Unveiling the Role and Mechanism of Mechanochemical Activation on

Subscriber access provided by Washington University | Libraries

Environmental Processes

Unveiling the Role and Mechanism of Mechanochemical Activation on Lithium Cobalt Oxide Powders from Spent Lithium-ion Batteries Mengmeng Wang, Quanyin Tan, and Jinhui Li Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.8b03469 • Publication Date (Web): 12 Sep 2018 Downloaded from http://pubs.acs.org on September 14, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 32

Environmental Science & Technology

1

Unveiling the Role and Mechanism of

2

Mechanochemical Activation on Lithium Cobalt Oxide

3

Powders from Spent Lithium-ion Batteries

4

Mengmeng Wang†, Quanyin Tan†, Jinhui Li†,*

5

†State Key Joint Laboratory of Environment Simulation and Pollution Control,

6

School of Environment, Tsinghua University, Beijing 100084, China

7

* Corresponding Author

8

Mailing address: Room 804, Sino-Italian Environmental and Energy-efficient

9

Building, School of Environment, Tsinghua University, Haidian District, Beijing

10

100084, China

11

E-mail address: [email protected]

12

Tel.: +86-10-62794143

13

Fax: +86-10-62772048

1

ACS Paragon Plus Environment


14

TABLE OF CONTENTS

15 16

2


Page 2 of 32

Page 3 of 32


17

ABSTRACT

18

This research presented the impacts of mechanochemical activation (MCA) on

19

the physiochemical properties of lithium cobalt oxide (LiCoO2) powders of cathode

20

materials from spent lithium-ion batteries, and analyzed the relevant effects of these

21

changes on the leaching efficiency of lithium (Li) and cobalt (Co) and the leaching

22

kinetics of LiCoO2 powders. The results revealed the superiority of MCA in the

23

following levels of changes in the LiCoO2 powders: first, the physical properties

24

included a decrease in the average particle size, an increase in the specific surface

25

area, and the appearance of a mesoporous structure change; second, changes in

26

crystal-phase structures were reflected in the grain refinement of LiCoO2 powders,

27

lattice distortions, lattice dislocations, storage and increment of internal energy; third,

28

the surface characteristics included a chemical shift of lithium element electrons, a

29

reduction in Co3+ concentration, and an increment in the surface hydroxyl oxygen

30

concentration. These changes in physiochemical properties and structures enhanced

31

the hydrophilicity and interface reactivity of the activated LiCoO2 powders, and

32

significantly improved the leaching efficiencies of Li and Co in organic acid solutions.

33

The rate-limiting step of metal leaching was also altered, from a surface chemical

34

reaction-controlled one before MCA to an ash layer diffusion-controlled one after

35

MCA.

36

3



37

INTRODUCTION

38

With the increased production and use of portable electronic devices and

39

electric-vehicle power batteries, the amount of spent lithium-ion batteries (LIBs) has

40

also been rapidly increasing, and both academic researchers and industrial analysts

41

have focused more attention on recycling LIB metals.1, 2 The valuable LIB-cathode

42

metals lithium (Li) and cobalt (Co), in the form of lithium cobalt oxide (LiCoO2),

43

provide a major economic incentive for the recovery of spent LIBs.3-10 Although

44

several recovery methods have been used, hydrometallurgy has always been the major

45

one, because of its high metal recovery rate, mild reaction conditions, controllability,

46

and low environmental load.11-14 As for environmentally friendly reaction reagents,

47

organic acids are generally the first choice for Li and Co leaching. A series of organic

48

acids, including L-tartaric,15 aspartic,16 malic,17 oxalic,18 formic,19 ascorbic,20

49

succinic,21 and citric22 acids have been employed to leach Li and Co from LiCoO2

50

powders. Yet despite excellent technical prospects and environmental benefits, the

51

industrial application of organic acid leaching has still been limited by technical

52

bottlenecks, such as long reaction time and high reagent cost. Thus, significantly

53

shortening the metal leaching time and further reducing the costs of reagents are the

54

current challenges for the hydrometallurgic recovery of metals from spent LIBs.15, 23,

55

24

56

In recent years, mechanochemical activation (MCA) technology has been widely

57

applied for enhancing the recovery efficiency of valuable metals from solid wastes.25,

58

26

During MCA, the solid materials, under the actions of friction, collision, impact, 4


Page 4 of 32

Page 5 of 32


59

cutting, and other mechanical forces, would obviously experience changes in

60

physiochemical properties and material structures, even as those forces efficiently

61

convert a portion of mechanical energy into internal energy, thereby improving the

62

chemical reaction activity of solid materials.27, 28 MCA, therefore—because of its

63

unique reaction mechanism, kinetics, thermodynamics, low operating costs, and ease

64

of use—is a good candidate for metal recovery from e-waste.29, 30

65

Yuan et al.31 used MCA to activate waste cathode ray tube glass, and discovered

66

that mechanical forces could significantly enhance the lead leaching efficiency in

67

nitric acid solution by destroying the Si-O bonds of network structures in the glass.

68

Yang et al.32 used MCA to activate spent lithium iron phosphate battery cathode

69

materials, and found that this activation could significantly enhance the leaching of

70

lithium and iron. While MCA has proved to be an effective approach for accelerating

71

the recycling performance of valuable metals from e-waste, the role and mechanism

72

of MCA has seldom been fully investigated. Moreover, there is still a lack of

73

systematic research concerning the effects of MCA on the physiochemical properties

74

(physical properties, crystal-phase structures, surface characteristics, and solid-liquid

75

interfacial behaviors) and structures of solid waste materials. Yet changes in these

76

properties and structures could profoundly affect the efficiency and behaviors of metal

77

leaching, making MCA an important area for further research.

78

This study therefore focused on the role of MCA and its effects on the physical

79

properties and material structures of LiCoO2 powders in spent LIBs. Using acetic acid

80

leaching as a probe reaction, the effects of these physiochemical properties and 5



81

structural changes on the metal leaching rate, leaching efficiency, and metal leaching

82

kinetics were fully investigated. This study aimed to (1) discover the effects of MCA

83

on the physical properties, crystal-phase structures, surface characteristics, and

84

solid-liquid interfacial behaviors of LiCoO2 powders; (2) clarify the strengthening

85

effect and mechanism of MCA on metal leaching; (3) investigate the effects of MCA

86

on metal leaching kinetics; and (4) evaluate the economic and environmental benefits

87

of MCA combined with acetic acid leaching for metal recovery from spent LIBs.

88

MATERIALS AND METHODS

89

Materials and reagents Waste LiCoO2 powders were provided by Huaxin

90

Environmental Co. Ltd, Beijing, China. The Li and Co contents in the LiCoO2

91

powders were 3.4 wt%, and 29.1 wt%, respectively. The acetic acid and hydrogen

92

peroxide used were all of analytical grade and were purchased from the Chemical

93

Reagent Company of Beijing, China. Deionized water was used for the preparation

94

and dilution of chemical solutions.

95

Experimental procedure The schematic diagram for this study is shown in Figure

96

1. In the MCA stage, 0.5 g of LiCoO2 powders were placed in a zirconia pot with an

97

inner volume of 45 mL and ground with 14 zirconia balls of 10 mm diameter. The

98

LiCoO2 powders were then activated using a planetary ball-mill apparatus

99

(Pulverisette-7, Fritsch, Idar-Oberstein, Germany) at several different rotary speeds (0,

100

100, 200, 300, 400, and 500 rpm, where 0 rpm represents non-activated LiCoO2

101

powders) for 30 min. The LiCoO2 powders were leached with acetic acid in a closed

102

100-mL three-necked flask placed in a water bath with a magnetic stirrer. Various 6


Page 6 of 32

Page 7 of 32


103

acetic acid concentrations (1, 5, 10, and 20 vol.%), H2O2 concentrations (0, 1, 3, 5,

104

and 7 vol.%), and leaching temperatures (25, 35, 45, 55, and 65 oC) were analyzed for

105

their effects on metal leaching from the LiCoO2 powders. Lithium cobalt oxide powders (C/LiCoO2) Mechanochemical activation Material characterization

Physical properties

Surface characteristics

Phase structure

Interfacial behavior

Organic acid leaching (Acetic acid) Leaching rate of metals

Parameter optimization

Leaching kinetics of metals

Economic assessment

106 107

Figure 1. Schematic diagram of this study.

108

Analytical methods The metal contents of the LiCoO2 powders were determined

109

using an inductively coupled plasma-optical emission spectrometer (ICP-OES,

110

OPTIMA 2000, PerkinElmer, USA) after digestion with an HNO3-HCl mixture. The

111

contents of Li and Co in the acetic acid leaching solution were measured with

112

ICP-OES and the leaching percentages expressed by the following equation:

113

WLi/Co (wt%) =

C ×100% C0

Eq. (1)

114

where C is the final mass of metal ions in the filtrate after leaching and C0 is the

115

original mass of metal ions in the LiCoO2 powders before leaching.

116

The average sizes of the LiCoO2 particles before and after MCA were measured 7



Page 8 of 32

117

with a Microtrac particle size analyzer (MT3300, Tokyo, Japan). The specific surface

118

areas (SSAs) of the LiCoO2 powders were measured with a nitrogen gas adsorption

119

instrument

120

Brunauer-Emmett-Teller (BET) method. The crystal structures of the LiCoO2 powders

121

were characterized by X-ray diffraction (XRD; Philips PW 1700, USA) using Cu Kα

122

radiation (γ=1.5418Å) with 30 kV voltage and 30 mA current. Analysis of the X-ray

123

diffraction data was carried out using MDI Jade 6.5 software. The morphologies and

124

structures of the LiCoO2 powders were characterized with field emission scanning

125

electron microscopy (FESEM; Carl Zeiss MERLIN Compact, Germany) and a

126

transmission electron microscope (TEM; FEI, Tecnai G2 Spirit). X-ray photoelectron

127

spectroscopy analysis was conducted using a PHI Quantera SXM (XPS;

128

PHI-5300/ESCA, ULVAC-PHI, Inc, Japan). Thermogravimetric analysis combined

129

with the differential scanning calorimetry (TGA-DSC) was conducted using a thermo

130

gravimetric analyzer (TGA/DSC 1, Mettler Toledo, Switzerland) under argon

131

atmosphere. The contact angle of the LiCoO2 powders was measured with the sessile

132

drop method using a contact angle meter (OCA15Pro, Dataphysics Instrument Co.,

133

Ltd., Germany). The zeta potential was measured via dynamic light scattering using

134

particle size analyzer (SZ-100Z, Horiba Ltd., Japan).

135

RESULTS AND DISCUSSION

136

Physical properties of the LiCoO2 powders The properties and structures of

137

LiCoO2 powders will affect the powders’ chemical reaction activity. Figure 2 shows

138

the physical property changes of the activated LiCoO2 powders at different rotary

(ASAP2010,

Micromeritics,

Georgia,

8


USA)

based

on

the

Page 9 of 32


139

speeds. Figure 2a shows that the average particle sizes of LiCoO2 powders decreased

140

as the rotary speed increased. At the rotary speed of 0 rpm, the average particle size

141

was about 13 µm, but when the rotary speed exceeded 300 rpm, the average particle

142

size was 0.206 µm. Yet as the rotary speed continued to increase to 500 rpm, the

143

downward trend in average particle size was barely perceptible, possibly because at

144

low rotary speeds, MCA had a significant effect on the crushing and grinding of

145

LiCoO2 powders, whereas at high rotary speeds, agglomeration occurred among the

146

LiCoO2 powder particles, and when the particle crushing speed and aggregation were

147

balanced, the average particle sizes no longer decreased significantly. In contrast to

148

the average particle size results, the specific surface areas of the LiCoO2 powders

149

were gradually enlarged with an increase in the rotary speed. At 0 rpm, the LiCoO2

150

powders had a specific surface area of 0.61 m2/g, but at 500 rpm, the specific surface

151

area was enlarged by 40 times, to 24.56 m2/g. The combined results indicate that with

152

an increase in rotary speed, MCA led to a decline in the particle sizes of LiCoO2

153

powders, and gradually exposed numerous fresh surfaces and enlarged the specific

154

surface areas. Moreover, the pore volumes of LiCoO2 powders were also enlarged

155

with increases in the rotary speed (Figure 2b).

156

Figure 2c indicates that at 0 and 100 rpm, the N2 adsorption/desorption curves of

157

LiCoO2 powders at low-pressure clung to the X-axis, with little adsorption and weak

158

interaction between nitrogen molecules and LiCoO2 powders, and no evident

159

hysteretic loop was observed. These results indicate that the LiCoO2 powders did not

160

develop pore structures after activation at low rotary speeds. With the rise of rotary 9



161

speed to 300, 400, and 500 rpm, the N2 adsorption/desorption curves of the activated

162

LiCoO2 powders all belonged to IV-type curves, indicating that the LiCoO2 powders

163

began to develop pore structures after activation at high rotary speeds. Moreover, a

164

clearly evident H3 hysteretic loop appeared at high relative pressures. Thus, it could

165

be concluded that the LiCoO2 powders activated at high rotary speeds developed

166

seam-shaped pore structures accumulated from sheet-like particles. The pore size

167

distributions in Figure 2d also show that the LiCoO2 powders at 0 and 100 rpm had no

168

pore structure, while with the rise of rotary speed, mesoporous structures sized at

169

2.5-5 nm began to appear in the LiCoO2 powders.

170 171

Figure 2. Physical properties of the LiCoO2 powders activated at different rotary

172

speeds: (a) average size and specific surface area, (b) pore volume and pore size, (c)

173

N2 absorption-desorption curves, and (d) pore diameter distribution.

174

The above results indicate that the overall structure of LiCoO2 powders was 10


Page 10 of 32

Page 11 of 32


175

destroyed after MCA, as the average particle sizes decreased, further facilitating the

176

dispersion and mass transfer of LiCoO2 powders in the liquid phase. A large specific

177

surface area will provide more active sites for chemical reactions, and well-developed

178

pore structures will facilitate the solvent and solute molecules to infiltrate and diffuse

179

into the inner part of the activated LiCoO2 powders. Changes in these physical

180

properties favor a liquid-phase reaction of LiCoO2 powders.33

181

Phase structure of the LiCoO2 powders XRD patterns in Figure 3a show that

182

the LiCoO2 powders at 0 rpm exhibited major diffraction peaks at the (003), (101),

183

(104), (015), (107), (018), (110), and (113) planes of the LiCoO2 crystals,

184

accompanied by numerous impurity peaks—the amorphous peaks of carbon. With an

185

increase in the rotary speed, the diffraction peak intensities of major crystal planes

186

(003), (101), and (104) were weakened (Figure 3b), while the full widths at half

187

maximum (FWHM) of the diffraction peaks were enlarged (Figure 3c). These results

188

indicate that the mechanical impact, friction, and shear force during MCA led to grain

189

refinement and lattice distortion of the LiCoO2 crystals.32

190

SEM results (Figure S1) showed that the LiCoO2 powders at 0 rpm were

191

irregular complete particles, and increase in the rotary speed induced the increasing

192

destruction of LiCoO2 crystal particles. After activation at 500 rpm, no obvious

193

interfaces were observed between LiCoO2 powder particles, and the surfaces of the

194

activated LiCoO2 powders became loose and cloud-like. TEM results showed that the

195

LiCoO2 powders at 0 rpm were large irregularly shaped spherical particles (Figure 3d).

196

The LiCoO2 powders activated at 500 rpm were loose, layer-like, stacked structures 11



197

with significantly reduced particle sizes (Figure 3e). HRTEM results showed that the

198

lattices of the LiCoO2 crystals changed from an orderly state to a disorderly state after

199

MCA, further confirming that the mechanical forces destroyed the LiCoO2 crystal

200

lattices, thereby inducing lattice dislocation and distortion. Selected area electron

201

diffraction (SAED) showed that the LiCoO2 crystals changed from layer-like

202

hexahedron single crystals to polycrystals after activation.

203

TGA-DSC results confirmed that the LiCoO2 powders activated at 500 rpm were

204

more prone to pyrolysis than those at 0 rpm (Figure S2). From the perspective of

205

energy, the MCA subjected LiCoO2 crystals to grain refinement and lattice distortion,

206

and a portion of the mechanical energy was stored in the LiCoO2 powders in the form

207

of internal energy. The LiCoO2 powders were therefore more susceptible to pyrolysis,

208

since they were in a metastable state after MCA.28, 34

209

The above results indicate that during MCA, mechanical impact, shear force, and

210

friction led to the lattice deformation and defects of LiCoO2 crystalline internal

211

structures. After MCA, the LiCoO2 powders’ chemical energy was obtained from the

212

external environment, and their crystalline interior underwent lattice distortion and

213

defects, increasing the internal energy. As a result, the LiCoO2 powder surfaces were

214

manifested as a layer of high-activity and high-energy floccules. The existence of

215

floccules was the major cause of the intensified leaching reaction of solid materials

216

after MCA.

12


Page 12 of 32

Page 13 of 32


217 218

Figure 3. (a) XRD patterns, (b) XRD peak intensity, and (c) FWHM of the LiCoO2

219

powders activated at different rotary speeds; TEM, HRTEM, and SAED of the

220

LiCoO2 powders activated at (d) 0 rpm and (e) 500 rpm.

221

Surface characteristics of the LiCoO2 powders XPS survey scan spectra of the

222

LiCoO2 powders at different rotary speeds (Figure S3) show that the surface

223

characteristic peaks of LiCoO2 powders were mainly Co2p, O1s, and C1s, while the

224

characteristic peaks of Li1s were not obvious, due to the low Li concentration. The

225

high-resolution XPS spectra of Li1s (Figure 4a) show that the binding energy of Li1s

226

peak shifted about ∆E=0.61 eV to the low-energy field with an increase in the rotary

227

speed, indicating that the Li element experienced a chemical shift during MCA, and

228

the bonding interaction was destroyed. When the rotary speed exceeded 300 rpm, a 13



Page 14 of 32

229

portion of the lithium oxide in the LiCoO2 powders reacted with carbon black to form

230

lithium carbonate (Table S1).35 The high-resolution XPS spectra of C1s also

231

confirmed that a portion of the C element was converted to carbonate after activation

232

at 300, 400, and 500 rpm (Figure 4b and Table S2). The FT-IR results in Figure S4a

233

further confirmed the appearance of carbonate characteristic peaks (864.7, 1435.3,

234

and 1487.5 cm-1) in the MCA products. The possible formation mechanism of Li2CO3

235

is as follows (Figure S4b):

236

3LiCoO2 + C → 3Li + Co3O4 + CO2 ↑

(R1)

237

12LiCoO2 + 6CO2 → 6Li2CO3 + 4Co3O4 + O2 ↑

(R2)

238

4Li + 2CO2 + O2 → 2Li2CO3

(R3)

239

Figure 4c shows that each high-resolution XPS spectrum of Co2p was

240

composed of a Co2p3/2 main peak, a satellite peak (S1), a Co2p1/2 main peak, and

241

another satellite peak (S2). The energy difference between Co2p3/2 and Co2p1/2

242

splitting is approximately 15 eV, which indicates the presence of both Co2+/Co3+

243

species in all LiCoO2 samples.36 The peak fitting results indicated that the main peak

244

of Co2p3/2 could be split into Peak 1 and Peak 2, while the Co2p1/2 main peak could

245

be split into Peak 3 and Peak 4. Since the FWHM of the Co2+ peak was broader than

246

that of the Co3+ peak (Table S3), and the Co2+ had a larger spin-splitting distance ∆E

247

(∆E2>∆E1) than the Co3+ one (Table S4), it can be deduced that the fitted Peaks 1 and

248

3 correspond to Co3+, while Peaks 2 and 4 correspond to Co2+.

249

rotary speed, the I(Co3+/Co2+) values decreased to varying degrees, indicating that the

250

Co3+ proportion declined during MCA, while the Co2+ proportion increased, due to 14


37, 38

With the rise in

Page 15 of 32


251

the reduction effect of carbon black on Co3+ under the action of mechanical forces

252

(Table S4). Compared with Co3+, Co2+ reacted faster during leaching in organic acid,

253

and the usage of the reductant could be therefore reduced.39

254

The high-resolution XPS spectra of O1s (Figure 4d) show that the oxygen

255

species on the surface of LiCoO2 crystals were mainly lattice oxygen (Olatt) and

256

surface hydroxyl oxygen (Osur); the Olatt originated from the internal structure of

257

LiCoO2 crystals, and the Osur resulted from the hydrothermal synthesis of LiCoO2

258

crystals.37 With an increase in the rotary speed, the I(Olatt/Osur) values continually

259

decreased, implying that the proportion of Olatt on the LiCoO2 crystal surface declined,

260

while the proportion of Osur increased (Table S5). The decrease in the Olatt proportion

261

implied an increase in oxygen vacancy concentration, which improved the surface

262

hydroxylation of the activated LiCoO2 powders. Moreover, the inner electron binding

263

energy of Li1s (from 0 to 100 rpm), Co2p, and O1s all shifted to the high-energy

264

fields with an increase in the rotary speed, a result that could be attributed to the

265

differences in the effects of extra-atomic relaxation.40

15



266

Figure 4. High-resolution XPS spectra of (a) Li1s, (b) C1s, (c) Co2p, and (d) O1s of

267

the LiCoO2 powders activated at different rotary speeds.

268

Interface behavior of the LiCoO2 powders The contact angles of water and

269

ethanol on the surface of LiCoO2 powders activated at different rotary speeds were

270

measured using the contour image method (Figure S5). The values of the contact

271

angles were calculated according to the Young-Laplace equation (γSV = γSL + γLV ×

272

cosθe). Table 1 shows that the contact angles of water on the surface of the LiCoO2

273

powders decreased with an increase in the rotary speed, indicating that the surfaces of

274

LiCoO2 powders became more hydrophilic after MCA. Combined with the O1s XPS

275

results, it can be concluded that the enhancement of the surface hydrophilicity can be

276

attributed to the increasing proportion of Osur on the surfaces of the LiCoO2 powders.

277

As a hydrophilic functional group, the Osur can easily bind with water molecules to 16


Page 16 of 32

Page 17 of 32


278 279

form hydrogen bonding, thus enhancing the hydrophilicity of the powders.35 Using the contact angles of water and ethanol, the surface free energy of LiCoO2

280

powders

activated

at

different

rotary

speeds

were

281

Owens-Wendt-Rabel-Kaelble method. Table 1 shows that the surface free energy of

282

the LiCoO2 powders increased gradually with the increase in rotary speed. During

283

MCA, the LiCoO2 powders were crushed into smaller sizes under the action of

284

mechanical forces, and developed numerous fresh surfaces, thus enlarging the specific

285

surface area and increasing the surface free energy and interface activity of the

286

LiCoO2 powders. Zeta potential results showed that MCA could significantly enhance

287

the surface negative charge of the LiCoO2 powders. During liquid-phase leaching, H+

288

could be better diffused via electrostatic attraction and combined with the surface

289

hydroxyl of the LiCoO2 powders. These changes were all favorable for the

290

liquid-phase interfacial infiltration and dispersion of the activated LiCoO2 powders,

291

and accelerated the liquid-phase reactions of the activated LiCoO2 powders.

17


calculated

via

the


Page 18 of 32

292

Table 1. Contact angle, surface free energy, and zeta potential of the LiCoO2 powders

293

activated at different rotary speeds. Rotary speed

Contact angle (°)

Surface free energy

Zeta potential

(rpm)

Water

Ethanol

(mN/m2)

(mV)

0

37.0

22.0

97.7

-0.6

100

30.0

21.8

110.7

-3.9

200

22.5

20.7

122.2

-43.6

300

19.8

21.0

126.0

-45.4

400

19.1

26.5

130.4

-47.0

500

17.6

25.5

131.6

-48.7

294

Analysis of metal leaching and kinetics Figures 5a and 5b show that the

295

leaching percentages of Li and Co varied with leaching time from the LiCoO2

296

powders activated at different rotary speeds. The following results can be observed: (1)

297

under identical conditions, the Li leaching percentage was always higher than that of

298

Co, indicating that Li was preferentially leached out due to its higher activity; (2) the

299

leaching percentages of both Li and Co were enhanced with increasing activation

300

rotary speed. These results indicate that the LiCoO2 powders were more activated at

301

higher rotary speeds. Combined with the characterization results, it was obvious that

302

the average particle sizes of the LiCoO2 powders decreased after MCA, thus

303

improving both the specific surface areas and surface activity. More importantly, the

304

LiCoO2 crystals were lattice-deformed and experienced numerous structural defects,

305

increasing the internal energy and enhancing the chemical reaction activity of the

306

solid materials. This is the core influencing factor for the rapid leaching of metals in

307

LiCoO2 powders after MCA. During the leaching reactions, the highly activated 18


Page 19 of 32


308

surface layer of the LiCoO2 powders was rapidly dissolved in acetic acid solution, and

309

the metal leaching rate and percentage were therefore improved within a very short

310

time. The effects of volume concentrations of acetic acid and hydrogen peroxide

311

(H2O2) on the metal leaching percentages of Li and Co are shown in Figure S6.

312

The effects of MCA on the metal leaching kinetics were investigated by

313

recording Li and Co leaching percentages varied within 5 min, at five different

314

temperatures, from LiCoO2 powders activated at 0 rpm (Figures 5c and 5d) and at 500

315

rpm (Figures 5e and 5f), respectively. The contrasting experiments showed that the

316

increase in leaching temperature significantly accelerated the metal leaching under

317

identical conditions, possibly because the temperature increase accelerated the mass

318

transfer behaviors. With an increase in the leaching temperature, more energy was

319

accumulated in the LiCoO2 powders, enhancing their ability to weaken or destroy the

320

chemical bonds in the LiCoO2 particles and increasing the number of molecules

321

containing kinetic energy equal to or greater than the leaching apparent activation

322

energy. As a result, the metal leaching rate was enhanced and the metal leaching

323

percentage per unit time was significantly improved.

19



324 325

Figure 5. Effect of rotary speed on the leaching percentages of (a) Li and (b) Co

326

(conditions: 25 oC, 20 vol.% acetic acid, and 5 vol.% H2O2); effect of temperature on

327

the leaching percentages of (c) Li and (d) Co (conditions: 0 rpm, 20 vol.% acetic acid,

328

and 5 vol.% H2O2); effect of temperature on the leaching percentages of (e) Li and (f)

329

Co (conditions: 500 rpm, 20 vol.% acetic acid, and 5 vol.% H2O2). 20


Page 20 of 32

Page 21 of 32


330

Since the LiCoO2 powder particles before the leaching reaction were dense and

331

poreless, the reaction interface gradually contracted toward the cores after the acetic

332

acid molecules reacted with the LiCoO2 powder particles. Thus, metal leaching from

333

the LiCoO2 powders could be described by the shrinking unreacted-core model

334

(Figure S7). The metal leaching percentage versus leaching time at different leaching

335

temperatures was fitted with the use of LiCoO2 powders activated at 0 and 500 rpm,

336

respectively; ka is the slope of the fitted straight line, or the apparent rate constant of

337

the leaching reaction (min-1); R2 is the coefficient of determination, and a larger R2

338

means the linear relationship of the regression equation is better and the fitting result

339

is more reliable (Tables S6 and S7).41 At 0 rpm, both Li and Co, 1-(1-x)1/3 were well

340

linearly related with the leaching time t (R2 > 0.98), indicating that the Li/Co leaching

341

from the LiCoO2 powders followed the shrinking unreacted-core model with surface

342

chemical-reaction-control as the rate-limiting step (Table S6). At 500 rpm, for both Li

343

and Co, 1-3(1-x)2/3+2(1-x) is well linearly related with the leaching time t (R2 > 0.98),

344

indicating that the Li/Co leaching from the LiCoO2 powders followed the shrinking

345

unreacted-core model with ash layer diffusion control as the rate-limiting step (Table

346

S7). The contrast analysis showed that MCA profoundly affects the Li/Co leaching

347

kinetics from LiCoO2 powders. The rate-limiting step of metal leaching changed from

348

a surface chemical reaction-controlled one before MCA to an ash layer

349

diffusion-controlled one after MCA.

350

Apparent activation energy of the metal leaching reaction On the basis of

351

the ka from Tables S6 and S7, the Arrhenius equation (Eq. (2)) was employed to 21



352

Page 22 of 32

determine the apparent activation energy:

k a = Ae

353

−

Ea RT

Eq. (2)

354

where A is the pre-exponential factor (min-1); Ea is the apparent activation energy of

355

reaction (kJ·mol-1); R is the molar gas constant (R=8.3145, J·mol-1·K-1); and T is the

356

reaction absolute temperature (K). Logarithm of both sides of Eq. (2) yields:

ln ka = ln A −

357

Ea RT

Eq. (3)

358

Obviously, lnka and 1/T are linear relations, and the slope of the straight line is -Ea/R.

359

Thus, according to the rate constant at different reaction temperatures, the Ea can be

360

calculated from Eq. (3).

361

The leaching rate constant ka at different reaction temperatures in Tables S6 and

362

S7 was substituted into Eq. (3). Arrhenius plots were plotted with the intercept lnka as

363

the Y-axis and 1/T as the X-axis, and the slope of the straight line was exactly -Ea/R.

364

The leaching apparent activation energies of Li and Co before and after the MCA

365

were then obtained (Figure S8). The apparent activation energy of Li decreased from

366

43.09 to 11.68 kJ·mol-1 after MCA (Figure S8a), while that of Co declined from 47.74

367

to 22.92 kJ·mol-1 (Figure S8b). These results indicated that MCA enhanced the

368

chemical reaction activity of the LiCoO2 powders, reduced the Ea of the metal

369

leaching reaction, and lowered the temperature and time dependence of the leaching

370

reactions.

371

Environmental implications A comparison of the methods revealed that MCA

372

combined with acetic acid leaching could achieve the goal of metal leaching at room

373

temperature in a shorter time (Table S8). Further economic analysis showed that 22


Page 23 of 32


374

acetic acid was more effective as a leaching reagent for Li and Co leaching than other

375

traditional inorganic or organic acids (Table S9). And in terms of environmental

376

benefits, acetic acid is much safer, in both transportation and storage, than high-risk

377

HCl and H2SO4. In addition, the acetic acid reagent can be regenerated into sodium

378

acetate, as depicted in a designed flow chart (Figure S9), to further reduce the reagent

379

cost and complete the separation of Li and Co.30 Economic assessment (Figure S10

380

and Table S10) for the recovery of 1 kg spent LIBs at the laboratory scale, based on

381

MCA combined with an acetic acid leaching process, demonstrated economic

382

feasibility. Thus, acetic acid is a better reagent for metal recovery from spent LIBs, in

383

terms of leaching percentage, security, and economy, than other chemical reagents.

384

In summary, MCA can obviously change the physical properties, crystal-phase

385

structure, surface characteristics, and solid-liquid interfacial behaviors of LiCoO2

386

powders and significantly improve the leaching efficiencies of Li and Co in acetic

387

acid solution. The rate-limiting step of metal leaching from LiCoO2 powders was

388

altered from a surface chemical reaction-controlled one before MCA to an ash layer

389

diffusion-controlled one after MCA, and the apparent activation energies of the

390

leaching reactions were significantly lowered. Rapid leaching of Li (99.8 wt%) and

391

Co (99.7 wt%) was achieved within a short time of 15 min at room temperature. MCA

392

combined with acetic acid leaching presents outstanding practical application

393

prospects and may be an environmentally friendly technology worth popularizing for

394

the recovery of valuable metals from spent LIBs.

395

SUPPORTING INFORMATION 23



396

SEM images of the LiCoO2 powders activated at different rotary speeds (Figure S1);

397

TGA-DSC curves of the LiCoO2 powders activated at 0 and 500 rpm (Heating rate of

398

15 °C/min in argon atmosphere) (Figure S2); XPS survey scan spectra of the LiCoO2

399

powders activated at different rotary speeds (Figure S3); (a) FT-IR spectra of the

400

LiCoO2 powders activated at different rotary speeds, and (b) the possible formation

401

mechanism of Li2CO3 (Figure S4); Contact angle images of (a) water and (b) ethanol

402

on the surface of the LiCoO2 powders activated at different rotary speeds, and (c)

403

schematic of a liquid drop showing the quantities for the Young–Laplace equation

404

(Figure S5); Effects of different acetic acid concentrations on the leaching

405

percentages of (a) Li and (b) Co (conditions: rotary speed of 500 rpm, acetic acid

406

concentration of 20 vol.%, and H2O2 concentration of 5 vol.%); and effects of

407

different H2O2 concentrations on the leaching percentages of (c) Li and (d) Co

408

(conditions: rotary speed of 500 rpm, acetic acid concentration of 20 vol.%, and H2O2

409

concentration of 5 vol.%) (Figure S6); Schematic diagram of shrinking

410

unreacted-core model (Figure S7); Arrhenius plots for leaching of (a) Li and (b) Co

411

from the LiCoO2 powders activated at 0 and 500 rpm (Figure S8); Designed flow

412

chart for Li and Co recovery from spent LIBs (Figure S9); Materials balance and cost

413

assessment for spent LIBs recovery based on MCA combined with acetic acid

414

leaching (Figure S10); Fitting peaks of the Li1s XPS spectra of the LiCoO2 powders

415

activated at different rotary speeds (Table S1); Fitting peaks of the C1s XPS spectra

416

of the LiCoO2 powders activated at different rotary speeds (Table S2); FWHM of the

417

Co2p fitting peaks of the LiCoO2 powders activated at different rotary speeds (Table 24


Page 24 of 32

Page 25 of 32


418

S3); Fitting peaks of the Co2p XPS spectra of the LiCoO2 powders activated at

419

different rotary speeds (Table S4); Fitting peaks of the O1s XPS spectra of the

420

LiCoO2 powders activated at different rotary speeds (Table S5); The rate constant (ka)

421

and the coefficient of determination (R2) for Li and Co leaching from the LiCoO2

422

powders activated at 0 rpm for different temperatures (Table S6); The rate constant

423

(ka) and the coefficient of determination (R2) for Li and Co leaching from the LiCoO2

424

powders activated at 500 rpm for different temperatures (Table S7); Key operational

425

parameters of different methods used for Li and Co recovery from the LiCoO2

426

powders (Table S8); Economic comparison of the Li and Co leaching from the

427

LiCoO2 powders by various inorganic acids and organic acids (Table S9); Economic

428

benefit assessment of the proposed MCA combined with acetic acid leaching process

429

(Table S10). Supporting Information is available free of charge via Internet at

430

http://pubs.acs.org.

431

AUTHOR INFORMATION

432

Corresponding author

433

Jinhui Li*,

434

Tel.: +86-10-62794143.

435

Fax: +86-10-62772048.

436

E-mail address: [email protected]

437

Notes

438

The authors declare no competing financial interest.

439

ACKNOWLEDGEMENTS 25



Page 26 of 32

440

This study was financially supported by major project of “The National Social

441

Science Fund of China” (16ZDA071) and the China Postdoctoral Science Foundation

442

(2016M601051). The authors thank Prof. Joseph F. Chiang from State University of

443

New York College at Oneonta for his valuable advice. The authors also thank Dr.

444

Kang Liu from Huazhong University of Science and Technology for his valuable

445

advice.

446

REFERENCES

447

1.

448

and recovery of spent lithium-ion batteries. Renewable and Sustainable Energy

449

Reviews 2016, 60, 195-205.

450

2.

451

review. Critical Reviews in Environmental Science and Technology 2014, 44, (10),

452

1129-1165.

453

3.

454

magnetic separation technology for in situ recycling cobalt, lithium carbonate and

455

graphite from spent LiCoO2/graphite lithium batteries. Journal of Hazardous

456

Materials 2016, 302, 97-104.

457

4.

458

Carbonate from

459

Environmental Science & Technology 2017, 51, (20), 11960-11966.

460

5.

461

cathode materials of spent lithium-ion batteries using mild phosphoric acid. Journal of

Ordoñez, J.; Gago, E.; Girard, A., Processes and technologies for the recycling

Zeng, X.; Li, J.; Singh, N., Recycling of spent lithium-ion battery: a critical

Li, J.; Wang, G.; Xu, Z., Environmentally-friendly oxygen-free roasting/wet

Xiao, J.; Li, J.; Xu, Z., Novel Approach for in Situ Recovery of Lithium Spent Lithium Ion Batteries Using

Vacuum Metallurgy.

Chen, X.; Ma, H.; Luo, C.; Zhou, T., Recovery of valuable metals from waste

26


Page 27 of 32


462

Hazardous Materials 2017, 326, 77-86.

463

6.

464

and graphite from spent lithium-ion batteries by Fenton reagent-assisted flotation.

465

Journal of Cleaner Production 2017, 143, 319-325.

466

7.

467

recovery of high value-added metals from spent lithium-ion batteries. Journal of

468

Power Sources 2017, 351, 192-199.

469

8.

470

Extraction and recovery of Co2+ ions from spent lithium-ion batteries using

471

hierarchical mesosponge γ-Al2O3 monolith extractors. Green Chemistry 2018, 20, (8),

472

1841-1857.

473

9.

474

for leaching of cobalt from spent lithium-ion batteries. Journal of Cleaner Production

475

2018, 180, 64-70.

476

10. Huang, L.; Guo, R.; Jiang, L.; Quan, X.; Sun, Y.; Chen, G., Cobalt leaching from

477

lithium cobalt oxide in microbial electrolysis cells. Chemical Engineering Journal

478

2013, 220, 72-80.

479

11. Zhang, X.; Xie, Y.; Lin, X.; Li, H.; Cao, H., An overview on the processes and

480

technologies for recycling cathodic active materials from spent lithium-ion batteries.

481

Journal of Material Cycles and Waste Management 2013, 15, (4), 420-430.

482

12. Chagnes, A.; Pospiech, B., A brief review on hydrometallurgical technologies for

483

recycling spent lithium-ion batteries. Journal of Chemical Technology and

He, Y.; Zhang, T.; Wang, F.; Zhang, G.; Zhang, W.; Wang, J., Recovery of LiCoO2

Hu, J.; Zhang, J.; Li, H.; Chen, Y.; Wang, C., A promising approach for the

Gomaa, H.; Shenashen, M.; Yamaguchi, H.; Alamoudi, A.; El-Safty, S.,

Meng, Q.; Zhang, Y.; Dong, P., Use of electrochemical cathode-reduction method

27



484

Biotechnology 2013, 88, (7), 1191-1199.

485

13. Lv, W.; Wang, Z.; Cao, H.; Sun, Y.; Zhang, Y.; Sun, Z., A critical review and

486

analysis on the recycling of spent lithium-ion batteries. ACS Sustainable Chemistry &

487

Engineering 2018, 6, (2), 1504-1521.

488

14. Ku, H.; Jung, Y.; Jo, M.; Park, S.; Kim, S.; Yang, D.; Rhee, K.; An, E.-M.; Sohn,

489

J.; Kwon, K., Recycling of spent lithium-ion battery cathode materials by ammoniacal

490

leaching. Journal of Hazardous Materials 2016, 313, 138-146.

491

15. Liu, K.; Zhang, F.-S., Innovative leaching of cobalt and lithium from spent

492

lithium-ion batteries and simultaneous dechlorination of polyvinyl chloride in

493

subcritical water. Journal of Hazardous Materials 2016, 316, 19-25.

494

16. Li, L.; Dunn, J. B.; Zhang, X. X.; Gaines, L.; Chen, R. J.; Wu, F.; Amine, K.,

495

Recovery of metals from spent lithium-ion batteries with organic acids as leaching

496

reagents and environmental assessment. Journal of Power Sources 2013, 233,

497

180-189.

498

17. Li, L.; Ge, J.; Chen, R.; Wu, F.; Chen, S.; Zhang, X., Environmental friendly

499

leaching reagent for cobalt and lithium recovery from spent lithium-ion batteries.

500

Waste Management 2010, 30, (12), 2615-2621.

501

18. Zeng, X.; Li, J.; Shen, B., Novel approach to recover cobalt and lithium from

502

spent lithium-ion battery using oxalic acid. Journal of Hazardous Materials 2015, 295,

503

112-118.

504

19. Gao, W.; Zhang, X.; Zheng, X.; Lin, X.; Cao, H.; Zhang, Y.; Sun, Z., Lithium

505

carbonate recovery from cathode scrap of spent lithium-ion battery: a closed-loop 28


Page 28 of 32

Page 29 of 32


506

process. Environmental Science & Technology 2017, 51, (3), 1662-1669.

507

20. Li, L.; Lu, J.; Ren, Y.; Zhang, X. X.; Chen, R. J.; Wu, F.; Amine, K.,

508

Ascorbic-acid-assisted recovery of cobalt and lithium from spent Li-ion batteries.

509

Journal of Power Sources 2012, 218, 21-27.

510

21. Li, L.; Qu, W.; Zhang, X.; Lu, J.; Chen, R.; Wu, F.; Amine, K., Succinic

511

acid-based leaching system: a sustainable process for recovery of valuable metals

512

from spent Li-ion batteries. Journal of Power Sources 2015, 282, 544-551.

513

22. Chen, X.; Luo, C.; Zhang, J.; Kong, J.; Zhou, T., Sustainable recovery of metals

514

from spent lithium-ion batteries: a green process. ACS Sustainable Chemistry &

515

Engineering 2015, 3, (12), 3104-3113.

516

23. Li, L.; Zhai, L.; Zhang, X.; Lu, J.; Chen, R.; Wu, F.; Amine, K., Recovery of

517

valuable metals from spent lithium-ion batteries by ultrasonic-assisted leaching

518

process. Journal of Power Sources 2014, 262, 380-385.

519

24. Bertuol, D. A.; Machado, C. M.; Silva, M. L.; Calgaro, C. O.; Dotto, G. L.;

520

Tanabe, E. H., Recovery of cobalt from spent lithium-ion batteries using supercritical

521

carbon dioxide extraction. Waste Management 2016, 51, 245-251.

522

25. Ou, Z.; Li, J.; Wang, Z., Application of mechanochemistry to metal recovery from

523

second-hand resources: a technical overview. Environmental Science: Processes &

524

Impacts 2015, 17, (9), 1522-1530.

525

26. Guo, X.; Xiang, D.; Duan, G.; Mou, P., A review of mechanochemistry

526

applications in waste management. Waste Management 2010, 30, (1), 4-10.

527

27. Tan, Q.; Li, J., Recycling metals from wastes: a novel application of 29



528

mechanochemistry. Environmental Science & Technology 2015, 49, (10), 5849-5861.

529

28. Beyer, M. K.; Clausen-Schaumann, H., Mechanochemistry: the mechanical

530

activation of covalent bonds. Chemical Reviews 2005, 105, (8), 2921-2948.

531

29. Sasai, R.; Kubo, H.; Kamiya, M.; Itoh, H., Development of an eco-friendly

532

material recycling process for spent lead glass using a mechanochemical process and

533

Na2EDTA reagent. Environmental Science & Technology 2008, 42, (11), 4159-4164.

534

30. Wang, M.-M.; Zhang, C.-C.; Zhang, F.-S., An environmental benign process for

535

cobalt and lithium recovery from spent lithium-ion batteries by mechanochemical

536

approach. Waste Management 2016, 51, 239-244.

537

31. Yuan, W.; Li, J.; Zhang, Q.; Saito, F., Innovated application of mechanical

538

activation to separate lead from scrap cathode ray tube funnel glass. Environmental

539

Science & Technology 2012, 46, (7), 4109-4114.

540

32. Yang, Y.; Zheng, X.; Cao, H.; Zhao, C.; Lin, X.; Ning, P.; Zhang, Y.; Jin, W.; Sun,

541

Z., A Closed-Loop Process for Selective Metal Recovery from Spent Lithium Iron

542

Phosphate Batteries through Mechanochemical Activation. ACS Sustainable

543

Chemistry & Engineering 2017, 5, (11), 9972-9980.

544

33. Nasser, A.; Mingelgrin, U., Mechanochemistry: a review of surface reactions and

545

environmental applications. Applied Clay Science 2012, 67, 141-150.

546

34. Tromans, D.; Meech, J., Enhanced dissolution of minerals: stored energy,

547

amorphism and mechanical activation. Minerals Engineering 2001, 14, (11),

548

1359-1377.

549

35. Moses, A. W.; Flores, H. G. G.; Kim, J.-G.; Langell, M. A., Surface properties of 30


Page 30 of 32

Page 31 of 32


550

LiCoO2, LiNiO2 and LiNi1−xCoxO2. Applied Surface Science 2007, 253, (10),

551

4782-4791.

552

36. Zhang, G.; Li, C.; Liu, J.; Zhou, L.; Liu, R.; Han, X.; Huang, H.; Hu, H.; Liu, Y.;

553

Kang, Z., One-step conversion from metal–organic frameworks to Co3O4@N-doped

554

carbon nanocomposites towards highly efficient oxygen reduction catalysts. Journal

555

of Materials Chemistry A 2014, 2, (22), 8184-8189.

556

37. Kosova, N.; Kaichev, V.; Bukhtiyarov, V.; Kellerman, D.; Devyatkina, E.; Larina,

557

T., Electronic state of cobalt and oxygen ions in stoichiometric and nonstoichiometric

558

Li1+xCoO2 before and after delithiation according to XPS and DRS. Journal of Power

559

Sources 2003, 119, 669-673.

560

38. Ma, D.; Li, Y.; Zhang, P.; Cooper, A. J.; Abdelkader, A. M.; Ren, X.; Deng, L.,

561

Mesoporous Li1.2Mn0.54Ni0.13Co0.13O2 nanotubes for high-performance cathodes in

562

Li-ion batteries. Journal of Power Sources 2016, 311, 35-41.

563

39. Meshram, P.; Pandey, B.; Mankhand, T., Hydrometallurgical processing of spent

564

lithium ion batteries (LIBs) in the presence of a reducing agent with emphasis on

565

kinetics of leaching. Chemical Engineering Journal 2015, 281, 418-427.

566

40. Zhang, K.; Banaszak Holl, M.; McFeely, F., Extra-atomic relaxation and

567

core-level binding energy shifts at silicon/silicon oxide interfaces: Effects of cluster

568

size on physical models. The Journal of Physical Chemistry B 1998, 102, (20),

569

3930-3935.

570

41. Zhang, X.; Cao, H.; Xie, Y.; Ning, P.; An, H.; You, H.; Nawaz, F., A closed-loop

571

process for recycling LiNi1/3Co1/3Mn1/3O2 from the cathode scraps of lithium-ion 31



572

batteries: Process optimization and kinetics analysis. Separation and Purification

573

Technology 2015, 150, 186-195.

32


Page 32 of 32

Unveiling the Role and Mechanism of Mechanochemical Activation on

Recommend Documents