The Use of Activated Carbons with Basic Properties

451TheUseofActivatedCarbonswithBasicPropertiesfortheTreatmentof2-ChlorophenolAmjadH.El-Sheikh,AlanP.Newman*,HafidK.Al-Daffaee,SukiS.PhullandDanielE.LynchSchoolofScienceandtheEnvironment,CoventryUniversity,PrioryStreet,CoventryCV15FB,UK.(Received4July2003;revisedformaccepted11March2004)ABSTRACT:ArangeofbasicactivatedcarbonswaspreparedfromsinglecultivarJordanianolivestonesandtheirchemicalcomposition,texturalproper-tiesandsurfacegroupsinvestigated.Oneofthesampleswasde-ashedandthenoxidizedusingconcentratednitricacidtostudytheeffectsofinorganiccontentandsurfaceoxidationonitsadsorptioncapacitytowards2-chlorophenol(2-CP).Commercialsampleswithcombinedacidicandbasicpropertieswerealsotestedwithrespectto2-CPadsorption.Anattemptwasmadetocorrelatethetotalbasicitywiththeadsorptioncon-stantsoftheLangmuirequationandwithotherproperties.Thesepropertiesincludedburn-off,apparentsurfacearea,microporevolume,totalporevolumeandMethyleneBlue(MB)adsorptionsurfacearea.Thetotalbasicityhadnorelationshipwithanyadsorptionparameter.However,totalbasicitywasfoundtohavearelationshipwiththetotalporevolume,themicroporevolume,MBadsorptionandburn-off.TheBETsurfaceareashowedonlyaveryweakrela-tionshipwiththetotalbasicity.Burn-offhadarelationshipwiththerelativeaffinityoftheadsorbateandthesurfaceandLangmuirconstants,butnotwiththeadsorptioncapacity.De-ashingthesampleusingHF/HCldecreasedthetotalbasicityandMBadsorptionbutincreasedthetotalacidityandthecapacitytowards2-CPuptake.Themineralcontentsofbothpreparedandcommercialsampleswereanalyzedandfoundtoplaynoroleintheadsorptionof2-CP.INTRODUCTIONTheuseofagriculturalby-productsforthepreparationofactivatedcarbons(ACs)hasbeenreportedwidely(Overendetal.1985;Bridgwater1994;Bansaletal.1988).Morespecifically,thecarbonizationofolivestonestoformACshasbeenreportedbygroupsinSpain(Lopez-Gonzalezetal.1980;Gonzalezetal.1994;Molina-Sabioetal.1996;Rodriguez-Valeroetal.2001)andGreece(Galiatsatouetal.2001).Unfortunately,inthesestudiestheauthorsneithernamedthevariety(orvarieties)ofoliveusednordidtheystatewhetherasinglevarietyoramixturewasused.However,apreviousreportfromourgroup(El-Sheikhetal.2004)presentedtheeffectsthatdifferentpreparativeconditionshadonthesurfacepropertiesofACspreparedfromsinglecultivarolivestones.Otherreportshavealsoexploredtheroleofsurfaceacidity,oxygencontentandtexturalfeaturesofACs(Diamadopoulosetal.1992;Aniaetal.2002a,b;Huetal.2000;LengandPinto1997;Vidicetal.1997;VidicandSuidan1992)thathadbeenpreparedfromdiffering*Authortowhomallcorrespondenceshouldbeaddressed.E-mail:[e-mail]22(6)_36.qxd21-10-042:15pmPage451naturalsources.Inthesestudies,particularinterestwasgiventotheadsorptionofphenolasarepresentativecompoundforthelargergroupofsubstitutedphenols,suchasthetoxicchlorinatedphenols.TheresultsshowedthatbasicACswithlowoxygencontentaremorecapableofphenoluptake.TheyalsoshowedthatincreasedashcontentdecreasedtheabilityofanACtoabsorbphenol(Aniaetal.2002a,b).Furthermore,theashcontent,whichmayalsoaffecttheregenera-tionoftheAC,maybereleasedduringthetreatmentprocessthusre-contaminatingthesupposedlytreatedwater.ThesurfacepropertiesofACsplayanimportantroleintheadsorptionprocessofanytargetspecies.Whethervariousfunctionalgroupsarepresentonthecarbonsurfacedependsontheprecursorandtheactivationtechniqueemployedinthemanufacturingprocess.Boththepresenceofimpuritiesinthebasematerialandthemethodofpreparationinfluencetheformationofringedstruc-turesattheedgesofbasalplanesandyieldfreevalencieswhichareveryreactive(Vidicetal.1997).TheacidicorbasicnatureofanACdependsonthepresenceofspecificsurfacefunctionalgroups.AcidicgroupspotentiallyhindertheabilityofanACtoadsorbphenoliccompounds(Aniaetal.2002b).Resultsfortheadsorptionofphenoland4-chlorophenolshowedthatthelowerthehydrophilicity,thelargertheuptakecapacity(Huetal.2000).Theremovalofhydrophilicstruc-turessuchascarboxylicacidgroupsfromthesurfaceofanACincreasesthephysisorptionandsurfacepolymerizationofphenol(LengandPinto1997).Fortheworkreportedhere,basicACswerepreparedandinvestigatedfortheadsorptionof2-chlorophenol(2-CP)inacidicmediaandcomparedwithcommercialsamples.Acidicconditions(pH2)wereusedtomaximizethesorptionof2-CPbysuppressingitsionization.TheadsorptionconstantsoftheLangmuirequationweredeterminedforallsamplesandcomparedagainstburn-off,apparentsurfacearea,microporevolume,totalporevolumeandMethyleneBlueadsorptionsurfacearea.EXPERIMENTALMaterialsNabaliolivestones,grownnearAmman,wereobtainedfromalocalmarketinJordan.Thegeo-chemistryofthesoilinN.W.Jordan(highlimestonecontent)wouldexplainthepredominanceofcalciumandmagnesiumintheactivatedcarbonsproducedfromthesestonesasdetailedinTable6below.OliveproductioninJordanin2000amountedto134·103tonne()withthemainvarietiesbeingNabali,Carotina,SouriandGrossadeEspagna().AllchemicalswereobtainedfromAldrichandusedwithoutfurtherpurification.ThethreecommercialACsusedforcomparisonwiththepreparedsampleswereDarcoG-60(DARCOG-60)powder(100mesh),Darcogranular(20–40mesh)(DARCO20–40)andDarcoKB(D