treatment of uranium-contaminated waters using organic-based permeable reactive barriers

Treatment of Uranium-Contaminated WatersUsing Organic-BasedPermeable ReactiveBarriers

Ellen C. England

A literature review and screening study suggest the feasibility of using low-cost organic materials within a permeable reactive barrier (PRB) to treat ura-nium-contaminated water. Natural peat deposits remove and sequester ura-nium from ground water under certain geochemical conditions while severalspecies of bacteria, including Desulfovibrio desulfuricans precipitate solubleuranium from solution. Cation exchange capacities were measured for saw-dust and peat, materials to be used in construction of a small-scale PRB. Re-sults of a literature review and the cation exchange capacity measurementssuggest that organic materials, such as peat, can be used to remove solubleuranium from contaminated water. © 2006 Wiley Periodicals, Inc.*

INTRODUCTIONUranium contamination of soils, surfacewater, and groundwater

can come from both natural and man-made processes, includingleaching/mobilization from geological deposits, low-level radioactivewaste burial facilities, wastes generated during the nuclear fuel cycle,wastes from the phosphate fertilizer industry, nuclear weapons pro-duction, and wastes generated during other radioactive waste reme-diation processes. Uranium-contaminated sites can be found at manyfederal facilities.1

Whatever the ultimate source, uranium released from theseprocesses can cause water concentrations to exceed the EnvironmentalProtection Agency’s drinking water standard or the Nuclear Regula-tory Commission’s effluent regulations.2 Uranium in water or soil mayenter the food chain and pose a health risk. The most common ra-dioisotopes, 235U, 234U, and 238U, are alpha particle emitters and may

Federal Facilities Environmental Journal/ Spring 2006 19© 2006 Wiley Periodicals, Inc. *This article is a government work and, as such, is in the public domain of the United States of America.Published online in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/ffej.20078

Lt. Col. Ellen C. England, PhD, is an assistant professor of engineering and environmentalmanagement at the Air Force Institute of Technology, Wright-Patterson AFB, Ohio. Her re-search interests include air pollution control using membrane biofiltration, environmentalsafety and health exposure monitoring, and sustainable design.

20 Federal Facilities Environmental Journal/ Spring 2006DOI: 10.1002/ffej

Treatment of Uranium-Contaminated Waters Using Organic-Based Permeable Reactive Barriers

deliver a radiation dose to tissues upon inhalation or ingestion, or pro-duce damage from chemical toxicity, primarily in the kidney.3

Uranium is commonly found in the tetra- (uranous), penta-, or hexa-valent (uranyl) forms.4 However, most important in nature are the ura-nous U(IV) and uranyl U(VI) oxidation states.5 Predicting the exact ura-nium complexes likely to exist in soil or water at a particular locationmay be difficult without specific physical or chemical analyses of thewater and/or soil. Complexes formed in soil or water are influenced bysoil and water properties such as pH, organic content, other inorganicspecies including carbonate and phosphate, and the reducing potential(Eh) of the environment, among others.6 Uranium speciation can bepredicted from Eh pH diagrams or by using one of several geochemi-cal computer codes.7 Generally, the UO2�2 ion dominates in aerobicacidic groundwater environments and carbonate species such asUO2(CO3)3-4 in alkaline, with a full discourse on uranium mineralogyfound by the Mineralogical Society of America in 1999.8

Removal of uranium from water sources has frequently been ac-complished by ion exchange during or after pumping an aquifer or sur-facewater body, a relatively expensive and energy-intensive process.9

This work reports the initial screening of an inexpensive in situ ap-proach to remove uranium contamination from ground- or surfacewa-ter. The use of organic materials within permeable reactive barriers(PRBs) for uranium removal is suggested by sequestration of uraniumunder certain geochemical conditions, the removal of soluble uranium(UO2�2) from solution by bacteria, and the recent proliferation of PRBsto effectively treat inorganic groundwater contaminants. An extensiveliterature search and preliminary lab-scale investigation suggest thepotential for removal of uranium from groundwater using organic ma-terials such as peat, under reducing conditions, contained within PRBs.Indeed, the concept of metal removal using anaerobic organisms ingeochemical barriers has already been suggested by others.10

BACKGROUNDThe case for uranium removal from water using organic substrates

contained with a permeable reactive barrier begins with an examina-tion of geological studies of secondary uranium deposits. Studies haveshown the potential for uranium to mobilize from one geological de-posit and settle in peat or gypsum or to precipitate as silicates, phos-phates, and silicophosphates, coprecipitate, or adsorb onto iron oxy-hydroxides.11 The case is further supported by radioisotopes,including uranium, found concentrated at a peat interface below a tail-ings pile and virtually no radionuclides deposited beneath the tailingspile/soil interface at another.12 Solubilized uranium was found to ad-here to rock substrates under the correct geochemical conditions andsorb to natural barriers and positively charged uranyl species, as wellas other metals and humic substances, with the radionuclide bindingoccurring primarily at the carboxylate groups.13 Uranium activity wasassociated primarily with an exchangeable phase, a carbonate phase,

Removal of uranium from water sources has frequently beenaccomplished by ionexchange during or afterpumping an aquifer orsurfacewater body, arelatively expensive andenergy-intensive process.

Federal Facilities Environmental Journal/ Spring 2006DOI: 10.1002/ffej

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Ellen C. England

and an iron oxide phase, when soils from two radioactive waste siteswere examined.14

A combined laboratory and field study, using spray irrigation ofsimulated mine water, showed radionuclides were retained at the sur-face of soil columns and would not leach to any significant soildepths.15 Uranium exhibited strong sorption onto fine till soils, with97 percent of that applied remaining after four years in a soil corestudy, and after one year, most was still confined to the soil surface.16

When phosphogypsum fertilizer plant process water passed throughcalcareous soils during a sequential batch procedure, soils became en-riched in uranium; uranium removal was controlled by a combinationof sorption and precipitation processes, while calcareous soils werepreviously shown to sorb uranium.17 Uranium migration was pro-gressively retarded as the amount of peat within a peat/soil mixturecontained within a geochemical barrier for radioactive waste disposalcells was increased.18 Oxidant addition and heating experiments sug-gest that uranium is fixed to peat as U(VI).19 In another study, ura-nium was found associated with iron and manganese oxides in thesource term, complexed by fulvic acids in the groundwater and asso-ciated with carboxyl functional groups within peat.20

BIOREMEDIATION OF URANIUM-CONTAMINATED SOILS AND WATERS

The case for removal of U from solution is strengthened by an ex-amination of extensive reviews detailing the influence of microorgan-isms on radionuclides and other metals and the characterization of in-digenous bacteria in uranium mine waste heaps.21 A summary ofjournal articles and the organisms studied is shown in Exhibit 1. Bac-terially mediated metal-removal mechanisms, as reported by thesesources, include biosorption-adsorption, ion exchange, and entrap-ment by living or dead, freely suspended or immobilized biomass;precipitation of metals on the cell wall; the existence of metal-bindingproteins and peptides; complexation with siderophores; and microbialmetal transformations where metals are oxidized, reduced, methy-lated, sulfonated, or dealkylated. Several of these removal mecha-nisms for uranium have been extensively studied. Those mechanismsinclude biosorption, bioprecipitation onto cell walls, and microbialmetal transformation via enzymatic reduction of U(VI) to U(IV).

In most accounts, biosorption involves bringing uranium-bearingwater into contact with living or dead bacteria, fungi, or algae.22 Inbiosorption, the uranium in solution binds to the biomass throughpassive, physical-chemical mechanisms, and removal of uranium maynot depend upon the life of the organism.23

As with biosorption, uranium may accumulate or precipitate on thebiomass. Bioprecipitation of uranium onto the cell walls was found tooccur readily with Citrobacter sp., while suspended and fixed cells ofCitrobacter N14 removed uranium from acidic mine drainage water inbioreactor cells.24 Uranium accumulation on the cell wall of Thiobacil-

In most accounts,biosorption involvesbringing uranium-bearingwater into contact withliving or dead bacteria,fungi, or algae.



Exhibit 1. Summary of Uranium Removal and the Microorganisms Responsible

Authors Year Organism

Duff et al. 1999 Chlorella

Spear et al. 1999 Desulfovibrio desulfuricans, ATCC7757

Panak et al. 1998 Desulfovibrio desulfuricans, Thiobacillus ferrooxidans, ATCC 23270 and ATCC33020

Francis & Dodge 1998 Pseudomonas fluorescens

Gadd et al. 1998 Aspergillus niger

Basnakova et al. 1998 Citrobacter sp.

Blount 1998 Mixed culture

Robinson et al. 1998 D. desulfuricans

Abdelouas et al. 1998 Mixed culture

Tucker et al. 1998 D. desulfuricans

Ganesh et al. 1997 Pseudomonas aeruginosa, D. desulfuricans

Truex et al.a 1997 Shewanella alga BrY

Roig et al. 1997 Citrobacter N14

Hard & Babelb 1997 UFZ B 378

Barton et al. 1996 D. desulfuricans, gigas, baculatus, Pseudomonas sp., Pseudomonas putida

Uhrie et al. 1996 Mixed culture of sulfate reducers

Thomas & Macaskiec 1996 Mixed culture

Hu et al. 1996 Pseudomonas aeruginosa

Macaskie et al. 1995 Citrobacter sp.

Phillips et al. 1995 D. desulfuricans

Schippers et al. 1995 Mixed culture

Delwiche et al. 1994 Thiobacillus ferrooxidans

Francis et al. 1994 Clostridium sp.

Lovley et al. 1993 Desulfovibrio sp., Desulfobacterium autotrophicum, Desulfobulbus proprionicus

Lovley et al. 1993 Desulfovibrio vulgaris

Lovley & Phillips 1992 D. desulfuricans

Lovley & Phillips 1992 D. desulfuricans

a. Truex, M., Peyton, B., Valentine, N., & Gorby, Y. (1997). Kinetics of U(VI) reduction by a dissimilatory Fe(III)-reducingbacterium under non-growth conditions. Biotechnology and Bioengineering, 55(3), 490–496.

b. Hard, B., Friedrich, S., & Babel, W. (1997). Bioremediation of acid mine water using facultatively methylotrophic sulfate-reducing bacteria. Microbiology Research, 152, 65–73.

c. Thomas, R., & Macaskie, L. (1996). Biodegradation of tributyl phosphate by naturally occurring microbial isolates andcoupling to the removal of uranium from aqueous solution. Environmental Science & Technology, 30, 2371–2375.


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Ellen C. England

lus ferrooxidans and the ability to extract uranium from solution havebeen demonstrated.25 Extracellular polymeric substance involvementin the creation of intercellular deposits of nickel uranyl phosphate wassuggested for Citrobacter cells.26

Reduction of U(VI) to U(IV)Precipitation of uranium from solution was reported for several or-

ganisms, including Geobacter metallireducens, Shewanella putrefaciens,Clostridium sp., and Desulfovibrio desulfuricans. These organisms do notappear to precipitate uranium onto the cell wall but reduce U(VI) toU(IV).27 A previously unidentified bacterium, Desulfotomaculum re-ducens strain MI-1, isolated from marine sediments, was found capableof enzymatically reducing U(VI) and growing with U(VI) as the ter-minal electron acceptor.28 Bacterial consortia have also been impli-cated in reduction of U(VI) to U(IV).29

Probably the most intensively studied organism, D. desulfuricans,was found to reduce U(VI) directly, rather than indirectly through sul-fide production, as was previously believed; D. desulfuricans was iden-tified as an enzymatic reducer of U(VI).30 Lovley and his colleaguesfound D. desulfuricans could reduce U(VI) but did not grow with U(VI)as the sole electron acceptor.31 Removal of uranium from solution wasfound to be efficient, with 80 percent of uranium U(VI) in solution re-duced to U(IV) within 24 hours, and D. desulfuricans, immobilized inpolyacrylamide gels, removed uranium with residence times of lessthan 37 hours.32 A comparison of results between two organisms,S. alga and D. desulfuricans, showed the two bacteria reduced U(VI) atdifferent rates and in different efficiencies for the variety of organiccomplexes evaluated, while batch culture studies of D. desulfuricansshowed ligand concentration may limit the precipitation of uranium.33

A study of five species of Desulfovibrio, Desulfobacterium autotrophicum,and Desulfobulbus propionicus showed that only the Desulfovibriospecies reduced U(VI) and suggested the mechanism of U(VI) to U(IV)reduction was cytochrome c3.34 Further work indicated a nongrowthMonod model provided a best fit of U removal by D. desulfuricans(ATCC 7757) in batch studies.35

Permeable Reactive BarriersThe third component in the case for removal of U from ground-

water rests in the recent proliferation of PRBs. Permeable reactivebarriers are structures emplaced below grade, usually using trench-ing techniques. The barriers may be placed vertically (to intercept alaterally moving plume) or horizontally (to intercept a downward-moving plume of contaminant-laden water). Reactive barriers havebeen used predominantly to treat groundwater; however, somehave been used to treat domestically contaminated waters percolat-ing through the soil.36 Several documents produced or funded bythe Environmental Protection Agency and others provide summaryand design information on PRBs.37 Both organic and inorganic con-

Permeable reactivebarriers are structuresemplaced below grade,usually using trenchingtechniques.



taminants singly or in combination have been effectively removedfrom groundwater using PRBs. Blowes and his colleagues reviewedinformation concerning the ability of reactive barriers to remove in-organic materials with removal of inorganics demonstrated for acidmine drainage, domestic septic system effluent, and agriculturaldrainage.38

Numerous substrates, both natural and manufactured, have beenemployed in PRB systems for the treatment of contaminants. Includedin the list of substrates for metals removal were a pea gravel-compostmix, phosphate-containing materials, a biodegradable plastic and ironpowder combination, iron filings, an iron-silica alloy, a sand/Huma-sorb mix, and iron powder, among others.39 Even paper mill sludge, awaste itself, was found to adsorb heavy metals and offers the potentialfor use in PRBs.40 Zero-valent iron and iron-containing compounds,however, appear to be the most frequently used material in opera-tional PRBs.

Mechanisms responsible for metal removal in PRBs have been atleast partially elucidated. The predominant removal mechanisms re-ported include adsorption, chemically mediated reduction, and bacte-rially mediated reduction, or a combination of these mechanisms.Cu(II), Cr(VI), and As(V) were removed from a wood preservativewaste stream by adsorption and chemical reduction of dissolved met-als, while bacterially mediated sulfate reduction was determined to beresponsible for beneficial changes in effluent water quality from minedrainage PRBs and removal of copper, zinc, and cadmium within an-other PRB.41

Uranium-removal mechanisms have already been examined forPRBs actually constructed of other natural materials. Cantrell foundrapid removal rates of CrO4–2, Tc4O–, UO2�2, and MoO2–2 usingzero-valent iron in batch studies while Gu and his colleagues deter-mined that adsorption by zero-valent iron accounted for less than 4percent of the UO2�2 removed from solution—reduction to U(IV)accounted for the remainder.42 Morrison and his colleagues studiedthe removal of uranium from groundwater using zero-valent iron ina PRB and column tests and found that chemical reaction/precipita-tion, not adsorption, was the mechanism of removal, while Fullerand his colleagues examined uranium removal using hydroxyap-atite.43 Pilot-scale studies for removal of uranium from water in-clude the use of permeable reactive barriers constructed with phos-phate-rich, zero-valent iron or amorphous ferric oxyhydroxide.44

Three full-scale PRBs were constructed to treat U-containinggroundwater, with the zero-valent iron barrier found to be most ef-fective in removing U; 99.5 percent of influent U concentrationswere removed, primarily in the first foot of the barrier. Bone charphosphate and amorphous ferric oxide barriers also removed U in afunnel and gate system.45 More recent work has been aimed at fur-ther elucidating the mechanisms of removal using radioindicatorsand evaluating PRBs in the field.46

Zero-valent iron and iron-containingcompounds, however,appear to be the mostfrequently used materialin operational PRBs.


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Ellen C. England

METHODS AND MATERIALSRadioactively contaminated water from the St. Louis Airport Ra-

dioactive Waste Disposal Site was supplied by the Army Corps of En-gineers for laboratory-scale studies. Inorganic chemical analysis of thewater supplied by Stone and Webster, the on-site environmental con-sulting firm, indicated high levels of nitrate (920 mg L–1), selenium(0.659 mg L–1), and uranium (4.00 mg L–1), with other inorganics pres-ent in low quantities. The combination of ground- and surfacewaterhad been collected over a period of months and stored on-site, await-ing treatment.

Small-column studies were used to determine the ability of the or-ganic substrates to remove uranium from solution. A 12-cm columnwith a volume of 12 mL was filled with a mixture of commercialsphagnum peat moss (1 g), cedar/pine sawdust (1 g), and sand (0.5 g)(Exhibit 2). Water was passed through the columns at various flowrates (1, 2, 5, and 10 mL min–1), the effluents analyzed, and break-through curves plotted.

A laboratory-scale PRB was constructed of Plexi-glass® with threeequally sized compartments. Compartments were separated by metal-lic screening, with flow-equalizing compartments 1 and 3 containingclear plastic beads and compartment 2 containing the same mix of or-ganic materials (40 percent peat, 40 percent sawdust, and 20 percentsand) used in the column studies. Plastic beads, instead of sand, were

Exhibit 2. Column Study Experimental Configuration

Note: Influent water was passedthrough a substrate-filled columninto test tubes automatically time-advanced by the Isco sampler.



used to limit possible adsorption of soluble uranium. After construc-tion, the PRB organic material was inoculated with activated sludgefrom the Rolla, Missouri, wastewater treatment plant and 10 g of sub-strate from an operational lab-scale constructed wetland. Twentygrams of potassium sulfate were added to compartment 2 to providean initial sulfate source for sulfate-reducing bacteria. A diagram of thelab-scale PRB is shown in Exhibit 3.

Influent and effluent samples from column studies and the lab-scale PRB were analyzed using gross alpha measurement. Ten-milli-liter samples of radioactive water were evaporated in aluminumplanchets, placed 1 cm from the detector, and counted individuallyusing a Tennelec® alpha spectrometer and counter. Gross alpha count-ing time was three hours per sample. Standard error of the net count-ing rate (�r) was calculated for each sample in accordance with the fol-lowing formula:

where G (gross count) is the number of counts recorded in the scalerwith sample present, tG the time of the gross count, B (backgroundcount) the number of counts recorded in the scaler with sample absent,and tB the time of the background count.47

Other tests included sulfate-reducing bacteria enumeration, dis-solved oxygen concentration determination, and nitrate measurement.

Exhibit 3. Lab-Scale PRB Experimental Configuration

Note: Chamber 2 contained thepeat/sawdust/sand substrate.


27

Ellen C. England

Sulfate-reducing bacteria enumeration was completed in accordancewith a technique used by Jain, while colony counting was accom-plished using a typical spread plate method with Rza agar.48 Dis-solved oxygen concentrations were measured using a calibrated Dow-Corning® dissolved oxygen meter. Nitrate measurements werecompleted using the Hach® High Range Nitrate Method 8039 and aHach® DR/2010 Portable Datalogging Spectrophotometer. Influentand effluent samples were taken directly before entering or exiting thePRB, respectively, and were diluted 1:50 before nitrate measurements.Cation exchange capacities of the peat moss, sawdust, and sand weremeasured using a method by Petry.49 One modification to the methodwas made; samples were filtered using 0.2 nitrocellulose filters (FisherScientific), rather than centrifuged.

RESULTS/DISCUSSIONResults of the column breakthrough studies at the varying flow

rates are shown in Exhibit 4, with error bars calculated but not shownfor ease of viewing. Breakthrough was compared for each flow rate ona bed volume basis. Breakthrough occurred most rapidly for the 10 mLmin–1 flow rate, while the other flow rate results were mixed. Break-through curve shapes differed and suggest a mechanism, other thanadsorption alone, may be responsible for the removal of soluble ura-nium. Had adsorption alone been responsible for the removal, break-through bed volumes and breakthrough curve shapes might havebeen more similar between the flow rates; the same number of bedvolumes would have been exhausted for identical mass loadings.

The fixation of U onto organic matter is postulated to involve sev-eral mechanisms, including adsorption, cation exchange, reduction, or

Exhibit 4. Comparison of Column Breakthrough Curves for a Variety of Flow Rates



a combination of the processes.50 Indeed, Zielinski and Meier pre-sented a cation exchange model of import and calculated rate con-stants to explain U removal from peat.51 The model equations sug-gested were as follows, where (Hu) refers to poorly characterizedhumic substances in the peat:

UO2(Hu) � 2H�]^ H2(Hu) � UO22�

UO2(Hu)2 � 2H�]^ H2(Hu)2 � UO22�

The variation in shape and breakthrough time might also be relatedto the relatively small amount of material contained within thecolumns and the lack of particle-size fractionation. Although there wasthe same weight of each type of substrate material in each test, visualinspection identified inhomogeneities in the substrate from test to test.

A comparison of the results of one column study (2 mL min–1) andthe lab-scale PRB are shown in Exhibit 5. The lab-scale test was termi-nated early due to a change in water supply characteristics from thesupplier. Results of this comparison indicate reasonable scaling be-tween the column and lab-scale test conducted at the same flow rate.

Effluent and pore water test results indicated high levels of nitratepresent and the absence of sulfate-reducing bacteria. Dissolved oxy-gen was also present in the effluent and pore water, indicating that inthis lab-scale PRB, the desired anaerobic conditions were not achieved.The lab-scale PRB depth was only 7.6 cm, promoting aerobic ratherthan anaerobic conditions. No sulfate-reducing bacteria were identi-fied in the effluent of the lab-scale PRB. Additionally, the presence ofnitrate was determined to be detrimental, as nitrate and oxygen, ratherthan sulfate, would be the preferred electron acceptors under the aer-obic conditions.

Exhibit 5. Comparison of Lab-Scale PRB Breakthrough with 2 mL min–1 Column Study


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Ellen C. England

Measured cation exchange capacities were found to be 0.16, 0.04,and 0.006 meq Ca2� g–1 for peat, sawdust, and sand, respectively.Cation ion exchange capacities of the peat and sawdust were lowerthan reported elsewhere (Heikkinen and his colleagues reported arange of 0.214–0.927 meq g–1; Zielinski and Meier reported 2.2 meqCa2� g–1) for natural organic or commercially processed materials(Marson reported 1.2 meq g–1), with the exception of Schwenden-mann, who reports cation exchange capacity values less than 1 meqCa2� g–1 for organic materials of a forest floor.52 Decreased exchangecapacities might have been related to the commercial processing of thepeat, which includes sun and wind drying.53 Moisture content of thecommercial peat was 24 percent, while peat from the field was foundto have a moisture content of 82 percent.54 Drying may have impactedor changed the structure of the organic material surface, resulting insome change in the cation exchange capacity.55 The lower exchange ca-pacities measured might also have been the result of a difference incation exchange measurement methodologies, as several measure-ment and reporting methods exist for cation exchange capacities.56

During the course of the lab-scale PRB operation, three plate countsof bacteria were completed using the effluent of the PRB. The platecounts yielded numerous distinguishable colonies, indicating bacteriawere present. However, visual observations indicated the organic ma-terial was not breaking down as readily as anticipated. Rather thanturning black like soil, the peat and sawdust components remainedreadily identifiable. The lack of degradation is contrary to thatrecorded in constructed wetland research, where the constructed wet-land substrate mixture (bark/peat/manure) took on the appearance ofa rich soil within three to four months.57 The apparent lack of materialdegradation in the lab-scale PRB might have been related to the choiceof Northern white cedar sawdust as the substrate. Northern whitecedar was found to be decay-resistant, and the lignin components con-tained within the sawdust are difficult for bacteria to degrade.58 Theaerobic conditions would have prevented sulfide formation.

CONCLUSIONSAlthough extensive, further study is necessary, literature informa-

tion and preliminary lab-scale studies suggest the potential for usinglow-cost organic materials such as peat, contained within permeablereactive barriers, to remove soluble uranium from ground- or surface-water. For successful, continued removal of soluble uranium, a reduc-ing environment must be maintained, in addition to the presence ofthe organic adsorbent material; the aerobic environment present inthis study’s lab-scale PRB did not achieve the desired results of sus-tained uranium removal. Additionally, air-dried peat, and wood chipbark, combined with a highly accessible carbon source, such as waste-water treatment plant biosolids, rather than the commercially pre-pared peat/sawdust/activated sludge mixture, might be more appro-priate initial choices for placement within a PRB. �

For successful, continuedremoval of solubleuranium, a reducingenvironment must bemaintained, in additionto the presence of theorganic adsorbentmaterial. . .



NOTES1. Ilani, S., & Strull, A. (1989). Uranium mineralization in the Judean Desert and in theNorthern Negev, Israel. Ore Geology Reviews, 4, 305–314; Rosholt, J. (1982). Mobi-lization and weathering. In M. Ivanovich & R. S. Harmon (Eds.), Uranium series dis-equilbrium (Vol. 1, pp. 167–180). Oxford, UK: Clarendon Press; Macaskie, L., Yong, P.,Doyle, T., Roig, M., Diaz, M., & Manzano, T. (1997). Bioremediation of uranium-bear-ing wastewater: Biochemical and chemical factors influencing bioprocess application.Biotechnology and Bioengineering, 53, 100–109; Tang, Y. (1990). Radioactive wastemanagement. Philadelphia, PA: Hemisphere Publishing; Bolivar, J., Garciatenorio, R.,& Garcialeon, M. (1995). Enhancement of natural radioactivity in soils and salt-marshes surrounding a non-nuclear industrial complex. Science of the Total Environ-ment, 9, 125–136; Rutherford, P., Dudas, M., & Arocena, J. (1995). Trace elements andfluoride in phosphogypsum leachates. Environmental Technology, 16, 343–354;Kramer, D. (1995). Hanford’s high price of peace. Engineering News-Record, pp.22–29; Francis, C., Timpson, M., Lee, S., Elless, M., & Wilson, J. (1998). The use of car-bonate lixiviants to remove uranium from uranium-contaminated soils. Journal of Ra-dioanalytical and Nuclear Chemistry, 228, 15–20.

2. United States Environmental Protection Agency. (2000, December 7). The radionu-clides rule. Federal Register; United States Nuclear Regulatory Commission. (1999).Table 2, Uranium in 10 CFR Part 20, Appendix B, U.S. Government Printing Office.

3. United States Department of Health, Education, and Welfare. (1970). Radiologicalhealth handbook. Rockville, MD: Bureau of Radiological Health; Klassen, C. (1996).Casarett and Doull’s toxicology (5th ed.). New York: McGraw-Hill.

4. Langmuir, D. (1997). Aqueous environmental geochemistry. Upper Saddle River,NJ: Prentice Hall.

5. Koss, V., & Buetow, E. (1993). Modeling of heavy metal adsorption on the site of theEllweiler uranium mill. Soil and Environment, 1, 517–518.

6. See note 4.

7. Allison, J., Brown, D., & Novo-Gradac, K. (1991). MINTEQA2. A geochemical as-sessment data base and test cases for environmental systems: Version 3.0 user’s man-ual. Report EPA/600/3-91/-21. Athens, GA: US EPA; Garrels, R., & Christ, C. (1965).Solutions, minerals and equilibria. New York: Harper and Row; Parkhurst, D. (1995).User’s guide to PHREEQC—A computer program for speciation, reaction-path, ad-vective transport, and inverse geochemical calculations. U.S. Geological Survey WaterResources Inv. Report 95-4227.

8. Barton, L., Choudhury, K., Thomson, B., Steenhoudt, K., & Groffman, A. (1996). Bac-terial reduction of soluble uranium: The first step of in situ immobilization of uranium.Radioactive Waste Management and Environmental Restoration, 20, 141–151; Miner-alogical Society of America (1999). Uranium: Mineralogy, geochemistry and the envi-ronment. Washington, DC: Mineralogical Society of America.

9. M. Lyerla, Stone and Webster Environmental Consultant (personal communication,June 2001).

10. Uhrie, J., Drever, J., Colberg, P., & Nesbitt, C. (1996). In situ immobilization of heavymetals associated with uranium leach mines by bacterial sulfate reduction. Hy-drometallurgy, 43, 231-–239; Blount, J. (1998). Physicochemical and biogeochemicalstabilization of uranium in a low-level radioactive waste disposal cell. Environmentaland Engineering Geoscience, 4, 491–502.

11. Halbach, P., Von Borstel, D., & Gundermann, K. (1980). The uptake of uranium byorganic substances in a peat bog environment of a granitic bedrock. Chemical Geol-ogy, 29, 117–138; Culbert, R., & Leighton, D. (1988). Young uranium. Geology Reviews,3, 313–330; Lopatkina, A. (1967). Conditions of accumulation of uranium in peat.


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Geokhimiya. 6, 708–719; Zielinski, R., & Meier, A. (1988). The association of uraniumwith organic matter in holocene peat: An experimental leaching study. Applied Geo-chemistry, 3, 631–643; Ilani, S., & Strull, A. (1989). Uranium mineralization in theJudean Desert and in the Northern Negev, Israel. Ore Geology Reviews, 4, 305–314;Villar, L., Pelayo, M., Cozar, J., De La Cruz, B., Pardillo, J., Reyes, E., et al. (1997). Min-eralogical and geochemical evidence of the migration/retention processes of U and Thin fracture fillings from the El Berrocal granitic site (Spain). Journal of ContaminantHydrology, 26, 45–60.

12. Dave, N., Lim, T., & Vivyurka, A. (1981). Chemical and radioisotope stratificationin an abandoned uranium tailings pile. In Radiation hazards in mining: Control, meas-urement, and medical aspects (pp. 180–188). Golden, CO: Society of Mining Engineersof the American Institute of Mining, Metallurgical and Petroleum Engineers; Jeffery, J.,Sinclair, G., & Lowson, R. (1988). Radium and heavy metal transport beneath an aban-doned uranium tailings dam. Australian Nuclear Science and Technology Organisa-tion, pp. 1–14.

13. Abdelouas, A., Lutze, W., & Nuttall, E. (1998). Chemical reactions of uranium inground water at a mill tailings site. Journal of Contaminant Hydrology, 34, 343–361;Al-Hashimi, A., Evans, G., & Cox, B. (1996). Aspects of the permanent storage of ura-nium tailings. Water, Air and Soil Pollution, 88, 83–92; Gaffney, J., Marley, N., & Clark,S. (Eds.). (1996). Humic and fulvic acids: Isolation, structure, and environmental role.Washington, DC: American Chemical Society.

14. Lewis, B., & Gnanapragasam, E. (1993). Coupling of equilibrium chemistry to thetransport of radionuclides in contaminated soils. USA/CIS Joint Conference of Envi-ronmental Hydrology and Hydrogeology (pp. 333–344). Alexandria, VA; Wang, Y.(1991). The desorption of uranium and thorium from contaminated soils: The role ofgeochemistry and distribution coefficients in modeling contaminants leaching. Un-published doctoral dissertation, Northwestern University, Evanston, IL.

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