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Sediment-copper

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Sediment-copper

    Sediment-copper

    Availableonlineatwww.sciencedirect.com

    .瓤二:ScienceDirect

    JournalofEnvironmentalSciences1~2007)123127

    JOURNALOF

    ENVIRONMENTAL

    SClENCES

    ISSNl001-0742

    CNl1-2629/X

    wwwoes~-8c.ell

    Sediment-copperdistributionsinhyper-concentratedturbulent

    solid-liquidsystem

    YANGJunNIJin.ren2

    J.DepartmentofEnvironmentalEngineering,BeihangUniversity,Beijing100083,China.E-mail:yangjun@buaa.edu.cn

    2.CollegeofEnvironmentalSciences,PekingUniversity,KeyLaboratoryfo,WaterandSedimentSciences,

    MinistryofEducation,Beijing100871,China

    Received23January2006;revised10March2006;accepted10April2006

    Abstract

    Thisstudypresentsaspecialproblemonverticaldistributionforsedimentandcopperinhyper-concentratedturbulentsolid-

    liquidsystemthatisessentiallydifferentfromtheordinarylow

    concentratedturbulentsystem.Aresonancetypeturbulentsimulation

    equipmentisusedfortheexperimentalstudyinwhichaverticallyuniforillturbulenttieldofthemixtureofloessandwaterisproduced

    inatestingcylinderwithagrillestirrerthatmovesupanddownharmoniouslywithvaryingvibr

ationfrequencies.inordertocompare

    thevariationsoftheverticalprofilesofsedimentandcopperinlow

    andhyper-concentratedsolid-liquidsystem,differentscenariosfor

    inputsedimentcontentrangingfrom5to800kg/mwasconsideredintheexperimentalstudies.Itwasfoundthatsolidscoppercontent

    increaseswithinputsedimentcontent,So,andreachesitspeakasSogoesto10ke,/mandthendecreasesrapidlywithincreasinginput

    sedimentcontent.SuchabehaviorispossiblyresultedfromthejointefI.ectofthespecificadsorptionofcopperonloess,precipitation

    ofcarbonateandhydroxideofcopperduetohighcarbonatecontentintheloessandtheso.called"particulateconcentrationeffect''due

    tothepresentofthesedimentvariationinwa~r.Theverticalsedimentconcentrationdistributionresultedfromtheuniformturbulence

    isgenerallyuniform,butslightnon.uniformitydoesOCCurassedimentconcentrationexceedscertainvalue.Howeve~thevertical

    concentrationdistributionsofsolublecopperseemnottobeaffectedmuchbythevariationofseAimentconcentrations.

    Keywords:hyper-concentraledsystem;loess;copper;verticalsedimentdistribution Introduction

    Chineseriversarenotedfortheirhighsedimentcon-

    centrations.Thus,thehyper-concentratedflowinlarge

    rivershasbeenthemainconcerninChina.Forexample,

    therecordedmaximumsedimentconcentrationinYellow

    Riverisupto1650km(Chien.1989).Unlikeordinary

    turbulentflowswithsedimentconcentrationlowerthan

    100kg/m3,mostofthephysical.chemicalandbiological

    characteristicsinhyper.concentratedflowswillbeessen--

    tiallychanged.whichimplieseitherthesedimenttransport

    orthepollutantmigrationandtrans}formationprocesses

    maybequitedifierent.Inordertodescribethedifferent

    mechanismsofthespecificflows,newexplorationsmust bemadebothexperimentallyandtheoretically. Muchefforthasbeenmadebyhydraulicscientistsonthe investigationsofhype~concentratedsystems,particularly ontheirformationcauses,transportprocessesandthe changesofthephysicalcharacteristiessuchasviscosity, settlingvelocityandflocculation.Static,kinematicand dynamiccharacteristicshavebeenwidelystudiedbvthe Chinesescientists(Chien.1989)inthepastdecades.How

    ever,thepreviousstudiesonhyper-concentratedflows,to Proj~tsupportedbytheNationalBasicResearchProgramofChina(No G1999043603).*Correspondingauthor,E-mail.:yanKiun@buan.edu.cn. alargeextent.wererelatedtothevariationsofphysical characterstiesratherthanthoseofchemicalandbiological characteristics,whichareofsignificancetothemotionof pollutants.

    Ontheotherhand,mostofthepreviousresearches ontheinteractionsbetweenheavymetalsandsediments havebeencarriedoutundertheconditionsofthelow. concentratedsolid.1iquidsystemssuchasthoseinrivers, lakes.seaandestuaries.Since1970s.manygeographical andenvironmentalscientistshaveinvestigatedtheheavy metalcontentsonsedimentsinnaturalwaters(Chenet a1.,1991:ZhangandSelinus,1997).Meanwhile,im. provementsofanalyticaltechniquesformetalspeciations havebeenmade(Tessiereta1.,1979).Mechanismsof adsorptionandtransport.transformationprocesshavebeen studied(Forstner,1989)intermsofvariousmodels. Moreover,methodshavebeenproposedforevaluatingthe ecologicalandhealtheffectsofmetalspeciations(Grahn

andHakanson,1987).

    Nevertheless,whatarethechemicalandbiologicalbe- haviorsinthehyper-concentratedsystems?atkindsof essentialchangeswilloccurwhenasystemtransfersfrom lowertohighersedimentcOncen廿atiOns?Theprevious

    studiescanhardlygivesatisfactoryanswers,andnew understandingsarescarcelyneeded.

GJuneta1.,,01.19

    Thepresentpaper,initiatedfromseriesoffundamental experimentsonverticalprofilesforsedimentandcopper distributionsinacylinder,aimsatgainingnewunder- standingsoftheseldomreportedfieldbyfocusingon theadsorptionanddiflusioncharacteristicsinahyper

    concentratedturbulentsystem.Thisstudyisexpectedtobe ofgreathelptointerprettheabnormalpollutingprocesses inhyper-concentratedsedimentladenflows.whichcannot

    beexplainedbytheordinarytheoryplicableforthelow

    concentratedturbulentsystem.

    1Materialsandmethods

    1-1Apparatus

    Theapparatusemployedintheexperimentalstudywasa self-designedresonancetypeturbulentsimulationsystem. Themainbodyisaplexiglasscylinderof西24cmx50cm

    asshowninFig.1.A9.1ayergrillestirrerwasfixedinthe cylinderwithequaldistanceof4cmbetweenanytwo neighboringlayers.Thegrillestirrerisdrivenbydirect currentmotorthroughaneccentricwhee1.Whenthegrille stirrermovesupanddownharmoniouslywithvarying

    vibrationfrequencies,theverticallyuniformturbulentfield willbegeneratedinthemixtureofloessandwaterinthe cylinder.Eightsamplingopeningswerearrangedonthe wallofthecylinderwithdifferentverticaldistance(H) fromebottom,i.e.4,7,10,16,28,34,40,and46cm, respectively.

    1.2Materials

    TheporousMalanloesswasusedforsolidsediment materialintheexperiments.ThesoilwasfromtheMiddle Fig.1Schemeoftheresonancetypeturbulentsimulationsystem.(1) siliconcor.0Uedrectifier;(2)directcurrentmotor;(3)beltpulley;(4) eccentricwheel;(5)plexiglasscylinder;(6)samplingopenings;(7)solid-

    liquidmixture;(8)griliestirrer.

    YellowRiverwheresubjecttoseriouserosion.Physically theloessiscomposedof>50%siltwitlldiametersofO.05- 0.005iilln.10%35%clayparticleswithdiameterssmaller than0.005mmandof<5%finesandwithdiameters greaterthan0.1iilln.Theloessischemicallycomposed OfSi02,Al203,solidorganicmatterlessthan1%and carbonatesalt.Thehighcontentofcarbonatemaygreatly affectitsadsorptioncharacteristicontheheavymetals ranged10%-16%.TheloessismarkedbyitspHvalueof 7.5-8.6anditsnegativechargecharacteristies. Theremainingfineparticlesaftergrindingandsieving ofloessareofdiameterssmallerthan0.076iilln.Astock coppersolution(10000mg/L)waspreparedindistilled waterwithCuS04.5H2O(A.R.).Distilledwaterwasused toprepareallthesolutions.A1ltllelaboratoryglassware waspre,cleanedbysoakingin10%HN03.

    1.3Procedureandanalysismethods

    Theexperimentalproceduresincludefivesteps.First, dispersethepreparedloessintodistilledwaterandactivate thesedimentsfor24h.Second,transfercompletelythe activatedwater-sedimentmixtureandaddlLofthestock coppersolutionintoa20Lsizedtestingcylinder.Third,

    shakethewater-sediment-coppermixturefor1.5hata constantvibrationfrequency.Fourth,takesamples(50

    100m1)fromthesamplingopeningsandmeasurethe finalpH.temperatureandt0talsamplingvolume.Finally, analyzethesolubleandsolidscopperconcentration.Input sedimentcontentsintheexperimentalserieswere5,10, 40,70,100,200,400,600,800kg/m3,respectively.The detailedexperimentalparametersarepresentedinle 1.Analyticalduplicate.methodblanksandmatrixspike sampleswereconsidered.

    Samplesoftheequilibratedcopper-sedimentmixture postvibrationwerecentrifugedtodeterminethesoluble copperconcentration.Thesupematantwasdecantedinto anultra.filtrationsystemandfilteredthrougha0.45mn

    membraneofeel1ulloseacetate.Thefiltratewasanalyzed forcopperconcentrationbyflameatomicabsorptionspec

    trophotometer(AAS.HitachiModel1808o).

    Thecoppercontentofthesolidswasdeterminedbvre. suspendingthesolidsinNaOAc/HOAcbuffersolution(pH 51madeof8mlof1mol/LNa0Ac+5dropsofconcen. H0Acpergramsolid.Themixturewasagitatedusinga reciprocatingshakerfor6hatroomtemperature(202.C1.

    CoppercontentinthemixturewasaIlalyzedthroughthe processofcentrifuge,fiItration,dilutionandAAS. Coppercontentcouldbedeterminedbythesampling

Table1Summaryofexperimentalparameters

No.1Sediment-copperdistributionsinhyper-concentratedturbulentsolid-liquidsystem12

    5

    copperconcentrationmultipliedbythevolumeofthe originalsample,whereassolidscoppercontent(mg/g) couldbeobtainedfromthecoppercontentdividedbythe solidscontent.

    2Resultsanddiscussion

    2.1Relationshipsbetweenmainvariables

    Themainvatiablesinthepresentexperimentsinclude meansolidcoppercontent,solublecopperconcentration, pHandmeanactualsedimentconcentration.Fig.2de

    sctibestherelationshipsbetweenthevariables,inwhich thexaxisdenotesclassification.Theactualsedimentcon. centration(S)isthemeasuredcontentatdifferentheights inthevertica1.whichisdifferentfromtheinputsediment content(So)atthebeginningoftheexperiments.Under theuniformturbulentconditions,solidcoppercontent increaseswhen<1kg/m3andreachesitspeakatS=I kg/m3,orwhenSogoesto10kg/m.Onthecontrary,it dropsrapidlywithincreasingS.Thesenewfindingson adsorptionorsorptioncharactedsticsarequitedifferent fromthoseobtainedinpreviousstudieswherethedecreas- ingtrendofsolidcoppercontentwithincreasingsediment concentrationatnegativeexponentwasoftenexplained bythesocalled"particleconcentrationeffect".Withthe initialcopperconcentrationof500mg/L.theexperimental curveinFig.2indicatesthatthesolublecopperconcentra. tiondecreasesrapidlyastheactualsedimentconcentration

    )increasesfrom0.88to79.8kg/m3,whiletheinput sedimentcontentisrangedfrom5kg/m3to200km3. However,itdecreasesto0.2-0.6me/t,asactualsediment concentrationincreasesfrom273to707kg/m,while largerinputsedimentcontentranged400-800kg/mis used.Theexperimentalresultsshowedgreatersorption capacityofhyper-concentratedloess.

    Theadsorbedcopperspeciesonloessweredetermined byusingrevised"ressier'ssequencingextractmethod (Tessierela1..1979).Itisindicatedthatsolidscop. periscomprisedof>93%carbonatebound.2%4%

    Meanactualsedimentconcentration(kgm)

    0

    Fig.2Relationshipsbetweenmeansolidcoppercontent,solublecopper

    eoncenlzation,pHandmeanactualsedimentconcentration. Fe/Mnoxideboundand0.001%_0.1%exchangeableand organicallybound.whichisconsistentwitIlthemonitored resultsofsuspendedsedimentsintheYellowRiver(Yellow RiverInstituteofWaterResourceProtection,1988).The highcontentofcarbonate(10%16%)andloworganic

    matter(<1%)intheoriginalloessappeartoplayakeyrole intheabovecopperspeciesdistribution.Thespeciation ofcopperinsedimentisrelatedtotheirbiogeochemical reactivity,whichinturniscontrolledbythelocalwater andporoussolidproperties.Sincethehighcontentof carbonateboundofcopperissensitivetosolutionacidity andeasytobere.dissolvedwhenpH<5,particularatten

    tionmustbepaidtopreventlocalacidicpollutionwhich couldleadtosecondpollutionofheavymeta1.

    Theadsorptionkineticanalysisindicatesthatthetime

    forattainingtheadsorptionequilibriumisnormallyless than20min.Theadsorptionofstronglyhydratedcopper ontheloessbelongstospecificadsorptionthathasbeen studiedusingm,ESR.andXI(Picketing,1979),and COUldbeexplalnedbythesurfacecomplexationmode1. Moreover,bluegreenprecipitateswerevisuallyobserved astheinputsedimentcontentincreasescompanionedby theriseofpHvaluesinthemixture.Theprecipitatemay beamixtureofCu3(OH)2(CO3)2(azutite),Cu2(OH)2CO3 (malachite)andCu(OH)2,whosePKsD(negativelogarithm ofsolubilityproduct)are21.53,21.51and19.66.re

    spectively.Theprecipitationorco-precipitationprocesses greatlydependonthePHvalueandthebicarbonate concentrationinthesolution.ThepHvalueofmostfresh watersiscontrolledbytheconcentrat.ionofdissolved carbondioxideorbicarbonateinthesolution.Inthe presenceofbicarbonate.copperionsstarttoformCu(OH), andcarbonateprecipitatesatpH5,andthenover8O%Of t0talcopperiontransformedintoprecipitatesatpH7.5.It isrecognizedthatthereshouldbeasteepriseofadsorption atpHvaluessimilartothefirstpKhofthehydratedcation. Thedifficultyindistinguishingtheprecipitatesfromeach otherintheexperimentsisprimarilyduetothegreaterpKh (about7.51forcopperthanthepHfortotalprecipitation (Picketing,1979).Therefore,twoprocessesexistincopper adsorptionontheloess,oneisspecificadsorptionand anotherisprecipitationofcarbonateandhydroxide.The chemicalextractsolutionofHOAc.NaOAcbuffer(pH5, usedinthisstudycoulddissolveandpickupatleastthe mixtureoftheabovethreeprecipitates.

    ThesolidscoppercontentreachesapeakwhenSo=10 kg/m3+Inprinciple.thectiticalinputsedimentcontent correspondingtothepeakmaydependonthepropertiesof theloessandcopper.Forthepresentstudy,whenS=0.88 kg/m3(orSo=5kg/m),aspecificadsorptionplayeda mainroleinadsorptionofcopperonloesssincetheloess haslittleeffectonthecoppersolutionaspHvaluebeing 5.20.However,whenthesedimentconcenU'ationincreases to1.06kg/m3(orSo=10kg/m3),thespecificadsorption inadditiontotheprecipitatesofCu3(OH)2(CO3)2and Cu2(OH)2CO3formedby500mg/Lcopperionandcar- bonateaswellasCu(OH)2formedthroughhydrolysisat pH5.35.Insuchacase.''particleconcentrationef}ct"

    doesnotremarkablyaffectthesolidscoppercontentowing 目一目口售E8—鲁8B"Iq?1盆目善

    0000蚰?m

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    tothelowsedimentconcentration.Thedissolvedcarbonate andtheslightincreaseofpHareresultedfromhighcontent ofcarbonateintheloess.?enSfurtherincreasesfrom

    1.06kg/m3.theprecipitationeffectbecomeseminentand the"particleconcentrationeffect''shadowsitssignificance totherapiddecreaseofsolidscoppercontent. Insummary.themechanismofpeak/maximumadsorp

    tioncapacityofcopperontheloesscouldbeaiointefl'ect ofcopperspecificadsorptiononloess,precipitationof carbonateandhydroxideofcopperduetohighcontent ofcarbonateintheloessandthe"particleconcentration

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