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

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Extraction of humic acid by coacervate: Investigation of

direct and back processes

H. Ghouas, Boumediene Haddou, Mohamed Kameche, Zoubir Derriche,

Christophe Gourdon

To cite this version:

H. Ghouas, Boumediene Haddou, Mohamed Kameche, Zoubir Derriche, Christophe Gourdon.

Extrac-tion of humic acid by coacervate: InvestigaExtrac-tion of direct and back processes. Journal of Hazardous

Materials, Elsevier, 2012, vol. 205-206, pp. 171-178. �10.1016/j.jhazmat.2011.12.057�. �hal-00878996�

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_{: DOI:10.1016/j.jhazmat.2011.12.057}

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To cite this version

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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

Any correspondance concerning this service should be sent to the repository

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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

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

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

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