Research Article Galvanic Interaction between Chalcopyrite and...

Hindawi Publishing CorporationJournal of ChemistryVolume 2013 Article ID 817218 9 pageshttpdxdoiorg1011552013817218

Research ArticleGalvanic Interaction between Chalcopyrite and Pyrite withLow Alloy and High Carbon Chromium Steel Ball

Asghar Azizi1 Seid Ziaoddin Shafaei2 Mohammad Noaparast2

and Mohammad Karamoozian1

1 Department of Mining Petroleum and Geophysics Shahrood University of Technology Shahrood Iran2 School of Mining Engineering College of Engineering University of Tehran Iran

Correspondence should be addressed to Asghar Azizi aziziasghar22yahoocom

Received 12 May 2013 Revised 17 July 2013 Accepted 17 July 2013

Academic Editor Svetlana Ibric

Copyright copy 2013 Asghar Azizi et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

This study was aimed to investigate the galvanic interaction between pyrite and chalcopyrite with two types of grinding media(low alloy and high carbon chromium steel ball) in grinding of a porphyry copper sulphide ore Results indicated that injectionof different gases into mill altered the oxidation-reduction environment during grinding High carbon chromium steel ball undernitrogen gas has the lowest galvanic current and low alloy steel ball under oxygen gas had the highest galvanic current Also resultsshowed that the media is anodic relative to pyrite and chalcopyrite and therefore pyrite or chalcopyrite with a higher rest potentialacted as the cathode whilst the grinding media with a lower rest potential acted as the anode when they are electrochemicallycontacted It was also found that low alloy steel under oxygen produced the highest amount of EDTA extractable iron in the slurrywhilst high carbon chromium steel under nitrogen atmosphere led to the lowest amount

1 Introduction

The key to a successful separation in mineral processing isthe preparation of particles with adequate liberation underthe correct pulp chemical conditions [1] Wet milling in ballmills followed by flotation is the general practice employedin the beneficiation of copper sulphide ores in which themajor minerals of commercial significance typically arechalcopyrite (CuFeS

2) bornite (Cu

5FeS4) covellite (CuS)

and chalcocite (Cu2S) [2]

It has been widely accepted that the grinding environ-ment of sulfide minerals such as pyrite arsenopyrite chal-copyrite galena pyrrhotite and sphalerite has a pronouncedeffect on the recovery and selectivity of sulphide minerals [3ndash10]

Galvanic interaction is one of the most important elec-trochemical factors which governs the dissolution rate ofsulphide minerals in hydrometallurgical systems [11] It mayoccur in many minerals processing systems flotation [12ndash14] leaching of sulfide [15ndash17] and particularly wet grinding

[18 19] Most sulfides are at best semiconductors Thereforeduring grinding due to sulphide mineral electrical conduc-tivity a contact between mineral in ore and grinding mediaoccurs which results in a galvanic couple between the mediaand the sulphide mineral This increases dissolution of fer-rous ions fromgrindingmedia which are usually precipitatedin the form of iron oxy-hydroxides on the surfaces of thesulphide minerals [20ndash22]

The extent of galvanic interaction between mineral andgrinding media is dependent on the media type mineralsmineralogy rest potential (open circuit potential) differencesbetween sulphide minerals and grinding media polarizationbehavior of the materials comparative geometric ratio ofthe sulphide mineral to the medium in the couple andgrinding environment such as pH percent solid viscosityEh gas purging (air O

2and N

2) temperature rheologi-

cal properties and water chemistry (ie anions Clminus SOminus24

cations Ca+2 Mg+2 Fe+2 Fe+3) [9ndash23]A vast number of studies were carried out in inves-

tigating the electrochemical interactions between grinding

2 Journal of Chemistry

media and sulphide minerals [13 14 24 25] Generallythese studies indicate that most sulphide minerals are noblerthan the grinding media used during grinding thereforea galvanic couple between the media and the sulphidemineral(s) exists which increases the corrosion rate of thegrinding media In addition these studies show that galvanicinteraction between media and mineral not only promotesthe corrosion rate of steel grinding media but also hasa deleterious influence on the floatability of the groundsulphide minerals Although extensive studies were carriedout on the electrochemical interactions between grindingmedia and minerals in grinding of sulphide minerals andorores but these investigations were not reported in grindingof porphyry copper sulphide ore Pyrite and chalcopyritethe most common and exploitable sulphide minerals usuallyoccur together and in contact with each other Thereforethis paper was aimed to investigate the effect of galvanicinteraction among chalcopyrite and pyrite with grindingmedia in grinding the Sarcheshmeh copper ore In this studyinfluence of two factors including media type and dissolvedoxygen were investigated in galvanic interaction betweenminerals (chalcopyrite and pyrite) and media

The Sarcheshmeh copper ore is a major porphyry cop-per deposit which is located in Kerman Province in thesoutheastern part of Iran The Sarcheshmeh copper mine isthe largest copper producer in Iran and one of the majorproducers in the world market In the concentrator plantafter three stages of crushing the ore feeds to ball mills ina closed circuit with cyclones to produce 70 of the productfiner than 75120583m [26]

2 Experimental

21 Materials and Reagents The Sarcheshmeh copper oresamples were obtained from the input feed to ball millsSamples were crushed in a jaw crusher and then screenedto collect the +025ndash2mm particle size fraction Sampleswere then homogenized and sealed in polyethylene bagsRepresentative samples were chemically analyzed which theirchemical compositions listed in Table 1

In order to construct electrodes samples of pure pyriteand chalcopyrite were collected from the Meiduck coppermine in the Babak city in Kerman Province of Iran andthe Ghaleh Zari mine in Nehbandan city in south KhorasanProvince of Iran respectivelyThese samples were chemicallyanalyzed It is specified that pure pyrite and chalcopyriteminerals have 993 and 9744 pyrite and chalcopyriterespectively

Two types of steel ball were applied as grinding mediawhich their chemical compositions are presented in Table 2In this research samples were groundwith 8 kg ball inmixingof 05 075 and 1 inch in diameter

For preparing minerals and medium electrodes mediumand mineral samples were cut into a size of 7 times 7mm tofill in a Teflon tube Then a copper wire was connected tothe back of the medium with electrically conductive silverepoxy After that the sample was mounted in a Teflon tubewith the working surface exposed and the central part of

Table 1 Chemical composition of the Sarcheshmeh ore sample (Wt)

Particle range Chemical compositions (Weight )Cu Fe Mo S SiO2 Al2O3

025 to 2 millimeters 074 434 0032 305 5507 1435

Table 2 Chemical compositions of the grinding media

Ball type Chemical compositions (Weight )C Si S P Mn Cr Mo Cu

High carbonchrome steel 228 0698 0049 0 1 1325 0177 0044

Low alloysteel 0249 0173 0024 0018 0586 0019 0002 0012

the tube was sealed with nonconductive epoxy resin Theelectrodes surface was gently polished with 500 grit siliconcarbide paper prior to each test and cleaned with acetoneand double distilled water After each experiment the usedmedium electrodes were repolished and then reused

22 Grinding The prepared representative samples (365 g)were ground in a specialized ball mill with 8 kg balls in pH7ndash75 solid percentage 35 and rotation speed 75 rpm for125 minutes so that 70 of particles were finer than 75120583min diameter This specialized grinding system was designedin RampD of the Sarcheshmeh copper Mine Ball mill wasconstructed using a stainless steel pipe with diameter of 21 cmand length of 30 cm with a wall thickness of 07 cm In orderto study the electrochemistry of inside the mill that is tomeasure the slurry chemical conditions polarization curvesof balls and minerals and their electrochemical interactionsan electrochemical apparatus associated with gas purgingsystem was also linked to the mill Schematic representationof specially designed grinding system illustrated in Figure 1

The setup of experiments included a specialized ball millelectrochemical tools including potentiostatgalvanostatcoupled with a personal computer for data acquisition andpotential control accompanied by a three-electrode systemthe gas purging system and meters for monitoring chemicalconditions (Eh pH and DO)

Polarization curves of balls and minerals were deter-mined using the computerized potentiostatgalvanostat(SAMA500 Electrochemical Analysis System SAMA re-search center Iran) and three-electrode system by Tafelextrapolation method and technique of linear sweepvoltammetry (LSV)

The three-electrode systemwas comprised of an AgAgCl(30M KCl) electrode as a reference electrode Pt wire as thecounter electrode and grinding media electrode as workingelectrode All potentials were measured and reported versustheAgAgCl (30MKCl) reference electrode (+210mVversusSHE) All polarization experiments were also carried out witha sweep rate of 50mVs

Moreover in experiments different gases (nitrogen airor oxygen) were continuously injected at the rate of 6 Lmininto themill to change the oxidation conditionsThe pulpwas

Journal of Chemistry 3

Measuring chamber

Gas purging

Probes (DO Eh Pt reference and working electrode)

Grate Pumping

Grinding chamber

Figure 1 Schematic plan of specially designed ball mill

also pumped out of the mill and mixed with the gases andthen returned into the mill

23 EDTA Extraction Technique An EDTA (ethylenediamine-tetra acetic acid disodium) extraction technique hasbeen widely used to determine the magnitude of oxidizediron species in the slurry [27] Thus EDTA extractiontechnique was carried out to determine the amount ofoxidized iron species from minerals andor grinding mediaon ball mill discharge as follows [27ndash29]

A 3 percent by weight solution of ethylene diamine-tetraacetic acid disodium salt was made up and solution pHwas adjusted to 75 sodium hydroxide 250mL of the EDTAsolutionwas placed into a beaker and stirred using amagneticstirrer A 25mL sample of the pulp was collected from milldischarge Samples were weighted to determine the mass ofpulp The pulp was injected into the EDTA solution and thenstirred for 5 minutes At the end of the 5 minutes extractiontime the sample was filtered through a 022micronMilliporefilter paper using a vacuum filter The filtrate was analyzedusing atomic absorption spectroscopy (AAS) The solid frombulk sample from which have collected the 25mL of pulpwas assayed Finally the percent EDTA extractable iron wasdetermined by dividing themass of iron in the solution by thetotal mass of iron in the solids

The EDTA extractable Fe percentage follows the method-ology developed by Rumball and Richmond (1996) [27]

3 Results and Discussion

Potentiodynamic polarization is a direct current techniquethat gives fundamental information from the corrosion ratebehavior of activity passivity and susceptibility to corrosionof the material Also polarization diagrams can be suitableto study galvanic interaction between minerals and grindingmedia In the measurement a potentiostatgalvanostat isused to control the driving force for the electrochemicalreactions taking place on the working electrode (mineralor medium) Polarization curves of medium (low alloy andhigh carbon chromium steel balls) pyrite and chalcopyriteelectrodes were obtained using described electrochemical

equipments Results of potentiodynamic polarization studiesfor pyrite chalcopyrite and low alloy and high carbonchromium steel balls under different aeration conditions ata scanning rate of 50mVsec are illustrated in Figures 2 and3 According to the results of Figures 2 and 3 the followingobservations can be obtained

Figure 2 indicates polarization curves of low alloy steelball pyrite and chalcopyrite under different aeration condi-tions and without aeration during grinding of the Sarchesh-meh copper ore with low alloy steel ball Figure 2(a) exhibitsthat the cathodic polarization curves were extended fromminus990mV to minus585 minus377 and minus239mV for medium chalcopy-rite and pyrite respectively whereas anodic polarization ofmedium chalcopyrite and pyritewere extended respectivelyfrom minus585 minus377 and minus239mV to +0290mV

In Figure 2(a) the activity passivity and transpassivityregions can be clearly distinguished both for chalcopyriteand for pyrite In the case of chalcopyrite a passivationbehavior around minus175mV and a transpassivation behaviorwas observed around +180mV whereas for pyrite passiva-tion and transpassivation behavior was seen around minus63and 199mV respectively It was also observed active-passive-transpassive behavior for low alloy steel ball

Figure 2(b) indicates that starting of passivity andtranspassivity regions for low steel and chalcopyrite areattained 49 and 125mV and 218 and 257mV in air purgingconditions respectively whilst no passive phenomenon isfound for pyrite

As can be observed in Figures 2(c) and 2(d) all of thecurves follow a typical form of active-passive-transpassiveanodic behavior

Figure 3 indicates polarization curves of high carbonchrome steel ball pyrite and chalcopyrite under differentaeration conditions and without aeration during grindingof the Sarcheshmeh copper ore All of polarization curvesfor pyrite and chalcopyrite exhibit passivation behaviourhowever they differ in nature of transition from active topassive stateThe polarization plots for medium show a smallpassivating region which may be due to the iron hydroxidespecies which passivates the steel ball surface and preventsfurther oxidation The magnitude of passivity region undernitrogen atmosphere is the greater than other conditions inall of curves

As seen in Figure 3 the current reach a limiting valuearound a potential of minus900mV for pyrite and chalcopyriteand minus940mV for high carbon chrome steel during cathodicpolarization under nitrogen atmosphere (Figure 3(a)) Underair atmosphere limiting current values attain around apotential ofminus910mV for pyrite and chalcopyrite andminus860mVfor high carbon chrome steel during cathodic polarizationin air purging (Figure 3(b)) Limiting current value reachto a potential of minus745 and minus930mV for minerals (pyriteand chalcopyrite) and high carbon chrome steel ball in O

2

purging respectively whereas is achieved value around apotential of minus920mV for both minerals and medium withoutaeration conditions (Figures 3(c) and 3(d)) Limiting currentvalue is not observed for pyrite and chalcopyrite in the anodicpolarization while for the grinding media limiting currentvalue is attained at potentials above +160mV in all of curves


00 02 04

Critical passivation pointTrans-passivation point

Active region

Galvanic current density

Passive region

minus12 minus10 minus08 minus06 minus04 minus02

minus30

minus35

minus40

minus45

minus50

minus55

minus60

minus65

minus70

Log

(J)

Log

(Ac

m2)

Potential versus AgAgCl (300M KCl) (V)

(a)


minus30

minus35

minus40

minus45

minus50

minus55

minus60

minus25

minus20

00 02 04minus12 minus10 minus08 minus06 minus04 minus02

Log

(J)

Log

(Ac

m2)


(b)



Low steel PyriteChalcopyrite

minus30

minus35

minus40

minus45

minus50

minus15

minus20

minus25

Log

(J)

Log

(Ac

m2)


(c)




minus30

minus35

minus40

minus45

minus50

minus55

minus60

minus25

Log

(J)

Log

(Ac

m2)


(d)

Figure 2 Potentiodynamic polarization sweep curves of grinding medium pyrite and chalcopyrite during grinding of ore with low alloysteel ball under nitrogen (a) air (b) and oxygen atmosphere (c) and without aeration (d) at a sweep rate of 50mVs

In addition Figures 2 and 3 exhibit a method of how tocalculate the galvanic current from the polarization curvesof the minerals and medium Current in the polarizationcurves represents rate of all electrons exchange reactions atthe surface of the electrodes Table 3 presents the steady-statecombination potentials and the galvanic current densitiesof pyrite and chalcopyrite with low alloy and high carbonchromium steel ball measured in mill by using polarizationcurves exposed to the different gases (nitrogen air and oxy-gen) and at pH of 7ndash75 during grinding of the Sarcheshmehcopper sulphide ore

As can be considered in Table 3 different aeration con-ditions alter the oxidation-reduction environment duringgrinding Oxygen in the grinding system produces the high-est galvanic current in the medium-mineral (pyrite andorchalcopyrite) couple during grinding whilst nitrogenation

resulted in the lowest galvanic current As seen high carbonchromium steel ball under nitrogen gas has the lowestgalvanic current for mineral-grinding media system and lowalloy steel ball under oxygenation has the highest currentTherefore the galvanic interaction between the grindingmedia and sulphide mineral was affected by type of mediagrinding and the injected gas (nitrogen air and oxygen) typeinto mill during grinding

Moreover the derived results from Figures 2 and 3 andTable 3 show that the grinding media is anodic relative tothe all sulphide minerals (pyrite and chalcopyrite) and theelectrons flow from the media to the minerals Thus pyriteor chalcopyrite with a higher rest potential (open circuitpotential when net current is equal to zero) would act as thecathode whilst the grindingmedia with a lower rest potentialwould act as the anode when they are electrochemically



minus30

minus35

minus40

minus45

minus50

minus55

minus65

minus60

minus25


Log

(J)

Log

(Ac

m2)


(a)



minus30

minus35

minus40

minus45

minus50

minus55

minus20

minus25

Log

(J)

Log

(Ac

m2)


(b)


High steel PyriteChalcopyrite


minus30

minus35

minus40

minus45

minus50

minus55

minus15

minus20

minus25

Log

(J)

Log

(Ac

m2)


(c)



minus30

minus35

minus40

minus45

minus50

minus55

minus60

minus25


Log

(J)

Log

(Ac

m2)


(d)

Figure 3 Potentiodynamic polarization sweep curves of grinding medium pyrite and chalcopyrite during grinding of ore with high carbonchrome steel ball under nitrogen (a) air (b) and oxygen atmosphere (c) and without aeration (d) at a sweep rate of 50mVs

contactedModel of galvanic interaction occurring between asingle sulphide mineral (pyrite or chalcopyrite) and grindingmedia is illustrated in Figure 4(a) based on mixed potentialmodel [30] Pozzo et al (1990) [31] described an electrochem-ical model for a two-sulphide mineralgrinding medium sys-tem as shown in Figure 4(b) According to Pozzo et al (1990)in grinding of the Sarcheshmeh sulphide ore composed ofchalcopyrite pyrite (as two main mineral) with low alloy orhigh carbon chromium steel ball the noblest electrode (thehighest rest potential) in the series is pyrite (see Table 4)Therefore pyrite will act as cathode and the grinding mediaalways as anode The other sulphide mineral (chalcopyrite)with lower rest potential than pyrite but higher rest potentialthan the grindingmedium developed an intermediate anodic(Figure 4) depending on its rest potential

Under the above conditions the following electrochem-ical reactions may be occurred on sulphide minerals andgrinding media surface [22 32ndash34]

Cathodic reaction on cathodic mineral surface

1

2O2+H2O + 2eminus 997888rarr 2OHminus (1)

Anodic reactions on medium surface

Fe 997888rarr Fe2+ + 2eminus

Fe 997888rarr Fe3+ + 3eminus(2)


Table 3 The measured galvanic current densities (120583Acm2) and combination potentials (mV) (versus AgAgCl (30MKCl)) of pyritechalcopyrite with low alloy and high carbon chromium steel ball under different aeration conditions in mill

Aeration conditions Galvanic current density of pyrite andlow alloy steel

Combination potentials (potentialbetween pyrite and low steel ball)

Without aeration 10963 minus345Nitrogen 6341 minus538Air 11197 minus203Oxygen 27750 minus179

Aeration conditions Galvanic current density of chalcopyriteand low alloy steel ball

Combination potentials (potentialbetween chalcopyrite and low steel ball)


Aeration conditions Galvanic current density of pyrite andhigh carbon chromium steel ball

Combination potentials (potentialbetween pyrite and high carbon

chromium steel ball)Without aeration 8653 minus531Nitrogen 2633 minus535Air 8998 minus372Oxygen 21218 minus172

Aeration conditions Galvanic current density of chalcopyriteand high carbon chromium steel ball



Table 4 Rest potential of sulphide minerals and steel media at near neutral pH [7 32]

Mineral Solution Rest potential versus SHEmVN2

Air O2

Galena Distilled water 142 172 21805molL NaCl (pH = 105) 45 95

Pyrite Distilled water 405 445 4850001molL Na2SO4 45 95

Pyrrhotite Distilled water 125 262 295Arsenopyrite Distilled water 277 303 323

ChalcopyriteDistilled water 190 355 371

005molL Na2SO4 115 2650 5molL NaCl (pH = 105) 65 115

Sphalerite 0 5molL NaCl (pH = 105) 30 60Mild steel Distilled water minus515 minus335 minus175

05molL NaCl minus395Ferronickel steel 05molL NaCl pH = 105 minus255 minus205

Precipitation

Fe2+ + 2OHminus 997888rarr Fe(OH)2

Fe(OH)2+OHminus larrrarr Fe(OH)

3+ eminus

(3)

Reaction on anodic mineral surface (two sulphide min-eral and medium system)

MSlarrrarr M2+ + S + 2eminus (4)

As can be considered in above reactions ferrous ions arereleased into the solution as a result of anodic oxidation of


Grinding media Sulphide

mineral

Fe2+ Fe2+

1

2O2

+ H2O

eminus OHminus

(a)

Steel ball

Anodic mineral

Cathodic mineral(pyrite)

1

2O2

+ H2O

eminus

eminus

eminuseminus

eminusOHminus

Me2+ + S0 rarr SO2minus

4

Fe2

(b)

Figure 4 Model galvanic interactions between a single sulphide mineral (a) [31] and two sulphide minerals (b) [33] and steel ball duringgrinding

grinding media simultaneously with the cathodic reductionof dissolved oxygen

The flow of electrons from the grindingmedia to sulphideminerals increases the oxidation of grinding media [35]leading to more oxidized iron species in the slurry In thiswork the EDTA extraction technique was used as a measureof the corrosion of the system It is not an accurate measurebut it gives general information on the process The amountof oxidized iron species fromminerals andor grindingmediain the mill discharge under different aeration conditions forlow alloy and high carbon chrome steel balls were obtainedby EDTA extraction technique as shown in Figure 5 It isobserved that the grinding media as well as the type ofaeration influence the amount of EDTA extractable iron Itis seen that low alloy steel ball under oxygen atmosphereproduces the highest amount of EDTA extractable iron in theslurry whilst high carbon chromium steel ball under nitrogenatmosphere leads to the lowest amount

4 Conclusion

The purpose of this study was to investigate the galvanicinteraction between pyrite and chalcopyrite with low alloyand high carbon chromium steel balls in grinding of theSarcheshmeh porphyry copper sulphide ore A specializedlaboratory grinding system which linked to electrochemicalequipment was constructed to study the grinding environ-ment electrochemistry and quantify the galvanic currentbetween pyrite and chalcopyrite with grinding media Themajor conclusions based on this research work can besummarized as follows

(i) High carbon chromium steel ball under nitrogen gashas the lowest galvanic current and low alloy steel ballunder oxygen gas had the highest galvanic current inmineral-grinding media system

(ii) Grinding media was anodic relative to pyrite andchalcopyrite and therefore the electrons flowed fromthe media to the minerals Pyrite or chalcopyrite with

Different aeration conditionsWithout aeration Nitrogen Air Oxygen

EDTA

extr

acta

ble i

ron

()

00

01

02

03

04

05

06

Low alloy steel ballHigh carbon chromium steel ball

Figure 5 EDTA extractable iron in the mill discharge underdifferent aeration conditions for two types of grinding media

a higher rest potential acted as the cathode whilst thegrindingmedia with a lower rest potential acted as theanode when they were electrochemically contactedin single mineral-media system

(iii) In two sulphide minerals-media (pyritechalcopyritemedia) systems pyrite is the noblest electrode actedas cathode and the grinding media always as anodewhilst chalcopyrite with lower rest potential thanpyrite but higher rest potential than the mediumdeveloped an intermediate anodic depending on itsrest potential

(iv) Low alloy steel ball under oxygen produced thehighest amount of EDTA extractable iron in theslurry whilst high carbon chromium steel ball undernitrogen atmosphere produced the lowest amount


(v) Polarization curves for pyrite chalcopyrite andmedium (low alloy and high carbon chromium steelballs) were obtained by electrochemical equipmentand using linear sweep voltammetry technique underdifferent aeration conditions and without aerationApproximately in all of polarization curves of miner-als and steel balls the activity passivity and transpas-sivity regions could be distinguishedThepolarizationplots for balls showed a small passivating regionwhich may be due to the iron hydroxide specieswhich passivates the steel ball surface and preventsfurther oxidation In addition limiting current valuewas also attained based on polarization plots

Acknowledgments

This work was supported by Research and developmentdivision and funded by National Iranian Copper IndustriesCompany The authors wish to thank the manager andpersonnel of the Sarcheshmeh copper mine for their supportduring this research

References

[1] C J Greet ldquoThe significance of grinding environment on theflotation of UG2 oresrdquo in Proceedings of the 3th InternationalPlatinum Conference Platinum in Transformation p 29 TheSouthern African Institute of Mining and Metallurgy Sun CitySouth Africa 2008

[2] W J Bruckard G J Sparrow and J T Woodcock ldquoA reviewof the effects of the grinding environment on the flotation ofcopper sulphidesrdquo International Journal of Mineral Processingvol 100 no 1-2 pp 1ndash13 2011

[3] M Rey and V Formanek ldquoSome factors affecting selectivityin the differential flotation of lead-zinc ores in the presence ofoxidized lead mineralrdquo in Proceedings of the 5th InternationalMineral Processing Congress pp 343ndash352 Institution of Miningand Metallurgy London UK 1960

[4] R L Pozzo and I Iwasaki ldquoAn electrochemical study ofpyrrhotite-grinding media interaction under abrasive condi-tionrdquo Corrosion vol 43 no 3 pp 159ndash164 1987

[5] R L Pozzo and I Iwasaki ldquoPyrite-pyrrhotite grinding mediainteractions and their effects on media wear and flotationrdquoJournal of the Electrochemical Society vol 136 no 6 pp 1734ndash1740 1989

[6] Y Peng S Grano D Fornasiero and J Ralston ldquoControlof grinding conditions in the flotation of chalcopyrite andits separation from pyriterdquo International Journal of MineralProcessing vol 69 no 1ndash4 pp 87ndash100 2003

[7] Y Peng S Grano D Fornasiero and J Ralston ldquoControl ofgrinding conditions in the flotation of galena and its separationfrom pyriterdquo International Journal of Mineral Processing vol 70no 1ndash4 pp 67ndash82 2003

[8] GHuang and S Grano ldquoGalvanic interaction between grindingmedia and arsenopyrite and its effect on flotation part IQuantifying galvanic interaction during grindingrdquo Interna-tional Journal of Mineral Processing vol 78 no 3 pp 182ndash1972006

[9] GHuang and SGrano ldquoGalvanic interaction of grindingmediawith pyrite and its effect on floatationrdquo Minerals Engineeringvol 18 no 12 pp 1152ndash1163 2005

[10] S Grano ldquoThe critical importance of the grinding environmenton fine particle recovery in flotationrdquoMinerals Engineering vol22 no 4 pp 386ndash394 2009

[11] H Majima and E Peter ldquoElectrochemistry of sulphide dis-solution in hydrometallurgical systemsrdquo in Proceedings of theinternational Mineral Processing Congress p 13 LeningradRussia 1968

[12] V Vathsala and K A Natarajan ldquoSome electrochemical aspectsof grinding media corrosion and sphalerite flotationrdquo Interna-tional Journal ofMineral Processing vol 26 no 3-4 pp 193ndash2031989

[13] M K Yelloji Rao and K A Natarajan ldquoEffect of galvanicinteraction between grinding media and minerals on sphaleriteflotationrdquo International Journal ofMineral Processing vol 27 no1-2 pp 95ndash109 1989

[14] M K Yelloji Rao andK A Natarajan ldquoEffect of electrochemicalinteractions among sulfide minerals and grinding medium onchalcopyrite flotationrdquo Minerals and Metallurgical Processingvol 6 no 3 pp 146ndash151 1989

[15] J EDutrizac R J CMacDonald andT R Ingraham ldquoEffect ofpyrite chalcopyrite and digenite on rate of bornite dissolutionin acidic ferric sulphate solutionsrdquo Canadian MetallurgicalQuarterly vol 5 no 1 pp 3ndash7 1971

[16] J E Dutrizac and R J C Mac Donald ldquoEffect of impuritieson the rate of chalcopyrite dissolutionrdquo Canadian MetallurgicalQuarterly vol 12 no 4 pp 409ndash420 1973

[17] H G Linge ldquoReactivity comparison of Australian chalcopyriteconcentrates in acidified ferric solutionrdquo Hydrometallurgy vol2 no 3 pp 219ndash233 1977

[18] K A Natarajan S C Riemer and I Iwasaki ldquoCorrosive anderosive wear in magnetite taconite grindingrdquo Minerals andMetallurgical Processing vol 1 no 1 pp 10ndash14 1984

[19] R L Pozzo and I Iwasaki ldquoEffect of pyrite and pryyhotite on thecorrosive wear of grinding mediardquo Minerals and MetallurgicalProcessing vol 4 no 3 pp 166ndash171 1987

[20] J W Jang I Iwasaki and J J Moore ldquoEffect of galvanicinteraction between martensite and ferrite grinding mediawearrdquo Corrosion vol 45 no 5 pp 402ndash407 1989

[21] M K Yelloji Rao and K A Natarajan ldquoFactors influencingball wear and flotation with respect to ore grindingrdquo MineralProcessing and Extractive Metallurgy Review vol 7 no 3-4 pp137ndash173 1991

[22] K A Natarajan ldquoLaboratory studies on ball wear in thegrinding of a chalcopyrite orerdquo International Journal of MineralProcessing vol 46 no 3-4 pp 205ndash213 1996

[23] J H Ahn and J E Gebhardt ldquoEffect of grinding media-chalcopyrite interaction on the self-induced flotation of chal-copyriterdquo International Journal ofMineral Processing vol 33 no1ndash4 pp 243ndash262 1991

[24] K A Natarajan and I Iwasaki ldquoElectrochemical aspects ofgrinding media-mineral interactions in magnetite ore grind-ingrdquo International Journal of Mineral Processing vol 13 no 1pp 53ndash71 1984

[25] C J Greet G L Small P Steinier and S R Grano ldquoTheMagot-teaux Mill investigating the effect of grinding media on pulpchemistry and flotation performancerdquo Minerals Engineeringvol 17 no 7-8 pp 891ndash896 2004

[26] H R Barkhordari E Jorjani A Eslami and M NoaparastldquoOccurrence mechanism of silicate and aluminosilicate miner-als in Sarcheshmeh copper flotation concentraterdquo InternationalJournal of Minerals Metallurgy and Materials vol 16 no 5 pp494ndash499 2009


[27] J A Rumball and G D Richmond ldquoMeasurement of oxidationin a base metal flotation circuit by selective leaching withEDTArdquo International Journal of Mineral Processing vol 48 no1-2 pp 1ndash20 1996

[28] V J Cullinan S R Grano C J Greet N W Johnson andJ Ralston ldquoInvestigating fine galena recovery problems in thelead circuit of Mount Isa Mines LeadZinc Concentrator part 1grinding media effectsrdquoMinerals Engineering vol 12 no 2 pp147ndash163 1999

[29] C Greet and R S C Smart ldquoDiagnostic leaching of galena andits oxidation products with EDTArdquo Minerals Engineering vol15 no 7 pp 515ndash522 2002

[30] Y Peng and S Grano ldquoInferring the distribution of ironoxidation species on mineral surfaces during grinding of basemetal sulphidesrdquo Electrochimica Acta vol 55 no 19 pp 5470ndash5477 2010

[31] R L Pozzo A S Malicsi and I Iwasaki ldquoPyrite-pyrrhotite-grindingmedia contact and its effect on flotationrdquoMinerals andMetallurgical Processing vol 7 no 1 pp 16ndash21 1990

[32] J J Pavlica and I Iwasaki ldquoElectrochemical and magneticinteraction in pyrrhotite flotationrdquo SME-AIME Transactionsvol 272 pp 1885ndash1890 1982

[33] X Cheng and I Iwasaki ldquoPulp potential and its implicationsto sulphide flotationrdquoMineral Processing and Extractive Metal-lurgy Review vol 11 no 4 pp 187ndash210 1992

[34] K A Natarajan S C Riemer and I Iwasaki ldquoInfluence ofpyrrhotite on the corrosive wear of grinding balls in magnetiteore grindingrdquo International Journal of Mineral Processing vol13 no 1 pp 73ndash81 1984

[35] C J Martin R E McIvor J A Finch and S R Rao ldquoReview ofthe effect of grinding media on flotation of sulphide mineralsrdquoMinerals Engineering vol 4 no 2 pp 121ndash132 1991

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media and sulphide minerals [13 14 24 25] Generallythese studies indicate that most sulphide minerals are noblerthan the grinding media used during grinding thereforea galvanic couple between the media and the sulphidemineral(s) exists which increases the corrosion rate of thegrinding media In addition these studies show that galvanicinteraction between media and mineral not only promotesthe corrosion rate of steel grinding media but also hasa deleterious influence on the floatability of the groundsulphide minerals Although extensive studies were carriedout on the electrochemical interactions between grindingmedia and minerals in grinding of sulphide minerals andorores but these investigations were not reported in grindingof porphyry copper sulphide ore Pyrite and chalcopyritethe most common and exploitable sulphide minerals usuallyoccur together and in contact with each other Thereforethis paper was aimed to investigate the effect of galvanicinteraction among chalcopyrite and pyrite with grindingmedia in grinding the Sarcheshmeh copper ore In this studyinfluence of two factors including media type and dissolvedoxygen were investigated in galvanic interaction betweenminerals (chalcopyrite and pyrite) and media

The Sarcheshmeh copper ore is a major porphyry cop-per deposit which is located in Kerman Province in thesoutheastern part of Iran The Sarcheshmeh copper mine isthe largest copper producer in Iran and one of the majorproducers in the world market In the concentrator plantafter three stages of crushing the ore feeds to ball mills ina closed circuit with cyclones to produce 70 of the productfiner than 75120583m [26]

2 Experimental

21 Materials and Reagents The Sarcheshmeh copper oresamples were obtained from the input feed to ball millsSamples were crushed in a jaw crusher and then screenedto collect the +025ndash2mm particle size fraction Sampleswere then homogenized and sealed in polyethylene bagsRepresentative samples were chemically analyzed which theirchemical compositions listed in Table 1

In order to construct electrodes samples of pure pyriteand chalcopyrite were collected from the Meiduck coppermine in the Babak city in Kerman Province of Iran andthe Ghaleh Zari mine in Nehbandan city in south KhorasanProvince of Iran respectivelyThese samples were chemicallyanalyzed It is specified that pure pyrite and chalcopyriteminerals have 993 and 9744 pyrite and chalcopyriterespectively

Two types of steel ball were applied as grinding mediawhich their chemical compositions are presented in Table 2In this research samples were groundwith 8 kg ball inmixingof 05 075 and 1 inch in diameter

For preparing minerals and medium electrodes mediumand mineral samples were cut into a size of 7 times 7mm tofill in a Teflon tube Then a copper wire was connected tothe back of the medium with electrically conductive silverepoxy After that the sample was mounted in a Teflon tubewith the working surface exposed and the central part of

Table 1 Chemical composition of the Sarcheshmeh ore sample (Wt)

Particle range Chemical compositions (Weight )Cu Fe Mo S SiO2 Al2O3

025 to 2 millimeters 074 434 0032 305 5507 1435

Table 2 Chemical compositions of the grinding media

Ball type Chemical compositions (Weight )C Si S P Mn Cr Mo Cu

High carbonchrome steel 228 0698 0049 0 1 1325 0177 0044

Low alloysteel 0249 0173 0024 0018 0586 0019 0002 0012

the tube was sealed with nonconductive epoxy resin Theelectrodes surface was gently polished with 500 grit siliconcarbide paper prior to each test and cleaned with acetoneand double distilled water After each experiment the usedmedium electrodes were repolished and then reused

22 Grinding The prepared representative samples (365 g)were ground in a specialized ball mill with 8 kg balls in pH7ndash75 solid percentage 35 and rotation speed 75 rpm for125 minutes so that 70 of particles were finer than 75120583min diameter This specialized grinding system was designedin RampD of the Sarcheshmeh copper Mine Ball mill wasconstructed using a stainless steel pipe with diameter of 21 cmand length of 30 cm with a wall thickness of 07 cm In orderto study the electrochemistry of inside the mill that is tomeasure the slurry chemical conditions polarization curvesof balls and minerals and their electrochemical interactionsan electrochemical apparatus associated with gas purgingsystem was also linked to the mill Schematic representationof specially designed grinding system illustrated in Figure 1

The setup of experiments included a specialized ball millelectrochemical tools including potentiostatgalvanostatcoupled with a personal computer for data acquisition andpotential control accompanied by a three-electrode systemthe gas purging system and meters for monitoring chemicalconditions (Eh pH and DO)

Polarization curves of balls and minerals were deter-mined using the computerized potentiostatgalvanostat(SAMA500 Electrochemical Analysis System SAMA re-search center Iran) and three-electrode system by Tafelextrapolation method and technique of linear sweepvoltammetry (LSV)

The three-electrode systemwas comprised of an AgAgCl(30M KCl) electrode as a reference electrode Pt wire as thecounter electrode and grinding media electrode as workingelectrode All potentials were measured and reported versustheAgAgCl (30MKCl) reference electrode (+210mVversusSHE) All polarization experiments were also carried out witha sweep rate of 50mVs

Moreover in experiments different gases (nitrogen airor oxygen) were continuously injected at the rate of 6 Lmininto themill to change the oxidation conditionsThe pulpwas


Measuring chamber

Gas purging


Grate Pumping

Grinding chamber















2



00 02 04


Active region


Passive region


minus30

minus35

minus40

minus45

minus50

minus55

minus60

minus65

minus70

Log

(J)

Log

(Ac

m2)


(a)


minus30

minus35

minus40

minus45

minus50

minus55

minus60

minus25

minus20


Log

(J)

Log

(Ac

m2)


(b)




minus30

minus35

minus40

minus45

minus50

minus15

minus20

minus25

Log

(J)

Log

(Ac

m2)


(c)




minus30

minus35

minus40

minus45

minus50

minus55

minus60

minus25

Log

(J)

Log

(Ac

m2)


(d)








minus30

minus35

minus40

minus45

minus50

minus55

minus65

minus60

minus25


Log

(J)

Log

(Ac

m2)


(a)



minus30

minus35

minus40

minus45

minus50

minus55

minus20

minus25

Log

(J)

Log

(Ac

m2)


(b)




minus30

minus35

minus40

minus45

minus50

minus55

minus15

minus20

minus25

Log

(J)

Log

(Ac

m2)


(c)



minus30

minus35

minus40

minus45

minus50

minus55

minus60

minus25


Log

(J)

Log

(Ac

m2)


(d)





1





















Air O2








Precipitation



3+ eminus

(3)






mineral

Fe2+ Fe2+

1

2O2

+ H2O

eminus OHminus

(a)

Steel ball

Anodic mineral


1

2O2

+ H2O

eminus

eminus

eminuseminus

eminusOHminus


4

Fe2

(b)




4 Conclusion





EDTA

extr

acta

ble i

ron

()

00

01

02

03

04

05

06








Acknowledgments


References














































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


Measuring chamber

Gas purging


Grate Pumping

Grinding chamber















2



00 02 04


Active region


Passive region


minus30

minus35

minus40

minus45

minus50

minus55

minus60

minus65

minus70

Log

(J)

Log

(Ac

m2)


(a)


minus30

minus35

minus40

minus45

minus50

minus55

minus60

minus25

minus20


Log

(J)

Log

(Ac

m2)


(b)




minus30

minus35

minus40

minus45

minus50

minus15

minus20

minus25

Log

(J)

Log

(Ac

m2)


(c)




minus30

minus35

minus40

minus45

minus50

minus55

minus60

minus25

Log

(J)

Log

(Ac

m2)


(d)








minus30

minus35

minus40

minus45

minus50

minus55

minus65

minus60

minus25


Log

(J)

Log

(Ac

m2)


(a)



minus30

minus35

minus40

minus45

minus50

minus55

minus20

minus25

Log

(J)

Log

(Ac

m2)


(b)




minus30

minus35

minus40

minus45

minus50

minus55

minus15

minus20

minus25

Log

(J)

Log

(Ac

m2)


(c)



minus30

minus35

minus40

minus45

minus50

minus55

minus60

minus25


Log

(J)

Log

(Ac

m2)


(d)





1





















Air O2








Precipitation



3+ eminus

(3)






mineral

Fe2+ Fe2+

1

2O2

+ H2O

eminus OHminus

(a)

Steel ball

Anodic mineral


1

2O2

+ H2O

eminus

eminus

eminuseminus

eminusOHminus


4

Fe2

(b)




4 Conclusion





EDTA

extr

acta

ble i

ron

()

00

01

02

03

04

05

06








Acknowledgments


References














































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


00 02 04


Active region


Passive region


minus30

minus35

minus40

minus45

minus50

minus55

minus60

minus65

minus70

Log

(J)

Log

(Ac

m2)


(a)


minus30

minus35

minus40

minus45

minus50

minus55

minus60

minus25

minus20


Log

(J)

Log

(Ac

m2)


(b)




minus30

minus35

minus40

minus45

minus50

minus15

minus20

minus25

Log

(J)

Log

(Ac

m2)


(c)




minus30

minus35

minus40

minus45

minus50

minus55

minus60

minus25

Log

(J)

Log

(Ac

m2)


(d)








minus30

minus35

minus40

minus45

minus50

minus55

minus65

minus60

minus25


Log

(J)

Log

(Ac

m2)


(a)



minus30

minus35

minus40

minus45

minus50

minus55

minus20

minus25

Log

(J)

Log

(Ac

m2)


(b)




minus30

minus35

minus40

minus45

minus50

minus55

minus15

minus20

minus25

Log

(J)

Log

(Ac

m2)


(c)



minus30

minus35

minus40

minus45

minus50

minus55

minus60

minus25


Log

(J)

Log

(Ac

m2)


(d)





1





















Air O2








Precipitation



3+ eminus

(3)






mineral

Fe2+ Fe2+

1

2O2

+ H2O

eminus OHminus

(a)

Steel ball

Anodic mineral


1

2O2

+ H2O

eminus

eminus

eminuseminus

eminusOHminus


4

Fe2

(b)




4 Conclusion





EDTA

extr

acta

ble i

ron

()

00

01

02

03

04

05

06








Acknowledgments


References














































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of



minus30

minus35

minus40

minus45

minus50

minus55

minus65

minus60

minus25


Log

(J)

Log

(Ac

m2)


(a)



minus30

minus35

minus40

minus45

minus50

minus55

minus20

minus25

Log

(J)

Log

(Ac

m2)


(b)




minus30

minus35

minus40

minus45

minus50

minus55

minus15

minus20

minus25

Log

(J)

Log

(Ac

m2)


(c)



minus30

minus35

minus40

minus45

minus50

minus55

minus60

minus25


Log

(J)

Log

(Ac

m2)


(d)





1





















Air O2








Precipitation



3+ eminus

(3)






mineral

Fe2+ Fe2+

1

2O2

+ H2O

eminus OHminus

(a)

Steel ball

Anodic mineral


1

2O2

+ H2O

eminus

eminus

eminuseminus

eminusOHminus


4

Fe2

(b)




4 Conclusion





EDTA

extr

acta

ble i

ron

()

00

01

02

03

04

05

06








Acknowledgments


References














































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

















Air O2








Precipitation



3+ eminus

(3)






mineral

Fe2+ Fe2+

1

2O2

+ H2O

eminus OHminus

(a)

Steel ball

Anodic mineral


1

2O2

+ H2O

eminus

eminus

eminuseminus

eminusOHminus


4

Fe2

(b)




4 Conclusion





EDTA

extr

acta

ble i

ron

()

00

01

02

03

04

05

06








Acknowledgments


References














































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of



mineral

Fe2+ Fe2+

1

2O2

+ H2O

eminus OHminus

(a)

Steel ball

Anodic mineral


1

2O2

+ H2O

eminus

eminus

eminuseminus

eminusOHminus


4

Fe2

(b)




4 Conclusion





EDTA

extr

acta

ble i

ron

()

00

01

02

03

04

05

06








Acknowledgments


References














































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of



Acknowledgments


References














































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of




















Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

Research Article Galvanic Interaction between Chalcopyrite and...

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