Reductive dissolution of manganese from manganese dioxide ore by autotrophic mixed culture under aerobic conditions

Accepted Manuscript Reductive dissolution of manganese from manganese dioxide ore by autotrophic mixed culture under aerobic conditions Baoping Xin, Ting Li, Xin Li, Zhigang Dan, Fuyuan Xu, Ning Duan, Yongtao Zhang, Haiyan Zhang PII:

S0959-6526(14)01357-2

DOI:

10.1016/j.jclepro.2014.12.060

Reference:

JCLP 5031

To appear in:

Journal of Cleaner Production

Received Date: 12 January 2014 Revised Date:

11 December 2014

Accepted Date: 17 December 2014

Please cite this article as: Xin B, Li T, Li X, Dan Z, Xu F, Duan N, Zhang Y, Zhang H, Reductive dissolution of manganese from manganese dioxide ore by autotrophic mixed culture under aerobic conditions, Journal of Cleaner Production (2015), doi: 10.1016/j.jclepro.2014.12.060. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT The wordcount of the whole text file: 6839 characters.

2

Reductive dissolution of manganese from manganese dioxide ore by

3

autotrophic mixed culture under aerobic conditions

4

Baoping Xina, Ting Lia, Xin Lia, Zhigang Danb, Fuyuan Xub,∗, Ning Duanb, Yongtao

5

Zhanga, b, Haiyan Zhangb

RI PT

1

6

a

7

Beijing Institute of Technology, Beijing 100081 , P.R.China

8

b

9

Environmental Sciences, 8 Dayangfang, Beiyuan Road, Beijing 100012, P.R.China

M AN U

SC

Department of Environment and Energy, School of Chemical Engineering and Environment,

Center for Engineering Technology of Clearer Production, Chinese Research Academy of

Abstract: Reductive leaching of manganese from manganese dioxide ore has become

11

increasingly important for production of electrolytic manganese. The anaerobic

12

bioleaching has long received great concerns for reductive extraction of Mn by

13

heterotrophic microorganisms in the presence of sacchariferous substances.

14

Alternatively, the reductive dissolution of manganese from manganese dioxide ore by

15

autotrophic mixed culture under aerobic conditions was investigated in this work. The

16

results showed that the autotrophic mixed culture was capable of reductive liberation

17

of Mn in the presence of cheap sulfur and pyrite. 99% of Mn extraction was achieved

18

by the mixed culture at 10% of pulp density after 72-96 h under 24 g/L of mixed

AC C

EP

TE D

10

∗

Corresponding Author:E-mail address: [email protected] (F.Xu); Phone number: +86-10-84914256; Fax numbers: +86-10-84932378 Center for Engineering Technology of Clearer Production, Chinese Research Academy of Environmental Sciences, 8 Dayangfang, Beiyuan Road, Beijing 100012, P.R.China. 1

ACCEPTED MANUSCRIPT energy substrates, initial pH at 1.0 and pH control of process at 2.0. The diffusion

20

controlled model fitted best for describing dissolution of Mn. The acid dissolution was

21

the dominating mechanism for great improvement in leaching efficiency from 78%

22

without pH control to 99% with pH control.

23

Keywords: Reductive leaching; Manganese dioxide ore; Mn extraction; Anaerobic

24

bioleaching; Autotrophic mixed culture

25

1. Introduction

SC

Manganese is a strategically important nonferrous element used for production of

M AN U

26

RI PT

19

steel, ferromanganese, non-ferrous alloys, dry cell batteries, fertilizers, dietary

28

additives, paints and other chemicals (Sahoo et al., 2001; Duan et al., 2011). In

29

general, manganese is produced by electrolysis of manganese sulfate which is

30

prepared through leaching of manganese ore in sulfuric acid (Nayl et al., 2011; Duan

31

et al., 2011). Manganese ore exists mainly in the form of MnCO3 and MnO2 in nature.

32

When manganese is present in its divalent soluble form such as MnCO3, manganese

33

salts are obtained directly by acid leaching; whereas it is present in the insoluble form

34

such as MnO2, reducing agents are required to obtain the soluble Mn2+ for acid

35

mobilization into solution (De Michelis et al., 2009; Duan et al., 2011). Although

36

direct acid leaching of MnCO3 is preferred due to the much simpler leaching process

37

and lower leaching cost; in recent years, reductive leaching of manganese from MnO2

38

has drawn growing attentions due to rapid depletion of MnCO3 (Elsherief, 2000; Duan

39

et al., 2011).

40

AC C

EP

TE D

27

A large kinds of reducing agents, sulfur dioxide, sodium sulfite, hydrogen 2

ACCEPTED MANUSCRIPT peroxide, pyrite, methanol, oxalic acid, glucose, sucrose, lactose, molasses, saw dust,

42

corncob and so on, have been utilized for reductive leaching of manganese from

43

manganese dioxide ore in different strong acid media (Tian et al., 2012; Ghafarizadeh

44

et al., 2011; Su et al., 2008). These physical-chemical processes can quickly and

45

efficiently release manganese; however, they usually consume great energy and are

46

often associated with excessive corrosion as well as impose adverse impact on

47

environment due to high reaction temperature and dense strong acid (Mehta et al.,

48

2010; Tian et al., 2010; Hariprasad et al., 2007). Moreover, some agents are toxic and

49

dangerous (Senanayake, 2004; Nayl et al., 2011), some are expensive (Ghafarizadeh

50

et al., 2011; Ismail et al., 2004). These shortcomings limit their wide commercial

51

application.

SC

M AN U

Bioleaching technology permits migration of target metals from solid matters

TE D

52

RI PT

41

such as low-grade ores and nodules under mild conditions of room temperature and

54

ordinary pressure by direct or indirect actions of microorganisms (Rohwerder et al.,

55

2003). The advantages of the processes include the absence of noxious off-gas or

56

toxic effluents, simplicity of plant operation and maintenance, economic and simple

57

process requiring low-capital and low-operating cost, applicability to various metals

58

(Bosecker, 1997). At most cases, the aerobic microorganisms such as acidophilic

59

sulfur-oxidizing and iron-oxidizing bacteria are used to extract metals from reduced

60

sulfides through biological oxidation (Cui and Zhang, 2008). However, as a highly

61

oxidized metal compound, bioleaching of manganese dioxide ore is generally carried

62

out by the direct or indirect actions of heterotrophic microorganisms under anaerobic

AC C

EP

53

3

ACCEPTED MANUSCRIPT or microaerobic conditions for reductive extraction of Mn (Abbruzzese et al., 1990;

64

Veglio, 1996; Lee et al., 2001). Although the anaerobic bioleaching by heterotrophic

65

microorganisms using organic matters as electron donor exhibits a good technical

66

feasibility for reductive extraction of Mn, it has not been commercialized yet because

67

of low bioleaching efficiency, long bioleaching period and high bioleaching cost

68

(Veglio et al., 1997; Lee et al., 2001; Mehta et al., 2010). In recent years, it has been

69

demonstrated that metals present in oxidized ore bodies can, in some cases, also be

70

extracted using chemolithotrophic acidophilic bacteria, referred to as reductive

71

mineral dissolution (Johnson, 2013). By this way, the associated nickel was efficiently

72

leached from limonite ore, accompanying with reduction of the ferric iron present in

73

the mineral phase (goethite) into ferrous state by acidithiobacillus ferrooxidans using

74

elemental sulfur as electron donor under anaerobic conditions (Hallberg et al., 2011).

75

Compared with organic electron donor, the anaerobic bioleaching using sulfur as

76

electron donor driven by chemolithotrophic acidophilic bacteria sharply reduced the

77

leaching cost due to very low price of sulfur. However, a rather longer period of 14-30

78

days was still required for nickel extraction of 75% (Hallberg et al., 2011).

SC

M AN U

TE D

EP

AC C

79

RI PT

63

In our previous works, it was found that under aerobic conditions manganese was

80

efficiently extracted from spent Zn-Mn batteries as highly oxidized metal compound

81

by chemolithotrophic acidophilic bacteria using sulfur and pyrite as electron donor

82

(Xin et al., 2012). The mixed culture of the Alicyclobacillus sp. as sulfur-oxidizing

83

bacteria and the Sulfobacillus sp. as iron-oxidizing bacteria displayed the highest

84

bioleaching capacity of Mn (Xin et al., 2012). In this work, release of manganese

4

ACCEPTED MANUSCRIPT 85

from manganese dioxide ore by the autotrophic mixed culture under aerobic

86

conditions was investigated. The objectives of the current study were

87

the bioleaching conditions for efficient release of manganese;

88

bioleaching thermodynamics and kinetics of manganese dissolution;

89

bioleaching mechanisms of manganese liberation based on XRD and EDS analysis.

90

2. Materials and methods

91

2.1 Manganese dioxide ore and content of manganese

) to explore the

SC

RI PT

) to reveal the

Manganese dioxide ore particles with size of 70-80μm were kindly provided by

M AN U

92

) to optimize

an electrolytic manganese factory of Hunan Province, South Central China. The

94

manganese dioxide ore particles were digested by HF–HNO3–HCl digestion method

95

(USEPA, 1995). The content of manganese in the ore particles was determined as 155

96

g/kg by atomic absorption spectrophotometer (AAS), indicating the ores was

97

low-grade ones. Based on X-Ray Fluorescence (XRF) analysis, the raw manganese

98

dioxide ore contained 25.4% MnO2, 6.3% Fe2O3, 64.4% SiO2 and 2.9% CaO in

99

weight.

101

EP

2.2 Microorganisms and media

AC C

100

TE D

93

The Alicyclobacillus sp. with high sulfur-oxidizing ability and the Sulfobacillus

102

sp. with high ferrous-oxidizing ability were used for Mn extraction from the

103

manganese dioxide ores in this study (Xin et al., 2012). The detailed procedures about

104

their identification, culture, maintenance, inoculums were described in the previous

105

paper (Xin et al., 2011). Although the Alicyclobacillus was once regarded as obligate

106

heterotrophs, some newly isolated Alicyclobacillus including our isolate were verified 5

ACCEPTED MANUSCRIPT 107

as autotrophs or facultative autotrophs (Guo et al., 2009). The Sulfobacillus sp. is

108

mixotrophic bacteria, but it grows well using Fe2+ as sole energy substrate. Based on

109

preliminary experiments, both of them were proved to be mesophilic bacteria and

110

culture temperature of over 40

111

Therefore, elemental sulfur and FeSO4 were used as energy sources to culture the

112

Alicyclobacillus sp. and the Sulfobacillus sp. at 30

113

inoculums, respectively (Xin et al., 2011).

RI PT

ⅰadverselyⅰaffected their growth and activity.

SC

ⅰfor strain preservation and

The bioleaching media were prepared by adding different doses or types of

115

energy substrates (elemental sulfur, pyrite or the combined) according to varied

116

experimental objectives into the basic medium containing (NH4)2SO4, 2.0 g; KH2PO4,

117

1.0 g; MgSO4·7H2O, 1.0 g; CaCl2, 0.25 g; FeSO4·7H2O, 0.18 g; distilled water, 1000

118

ml; natural pH (ca. 5.5). Purity of elemental sulfur 98%; purity of pyrite

119

2.3 Behavior comparison of Mn dissolution from the manganese dioxide ores by

120

different bioleaching systems

TE D

80%.

Three kinds of bioleaching media respectively containing 24 g/Lelemental sulfur,

EP

121

M AN U

114

24 g/L pyrite, 12 g/L elemental sulfur + 12 g/L pyrite, were prepared and transferred

123

into 250 ml flasks at a portion of 100 ml per flask. The bioleaching media containing

124

elemental sulfur (S) only were inoculated at a rate of 10% (V/V) with the

125

sulfur-oxidizing bacteria (SOB) Alicyclobacillus sp., which was referred to as S-SOB

126

leaching system. At the case of pyrite (P) only, the iron-oxidizing bacteria (IOB)

127

Sulfobacillus sp. was inoculated, which was known as P-IOB leaching system. With

128

mixed energy sources (MS) of elemental sulfur + pyrite, both SOB and IOB were

AC C

122

6

ACCEPTED MANUSCRIPT 129

inoculated at 5% (V/V) for each strain serving as the mixed culture (MC), which was

130

called as MS-MC leaching system. And then the inoculated bioleaching systems were

131

incubated at a shaker (30

132

of S-SOB, MS-MC and P-IOB respectively decreased to ca.1.0, 1.5 and 2.3 due to

133

accumulation of biogenetic H2SO4 through bio-oxidization of sulfur. At that moment,

134

the pH value of MS-MC and P-IOB was adjusted to the same value (1.0) as S-SOB

135

with 0.5 mol/L H2SO4 solution in order to eliminate the effect of pH, and then 10 g of

136

powder ores (10% of pulp density) was added into S-SOB, MS-MC, P-IOB,

137

respectively. The flasks containing ores were continuously incubated in the shaker to

138

initiate bioleaching. During bioleaching period, the samples were taken periodically to

139

measure the oxidation–reduction potential (ORP) and pH value; the total iron dose,

140

Fe2+ dose, Fe3+ dose and dissolved doses of Mn were monitored after the samples

141

were centrifuged at 10000 g for 10 minutes to remove the cells and solid matters; the

142

cell density of the solutions was analyzed after the samples were treated by ultrasonic

143

to release the adherent bacteria. The bioleaching media were inoculated with sterile

144

water instead of bioleaching cells to serve as the sterile controls; the control groups

145

received the same procedure as the experiment groups. All the experiments including

146

the sterile controls were carried out in triplicates.

RI PT

SC

M AN U

TE D

EP

AC C

147

, 120 rpm). After about 8-10 days of culture, the pH value

In the above three bioleaching systems, the biogenetic H2SO4, Fe3+ and Fe2+

148

might play different role in Mn extraction. For quantitatively determine their

149

respective contribution to Mn dissolution, a set of chemical leaching experiments to

150

simulate bioleaching process was established. Pure H2SO4 solution at pH 1.0 (A),

7

ACCEPTED MANUSCRIPT H2SO4 solution at pH 1.0 + FeSO4·7H2O at 22.24 g/L (B), H2SO4 solution at pH 1.0 +

152

Fe2(SO4)3 at 15.99 g/L (C), were prepared and transferred into 250 ml flasks at a

153

portion of 100 ml per flask. In B and C solution, the dose of Fe3+ and Fe2+ was equal

154

to Fe dose in 12 g/L pyrite (FeS2). 10 g of powder ores (10% of pulp density) was

155

supplemented into A, B, C solution, respectively. The flasks containing ores were

156

placed in the shaker to conduct leaching. During leaching period of 24 hours, ORP

157

value, pH value and dissolved doses of Mn were measured at every 6 h.

158

2.4 Effect of doses of mixed energy sources on dissolution of Mn by the MS-MC

159

leaching system

M AN U

SC

RI PT

151

Bioleaching media respectively containing 4, 8, 16, 24 and 32 g/L of MS (sulfur

160

and pyrite, 1:1 in weight) were prepared and transferred into 250 ml flasks at a portion

162

of 100 ml per flask. Both SOB and IOB were inoculated at 5% (V/V) for each strain,

163

serving as the MC. The inoculated bioleaching media were incubated at a shaker

164

(30

165

containing 24 g/L of MS or higher firstly declined to ca.1.0. At that moment, the pH

166

value of all bioleaching media was adjusted to 1.0 with 0.5 mol/L H2SO4 solution,

167

followed by addition of 10 g of powder ores. The flasks containing ores were

168

continuously incubated in the shaker to perform bioleaching. In the course of

169

bioleaching, varied process parameters were monitored, and dissolved doses of Mn

170

were measured; the controls were also run as described above. All the experiments

171

were carried out in triplicates.

172

2.5 Effect of initial pH value on dissolution of Mn by MS-MC leaching system

TE D

161

AC C

EP

, 120rpm). After about 10 days of culture, the pH of bioleaching media

8

ACCEPTED MANUSCRIPT 173

Both IOB and SOB serving as MC were respectively inoculated into 250 ml flasks containing 100 ml of bioleaching media with 24 g/L MS. After about 10 days of

175

incubation at a shaker, the pH of bioleaching media dropped to ca.1.0. At that moment,

176

the pH value of bioleaching media was respectively adjusted to 1.0, 2.0 and 3.0 with

177

0.5 mol/L H2SO4 or NaOH solution to represent varied initial pH. And then 10 g of

178

powder ores was supplemented into the bioleaching media. The flasks receiving ores

179

were continuously incubated in the shaker to carry out bioleaching. In the process of

180

bioleaching, varied process parameters were monitored, and dissolved doses of Mn

181

were measured. All the experiments were conducted in triplicates.

182

2.6 Improving dissolution performance of Mn from ores by pH control of

183

bioleaching media with exogenous acid in MS-MC leaching system

SC

M AN U

Bioleaching media containing 24 g/L of MS were prepared, transferred into flasks,

TE D

184

RI PT

174

inoculated with the MC and inoculated at a shaker as described above. After about 10

186

days of incubation, the pH of bioleaching media dropped to ca.1.0. And then 10 g of

187

powder ores was added into the bioleaching media, followed by continuously

188

incubation in the shaker to initiate bioleaching. During bioleaching, the pH, ORP, total

189

iron dose, Fe3+ dose, Fe2+ dose, cell number, released content of Mn were measured at

190

every 24 hours. Once the pH value of the bioleaching media exceeded 2.0, it received

191

pH adjustment with 0.5 mol/L H2SO4 solution and returned to 2.0 for fitting the

192

growth of the mixed culture, especially the iron-oxidizing bacteria. Because addition

193

of exogenous H2SO4 for acidic adjustment maybe resulted in Mn release, the actual

194

extraction dose of Mn by bioleaching were the difference value of the

AC C

EP

185

9

ACCEPTED MANUSCRIPT above-mentioned measured value subtracting the released dose of Mn in controls

196

flasks without both energy matters and bioleaching bacteria, into which only the same

197

amount of exogenous H2SO4 was added synchronized with the bioleaching flasks. The

198

cases without any pH adjustment also run as controls. All the experiments were

199

conducted in triplicates.

200

2.7 Thermodynamics and kinetics exploration of Mn dissolution from manganese

201

dioxide ores by aerobic bioleaching

SC

RI PT

195

The important thermodynamics parameters ΔG, ΔH and ΔS of the

203

bioleaching reaction were calculated and compared with those of the traditional

204

chemical processes using different reducing agents (Dean, 1999).

M AN U

202

ΔrGθm (298K) = ViΔrGθm (298K) -

VjΔrGθm (298K)

(1)

206

ΔrHθm (298K) = ViΔrHθm (298K) -

VjΔrHθm (298K)

(2)

207

Where:

TE D

205

i: products;

209

j: reactants;

210

V:stoichiometric number of i or j.

212

AC C

211

EP

208

ΔrSθm (298K) =(ΔrGθm (298K) -ΔrHθm (298K))/298K

(3)

The most widely used four kinds of kinetics models, i.e. diffusion controlled

213

model, chemical reaction controlled model, shrinking sphere model (Stokes regime)

214

and product layer diffusion model, were use to present the bioleaching behavior of

215

Mn at the case of pH control or not by establishing the mathematical relationship

216

between the fraction of Mn dissolved and the leaching time. The detailed procedures

10

ACCEPTED MANUSCRIPT 217

were described by Mishra et al. (2008).

218

2.8 Apparatuses and conditions

219

The pH value of bioleaching media was determined using a precise pH meter, the oxidation reduction potential (ORP) value (Eh) was determined by portable ORP

221

meter (Ag/AgCl electrode as reference one); the released dose of Mn was determined

222

by atomic absorption spectrophotometer (361MC, Shanghai Precision Scientific

223

Instrument Co., Ltd., China). Total iron dose, Fe2+ dose and Fe3+ dose were measured

224

by chemical methods. Total iron dose and iron (

225

simultaneously by spectrophotometer at 396 nm and at 512 nm, respectively, after 1,

226

10-phenanthroline was added into the solution to form a reddish orange iron ( )

227

complex and a yellow iron ( ) complex; the iron ( ) dose was obtained by total iron

228

dose deducting iron ( ) dose. The detailed procedures were described by Harvey et

229

al. (1955). The cell number of the mixed culture was counted using a microscope.

230

Components analysis was performed by X-ray fluorescence (XRF-1800, Shimdzu).

231

Structure change analysis was performed by X-ray diffractometer (XRD, Shimdzu)

232

with Cu Ka radiation (k = 1.5418). Micro-area chemical analysis was performed using

233

energy dispersive X-ray analysis (EDX, Oxford) operating at 20.0 keV. Morphology

234

change of ores after bioleaching was analyzed by scanning electron microscope (SEM,

235

Hitachi S-4800, Japan) at an accelerating voltage of 20 kV.

236

3. Results and discussion

237

3.1 Behavior comparison of Mn dissolution from the manganese dioxide ores in

238

different bioleaching systems

SC

RI PT

220

AC C

EP

TE D

M AN U

) dose were measured

11

ACCEPTED MANUSCRIPT 239

The tested three kinds of bioleaching systems displayed very different dissolution efficiencies of Mn. The S-SOB leaching system using SOB only as leaching

241

microorganism and using sole elemental sulfur as energy substrate was almost

242

incapable of Mn release; only 4.2% of Mn dissolution efficiency, i.e. 0.65 g/L of

243

leaching concentration, was obtained after 4 days of contact (Fig. 1). Compared with

244

S-SOB, performance of P-IOB using sole pyrite as energy substance and using IOB

245

only as leaching microorganism was greatly improved, release efficiency and leaching

246

dose of Mn respectively reached 65.8% and 10.2 g/L after 4 days of incubation (Fig.

247

1). Among the tested leaching systems, the MS-MC system exhibited the highest

248

release capacity of Mn; the maximum leaching efficiency of 78.0% was achieved,

249

being equivalent to 12.1 g/L of released dose (Fig. 1). By contrast, the sterile controls

250

without any inoculum had no any extraction of Mn.

252

SC

M AN U

TE D

251

RI PT

240

In S-SOB leaching system, H2SO4 was generated due to biological oxidation of elemental sulfur according to the equation as followings: S + 1.5O2 + H2O = H2SO4 (biological reaction)

254

Therefore, acid dissolution by biogenic H2SO4 in S-SOB plays the dominant role

(4)

AC C

EP

253

255

in metals extraction (Xin et al., 2011). However, because MnO2 is insoluble and

256

resistant to acid dissolution, S-SOB leaching system yielded very low Mn extraction

257

despite that the pH of system kept rather low level of 1.5-2.0 during bioleaching

258

period (Sayilgan et al., 2009). Different with the S-SOB, P-IOB generates Fe3+ from

259

oxidation of pyrite by the IOB, and then the biogenetic Fe3+ triggers a series of

260

chemical reactions between Fe3+ and pyrite to produce Fe2+ (Xin et al., 2009). The

12

ACCEPTED MANUSCRIPT 261

major reaction equations were listed as followings: 2FeS2 + 7.5O2 + H2O = 2Fe3+ + 4SO42-+ 2H+ (biological reaction)

(5)

263

2Fe2+ + 0.5O2 + 2H+ = 2Fe3+ + H2O (biological reaction)

(6)

264

FeS2 + 14Fe3+ + 8H2O = 15Fe2+ + 2SO42- + 16H+ (chemical reaction)

(7)

265

FeS2 + 2Fe3+ = 3Fe2+ + 2S (chemical reaction)

(8)

266

The resulting Fe2+ reduced insoluble Mn4+ into soluble Mn2+ at cost of acid consumption, whose reaction equation was presented as below:

SC

267

RI PT

262

MnO2 + 4H++ 2Fe2+ = Mn2++ 2Fe3++ 2H2O

269

Thereby cyclic reaction of Fe2+/Fe3+ couple occurred in the P-IOB leaching

(9)

M AN U

268

270

system which evidently facilitated Mn liberation (Nayak et al., 1999), leading to great

271

increase in Mn extraction efficiency from 4.2% by S-SOB to 65.8% by P-IOB.

272

Although P-IOB could efficiently transform Mn4+ into Mn2+ owing to cyclic reaction of Fe2+/Fe3+ couple; dissolution of soluble Mn2+ into water strongly

274

consumed acid, resulting in continuous increase in pH value and decrease in ORP

275

value during bioleaching (Fig. 1). On the other hand, the P-IOB had relatively low

276

capacity in H2SO4 production owing to low release of sulfur from pyrite and low

277

activity of IOB in sulfur oxidation, so it kept the highest pH value among the three

278

bioleaching systems (Fig.1). In contrast, MS-MC not only produced a great amount of

279

Fe2+ due to the co-existance of pyrite and IOB like P-IOB, which converted insoluble

280

Mn4+ into soluble Mn2+ by reduction mechanism of Fe2+; but also generated a lot of

281

H2SO4 due to the co-existance of elemental sulfur and SOB like S-SOB, which

282

liberated the soluble Mn2+ from solid phase by acid dissolution. MS-MC merged

283

P-IOB with S-SOB, so it harvested the highest Mn leaching efficiency of 78% (Fig.

AC C

EP

TE D

273

13

ACCEPTED MANUSCRIPT 284 285

1). In order to further discern the role of H2SO4, Fe2+ and Fe3+ in Mn extraction, three kinds of chemical leaching systems, i.e. pure H2SO4 solution, H2SO4 solution

287

containing Fe2+ and H2SO4 solution containing Fe3+, were established for Mn

288

extraction. It was found that the pure H2SO4 solution only attained 3.1% of Mn

289

dissolution (Fig.2). H2SO4 solution containing Fe3+ harvested slightly greater Mn

290

extraction of 5.2% because hydrolysis of Fe3+ generated more H+ which enhanced

291

acid dissolution of a small amount of Mn2+ present in the ore (Fig.2). As expected, the

292

addition of Fe2+ evidently improved performance of Mn extraction and a final

293

leaching efficiency of 14.5 % was reached (Fig.2), a 3.7 fold increase compared to the

294

pure H2SO4 solution. Due to great acid consumption for Mn extraction, the case of

295

Fe2+ addition kept the highest pH value over leaching (Fig.2). Meantime, the ORP

296

value evidently rose owing to generation of Fe3+ at the case of Fe2+ addition; whereas

297

almost no ORP variation was occurred with the pure H2SO4 solution and H2SO4

298

solution containing Fe3+ (Fig.2). The results demonstrated that the Fe2+ really played a

299

very important role in Mn extraction from manganese dioxide ores.

SC

M AN U

TE D

EP

AC C

300

RI PT

286

Considering the important role of Fe metabolism in bioleaching of Mn, dose

301

variation of total iron, Fe2+ and Fe3+ in three kinds of bioleaching systems during

302

bioleaching were investigated (Fig.3). With S-SOB system, there was very low dose

303

of Fe3+ due to leaching of Fe2O3 as one of components of the manganese dioxide ore;

304

whereas Fe2+ was not detected throughout the bioleaching, as evidence that no

305

reduction reaction of Mn4+ by Fe2+ occurred and thus very low leaching efficiency of

14

ACCEPTED MANUSCRIPT Mn was obtained. As for P-IOB system, the greatest dose of pyrite and the highest

307

inoculation density of IOB harvested the greatest dose of Fe3+ due to oxidization of

308

pyrite by IOB. However, almost equal Fe2+ concentration even slightly higher Fe2+

309

concentration occurred in MS-MC system than P-IOB system throughout the

310

bioleaching (Fig.3), as evidence for reduction of Mn4+ into Mn2+ by Fe2+ in P-IOB and

311

MS-MC (Nayak et al., 1999).

Because Fe2+ played a crucial role in Mn dissolution, the H2SO4-FeSO4·7H2O

SC

312

RI PT

306

chemical leaching system with 4.48 g/L of Fe2+ attained 14.5% of Mn release;

314

however, the MS-MC biological leaching system containing 12 g/L pyrite in which

315

the dose of Fe2+ was also 4.48 g/L harvested as high as 78% of Mn extraction. The

316

remarkable difference in Mn extraction between the chemical leaching and biological

317

leaching implied that the S- in FeS2 maybe also act as electron donor to reduce Mn4+

318

into Mn2+, accounting for 78% of Mn dissolution in MS-MC. The active intermediates

319

such as S2O32- might directly participate in the reduction reaction, which was

320

produced through the reaction equation as followings (Johnson, 2013):

321

FeS2 + 6Fe3+ + 3H2O = 7Fe2+ + S2O32- + 6H+ (chemical reaction)

TE D

EP

(10)

AC C

322

M AN U

313

However, the detailed biological-chemical processes involving reduction Mn4+

323

into Mn2+ by S- in pyrite needed to be further studied, including identifying the active

324

intermediates and testing their contributions in Mn extraction. Another remarkable

325

difference in Mn extraction between MS-MC and S-SOB (78% vs. 4.2%) revealed

326

that elemental sulfur failed to act as electron donor to reduce Mn4+, but formed H2SO4

327

in the presence of O2 to perform acid dissolution. As conclusion, S- in pyrite and S0 in

15

ACCEPTED MANUSCRIPT 328

elemental sulfur played different role in Mn extraction. However, the intrinsic

329

mechanisms involving the difference in function between S- and S0 needed further

330

investigation. For a long time, anaerobic bioleaching technology has been receiving great

332

concerns for reductive extraction of Mn from manganese dioxide ore by the direct or

333

indirect actions of heterotrophic microorganisms in the presence of sacchariferous

334

substances (Ehrlich, 1987; Veglio et al., 2001; Mehta et al., 2010). In the case of

335

direct action, the microorganisms are capable of utilizing the MnO2 as a final acceptor

336

of electrons in the respiratory chain of their metabolism, instead of oxygen (Lee et al.,

337

2001). In the case of indirect action, the reductive process is associated with the

338

formation of reductive compounds such as oxalic and citric acid coming from their

339

metabolism (Mehta et al., 2010). Recently, a novel anaerobic bioleaching was

340

developed to deal with the highly oxidized ores, which was driven by

341

chemolithotrophic acidophilic bacteria and used cheap sulfur as electron donor instead

342

of organic electron donor (Johnson, 2013). Opposed to the both anaerobic bioleaching,

343

the current studies demonstrated that aerobic bioleaching was qualified for reductive

344

liberation of Mn from manganese dioxide ore by autotrophic microorganism in the

345

presence of cheap sulfur and pyrite as mixed energy substrates, in which some active

346

intermediates such as Fe2+ and suspected S2O32- acted as reducing agents to reduce the

347

oxidized metals.

348 349

AC C

EP

TE D

M AN U

SC

RI PT

331

The MS-MC bioleaching system displayed the best performance for reductive extraction of Mn from manganese dioxide ores. However, great acid consumption in

16

ACCEPTED MANUSCRIPT both reduction of Mn4+ into Mn2+ and following solubilization of Mn2+ into water in

351

such high pulp density of 10% resulted in a sharp rise in pH value from 1.0 to 3.5

352

after 4 days of culture, which harmed the growth and activity of the mixed culture and

353

caused a evident decline in cell density (Fig.4), attaining only 78% of leaching

354

efficiency (Fig. 1). In the following studies, the effect of MS dose, initial pH value

355

and pH control at 2.0 on the leaching efficiency of Mn were investigated to improve

356

the performance of MS-MC bioleaching system.

357

3.2 Effect of MS dose on dissolution of Mn from manganese dioxide ores by

358

MS-MC leaching system

SC

M AN U

359

RI PT

350

Dose variation of the MS had an evident influence on Mn dissolution performance by MS-MC leaching system. When MS dose increased from 4 to 24 g/L,

361

Mn extraction efficiency increased from 17.4% to 78% and leaching dose increased

362

from 2.7 to 12.1 g/L (Fig. 5). However, extraction efficiency and leaching

363

concentration of Mn did not further rise when MS dose increased from 24 to 32 g/L

364

(Fig. 5). The results suggested that 24 g/L of MS dose was sufficient for the maximum

365

dissolution of Mn by MS-MC leaching system at pulp density of 10%.

366

Increase in MS dose enhanced the production of biogenic Fe3+, increase in biogenic

367

Fe3+ dose promoted the generation of Fe2+, increase in Fe2+ dose finally boosted the

368

transformation of insoluble Mn4+ into soluble Mn2+, resulting in increase in leaching

369

efficiency of Mn (Xin et al., 2012). On the other hand, although increase in MS dose

370

enhanced the production of biogenic H2SO4, much more acid was required to dissolve

371

soluble Mn2+ into water in the case of higher MS dose, resulting in higher rise in pH

AC C

EP

TE D

360

17

ACCEPTED MANUSCRIPT 372

value and stronger drop in ORP value with increase in MS dose (Fig. 5).

373

3.3 Effect of initial pH value on dissolution of Mn by MS-MC leaching system

374

Initial pH value greatly affected the dissolution behavior of Mn. When initial pH value increased from 1.0 to 3.0, the maximum leaching efficiency of Mn drastically

376

dropped from 78% to 4.4%, being equivalent to fall from 12.1 to 0.68 g/L with the

377

maximum leaching dose (Fig. 6). On the other hand, due to massive acid consumption

378

the pH value rose to 3.5 in the case of initial 1.0; increase to 3.7 with initial pH 2.0,

379

increase to 4.0 with initial pH 3.0. Correspondingly, the ORP values decreased to

380

different degree with varied initial pH (Fig. 6). The results showed that low initial pH

381

was advantageous to the dissolution of Mn by MS-MC leaching system. The great

382

influence of the initial pH on Mn dissolution might attribute to various reasons. Firstly,

383

the pH value of bioleaching media affected growth of IOB and low pH benefited the

384

activity of IOB, resulting in production of much more amount of biogenic Fe3+ (Xin et

385

al., 2009). Secondly, the pH value of media affected the chemical reactions between

386

biogenic Fe3+ and pyrite and low pH benefited production of Fe2+, resulting in

387

stronger transformation of insoluble Mn4+ into soluble Mn2+ by Fe2+ reduction (Xin et

388

al., 2009). Thirdly, the pH value of media affected dissolution of soluble Mn2+ and low

389

pH benefited liberation of Mn2+ into water, resulting in higher leaching efficiency of

390

Mn (Xin et al., 2012). However, the detailed mechanisms about initial pH function on

391

Mn dissolution needed to be further studied.

392

3.4 Improving dissolution performance of Mn from ores by pH control of

393

bioleaching media with exogenous acid in MS-MC leaching system

AC C

EP

TE D

M AN U

SC

RI PT

375

18

ACCEPTED MANUSCRIPT 394

Control of media pH at ca. 2.0 during bioleaching evidently improved the dissolution performance of Mn. Compared with the case of no control, the maximum

396

leaching efficiency of Mn increased from 78% to 99%, the maximum extraction dose

397

increased from 12.1 to 15.35 g/L, achieving almost complete dissolution of Mn.

398

Although the pH value kept unchanged at 2.0 with pH control case, the ORP value

399

sharply dropped due to much more amount of released Mn2+ in the bioleaching media

400

than the no control case (Fig. 7). The leaching of Mn by MS-MC included reduction

401

of insoluble Mn4+ into soluble Mn2+ by Fe2+ and acid dissolution of soluble Mn2+ into

402

water by biogenic H2SO4. The control of pH at 2.0 benefited the growth and activity

403

of the mixed culture (Fig. 8), not only generating higher dose of Fe2+ which was favor

404

of reducing insoluble Mn4+ into soluble Mn2+ (Fig. 9) but also enhancing the acid

405

dissolution of soluble Mn2+ into water phase, accounting for 99% of Mn leaching

406

efficiency.

SC

M AN U

TE D

407

RI PT

395

Anaerobic bioleaching process exhibited technical feasibility for reductive extraction of Mn, but its commercial application still faces great challenges due to low

409

bioleaching efficiency, long bioleaching period and high bioleaching cost (Veglio et

410

al., 1997; Lee et al., 2001; Mehta et al., 2010). Anaerobic bioleaching process was

411

carried out by direct or indirect actions. In the former case, leaching efficiency of Mn

412

from nodules serving as electron acceptor was 77% by dissimilatory Mn-reducing

413

bacteria after 48 h of incubation; however, the much low pulp density of 1.0 g/L

414

meant that a massive quantity of leaching media was required (Lee et al., 2001). In the

415

second case, 91% of Mn was dissolved by Aspergillus niger at pulp density of 5%

AC C

EP

408

19

ACCEPTED MANUSCRIPT based on the reductive leaching of organic acids released from the fungus; however,

417

the much long leaching period of 30 days meant that a great volume of leaching

418

reactor was required (Mehta et al., 2010). Although 95-100% of Mn extraction by

419

heterotrophic mixed cultures was obtained after 36-48 h of treatment at pulp density

420

of 20%, the much high molasses dose of 100 g/L as carbon source meant that a huge

421

bioleaching cost was required (Veglio et al., 1997). The newly-developed anaerobic

422

bioleaching using sulfur as electron donor sharply reduced the leaching cost due to

423

very low price of sulfur. However, a rather longer period of 14-30 days was still

424

necessary for dissolution of target metals due to the nature of anaerobic reaction

425

(Hallberg et al., 2011). By contrast, 99% of Mn extraction was achieved by the

426

MS-MC leaching system at 10% of pulp density after 3-4 days of incubation using the

427

extremely cheap MS (12 g/L sulfur + 12 g/L pyrite) (Fig. 7). The results demonstrated

428

that the MS-MC leaching system could efficiently, safely and economically leach Mn

429

from manganese dioxide ore under mild conditions of room temperature and ordinary

430

pressure through pH adjustment. The current aerobic bioleaching was not only

431

cost-effective due to very cheap sulfur and pyrite as energy substrates but also rather

432

fast compared with the anaerobic bioleaching, displaying greater application potential.

433

3.5 Bioleaching thermodynamics and kinetics of Mn from MnO2 ores

SC

M AN U

TE D

EP

AC C

434

RI PT

416

The most widely used four kinds of kinetics models, i.e. diffusion controlled

435

model, chemical reaction controlled model, shrinking sphere model (Stokes regime)

436

and product layer diffusion model, were use to describe the bioleaching behavior of

437

Mn from manganese dioxide ore at the case of pH adjustment and not. Although

20

ACCEPTED MANUSCRIPT 438

bioleaching performances of Mn at the case of no pH adjustment were worse depicted

439

by the kinetics models (R2

440

(Table 1), the diffusion controlled model fitted best for describing dissolution of Mn

441

due to the highest correlation coefficients among the four kinds of kinetics models

442

independent of pH control. The results implied that the resistance to diffusion through

443

a product layer controlled the rate of bioleaching of manganese dioxide ore (Mishra et

444

al., 2008).

0.9)

SC

RI PT

0.7) than those at the case of pH adjustment ((R2

In order to better understand bioleaching mechanisms of Mn from manganese

446

dioxide ore, bioleaching thermodynamics of Mn was also explored. The reductive

447

leaching mechanism of Mn from MnO2 ore by aerobic bioleaching using MS was

448

described as the following equation:

M AN U

445

MnO2 + 0.5S + FeS2 + 4O2 = MnSO4 + 0.5Fe2(SO4)3 (biological reaction)

450

The reductive leaching equations of Mn by traditional chemical processes using

451

FeSO4, H2O2 and glucose as reducing agents in strong acid solution were described in

452

detail by Zhang and Cheng (2007).

EP

Thermodynamics parameters ΔG, ΔH and ΔS of the bioleaching reactions

AC C

453

(11)

TE D

449

454

were calculated and compared with that of the traditional chemical leaching using

455

different reducing agents (Table 2). It was observed that the bioleaching possessed a

456

huge negative value ofⅰΔG, being 8.8/18.8/7.2 times higher than that of traditional

457

chemical leaching in strong acid using FeSO4/H2O2/glucose as reactants. Bioleaching

458

has much greater potential to occur spontaneously than chemical leaching, although

459

its reaction speed is very low due to the solid nature of both sulfur and pyrite if

21

ACCEPTED MANUSCRIPT without help of leaching cells. However, it is MC consisting of IOB and SOB that

461

accelerated drastically reaction process as biocatalyst, realizing efficient dissolution of

462

Mn from manganese dioxide ore. The results showed the advantage and possibility of

463

aerobic bioleaching in reductive leaching of Mn based on thermodynamics analysis.

464

3.6 Mechanisms illustration of Mn bioleaching from ore using XRD and EDS

465

RI PT

460

Bioleaching slag collected from both pH adjustment case and not was analyzed

using XRD and EDS and compared with the raw ore. The EDS analysis showed that

467

the no-adjustment slag had higher-content residual of Mn due to incomplete Mn

468

dissolution (78% of leaching efficiency) (Fig. 10); however, no Mn-containing crystal

469

compounds were detected based on XRD analysis (Fig. 11), indicating that crystal

470

MnO2 in the manganese dioxide ore was completely transformed into MnO by

471

bioleaching and the remaining Mn existed in the form of amorphous state. In contrast,

472

pH-control slag had no residual of elemental Mn according to the EDS analysis

473

because of almost complete dissolution of Mn (Fig. 10), suggested that acid

474

dissolution was the dominating mechanisms for great improvment in leaching

475

efficiency from 78% without pH control to 99% with pH control.

476

4. Conclusion

M AN U

TE D

EP

AC C

477

SC

466

The aerobic bioleaching technology was qualified for reductive liberation of Mn

478

from manganese dioxide ore by autotrophic microorganism in the presence of cheap

479

sulfur and pyrite. 99% of Mn extraction was achieved by the mixed culture at 10% of

480

pulp density after 72-96 h under the conditions of 24 g/L of mixed energy substrates,

481

initial pH at 1.0 and pH control of process at 2.0. The diffusion controlled model fitted 22

ACCEPTED MANUSCRIPT 482

best for describing dissolution of Mn independent of pH adjustment. The acid

483

dissolution was the dominating mechanisms for great improve in leaching efficiency

484

from 78% without pH control to 99% with pH control.

486

RI PT

485

Acknowledgements

We highly appreciate financial support from the National Natural Science

488

Foundation of China (Grant No. 21277012) and Shandong Fund of Sciences and

489

Technology for Environment Protection.

490

References

491

Abbruzzese, C., Duarte, M.Y., Paponetti, B., Toro, L., 1990. Biological and chemical processing

494 495 496

M AN U

Bosecker, K., 1997. Bioleaching: metal solubilization by microorganisms. FEMS Microbial. Rev. 20: 591-604.

TE D

493

of low-grade manganese ore. Min. Eng. 3: 307-318.

Cui, J., Zhang, L., 2008. Metallurgical recovery of metals from electronic waste: a review.

J.

EP

492

SC

487

Hazard. Mater. 158: 228–256.

De Michelis, I., Ferella, F., Beolchini, F., Olivieri, A., Vegliò, F., 2009. Characterisation and

498

classification of solid wastes coming from reductive acid leaching of low-grade

499 500 501

AC C

497

manganiferous ore. J. Hazard. Mater. 162 (2–3), 1285–1291.

Dean, J.A., 1999. Section 6: thermodynamic properties in Lange’s Chemistry Handbook Version 15th. McGraw-Hill, UMich, New York.

502

Du Plessis C.A., Slabbert, W., Hallberg, K.B., Johnson, D.B., 2011. Ferredox: a

503

biohydrometallurgical processing concept for limonitic nickel laterites. Hydrometallurgy, 109: 23

ACCEPTED MANUSCRIPT 504

221– 229. Duan, N., Dan, Z.G., Wang, F., Pan, C.X., Zhou, C.B., Jiang, L.H., 2011. Electrolytic manganese

506

metal industry experience based China’s new model for cleaner production promotion. J.

507

Cleaner Prod. 19:2082-2087.

510 511

5 (3/4): 423-431.

Elsherief, A.E., 2000. A study of the electroleaching of manganese ore. Hydrometallurgy, 55:

SC

509

Ehrlich, H.L., 1987. Manganese oxide reduction as a form of anaerobic respiration. Geomicrobiol,

311–326.

M AN U

508

RI PT

505

Ghafarizadeh, B., Rashchi, F., Vahidi, E., 2011. Recovery of manganese from electric arc furnace

513

dust of ferromanganese production units by reductive leaching. Mine. Eng. 24: 174–176.

514

Guo, X., You, X.Y., Liu, L.J., Zhang, J.Y., Liu, S.J., Jiang, C.Y., 2009. Alicyclobacillus aerissp.

515

nov., a novel Fe2+ and sulfur-oxidizing bacterium isolated from a copper mine. International

516

Journal of Systematic and Evolutionary Microbiology, 59: 2415–2420.

519 520 521 522

iron minerals: a new approach for bioprocess ing nickel laterites. Miner. Eng. 24: 620–624.

EP

518

Hallberg, K., Grail, B.M., du Plessis, C.A., Johnson, D.B., 2011. Reductive dissolution of ferric

Hariprasad, D., Dash, B., Ghosh, M.K., Anand, S., 2007. Leaching of manganese ores using

AC C

517

TE D

512

sawdust as a reductant. Mine. Eng. 20: 1293- 1295.

Harvey, A.E., Smart, J.A., Amis, E.S., 1955. Simultaneous spectrophotometric determination of iron (

) and total iron with 1,10- Phenanthroline. Analytical Chemistry, 27: 26-29.

523

Ismail, A.A., Ali, E.A., Ibramhim, I.A., Ahmed, M.S., 2004. A comparative study on acid leaching

524

of low grade manganese ore using some industrial wastes as reductants. Can. J. Chem. Eng.

525

82: 1296-1300.

24

ACCEPTED MANUSCRIPT

527 528 529 530 531

Johnson, D.B., 2013. Development and application of biotechnologies in the metal mining industry. Environ. Sci. Pollut. Res. 20:7768–7776. Lee, E.Y., Noh, S.R., Cho, K.S., Ryu, H.W., 2001. Leaching of Mn, Co, and Ni from manganese nodules using an anaerobic bioleaching method. J. Biosci. Bioeng. 92: 354-359.

RI PT

526

Mehta, K.D., Das, B., Pandey, B.D., 2010. Leaching of copper, nickel and cobalt from Indian Ocean manganese nodules by Aspergillus niger. Hydrometallurgy, 105: 89- 95.

Mishra, D., Kim, D.J., Ralph, D.E., Ahn, J.G., Rhee, Y.H., 2008. Bioleaching of spent hydro

533

processing catalyst using acidophilic bacteria and its kinetics aspect. J. Hazard. Mater. 152:

534

1082–1091.

536

M AN U

535

SC

532

Nayak, B.B., Mishra, K.G., Paramguru, R.K., 1999. Kinetics and mechanism of MnO2 dissolution in H2SO4. J. Appl. Electrochem. 29: 191- 200.

Nayl, A.A., Ismail, I.M., Aly, H.F., 2011. Recovery of pure MnSO4·H2O by reductive leaching of

538

manganese from pyrolusite ore by sulfuric acid and hydrogen peroxide. Int. J. Miner. Process.

539

100: 116–123.

TE D

537

Rohwerder, T., Gehrke, T., Kinzler, K., Sand, W., 2003. Bioleaching review part A: progress in

541

bioleaching: fundamentals and mechanisms of bacterial metal sulfide oxidation. Appl.

543 544

AC C

542

EP

540

Microbiol. Biotechnol. 63: 239–248.

Sahoo, R.N., Naik, P.K., Das, S.C., 2001. Leaching of manganese ore using oxalic acid as reductant in sulphuric acid solution. Hydrometallurgy, 62: 157–163.

545

Sayilgan, E., Kukrer, T., Civelekoglu, G., Ferella, F., Akcil, A., Veglio, F., Kitis, M., 2009. A

546

review of technologies for the recovery of metals from spent alkaline and zinc–carbon

547

batteries. Hydrometallurgy, 97: 158–166.

25

ACCEPTED MANUSCRIPT 548 549

Senanayake, G., 2004. A mixed surface reaction kinetic model for the reductive leaching of manganese dioxide with acidic sulfur dioxide. Hydrometallurgy, 73: 215–224. Su, H.F., Wen, Y.X., Wang, F., Sun, Y.Y., Tong, Z.F., 2008. Reductive leaching of manganese from

551

low-grade manganese ore in H2SO4 using cane molasses as reductant. Hydrometallurgy, 93:

552

136–139.

554

Tian, Q.H., Jiao, C.Y., Guo, X.Y., 2012. Extraction of valuable metals from manganese–silver ore. Hydrometallurgy, 119-120: 8–15.

SC

553

RI PT

550

Tian, X.K., Wen, X.X., Yang, C., Liang, Y.J., Pi, Z.B., Wang, Y.X., 2010. Reductive leaching of

556

manganese from low-grade manganese dioxide ores using corncob as reductant in sulfuric

557

acid solution. Hydrometallurgy, 100: 157–160.

559 560 561

USEPA, 1995. Microwave Assisted Acid Digestion of Sediments, Sludge and Soil. Method 3052. US Environmental Protection Agency, Washington, DC.

TE D

558

M AN U

555

Veglio, F., 1996. The Optimization of manganese dioxide bioleaching media by fractional factorial experiments. Process Biochem. 31: 773-785. Veglio, F., Beolchini, F., Gasbarro, A., Toro, L., Ubaldini, S., Abbruzzese, c., 1997. Batch and

563

semi-continuous tests in the bioleaching of manganiferous minerals by heterotrophic mixed

565 566 567 568 569

AC C

564

EP

562

microorganisms. Int. J. Miner. Process. 50: 255-273.

Veglio, F., Trifoni, M., Abbruzzese, C., Toro, L., 2001. Column leaching of a manganese dioxide ore: a study by using fractional factorial design. Hydrometallurgy, 59: 31–44.

Xin, B.P., Chen, B., Duan, N., Zhou, C.B., 2011. Extraction of manganese from electrolytic manganese residue by bioleaching. Bioresour. Technol. 102: 1683–1687. Xin, B.P., Jiang, W.F., Aslam, H., Zhang, k., Liu, C.H., Wang, R.Q., Wang, Y.T., 2012.

26

ACCEPTED MANUSCRIPT 570

Bioleaching of zinc and manganese from spent Zn–Mn batteries and mechanism exploration.

571

Bioresour. Technol. 106: 147–153. Xin, B.P., Zhang, D., Zhang, X., Feng, W., Li, L., 2009. Bioleaching mechanism of Co and Li

573

from spent lithium-ion battery by the mixed culture of acidophilic sulfur-oxidizing and

574

iron-oxidizing bacteria. Bioresour. Technol. 100: 6163–6169.

575

RI PT

572

Zhang, W.S., Cheng, C.Y., 2007. Manganese metallurgy review. Part I: Leaching of

ores/secondary materials and recovery of electrolytic/chemical manganese dioxide.

577

Hydrometallurgy, 89: 137–159.

AC C

EP

TE D

M AN U

SC

576

27

ACCEPTED MANUSCRIPT

Table 1 Lines of best-fit equations and correlation factor for various kinetic leaching

RI PT

models describing the dissolution of Mn from the manganese dioxide ore at pulp density of 10% and initial pH value of 1.0 and 24 g/L of the mixed energy substrate.

Line of best-fit equations and correlation factor

SC

Kinetic model

With pH adjustment Product layer diffusion, parabolic

M AN U

Y= 0.0059x + 0.4235，R² = 0.9208

Without pH adjustment

Y = 0.0048x + 0.2232，R² = 0.6157

Y= 0.0022x + 0.0554，R² = 0.9484

Y = 0.0010x + 0.0335，R² = 0.6787

Chemical reaction controlled

Y= 0.0045x + 0.2684，R² = 0.9480

Y = 0.0026x + 0.1853，R² = 0.6209

Shrinking sphere, Stoke’s regime

Y= 0.0046x + 0.4964，R² = 0.9321

Y = 0.0038x + 0.3316，R² = 0.5865

AC C

EP

TE D

Diffusion controlled

ACCEPTED MANUSCRIPT

Table 2 Comparison of the thermodynamic parameter changes between chemical

Chemical leaching (H2O2 as reductant)

Chemical leaching (C6H12O6 as reductant)

-84.59

-220.22

△H（kJ·mol-1）

-191.62

M AN U

△S（J·deg-1·mol-1）

Chemical leaching (FeSO4 as reductant)

SC

standard state (298 K=25 , 1atm).

RI PT

leaching using FeSO4/ H2O2 /glucose as reducing agents and aerobic bioleaching at

327.85 -1

△G（kJ·mol ）

EP AC C

-1844.40

67.90

-270.10

-1069.97

-221.92

-184.86

-1817.65

TE D

-92.79

Bioleaching (S+FeS2 as reductant)

ACCEPTED MANUSCRIPT

Fig. 1

10 8 6 4

40 20 0

0

1

2 3 Leaching time(d)

0

1

4

2

3

4

Leaching time(d)

SC

0

680 660

4.0

640

3.5

620

Eh(mV)

3.0 pH

60

2

4.5

2.5 2.0

600 580 560

1.5

540 520

1.0

500

0

Fig. 1

1

2 3 Leaching time(d)

4

TE D

0.5

80

RI PT

Mn dissolution efficiency(%)

12

M AN U

Mn dissolution concentration(g/L)

100

14

0

1

2 3 Leaching time(d)

4

Time-courses for pH value, ORP value, Mn dissolution concentration and Mn dissolution

systems.

EP

efficiency during reductive leaching of manganese dioxide ore by different aerobic bioleaching

AC C

(-■- S-SOB leaching system, -●- P-IOB leaching system, -▲- MS-MC leaching system)

ACCEPTED MANUSCRIPT

Fig.2

750

14

2.0

RI PT

Mn dissolution efficiency (%)

16

1.8

700

12

6 4

pH

8

1.6

650

1.4

600

1.2

550

2

1.0

6

12 18 Leaching time(h)

500 0

24

6

12 18 Leaching time(h)

24

M AN U

0 0

SC

Eh(mV)

10

0

6

12 18 Leaching time(h)

Fig.2 Time-course for Mn release, pH change and ORP variation in three chemical leaching systems

AC C

EP

TE D

(-■- H2SO4, -○- H2SO4 + FeSO4, -▲- H2SO4 + Fe2(SO4)3)

24

ACCEPTED MANUSCRIPT

Fig. 3

1600

1400

1400

1200

800 600 400

1000 800 600 400

80

RI PT

1000

Fe2+ dose ( mg/L)

Fe3+ dose ( mg/L)

1200

60 40 20

200

0

0 1

2 3 Leaching time (d)

4

0

0

1

2 Leaching time (d)

3

4

0

1

2

Leaching time (d)

M AN U

Fig. 3 Time-courses for total iron dose, Fe3+ dose, Fe2+ dose during bioleaching of Mn from MnO2 ore in different leaching system.

TE D

(-■- S-SOB leaching system, -●- P-IOB leaching system, -▲- MS-MC leaching system)

EP

0

SC

200

AC C

Total iron dose (mg/L)

100

3

4

ACCEPTED MANUSCRIPT

Fig. 4 9

S-SOB leaching system P-IOB leaching system MS-MC leaching system

7 6 5 4 3 2 1 0

0

4 Leaching time (d)

RI PT

Cell number( 108/ml)

8

AC C

EP

TE D

M AN U

bioleaching in different leaching system.

SC

Fig. 4 Population variation of the mixed culture as leaching cells before and after

ACCEPTED MANUSCRIPT

12 10 8 6 4 2 0

0

1

2

3

80

60

40

20

0

4

0

660 640

4

620

2.8

Eh(mV)

2.4 pH

2 3 Leaching time(d)

M AN U

3.2

1

SC

Leaching time(d)

3.6

RI PT

14

Mn dissolution efficiency(%)

Mn dissolution concentration(g/L)

Fig.5

2.0 1.6

600 580 560

1.2

540

0.8 0

1

2

3

4

520

0

1

2 3 Leaching time(d)

TE D

Leaching time(d)

4

Fig. 5 Time-courses for pH value, ORP value, Mn dissolution concentration and Mn dissolution efficiency during reductive leaching of Mn from MnO2 ore by the MS-MC

EP

leaching system under different MS dose (sulfur and pyrite, fifty-fifty in weight).

AC C

（—■—4 g/L, —●—8 g/L, —▲—16 g/L, —▼—24 g/L, —□— 32 g/L）

ACCEPTED MANUSCRIPT

14 90

12 10 8 6 4 2 0

0

1

2

3

75 60 45 30 15 0

4

0

1

Leaching time(d)

3

4

650

3.5

600 Eh(mV)

2.5 2.0

SC

4.0

M AN U

700

3.0 pH

2

Leaching time(d)

4.5

550 500 450

1.5

400

1.0 0.5

RI PT

Mn dissolution efficiency(%)

Mn dissolution concentration(g/L)

Fig. 6

350

0

1

2 3 Leaching time(d)

4

0

1

2 3 Leaching time(d)

4

TE D

Fig. 6 Time-courses for pH value, ORP value, Mn dissolution concentration and Mn dissolution efficiency during reductive leaching of manganese dioxide ore by the MS-MC leaching system under different initial pH values.

AC C

EP

（—■—pH=1.0, —●—pH=2.0, —▲— pH=3.0）

ACCEPTED MANUSCRIPT

14 12 10 8 6 4 2

60 40 20 0

0

1

2 3 Leaching time(d)

4

0

2

625

4.0

600

M AN U

4.5

3

4

Eh(mV)

575

3.0 2.5 2.0

550 525 500

1.5

475

1.0 0

1

2 3 Leaching time(d)

4

0

1

2 3 Leaching time(d)

TE D

0.5

1

Leaching time(d)

3.5

4

Fig. 7 Time-courses for pH value, ORP value, Mn dissolution concentration and Mn dissolution efficiency during reductive leaching of Mn from manganese

EP

dioxide ore by the MS-MC leaching system with pH adjustment at 2.0 or not. (—■—without adjustment, —●—with adjustment)

AC C

pH

80

SC

0

100

RI PT

16 Mn dissolution efficiency(%)

Mn dissolution concentration(g/L)

Fig. 7

ACCEPTED MANUSCRIPT

Fig. 8 9

without pH adjustment with pH adjustment

7 6 5 4 3 2 1 0

0

4 Leaching time (d)

RI PT

Cell number ( 108/mL)

8

Fig. 8 Population variation of the mixed culture as leaching cells before and after

AC C

EP

TE D

M AN U

SC

bioleaching by MS-MC system at case of pH control or not.

ACCEPTED MANUSCRIPT

Fig. 9

120 1200

600 400

1000 800 600 400

100 80

RI PT

800

Fe2+ dose( mg/L)

Fe3+ dose ( mg/L)

1000

60 40 20

200

200

0

1

2

3

4

0

1

2 Leaching time (d)

Leaching time (d)

3

4

0

SC

0

1

2

M AN U

MS-MC system at case of pH control or not.

(-■-without pH adjustment, -●- with pH adjustment)

3

Leaching time (d)

Fig. 9 Time-courses for total iron dose, Fe3+ dose, Fe2+ dose during bioleaching of Mn by

TE D

0

EP

0

AC C

Total iron dose (mg/L)

1200

4

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

Fig. 10

Fig. 10 EDX images of manganese dioxide ore before and after bioleaching (a: raw sample; b: no pH adjustment; c: pH adjustment)

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

Fig. 11

Fig. 11 XRD images of manganese dioxide ore before and after bioleaching (a: raw sample; b: no pH adjustment; c: pH adjustment)

ACCEPTED MANUSCRIPT

Research Highlight 1. Aerobic bioleaching was qualified for reductive extraction of Mn from MnO2 ore

RI PT

2. 99% of Mn extraction was achieved at 10% of pulp density by MS-MC system. 3. The diffusion controlled model fitted best for describing Mn dissolution.

4. Bioleaching has greater potential to occur spontaneously than chemical leaching.

AC C

EP

TE D

M AN U

SC

5. Acid dissolution was dominating mechanism for improving leach by pH control.