Dissolution of pure chalcopyrite with manganese nodules and waste water

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Pleasecitethisarticleinpressas:ToroN,etal.Dissolutionofpurechalcopyritewithmanganesenodulesandwastewater.JMaterResTechnol.

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Original Article

Dissolution of pure chalcopyrite with manganese nodules and waste water

Norman Toro

^a,b,^∗

, Kevin Pérez

^a

, Manuel Salda ˜na

^a

, Ricardo I. Jeldres

^c

, Matías Jeldres

^c

, Manuel Cánovas

^a

aDepartamentodeIngenieríaMetalúrgicayMinas,UniversidadCatólicadelNorte,Antofagasta,Chile

bDepartmentofMining,GeologicalandCartographicDepartment,UniversidadPolitécnicadeCartagena,Murcia,Spain

cDepartamentodeIngenieríaQuímicayProcesosdeMinerales,FacultaddeIngeniería,UniversidaddeAntofagasta,Antofagasta 1240000,Chile

a r t i c l e i n f o

Articlehistory:

Received4September2019 Accepted10November2019 Availableonlinexxx

Keywords:

Leaching CuFeS2

Chloridemedia MnO₂

a bs t r a c t

Chalcopyriteisthemostabundantcopperoreand,consequently,themostutilisedtopro- ducemetalliccopper.Themainrouteoftreatmentisthroughpyrometallurgicalprocesses, buttheseemitsignificantquantitiesofSO2intotheatmosphere(e.g.182,000t/yearamongall Chileansmelters),producingmightyconcerninthecommunity.Inthiscontext,hydromet- allurgyispresentedasanalternativethatmaybemoreenvironmentallyfriendly;however, thedifficultiesofprocessingsulphidemineralspreventachievingsustainableefficiencies fortheindustry.Inthisresearch,apurechalcopyritemineralisleachedat25^◦Cwiththe additionofmanganesenodulesasanoxidizingagent,andwastewaterwithahighcon- centrationofchloridethatbothenhancesthedissolutionandavoidthepassivationofthe chalcopyrite.ThehighconcentrationsofMnO2(4/1and5/1)allowsthatthepotentialvalues canbebetween580and650mV,whichfavorsthedissolutionofCuFeS2.TheXRDshowed theformationofnon-pollutingspeciesand,besides,theydonotcauseobstaclestothecop- perdissolution.Highconcentrationsofchlorideenableincreasingcoppersolutionsfrom CuFeS2,attainingfavorableoutcomeswhenworkingwithwastewaterinsteadofseawater.

1. Introduction

Chalcopyrite is the most abundant copper mineral in the world[1–3], representing nearly70 % ofthe reserves[4–6].

For this reason, this copper mineral is the most adopted

∗ Correspondingauthor.

E-mail:[email protected](N.Toro).

toprovide metalliccopper [7].Currently, around80–85%of theworld’scopperproductionisconductedbyconventional pyrometallurgicalmethods,whichconsistsofflotation,smelt- ing,refining,andelectrorefining[8].However,despitethehigh levelsofproduction,deepconcernsariseaboutthesignificant emissions ofsulfurdioxide causedbytheseoperations;for example,theChileansmeltersproduceabout188ktofSO2per year[9].Inthiscontext,extendinghydrometallurgytosulfide mineralsispresentedasapromisedoptiontoreduceenviron-

https://doi.org/10.1016/j.jmrt.2019.11.020

creativecommons.org/licenses/by-nc-nd/4.0/).

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mentalimpacts[10];however,theperplexityliesinthelow efficiencyoftheoperations,especiallyatroomtemperature andatmosphericpressure[11].Diversestudieshavebeencar- riedoutfortherecoveryofcopperfromchalcopyriteinacid mediautilisingvariedoxidisingagentssuchasdissolvedoxy- gen[12,13],ferricchloride[14–16],ferricsulfate[17,18],cupric ions[19],andmanganesenodules[20,21].

Polymetallicnodules,calledmanganesenodulesaswell, arerockconcretionsformedbyconcentriclayersofFeandMn hydroxides[22].Theseareagoodalternativefortherecovery ofMn,whichisessentialfortheproductionofsteel[23–25].

Itseconomicinterestisduetothehighgradesofbase,critical, andraremetals[26,27],suchasCo,Ni,Te,Ti,Pt,andrareearth elements[28].

Inprevioustrials[20,21,29],itwasdisclosedthatMnO2isa goodoxidizingfortheleachingofchalcopyriteinacidmedia, especially atHCl concentration ranges between 3−4mol/L.

Threeroutes were discoveredforthe copperdissolution of copper:(i)thegalvanicinteractionbetweenchalcopyriteand MnO2,(ii)theactionoftheFe³⁺/Fe²⁺ratio,and(iii)theactionof chloridegasformedbythereactionbetweenMnO₂andHClin chalcopyrite.Beside,Havliketal.[21]gottenlowcoppersolu- tionsfor3mol/LHCl,indicatingthattheoptimalresultsmay bereachedat4mol/LHClandaratioof4/1MnO2/CuFeS2.

Several investigationshave reportedthat chloridestabi- lizescuprous ionsformingsolublecomplexesthatimprove chalcopyritedissolution[12,30–32].Thereason,leachingwith sulfuricacidandsodiumchlorideformsporouscrystalsofsul- furonthemineralsurfaceratherthanalayerofpassivesulfur thatblockstheflow[33,34].

Theproposedreactionforchalcopyriteleachingwithman- ganesenodulesisnextexpressed:

CuFeS_2(s)+2MnO_2(s)+8H⁺_(aq)+5Cl⁻_(aq)

=2Mn²_(aq)⁺ +4H₂O_(aq)+CuCl⁻_2(aq)+FeCl_3(s)+2S⁰_(s) (1)

G⁰ =−202.6kJ

Ca²_(aq)⁺ +SO²_4(aq)⁻ =CaSO_4(s) (2)

G⁰ =−28.0kJ

TheMn⁴⁺ (MnO2)presented in the manganese nodules wasusedastheoxidizingagent.Eq.(1)describesthecopper dissolvinginasulphate-chloridemedium,owingtothesulfu- ricacidandthehighpresenceofchloride(wastewater).The principalbenefitsofleachinginachlorinatedenvironment arerelatedto:i)enhancedleachingkinetics,ii)generationof elementalsulfurandnotresidualsulfate,andiii)thecupric and/orcuprous ions are stableas chloridecomplexes. The GibbsfreeenergyofEq.(1),beingnegative,isconsideredspon- taneousundernormalconditions, allowingastablecopper productand anon-contaminating elementalsulfurresidue.

Whilethecalciuminbothwastewaterandmanganesenod- ulesreactswiththesulfate(Eq.(2)),insolublecalciumsulfate isformedbecausethecationprecipitateswhenitcomesinto contact with sulfate, nitrates, and other elements. Eq. (1)

showsa2/1MnO2/CuFeS2ratioforleachingcopperusingman- ganesenodulesasanoxidizingagent,butthebestconditions toleachcopperisata4/1MnO2/CuFeS2ratio.Thevaluesof theGibbsfreeenergywerecalculatedusingthesoftwareHSC 5.1(OutotecCompany,Espoo,Finland).

Overall, the studies attest that mixing intensity instir- ring reactorswithchloridemediadoesnotalterthe rateof copperdissolution[35].Otherresearchesindicatedthatmix- ingdoesnotaffectoxidizationofchalcopyrite[30,36,37].The explanationisthatthedissolutionspeedisnotcontrolledby masstransferthroughtheliquidborderlayer[30].Otherwise, someauthorsstatedpositiveresultsindissolvingcopperfrom CuFeS2byincreasingstirringspeed[11,38].

Theoceansandothersalinewatersarethemostsignifi- cantwaterresourceontheplanet,representing97.4%ofthe availablewater.Theadditional2.5%forfreshwaterincludes 1.7%inthepolaricecapsandglaciers,makingitdifficultto use.Traditionalsources(groundwater,lakes,wetlands,rivers, amongothers)areonly0.8%[39].Theshortageoffreshwateris morenoticeableinaridareas,whereitbecomesaneconomic, environmentalandsocialproblem[40],especiallygiventhe demandofthelarge-scaleminingforthisresource. Mining isthefourthlargestconsumerofwaterinChile,occupying3

%ofthetotal.Thefirstuserisagriculture,whichrequires82

%;thenhumanconsumptionwith8%;andtheremaining7

%isforindustriesotherthanmining.Totalminingoccupied 14.9m³/sin2016,being13.6m³/sutilisedbycopper,smelters, andrefineries,whileothermineralsconsumed1.3m³/s,such as gold, iron, silver,polymetallic, and non-metallic mining [41].TheGeneralWaterDirectorateextendedtheprohibition zonesforwaterextraction,restrictingthewaterrightsformin- ing companies. Besides, authorities inChile indicated that large-scale miningprojectswouldnotbelongerauthorized forusingwaterfromaquifers.Thispromptedthenewfacili- tiestoconsiderseawaterordesalinatedwater[42],especially inthenorthofthecountry[43].Therefore,itisvitaltofind newalternativesthatcanimprovewateravailability,wherein avalidoptionisassociativitybetweenminingcompaniesand desalinationplants.

Inthepresentresearch,theleachingofchalcopyritewas studied,consideringmanganesenodulesasanoxidisingagent and the reuse ofwastewaterwithahigh chloridecontent.

Varied MnO₂/CuFeS₂ proportions, mixing intensity, H₂SO₄ concentration,andchlorideconcentrationwereexamined.

2. Materials and methods

2.1. Chalcopyritemineral

The sample of chalcopyrite was obtained from Minera Michilla,locatedinAntofagasta(northofChile).Thesample wastakenselectivelyfromacopperdeposit(800g)andthen crushed ina porcelainmortartoget asize rangebetween 38 and 47␮m (−47+38␮m).Weremoved the impuritiesby hand (withthehelpofamicroscope).Thehomogenisation ofthematerialwasdonebysamplingtechniques,selecting a representative fractionof40g(20gforchemical analysis and 20g for mineralogical analysis). The chemical analysis was performed by atomic emission spectrometry via

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Table1–Chemicalanalysisofchalcopyrite.

Component Cu Fe S

Mass(%) 33.89 30.62 35.49

induction-coupledplasma(ICP-AES),developedintheApplied GeochemistryLaboratoryoftheDepartmentofGeologicalSci- encesoftheUniversidadCatólicadelNorte.Table1showsthe chemicalcompositionofthesamples.

Inaddition,thesamplewasanalyzedmineralogicallyusing aBrukerbrandX-raydiffractometer,automaticandcomputer- izedmodelofD8.Accordingtotheinitialqualitativeanalysis ofXRD,theprimarymineralphasepresentinthesampleswas chalcopyrite,whichshowed99.9%purity,and whosemain peaksare at29,372,48,975and 48,684^◦. Thesepeaks corre- spondto those giveninthe reference pattern PDF35-0752 (ICDD,2004).Fig.1givestheresultsthatindicateapurityof 99.90%.

2.2. Manganesenodules(MnO2)

Themanganesenodulewascollectedduringthe1970sfrom thedeepoceanontheBlakePlateau(AtlanticOcean).Thesam- plewascrushedwithaporcelainmortartoreachaparticlesize between53and75␮m(−75+53␮m).Themineralogicalcom- positionispresentedinTable2.Thematerialwasanalyzed usinga Bruker® tabletopM4-Tornado ␮-FRX(Fremont,CA, USA).Theinterpretationofthe␮-XRFdatashowsthatthenod- uleswerecomposedbyfragmentsofpreexistingnodulesthat formedtheirnucleus,withconcentriclayersthatprecipitated aroundthenucleusinlaterstages.

2.3. Reactantandleachingtests

Thesulfuricacid(MerckMillipore)usedfortheleachingtests hadanalyticalgrade,purity95–97%,anddensity1.84kg/L.The wastewaterfromAguasAntofagastaDesalinationPlanthada concentrationof39.16g/Lofchloride.Tables3and4showsthe chemicalcomposition ofwastewaterand seawater, respec- tively.

Leachingassayswereconductedina50mLglassreactor witha0.01S/Lratio.Atotalof200mgofchalcopyriteandMnO2

(Manganesenodules)atdifferentconcentrationsweremain- tainedinsuspensionwitha5-positionmagneticstirrer(IKA ROS,CEP13087-534,Campinas,Brazil)at600rpm.Thetem- peraturewascontrolledat25^◦Cwithanoil-heatedcirculator (Julabo).Alltestswere triplicated,and measurementswere carriedoutin5mLundilutedsamples,usingatomicabsorp- tionspectrometrywithacoefficientofvariation≤5%,and arelativeerrorbetween5and10%.MeasurementsofpHand oxidation-reductionpotential(ORP)ofleachingsolutionswere madeusingapH-ORPmeter(HANNAHI-4222).TheORPsolu-

Table3–Chemicalcompositionofwastewater.

Compound Concentration(g/L)

Fluoride(F-) 0.002

Calcium(Ca²⁺) 0.8

Magnesium(Mg²⁺) 2.65

Bicarbonate(HCO3−) 1.1

Chloride(Cl⁻) 39.16

Calciumcarbonate(CaCO3) 13

Table4–Referencecompositionofseawater(datafrom CisternasandGálvez[39]).

Solute g/kgofsolution Solute g/kgofsolution

Na⁺ 10.78145 Br- 0.06728

Mg²⁺ 1.28372 CO32- 0.01434

Ca²⁺ 0.41208 B(OH)4- 0.00795

K⁺ 0.3991 F- 0.0013

Sr²⁺ 0.00795 OH- 0.00014

Cl⁻ 19.35271 B(OH)3 0.01944

SO42− 2.71235 CO2 0.00042

HCO3− 0.10481 Total 35.16504

tionwasmeasuredusingaredoxelectrode(internalAg/AgCl withelectrolyte3.5mol/LKCl).

2.4. EffectontheMnO2/CuFeS2ratio

Inpreviousstudies,itwasdemonstratedthatathighercon- centrationsofMnO2concerningCuFeS2,betterextractionsof coppercanbeobtainedfromchalcopyrite[20,29].

ThisresearchseekstooptimizetheMnO₂/CuFeS₂ratiofor the leachingofchalcopyriteinchloridemedia.Theworkis donewithaparticlesizeof−47+38␮mforchalcopyrite,and

−75+53␮mformanganesenodule,usingvariedproportions ofbothsamples,20mLofleachingsolution (1MofH₂SO4), 39.16g/Lofchloride,600rpm,and25^◦C.

2.5. Effectofmixing

The present work investigates the effect mixing intensity (200–1,000rpm)onthecopperdissolutionratefromchalcopy- rite, consideringa5/1ofMnO2/CuFeS2ratio, 1MofH₂SO4, 39.16g/Lofchloride(wastewater),and25^◦C.

2.6. EffectofH2SO4

Differentconcentrations ofH2SO4 were evaluatedforchal- copyrite leachingusingMnO2.Weworkedatachalcopyrite particle size of −47+38␮m and manganese nodule of

−75+53␮matdifferentconcentrationsofsulfuricacid(1,2, and 3mol/L),aMnO2/CuFeS2 ratioof5/1,600rpm,20mLof leachingsolutionandtemperatureof25^◦C.

Table2–Mineralogicalanalysisofthemanganesenodule.

Component MgO Al2O3 SiO2 P2O5 SO3 K2O CaO TiO2 MnO2 Fe2O3

Mass(%) 3.54 3.69 2.97 7.20 1.17 0.33 22.48 1.07 29.85 26.02

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Fig.1–X-raypowderdiffractionpatternsforthechalcopyrite.

Fig.2–EffectoftheMnO₂/CuFeS₂ratioonCuextraction (25^◦C,CuFeS₂size:−47+38␮m,MnO₂size:−75+53␮m, 1mol/LH2SO4and39.16g/Lofchloride).

2.7. Effectondifferentchlorideconcentrations

Theeffectofchloridewasevaluatedforchalcopyrite parti- clesizeof−47+38␮mandmanganesenoduleof−75+53␮m, aMnO2/CuFeS2 ratioof5/1,600rpm,aH2SO4concentration of1mol/L, and differentchlorideconcentrations (seawater:

20g/Landwastewater:39.16g/L).

3. Results and discussion

3.1. EffectontheMnO2/CuFeS2ratio

Fig. 2 shows the evolution of copper dissolution from chalcopyriteatdifferent MnO2/CuFeS2 proportions. Forlow MnO2/CuFeS2(2/1),passivationofthemineralappeared,and littleCusolutionswereobtained(31%in400min).Forthe3/1 ratio,therewasaconsiderableincreaseintheCuextractions (approximately10%)butstillslowkineticsofdissolution.In

bothpreviousconditions,thelowcopperextractionsweredue toadeficientamountofoxidisingagent(Mn⁴⁺)foritsdisso- lution.Thebestresultsforthisinvestigationwereobtainedat the4/1and5/1ratios,whereCusolutionsof68and77%were sequentiallyachievedat400min.TheresultsagreewithHav- liketal.[21],whoindicatedthatMnO2/CuFeS2at4/1present good outcomesforthedissolution ofCufrom chalcopyrite.

However,inthisstudy,itwasnotedthat4/1isanoptimum fordissolutionandoverthisproportion,nohigherextractions couldbegotten.Itshouldberemarkedthat,unlikeprevious studies [20,21],the chalcopyrite usedhere hadhigh purity.

Dutrizac[30]statedthechallengeofdeterminingtheeffects ofadditiveswhenworkingwithchalcopyriteinchlorinated media,sincesmallamountsofsecondarycoppermineralisa- tionsmayaffecttheinterpretationoftheresults.Then,itcan beestablishedthatourdissolutionisspecificforchalcopyrite.

Fig. 3showsthe potentialforthetestsperformedinFig.2.

ForthelowerMnO2/CuFeS2ratios(2/1and3/1),lowerpoten- tialwereobtained(between500−570mV),whilehavinghigher contentsofMnO₂thepotentialswerebetween580–650mV.For alltheexperimentalassays,thepHrangedbetween-0.6and 1.5.TheseresultsagreewiththestudyofVelásquez-Yévenes etal.[13].Theauthorsworkedwithachalcopyrite,concen- tratedinchloridemedia,andconcludedthatthebestpotential windowinwhichthechalcopyritedissolutionrateislinearis between550and620mV.Additionally,theauthorsindicated that athigh concentrationsofchloride,the potentialrange mightincrease.

3.2. Agitationevaluation

Fig. 4 shows that the stirringpromotes the copper extraction.Thebestresultswereobtainedat800rpm(54%copper extraction);however,theextractionrateat600rpmisnotsig- nificantly differing (52%). This concurs withother studies [13,18]wherethemixingintensitydidnotaffectthecopper

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Fig.3–EffectofthepotentialinthesolutionofCuatdifferentratiosofMnO₂/CuFeS_2.

0 10 20 30 40 50

0 20 40 60 80 100

200 rpm 400 rpm 600 rpm 800 rpm

Fig.4–Effectofmixingonthecopperextraction(25^◦C, MnO2/CuFeS2ratioof5/1,chalcopyritesizeto−47+38␮m, 1mol/LH2SO4and39.19g/Ldecloruro).

dissolutionratefromchalcopyrite.Moreloweringdissolution rateswereobtainedwithsloweragitation(200and400rpm), whereinnotall the particlesremained insuspension,hav- ingasignificantinfluenceontheresults.Velásquez-Yévenes [35]pointedoutthatoncekeepingthemineralparticlesdis- persed(nearto600rpm),themixingintensitydoesnotplay asignificant role incopper extraction.Ultimately, the copperdissolution rateat1000rpmwasbelowthatreachedat 800rpm.ThiscoincideswithSokicetal.[44]whofoundthat thechalcopyriteleachingratedeclinedslightlybyanincrease inmixing,sincealessenedcontactoccursbetweentheparti- clesandtheoxidant.Also,extremelyhighagitationmakethe mineralparticlesadheretothereactorwall[22].

3.3. EffectofH2SO4

Fig.5showsthedissolutionofchalcopyriteintimewiththe additionofMnO2andCl-atdifferentconcentrationsofH2SO4. Astheconcentrationoftheacidincreases,thecoppersolu- tionsenhance.For1mol/L,thefinalextractionofCuwas47%.

For2mol/L,therewasanincreaseof6%;however,for3mol/L, therewasnosignificantincreaseinthecopperextractionfrom chalcopyrite.TheseresultsinFig.5and thosepresentedin Fig.2,indicatethatitisnotnecessarytohaveahighconcen- trationofH₂SO₄whilehavinghighratiosofMnO₂/CuFeS₂and chloride.

Fig.5–Effectontheacidconcentrationinchalcopyrite leachingwiththeadditionofMnO₂(25^◦C,CuFeS₂size:

−47+38␮m,MnO2size:−75+53␮m,MnO2/CuFeS2to4/1 and39.16g/Lchloride).

0 10 20 30 40 50 60 70 80

0 100 200 300 400 500

H2SO4 sea water waste water

Fig.6–Effectonthechlorideconcentrationintheleaching ofchalcopyritewiththeadditionofMnO2(25^◦C,CuFeS2

size:−47+38␮m,MnO₂size:−75+53␮m,MnO₂/CuFeS₂to 5/1andH₂SO₄concentrationof1mol/L).

3.4. Effectofdifferentchlorideconcentrations

Fig.6showstheeffectonchlorideconcentrationforleach- ingchalcopyritebyaddingMnO₂asanoxidizingagent.The bestresultswereobtainedwhenworkingwithhighconcentra- tionsofchloride(wastewater,39.19g/Lofchloride)achieving

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Fig.7–X-raypowderdiffractionpatternsfortheresiduemineralafterbeingleachedwithwastewaterat25^◦Cinatimeof 90min.CuFeS2size:−47+38␮m,MnO2size:−75+53␮m,MnO2/CuFeS2to5/1and39.16g/Lchloride).

Fig.8–X-raypowderdiffractionpatternsfortheresiduemineralafterbeingleachedwithH2SO4at25^◦Cinatimeof90min.

CuFeS₂size:−47+38␮m,MnO₂size:−75+53␮m,MnO₂/CuFeS₂to5/1and39.16g/Lchloride).

extractionsof 77 % Cu atthe end of the experiment. The outcomesmatcheswiththeresearchofDevietal.[20],who achievedCuextractionsofupto77%after60min,although withhigherconcentrationsofHCl(4mol/L).Havliketal.[21]

gotbettercopperextractionwhileincreasingtheconcentra- tion ofHCl upto4Mol/L, butfurtherlevelsled toadecay ofCuremoval.Cusolutionsdecrease(71%)whenworkingat lowerconcentrationsofchloride(seawater),whatagreeswith whatwasexpected:theloweramountofchloride,thelower theextractionofCu.Inthecaseofleachingwithwastewa- ter,thesolutionwasnotnegativelyaffectedbythepresence ofimpurities, nor was it affected by contaminants contri- bution from the manganese nodules. According to several authors,phosphate precipitates and formscoatings inthe sulfidesgeneratingpassivation, butinthis case,itwas not a retardantin the dissolution of copper [45,46]. When not addingchloride,thedissolutiondecreasesand,besides,there wasatendencytopassivationafter90min.Thisispossibly becausethechlorideionspromotetheformationoflongsul- fidecrystals.Then,thereactantspenetratethesulfidelayer, preventingthepassivationofthemineral[47].Infutureworks, itisnecessarytostudythe optimalratios ofMnO2/CuFeS2, H2SO4andchloride.Moreover,itwouldbeinterestingtoeval- uateotherindustrialwatersthathavehighconcentrationsof chloride.

3.5. Mineralogyoftheresidue

Fig. 7shows anx-ray diffractogram ofthemineral residue thatwasleachedwithwastewater.Itwasfoundthatthecal- ciumprecipitateintheformofsulfate,butitdidnotaffectthe copperextraction(comparingwithseawaterinFig.6).Thecop- perremainingintheresiduewasintheformofchalcopyrite (approximately 20mg), whilesmall quantitiesofelemental sulfidewereestablishedasastableresidue.Therestwascom- posedofmagnesiumoxideand manganese,wherethe last oneisofinterestsinceitistheoxidizingagent.InFig.8,the residuesthatworkedwithH2SO4wereanalyzed,withoutthe additionofchloride(Fig.6).Itwasfoundthattheremainingis mostlycomposedofchalcopyriteandpyrolusite(MnO2).The unreactedchalcopyriteisexplainedbypassivationsinceatnot havingchloride,afilmofsulfurashcancoverthemineralsur- face. Thislayerpreventsthecontactbetweentheoxidizing agentwithcopper,mitigatingitsreaction.Hematiteresidues werealsofoundfrommanganesenodulesusedasanoxidizing agent.Dutrizac[31]explainedthemorphologicalformations ofsulfuraround achalcopyritemineral leachedwithFeCl₃ and HCl.It was observedgranular formations, hemispher- icalglobules, crystallisedaggregates,and irregular globular masses,whichtendtocovertheentiremineralsurface.How- ever, the crystal formation has enoughspace toallow the

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leachingsolutiontoenterintothemineral.Havliketal.[14]

leached chalcopyrite using FeCl3 and HCl.The researchers foundelementalsulfuron thesurface ofmineralresidues, whichrealize on chlorineand its effects onmorphological formation.CarneiroandLeao[17]analysedtheeffectofNaCl inachalcopyriteconcentrate.Consideringthemineralogical analysisoftheresidues,theauthorsevaluatedtheporosity, whichincreasedwiththepresenceofNaCl,facilitatingthe diffusionoftheleachingsolutionthroughthe mineral.The formationof asolid compound ofelemental sulfurwith a highporosityconvergestowhatwasobtainedinthisresearch.

TheassaysconductedwithH2SO4(Fig.6)reportedlowcopper extractions, while the mineralogical analyses (Fig. 8) indicated the presence of sulfur around the mineral. Despite notanalysingtheporosityofthisresidue,itistheoretically expectedthatthe lackofchlorine wasfundamental inthe non-formationofelongatedand poroussulfurcrystals[33].

Thispreventedahighextractionofcopper.Theanalysisand identificationofthecrystallinephaseswere obtainedusing the DIFFRAC.EVA V4.2.1 program, withthe Powder Diffrac- tionFileofICDD database(PDF-2(2004))(ManganeseOxide PDF 65-1298(ICDD, 2004), Sulfur PDF 08-0247 (ICDD, 2004), MagnesiumOxide,PDF04-0829(ICDD,2004),CalciumSulfate PDF86–2270(ICDD,2004) andIronOxidePDF89-8103(ICDD, 2004)).

4. Summary and conclusions

Thisresearchdisplaystheresultsofthecopperdissolution fromchalcopyritebyaddingMnO2asanoxidizingagent(manganesenodules),usingwastewaterat25^◦C.TheMnO2present inthe marine nodulesproved to beanexcellent oxidizing agentforthedissolutionofchalcopyrite.Themainfindings ofthisstudyarethefollowing:

• HighconcentrationsofMnO2(4/1and5/1)allowthepoten- tial values to be between 580 and 650mV, favoring the dissolutionofCuFeS2.

• Themixingintensitydidnothaveasignificanteffectonthe copperdissolutionratefromchalcopyrite.

• The best resultsforhigh ratios ofMnO2/CuFeS2 (5/1),in chloridemedia,wereobtained2mol/LofH₂SO4.

• High concentrations of chloride allow to significantly increase the copper dissolution from CuFeS2, achieving better results when working with discard (waste) water comparedtoseawater.

• Thewasteanalysedforleachingwithwastewaterdidnot reveal the formation of pollutants elements like stable elemental sulfur (S⁰). Besides, the elements present as MgO and CaSO4 did not significantly affect the copper extraction

• The best results ofthis investigation (77 % of Cu) were obtainedwhenworkingatMnO₂/CuFeS₂ratiosof5/1and aconcentrationof1mol/LofH2SO4at25^◦C.

Wastewaterprovedtobeanexcellentcontributiontothe processaswellasareusablewaterresourcethatprovideshigh amountsofchloride.Itisnecessarytoinvestigate:i)hydromet- allurgicalalternativesfortheinformationofsecondaryand

primary sulfides, since these are a more environmentally friendlyalternative,andii)toprovidesolutionsforthewater scarcity.

Author contributions

All oftheauthors contributed toanalyzingthe resultsand writingthepaper.

Conflicts of interest

Theauthorsdeclarenoconflictsofinterest.

Acknowledgments

Theauthors are gratefulforthe contributionof theScien- tificEquipmentUnit-MAINIoftheUniversidadCatólicadel Norteforaidingingeneratingdatabyautomatedelectronic microscopyQEMSCAN® andforfacilitatingthechemicalanal- ysisofthesolutions. Weare alsogratefultoMarinaVargas Aleuy, MaríaBarrazaBustosand CarolinaOssandón Cortés of the Universidad Católica del Norte for supporting the experimentaltests.R.I.JthanksCentroCRHIAMProjectConi- cyt/Fondap/15130015.

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