(2014) free production of copper from minerals through controlled andsustainable electrochemistry

8/16/2019 (2014) Free Production of Copper From Minerals Through Controlled Andsustainable Electrochemistry

http://slidepdf.com/reader/full/2014-free-production-of-copper-from-minerals-through-controlled-andsustainable 1/10

Electrochimica Acta 140 (2014)447–456

Contents lists available at ScienceDirect

Electrochimica Acta

journal homepage: www.elsevier .com/ locate /e lectacta

Production of copper from minerals through controlled and

sustainable electrochemistry

Aphichart Rodchanarowan a, Prashant K. Sarswatb, Ravindra Bhideb, Michael L. Freeb,∗

a Department ofMaterials Engineering andCenter of Advanced Studies in Industrial Technology, KasetsartUniversity, 50 Ngamwongwan Rd., Ladyao,

Chatuchak, Bangkok 10900, Thailandb Department ofMetallurgical Engineering, University of Utah, 135 S. 1460 E. Rm 412, Salt Lake City, UT 84112,USA

a r t i c l e i n f o

Article history:

Received 14 December 2013

Received in revised form 2 July 2014

Accepted 8 July 2014

Available online 15 July 2014

Keywords:

Copper

Electrowinning

Chalcopyrite

Mass transport

Electrodeposit roughness

Leaching

Halide media

Chloride

Electrochemical modeling

a b s t r a c t

Extraction of copper using halide media is more rapid than in sulfate media, and the resulting cuprous

ions require less energy to electrowin than cupric ions from sulfate media. The quality of the deposit

is influenced strongly by the deposit roughness, which is controlled by mass transport. Thus, coupled

halide leaching of chalcopyrite and subsequent electrowinning with controlled mass transport provide

an opportunity for more sustainable copper production. This paper presents new insights regarding cop-

per extraction and recovery methods from chalcopyrite ore in aqueous chloride media using leaching

and electrowinning as well as steps for deposit quality improvements. Viability of integrated leaching

and electrowinning was examinedusing low grade copper ore and continuous leaching solution recircu-

lation. Other sets of experiments were conducted where leaching and electrowinning were performed

separately, in order to find optimum experimental conditions for coupled leaching and electrowinning.

Analysis based on scientific and statistical tools are presented for comparative evaluation. Copper elec-

trodeposit morphology improvementbyuse of a variety of smoothing additives as well as mass transport

control was also evaluated.

© 2014 Elsevier Ltd. All rights reserved.

1. Introduction

Electrochemistry plays an important role in sustainable metal

extraction and recovery. Metals such as aluminum, copper, gold,

titanium, and zinc often rely on electrochemistry for important

processing steps. There are many new innovative ways to reduce

energy consumption and environmental challenges associated

with the production of these metals that are discussed in the lit-

erature [1]. This paper focusses on specific opportunities available

in copper extraction andrecovery that are associated directly with

electrochemistry and its potential role in enhancing sustainability

through reduced energyconsumption and improvedproduct qual-

ity.

Metal extraction begins with chemical dissolution of the metal.

In the case of copper, most of the world’s reserves are in the form

of chalcopyrite (CuFeS2). The importance of chalcopyrite to copper

production has led to extensive extraction research.

∗ Corresponding author. 1460East 135 S, Room 412, Salt Lake city, UT 84012.

Tel.:+1 801585 9798.

E-mail address:[email protected](M.L. Free).

Conventionalchalcopyriteprocessingbeginswithcomminution

using crushingand grinding. 100 to500 tonsofore are crushed and

ground at an energy cost of 10 to 20 kWhr per ton for every ton

of copper produced. Thus, energy consumption for comminution

can range from1,000 to 10,000 kWhr per ton of copper. After crus-

hing and grinding, the resulting fine particles of chalcopyrite are

separated from gangue minerals by flotation. Flotation results in

a concentrate of chalcopyrite containing nearly 30% copper that

is smelted and converted into blister copper, which is further

processed into copper anodes that are around 99.5% copper. The

anodes are electrorefined to produce 99.99% copper cathodes.

An alternative method of producing copper from copper oxides

and secondary sulfides utilizes heap leaching, solvent extraction,

and electrowinning. This process circumvents most or all of the

crushing and grinding as well as all of the flotation, smelting and

electrorefining.This approach has increased inuseover thepast 30

years because it is cost effective. This process is performed using

sulfuric acid media for copper oxide and secondary copper sulfide

ores. However, leaching chalcopyrite by conventional sulfuric acid

heap leaching is difficult and generally results in low recoveries.

Thus, thereareopportunities toadapt some of thechemistry devel-

opedfor chalcopyriteconcentrate leachingtochalcopyriteoreheap

leaching to create more sustainable practices.

http://dx.doi.org/10.1016/j.electacta.2014.07.015

0013-4686/©2014 Elsevier Ltd. All rights reserved.

http://localhost/var/www/apps/conversion/tmp/scratch_5/dx.doi.org/10.1016/j.electacta.2014.07.015

http://www.sciencedirect.com/science/journal/00134686

http://www.elsevier.com/locate/electacta

mailto:[email protected]



mailto:[email protected]

http://crossmark.crossref.org/dialog/?doi=10.1016/j.electacta.2014.07.015&domain=pdf

http://www.elsevier.com/locate/electacta

http://www.sciencedirect.com/science/journal/00134686




448 A. Rodchanarowan et al. / Electrochimica Acta 140 (2014) 447–456

Table 1

Comparison of leaching and electrowinning reactions for various processes.

Process Anticipated Leaching Reaction Electrowinning Reaction

Arbiter[2] CuFeS2 + 4.25O2 +4NH3 + H2O=Cu(NH3)42+

+0.5Fe2O3 +2SO42− +2H+

Cu2+ +H2O=0.5O2 +Cu+2H+

BacTech/Mintek[3] CuFeS2 + 4Fe3+ = Cu2+ +5Fe2+ + 2So Cu2+ +H2O=0.5O2 +Cu+2H+

BHAS[4] 3Cu2+ + CuFeS2 =4Cu+ + 2So + Fe2+

CuFeS2 + 3Fe3+ = Cu+ +4Fe2+ +2So

Cu2+ +H2O=0.5O2 +Cu+2H+

BioCOP[3] CuFeS2 + 4Fe3+ = Cu2+ +5Fe2+ + 2So Cu2+ +H2O=0.5O2 +Cu+2H+

BRISA[3] CuFeS2 + 4Fe3+

= Cu2+

+5Fe2+

+ 2So

Cu2+

+H2O=0.5O2 +Cu+2H+

Bromide[5] 3Cu2+ + CuFeS2 =4Cu+ + 2So + Fe2+ 2Cu+ =Cu+Cu2+

CANMET[6] 2H+ + (calcinedconc.)= CuCl2 + 2So Cu2+ +H2O=0.5O2 +Cu+2H+

CENIM-LINETI[7] 2CuFeS2 + 4O2 + 2NH4+ =2Cu2+ +2NH3 + Fe2O3H2O+SO4

2− + 3So Cu2+ +H2O=0.5O2 +Cu+2H+

CLEAR [8] CuFeS2 + 3Fe3+ = Cu+ +4Fe2+ +2So

3Cu2+ + CuFeS2 =4Cu+ + 2So + Fe2+

2Cu+ =Cu+Cu2+

Cuprex[4] CuFeS2 + 4Fe3+ = Cu2+ +5Fe2+ + 2So Cu2+ +2Cl− = Cl2 + Cu

Cymet[9] CuFeS2 + 3Fe3+ = Cu+ +4Fe2+ +2So

3Cu2+ + CuFeS2 =4Cu+ + 2So + Fe2+

Cu+ +4Fe2+ =3Fe3+ +Cu+Fe

Dextec[10] Cu2+ + CuFeS2 +0.75O2 + 0.5H2O=2Cu+ + 2So +FeOOH Cu2+ +2Fe2+ =2Fe3+ + Cu

Ecochem[11] 3Cu2+ + CuFeS2 =4Cu+ + 2So + Fe2+

+ some CuFeS2 +3Fe3+ = Cu+ +4Fe2+ + 2So

2Cu+ =Cu+Cu2+

some Cu+ + Fe2+ = Fe3+ + Cu

some Cu2+ +2Fe2+ =2Fe3+ +Cu

Electroreduction [22] 2CuFeS2 + 2H• + 4H+ = Cu2S + 3H2S + 2Fe2+

Cu2S(s) +2H (surf)= 2 Cu(s)+ H2S

H+ + e− = H•

H2S = S◦ + 2H+ + 2e−

Electroslurry[12] CuFeS2 + 4Fe3+ = Cu2+ +5Fe2+ + 2So Cu2+ +2Fe2+ =2Fe3+ + Cu

Elkem[13] 3Cu2+ + CuFeS2 =4Cu+ + 2So + Fe2+

CuFeS2 + 3Fe3+ = Cu+ +4Fe2+ +2So

2Cu+ =Cu+Cu2+

Galvanox[14] CuFeS2 + 4Fe3+ = Cu2+ +5Fe2+ + 2So Cu2+ +H2O=0.5O2 +Cu+2H+

HydroCopper[3] CuFeS2 + CuCl2 +0.75O2 = 2CuCl+ 0.5Fe2O3 + 2So NA (precip. CuO, hydrogen reductionto Cu)

Intec[15] Cu2+ + CuFeS2 +0.75O2 + 0.5H2O=

2Cu+ + 2So +FeOOH

2Cu+ =Cu+Cu2+

Leach/SX/EW (ore) CuS+ 2O2 = Cu2+ +SO42−

(for comparison to CuFeS2 leaching)

Cu2+ +H2O=0.5O2 +Cu+2H+

(for comparisononly)

Minemet[16,17] 3Cu2+ + CuFeS2 =4Cu+ + 2So + Fe2+ Cu2+ +H2O=0.5O2 +Cu+2H+

Nenatech[18,19] CuFeS2 + 4Fe3+ = Cu2+ +5Fe2+ + 2So Cu2+ +H2O=0.5O2 +Cu+2H+

Nitric Acid[20] 3CuFeS2 + 5HNO3 +15H+ =3Cu2+ +3Fe3+ +10H20+6So + 5NO Cu2+ +H2O=0.5O2 +Cu+2H+

USBM[21] CuFeS2 + 3Fe3+ = Cu+ +4Fe2+ +2So Cu+ + Fe2+ =Fe3+ +Cu

Considerable research has been performed to replace smelting

andconvertingwithhydrometallurgicalprocessingof chalcopyrite

ores [2–22]. A list of many of the processing methods that do notinvolvepressurizedvesselsarepresentedin Table1.Othermethods

have been developed for elevated pressure applications that will

not be discussed here.

1.1. Halide based leaching and electrowinning

Note that of the processes shown in Table 1, those with halide

are generally performed at lower temperature (near ambient con-

ditions) than those with sulfate. Halidebased leaching is generally

muchfaster thansulfate leaching at ambient temperature.Chloride

salts such as sodiumchlorideare readily availableandinexpensive,

and in some locations seawater brines are used out of necessity in

arid coastal areas. In addition,halides can in some cases be directlyintegrated with gold leaching. Thus, the halide based methods are

among those most likely to be used in a heap leaching scenario

for chalcopyrite ore. Metal recovery experiments using integrated

leaching-electrowinning [23,24], have also been performed for

recovery of metals such as Cu, Ag, Pd, Sn, and Pb from electronic

scrap in halide media. Copper recovery from IPC (Inco Pressure

Carbonyl) process has been reported, where multistage leaching

wasutilizedin order toproduce copperwithout solventextraction.

However, most of these experiments were performed for metal

rich residue leaching. Other methods, such as many of those in

Table 1, can be effective in concentrate leaching scenarios, but are

notlikelyto beutilizedin commercialheap leachenvironmentsdue

to reagent costs, heating costs, capital costs, and a variety of other

reasons.

Cupric chloride and ferric chloride solutions are very efficient

oxidizing agents for sulfide mineral leaching [9,10]. Leaching of

chalcopyrite in chloride media can be represented by [4,6].

CuFeS2+4FeCl3→ CuCl2+5FeCl2+2S0

CuFeS2+3CuCl2+4Cl−→ 4CuCl2−+FeCl2+2S0

These reactions suggest that chloride based leaching of chal-

copyrite using cupric chloride and ferric chloride as leachants,

produces cuprous as well as ferrous ions. The associated elec-

trowinning reactions can be expressed as:

CuCl2−+e−→ Cu + 2Cl−(cathode)

CuCl2−→ CuCl2+e−;FeCl2→ FeCl2

++e−(anode)

Some supplemental oxidation is needed to meet the stoichio-

metric requirements drivethe chalcopyrite leaching reactions. The

additional oxidation can be provided by air injection. Also, oxida-

tion of remaining ferrous ions after the electrowinning step helps

to facilitate FeO(OH) precipitation prior to leaching.

Producing quality copper in chloride media often requires

smooth deposits to avoid entrapped impurities as well as short-

circuiting. Appropriate additives and mass transport control are

generally required to achieve smooth deposits in industrial elec-

trowinning. Thus, this study will present research in this area that

is applied to copper chloride media.



A. Rodchanarowan et al. / Electrochimica Acta 140 (2014) 447–456 449

Fig. 1. Schematicdiagram of leaching and electrowinning experimental set up.

2. Experimental Procedures

2.1. Leaching Tests

Inorder toexamine theviability ofhalideleaching[25], f actorial

designsof experiments (twolevels, threefactors)wereestablished.

Factors chosen in this case are acid concentration, ratio of concen-

trationofferricandferrous ions,andratioofconcentrationof cupric

and cuprous ions. The amount of copper extracted (gm/gm of ore)

was chosen as the response variable. Laser induced breakdown

spectroscopy analysis of ore samples was performed for elemen-

tal characterization. Line identifications were done using PLASUS

Specline software. Chalcopyrite ore (5 grams) of size (-35 +100)

was taken and wet screened properly for removal of fines. Ore

was then dried for further use. A small 50ml burette was used for

leaching. Leaching solution from the reservoir was pumped into

theburette where it fluidized oreparticles. This fluid wassent back

to the reservoir. This operation was carried out for a period of two

days.

The experimental matrix for leaching test conditions is pre-

sented in Table 2. Eight different experiments were conducted.

After completion of leaching, solids were filtered out from the

column and dried. Leaching residue was completely ground and

digested in aqua regia. Inductively coupled plasma mass spec-

troscopy was conducted, in order to determine the amount of

leached copper.

2.2. Electrowinningwith combined leaching

Inorder toevaluateelectrowinningperformance, thesamesolu-

tions were used for both electrowinning and leaching as indicatedinTable2. Theseexperiments areessentialfor exploringthe validity

and performance evaluation of an overall integrated process.

Table 2

Factorial design test matrix for leaching and electrowinning.

Test ID Cu++(M) Cu+(M) Fe+++(M) Fe++(M) HCl(M)

Cu01-09Fe01-09H05 0.01 0.09 0.01 0.09 0.05

Cu09-01Fe01-09H05 0.09 0.01 0.01 0.09 0.05

Cu01-09Fe09-01H05 0.01 0.09 0.09 0.01 0.05

Cu09-01Fe09-01H05 0.09 0.01 0.09 0.01 0.05

Cu01-09Fe01-09H15 0.01 0.09 0.01 0.09 0.15

Cu09-01Fe01-09H15 0.09 0.01 0.01 0.09 0.15

Cu01-09Fe09-01H15 0.01 0.09 0.09 0.01 0.15

Cu09-01Fe09-01H15 0.09 0.01 0.09 0.01 0.15

Stainless steel cathodes (thickness =0.06mm andarea 2-3cm2)

were used. Cathodes and anodes were spaced 1cm apart. In order

to simulate an actual tank house environment, lead was used astheanode.The volumeof electrolyte foreach test was100 ml.Elec-

trowinning operations were carried out at 40◦C. The duration of

electrowinning (EW) was 20hours for each test.

Deposition was carried out using galvanostatic current at

5 mA/cm2. Theratio of cupric tocuprous ions, ferric to ferrous ions,

and HCl concentration were selected as factors. Current efficiency

was the response variable.

A labscale experimentalsetup wasestablished inorder toevalu-

atepreliminaryviabilityof simultaneous leachingandEWasshown

in Fig. 1. In this experiment, leaching solution was circulated from

the EW cell through the column, which is filled with ore, and then

returned to theEW cell. The recirculating solution wasmaintained

at a set pH by a pH controller. Eh and pH of the solution were con-

tinuously monitored. Electrowon copper was measured by weightat regular intervals. Stainless steel electrodes were used as the

working electrodes. A platinum mesh electrode was chosen as the

counter electrode. Scanning electron microscope (SEM) character-

ization of selected electroplated samples was performed using an

FEI Nova NanoSEMTM.

Thegeneral test conditions for ore leaching and electrowinning

were 1.9 M CaCl2, 0.1M CuCl2, 500 grams of -14+ 35 Mesh ore, 1

literof totalsolution, pH1.5, 2.8litersperhourof recirculatingflow.

It should benotedthat this integratedleaching-electrowinning test

was performed using cupric chloride in the leaching solution to

examine and validate the proof of concept. Calcium chloride has

been used to recovery of various heavy metals from soil [26,27] as

well as to recover copper from arsenicalCu-Co sulfideconcentrate.

In this study CaCl2 was added to enhance recovery and moderate

the free sulfate and iron concentrations.

2.3. Additive and Mass Transport Testing

A three component electrowinning cell was used in the exper-

imental deposition of copper to evaluate roughness. It consisted

of a platinum counter electrode and a saturated calomel electrode

(SCE), against which thepotentials are reported. Theworking elec-

trode was a copper disc (99.999% pure from Alfa Aesar) mounted

in a Teflon holder with an area of 0.203 cm2 exposed to the elec-

trolyte. Itwaspolishedwith600-grit polishingpaperto removethe

deposition products from the previous tests and then rinsed with

pure water. This electrode was further polished with Micropolish

alumina powder (0.05m) to obtain a smooth, clean, defect-free




Fig. 2. LIBS spectrum of chalcopyrite oresample. Inset showsa portion of oresurface, chosen for elemental analysis.

surface. Finally the electrode was cleaned in an ultrasonic water

bath to remove any polishing particles from the surface. All solu-

tionswere prepared using reagent grade chemicalsandASTM TypeI water. Electrochemical tests were performed using an EG&G 273

potentiostat, operated using PowerSuite software made by Prince-

ton Applied Research, and PCI4/750 potentiostat operated using

Virtual Front Panel software, both made by Gamry Instruments,

connected to an IBM compatible PC and AFASR rotator from Pine

Instruments forpotentiostaticand galvanostaticcurrent transients.

Surface roughnesswascharacterized bya CCDIris camerabySONY

with the help of LEAD CAPTURE and LEAD CONVERT software (by

LEAD technologies) along with Microimage software (University

of Utah). Surface roughness calculations were performed by MAT-

LAB (Mathworks Inc.). Surface roughness was quantified as the

quadratic mean for the vertical deviations of the area profile of

electrodeposited surface. Selected samples were examined using

an SEM to examine electrodeposit quality.

3. Results and Discussion

3.1. Application scenarios for chalcopyrite leaching in chloride

media

One approach to reducing energy in chalcopyrite ore leaching

is to utilize run-of-mine or crushed ore in heaps to reduce com-

minution costs. Elemental characterization of ore sample based

on LIBS spectrum suggests that it contains elements such as Cu,

Fe, S, Si and trace amount of other elements including Zn and Al

(See Fig. 2). Leaching can be performed using chloride media to

recover copper. The use of chloride media results in rapid leach-ing of chalcopyrite and the production of cuprous chlorides that

require only half of the electrons (Cu+ + e−↔ Cu) that are required

for conventional electrowinning of copper (Cu2+ +2e− ↔ Cu). In

addition, the cell voltage is reduced by approximately half due to

theuse ofcuprous andferrous ions oxidation(Cu+↔Cu2+ + e−; Fe2+

↔ Fe3++ e−) rather than the conventional water hydrolysis (2H2O

↔ 4H++ O2 + 4e−) at the anode. The change from water hydroly-

sis to cuprous and ferrous oxidation also eliminates acid misting

caused by oxygen evolution, thereby creating a more environmen-

tally sustainable practice. The cupric and ferric ions generated at

the anode can be used to leach more chalcopyrite, thereby cir-

cumventing the need for a separate reduction process. The main

negative aspects of chloride media are greater corrosion and the

potentialneed toseparateanolyte andcatholyte. It shouldbe noted

that theexperiments in this study didnotuseseparate anolyte and

catholyte.

3.1.1. Preliminary leaching and electrowining findings

Fig. 3 shows a 3D plot of copper recovery versus the ratio of

cupric to cuprous ions and ratio of ferric to ferrous ions, which has

been drawn using STATISTICA 9 software. The fraction of copper

dissolved for eightdifferent experiments (SeeTable 2) is presented

in graphical form. The leaching solution with low ferric ion, high

ferrous ion, high cupric ion, low cuprous ion and high acid con-

centration (Cu09-01Fe01-09H15), results in maximum leaching. It

was observed that maximum 2-day recovery was ∼ 0.005g Cu/g

Ore fromanore witha copper content of ∼ 0.0074g Cu/g Ore. Thus,

the extraction of copper reached 68% in 2 days.

From the results of the factorial design analysis of electrowin-

ning experiments, which are graphically presented in Fig. 4, it can

be concluded that a low ferric to ferrous ion ratio leads to max-imum current efficiency of approximately 70%. This corresponds

to 0.7 copper atoms per electron, which is much higher than the

copper yield of only 0.49 atoms per electron in conventional elec-

trowinning from sulfate media assuming 98% current efficiency.

Fig. 4 also shows that a high ferric to ferrous ion ratio has the max-

imum adverse effect on electrodeposition current efficiency (See

Fig. 3. 3 D contour plot for recovered copper vs. different factors, based on output

of factorial design experiments. Experimental details are represented in Table 2.




Fig. 4. Contour plot of current efficiency vs. different variables.

Table2). High acid content aswell ashigh cupric/cuprous ratio alsocauses an adverse effect on electrodeposition/current efficiency.

Fig. 5 shows an SEM micrograph of an electrodeposited sample

prepared from such a condition. It can be seen that surface of elec-

trodeposit is porousandgrainsarenotadjacent.Most of thegrains

are ellipsoidal and vertically oriented. Grains are ∼ 1-3m long,

grain distributionis such that porosity canbeobserved throughout

thefilm. Such anobservation supports lowcurrent efficiency. It has

been already reported that electrolysis of cupric chloride causes

corrosion of copper cathode and causes precipitation of CuCl [23].

Although the reduction in current efficiency associated with ferric

and cupric ions is expected, it is useful to note that reasonable cur-

rent efficiencies areachievable without theuseof a diaphragmcell

or anode bags. In an industrial application, electrolyte flow con-

trol or separation of anolyte and catholyte would result in greaterefficiencies.

Results of leaching and electrowinning tests suggest that there

is a possibility of effective integrated leaching-electrowinning,

if a proper combination of Fe3+, Fe2+, Cu2+, Cu+ and pH is

utilized. It can be seen that the high acid concentration, low

Fe3+ concentration combination can be utilized for integrated

Fig. 5. SEM micrograph of an electrodeposited sample prepared from high acid

content as well as high cupric/cuprous ratio.

leaching-electrowinning. More investigation is needed to deter-

mine appropriate solution species concentrations.

Integratedleaching-electrowinning experiments werealsoper-

formed using chalcopyrite ore following the procedures discussed

previously. Initially, 6.3 gram of cupric chloride was added in the

form of chloride salt in order to simulate a circulating leaching

solution. As the electrolysis and leaching occurred using the same

recirculated electrolyte through the leaching column and elec-

trowinning cell, thecopperproductionat thecathodeexceeded the

initial copper amount after 6 days. When the test was completed

after 15 days, it is estimated that more than 50% of the copper in

the ore was dissolved and recovered by electrodeposition.

3.1.2. Application Issues and Needed Adaptations

In order to utilize chloride media in commercial chalcopyrite

ore leaching thatis coupled withelectrowinning, someadaptations

need to be made. In order to do direct electrowinning of leach-

ing solutions, there must be a moderately high dissolved metal

concentration. Thus, heap leaching solutions would need to be

more concentrated than usual, which may require pulsed solu-

tion applications to reduce volume and increase dissolved copper

concentration.

In order to retain reasonable efficiency in electrodeposition and

in subsequent leaching, the anolyte and catholyte should be sep-

arated by directed laminar flow in the electrowinning cell or by

diaphragm use. The catholyte should originate from the leaching

solution, andtheanolyte shouldoriginatefrom thetopof thecath-

ode and be sent for further oxidation if needed to ensure good iron

precipitation and optimal electrochemical activity for leaching.

Althoughmostof the ironmay be removableby precipitation, it

may beadvantageousto concentratesome of thecopper insolution

by solvent extraction prior to electrowinning.

Electrolytepurificationthroughsomebleedingand treatingmay

be needed to keep unwanted ion concentrations within desired

limits.

Electrodeposit morphology needs to be controlled to be either

conventional copper cathodeplate ora granulatedproductthrough

appropriate control of current density. Moderate current den-sity and appropriate additives can be used to achieve plate

deposits. High current densities can be used to achieve granulated

product.

3.2. Electrodeposit Roughness Control for Improved Efficiency

andQuality Control

Surface morphology of electrodeposits is greatly affected by

the parameters such as substrate orientation and initial rough-

ness, density anddistributionof activenucleation sites, nucleation

andgrowth, impurity concentrations,andexperimental conditions

[28–30]. Deposit roughness can lead to increased product impu-

rity levels and short-circuiting. Rough deposits can trap solution

and particles into the deposit, thereby increasing product impu-ritylevels,whichincreasesproduct rejectionratesand productivity

[28–30]. In addition, rough deposits are associated with unde-

sirable localized growth. If local growth feature size exceeds the

separation between cathodes and anodes, short-circuiting occurs.

Short-circuiting creates current inefficiency and wastes power.

Thus,electrodeposit smoothingusingadditivesandmasstransport

control is important to sustainable electrometallurgy.

3.2.1. Effects of additives

Additive assisted smoothing is believed to cause a local

inhibition as well as acceleration of deposition rate. Copper

electrodeposition from sulfate bath was earlier examined using

an AFM. Examination of 5m×5m area suggests that sur-

face feature dimension is ∼ 1m, it was initially observed that




Fig. 6. A comparison of surface topography of copper electrodeposit with additive (a) and without additive (0.01g/L gelatin) (b), on a circular hole after 12minutes of

depositionperiod (height not to scale). Electrolyte contains∼ 0.1M CuCl, 4M NaCl and 0.01M HCl. The cathodic current density was ∼ 25mA/cm2 at 1000 rpm.

the average roughness value for 300s electrodeposition was ∼

250 nm [28]. For these experiments 500ppm of Ethylene gly-

col (MW 3400) was used. Other additives were also utilized

such as bis (3-sulfopropyl) disulfide, and l-(2-hydroxyethyl)-2-imidazolidinethione, which have been used by others for copper

electrodeposition to produce smoother deposits [29]. It has been

reported that Bis-(3-sulfopropyl)-disulfide sodium salt improve

tensile strengthandhardnessof copperdeposits [29]. Effectof acti-

vatedpolyacrylamide (APAM) on thesurfacemorphology of copper

wasalso examined. It was reported that long duration electrowin-

ning testsusingAPAM results in slightly columnardeposit whereas

use of Gaur results in relatively small grains [30].

Copper electrodeposition on the substrates containing micro-

size pores in chloride electrolytes without smoothing additive is

enhanced at the edges of pores due to enhanced localized mass

transportat pore edges. In contrast, useof additives such as gelatin

(∼ 0.012g/L) can cause preferential plating bottom of pore (See

Fig. 6a, b). A 3D diagram shows that uniformity in electrodepo-sition increased when additive is used. The effect of additives on

electrodeposit quality is shown in the topographic images pre-

sented in Figs. 7 (a, b). These Figs. show that gelatin significantly

reduces surface microroughness relative to a control test without

additive.

Gelatin is composed of amino acids which are connected by

peptide bonds. The molecular weight of gelatin in this study is

about 200,000. Themain amino acid component is glycine. Glycine

is found in almost one third of the amino acids found in gelatin.

Proline is the second most common amino acid found in gelatin.

Fig. 8 shows the effects of a variety of additives on electrode-

posit roughness. Fig. 8 reveals that glycine and proline do not

contribute significantly to smoothing as monomeric molecules.

However, when glycine and proline are combined in polymericform in the gelatin molecule, significant smoothing is achieved.

Similarly, when small molecular weight compounds are used, lit-

tle if any smoothing takes place (see PEG, PAA, PVP, and PEO data

in Fig. 8). In contrast, as the molecular weight increases above

approximately 100,000g/mole, smoothing was relatively consis-

tent, regardless of the polymer used in this study. Thus, molecular

size appears to be a critical factor associated with electrodeposit

smoothing for the system investigated in this study. SEM micro-

graphs of long term electroplated samples are shown (See Fig. 9).

It can be seen that most of the grains are long and adjacent to

each other. No preferential growth was observed at the surface of

electrodeposits.Selectedareasofelectrodepositswere slightlypol-

ished, inorder to observe pit holes or void inside the deposit. It can

be seen that most of the electrodeposit is free from such holes ordiscontinuity, which suggests filling is uniform.

One of the causes for rougher electrodeposits is the develop-

ment of an unstable interface front [31]. Another aspect is an

effect of chloride anions on the electrode surface as well as an

attractive interaction between chloride and copper ions, which

can result in formation of local structures [31–33]. In these struc-

tures, ionic species can be adsorbed easily. It should be noted

that diffusion characteristics of additives are different in chloride

and sulfate media. It also causes a difference in bottom up filling

as well as conformal growth, which results in different surface

Fig. 7. Surface topography map of copper electrodeposits a) in the absence of additives, andb) in the presence of 0.013g/L gelatin from an electrolyte containing 0.1mol/L

CuCl, 4mol/L NaCl, and0.01mol/L HClat room temperature,cathodic current density of 15mA/cm2

, 15hours, and1,000rpm.




Fig. 8. Effect of different additives on surface microroughness of copper electrode-

posits obtained from an electrolyte containing 0.1mol/L CuCl, 4 mol/L NaCl, and

0.01 mol/L HClat room temperature using a cathodic current density of 25mA/cm2

for3 hours with a rotational speed of 1,000rpm. (PEO is polyethyleneoxide, PEGis

polyethyleneglycol, PVAis polyvinylalchohol,PVP is polyvinylpyrrolidone, PAA is

polyacrylic acid).

quality [33]. The inhibition capacity of electrodeposition is dif-

ferent due to difference in nature of sulfate and chloride ions

[31–34]. Copperdeposition from sulfate media isbelievedto follow

progressive nucleation and subsequent growth of 3-dimensional

centers under diffusioncontrol. However, the presence of chloride

ions causes challenges such as localized grain corrosion. All these

challenges canbe mitigated to some extent by specific additivesor

hybrid additives [33].

In this study, some copper electrodeposits were collected from

several places, digested anddiluted for inductively coupled plasma

optical emission spectroscopy (ICP-OES) analysis using a Spectro

Geneses optical spectrometer. Data collectionand calibration were

performed using Smart Analyzer Vision software. The detection

limitof ICPanalysiswas∼0.0014ppmand regressioncoefficientfor

calibration curve fittingwas∼ 0.9999. Table 4 provides a summary

of the ICP analyses.

Additional testing indicatedthat largemoleculescontributed to

increased nucleation density, which contributed to the smoothing

effect of these molecules [35]. This effect is related to mass trans-

portthroughadsorbedmoleculelayerporesas describedelsewhere

[35].

3.2.2. Effects of mass transport

Effects of mass transport [36] f or copper electrodeposit mor-

phology was earlier studied and reported previously, mainly for

sulfate media electrolytes [37,38]. Methods such as impedance

and resistivity measurements, SEM imaging, and AFM character-

ization were used for roughness evaluations [36–38]. An effect of

direct andpulsedcurrent wasalso studied earlier forsulfate media

electrodeposition. Their results suggest, based on small area sur-

face examination, that smoother and homogeneous patterns are

more likely under dc-electrodeposition conditions [37]. However,

for chloride media electrolytes in our case, rms surface roughness

of thedepositsobtainedunderpulsedcurrent conditionswas lower

thanthat obtainedunderdirectcurrentconditionsfor highervalues

of i/iL with the same quantity of charge transferred. It is important

tomention that most ofourexperimentswere conductedfor longer

periods of time.

The rate of metal electrodeposition from its aqueous solution

is governed by the kinetics of the reactions occurring at the sur-

face of theelectrodes. Factors that usually control the rate of metal

removal from its aqueous solution by electrowinning are: 1) the

rate of electrochemical reaction occurringat theelectrodesurface;

and2) therateof transportof reacting ions to theelectrodesurface.The electrochemical reaction results in depletion of the reacting

ions at the electrode surface that are replenished by mass trans-

port. A modified version of the Butler-Volmer equation, that takes

into account the rate of transport of ions to the electrode surface,

can be written as [36]

i = k

[C ba(C saC ba

)a

exp(˛aF

RT )− C bc (

C sc C bc

)c

exp(−˛c F

RT )] (1)

Fig. 9. Scanning electron microscope imageof copper electrodeposit (as depositedand slightly polished), Electrolyte contains∼ 0.1M CuCl, 4M NaCland0.01M HCl.




Table 3

Comparison of surface roughness values fromrotating disc experiments for direct and pulsed electrodeposition condition.

Charge (C/cm2) DC Roughness (m) Time (min) Pulse Roughness (m) Time (min)

75 4.58 120 6.23 120.0

108 5.39 120 8.00 473.4

180 13.20 120 13.91 460.5

250 24.96 120 14.28 479.7

Fig.10. Surfacetopography image of copper rotatingdisc electrodesampleobtainedafterelectrodepositionat a cathodiccurrentdensityof 10mA/cm2 for30min at rotational

speed of 250 rot/min and500 rot/min. Bath contain 0.1mol/L CuCl, 4.0mol/L NaCl and0.01mol/L HCl.

where k’ is a constant that is directly related to the equilibrium

exchange current density, C b(a or c) is thebulk concentration for the

anodic (a)orcathodic(c) reactions,C s(a or c) is thesurfaceconcentra-

tion for the anodic (a) or cathodic (c) reactions, is overpotential,

R is the gas constant, T is absolute temperature, and is a factor

that depends upon reaction mechanisms and related factors and it

is usually between 0.25 and1. In subsequent expressions,will be

assumed to be 1.

If the overpotential becomes very large, then a limit is reachedwhere the rate of mass transport reaches a maximum level. The

current density measured under these complete mass transport

control conditions is known as the mass transport limiting current

density (iL). This limiting current density is governed by the diffu-

sion rates of the dissolved metal ions in the solution and hence it

is also known as diffusion controlled current density. This can be

written:

iL =nFD(C ba − C sa)

ı (2)

whereD is thediffusivityof thedissolvedspecies andı is thethick-

ness of the diffusion layer.

If mass transport is controlling the current flow in electrodepo-

sition, the limiting current density is an important parameter thatcanbeused tostudy this diffusionlimitedmass transfer.Therefore,

a series of experiments were carried out to study cathodic elec-

trodeposition of copper under direct current conditions. The effect

of mass transport on electrode surface of copper electrodeposit

morphology was studied by varying rotational speed of work-

ing electrode from 250 to 1000rpm. It has been observed that

surface roughness of electrodeposit decreases with increase in

rotational speed. Such an observation was for fixed direct cur-

rent conditions (See Fig. 10). On the other hand an increase in i/iL

ratio causes enhanced surface roughness. Pulsed potential results

in a short deposition period, during which the depositing ions

become depleted in solution near the electrode interface. A rest

period allows replenishing of depositing ions near the electrode-

electrolyte interface. Thus, the rest period allows for an increased

limiting current density for the short duration of the applied

pulsed voltage. For argon purged electrolyte containing 0.1mole/L

CuCl, 4mol/L NaCl, and 0.1mol/L HCl a ∼ 30% enhancement in

limiting current density wasobservedwhen thepulse-offtimewas

increasedfrom 10ms to50ms. It canbe understood that thelonger

relaxation time allowsgreater replenishment of ions in thebound-

ary layer, resulting in a higher mass transport limiting current.

It was observed that surface roughness of deposits obtained

under pulsed current is low compared to deposit obtained at dcconditionwithhigh i/iL value. Information fromtopographyexami-

nationsuggests that at i/iL =0.50, rmsroughnesswasalmostdouble

for pulsed plating condition compare to dc-electrodeposition. The

surface roughness of electrodeposits depends on nucleation and

growth rate. Growth wasmonitoredfor trapezoidal anomaly,it was

observed that highest point on growing surface receive higher cur-

rent andhavegreateraccessoffluxofincomingreactionions.Sucha

regionwhichreceive higherflux, highergrowthof electrodeposit is

expected. Increase in rotational speed causes lowering of preferen-

tial growthof electrodepositsdue to more uniform current density

distribution. Increase in cathodic overpotential results in higher

current density. However such higher overpotential increases the

difference in current density at top and bottom region of trape-

zoidal anomaly, which results in different growth rate in these

regions. Table 3 shows thecomparison of surface roughness values

from rotating disc experiments for direct and pulsed electrodepo-

sition condition.

For a given rotational speed of a rotating copper disc, a limiting

current density was observed in the cathodic direction as seen in

Fig. 11. In Fig. 11, it is seen that changes in the applied potential

Table 4

Copper electrodeposition purity (samples werecollected fromdifferent places).

Sample Copper purity

1 99.1%

2 99.0%

3 99.4%




Fig. 11. Potentiodynamic scans for argon purged electrolyte with 0.1mol/L CuCl,

4mol/L NaCl and 0.01mol/L HCl as a function of rotational speed of electrode at a

scan rate of 5mV/s. A calomel electrode was used as a reference electrode against

which all thepotentials were measured.

Fig. 12. Limiting current densities under direct current conditions in a bath con-

taining 0.1mol/L CuCl,4.0 mol/L NaCl and0.01mol/L HCl.

Fig. 13. Effect of i/iL on rms surface roughness of copper electrodeposits obtained

froma bathcontaining0.1 mol/LCuCl,4.0mol/LNaCland0.01mol/LHClunderdirect

current conditionsat various rotational speeds of copper working electrode.

result invery little change in the current in the regions where mass

transfer limitations dominate. In this region the electrochemical

reaction can only proceed as quickly as the reacting ions can be

transported to the electrode surface.

This region of nearly constant cathodic current density can be

viewedas thebalancebetween therateof electrochemicalreaction

and the rate at which the reacting ions are transported to the elec-

trode. With increase in the rotational speed of the disc, this rate of

mass transport increases, thereby increasing the limiting current

density as seen in Fig. 12.

One way to characterize the extent to which the deposition is

mass transport controlled is to determine the ratio of the applied

current density to the limiting current density. As this ratio (i/iL )

approaches1 thesystem approachescompletemasstransportcon-

trol. When i/iL is near zero the deposition process is controlled by

electron charge transfer kinetics. Therefore, the effect of i/iL on

root- mean-squared surface roughness of copper electrodeposits

wasstudied.It wasfoundthat thesurface roughness increasedwith

increase in i/iL for direct current conditions as seen in Fig. 13.

4. Conclusions

In summary, potential of copper recovery using chloride media

was examined using coupled leaching-electrowinning approach.

The 2-day copper extraction was as high as 68%. Deposit qual-

ity, percentage recovery, and electrowinning efficiency were also

examinedusingelectrolytescontainingdifferentlevels ofdissolvediron and copper. The copper electrodeposited per electron in chlo-

ridemedia washigherthan forconventional sulfateelectrowinning

systems. Analyses were done using statistical models and avail-

able theory for chloride media leaching. Electrodeposit quality

improvements were accomplished using proper choice additives

and mass transport conditions. A detailed investigation were per-

formed using more than ∼ 25 additives as well as different mass

transport conditions including rotationalspeedvariation,different

limiting current density, pulse and dc electrodeposition.

References

[1] M. L. Free, M. S. Moats, T., Robinson, N., Neelameggham, G., Houlachi, M.,Ginatta, D. Creber, and G. Holywell, Electrometallurgy–Now and in the Future,Proceedings ofElectrometallurgy2012 Symposium, Ed.M. L. Free, G.,Houlachi,E., Asselin, A.,Allanore, J., Yurko, S., Wang, TMS, Warrendale, 2012, p. 3.

[2] M.C. Kuhn, N. Arbiter, H. Kling, Anaconda’s Arbiter Process for Copper, CIMBulletin, February,1974, pp. 62–73.

[3] S. Wang, Copper Leaching from Chalcopyrite Concentrates, The Journal of TheMinerals, Metals & Materials Society 57 (2005) 48.

[4] R.F. Dalton, G. Diaz, R. Price, A.D. Zunkel, The CuprexMetal Extraction ProcessRecovering Copper from Sulfide Ores, The Journal of The Minerals, Metals &Materials Society 43 (1991) 51–56.

[5] G.W.McDonald,H. Darus, S.H.Langer,A Cupric BromideProcess forHydromet-allurgical Recovery of Copper, Hydrometallurgy 24 (1990)291–316.

[6] G. M. Ritcey, K. T. Price, and B. H. Lucas, Recovery of Copper and Zinc from-Complex Chloride Solutions, United States Patent, No. 4362607, 7 December1982.

[7] J.L. Limpo, J.M. Figueiredo, S. Amer, A. Luis, the CENIM-LNETI Process: A NewProcess for theHydrometallurgicalTreatment of ComplexSulphidesin Ammo-niumChloride Solutions, Hydrometallurgy 28 (1992)149.

[8] G. E. Atwoodand C. H. Curtis, HydrometallurgicalProcess forthe Production of Copper, UnitedStatesPatent, No. 3785944, 15 January 1974.

[9] P.R. Kruesi, E.S. Allen, J.L. Lake, Cymet Process-Hydrometallurgical Conversionof Base-Metal Sulfides to Pure Metals, CIMBulletin (1973) 81–87.

[10] P. K. Everett, The Dextec Radial Electrolytic DiaphragmCell, Reinhardt Schuh-mann InternationalSymposiumon Innovative Technology and Reactor Designin Extraction Metallurgy. Proceedings of a Symposium Held at the TMS-AIMEFall Meeting for Extractive and Process Metallurgy. Sponsored by: Metallurgi-cal Socof AIME, Warrendale, PA,USA; Mining & Metallurgical Instof Japan, Jpn;Inst of Mining & Metallurgy; Verein DeutscherEisenhuettenleute, Duesseldorf,West Ger; Technical Assoc for Iron & Steel Production; et al. Metallurgical Socof AIME, 1986, 727-740.

[11] G. Zoppi, Process forthe Production of High Purity CopperMetalfrom Primaryor SecondarySulphides, United States Patent,No.6159356, 12 December2000.

[12] D.A. Dahlstrom, F.A. Bacek, B.C. Wojcik, R.C. Emmett, The ElectroslurryTM

Process-Hydrometallurgical Processing of Chalcopyrite to Electrowon Copper,Proceedings of the Fourth JointMeeting MMIJ-AIME (1980), D-4-3.

[13] C. Haakonsen, Cupric and Ferric Chloride Leach of Metal Sulphide-ContainingMaterial, UnitedStatesPatent, No. 4337128, 29 June 1982.

http://refhub.elsevier.com/S0013-4686(14)01393-0/sbref0010
































































































































































































[14] D.G. Dixon,D.D. Mayne, K.G. Baxter, GalvanoxTM–a novel galvanically assistedatmospheric leaching technology for copper concentrate, Canadian Metallur-gical Quarterly 47 (2008) 327–336.

[15] M. L. Free, Electrochemical Coupling of Metal Extraction and Electrowin-ning, in Electrometallurgy 2001, (ed.) , J. A. Gonzales, J. Dutrizac, 2001,235-260.

[16] J. M. DeMarthe, A. Sonntag, and G. Andre, Method of Obtaining Copper fromCopper-Bearing Ores, UnitedStatesPatent, No. 4023964, 17 May 1977.

[17] J.M. DeMarthe, A. Sonntag, A. Georgeaux, A New Hydrometallurgical Processfor Copper, in: J.D. Yannopoulis, J. Agarrwal (Eds.), in: Extractive Metal-lurgy of Copper, 2, The Metallurgical Society of AIME, New York, 1976,

pp. 825–848.[18] M.M. Hourn and D. W. Turner, Atmospheric Mineral Leaching Process, United

StatesPatent, No. 5993635, 30 November 1999.[19] M. Hourn andD. Halbe, The Nenatech Process: Results on FriedaRiver Copper

GoldConcentrates, Randol’s Copper Hydromet Roundtable ‘99 - Phoenix”.[20] G.Bjorling, I.Faldt,E. Lindgren,I. Toromanov, ANitricAcidRoutein combination

with Solvent Extraction for Hydrometallurgical Treatment of Chalcopyrite, in: J.D. Yannopoulis, J. Agarrwal (Eds.), in: Extractive Metallurgy of Copper, 2, TheMetallurgical Society of AIME, NewYork, 1976, pp. 726–737.

[21] F.P. Haver, R.D. Baker, M.M. Wong, Improvements in Ferric Chloride Leachingof Chalcopyrite Concentrate, Report of Investigations No. 8007, United StatesDepartment of theInterior Bureau of Mines (1975) 1–16.

[22] J.C. Fuentes-Aceituno, G.T. Lapidus, F.M. Doyle, A kinetic study of the elec-troassisted reduction of chalcopyrite, Hydrometallurgy 92 (1–2) (2008)26–33.

[23] McKevitt, B. R. Removal of iron by ion exchange from copper electrowinningelectrolyte solutions containing antimony and bismuth. Master Thesis. TheUniversityof British Columbia, Nov 2007.

[24] N.P. Brandon, G.H. Kelsall, R. Olivje, M. Schmidt, Q. Yin, Metal Recovery from

Electronic Scrap by Leaching and Electrowinning, Energy and Electrochemi-cal Processes for a Cleaner Environment: Proceedings of the ElectrochemicalSociety Proceedings Volume (2001)322–323.

[25] T. Kekesi, M. Isshiki, Electrodeposition of copper from pure cupric chloridehydrochloric acid solutions, Journal of Applied Electrochemistry 27 (1997)982–990.

[26] L. Heasman, H.A. van der Sloot, Ph. Quevauviller, Harmonization of Leach-ing/Extraction Tests, Elsevier,Amsterdam, Jun10 1997, pp. 46–53.

[27] G.A. Smyres, R. L. Kral, K.P.V., Lei, T. G. Carnahan, Bureau of Mines Report of Investigations/1986, Calcium Chloride-Oxygen and Metals Recovery From anArsenical Copper-cobalt Concentrate.

[28] O. Timothy, Drews, C. Jason, Ganley, and Richard C. Alkire, Evolution of Sur-face Roughness during Copper Electrodeposition in the Presence of Additives:Comparison of Experiments andMonte Carlo Simulations, Journal of the Elec-trochemical Society 150 (5)(2003)C325–C334.

[29] Takuya Nagayama, Hiroaki Yoshida and Ikuo Shohji, Effect of Additives in anElectrolyte on Mechanical Properties of Electrolytic Copper Foil, ASME 2013International Technical Conference and Exhibition on Packaging and Integra-tion of Electronic andPhotonicMicrosystems,Burlingame, California, USA, July

16–18,2013.[30] C.P. Fabian, M.J. Ridd, M.E. Sheehan, Assessment of activated polyacrylamide

andguaras organic additivesin copperelectrodeposition, Hydrometallurgy 86(1–2) (2007) 44–55.

[31] N. Tantavichet, M. Pritzker, Copper electrodeposition in sulphate solutions inthe presence of benzotriazole, Journal of Applied Electrochemistry 36 (2006)49–61.

[32] M. Scendo, J. Malyszko, The Influence of Benzotriazole and Tolyltriazole ontheCopper Electrodeposition on PolycrystallinePlatinum fromAcidic ChlorideSolutions, Journal of TheElectrochemical Society 147 (2000) 1758–1762.

[33] K. Lin, J. Shieh, S. Chang, B. Dai, C. Chen, M. Feng, Y. Li, Leveling effects of cop-per electrolytes with hybrid-mode additives, J. Vac. Sci. Technol. B 20 (2002)2233–2237.

[34] B. Panda, Effects of Added Chloride Ion on Electrodeposition of Copper from aSimulatedAcidic Sulfate BathContaining Cobalt Ions, ISRNMetallurgyVolume2013 (2013), ArticleID 930890, 6 pages.

[35] M. L. Free, R. Bhide, and A. Rodchanarowan, Evaluation of mass transporteffects on the nucleation and growth of electrodeposits, Mineral Processingand Extractive Metallurgy (Trans. Inst. Min. Metall. C), in press,2013.

[36] J. Newman and K. E. Thomas-Alyea, Electrochemical Systems, 3rd Edition,Hoboken, NJ: John Wiley,(2004)p.274.

[37] Jean-Marie Quemper, Elisabeth Dufour-Gergam, Nad‘ege Frantz-Rodriguez, Jean-Paul Gilles, Jean-Paul Grandchamp, Alain Bosseboeuf, Effects of directand pulse current on copper electrodeposition through photoresist molds, J.Micromech. Microeng.10 (2000) 116–119.

[38] N.Ibl, K.Schadegg, SurfaceRoughnessEffectsin theElectrodepositionofCopperin theLimiting Current Range,J. Electrochem.Soc. 114 (1) (1967) 54–58.































































































































































































































































































































































































































































































































































(2014) free production of copper from minerals through controlled andsustainable electrochemistry

Documents