Facile and Cost-Effective Approach for Copper Recovery from Waste

Subscriber access provided by Iowa State University | Library

Sustainability Engineering and Green Chemistry

A facile and cost-effective approach for copper recovery from waste printed circuit boards via a sequential mechanochemical/leaching/recrystallization process Kang Liu, Jiakuan Yang, Huijie Hou, Sha Liang, Ye Chen, Junxiong Wang, Bingchuan Liu, Keke Xiao, Jingping Hu, and Huali Deng Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.8b06081 • Publication Date (Web): 30 Jan 2019 Downloaded from http://pubs.acs.org on February 4, 2019

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 30

Environmental Science & Technology

1

A facile and cost-effective approach for copper recovery

2

from waste printed circuit boards via a sequential

3

mechanochemical/leaching/recrystallization process

4

Kang Liu†‡, Jiakuan Yang*,†‡§, Huijie Hou*,†‡, Sha Liang†‡, Ye Chen†‡, Junxiong Wang†‡,

5

Bingchuan Liu†‡, Keke Xiao†‡, Jingping Hu†‡, Huali Deng∥

6

†

7

Technology (HUST), 1037 Luoyu Road, Wuhan, Hubei, 430074, China

8

‡

9

Recycling, 1037 Luoyu Road, Wuhan, Hubei, 430074, China

School of Environmental Science and Engineering, Huazhong University of Science and

Hubei Provincial Engineering Laboratory of Solid Waste Treatment, Disposal and

10

§

11

(HUST), 1037 Luoyu Road, Wuhan, Hubei 430074, China

12

∥

13

*Co-Corresponding author

14

* Prof. Jiakuan Yang

15

Tel: +86-27-87792102, Fax: +86-27-87792101.

16

E-mail: [email protected].

17

* Associate Prof. Huijie Hou

18

Tel.: +86-27-87793948.

19

E-mail: [email protected]

State Key Laboratory of Coal Combustion, Huazhong University of Science and Technology

Dongjiang Environmental Protection Co., Ltd., Shenzhen 518000, China

20

1

ACS Paragon Plus Environment


21

■ ABSTRACT

22

The recovery of copper (Cu0) from waste printed circuit boards (WPCBs) is a great

23

challenge due to its heterogeneous structural properties, with a mixture of metals,

24

epoxy resin, and fiberglass. In this study, a three-step sequential process—including

25

mechanochemical processing, water leaching, and recrystallization—for Cu0 recovery

26

from WPCB powder is reported. Potassium persulfate (K2S2O8), instead of acid/alkali

27

reagents, was employed as the sole reagent in the cupric sulfate (CuSO4) regeneration

28

process. Complete oxidation of the Cu0 in the WPCBs to copper oxide (CuO) and

29

CuSO4 was first achieved during mechanochemical processing with K2S2O8 as the

30

solid oxidant, and the K2S2O8 was simultaneously converted to sulfate compounds

31

(K3H(SO4)2) via a solid-solid reaction with epoxy resin (CnHmOy) as hydrogen

32

donator under mechanical force. The rapid leaching of Cu species in the forms of CuO

33

and CuSO4 was therefore easily realized with pure water as a non-toxic leaching

34

reagent. The kinetics of the leaching process of Cu species was confirmed to follow

35

the shrinking nucleus model controlled by solid-film diffusion. Finally, CuSO4·5H2O

36

was successfully separated by cooling crystallization of the hot saturated solution of

37

sulfate salt (K2Cu(SO4)2·6H2O). An efficient conversion of Cu0 to CuSO4·5H2O

38

product, for WPCB recycling, was therefore established.

39

2


Page 2 of 30

Page 3 of 30


40

TOC ART

41 42

3



Page 4 of 30

43

■ INTRODUCTION

44

According to statistics from the United Nations Environment Programme, in 2016, the

45

global e-waste generation has exceeded 40 million tons, while e-waste still maintains

46

an annual growth rate of 3-5%.1 As the main components of various electronic and

47

electrical equipment, it is estimated that about 2 million tons of printed circuit boards,

48

are discarded annually worldwide assuming the weight proportion of printed circuit

49

boards is 5 wt% of waste electronic and electrical equipment.2 Specifically, the

50

average copper content in waste printed circuit boards (WPCBs) comes to more than

51

20 wt%, much higher than the 0.2-0.7 wt% in copper ore, making it the main

52

economic drive for the recycling of WPCBs.

53

significant quantities of heavy metals (e.g., Pb, Hg, Cd, and Cr) and toxic substances

54

(e.g., organochlorine and organobromine) that pose serious environmental threats if

55

not properly managed (Table S1).9-12 Therefore, the recycling of WPCBs has become

56

an important issue of both global environment and human health. 13, 14

3-8

Furthermore, WPCBs also contain

57

The copper in WPCBs is generally in the form of Cu0. Conventional recycling

58

processes for Cu0 recovery from WPCBs include physical,15, 16 electrochemistry,17, 18

59

pyrometallurgical,19,

60

However, direct leaching and separation of Cu0 from WPCB powder is extremely

61

challenging, even when using a mineral acid as the leaching reagent.27, 28 Further, the

62

direct conversion of the Cu0 in WPCBs into high-value copper compounds is even

63

more daunting.29 Currently, hydrometallurgy is a widely accepted approach in mature

64

industrial recycling system for Cu0 recovery from WPCBs due to its advantages of

65

low recovery cost, high metal recovery rate, and mild operational conditions.22

66

However, the generation of waste acids and liquid wastes pose severe environmental

67

risks, requiring a complex supplementary wastewater treatment process.30,

20

hydrometallurgical,21-23 and biometallurgical24-26 method.

4


31

Page 5 of 30


68

Furthermore, the use of acid/base reagents and organic extractants increases the cost

69

of corrosion protection of the equipment and the potential risks to the practitioner.9

70

Therefore, new technology and methods for direct Cu0 recovery from WPCBs, or

71

faster conversion of Cu0 into high-value products, is urgently required.

72

Currently, a mechanochemical method is widely used for the recovery of valuable

73

metals from e-waste, because of its unique reaction mechanism.32, 33 First of all, the

74

mechanochemical method utilizes mechanical forces, including shearing, friction,

75

impact force, etc., to apply mechanical energy to condensed matter such as a solid or

76

liquid to induce chemical reactions: this is especially effective for highly dispersed

77

valuable metals in complex e-waste.34 In addition, because the driving force of

78

mechanochemical processing is mechanical energy rather than thermal energy, the

79

extraction reaction of valuable metals in electronic wastes can be easily completed

80

without harsh conditions such as high temperature or high pressure, fulfilling the goal

81

of green chemistry for e-waste recycling.35 Because of all these advantages, the

82

mechanochemical method has now become a popular metal recovery technology for

83

e-waste.36-42

84

Li et al.43 proposed detoxifying cathode ray tube funnel glass for lead recovery by

85

mechanochemical activation. Substantial physicochemical changes have been

86

observed after mechanochemical activation, including chemical breakage and the

87

formation of defects in the inner structure of glass. These changes contribute to the

88

easy dissolution of an activated sample in acid solution. Sun et al.44 proposed a

89

mechanochemical activation method to selectively recycle iron (Fe) and lithium (Li)

90

from the cathode scrap of spent lithium iron phosphate (LiFePO4) batteries. The

91

characterization results confirmed that the chemical bonding of LiFePO4 was

92

destroyed during mechanochemical activation, an effect that could be attributed to the 5



93

destructive effect of mechanical force. This approach also significantly promotes the

94

leaching of metals in the solid materials after mechanochemical activation. However,

95

few reports on Cu0 recovery from WPCBs using the mechanochemical method can be

96

found in existing research literature.

97

Here in this work, a facile process is proposed, including mechanochemical

98

processing, water leaching, and recrystalization, for the regeneration of Cu0 to

99

high-value chemicals from WPCBs. The integrated three-step process could realize

100

direct conversion of Cu0 from WPCBs into CuSO4·5H2O. The mechanochemical

101

processing paths of K2S2O8 and Cu0 in WPCB powder under the induction effect of

102

mechanical force were explored, and conversion paths of Cu0 to CuSO4·5H2O product

103

for WPCB metal recycling were established.

104

■ MATERIALS AND METHODS

105

■

106

DongJiang Co., Ltd (Xiamen, China). The Cu0 content in the WPCB powders

107

(0.1-0.15 mm) was 5.4 wt%. The XRF result of the WPCB powder (0.1-0.15 mm)

108

used in this study was provided in Table S2. The chemical reagents used were all of

109

analytical grade and were purchased from Chemical Reagent Company of Beijing

110

(Beijing, China). De-ionized water was used for preparation and dilution of the

111

chemical solutions.

112

■

113

resistance) were separated, the bare WPCB boards were shredded and crushed by a

114

cutting and grinding machine (Beijing Grinder Instrument Co., Ltd, China) and passed

115

through sieve mesh to obtain the WPCB powder of varying particle sizes. The particle

116

size distribution of the WPCB powder when passing through different sieve mesh is

Materials and reagents WPCB samples were obtained from Xiamen

Experimental procedure After the components (e.g., relays, capacitors, and

6


Page 6 of 30

Page 7 of 30


117

shown in Figure S1. The designed steps for Cu0 recovery from WPCB powder were

118

divided into three stages.

119

Stage I: All mechanochemical experiments were carried out in a planetary ball

120

mill (QM-3SP2J, Nanjing University Instrument Plant, China). Zirconia (ZrO2)

121

ball-milling pots of 100 mL inner volume and zirconia balls of 8 mm diameter were

122

used in the Cu0 recovery experiments. Conditions for mechanochemical processing

123

are listed in Table S3. First, WPCB powder (0.1-0.15 mm) of 0.5 g and K2S2O8 with

124

various mass ratios (K2S2O8/WPCBs mass ratio = 2:1, 1:1, 2:3, 1:2, 1:3, and 1:4),

125

together with grinding balls, were sealed in the ZrO2 pot. The mixture was then

126

co-ground at different rotary speeds (0, 100, 200, 300, 400, and 500 rpm) under

127

ambient conditions for different periods of time (0, 1, 2, 3, 4, 5, and 6 h).

128

Stage II: Co-ground products of 0.5 g were leached in 50 mL of de-ionized water

129

with constant magnetic stirring (300 rpm). The leaching temperature was set at

130

different temperatures: 25, 35, 45, and 55 oC. The leaching solution and solid residues

131

were rapidly separated by vacuum filtration after the reaction was complete.

132

Stage III: CuSO4·5H2O was separated from the filtrate by a heating concentration

133

and cooling recrystallization process. First, the leaching solution obtained in stage II

134

was converted into a saturated solution of sulfate salt (K2Cu(SO4)2·6H2O) by

135

continuous heating, and then the saturated solution was cooled to room temperature.

136

After filtration, CuSO4·5H2O could be easily separated from K2SO4 solution because

137

of their differences in solubility. The proposed flow chart for Cu0 recovery from

138

WPCB powder is shown in Figure 1.

7



Page 8 of 30

WPCBs (Cu0) Crushing and sorting WPCB powders (Cu0) Solid oxidant (K2S2O8)

Stage I

Mechanochemical processing Reaction products (CuSO4 + CuO + K3H (SO4)2) Stage II Water leaching Vacuum filtration

Residues

Leaching products (K2Cu(SO4)2 ·6H2O) Stage III Cooling recrystallization CuSO4·5H2O

139

K2SO4

140

Figure 1 Proposed flow chart for Cu0 recovery from WPCB powder

141

■ Analytical methods The percentage of Cu recovery after the mechanochemical

142

processing and water leaching process was calculated as follows:

143

Cu recovery percentage (%) = W1/W2 × 100%

144

where W1 is the Cu element in the leaching solution (g); and W2 is the original Cu

145

element in the WPCB powders (g).

146

The residual ratio of K2S2O8 after the mechanochemical and water leaching processes

147

was calculated as follows:

148

Residual ratio of K2S2O8 = C/C0 × 100%

149

where C is the measured S2O82− residual amount in the leaching solution (g); and C0 is

150

the initial amount of S2O82− in the starting material of K2S2O8 (g).

(1)

(2)

8


Page 9 of 30


151

Metal contents of the WPCB powder were determined using an inductively

152

coupled

153

PerkinElmer, USA) after digestion with a HNO3-HCl-HClO4-HF mixture. The

154

concentrations of copper ions in the leaching solution were measured using ICP-OES,

155

and the concentrations of S2O82− in the leaching solution were measured using the

156

potassium iodide colorimetric method (Content S1) with a Lambda-14 UV

157

spectrophotometer (PerkinElmer Inc., Waltham, MA). The error bars in all data plots

158

represent the maximum and the minimum values of triplicate runs.

plasma-optical

emission

spectrometer

(ICP-OES,

OPTIMA

8300,

159

XPS analysis was conducted using a PHI Quantera SXM (PHI-5300/ESCA,

160

ULVAC-PHI, Inc, Japan). FT-IR spectra (Thermo Scientific Nicolet iS10 FR-IR

161

Spectrometer, USA) were employed for the identification of relevant characteristic

162

bands of different reaction products. The crystalline phases of samples before and

163

after the mechanochemical processing were characterized with XRD (PW 1700,

164

Philips, USA) using Cu Kα radiation with 30 kV voltage and 30 mA current. The

165

morphological properties of the K2S2O8/WPCBs samples before and after the

166

mechanochemical processing were examined with a scanning electron microscope

167

with energy dispersive X-ray analysis (SEM-EDAX, Hitachi S-3000N, Japan). The

168

carbon and sulfur contents in various solid samples were analyzed using a

169

high-frequency infrared carbon and sulfur analyzer (HCS-140, Shanghai DeKai

170

Instrument Co., Ltd. China).

171

■ RESULTS AND DISCUSSION

172

■

173

before and after mechanochemical processing were first analyzed with XPS. Figure

174

2a shows that the characteristic peaks of Cu 2p and S 2p could be observed from the

The oxidation of Cu0 The conversion of Cu0 in the K2S2O8/WPCBs samples

9



175

K2S2O8/WPCBs samples after mechanochemical processing. Figure 2b is the XPS

176

spectra of Cu 2p in the K2S2O8/WPCBs samples before and after mechanochemical

177

processing. A significant shake-up peak can be observed at the side of high binding

178

energy of Cu 2p3/2 in the K2S2O8/WPCBs sample after the mechanochemical

179

processing, and a significant satellite peak is observed at EB = 940-950 eV, implying

180

that Cu2+ occupied the main valent states in the K2S2O8/WPCBs sample after

181

mechanochemical processing.45 Further fitting results of Cu 2p XPS high-resolution

182

spectra in Figure 2c show that the peak of Cu 2p3/2 was split into three components,

183

with binding energies of 932.8, 933.5, and 935.7 eV, which correspond to the binding

184

energies of CuO, CuO, and CuSO4, respectively. In addition, the intensity peak of Cu

185

2p1/2 binding energy in 953.0 eV also corresponds to the binding energy of CuO,

186

indicating that the Cu0 in the WPCB powder was converted into CuO and CuSO4 by

187

mechanochemical processing with K2S2O8. From the fitting result of S 2p XPS spectra

188

of Figure 2d, the characteristic peaks of sulfate occurred at 169.2 and 170.1 eV in the

189

S 2p spectra of the ball-milling sample at 400 rpm at a reaction time of 4 h. Therefore,

190

Cu0 in the WPCB powder was converted into CuO and CuSO4 after mechanochemical

191

processing. Furthermore, the possible decomposition products of K2S2O8 after

192

mechanochemical processing were conjectured to be sulfates, a speculation confirmed

193

by XRD and FT-IR analysis.

10


Page 10 of 30

Page 11 of 30


(b)

O1s

S2p

Cu2p

C1s O1s

After reaction

C1s

Cu2p

Cu2p1/2

Cu 2p3/2

Intensity (a.u.)

Intensity (a.u.)

(a)

Shake-up peak After reaction

Before reaction

(c)

200

400 600 800 Binding energy (eV)

1200 930

(d)

Cu2p

Cu2p3/2 CuO (932.8 eV)

Intensity (a.u.)

1000

CuO (953.0 eV)

CuO (933.5 eV) CuSO4

940 950 Binding energy (eV)

Cu2p1/2

(935.7 eV)

960

S2p Sulfate (169.2 eV)

Intensity (a.u.)

0

Before reaction

Sulfate (170.1 eV)

Shake-up peak 930

940 950 Binding energy (eV)

960

166

168 170 172 Binding energy (eV)

174

194 195

Figure 2 XPS spectra of K2S2O8/WPCBs samples before and after mechanochemical

196

processing (Conditions: ball-milling time of 4 h, K2S2O8/WPCBs mass ratio of 3:2,

197

ball-to-powder mass ratio of 60:1, and rotary speed of 400 rpm). (a) full spectra

198

analysis; (b) Cu 2p XPS spectra before and after mechanochemical processing; (c)

199

fitting result of Cu 2p XPS high-resolution spectra of the sample after

200

mechanochemical processing; and (d) fitting result of S 2p XPS high-resolution

201

spectra of the sample after mechanochemical processing.

202

■

203

show that the diffraction peaks of Cu0 in the K2S2O8/WPCB sample before

204

mechanochemical processing were difficult to identify due to a much stronger

205

diffraction peak intensity of K2S2O8, compared to Cu0. After mechanochemical

206

processing at different speeds for 4 h, the diffraction peaks of K2S2O8 gradually

207

weakened. The decrease of diffraction peak intensities can be attributed to the grain

Decomposition of potassium persulfate The XRD patterns in Figure 3a

11



Page 12 of 30

208

refinement and lattice distortion of the mixture under the action of mechanical force.46

209

As shown in Figure 3b, the sample after ball-milling at 400 rpm for 4 h was identified

210

as K3H(SO4)2 (a mixture of KHSO4·K2SO4), implying that the organic compounds in

211

the WPCB powder were also involved in the mechanochemical processing. Further

212

FT-IR analysis (Figures S2a and S2b) shows that compared with WPCB powder,

213

K2S2O8 had relatively stronger characteristic peaks, so that the characteristic bands of

214

K2S2O8 mainly occurred in the K2S2O8/WPCBs sample before the mechanochemical

215

processing (Figure S2c). After mechanochemical processing at different speeds, the

216

bending vibrations at m = 592.7 and 703 cm−1 appearing in the K2S2O8/WPCBs

217

sample after 400 rpm can be attributed to the medium characteristic absorption peaks

218

of SO42−. The symmetric stretching vibrations appearing in the K2S2O8/WPCBs

219

sample after 400 rpm at v = 1052 and 1210 cm−1 can be attributed to the strong

220

characteristic absorption peaks of SO42− (Figure S2d-S2g). This result strongly

221

confirms that the decomposition products of K2S2O8 after mechanochemical

222

processing with WPCB powder were mainly sulfates. The SEM images of the

223

K2S2O8/WPCB samples before and after the mechanochemical processing are shown

224

in Figure S3.

225

It is well known that K2S2O8 can be converted to KHSO4 and O2 in water at

226

temperatures above 60 oC (2K2S2O8 + 2H2O → 4KHSO4 + O2↑), and the local

227

chemical temperature of the mechanochemical processing could reach 1000 oC or

228

even higher.32,

229

elementary C, H, and O, the production of KHSO4 may be a result of the solid-solid

230

reaction of K2S2O8 with the epoxy resin. Epoxy resin containing the C, H, and O

231

elements in WPCB powder, therefore, played the role of hydrogen donor: 47-49

232

2K2S2O8 + 2H2O (CnHmOy) → 4KHSO4 + O2 (g)

34

Since the composition of the epoxy resin (CnHmOy) is mainly

12


(R1)

Page 13 of 30


233

The verification experiments in Figure S4 showed that the presence of pure epoxy

234

resin alone or with WPCB powder could significantly increase the production of

235

sulfate, confirming that the hydrogen in CnHmOy could be used as a hydrogen donor

236

for promoting the conversion of K2S2O8 to KHSO4.

Intensity (a.u.)

400 rpm 300 rpm 200 rpm



20

237

 

30 40 50 2 Theta (degree)

 K3H(SO4)2

     



JCPDS No: 01-087-1987

 

400 rpm 

 K 2S 2O 8  

10

100 rpm





(b)

Intensity (a.u.)

(a)

0 rpm 70 10

60

20

30 40 50 2 Theta (degree)

60

238

Figure 3 (a) XRD patterns of the K2S2O8/WPCB sample before and after

239

mechanochemical processing at different speeds (Conditions: ball-milling time of 4 h,

240

K2S2O8/WPCB mass ratio of 3:2, and ball-to-powder mass ratio of 60:1); (b) XRD

241

pattern of the K2S2O8/WPCB sample after mechanochemical processing at 400 rpm

242

(enlarged view).

243

■

244

during the water leaching process can be attributed to the effect of H+ in the leaching

245

solution, as shown in Eq. (R2):

246

CuO + 2KHSO4 = CuSO4 + K2SO4 + H2O

247

Figure 4a indicates that Cu leaching from the K2S2O8/WPCB mechanochemical

248

processing product is a very fast process. When the temperature reaches 25 oC, only

249

9.0 min are required to reach a Cu leaching efficiency of 99.8 wt%. During the

250

ball-milling process, mechanical energy is transmitted to the materials in the pot by

Leaching kinetics of copper species The rapid dissolution of Cu species

(R2)

13


70


251

the grinding balls. Meanwhile, collisions at varying strengths and frequencies could

252

initiate physical and chemical reactions. Due to the distortion of the lattice in the

253

internal structure of the materials caused by the mechanical force activation, a part of

254

the mechanical energy is stored in the mineral crystal structure, promoting Cu

255

leaching. Besides, raising the leaching temperature can obviously promote Cu

256

leaching from the mechanochemical processing products. This result can be attributed

257

to the accelerated reaction process and the mass transfer process in the solution.

258

The kinetics of the Cu leaching process can be described by a shrinking nucleus

259

model. This model can be divided into diffusion control, chemical reaction control,

260

and mixed reaction control, according to the different control steps. Figure 4b and

261

Table S4 indicate that the kinetic equation (1-2/3α-(1-α)1/3=kt; α is the leaching

262

percentage of Cu; k is the diffusion rate constant; and t is the reaction time) of

263

diffusion control at different leaching temperatures presented a sound linear

264

regression relation with time, indicating that the leaching of Cu from the

265

mechanochemical processing products follows the shrinking nucleus model of

266

diffusion control.

267

Based on the diffusion rate constant (k, min-1) of Cu leaching at different leaching

268

temperatures, a linear fitting relation between lnk and 1,000/T was plotted. Figure 4c

269

indicates that the slope between lnk and 1/T was -1847.0. According to the Arrhenius

270

equation, the apparent activation energy was Ea = 15.4 kJ/mo1. This value shows that

271

the Cu leaching from mechanochemical processing products belonged to solid-film

272

diffusion control. Figure S5 indicates that with the disappearance of diffraction peaks

273

of the metallic copper phase, Cu0 had been successfully leached from the WPCB

274

powder after the mechanochemical processing and water leaching processes.

14


Page 14 of 30

Page 15 of 30


275

Therefore, after filtration and separation from the residue, the final products recovered

276

from the leaching solution should be CuSO4 and K2SO4. (a)

0.6

(b)

25 oC Adj.R2= 0.9946 35 oC Adj.R2= 0.9974 45 oC Adj.R2= 0.9980 55 oC Adj.R2= 0.9983

1/3

80

1-2/3α-(1-α)

Cu leaching percentage (wt%)

100

60

25oC 35oC 45oC 55oC

40 20 0

0.4

0.2

0.0

0

1

2

3 4 5 6 7 Leaching time (min) -2.0

8

9

0

1 2 3 4 Leaching time (min)

5

(c)

InK

-2.2

-2.4 Slope = -1847.0 Ea = 15.4 kJ/mol

-2.6

R2-Square = 0.9173 3.0

3.1

3.2 1,000/T

277

3.3

3.4

278

Figure 4 (a) Leaching percentage of Cu species from the K2S2O8/WPCB

279

mechanochemical processing product under different temperatures; (b) kinetic curves

280

for different leaching temperatures; (c) Arrhenius curves plot of the leaching reaction

281

(Conditions: ball-milling time 4 h, K2S2O8/WPCB mass ratio 3:2, ball-to-powder

282

mass ratio 60:1, and rotary speed 400 rpm)

283

■

284

solution after vacuum filtration in Figure 5a shows that the crystallization product of

285

the separated leaching solution was mainly a composite sulfate salt (cyanochroite,

286

K2Cu(SO4)2·6H2O; JCPDS No:96-901-2781). This result is consistent with the above

287

characterization analysis. CuSO4 could be effectively separated from the K2SO4

Separation of cupric sulphate The crystallization of the separated leaching

15



Page 16 of 30

288

solution by cooling recrystallization, because of the difference in the solubility of

289

these two sulfate compounds (Figure S6). The XRD pattern in Figure 5b shows that

290

the CuSO4·5H2O products separated by cooling recrystallization agreed well with the

291

XRD diffraction peaks in the standard cards (CuSO4·5H2O, JCPDS No: 01-072-2355).

292

The SEM image shows that the CuSO4·5H2O product presented an irregular sheet

293

stacking structure (Figure 5c). EDAX analysis (Figure 5d) shows that the atomic

294

percentages of Cu, S, and O in the CuSO4·5H2O product were 17.89, 15.17, and 66.94

295

wt%, respectively—close to a pure CuSO4·5H2O product. Therefore, after a three-step

296

sequential process, including mechanochemical processing, water leaching, and

297

recrystallization, Cu0 in the WPCB powders was successfully recovered in the form of

298

CuSO4·5H2O product.

(a)

(b)

Copper sulfate hydrate [CuSO4·5H2O]

Intensity (a.u.)

Intensity (a.u.)

Cyanochroite [K2Cu(SO4)2·6H2O]

JCPDS No: 96-901-2781 10

20

30 40 50 2Theta (degree)

60

JCPDS No:01-072-2355 70

10

20

30 40 50 2Theta (degree)

(d)

(c)

60

70

Area I

Area I

(b)

Element

Atomic percentage

Cu

17.89 wt%

S

15.17 wt%

O

66.94 wt%

10 μm

299 300

Figure 5 (a) XRD pattern of the crystallization of the separated leaching solution

301

(obtained from WPCB particle size = 0.6-0.8 mm), (b) XRD pattern, (c) SEM image,

16


Page 17 of 30


302

and (d) EDAX analysis of the obtained CuSO4·5H2O product (Conditions: reaction

303

time of 4 h, K2S2O8/Cu0 mass ratio of 30:1, and rotary speed of 400 rpm).

304

■

305

metals, organic materials, and inorganic materials in WPCB powder will increase

306

during the mechanochemical processing, resulting in an increase of solid reactivity.

307

The mechanochemical processing can not only reduce the activation energy of

308

chemical reaction, but can also induce a variety of solid chemical reactions.

309

According to the state of the raw materials (K2S2O8/WPCB powder), the possible

310

reactions in the ZrO2 pot during the mechanochemical processing can be divided into

311

a solid-solid reaction and a solid-gas reaction.46 The entire possible reaction paths of

312

Cu0 are shown in Figure 6.

Exploration of the possible reaction paths of Cu0 The inner energies of

313 314

Figure 6 Schematic diagram of the proposed Cu0 recovery paths

315

(Note: R1-R6 in Figure 6 represent reactions of Eq.(R1)–(R6)) 17



Page 18 of 30

316

In the mechanochemical processing stage (Figure 6a-I), many possible reaction

317

paths for the K2S2O8 and Cu0 were induced under the mechanical force. Based on the

318

identified K2S2O8/WPCB reaction products, a schematic diagram of the proposed Cu0

319

reaction paths is shown in Figure 6b. The possible reaction paths for Cu0 conversion

320

can be summarized as follows:

321

(1) Cu0 could react with K2S2O8 to produce CuSO4 directly due to the redox activities

322

of K2S2O8 as an oxidant and Cu0 as a reducing agent.

323

Cu + K2S2O8 → CuSO4 + K2SO4

324

(2) Cu0 could react with K2S2O8 to form CuO and SO3. However, in a closed reaction

325

system, the new-generated CuO may be corroded by SO3, and CuSO4 will ultimately

326

be generated.

327

Cu + K2S2O8 → CuO + SO3 (g) + K2SO4

328

The results of the carbon and sulfur analyzer in Figure S7 show that the carbon and

329

sulfur percentages of the K2S2O8/WPCBs samples after treatment at different rotary

330

speeds decreased continuously, indicating that the carbon and sulfur species in the

331

K2S2O8/WPCBs sample were partially involved in the mechanochemical processing

332

and were converted to gaseous compounds. The sulfur element conservation of the

333

K2S2O8/WPCBs sample after treatment at different rotary speeds also indicates that

334

some sulfur species was converted into gaseous sulfur compounds (Figure S4b).

335

Nevertheless, the release of gaseous sulfur compounds can be effectively controlled

336

by absorption with the Ca(OH)2 solution.

337

(3) Epoxy resin has a high content of reducible carbon materials. CuSO4 therefore

338

reacted with carbon materials to produce CuO, CO, and SO2.

339

C + CuSO4 → CuO + CO (g) + SO2 (g)

(R3)

(R4)

(R5)

18


Page 19 of 30


340

During the water leaching stage (Figure 6a-II), the produced CuSO4 can be

341

dissolved directly in pure water. H+, generated from the hydrolysis of KHSO4, was

342

responsible for the rapid leaching of CuO in solution. CuO was therefore converted to

343

CuSO4 by reacting with KHSO4.

344

In the recrystallization stage (Figure 6a-III), with the difference in solubility

345

between K2SO4 and CuSO4, the separation of CuSO4 can be successfully realized by

346

evaporation recrystallization. Finally, after three steps of transformation, Cu0 was

347

converted to a high-value CuSO4·5H2O product.

348

■

349

The effects of different mechanochemical processing parameters, including time,

350

K2S2O8/WPCBs mass ratio, ball-to-powder mass ratio, and ball-milling speed, on Cu

351

recovery and K2S2O8 decomposition percentage, were studied. The left vertical axes

352

in Figure 7 show the Cu recovery percentages for different mechanochemical

353

processing parameters. In the beginning of the mechanochemical processing, the

354

reactant concentrations of both the Cu in the WPCB powder and the K2S2O8 were

355

high, which would contribute to more effective contacts and hence faster reaction

356

rates (Figure 7a). At the end of 4 h, the Cu recovery percentage reached 90.1 wt%.

357

Obviously, mechanochemical processing significantly promoted the leaching of Cu

358

species from WPCB powder. Beyond that time, the solid materials in the ball mill pot,

359

firmly adhered to each other by the continuous impact of mechanical force, were not

360

easily dispersed during the process of water leaching and thus the Cu recovery

361

percentage decreased gradually.

Influence of different mechanochemical parameters on Cu0 recovery

362

Figure 7b shows that the Cu recovery percentage reached the maximum of 99.6

363

wt% when the mass ratio of K2S2O8 to the WPCBs was 3:2. With a longer

364

ball-milling time and a higher K2S2O8/WPCBs mass ratio, the solid materials in the 19



365

ball mill pot were also prone to cohere, thus affecting the subsequent water leaching

366

process, which was not favorable for Cu species leaching.

367

Figure 7c shows that the Cu recovery percentage increased with the

368

ball-to-powder mass ratio when the ratio ranged from 20:1 to 60:1, because more balls

369

led to more collisions per unit of time, resulting in the transmission of more energy to

370

the materials. When the ball-to-powder mass ratio exceeded 60:1, less effective

371

collisions occurred since more reactor space was occupied by the larger number of

372

grinding balls, which had negative influences on the interaction between Cu and

373

K2S2O8. Thus, the optimal ball-to-powder mass ratio was proposed to be 60:1.

374

It is generally believed that a higher rotary speed will lead to higher specific

375

collision energy on a substance. The specific collision energy can be expressed in the

376

equation below: 50 n

1 mV j2 j 1 2W

377

Ew  

378

(3)

379

where Ew is the specific collision energy (KJ); Vj is the relative speed between balls or

380

between the balls and the wall (m/s); m is the ball mass (g); n is the collision

381

frequency per second; and W is the sample mass in the ball-milling pot (g). The

382

specific collision energy, Ew, would increase with increase in the ball mass (m) and

383

the relative speed (Vj). Figure 7d shows that the Cu recovery percentage was

384

proportional to the specific collision energy. However, too high a rotary speed would

385

lead to more coherence of the K2S2O8/WPCBs materials, causing an adverse effect on

386

the Cu recovery. An optimal rotary speed for Cu recovery was thus chosen to be 400

387

rpm.

20


Page 20 of 30

Page 21 of 30


388

In summary, the optimal mechanochemical processing parameters for Cu recovery

389

were a ball-milling time of 4 h, a K2S2O8/WPCBs mass ratio of 3:2, a ball-to-powder

390

mass ratio of 60:1, and a rotary speed of 400 rpm. Under the optimal conditions, the

391

Cu recovery percentage could be as high as 99.8 wt%. The valence change and

392

leaching behaviors of the impurity metals are shown in Figure S8 and Figure S9,

393

respectively. The XPS results in Figure S8 show that Sn0 and Pb0 in the raw material

394

WPCB powders were oxidized to oxides under the effect of mechanical force and

395

K2S2O8. The leaching results in Figure S9 show that the leaching percentages of Ca,

396

Sn and Pb were lower than 2.8, 0.01, and 0.77 wt%. Thus, the proposed

397

mechanochemical process for Cu0 recycling from WPCBs exhibited excellent

398

selectivity.

399

It is also desirable to minimize the residual ratio of K2S2O8. The right vertical axes

400

in Figure 7 show this residual ratio in the presence of WPCB powder under different

401

mechanochemical processing parameters. Under the optimal mechanochemical

402

processing conditions for maximum Cu recovery, the residual ratio of K2S2O8 in the

403

presence of WPCB powder was only 0.10.

21



0.4

60

0.2 40

0

1

2

3

4

5

0.0

6

0.8 0.6 80

0.4 0.2

60

0.0 0

1

(c)

1.0 0.8 0.6

80

0.4 0.2

60

0.0 20

40 60 80 Ball-to-powder mass ratio

100

Recovery percentage of Cu (wt%)

Time (h) 100

1.0

2 3 4 K2S2O8/WPCBs mass ratio

(d)

100

1.0 0.8

80

0.6 0.4

60 0.2 40

0.0 100

200 300 400 500 Ball-milling speed (rpm)

404 405

Figure 7 Effect of (a) time (Conditions: K2S2O8/WPCBs mass ratio of 4:1,

406

ball-to-powder mass ratio of 60:1 and rotary speed of 400 rpm), (b) K2S2O8/WPCBs

407

mass ratio (Conditions: reaction time of 4 h, ball-to-powder mass ratio of 60:1 and

408

rotary speed of 400 rpm), (c) ball-to-powder mass ratio (Conditions: reaction time of

409

4 h, K2S2O8/WPCBs mass ratio of 3:2 and rotary speed of 400 rpm), and (d)

410

ball-milling speed (Conditions: reaction time of 4 h, K2S2O8/WPCBs mass ratio of 3:2

411

and ball-to-powder mass ratio of 60:1), on Cu recovery percentage and K2S2O8

412

decomposition percentage.

413

■ Environmental implications

414

The direct conversion of Cu0 into high value-added products may be a more

415

promising approach for WPCBs recycling. This study therefore designed a three-step

416

sequential process for converting Cu0 into a CuSO4·5H2O product. The engineering

417

application results in Figure S10 show that the Cu recovery percentage generally 22


Residual ratio of K2S2O8 (C/C0)

0.6

(b)

100


0.8 80


1.0

K 2S 2O 8 Recovery percentage of Cu (wt%)

(a)




Cu 100

Page 22 of 30

Page 23 of 30


418

exceeded 98 wt%, and the residual ratio of K2S2O8 was negligible, showing that the

419

proposed mechanochemical processing and water leaching process is a promising

420

strategy for Cu recovery from WPCB powder of varying particle sizes. A

421

comprehensive process comparison in Table S5 present that the highlight of the

422

proposed mechanochemical/leaching/recrystallization process for Cu0 recovery from

423

WPCBs is the production of high-value CuSO4·5H2O product at room temperature

424

and high-value CuSO4·5H2O products. Furthermore, economic evaluation in Table S6

425

shows that the proposed strategy could benefit from the high-value products of

426

CuSO4·5H2O and K2SO4 as well as the low energy consumption of mechanochemical

427

process, the proposed three-step process for Cu0 recovery from WPCBs presents

428

considerable economic profits at the current laboratory stage, and could be considered

429

economically favorable and feasible for practical applications.

430

In summary, Cu0 in the WPCB powder was successfully recovered in the form of

431

CuSO4·5H2O after a three-step process: mechanochemical processing, water leaching,

432

and cooling recrystallization. The proposed strategy provides a feasible solution for

433

large-scale conversion of Cu0 in WPCB powder into CuSO4·5H2O products.

434

■ SUPPORTING INFORMATION

435

Supporting Information is available free of charge via Internet at

436

http://pubs.acs.org.

437

■ AUTHOR INFORMATION

438

Co-Corresponding authors*

439

* Prof. Jiakuan Yang

440

Tel: 86+27+87792102.

441

E-mail: [email protected] (Prof. Jiakuan Yang).

442

* Associate Prof. Huijie Hou 23



443

Tel.: +86-27-87793948

444

E-mail: [email protected] (Associate Prof. Huijie Hou).

445

Notes

446

The authors declare no competing financial interest.

447

■ ACKNOWLEDGMENTS

448

The research is supported by the China Postdoctoral Science Foundation

449

(2016M602306), the Foundation of State Key Laboratory of Coal Combustion

450

(FSKLCCA1604), and National Key Research and Development Program of China

451

(2018YFC1900105). Additionally, we would also like to thank the Analytical and

452

Testing Center of Huazhong University of Science and Technology for providing

453

experimental measurements.

454

■ REFERENCE

455

1.

456

Petersen, J., E-waste in the international context – A review of trade flows,

457

regulations, hazards, waste management strategies and technologies for value

458

recovery. Waste Manage. 2018, 82, 258-275.

459

2.

460

comparative evaluation of China and India. Renewable and Sustainable Energy Rev.

461

2017, 76, 434-447.

462

3.

463

Disconnecting, Resource Recovery, and Pollution Control. Environ. Sci. Technol.

464

2015, 49, (2), 721-733.

465

4.

466

printed circuit boards (WPCBs) using molten salts. J. Hazard. Mater. 2012, 213-214,

Ilankoon, I. M. S. K.; Ghorbani, Y.; Chong, M. N.; Herath, G.; Moyo, T.;

Awasthi, A. K.; Li, J., Management of electrical and electronic waste: A

Wang, J.; Xu, Z., Disposing and Recycling Waste Printed Circuit Boards:

Flandinet, L.; Tedjar, F.; Ghetta, V.; Fouletier, J., Metals recovering from waste

24


Page 24 of 30

Page 25 of 30


467

485-490.

468

5.

469

Dissolution of Brominated Epoxy Resins by Dimethyl Sulfoxide To Separate Waste

470

Printed Circuit Boards. Environ. Sci. Technol. 2013, 47, (6), 2654-2660.

471

6.

472

recovery from waste printed circuit boards through batch sub/supercritical water

473

treatments. Chem. Eng. J. 2013, 219, 131-136.

474

7.

475

Electronic Waste Disassembly with Industrial Waste Heat. Environ. Sci. Technol.

476

2013, 47, (21), 12409-12416.

477

8.

478

Cost-Effective Than Virgin Mining. Environ. Sci. Technol. 2018, 52, (8), 4835-4841.

479

9.

480

of current technologies and treatment status in China. J. Hazard. Mater. 2009, 164,

481

(2), 399-408.

482

10. Duan, H.; Li, J.; Liu, Y.; Yamazaki, N.; Jiang, W., Characterization and

483

Inventory of PCDD/Fs and PBDD/Fs Emissions from the Incineration of Waste

484

Printed Circuit Board. Environ. Sci. Technol. 2011, 45, (15), 6322-6328.

485

11. Duan, H.; Li, J.; Liu, Y.; Yamazaki, N.; Jiang, W., Characterizing the emission of

486

chlorinated/brominated dibenzo-p-dioxins and furans from low-temperature thermal

487

processing of waste printed circuit board. Environ. Pollut. 2012, 161, 185-191.

488

12. Li, T.-Y.; Zhou, J.-F.; Wu, C.-C.; Bao, L.-J.; Shi, L.; Zeng, E. Y., Characteristics

489

of Polybrominated Diphenyl Ethers Released from Thermal Treatment and Open

490

Burning of E-Waste. Environ. Sci. Technol. 2018, 52, (8), 4650-4657.

491

13. Hadi, P.; Xu, M.; Lin, C. S. K.; Hui, C.-W.; McKay, G., Waste printed circuit

Zhu, P.; Chen, Y.; Wang, L.; Qian, G.; Zhang, W. J.; Zhou, M.; Zhou, J.,

Xing, M.; Zhang, F.-S., Degradation of brominated epoxy resin and metal

Chen, M.; Wang, J.; Chen, H.; Ogunseitan, O. A.; Zhang, M.; Zang, H.; Hu, J.,

Zeng, X.; Mathews, J. A.; Li, J., Urban Mining of E-Waste is Becoming More

Huang, K.; Guo, J.; Xu, Z., Recycling of waste printed circuit boards: A review

25



492

board recycling techniques and product utilization. J. Hazard. Mater. 2015, 283,

493

234-243.

494

14. Guo, J.; Guo, J.; Xu, Z., Recycling of non-metallic fractions from waste printed

495

circuit boards: A review. J. Hazard. Mater. 2009, 168, (2), 567-590.

496

15. Wu, J.; Li, J.; Xu, Z., Electrostatic Separation for Recovering Metals and

497

Nonmetals from Waste Printed Circuit Board: Problems and Improvements. Environ.

498

Sci. Technol. 2008, 42, (14), 5272-5276.

499

16. Hou, S.; Wu, J.; Qin, Y.; Xu, Z., Electrostatic Separation for Recycling Waste

500

Printed Circuit Board: A Study on External Factor and a Robust Design for

501

Optimization. Environ. Sci. Technol. 2010, 44, (13), 5177-5181.

502

17. Ping, Z.; ZeYun, F.; Jie, L.; Qiang, L.; GuangRen, Q.; Ming, Z., Enhancement of

503

leaching copper by electro-oxidation from metal powders of waste printed circuit

504

board. J. Hazard. Mater. 2009, 166, (2), 746-750.

505

18. Fogarasi, S.; Imre-Lucaci, F.; Imre-Lucaci, Á.; Ilea, P., Copper recovery and gold

506

enrichment from waste printed circuit boards by mediated electrochemical oxidation.

507

J. Hazard. Mater. 2014, 273, 215-221.

508

19. Zhan, L.; Xu, Z., Application of Vacuum Metallurgy to Separate Pure Metal from

509

Mixed Metallic Particles of Crushed Waste Printed Circuit Board Scraps. Environ. Sci.

510

Technol. 2008, 42, (20), 7676-7681.

511

20. Zhou, Y.; Wu, W.; Qiu, K., Recycling of organic materials and solder from waste

512

printed circuit boards by vacuum pyrolysis-centrifugation coupling technology. Waste

513

Manage. 2011, 31, (12), 2569-2576.

514

21. Yang, H.; Liu, J.; Yang, J., Leaching copper from shredded particles of waste

515

printed circuit boards. J. Hazard. Mater. 2011, 187, (1), 393-400.

516

22. Akcil, A.; Erust, C.; Gahan, C. S.; Ozgun, M.; Sahin, M.; Tuncuk, A., Precious 26


Page 26 of 30

Page 27 of 30


517

metal recovery from waste printed circuit boards using cyanide and non-cyanide

518

lixiviants – A review. Waste Manage. 2015, 45, 258-271.

519

23. Li, K.; Xu, Z., Application of Supercritical Water To Decompose Brominated

520

Epoxy Resin and Environmental Friendly Recovery of Metals from Waste Memory

521

Module. Environ. Sci. Technol. 2015, 49, (3), 1761-1767.

522

24. Zhu, N.; Xiang, Y.; Zhang, T.; Wu, P.; Dang, Z.; Li, P.; Wu, J., Bioleaching of

523

metal concentrates of waste printed circuit boards by mixed culture of acidophilic

524

bacteria. J. Hazard. Mater. 2011, 192, (2), 614-619.

525

25. Yang, Y.; Chen, S.; Li, S.; Chen, M.; Chen, H.; Liu, B., Bioleaching waste

526

printed circuit boards by Acidithiobacillus ferrooxidans and its kinetics aspect. J.

527

Biotechnol. 2014, 173, 24-30.

528

26. Xiang, Y.; Wu, P.; Zhu, N.; Zhang, T.; Liu, W.; Wu, J.; Li, P., Bioleaching of

529

copper from waste printed circuit boards by bacterial consortium enriched from acid

530

mine drainage. J. Hazard. Mater. 2010, 184, (1), 812-818.

531

27. Xiu, F.-R.; Qi, Y.; Zhang, F.-S., Recovery of metals from waste printed circuit

532

boards by supercritical water pre-treatment combined with acid leaching process.

533

Waste Manage. 2013, 33, (5), 1251-1257.

534

28. Huang, J.; Chen, M.; Chen, H.; Chen, S.; Sun, Q., Leaching behavior of copper

535

from waste printed circuit boards with Brønsted acidic ionic liquid. Waste Manage.

536

2014, 34, (2), 483-488.

537

29. Zhang, Z.; Zhang, F.-S., Synthesis of cuprous chloride and simultaneous recovery

538

of Ag and Pd from waste printed circuit boards. J. Hazard. Mater. 2013, 261,

539

398-404.

540

30. Chen, M.; Zhang, S.; Huang, J.; Chen, H., Lead during the leaching process of

541

copper from waste printed circuit boards by five typical ionic liquid acids. J. Cleaner 27



542

Prod. 2015, 95, 142-147.

543

31. Xiu, F.-R.; Qi, Y.; Zhang, F.-S., Co-treatment of waste printed circuit boards and

544

polyvinyl chloride by subcritical water oxidation: Removal of brominated flame

545

retardants and recovery of Cu and Pb. Chem. Eng. J. 2014, 237, 242-249.

546

32. Tan, Q.; Li, J., Recycling Metals from Wastes: A Novel Application of

547

Mechanochemistry. Environ. Sci. Technol. 2015, 49, (10), 5849-5861.

548

33. Wang, M.; Tan, Q.; Chiang, J. F.; Li, J., Recovery of rare and precious metals

549

from urban mines—A review. Front. Env. Sci. Eng. 2017, 11, (5), 1.

550

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

551

from second-hand resources: a technical overview. Environ. Sci-proc. Imp. 2015, 17,

552

(9), 1522-1530.

553

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

554

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

555

36. Zhang, Z.-Y.; Zhang, F.-S.; Yao, T., An environmentally friendly ball milling

556

process for recovery of valuable metals from e-waste scraps. Waste Manage. 2017, 68,

557

490-497.

558

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

559

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

560

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

561

38. Sasai, R.; Kubo, H.; Kamiya, M.; Itoh, H., Development of an Eco-Friendly

562

Material Recycling Process for Spent Lead Glass Using a Mechanochemical Process

563

and Na2EDTA Reagent. Environ. Sci. Technol. 2008, 42, (11), 4159-4164.

564

39. Guan, J.; Li, Y.; Guo, Y.; Su, R.; Gao, G.; Song, H.; Yuan, H.; Liang, B.; Guo, Z.,

565

Mechanochemical process enhanced cobalt and lithium recycling from wasted

566

lithium-ion batteries. ACS Sustainable Chem. Eng. 2016, 5, (1), 1026-1032. 28


Page 28 of 30

Page 29 of 30


567

40. Fan, E.; Li, L.; Zhang, X.; Bian, Y.; Xue, Q.; Wu, J.; Wu, F.; Chen, R., Selective

568

Recovery of Li and Fe from Spent Lithium-Ion Batteries by an Environmentally

569

Friendly Mechanochemical Approach. ACS Sustainable Chem. Eng. 2018, 6, (8),

570

11029-11035.

571

41. Zhang, L.; Xu, Z., A review of current progress of recycling technologies for

572

metals from waste electrical and electronic equipment. J. Cleaner Prod. 2016, 127,

573

19-36.

574

42. Tan, Q.; Deng, C.; Li, J., Enhanced recovery of rare earth elements from waste

575

phosphors by mechanical activation. J. Cleaner Prod. 2017, 142, 2187-2191.

576

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

577

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

578

Technol. 2012, 46, (7), 4109-4114.

579

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

580

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

581

Iron Phosphate Batteries through Mechanochemical Activation. ACS Sustainable

582

Chem. Eng. 2017, 5, (11), 9972-9980.

583

45. Zhao, X.; Guo, L.; Zhang, B.; Liu, H.; Qu, J., Photoelectrocatalytic Oxidation of

584

CuII–EDTA at the TiO2 Electrode and Simultaneous Recovery of CuII by

585

Electrodeposition. Environ. Sci. Technol. 2013, 47, (9), 4480-4488.

586

46. Wang, M.; Tan, Q.; Li, J., Unveiling the Role and Mechanism of

587

Mechanochemical Activation on Lithium Cobalt Oxide Powders from Spent

588

Lithium-ion Batteries. Environ. Sci. Technol. 2018, 52, (22), 13136-13143.

589

47. Nomura, Y.; Nakai, S.; Hosomi, M., Elucidation of Degradation Mechanism of

590

Dioxins during Mechanochemical Treatment. Environ. Sci. Technol. 2005, 39, (10),

591

3799-3804. 29



592

48. Zhang, T.; Huang, J.; Zhang, W.; Yu, Y.; Deng, S.; Wang, B.; Yu, G., Coupling

593

the dechlorination of aqueous 4-CP with the mechanochemical destruction of solid

594

PCNB using Fe–Ni–SiO2. J. Hazard. Mater. 2013, 250-251, 175-180.

595

49. Cagnetta, G.; Robertson, J.; Huang, J.; Zhang, K.; Yu, G., Mechanochemical

596

destruction of halogenated organic pollutants: A critical review. J. Hazard. Mater.

597

2016, 313, 85-102.

598

50. Yinglei, W.; Jianhua, Y.; Shengyong, L.; Xiaodong, L., Mechanochemical

599

decomposition of pentachlorophenol by ball milling. J. Environ. Sci. 2009, 21, (12),

600

1761-1768.

601

30


Page 30 of 30

Facile and Cost-Effective Approach for Copper Recovery from Waste

Recommend Documents