Adsorption of heavy metals from multi-metal aqueous solution

ORIGINALPAPER

Adsorptionofheavymetalsfrommulti-metalaqueoussolutionbysunflowerplantbiomass-basedcarbons

¨a¨4M.Jain1,4•V.K.Garg1•K.Kadirvelu2,3•M.Sillanpa

Received:3September2014/Revised:4May2015/Accepted:6July2015

ÓIslamicAzadUniversity(IAU)2015

AbstractThisstudyreportsthecompetitiveadsorptionofNi(II),Cd(II)andCr(VI)ontosunflowerwastebiomasscarbons,viz.sunflowerheadcarbonandsunflowerstemcarbonfrommulti-metalaqueoussolution.Theadsorptioncapacityoftheadsorbentswashighestinmono-metalsystembutdecreasedwithincreaseinthenumberofco-ions.Theadsorptioncapacityinmono-metalsystemwas0.32and0.45mM/gforNi(II),0.25and0.32mM/gforCd(II)and0.20and0.28forCr(VI)bysunflowerheadcarbonandsunflowerstemcarbon,respectively,whereas,inabinarysystem,adsorptioncapacityofsunflowerheadcarbonforNi(II)was0.24mM/gin0.5mMCd(II)solu-tionwhichwasfurtherreducedto0.18mM/gin2.0mMCd(II).Theeffectofco-cationswasmorepronouncedintertiarysystems.Similarbehaviorwasobservedforothersystemsalso.Theinteractiveeffectofmulti-metalionsinbinaryandtertiarycomponentsystemswasantagonisticinnature,i.e.,theeffectofmixtureislessthanthesumofindividualeffectoftheconstituentsorwhentheeffectofindividualsubstancesaddedtogetherislessthanthe

&V.K.Garg

vinodkgarg@yahoo.com

1expectedinresponsetomultiplesubstances.Langmuirmodelbestfittedthedataforallthesystemswithr2value[0.95.

KeywordsCompetitiveadsorptionÁChromiumÁCadmiumÁNickelÁHelianthusannuus

Introduction

Variousindustrialprocessesgeneratemetal-ladenwastewaters.Themultiplecomponentsofwastewaterscauseinteractiveeffectsdependingonseveralfactorssuchasnumberofco-cationscompetingforbindingsites,metalconcentration,equilibriumconcentrationofmetalionspecies,pH,natureandquantityoftheadsorbentbiomass(Saeedetal.2005).Treatmentofsuchwastewatersisachallengeforenvironmentalengineers,municipalitiesandpolicymakers.Severaltechnologiesareavailableforthetreatmentofheavymetalscontainingwastewaters.Amongthem,chemicalprecipitation,reverseosmosis,oxidation–reduction,electrodialysis,solventextractionandadsorptionarecommon.Butadsorptionisthemostsoughtouttech-nologyforsuchkindofwaterswhichcontainstraceamountofheavymetalsandthatcannotberemovedbyothermethods.Adsorptioncanbeappliedfortreatmentofwastewaterusingvariousmaterialslikeagriculturalwaste,algae,bacteria,fungi,zeolites,clay,mudandflyashasadsorbent.

Alargevolumeofworkontheadsorptionofheavymetalionsfrommono-metalsolutionsbyvariousadsor-bentsisavailableinliteratures(Vinhetal.2015;Reddyetal.2015;Ghasemietal.2014;MahajanandSud2013;Machidaetal.2006;Kadirveluetal.2004;Lietal.2003;Nguyenetal.2013).Multi-metaladsorptionstudiesare

DepartmentofEnvironmentalScienceandEngineering,GuruJambheshwarUniversityofScienceandTechnology,Hisar125001,Haryana,India

Defence,BioengineeringandElectromedicalLaboratory(DEBEL),DefenceResearchandDevelopmentOrganization,RamanNagar,Bangalore560093,India

PresentAddress:DRDOBUCentreforLifeSciences,BharathiarUniversityCampus,Coimbatore1046,TamilNadu,India

LaboratoryofGreenChemistry,DepartmentofChemistry,LappeenrantaUniversityofTechnology,Sammonkatu12,50130Mikkeli,Finland

234123

importanttoassessthelevelofinterferencecausedbyco-ionspresentinthewastewaterandtheefficiencyofadsorbenttoremovethoseionsfromwastewaters(Sri-vastvaetal.2006).Competitiveadsorptionofvariousheavymetalsinmulti-metalsystemhasbeenreportedinyesteryearsonlybyafewworkers.Hadietal.(2014)reportedtheadsorptionofCu,PbandZnfromsingle,binaryandternarysystemusinge-waste-basedadsorbent.MohanandSingh(2002)foundthatadsorptioncapacityofactivatedcarbonforCd(II)andZn(II)decreasedinmulti-metalsystemascomparedtobinarysystem.Chibanetal.(2011)reportedthatadsorptioncapacityofPb(II)bydriedCarpobrothusedulisdecreasedinthepresenceofCd(II)inbinarysystem.TingandTeo(1994)reportedthatinmulti-componentsystem,metalionsinteractwitheachotherinsynergistic,antagonisticornon-interactivemannerandtheresultscannotbepredictedonthebasisofsinglemetalstudies.Therefore,itisworthwhiletostudythesimulta-neousadsorptionoftwoormoremetalsandalsotoquantifytheinterferenceofametalwiththeadsorptionofother.

Plantbiomassiscomposedofbiopolymers,mainlycontaininglignocelluloseandtanninswhichmayleadtobindingofmetalionsduetothepresenceoffunctionalgroupslikehydroxyl,carboxyl,carbonyl,thiolandamine(Witek-Krowiak2012).Inthepresentstudy,sunflowerwastebiomasswaschosenastheprospectiveprecursorforpreparationofadsorbents.Sunflowerisoneofthefivelargestoilproducingcropsintheworldandisknownforedibleoilandbioethanolproduction.Afterextractionofoil,hugequantitiesofsunflowerheadsandstalksaregeneratedthatdonotfindanysuitableenduseandareburntinthefieldscausingenvironmentalpollution(Sharmaetal.2012).

Thesunflowerwastebiomassalsocontainsfunctionalgroupslikehydroxyl,carboxylandcarbonylasindicatedbyFT-IRanalysisreportedelsewhere(Jainetal.2010).TheadsorbentspreparedfromthisbiomasshadgoodadsorptionpotentialforCr(VI),Ni(II)andCd(II)frommono-metalsystems(Jainetal.2009,2013,2014).Yet,nodataareavailableontheusageofsunflowerwastebiomassfortheremovalofheavymetalsfrommulti-metalsystem.So,incontinuationofourearlierwork,thisstudyreportstheperformanceoftwoadsorbents,viz.sunflowerheadcarbon(SHC)andsunflowerstemcarbon(SSC)fortheremovalofmetalsfrommulti-metalaqueoussystems.Inthisstudy,themetalsofinterestwerechromium,nickelandcadmium,whicharecommonlyencounteredinmanyoftheindustrialeffluents.

DateandLocationoftheresearch:March,2011;GuruJambheshwarUniversityofScience&Technology,Hisar(HARYANA).

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Materialsandmethods

Adsorbents

Twoadsorbentswerepreparedfromdeseededheadsandstemsofsunflower(Helianthusannuus)wastebiomass,viz.sunflowerheadcarbon(SHC)andsunflowerstemcarbon(SSC)asreportedbyJainetal.(2010).Abriefdescriptionofthepreparationofadsorbentshasbeengivenhere.Thesunflowerheadsandstems(H.annuus)werecollecteddirectlyfromtheagriculturalfields.Theyweregroundseparatelyintofinepowderandweremixedwithconcen-tratedH2SO4intheratioof2:1(H2SO4:sunflower,v/w)andcarbonizedat150°Cinhotairovenfor24h.Thecharredmaterialwasrepeatedlywashedwithdeionizedwateruntilexcessacidwasremovedandfinallysoakedin2%Na2-HCO3(w/v)overnighttoremoveanyresidualacidfromthematerial.Theadsorbentwaswashedagainwithdeionizedwaterseveraltimesanddriedinhotairovenat105°Cfor8h.Theadsorbentobtainedwassievedfromstandardsieve(ASTMNo.50,I.S.S.No.30)togettheparticlesizeofB300lm.Theadsorbentwasdesignatedassunflowerheadcarbon(SHC)andsunflowerstemcarbon(SSC).

ThesurfacecharacterizationoftheadsorbentswasdoneusingSEM,EDX,FT-IRandBETsurfaceareaasreportedelsewhere(Jainetal.2010),whilethephysico-chemicalparameterswerefoundtobepH=3.7and4.1,ashcon-tent=4.2and3.8%,moisturecontent=2.5and2.8%,bulkdensity=0.8and0.6gcc-1,watersolublemat-ter=2.3and1.8%,acidsolublematter=10.3and8.3%,elementalanalysis=C—51and41%,H—3.1and2.8%,N—0and8.5%,O—45.9and44.7%forSHCandSSC,respectively.AmongSHCandSSC,SSCprovedtobethebetteradsorbentduetohighsurfaceareaandadsorptioncapacity.Thiscanbeexplainedonthebasisofstructureofsunflowerstems.Thesunflowerstemsaremadeofanoutercoveringcalledskinandaninnersofttissuecalledpith.Skinisafibrousandcellulose-basedstructure,whilepithissoft,spongyandporous(SunandXu1997).SunandXu(1997)alsorevealedthattheBETsurfaceareaofsunflowerskinis1.11andthatofpithis2.31m2/g.Butwhentotalareaofbothskinandpithisconsidered,thenitdecreasesto1.20m2/g.TheresultsfromourpreviousstudyareinagreementwithSunandXushowingthattheBETsurfaceareaofSHCwas1.17andthatofSSCwas1.28m2/g(Jainetal.2010).BatchstudiesMono-componentstudy

BatchmodeadsorptionstudiesofNi(II),Cd(II)andCr(VI)bySHCandSSCwereperformedtodeterminetheir

Int.J.Environ.Sci.Technol.

adsorptioncapacityinmono-componentsystem.Fiftymillilitersofmetalionsolutionofconcentra-tion=1.0mMwithanadsorbentdoseof0.2g/50mLwasagitatedatatemperatureof25±1°Cinanorbitalshakerfor180minat180rpm.AlltheexperimentswerecarriedoutatanoptimumpHof2.0forCr(VI),6.0forCd(II)andNi(II)basedonourearlierfindings(Jainetal.2010,2013,2014).Themetaluptakeloadingcapacityqe(mMofmetalpergofadsorbent)foreachsorptionsystemwasdeter-minedusingEq.1:

q CeðmM/gÞ¼iÀCe

!MÂVð1Þ

whereCiandCearetheinitialandequilibriumconcen-tration,Visthevolumeofthesolutionin(L)andMisthemassoftheadsorbent(g).Metalsolutionswerepreparedusingpotassiumdichromate(K2Cr2O7),nickelnitrate[Ni(NO3)2Á6H2O]andcadmiumsulfate(3CdSO4Á8H2O).Residualmetalionconcentrationinthesolutionwasdeterminedusingatomicabsorptionspectrophotometer(ShimadzuAA6300,Japan).Multi-componentstudy

Theeffectofco-cationsontheadsorptionofNi(II),Cd(II)andCr(VI)bySHCandSSCwasstudiedinbinaryandtertiarycomponentsystems.Experimentaldesignusedinthestudyconsistedofbinarysystem,viz.Ni(II)?Cd(II),Ni(II)?Cr(VI),Cd(II)?Ni(II),Cd(II)?Cr(VI),Cr(VI)?Ni(II),Cr(VI)?Cd(II)andtertiarysystem,viz.Ni(II)?Cr(VI)?Cd(II),Cd(II)?Cr(VI)?Ni(II),Cr(VI)?Ni(II)?Cd(II).

Theeffectofco-cationsonNi(II),Cd(II)andCr(VI)adsorptioncapacityhasbeenstudiedatdifferentco-ca-tionconcentrations.Forbinaryandtertiarycomponentsystem,themetalandco-cationconcentrations(mM)weremaintainedataratioof1:1and1:1:1.Adsorptionstudieswerecarriedoutbykeepingtheconcentrationoffirstmetalconstantandvaryingtheconcentrationofothermetal(s)ionsatoptimumpHoftheformermetalionobtainedincaseofsinglemetalsystem.Theprocessparametersoptimizedformono-metalsolutionswereappliedforbinaryandtertiarysystems,viz.pH2.0forCr(VI)and6.0forNi(II)andCd(II),volume=50mL,co-cationconcentrationvariedbetween0.5mMand2.0mMforbinarysystemandbetween0.25:0.25and1.0:1.0fortertiarysystem,adsorbentdose=0.2g/50mL,contacttime=180min,stirringspeed=180rpmandtemperature=25±1°C(Jainetal.2010).

Adsorptionisotherms

AdsorptiondataweremodeledusingLangmuirandFre-undlichequations.ThesemodelsaregivenbelowinEqs.2and3:Ceq¼

1þCe

ð2Þ

eQ0bQ0log10qe¼log10ÀKf

Á

þ󰀆1󰀇n

log10ðCeÞ

ð3Þ

whereCeistheequilibriumconcentrationofmetalion(mM/L),qeistheamountofmetaladsorbed(mM/g),QoisLangmuirmaximumadsorptioncapacity(mM/g),bistheconstantrelatedtofreeenergyofadsorption(L/mM),KfistheFreundlichrelativeadsorptioncapacity(mM/g)andnistheintensityoftheadsorbent.

Resultsanddiscussion

ItwasevidentfromtheresultsthatadsorptioncapacityofNi(II),Cd(II)andCr(VI)bySHCandSSCinmono-metalsystemwashigherthanmulti-metalsystems.Amongthetwoadsorbents,SSChadhigheradsorptioncapacitythanSHCforNi(II),Cd(II)andCr(VI)inmono-componentsystem.Itwas0.32,0.25and0.20mM/gforNi(II),Cd(II)andCr(VI),respectively,bySHC,whereas0.45,0.32and0.28mM/gforNi(II),Cd(II)andCr(VI),respectively,bySSC(Figs.1a,2a,3a).ThisvariationmaybeduetothefactthatSSCwaspreparedfromsunflowerstemwhichismoreporousduetothepresenceofpithinitandhashighersurfaceareathansunflowerheads.Theorderofadsorptioncapacityinmono-componentsystembySHCandSSCwasNi(II)[Cd(II)[Cr(VI).

Nickeladsorptioninmulti-metalsystem(binaryandtertiarysystem)

Theeffectofvariousco-cationsontheadsorptioncapacityofSHCandSSCinbinaryandtertiarysystemforNi(II)hasbeendepictedinFig.1a,b.Theresultsshowedthatastheconcentrationoftheco-cationswasincreasedfrom0.5to2.0mMinthesolution,theadsorptioncapacityoftheadsorbentsforNi(II)decreased.TheadsorptioncapacityofSHCdecreasedfrom0.24mM/gto0.18mM/gandthatofSSCfrom0.27mM/gto0.21mM/gforNi(II)inNi(II)?Cd(II)binarysystem(Fig.1a).TheadsorptioncapacityofSHCdecreasedfrom0.20mM/gto0.14mM/gandthatofSSCfrom0.22mM/gto0.16mM/gforNi(II)inNi(II)?Cr(VI)binarysystem(Fig.1a).

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Fig.1aEffectofco-cationconc.onNi(II)sorptionbySHCandSSCinbinarysystematNi(II)conc.=1.0mM,pH=6.0,dose=4.0g/L,contacttime=180min,stirringspeed=180rpm,temp.=25±1°C.bEffectofco-cationconc.onNi(II)sorptionbySHCandSSCintertiarysystematNi(II)conc.=1.0mM,pH=6.0,dose=4.0g/L,contacttime=180min,stirringspeed=180rpm,temp.=25±1°C

TheadsorptioncapacityofSHCdecreasedfrom0.15mM/gto0.09mM/gandthatofSSCdecreasedfrom0.17mM/gto0.11mM/ginNi(II)?Cd(II)?Cr(VI)tertiarysystem(Fig.1b).Theadsorptioncapacitywasminimumat2.0mMconcentrationinallthethreesystems,i.e.,Ni(II)?Cd(II),Ni(II)?Cr(VI)andNi(II)?C-d(II)?Cr(VI),whereastheadsorptioncapacityofNi(II)washighest,i.e.,0.32mM/gbySHCand0.45mM/gbySSCat1.0mMNi(II)concentrationinmono-metalsystem(Fig.1a,b).

Cadmiumadsorptioninmulti-metalsystem(binaryandtertiarysystem)

Theeffectofvariousco-cationsontheadsorptioncapacityofSHCandSSCinbinaryandtertiarysystemforCd(II)

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Fig.2aEffectofco-cationconc.onCd(II)sorptionbySHCandSSCinbinarysystematCd(II)conc.=1.0mM,pH=6.0,dose=4.0g/L,contacttime=180min,stirringspeed=180rpm,temp.=25±1°C.bEffectofco-cationsconc.onCd(II)sorptionbySHCandSSCintertiarysystematCd(II)conc.=1.0mM,pH=6.0,dose=4.0g/L,contacttime=180min,stirringspeed=180rpm,temp.=25±1°C

adsorptionisdepictedinFig.2a,b.TheadsorptioncapacityofSHCforCd(II)decreasedfrom0.18mM/gto0.12mM/gandthatofSSCdecreasedfrom0.20mM/gto0.13mM/ginCd(II)?Ni(II)binarysystemasthecon-centrationoftheco-cationincreasedinthesolutionfrom0.5to2.0mM(Fig.2a).TheadsorptioncapacityofSHCdecreasedfrom0.16mM/gto0.10mM/gandthatofSSCdecreasedfrom0.18mM/gto0.12mM/gforCd(II)inCd(II)?Cr(VI)binarysystem(Fig.2a).

TheadsorptioncapacityofSHCforCd(II)decreasedfrom0.13mM/gto0.07mM/gandthatofSSCdecreasedfrom0.15mM/gto0.09mM/ginCd(II)?-Ni(II)?Cr(VI)intertiarysystem(Fig.2b).Theadsorp-tioncapacitywasminimumat2.0mMconcentrationinallthethreesystemsthatareCd(II)?Ni(II),Cd(II)?Cr(VI)andCd(II)?Ni(II)?Cr(VI).

Int.J.Environ.Sci.Technol.

Chromiumadsorptioninmulti-metalsystem(binaryandtertiarysystem)

Theeffectofvariousco-cationsontheadsorptioncapacityofSHCandSSCforCr(VI)inbinaryandtertiarysystemisdepictedinFig.3a,b.Astheconcentrationoftheco-ca-tionswasincreasedinthesolutionfrom0.5to2.0mM,theadsorptioncapacityofthestudiedadsorbentsforCr(VI)decreased.TheadsorptioncapacityofSHCdecreasedfrom0.14mM/gto0.08mM/gandthatofSSCdecreasedfrom0.16mM/gto0.10mM/gforCr(VI)inCr(VI)?Ni(II)binarysystem(Fig.3a).TheadsorptioncapacityofSHCdecreasedfrom0.12mM/gto0.06mM/gandthatofSSCdecreasedfrom0.14mM/gto0.08mM/gforCr(VI)inCr(VI)?Cd(II)binarysystem(Fig.3a).TheadsorptioncapacityofSHCforCr(VI)decreasedfrom0.11mM/gto0.05mM/gandthatofSSCdecreasedfrom0.13mM/gto0.07mM/ginCr(VI)?Ni(II)?Cd(II)tertiarysystem(Fig.3b).

Itisevidentfromtheresultsthatco-adsorptionresultedinloweringoftheadsorptioncapacityforaparticularion.Theresultsalsoindicatedthattheco-cationsinthesystemcompetedwithNi(II),Cd(II)andCr(VI)foradsorptionsites.Relativelylessadsorptioncapacityinbinaryandtertiarycomponentsystemmaybeduetothecompetitionamongdifferentmetalionsfortheavailablebindingsitesontheadsorbents(Aksuetal.1999).deCarvalhoetal.(1995)reportedthatdecreaseinadsorptioncapacityinthepresenceofco-ionsmaybeduetotheprogressiveinter-ferenceofionsbecauseofoverlappingonsorptionsitesathigherconcentration.Factorsthataffecttheadsorptionpreferenceofanadsorbentformetalsinmulti-metalsystemarerelatedtothephysico-chemicalpropertiesofthesolu-tionsuchaspH,temperaturesurfacepropertiesoftheadsorbentandthepropertiesofthemetalssuchaselec-tronicconfiguration,electronegativityandionicradius(Srivastavaetal.2006).

Fig.3aEffectofco-cationconc.onCr(VI)sorptionbySHCandSSCinbinarysystematCr(VI)conc.=1.0mM,pH=2.0,dose=4.0g/L,contacttime=180min,stirringspeed=180rpm,temp.=25±1°C.bEffectofco-cationsconc.onCr(VI)sorptionbySHCandSSCintertiarysystematCr(VI)conc.=1.0mM,pH=2.0,dose=4.0g/L,contacttime=180min,stirringspeed=180rpm,temp.=25±1°C

Table1IonicpropertiesofstudiedmetalionsPropertyAtomicweightMolecularweightElectronicconfigurationElectronegativityIonicradii(A°)Hydratedradii(A°)CoordinationnumberStandardReductionPot.(V)

Cr(VI)51.01294.18[Ar]3d4s1.660.524.616&4

Cr6þ+3eÀ!Cr3þð1:1ÞCr3þ3eÀ!CrðÀ0:74Þ

Source(Kadirveluetal.2008)

51Ni(II)58.69290.81[Ar]3d4s1.910.724.044

Ni2þ+2eÀ!NiðÀ0:25Þ

82Cd(II)112.41769.52[Kr]4d105s21.690.954.266&4

Cd2þ+2eÀ!CdðÀ0:403Þ

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Table2Interactiveeffectofamixtureofmetalionsinbinaryandtertiarysystems

Metalsystem

SHCRi(%)

Nickel

Ni(II)?Cd(II)Ni(II)?Cr(VI)Ni(II)?Cd(II)?Cr(VI)CadmiumCd(II)?Ni(II)Cd(II)?Cr(VI)Cd(II)?Ni(II)?Cr(VI)ChromiumCr(VI)?Ni(II)Cr(VI)?Cd(II)

Cr(VI)?Ni(II)?Cd(II)RiRelativeadsorptioncapacity

60.050.025.0

AntagonisticAntagonisticAntagonistic

50.042.925.0

AntagonisticAntagonisticAntagonistic

.056.028.0

AntagonisticAntagonisticAntagonistic

53.050.028.1

AntagonisticAntagonisticAntagonistic

68.856.328.1

AntagonisticAntagonisticAntagonistic

57.844.424.4

AntagonisticAntagonisticAntagonistic

Interactiveeffect

SSCRi(%)

Interactiveeffect

Table3LangmuirandFreundlichparametersforNi(II),Cd(II)andCr(VI)inmono,binaryandtertiarysystembySHC

MetalCombinationsSHCLangmuirQob

r2FreundlichKfn

r2Mono-componentNi(II)Cd(II)Cr(VI)

BinarycomponentNi(II)?Cd(II)Ni(II)?Cr(VI)Cd(II)?Ni(II)Cd(II)?Cr(VI)Cr(VI)?Ni(II)Cr(VI)?Cd(II)TertiarycomponentNi(II)?Cd(II)?Cr(VI)Cd(II)?Ni(II)?Cr(VI)Cr(VI)?Ni(II)?Cd(II)

0.050.030.02

-3.7-2.8-2.1

0.98080.96850.9494

0.060.40.3

0.90.50.5

0.97850.1470.0667

0.150.110.090.060.040.02

-5.1-10.2-6.4-4.4-3.2-2.2

0.960.940.980.98170.97420.8539

0.150.100.080.060.051.3

0.52.21.51.10.80.2

0.85990.97340.97850.98030.97980.4378

0.260.200.18

0.20.40.6

0.99670.99850.9932

0.210.170.14

1.72.11.9

0.76540.82810.8712

Themechanismofadsorptioninmulti-metalsystemcanbepredictedonthebasisofionicpropertiesofthemetalions.TheresultssignifythatNi(II)isthemostadsorbedionamongthethreestudiedmetalionsduetomoreaccessibilitytotheporesasithasthesmallesthydratedradiiascomparedtoothertwoions(Table1).Also,ithasthehigheststandardreductionpotential(Table1)whichimpliesthatmetalswithhigherstandardreductionpotentialtendtoexhibitastron-gerionicinteractionwithanelectron-richsurfaceoftheadsorbents(MohanandSingh2002).Further,itisthemostelectronegativeionamongthethree,soitismorestronglyattractedtothesurfaceoftheadsorbents.

Interactivebehaviorofmetalions

TheselectivityofadsorbentsforNi(II),Cd(II)andCr(VI)inbothbinaryandtertiarymixturewasevaluatedintermsofrelativemetaliadsorptionthatisRi(%)whichisdefinedasinChangandChen(1998).ThepercentageRiwilldeterminewhetherthecombinationsinbinaryandtertiarysystemareantagonisticorsynergisticinnature.

Ri¼

metaliadsorptioncapacitywithcoexistenceofmetaljandk

Â100

metaliadsorptioncapacitywithoutcoexistenceofmetaljandk

ð4Þ

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Int.J.Environ.Sci.Technol.Table4LangmuirandFreundlichparametersforNi(II),Cd(II)andCr(VI)inmono,binaryandtertiarysystembySSC

Metalcombinations

SSCLangmuirQoMono-componentCr(VI)Ni(II)Cd(II)

BinarycomponentNi(II)?Cd(II)Ni(II)?Cr(VI)Cd(II)?Ni(II)Cd(II)?Cr(VI)Cr(VI)?Ni(II)Cr(VI)?Cd(II)TertiarycomponentNi(II)?Cd(II)?Cr(VI)Cd(II)?Ni(II)?Cr(VI)Cr(VI)?Ni(II)?Cd(II)

0.080.050.03

-5.2-3.7-2.8

0.98430.97850.9685

0.070.060.3

1.30.90.5

0.97970.98080.1470

0.120.140.100.090.060.05

-158.7-18.9-8.8-6.3-4.4-3.2

0.98780.99160.98240.980.98170.9742

0.70.120.10.080.060.05

2.43.42.11.51.10.7

0.67370.95180.95960.97850.98030.9798

0.290.240.20

0.81.52.5

0.98730.99910.9986

1.82.10.9

3.62.51.8

0.85420.91230.9063

b

r2FreundlichKfn

r2IfRi[100percent,itindicatesthattheinteractiveeffectofamixtureofmetals(say,jandk)issynergistic,Ri\\100%indicatesantagonisticbehaviorandRi=100%indicatesnon-interactivebehavior.ThevaluesofRiwere\\100%inallthebinaryandtertiarymetalsystems(Table2).So,itwasinferredthattheinteractionsbetweendifferentmetalionsareantagonisticinnature.Thismaybeduetothescreeningeffectbythemetalspresentinthesolution(SagandKutsal1996).Adsorptionisotherms

TheLangmuirandFreundlichadsorptionisothermswereappliedformono,binaryandtertiarysystems.Thevalueofcorrelationcoefficientr2forLangmuirisothermwasfoundtobe[0.95forallthesystemsbyboththeadsorbents(Tables3,4).Whilethevalueofcorrelationcoefficientr2forFreundlichisothermvariedforallthesystemsforboththeadsorbents,itwasverylessfortertiarysystem(Tables3,4).Theresultsclearlyrevealedthattheadsorptioncapacitydecreasedfrommonotobinaryandfrombinarytotertiarysystemduetothepresenceofothermetalionsinthesystem.ThemaximumLangmuircapacitywasfoundtobethehighestformono-componentsystem,i.e.,0.26,0.20and0.18mg/gforNi(II),Cd(II)andCr(VI),respectively,bySHCand0.29,0.24and0.20mg/gforNi(II),Cd(II)andCr(VI),respectively,bySSC,whileitrangedbetween0.15and0.02mg/gforthebinarysystemandbetween0.05and0.02mg/gfortertiarycomponentsystembySHC.Theadsorptioncapacityrangedbetween0.12and0.05mg/gforthebinarysystemandbetween0.08

and0.03mg/gfortertiarycomponentsystembySSC(Tables3,4).Theorderofmaximumadsorptioncapacitywasfoundtobemono-component[binarycompo-nent[tertiarycomponent.

Conclusion

Differentpartsofsunflowerplantbiomasswereconvertedintotwoadsorbents.TheseadsorbentswereemployedfortheadsorptionofNi(II),Cd(II)andCr(VI)inmono,binaryandmulti-metalsystems.Theresultsshowedtheadsorp-tioncapacityofsunflowerstemcarbonwasmorethansunflowerheadcarbon.Itwasalsoinferredfromthedatathatadsorptioncapacityoftheadsorbentsdecreasedinthepresenceofco-cations.Theadsorptioncapacityofboththeadsorbentswaslesserinmulti-metalsystemsthanbinaryandmono-metalsystems,foranyparticularmetal.Thisinhibitoryeffectofco-cationsmaybeduetothecompe-titionandaffinityofmetalionsfordifferentsitesontheadsorbents.Thevalueofr2was[0.95forLangmuiriso-therminallthesystemsforboththeadsorbents,thusshowingtheapplicabilityofLangmuirmodel.Theinter-activeeffectwasfoundtobeantagonisticinbothbinaryandtertiarysystemsindicatedbyvalues\\100inallthesystems.

AcknowledgmentsThepresentworkwassupportedbyCouncilofScientificandIndustrialResearch(CSIR),Govt.ofIndia,NewDelhi,intheformofSeniorResearchFellowship(Grantnumber09/752(0022)/2009/EMR-I.Theauthorsexpresstheirthanksforfinancialsupporttothiswork.

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NomenclatureSHCSunflowerheadcarbonSSCSunflowerstemcarbonBETBrunauer–Emmett–TellerSEMScanningelectronmicroscopeEDXEnergydispersiveX-rayanalysis

FT-IR

Fouriertransforminfraredmicroscopy

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