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Hydrometallurgy 89

Manganese metallurgy review. Part III: Manganese control inzinc and copper electrolytes

Wensheng Zhang ⁎, Chu Yong Cheng

Parker Centre for Integrated Hydrometallurgy Solutions, CSIRO Minerals, PO Box 7229, Karawara, WA 6152, Australia

Received 6 July 2007; received in revised form 24 August 2007; accepted 25 August 2007Available online 1 September 2007

Abstract

Manganese is often associated with zinc and copper minerals, and can build up in the processing circuits. Part III of the reviewoutlines the current practice and new developments to get a better understanding of manganese behaviour and control inelectrowinning of zinc and copper, and identifies suitable methods and processes to control manganese.

In zinc electrowinning, the presence of small amounts of manganese (1–5 g/L) can minimise the corrosion rate of the anodesand reduce the contamination of the cathodic zinc with lead, but excess manganese results in significant decreases in the currentefficiency. The neutralized zinc feed solution that contains little acid is considered to be the best place to implement manganesecontrol. Various methods and processes for manganese control in zinc electrowinning have been developed. Oxidative precipitationand solvent extraction are the most important methods. For the neutralized zinc solution at pH 5, oxidative precipitation using astrong oxidant such as Caro's acid and SO2/O2 can selectively precipitate manganese as insoluble MnO2 or Mn(OOH), leavingother impurities, e.g., Mg, Cl−, F−, etc. in the circuit. Solvent extraction of zinc using D2EHPA (di-2-ethylhexyl phosphoric acid)can selectively recover zinc from the solution and leave other impurities including manganese in the raffinate.

In copper solvent and electrowinning circuits, the problem of manganese is mainly associated with the decrease in the currentefficiency and degradation of the solvent caused by the higher valent manganese species generated on the anode. The prevention orminimisation of Mn(II) oxidation during the electrowinning is critical. This can be achieved by adding ferrous ions or sulfurdioxide to control the cell potential.© 2007 Elsevier B.V. All rights reserved.

Keywords: Manganese control; Zinc electrowinning; Copper electrowinning

1. Introduction

In the roasting–leaching–electrowinning process forprocessing zinc sphalerite flotation concentrates, somenon-ferritic zinc and manganese are first dissolved in aneutral leach liquor while most of the ferritic zinc andmanganese are then dissolved in a hot acid leach (Harris

⁎ Corresponding author.E-mail address: wensheng.zhang@csiro.au (W. Zhang).

0304-386X/$ - see front matter © 2007 Elsevier B.V. All rights reserved.doi:10.1016/j.hydromet.2007.08.011

and Hanson, 1978). High extractions of zinc andmanganese are achieved in the oxidative pressure-leach process (Bolton et al., 1981). In both processes,most of the manganese reports to the leach liquor.Secondary sources of manganese come from addition ofmanganese, usually as MnO4

−, to the leaching circuit toserve as an oxidant (Filippou, 2004). Additionalmanganese dioxide or potassium permanganate isusually introduced to the zinc sulfate electrolyte fromthe leaching process in order to oxidise iron impurities.

179W. Zhang, C.Y. Cheng / Hydrometallurgy 89 (2007) 178–188

The amount of manganese added varies widely with theamount of iron and other impurities in the solution. Thepurified industrial zinc sulfate electrolyte usuallycontains a substantial amount of manganese (MacK-innon and Brannen, 1991).

In zinc electrowinning, the presence of manganese hasdual effects, positive and negative, depending on itsconcentration in the electrolytes (Krupkowa et al., 1977;Verbaan and Mullinder, 1981). Small amount of manga-nese is needed to present in the electrolyte to reduce thecorrosion of anodes and minimise the contamination ofcathodic zinc by the dissolved lead. Higher concentrationsof manganese in the electrowinning can cause asignificant decrease in current efficiency and it has to beremoved or controlled when building up to a certain level.

In the copper solvent extraction and electrowinning(SX–EW) process, manganese must be controlled toobtain high current efficiency and to ensure the qualityof copper cathodes (Cheng et al., 2000). Higher valentmanganese ions which are generated on the anodes cancause severe degradation of organic extractants in theSX circuit. It is therefore essential to maintain amanganese balance throughout the plant circuit. Thecontrol of impurities involving manganese is still underdevelopment for novel methods and processes.

This paper reviews current practice and new devel-opments to get a better understanding of manganesebehaviour and control in the electrowinning of zinc andcopper, and identifies suitable methods and processes tocontrol manganese.

2. Effect of manganese on zinc electrowinning

Mn2+ ions in the electrolyte could be oxidised toMnO4

− (Vereecken and Winand, 1972) which wasproposed to react immediately with Mn2+ to form Mn3+

and finally MnO2 (Yu and O'Keefe, 2002). MnO2

formation initiated at about 1.6V, evidenced by formationof a brown film on the electrode (Vereecken and Winand,1972). Both MnO4

− and Mn3+ ions decreased the currentefficiency of zinc deposition because they depolariseddischarge of the H+ ions. The positive and negative effectson zinc electrowinning are summarised below.

2.1. Positive effects

2.1.1. Effect on anodesLead alloys containing silver are the primary insoluble

anodes used for zinc electrowinning. These anodes sufferfrom corrosion and have a detrimental effect on cathodepurity from incorporation of lead corrosion products.About 1–3 g/L Mn2+ ions are usually required in the

electrolyte tominimise the corrosion rate and to reduce thecontamination of the cathodic zinc with lead and thus topromote the purity of cathodic zinc products (Krupkowaet al., 1977;MacKinnon andBrannen, 1991).Schierle andHein (1993) identified that the MnO2 layer formed had adepolarizing effect on the Pb–Ag–Ca anodes in asynthetic zinc and manganese sulfate electrolyte. Newn-ham (1992) investigated the corrosion rates of anodesmade from various lead/silver alloys under variousconditions. In the absence of manganese, the corrosionrate was effectively independent of current density in therange studied, whereas in the presence of manganese, thecorrosion rate decreased with decreasing current density.Saba and Elsherief (2000) observed that the presence ofmanganese up to 1.8 g/L in the electrolyte had little effecton zinc polarization while Ivanov and Stefanov (2002)found that up to 5 g/L of Mn(II) present in the zinc sulfateelectrolyte did not exert a large effect on zinc deposition.

2.1.2. Effect on higher electropositive metalsIn addition to the inherent over-potential, impurities

such as Cu, Co, Ni and Sb in the electrolyte could have asignificant polarization impact (Ivanov, 2004). Thepresence of manganese ions decreased the deleteriousinfluence of the above metals that are more electropos-itive than zinc. It was proposed that the manganesehydrates block the active hydrogen spots of theimpurities on the zinc cathodic surface. Thus, theprocess of zinc re-dissolution was inhibited. This effectwas more pronounced at high temperatures. A smallamount of MnO4

− (15–80 mg/L) had a beneficial effecton zinc deposition when the electrolyte also containedSb3+ (Hosny et al., 1989; Ivanov and Stefanov, 2002).

2.1.3. Effect on anode chlorine gas evolutionA substantial amount of chloride ions may be present

in the zinc electrolyte when processing steel industrialdust (Yoshida et al., 1997). Chloride anions in theelectrolyte attack the anodes which are commonly madeof Pb alloy and increase the corrosion rate (Newnham,1992). It was proposed by Kelsall et al. (2000) thatdeposition of manganese dioxide on anode surfacesprobably produced a diffusion barrier to anodic chlorineevolution, and Mn(II) species scavenged any chlorinethat did form in the electrolyte. Hence, current efficiencylosses for zinc deposition were limited. In addition, theinhibiting chlorine generation also has a major benefitfor the cell house hygiene.

2.1.4. Effect on positive interaction with other ionsMacKinnon (1994) studied the effects of foaming

agents, and their interactions with antimony, manganese

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and magnesium, on zinc deposition current efficiency,morphology and orientation. Both Dowfroth andSaponin decreased the zinc deposition current efficiencyand also changed the deposit morphology and orienta-tion. The addition of MnSO4 to an electrolyte containing10 mg/L Dowfroth increased the current efficiency forzinc deposition and changed the deposit morphologydue to a positive interaction with manganese.

2.2. Negative effects

2.2.1. Effect on current efficiencyA concentration of Mn2+ ions higher than 3 g/L in the

electrolyte could result in a significant decrease in thecurrent efficiency (Cathro, 1991). The particles ofMnO2, produced on the anodes, were found to bedeposited on the cathode and formed galvanic pairs withzinc, and the latter dissolved anodically. An increase of10–15% in energy consumption at a high currentdensity (5000A/m2) was observed for industrial electro-lytes containing manganese.

In a study on the effects of manganese, magnesium,sodium and potassium sulfates on the current efficiency,morphology and orientation (MacKinnon and Brannen,1991), it was found that an increase in the concentrationof Mn(II) (sulfate) up to 5.5 g/L in the electrolyteresulted in a decrease in the current efficiency and anincrease in the size of the zinc platelets.

2.2.2. Effect on oxygen over-potentialThe reaction potential and over-potential required for

oxygen evolution is one of the important factors forprocess economics. Rerolle andWiart (1996) studied thekinetics of oxygen evolution on Pb and Pb–Ag anodesduring zinc electrowinning in the absence and presenceof Mn2+ in a sulfate medium using impedance spec-troscopy. It was found that the presence of silver in thelead anode modified both the kinetic parameters of themain reaction of oxygen evolution, and the potentialdependence of the condensed oxide layer. The reactionof oxygen evolution was proposed to be inhibited by asilver salt adsorbate. The electrode coverage by thisadsorbate appeared to be increased in the presence ofMn2+ in the electrolyte, thus changing the inhibition intoa passivation process.

2.2.3. Effect on anode disposal and cleaningToo much Mn2+ (N4 g/L) was found to create an

anode disposal problem and increase the frequency ofanode cleaning (Pajunen et al., 2003). The manganesedioxide layer formed on the anode could not be removedwithout losing the active coating of the anode. The same

problem was also found for hybrid anodes in which amixed metal oxide coated titanium mesh was attached toa lead base material.

2.2.4. Effect on organic reagents in zinc SX–EW circuitIn zinc SX–EW circuit, the presence of manganese

may result in decrease in organic reagent kinetics andcapacity due to reagent oxidation and degradation byMnO2. It may also cause long phase disengagement timeand stable emulsion formation in SX settlers as a resultof surface-active degradation products and high organicloss to the raffinate and high electrolyte loss to theorganic by entrainment.

3. Pre-treatment of anodes in zinc electrowinning

Anode composition and pre-treatment are two of theimportant aspects in zinc electrowinning in terms ofMnO2 formation and tolerance of manganese levels inthe system. Some interesting methods are summarised inthis section, which may also be applied to copperelectrowinning.

3.1. Composite anode technology

Dattilo and Lutz (2001) reported the Merrlincomposite anode technology for metal electrowinning.The Merrlin composite anode is a coating applied to aconventional lead alloy anode that alters the electro-chemical reactions during metal electrowinning. Thecomposite is a mixture of lead and manganese oxides,which are bound to the surface with heat and pressure.The use of this anode, relative to the normal lead alloy,was evaluated both in zinc and copper electrowinning.In zinc electrowinning, a significant reduction of anodescale and cell sludge was observed. The reasons for thisalteration in cell operation were believed to be due to thedecreased oxidation of manganese.

A lead fluoride coating for passivation of 0.8% Ag-alloyed lead anodes by a preconditioning process wasreported by Jaksic et al. (1987) and Rajkovic et al.(1987, 1998). Anodic polarization from acidic sulfatesolution in the presence of F− ions produces a thin PbF2layer, which catalytically affects the transformation ofthe isolating PbSO4 layer into the protecting β-PbO2

layer and hinders crystallisation of α-PbO2 which hasmuch lower corrosion protecting capability. Further,anodic polarization in the cells for zinc electrowinningin the presence of Mn2+ ions created a glassy deposit ofmixed oxides, MnO2–β-PbO2, which exhibited ad-vanced protecting properties, hindered further produc-tion and precipitation of MnO2, and extended the life-

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time of alloyed Pb electrodes from two to six or evenmore than 10 years. An additional contribution was thatthe detrimental MnO2 production was dramaticallyreduced (Rajkovic et al., 1998).

An anode composite containing bismuth was appliedto zinc electrowinning by Harlamovs et al. (2003). Theelectrowinning anodes were optionally manufacturedfrom Pb alloy containing 0.7–0.8% Ag and 1.7–1.9%Bi, as an alternative to the Pb–(2%)Ag alloy. The zinccould be recovered from the concentrated solution byelectrowinning in the absence or presence of manganese.

3.2. Treatment of anode by sulfite solution

Joslin (1985) reported that anodically depositedmanganese dioxide was removed by an aqueous sulfitesolution. The treatment of catalytic anodes with aqueoussulfite solution caused the MnO2 deposit to flake off andthereby restored its catalytic activity. The anodes weretreated every 3–4 weeks with the Na2SO3 solution andthe MnO2 was removed from the anodes withoutdissolution.

4. Methods for manganese control in zincelectrowinning

The concentration of manganese and other impuritiesin the zinc electrolytes from the leach-EW circuit isconventionally controlled by treating a bleed stream ofelectrolyte with limestone at temperatures in the range of50–90 °C at a pH between 6 and 8 to precipitate the zincas basic zinc sulfate and then at a final pH above 10 toprecipitate manganese hydroxide and other impurities.The basic zinc sulfate can be used as a neutralizing agentelsewhere in the circuit. For newer flowsheets includeSX–EW, the zinc electrolytes are usually manganesedeficient and some forms of manganese are added tomaintain manganese levels for its positive effects.

Various methods and processes for manganesecontrol in zinc electrowinning have been studied anddeveloped. Among these, oxidative precipitation, com-bined precipitation and evaporation, solvent extraction,electrolysis and electrowinning, are potentially usefulfor manganese control in zinc electrowinning.

4.1. Manganese removal by oxidative precipitation

Oxidative precipitation of Mn(II) is based on forminginsoluble manganese dioxide (MnO2) by oxidation witha strong oxidant. Mn3+ is proposed to be the initialoxidised species which then disproportionates to formMnO2 and Mn2+. The oxidative precipitation of Mn(II)

has found application in zinc electrowinning for con-trolling the manganese concentration to an acceptablelevel (b5 g/L). Various oxidants have been investigatedfor the oxidation, including ozone, catalysed SO2/O2

mixtures, Caro's acid (H2SO5), persulfate salts (Zhangand Cheng, in press). In addition to controlling theamount of manganese in the electrowinning, oxidativeprecipitation is also of importance for recovery ofmanganese as manganese dioxide from solutions.

4.1.1. Oxidation by ozonePonelis (1995) investigated oxidative precipitation of

a high concentration of manganese (15 g/L in zincelectrolyte) by ozonation. The experimental work wascarried out in a laboratory scale bubble reactor, whichwas coupled with a small scale ozone generator. Anindustrial electrolyte was used for the experiments in asemi-batch mode for different reaction times in thetemperature range of 20–70 °C and the pressure range of88–400kPa. An ozone demand of 0.94mol ozone permol manganese was determined. The reaction dependedon temperature with the apparent activation energybeing 56.6kJ/mol.

4.1.2. Oxidation by SO2/O2 mixtureFerron (2000) patented a method for purification of

zinc ore leach solutions by oxidation of manganeseimpurity by a SO2/O2 mixture. The manganese impurityin the zinc ore leach solutions could be removed by thetreatment with an O2/(0.5–10%) SO2 gas mixture at 40–80 °C and pH of 3–4, in which the Mn(II) wasoxidatively precipitated as manganese dioxides with aminimised loss of zinc by co-precipitation. This processwas proposed for a removal of the manganese impurityin a neutral zinc electrolyte.

A similar method for removal of manganese in zincore leach solutions by SO2/O2 was patented byDemopoulos et al. (2001). With this method, the Mn2+

ions in acidic sulfate leach solutions, especially fromroasted Zn-sulfide ores, could be precipitated withoutthe loss of zinc and other metal values. The weaklyacidic sulfate solution could be treated with anoxidising SO2–O2 gas mixture at controlled pH N2and bath temperature of 60–90 °C to precipitate thesoluble Mn2+ ions as Mn3+ or Mn4+ hydroxides and/oroxides for removal from the Zn-containing leachsolutions. The manganese precipitation as MnO2 froman aqueous leach solution containing zinc at 30–170 g/L is typically increased to 100% by neutralizing thefreshly formed acid with soda or ore calcine. By com-parison, there was no manganese removal in the ab-sence of SO2. The precipitated manganese compounds

182 W. Zhang, C.Y. Cheng / Hydrometallurgy 89 (2007) 178–188

could be optionally used as oxidants in other parts of theore leach circuit.

4.1.3. Oxidation by Caro's acid and peroxydisufuric acidAmmonium persulfate ((NH4)2S2O8) was used at a

pilot-plant scale for the control of excess manganese ionsin the zinc electrolyte in the processing of Gamsbergdeposit in South Africa (Deguire et al., 1978; Burkin andChouzajian, 1983). This chemical oxidation method wascomparatively tested with anodic oxidation method. Thechemical oxidation with ammonium persulfate wasperformed at 90 °C for 2 h and the resulting pulp wasfiltered to separate the precipitated manganese. Theanodic oxidation was carried out by electrolysing aportion of the feed electrolyte (1000L/day) in a smallelectrolytic cell with aluminium cathodes and lead anodesat a current density of 600A/m2. The heavy accumulationof manganese dioxide in the spent electrolyte neededfiltering and frequent cleaning of the anodes.

Compared with the anodic oxidation method, thechemical oxidation was found to be viable with theprecipitated manganese dioxide being battery grade andflexible in terms of varying concentrations of manganesein the solution without affecting the process efficiency orquality of the manganese dioxide produced. The maindisadvantage using the anodic oxidation was theproduction of off-grade cathodic zinc and erratic cathodecurrent efficiency obtained during electrolysis.

The use of Caro's acid (H2SO5) to remove manganesefrom a zinc electrolyte containing 150 g/L Zn and 6–7 g/LMn was reported (Burkin et al., 1981; Burkin andChouzajian, 1983). About 70–80% precipitation ofmanganese could be achieved using Caro's acid at a pHof about 2. It was concluded that removal of manganeseby ammonium persulfate was more convenient than theuse of Caro's acid, but the cost of peroxydisulfate wasexpected to be higher than Caro's acid because Caro'sacid could be produced easily on site.

4.1.4. Oxidation by halide species from anodecompartment

Moyes and Houlis (2003) developed a halide-basedleaching for zinc recovery from complex ores with astep for removal of manganese as MnO2 by the halidespecies which were generated at the anodes. The processwas comprised of the following steps:

(1) The complex zinc ore feed was processed byleaching the zinc with an aqueous solution contain-ing halides with copper as catalyst.

(2) The resulting zinc leach solution was purified withzinc dust, which was then processed by electro-

winning to deposit the zinc metal, and to generatethe halide species (preferably Halex, BrCl2

−) forrecycling to the leaching stage.

(3) A portion of the spent electrolyte (up to 20%) wasoptionally removed as a bleed stream from thecathode compartment, and was treated with Halexvapour and limestone to precipitate the manga-nese as MnO2.

Among the above oxidants, SO2/O2 appears to be thecheapest, particularly if the process involves roastingzinc sulfide concentrates. However, it may need moreanalytical and automatic control to enable the SO2/O2

mixture to function as an oxidant for Mn(II). There arealso significant problems associated with the scale-up ofreactors for SO2/O2 (or air) precipitation due to thediffering solubilities of the gases. In this regard, Caro'sacid offers better controls in real applications. Com-pared with the conventional precipitation method,oxidative precipitation has the following advantages:

(1) It is selective for oxidation of Mn(II) to insolubleforms of manganese oxides, without first requiringseparation and recovery of zinc from the electrolyte.

(2) It can be used to treat the whole leach liquor or totreat a bleed stream of the electrolyte.

(3) The oxidation is operative at relative lower pHrange (pH 3–6) and nearly a stoichiometricamount of base reagent needed for neutralisationunder well-controlled conditions due to littleprecipitation of other impurities.

(4) The manganese could be recovered as a relativelypure marketable product with or without furtherpurification.

Its disadvantages are:

(1) Oxidative precipitation cannot remove otherimpurities which accumulate in the electrolyte.

(2) More controls for the operation are expected, e.g.,optimum SO2/O2 ratios and optimum solution pH.

(3) Significant difference in gas solubility between SO2

and O2 or air and subsequent problem of scale-up.

4.2. Manganese removal by hydroxide precipitation

The hydroxide precipitation method for recovery ofzinc and removal of manganese is one of the effectivemethods for control of manganese in the zinc processingcircuit based on the significant difference between the pHfor precipitation of zinc hydroxide and that for manganesehydroxide. Stolbova et al. (1989) investigated the removal

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of manganese and magnesium from zinc-industry solu-tions by an ammonia method. The purification of elec-trolyte in zinc electrowinning was improved by treatingpart of the electrolyte (Zn 130–140, Mg 5–7, Mn 2–8, K1–3, Na 2–4, andCl 0.2–0.4 g/L)with 25%NH4OH at pH7–7.2 and 50 °C. The precipitation recovered 95–96% Znwhile the impurities (Mg 98–99 and Mn 85–95%, K, Na,and Cl) were accumulated in the (NH4)2SO4 solutionwhich was evaporated and used as fertilizer. The zinc-containing precipitate was dissolved in H2SO4 to preparepure ZnSO4. Compared with oxidative precipitationmethods, hydroxide precipitation does not need anexpensive oxidant but more base reagents for the two-stage precipitation of both zinc and manganese togetherwith other impurities at higher pH. The precipitated basezinc sulfate may be used as a neutralisation reagent in thecircuit. The hydroxide precipitation method has beencommercially adopted for manganese control in processesfor both zinc sulphide ores and zinc oxide ores. Two of theprocesses are summarised below.

4.2.1. HydroZinc process for sulfide oresTheCanadian zinc producer, TeckCominco, developed

a process, called HydroZinc, for recovery of zinc fromlow-grade sulfide ores through heap bioleaching, solventextraction, and electrowinning (Lizama et al., 2003;Filippou, 2004). In order to minimise the corrosion ofthe Pb–Ag anodes and lead contamination of cathode zincproduct, manganese has to be added, usually as potassiumpermanganate (KMnO4), into the zinc electrolyte. Eitherthe use of lead anodes with elevated silver content (2%) orof lead anodes alloyed with bismuth (1.7–1.9%) and silver(0.7–0.8%) are proposed to avoid a significant drop in thecurrent efficiency caused by the presence of MnO4

−. Themajor steps can be summarised as follows:

(1) The pregnant leach solution, which contained 10–50 g/L zinc, was neutralized in stirred-tankreactors to pH 4 with limestone slurry toprecipitate all the ferric iron.

(2) Zinc was extracted in two stages with 20% (v/v)D2EHPA (di-2-ethylhexyl phosphoric acid) dilut-ed in kerosene. Typically, only 30–50% of thezinc was extracted.

(3) The zinc pregnant solution from the stripping ofthe loaded organic phase reported to electrowin-ning process.

(4) Part of the neutralized solution (about 5% v/v)was further neutralized to pH 6.0 to recover all thecontained zinc as basic zinc sulfate.

(5) The bleed was treated with zinc powder to removecadmium and was then neutralized to pH 10 to

precipitate manganese and some other impurities(Mg, Ca, etc.) as hydroxides.

(6) The rest of the neutralized pregnant leach solutionwas fed to the solvent extraction circuit.

4.2.2. ZINCEX and Skorpion processes for zinc oxideores

The ZINCEX process was initially developed in theearly 1970s by TR (Técnicas Reunidas), Spain, and useda solvent extraction process for the recovery of zincfrom chloride leach solutions (Martin San Lorenzo et al.,2001). It included two separate sections using twodifferent extractants: an anionic extractant (a secondaryamine such as Amberlite LA-2) to extract pure zincchloride, and a cationic extractant (D2EHPA) to transferzinc into a sulfate electrolyte, from which zinc metalwas recovered by conventional electrolysis. Thisprocess was then modified to recovery of zinc fromsulfuric leach solutions, the modified ZINCEX process(Martin San Lorenzo et al., 2001, 2004, 2005).

The modified ZINCEX process has recently beenused by the Skorpion Zinc plant which is the firstcommercial application of zinc SX–EW for processingprimary leach liquor (Cole and Sole, 2003; Sole et al.,2005). The pregnant sulfuric acid leach solution is firstneutralized by lime to precipitate impurities includingiron, aluminium and silica. Zinc is then extracted usingD2EHPA reagent and electrowon onto aluminiumcathodes. The levels of soluble impurities includingmanganese are controlled by bleeding about 8–15% ofthe pregnant leach solution or the acid raffinate andneutralizing the bleed with lime or limestone in twosteps at 70–90 °C. First, the solution is neutralized at apH between 6 and 8 to precipitate its zinc content in theform of basic zinc sulfate, and then is further neutralizedto a final pH above 10 to precipitate the impuritiesincluding manganese (Filippou, 2004). The basic zincsulfate is used as a neutralizing agent elsewhere in theprocess while the impurity residue containing manga-nese hydroxide is discarded. Manganese is actuallyadded back into the zinc electrolyte for maintaining acertain manganese level for its positive effects.

4.3. Manganese removal by evaporation

Dyvik and Mioen (1987) patented a hydrometallur-gical process for zinc production from its concentrate. Inelectrowinning, a portion of the acidic solution waswithdrawn and vaporized to concentrate H2SO4 toapproximately 60% for precipitation of zinc, magnesiumand manganese impurities as sulfates to preventmanganese accumulation. The residual H2SO4 solution

184 W. Zhang, C.Y. Cheng / Hydrometallurgy 89 (2007) 178–188

containing 1–5 g/L Zn was recycled to the leachingstage. The metal sulfate crystals could be dissolved inwater for further treatment. Zinc could be precipitated asbasic zinc sulfate or electrowon to produce zinc metalwhilst manganese was discarded after lime treatment ofthe liquor.

4.4. Manganese removal by solvent extraction

In conventional treatment of a bleeding of the spentelectrolyte, the acid is lost by neutralization. Recoveryof acid by solvent extraction offers a useful step andprovides the conditioning of pH for subsequentseparation and recovery of zinc and/or manganese. Aniso-butyl alcohol was used for recovery of H2SO4

followed by recovery of zinc by D2EHPA or both zincand manganese by naphthenic acid in kerosene fromzinc spent electrolytes (Buttinelli and Giavarini, 1982).In addition to alcohols, some stronger acid extractantssuch as Tri(2-ethylhexyl)amine (TEHA) and Cyanex923 were also investigated (Eyal and Baniel, 1991; Eyalet al., 1991a,b; Alguacil and López, 1996).

So far not much work has been devoted to the use ofsolvent extraction for the control of manganese in zincelectrowinning; however, solvent extraction has shownpromise in several methods:

(1) For a neutralized zinc electrolyte containing a highconcentration of zinc, D2EHPA is selective forzinc over manganese at pH 2.5. While the raffinatecontaining manganese can be further treated ordiscarded, the zinc stripped from the organicsolution can be recycled back to the circuit.

(2) Cyanex 272 can also be used for extraction of zincfrom a neutralized electrolyte at pH 2.5, leavingmanganese and other impurities in the raffinate.However, Cyanex 272 is more expensive thanD2EHPA.

(3) For spent electrolyte containing a high concentra-tion of sulfuric acid, Cyanex 923 could be used forrecovery of acid followed by extraction of zincwith Cyanex 272 or D2EHPA.

The major advantage of using solvent extraction liesin the separation and recovery of zinc in the electrolytefrom manganese and other impurities which remain inthe raffinate for further treatment or disposal. However,there is a high cost of base for the extraction of highconcentrations of zinc in both (1) and (2) except whereassociated with an RLE process. Up to 90% of the acidcould be recovered with method (3), but two SX circuitsare required.

4.5. Simultaneous electrolysis and electrowinning

Simultaneous electrolysis to deposit Mn as MnO2 onthe anode and Zn on the cathode for manganese removalis used in the Glencore's Sulfacid plant in Argentinean.Manganese is removed during the process typically 0.1 to0.4 g/L per pass depending on the conditions (Harlamovs,2007). The process is based on the following simplifiedEqs. (1) and (2).

At the anode,

Mn2þ þ 2H2O→MnO2 þ 4Hþ þ 2e− ð1ÞAt the cathode,

Zn2þ þ 2e−→Zn ð2ÞThe overall cell reaction can then be expressed by:

ZnSO4 þMnSO4 þ 2H2O→Zn þMnO2

þ 2H2SO4 ð3ÞThis process could be applied to treatment of a bleed

stream of zinc electrolyte containing a sufficiently highconcentration of manganese.

Verbaan (1980) first patented a simultaneous electrol-ysis and electrowinning method for removal of manga-nese. In this method, the Zn- and Mn-containing solutionwas electrolysed in the first electrolysis step to produceMnO2 and zinc on the anode and cathode, respectively,and the rest of the zinc was recovered in the final elec-trolysis step. The preferred cathode material was alu-minium, and the anode was carbon (graphite). TheproducedMnO2 was reported to suit battery manufacture.Simultaneous electrolysis was also used for removal ofmanganese from some or all of the purified leach liquorwhich contained up to 20 g/L Mn2+ (Verbaan andMullinder, 1981). H2SO4 in the range of 0–30 g/L wasfound to maximise zinc current efficiency while thatbelow 50 g/L to maximalise manganese current efficien-cy. A decrease in Mn concentration from 20 to 10 g/Ldecreased Mn current efficiency from 74.7 to 61%.

A similar process for simultaneous electrowinning ofzinc and manganese dioxide was also developed by TohoZinc, Japan (1982). In this process, a solution containing5–80 g/L Zn and 20–80 g/LMnwas electrolysed at a bathtemperature of 75–95 °C. The MnO2 product from thesimultaneous electrolysis was reported to be superior tonatural MnO2, but did not meet the specifications forconventional EMD (Rodrigues and Dry, 1990).

In another patented process by Nattrass (1986) for thecontrol of manganese build-up in the electrolyte in zincplants, two-step electrolysis was used: (i) electrolysing azinc electrolyte containing manganese ions to produceelectrolytic zinc and a spent electrolyte, (ii) further

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electrolysing the spent electrolyte under agitated condi-tions to produce solid MnO2, which could be used in themanufacture of dry battery cells.

The efficiency of the simultaneous electrolysis processfor removal of manganese was reported to be promoted byusing a cold electrolysis at 10–15 °C (Fussi et al., 1998). Inthis process, the feed was acidified to 50–90 g/L H2SO4,cooled to below 15 °C, and electrolysed at 200–400A/m2

using Pb anodes and Al cathodes with air injection forstirring, followed by settling the slurry product withaddition of a flocculant. The manganese removal wasincreased by tenfold compared with conventional chem-ical pre-treatment, and the same anodes could be used for30 days, resulting in low operating cost.

Simultaneous electrolysis and electrowinning areattractive means to control the manganese level in a zincelectrolyte by treating part or all of the electrolyte usinggraphite as anodes for MnO2 deposition and aluminiumas cathodes for zinc deposition. Their advantages are:

(1) The same electrowinning equipment can be usedwithout many modifications.

(2) The treatment does not alter the acidity and otherconditions significantly.

(3) Recovery of manganese as a quality product closeto EMD is achievable under well-controlledconditions.

However, their disadvantages are:

(1) Other impurities remain in the electrolyte.(2) The optimum conditions for deposition of MnO2

and zinc are not identical and need separatecontrols.

(3) Current efficiencies for zinc and MnO2 productionare low.

(4) High energy requirements are expected if theconcentrations of manganese are low in theelectrolyte.

5. Effect of manganese in copper SX–EWoperations

Some problems caused by manganese during copperSX–EW commissioning and operations were reportedby Miller (1995) and Miller et al. (1997). They include:

(1) Decrease in organic reagent kinetics and capacitywith high copper concentrations in raffinate due toreagent oxidation and degradation by MnO2.

(2) Long phase disengagement time and stableemulsion formation in SX settlers as a result ofsurface-active degradation products.

(3) High organic loss to the raffinate and highelectrolyte loss to the organic by entrainment.

(4) MnO2 precipitating on electrode surfaces.(5) Sticky cathodes and nodular growth on copper

cathodes.

It has been established that Mn2+ itself has no effecton the operation of the SX plant. However, when themanganese is transferred into the copper EWelectrolyte,the Mn2+ is oxidised to higher valent species (MnO4

−

and MnO2) in the highly oxidising environment in theEW cells. These, in turn, generate further symptomswhich can form positive feedback loops and veryquickly lead to a catastrophic reduction in plantperformance.

The mechanism of organic degradation caused bymanganese was identified by Cheng et al. (2000) with acoupled SX–EW circuit using Acorga M5640 and LIX984N as extractants. It was observed by visible spectrathat Mn2+ in the electrolyte was primarily oxidised toMn3+, which was further oxidised to MnO4

−. Theformation of these high valent manganese specieswere evidenced by the high redox potentials measured.Solid MnO2 particles were also formed. It was furtherdetermined that most of the observed organic oxidationand consequent emulsion formation were associatedwith the presence of Mn3+ rather than MnO4

− species. Anumber of degradation products of the hydroxyoximeextractants were detected by a combination of gaschromatography (GC), high performance liquid chro-matography (HPLC) and pre-concentration techniques,including an acidic oxidation product of 5-nonylsalicy-laldehyde which was consistent with a 5-nonylsalicylicacid. There was also evidence for oxidative cleavage ofthe nonyl chain of the aldoximes or their degradationproducts, the formation of a nonyl phenol dimer, andpossibly also polymerisation of the related hydroxyox-imes or their degradation products.

Ipinza et al. (2003, 2004) studied the formation ofanodic slime in copper electrowinning. It was observedthat in the presence of manganese in the electrolyte, amanganese dioxide double layer was formed at theanode. This double layer was always composed of athick external layer of non-adhering and easily remov-able scales, and a thin internal layer adhering relativelywell to the surface of the electrode. Manganesedeposited on the anode surface and reduced the presenceof lead compounds in the slime, which was interpretedas a protective effect of this ion on the anodic corrosion.The presence of iron in the electrolytes only inhibitedthe formation of tetragonal manganese oxide, reducingthe volume of the slime formed.

186 W. Zhang, C.Y. Cheng / Hydrometallurgy 89 (2007) 178–188

The presence of Mn2+ increased the density andviscosity of copper electrolyte (Subbaiah and Das, 1994).For example, the conductivity of copper electrolytedropped from 420 mΩ/cm to 370 mΩ/cm in the presenceof 19.9 g/L of Mn2+. The limiting current density andcopper mass transfer coefficient were found optimum at aconcentration of 5 g/L Mn2+. The manganese impurityalso significantly affected the surface morphology andcrystal orientation of the cathode copper, promoting agrowth of pyramidal and planar structures, while restrict-ing the growth of ridge-type structures.

6. Methods for control of manganese in copperelectrowinning

6.1. Control of electrolyte Eh by addition of reductants

A number of solutions for the manganese problems incopper SX–EW operations at Girilambone CopperCompany were reported (Miller, 1995; Miller et al.,1997). As the main problems of manganese in copperelectrowinning were related to the high valent manganesespecies generated in EW environment, a method formaintaining the electrolyte Eh at an appropriate value(around400mV) and thus keepingmanganese in theMn2+

state by addition of reductants was attempted. An initialtrial on the reduction of Eh by addition of ferrous sulfate tothe electrolyte was found kinetically slow. An addition ofSO2 successfully controlled the Eh in the range of 400–450 mV. A concentration of 1 g/L Fe2+ was required tomaintain the Eh and the manganese in the Mn2+ state.

6.2. Oxidative precipitation

Shaw et al. (1999) reported a patented process forcontrol of manganese, iron, and chloride in copperelectrowinning tank houses which was tested in a pilotplant. In the process, manganese was removed asinsoluble manganese dioxide by oxidative precipitationwith permanganate salts.

6.3. Solvent extraction of acid from bleed prior tomanganese hydroxide precipitation

For conventional impurity control in copper electro-winning by bleeding, the acid can be recovered by solventextraction. A process using Cyanex 923 and a branchedlong-chain aliphatic tertiary amine, tris(2-ethylhexyl)amine (TEHA) for selective recovery of up to 90% ofthe sulfuric acid from electrolyte bleed streams, wasdeveloped by Gottliebsen et al. (2000). The processinvolved extraction at ambient temperature and stripping

with water at elevated temperatures. Both extractants hadthe ability to produce acid with a concentration of N120 g/L sulfuric acid, which could be recycled back into the tankhouse, reducing both neutralisation and acid make-upcosts. The weakly acidic raffinate could be further treatedby the conventional bleeding procedures to precipitatemanganese hydroxide. The reactionmechanisms betweenTEHA and H2SO4 depended on acid concentrations. Atacid concentrations below 1M, it involved the formationof the amine sulfate salt, combining two amines for everysulfate, which can be expressed by Eq. (4).

H2SO4 þP2R3N ¼PR3NHð Þ2SO4 ð4ÞAt higher concentrations of sulfuric acid, the formation ofamine bisulfate dominated as described by Eq. (5).

H2SO4 þPR3NHð Þ2SO4 ¼ 2PR3NHð ÞHSO4 ð5Þ

7. Summary of manganese control in zinc andcopper electrowinning

The presence of higher valent species of manganeseresulting from the oxidation at the anodes hasdetrimental effects on both copper and zinc solventextraction and on the electrowinning of zinc and copper.

Various methods have been investigated for manga-nese control in zinc and copper electrowinning. Theseinclude:

(1) Addition of a reductant, e.g. ferrous iron andaqueous SO2 to the electrolyte to maintain a lowEh value (400–450 mV) and to avoid occurrenceof any higher valent manganese species.

(2) Oxidative precipitation of manganese from neu-tralized electrolyte as insoluble MnO2 using Caro'sacid or SO2/O2. A drawback of this strategy is thatother impurities, e.g.Mg, Cl−, F− etc., remain in thecircuit, which have to be treated when it exceed theacceptable levels.

(3) Solvent extraction of zinc or copper using acation-exchange extractant, e.g. D2EHPA orhydroxyloximes can selectively recover zinc orcopper from the solution and leave other impuri-ties including manganese in the raffinate whichcould be further treated for recovery of manganeseor discarded. The loaded organic phase can bestripped using the spent electrolyte to produce ametal-rich sulfate solution for electrowinning.

(4) The use of composite anodes to increase thecurrent efficiency with less anode scale and cellsludge.

187W. Zhang, C.Y. Cheng / Hydrometallurgy 89 (2007) 178–188

For separation methods such as sulfide precipitation,carbonate precipitation, and hydroxide precipitation, therecovery of a large amount of zinc prior to removal ofmanganese or copper makes these methods lesseconomically viable. Among various separation techni-ques, oxidative precipitation and solvent extraction arerecommended for future work.

Acknowledgments

The authors would like to thank CSIRO Mineralslibrary staff for collecting some references, and DrDavid Muir for reviewing this paper and providingvaluable comments. We would also like to thank thereviewer, Mr Juris Harlamovs (TeckCominco), andanother anonymous reviewer for some helpful com-ments and useful information provided.

References

Alguacil, F.J., López, F.A., 1996. The extraction of mineral acids bythe phosphine oxide Cyanex 923. Hydrometallurgy 42 (2),245–255.

Bolton, G.L., Sefton, V.B. and Zubryckyj, N., 1981. Removal ofmanganese ions from zinc and manganese containing solutions.US Patent No. 4290866.

Burkin, A.R., Chouzajian, K.A., 1983. Precipitation of manganesedioxide from zinc electrolyte solution using peroxymonosulfuricacid. In: Osseo-Asare, K., Miller, J.D. (Eds.), HydrometallurgyResearch, Development and Plant Practice, Proceedings 3rdInternational Symposium on Hydrometallurgy. The MetallurgicalSociety of AIME, Atlanta, Georgia, pp. 603–615.

Burkin, A.R., Manning, G.D., Monhemius, A.J., 1981. Application ofhydrogen peroxide and peroxysulfuric acids in hydrometallurgy.Hydrometallurgy, vol. 81. Society of Chemical Industry, Manche-ster, England, pp. 11–B5/2.

Buttinelli, D., Giavarini, C., 1982. Zinc and manganese recovery byextraction with naphthenic acid. Chemistry and Industry 64 (10),634–635.

Cathro, K.J., 1991. Electrowinning of zinc at high current density.Chemistry in Australia 58 (11), 490.

Cheng, C.Y., Hughes, C.A., Barnard, K.R., Larcombe, K., 2000.Manganese in copper solvent extraction and electrowinning.Hydrometallurgy 58 (2), 135–150.

Cole, P.M., Sole, K.C., 2003. Zinc solvent extraction in the processindustries. Mineral Processing and Extractive Metallurgy Review24 (2), 91–137.

Dattilo, M., Lutz, L.J., 2001. Merrlin composite anode technology formetal electrowinning. In: Gonzalez, A., Dutrizac, J.E., Kelsall, G.H.(Eds.), Electrometallurgy 2001, Proceedings of Annual Hydromet-allurgy Meeting. The Metallurgical Society of Minerals EngineeringInternational, Toronto, pp. 447–452.

Deguire, M.F., Hannaford, A.L., Harris, L., 1978. Electrolytic Zn recoveryfrom manganiferous concentrate. World Mining 31 (10), 92–99.

Demopoulos, G., Rosato, L. and Wang, Q., 2001. Removal ofmanganese for control of zinc-ore leach flow circuits. WO PatentNo. 2001048255.

Dyvik, F. and Mioen, T.K., 1987. A method for hydrometallurgicallymanufacturing zinc. EP Patent No. 227626.

Eyal, A.M., Baniel, A.M., 1991. Recovery and concentration of strongmineral acids from dilute-solutions through LlX .1. Review ofparameters for adjusting extractant properties and analysis of processoptions. Solvent Extraction and Ion Exchange 9 (2), 195–210.

Eyal, A.M., Hazan, B., Bloch, R., 1991a. Recovery and concentrationof strong mineral acids from dilute-solutions through LlX .2.Reversible extraction with branched-chain amines. SolventExtraction and Ion Exchange 9 (2), 211–222.

Eyal, A., Hazan, B., Bloch, R., 1991b. Recovery and concentration ofstrong mineral acids from dilute-solutions through LlX .3. Atemperature swing based process. Solvent Extraction and IonExchange 9 (2), 223–236.

Ferron, C.J., 2000. Purification of zinc-ore leach solutions byoxidation of manganese impurity. WO Patent No. 2000061826.

Filippou, D., 2004. Innovative hydrometallurgical processes for theprimary processing of zinc. Mineral Processing and ExtractiveMetallurgy Review 25 (3), 205–252.

Fussi, J.L., Quintero, O., Cornaglia, A. and Morosini, C., 1998.Electrowinning of high-purity zinc metal from an ore-leachsolution pretreated by cold electrolytic removal of manganese.EP Patent No. 885976.

Gottliebsen, K., Grinbaum, B., Chen, D., Stevens, G.W., 2000.Recovery of sulfuric acid from copper tank house electrolytebleeds. Hydrometallurgy 56 (3), 293–307.

Harlamovs, J.R. (TeckCominco), 2007. Private communication.Harlamovs, J.R., Ashman, D.W., Gonzalez Dominguez, J.A., Lizama,

H.M., Makwana, D.D. and Stradling, A.W., 2003. Heap bioleach-ing process for zinc recovery from sulfide ores followed by solventextraction and electrowinning stages. WO Patent No. 2003006696.

Harris, L. and Hanson, A.K. Jr., 1978. Process for manganese removalfrom zinc metal-bearing solutions. US Patent No. 4067789.

Hosny, A.Y., O'Keefe, T.J., James, W.J., 1989. Hull cell technique forevaluating zinc sulfate electrolytes. Minerals Engineering 2 (3),415–423.

Ipinza, J., Ibanez, J.P., Vergara, F., Pagliero, A., 2003. Study of anodicslime from Chilean copper electrowinning plants. In: Young, C.A.,Alfantazi, A.M., Anderson, C.G., Dreisinger, D.B., Harris, B.,James, A. (Eds.), Hydrometallurgy 2003, Proceedings of the 5thInternational Symposium. The Minerals, Metals and MaterialsSociety, Vancouver, Canada, pp. 1267–1277.

Ipinza, J., Ibanez, J.P., Vergara, F., Pagliero, A., 2004. Anodic slimesformation in copper electrowinning. Revista De Metalurgia 40 (1),13–20.

Ivanov, I., 2004. Increased current efficiency of zinc electrowinning inthe presence of metal impurities by addition of organic inhibitors.Hydrometallurgy 72 (1–2), 73–78.

Ivanov, I., Stefanov, Y., 2002. Electroextraction of zinc from sulfateelectrolytes containing antimony ions and hydroxyethylated-butyne-2-diol-1,4: part 3. The influence of manganese ions and adivided cell. Hydrometallurgy 64 (3), 181–186.

Jaksic, M., Rajkovic, M., Stanojevic, D., 1987. Development andapplication of the preconditioned alloyed lead anode for zincelectrowinning. I. Theoretical basis of the preconditioning process.Hemijska Industrija 41 (6–7), 226–232.

Joslin, T., 1985. Removing anodically deposited manganese dioxide.EP Patent No. 157951.

Kelsall, G.H., Guerra, E., Li, G., Bestetti, M., 2000. Effects ofmanganese(II) and chloride ions in zinc electrowinning reactors.Proceedings––Electrochemical Society, 2000-14 (Electrochemis-try in Mineral and Metal Processing V), pp. 350–361.

Krupkowa, D., Jurczyk, H., Krezel, K., Nosel, J., Gluszczyszyn, A. andMendyka, M., 1977. Zinc electrowinning. Pl Patent No. 89821.

188 W. Zhang, C.Y. Cheng / Hydrometallurgy 89 (2007) 178–188

Lizama, J.L., Harlomoves, J.R., Belanger, S., Brienne, S.H.R., 2003.The Teck Cominco HydroZinc process. In: Young, C.A., Alfantazi,A.M., Anderson, C.G., Dreisinger, D.B., Harris, B., James, A.(Eds.), Hydrometallurgy 2003, Proceedings of the 5th InternationalSymposium. The Minerals, Metals and Materials Society,Vancouver, Canada, pp. 1503–1516.

MacKinnon, D.J., 1994. The effects of foaming agents, and theirinteraction with antimony, manganese and magnesium, on zincelectrowinning from synthetic acid sulfate electrolyte. Hydromet-allurgy 35 (1), 11–26.

MacKinnon, D.J., Brannen, J.M., 1991. Effect of manganese, magne-sium, sodium and potassium sulfates on zinc electrowinning fromsynthetic acid sulfate electrolytes. Hydrometallurgy 27 (1), 99–111.

Martin San Lorenzo, D., Garcia Leon, M.A., Nogueira Diaz, G.,Falgueras, J., 2001. A new zinc solvent extraction application:spent domestic batteries treatment plant. In: Cox, M., Hidalgo, M.,Valiente, M. (Eds.), solvent extraction for the 21st century.Proceedings of ISEC '99, vol. 1. Society of Chemical Industry,London, UK, pp. 201–206.

Martin San Lorenzo, D., Nogueira Diaz, G., and Garcia Leon, M.A.,2004. Process for electrolytic production of ultra-pure zinc or zinccompounds from zinc primary and secondary raw materials. USPatent No. 2004031356.

Martin San Lorenzo, D., Nogueira Diaz, G., and Garcia Leon, M.A.,2005. Process for the continuous production of high pureelectrolytic zinc or zinc compounds from zinc primary andsecondary raw materials. US Patent No. 6869520.

Miller, G.M., 1995. The problem of manganese and its effects oncopper SX–EW operations. In: Cooper, W.C., Dreisinger, D.B.,Dutrizac, J.E., Hein, H., Ugarte, G. (Eds.), Proc. Copper'95––Cobre'95 Int. Conf. Can. Inst. Min. Met., Montreal, Canada, vol. 3,pp. 649–663.

Miller, G.M., Readett, D.J., Hutchinson, P., 1997. Experience inoperating the Girilambone copper SX–EW plant in changingchemical environments. Minerals Engineering 10 (5), 467–481.

Moyes, J. andHoulis, F., 2003. Halide-based leaching for zinc recoveryfrom complex ores with purification. WO Patent No. 2003023077.

Nattrass, W.A., 1986. Control of manganese buildup in the electrolytein zinc plants. ZA Patent No. 8601104.

Newnham, R.H., 1992. Corrosion rates of lead-based anodes for zincelectrowinning at high current densities. Journal of AppliedElectrochemistry 22 (2), 116–124.

Pajunen, L., Aromaa, J., Forsen, O., 2003. The effect of dissolvedmanganese on anode activity in electrowinning. In: Young, C.A.,Alfantazi, A.M., Anderson, C.G., Dreisinger, D.B., Harris, B.,James, A. (Eds.), Hydrometallurgy 2003, Proceedings of the 5thInternational Symposium. The Minerals, Metals and MaterialsSociety, Vancouver, Canada, pp. 1255–1265.

Ponelis, A.A., 1995. Ozonation of high concentration manganese––temperature and pressure dependence of mass transfer and kineticcoefficients. South African Journal of Chemical Engineering 7 (2),1–11.

Rajkovic, M., Stanojevic, D., Jaksic, M., 1987. Development andapplication of the preconditioned alloyed lead anode for zincelectrowinning. II. Experiment confirmation of preconditioning

under industrial process conditions. Hemijska Industrija 41 (9),369–379.

Rajkovic, M.B., Vladisavljevic, G.T., Ristic, N.M., Jaksic, M.M.,1998. A preconditioning process for extended passivation ofalloyed lead anodes in zinc electrowinning. Bulletin of Electro-chemistry 14 (3), 107–114.

Rerolle, C., Wiart, R., 1996. Kinetics of oxygen evolution on Pb andPb–Ag anodes during zinc electrowinning. Electrochimica Acta 41(7/8), 1063–1069.

Rodrigues, J.M.S., Dry, M.J., 1990. The production of particulatemanganese dioxide during zinc electrowinning. In: Claessens, P.L.,Harris, G.B. (Eds.), Proceedings of the International Symposiumon Electrometallurgical Plant Practice. Pergamon Press, New York,pp. 199–220.

Saba, A.E., Elsherief, A.E., 2000. Continuous electrowinning of zinc.Hydrometallurgy 54 (2,3), 91–106.

Schierle, T., Hein, K., 1993. Anode depolarization in the metal winningelectrolysis. Erzmetall World of Metallurgy 46 (3), 164–169.

Shaw, D.R., Illescas, J., Tomasek, C., Jupp, S., Dreisinger, D.,Wassink, B., Readett, D., Lancaster, T., 1999. Iron, chloride andpermanganate control in copper electrowinning tankhouses.Proceedings of the COPPER 99––COBRE 99 InternationalConference. Phoenix, vol. 3, pp. 653–668.

Sole, K.C., Feather, A.M., Cole, P.M., 2005. Solvent extraction insouthern Africa: An update of some recent hydrometallurgicaldevelopments. Hydrometallurgy 78 (1–2), 52–78.

Stolbova, E.F., Piskunov, V.M., Matveev, A.F., 1989. Removal ofmanganese and magnesium from zinc-industry solutions by theammonia method. Tsvetnye Metally (10), 42–45 (Moscow,Russian Federation).

Subbaiah, T., Das, S.C., 1994. Effect of some common impurities onmass transfer coefficient and deposit quality during copperelectrowinning. Hydrometallurgy 36 (3), 271–283.

Toho Zinc Co., Ltd. Japan, 1982. Simultaneous electrowinning of zincand manganese dioxide. JP Patent No. 57149481.

Verbaan, B., 1980. Simultaneous recovery of zinc and manganese. ZAPatent No. 8001590.

Verbaan, B., Mullinder, B., 1981. The simultaneous electrowinning ofmanganese dioxide and zinc from purified neutral zinc sulfate athigh current efficiencies. Hydrometallurgy 7 (4), 339–352.

Vereecken, J., Winand, R., 1972. Influence of manganese(II) ions onthe anodic oxidation of methanol. Electrochimica Acta 17 (2),271–278.

Yoshida, T., Kahata, M., Dobashi, M., Suzuki, M., 1997. Chlorineanion elimination from zinc sulfate solution by periodic currentreverse electrolytic system, Aqueous Electrotechnologies: Prog-ress in Theory and Practice. Proceedings of Symposium. TheMinerals, Metals and Materials Society, Warrendale, pp. 177–188.

Yu, P., O'Keefe, T.J., 2002. Evaluation of lead anode reactions in acidsulfate electrolytes––II. Manganese reactions. Journal of theElectrochemical Society 149 (5), A558–A569.

Zhang, W., Cheng, C.Y., in press. Manganese Metallurgy Review. PartII: Manganese Separation and Recovery from Solution. Hydro-metallurgy. doi:10.1016/j.hydromet.2007.08.009.