Oxalate Extraction of Pb and Zn from Polluted Soils: Solubility Limitations

Home , Oxalate

Downloaded By: [NEICON Consortium] At: 08:12 12 May 2007 Agricultural and Biological Engineering Biological and Herzig M. Agricultural L. and Elliott A. H. of thismaterialwithouttheconsent ofthepublisherisprohibited. Copyright Department, Pennsylvania State University, State Pennsylvania Department, University Park, PA 16802 PA Park, University Oxalate ExtractionofPbandZnfrom Polluted Soils: SolubilityLimitations KEY WORDS: © 1999,CRCPressLLC—Filesmay bedownloadedforpersonaluseonly.Reproduction soilremediation,heavymetals,metal-contaminatedsoils,chelation. Journal ofSoilContamination, 105 Oxalate (Ox) was used to extract Pb and Pb extract to used was (Ox) Oxalate Zn from industrially contaminated soils. contaminated industrially from Zn as a single-step extractant even for soils for even extractant single-step a as Although Ox effectively releases metals releases effectively Ox Although mildly contaminated with Pb. The useful- The Pb. with contaminated mildly bound by hydrous oxide soil components, soil oxide hydrous by bound ness of Ox as a Zn extractant, however, extractant, Zn a as Ox of ness sp it forms insoluble salts with some heavy some with salts insoluble forms it depends on the level of soil contamination. soil of level the on depends metals unlike conventional extractants conventional unlike metals A Zn solubility model, based on published on based model, solubility Zn A (e.g., EDTA). The insolubility of PbOx(s) of insolubility The EDTA). (e.g., equilibrium constants, was developed to developed was constants, equilibrium = 2.74 2.74 = (K assess Ox suitability as a function of sys- of function a as suitability Ox assess tem conditions. Precipitation of ZnOx(s) hin- ZnOx(s) of Precipitation conditions. tem dered Zn recovery under acidic conditions acidic under recovery Zn dered where formation of soluble oxalato com- oxalato soluble of formation where plexes was small. For pH < 3, the presence the 3, < pH For small. was plexes of 1 M Ox actually reduced Zn release Zn reduced actually Ox M 1 of compared to simple acid washing. Although washing. acid simple to compared Ox displaces oxide-bound metals and thus and metals oxide-bound displaces Ox is potentially useful in soil washing, solubil- washing, soil in useful potentially is ity limitations must be defined for effective for defined be must limitations ity remediation of metal-laden soils. metal-laden of remediation × 10 –11 ) precluded the use of Ox of use the precluded ) 8(1):105–116(1999) Downloaded By: [NEICON Consortium] At: 08:12 12 May 2007 O 0.1 to wheatplants(MisraandPandey,1976).FarrahPickering(1978)foundthat mended asanextractantforevaluatingthefractionofsoilheavymetalsavailable trations insoils.Grigg’sreagent(acidifiedammoniumoxalate)hasbeenrecom- solutions usedtoevaluatetheplant-availableorbiologicallyactivemetalconcen- metal ionsfromsoilshasbeenemployedformanyyears,particularlyinextracting in desorbingmetalsoccludedwithinhydrousoxides(ElliottandShastri,1998). Shem, 1992),althoughslowdissolutionofoxidicsoilcomponentshindersitsuse been showntobeextremelyeffectiveindesorbingmetalsfromsoils(Petersand probably isthemostcommonlyreportedreagentinsoilwashingstudies.Ithas they formremarkablystablecomplexeswithawidearrayofmetals.EDTA (NTA, EDTA,DTPA)havebeenusedbothanalyticallyandcommerciallybecause from contaminatedsoils(Pickering,1986).Severalaminopolycarboxylicacids appreciation ofoperationalconditionsthatoptimizemetalrecovery. process detailsaregenerallyconsideredproprietary.Thishashinderedabroad There areanumberoffull-scalesoilwashingtechnologies(Anderson,1993),but pleted inNorthAmerica,roughlyone-tenthinvolvedsoilwashing(USEPA,1997). government-sponsored innovativetechnologyfielddemonstrationprojectscom- and themetal-ladensolutionundergoesfurthertreatment.Ofmorethan300 into aqueoussolution.Afterseparation,thecleanedsoilisredepositedatsite ex situ for otherremediationtechniques(Anderson,1993).Typically,soilwashingisan be usedtoremoveinorganiccontaminantslikeheavymetalsorasapretreatmentstep soil followingOxextraction mayalsoconstrainitsusefordecontaminatingZn- Based onpublishedsolubilityconstants,precipitation ofmetalsdisplacedfromthe reported thatOxwasineffectiveinremovingPbfrom ahighlycontaminatedsoil. tions tothesparingsolubilityofPb-oxalatespecies. ElliottandShastri(1998) metals. Pickering(1986)attributedlowPbrecovery from sedimentsbyOxsolu- agents. ligand andispotentiallylessexpensivethansome commonlyinvestigatedre- oxide components(ElliottandShastri,1998).Oxis alsoanaturallyoccurring related extractants,Oxisextremelyeffectiveinreleasing metalsboundtosoil release Cdfromsoilsthroughorganiccomplexation. IncontrasttoEDTAand surfaces. Recently,Krishnamurtietal.(1997)documentedtheabilityofOxto of anionicoxalatocomplexesandtheaffinityprotonatedOxspeciesforclay clays. Theyattributedthemetal-displacingabilityofoxalicacidtoformation of thismaterialwithouttheconsent ofthepublisherisprohibited. Copyright The abilityofoxalicacidandotheroxalate(Ox)-containingreagentstodisplace A widerangeofcomplexingligandshavebeenemployedforextractingmetals On thenegativeside,Oxtendstoformsparinglysoluble oxalatesaltswithsome M oxalicacidwasabletoreleasePb,Zn,Cu,andCdpreadsorbedonseveral processthatemploysextractingreagentstodisplacemetalsfromthesoil complete cleanupofhazardouswastesites.Insomecases,soilwashingcan N-SITE remediationofmetal-contaminatedsoilsisoftenamajorobstacleto © 1999,CRCPressLLC—Filesmay bedownloadedforpersonaluseonly.Reproduction I NTRODUCTION 106 Downloaded By: [NEICON Consortium] At: 08:12 12 May 2007 using atripleacid(HF-HNO dried atnearroomtemperaturepriortouse.Thetotalmetallevelswereassessed particular soilseriesorclassification.Soilsweregroundtopassa2-mmsieveand ferred toasthe“Indiana”and“Palmerton”soil;namesdonotdesignateany downwind fromthePalmerton,Pennsylvania,smelterfacility.Thesoilsarere- had elevatedZnandwascollectedfromthemountainimmediatelyadjacent Pb, withlevelsashigh46%reported(SimsandWagner,1983).Thesecondsoil and hadextremelyhighPb(21%).Soilsatbatterysitestypicallyhaveroughly5% collected fromanautomobilebatteryrecyclingfacilitynearIndianapolis,Indiana, Two metal-contaminatedsurfacesoilswereusedinthisstudy(Table1).Onewas process conditionsthatmaximizemetalrecoveryinsoilwashingsystems. illustrates theuseofafundamentalsolutionequilibriumapproachinestablishing modeled usingpublishedthermodynamicequilibriumconstants.Thismodeling behavior ofOx.Tohelpinterpretthedata,ZnsolubilityinpresenceOxwas the pHandconcentrationdependenceofaminocarboxylicacidswith has beeninvestigated.MetalreleasebyEDTAextractionwaschosentocompare as anextractant.RecoveryofPbandZnfromtwoindustriallycontaminatedsoils conditions underwhichinsolubilityofmetal-oxalatesaltslimitstheutilityOx eters (pH,soil/solutionratio,ionicstrength). could beinfluencedbythelevelofcontaminationandvariousoperationalparam- generally notobservedinmostsoilwashingsystems.However,suchprecipitation polluted soils.Precipitationofthedisplacedmetalwithextractingreagentis pylene Erlenmeyerflasksanddilutedto100mltotalvolumewithdistilledwater. prepared fromoxalicacidandtetrasodiumEDTA,wereaddedto125-mlpolypro- desired finalconcentration,variableamountsofOxorEDTAstocksolutions, 1988). provide superiorrecoveryfromhighlycontaminatedsoils(ElliottandShields, of thismaterialwithouttheconsent ofthepublisherisprohibited. Copyright Therefore, thepurposeofthisinvestigationwastomorepreciselydefined ol%mgkg 280 197 2700 521 812 210,000 17 18 32 23 51 59 % 6.5 2.6 a Palmerton Indiana Soil Batch desorptionexperimentswereperformedasfollows.Dependingonthe Typical backgroundsoilvalues(Lindsay, 1979;Alloway,1990). © 1999,CRCPressLLC—Filesmay bedownloadedforpersonaluseonly.Reproduction rai atrSn itCa bZ Cd Zn Pb Clay Silt Sand Organic matter Selected PropertiesoftheSoils M ATERIALS 3 -HClO TABLE 1 4

) digestionmethod,previouslyshownto 107 AND M ETHODS 10 a 50 a –1 0.2 a Downloaded By: [NEICON Consortium] At: 08:12 12 May 2007 1.0 0.01 mgL (Perkin-Elmer, Norwalk,CT).Detectionlimitsreportedbythemanufacturerare flame atomicabsorptionusingaPerkin-Elmermodel2380spectrophotometer Scientific, AnnArbor,MI),andmetalanalysisofthefiltratewasdoneby release data.Thesoilwasremovedbyfiltrationthrough0.45- final pHofthesampleswasmeasuredandthesevalueswereusedtoplotmetal to catalyzeOxdissolutionofoxyhydroxides(Pickering,1986).Aftershaking,the Pittsburgh). Theextractingsolutionswereopentolightexposure,whichisknown at roomtemperatureonaBurrellmodel75wrist-actionshaker(BurrellCorp., pH valueswouldcoverthe3to10range.Thesampleswereagitatedfor24h initial pHadjustment.ThewasadjustedwithNaOHandHNO g,dependingonthesystem)wasaddedtoflasksjustprior The soil(2to4 of thismaterialwithouttheconsent ofthepublisherisprohibited. Copyright shown inFigure1.At0.08 The influenceofOxandEDTAonsolubilizationPbfromtheIndianasoilis ments. separation, andZnanalysisfollowedthesameproceduresasdesorptionexperi- The pH-dependent release of Pb from the Indiana soil as influenced by EDTA and Ox. and EDTA by influenced as soil Indiana the from Pb of release pH-dependent The Zinc solubility,intheabsenceandpresenceofOx,wasevaluatedusing0.01to M solutionsofZn(NO © 1999,CRCPressLLC—Filesmay bedownloadedforpersonaluseonly.Reproduction –1 (Pb)and0.0008mgL Comparison ofOxalatewithEDTA 3 ) 2 R M .6H ESULTS , theEDTAconcentrationrepresentsa2:1ligand/ 2 O. AdjustmentofpH,shakingconditions,solids –1 FIGURE 1 FIGURE

(Zn). AND 108 D ISCUSSION µ m filters(Gelman 3 sothatthefinal Downloaded By: [NEICON Consortium] At: 08:12 12 May 2007 solubility productconstant(K species formedinsolution.ThesparingsolubilityofPbOx(s)isindicatedbyits soil butsubsequentlyprecipitatedfromthesolutionphase. distinguish betweenPbremainingonthesoilandthatwhichisdisplacedfrom filtration techniqueusedtoseparatethewashedsoilfromsolutiondoesnot that Pbisremovedfromsolutionsubsequenttoitsdisplacementthesoil.The lution ofPb-containingphases)shouldoperateevenwithOxpresent.Thisimplies under acidicconditions(i.e.,exchangedisplacementbyH acidic conditions,whereitwasexpected.Theprocessesthatreleasesoil-boundPb tion mustbeconsideredforacompletepictureofPbsolubilityinthissystem. even at1 stable Pb-oxalatocomplexes(Table2),OxwasunabletopromoterecoveryofPb high metalrecoveries(FarrahandPickering,1977).Despiteformingreasonably As ageneralrule,reagentsthatconvertsorbedmetalsintoanioniccomplexeseffect is greatlysuperiortoOxasindicatedbytherelevantformationconstants(Table2). release relativetoOx.TheabilityofEDTAcomplexPb,andmetalsingeneral, soils. Althoughpresentinlowerconcentration,EDTAdramaticallyenhancedPb excess, arequirementforsubstantialmetalrecoveryinwashingofcontaminated ligand/metal ratiowas12:1.Thus,bothligandsarepresentinstoichiometric metal molarratioassumingtotalsolubilizationofthePb.For1 Pb catalyzed dissolutionofPb-containingsoilcomponentsandthedisplacement recovery occurredbelowpH5.Thisbehaviorcanbeattributedtotheacid- ation areinvolved.Evenintheabsenceofligands,asubstantialupturnPb solution pH(designated“noligands”)revealsthatprocessesotherthancomplex- of thismaterialwithouttheconsent ofthepublisherisprohibited. Copyright 2+ This behaviorismostreadilyexplainedbytheinsolubilityofPb-oxalate Figure 1showsthatOxdidnotresultinsolubilizationofPbevenunderstrongly The effectssolubleoxalatocomplexformation,Pbhydrolysis,andOxprotona- fromexchangesitesbyH b41 772.74 17.7 4.16 Pb d27 659.0 1.35 16.5 16.5 2.73 3.4 Cd Zn Oxalate Metal © 1999,CRCPressLLC—Filesmay bedownloadedforpersonaluseonly.Reproduction M levels.ComparingtheOxdatawithPbreleasesimplybyadjusting log formationconstantsfor 1:1 complex(I=1 (Martell andSmith,1976;CRC,1977) Equilibria RelevanttotheSystem KPbOx sp = sp [][] + ): (seeElliottandBrown,1989). EDTA 211 22 M TABLE 2 + , 25 109 ° C) =× 7 10 274 . Oxalate solubilityproduct K sp ± (I=0,18 + × × × , acid-catalyzeddisso- 10 10 10 –11 –8 –9 ° M C) Ox,theinitial (1) Downloaded By: [NEICON Consortium] At: 08:12 12 May 2007 conditions, thesolutionwouldbesaturatedwithrespecttoPbOx(s)ifPb ceeded 2.74 concentration (Ox However, Eq.1isusefulforagrossestimationofthiseffect.Ifthetotaloxalate of thismaterialwithouttheconsent ofthepublisherisprohibited. Copyright cause oflowPbrecoverieswithOx(Pickering,1986),weinvestigatedtheextent different (Figure1). for soilshighlyenrichedwithPb,therelativeextractionefficiencywasquite and 0.1 reagent (acidammoniumoxalate)extractedmorePbfromsoilsthan0.02 apparently, hinderPbreleasefromsoils.MisraandPandey(1976)reportedGrigg’s elevated Pb.Forunpollutedsoils,however,theinsolubilityofPbOx(s)doesnot, that Oxisunsuitableasasinglestepextractantevenforsoilswithmoderately soil, theresultingsolutionlevelshouldbe7.8 recovery ofPbevenfromthePalmertonsoil.Assumingtotalreleasethis tracted with1 Palmerton soil,onlymodestlycontaminatedwithPb(812mg/kg),wasalsoex- ciable displacementwillresultinhighPblevelstheextractsolution.The low inthepresenceof1 of PbOx(s)wasreached.ThisroughcalculationexplainswhyPbrecoveryso into asolutioncontaininghighenoughlevelofOxsuchthatthesaturationpoint the solutionconcentrationofPbwouldbe0.04 protonation characteristicsofoxalicacid(pK The pH-dependent removal of Zn and Pb from the Palmerton soil as influenced by Ox. by influenced as soil Palmerton the from Pb and Zn of removal pH-dependent The Although thesparingsolubilityofPbOx(s)hasbeenidentifiedpreviouslyas The Indianasoil,however,isgrosslycontaminatedwithPbsothatanyappre- N © 1999,CRCPressLLC—Filesmay bedownloadedforpersonaluseonly.Reproduction HCl,butintheircasesoil-extractablePbwaslessthan3mg/kg.Clearly, × 10 M Ox.Figure2showsthatOxwasunabletoeffectanyappreciable –11 T

) is1 M suig10 brcvr o h odtosi iue1, . Assuming100%PbrecoveryfortheconditionsinFigure M M Ox. athighpH,Ox FIGURE 2 FIGURE 110 a1 × 2– = 1.25,pK 10 M willberoughly1 . ThePbionswerethendisplaced –6 M . ThePbOx(s)issoinsoluble a2 = 4.28).Basedonthese M giventhe M EDTA 2+ ex- Downloaded By: [NEICON Consortium] At: 08:12 12 May 2007 (Zn equilibrium modelslikeMINTEQA2. carbonate-containing Znphasesandcannotbeneglectedthusrequirechemical complexation withsoilorganicmatter,precipitationofCaOx(s),andformation be quantifiedtomodelmorepreciselysuchcomplexsystems.Forsomesystems, (ZnOx(s) andZnO(s)).Onecautioniswarranted.Ahostofotherreactionsmust level onZnrecoveryinthissystem. These reactionscanbemodeledtoquantifyandpredicttheeffectofpHOx ation) thatcollectivelydefinetheamountofZncanexistinsolutionphase. interplay ofequilibria(precipitation,hydrolysis,Oxprotonation,Zncomplex- under acidicconditionsaswasobservedforPb.Thesedatareflectthecomplex noteworthy inFigure2wasthefailureofOxtocompletelysurppressZnremoval basic conditions,thepresenceofOxhadlittleimpactonZnrelease.Particularly neutral conditions,OxenhancedZnremoval.However,understronglyacidicor ability ofOxtomodifyZnremovalexhibitedastrongpHdependence.Undernear- be enhancedsimplybyloweringthepHofwashingsolution.Inourstudy, 1).DavisandSingh(1995)similarlyfoundthatZn(II)removalfromsoilcan ure recovery increasedunderacidicconditionsanalogoustothebehaviorofPb(Fig- release withandwithoutOxintheextractingsolvent.InabsenceofOx,Zn forms lessstablesolublecomplexeswithZn(Table2).Figure2compares tation ofZnOx(s).Similarly, thetotalconcentrationofOxinsystemincludes (both ZnOx Zn, theprotonationbehaviorofoxalicacid,formationZn-oxalatocomplexes taken intoaccount,includingtheformationofmononuclearhydroxocomplexes patterns observedintheextractionexperiments.Severalsolutionreactionswere if thebehaviorofZninpresenceOxcouldexplaingeneralrelease A Znsolubilitymodelwasdeveloped,basedonpublishedequilibria,todetermine polluted soils.WhiletheK to whichthesamephenomenamightlimitextractivedecontaminationofZn- where P in themassbalanceexpression: aquo ion(Zn of thismaterialwithouttheconsent ofthepublisherisprohibited. Copyright The Znsolubilitymodelisbasedonmassbalanceexpressionsforthetotalzinc T ) andtotaloxalate(Ox nPZ nHZ HZ HZ OH Zn OH Zn OH Zn ZnOH Zn P Zn Zn TZn © 1999,CRCPressLLC—Filesmay bedownloadedforpersonaluseonly.Reproduction represents themolesperliterofZnremovedfromsolution byprecipi- =+ + ° 2+ []

and Zn(Ox) nxZ Ox Zn ZnOx ), fourhydrolysisspeciesandtwooxalatocomplexes were included [] Zinc SolubilityinthePresenceofOxalate o 2 + ++ [] + 2 [] sp 2– ( T forZnOx(s)isroughly100timesthatofPbOx(s),Ox ), andtheformationofZn-containingsolidphases ) concentrationsinthesystem.ForZn,divalent ) 2 2 ± + [] 111 ( ) 234 o + [] ( ) ±± + [] ( ) 2 (2) Downloaded By: [NEICON Consortium] At: 08:12 12 May 2007 (Figure 3a),Znsolubilityisabout10 illustrates howligandsenhancemetalsolubility.Forexample,intheabsenceofOx becomes thestable(lesssoluble)phase.AcomparisonofFigures3aand3b ZnOx(s) phaseforpHlessthanabout9.7,andmorealkalineconditions,ZnO(s) 3b). ThedataandcalculationsclearlyshowthatZnsolubilityisdeterminedbythe as illustratedforPb(Figure1)andZn2). simply loweringthepHofanaqueouswashingsolutionwillenhancemetalrelease, is acommonandwidelyrecognizedfeatureofheavymetalsexplainswhy around pH10andprogressivelyincreasesatlowerhigher(Figure3a).This solubility experiments.IntheabsenceofOx,ZnO(s)isaminimum the solidlinesreflectingmodelcalculationsanddatageneratedfrombatch conditions. Thissameprocedurewasrepeatedforzincite,ZnO(s). soluble Znconcentration,thatis,thesolubilityofZnOx(s)underassumed The individualZnspeciescanthenbedeterminedandsummedtoderivethetotal explicitly (viathequadraticequation)forfreeoxalateconcentration,[Ox P the amountprecipitatedasZnOx(s),P of thismaterialwithouttheconsent ofthepublisherisprohibited. Copyright extraction data.Noticethat thepresenceofOxcausedasubstantialincreaseinZn This interplayofcomplexation andsolubilityreactionswasreflectedintheOx expression: [Zn roughly 10 metal releaseunderacidicconditions.AtpH6.0without Ox,Znsolubilityis ligand-free systemoverthepH5to10range. Figure 2showsthatOxdid,infact,enhanceZnsolubilitycomparedwiththe This solubilityincreaseexplainswhysuchreagentscandisplacemetalsfromsoils. 3b), ZnsolubilitywasincreasedroughlyfourordersofmagnitudeatthesamepH. of theoxalatesaltcanbebroughtintocombinedexpressionthroughK complexed formsofsolubleOx: in Znsolubility. to moreacidicconditionsrevealsanevendramatic oxalate-inducedreduction by morethananorderofmagnitude(Figure3b).Extending theZnO(s)solubility Zn Because eachspeciesinEq.2canbeexpressedtermsof[Zn The presenceof0.25 Figure 3showsthepH-dependentsolubilityofZnasinfluencedbyOx,with Because ZnandOxareprecipitatedfromsolutionina1:1stoichiometricratio, These diagramsalsoshowpreciselywhyOx can potentiallyinhibit =P Ox xPHO O xZO nOx Zn ZnOx Ox HOx Ox H P Ox © 1999,CRCPressLLC—Filesmay bedownloadedforpersonaluseonly.Reproduction . ThisallowsEq.2tobesolvedforP –1 TOx M =+ (Figure3a).ThepresenceofOxcausedZnsolubility todecrease 2+ ] =K Solubility LimitationsonZnDisplacement [] 2 sp M /[Ox OxhadadramaticinfluenceonZnsolubility(Figure oo + [] 2– ]. Theresultingexpressioncanthenbesolved _± –6 112 M + Ox [] atpH9.InthepresenceofOx(Figure , aswelltheprotonatedandZn- 2 Zn + andsubstitutedforP [] + 2 [] 2+ ( ], thesolubility ) Ox 2 2 ± in Eq.3. 2– (3) ]. sp Downloaded By: [NEICON Consortium] At: 08:12 12 May 2007 potentially bereleasedinto thesolution. solubility effectsinfluencemetalreleasedependson the amountofmetalthatcan acidic conditionsbasedoncalculations(Figure3b).However, theextenttowhich that anappreciablereductioninZnrecoverywould beobservedunderstrongly the presenceofOxhadlittleclear-cuteffectonZnsolubility. Itmightbeexpected removal overthe“noligand”datainpH4to10range (Figure2).ForpH<4, of thismaterialwithouttheconsent ofthepublisherisprohibited. Copyright are from batch solubility experiments. The dashed line (3a) is the calculated solubility calculated the is (3a) line dashed The experiments. solubility batch from are The pH-dependent solubility of Zn: (a) Solubility of ZnO(s) and (b) solubility of ZnOx(s) and ZnOx(s) of solubility (b) and ZnO(s) of Solubility (a) Zn: of solubility pH-dependent The neglecting the uncharged hydrolysis species (Zn(OH) species hydrolysis uncharged the neglecting ZnO(s) in the presence of 0.25 0.25 of presence the in ZnO(s) © 1999,CRCPressLLC—Filesmay bedownloadedforpersonaluseonly.Reproduction FIGURE 3A FIGURE M Ox. Lines were generated from the solubility model, data model, solubility the from generated were Lines Ox. FIGURE 3B FIGURE 113 2 o because its existence is questioned. is existence its because Downloaded By: [NEICON Consortium] At: 08:12 12 May 2007 the soilZnisreleased.Ifmaximumreleasewouldpotentiallyresultin10 because thesolutioncanneverbeoversaturatedwithrespecttoZnOx(s)evenifall bility willnotadverselyimpactZnrecoveryfromthecontaminatedsoil.Thisis maximum Znreleasableintosolutionis10 of thesoilZnwerereleasedintosolution.Ifsystemconditionsaresuchthat of thismaterialwithouttheconsent ofthepublisherisprohibited. Copyright increasing themaximumreleasableZnto10 increased byaddingasolutionofZnnitratetothesoil.Thishadeffect (pH 1to4rangeofFigure2). capable ofbeingdesorbedunderthesystemconditions.Thiswas,infact,case or noimpactonZnrecovery,dependingwhatfractionofthetotalisactually with thesolubilitycurveforZnOx(s),suggestingthatmighthavelittle “y”. TheselinesrepresentpossibleZn Figure 2,themaximumreleasableZnwasroughly10 to soildecontaminationbywashing.Forthedesorptionexperimentsshownin level ofZnisreached.Inthiscase,solubilitytheoxalatesaltanimpediment in solution(arrow“y”),thesolubilityofZnOx(s)isexceededbeforethis predicted Znsolubilityexceedsthe10 release inFigure4(aboutpH3to4)correspondscloselytheatwhich is noteworthythatthecrossoverpHatwhichpresenceofOxenhancesZn analysis, thepresenceofOxhadamoredramaticabilitytohinderZnrecovery.It artificially contaminatedsoilisshowninFigure4.Consistentwiththeforegoing soil so that total Zn removal would correspond to Zn to correspond would removal Zn total that so soil Effect of 1.0 1.0 of Effect To furtherinvestigatethiseffect,theZnconcentrationofPalmertonsoilwas This isillustratedinFigure3bbytwohorizontaldashedarrowslabeled“x”and © 1999,CRCPressLLC—Filesmay bedownloadedforpersonaluseonly.Reproduction M Ox on Zn release from the Zn-amended Palmerton soil. Zn was added to the to added was Zn soil. Palmerton Zn-amended the from release Zn on Ox FIGURE 4 FIGURE –2.8 T 114 levelsthatcouldexistinsolutionif100% M maximumreleasablelevel(Figure3b). –5.5 M –2.8 T = 10 = (arrow“x”),oxalate-saltinsolu- M . TheOxextractionofthis –3 – 2.8 2.8 M M . Thisvaluejustoverlaps in the extracting solution. extracting the in –1.5 M Zn Downloaded By: [NEICON Consortium] At: 08:12 12 May 2007 Gyliene, O.andSalkauskas,M.1995.Metalrecoveryfromspent electrolessplatingsolutionsby Farrah, H.andPickering,W.F.1978.Extractionofheavymetals sorbedonclays. Elliott, H.A.andShields,G.1988.Comparativeevaluationof residualandtotalmetalanalyses Elliott, H.A.andShastri,N.L.1998.Extractivedecontamination ofmetalpollutedsoilsusing Alloway, B.J.1990. conditions whereprecipitationhindersmetalrecoveryfromcontaminatedsoils. carbonate-containing Znprecipitates,solubilitymodelshelpdefineandavoid quantifying sidereactionsnotconsideredhere,suchasformationofCaOx(s)or Ni, andCo(GylieneSalkauskas,1995).Althoughsomesystemsnecessitate oxalate saltsmayalsobeanissueforCd(Krishnamurtietal.,1997)aswellCu, acidic conditionsmayconstrainuseofOxasasoilwashingagent.Insolubility reagents. ResultsindicatethatforPbandZn,precipitationofoxalatesaltsunder with thetraditionalaminopolycarboxylicacids(e.g.,EDTA)usedassoilwashing ciency. Thishasnotbeenfullyappreciatedheretoforebecauseitisanissue aqueous phasetoaccommodatethecomplexedmetalalsodictatesrecoveryeffi- of metalcomplexationreactions.Thisworkindicatesthatthecapacity divided intothoseinfluencingthenatureofsoil-boundmetalsorstrength for washingofmetalsfromcontaminatedsoils.Theseparameterscanbebroadly A hostofchemicalparametersinfluencetheselectionandusechelatingreagents Davis, A.P.andSingh,I.1995.WashingofZn(II)fromacontaminated soilcolumn. case, willeffectgreaterZnrecoverythanligand-enhancedextractionusingOx. of OxcanactuallyhinderZnrecovery(Figure4).Simpleacidleaching,inthis Ox asanextractantiscompromised.Indeed,underacidicconditions,thepresence exceeded thesolubilityofZnOx(s)underprocessconditions,usefulness the soil.WhencontaminationlevelwashighenoughsothatdisplacedZn contamination, itsutilityforZndependsonthedegreeofcontaminationwithin Elliott, H.A.andBrown,G.1989.Comparativeevaluation ofNTAandEDTAforextractive Anderson, W.C.1993. CRC, 1967. of thismaterialwithouttheconsent ofthepublisherisprohibited. Copyright oxalate precipitation. Pollut. in pollutedsoils. oxalate. Thus, whileOxisanunsuitableextractantforPbatalmostanylevelof decontamination ofPb-pollutedsoils. ASCE. napolis, MD,Amer.Acad.Environ.Engr.

© 121(2), 9, Water,Air,SoilPollut. 1999,CRCPressLLC—Filesmay bedownloadedforpersonaluseonly.Reproduction Handbook ofChemistryandPhysics 491–498. 174–185. Comm. SoilSci.PlantAnal. Heavy MetalsinSoils Innovative SiteRemediationTechnology:SoilWashing/SoilFlushing Plating Surf.Finishing inpress. REFERENCES C Water, Air,SoilPolut. ONCLUSIONS , NewYork,JohnWiley&Sons. 115

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45, 361–369. J. Environ.Eng., Water, Air,Soil . An- Downloaded By: [NEICON Consortium] At: 08:12 12 May 2007 USEPA. 1997.CompletedNorthAmericaninnovativeremediationtechnologydemonstrationprojects. Sims, R.andWagner,K.1983.In-situtreatmenttechniquesapplicabletolargequantitiesof Peters, R.W.andShem,L.1992.Useofchelatingagentsforremediationheavymetalcontami- Pickering, W.F.1986.Metalionspeciationinsoilsandsediments. Martell, A.E.andSmith,R.M.1976. Lindsay, W.L.1979. Krishnamurti, G.S.R.,Cieslinski,G.,Huang,P.M.,andVanRees,K.C.J.1997.Kineticsof of thismaterialwithouttheconsent ofthepublisherisprohibited. Copyright Misra, S.G.andPandey,1976.Evaluationofsuitableextractantforavailableleadinsoils. EPA 542–F–96–002a. Office ofSolidWasteandEmergencyResponse,UnitedStatesEnvironmentalProtectionAgency, Sites, SilverSprings,MD,HazardousMaterialsControlRes.Inst. hazardous wastecontaminatedsoilsinProc.ManagementofUncontrolledHazardousWaste nated soil.In: .F.,Reed,D.T.,andTasker,I.R.,Eds.),Wash.,D.C.,Amer.Chem.Soc. G. J. Environ.Qual. cadmium releasefromsoilsasinfluencedbyorganicacids:Implicationinavailability. Soil.

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1, 83–146. Plant