英文翻译.docx

英文翻译.docx

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英文翻译

Removalofchromium（III）andcadmium（II）fromaqueoussolutions

Abstract

Chromiumandcadmiumaretoxicheavymetalspresentinwastewatersfromavarietyofindustries.Astrongcationexchangeresin,AmberliteIR120,wasusedfortheremovalofchromiumandcadmium.Theresinwaspreparedintwodifferentcationicforms,asNa+andH+.Theoptimumconditionswereconcentration,pH,stirringtimeandresinamount.Theconcentrationrangewasbetween2-50rag/L,pHrangebetween2-10,stirringtimebetween5-60min,andtheamountofresinwasfrom50-1000rag.Exchangecapacities,moisturecontentandoptimumconditionsofthisresinweredeterminedinabatchsystem.Thestirringspeedwas2000rpmduringallofthebatchexperiments.Theinitialandfinalchromiumandcadmiumamountsweredeterminedbyatomicabsorptionspectrophotometry.Theoptimumconditionswerefoundtobeaconcentrationof20mg/L,pHof5.5,stirringtimeof20minand100mgofresin.TheresultsobtainedshowthattheAmberliteIR120strongcation-exchangeresinperformedwellfortheremovalandrecoveryofchromiumandcadmium.

Keywords:

Chromium（III）;Cadmium（II）;Ion-exchangeresins;Toxicity;Conservativetechnologies

1.Introduction

Bothmetalsarecommonandimportantwaterpollutants.Theyareoftendischargedsimultaneouslyfromavarietyofindustrialsourcesincludingelectroplatingrinsewaters.Duetotheirtoxicityevenatlowconcentrations,themaximumlevelsallowedofmetalsareregulatedbylegislationineachcountry.

Thereleaseoflargequantitiesofheavymetalsintothenaturalenvironmenthasresultedinanumberofenvironmentalproblems.Cadmium,whichiswidelyusedandextremelytoxicatrelativelylowdosages,isoneoftheprincipalheavymetalsresponsibleforcausingtheseproblems.Themainanthropogenicpathwaythroughwhichcadmium（II）andchromium（III）entertheenvironmentisviawastesfromindustrialprocesses.Asheavymetalscannotbedestroyedinthenaturalenvironment,technologiesthatcanremoveandrecoveryheavymetalsfromwastewaterareneeded.

Classicaltechniquesofheavymetalremovalfromsolutionsincludethefollowingprocesses:

precipitation,electrolyticmethods,ionexchange,evaporationandadsorption.Chemicalprecipitationiscurrentlythemostwidelyusedtreatmenttechniqueforremovalofheavymetals.Nevertheless,particularlyfrustratingaspectsofthismethodaresignificantsludgeproduction,theever-increasingcostforlandfilldisposaloftheresultingtoxicsludge,andmostimportantly,thelong-termenvironmentalconsequences.Therefore,alternativetreatmentprocessesfortheremovalandpossiblytherecoveryoftoxicmetalshavetobeapplied.

Sorption,usedhereasageneraltermincludingseveralmechanismssuchasionexchange,surfacecomplexation,etc.,isconsideredasacommontreatmentmethodinmanywaterandwastewatertreatmentschemes,regulatingalsothetransportofchemicalspeciesinaquaticsystems.Activatedcarbon,biomassandionexchangearecommonlyusedforremovalofheavymetals.Chromiumisusedinavarietyofindustrialapplications,includingetectroplatingandasacorrosioninhibitorincoolingtowers.Chromiumsaltsareusedtotanatreatedanimalhidetoproduceleather.

Ionexchangeisoneofthemosteffectivetechniquesfortheremovalofchromiumfromtannerywastewaters.Chromiumexistsintwostableoxidationstates,Cr（III）andCr（VI）.TheCr（VI）stateisofparticularconcernbecausethisformishazardoustohealth.Chromiumisintroducedintonaturalbodiesofwaterfromindustriessuchaselectroplating,leathertanning,cement,steelandphotography.Itisfoundinsolutionindifferentchemicalforms,forexample,textile

andtanningwastesmaycontaineitherthehexavalentortrivalentchromiumspecies,whileelectroplatingandmetalfinishingwastescontainprimarilythetrivalentchromiumspecies.

Cadmiumisoneofthemosttoxicheavymetalsandisconsiderednon-essentialforlivingorganisms.Thiselementisfoundatlowconcentrationsinnaturalenvironments,buthumanactivitieshaveledtoincreasedlevelsonallthecontinents.Cadmiumispresentinwastewatersfrommetallurgicalalloying,ceramics,electroplating,photography,pigmentworks,textileprinting,chemicalindustriesandleadminedrainage.Cadmiumisremovedfromwastewatersbyprecipitation,electrocoagulation,adsorption,biosorption,activatedcarbonfiltrationandionexchange.AmberliteIR120isagel-typepolystyrene,sulphonatedstrongcation-exchangeresin.RohmandHaas[24]showedthatitsprincipalcharacteristicshaveexcellentphysical,chemicalandthermalstability,goodion-exchangekineticsandhighexchangecapacity.

Conservativetechnologiesformetalcontrolhaveanincreasinginterest,astheyareabletoremovepollutantsandreusevaluableby-productsobtainedfromwastesand/orsidestreamsfrommanufacturingprocesses.Thepresentpaperexaminesoptimumconditionsofastrongcation-

exchangeresin（AmberliteIR120）fortheremovalandrecoveryofchromiumandcadmium.

2.Materialandmethods

2:

1.Reagents,solutions,resinsandequipment

TheresinusedinthisworkwasAmberliteIR120（RohmandHaasCompany）,astrongacidiccation-exchangeresinbasedonastyrenematrix.Table1showsthemainphysicochemicalpropertiesoftheresininvestigated,andTable2showssuggestedoperationalconditionsoftheresin.ThisresinwaspreparedintwodifferentcationicformsasNa+andH+.Underthesetwoconditions,exchangecapacities,moisturecontentandotheroptimumconditionsweredeterminedinabatchsystem.

Theoptimumconditionswereconcentration,pH,stirringtimeandresinamount.Chromiumandcadmiumamountsweredeterminedbyatomicabsorptionspectrophotometry（AAS）onaModelSpect.AA20（Varian）withanairacetyleneflameusedfordeterminationofthechromiumamountsintheaqueousphasewiththefollowingsettings:

wavelength,357.9;lampcurrent,7mA;slit,0.2nm;air/acetyleneratio,3.5/1.5;andforcadmiumwiththefollowingsettings:

wavelength,228.8;lampcurrent,4mA;slit,0.5nm;air/acetyleneratio,3.5/1.5.AllpHmeasurementsweremadewithapH-meter（Metrohm）andacombinationglasselectrode.

Analyticalreagent-gradebasicchromicsulphate[Cr4（SO4）5（OH）2],[Cd（NO3）2.4H20],HCI,NaCINaOH,andchemicals（Merck,Germany）wereused.Freshlypreparedsolutionswereusedthroughouttheexperiments.WaterwasdeionizedandpurifiedfurtherwithaMilli-Qwaterpurificationsystem（Millipore,USA）.

Table1

PhysicochemicalpropertiesoftheAmberliteIR120resin

FunctionalgroupSulphonic

MatrixStyrene

Moisture-holdingcapacity,%:

Na+form44-49

H+form41-56

Totalexchangecapacity,eq/L:

Naform≥2.00

Hform≥1.80

Table2

SuggestedoperatingconditionsofAmberliteIR120

Operationtemperature,C120max.

Serviceflowrate,BV/h5-40

RegenerantsHC1、H2SO4、NaCI

Flowrate,bedvolume/h2-82-202-8

Concentration,%5-80.7-610

Level,g/L50-15060-24080-250

Slowrinse,BVat2

regenerationflowrate

Fastrinse,BVatservice4-8

flowrate

2.2.Procedures

2.2.1.Conditioningofresin

Afterthreepreliminaryrecyclingsoftheresininacolumnsystemwith1MHC1andNaOHsolutionstoremoveeventualchemicalresidues（solvents,functionalizingagents）trappedinthematrixesoftheresinsduringtheirpreparation,thesampleswerefinallyconvertedintosodiumandhydrogenformsby1MNaClorHCl.

2.2.2.Determinationoftheresinmoisturecontent

Samplesof1gofionexchangersintheNaandH+formsweredriedat110Cfor1h,cooledinadesiccatorandweighed.Thiswascontinueduntiltheattainmentofaconstantweight.

2.2.3.Determinationofion-exchangecapacity

Theion-exchangecapacitywasdeterminedinreferencetobothNaandHformsbyusingcolumntechniques.Accordingly,afterloadingthesample（3g）intoaglasscolumn,theresinwaselutedwith20mgL-1concentrationofchromiumandcadmiumsolutionsata2BV/hflowrate.TheresultsaregiveninTable3withdeterminedmoisturecontents.

Table3

Exchangecapacitiesandmoisturecontentoftheresin

Resin（AmberliteIR120）NaformHform

Capacity（eq/L）（column）1.120.97

Capacity（eq/L）（titrimetric）1.471.36

Moisturecontent（%）47.4555.20

2.2.4.Generalstudyprocedure

Theconditionedresinsamples（Na+andHforms）wereusedforremovalofchromiumandcadmiuminthebatchmethod.Theeffectsofconcentration,pH,stirringtimeandresinamountwereinvestigatedfordeterminationofoptimumconditions.Anamountof0.1gresinsampleswasputintocontactwith50mLofsolutioncontainingchromiumandcadmiumfor20min（pH5）.Stirringspeedwas2000rpmduringthebatchexperiments.Alltheoperationswereconductedatroomtemperature.Afterfiltrationofthe

solidphase,thecontentofchromiumandcadmiumintheliquidphaseweredeterminedbyAAS.

3.Results

3.1.OperatingconditionsfortheAmberliteIR120resin

3.1.1.Concentration

Chromium（III）andcadmium（II）concentrationswereselectedintherangeof2to50mg/Lfortwodifferentionicformsofresin（studiedpH:

5.5）.TheeffectofconcentrationonmetaladsorptionwasinvestigatedandtheresultsaregiveninFigs.1and2.Experimentsweredoneusing0.1gofresinwithdifferentmetalconcentrations（2-50rag/L）.Itwasfoundthatthemetalamountsretainedwerealmoststableinthisconcentrationrangeforboththemetalandionicformsofresin.Adsorptionofcadmiumwasabithigherthanchromiumforbothformsofthisresin.Inthebeginningvaluesofconcentration,theresultsshowthattherewashigheradsorptionoftheNa+form.Themaximumadsorptionwasobtainedas93.4%forcadmiumand90.27%forchromiu