Extraction of humic acid by coacervate: Investigation of direct and back processes

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OULOUSE

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DOI:10.1016/j.jhazmat.2011.12.057

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To cite this version :

Ghouas, H. and Haddou, Boumediene and Kameche, Mohamed and

Derriche, Zoubir and Gourdon, Christophe Extraction of humic acid

by coacervate: Investigation of direct and back processes. (2012)

Journal of Hazardous Materials, vol. 205-206 . pp. 171-178. ISSN

0304-3894

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Extraction

of

humic

acid

by

coacervate:

Investigation

of

direct

and

back

processes

H.

Ghouas

_{, B.}

_Haddou

_{, M.}

_Kameche

_{, Z.}

_Derriche

_,

_C.

_Gourdon

a_{U.S.T.Oran,FacultédesSciences,DépartementdeChimieBP1505,M’Nouar,Oran,Algeria}

b_{LaboratoiredeGénieChimique,UMR5503,BP84234,CampusINP-ENSIACET,N}◦_{4AlléeEmileMonso,ToulouseCedex4,France}

Keywords: Extraction Humicacid Surfactant Coacervate Cloudpoint

a

b

s

t

r

a

c

t

Thetwoaqueousphasesextractionprocessiswidelyusedinenvironmentalcleanupofindustrial effluents andfinechemical productsfortheir reuse.This processcanbe madebycloud point of polyethoxylatedalcoholsandmicellarsolubilizationphenomenon.Itiscommonlycalled“coacervate extraction”andisused,inourcase,forhumicacidextractionfromaqueoussolutionat100mg/L.The surfactantsusedarealcoholpolyethoxylateandalkylphenolpolyethoxylate.Phasediagramsofbinary water/surfactantandpseudo-binaryareplotted.Theextractionresultsareexpressedbythefollowing responses:percentageofsoluteextracted,E(%),residualconcentrationsofsoluteandsurfactantindilute phase(Xs,w,andXt,wrespectively)andvolumefractionofcoacervateatequilibrium().Foreach

parame-ter,theexperimentalresultsarefittedtoempiricalequationsinthreedimensions.Theaimofthisstudyis tofindoutthebestcompromisebetweenEandC.Thecomparisonbetweenexperimentalandcalculated

valuesallowsmodelsvalidation.Sodiumsulfate,cetyltrimethylammoniumbromide(CTAB)additionand pHeffectarealsostudied.Finally,thepossibilityofrecyclingthesurfactanthasbeenproved.

1. Introduction

Humicsubstancesarepolyelectrolyticmacromoleculeshaving highmolecularweights[1–4].Theyaresignificantinaquatic sys-temsforseveralreasons.Theygiveyellowbrowncolortowater

[5]andcancomplexmetals[6,7]andorganicpollutantssuchas pesticides[8].Theyareprecursorstotheformationofmutagenic halogenatedcompoundsinwaterafterchlorination[9].Especially humicacidrepresentsthemajoradvantageofthenaturalorganic matterinsoilandsurfacewater[1].However,itspresenceinraw watercansignificantlyaffectthequalityduringthepurification process [10]. It is widely agreed that trihalomethanes (THMs), one of disinfection byproducts, can begenerated by step chlo-rinationinwatertreatmentwhentheycontainhumicacid[11]. Severalresearcheshavebeencarriedoutasanalternativeforthe degradationofaquatichumicsubstances[12–15].Besides, differ-enttechniquesfortreatmentofcontaminatedreleasewithhumic acid,havebeenproposedsuchas:biologicaltreatment[16], filtra-tion[17,18],adsorption[7,9],ozoneoxidation[19],heterogeneous photocatalysis[20,21],coagulationandionexchange[22], electro-chemistry[23],photocatalytictreatment[24,25].

∗ Correspondingauthor.Tel.:+213041425763;fax:+213041425763. E-mailaddress:Boumediene74@yahoo.fr(B.Haddou).

Thepresentworkconcernsthestudyofcloudpointextraction (CPE)asamethodofrecoveryandvalorizationofhumicacidof aqueoussolutionusingthepowerfulsolubilizingcharacteristicof nonionicsurfactantaqueoussolutions. Ineffect,above alineof lowcriticaldemixingpointofsuchsystemsdefinedascloudpoint (tc),aqueoussolutionsofmostnonionicpolyethoxylated(orinthe

presenceofpolyethyleneglycolelectrolyte)formtwophases:the coacervate,richinsurfactant,andthedilutephase.Inthelatter,the surfactantconcentrationisclosetoitscriticalmicelle concentra-tion(cmc).Therefore,duetothemicellarsolubilizationpropertyof thesurfactant,hydrophobic,amphiphilicorevenionicsoluteshave beenextractedinthecoacervateafterincreasingthetemperature aboveitscriticalvalueTc.Theextractionprocesswithtwoaqueous

phases, initially applied tothe case of metal ionsin the pres-enceofchelatingagent[26],waslaterappliedtomanychemical species:variousmetalions,smallorganicmoleculesand biologi-calmolecules[27,28].ThistechniqueallowsmovingtowardGreen Chemistry.Thesmallvolumeofthebiodegradablesurfactant-rich phaseobtainedbyusingthecloudpointmethodology,permitsto setupanexperimentalprocessoflowercost,betterextraction effi-ciencyandlowertoxicitythanthoseusingorganicsolvents.This factisparticularlyattractive,becausethe“GreenChemistry” con-ceptcanbeemployed here.CPEisconsideredtobeconvenient and environmentallysafealternativetoextraction withorganic solvents[28,29].ManyadvantageswereclaimedtoCPEcompared toconventionalliquid–liquidextraction,includinghighextraction

efficiency,easeofwastedisposalandtheuseofnon-toxicandless dangerousreagents[29].

2. Materialsandmethods 2.1. Reagents

Thesurfactantsusedinthisworkarebiodegradablenonionic surfactants:

1) Apolyethoxylatedoctylphenolknownas“Dowfax20B102”, sup-pliedbyDowChemicalcompany.Ithasthechemicalformula C16–18H33–37-8-(OCH2 CH2)9 OHandbelongstothefamilyof

ethoxylatedalkylphenols(EPA).

2)Analcohol polyethoxylate (AE) experienced by Lutensol ON 30andequivalenttoC10H21(OCH2 CH2)3OH.Itisprovidedby

BASF.

Thesesurfactantswarrantedgreatdealofresearch,both theo-retically[30]andexperimentally[25].Theyarenotsoexpensive andhaveexcellentextractionperformances.Humicacidwas sup-pliedbySigma–Aldrich.

2.2. Methods 2.2.1. Cloudpoint

Aqueous solutions of ethoxylated alcohols and ethoxy-lated alkylphenols are sensitive to temperature, because their hydrophilicgroupstodésolvategraduallyduringheating[31–33]. Thedeterminationofcloudpointwasmadebyusingtheapparatus MettlerFP900whichconsistsoftheoperatingFP900,acontrolunit, andseveralmeasuringcells.Thecelltemperaturemeasurement isperformedwithahighly accuratesensor Pt100(probe), inte-gratedinthebodyofafurnace.Inthelowerpartofthecloudpoint measuringcell,PF81Cisalightsourceandanopticalfiberwhich illuminatesthethree specimens. The light passing throughthe specimensisconvertedbythreephotoelectriccellsintoelectrical signalsproportionaltotheintensityremains.Thelight transmis-sionismeasuredcontinuouslywhilethecelltemperatureincreases linearlywiththeheatingratechosen.Thecloudpointdesignates thetemperatureatwhichthesinglelimpidphaseistroubled,asa resultoftheappearanceofasecondphase.

Fortheextractiontests,10mLofsolutioncontainingthe sur-factantconcentrations(1–12wt.%)andthesolute(humicacidat 100mg/L)indeionizedwater,wereheatedinaprecisionovenfor 2htoreachequilibrium.Theheatingtemperaturerangewas cho-senfromthecloudpointtemperaturetoabout20◦_{C.Ineffect,for}

thesurfactantLutensolON30,thetemperaturerangeis(27–47◦_C)

whilethatforDowfax20B102is(33–53◦_{C).Thevolumesofboth}

phaseswereregistered.Asmallamountofthedilutephasewas takenusingasyringeandanalyzed.

2.2.2. Analysis

TheconcentrationofDowfax20B102inthedilutephasewas achieved by high performance liquid chromatography reverse phase,underthefollowingconditions:RP18column(ODS),95bar pressure,eluentH2O/CH3CN/CH3OH,7.5/60/32.5(vol.%),flowrate

1mL/minand260nmwavelengthdetector(UV).

ForLutensolON30,thelightscatteringdetectorLS31(EUROSEP instruments)wasused.Thethreeparameterstooptimizethe sen-sitivityofthedetectorweretheflowofairintothenebulizer,the temperatureoftheevaporatorandthegainofthephotomultiplier. Duringtheanalysis,theairpressurewassetto1bar,the evapora-tortemperaturefixedat55◦_{Candthegainofphotomultiplierwas}

equalto400mV.Humicacidconcentrationwasdeterminedusing thespectrophotometer(SAFAStypeMC2)at400nm.

3. Resultsanddiscussion

3.1. Binaryandpseudo-binaryphasediagrams

Organic solubilizates can interact with the surfactant polar head group or with its hydrophobic lengthafter solubilization in micelles. According to their chemical nature, organic com-pounds can vary the surfactants cloud point [31,34].The cloud pointincreasingofLutensolON30andDowfax20B102surfactants by humic acid addition, this phenomenon is especially notice-ableforlowsurfactantconcentrations.Thisindicatesasignificant interactionbetweenhumicacidandthesurfactant.Indeed,the sur-factantssolubilityinwaterwasincreasedbyinducingthecloud pointincrease[34,35].Furthermore,evenatverylow concentra-tion(0.1wt.%), thepresence ofCTAB significantlyenhancesthe cloudpointofLutensolON30.Toexplainthisphenomenon,various mechanismshavebeensuggestedincludingformationofmicelles, solubilizationandcomplexformation.Theincorporationofionic surfactantintothenonionic micellescauses electrostatic repul-sionbetweenthemicelles,thus hinderingthecoacervatephase formationandraisingupthecloudpoint[36,37].

4. Modelingofextraction

Theextractionresultsofhumicacidfromitsaqueoussolutions at100mg/Lbydifferentsurfactants,accordingtotwovariables: wt.%surfactant(Xt),andtemperature(T),wereexpressedbythree

responses(Y):percentageofextractedsolute(E),residual concen-trationsof solute(Xs,w)in thedilute phase and the coacervate

volumefractionatequilibrium(C)[34,38].Foreachparameter

determinedand by consideringcentral composite designs [39], theresultswereanalyzedbyanempiricalfitting.Inthismethod, theexperimentalvalues can beused todeterminethe polyno-mial model constants which were adjusted. The models were checkedbyplottingcomputingdataagainstexperimentalresults. Thequadratic correlationwaschosen togivetheslope andthe regressioncoefficient(R2_{)closertounity.}

Y=a0+a1Xt+a2T+a12XtT+a11Xt2+a22T2 (1)

Suchcorrelationallowsbuildingtheresponsesurface.However, onecannotallowphysicalsignificancetotheportionofhorizontal planescorrespondingtothemaximumvalueoftheresponse.

Thequadraticequationsfortheproperties(E,Xs,w,Xt.wandC),

whosereliabilitywaschecked,areasfollows: E(Dowfax)=26.993+11.314Xt+1.21T−0.103XtT −0.395X_t2−8.788 10−3T2 (2) E(Lutensol)=14.687+5.592Xt+2.607T−0.033XtT −0.216Xt2−0.027T2 (3) Xs.w(Dowfax) =106.276+0.063Xt−2.92T−0.125XtT +0.344Xt2+0.03T2 (4) Xs.w(Lutensol)=83.753−2.485Xt−2.543T−0.051XtT +0.225Xt2+0.027T2 (5)

Xt.w(Dowfax)=106.276+0.063Xt−2.92T−0.125XtT +0.344X2t +0.03T2 (6) Xt.w(Lutensol)=0.506+0.035Xt−0.023T−1.046 10−3XtT −1.159 10−3X2_t +3.11 10−4T2 (7) C(Dowfax)=0.403+0.479Xt−0.027T−0.009XtT −0.001Xt2+4 10−4T2 (8) C(Lutensol) =0.2939+0.0009Xt−0.0136T −0.002XtT−0.0054X2−0.0006T2 (9) 4.1. Extractionefficiency

Fig.2representsthethree-dimensionalisoresponsecurvesof thestudiedpropertiessmoothedbythequadraticmodel(Eqs.(2) and(3)).Fig.3ashowsthattheextentofhumicacidextraction(E) increaseswithXt.Inthiswork,Ereaches98%for10%LutensolON

30.However,thetemperatureincreasehasslighteffectofhumic acidextraction.Thistrendwasalsoobservedbyotherresearchers in otherextractionsystems [34,35,38].Indeed,thetemperature raiseinducessimultaneousandoppositeeffects:itincreasesthe concentrationofsoluteinthemicellaraggregatesasaresultofthe decreaseof(C)[38].Besides,onecannoticethattheextraction

extentobtainedwithLutensolON30,ishigherthanobservedusing Dowfax20B102.Thepresenceofabenzeneringinthehydrophobic chainofDowfax20B102,seemstohaveanegativeeffectonhumic acidsolubilization.

4.2. Concentrationofresidualhumicacid(Xs.w)

Fig.3representsthethree-dimensionalisoresponsecurvesof thestudiedproperty(Xs.w),smoothedbythequadraticmodel(Eqs.

(4)and(5)).Inthisfigure, itisshownthattheconcentrationof humicacidinthedilutephaseXs.wdecreasesasXtantTincrease.

Hence,thefirstcontactbetweenthesurfactantandtheeffluent solutions,allowssoluteconcentrationreductiontoabout10and

60timesusingDowfax20B102andLutensolON30,respectively (Table1).

4.3. Concentrationofresidualsurfactant(Xt.w)

Theconcentrationofresidualsurfactant(Xt.w)isavery

impor-tantparameter.Thehighlossofsurfactantinthedilutephasecan compromisetheprocessreliability.Indeed,thepresenceofanother contaminant inthe dilute phase, issufficient tomake the pro-cessuseless.Althoughthesesurfactantsareknownbytheirgood biodegradabilityproprieties,itwouldbedetrimentaltosquander theminthedilutephase.

Thebehaviorof(Xt.w)accordingtoXtandTisshowninFig.4

(smoothedbythequadraticmodelEqs.(6) and(7)).Thisfigure showsthattheresidualconcentrationofsurfactantislowathigh temperatureandlowsurfactantconcentration.Theseresultsare ingood agreementwithpreviousstudiesusingpolyethoxylated alkylphenols[37]aswellasotherpolyethoxylatedalcohols[38]. Indeed,theheatingdesolvatesgraduallythesurfactanthydrophilic groupsandthusitreducesitshydrophiliccharacter.Ingeneral,the desolvationenergyofthesurfactantmolecule canbeassociated withitsenergytransferfromthehydrophilic(aqueoussolution) tothehydrophobicmedium(micellarsystem).Onecannoticein

Fig.4thattheremainingconcentrationofLutensolON30inthe dilutephaseaftertheextraction,ishigherthanthatobtainedusing Dowfax20B102.Suchresultcanbeexplainedbythefactthatthe cmcofLutensolON30(cmc=0.2g/L)ishigherthanthatofDowfax 20B102(cmc=0.08g/L).Hence,LutensolON30ismoresolublein waterthanDowfax20B102.

4.4. Volumefractionofcoacervate

Inordertoincreasetheconcentrationfactorofsolute,a mini-malvolumefractionofcoacervate(C)shouldbeobtainedwhen

temperatureincreases.Ineffect,accordingtoFig.5,thesmoothed valueofCusingEqs.(8)and(9)islowathightemperatureandlow

surfactantconcentration.However,highsurfactantconcentrations inducemoresurfactantlossinthedilutephase(Fig.4).Although thesurfactantisbiodegradable,thislossisnoteconomical.Sothe optimizationoftheprocessneedstocompromisebetweenthefour studiedparametersE,Xs,w,Xt.wandC.Itshouldbepointedout

thatthisobservationhadalsobeendoneeitherbyusandothers

[34,37,38,40].Indeed,lesssurfactantconcentrationshouldbeused tohaveasmallervolumefractionofcoacervate.Onthebasisofthis finding,optimalvaluesofC(i.e.0.1and0.3)wereobtainedusing

4wt.%Dowfax20B10and4wt.%LutensolON30at50◦_Cand40◦_C,

respectively.

Table1

Someexperimentalresultsoftheextractionparameters(E,Xs,w,C,R2andXs,0/Xs,w).

[XT(wt.%),T(◦C)] E(%) Xs,w(mg/L) Xt,w(wt.%) C Xs,0/Xs,wa LutensolON30 R2_{=0.994 R}2_{=0.990 R}2_{=0.968 R}2_=0.957 [2,30] 76.681 23.319 0.102 0.060 4.288 [2,36] 79.864 20.136 0.090 0.050 4.966 [2,42] 81.080 18.920 0.078 0.050 5.285 [6,36] 92.201 7.799 0.087 0.200 12.822 [6,42] 94.027 5.973 0.072 0.070 16.742 [10,42] 98.340 1.660 0.115 0.050 60.240 Dowfax20B102 R2_{=0.989 R}2_{=0.995 R}2_{=0.959 R}2_=0.962 [1,36] 67.026 32.974 0.024 0.075 3.032 [1,42] 70.012 29.988 0.021 0.050 3.334 [1,48] 71.089 28.911 0.012 0.030 3.458 [5,42] 88.102 11.898 0.041 0.300 8.404 [5,48] 89.017 10.983 0.023 0.100 9.104 [9,48] 92.287 7.713 0.051 0.150 12.965 a_X

Fig.1.EffectofhumicacidandCTABonthecloudpointofLutensolON30andDowfax20B102.

5. Parametersaffectingextractionefficiency 5.1. Effectofsodiumsulfate

OnecanseeclearlyinFig.6thattheelectrolyteincreasesthe extraction extent(E%)of humicacid. The presenceof the elec-trolyteinducesadecreaseinthesolubilityofhumicacidinwaterby salting-outphenomenon.AccordingtoSaitoandShinoda[41],the additionofelectrolytetonon-ionicsurfactantsolutionsincreases theirhydrocarbonsolubilizationcapacity, byloweringcmc.This behaviormaybetheresultofanincreaseinmicellarnumberin

thepresenceofelectrolyte.So,theadditionofelectrolyteto non-ionicsurfactants solutionsincreasestheirsolubilizationcapacity towardorganicsoluteandconsequentlyimprovestheefficiencyof itscoacervateextraction(Fig.6).

5.2. Effectofcetyltrimethylammoniumbromide(CTAB): extractionbymixedmicelles

When nonionic and ionic surfactant co-exist together, they interactandprovideadditionalbeneficialpropertiestothesystem. Thisinteractionresultsinmostcasesbyaspecificassociationand

Fig.3.Three-dimensionalisoresponsecurvessmoothedbyaquadraticmodel,Xs.w=f(Xt.T),calculatedbythequadraticmodel(Eqs.(4)and(5)).

Fig.4.Three-dimensionalisoresponsecurvessmoothedbyaquadraticmodel,Xt.w=f(Xt.T),calculatedbythequadraticmodel(Eqs.(6)and(7)).

Fig.6. EffectoftheNa2SO4ontheextractionextentofhumicacid(E%).

theformationofnewandoriginalstructuresthatcanleadto syn-ergisticeffects.Thesemicellesareknownas“mixedmicelles”.The cloudtemperatureanalysis(Fig.1)allowsustoconfirmthe forma-tionofmixedmicelles.Onecanseeclearlythatthecloudpointof 1wt.%LutensolON30risesdramaticallyinthepresenceofCTAB.

Mixedmicelleshavepositiveeffectsontheextractionratioof humicacid(E%).OnecanseeinFig.7thatEincreasessignificantly withincreasingCTABconcentration.ThepositivechargeofCTAB moleculesincreasestheaffinityofthenegativelychargedhumic acidtowardthemicellaraggregates[42],suchresultswasobtained inothersystemsusingmixedmicelles[37].

5.3. EffectofpHonextractionrateofhumicacid:recyclingof surfactant

Humicsubstancesaremixturesofweakacidpolyelectrolytes, widelyspreadoutinsoilandnaturalaquaticenvironments[37,43]. Followingthecomplexityoftheirchemicalnature,alarge num-berof modelshave beendeveloped todescribe theiracid-base properties[44,45].Models knownascontinuous distributionof acidityconstantsvalues(expressedintermsofpK_i=−logK_i),have beendeveloped.Inthis model,theaciditydistributionofhumic

Fig.7. EffectofCTABontheextractionextentofhumicacid(E%).

Fig.8. EffectofpHontheextractionextentofhumicacid(E%).

substances molecules may be expressed by several functions

[46–48].Posner [48] showed that thedissociation constants of humicacidcanbedescribedbyamodelofpKivaluesdistribution

ofitsacidsites(4.0≤pK≤9.0),whereastherelativeconcentration ofeachsiteisnormallydistributedaccordingtothepKivalues.

HAi+H2O⇆Ai−+H3O+ (10)

Itisalsowellknownthatthesolute–micelleinteractionsare stronglyinfluencedbysoluteionization[38].Afterthe deproto-nationofa weakacidortheprotonationofa weakbase,slight interactionsmayoccurwiththesurfactant.In theseconditions, a small amountof those species maysolubilize, unlike neutral molecules.Consequently,asmallamountofionizedsolutecanbe extracted.

InFig.8,theresultsshowthatthedistributionofhumicacid betweenaqueousandsurfactant-richphase,depends greatlyon thesolutionacidity.Theextractionratio(E%)increaseswhenthe pHdecreases(Fig.8).Thisbehaviorcanbeexplainedbythe trans-formationofhumicacidtotheneutralmolecularformatacidpH. Theneutralformofhumicacidinteractsstronglywiththe micel-laraggregatesofnonionicsurfactant.Thisphenomenonwasalso observedwithfulvicacid(pKa=4.15)[49].Hence,separation of

humicacidisfavoredbyacidpH.

Indeed,pHis thekey-parameterforsurfactant regeneration. Severalworks havebeendoneontherecyclingandrecoveryof surfactantsolutionaftertheextractionsteps,byasimplepH con-trol[38,50,51].Thisrequirestwosteps:thefirstoneconcernsthe back-extractionofsolutesfromcoacervatewhilethesecondone relatestotheregenerationofthesurfactant.

Afterafirstextractionprocessofhumicacid(asweakacid)at 4wt.%ofLutensolON30and40◦_{C,thecoacervatepHwasincreased}

beyonditspKaequalto9.0,usingCa(OH)2togiveacomplete

disso-ciationofthesolute(Table2)[38,48].Hence,87.15%ofhumicacid extractedat40◦_{Ccanbereleasedfromthecoacervatetoanew}

dilutephase(at75◦_{CandpH12.4).ItisthemaximumpHwhich}

canbereachedusingCa(OH)2withasolubilitylimitof1.53g/L[52].

Moreover,thepreviouscoacervatewasseparatedintotwonew phasesat75◦_{C:asmallquantityoftheaqueousphasecontaining}

theconcentratedsolute,andanewcoacervatephasecontaining mostofthesurfactant.Inordertousethesurfactantagain,itis necessarytodecreaseitspHandtoprecipitatethebase(Ca(OH)2).

Therefore,itisbettertochooseanacidforminganinsolublesalt withthebasecation,suchasH2C2O4).

Table2

Conditionsforregenerationofcoacervate. [Ca(OH)2](g/L) inthe coacervate pHof coacervate Concentration(mg/L) ofhumicacidrelease fromthecoacervate

0 7.62 13.60 0.05 8.24 26.15 0.12 9.56 31.14 0.24 10.08 38.89 0.36 11.12 46.72 0.65 11.56 57.06 0.75 11.89 72.62 1.25 12.21 75.24 1.53 12.40 77.91 Table3

ResultsofthreecycleregenerationofLutensolON30coacervate. Settings Surfactantfrom

thefirstback extraction

Surfactantfrom thesecond backextraction

Surfactantfrom thethirdback extraction

Es(%) 96.587 81.298 69.758

XTs(%) 11.23 10.13 8.97

Et(%) 93.58 84.41 74.75

Table3summariestheresultsofsurfactantreuseforthree suc-cessivecyclesafterback-extractionofhumicacid,solubilizedin LutensolON30micelles.Thefirststageextractionwasperformed at40◦_{Cusing10wt.%ofsurfactantwhereasthebackextractionwas}

achievedat75◦_{C.Onecannoticethattheextractionextent(Es%)}

recoveredafterhumicacidreleaseatpH12.4usingfresh surfac-tant,ishigherthanthatobtainedwithrecycledsurfactant.Asthe backextractionofhumicacidisaround87%atpH12.4,micelles keep13%ofthehumicacidconcentrationateach extraction/back-extractionstage.Therefore,Esdecreasesusingrecycledsurfactant.

Table3showsalsothatthesurfactantconcentrationobtainedafter humicacidreleasefromcoacervate(XTs%),decreasesafterthe

sur-factantrecycling.Indeed,ateachextraction/back-extractionstage, asmallamountofsurfactantislostinthedilutephase,inducinga lowersurfactantrecoverypercentage.

6. Conclusion

Coacervateextractionwasusedtoseparatehumicacidfrom water.Thebestcompromise betweentheparametersgoverning the extraction effectiveness (surfactant concentrationand tem-perature) was foundusing a suitable experimentaldesign and three-dimensionalempiricalcurvefitting.Thestudyshowedthat cloudpointextractiontechniquewasabletoremovesoluble pollu-tantsfromeffluent.Extractionsattemperaturesrangingbetween 40◦_Cand50◦_{C,allowedtoobtaintheextractionextents94%and}

97%using4wt.%ofDowfax20B102andLutensolON30 respec-tively.Whereaslowsurfactantconcentration(<5wt.%)shouldbe usedtohavesmallervolumefractionofcoacervate.Na2SO4 and

CTABincreasedtheextractionextentofhumicacid.Theextraction ofthesolutewashighatacidpHrange.Moreover,extractionextent obtainedwithLutensolON30washigherthanthatusingDowfax 20B102.However,humicacidwaslessextractibleatpHaboveits pKa.Indeed,thepHcanbeakey-parameterforsurfactant

regenera-tionincloudpointextractionprocessofhumicacid.Thesurfactant recyclinginacloudpointextractionprocessseemstobepossible atpH>pKaofthesolute.

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