Leaching kinetics of colemanite in ammonium hydrogen sulphate solutions

Review

Leaching

kinetics

of

colemanite

in

ammonium

hydrogen

sulphate

solutions

Ro¨vs¸

en

Guliyev

,

Soner

Kus¸

lu

*

,

Turan

C¸alban

,

Sabri

C¸olak

Contents

1. Introduction... 1202

2. Methodsandmaterials... 1203

2.1. Experimentalprocedure... 1204

3. Resultsandanalysis... 1204

3.1. Dissolutionreactions ... 1204

3.2. Effectofparameters... 1204

3.3. Effectofreactiontemperature... 1204

3.4. Effectofconcentrationofammoniumhydrogensulphate... 1205

3.5. Effectofstirringspeed... 1205

3.6. Effectofsolid/liquidratio ... 1205

3.7. Effectofcolemaniteparticlesize... 1205

4. Kineticsanalysis... 1205

5. Discussionandconclusion... 1207

References... 1207

1. Introduction

Boroniswidelydistributedelementinnature.Itusuallyappears

intheformofboratsaltsorboricacid.Itisoneofthemostimportant

undergroundrichnessesofTurkey.Turkeyhas72%oftotalworld

boronreserveson the basis of B2O3.Ithas moreindustrialand

strategicimportance.Itoccursintracesinmostsoilsandplants,but isonlyfoundinaconcentratedforminafewplaces[1].

Boron compounds have found more increasingly field of

application.Ithavegainmorestrategicimportanceandareused

in hundreds ofdifferentfieldsas spacetechnology, agriculture,

nuclear industry or cleaning products. In recent years the

productionofboronanditscompoundshasincreasedgreatly,as

itcanbeusedinnuclearengineering,asfuelforrocketmotors,in

ARTICLE INFO Articlehistory: Received3August2011 Accepted25January2012 Availableonline2February2012 Keywords:

Colemanite

Ammoniumhydrogensulphate Leachingkinetics

ABSTRACT

The aim of the study was to investigate the dissolution kinetics of colemanite in ammonium hydrogensulphatesolutionsinamechanicalagitationsystemandtodeclareanalternativereactant toproduceboricacid.Reactiontemperature,concentrationofammoniumhydrogensulphate,stirring speed,solid/liquidratioandparticle sizewere selected asparameterson thedissolutionrateof colemanite. The experimental results were successfully correlated by linear regression using StatisticaPackageProgram.Dissolutioncurveswereevaluatedinordertotestshrinkingcoremodels forsolid–fluidsystems.Itwasobservedthatincreaseinthereactiontemperatureanddecreaseinthe solid/liquidratiocausesanincreasethedissolutionrateof colemanite.Thedissolutionextentis highlyincreasedwithincreasethestirringspeedratebetween100and500rpmandthedissolution extentisslowlyincreasedwithincreasethestirringspeedbetween500and700rpminexperimental conditions. Theactivationenergy wasfoundtobe32.66kJ/mol. Theleaching of colemanitewas controlledbydiffusionthroughtheashorproductlayer.Therateexpressionassociatedwiththe dissolutionrateofcolemanitedependingontheparameterschosenmaybesummarizedasfollows: 13(1X)2/3₊₂₍₁

X)=8.99C1.08

W1.39

D1.27_(S/L)0.54_e(32.66/RT)_t.

ß2012TheKoreanSocietyofIndustrialandEngineeringChemistry.PublishedbyElsevierB.V.Allrights reserved.

*Correspondingauthor.Tel.:+904422314586;fax:+904422314544. E-mailaddress:ksoner90@hotmail.com(S.Kus¸lu).

ContentslistsavailableatSciVerseScienceDirect

Journal

of

Industrial

and

Engineering

Chemistry

j o urna l hom e pa ge : ww w. e l s e v i e r. c om/ l o ca t e / j i e c

1226-086X/$–seefrontmatterß2012TheKoreanSocietyofIndustrialandEngineeringChemistry.PublishedbyElsevierB.V.Allrightsreserved.

hardandrefractoryalloys,inhighqualitysteels,intheproduction

of heat resistant polymers, for the production of optic and

chemicallystableglassintheglassindustry.Thecompoundsare

alsousedincosmetic,leather,ceramics,rubber,paint,textileand

agriculturalareaandalsoascatalysts[2].Theyalsofindapplication

inthewood-processingindustryasaprotectionagainstmoulds.

Boratandboricacidareusedasrawmaterialsforthemanufacture

ofglass,soap,detergent,cosmeticsand photographicchemicals,

flameretardantsandfornuclearinstallationsasneutronabsorbers.

Colemanitehasamonocliniccrystalstructureandadensityof

2.40gcm3_{.Itschemicalformulais2CaO3B}

2O35H2O.Itisusedto

produceboricacid.BoricacidisusedasasourceofB2O3inmany

fusedproductsandasstartingmaterialinthepreparationofmany

boronchemicalssuchasboronphosphate,borontrihalides,boron

esters,boroncarbide,organicboronsaltsandfluoroborates[3,4].

Ithasbeenknownthattheinvestigationofthedissolutionof

colemanite ore in various solutions have been studied for

productionofboroncompounds.Therearemany studiesin the

literatureconnectedwiththedissolutionkineticsofcolemanitein

varioussolutions.

Leachingkinetics of colemanitewithdifferent solutions has

been studied by a number of investigators. These studies are

summarized as follows:Alkan et al.,studied colemaniteorein

watersaturatedwithCO2.Theprocesswasfoundbychemically

reaction controlled and the activation energy was calculated

57.7kJ/mol [5]. Kocakerim and Alkan investigated it in water

saturatedwithSO2.Theprocesswasfoundbychemicallyreaction

controlledandtheactivationenergywascalculated53.97kJ/mol

[6].Karago¨lgeetal.carriedoutitinethylenediaminetetraacetic

acid(EDTA).Theyfoundthattheprocesswasfoundbychemically

reactioncontrolled andtheactivationenergy wascalculatedas

50.60kJ/mol [7]. The dissolution kinetics of colemanite was

investigatedinammoniumchloridebyKumetal.,andtheyfound

that thedissolutionwascontrolled by chemicallyreaction.The

activation energy was found as 89kJ/mol [8]. O¨ zmetin et al.

studied it in acetic acid. They carried out the process rate

controllingstepisthefirstorderpseudohomogeneousreaction

model.Theactivationenergywasfoundas51.49kJ/mol[9].The

dissolutionkineticsofcolemanitewasinvestigatedinboricacidby

Yartasi et al., and they found that therate controlling step is

diffusionthroughproductfilmaroundunreactedcoreof

coleman-iteparticles[10].Temuretal.investigatedthedissolutionkinetics

of colemanite in phosphoric acid and they found the rate

controlling step is surface chemically reaction process. The

activation energy was calculated by 53.91kJ/mol [11]. The

dissolution of colemanitewas carried out in sulphuric acid by

C¸etin etal. Theprocess ratecontrollingstepwasfoundsecond

orderwithrespecttosaturationlevelandtheactivationenergy

wasfoundas34.0kJ/mol[12].AlkanandDog˘anwerecarriedout

experimentsinoxalicacidanddescribedtheratecontrollingstep

as product layer diffusion process. They found the activation

energy as 39.70kJ/mol [13]. C¸avus¸ and Kus¸lu studied the

dissolutionofcolemaniteincitricacidsolutionandtheactivation

energywasfoundas28.65kJ/mol.Theratecontrollingstepwas

diffusionthoroughtheproductlayer[14].Tunc¸etal.investigatedit

in ammonium sulphate solutions. The rate controlling step is

chemically reaction and the activation energy was found as

40.46kJ/mol [15]. The dissolution kinetics of colemanite in

perchloric acid was carried out by Gu¨r and Alkan. Chemical

reaction was found as rate controllingstep and the activation

energywasfoundas46.47kJ/mol[16].Kubilayetal.wasstudiedit

in perchloric acid. Rate controlling step was heterogeneous

chemical reaction and the activation energy was found as

41.07kJ/mol [16]. Gu¨r studied the dissolution kinetics of

colemanitein amonioum nitratesolutions. The ratecontrolling

stepwaschemicallycontrolandtheactivationenergywasfoundas

41.40kJ/mol [17]. Kuslu etal. wasinvestigated it inpotassium

hydrogensulphatesolutions.Ratecontrollingstepwasdiffusion

throughtheashorproductlayerandtheactivationenergywas

foundas26.34kJ/mol[19].

Theboricacidisindustriallyproducedwithareactionbetween

colemanite and sulphuric acid solution. As sulphuric acid is a

stronglyacid,theimpuritiesinboronorearedissolved.Thiscase

causesimpuritiesinboricacidsolutions.Thequalityofboricacidis

reduced. Therefore, weak acid solutions should be used for

productionofboricacid.

Theaimofourstudyistoinvestigatethedissolutionkineticsof

colemanite in ammonium hydrogen sulphate solutions in a

mechanical agitation system and alsoto declarean alternative

reactanttoproducetheboricacid.Thereisnostudyreportedinthe

literatureaboutsuchaprocedure.Investigationonthedissolution

conditionsandthedissolutionkineticsofcolemanitein

ammoni-umhydrogensulphatewillbebeneficialtothesolutionofsome

problems appeared during boric acid production. So that, the

kinetic data for the reaction of colemanite with ammonium

hydrogensulphateareveryimportantforindustrialapplication.

Thedissolutionkineticsofcolemaniteinammoniumhydrogen

sulphatewasexaminedaccordingtotheheterogeneousreaction

models. In our study, reaction temperature, concentration of

ammoniumhydrogen sulphate, stirring speed,solid/liquid ratio

andparticlesizewerechosenasprocessparameters.

2. Methodsandmaterials

Leaching experiments were conducted under atmospheric

pressure conditions.Allreagentsused intheexperimentswere

prepared fromanalyticalgrade chemicals (Merck)and distilled

water. A constant temperature water circulator was used in

combination with the reactor to maintain the mixture in the

reactorataconstanttemperature.Theexperimentswerecarried

outina500mLsphericalglassreactor.Thereactorwasequipped

witharefluxcondensertopreventevaporationduringheatingand

Nomenclature

b stoichiometriccoefficient

C concentration of borax decahydrate solution

(molm3₎

CAg concentrationofAinthebulksolution(molm3)

D meanparticlesize(m)

De diffusioncoefficient(m2min1)

EA activationenergy(kJkmol1)

kd masstransfercoefficient(mmin1)

ks reaction rate constant for surface reaction

(molmin1₎

ko frequencyorpre-exponentialfactor(min1)

L amountofliquid(mL)

n molnumber(mol)

r correlationcoefficient(–)

R universalgasconstant(kJkmol1₎

R initialradiusofasolidparticle(m)

S amountofsolid(g)

T reactiontemperature(K)

t reactiontime(min)

t* reactiontimeforcompleteconversion(min)

X fractionalconversionofB2O3

W stirringspeed(rpm)

amechanicalstirrertoobtainahomogeneoussuspensioninthe

reactor.Themechanical agitation experimental systemis fairly

common,sonoillustrationofitappearsinthispaper.

2.1. Experimentalprocedure

A typical experiment conducted was as follows: 250mL of

ammoniumhydrogensulphatesolutionswaspouredintotheflask.

Thesolutionwasheatedtothedesiredtemperature,atwhichit

was kept constant. All experiments were carried out using

337.5

m

ofparticlesizeonthereactionratewasinvestigated.After this,

largequalities ofsolid colemanitewereaddedtothesolutions.

Stirringofthesolutionwasstarted immediatelythereafter.The

durationofthetreatmentdependedontheexperimental

condi-tions. At definite time intervals, 1mL samples of the reacted

solution were taken for the assay of B2O3 and analyzed by

potentiometricandtitrimetricmethods[18,20].BasedontheB2O3

estimated,thedegreeofdissolutionofcolemanitewasdetermined

asafunctionoftime.

Colemanite samples usedin theexperimentswere obtained

fromBandırma Borax Corporation, Turkey. The colemanite ore

sampleswerecrushed,driedundervacuumandsievedwithASTM

standard sievesto give fractions of average sizes 637.5,337.5,

215.0and 165.0

m

analysisofcolemanitesamplesusedintheexperimentsasfollows:

%24.42CaO,%43.52B2O3,%18.9H2O,%13.16SiO2andothers.

Eachexperimentwasrepeatedtwice,andthearithmeticaverageof

theresultsofthetwoexperimentswasusedinthekineticanalysis.

3. Resultsandanalysis

3.1. Dissolutionreactions

The reaction taking place in the solution can bewritten as

follows[20]:

4NH4HSO4ðaqÞ!4NH4þðaqÞþ4HSO41ðaqÞ (1)

4HSO41ðaqÞþ4H2OðaqÞ$4H3OþðaqÞþ4SO42ðaqÞ (2)

When colemanite is added to the ammonium hydrogen

sulphatesolutions,thereactiontakingplaceinthesolutioncan

bewrittenasfollows[19,20]:

2CaO3B2O35H2OðsÞþ4H3OþðaqÞ!2CaþðaqÞþ6H3BO3ðaqÞþ2H2OðlÞ

(3) 2Caþ2

ðaqÞþ2SO42ðaqÞ!2ðCaSO42H2OÞðsÞ (4)

Thetotalreactionisasfollows:

2CaO3B2O35H2OðsÞþ4NH4HSO4ðaqÞþ6H2OðaqÞ

!2ðCaSO42H2OÞðsÞþ6H3BO3ðaqÞþ2ðNH4Þ2SO4ðaqÞ (5)

Ascanbeseenfromthetotalreaction(5),CaSO42H2O,boric

acid and ammonium sulphate has been obtained. As know,

ammonium sulphate solutions can dissolve the colemanite

minerals. So that the dissolution of colemanite minerals has

increased.

3.2. Effectofparameters

Reactiontemperature,concentrationofammoniumhydrogen

sulphate,stirringspeed,solid/liquidratioandcolemaniteparticle

sizewereselectedasprocessvariablestoinvestigatetheireffects

onthedissolutionlevelofcolemanite.Intheexperiments,while

the effect of one parameter was studied, the values of other

parameters were kept constant. The kept constant values for

reactiontemperatureof 353K,for concentrationof ammonium

hydrogensulphateof1.5M,forstirringspeedof500rpm,forsolid/

liquid ratio of 1/50g/mL and for colemanite particle size of

337.5

m

A quantity of 250mL of ammonium hydrogen sulphate

solutions was used and kept constant in all experiments.

Homogeneity ofsuspensionin thereactorwasobtainedwitha

stirringspeedof500rpm,keptconstantinallexperiments.The

dataobtainedwereplottedintheformoftimeversusfractional

conversionasappearinginFigs.1–5.Inthesefigures,thefractional

conversionX(%)isdefined:

Xð%Þ¼ðamountofdissolved B2O3 inthesolutionÞ

ðamountof B2O3 intheoriginalsampleÞ

100 (6)

3.3. Effectofreactiontemperature

Thetemperatureisafactorofgreatimportancefortheleaching

kinetics.Theeffectofreactiontemperaturewasexaminedat323,

328,333,338,343,348and353K.Thedissolutioncurvesobtained

areshowninFig.1.AscanbeshownfromFig.1thatthequantityof

16 14 12 10 8 6 4 2 0 t (min.) 40 50 60 70 80 90 100 X (% B 2 O3 ) 323 K 328 K 333 K 338 K 343 K 348 K 353 K

Fig.1.Effectofreactiontemperatureondissolutionrateofcolemanite.

22 20 18 16 14 12 10 8 6 4 2 0 t (min.) 71,50 90,76 98,41 % B 2 O3 C=1.0 M C=1.5 M C=2.0 M C=2.5 M C=3.0 M

Fig.2.Effectofconcentrationofammoniumhydrogensulphateondissolutionrate ofcolemanite.

colemanitedissolvedincreaseswithincreasingreaction

tempera-ture.The reaction rateconstant is exponentially dependent on

reactiontemperature.

3.4. Effectofconcentrationofammoniumhydrogensulphate

Theexperimentsforobservingtheeffectof concentrationof

ammonium hydrogen sulphate solutions on the dissolution

processwerestudiedby varyingto1.0, 1.5,2.0, 2.5 and3.0M.

ThedissolutioncurvesaregiveninFig.2.ItcanbeseenfromFig.2 that,thedissolutionleveloftheprocessincreaseswithincreasein

theconcentrationofammoniumhydrogensulphatesolutionsuntil

about1.5M.Ingeneral,theleachingrateincreaseswithincreased

concentrationofreagent,butonlyuptoacertainmaximumlevel.

Thedissolutionrateofcolemaniteremainedalmostconstantat

concentration of ammonium hydrogen sulphate solution of

between1.5Mand3.0M.

3.5. Effectofstirringspeed

The effect of the stirring speed on the dissolution rate of

colemanitewasinvestigatedat100, 300,500 and700rpm.The

experimental results for the effects of stirring speed on the

dissolutionprocesscanbeseeninFig.3.ItcanbeseenfromFig.3 that,thedissolutionleveloftheprocessincreaseswithincreasein

thestirringspeedrateuntilabout500rpm.Itisevidentthatthe

dissolution rateis practically independentof thestirring speed

between 500and700rpm.Homogeneityofthesuspensionwas

exactlyobtainedatastirringspeedof500rpm.Becauseofthis,the

stirring speed rate of 500rpm was as constant value in all

experimentstogetguaranteedtoobtainhomogeneityinthebatch

reactor.

3.6. Effectofsolid/liquidratio

The effect of solid/liquid ratio on the dissolution rate of

colemanitewasinvestigatedbyvaryingratioto1/50,1/25,1/10

and1/5g/mL.Thevariationofthedissolutionrateforvarioussolid toliquidratioscanbeseenFig.4.ItcanbeseenfromFig.4that,

decreasingsolidtoliquidratiosfavorthedissolutionprocess.The

dissolutionratedecreaseswithincreasingsolid/liquidratio.This

situationcanbeexplainedbythedecreaseintheamountofsolid

colemaniteparticlesperamountofreagentammoniumhydrogen

sulphateinthereactionmixture.

3.7. Effectofcolemaniteparticlesize

Theeffectofparticlesizewasstudiedbytreatingfivesizesof

fractionsofthismineral,namely637.5,337.5,215.0and165.0

m

ThedissolutioncurvesarepresentedinFig.5.Ascanbeseenfrom

Fig.5,astheparticlesizedecreasesthedissolutionratesincreased. Thissituationcanbeattributedtotheincreasingcontactsurfaceof

thesamplesastheparticlesizedecreases.

4. Kineticsanalysis

The solid–fluidheterogeneous reactionrate canbeobtained

fromtheheterogeneous reactionmodel. Theexperimental data

wereanalyzedbasedontheun-reactedshrinkingcoremodelto

evaluate the rate-controlling step [21,22]. The heterogeneous

reactionmodelgivesrateequationsforeachcontrolmechanisms.

Thestepwiththehighestresistanceistherate-controllingstep.

Themodelhasbeenusedforsolid–liquidheterogeneoussystems

in both analytical and numerical methods. Integrated rate

equationsfortheun-reactedshrinking-coremodelandtheother

modelsareshowninTable1.Accordingtothemodel,thekinetic

dataweretreatedbyequationsinTable1.Theapplicationofthe

abovemodelstotheexperimentaldatawillhelpintodetermining

thedissolutionkineticsoftheprocess.Inthecasesinwhichthe

chemicalreactionismuchfasterthanthediffusiontheleachingis

said to be diffusion-controlled. The leaching mechanism often

becomesdiffusioncontrolledwhen,duringtheleaching,aporous

22 20 18 16 14 12 10 8 6 4 2 0 t (min.) 68,43 88,50 96,71 % B 2 O3 100 rpm 300 rpm 500 rpm 700 rpm

Fig.3.Effectofstirringspeedondissolutionrateofcolemanite.

30 25 20 15 10 5 0 t (min.) 40 50 60 70 80 90 100 X (% B 2 O3 ) 1/50 g/mL 1/25 g/mL 1/10 g/mL 1/5 g/mL

Fig.4.Effectofsolid/liquidratioondissolutionrateofcolemanite.

22 20 18 16 14 12 10 8 6 4 2 0 t (min.) 81,50 95,72 % B 2 O3 637,5µm 337,5µm 215,0µm 165,0µm

productlayerformsonthesurfaceoftheparticletobeleached.The

mechanismofdiffusioncontrolledleachingofsphericalparticleis

oftencalledtheshrinkingcoremodel[22,23].Experimentaldata

that fitsthe heterogeneous diffusion controlled ashor product

layerintheformoft/t*=13(1X)2/3_{+2(1X).Theregression}

coefficientsfortheallmodelsobtainedthestudycanbeshownin

Table2.Diffusioncoefficients(De)throughproductfilmsforthe

systemwereobtainedfromEq.(9).Timeforcompleteconversion

(t*)andthediffusioncoefficients(De)obtainedintheexperimental

systemcanbeseeninTable3.Theevidenceforthisproposalisas

follows: Regressionanalysis hasshown that experimental data

correlate well with Eq. (9) in Table 1, which means that the

dissolutionisdiffusioncontrolledashorproductlayer.Duringthe

reaction,CaSO42H2Oprecipitates.Therefore,itmayappearthat

the process is controlled diffusion product or ash film. The

regressioncoefficientwasfoundtobe0.9932ashigherlinearity.

Thevariationof13(1X)2/3_{+2(1X)withtime(t)isplotted}

for reaction temperature in Fig. 6. Eq. (9) in Table 1 is the

expression for diffusion controlled leaching according to the

shrinkingcoremodel.Asisevidentfromtheequation,thereaction

timeforcompleteconversionisproportionaltothesquareofthe

radiusoftheparticle.Fordiffusioncontrolledleaching,thereaction

time for complete conversion is proportional to R2_{. Using the}

heterogeneous diffusion controlled throughthe ash or product

layer, the t* values wereplotted versus R2. The highlinearity

betweent*andR2_{isseeninFig.7.Theregressioncoefficient(r}2₎

wasfoundtobe0.9916.Otherwise,theregressioncoefficient(r2₎

betweent*andRwasfoundtobe0.9491.TheArrheniusplotsof

lnksversus1/Tweredrawnfortofoundtheactivationenergyof

thereaction[22–25].Arrheniusplotsoflnksversus1/Tareshown

inFig.8.Fromtheslopesofthestraightlinestheactivationenergy ofthereactionisfoundtobe32.66kJ/mol.Ithasbeenreportedthat

the activation energy of the reaction controlled by surface

chemicalreactionsareabove40kJ/mol[26].Similarresultswere

foundintheliterature[10,14]. Further,this valueindicates the

dissolution rateof colemaniteis a diffusion controlled through

product or ash layer. The fact that the dissolution rate of

colemaniteis dependent of thestirring speed is shown by the

Table3

Valuesoft*andDeobtainedintheexperimentalsystem.

T(K) C(mol/L) W(rpm) S/L(g/mL) D(mm) t*(min) De(m2/s) 323 1.5 500 1/50 337.5 15.432 0.861010 328 1.5 500 1/50 337.5 14.978 0.891010 333 1.5 500 1/50 337.5 10.627 1.251010 338 1.5 500 1/50 337.5 10.493 1.271010 343 1.5 500 1/50 337.5 7.722 1.721010 348 1.5 500 1/50 337.5 7.496 1.781010 353 1.5 500 1/50 337.5 5.452 2.451010 353 1.0 500 1/50 337.5 5.023 2.661010 353 2.0 500 1/50 337.5 4.102 2.451010 353 2.5 500 1/50 337.5 3.160 2.541010 353 3.0 500 1/50 337.5 2.951 2.261010 353 1.5 100 1/50 337.5 21.832 6.121011 353 1.5 300 1/50 337.5 10.520 1.261010 353 1.5 700 1/50 337.5 4.108 3.251010 353 1.5 500 1/25 337.5 10.905 1.221010 353 1.5 500 1/10 337.5 16.025 0.831010 353 1.5 500 1/5 337.5 72.463 1.841011 353 1.5 500 1/50 637.5 23.364 2.041010 353 1.5 500 1/50 215.0 3.345 1.621010 353 1.5 500 1/50 165.0 2.642 1.201010 16 14 12 10 8 6 4 2 0 t (min.) 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1-3(1-X) 2/3 +2(1-X) 323 K r2 _{= 0,9919} 328 K r2 _{= 0,9978} 333 K r2 _{= 0,9975} 338 K r2 _{= 0,9895} 343 K r2 _{= 0,9564} 348 K r2 _{= 0,9909} 353 K r2 _{= 0,9584} Fig.6.Variationof13(1X)2/3₊₂₍₁

X)withtimeforreactiontemperatures. Table1

Integratedrateequationsfortheun-reactedshrinkingcoremodelandtheother models.

Rate-controllingstep Rateequation

Surfacechemicalreaction t=t¼½1ð1XBÞ1=3 t¼rBR=bksCAg Filmdiffusioncontrol t=t¼XB t¼rBR=3bkgCAg

Diffusioncontrolthrough

theashorproductlayer t=t¼½13ð1XBÞ2=3

þ2ð1XBÞ t¼rBR2=6bDeCAg First-order pseudo-homogeneousmodel _{lnð1XÞ¼kt} Second-order pseudo-homogeneousmodel ð1XÞ1¼kt Avramimodel lnð1XÞ¼ktm Table2

TheregressioncoefficientsforthemodelsshowninTable1.

Model Equation r2 _Act.energy

(kJ/mol)

Surfacechemicalreaction (7) 0.9760 32.80

Filmdiffusioncontrol (8) 0.8374 20.42

Diffusioncontrolthroughthe ashorproductlayer

(9) 0.9932 32.66 First-orderpseudo-homogeneous model (10) 0.8183 37.38 Second-orderpseudo-homogeneous model (11) 0.5840 38.44 Avramimodel (12) 0.8928 23.15

factthatthecontrolmechanismisdiffusioncontrolledthroughthe

productorashlayer.

The values were found by non-linear regression analyses

(Statistica 7.0, non linear estimation model, user-specified

regression-least squares, security value of %95, comparison

value of 1Exp(6), and maximum iteration values of

1000) and the analyses gave the mathematically model as

follows:

13ð1XÞ2=3þ2ð1XÞ¼8:99C1:08

W1:39

D1:27

ðS=LÞ0:54eð32:66=RTÞ_{t (13)}

5. Discussionandconclusion

Theaimofthestudywastoinvestigatethedissolutionkinetics

of colemanitein ammonium hydrogen sulphate solutions in a

mechanicalagitationsystemandtodeclareanalternativereactant

to produce boric acid. Based on the results obtained in this

research,thefollowingconclusionmaybedrawn:

The dissolution rateofcolemanite increasedwithincrease in

reactiontemperatureanddecreaseinthesolid/liquidratio.

The dissolution extent is highly increased with increase the

stirringspeedratebetween100and500rpmandthedissolution

extent is slowly increased with increase the stirring speed

between500and700rpminexperimentalconditions.

Thedissolutionprocessfollowsashrinkingcoremodelwiththe

heterogeneousdiffusioncontrolledthroughtheashorproduct

layerastheratecontrollingstep.

Theactivationenergywasfoundtobe32.66kJ/mol.

Weak acid solutions such as ammonium hydrogen sulphate

shouldbeusedforproductionofboricacid.Sothattheimpurities

inboricacidproducedwasreduced.

The mathematical form of the model depended on the

parameterschosenwasfoundasfollows:

13ð1XÞ2=3þ2ð1XÞ¼8:99C1:08W1:39D1:27

ðS=LÞ0:54eð32:66=RTÞ_t

References

[1]M.Tunc¸,M.M.Kocakerim,O¨ .Ku¨c¸u¨k,M.Aluz,KoreanJ.Chem.Eng.24(2007)55. [2]T.W.Davies,S.C¸olak,R.M.Hooper,PowderTechnol.65(1991)433.

[3]H.P.. Kemp,TheChemistryofBorates:PartI,BoraxConsolidatedLtd,London,1956 [4]A.Gur,KoreanJ.Chem.Eng.24(4)(2007)588.

[5]M.Alkan,M.M.Kocakerim,S.C¸olak,J.Chem.Tech.Biotechnol.35(A)(1985)382. [6]M.M.Kocakerim,M.Alkan,Hydrometallurgy19(1988)385.

[7]Z.Karago¨lge,M.Alkan,M.M.Kocakerim,Metall.Mater.Trans.B23B(1992)409. [8]C.Kum,M.Alkan,A.Yapıcı,M.M.Kocakerim,Hydrometallurgy36(1994)259. [9]C.Ozmetin,M.M.Kocakerim,S.Yapıcı,A.Yartası,Ind.Eng.Chem.Res.35(1996)

2355.

[10]A.Yartasi,C.O¨ zmetin,M.M. Kocakerim,M.H.Demirhan,Chim.ActaTurc26 (1998)7.

[11]H.Temur,A.Yartası,M.Copur,M.M.Kocakerim,Ind.Eng.Chem.Res.39(2000) 4114.

[12]E.C¸etin,I˙.Erog˘lu,S.S.O¨ zkar,J.Cryst.Growth231(2001)559.

[13]O¨ .Ku¨cu¨k,M.M.Kocakerim,A.Yartası,M.Copur,Ind.Eng.Chem.Res.41(2002) 2853.

[14]M.Alkan,M.Dog˘an,Chem.Eng.Process.43(2004)867. [15]F.C¸avus¸,S.Kus¸lu,Ind.Eng.Chem.Res.44(2005)8164. [16]A.Gur,M.E.Alkan,J.Chem.Eng.Jpn.(2008)354.

[17]S.Kubilay,Z.Yalc¸ınkaya,S.Aklan,AsianJ.Chem.(2008)2311. [18]A.Gur,Chin.J.Inorg.Chem.24(2008)467.

[19]R.Guliyev,S.Kus¸lu,T.C¸alban,S.Colak,J.Ind.Eng.Chem.18(2012)38. [20]A.A.Nemodruk,Z.K.Karalova,AnalyticalChemistryofBoron,vol.1.Section2,

IsraelProgramforScientificTranslations,Jerusalem,1965,p.33.

[21]D.A.Sookg,D.W.West,F.J.Holler,FundamentalsofAnalyticalChemistry,seventh ed., SaundersCollegePublishing,1996.

[22]O.Levenspiel,ChemicalReactionEngineering, 2nded., Wiley,NewYork,1972. [23]F.Habashi,KineticsofMetallurgicalProcesses,MetallurgieExtractiveQuebec,

QuebecCity,Canada,1999.

[24]B.Do¨nmez,F.Demir,O.Lacin,J.Ind.Eng.Chem.15(2009)865. [25]S.Kus¸lu,F.C¸.Dis¸li,S.C¸olak,J.Ind.Eng.Chem.16(2010)673.

[26]E.Jackson,HydrometallurgicalExtractionandReclamation,EllisHorwoodLtd, Chichester,1986,400. 0,00282 0,002840,002860,002880,002900,002920,002940,002960,002980,003000,003020,003040,003060,003080,003100,00312 1/T -2,7364 -2,3634 -2,0441 -1,6950 ln k r2 _{= 0,9993}

Fig.8.Arrheniusplotofthedissolutionprocess.

4,5E5 4E5 3,5E5 3E5 2,5E5 2E5 1,5E5 1E5 50000 0 R2_(µm2₎ 0 2 4 6 8 10 12 14 16 18 20 22 24 26 t* (min.) r2 _{= 0,9916}