Mn metallurgy review

Available online at www.sciencedirect.com

(2007) 160–177www.elsevier.com/locate/hydromet

Hydrometallurgy 89

Manganese metallurgy review. Part II: Manganese separation andrecovery from solution

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

Various methods for manganese separation and recovery from solution are reviewed, which are potentially applicable to leachsolutions of secondary manganese sources, particularly nickel laterite waste effluents. The main methods include solventextraction, sulfide precipitation, ion exchange, hydroxide precipitation and oxidative precipitation. These methods are brieflycompared and assessed for both purification of manganese solutions and recovery of manganese from the solutions in terms of theirselectivity, efficiency, reagent costs and product quality. The strategies for co-recovery of valuable metals including nickel andcobalt are discussed.

Among these methods, oxidative precipitation with cheap oxidants such as SO2/O2 mixture is highly selective for recovery ofmanganese and the most promising method recommended for future research and development. Solvent extraction with cheapextractants is next for selective extraction of manganese, purification of manganese solutions or co-recovery of other valuablemetals. The cost of base needed for neutralisation in solvent extraction is a major consideration. Carbonate precipitation is moreselective for manganese than hydroxide precipitation with respect to magnesium impurity. Manganese carbonate is a favourableform for further processing to final manganese products, but its applicability will largely depend on the relative concentrations ofmanganese to magnesium and calcium impurities. Sulfide precipitation and ion exchange offer useful means for purification and/orco-recovery of other base metal impurities.© 2007 Elsevier B.V. All rights reserved.

Keywords: Manganese; Separation; Recovery; Solvent extraction; Precipitation

1. Introduction

Manganese separation and recovery from solutionsare crucial to make a process economically viable. Thisis particularly important to separate metal values andrecover manganese in the solutions from secondarymanganese materials including Mn-bearing steel scraps,spent electrodes, waste electrolytes, spent catalysts, andfrom industrial mineral processing waste effluents.

⁎ Corresponding author.E-mail address: [email protected] (W. Zhang).

0304-386X/$ - see front matter © 2007 Elsevier B.V. All rights reserved.doi:10.1016/j.hydromet.2007.08.009

Industrial waste effluents containing a substantialamount of manganese are a potential source of manga-nese. For example, most manganese contents in sphaleriteflotation concentrates are leached together with zinc andrejected to the waste effluents in its downstream pro-cessing. In recent years, an increasing world demand fornickel and cobalt has motivated the development ofprocesses for the treatment of nickel–cobalt laterite ores.In Western Australia, several laterite plants are incommercial operation, including the Cawse and MurrinMurrin projects, and more recently the Ravensthorpeproject of BHP Billiton. Worldwide, more than ten nickel

mailto:[email protected]

http://dx.doi.org/10.1016/j.hydromet.2007.08.009

161W. Zhang, C.Y. Cheng / Hydrometallurgy 89 (2007) 160–177

projects are in different stages of development. In allthese plants, manganese is one of the impurities that areleached together with nickel and cobalt and disposed inthe subsequent separation processes. Different separationstrategies are used in the downstream processes by dif-ferent plants and projects. The total recoverable manga-nese from laterite waste streams has been estimated to bemore than 45,000 t per annum in Western Australia aloneand 121,500 t per annum worldwide, which are valued atUS $71.5million per annum and $193million per annum,respectively (Zhang and Cheng 2006). The value esti-mations are based on the latest statistics on Mn metalaverage international prices (US $1590/t for Mn metal)(Corathers and Arguelles 2007).

The challenge to recovery of manganese from thesewaste solutions lies in the relatively low manganeseconcentration (1–5 g/L) together with large amounts ofimpurities, e.g. about 10 g/L magnesium in a typicalnickel laterite waste effluent. Selectivity, reagents costs,efficiency and product quality are important economicalfactors for developing a method or a process.

In Part I, various leaching processes for manganeseores and secondary materials are reviewed. Part II of thisreview covers various separation and recovery methodsincluding solvent extraction, ion exchange, and hydrox-ide, carbonate, sulfide, and oxidative precipitations.Their applicability is briefly discussed.

The aims of this literature review are to searchmethods and techniques which are potentially applicablefor the separation and recovery of manganese fromindustrial streams and to suggest suitable methods andprocesses for further research and development.

2. Solvent extraction of manganese

In hydrometallurgical processing of manganese-containing materials, the leach liquors often containdivalent iron, manganese, copper, nickel, cobalt and zincalong with other impurities. Solvent extraction plays avital role in purification and separation of manganese.A number of organic SX reagents have been used forfundamental research, focusing on the phosphorus acidand carboxylic acid cation exchange reagents.

2.1. Metal ion selectivity and manganese speciation incation exchange reagents

2.1.1. D2EHPA-phosphoric acid extractantD2EHPA, di-2-ethylhexyl phosphoric acid, is by far

the most widely used extractant for manganese. Sato andNakamura (1985) investigated solvent extraction ofdivalent metals: Mn, Co, Ni, Cu, Zn Cd, and Hg, from

sulfuric acid solutions by D2EHPA. The distributioncoefficient was found to be dependent on the concentra-tions of acid and D2EHPA, suggesting that these metalswere extracted through a cation-exchange mechanism:

M 2þ þ 2PðHAÞ2 ¼PMA4H2 þ 2Hþ ð1Þ

where M denotes Mn, Co, Ni, Cu, Zn, Cd and Hg,PHA=D2EHPA in the organic phase and

PMA4H2 the

metal–organic complex in organic solution. The metalextraction lies in the order:

ZnNCdNMnNCuNCoNNiNHg:

Cheng (2000) reported a similar extraction order forZn, Mn, Cu, Co and Ni with D2EHPA in the presence ofCa and Mg (pH50 in bracket):

Znð1:70Þ∼Cað1:72ÞNMnð2:71Þ∼Cuð2:80ÞNCoð3:7Þ∼Nið3:82ÞNMgð4:3Þ:

In chloride medium, the kinetics of both forward andbackward extractions of manganese with D2EHPA wereinvestigated by Biswas et al. (1996, 1997) using a singledrop technique. The formation of 1:1 complex of Mn2+

withPHA�

2 (dimeric anion) at the interface was proposedto be the rate limiting step. In the range of 0.04–0.50 mol/L D2EHPA and aqueous pH range of 1.0–3.0, the processis under mixed chemical and diffusion control. Theactivation energy depends on the back-extraction para-meters and is of the order of 20–40 kJ/mol.

In sulfate medium, the extraction kinetics of Mn(II)with D2EHPA in n-hexane was investigated by Hughesand Biswas (1993) using a rotating diffusion techniquein the pH range 2.70–3.57. With the concentration ofMn(II) ≤0.5 mol/L and that of the organic extractant≤1.13 mol/L, the formation of a 1:1 complex in theaqueous film was identified to be the rate-limiting step.In the lower temperature region (∼25 °C), the activationenergy was about 20 kJ/mol, indicating a mixeddiffusion and chemically controlled mechanism.

The extraction kinetics of Mn(II) from 0.1 M sulfatemedium by D2EHPA solution in kerosene was againstudied by Biswas and Mondal (2003) using the LewisCell (stirred cell) and Hahn Cell (non-stirred cell)techniques. The rate constant values and activationenergy was found to vary significantly with the phasecontacting techniques.

Alkylphosphoric acids related to D2EHPA have alsobeen studied. Wang and Nagaosa (2002) investigatedthe extraction of divalent metal ions using Di-2-methylnonylphosphoric acid (D2MNPA) in heptane at

162 W. Zhang, C.Y. Cheng / Hydrometallurgy 89 (2007) 160–177

an aqueous ionic strength of 0.10 mol/L (NaClO4) at25 °C. The extraction order of metals is:

Cd≈MnNCuNCoNNi

The metal complexes extracted were found to be allmonomeric species by using a slope analysis method. Acurve fitting method was used to determine the types ofmetal–organic complexes extracted.

PMnA23ðHAÞ and

PMnA24ðHAÞ complexes were found for Mn(II).

2.1.2. Ionquest 801/P507/PC 88A-phosphonic acidextractant

Metal pH isothermswith 2-ethylhexyl phosphonic acidmono-2-ethylhexyl ester (PC88A) were investigated inboth sulfate and chloride media by Dreisinger and Cooper(1984). The extraction orders differ in different media.

In sulfate medium, the order was found to be (pH50 inbracket):

FeðIIIÞð0:15ÞNZnð1:46ÞNPbð3:05ÞNCuð3:15ÞNMnð3:19ÞNCdð3:37ÞNCað3:48ÞNFeðIIÞð3:5ÞNCoð3:55ÞNMgð4:07ÞNNið4:85Þ:

It indicates a good possibility of separation of zincfrom manganese and manganese from nickel in sulfatemedium with PC 88A.

In chloride medium, the isotherms of cobalt andmanganese shifted significantly to lower pH values andthe order became (pH50 in bracket):

FeðIIIÞð0:30ÞNZnð1:28ÞNCoð2:03ÞNMnð2:64ÞNCuð2:69ÞNFeðIIÞð2:88ÞNPbð2:93ÞNCað2:96ÞNMgð3:62ÞNCdð3:70ÞNNið4:27Þ:

These shifts increase the ease of separation ofmanganese from nickel and the separation of manganesefrom magnesium, but reduce that of separation of zincfrom manganese.

The extraction order was also found to depend on theratio of the molar concentrations of the extractant to themetal in the organic phase (Thakur, 1998).At low loading,the extraction order was established as MnNCuNCoNNiand the equilibrium reaction proceeded via Eq. (2):

M 2þ þ 2PðHAÞ2 ¼PMðHA2Þ2 þ 2Hþ ð2Þ

At high loading, the extraction order becameCuNMnNCoNNi and the following equilibrium reac-tion predominates:

M 2þ þPðHAÞ2 ¼PMA2 þ 2Hþ ð3Þ

2.1.3. Cyanex 272 and PIA-8-phosphinic acidThe extraction of metals from a sulfate medium with

Cyanex 272 in toluene was established in the order(pH50 in bracket) (Cole 2002):

Znð2:51ÞNCuð4:13ÞNMnð4:60ÞNCoð4:65ÞNMgð5:59ÞNCað6:15ÞNNið6:58Þ:

The pH50 values suggest that Cyanex 272 is a goodextractant in terms of separation of cobalt from nickel,zinc from manganese, and manganese from nickel.

The research results by Devi et al. (1997) showed thatthe extraction of metal ions with Cyanex 272 increasedwith increasing equilibrium pH and the extractantconcentration up to 0.05 M. The separation factor ofzinc over manganese (βZn/Mn) was pH dependent,maximum at pH 3.5 and minimum at pH 5.7. Theextracted species were determined to be

PZnA23ðHAÞ

andPMnA23ðHAÞ.

2.1.4. Carboxylic acid extractantsThe extraction of Mn, Cu, Co, and Ni in nitric

medium with Versatic 911 acid in benzene was reported(Shibata et al., 1974; Shibata and Nishimura, 1979).PMnA24HA and

PðMnA22HAÞ2 were observed to be thepredominant extracted species of manganese. Theextraction reaction of these metals was endothermicand temperature had a significant effect on extraction ofCo2+ and Mn2+ (Mukai et al., 1975).

The extraction of Mn(II) from NH4Cl solutions withheptanoic acid was studied by Apostoluk (1989). It wasfound that the prevailing species in the organic phasewere mononuclear Mn(II) complexes, but when Mn(II)concentration in the system was 10.0 mM, the organicphase contained

PðMnA22HAÞj complexes, wherej=1, 2 or 3.

2.2. Applications of SX for manganese separation/removal

Manganese is closely associated with zinc ores andnickel–cobalt laterite ores and leached together withthese metals. Solvent extraction plays an important rolein separation of these metal values from manganese, inwhich manganese is left as an impurity in the raffinate.The major solvent extraction processes developed arereviewed below.

2.2.1. Separation of manganese from cobalt and nickelThe reported extractants for the separation of

manganese from cobalt and nickel are summarised inTable 1.

Table 1Summary of Mn separation from Co and Ni and recovery from manganese solutions

Extractant Remark Reference

D2EHPA-phosphoric acid Mn removed for Co EW in the pilot Mn SX circuit Dry et al. (1998)Continuous operation for separation of Mn from Co at pH 4.2 Feather et al. (1999)Extn. order: Zn∼CaNMnNCuNCoNNiNMg Hoh et al. (1984)Optimum pH 3.5 for Mn from Ni at 40–60 °C Cheng (1999, 2000)Optimum pH 3 for Mn from Co at 23 °C

PC 88A-phosphonic acid Fe(III)NZnNPbNCuNMnNCdNCaNFe(II)NCoNMgNNi Dreisinger and Cooper (1984)Mn over Mg and Ni

Cyanex 272-phosphinic acid Bulong process:Co, Cu, Zn and Mn from Ni, Ca and MgCo and Mn from Ni at pH 6 and 50 °C Taylor and Cairns (1997)ZnNCuNMnNCoNMgNCaNNi Hubicki and Hubicka (1996)Separation of Mn from Ca and Ni Cole (2002)

D2EHPA D2EHPA best with βMn/Co max at pH 4.45 Devi et al. (2000)PC88A D2EHPANPC88ANCyanex 272Cyanex 272


In the Kakanda project of the Democratic Republic ofCongo, after leaching, copper SX and iron removal,manganese was removed from the leach solution usingD2EHPA before cobalt electrowinning (Dry et al., 1998;Feather et al., 1999). The pilot manganese SX circuitconsisted of three extraction stages, one scrubbing stageand two stripping stages. A bleed stream of the strippedorganic phase was treated with 6 M HCl in one re-stripstage to control the accumulation of ferric ion in theorganic solution.

Hoh et al. (1984) performed a continuous mixer-settler operation for separation of manganese fromcobalt in sulfate solution by D2EHPA. A high degree ofseparation could be achieved by controlling the solutionpH at 4.2. Four extraction stages at O/A=2 and twostripping stages at O/A=1 were used to separatemanganese from cobalt.

Devi et al. (2000) compared separation of divalentmanganese and cobalt from sulfate solutions usingsodium salts of D2EHPA, PC 88A and Cyanex 272 inkerosene. Manganese and cobalt pH isotherms with thethree extractants indicated a preferential extraction ofmanganese over cobalt. The selectivity of manganeseover cobalt by PC 88A and Cyanex 272 was too small tobe used for their separation. In the case of D2EHPA, theseparation factor of manganese over cobalt was maxi-mum (79.3) at equilibrium pH of 4.45. The order ofmanganese extraction with the three extractants wasD2EHPANPC88ANCyanex 272. D2EHPA was themost suitable extractant for separation of manganesefrom cobalt.

The separation of copper and manganese from cobaltand nickel in synthetic nickel laterite leach solution wasstudied by Cheng (1999, 2000) with D2EHPA. It was

found that relatively high temperatures in the range of 40–60 °C and pH at 3.5 were favourable for separation ofmanganese from nickel while a low temperature at 23 °Cand pH 3 was optimum for separation of manganese fromcobalt. A complete removal of manganese and copperfrom the aqueous solution was achieved bymultiple stageextraction and scrubbing of the loaded organic solutionwith manganese solution. After one stage of contact, onlyabout 3 ppm Co and Ni were present in the organicsolution.

The Bulong Nickel Operation in Western Australia,processed a nickel–cobalt laterite ore and produced high-grade nickel and cobalt cathode products (Taylor andCairns, 1997). In this process, cobalt, copper, zinc andmanganese were separated from nickel, calcium andmagnesium by solvent extraction with Cyanex 272. Thenickel in the raffinate was separated from calcium andmagnesium by solvent extraction with Versatic 10 andthen electrowon. The strip solution from Cyanex 272containing cobalt, copper, zinc and manganese subjectedto sulfide precipitation, solids/liquid separation and acidre-leach to separate cobalt, copper and zinc frommanganese. The zincwas eliminated by solvent extractionwith D2EHPA and the copper by ion exchange (IX). Thecobalt was then recovered from the purified solution byelectrowinning. Compared with the direct solvent ex-traction approach (see below), the Bulong process isinefficient because of the twice extraction of the largevolume of dilute feed solution, subsequent sulfide pre-cipitation and re-leach to separate cobalt frommanganese.

Purification of a nickel sulfate solution containingimpurities such as Co, Zn, Cu, Mn and Fe was alsocarried out by Hubicki and Hubicka (1996) usingCyanex 272. After two stages of extraction at a phase

Table 2Summary of Ni, Co separation and recovery from manganese solutions


Cyanex 301 (20%) and TBP (5%)in Exxsol D-80

N99.9% Co and Ni only 0.2% Mn Tsakiridis and Agatzini (2004)

Cyanex 301-Goro process but needs strip with 5–6 M HCl at 50–60 °C Price and Reid 1993; Mihaylov et al., 1995;Bacon and Mihaynov, 2002

Cyanex 301, Cyanex 302 with Aliquat 336 Cyanex 301 more efficient than Cyanex 302 Niand Co from Mn, Ca and Mg

Tait 1992; Jakovljevic et al., 2004

Carboxylic acid- hydroxyoxime Versatic911-(LIX 63, 64, 64 N, 65 N, and 70)

First observed synergism for Ni with 3 pH unit shift Flett and West 1971; Tammi, 1976

Carboxylic acid-aldoximes (non chelating) Synergism for Ni and Co Preston (1983, 1985)Separation of Ni, Zn and Co from Mn, Ca and Mg

Versatic 10 and LIX 63(CSIRO DSX synergist system)

ΔpH50 (Mn–Ni)=1.96 Cheng and Urbani 2005a,b; Cheng 2006

ΔpH50 (Mn–Co)=2.53Versatic 10-alkylpyridine synergistand neodecanoic acid

N99.9% extraction for Ni, Co, Zn, Cu Preston and Du Preez (2000)

Versatic 10-decyl-4-pyridinecarboxylic acid(CSIRO DSX synergist system)

Reject Mn impurities in raffinate Cheng and Urbani 2005c; Cheng et al., 2005

Pyridine (BNPP) and sulphonic acid(HDDNS)

Useful for separation at very acidic solution(pH b0.5), but needs strong acid to strip Ni and Co

Zhou and Pesic (1997)


ratio of 1:1, pH 6 and 50 °C, the manganese and cobaltcontent in the purified NiSO4 solution decreases severalhundred times compared to the initial content. Thepurified nickel sulfate contained 10 ppm Co, 1 ppm Zn,0.5 ppm Fe, Cu and Mn.

2.2.2. Separation of cobalt and nickel from manganeseThe reported extractants for the separation of cobalt

and nickel from manganese are summarised in Table 2.Synergist effect on nickel extraction by mixtures of

carboxylic acid and a hydroxyoxime was observed inearly 1970s (Flett and West, 1971; Tammi, 1976). Thesynergistic systemswere further studied byPreston (1983,1985). Recently, a number of synergistic SX systemscomprising carboxylic acids and oxime reagents weredeveloped to recover nickel and cobalt and separationfrom manganese, magnesium and calcium impurities inthe nickel laterite leach solutions (Cheng and Urbani2005a,b; Cheng 2006). For the system containingVersatic10 (an alkyl monocarboxylic acid) and LIX63, thedifference in pH50 values between manganese, and nickeland cobalt was 1.96 and 2.53 pH units, respectively,indicating easy separation of nickel and cobalt frommanganese impurities.

Synergist systems containing carboxylic acids, andalkyl pyridines and pyridinecarboxylate esters as syner-gists have been intensively studied by Preston and co-workers. The pyridinecarboxylate ester synergists withcarboxylic acid extractant, Versatic 10, were found tocause appreciable synergistic shifts for the extraction ofNi and Co (Preston and du Preez, 1994; du Preez and

Preston, 2004). With n-octyl 3-pyridinecarboxylate, thesynergistic shifts decreased in the order:

NiNCoNCdNCu∼FeðIIÞNMnNZn

And with Acorga DS5443A or CLX50 (a pyridine di-carboxylate ester manufactured by Avecia) in the order:

NiNCuNCoNFeðIIÞNCdNMnNZn

With an alkylpyridine synergist, large synergisticshifts were found for nickel, e.g. from 1.04 pH units withVersatic 10 alone to 3.48 pH units for its mixture (Prestonand du Preez, 2000). The selectivity series for theextraction of divalent metals from sulfate media by theabove-mentioned mixture lied in the order (pH50 inbracket):

Cuð3:16ÞNNið4:73ÞNZnð4:94ÞNCoð5:41ÞNFeðIIÞð5:65ÞNMnð6:45ÞNCað7:96ÞNMgð8:43Þ:

This series suggests that in the recovery of nickelfrom laterite leach liquors, the mixed extractant systemswould allow the early rejection of manganese, ferrousiron, calcium and magnesium to the raffinate, whilst themore valuable impurity metals (copper, cobalt and zinc)would report to the nickel strip liquor.

Based on the earlier work, the direct solvent extraction(DSX) process (Fig. 1) has been developed to directlyseparate nickel and cobalt from manganese, magnesiumand calcium without intermediate precipitation (Cheng

Fig. 1. A conceptual flowsheet of the direct SX Process for nickel laterites (Cheng et al., 2004).


et al., 2004; Cheng and Urbani, 2005c). The core of theDSX process is the synergistic solvent extraction tech-nology using Versatic 10 as extractant in combination witha synergist including decyl-4-pyridinecarboxylic acid(4PC) (Cheng and Urbani, 2005c; Cheng et al., 2005)and LIX 63 (Cheng and Urbani, 2005a,b; Cheng, 2006).Batch and semi-continuous tests using the system con-taining Versatic 10 and 4PC and nickel laterite pilot plantsolutions from BHP Billiton were carried out. Excellentselectivity for nickel and cobalt over Mn, Mg and Ca weredemonstrated. The pH50 of cobalt was found to be 5.47 andthe pH50 of manganese 6.63, resulting in aΔ pH50 of 1.17pHunits betweenmanganese and cobalt, suggesting a goodseparation of cobalt and nickel from manganese, magne-sium and calcium. Fast extraction and stripping kineticswere also observed. In semi-continuous extraction tests, theorganic synergist solution effectively extracted all of thecobalt, zinc and copper and 99.97% of the nickel, leavingmost of manganese, magnesium, calcium and chloride inthe raffinate. About 96% of the co-extracted manganese,100% of the co-extracted magnesium and 61% of the co-extracted calcium were scrubbed in the semi-continuousscrubbing tests.

A synergistic extraction system involving a pyridine-based chelating extractant, 2,6-bis-[5-n-nonylpyrazol-3-yl] pyridine (BNPP) and dinonyl naphthalene sulfonicacid (DNNSA) has also been reported for selectiveextraction of nickel and cobalt at pH 0.5 from impuritiessuch as Fe, Mn, Ca, Mg and Al (Zhou and Pesic, 1997).The extraction sequence of the metals (pH50 in bracket)is:

Cuðb0:0ÞNNiðb0:0ÞNCoðb0:0ÞNZnð0:15ÞNFeðIIÞð0:6ÞNFeðIIIÞð0:65ÞNNMnð1:51Þ

NCað2:4ÞNAlð3:1ÞNMg

This synergistic system showed good separation ofnickel and cobalt from manganese in highly acidicsolutions. However, the stripping of cobalt and nickelneeds strong HCl acid. The stripping kinetics of nickel isslow and needs both strong HCl and high temperature.

A better direct SX process to separate nickel andcobalt from the major impurities (Mn, Mg and Ca) in thehighly acidic nickel leach solution of the Goro Processin New Caledonia has been developed by Inco Ltd(Price and Reid, 1993; Mihaylov et al., 1995; Bacon andMihaynov, 2002). After the removal of copper by IX,the leach solution is subjected to solvent extractionusing Cyanex 301 (bis-(2,4,4-trimethylpentyl)-dithio-phosphinic acid) to reject the major impurities, Mn, Mgand Ca. Cobalt, nickel and zinc are stripped using 6 MHCl. The zinc is then separated by IX and the cobalt isseparated from the nickel by SX using tertiary octylamine (TOA). After pyro-hydrolysis of the concentratedNiCl2 solution, nickel is recovered as nickel oxide andHCl is recycled for stripping and cobalt is precipitated ascarbonate.

Problem with Cyanex 301 is its affinity for copper,making it impossible to strip and hence completeremoval of copper is necessary. Therefore, the majordisadvantages of the Goro Process lie in the need to useion exchange for complete copper removal before thesolvent extraction and the need for 6 M HCl and hightemperatures (50–60 °C) for stripping the metals.Consequently, the use of 6 M HCl in stripping forcesthe nickel recovery via pyrohydrolysis route. 6 M HClmay not be necessary strong and expensive if it isrecycled and regenerated.

Tsakiridis and Agatzini (2004) recently studied asimultaneous extraction and separation of cobalt andnickel from manganese and magnesium in sulfate

Table 3Summary of Zn separation and recovery from manganese solutions


D2EHPA βZn/Mn maximum at pH 3 and A/O=2 Ritcey and Lucas (1971)pH 1.8–3.0 for Zn; pH 3.3–6.5 for Mn Urbanski (1988)Optimum pH 2.75 for Zn from Mn Cho and Dai (1994)

Cyanex 272 pH 2.5 for Zn; pH 4.5 for Mn Salgado et al., (2003)LIX1104 Fe(III)NCuNZnNNi∼CoNCaNMn Tait et al. (1995)

Easy separation of Zn from MnVersatic 10-LIX 63 (CSIRO Synergistic SX) Separation of Co/Zn from Mn (Baja Mining Boleo Project) Dreisinger et al. (2005)TBP (30–50 g/L NaCl) N90% Zn extraction in 4–5 stages Bressa et al., (1979)Naphthenic acid pH 5.2–5.5 Buttinelli and Giavarini (1982)


solutions using Cyanex 301. The results showed that theextractant Cyanex 301 in the presence of TBP could beused for the separation of cobalt and nickel frommanganese and magnesium in sulfate solutions with animproved stripping efficiency. Cyanex 301 (20%) andTBP (5%) in Exxsol D-80 could extract cobalt andnickel by 99.9% and 99.7%, respectively, in one stage atpH 2.0 and 50 °C. After scrubbing with 1 M HCl atpH=2.0, manganese co-extraction in the loaded Cyanex301 could be reduced to 0.2%, whereas no magnesiumextraction occurred in the pH range 1.0–2.0. Cobalt andnickel stripping from the loaded organic phase by 5 MHCl reached 99.6% and 99.2%, respectively, in onestage at 50 °C and phase ratio O/A=2/1.

Tait (1992) compared the extraction behaviour ofCyanex 301, Cyanex 302 and their binary extractantmixtures with Aliquat 336 toward Cu, Zn, Fe(III), Fe(II),Co, Ni, and Mn in sulfate solutions. Cyanex 301 wasfound more efficient as an extractant than Cyanex 302,and was able to effect extraction at greater acidities. Thepresence of base Aliquat 336 resulted in a decrease in itsextraction power. This could be ascribed to the highstability of the acid-base couple which must dissociate toeffect extraction.

Jakovljevic et al. (2004) also investigated the solventextraction and stripping characteristics of Cyanex 301binary extractant systems for recovery of cobalt andnickel from chloride solutions. These binary extractantsystems consisted of the mixtures of Cyanex 301 withbasic extractants Primene JMT, Amberlite LA-2,Alamine 336 and Aliquat 336. The Cyanex 301-aminesystems all demonstrated that cobalt and nickel couldbe selectively extracted from calcium, manganese andmagnesium. Among the amine extractant systems,Cyanex 301-Aliquat 336 was found most promising.A decrease in cobalt stripping was observed when thehydrochloric acid concentration was increased from 2 to4 M. The hydrochloric acid concentration had a reverseeffect on nickel.

2.2.3. Separation of zinc from manganeseThe reported extractants for separation of zinc from

manganese are summarised in Table 3.Salgado et al. (2003) reported a process for recovery

of zinc and manganese from spent alkaline batteries bysolvent extraction with 20% (v/v) Cyanex 272 dissolvedin Escaid 110 at 50 °C. The process is of particularimportance for separation of zinc and manganesemetals. The leach solution contained 18.96 g/L Zn and12.95 g/L Mn. The bench scale results showed that theorganic system is selective for zinc at pH 2.5, leavingmanganese in the raffinate. This method has beenproposed to treat residues from both zinc–carbon andalkaline batteries because metal compositions of thesebatteries are quite similar.

Buttinelli and Giavarini (1982), Buttinelli et al.,(1985) developed a process for the recovery of H2SO4,zinc and manganese from zinc spent electrolytes. In thisprocess, sulfuric acid was extracted by an iso-butylalcohol. Zinc was extracted by D2EHPA, leavingmanganese in the solution or zinc and manganese co-extraction by 1 M naphthenic acid in kerosene afterpartial neutralization to pH 5.2-5.5. The strippedsolution containing zinc and manganese could bedirectly recycled to the zinc electrowinning circuit.

In Baja Mining Corporation's Boleo project, zinc andcobalt were recovered in a pilot plant operation usingCSIRO synergistic solvent extraction technology in aDSX process (Dreisinger et al., 2005). The feed solutioncontained 23 g/L Mn, 0.13 g/L Co and 0.6 g/L Zn.Cobalt and zinc were separated from the manganese.About 69% zinc was selectively stripped from theorganic solution at pH 3.0 using weak sulfuric acid andrecovered as zinc sulfate by evaporation while the cobaltand remaining zinc were further bulk stripped at pH 1.0.The Zn and Co in the strip liquor was separated by SXextraction with Cyanex 272 at pH 3 for zinc and pH 5for cobalt which was then recovered by electrowinningafter stripping.


A process was patented by Urbanski (1988) for therecovery of zinc, manganese, and magnesium salts fromaqueous solutions of their mixtures, especially from spentzinc electrolyte. In this process, the spent zinc electrolytecontaining Zn, Mn, Mg, and optionally NH4 was firstsubjected to selective extraction of zinc at pH 1.8–3.0using D2EHPA. The organic phase was stripped usingH2SO4. Then, the zinc-free electrolyte was subjected toselective extraction of manganese at pH 3.3–6.5 usingD2EHPA. The organic phase was stripped using a mineralacid solution. A study of solvent extraction with DEHPAshowed that zinc in the leach solution from an acid minedrainage sludge sample could be extracted without Ni, Coand Mn up to a pH of 2.75 (Cho and Dai, 1994).

A combined chemical precipitation with solvent ex-traction for separation of nickel and cobalt from sulfuricacid leaching solution of ocean polymetallic nodules wasreported by Jiang et al. (1998) The leach liquor containingNi, Co,Mn and Znwas subjected to selective extraction ofZn from Mn with P204 (Chinese version of D2EHPA),followed by scrubbing and stripping to yield zinc sulfatesolution. Nickel–cobalt separation was achieved usingCyanex272. The compositions of the resultant sulfatesolutions had b20 ppm impurity.

Ritcey and Lucas (1971) developed a process forrecovery and separation of manganese and zinc fromcalcine leach liquor. In this process, the separation ofcopper was accomplished by using LIX 63with very littlezinc and no manganese extraction in the equilibrium pHrange of 0.8–1.5. After removal of the copper using LIX63 at a pH range of 0.8–1.5, zinc was extracted at pH 3.0using 20% D2EHPA and 2% TBP in kerosene. Themaximum separation of Zn/Mnwas observed at pH 3.0 atan A/O ratio of 2. Any co-extracted manganese wasremoved by scrubbing with ZnSO4 solution.

The extraction of metals with LIX 1104 (branchedhydroxamic acid) dissolved in toluene and aqueous sulfatesolutions has been investigated by Tait et al. (1995). Theextraction of metals was found to be of the following order(pH50 in bracket):

FeðIIIÞNCuð2:3ÞNZnð5:0ÞNNið5:5Þ≈Coð5:5ÞNCað5:9ÞNMnð6:5Þ

Slope analysis showed that LIX 1104 forms chelatesof ML2 with manganese, cobalt, zinc and cadmium andML2 (HL) with nickel and copper. Table 3 gives thepH50 values at which 50% extractions were achievedunder the conditions of 0.02 M metal ions, 1 M Na2SO4,and 25 °C. It shows an ease of separation of zinc frommanganese and a good possibility of separation of nickeland cobalt from manganese.

Bressa et al. (1979) investigated the recovery of zincand its separation from manganese and magnesium inacidic and industrial solutions (ZnCl2 and ZnSO4) bysolvent extraction with Tributylphosphate (TBP) inkerosene. Adding NaCl (30–40 g/l) was found to benecessary, and extraction could be carried out at roomtemperature with a mixture containing kerosene 20–30%. Except for iron, the separation was very selective.

The separation of iron, manganese and zinc usingAlamine 336 in xylene from hydrochloric leachingsolutions of manganese nodules containing cobalt andnickel has been reported by Ahn et al. (2003). In thepresence of minimum 5.0 M chloride ion, cobalt couldbe selectively extracted from nickel due to cobaltchloro-complex in solution, but co-extracted with theimpurity metals such as Cu, Fe, Mn and Zn. Manganeseand nickel were effectively removed in the scrubbingstep with 6.0 M HCl solution, and copper, iron and zincby controlling the concentration of chloride ions in thecobalt stripping step.

3. Purification of manganese solutions

3.1. Sulfide precipitation of metals from Mn2+ solution

The precipitation of metal sulfides and separation isbased on different sulfide solubilities of metals at acertain pH and temperature. Gaseous hydrogen sulfide(H2S) or sodium sulfides (Na2S) or ammonium sulfide(NH4)2S is usually employed in the precipitation ofmetal sulfides. The thermodynamic equilibria involvedin the sulfide precipitation can be expressed as:

H2SðgÞ ¼ 2Hþ þ S2� Kp ¼ ½Hþ�2½S2��PH2S

ð4Þ

Mnþ þ n

2S2� ¼ MSn=2 K ¼ 1

½Mnþ�½S2��n2

¼ 1

KSð5Þ

where Ks is the solubility product of the metal sulfide.These relationships can be written in the forms:

pH ¼ � n2ðlogKp � logPH2S þ log½S2��Þ ð6Þ

log½Mnþ� ¼ logKS � n2log½S2�� ð7Þ

For a given PH2S, each can be plotted on a sulfidesolubility diagram as shown in Fig. 2 (Based onMonhemius, 1977).

Fig. 2. Sulfide solubility diagram at 25 °C (Based on Monhemius, 1977).


It can be seen that the line of Mn2+ is far to the righthand side of the diagram, indicating that manganesesulfide is more soluble than most other metal sulfides.This offers a theoretical basis for separation of Mn2+

from other metals such as Cu2+, Zn2+, Co2+, Ni2+, andFe2+ in hydrometallurgical processes, where other metalions are precipitated as metal sulfides while Mn2+ ionsremain in solution.

Sulfide precipitation for purification of MnSO4 solu-tions was used in electrodeposition of manganese byHannay and Walsh (1944). The MnSO4 solution wasfreed of impurities such as Ni, Co, Zn, Pb, As, Sb, Fe,Cu and Cd by the treatment with H2S at pH 5–6 and at atemperature not higher than 25 °C.

Roehrborn and Amirzadeh-Asl (1994) reported thesulfide precipitation for the separation of zinc frommanganese in the leach solution of the sludges from theprocessing of raw zinc liquor. The zinc in the solutionwas precipitated with Na2S solution to pH 5–7, leavingmanganese in solution for subsequent recovery.

The sulfide precipitation has been commercially prac-ticed inMurrinMurrin nickel laterite processes (Motteramet al., 1996). The separation of nickel, cobalt, copper andzinc frommanganese, magnesium and calcium impuritiesis achieved in one step sulfide precipitation andmanganese is discarded. The nickel, cobalt, copper andzinc in the precipitate are re-leached under pressure withoxygen followed by solvent extraction with Cyanex 272to separate the zinc, cobalt and nickel. The nickel andcobalt are recovered by reduction with hydrogen.

Jandova et al. (2005) studied a controlled sulfideprecipitation for recovery of copper and nickel–cobaltconcentrates from the liquors originating from leachingmanganese deep ocean nodules in FeSO4–H2SO4–H2Osolutions. The metal ions studied include Co2+, Cu2+,Fe2+, Ni2+, Mn2+ and Zn2+. Promising results were

obtained when copper and nickel–cobalt concentrateswere precipitated with 5.5% solution of (NH4)2S.Copper precipitation was conducted at pH 1.0 andnickel–cobalt precipitation at pH 3.0 at the laboratorytemperature, and leaving manganese in solution forpossible recovery or discharge.

3.2. Adsorption and ion exchange

A method using ion exchange for purification ofmanganese sulfate solutions was reported by Kholmo-gorov et al. (1997). It was found that cobalt sorptionincreased with pH increase up to 5.5. The cobalt andmanganese separation was achieved by substituting themanganese ions with cobalt ions at pH more than 3.5using chelating resins ANKB-35 and AMF-2M. Thecobalt content in the resulting manganese sulfate solu-tions was below 0.6 mg/l.

Kudryavtsev et al. (1991) used a polyethylenepolya-mine-type ion exchanger for separation of cobalt andmanganese in sulfate solutions. The ion exchanger waspre-treated with mineral acids at pH 3–3.5.

Amino-carboxylic amphoteric ion exchangers weretested (Kononova et al., 2000) for the separation of nickelfrom the Mn(NO3)2–H2O system. The examined ionexchanger included aminocarboxylic amphoteric ionexchangers AMF-1T, AMF-2T, AMF-2M, ANKB-35 aswell as carboxylic cation exchanger KB-2T. Of theexchangers examined, the ion exchanger AMF-2T wasfound to be the best for the selectivity ofNi(II) overMn(II).

Diniz et al. (2005) has reported an uptake of copper,nickel, cobalt, lead, iron and manganese from manganesechloride leach solution onto the chelating resin DowexM-4195 in the column experiments. The solution contained85 mg/L Cu, 100 mg/L Ni, 47.5 mg/L Co, 40 mg/L Pb,6.0 g/L Fe, 47.5 g/L Mn with 1.0 M free acid and 3.6 M

Fig. 3. A solubility diagram of metal hydroxides at 25 °C (Based on Monhemius, 1977).


total chloride. The results indicate a sequence of affinityof metals in the order:

CuNNiNPbNFeNCoNMn

The results demonstrated the ability to remove con-taminants to an extent satisfying the quality criteria re-quired for the utilisation of themanganese chloride solutionfor preparing manganese chemicals. The column elutiontests confirmed that a two-stage elution scheme, wherebysulfuric acid was first used to elute iron, nickel and cobaltfrom the resin, and then a subsequent ammonium hydro-xide elution recovered almost all of the copper.

4. Precipitation of manganese compounds

4.1. Hydroxide precipitation

The precipitation of metals in solutions as metalhydroxides is the most common way to remove metalsfrom solutions in hydrometallurgical processes. Theequilibrium of a metal hydroxide precipitation can beexpressed by the general equation:

Mnþ þ nOH� ¼ MðOHÞn ð8Þ

The equilibrium constants can be written as:

K1 ¼ 1½Mnþ�½OH��n ¼

1KS

ð9Þ

where Ks is the solubility product. The equilibria of metalhydroxide precipitation can be presented graphically in asolubility diagram Fig. 3 (based on Monhemius, 1977).From the diagram, it is predicted that Fe3+, Al3+, Pb2+ andCu2+ can be readily separated from Mn2+ by hydroxide

precipitation while separation of Zn2+ from Mn2+ ispossible but that of Co2+, Ni2+ fromMn2+ is difficult by ahydroxide precipitation method.

Thus, in hydrometallurgical separation processes,hydroxide precipitation alone does not provide a usefulmeans for separation and recovery of manganese.Generally, hydroxide precipitation in separation and/orrecovery of manganese is only useful in some specialcases in combination with other methods.

One practical strategy is to use hydroxide precipitationfor valuable metals together with manganese followed byselective leaching to separate valuablemetals frommanga-nese. This is used in the Cawse laterite process (Mansonet al., 1997), which comprises the following steps:

(1) Precipitation of copper, zinc, nickel and cobalttogether with some of the manganese as hydro-xides using MgO.

(2) Leaching with ammonia in the presence of air andCO2 to selectively dissolve the nickel, cobalt,copper and zinc in the precipitate as ammine com-plexes in the leach liquor, leaving manganese in theleach residue as manganese carbonate or oxides.

(3) Nickel and copper are separated from cobalt andzinc by SX with LIX84I. The nickel is recoveredby electrowinning while cobalt, together withzinc, is precipitated as sulfide.

In CESL nickel laterite process, a similar principle isused for separation of nickel and cobalt from manganesewith the ammonia carbonate re-leach (Jones and Moore,2001).

The major advantage of this strategy is the eliminationof a large volume of the feed solution at a very earlystage from the process circuit by hydroxide precipitationof the metals. However, the operation cost with respect


to the re-leach and subsequent separation processes ishigh.

A different strategy was investigated for separation andrecovery of cobalt and manganese from spent bromideoxidation catalysts by Clark et al. (1996). Instead ofhydroxide precipitation followed by selective leachingwith ammonia, a selective precipitation ofmanganesewithammonia was used. The spent catalysts containing 27–31%Co, 25–33%Mn, 0–14%Fe togetherwithCr, Cu andNi, were leached with 4MHCl at 80 °C for 4 h. The leachliquor was then purified with successive neutralisations:

(1) Addition of NaOH to remove iron and chromiumas hydroxide at pH 2.

(2) Addition of ammonia to precipitate manganesefrom an aerated solution leaving cobalt as a Co(III) hexammine complex in the solution.

(3) Recovery of cobalt from this solution by chemicalor electrochemical processes.

Compared with the first strategy, the selectiveprecipitation simplifies the process by omitting the re-leach step. However, more ammonia would be used forstabilising the valuable metals as hexammine complex ifthe solution volume is large. For the case of lateriteprocessing with a large volume of leach liquor, the firststrategy is advantageous in saving expensive ammonia atthe expense of comparatively cheap neutralisation agent.

4.2. Ammonia/carbonate precipitation of MnCO3

Carbonate precipitation of manganese is an importantpractical process for recovery of manganese. The use ofammonia in the carbonate process, instead of sulfideprecipitation, provides an alternative strategy for separa-tion of other valuable metals such as nickel and cobaltfrom manganese. In this case, manganese precipitates outas solid manganese carbonate while cobalt and nickel arestabilised in the solution as ammine complexes. Severalsuch processes have been reported in the literature.

INCO (Illis and Brandt 1975) developed a processfor selective recovery of metal values from sea nodulescontaining Mn 24.2%, Fe 5.8%, Ni 1.2%, Cu 0.85%,and Co 0.17%. The process comprised a reductiveroasting followed by leaching with 3–8% NH3 and 1–6% CO2 to extract nickel, cobalt and copper intosolution whilst most of soluble manganese was stab-ilised in solid residue by forming MnCO3 compoundwhich was then re-leached and recovered by crystal-lisation and calcination.

In processing nickel laterite ores, a similar strategy hasbeen adopted by Queensland Nickel (QNI) (Reid and

Price, 1993; Price and Reid, 1993; Skepper and Fittock,1996).After roasting the ore to reduce the nickel and cobaltto their metallic form, both metals are leached with anammoniacal carbonate solution. The manganese leachedinto the solution is minimised by forming stable manga-nese carbonate precipitate. The dissolved nickel, cobaltand zinc are separated by a series of selective solventextractions followed by precipitation of nickel from thestrip liquor as nickel carbonate and cobalt as sulfide.

Kono et al. (1986) studied separation and recovery ofMn, Cu, Ni and Co from sulfurous acid leach liquor ofsea nodules. In this process, Cu, Ni, Co, and Mn werecompletely leached with 0.2MH2SO3 while 30% of ironwas undissolved. After oxidation by aeration, Fe2+ wasprecipitated as Fe(OH)3 at pH 4.3–4.4. Subsequently,manganese was precipitated as MnCO3 by addition of(NH4)2CO3, while Cu, Ni, and Co in the solution werestabilized as ammine-complexes with NH3.

4.3. Oxidative precipitation of MnO2

Oxidative precipitation of manganese as insolublemanganese oxides, mainly MnO2, has found a wideapplication for removal of manganese impurity from Zn,Co, and Ni processing circuits. Manganese dioxide(MnO2) is a strong oxidising agent with the standardreduction potential being 1.224 V. It needs a strongeroxidant to oxidise Mn(II) to higher valence oxides,initiallyMn3+and thenMnO2. Various oxidants forMn(II)have been studied and applied to the practical processes,including ozone, SO2/O2 oxidising mixture, Caro's acid,peroxydisulfuric acid, hypochlorite and chlorate.

4.3.1. Ozone as oxidantBolton et al. (1981) reported a process for removing

manganese from an aqueous acidic sulfate solutioncontaining zinc and manganese without removing asubstantial amount of zinc from the solution. The solutionhad a free acid of 0.1–2 M, and contained 5–170 g/L Znand 1–25 g/L Mn. The process comprised treating thesolution with ozone to oxidise manganese to manganesedioxide and removing manganese dioxide from thesolution. The process was further patented for removalof both manganese and chloride ions from aqueous acidiczinc sulfate solutions (Bolton et al., 1982). In this process,acidified aqueous ZnSO4 solutions were treated withozone for the sequential precipitation of manganese asMnO2, and removal of chloride as chlorine gas. Theprocess was proposed for the treatment of spentelectrolytes from H2SO4 leaching of ZnS ores. Forexample, O2 containing 57.5 mg/L O3 was passedcountercurrently through a solution containing H2SO4


150 g/L, Zn 50 g/L, Mn 3.74 g/L and Cl− 107 mg/L in athree-cell series at approximately 23 °C. The manganeseremoval occurred mainly in the first and second cell, butchloride removal occurred in the second and third cell.The final solution containedMn 30mg/L and Cl− 3mg/L.The ozone oxidant is an effective but rather expensiveoxidant for Mn(II) and thus is less feasible than cheaperoxidants such as SO2/O2 mixture.

4.3.2. Chloric acid, chlorine dioxide and hypochloriteas oxidants

Chloric acid (HClO3) was used in a patented processto separate zinc oxide and manganese oxide byCawlfield and Ward (1995). The process comprisedthe following basic steps:

(1) Reacting a mixture of zinc oxide and manganeseoxide with an aqueous chloric acid solutionwherein the chloric acid was in molar excess ofthe manganese oxide to form a chlorine gas phase,a solid phase containing manganese dioxide and asolution phase containing zinc chloride.

(2) Separating the solid phase containing manganesedioxide from the liquid phase.

(3) Recovering the zincmetal from the electrolytic cell.

Yuan et al. (2000) studied oxidation and recovery ofmanganese in the leaching solution from a manganeseore using chloric salt (NaClO3) as the oxidant for Mn(II)in the acidic solutions. Optimum conditions werestepwise addition of the oxidant at a NaClO3:ore ratioof 0.25:1 (w/w), a acid:ore ratio of 0.54–0.55:1 (w/w),and liquid:solid ratio of 3:1, and a reaction time of 6 h.More than 90% of manganese was recovered under theoptimum conditions.

Chlorine dioxide (ClO2) oxidant was used by Parket al. (2005) for selective leaching of nickel and cobaltfrom the precipitated manganese hydroxide. The pro-cess is selective because manganese is dissolved and re-precipitated as MnO2 under the strong oxidising con-ditions while nickel and cobalt tend to be preferentiallyleached into the solution.

In the patent by Ferron (2003), a process wasreported involving oxidative separation of cobalt andmanganese from nickel in a leach solution containingNi, Co, Fe, and Mn. The process involved:

(1) Removing the iron from solution by oxidation andpartial neutralisation;

(2) Removing cobalt andmanganese from the solutionby oxidation and precipitation at pH from 1 to 4with hypochlorite, and

(3) Conventional nickel recovery from the resultantsolution.

One problem of using chloric acid or chlorine in theprocess is its highly corrosive nature and the costs for itscontrol and handling would be high.

4.3.3. Sulfur dioxide/oxygen as oxidantSulfur dioxide/oxygen (SO2/O2) at a correct ratio is a

strong oxidant for Fe(II) and Mn(II). Manganese isprecipitated as MnO2/Mn2O3 spontaneously using SO2/O2 gas mixtures in the pH range of 3–6. The mixture canalso oxidise Co(II) and Ni(II) at pH above 5 and 7,respectively. The study by Zhang et al. (2002) showedthat the rate of Mn(II) oxidation with SO2/O2 was thefirst order with respect to SO2 partial pressure up to5.7% SO2 at 80 °C and half order with respect to [H+].The rate of oxidation of Mn(II) was slow at pH b3 andincreased rapidly at pH N4. Any Fe(II) present wasoxidised and precipitated before Mn(II) removal. Theselectivity of manganese precipitation at pH 3–6 wasconsistent with thermodynamic data for the Mn–Ni/Co–H2O systems.

The SO2/O2 oxidant is comparably cheap and easy tomake or extract from smelter off-gas. These character-istics have made it a competitive oxidant and found awide application for separation or removal of manga-nese from valuable metals such as nickel, cobalt andzinc. Several processes have been patented as describedbelow.

Kniprath (1970) was the first to develop a method forsimultaneous precipitation of MnO2 or CoOOH at pH 5with oxygen or air and a reducing agent, e.g. SO2 orNa2SO3. The method was useful in purification of nickelliquors containing Fe, Mn, Co, and other metals, fromelectrolytic copper refining. Thus, 416 mL/min O2 and183 mL/min SO2 were passed into a litre of solutioncontaining 2 g Mn2+ (as sulfate) at 50 °C and pH 5.0adjusted by addition of NaOH. After 2 h, manganesewas precipitated quantitatively as MnO2.H2O.

Okajima (1975) disclosed a process for the treatmentof manganese nodules, in which, manganese and ironwere oxidatively precipitated as respective oxides byaeration of the solution containing 50 g/L Na2SO3. Thesolid leach residue, after combining it with the pre-cipitate was used for making ferromanganese containing43%Mn and 16%Fe. The ferromanganese can be readilyenriched for metallurgical applications. An addition ofchloride and use of the mixture of SO2/Air improved theseparation of iron and manganese (Okajima, 1977).

Manganese could be effectively separated from zincsolutionswith optimummixture of SO2 (0.5–10%) andO2


at 40–80 °C and pH 3–5, preferably pH 3–4 to minimiseloss of zinc by coprecipitation (Ferron, 2000; Demopouloset al., 2001). A distribution of nucleation sites in thereaction such asMnO2 crystals enhances the reaction. Theprocess is suitable for decreasing the manganese impurityin acidic solution for zinc electrowinning.

Similar principles can also be applied for separationof manganese from cobalt in cobalt leach solutions(Ferron and Turner, 2000; Lunt et al., 2003). In the co-presence of iron and manganese in the cobalt solutions,iron (II) can be first oxidised with the SO2/O2 gasmixture at 60 °C and then precipitated by hydrolysis atpH control 2.5–3.5, followed by oxidative precipitationof manganese in the second stage. Optionally, air can beused in the mixture with 0.1–2% SO2.

4.3.4. Persulfate as oxidantThe oxidation of manganese by peroxy-monosulfuric

acid (Caro's acid) and peroxy-disulfuric acid (H2S2O8)was reviewed by Burkin et al. (1981), and Burkin andChouzadjian (1983). The oxidation by these oxidantscan be expressed by the following reactions:

Oxidation by Caro's acid

Mn2þ þ H2SO5 þ H2OYMnO2 þ 2Hþ þ H2SO4

ð10Þand oxidation by peroxy-disulfuric acid

Mn2þ þ H2S2O8 þ 2H2OYMnO2 þ 2Hþ þ 2H2SO4

ð11ÞCaro's acid was used for the recovery of manganese

from aqueous acidic leach solutions (Burkin andChouzadjian, 1979). The developed process consisted of:

(1) Oxidation of Mn(II) to the Mn(IV) state in 2stages at 70–90 °C with 110–160% of stoichio-metric amount of Caro's acid relative to that ofmanganese;

(2) Neutralisation of the residual Caro's acid with aneutralizing agent (preferably a hydroxide) in oneor more stages at 100–133% of stoichiometricamount;

(3) Separation of the precipitated manganese saltfrom the preferred solutions at Caro's acid/H2O2

ratio of 30:1.

Wang and Zhou (2002) investigated a hydrometallur-gical process for the recovery of cobalt from zinc plantresidue, in which ammonium peroxy-disulfate((NH4)2S2O8) was used for oxidative precipitation of

iron and then manganese as MnO2. It was found thatchloride ion seriously affected the precipitation ofmanganese, which was attributed to the reduction of themanganese oxide. The standard redox potential ofMn3O4/Mn2+ pair is 1.76 V and that of Cl2/Cl

− pair is1.39. Therefore, the manganese oxide can be thermody-namically reduced to Mn2+ by chloride. The oxidation–reduction reaction betweenMn2+ and ammonium peroxy-disulfate was proposed to proceed according to Eq. (12):

3Mn2þ þ ðNH4Þ2S2O8 þ 4H2O¼ Mn3O4 þ ðNH4Þ2SO4 þ H2SO4 þ 6Hþ ð12Þ

The above reaction indicates that the addition ofammonium peroxy-disulfate will cause a decrease of pH,which may affect the precipitation significantly. The acidcan be neutralised by the addition of a dilute sodiumcarbonate solution. Furthermore, at pH 4.0–4.5, precip-itation of iron and manganese could be completed byapplying sufficient ammonium peroxy-disulfate solution.

Sarma et al. (1987) and Nathsarma and Sarma (1987)reported a process for the recovery of Ni, Co, and Cuand oxidative precipitation of the iron and manganesewith potassium persulfate in solutions from threedifferent raw materials: lateritic nickel ores, copperconverter slag and Indian Ocean manganese nodules.This removal also resulted in some loss of cobalt due toits adsorption on the manganese dioxide matrix.

5. Evaluations of methods for manganese recovery

Fig. 4 graphically summarises the major routes forrecovery of manganese from solutions containing one ormore of metal impurities such as Fe, Zn, Cu, Ni, and Co.The applicability of a route for recovery of manganeseor other valuable metals from a solution depends on anumber of cost sensitive factors, including the concen-tration of manganese in the solution, levels of otherimpurities, and purity of final manganese products. Ageneral evaluation of each route is outlined below.

Solvent extraction. Little work has been reported in theliterature for the recovery of manganese using solventextraction in the manganese industry. Solvent extractionsystems can be applied to both the recovery of manganeseand separation of othermetal impurities. DEHPAhas beenidentified and is the cheapest of the reagents for selectiveextraction ofmanganese over other impurities, e.g. Ni, Coand Mg. However, DEHPA cannot separate manganesefrom Ca. Synergistic SX systems offer better selectivityfor purification of manganese solution, but they aregenerally more costly due to involving expensive syn-ergists such as hydroxyoxime and pyridinecarboxylate

Fig. 4. Simplified possible routes for recovery of Mn from waste effluents.


esters. Themain operating cost by solvent extraction is thebase for pH adjustment. Ammonia is the most appropriateneutralisation agent in terms of cost and convenience foruse in solvent extraction. The cost of anhydrous ammoniais about 16% of the selling price for the manganese metalproduct, based on the current manganese metal price (US$1590 per tonne). This seems acceptable to the industry.Therefore, solvent extraction may offer an alternative tohydroxide and carbonate precipitation for recovery ofmanganese from the industrial effluents.

Sulfide precipitation. Sulfide precipitation is notconsidered for use for recovery of manganese fromindustrial waste solutions because of some unfavourableattributes. First, this method requires pollution controland management. Second, it needs stages to separatefrom other impurities. Last, but most importantly, themanganese sulfide is not a favourable product for themanganese industry, needing further conversion. How-ever, it provides a useful means for optional purificationof small amounts of metal impurities such as Cu, Zn, Niand Co before the step for production of highly puremanganese CMD, EM and EMD products. It has foundwide applications for purification of solutions fromleaching polymetallic manganese nodules, Zn–Mnbearing sludges, battery wastes, organic wastes, andmanganese-bearing laterite ores.

Ion exchange. Ion exchange is a useful method forpurification of manganese solution to separate metals

including Cu, Fe, Co, Ni and Pb. Compared with sulfideprecipitation method, ion exchange is more environ-mentally friendly and easier to control. However, a resinhas a limited capacity for adsorption of particular metalsand therefore more suitable for removal of traceamounts of metal impurities for preparation of highlypure manganese solutions.

Hydroxide precipitation. Manganese can be precip-itated as manganese hydroxide, Mn(OH)2 which is thenslowly oxidized to a mixture of hydrated manganeseoxides in the presence of air, or which can be calcined at300–450 °C with aeration to yield MnO2. However, theprecipitation requires solution pH above 9 and is lessselective. Based on the stability constants reported byMonhemius (1977), the selectivity of Mn from Mg andCa can be expressed by reactions (13) and (14):

MgðOHÞ2 þMn2þ

¼ MnðOHÞ2 þMg2þ Log K ¼ 1:44ð13Þ

CaðOHÞ2 þMn2þ

¼ MnðOHÞ2 þ Ca2þ Log K ¼ 7:36ð14Þ

The values of the equilibrium constants K indicatethat the selectivity for manganese hydroxide is thermo-dynamically more favourable with respect to Ca thanMg. However, this is not desirable for the separation of


manganese in the waste effluents which usually containmuch more Mg (N10 g/L) than Ca (b1 g/L). In apractical application, substantial amount of magnesiumis expected to be co-precipitated. Furthermore, for theproduction of purer manganese product, more expensivebase reagents such as ammonia or sodium hydroxide arepreferred to lime which would form calcium sulfate andco-precipitate with manganese.

In hydrometallurgical processes, hydroxide precipi-tation alone does not provide a useful means forseparation and recovery of manganese. Generally,hydroxide precipitation in separation and/or recoveryof manganese is only useful in some special cases. Onestrategy is to precipitate manganese and other valuablemetals as mixed hydroxides which is then leached byacid in the presence of an oxidant for Mn(II). Thisresults in insoluble MnO2 and soluble value metals (Zn,Cu, Ni and Co) in solution.

Carbonate precipitation. Carbonate precipitation ofmanganese as manganese carbonate can occur at pHabout 8.5 and the selectivity for manganese isthermodynamically more favourable with respect tomagnesium than calcium. This is indicated in reactions(15) and (16) (Stability constants based on Lide 2007):

MgCO3 þMn2þ ¼ MnCO3 þMg2þ Log K ¼ 5:48

ð15Þ

CaCO3 þMn2þ ¼ MnCO3 þ Ca2þ LogK ¼ 2:35

ð16Þ

This would be suitable for the separation ofmanganese in solutions containing more magnesiumthan calcium impurities compared with hydroxideprecipitation. In addition, manganese carbonate is afavourable form which can, after drying, be sold directlyto the manganese industry or further processed forproduction of CMD, EM and EMD.

In separation process, carbonate salts or carbondioxide together with ammonia can selectively precip-itate manganese as manganese carbonate while copper,nickel and cobalt are stabilised in solution as amminecomplexes. However, for the industrial waste solutionscontaining relatively low manganese and high magne-sium, the coprecipitation of magnesium and calciummay be considerable and need further purification stepsfor production of highly pure manganese products.Therefore, the applicability of carbonate precipitationfor recovery of manganese would depend on theconcentration of manganese relative to that of impuritiessuch as magnesium and calcium.

Oxidative precipitation. Oxidative precipitation ofmanganese as insoluble MnO2/Mn2O3 is highly selec-tive, especially when the solutions are free from iron.Small amounts of nickel and cobalt may be co-precipitated through oxidative precipitation and/oradsorption mechanism, depending on the solution pHand the types of oxidants used. The co-precipitatednickel and cobalt could be further separated andrecovered as by-products and may provide additionalbenefits as nickel and cobalt are more valuable metalsthan manganese. The main concern for use of oxidativeprecipitation method is the cost of some oxidants such asozone, Caro's acid, and peroxy-disulfuric acid. This maynot justify its use for recovery of manganese from asolution containing a low manganese concentration, e.g.laterite waste solutions containing 1–5 g/L manganese.The SO2/air oxidising mixture is a relatively cheapoxidant which is considered to be the most suitableoxidant for recovery of manganese fromwaste solutions.In the separation of manganese from other valuablemetals such as zinc, cobalt and nickel, the unique featureof the oxidative precipitation is that manganese can beselectively separated at lower pH range 3–6.

6. Conclusions

Solvent extraction is a promising alternative to theprecipitation methods for recovery of manganese fromsolutions.DEHPAhas been identified as the cheapest of thereagents for selective extraction of manganese over otherimpurities including Ni, Co, and Mg. The main operatingcost is the base for pH adjustment, for which ammoniaappears to be acceptable to the industry based on the currentprices of manganese products and ammonia reagent.

Manganese sulfide is an unfavourable form for man-ganese industry and not suitable for manganese recoverybut sulfide precipitation has been widely applied forpurification of manganese solutions and for the prepara-tion of highly pure manganese solution for production ofCMD, EM and EMD. Ion exchange is only suited for theremoval of small amounts of impurities due to a limitedcapacity of a resin.

Hydroxide precipitation is usually used for removal ofiron and aluminium impurities in manganese solutions,but it is less selective and is not suitable for the recovery ofmanganese from a solution containing a relatively largeamount of magnesium.

Carbonate precipitation is more selective and providesa more suitable form of manganese product for furtherprocessing. However, for the waste solutions containinglow manganese and high magnesium, its product qualityand further purification costs are the major concerns.


Oxidative precipitation offers the best selectivity forrecovery of manganese as MnO2/Mn2O3 over othermetals including Zn, Ni, Co, Mg and Ca in a pH range of3–6. The manganese oxides precipitated are expected tobe relatively pure and may need minimum purificationor processing for production of CMD product. Forindustrial waste solutions containing residual Ni and Co,the co-recovery of Ni and Co values is possible throughadsorption mechanism or co-precipitation as their oxideforms at higher pH range. The key issue for itsapplication is the cost of oxidants, for which the SO2/O2(Air) mixture is an effective and cheap oxidant.

Both oxidative precipitation and solvent extractionare recommended for future research and develop-ment for recovery of manganese from industrial wastesolutions.

Acknowledgements

The authors would like to thank CSIRO Mineralslibrary staff for collecting some references and Dr DavidMuir for reviewing this paper and providing valuablecomments.

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