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Use of bone meal amendments to immobilise Pb, Zn and Cd in soil, A leaching column study.pdfUse of bone meal amendments to immobilise Pb, Zn and Cd in soil, A leaching column study.pdf -- 5 元

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,MuseumReceived25August2005receivedinrevisedform7February2006accepted10February2006Anextended18monthsleachingcolumnstudyofmetalPb,Zn,Cdimmobilisationusingbonemealasasourceofphosphate,demonstratingpositiveresults.AbstractTheaimofthisstudyistotestthestabilisationofmetalsincontaminatedsoilsviatheformationoflowsolubilitymetalphosphates.Boneapatite,intheformofcommerciallyavailablebonemeal,wastestedasaphosphatesourceonaminewastecontaminatedmadegroundwithhighlevelsofPb,ZnandCd.Triplicateleachingcolumnsweresetupatbonemealtosoilratiosof125and110,inadditiontounamendedcontrols,andwererunfor18months.ThecolumnswereirrigateddailywithasyntheticrainsolutionatpHof2,3,and4.4.After100days,theleachatePb,ZnandCdconcentrationsofallamendedcolumnsweresignificantlyreduced.For110treatments,releaseofthesemetalswassuppressedthroughoutthetrial.For125treatments,ZnandCdconcentrationsintheleachatesbegantoincreaseafter300days.DTPAandwaterextractionsshowedthatPbandCdweremorestronglyheldintheamendedsoils.Thisstudyconcludesthatthecomplexityofsoilprocessesandthesmallquantitiesofmetalssequesteredprecludeddeterminationofametalimmobilisationmechanism.C2112006ElsevierLtd.Allrightsreserved.KeywordsMetalimmobilisationPhosphateBonemealApatiteLeadZincCadmiumSoilcolumn1.IntroductionMetalsmaybepresentinsoilsfromavarietyofsourcesandcanrepresentapotentialhazardtohumansandtheenvironmentiftheyarereadilyreleasedintosoilsolutionorareotherwiseavailabletobiologicalprocesses.However,ifsuchmetalsareboundupinrelativelyinertandinsolublecompounds,thedangertheyrepresentisreducedsubstantially.ThephosphatesofmanymetalsincludingPb,Zn,Cd,CuandarestableacrossaverywiderangeofenvironmentalEhandpHconditions.Therenowexistsasignificantbodyofresearchshowingsuchcompoundsmayreadilyform,giventhepresenceofasourcewhichreleasessufficientphosphatetosolutione.g.ValsamiJonesetal.,1998Caoetal.,2003HettiarachchiandPierzynski,2004.Theamendmentofsoilswithphosphatemayhavethepotentialtoreducesignificantlymetalbioavailabilityandreleasetogroundandsurfacewaters.MuchofthisresearchhaslargelybeenconcernedwithPbUseofbonemealamendmentsinsoilAleachingI.R.Sneddona,1,M.OrueetxebarriaaE.ValsamiJonesaDepartmentofMineralogy,TheNaturalHistorybEnvironmentalScience,SchoolofBioscience,TheUniversitycDepartmentofSoilScience,SchoolofHumanandEnvironmentalSciences,EnvironmentalPollution144andNicanhaveexceptionallylowsolubilitiesNriagu,1984Correspondingauthor.Tel.þ4421079425334faxþ4421079425537.Emailaddresse.valsamijonesnhm.ac.ukE.ValsamiJones.1PresentaddressCawthronInstitute,98HalifaxStreetEast,PrivateBag2,Nelson,NewZealand02697491/seefrontmatterC2112006ElsevierLtd.Allrightsreserved.doi10.1016/j.envpol.2006.02.008toimmobilisePb,ZnandCdcolumnstudyb,M.E.Hodsona,c,P.F.Schofielda,a,,CromwellRoad,LondonSW75BD,UKofNottingham,UniversityPark,NottinghamNG72RD,UKTheUniversityofReading,Whiteknights,ReadingRG66DW,UK2006816e825www.elsevier.com/locate/envpolimmobilisationviatheprecipitationofthePbapatitegroupmineralpyromorphitePb5PO43OHinthepresenceofsolublephosphate.Insyntheticsolutions,pyromorphitehasbeenshowntoformrapidlyinconditionsconsistentwiththosefoundinmanysoilenvironmentsXuandSchwartz,1994.Inseveralexperimentsusingmetalcontaminatedsoils,evidenceforPbphosphateformationhasbeenobtainede.g.CotterHowellsetal.,1994.ExperimentswherePbuptakebyplantswasmeasuredhaveindicatedthatitsavailabilityisreducedinphosphatetreatedcontaminatedsoilsLapercheetal.,1997Brownetal.,1999.Theformationofothermetalphosphates,includingthoseofZn,Cu,CdandU,hasalsobeenimplicatedMaetal.,1994Chenetal.,1997ValsamiJonesetal.,1998andinsoils,thebioavailabilityofmetalshasbeenreducedsignificantlyafterphosphateadditionHettiarachchiandPierzynski,1999.Giventhatphosphateitselfcanleadtoenvironmentalproblemssuchaseutrophicationofsurfacewaters,duetoitsroleasanutrient,thechoiceofphosphatesourceforsoilremediationisanimportantone.Furthermorethepresenceofarsenicinmanymetalcontaminatedsoilsshouldbetakenintoconsideration,asaqueousphosphatemaycompetewitharsenateforadsorptionsitesandmaycauseAsmobilizatione.g.Boissonetal.,1999.ThecalciumphosphatemineralhydroxylapatiteCa5PO43OHhasarelativelylowsolubilitywhenpresentinitsrockcrystalformthoughworkbysomeresearcherssupportsitspotentialforremediationoftoxicmetalcontaminationinsoilsHettiarachchiandPierzynski,2002Caoetal.,2003.Hydroxylapatiteisalsotheprincipalmineralconstituentofbone,andbonemealhasbeenidentifiedasapotentiallyappropriatesourceofphosphateduetothemoderatesolubilityassociatedwithitscarbonatecontentTung,1998ValsamiJonesetal.,1998andpoorlycrystallinestructureCheungetal.,2002.Earlierworkwithbonemealamendmentshasbeenencouraging.Laboratoryexperimentsusingavarietyofsoilshaveshownreleaseofmetalstoporewaterstobereducedsignificantly,withacorrespondingreductioninmetalsavailabilitytoplantsandsoilorganismsHodsonandValsamiJones,2000aDaviesetal.,2003.IthasalsobeenshownrecentlythatincineratedbonemealisaveryeffectivesorbingagentforAsVSneddonetal.,2005.Thepreviousworkonmetalimmobilizationbybonemealwascarriedoutmostlyonacidicsoilsandforshortperiodsoftimeupto4months.Therefore,thepermanenceofsuchreductionsneedstobedemonstratedfurther,especiallyinsoilswithhighmetalloadingsacrossarangeofsoilcomponentfractions.Thispaperreportsontheresultsofanextended18monthsleachingstudycarriedouttoinvestigatetheeffectivenessofbonemealamendmentsinreducingthemobilityofthemetalsPb,ZnandCdinacontaminatedminewastemadegroundofaboveneutralpH.2.Materialsandmethods2.1.SoilThechosensoilactuallymadegroundwasfromanareaofextensivegraveltailingsassociatedwithhistoricalPbminingatNentheadinCumbria,UK.Thiswasaheterogeneousmadeground,derivedfromacarbonatehostedI.R.Sneddonetal./Environmentalore.Metalsleachintosurfacewatersfromthespoilheapsandtailingsdamsandalsofromdisusedmineadits.Duetointeractionwithcalcareouscarboniferousrocks,catchmentwatershavehighhardnessgenerallygreaterthan200mg/LasCaCO3,highalkalinitygenerallygreaterthan100mg/LasHCO3C255andpHintherange7.4e8.0NuttallandYounger,2000.DuetoelevatedlevelsofZn,theriverNenthasaverylimitedaquaticfauna.OtherecotoxicmetalssuchasPb,CdandAsarealsopresentNuttallandYounger,1999.AttheNentheadsite,madegroundusedinthetrialwasremovedtoadepthof20cmandtoensurehomogeneity,wasdrysievedto2mmsizefractionandafurther26between2mmand75mm.2.2.LeachingcolumnssetupInordertofacilitatecomparisontoearlierworkwithothersoils,theleachingcolumnexperimentsweresetupfollowingamethodologyusedpreviouslyanddescribedindetailinHodsonandValsamiJones2000bseealsoHodsonetal.,2001,andaschematicinHodsonandLangan,1999.Thecolumnsweremadefrominverted250mLpolypropylenebottleswiththeirbasesremovedandasmallholedrilledintheircaps.Thesoilwasunderlainbyalayerofquartzwoolandanotherofpolypropylenebeadstofiltertheleachateandensurefreedrainage.Theselayerswererepeatedatthetopofthesoilcolumntoaidinevenirrigantdistributionandlimitevaporativelosses.Thecolumnswereprotectedfromlighttoinhibitalgalgrowth.Bonemealandsoilweremixedtogetherthoroughlytoensurehomogeneity200gofairdriedsoilor200gsoilinsoil/bonemealmixwasaddedtoeachcolumn.Thediameterofthe250mLpolypropylenebottleswas57mmandthedepthofthesoilcolumnwasapproximately65mm.Thevariablesexaminedwerebonemealtosoilrationoamendment,125and110andirrigantpH2,3and4.4pHwasadjustedbysmalladditionsofnitricacid,fromastartingvalueof4.8.Alloftheexperimentswerecarriedoutintriplicate.Irrigationwascarriedoutmanuallybypipette.Fivedaysperweek,10mLofasyntheticrainsolutionwasdistributedevenlytothetopofthecolumns.TheirrigantwasformulatedsoastoapproximatethecompositionofnaturalrainTable1andappliestoirrigantpHof4.4.ThetwolowerpHvalueswereusedtotestthepotentialeffectsofacidificatione.g.viaacidraintothetreatment.Theirrigationratewaschosendbasedonsurfaceareaforinfiltrationdequivalenttoannualprecipitationof1300mmrainfallfortheNentheadareafortheyeartoOctober1,2001was1247mmdatafromBoltshopeParksynopticstationhttp//www.metoffice.com/climate/uk/networks/index.html.Theleachatecollectedbeneaththecolumns,wassampledatintervalsoverthecourseofthetrialandanalysedformetals,CaandPbyICPOESInductivelyCoupledPlasmaeOpticalEmissionSpectrometry.Leachateswerecollectedin100mLpolypropylenesamplebottlestowhich1mLconcentratedAristargradenitricacidhadbeenadded.Leachateswerecollectedweekly,andthepreacidificationwasundertakentostabilisetheleachateduringthecollectionperiod.Onoccasions,unacidifiedleachateswerecollected,filteredandthenacidified,toascertainthatpreacidificationofcolumnfilteredleachatesdidnotintroduceanyerrorsinthemeasuredconcentrations.Leachateswerevisuallyexaminedforturbiditybutnonewaseverobserved.2.3.SamplepreparationandanalysisThepreacidifiedleachateswereweighedtoallowfordilution,thenfilteredMillipore0.22mintopolypropylenevials.Sampleswerestoredat4C14Cfornomorethan5daysbeforeanalysis.PreacidificationoftheleachateTable1ColumnirrigantcompositionaNitrateAmmoniumNaMgCaChlorideSulphate2.470.471.800.360.293.481.06Unitsaremg/L.817Pollution1442006816e825aConcentrationsmeasuredatpH4.8andpriortopHadjustmentforeachindividualirrigantpH.2.2istrywereperformedusingaVarianVistaproaxialICPOES1.2kWRFpowerandusingaMeinhardtconcentricnebuliser.Matrixmatchedstandardsandblankswereused,togetherwithamonitoringstandardofknowncompositionevery10samples.FortheanalysesperformedbyICPOES,acalibrationstandardwasanalysedatregularintervalswithineachruntomonitorinstrumentstability.Onthebasisofthiscalibrationstandardananalyticalprecisionofbetterthan2isestimatedforallanalytes.Inhousedetectionslevelswereestablishedas1mg/LforCd,5mg/LforPband10mg/LforZn,Cu,Fe,Al,Ca,Mg,NaandP.AnalysesfororganiccarbonwereperformedonaShimadzuTOC5000analyser,withaprecisionof2anddetectionlevelof200mg/L.Anionsnitrate,ammonium,chlorideandsulphatewereanalysedbyionchromatographyusingaDionexDX300columnAS4Aprecisionisestimatedat5anddetectionlevelsat100mg/Lfortheseanalyses.2.4.MaterialscharacterisationLaboratoryanalysisindicatedasoilpHrangingfrom7.6to8.0basedona11ratioofsoilanddeionisedwaterandrelativelyhighmetalconcentrationsTable2.XraypowderdiffractiondatawerecollectedusingaNoniusPDS120powderdiffractionsystemconsistingofanInelcurved,positionsensitivedetectorPSD.ThisdetectorpermitsthesimultaneousmeasurementofthediffractedXrayintensitiesatallanglesof2qacross120C14withinastaticbeamsampledetectorgeometry.Measurementsweremadeinreflectiongeometrywiththesamplesurfaceatanangleof7.5C14totheincidentbeam.CuKa1radiationwasselectedfromtheprimarybeambyagermanium111crystalmonochromatorwiththeXraytubeoperatingconditionsat45kVand32mA.Beamdimensionsweresettoaheightof0.24mmandlengthof4.0mm.Powderedsamplesofthesoilandmineralstandardsweretoploaded,inturn,intoacircularwellmount,15mmindiameterand1mmdeep.Powderswerepackedandsmoothed,usingthenarrowedgeofaspatulainamannersuchthattheyhadaneven,flatsurfacelevelwiththerimofthewellmount.Sampleswerespuncontinuouslyduringdatacollectionof10minforthesampleandeachstandard.NISTsiliconpowderSRM640wasusedasanexternal2qcalibrationstandard,andthe2qlinearisationwasperformedusingaleastsquarescubicsplinefunction.FurtherpracticaldetailsandtheirjustificationaredescribedbySchofieldetal.2002.QuantitativephaseanalysiswasperformedintwostagesusingthewellestablishedsequentialwholepatternstrippingprocedureinthesamemannerasdescribedbySchofieldetal.2002.ThesoilmineralogyisshowninTable3.MetalbearingphasesdprincipallythoseofZn,PbandFedarelikelytobeunderrepresentedwhencomparedtototalmetalloadingsreturnedbysoildigestion.Thismaybeduetothefactthatsulphideswithinthesoilarelikelytohavebeenhighlyweathered,givingrisetosuchsecondaryphasesasZnTable2MetalloadingforsoilsandbonemealZnNiCuMedianUKsoilconcentrations82.022.618.1Nentheadsoila2mmsizefraction3230050130Bonemeal80BDUnitsaremgmetal/g.UKmedianvaluesfromMcGrathandLoveland1992.Nentheadbelowdetection.aICPOESanalysisafterHNO3/HF/HClO4totaldigestion,exceptforFeandhydroxycarbonatesandironoxidesandoxyhydroxides.Thedifficultyliesindetectingandquantifyingsecondaryphases,whichmaybepoorlycrystallineoramorphousandpresentinlowproportionscomparedtoprimaryphasesLanfrancoetal.,2003.SizefractionationtoimproveXRDresolutionwasnotcarriedout,aspreviousworkhasshownittobeineffectivee.g.Hodsonetal.,2000.Bonemealiscrushed,sterilisedboneandassociatedorganicmaterial,abyproductofmeatprocessing.BonemealforthetrialwasobtainedfromJohnHallAnimalFeedsLtd,acommercialsupplier.Thewaterandorganiccomponentwasapproximately40wtbaseduponincineration.Grainsizewas0e2mmassupplied.DigestionsyieldedatotalPcontentof11wtandCaPmolarratioof1.82thesevaluesaretypicalforbonee.g.LeGerosandLeGeros,1984.TracemetalanalysisisshowninTable2.2.5.DTPA/waterextractionofsoilmetalsTogainanindicationofthepotentialbioavailabilityofmetalsretainedbythesoilcolumns,astandardDTPAdiethylenetriaminepentaaceticacidextractionprocedurewascarriedoutwhenthecolumnsweredismantledafter550daysofirrigation.ThemethodusedwasthatofSoonandAbboud1993.Thesoilfromeachsetofthreereplicatecolumnswascombined,airdried,homogenised,thensplitdowntorepresentative5gsamplesforuseintheextractions.Theextractingsolutionwasmadeupof5mMDTPA,10mMCaCl2and0.1MTEAtriethanolamineindeionisedwater.ThepHwasadjustedto7.3C60.05with11HCl.Extractionswerecarriedoutintriplicateusing5gsoilto25mLextractingsolutionin60mLHDPEsamplebottles.Theweightfortreatedsoilwasadjustedupwardsbytheamountofaddedbonemealtoensurethatthesameamountoforiginalsoilwasused.Thesewereshakenfor2h120cycles/mininawaterbathat20C14CafterwhichthesupernatantwasfilteredMillipore0.22mandacidifiedforanalysisbyICPOES.Inparallel,anextractionfollowingthesamemethodwascarriedoutusingdeionisedwateronly.3.Resultsanddiscussion3.1.LeachateanalysisThemeanleachateconcentrationcurvesforcolumnsusingirrigantatpH4.4areshowninFig.1.SimilarleachatePbCdFeAl40.00.726786279178900604710027400BDBD157203soilandbonemealvaluesareroundedmeansoftriplicateanalyses.BD,Sphalerite0.7collectionbottlespreventedpHdeterminationforthesamplesanalysedhowever,onfouroccasionsoverthecourseofthetrialsampleswerecollectedwithoutprioracidaddition,andpHmeasurementswerecarriedoutontheseunacidifiedleachatesusinganOrionmodel720AbenchtoppH/ISEmeter,whichwascalibratedwithstandardbuffersolutionsimmediatelybeforeeachsamplebatchseeSection3.Allcalibrationandreferencestandardsweremadeupusingwaterdeionisedto18.2MUcmC2551andappropriate10,000mg/Linstrumentmasterstandards.Calibrationblanksweremadeupusingthesamesyntheticrainsolutionusedasaleachingcolumnirrigant.AnalysesforcationsolutionchemTable3PrincipalsoilmineralphasesbyXRDMineralCalcite1.3Dolomite/ankerite2.2Fluorite2.0Galena0.2Quartz35.0Smectite/illite58.6818I.R.Sneddonetal./EnvironmentalPollution1442006816e825AlLiBO2fusiondigestion.concentrationpatternswereobservedatallirrigantpHlevels.Thisismostlikelyduetothestrongbufferingcapacityofthesoil.HenceanalysisofdatareferstothepH4.4seriesunlessotherwisestated.Thefirst100daysofthetrialwascharacterisedbyhighvariabilitybothbetweentreatmentsandbetweenindividualcolumns.However,forCdandZnduringthisinitialperiod,significantlymoremetalwasreleasedfromthesoilatthe110bonemealamendmentratethanat125.Towardstheendofthisperiod,decreasingmetalsconcentrationsinleachatesfromtheamendedcolumnssawconsistentlylowerreleasesthanfromthecontrols.Thisdifferencewasstatisticallysignificantatthe95confidencelevelforallmetalsby120daysofirrigationsinglefactoranalysisofvarianceirrigantatpH3andpH4.4.At170days,leachateconcentrationsforalltreatmentswereapproximately35,13and9thoseoftherespectivecontrolsforPb,ZnandCd.For110treatments,thissuppressionofmetalsreleasewasmaintainedfortheremainderofthetrialwithleachateconcentrationsdecreasingfurtheruntil477dayswheretheywere6Pb,3Znand1CdofmeanlevelsCdandZnreleasefrom125amendedsoilswasrelativelystablefortheperiod120e300daysbutappearedtobetemporaryonly,withconcentrationsrisingsteadilyafterapproximately300daysand,inthecaseofZn,eventuallyconvergingwithcontrollevels.ThischangewasseentocorrespondwithdecreasingPandincreasingCaconcentrationintheleachatesFig.1.ZincandCdreleasebegantoincreaseasleachatePdecreasedbelowapproximately80mg/L.Theincreaseinvariabilityindicatedbytheerrorbarsofthe125CdandZncurvesFig.1arisesfromdifferencesinthetimingoftheconcentrationincreaseinthethreereplicatecolumns.Inthecaseof110bonemealtreatments,whereforallirrigantsdecreasingleachateconcentrationsofallthreemetalswereobservedforthedurationofthetrial,Pconcentrationsdidnotdropbelow150mg/L.CadmiumandZnleachateconcentrationsinthecontrolsgraduallyincreasedoverthecourseofthetrialand,ingeneral,thecontrolsshowedmorevariabilityovertimethanthebonemealtreatments.ThesuppressionofPbrelease,thoughnotassubstantialasforCdandZn,remainedrelativelystableforthe125treatedsoilsforthedurationofthetrial.In110treatFig.1.SoilcolumnleachateconcentrationsirrigantatpH4.4.Datapointsaremeansoftriplicatecolumns.Errorbarsrepresentonestandarddeviationeithersideofthemean.I.R.Sneddonetal./EnvironmentalinthecontrolleachatesirrigantatpH4.4.Thesuppressionof819Pollution1442006816e825ments,Pbconcentrationscontinuedtodecreaseuntil470days.
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