Leaching of iron and chromium from an indigenous ferro chromium alloy via a rotary evaporator: Optimum conditions determination and kinetic analysis

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https://www.journals.elsevier.com/journal-of-materials-research-and-technology Availableonlineatwww.sciencedirect.com

Original

Article

Leaching

of

iron

and

chromium

from

an

indigenous

ferro

chromium

alloy

via

a

rotary

evaporator:

optimum

conditions

determination

and

kinetic

analysis

Mehmet

Feryat

Gülcan

a

_,

_Billur

_Deniz

_Karahan

b,c,∗

_,

_Sebahattin

_Gürmen

a a_Istanbul_Technical_University,_Department_of_{Metallurgical}_and_Materials_Engineering,₃₄₄₆₉_{Maslak-Istanbul,}_Turkey b_Istanbul_Medipol_University,_Department_of_Civil_Engineering,₃₄₈₁₀_{Beykoz-Istanbul,}_Turkey

c_Istanbul_Medipol_University,_Research_Institute_for_Health_Sciences_and_Technologies_(SABITA),₃₄₈₁₀_{Beykoz-Istanbul,}_Turkey

a

r

t

i

c

l

e

i

n

f

o

Articlehistory:

Received5May2020

Accepted30September2020

Availableonline17October2020

Keywords:

Leach

Ferrochromiumalloy

Rotaryevaporator

Taguchimethod

Kineticstudy

a

b

s

t

r

a

c

t

Intheleachingprocessofchromium-containingprecursorhexavalentchromiummayform,

whichprovokesdamagestoenvironmentandhumanhealth.Asasolution,leachingthe

chromiumcontainingprecursorwithsulphuricacidtogetchromiumionsintosolution

withoutforminghexavalentionshasbeenproposed.Theseexperimentsaremostlycarried

outathightemperaturestoincreasetheyield,whilethedetrimentaleffectofevaporation

isstillunderinvestigation.Inthisstudy,indigenousferrochromiumalloys(>60wt%Cr)

havebeenleachedwithsulphuricacidbyusingarotaryevaporatorwherenoevaporation

occurs.Theacidmolarity,solid:liquidratio,temperatureandrotationrateoftherotaryﬂask

havebeenoptimizedusingTaguchimethodtomaximizeFeandCrdissolutions’

efﬁcien-cies.Leachingin5Msulphuricacidsolutionwith1:50solid:liquidratio,at90◦C,30rpm

for150mincouldsustainyieldsaround73%and56%forCrandFerecoveries,respectively.

Withinthescopeofthisresearch,theeffectsofthementionedparametersontheleaching

efﬁciencyhavebeenalsoanalyzedviatheANOVAmethod.Themosteffectiveparameters

forCrandFehavebeenfoundastemperatureandsolid:liquidratio,respectively.Finally,

thekinetichasbeenalsostudiedanduniversalequationshavebeensuccessfullytested.

−ln(1−x)=k*tn_gives_the_best_ﬁtting_result_(where_n₌_0.4_and_0.6_are_calculated_for_Fe_and

Cr,respectively).Thesevaluesindicatethattheleachingreactionfollowsthemixedkinetic

controlmodel.Theactivationenergiesarecalculatedas46.12kJ/molforFeand142.8kJ/mol

forCr.

CCBY-NC-NDlicense(http://creativecommons.org/licenses/by-nc-nd/4.0/).

∗ _{Corresponding}_author.

E-mail:bdkarahan@medipol.edu.tr(B.D.Karahan).

https://doi.org/10.1016/j.jmrt.2020.09.133

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14104

j mater res technol.2020;9(6):14103–14115

Nomenclature

CCC CrossCorrelationCoefﬁcient

FeCr ferrochromium

Wt.% weightpercentage

kJ/mol kilojoulepermole

AAS atomicabsorptionspectroscopy

S/L solid/liquidratio(vol./vol.)

SSE sumofsquarederrors

vol. volume

XRD X-raydiffraction

XRF X-rayﬂuorescence

S/N signaltonoiseratio

EA activationenergy

R gasconstant

1. Introduction

Lately,environmentalpollutioncausedbypyrometallurgical

processesandincreaseinenergycostshaveledtothesearch

forproducinghighvalue-addedtransitionmetaloxides

pow-ders bya cheaper, environmentally sensitiveand practical

method.Recently,Guoetal.[1]haveproposedthatthe

pro-ductionoftransitionmetaloxide(TMO)powdersthrougha

liquidphasepresentsoutstandingadvantagessuchas

regu-latingmorphologyandsizeoftheﬁnalpowders.Therefore,

instead ofusing syntheticproductionmethodswherehigh

qualityprimarymaterialshavebeenselectedasprecursor;it

isbelievedthatdesigningaprocesscapableofleaching

dif-ferenttransitionmetalsfromanytypeofprecursormaterial

mayattractattentionoflargeaudienceasthesolutioncould

beusedintheTMO’spowderproduction.

Inthisstudy,tosetanexampleforthisidea,acheap,clean

andpracticalprocessisproposedforobtainingasolutionthat

containstransitionmetalsions(i.e.ironandchromiumions).

In view ofthis, anindigenous ferro chromium alloy being

widelyusedinrefractory,chemicaland steelindustrieshas

beenparticularlychosenastheprecursormaterial.Thereason

forchoosingferrochromiumalloyastheindigenous

precur-soristhefactthatTurkeyisawell-recognizedproducerofhigh

qualityferrochromiuminlargequantities[2].

Itisknownthatthechoiceofchemicalsandexperimental

parameterstobeusedinsuchresearchareofcritical

impor-tanceaschromiumtendstoassumehexavalentvalueathigh

and lowpHvalues ofthesolution. Itisto benoted, these

hexavalentchromium ionsthatharmtheenvironmentand

humanhealth are universally prohibited. Within this

con-text,Luietal.[3]havestatedthatsulphuricacidleachingof

chromiteorespreventshexavalentchromiumformationinthe

solution.Inpursuitofthat,Mohantyetal.[4]haveleacheda

rawmaterialcontaining24%ironwithvarioustypesofacids

(HCl,H2SO4 andHNO3), saltmixture(NaCl andCuCl3)and

bases(NaOH).Theyhaverevealedthat1.93Msulphuricacid

achievesthehighestefﬁciency[4].Subsequently,Tzeferisatal.

[5]haveleachedlateriticnickelorebyorganicacids,sulphuric

acid andtheir mixtures.Theoutcomes havedemonstrated

thesuperiorityofsulphuricacidtoachievethehighest

efﬁ-ciencyinleachingoftransitionmetals.Later,researchershave

investigatedtheeffectsoftemperature,processduration,acid

concentration,precursorparticlesizeandsolid:liquidratioon

transitionmetals’ leachingefﬁciencies[3,6,7].Therefore, to

deﬁnethemaximumleachingefﬁciencyconditions,Taguchi

methodhasbeenpreferredsimilartopreviousleaching

stud-ies[8–11]sinceitcanpredictcontributionofeachvariableonto

theoutcomeandpermitsoptimizationofnumerouscontrol

factors withleastnumber oftrials. Thus,byusingTaguchi

methodnotonlythecostand timearedecreased, butalso

thequalityisimproved,eventually[12,13].

Within the scope of the paper, an indigenous ferro

chromiumalloyisleachedwithsulphuricacidtosuccessfully

transferchromiumandiron(aswell asother traceamount

oftransitionmetals)intothesolutionastrivalentand

diva-lentions.Duringtheexperiments,arotaryevaporatorisused

fortheﬁrsttimetoleachanindigenousferrochromealloy

with5%wtCcontentincontrasttotraditionalstirringoptions

(suchasmechanicalandmagneticstirring).Therotary

evapo-ratorhasbeenparticularlychosensinceinhydrometallurgical

processingofchromium,pHadjustmentandevaporationare

importantcriteriatobeconsideredtoalleviateharmon

envi-ronmentandlivingcreatures.Itisexpectedthatthechange

inthereactortypenotonlymodiﬁestheinteractionbetween

theactiveparticles(ferrochromiumalloys)andtheleaching

media (sulphuricacid)but alsoenhances the safety ofthe

leachingprocess.

Fortheﬁrsttimeintheopenliterature,Taguchi

experimen-taldesigntechniqueandtheANOVAanalysishavebeenused

tomaximizetheleachingefﬁciencyandanalyzethe

param-eters’ effect on the leaching process when an indigenous

ferrochromiumalloywith5%Ccontenthasbeenleachedout

withsulphuricacidinarotaryevaporator.Todeﬁnethe

opti-mumprocessparameters,Taguchiorthogonalarraymethod

isappliedviafourparameterswiththreelevels,aspresented

inTable1.Thecontrolexperimenthasbeenruninadditionto

demonstratetheconsistencyandrepeatabilityoftheleaching

experiments’results.Furthermore,akineticstudyisalso

real-izedtorevealthecontrolmechanismofFeandCrdissolutions

undertheoptimumsulphuricacidleachingconditionsofthe

ferrochromiumalloy.

2. Experimental

2.1. Materials

Duringtheexperiments,anindigenousferrochromiumalloy

is used. Sulphuricacid is MerckQuality(1.00713.2500) and

deionizedwaterisofanalyticalgrade.Ethanolissuppliedby

Merck(1.00983.2511).

2.2. Ferrochromiumpreparation

Prior to starting the leaching operation, ferro chromium

chunksaremilledtoreducegrainsize,inordertoincreasethe

solid/liquid(acid)interactionduringleaching.Particleswith

grain sizeunder140meshare milledfor4hat235rpmby

planetaryballmill(RetschPM100).5mlethanolisusedas

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Table1–ExperimentlevelsforTaguchiorthogonalmethodL9(34).

Parameters Units Firstlevel Secondlevel Thirdlevel

Molarity (M) 0.5 2 5

Solid:liquidratio (vol:vol.) 1:50 1:100 1:200

Temperature (◦C) 25 60 90

Rotationrateoftheﬂask (rpm) 30 100 200

diameterareemployed.Duringtheexperiments,ball/powder ratio is ﬁxed as 10:1 in weight. Then, milled powders are cleansedat60◦Cfor4hwith500rpminamagneticstirrer toremovewatersolublespeciesfromtheprecursor.

2.3. Leachingprocedure

Allleachingexperimentshavebeen doneinarotary evap-orator system (Buchi Rotavapor® R-300). To optimize the leachingprocessparameters,nineexperimentsaredesigned viaTaguchiorthogonalarraymethod.Fourparameterswith threelevels(L9(34))havebeeninvestigated:Molarity(0.5M,2M and5M),volumetricsolid:liquidratio(1:50,1:100and1:200), temperature(25◦C,60◦Cand90◦C)androtationrateofthe ﬂask(30,100and200rpm).Theleachingduration(150min)is keptconstantforthesenineexperiments.Theparametersand theirlevelsaregiveninTable1.AfterTaguchiandANOVA

anal-yses,anadditionalcontrolexperimenthasbeendoneatthe

optimumparameterstoachievemaximumleachingefﬁciency

ofironandchromiumwithinthedeﬁnedexperimentalframe.

Finally,theeffectsofprocessdurationaswellasthestirring

rateoftheﬂaskontheleachingefﬁciencyhavebeen

investi-gatedandkineticcalculationshavebeenmadetodiscussthe

leachingcontrollingmechanismsofFeandCr,respectively.

2.4. Chemical,morphologicalandstructuralanalyses

Chemicalcompositionoftheferrochromium alloyandthe

solidresidueremainedafterleachinghavebeenanalyzedby

X-rayﬂuorescence(XRF, HitachiX-MET8000, Malvern

Pana-lytical–Epsilon1)andEnergyDispersiveX-rayspectrometer

(EDS,Bruker).Carbonandsulphurcontentoftheprecursor

material(aftercleansing)aredeterminedbyEltraCS800.For

determiningtherecoveriesofironandchromiuminthe

leach-ingsolution,atomicabsorptionspectroscopy(AAS,Shimadzu

AA160)isused.Insampling,tokeepthesolid/liquidratioas

stable,each time5mlofleachate istakenforAASanalysis

andrightafter5mlofsulphuricacidsolution(withthesame

molarity)isaddedintotheleachateatthesametemperature.

Thetakensamplesaredilutedviadeionizedwaterbeforethe

AASanalysis.Therecoveryofmetalsarecalculatedbasedon

Eq.(1)[14];

Recovery(%)=

(MetalinsolutionfromAAS(g/L))

∗ (Leachatevolume(L))

(MetalamountinFe−Cr(%)fromXRF)

∗(InitialFe−Cramount(g)

∗100

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Fig.1–Particlesizedistributionofmilledferrochromium.

Investigationonparticlesizedistributionandmorphology

have been made by Malvern–Mastersizer 3001 and

scan-ning electron microscope (Zeiss Gemini 500), respectively.

Thestructuresofthe precursor alloyand theresidue have

beencharacterizedbyX-raydiffractionmethod(XRD,Bruker

AXS/DiscoveryD8)usingCuK␣astheX-raysources(0.02◦/s,

between2=15◦–90◦).

Finally,thepresenceofCr6+ _in_the_leaching_solution_has

beentestedusingtheColorometricanalysismethod(Standard

Methods–3500–Cr.B)[15].Allchemicalsusedforthis

experi-mentareofanalyticalreagentgrade.Ahexavalentchromium

(Cr6+₎_containing_stock_solution_of₁₀₀_ml_volume_is_prepared

bydissolving141.4mgofpotassiumdichromate(K2Cr2O7)in

distilledwater.Then1mlofthisstocksolutionisdilutedto

100mlbyusingDIwater.ThissampleisnamedasCRM

dur-ingtheanalysis.Inanothervolumetricﬂask,distilledwater

is added (as transparent solution) and named as BLANK.

Finally, the FeCrleachingsolutionisdiluted100times and

addedinto anothervolumetricﬂask,thelatterisnamedas

NUM. The colour chelating agent used for this analysis is

1,5-diphenylcarbazide(DPC,SpecialGrade,Merck).Duringthe

analysis,thestepsdeﬁnedinthestandardarefollowed.

3. Results

and

discussion

3.1. Materials

Thechemicalcompositionoftheprecursormaterialhasbeen

determined byXRF(Table2)and EDSanalyses.Theresults

showthatferro chromiumalloycontainsahighamountof

chromium(∼68%)andiron(∼29%)withtraceamountofother

transitionmetalssuchasMn,CoandNi.

An additionalexperimenthas been conductedto

deter-minethecarboncontentofthepowder.Theresultrevealsthat

theindigenousalloycontains∼5wt.%carbon.

Theparticlesizeanalysisoftheferrochromiumalloy,after

the ball milling,showsthat anaverageparticle size(Dv50)

of2.78␮misachieved,eventually(Fig.1).SEMimagesofthe

milled powder justify the particle sizeanalysis’ result and

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14106

Table2–XRFanalysisofanindigenousferrochromiumalloyandtheresidueafterleaching(el.%).

Fe Co Ni Si Cr Other

Precursor 29.49 0.08 0.54 0.66 68.34 Balance

Residue 14.479 0 0.417 8.77 52.235 Balance

Fig.2–SEMimagesoftheballmilledferrochromiumalloy 10,000×magniﬁcation(4h,235rpm,10:1BPR)(SEMimage atsmallermagniﬁcation(5000×)inupperleft-handis given).

Fig.3–XRDpatternoftheprecursorferrochromiumalloy (redline)andtheresidueafterleaching(blackline).(For interpretationofthereferencestocolorinthisﬁgurelegend, thereaderisreferredtothewebversionofthisarticle.)

XRDresultoftheprecursormaterialshowsthatthemain sourcesofironintheferrochromiumareCrFe(03-065-4528), CrFeC(00-005-0720),Fe2SiO4(01-074-1002)andFe3O4 (01-076-0956).AndthemainsourcesforchromiumareCrFe,CrFeCand Cr7C3(00-036-1482)asgiveninFig.3.Allthosecompoundsare

commonlyencounteredspeciesduringthe characterization

ofthehighcarbon-ferrochromiumalloy[17–21].Moreover,a

smallamountofcalciumcarbonate(01-072-1652)isdetected

inhighcarboncontainedferrochromiumalloywhichis

orig-inatedfrom the productionprocess,asdescribed byNeizel

etal.[18]

3.2. Leachingreactionsoftheferrochromiumwith

sulphuricacid

FeCrisfoundtobehighlyresistanttosulfuricacidleaching.

CapillaandDelgado[22]claimthatwhentheleachingoccurs

at200◦C,it leadssulphatebasedprecipitate formation

fol-lowingtheEq.(2).ThenNadirovetal.[23]haveproposedthat

athightemperature (>80◦C)sulfuricacidleaching,fayalitic

dissolution may happenfollowingEq.(3). Then,Salmimies

etal.[24]havestudiedthesulfuricacidleachingofmagnetite

andindicatedthatmagnetitehasrelativelyhighresistanceto

sulfuricacidleaching(Eq.(4)).Finally,carbidesbeingagood

refractorareknowntoberesistanttosulfuricacidleachingas

statedbyKuznetsovetal.[25].Herein,itisalsoimportantto

mentionthatcalciumcarbonatethatispresentinthe

precur-sortransformsintocalciumsulphatefollowingtheEq.(5),as

suggestedbyHavliketal.[26].

Moreover,Liu etal. [14]havedeﬁnedthe sulphuricacid

reactionofthetraceamountofother transitionmetals(Ni,

Co) thatare present inthe precursor (asdetectedbyXRF),

followingEqs.(6)and(7).

Thepossiblereactionsthatmayoccurduringthe

interac-tionoftheprecursormaterial(ferrochromium)withsulphuric

acidaredescribedbelow(seeEq.(2)–(7))[14,23–28];

CrFe+H2SO4→ FeSO4+Cr2(SO4)3+H2 (2)

2FeO∗SiO2+2H2SO4→ 2FeSO4+H4SiO4 (3)

Fe3O4+4H2SO4→FeSO4+Fe2(SO4)3+4H2O (4)

CaCO3+H2SO4(aq)→ CaSO4+CO2+H2O (5)

H2SO4+Co→ CoSO4+H2 (6)

H2SO4+Ni→ NiSO4+H2 (7)

Additional characterization to detect hexavalent

chromium existence in the leaching solution is done (see

Supplementaryﬁle).ThecolouroftheFeCrleachingsolution

(namedas‘NUM’)isdetectedtobebetweengreenandblue,

whichissimilartoothertrivalentsolutionsgiveninthe

liter-ature[29]anddifferentthanthesyntheticallypreparedCr6+

solution(namedas‘CRM’,pinkincolour).Thisobservation

can be explainedbythe fact that the Cr3+ inthe leaching

solutioncannotbeoxidizedtoadifferentvalencestatedue

to the insufﬁcientoxidationpotentialof sulphuricacid,as

statedpreviouslybyGevecietal.[30].

3.3. Taguchiexperimentalanalysisofleachingprocess

Nine different experiments have been designed following

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Table3–TheparametersandtheresultsofexperimentsbasedonL9(34)Taguchi’sorthogonalarrays. Experiment No. s Molarofacid solution(M) Solid:liquid ratio(vol.) Temperature (◦_C) Rotationrate oftheﬂask (rpm) AASFe (g/L) S/NforFe (db) AASCr (g/L) S/NforCr (db) 1 0.5 1:50 RT 30 10.81 20.67 18.15 25.18 2 0.5 1:100 60 100 9.59 19.64 10.16 20.14 3 0.5 1:200 90 200 9.1 19.19 28.32 29.04 4 2 1:50 60 200 12.38 21.86 36.64 3128 5 2 1:100 90 30 10.82 20.68 36.64 31.28 6 2 1:200 RT 100 7.04 16.95 4.99 13.97 7 5 1:50 90 100 13.1 22.35 38.31 31.67 8 5 1:100 RT 200 9.35 19.42 13.83 22.81 9 5 1:200 60 30 10.03 20.03 31.65 30.01

Fig.4–S/Nvaluesforironof(a)molarity(M);(b)S:L(ml:ml)ratio;(c)temperature(◦C);(d)rotationrateofﬂask(rpm).

each experiment withAAS analysis’ result havebeen pre-sentedinTable3.Inleachingoperation,theamountofmetal

ions is desired to be maximized. Thus, “larger is better”

approach is chosen, accordingly. S/N ratios are calculated

using the Eq. (8), where n represents the total number of

replicationsofeachtestrun;yrepresentstheextractionyield

ofmetals(chromiumandiron)achievedineachexperiment

[32–33].TheS/Ncurvaturesforallparametersincaseofiron

andchromiumhavebeengiveninFigs.4and5(a–d),

respec-tively. S/N=−10∗log

1 n∗ i=0

n

1 yi2

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AnalysisofVariance(ANOVA)isusedtoidentifytheeffect

ofeachparameteronthemetalextractionyields.Themost

effectiveparametersonCrleachingarerevealedtobe:

tem-peratureandrotation rateoftheﬂask(Tables4and5).On

theotherhand,themosteffectiveparametersonFeleaching

arerevealedtobe:solid:liquidratio(vol:vol)andtemperature

(Tables6and7).

Whentheleachingefﬁcienciesofchromiumandironfrom

theindigenous alloyhavebeencalculated,∼73%and∼56%

havebeendetermined,respectively.Thesevalueshavebeen

determined byusingAASresults,according toEq.(1).This

equation isusedinLui etal.[14]work andElbaret al.[7]

work,previously.

Then,byusingEq.(9)atheoreticalcalculationabouttheFe

andCrrecoveriesbasedonTaguchiapproachisdone.“T”refers

totheaverageS/Nratiosofallexperiments,‘C’demonstrates

theestimatedS/Nvaluerelatedtotheoptimumleaching

con-ditions.a3,b1,c3andd1arechosenastheyarethelevelsof

parameterstogetmaximumamountofmetalionsintothe

solution(Figs.4and5).Theestimatedvalue(C)iscalculated

as23.165dband 35.56dbforFeand Cr,respectively. These

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leach-14108

Fig.5–S/Nvaluesforchromiumof(a)molarity(M);(b)S:L(ml:ml)ratio;(c)temperature(◦C);(d)rotationrateofﬂask(rpm).

Table4–ANOVAanalysisofchromium’sleachingfromferrochromiumalloy.

Parameter Degreeoffreedom Sumofsquare Meanofsquare Fvalue

Molarity 2 18.95

Solid:liquid 2 46.97

Temperature 2 154.59

Rotationrateoftheﬂask 2 82.26

Error

Total 8 302.76

Table5–RevisedANOVAanalysisofchromium’sleachingfromferrochromiumalloy.

Temperature 2 154.59 77.30 4.69

Rotationrateoftheﬂask 2 82.26 41.13 2.50

Error 4 65.91 16.48

Total 8 302.76

Table6–ANOVAanalysisofiron’sleachingfromferrochromiumalloy.

Molarity 2 1.17

Solid:liquid 2 12.78

Temperature 2 5.26

Rotationrateoftheﬂask 2 1.02

Error

Total 8 20.22

Table7–RevisedANOVAanalysisofiron’sleachingfromferrochromiumalloy.

Solid:liquid 2 12.78 6.39 11.73

Temperature 2 5.26 2.62 4.82

Error 4 2.18 0.54

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ingsolution,respectively.Anadditionalcontrolexperimentis

conductedat90◦C,30rpm,1:50volumetricsolid:liquidratio

(vol:vol),in5Msulphuricacidsolution,for150mintoconﬁrm

theexperimentalresults.FeandCrconcentrationsinthe

con-trolexperiment’ssolutionaredetectedas13.22±.1.3g/Land

39.0±.0.82g/L,respectively.

C=T+ (a3−T) + (b1−T) + (c3−T) + (d1−T) (9)

Thecorrelationsbetweenthenumericalvaluesobtained

inpursuitofEq.(9)andAASresultsarefoundtobe46%for

chromiumand92%foriron.Thesevalueshaveharmonywith

characterizationsresultsandtheoutcomesgivenintheopen

literature[33–36].

As stated previously, the high resistance of

intermetal-lic and carbide particles to sulphuric acid leaching could

explainthisobservation.Meanwhile,lowleachingkineticof

chromiuminsulphuricacidaswellaspossibleformationof

chromiumsulphateparticles duringleachingprocesscould

representotherreasons[31].Bythesametoken,Gevecietal.

[30]havestatedthatlostinleachingefﬁciencyofchromium

canbeattributedtotheformationofstablechromium

sul-phate layer over the chromium particles during sulphuric

acidleaching.TojustifyourhypothesisXRDanalysisofthe

residuehasbeencarriedout(seeFig.3,blackline).XRDresult

oftheresidueshowingthepresenceofchromiumsulphate

(Cr2(SO4)3) veriﬁes the reaction given as Eq. (2). Moreover,

the presences ofCrFeC, Cr7C3, Fe3O4, Fe2SiO4 and CrFe in

theresiduesubstantiatethefactthatsomeamountof

inter-metallics,carbideandoxide(CrFeC,Cr7C3,Fe3O4,Fe2SiO4and

CrFe) have dissolved, some remain without being leached

[25,31,37].

ChromiumsulphatepeaksidentiﬁedinXRDresults

indi-cate theformation ofanewphase asaresultofleaching.

Previousworkonsulphuricacidleachingofchromium

con-taining particles reveal that upon the leaching reaction

chromiumsulphateformsandcoverstheparticlesurface[30].

When comparing the residue’s and the precursor’s XRF

analysesCaamountisalwaysfoundtobelessthan1%bothin

theprecursorandtheresidue(Table2).And,theamountofFe,

Cr,Ni,Coarenotedtobedecreasedfromtheprecursortothe

residueduetothedissolutionreactionsindicatedinEqs.2–7.

Ontheotherhand,sulphurcontentisfoundtobeincreased

afterleachingoperation(from452ppmto14.095%el.)

follow-ing the sulphate particles’ formation, which isbelieved to

negativelyaffecttheleachingkinetic[28–30].

Furtherdiscussionontheindependentparameters’effect

onFeandCrleachingefﬁcienciesisdonebasedonFigs.4and5.

Figs.4aand5arevealthattheS/Nratiosofmolarityfor

leach-ingofironandchromiumrevealsimilartrends:ﬁrstaslight

thenaremarkableimprovementisnotedwhenacid

molar-ity isincreasedfrom 0.5to 2M, then 2Mto 5M. Ige etal.

[6]havereportedasimilarresultandclaimedthatironion

concentrationintheleachateisincreasedinmore

concen-trated sulphuric acid solutions. This fact is also valid for

chromiumleachingwherehigherchromiumion

concentra-tionisdetectedinmoreconcentratedsulphuricacidsolutions

[6,14].

Ontheotherhand,solid:liquidratioisfoundtobeinversely

interacting with the leaching efﬁciencies ofboth iron and

chromium,asexpected:highersolidamountmeaningmore

availablematerialtobeleachedout,whichresultsinhigher

leachingefﬁciency,eventually(Figs.4b,5b).

Figs.4c,5cdemonstratethattemperaturehasapositive

correlationwiththeironandchromiumconcentrationsinthe

leachate.Anincreaseintemperature(from25◦Cto90◦C)

pro-motestheactivityofatomsandmoleculesintheleachateas

statedinpreviousstudies[6,14],leadinginanincreaseinthe

leachingefﬁciencies.

Finally,therotationrateoftheﬂaskintherotary

evapora-torsystemﬁrstdecreases(from30to100rpm)thenincreases

(from 100 to 200rpm) the leachingefﬁciencies ofiron and

chromium.Possiblechangesatthesolid/liquidinterfaceupon

leachinganddeteriorationofchromiumsulphatelayerover

theparticlesmightexplainthisperformance.

3.4. Kineticanalysisofferrochromium’sleaching

Oncetheoptimumparametershavebeendeterminedto

max-imizetheleachingefﬁcienciesofironandchromium(5M,1:50

s:l(vol:vol)ratio,90◦C,30rpmand150min),additional

exper-imentshavebeenruntokineticallyinvestigatetheprocess.

First,anexperimentattheoptimumconditionsdeﬁnedby

Taguchihasbeenperformedfor360mintoobservethechange

inmetalrecoveriesofCr(redlineinFig.6b)andFe(blackline

inFig.6a)upontheleachingduration.Duringtheexperiment,

12sampleshavebeentakenoutoftheleachingsolutionat

dif-ferenttimelapse(0,1,5,15,60,90,120,150,180,240,300and

360min).BothCrandFerecoverieshavebeennotedtorapidly

increaseintheﬁrst60minofleaching,thenroughlyget

sta-bilizedafter150min.AscrutinylookinFig.6aandbreveal

thatintheﬁrst15min.oftheleachingreaction,the

efﬁcien-ciesincreaseexponentially,thenbetween15and60minthe

efﬁcienciesrisewithdifferentslopes,andﬁnallyfrom60to

150minﬂuctuationsintherecoverieswithapositiveslopeare

observedinFig.6aandb.Thistrendisverysimilartowhathas

beenstatedintheliterature[38].Ruizetal.[38]haveclassiﬁed

thistypeofleachingkineticinthreeparts:induction,

conver-sionandstabilization.Theyhaveexplainedthattheinduction

istheshortestperiodlastingaround20minandafterwards

theconversionhastakenplacewheremetalcomplexing

hap-penedinthesolution,andlastlyatthestabilization,leaching

operationendedwithitshighestrecoveryefﬁciency[38].

Noting that leaching is a heterogeneous reaction that

occursbetweensolidandliquidphases,thereactionbegins

primarilyatthepowder/acidsolutioninterfaceandthe

disso-lutionprogressivelyoccursbyreducingthesizeofthepowder.

Therefore,fortheleachingprocessoftheferrochromiumalloy

(with5%Ccontent),asagreedwithSokicetal.’s[39]study,not

onlythechemicalreactionofsulphateionswiththepowder,

butalsothediffusionoflixiviantspeciesshouldbeconsidered

toexplainthemechanism.Consideringthisfact,the

univer-salformulausedforkineticmodellingofleachingreactionare

reviewedand theR2 ₍_Table₈₎ _values_and_Cross _Correlation

Coefﬁcient(CCC)(Table9)valuesofCrandFerecoveriesat

differenttemperaturesare calculatedaccordingtoS¸en[44].

Herein x, a, t and n stand for metal fraction, initialmetal

amount,time(min)andconstantvalues.

ThemaximumvaluesofR2_,_R2

adjandCCCforFeandCr

(8)

14110

j m a t e r r e s t e c h n o l . 2 0 2 0; 9(6) :14103–14115

Table8–KineticmodelsandthecalculatedR2_,_adjusted_R2_and_mean_of_squares_values_for_Cr_and_Fe_leaching.

Expression Controllingmechanism R2_(adjusted_R2₎ _SSE

Fe45◦C Fe60◦C Fe90◦C Cr45◦C Cr60◦C Cr90◦C Fe45◦C Fe60◦C Fe90◦C Cr45◦C Cr60◦C Cr90◦C Ref. 1−2 3∗x− (1−x)23=_k∗_tn Diffusionthrough productlayer 0.617 (0.5532) 0.8582 (0.8346) 0.6426 (0.583) 0.6408 (0.5809) 0.9241 (0.9114) 0.7384 (0.6948) 0.002863 0.003698 0.007638 0.000704 0.003394 0.01658 [40] ln(a/a-x)=k*tn _Chemical_reaction

controlmodel 0.6766 (0.6227) 0.942 (0.9323) 0.8045 (0.772) 0.762 (0.7226) 0.994 (0.9929) 0.8992 (0.8824) 0.000163 0.000561 0.005114 0.000001 0.000007 0.001160 [41] −ln(1−x)=k*tn _Mixed_model (surfacereaction control;lixiviant diffusionmodel) 0.6784 (0.6248) 0.9392 (0.9290) 0.8357 (0.8083) 0.763 (0.7235) 0.9945 (0.9936) 0.9363 (0.9256) 0.001201 0.005271 0.04945 0.000031 0.000299 0.05841 [39] 1− (1−x)13= k∗tn Chemicalreaction control 0.6755 (0.6237) 0.9409 (0.9310) 0.8213 (0.7915) 0.762 (0.7231) 0.9944 (0.9935) 0.9232 (0.9104) 0.000130 0.000503 0.004668 0.000003 0.000031 0.005820 [42] 1− (1−0.45∗x)13 = k∗tn Surfacereaction controlbyshrinking coremodel 0.6764 (0.6225) 0.9421 (0.9324) 0.802 (0.769) 0.7623 (0.7227) 0.9941 (0.9931) 0.9044 (0.8884) 0.000026 0.000087 0.000785 0.000001 0.000006 0.001038 [43] 1− (1−x)23₌ k∗tn Shrinkingcore model(Film diffusion control-dense-shrinking model) 0.6726 (0.618) 0.9387 (0.9285) 0.7398 (0.6964) 0.7610 (0.7212) 0.9912 (0.9898) 0.8464 (0.8208) 0.000468 0.001159 0.008566 0.000014 0.000141 0.01272 [42]

(9)

Fig.6–Recovery-timegraphsof(a)ironand(b)chromium.

Table9–KineticmodelsandthecalculatedCCCvaluesforCrandFeleaching.

Expression Controllingmechanism Fe45◦C Fe60◦C Fe90◦C Cr45◦C Cr60◦C Cr90◦C Refs. 1−2

3∗x− (1−x) 2

3₌_k_∗_tn _Diffusion_through_product_layer _0.6875 _0.8106 _0.7013 _0.7002 _0.8411 _0.7518 _[40]

ln(a/a-x)=k*tn _Chemical_reaction_control_model _0.7209 _0.8494 _0.7850 _0.7643 _0.8723 _0.8297 _[41]

−ln(1−x)=k*tn _Mixed_model_(surface_reaction

control;lixiviantdiffusionmodel

0.7207 0.8480 0.7999 0.7650 0.8726 0.8467 [39]

1− (1−x)13 =_k∗_tn Chemicalreactioncontrol 0.7211 0.8488 0.7930 0.7617 0.8726 0.8407 [42] 1− (1−0.45∗x)13=_k∗_tn _Surface_reaction_control_by

shrinkingcoremodel

0.7206 0.8493 0.7834 0.7679 0.8725 0.8321 [43]

1− (1−x)23 =_k∗_tn _Shrinking_core_model_(Film

diffusioncontrol-dense-shrinking model)

0.7175 0.8478 0.7526 0.7599 0.8712 0.8050 [42]

(10)

14112

j m a t e r r e s t e c h n o l . 2 0 2 0; 9(6) :14103–14115

Table10–CalculatedR2_,_R2_adj_and_SSE_values_for_different_n_(n₌_1-0.3)_in_kinetic_expression_of_this_study.

nvalues R2_(R2_adj) _SSE

Fe45◦_C _Fe₆₀◦_C _Fe₉₀◦_C _Cr₄₅◦_C _Cr₆₀◦_C _Cr₉₀◦_C _Average ofFe Average ofCr Fe45◦_C _Fe₆₀◦_C _Fe₉₀◦_C _Cr₄₅◦_C _Cr₆₀◦_C _Cr₉₀◦_C _Average ofFe Average ofCr 1 0.6784 (0.6248) 0.9392 (0.9290) 0.8357 (0.8083) 0.763 (0.7235) 0.9945 (0.9936) 0.9363 (0.9256) 0.8178 (0.7874) 0.8979 (0.8809) 0.001201 0.005271 0.04945 0.000031 0.000299 0.05841 0.0186 0.0196 0.9 0.6921 (0.6491) 0.9356 (0.9249) 0.8594 (0.8360) 0.7720 (0.734) 0.9939 (0.9929) 0.9514 (0.9433) 0.8290 (0.8033) 0.9058 (0.8901) 0.001150 0.005576 0.04230 0.000030 0.000330 0.04455 0.0163 0.0150 0.8 0.7078 (0.6591) 0.9306 (0.9191) 0.8841 (0.8648) 0.7819 (0.7455) 0.9905 (0.9889) 0.9650 (0.9592) 0.8408 (0.8143) 0.9125 (0.8979) 0.001091 0.006010 0.03488 0.000028 0.000517 0.03204 0.0140 0.0109 0.7 0.7259 (0.6803) 0.9238 (0.9111) 0.9095 (0.8944) 0.7928 (0.783) 0.9833 (0.9805) 0.9764 (0.9725) 0.8531 (0.8286) 0.9175 (0.9120) 0.001023 0.006604 0.02723 0.000027 0.000909 0.02163 0.0116 0.0075 0.6 0.7470 (0.7048) 0.9143 (0.9001) 0.9353 (0.9246) 0.8049 (0.7724) 0.9708 (0.9660) 0.9841 (0.9814) 0.8655 (0.8432) 0.9199 (0.9066) 0.000945 0.007423 0.01946 0.000025 0.001588 0.01459 0.0093 0.0054 0.5 0.7710 (0.7329) 0.9008 (0.8842) 0.9605 (0.9539) 0.8176 (0.7872) 0.9503 (0.9421) 0.9854 (0.983) 0.8774 (0.8570) 0.9178 (0.9041) 0.000855 0.008598 0.01188 0.000024 0.002702 0.01334 0.0071 0.0054 0.4 0.7967 (0.7629) 0.8795 (0.8594) 0.9818 (0.9788) 0.8282 (0.7996) 0.9164 (0.9024) 0.9749 (0.9707) 0.8860 (0.8670) 0.9065 (0.8909) 0.000759 0.01044 0.005472 0.000108 0.004551 0.02301 0.0056 0.0092 0.3 0.8178 (0.7974) 0.8409 (0.8144) 0.9893 (0.9875) 0.8282 (0.7998) 0.8564 (0.9325) 0.9391 (0.929) 0.8827 (0.8654) 0.8746 (0.8871) 0.000681 0.01378 0.003216 0.000022 0.007814 0.05580 0.0059 0.0212

(11)

Fig.8– Kineticcurvesofsulphuricacidleachingof(a)iron;(b)chromium.

Fig.9–lnK−1/Tplots(a)iron;(b)chromium.

isused(n=1).Additionally,SSEvaluesarealsocalculated(see

Table8).Theresultsagreewiththeliterature’soutcomeand

conﬁrmthat[39]bothsurfacereactionandlixiviantdiffusion

tosolidparticlesareimportantinleachingofferrochromium

alloy.Tofurthersupportthisobservation,experimentsatthe

optimumleachingconditions withdifferentﬂask’srotation

rates(0,30and60rpm)havebeenconducted(Fig.7aandb).

Thestagnantacid solutionyieldstheworstefﬁciency.Such

behaviourhasbeenalsoobservedinLuietal.’s[14]work.Fig.7a

andbdemonstratethatthedifferenceintheleaching

efﬁcien-cies(recovery%)atthedifferentﬂask’srotationratesisalways

lowerthan 40%,whichsubstantiatesthe effectofchemical

reactiononleaching[39]mechanism.

Toevaluatethe leachingmechanism indetail,ﬁtting of

kineticmodelcouldbemadebymodifyingnvalueinthe

for-mula−ln(1−x)=k*tn_._If_n_is_near_to_1,_the_reaction_is_described

asanidealchemicalreactioncontrol,thenwhennvalueis

equaltoorlowerthan0.5diffusioncontrolmechanism

over-comes.Thecalculationsdemonstratethatthehighestaverage

R2_(and_R2

adj)andCCCvalues(for45◦C,60◦Cand90◦C)are

achievedwhenn=0.4isused(R2:0.886)foriron(Fig.8a),and

n=0.6isutilizedfor(AvergaerAR2_:_0.9199)_chromium_leaching

(Fig.8b)whichcouldbeseeninTable10.

Further, activation energy of each leaching reaction is

calculated based on Arrhenius equation (Eq. (10)). EA, R

and T stand for activation energy (kJ/mol), gas constant

(8.314J/molK)andtemperature(K)respectively.

lnK=lnA− EA

R∗T (10)

FollowingEq.(10)theactivationenergiesarecalculatedas

46.12kJ/moland142.8kJ/molforironandchromiumleaching

(Fig.9),respectively.Theseenergyvaluesshowresemblance

withtheactivation energiesreportedintheopenliterature

[14,36,45].

4. Conclusion

Theoutcomesofthisstudycanbesummarizedasfollows:

- Fortheﬁrsttimeintheopenliterature,anindigenousferro

chromiumalloywith5%Ccontentisleachedwithsulphuric

acidinarotaryevaporatorsystem.

- The optimizationof the leachingprocess is achievedby

Taguchiexperimentaldesign.Then,furtherkineticanalysis

isrealizedtodiscusstheleachingmechanismindetail.

- The highest efﬁciency is achieved when FeCr alloy is

leachedin5Msulphuricacidsolutionwith1:50

volumet-ricsolid:liquidratioat90◦Cfor150min,withaﬂaskrotation

speedof30rpm.Leachingefﬁcienciesofironandchromium

arefoundtobe∼56%and∼73%,respectively.Thereason

ofsuchefﬁciencyisbelievedtoberelatedtotheexistence

ofcarbides(CrFeC,Cr7C3,),ironsiliconoxide(Fe2SiO4)and

CrFeintermetallicsintheprecursorand theformationof

chromium sulphate ((Cr2(SO4)3)particles duringleaching

process.

- ANOVA analysisreveals that volumetricsolid:liquidratio

(vol:vol)andtemperatureareimportantparametersforiron

leaching;whereasinthecaseofchromiumleaching,

rota-tion rate of the ﬂask and temperature are found to be

signiﬁcantparameters.

- Thekineticinvestigationofferrochromiumleachingshows

thatbothleachingofironandchromium havebeen

con-trolledbysurfacereactionandlixiviantdiffusionthrough

(12)

14114

arecalculatedtobe:46.12kJ/molforironand142.8kJ/molfor

chromium.

Conﬂicts

of

interest

The authors declare that they have no known competing

ﬁnancialinterestsorpersonalrelationshipsthatcouldhave

appearedtoinﬂuencetheworkreportedinthispaper.

Acknowledgements

The authors would like to greatly acknowledge

TUBITAK/Turkey (Project No: 218M768) for ﬁnancial

sup-port.TheauthorsthankEtiKromA.S¸.forsupplyingthealloy.

Theauthors thank Prof.Dr.Süheyla Aydın, Prof.Dr. Özgül

Keles¸ (IstanbulTechnicalUniversity)andOnurC¸etin(Arc¸elik

Global)fortheirhelpsincharacterizations.

Appendix

A. Supplementary

data

Supplementarydataassociatedwiththisarticlecanbefound,

intheonlineversion,atdoi:10.1016/j.jmrt.2020.09.133.

r

e

f

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n

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Leaching of iron and chromium from an indigenous ferro chromium alloy via a rotary evaporator: Optimum conditions determination and kinetic analysis

Original

Article

Leaching

of

iron

and

chromium

from

an

indigenous

ferro

chromium

alloy

via

a

rotary

evaporator:

optimum

conditions

determination

and

kinetic

analysis

Mehmet

Feryat

Gülcan

,

Billur

Deniz

Karahan

,

Sebahattin

Gürmen

a

r

t

i

c

l

e

i

n

f

o

a

b

s

t

r

a

c

t

14104

1.

Introduction

2.

Experimental

3.

Results

and

discussion

14106



leach-14108

14110

14112

4.

Conclusion

14114

Conﬂicts

of

interest

Acknowledgements

Appendix

A.

Supplementary

data

r

e

_,

_Billur

_Deniz

_Karahan

_,

_Sebahattin

_Gürmen