—........... 46

Figure 14 Concentration of Soluble Silica Species in Equilibrium with2.6 nm Diameter Silica Particles ai pH = 8.5-10.5.....———............................ 49

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TABLES

Table I Physical and Chemical Characterization of Soils...-...™.™.............™.............. 14

Table n Adsorption of Chromate on Soil......™.........™.—.._........_..............,............... 17

Table HI Experimental Parameters Used to Determine the HydraulicConductivity of Colorado Soil Treated with Zeolite GeL.._.............™............. 20

Table IV Extraction Results of Heavy Metals Protected by an Acid Gel (No Soil)........ 21

Table V Treatment Evaluation of Soils Impregnated with Cr VI——........—........... 24

Table VI Chromate Reduction and Fixation of Cr, Pb. Zn. Cu. Cd. Niby Iron D and Acid Gels ~..........__........——......——..........——.......... 31

Table VII Lead Protection by Iron. Acid Gels and Zeolite Gels in the

Table VTH Protection of Pb, Zn. Cu. Cd, Ni by 6600 ppm Fe m and ZeoliteGel 2-10™....™...........__......._.__......____..__..-..»_......_.... 39

Table DC Comparison of Results Obtained in Columns with Dried Gels andwith Wet Gels (In Situ Treatment).—.........———...™.................................. 48

Table X Sequential Batch Extractions using 1) Gels Air Dried at 35°C;2) Gels Wet Cured at Room Temperature; 3) Gels Wet Cured at 35°C........... 50

VI

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ABSTRACT

The in..sint reduction of chromates and the fixation of the metals Cr. Pb, Zn. Cu. Cd and Ni insoil was investigated using Iron n and soluble silica.

Iron n fulfills two functions. It reduces chromates (CrVI) at soil pH to CrUl and the reactionproducts, Fe(OH)3 and Cr(OH>3. coprecipitate/adsorb heavy metals. In the absence of CrVlJronis added as Fein. Destabilized silica also fulfills two functions. It reacts with the metal andmetal hydroxides and reduces the soil permeability.

The leaching rate (mg/m2sec) of a metal is the product of leachate flow rate (l/m2sec) and theleachate concentration (rug/0. The leachate flow rate is directly proportional to the hydrauliccoefficient (Darcy's Law).

Treatment with destabilized silica reduces the hydraulic coefficient of virgin soil (Kn = 10-2... 10*4) to Kn=10*7 (cm/sec). This results in a flow rate reduction of three to five orders of magnitudecompared to virgin soil

Iron plus silica treatment results in a leachate concentration reduction of up to 2 orders ofmagnitude (Cn 95-99%; Pb: 99 %; Zn 95-99 %; Cd: 93-99%; NU 75-94%;)The combined effect of flow rate reduction and leachate concentration reduction results in apotential leaching rate reduction of five to seven orders of magnitude.

Iron-silica treatment may be developed into an efficient containment technology, provided thesilica gel integrity does not change with time.

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Executive Summary

Government and industry are in need of a new technology for the remediation of contaminated sites.Innovative approaches are needed to prevent the migration of contaminants, to isolate volumes throughimpermeable barriers and to provide permanent containment. The pollutants comprise organic*.inorganics, and radionuclides.

The present study was sponsored by the Department of Energy under the auspices of Argonne NationalLaboratory (Contract 02112401). The objective was to investigate the in situ reduction of chromatesand the fixation of the heavy metals, chrome, lead, zinc, copper, cadmium and nickeL

The approach was in situ reduction of chromates with a ferrous salt at soil pH and fixation of themetals using a destabilized aqueous sodium silica solution.The reactants in this treatment scheme are insolution and are not filtered out by soil as are the particles in pordand cement based treatmentapproaches.A literature search indicated that in tint chromate reduction and fixation of metals in soil using Fe anddestabilized silica is a novel approach. The use of iron and silica is mentioned in a few patents whichclaim that these ingredients in conjunction with cement, blast furnace slag, kiln dust, lime, etc.. solidifywastes and sludges into a monolith.

The iron n fulfills two functions. It reduces the Cr VI to Cr III. Cr III and Fe HI formed in thisreaction are precipitated at soil pH. In this precipitation step, other metals are coprecipitated andadsorbed on the Cr(OH)3 and Fe(OH)3. In the absence of Cr VI, iron HI must be substituted for Fe ILThe silica treatment step also fulfills two functions. Silica reduces metal solubility and lowers the soilpermeability.

Metal containment is therefore attacked on two fronts, because the leaching rate of a metal is the productof leachate flow rate and leachate concentration.

(1)

Metal Leaching Rate (mg/m sec) = Leachate Flow Rate (Ic/m2sec)x Leachate Concentration (mg/ltr)

The leachate flow rate can be calculated from Darcy's law if the hydraulic coefficient K is known andthe pressure gradient is given.The leachate concentration is measured in column experiments.

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The combined protection percentage achieved by reduction of the leachate flow rate and by reduction ofthe leachate concentration can be defined as:

(2)

Combined Protection % ,(,. unprotected •

= leachate concentration of treated soil3 leachate concentration of untreated soil

Kpotected a hydraulic coefficient of gel treated soil3 hydraulic coefficient of virgin soil

Equation (2) gives for Kprotected = Ksoii the protection percent achieved by leachate concentrationreduction, and for Cprwected = Qmprotected, the protection percent achieved by fow rate reduction.The experimental approach compiised the following six research areas:

. 1) chemical and physical characterization of three soils.2) measurement of soil-metal isotherms3) determination of the hydraulic coefficients Kh of untreated and silica treated soils4) in situ chromate reduction with iron n at soil pH5) metal fixation through iron plus silica treatment6) estimation of the combined protection achieved by chemical fixation and reduction

of soil permeability

Soils were collected from Travis and Williamson counties in Central Texas. All three soils show a highpercentage of limestone. As a consequence, the pH values of a 50% aqueous slurry range from 7.7 to8-5 and the soils exhibit high neutralization capacity against attack by TCLP extraction fluid #1 (pH =4.93 ± 0.05) and #2 (pH - 2.88 ± 0.05).

Soil loading levels with the heavy metals are described in the following matrix.Totaling Metals/

Abbreviation Crfripml Pbfppml Cdf;ym> Znfppnrt Cufppml Nifppmi IQOOgsoiL

Cr40 40 - 40CT400 400 - - - 400Met 40 40 40 40 40 40 200Met 100 100 100 100 100 100 500Met 400 - 400 400 400 400 400 2000Cr 40 Met 40 40 40 40 40 40 40 240Cr 400 Met 400 400 400 400 400 400 400 2400

Metal soil isotherms were determined for single metals at pH = 7.8. Chromate was not adsorbed at allCadmium, lead, zinc, and copper are more readily adsorbed than nickel These five metals showFreundtich type adsorption behavior up to a metal loading were the solubility product of the hydroxideis reached.

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The natural soil adsorption capacities at pH=7.8 reach 4-6 mg single meta!/g soil for Cd, Pb. Zn. andCu at an equilibrium concentration in a solution of 1 ppm. Nickel is adsorbed less strongly. This is inagreement with leaching results using DI water.

Hydraulic conductivity for the soils investigated ranged from Kh = 1.2 x I0~2(cm/sec) toKh = 3.8 x 10*4<cm/scc). Silica tret :nt decreases the hydraulic coefficient toKH = 6 x 10*7(cm/sec). This decrease co onds to a metal protection by flow reductiononly (Equation 2), of 99.8% to 99.995%.

In situ chromate reduction and metal fixation was researched in four stages using the above soil loadingmatrix with iron plus acid gels (silica solution destabilized with acid) and zeolite gels (silica solutiondestabilized with sodium aluminau).

The averaged column effluent concentrations and the TCLP Standards are as presented below:

Cd Zn Cu _ NJTCLP Standard 5.0 5.0 1.0

iron Plus Arida Cr40 0.124)30

Cr 40 Met 40 0.09 <0.02 O.OS 0.01 0.18 0.18Cr400 1.4-4.3 - ...Cr 400 Met 400 0.84 0.03 2.7 0.21 OJO 1.3

TCLPfl Cr40 0.12-0.30 - ...Cr 40 Met 40 0.10 0.02 0.77 0.25 0.15 0.54Cr400 0.14-0.22 - - ...

TCLP#2 Cr40 0.01-0.03 - - -Cr 40 Met 40 0.09 <0.02 0.93 0.41 0.13 0.89Cr400 0.05-0.18 - - ...Cr400M«400 0.41 0.13 37. 31. 2.5 25.

Iron Pins Ttnlitt fieha Colorado Met 40 - <0.02 0.004 0.015 0.18 0.10

Colorado Met 100 - <0.02 0.012 0.006 027 0.15Colorado Met 400 - <0.02 0.037 0.004 0.35 0.12Round Rock Met 400 - <0.02 0.091 <0.004 0.52 C.10Balcones Met 400 - <0.02 0.044 <0.004 0.10 0.05

TCLP*1 Colorado Met 40 • <0.02 0.04 0.02 0.12 0.12Colorado Me; 100 - <0.02 0.18 0.19 0.19 0.46Colorado Met 400 - <0.02 1.05 0.76 0.57 3.9iRound Rock Met 400 - <0.02 0.22 0.05 0.43 1.9CBalcones Met 400 - <0.02 0.06 0.04 0.10 2.59

Leachate concentration reduction percentages were as follows:

Chromium: 95 to 99% protection at Cr 40. Cr, 400, Cr 40 Met 40, Cr 400 Met 400soil loadings, using DI. TCLP #1 and TCLP #2 as leaching fluid, withFe II and acid gel treatment

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Lead: Up to 99+%Up to 99+% protection at Met 40. Met 100. Met 400 soil loadings, usingDI and TCLP #1 as leaching fluid, with Fe HI and zeolite gels treatment

Zinc; 89 to 99+% protection at Met 40, Met 100. Met 400 soil loadings, usingDI and TCLP #1 as leaching fluids, with Fe III and zeolite gel treatment

Copper No treatment effect against DI as leaching fluid at Met 40, Met 100,Met 400 soil loadings37-83% protection using TCLP #1 as leaching fluid, with Fe m andzeolite gel treatment

Cadmium: 89-99% protection at Met 40, Met 100. Met 400 soil loadings, using DI andTCLP #1 as leaching fluid, with Iron ED and zeolite gel treatment

Nickel: 50-90% protection at Met 40, Met 100. Met 400 soil loadings, usingDi and TCLP #1 as leaching fluid, with Fe m and zeolite gel treatment.

The column experiments were extended to approximately 500 ml eluate which corresponds to 40 porevolumes wher. leaching 30 g soil.

Combined Protection

It was found that the leachate flow rate is reduced by three to five orders of magnitude while theleachate concentration is reduced by one to two orders of magnitude.A reduction of the leachate concentration of 94% combined with a flow rate reduction of five orders ofmagnitude yields a combined protection of 99.9999+%.

The flow rate through a cube of 1 m3 treated Colorado soil under a pressure gradient of 1 cm/ra isestimated to be 1.9 Itr/year compared to 37.800 In/year for untreated Colorado soil

This would result in effective containment provided that gel integrity does not change with time. Thegel integrity over time can be ascertained through the investigation of sites treated with silica in the past.Beginning in the late 1880's and continuing to the present, the construction industry has used silica gelsto reduce soil permeability. Therefore, long terra data on gel behavior is available if these constructionsites could be identified.Conclusions

h Situ Cr VI reduction with Fe n was successful. This technique is ready for field evaluation for soilscontaining up to 400 ppm Cr Vfc, At higher Cr VI concentrations, treatment in combination with soilwashing may be necessary.

Metal fixation up to a Met 100 level was successful using 6000 ppm Fe addition and zeolite gel fixation.The equipment for in situ soil mixinf with simultaneous addition of liquids has been developed and iscurrently in use. However, more work in gel refinement is recommended. An extraction pH. using DIwater, not greater than pH 8.5-9.0 is desirable. Above this regime, the Pb was observed to increase inthe leachate. Also, the solubility of silici increases drastically above this pH range.

The long term gel behavior is of paramount importance and needs to be addressed.

xt

1.0 Introduction

This report describes the research results of Contract 02112401 performed under the auspices ofArgonne National Laboratory for the Department of Energy. The research addresses theremediation of soils contaminated with lead. zinc, copper, cadmium and nickel, with and withoutchromate. and with chromate alone.

The researched approach was a two-fold attack: (1) the reduction in the teachability of metals byreducing the metal solubilities; and (2) the reduction of soil permeability, thereby reducingleachate flow rate.The reduction in metal solubilities was achieved by reducing Cr VI to Cr III using Fe n. whichoxidizes to Fe IE. which in turn coprecipitates and adsorbs other heavy metals. The resultingmetal hydroxide matrix is reacted with silica to further reduce solubility. Fe HI was substitutedfor Fe U in the absence of Cr VL

The silica is added as a soluble destabilized aqueous solution which gels within hours. Thisreduces soil permeability close to the regime observed for unweathered marine clays. In thisfashion, the leachate flow rate is reduced by three to five orders of magnitude compared to virginsoils (Section 3.4).

The reduction of metal solubilities was researched in four stages:

1) in situ chromate reduction and fixation in •: matrix containing chromate onlyusing Fe II and silica destabilized with acid (acid gels) (Section 3.6. Exp. #1 -126);

2) in situ reduction of chromate in the presence of lead. zinc, copper, cadmium andnickel using Fe n and acid gels (Section 3.7. Exp. 127 - ISO);

i 3) fixation of lead, zinc, copper, cadmium and :ickel in the absence of chromium.using Iron in with acid and zeolite gels (silica solution destabilized with sodiumaluminate) (Section 3.8, Exp. 181 - 249); and

4) the fixation of lead, zinc, copper, cadmium and nickel in the absence of chromiumusing Iron HI and zeolite gels (Section 3.9, 3.10, 3.11 and 3.12. Exp. 250 -316).

Treatment effectiveness was evaluated in column leaching experiments.

Background

1.1 Chromate Reduction by Iron II in Neutral and Alkaline Medium

In earlier research it was found that Fe II salts reduce Cr VI not only in acidic region but also inan alkaline aqueous medium. The first objective of the present research was to determine if thisreaction goes to completeness in a soil environment.

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In the reaction between Cr VI and Fe n

2K2CrO4 + 6 FeSO4 + 16 HjO -* 2 [CrtOHfc • 3Fe(OH)j] + 2K2SO4 + 4 K2SO4 [1]

Chromium IE and iron in hydroxides are precipitated if the pH value of the environment issufficiently alkaline. An aqueous slurry of calcite containing soils shows pH values in the rangeof 7.5 to 8.5. Under this condition Fe m. Cr m and Fe n form hydroxide precipitates. TheNemst equation describing the Redox Potential of the Fe ffl/Fe n chain:

I

reduces to

231-59xpH(raV] (2)

E 3 potentialEQ 3 standard potentialR 3 gas constantT 3 absolute temperatureF 3 Faraday constant

3 activity of FelTJs activity of Fell

if the Fe ffl and Fe n activities are expressed as functions of pH and of the solubility products(Kjp) of the corresponding hydroxides. This potential is more negative in the entire alkalinerange than the oxidation potential of the Cr Vl/Cr ffl chain. This makes uLOQt reduction ofchromate feasible in a soil pH range of 7-10.The iron n is oxidized to iron EL In the pH range of 7-10 the iron ffl hydroxide coprecipitatesmost heavy metals. In the absence of CrVLFe ffl can be substituted for FeU In an aqueousenvironment it was observed that the residual metal concentrations are up to two orders ofmagnitude lower than would be expected from the hydroxide solubilities measured on singlemetals. A similar reduction is expected in a soil environment.Iron hydroxide precipitates tend to carry a positive surface charge while particles in a silica sol(pH-range >7) are charged negatively. This enhances the reaction of metal hydroxides and silica.1.2 Silica Gels

The second objective of the research was to determine if a silica treatment will further reduce thesolubility of heavy metals if exposed to leaching fluids of increasing acidity and to screen thechemical parameters for this in situ remediation approach in a sou pH range of 7-9. Silicasolutions, in contrast to pordand cement slurry, contain no particles which can be filtered out bythe soil They can be applied as aqueous solutions with good penetration properties.

Destabilized silica solutions set up a three dimensional network. Metal salts have a stronginfluence on the nature of the final gel structure (Figure 1).

FIGURE 1

COM

CcL NETWORKS

nm = nanometer

Polymerization behavior of silica. In basic solution (6) panicles in sol grow in size whiledecreasing in numbers; in acid solution or in presence of flocculating salts (A), particlesaggregate into three-dimensional networks and form gels (Den The Chemistry of Silica, JohnWiley & Sons, 1979, pg 174)

1.3 Leaching Rate Minimization through Permeability and Solubility Redaction

The silica solutions used in the present study were destabilized by addition of sulfuric acid (acidgels) or sodium aluminate (zeolite gels). These destabilized solutions form gels in t period ofminutes to hours depending on the pretreatment. See Section 3.3. A gel network is set up in thisfashion in the void volume of the soil which reduces the permeability of die treated soil by three tofive orders of magnitude.The leaching rate of a metal is the product of flow rate and concentration:

Leaching Rate (mg/m2 sec) = Flow Rate (I/m2 sec) x Concentration (mg/1) (3)

The proposed iron-silica treatment affects both parameters, reducing the concentration and the flowrate.

IThe metal concentration in the leachate is reduced by up to two orders of magnitude. Thereduction of the flow rate is much greater and can reach five orders of magnitude. The combinedprotection is discussed in Section 3.13.

1.4 Technology Use and Environmental Considerations

This technology can be used to:li prevent the nuzrstion of cont3nnn3nts2) isolate contiminated volumes using impermeable barriers, and3) provide permanent containment

The chemicals used in the treatment methodology pose no health or environmental risk.

The iron sulfate proposed for chromate reduction is widely used as fertilizer. Health riskscompared to other chemicals currently in use for chromate reduction, like sulfite in acidicmedium, are greatly reduced. FeSO4 treatment is odorless, non-corrosive, and non-toxic.Silica gels were applied for over a century for mechanical and hydrological soil stabilizationprojects and are considered environmentally safe.

I2.0 Methodology and Approach

Three soils were selected from the Central Texas area, contaminated with the metals to bestudied, treated with iron and silica and leached with DI water. TCLP extraction fluids # 1 or #2.The protection achieved by iron-silica treatment was measured in column and sequential batchexperiments.

2.1 Facilities and Equipment \1 1

The Pyrex columns for the experiments were 45 cm long with an internal diameter of 20 mm andwere fitted with a coarse frit or plugged with glass wool and sand in the effluent end.

PH determinations were performed with an Orion Research Expandable Ion Analyzer EA 920equipped with a glass electrode.

An AA/AE spectrophotometer 157 built by Instrumentation Laboratory was available for thef metal determination. This instrument provides for background correction using an UV lamp.' The detection limits in ppm are: Cr (.02); Pb (.02); Zn (.004); Cu (.007); Cd (.004) and Ni

(.02).

Silica was analyzed by the gravimetric procedure. A titrimetric method was used to determine thesodium content of the silica stock solution.

The carbon dioxide content in the soils was analyzed in a closed system, consisting of aevolution flask (HjSO<). a carbon dioxide absorber (Ba(OH)}). an expansion bladder and acirculation pump (ASTM D513). Total organic carbon was measured by burning the sample inan argon-oxygen stream at 600°C in an MCI TOX- 10 analyzer and absorbing the evolved COi >na barium hydroxide scrubber. The barium hydroxide consumption was determined in both casesthrough backtitration with 1 N HjSO* to the phenolphthalein end point.

2.2 Reagents and Supplies

The following chemicals were used in the experiments.For Soil Impregnation:

Potassium dichromate KjCrjO? Baker. ReagentNickel chloride 6-Hydrate NiCl2 • 6H:O Spectrum, ReagentCadmium chloride CdClj Spectrum. ReagentCupric chloride 2-Hydrate CuCl2 • 2H2O Spectrum, ReagentZinc chloride ZnClj Spectrum, ReagentLead chloride PbCh Spectrum. Reagent

AR302628

IFor Gel Preparation:

Silica: N-silica, (NajOSiOj ratio 1:3.22by weight) P.Q.Corporation

Sulruric Acid IN Thomas ScientificSodium aluminate NajO • AlzOs • 3H2O Spectrum. Technical

For CQj Analysis:Barium hydroxide Ba (OH)} • 8H2O Baker, Reagent

For TCLP Extraction Fluid Preparation:Glacial Acetic Acid Spectrum. TracegradeDdonized waterSodium Hydroxide NaOH Baker. Reagent

Fof yon. TrcatrnciitFerrous sulfate 7-Hydrase FeSO4 • 7H2O Baker. Reagent

For Fe II OxidationHydrogen Peroxide HjOj Baker, Reagent

AA Standards Baker, Analyzed

2.3 Experimental

2.3.1 Soils

The three soils studied were selected from Travis and Willfamson counties in Central Texas.Balconea Sofl (Bale.! was collected west of the Balcones Fault This soil is of the Brackett seriesand is shallow and well drained, It developed under prairie vegetation. It shows a graveflysurface layer and is underlain by imbedded limestone and marl This soil was collected from apile generated during a drainage ditch excavation using a ditch-witch. A high percentage ofground up limestone became intermixed with the soil during the excavation work.Round Rock Sofl fR.R.1 was collected east of the Balcones fault This sofl is of the HoustonBlack-Heiden soil series, which are composed of moderately well drained, deep clay thatdeveloped in calcareous marl, aHovial clays and chalk.Colorado Soil (CoU was collected from the alluvial deposits found in the vicinity of theColorado River. This soil is of the Lewisville- Patrick series. It consists of deep, well-drainedsilty clays. This sofl is calcareous and moderately alkaline.These soils were sieved; particles smaller than 2 mm were used in the experiments.

2.3.2 Soil Treatment

Soil impregnation with metaljj (Cr VI. Pb, Zn, Cu. Cd, Ni) was achieved by dissolving the metalsalts in one soil pore volume of DI water and mechanically mixing the aqueous solution into thesoil. The mixture was allowed to soak for several hours and was then air dried overnight at35°C and lepulverized. The contamination matrices are shown below.

Soil Contamination MatrixTotal mg Meals/

Abbreviation CrfppnO Ebfppm) Zn (ppm) Cufppcrt Cdfppm) Nifppnfl IQQQg sofl

Cr40 40 - - - - 40Cr400 400 - 400Met 40 40 40 40 40 40 200Met 100 100 100 100 100 100 500Met 400 - 400 400 400 400 400 2000 •Cr 40 Met 40 40 40 40 40 40 40 240Cr 400 Met 400 400 400 400 400 400 400 2400

30 g soil were used in the experiments:

400 ppm metal cone, dto 12 rag/30 g soil = 12,000 ug/30g soil100 ppm metal correspond to 3mg/30gsoil = 3,000 ug/30g soil40 ppm metal correspond to 1.2 mg/30 g soil = 1.200 u,g/30g soil

Iron treatment was achieved in the same fashion. Fe n was added to chromate containing soils(Section 3.6,3.7. Exp. #1 - 181). However, in the absence of chromate the Fe II was oxidizedwith H20j after addition to the soils (Section 3.8. Exp. # 181 - 249 and Section 3.9.3.10.3.11.3.12, Exp. # 250 - 316). This step could be eliminated by the direct application of Fe m to thesoil.

Silica treatment consisted of two approaches. In the experiments using acid gels, the silicasolution was destabilized with sulfunc acid before addition to the soiL In the experiments usingzeolite gels, destabilization was triggered by sodium aluminate addition. Following the additionof the destabilized silica solutions to the sofl, the mixture was air dried at 35°C and repurverized.This wss done for the following reasons:

1) the literature indicates no chemical changes with the exception of acceleratedcuring in gels up to 80°C (Her. The Chemistry of Silica, 1979);

2) accelerated curing by air drying also can occur in the field during hot, drysummers; and

3) air drying and repulverizing results in column flow rates fast enough for gelscreening studies.

In situ treatment was included also. In these experiments, silica treatment of the soil wasperformed in the column, leaving the gels undried. A stirring rod was used for manually mixingthe soils and silica solutions. This approach yielded inconsistent flow rates, sometimes resultingin channelling or complete blockage.

Next, the destabilized silica solution was forced into the sofl by applying a slight pressure on topof the glass column, combined with a slight vacuum from the bottom. This approach produced

column flow rates too slow for experimental purposes, especially before the development of thefinal gel formula. This procedure evidently resulted in a very homogeneous distribution of thegel in the soil causing nearly complete blockage. Column studies on in situ wet gels weretherefore abandoned in favor of sequential batch leaching experiments.

The equivalency of the leaching behavior of 1) gels dried at 35°C; 2) wet gels cured at roomtemperature; and 3) wet gels cured at 35°C; was proven experimentally in sequential batchleaching experiments (Section 3.12). Also, the leaching behavior of columns loaded with driedgels was compared to die leaching behavior of columns with in situ gels (Section 3.11).

2.3.3 Column and Sequential Batch Experiments

30 g soil was normally used in the column and sequential batch leaching experiments. Thisresulted in a soil column of 7 J cm. The pressure head was adjusted to yield 10 ml of effluentin 1-2 hours, if possible.The column effluents were captured in pore volume fractions in 40 ml borosilicate vials equippedwith screw caps and Teflon septums. The pH determination of each fraction was doneimmediately. Subsequently, the samples were acidified with concentrated nitric acid andanalyzed by AA (Atomic Absorption).

Sequential batch experiment samples were equilibrated for 24 hours and filtered. The solidswere re-exposed to 50 ml of fresh leaching fluid. This sequence was repeated 10 times. Thefiltrates were analyzed for pH and heavy metals.

2.3.4 Soil-Metal Isotherms for Single Metals

Soil-metal isotherm* were determined by equilibrating M gram of soil with V ml of metalsolution of concentration Co at room temperature (see Volume E, Appendix fl). Eight ouncewide mouth jars with closed-top caps and Teflon cap liners served as equilibration vessels. Thedesired pH was approached iteratively by adding acid or base. The samples were allowed toequilibrate in between pH adjustments for 8-16 hrs. The samples were filtered and Cf. the metalequilibrium concentration in solution, determined by atomic absorption. The isothermsdetermined for a single metal are not valid for a multi-metal matrix.

2.3.5 Metal Adsorption on Gels

Heavy tngtal protection by gels as a function of pH in the absence of soil was determined. Silica-heavy metal mixtures were allowed to gel 10 g gel were extracted with aqueous solutions atdifferent pH values. The metal concentration in the extraction fluid as a function of pH wasdetermined.

2.4 Data Reduction and Interpretation

2.4.1 Soil Metal Isotherms

When soil is exposed to a solution containing a heavy metal, adsorption of the metal on the soil isobserved. The amount of metal adsorbed is a function of pH. An increase of the metalconcentration in the system leads to an increased metal adsorption on the soil up to the pointwhere metal hydroxide precipitates. Further addition of metals leads to an increase of the amountprecipitated. The metal concentration in solution, however, stays constant

The adsorption behavior below the hydroxide saturation point can be described by a FreundlichIsotherm correlation:

Ax = (5)

= empirical constantsM = amount of soil added to <_V = volume of solution added to system (ml)C0 = starting concentration of metal in solution (mg/1)Cf = concentration of metal in solution after equilibration with soil (mg/I)

In the realm of validity of the Freundlich adsorption behavior we obtain a straight line in a doublelogarithmic plot Gog Ax/M over log Q). The slope of the line gives 1/n.

2.4.2 Reduction of Column Effluent and Sequential Batch Data

The results of the experiments #1 - 316 are tabulated in Appendix V. The leachate fractionvolumes for each experiment and the corresponding metal concentrations are shown.

VFurther data reduction was achieved by numerical evaluation of the integral:

V n nc(V) • dV « I ci • A Vj = Masseluted (ng) in I AVi (ml) (6)

c(V) = column effluent concentration (mg/I) as function of elution volume V (ml)i * l...n = number of elution fractionCi = metal concentration in fraction i (mg/1)AV{ s volume of i* fraction in (ml)

fiR302632

This numerical integration yields the micrograms ftig) of a metal leached in V ml if the fractionalamount eluted AV§ is measured in ml and the metal concentration in ppm.

Each series consisted of an experiment using soil contaminated with metals, but not treated(control experiment) and several experiments using identically contaminated soil which wastreated using different treatment schemes. The protection achieved by each treatment method wascalculated from the total mass eluted in V mis:

_ __ . /. mass eluted from treated soil \ ...% PTOtecuon = (l- ^ e,Kted conaol experiment ) * 10° (7)

2.4.3 Hydraulic Condpctivitv

The hydraulic conductivity is measured either in a constant-head or falling head permeameter. Asoil sample of length L and cross sectional area A is enclosed between two porous plates in acylindrical tube. A constant pressure head is applied and the effluent measured as function oftime.

FIGURE 2

Determination of the Hydraulic Coefficient

t. »•«— Continuous -,1 1 supply '7 •— T-J

• ' ~!-r! V^*•

H

r-T|-I ."'•".•** "•••"•*. L,.A. ;JL

^ i HOverflow

I— !Z1[j~ SSSS5i ;->-.: -1

. — .

0

THI1r

T ••-.•: • |7 --••• t

^— Head falls fromHO Hl in tifne Y

,fc— Cross -sectionalarea a

1 k • tii=l r Volume V Cross- sectional ^ Cross -sectionalin time t: area A area AQ»V/t

(ol (b)

(a) Constant-head permeameter; (b) falling-head permeameterTodd, D. K: Groundwater Technology (1959), Prentice-Hall

10

AR302633

It follows from Darcy's law for a constant head experiment:

Q-LHydraulic Coefficient Kn= [cm/sec]A * O

(8)

Q = V/t = effluent flow rate (cra3/sec)L = height of soil column (cm)A = cross sectional area of soil column (cm2)H = static head (cm)

and for a falling head experiment:

Hydraulic Coefficient Kh = 7 In ][j (cm/sec) (9)

a = cross sectional area of the static head column (cm2)HO = static head at beginning of experiment (mm)HI = static head at end of experiment (mm)t s duration of experiment (sec)Correlation (8) was used to estimate the hydraulic coefficient of sot! columns treated with in situgels and correlation (9) for virgin sou's.The range of values for unconsolidated natural deposits (Freeze and Cherry, Ground Water pg.29, Prentice-Hall, 1979) are as follows:

gravel: Kh = 10** to 10-> (cm/sec)clear sand: Kn= 1 tolO*3 (cm/sec)siltysand: Kh- UH to 10"5 (cm/sec)silt, loess: Kh = 10-' to Ifr7 (cm/sec)unweathered marine clay: Kn= 10-7 to 10*10 (cm/sec)

Hydraulic constants measured in Section 3.4 are 10r* to Ifr4 for virgin soils and 10-7 for geltreated samples.

11

ftR30263U

2.5 QA/QC (Quality Assurance and Quality Control)

The program required extensive analytical work. The methods employed were selected from SW346, EPA 600 and Standard Method protocols.

In particular, the following methods were employed: soil digestion (SW 846-3050); soil pH(SW 846-9045). aqueous pH (SW 9040). Metal determinations were performed by AA (Directaspiration). Cr-Method 7190, Pb-7420. Cu-7210. Cd-7130. Zn-7951. Ni-7520, Ca-7140.Mg-7450, Fe-7380, Mn-7460. The linear range of the spectrophotometer was determined andthe samples diluted so that the instrument readings fell within this range.

Recalibration of the instrument was done after 10-15 measurements. One sample of each testseries (10-15 samples) was chosen for duplicate analysis. Matrix interferences were checked forthe same sample by determining spike recoveries. The results of the duplicates and the spikerecoveries are given in the result tables contained in the Appendix V.

The matrix effect of silica could be overcome through sample acidification. This was proven bycomparing results for each element obtained by direct aspiration of acidified samples with resultsobtained by a 5-point method of addition determination.

The silica and sodium content of the N-silica were determined in duplicate.

SiO* Manufacturer 28.48% Found 28.1%; 28.1%Na2O: Manufacturer 8.97% Found 8.93%; 8.89%

The pH meter was calibrated using a two-point calibration at pH = 7.0 and pH = 10.0, if thesample pH was in the alkaline domain; and at pH 7.0 and pH 4.0, if the sample was in the acidicdomain.

12

AR302635

3.0 Results and Discussion

In this chapter the soils are characterized (Section 3.1); the adsorption capacity for single metalsare determined (Section 3.2); the composition of the silica gels and behavior are shown (Section3.3); the flow rate reduction achieved by silica treatment is determined (Section 3.4); chromatereduction and chemical fixation are addressed (Sec dons 3.5-3. 10); and tfce influence of gel curingmethods are studied (Section 3. 11-3. 12).

3.1 Soil Characterization

The physical and chemical characteristics of the soils are shown in Table 1. The X-raydiffraction patterns are provided in Appendix L

The aqueous soil extracts show pH values ranging from 7.7 to 8.5, which are expected in acalcite containing matrix.

The Round Rock soil was collected within the city. The elevated levels for copper, zinc.chromium and lead may have been caused by pollution.

Organic matter is highest in the Round Rock soil and lowest in the Balcones samples, asindicated by the analysis for total organic carbon. Round Rock soil contains the highest amountof clay. This was evident from its swelling characteristics when exposed to water.

X-ray diffraction results (Cu Kct radiation) show the presence of the following crystallinephases:

Balcones: Calcite: CaCC«3 major componentDolomite: Ca Mg(CO3)2 major component

Round Rock: Calcite: CaCO3 major componenta-Quartz: a-SiO2 major componentDolomite Ca Mg: (CO minor component

Colorado Calcite: CaCO3 major componentcc-Quartr a- SiOj major componentDolomite: CaMg(COj)2 minor component

The Balcones soil showed the most intense peak of cc-Quaitz at d = 3.35 (A) and possibly couldcontain small amounts of a-Si

Based on the X-ray results and the results of the chemical analysis, the Dolomite and Calcitecontent of the soils can be estimated:

Balcones: 46% Dolomite 18% CalciteRound Rock 6% Dolomite 16% CalciteColorado 4% Dolomite 19% Calcite

In these estimates it is assumed that the total amount of magnesium is bound in Dolomite.

&R302636

TABLE I

ParameterPacking Density (g/ml)Void Volume [ml/100 g soil]Moisture Weight %pH of 50% Slurry

Calcium (ppm)Magnesium (ppm)Iron (ppm)Manganese (ppm)Copper (ppm)Zinc (ppm)Chromium (ppm)Lead (ppm)Cftflfflitrnii Cpftfw jNickel (ppm)C0i%Organic Carbon (pom)

Balcones1.40332.98.50

320,00061.0002905.36.0111.30.120.030.7430.12,100

Round Rock1.20564.27.90

120.0007.6003308809.0341202

<0.012.009.65.600

Colorado1.15413.37.70

100.0005.1003103203.7283.40.91<0.011.5010.33.700

14

3.2 foil-Metal Adsorption Isotherms

The soil isotherms were determined for each soil to gain an understanding of the loadingcapacities for each metal and to discover any adsorption peculiarities.

The rate of nickel adsorption on soil was measured by exposing 15 g Balcones soil to 150 ml ofa 262 ppm nickel solution. The pH was held constant at 7.8. The nickel concentration insolution decreases from 262 ppm to 14 ppm in 23 hrs. After five hours 90% of the adsorptioncapacity was reached. In the studies to establish the isotherms, the solid-liquid equilibrium wasallowed approximately 12 hours equilibration time.

FIGURE 3

So.CL

.

Adsorption of Nickel in Balcones Soilas a Function of Time (pH = 7.8)

15 g Balcones Soil Equilibrated with150 ml of 262 ppm Ni

Time 10 reach » 90% equilibrium

Time (h)

The metal isotherms were determined by exposing soil to metal bearing solutions as discussed in2.3.4. Figure 4 shows the Cd soil isotherms for the three soils investigated at pH 7.8.

The solubility of the hydroxide limits the isotherms at their upper end. The limit for Cd is at aliquid equilibrium concentration of - 1 ppm at pH = 7.8. The soil adsorption capacity at thispoint is about 5 mg/g or 5000 ppm. The soil adsorption below this solubility barrier can bedescribed by a Freundlich type adsorption correlation. The equilibrium data for Pb, Zn, Cu. andNi are described in Appendix 0. The Pb. Zn, and Cu isotherms look similar to the Cd isotherm.The Ni isotherm lies closer to the Cf axis and the Ni(OH)2 regime is in the Cf=60 pprn range.

AR3Q2638

FIGURE 4

Cd Adsorption Isotherms for Colorado, Balcones and Round Rock Soil at pH = 7.8.

100

I :*"a"IH-|

10

i

.1 I

•/'*

.01

V-s <

JL[/

t

X\ f

ru

//

J

'!

K n s~ fS

rf

/

'f~

.1

/

,

a

^

''

'

I)T

f

HydroxidePretipctatfon

x^ >' X<t

\

r f

r a

8

Ba

Ro

Co

ben

aid

tom

M

(ta

to

{{UCOUS CHUIIII.IIMIIU buuu>uu«uuH »-tv

*

III,10

RPO)

16

* • *•

Chromate behaves differently. No adsorption was observed. This is indicated by comparing thechromium equilibrium concentrations with the starting concentrations in Table 0, which are inmost cases the same. The small amounts seemingly adsorbed at the 100 ppm concentration levelmay be lost by oxidation of organic matter in the soil rather than by adsorption. The ChemicalOxygen Demand (Procedure CWA 410.1) is based on oxidation of organic constituents bychromate. The reduction of Cr VI to Cr m by organic matter also may be the reason that thechromate elution never reached 100% in the column studies presented later (Section 3.6 and 3.7).

The isotherms were determined with single metals in solution. The adsorption characteristicsdetermined for a single element will change in a multi-metal environment

Table nAdsorption of Chromate on Soil

SoU Type

Sample*

Bclconcs1)2)3)4)5)

Rovad Rock1)2)3)4)5)

Colorado1)2)3)4)5)

SoU 100 ml ofCooccntntiOD

C.

1 100 ppm50 ppm25 ppm12.5 ppm6.25 ppm

100 ppm50 ppm25 ppmUJppm

Ig 6.25 ppm

100 ppm50 ppm25 ppm12.5 ppm6.25 ppm

EotiiliofinniPH

8.28.2128.212

8.18.08.18.18.1

7.77.77.77.97.9

cQtti n iM impCooccuuMion

Cf




AxAC

gSoil

0.2mg/gOmg/gOmg/gOmg/gOmg/g

Omg/gOmg/gOmg/gOmg/gOmg/g

0-6mg/g02 mg/gOmg/gOmg/gOmg/g

17

AR3026UO

3.3 SiHca Gel Composition (Add Gels and Zeolite

Two types of gels were used in the investigation, acid gels and zeolite type gels.Acid gels are generated by destabilizing sodium silicate solutions using sulfuric acid. Gel timedepends upon the pH and silica concentration as shown in Figure 5. Acid gels used in the studycontained up to 3% silica.

FIGURE 5

Gel Time of Sols Made from Sodium Silica Solutions and H}SO4as Function of Concentration and pH.

«.0 3.0 10 7.0 10 tO

ordicate-Time (minutes) required before gelationdetermined by arbitrary end point

abscissa-pH(Vail. Soluble Silicates. Volume 1.1952. page 197)

Gel times at 25.0*C of 3.3 ratio sodium silicate-sulfuric acidmixtures show most rapid gelation around an initial pH of7.5. (1) 1.00% SiOj; (2) 1.50% SiCfc (3) 2.00% SiOa; (4)2.50% SiO2; (5) 3.00% SiOj; (6) 3.50% SiO*

18

Zeolite pels were proposed by .Vail in 1938 (U.S. Pat. 2.131.338). Vail used sodium aluminatefor destabilizing sodium silicate solutions. Vail's basic recipe was modified to obtain gels with alower silica content One advantage of the zeolite gels is that most of the alkalinity of uSe sodiumsilicate is preserved due to the alkaline nature of sodium aluminate. This renders the gels morestable against acid attack, and more suitable for treating soils containing acidic reactingconstituents like the metal salts of strong inorganic acids.

The following zeolite gel formulations were used in the experiments.Gel #6: 2.25 parts 14.24% N-silica; 1.50 parts 5.3% sodium

aluminate (NajO. Al . 3HjO);2.00 parts 1 N H2SO4; 6.75 parts HjO;Gel Time: 3 hours

Gel.#6 Ml: 2.25 parts 14.24% N-silica; 1.50 parts 53% sodium aluminate;0.80 pans 1 N H2SO4; 7.95 parts H ;Gel Time: 25 minutes

Gel #6 M2 2.25 parts 14.24% N-silica; 150 parts 5.3% sodium aluminate;8.75jparts HjO;Gel Time: 40 minutes

Gel #2 3 parts 14.24% N-silica; 3 parts 5.3% sodium aluminate;6.5 parts HjO;Gel time: 4 rain.

Gel #2-10: 1 pan 7.12% N-silica; 1 pan 1.72% sodium aluminate(NaTO-AljOrSHzO);Gel Tune: 60 rain.

3.4 Hydraulic Conductivity of Soil Treated with Silica Gels

The hydraulic conductivity of soils treated with the zeolite gel 2-10 was estimated from thecolumn flow rate observed as a function of time using the constant head technique (Equation 8).The parameters valid for the column experiments themselves were used to determine the Khvalue in the Darcy equation. For the zeolite gel 2-10 a hydraulic conductivity of Kh = 6 x 10~7(cm/sec) was determined. The SiOj concentration in the zeolite gels was: 3.6%.

The determination of the hydraulic coefficient for Colorado sofl treated with acid gels yieldedKb = 15 x 10-7 (cm/sec). The SiO: concentration in the acid gels used in the experiments was2.4%.

The hydraulic conductivity for virgin Colorado soil was measured using the falling headtechnique (Equation 9). This determination yielded Kh = 1.2 x 10"2 (cm/sec). Results forBalcones soil and Round Rock soil gave Kh = 3.8 x IO*4 (cm/sec) and Kh = 1.3 x 10*3 (cm/sec)respectively.

19

fiR3026i*2

The silica treatment reduces the leachate flow rate by three to five orders of magnitude,depending upon the virgin soil characteristics.

Colorado soil plus acid gel: Kb= 1.5xlO*7 (cm/sec)Colorado soil plus zeolite gel: Kh= 6 x 10*7 (cm/sec)Virgin Colorado soil: Kn= 1.5 x Ifr2 (cm/sec)Virgin Round Rock soil Kh= 1.3 xlO*3 (cm/sec)Virgin Balcones soil: Kn= 1.8 x UH (cm/sec)

TABLEm

Experimental Parameters Used to Determine the Hydraulic Conductivityof Colorado Soil Treated with Zeolite Gel

Q(cra3/sec)L(cra)A (cm2)H(cra)

Kh(cm/sec)

Exn. 279

1.11x10-*7J93.1432.89

8.5 x 10-7

Exp 280

8.0 x 10-67.593.1432.89

5.8 x 10-7

Exo. 281

1.27 x 10-*6.333.1436.69

7.0 x 10-7

Exp. 282

7.75 x 10-'5.693.1435.42

4.0 x 10-7

Kh - 6 x 10-7 (cm/sec) for Gel 2-10

3.5 Metal Protection bv Add Gels in the Absence of Soil

A sodium silicate from Thomas Scientific with a NajOiSiOj ratio of 1:2.5 was used for theseexperiments. (All other experiments in the report were performed with N-silica.)

The objective was to investigate the leaching protection provided by acid gels for metals in theabsence of soil. The bulk of the data are described in Appendix EL

A mixture containing 1.35% SiOj. 300 ppm Fe n, and 50 ppm each of Cr VI, Zn, Cu. Pb, Cd.and Ni (300 ppm total metals) was gelled at apH =» 83 (gel time: 45 rain).10 g of the gel was subsequently extracted with 40 ml aqueous solution of a different pH. Theextraction fluid was analyzed for heavy metals (Table IV).

20

rTABLE IV

Extraction Results of Heavy Metals Protected by an Acid GelContaining 135% SiOj (No Soil)

(Concentrations in ppm)

Extraction pH

8.98.47.87.46.76.45.44.6

Cd

0.070.030.090.301.1 .1.8

Cr

0.070.020.060.040.080.020.080.04

Cu

0.080.010.030.030.030.202.14.5

Ni

0.100.070.070.160.280.350.751.3

Zn

0.070.030.030.050.130.471.6

Pb

<0.02<0.02<0.02<0.02<0.02<0.020.70.5

Fe

0.290.120.180.120.060.140.161.2

Maximum possible concentration in 40 ml extract:10.3 ppm Cd, Cr, Cu. Ni. Zn. Pb61.8 ppm Fe

The fixation of divalent metals is strong in the pH range 7-9. which is the expected pH range ofmost soils. Protection of Bivalent Fe and Cris observed at pH values as low as 4-5. From thedata presented in Table IV and in Appendix m we can derive the pH ranges for 99% protectionby the 135% SiOj gel containing 50 ppm each of the metals:

Cr pH=4-9Pb pH = 65-9Cu pH = 6.5-9Zn PH = 7-9Ni pH= 7.5-9Cd pH = 8-9.

The lead values need to be verified in a matrix free of chromates (see Section 3.8). Leadchromate (PbCKXO is very insoluble (0.058 mg/I. Handbook of Chemistry and Physics). Thetow lead values could be caused by precipitation of lead chromate, but experiments presented inSection 3.8 show an excellent protection for lead in the absence of chromate.

21

AR3026UU

3.6 Iron II and Acid Gels; Fixation of Chromates (Exp. <1 - 126)

fa situ chromate reduction using FeSO4 • 7HjO was tested on all three soils in experiments #1 -126.

Cr VI was the only metal loaded into the soil in this series. The chromate levels chosen were 40and 400 ppm.

Fixation was achieved through Fe n and acid gel treatment. Three moles of iron n are oxidizedby 1 mole Cr VI reduced to Cr IE (see Equation 1). An iron n addition of 220 ppm correspondsto 1.7 times the necessary stotchiometry at the 40 ppm Cr VI loading level. The iron addition for400 ppm Cr VI soil was 1680 and 2200 pprn Fe U. This corresponds to a stoichiometry of 1.3and 1.7. respectively.

The soil samples were treated with silica gels formed by destabilization of N-silica with sulfuncacid. The silica concentrations chosen were varied up to 3.0%. The silica treated soil was driedat 35°C and repulverizedDI water and TCLP extraction fluid #1 (pH=4.93± 0.05) and #2 (pH = 2.88 ± 0.05) were usedin column experiments to determine the leaching resistance of the treated soilThe experimental data are listed in Appendix V. These data were further condensed byintegrating the elution curves numerically up to 100 ml or 200 ml e&Iuent (see Section 2.4.2).These integrations yield the total amount of each metal leached in micrograms. See Table V.

30 g soil loaded with 400 ppm Cr VI contains a total of 12.000 jig Cr. The recovery in thecontrol column experiments (no iron and no silica treatment) ranged from 7,600 jig (Coloradosoil) to 1 1,900 |ig (Balcones soil). This variation may have been caused by organic matterwhich reduces chroraate. The organic matter found in the soils was lowest in the Balcones soil(2100 ppm organic C) and highest in Round Rock soil (5600 ppm organic Q. See Table L

30 g soil impregnated with 40 ppm Cr VI contains 1200 pg Cr. The eluents of the controlcolumn showed recoveries ranging from 700 to 1024 pg. Again the presence of organic mattermay have caused Cr VI reduction.

The findings in Table V are summarized as follows:Treatment with iron only yields protection similar to treatment with iron plus silica. The

averaged treatment results (c) show the following:

Cr40 Colorado: pH = 7.8 95.7% Protection 6 = 0.30 ppmRound Rock: pH = 7.8 96.8% Protection c = 0.25 ppmBalcones: pH = 8.3 98.7% Protection C = 0.12 ppm

Cr400 Colorado: pH = 7.8 96.8% Protection c= 1.4 ppmRound Rock: pH = 7.9 95.9% Protection 5 = 4.3 pprnBalcones: pH = 7.9 98.5% Prot: -lion c = 1.9 pprn

22

TCLP fflCr40 Colorado: pH = 7.6 95.8% Protection c = 0.30 ppm

Round Rock: pH = 7.4. 97.1% Protection C = 0.12 ppmBalcones: pH = 7.6 97.9 % Protection t = 0.24 ppm

Cr400 Colorado: pH = 7.4 98.4% Protection C = 0.14 ppmRound Rock: pH = 75 98.6% Protection £ = 0.22 ppmBalcones: pH = 7.7 98.4% Protection c = 0.18 ppm

TCLP #2Cr40 Colorado: pH = 75 95.1% Protection c = 0.03 ppm

Round Rock pH = 6.7 973% Protection C = 0.02 ppmBalcones: pH = 73 99.2 % Protection £ = 0.01 ppm

Cr400 Colorado: pH = 6.7 98.8% Protection c = 0.09 ppmRound Rock: pH = 7.2 995% Protection c = 0.05 ppmBalcones: pH=7.7 98.4% Protection C = 0.18 ppm

3.6.1 Snmmary

The column effluent chromium concentrations are highest in die leachatcs of treated Cr400 soilsleached with pi water. The column effluents contained between 1.4 ppm and 43 ppm Cr.

When TCLP #1 and TCLP #2 are used to teach Cr 400 soils, the effluent concentrationsdecrease to 0.14- 0.22 ppm (TCLP* 1) and to 0.05 - 0.18 ppm (TCLPt2). The acidity of theseteaching fluids is neutralized to a large extent by the calcite in the sofl as fe obvious from the onlyslight decrease in effluent pH. The amphoteric character of chromium may be responsible for thedecrease of chromium with decreasing pH.The low sofl adsorption of chromate observed in Table n causes the extremely high concentrationof Crin the first pore volumes of leachate through soil not treated with iron. This behavior is thebasis for Cr VI removal by soil washing as is currently practiced.Figure 6 illustrates the leaching behavior of treated and untreated Cr VI contaminated sofl.

23

AR3026U6

Table V

Treatment Evaluation of Soils Impregnated with Cf VI

Expf

74737778

80318384

86878990

92939396

9899101102

0410S107103

Tie111113114

s117119120

SoU

CoLCol.Col.Col.

Col.Coi.Col.Col.

Col.Col.CoLCoL

BafcBafcBafcBafc

BafcBafcBafcBafc

BafcBafcBafcBafc

RRRRRRRR

RRRRRRRR

Treatmentppm Cr VI

40404040

40404040

40404040

40404040

40404040

40404040

40404040

40404040

ppniFeU

220220220

_220220220

220220220

220220220

220220220

-

220220220

-

220220220

-

220220220

% Silicain fel

—1.8%17%

_ _-.U%17%

. _ '_

1.8%17%

— —11%3.0%

___ ~11%3.0%

.._11%3.0%

_1.4%11%

._

1.4%11%

Eztr.Fluid

DICIaa

TCLPflTCLPflTCLPflTCLPfl

TCLPf2TCLPflTCLPflTCLPfl

DIDIraa



DIDIDIDI


Button inpH Cm 100 ad Protection

efrineei

7.4 -#7.97J-»7.97.4-* 8.17.8 -»8J

7.6 -» 7.37.6 -» 7.67.7-»7J3.0-* 7.6

7.4 -#7.37.1 -#7.28.0 -* 7.77.7 -» 7.6

8.2 -» 8.07.9 -#8.17.7 -+8.68J-#9J

7.6 -#7.47 J -# 7.47.7 -» 7.47.9 -# 7.4

7.3 -#7.37.3 -# 7.37.3 -#6.97J -» 7.1

7.6 -» 8.07.3 -» 7.67J-+7J7J-»8J

7 J -# 7.47J-»7J7.6 -» 7.67 J -» 7.6

(•200ml)

697.128J29.7312

710.329.931.127.9

684.423.946328.4

931914.28.813.0

1.00349.611.711.1

1.0246139.337.99

77330J21021J>

•833•27.0*24.0•210 -

*

93.9%93.7%93.4%

95.8%93.6%96.1%

96J%93.2%45.9%

98J%99.1%98.6%

.93.1%981%98.9%

_99.3%99.0%99.2%

96.0%97.2%973%

.96.8%97.1%97.4%

24

aR3026l*7

Table V(continued)

Treatment Evaluation of Soils Impregnated with Cr VI

Erpf

1221?3121126

111224

262730

323336

8921

141516

138443942

50565760

61686366

Soil TratrppmCrVI ppm Ft IE

RRRRRRRR

Col.Col.Col.

Col.Col.Col.

Cot.Col.Col.

Bale.Bale.Bale.

Bale.Bale.Bale.

RRRRRRRRRR

RRRRRRRR

RRRRRRRR

40404040

400400400

400400400

400400400

400400400

400400400

400400400400400

400400400400

400400400400

120120120

16801680

^

16801680

_16801680

16801680

_16801680

——

22002200

_—

22002200

_—

22002200

nent% Silicain f el

—1.4%11%

—1Mb

—1.4%

—1.4%

—11%

__11%

—_—

3.0%

..—_

3.0%

„—_

3.0%

Ear.'Raid

TCLP f 2TCLPflTCLPflTCLPfl

OfDIOf

TCLPflTCLPflTCLPfl

TCLPflTCLPflTCLPfl

CfnCf

TCLPflTCLPflTCLPfl

CfCfCfCfCf



PHrange ofeffluent

7.0-»6.96.9 -* 7363-4 636.6-»63

»..u73 -+7.67.7 -#83

75-»73' .7 -+ 737.7 -+ 7.0

6.4-* 6161-* 6.47.0 -» 6.6

7.9-* 8.07.6 -* 7.97.7-* 8.0

7.9 -» 7.67.9 -» 7371 -» 7.6

71 -» 7.68.0 -» 7.97.9 -»8X)7.6 -* 8.07.9-* 83

73-* 7.47.7-»7371 -» 737.7 -» 73

7.1 -* 7.07.1 -* 7373-»737.6-* 73

Botioo inCm 100ml(•200 ml)

fuel

•773•18.7•153•193

9.619169108

8384137149

74619774

11168169107

11.074150207

11.9009.6099.920437428

9.7978.113295138

9.1159104

1688

Pnxectica*

97.6%96.7%973%

983%98.9%

98.4%98.3%

98.7%99.0*

98.6%983%

98.6%98.1%

—_

951%95.9%

_—

96.7%983%

.—

991%99.1%

25

ftR3026l*8

i j i i i i i i

It!!!!!!4*2U!!! IIiiiiiilii!WWrW

J

1 I I IIJMMa s * * *3 33 H

Wdd

26

3

flR3026U9

3.7 Iron II and Acid Gels; Fixation of Chromate* Plus Metals

In these experiments the heavy metal matrix was expanded to include the metals Pb, Zn. Cu. Cd,and Ni in addition to chromate. The results are summarized in Table VL

Fixation was achieved through Fe II and add_g£l treatment

The soils were dried and repulverized after silica treatment The experimental matrixencompassed the following variables:

1) Soil: 30 g Colorado

2) Leaching fluids: DI. TCLP ffl. TCLP« .

3) Metalloading: Cr 40 Met 40 (Total Metals -240 ppm)Cr 400 Met 400 (Total Metals - 2400 ppm)

4) Ironkvel: 220 ppm Fe U in Cr 40 Met 40corresponding to 1.7 x stoiduometry

2200 ppm Fe n in Cr 400 Met 400corresponding to 1.7 x stoidaometry

5) Gel Type Add Gets

Each set of experiments consisted of

1) sofl impregnated with Cr VI and metals, untreated (control column); ,..,.2) soil impregnated with metals, treated with iron only, and3) soil impregnated with metals, treated with iron and silica at two concentration levels.

The leachate curves were integrated up to 200 ml column effluent to arrive ax the mkrograms ofeach metal eluted in the first 200 ml of column effluent The protection percentage was calculatedfor the treated samples in relation to the control column, using Equation 7 (Section 2.4 J).

3.7.1 Chromium

Chromium shows behavior similar to that discussed in Section 3.6. Treatment with iron onlyprovides the same protection as treatment with iron plus silica. The treatment result averages for200 ml elution volume are listed below:

DL Cr 40 Met 40 pH = 7.2 96.8% Protection c-0.09 ppmCr 400 Met 400 pH = 7J 96.5% Protection c = 0.84 ppm

TCLP if 1 Cr40Met40 pH = 7.3 962% Protection C = 0.10ppm

TCLP #2 Cr40Met40 pH = 7.1 97 J% Protection c = 0.09ppmCr 400 Met 400: pH = 6.8 98.1% Protection t = 0.41 ppm

27

AR302650

3.7.2There is no significant difference between iron treatment alone and treatment with iron plus silica.The treatment result averages are listed below:

EL Cr 40 Met 40 fH = 7.2 -100% Protection c<0.02ppmCr 400 Met 400 pH = 7J 93.4% Protection c = 0.03 ppm

TCLP Ml Cr 40 Met 40 pH = 7.3 74.3% Protection c<O02ppm

TCLP*2 Cr 40 Met 40 pH = 7.1 -100% Protection C<0.02ppraCr400Met400 pH = 6.8 -143%* Protection £* O.I3 pprn

*Tbe negative rmtectior percentage found for Cr 400 Met 400 using TCLP #2 hinges on 11 figPb leached from the control column, which is unrealisticafly tow.

3.7.3 ZincIron i lus silica treatment proved superior over iron treatment alone. No marked difference isobvio is between the silica levels. The silica treatment result averages are listed below:

£>£ Cr 40 Met 40 pH = T-2 57.5% Protection C = 0.01 ppmCr 400 Met 400 pH = 7.5 89% Protection c = 0.21 ppm

TCLP Ml Cr 40 Met 40 pH = 7.3 42% Protection C = 0.25 ppm

TCLP if! Cr 40 Met 40 pH = 7.1 47% Protection t = 0.41 ppmCr40GMet400 pH>6.8 45% Protection c = 31.ppra

3.7.4 Copper

Iron plus silica treatment showed no clear advantage over iron treatment alone. Also, no cleardifference between the two silica levels is obvious. The silica treatment result averages are listedbelow:

QL Cr 40 Met 40 pH = 7.2 6% Protection £ = 0.18 ppmCr 400 Met 400 pH = 7.5 16% Protection c = 0.50 ppm

TCLP MI Cr 40 Met 40 pH = 7.3 8% Protection c=>0.15ppm

TCLP #2 Cr 40 Met 40 pH>7.1 17% Protectioa C = 0.13 ppmOr 400 Met 400 pH = 6.8 66% Protection

28

3.7.5 Cadmium

Iron plus silica treatment provided greater protection than iron treatment alone. There is nopattern in the differences between the two silica levels. The silica treatment result averages arelisted below:

& Cr40Met40 pH = 7.2 10% Protection C = 0.05 ppmCr 400 Met 400 pH = 7.5 25% Protection C = 2.7 ppm

TCLP Ml Cr 40 Met 40 pH = 7.3 8% Protection c = 0.77 ppm

TCLPM2 Cr 40 Met 40 pH = 7.1 37% Protection c = 0.93ppraCr400Met400 pH = 6.8 23% Protection t = 37.ppm

••

3.7.6 Hi£fc£l

Silica plus iron treatment proved superior to iron treatment alone. No significant difference isobserved for the two levels of silica. The two values were averaged.

QL Cr 40 Met 40 pH = 7.2 20% Protection c = 0.18 ppmCr 400 Met 400 pH = 7.5 60% Protection 5=1.3 ppm

TCLP Ml Cr 40 Met 40 pH = 7.3 38% Protection C = 0.54 ppm

TCLPM2 Cr40Met40 pH = 7.1 57% Protection £ = 0.89ppmCr 400 Met 400 pH = 6.8 48% Protection c = 25.ppm

29

3.7.7 Summary

Cr and Cu: The addition of silica provided no improvement over iron n treatment alone.

Zn. Cd. and Ni: Iron n phis silica treatment increased protection over iron n treatment alone.

CrandPb showed in all cases concentrations below 1 ppm.

Leachate concentrations above 1 ppm were only found at the Cr 400 Met 400 level for Cd and Niin DI water, for Zn, Cu,Cd and Ni in TCLP #2.Group I: Leachate concentration below 1 ppm

Cr 40 Met 40 Cr £ 0.1 ppm for all three leaching fluidsPb £ 0.02 ppm for all three leaching fluidsZn S 0.41 ppm for all three leaching fluidsCu £ 0.18 ppm for all three leaching fluidsCd S 0.93 ppm for all three leaching fluidsNi £ 0.89 ppm for all three leaching fluids

Cr 400 Met 400 Cr = 0.84 ppm for DI 0.41 for TCLP #2Pb = 0.03 ppm for DI 0.13 for TCLP #2Zn =0.21 for DI see belowCu = 0.50 for DI see below

Group 2: Leachate concentraions above 1 ppm

Cr 400 Met 400 Zn see above 31 for TCLP #2Cu see above 2.5 for TCLP #2Cd = 2.7 for DI 37 for TCLP #2Ni = UforDI 25TCLP#2

The higher metal concentration in the leachate observed at the Cr 400 Met 400 loading level,indicated above, led to the examination of other gel formulations as described in Section 3.9.

30

z1 5

ai <$

> C<

i s «* £• .5 —

1 fgp

6I j 1?

if J«fmlfffJjJiJSl

z

2

£

i

d

I'

ii

1'H

J*a.

|1i!

j.1ii_^

1|(a

&•

'•• r'«•-•. ' •> « '««(• '»•<• '•>«•

— « • « n «••>.• • e e e oeoo e e e o2 (tv** n — b » n *i b •' •'•>•» •' « N b

• K Ml «

oeo « e e ee ooe 00.0

•• v • • O ' B • • <•«•« *.».•» • K. • _i •• — ••«<• •**• «••* •••«

oo« oeo. • • « . ». — • ,K.O« .•*• .»•••« — - - MM •••

S*«*>» «i O • — ^ • « • • • 0 • O — <• ••• •• *» « •» n w A ft w w w w * So i^ • • «

.MAO. . • K. K. ,O»» . AOO .•>•!•»•>• .w« ««* •«•• ww

_ **"£ ••.•o >o«o eooo oeoe£ «b*w ik «» • ri^oti «bb«i «>*i^b

**. * *•**

"y ooeo •« — b b ooeb b • •» •" — — • W

— *« ••— — •» ««t> on —sss srs is: sss :ss2 »' • •' b • — b v<*e*i <•' • b b »•'•"•!

V V«•••» •>•»>»» •».«e ••••>• »«««*:»»:*: ^w«>: «««•: ^^^w ••••

ssss sees erst555S Siii iiii 5SS5 5555OOOu OO O O OvOO

«*« Mfb «|p O* O~

SSSS '£££ -222 -SSS -SSS«••!•»•• «••«•• *»«*•• •»•§•• **£**

fifififi fifififi

2222 hi! IIIl 2222 2222«««« «««« «««« mi finoooo coco ooeo ooao oooo

S W«.l«» ««•>•• »»»• S fkfclk*. >.•»»•

3.8 Iron fll. Acid C«is. Zeolite Gels; Fixation of Metals (Eip.t 181 . 249)

In the experiments #1-126 soils impregnated with Cr VI only were researched (Section 3.6) andin experiments #127 - 180 soils containing Cr VI plus metals were investigated (Section 3.7). Inexperiments #181 - 249 discussed below, the leaching behaviors of soils impregnated with Pb.Zn. Cu. Cd and Ni, in the absence of chromate were studied.

Fixation was achieved by Fe HI and acid /zeolite gel treatment At the start of the test series acidgels were screened for effectiveness. Toward the end, zeolite type gels of different compositionswere included in the program. The formulation of the zeolite gels was described in Section 3.3.

Lead protection through PbCrQi precipitation was impossible in the absence of chromate.

3.8.1 Protection of Lead bv Iron HI. Acid Gels, and Zeolite Type Gels in The Absence of

Table VII summarizes the leaching behavior of Pb in Colorado soil impregnated at the 40 ppmand 400 pprn level with Pb, Zn, Cu, Cd and Ni and no chromate.

The experiments showed no detectable Pb in the effluents of Met 40 soils whether treated oruntreated. This is true for DI and TCLP #1 as leaching fluid.

Lead (Figure 7Ql Met 40 pH = 7.7 -100% Protection c<0.02ppm

TCLP Ml Met 40 pH = 7.6 «100% Protection c<0.02ppmMet 400

Acid gel treatment only pH = 7.4 4-13% Protection c = 2.1 ppmIron IH treatment only pH = 7.4 74% Protection c = 0.57 ppmAcid gel -f iron m treatment pH = 7.4 74% Protection c = O.57 ppra6600ppraFeIII + Gel2-10 pH = 8.6 - 100% Protection c<0.02ppm

Of interest are the results obtained on Met 400 soil using TCLP #1 as shown in Figure 7. Thegraph en the left describes the results obtained with iron ffl and acid gels. Reduction in theleachate concentration is mainly caused by iron HI; silica treatments using acid gels iiiconjunction with iron show no further improvement. The graph on the right illustrates thedramatic improvement in protection provided by iron fll in combination with zeolite gels.

3.8.2 Protection of Zinc. Copper. Cadmium and Nictel by Iron HI. Acid Gels, and ZeoliteType Gets in the Absence of Chromate

Zn. Cu. Cd and Ni in the absence of chromate show a similar behavior if protected by iron andacid gels as was observed earlier in the presence of chromate (Chapter 3.7). Therefore, nofurther discussion is necessary. The findings are listed in Appendix V.

A marked increase in protection was observed using the 6600 ppm Fe ffl - gel 2-10 treatmentTherefore, the effort in the remainder of the program centered on this treatment strategy and isdiscussed in the following sections.

32

Table VTI #;£•

Pb Protection by Iron, Acid Gels, and Zeolite Gelsin the Absence of Cr

Soil Loading: Met 40 (Total Metals - 200ppm), and Met 400 (Total Metals- 2000 ppm)

Exp*

Acid Cell181182183184185186

Acid Geb191192193194195196

Acid Geb202203204205206207

Soil30f

Col.Col.Col.Col.Col.Col.

Col.Col.Col.Col.Col.Col.

CoLCol.Col.Col.Col.Col.

Pbppm

404040404040

404040404040

400400400400400400

j tjjj fflltppmFein

.-.220220220

.-.220220220

.

.

.220022002200

% Silicain eel

..34%.87%.

.34%

.87%

..34%.87%.34%.87%

..34%.87%-

.34%

.87%

Extr.Fluid

IXIXIXIXIXM

TCLP«1TCLP«1TCLP«1TCLP«1TCLP*lTCLP«1

TCLPflTCLP*1TCLPflTCLPflTCLPflTCLPfl

PHrange of

——— effluent

7.5 -> 7.97.4 -» 7.97.5 -» 827.6 -* 7.973 -» 8.012 -» 8.1

7.8 -» 7.17.8 -» 7.57.5 -» 7.47.6 -» 7.67.7 -» 7.87.5 -» 7.3

6.6 -» 7.87.1 -» 7.86.8 -» 6.87.3 -» 8.17.6 -» 7.77.4 -» 7.7

Ehitiooto fint 2

— 200 ml tig

<4w<4|ig<4|»g<4|ig<4juj<4|»g

<*vt<4|Uj<4|uj<4|tg<<M<<W

433 JM414.9 |ig376.0 »tg114.8|l«118.4 n101 .4 ut

PnxcctioQ%

.. 4%13%74%73%75%

Zeolite Cell238239240241242243298

Col.Col.Col.Col.Col.Col.Col.

400400400400400400400

.220022006600220066006607

,

gel* 6gelfcSMlfe!*6M2gel*2*d*2Cd 2-10

TCLPflTCLPflTCLPflTCLPflTCLPflTCLPflTCLPfl

6.6 -» 7.175-»7J8.2 -» 7.58.3 -» 7.48.6 -» 7.78.4 -» 7 J8.5 -» 8.2

273 JW24 2MU.7 «<<M«2.7 W<<W<4W

.fl.2%94.7%

«1H%99.0%

»1H%»1M%

33

AR302656

1 LEACHING BEHAVIOR OF PbPROTECTED BY Fa AND AOO CBS

o

O

# Exp. 2C* 2200 ppm F*m;NaSIci

•

O Dp. 207 2200 ppm P* 10; 0.17%

O •

iH. 1H

100 200 300

3-

Exp. 29ft MOO ppm F* It M 2-«9

2-

0

LEACHNQ BBHAVKJfl OF FbPROTECTED BY F« AND ZEOUTE GS2

a Et9L23fcUrWMl«i

Bcpk 24* 2200 ppnF»*G*tt

*A*

100 200

ml EFFLUENT

Figure 7: Comparison of Pb concentration in column effluents using addand zeolite eelsLoading: Pb. Cu. Zn, Ni, Cd: 400 ppm eachLeachate: TCLP Extraction Fluid #1

34

3.9 Iron m and Zeolite Get 2-10: Fixation of Metals (Exp. #250 - 316)

The remainder of the experiments centered on the treatment with 6600 ppm Fe JH and the zeolitegel 2-10.

The results obtained on soils which were dried and repulverized after silica treatment arepresented below. (Results obtained on in situ gels and the data obtained on sequential batchextractions are presented in Sections 3.10 and 3.11. respectively.)

The experimental matrix comprised the following variables:

1) Soil: Colorado. Round Rock. Balcones; 30 g in each experiment

2) Leaching Fluids: DI and TCLP #1

3) Metal Loading: Colorado: Met 40. Met 100, Met 400Round Rock: Met400Balcones: Met 400

4) Iron Level: Constant at 6600 ppm Fe m

5) Gel Type: Gel 2-10

The experimental data are summarized in Table VDX The data arrangement is the same as wasadopted in previous tables. The metals leached in ug were calculated for the first 500 ml ofleachate, which equals 40 pore volumes.

The graphical representations in Figures 8-12 illustrate the column dynamics for each metal.The behavior of each element is discussed below.

3.9.1 Lead Figure 8):

QL Colorado Met 40 No lead detected in effluent c<0.02ppmColorado Met 100 of treated and untreated soil c <0.02 ppmColorado Met 400 -100% Protection c<0.02ppmRound Rock Met 400 37% Protection c<0.02ppmBalcones Met 400 95% Protection -c<0.02ppm

The detection limit for lead by flame AA is 0.02 ppm. The lead detected in Round Rock Met 400and Balcones Met 400 was contained in the first pore volume of column effluent.

Average cohsnn effluents pH: = 8.3.

35

flR302658

1TCLP Ml Colorado Met 40 -100% Protection c<0.02ppm

Colorado Met 100 - 100% Protection c <0.02 ppmColorado Met 400 ». 100% Protection C <0.02 ppmRound Rock Met 400 - 100% Protection c <0.02 ppmBalcones Met 400 - 100% Protection c <0.02 ppm

Average column effluents: pH = 7.9.

3.9.2. Ztne. (Figure 9V

QL Colorado Met 40 -7% Protection C = 0.015 ppmColorado Met 100 89% Protection c = 0.006 ppmColorado Met 400 99.5% Protection c = 0.004 ppmRound Rock Met 400 . - 100% Protection c<0.004ppmBalcones Met 400 -100% Protection c<0.004ppm

The detection limit for Zinc by flame AA was 0.004 ppm.

Average column effluents pH = 8.2.

TCLP Ml Colorado Met 40 95% Protection c = 0.02 ppmColorado Met 100 94% Protection c = 0.19 ppmColorado Met 400 97% Protection c = 0.76 ppmRound Rock Met 400 99.2% Protection c = 0.05 ppmBalcones Met 400 99.3% Protection C = 0.04 ppm

Average column effluents: pH * 7.9Unprotected soil showed the highest effluent concentration in Colorado Met 400 with 24 ppm.

3.9.3 Copper (Figure 10)

121 Colorado Met 40 No Protection c = 0.18 ppmColorado Met 100 No Protection c = 0.27 ppmColorado Met 400 No Protection c = 0.35 ppmRound Rock Met 400 No Protection c = 0.52 ppmBalcones Met 400 No Protection C = 0.10 ppm

The detection limit for Cu is 0.007 ppm.

Avenge column effluent pH s 8.2

36

TCLP Ml Colorado Met 40 28% Protection c = 0.12 ppmColorado Met 100 37% Protection c = 0.19 ppmColorado Met 400 80% Protection c = 0.57 ppmRound Rock Met 400 32% Protection c = 0.43 ppmBalcones Met 400 83% Protection c = 0.10 ppm

Average column effluent: pH = 7.9Copper was observed in all cases to show an exceptionally high concentration in the first porevolumes (see Figure 10).

3.9.4 Cmdmium (Figure 11)

QL Colorado Met 40 89% Protection c = 0.004 ppmColorado Met 100 94% Protection is 0.012 ppmColorado Met 400 99.4% Protection c = 0.037 ppmRound Rock Met 400 96% Protection c = 0.091 ppmBalcones Met 400 98% Protection c = 0.044 ppm

Average column effluent: pH = 8.2

TCLP Ml Colorado Met 40 95% Protection t = 0.04 ppmColorado Met 100 93% Protection c = 0.18 ppmColorado Met 400 94% Protection c = 1.05 ppmRound Rock Met 400 97% Protection £ = 0.22 ppmBalcones Met 400 97% Protection c = 0.06 pprn

The detection limit for cadmium is 0.004 ppm.


3.9.5 Nickel fFipure 12)

Qi Colorado Met 40 9% Protection c = 0.10 ppmColorado Met 100 53% Protection c = 0.15 ppmColorado Met 400 94% Protection c = 0.12 ppmRound Rock Met 400 82% Protection c = 0.10 ppmBalcones Met 400 74% Protection c = 0.05 ppm

The detection limit for nickel is 0.02 ppm.


37

AR302660

TCLP Ml Colorado Met 40 32% Protection c = 0.12 ppmColorado Met 100 90% Protection e = 0.46 ppmColorado Met 400 75% Protection £ = 3.92 ppmRound Rock Met 400 85% Protection C = 1.90 ppmBalcones Met 400 76% Protection C = 2.59 ppm


3.9.6 Summary: Treatment Effect of Iron plus Gei 2-1Q fZcoHt* Cell

The treatment strategy using Fe HI in conjunction with zeolite gel 2-10 provided effective treatmentfor the conditions shown in Group I and partial effectiveness under the conditions shown inGroup II.Group 1: The following soil-metal combinations show less than 1 ppm concentration in effluentswith DI water and TCLP #1 teaching fluid:

DI TCLPJHLead; Colorado Met 40. Met 100. Met 400 <0.02 ppm <0.02 ppm

Round Rock Met 400; Balcones Met 400

Zinc: Colorado Met 40. Met 100. Met 400 50.015 ppra 20.76 ppmRound Rock Met 400; Balcones Met 400

Copper Colorado Met 40. Met lOOjn Met 400 50.52 ppm 50.57 ppmRound Rock Met 400; Balcones Met 400

Cadmium Colorado Met 40. Met 100 50.09 ppm 50.22 ppm

Nickel Colorado Met 40. Met 100 50.15 ppm 50.46 ppm

Group n The following soil-metal loading combinations produced effluents of less than 1 ppmconcentrations with DI water as the leachate and of more than 1 ppm concentration with TCLP #1 as

Nickel Colorado Met 400 0.12 ppm 3.92 ppmRound Rock Met 400 0.10 ppm 1.90 ppmBalcones Met 400 0.05 ppm 2.59 ppm

Cadmium Colorado Met 400 0.04 ppm 1.1 ppm

Effluent concentrations above 1 ppm are only found at the Met 400 level using TCLP f 1:

Nickel reaches values > 1 ppm in all three soils.Cadmium reaches values > 1 ppm only in Colorado sofl.

The treatment shows no effect on copper in DI water. In TCLP #1 protection from 28% to 83%was measured.

38

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AR302662

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AR302663

Figure 9:

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AR302661*

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42

Figure 11: Cd

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3.10 Coiuron Behavior up to QOQ ml Effluent for Zinc. Cadmfum. and Nickci(Colorado Met 400: TCLP »1>

In Section 3.9, the teachates for Colorado soil loaded at the Met 400 level and leached by TCLP#1 contained the largest concentrations of zinc, cadmium and nickel. Therefore, columnexperiments were extended to 1000 ml eluate to determine long-term eluate characteristics. SeeFigure 13.

The zinc and cadmium curves reach a plateau at 5 ppm and seem to stay constant, while theleachate concentration for nickel reaches a broad maximum at 10 ppm and falls slowly back to theeffluent axis.In all three cases no breakdown of the iron plus silica gel protection is observed.

45

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Loading: Pb. Cu. Zn. Ni and Cd; 400 ppm eachLeachate: TCLP Extraction Fluid ilTreatment: 6600 ppm Fe HI and Gel 2-10

46

3.11 Comparison of in Situ and Dried Gel Experiments

The results contained in previous sections are for experiments conducted with soils which weredried and repulverized after treatment This step was necessary to obtain samples amenable totimely screening experiments. However, several experiments with in situ gels also wereperformed. The silica-soil contact was achieved by manual mixing in the columns using a rod orby the pressure/vacuum technique. See Section 2.3.2.

Manual mixing resulted in erratic flow rates: Exp 228 (11 ml/hr); Exp 229 (2 ral/hr): Exp 230(3 ml/hr); Exp 231 (3 ml/hr); Exp 232 (0.1 ml/hr); Exp 233 (4 ml/hr). Evidently the soil-silicamixture was not homogeneous in columns prepared by manual mixing. The flow rates variedmuch less if the pressure/vacuum technique was used: Exp. 279 (0.040 ml/hr); Exp 280(0.029 ml/hr); Exp 281 (0.046 ml/hr); Exp 282 (0.028 ml/hr). The pressure vacuum techniqueyielded flow rates too slow for timely experimentation.

In Table DC the leaching results obtained on in situ experiments are compared with resultsobtained on soils which were dried and repulverized after silica treatment. The amount, of metaleluted in the first 200 ml of eluate are listed. The amounts are generally within a factor of two.Larger deviations especially for Cd and Ni in experiments #220 and f 228 may be caused bychanneling in Experiment #228; the flow rate of 11 ml/hr is much higher than that observed inother ULfjni, experiments. The channeling effect also could explain the smaller amount ofmetals found in in situ experiment #228.

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3.12 Sequential Batch Extractions

Sequential batch experiments were performed to study further the influence of air drying. Soils.impregnated with 400 ppm each Pb, Zn, Cu. Cd, and Ni, were treated with iron and gel 2-10.Following the silica treatment. the soil was:

1) Air dried at 35°C and repulverized,2) Wet cured at room temperature for 3 days,3) Wet cured at 35°C for 3 days.

The samples were sequentially batch extracted with 50 ml leaching fluid. The results axe shownin Table X. The variations observed are much smaller than those observed in Section 3.11using in situ gels. All three treatment methods yielded essentially the same results. It caa beconcluded that the soil drying step at 35°C does not alter the wet gel properties.

Thtf lead values in the DI water extracts are higher than those in TCLP f 1. See Table X. Theaverage pH value in the DI water extracts is pH = 9.2, compared to pH = 7.6 in the TCLP f 1extract.

The arcphoteric nature of lead and/or the increase in silica solubility are most lOcelj responsiblefor this behavior. Similar results were observed in column experiments. The lead valuesincreased at pH values greater than pH = 9. Also at pH range of 9.5-10. the first columneffluents had a high silica content in conjunction with increased concentrations of copper andnickel

A gel formulation yielding a pH range of about 8.5 in the DI kashate seems to be optimum andneeds to be developed. Also, this pH range is desirable in view of the increasing solobilirjr ofsilica above pH = 8.5. See Figure 14.

FIGURE 14Concentration of Soluble Silica Species in Equilibriumwith 2.6 nm Diameter Silica Particles at pH 8.5-10.5

10 /

" 2,H «5 I"

A, Si(OH>4 in equilibrium with 2.6 nm particles; B, calculated total concentrations of Si(OH)4and HSiOj •; C, calculated total concentrations of Si(OH)4, HSiO . and SiQj2-; D. observedtotal soluble silica. Den The Chemistry of Silica, (1979)

49

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• . f3.13 Combined Protection by Reduction of Soil Permeability and Chemical

Fixation

The following calculations have a practical implication only if the gel integrity does not weakenwith age. Three scenarios are analyzed:

1) the protection achieved by reducing the soil permeability, assuming zero percentchemical fixation (Section 3.13.1);

2) the combined protection of flow reduction plus chemical fixation (Section3.13.2); and

3) the time necessary to elute 40 pore volumes from a 1 m3 cube under a pressuregradient of 1 cm/m is estimated ( Section 3.13.3). In Section 3.9 columneffluents up to 500 ml corresponding to 40 pore volumes were collected andanalyzed.

Combining Darcy's law

• An A(10)

with equations (3) and (7) we derive Equation (11):

• a* - - - - — - *^

(IDProtection % =( 1 - J-PraraM ' KPpttcttdV 100

= leachate concentration of treated soil= leachate concentration of untreated soU= hydraulic coefficient of gel treated soil= hydraulic coefficient of virgin soil

3.13.1 Protection bv Flow Rate Reduction

For no chemical protection Cprotected equals Conpnxected in Equation (11). In Section 3.4 wefound the hydraulic coefficients to be:

Kpnxeocd = 6 x 10 •'(cm/sec) for Colorado soil treated with zeolite gelKsoil = 1.2 x 10*2 (cm/sec) for virgin Colorado soil

The protection for any element by flow rate reduction in gel treated Colorado soil is therefore

6 • 10-7Protection* = (l- *. 2'. JQ.2V 10° * 59-595%

51

AR302671*

3.13.2 Protection bv Flow Rate Reduction and Chemical Fixation

We found in experiments #257 and #266 (Colorado Met 100. TCLP #1)

Cproteaed=0.19ppraZn and Cunpocected = 3.3 ppm Zn.

This results in protection by chemical fixation of 94%.

From Equation (11) we calculate a combined protection of:

Protection* = (l- Vs* x |V""* ' 10° = "•9997%

3.13.3 Time Estimate to Elute 40 Pore Volumes from a Cube of I m* under a PressureGradient of 1 cm/m

(In Section 3.9 the volume effluent from 30 g soil was collected and analyzed up to 500 mlThe void volume in 30 g Colorado soil is 12.5 mL 500 ml effluent therefore corresponds to40 pore volumes.)

We use the following data:

Permeability of untreated Colorado soil 1.2xlO*2 (cm/sec)Permeability of treated Colorado soil 6 x 10*7 (cm/sec)Density of Colorado soil 1.15 (g/cm3*Void Volume of Colorado soil 41 (cm /lOOg)

We find:

Void volume of 1m3 Colorado soil 472 0)Flow rate through 1m3 untreated sofl 37.800 (I/year)Flow rate through 1 m3 treated soil 1.9 (I/year)

Since 40 pore volumes in I m3 corresponds to 40 x 472 = 18.800 U we calculate fur a flow rateof 1.9 I/year, that h will take

18.8001/1.9 (I/year) = 9,900 years

to elute 40 pore volumes under the assumed conditions, provided the gel integrity does notchange.Beginning in the late 1880's and continuing to the present, the construction industry has usedsilica gels to reduce soil permeability. Therefore, long term data on gel behavior is available ifthese construction sites could be identified and investigated.

52

AR302675

4.0 Technology Status

The literature was searched by computer for treatment methods used in the remediation of soil,sludges and waste contaminated with chromate and heavy metals. The search covered ChemicalAbstracts (1967-Nov. 91); NTTS (1964-Nov. 91); Engineering Index (1970-Dec. 1991); Enviroline(1970-Nov. 91); Pollution Abstracts (1970-Nov. 1991); and Energy Science and Technology (1974-Dec. 1991).

Key words entered were as follows:

Soil. Groundwater, Sludge, Waste, AND Remediation. Fixation, Stabilization. Encapsulation, ANDMetals, Heavy Metals, Chromium, Chromates, Radionuclides, AND Silica. Silicates. Soluble Silica.Cement. Fly Ash. Slag. Kiln Dust. AND/OR Iron. Iron Compounds. Iron Sulfate. Iron Salts.

We separate the findings into three categories: Soil chemistry 2nd chemical treatment methods,mechanical soil mixing techniques, and chromate in situ treatment

4.1 Sofl Chemistry and Chemical Treatment Methods for Sludges and Wastes

No articles were found describing chromate reduction and metal fixation in soils using a treatmentmethodology based on iron plus soluble silica.

The articles identified in the literature search deal with heavy metals and their interaction with the soilbiology. Fixation of heavy metals in sludges and wastes is covered predominantly in the patentliterature.

Of interest are the following publications and patents:

1. CA 103 (26): 2205531Haeger. Bror Olof, Swed.. Ger. Offen.. 12 pp.

Salt mixtures for binding H3AsO4 in soil to prevent pentavaknt arsenic migration consist primarilyof Fe. Al. and/or Cr salts of a weak acid.2. CA 100 (14): 106982V

Davis. CA. USA.166 pp. Avail. Univ. Microfilms InU Order No DA 8326072

Cobalt, nickel, copper and zinc are associated with iron and manganese oxides in soils.

3. CA 104 (26): 2279881Li, Hong Ryol; Li. Son Dak, N. Korea

Amorphous iron compounds show the greatest affinity for absorbing and fixing Boron.4. CA97(24):200845u

Gueniot. Bernard. FranceCR. Seances Acad. Sci. Scr.2.295 (l),31-6

53

AR302676

Uranium is fixed on the surface of iron oxyhydroxides in placic horizons of hydromorphic soils.The uranium adsorbed on the amorphous surface of the leptdocrocite is concentrated by a factor of

5. CA 840 18); 12 72 78mShigemasu, Tsunenobu; JapanBull. Inst Chem. Res. Kyoto Univ., 53(5). 435-45

Coprecipitation behavior of zinc in the oxygenation process of ferrous iron.

6. CA84(7):42409eMisra. S.G; Pande Padmakar. IndiaVijnana Parishad Anasandhan Patrica, 17(4) 81-5

About 80-90% of added manganese, copper and nickel sulfates (15-50 ppm) become fixed in soilwithin 15 days. The amount increased on adding 7-30 ppm FeSO.4.

Techniques applied for the fixation of hazardous material before burial into hazardous waste landfillscomprise treatment with portland cement or with fly ash of good pozzolanic properties. Thefollowing processes make use of soluble silicates for stabilization of sludges and fixation of heavymetals:

7. Chemfix: US Patent 3.837.872 (1974)

An aqueous solution of an alkali metal silicate is mixed with waste material and a silicate setting agentis used. Setting agent: Portland cement, lime, gypsum, calcium chloride. The main emphasis isgiven to portland cement in the examples cited.

8. Hitman Nuclear Proc. of Nad. Conf. on Management of Uncontrolled Hazardous WasteSites. Washington. D.C. Oct. 1931.206.

This company is engaged in the fixation of low level nuclear waste. The approach differs in twoways from the Chemfix method. Cement is the main ingredient and a solid anhydrous metasilicate isused instead of a high ratio liquid.

9. Hayes Method: U.S. Patent #4,173,546 (1979)

A method is provided for treating waste materials containing radioactive cesium. An aqueoussolution of an alkali metal silicate, shale particles and a hardening agent like portland cement, lime,gypsum and calcium carbonate are claimed. Again, cement is the hardening agent used in theexamples illustrated.

10. Siliroc Process: Brit Patent 1.5 18,024 (1978)

The first phase of this invention comprises treatment of a sflkate. like blast furnace slag, with acid toobtain silicic acid of bw molecular weight at pH= 1 to 3. The liquid portion of this reaction is rpfoedwith the waste to be treated in an acid medium to ensure partial dissolution of the waste. Next thepH is increased to 8. Cementation is finally achieved by setting components consisting of granulatedslag, cement and time. An increase in temperature invohes a reduction in the setting time required.

Organic constituents like carboxylic acids and phenols, latex waste, amines, stearates are directlyadsorbed and chemi-absorbed on the gel. Metals are fixed. No leaching data are given in the

54

flR302677

disclosure. The process was evaluated by Rousseau* and Craig (USEPA. Off. Res. De.., [Rep.]EPA 1981. EPA-600/2-81-028). They found the following leaching ranges (mg/I); Cd: 0.01-5.6;Cr 0.01-0.5; Cu: 0.05-0.64; Ni: 0.01-1.30; Pb: O.008-0.017; Zn: 0.41-34.8.

11. Ontario Liquid Waste Disposal Ltd.: Krofchak, Can. Pat 1.024.277 (1978)

The liquid waste is first reacted with an acid ferrous solution at pH-2 to 3 "so that highly toxicchemicals such as cyanide and hexavalent chromium would be converted to an ea5ily treatable form."In other words, Cr(VI) is reduced by Fe(Q) in acidic medium.

Next, the mixture is neutralized with a base (NaOH or lime) to raise the pH into die range 9-12.Metal hydroxides are precipitated.

The addition of a silicic compound follows at this stage. It is selected from the group consisting ofsodium silicate, cement, fly ash, general ash, siliceous slag, clays, silts, sand, stcne and sciL Insome cases these components were present in the waste, so no addition of siliceous material wasnecessary. Finally Ca(OH)2 is added to initiate hardening. Leaching in distilled H2O of a mixedwaste yielded the following results (mg/1): Mn=0.02; Cu = 0.02; Zn = 0.04; Pb = 0.10; Ni s 0.04;Fe = 0.26; Cr = 0.06; pH = 9;

12. Stabfcx Process: U. S. Patent 4,116,705

Hazardous waste is mixed with an aluminum silicate and portland cement The source of thealuminum silicate is conveniently fly ash. Low concentrations for trace metals in leachates andhydraulic conductivities in the range from 10*5 to 10~8 cm/sec are reported.13. Langer U.S. Patent 2,227,653 (1941)

The pH of silicate solutions ;s (fscreased by the addition of an acid. By further adding a suitable saltof a heavy metal (iron, copper, lead, zinc) as an electrolyte, the latter solution is coagulated to a geLPermeabilities of 10~8 (cm/sec) were measured.

14. Kokai Tokkyo Koho: Jap.. Fat 55.109,260 Showa (1980)

Treatment of Cr VI containing sludge with portland cement, zeolite (calcined at 900°Q, iron sulfateandaCaCOj-CaClj mixture.

15. Kokai Tokkyo Koho: Jap. Pat 54.074.273 Showa (1979)Industrial sludges and incinerator ash are solidified with iron sulfate, thiourea and cement No Cr VIeluted after treatment

16. Kokai Tokkyo Koho: Jap. Pat 53,133,578 Showa (1978)

Cr ffl containing wastes are solidified with cement, blast furnace slag and FeSOvOrFeClj.17. U.S. Patent 4,840.071; Lynn. Jablonski (1990)

Heavy metals in dusts and sludges are stabilized with fly ash, lime kiln dust, iron suifats andhydrated lime.

18. European Pat 352.096; Falk (1990)

55

flR302678

Toxic metals in solid wastes, sludges and slurries are encapsulated using FeSO4 or NajSOj. CaO orMgO, glycerin, aqueous silicate solution and fly ash.

19. International Application WO 8.810.243; Lynn, Jablonski (1988)

Dust and sludges are stabilized with anhydrous alumino silicates (fly ash. blast furnace slag). lime,and ferrous tons.

20. German Patent DE 3.505.293; Haeger. Bror Olof (1985)

Iron, aluminum and chromium salts are used to bind H3AsO4 in soil

21. Kokai Tokkyo Koho: Jap. Pat 57.184,498 Showa (1982)

Cyanide and Cr VI containing sludges are mixed with converter slag, gypsum. FeCl2 or aninorganic sulfide for stabilization.

22. Japan Kokai: Jap. Pat 51.123.775 Showa (1976)

Industrial wastes are treated with thiourea. Fe n and cement

4.2 Mechanical Soil Mixiny

There are two approaches developed for mechanical on-site mixing: mobile plant mixing and asitu mixing. Mobile plant mixing comprises systems that incorporate mobile or fixed units tomix solidification/stabilization agents with the wastes. In this approach the soil is physicallyremoved from its location, treated and redeposited or transported to a prepared disposal site.

/,t situ soil mixing was developed in the 1960's by Intrusion Prepaid Co. for geotechnicalprojects. It was refined by the Japanese in the 1970's and is now available for shallow soilmixing (SSM) and deep soil mixing (DSM) (Jasperse. B.H.. Havnat World, Nov. 1989)

DSM is a relatively simple process involving standard construction equipment A cranesupports a set of leads that guide two to four mixing paddles and augers with a diameter of 30-36 inches. In situ mixing is possible to depths of 100 feet

SSM is an economical approach to treat soil masses up to a depth of 30 feet A single auger of3 to 12 feet in diameter is used. The large type equipment b usable u. soft soils and sludges.

Treatment chemicals can be added at the same time the mixing operation occurs. They areinjected through the tip of the hollow stem auger. Solids can be precisely weighed, fluids arevolumetrically measured. If solidification is desired, cement, lime, kiln dust or fly ash ran beadded. If fixation is desired, other chemicals can be applied. This technique also u suitable foradding a two component system to the sofl. Component I can be added during the downwardmovement of the auger while component n can be mixed into the sofl upon retraction.

56

4.3 In Situ Chromate Reduction

(Rouse, J.V.: Haztech News, Vol. 5. No. 22 1990. p. 167)

Chromium contaminated ground water is pumped from the center of the plume of contaminationand treated above ground. Excess reducing agents are introduced into the treated water which isreturned through wells on the periphery of the plume. When the reductant contacts chromiumVI in the soil, Cr HI is generated and fixed on the subsurface. The article gives no specificsregarding the nature of the reductant

With this process only 10-25% of the water normally circulated in pump and treat operationsmust be processed. Using a reductant, only 5-10 pore volumes need to be processed comparedto 50-60 pore volumes using no reductant Treatment time is reduced by a factor of four whLetreatment costs are lowered to 50-75%. Capital costs are about the same.

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5.0 Acknowledgements

This work was funded by Argonne National Laboratory (Contract No. 02112401) through theresearch and development program sponsored and funded by the Office of TechnologyDevelopment, Office of Environmental Restoration and Waste Management. US Department ofEnergy.

The P.Q. Corporation of Valley Forge, Pa., supplied the N-silica and literature on inhouseresearch performed by J. S. Falcone. R. W. Spencer. R. H. Reifsnyder and E. P. Katsanis.

58

Distribution for DOE/CH-9214

Internal:

J. E Battles D. E Edgar K. M. MylesN. J. Beskid M. D. Erickson PCO Office (50)S. K. Bhattacharyya N. L. Gcetz A. D. PflugA. S. Boparai M. Harkins G. T. ReedyS.S. Borys J.EHelt(5) N.F. SathcrD. E Bugielski D. O. Johnson M. J. SteindlerD. J. Chaiko R. Kolpa M. ZielkeS. M. Cross T. R. Krause ANL Patent Dept.J. C. Cunnane R.Martello ANL Contract FileJ. S. Devgun N. K. Meshkov US Files (3)J. D. Ditmars

External:

DOE-OSTI. for distribution per UC-600 (2)ANL LibraryManager, Chicago Operations Office, DOEA. Bindokas. DOE-CHJ. C. Haugen, DOE-CHS.L. Webster. DOE-CHA. H. Aitken. Nuclear Diagnostic Systems, Inc., Springfield. VAD. H. Alexander. USDOE. Office of Technology Development. Washington, DCJ. Allison. USDOE. Office of Waste Operations. Washington. DCT. D. Anderson. USDOE, Office of Technology Development. Washington, DCM. S. Anderson, Amcs Laboratory, Iowa State University. Ames, IAG. Andrews. EG&G Idaho, Idaho Falls, IDF. Augustine, USDOE Office of Technology Development. Washington, DCD. H. Bandy, USDOE Albuquerque Operations Office. Albuquerque, NMM. J. Barainca, USDOE Office of Technology Development, Washington, DCS. Bath. Westinghouse Hanford Company. Richland, WAS. A. Banerman. University of Michigan, Ann Arbor. MIJ. Baublitz. USDOE Office of Environmental Restoration, Washington. DCJ. Bauer. USDOE Office of Environmental Restoration, Washington, DCB. G. Beck, Coleman Research Corporation, Fairfax. VAR. C. Bedick, USDOE Morgantown Energy Technology Center. Morgantown, WVM. Berger, Los Alamos National Laboratory, Los Alamos, NM (5)J. D. Berger. Westinghouse Hanford Company. Richland, WA (5)D. Berry. Sandia National Laboratories. Albuquerque, NM (5)D. Biancosino, USDOE Office of Technology Development, Washington, DCJ. Bickcl USDOE Albuquerque Operations Office. Albuquerque. NMJ. J. Blakeslee. EG&G Rocky Flats. Inc.. Golden, CO (5)T. Blayden, STC Library. Westinghouse Electric Corp.. Pittsburgh. PA

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W. Bliss, Reynolds Electric & Engineering Co., Las Vegas, NV (5)L. C Borduin, Los Alamos National Laboratory, Los Alamos, NMD. Bottrell, USDOE, Office of Technology Development, Washington, DCG. G. Boyd, USDOE, Office of Technology Development, Washington, DCJ. L. Bratton, Applied Research Associates, Inc., Albuquerque, NMJ. Buelt, Battelle Pacific Northwest Laboratory, Richland, WA (5)T. Burns, S-Cubed, Division of Maxwell Labs, San Diego. CAJ. Bursell, EIC Laboratories, Norwood, MAW. Buttner. Transducer Research, Naperville, ILJ. W. Cammann, Westinghouse Hanford Company, Rirhland, WAM. M. Carrabba. EIC Laboratories, Inc.. Norwood, MAR. A. Carrington, Mountain States Energy, Inc., Butte, MT (5)M. Carter, USDOE, Laboratory Management Division, Germantown, MDK. A. Chacey, USDOE, Office of Waste Operations, Washington, DCP: Colombo, Brookhaven National Laboratories, Upton, NY (5)D. Constant, South/Southwest HSRC, Louisianna State University. Baton Rouge, LAS. Conway, Colorado Center for Environmental Management, Golden, CO (5)J. Corones, Ames Laboratory, Iowa State University, Ames, IA (5)S. P. Cowan, USDOE Office of Waste Operations, Washington. DCR. B. Craig, Hazardous Waste Remedial Actions Program, Oak Ridge, TND. Daffern, Reynolds Electrical & Engineering Company, Las Vegas, NVW. Daily, Lawrence Livennore National Laboratory, Livermore, CAR. C. Doyle. IIT Research Institute. Virginia Tech. Center, Newington, VAL. P. Duffy, USDOE, Environmental Restoration and Waste Management. Washington, DCH. Duggcr, Kaiser Engineers Hanford Company. Richland. WA (5)A. J. Eirich, Kaiser Engineers Hanford Company, Richland. WAD. Emilia, Chem-Nuclear Geotech, Grand Junction, CO (5)B. D. Ensley, Environgen, Inc., Princeton Research Center. LawrencevUle. NJL. Erickson, Center for HSR, Kansas State University, Manhattan, KSL. Feder. Institute of Gas Technology, Chicago, ILH. D. Feiler, Science Applications International Corp., Oak Ridge. TNH. Feiner. Science Applications International Corp., Oak Ridge. TNJ. J. Fiorc, USDOE. Office of Environmental Restoration, Washington. DCW. Fitch. USDOE Idaho Field Office, Idaho Falls, IDJ. Ford, Hazardous Waste Remedial Action Program. Oak Ridge, TN (5)A. J. Francis, Brookhaven National Laboratory, Upton. NYC. Frank, USDOE Office of Technology Development. Washington, DCJ. French. EG&G Idaho. Idaho Falls. IDR. B. Gammage, Oak Ridge National Laboratory, Oak Ridge, TNC Gehrs, Oak Ridge National Laboratory, Oak Ridge. TNG. Gibb, USDOE Office of Technology Development, Washington. DCJ. F. Gibbons, Applied Research Associates, Albuquerque. NMR. Gilchrist, Westinghouse Hanford Company, Richland, WA (5)R. Gillies. Energy Technology Engineering Center, Canoga Park. CA (5)G. Glatzmaier, Solar Energy Research Institute, Golden, COS. Goforth. Westinghouse Savannah River Company, Aiken, SC

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S. R. Grace. USDOE, Rocky Rats Office, Golden. COS. Grant, Center for HSR, Kansas State University, Manhattan, KSW. Grceman, Duratek Corporation, Beltsville, MDT. C. Greengard, Rocky Flats Plant, Golden, COB. Gupta, National Renewable Energy Laboratory, Golden, CO (S)K. Hain. USDOE, Office of Technology Development, Washington, DCJ. Hall. USDOE, Nevada Field Office, Las Vegas. NVM. S. Hanson, Battelle Pacific Northwest Laboratories, Richland, WAL. H. Harmon, USDOE, Office of Waste Operations, Washington, DCK. A. Hayes, USDOE, Office of Environmental Restoration, Washington, DCE. L. Helminski, Weapons Complex Monitor. Washington, DCJ. M. Hennig, USDOE, Richland Operations Office, Richland, WAR. Hill, U.S. Environmental Protection Agency, Cincinnati, OHW. Holman, USDOE, San Francisco Operations Office, Oakland, CAJ. P. Hopper, Westinghouse Materials Company of Ohio, Cincinnati, OH (5)D. Huff, Martin Marietta Energy Systems, Inc.. Oak Ridge. TNJ. Hyde, USDOE. Office of Technology Development, Washington, DCR. Jacobson, University of Nevada, Water Resources Center, Las Vegas, NV (S)S. James, U.S. Environmental Protection Agency. Cincinnati. OHS. Janikowski, EG&G Idaho, Idaho Falls, IDW. J. Johnson, Paul C. Rizzo Associates, Inc., Monroeville, PAD. W. Jones, Nuclear Diagnostics Systems, Inc.. Brunswick. TND. Kabach, Westinghouse Savannah River Company, Aiken, SCC. Keller, Science and Engineering Associates, Inc.. Santa Fe, NMD. Keish, USDOE, Office of Technology Development. Washington, DCJ. Kitchens, IIT Research Institute, Ncwington, VAJ. Koger. Martin Marietta Energy Systems, Oak Ridge, TN (5)E. Koglin, U.S. Environmental Protection Agency, Las Vegas, NVK. Koller, EG&G Idaho, Idaho Falls, ID (5)G. Kosinski. Technics Development Corporation, Oak Ridge, TND. R. Kozlowski, USDOE, Office of Environmental Restoration, Washington, DCR. Kuhl. EG&G Idaho, Idaho Falls, IDJ. Lankford, USDOE, Office of Technology Development, Washington. DCJ. C. Lehr, USDOE Office of Environmental Restoration. Washington, DCR. Levine. USDOE Office of Technology Development, Washington, DCS. C. Lien, USDOE, Office of Technology Development, Washington, DCR. G. Lightner, USDOE, Office of Environmental Restoration, Washington. DCD. Lillian. USDOE, Office of Technology Development, Washington. DCE. Lindgren, Sandia National Laboratory, Albuquerque, NMB. Looney, Westinghouse Savannah River Company, Aiken, SCP. Lurk, USDOE Office of Technology Development, Washington, DCR. W. Lynch, Sandia National Laboratories, Albuquerque, NM (5)J. E. Lytle, USDOE, Office of Waste Management, Washington, DCR. S. Magee, New Jersey Inst. Technol., Hazardous Substance Research Center. Newark, NJK. Magrini, Solar Energy Research Insitute, Golden, COA. Malinauskas. Oak Ridge National Laboratory, Oak Ridge. TN (5)

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IS. A. Mann, USDOE, Office of Environmental Restoration, Washington, DCD. Manty, Exploratory Research, U.S. Environ. Protection Agency, Washington, DCJ. Marcheni, USDOE, Defense Programs, Washington, DCR. G. McCain, Westinghouse Hanford Company, Richland, WAP. L. McCarty. Hazardous Substance Research Center. Stanford University, Stanford, CAL. W. McClure, Westinghouse Idaho Nuclear Company, Inc.. Idaho Falls, ID (5)T. McEvilly, Lawrence Berkeley Laboratory, Berkeley, CA (5)C. P. McGinnis, Oak Ridge National Laboratory, Oak Ridge. TNK. Merrill, EG&G Idaho, Idaho Falls, ID (5)D. J. Moak, Westinghouse Hanford Company, Richland, WAJ. Moore. USDOE, Oak Ridge Field Office, Oak Ridge, TNK. Morehouse, Exploratory Research, U.S. Environ. Protection Agency. Washington, DCH. D. Murphy. Los Alamos National Laboratory, Los Alamos, NM (5)C. Myler, West Point Chemistry Department. West Point, NYB. Nielsen. Tyndall Air Force Base, Tyndall Air Force Base, FLR. Nimmo, QT Research Institute, Newington, VAK. Nuhfer, Westinghouse Materials Company of Ohio. Cincinnati, OH (5)M. O'Rear, USDOE, Savannah River Field Office, Aiken, SCR. Olexsi, U.S. Environmental Protection Agency, Cincinnati, OHT. Oppelt. U.S. Environmental Protection Agency, Cincinnati, OHD. F. Oren, Geotech, Inc., Grand Junction, COV. M. Oversby, Lawrence Livermore National Laboratory, Livermore, CAJ. Paladino, USDOE, Office of Technology Development, Washington. DCS. Pamukcu, Lehigh University, Bethlehem, PAJ. M. Passaglia. USDOE Office of Technology Development. Washington. DCG. S. Patton, USDOE, Office of Technology Development, Washington, DCI. L. Pegg, Duratek Corp., Columbia, MDC. Peters, Nuclear Diagnostics Systems, Inc., Springfield, VAM. Peterson, Battelle Pacific Northwest Laboratory, Richland, WAJ. Poppiti, USDOE Office of Technology Development, Washington, DCE. J. Poziomek, University of Nevada, Las Vegas, NVS. Prestwich, USDOE Office of Technology Development, Washington. DCR. E. Prince, Duratek Corporation, Columbia. MDR. F. Probstein, Massachusetts Institute of Technology, Cambridge. MAR. S. Ramsey. Oak Ridge National Laboratory, Oak Ridge, TNN. Rankin, Savannah River Technology Center, Aiken. SCC. Rivard, Solar Energy Research Institute. Golden. COR. Rizzo, Paul C Rizzo Associates, Inc., Monroeville, PAA. Robbat, Tufts University, Medford, MAW. Robson. Lawrence Livermore National Laboratory, Livermore, CAL. Rogers, EG&G Energy Measurements, Inc., Las Vegas, NV (5)V. J. Rohey, Westinghouse Hanford Co., Richland, WAB. Ross, Science and Engineering Associates, Albuquerque, NMN. E. Rothermich, Hazardous Waste Remedial Actions Program, Oak Ridge, TNG. Sandness, Pacific Northwest Laboratory, Richland, WAG. Sandquist, University of Utah, Salt Lake City, UT

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P. A. Saxmun, USDOE, Albuquerque Operations Office, Albuquerque, NMW. C. Schutte, USDOE. Office of Technology Development, Washington, DCK. Schwitzgebel, Sizemore Technical Services, Round Rock, TXJ. A. Scroppo, Blandon International. Inc., Des Plaines, ILM. W. Shupe, USDOE, Office of Technology Development, Washington, DCJ. Simpson. USDOE, Office of Technology Development. Washington, DCC. Sink, USDOE, Office of Technology Development, Washington, DCS. C. Sla.2, Battelle Pacific Northwest Laboratories. Richland, WA (5)R. Snipes, Hazardous Waste Remedial Actions Program, Oak Ridge, TNR. Spair, Envirogen, Inc., Lawrenceville, NJJ. L. Steete, Westinghouse Savannah River Company, Aiken. SC (5)S. Stein. Environmental Management Organization. Seattle. WA (5)K. Stevenson. USDOE, New York. NY (5)R. R. Stiger, EG&G Idaho. Idaho Falls. ID (5)D. Stoner. EG&G Idaho, Idaho Falls, IDL. Taylor. USDOE, Office of Environmental Restoration, Washington, DCL. J. Thibodcaux, South/Southwest HSRC, Louisianna State University, Baton Rouge, LAT. M. Thompson, Science Applications International Corp., Oak Ridge, TNJ. Tipton, Remote Sensing Laboratory, Las Vegas, NV (5)E. S. Tucker. Clemson Technical Center. Inc., Anderson, SCJ. A. Tun. USDOE, Office of Waste Operations, Washington, DCG. P. Tun, USDOE Office of Environmental Restoration, Washington. DCR. Tyler, USDOE, Rocky Rats Office. Golden, COL. D. Tyler, Sandia National Laboratories, Albuquerque, NM (5)C. L. Valle, Allied Signal Aerospace, Kansas City, MO (5)G. E. Voelker, USDOE, Office of Technology Development, Washington, DCJ. W, Wagoner, USDOE, Office of Environmental Restoration, Washington, DCH. Wang, University of Wisconsin, Madison, WIS. Weber, USDOE, Office of Technology Development, Washington, DCW. J. Weber. Hazardous Substance Research Center, University of Michigan, Ann Arbor, MIE. Weiss. Membrane Technology and Research, Inc., Menlo Park, CAT. WheelU, Sandia National Laboratories, Albuquerque, NM (5)M. Whitbeck, University of Nevada, Desert Research Institute, Reno, NVR. P. Whitfield, USDOE. Office of Environmental Restoration, Washington, DCP. Wichlacz, EG&G Idaho. Idaho Falls, ID (5)

1 C. L. Wklrig. Battelle Pacific Northwest Laboratories, Richland, WAH. Wijmans, Membrane Technology & Research, Inc., Menlo Park, CAJ. Wilson, Oak Ridge National Laboratory. Oak Ridge, TNW. Wisenbaker, USDOE Office of Environmental Restoration, Washington. DCJ. K. Wittle, Electro-Petroleum, Inc., Wayne, PAS. Wolf, USDOE, Office of Technology Development. Washington. DCT. Wood. EG&G Idaho. Idaho Falls. IDJ. L. Yow, Livermore. CA (5)C. Zeh, USDOE, Morgantown Energy Technoloy Center. Morgantown, WVL. P. Buckley. Atomic Energy of Canada, Ltd., Chalk River, Ontario, CANADAL. A. Moschuk, Atomic Energy of Canada Limited, Ontario, CANADA

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