Improved Electrocoagulation Reactor for Rapid Removal of Phosphate

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An improved electrocoagulation reactor for rapid removal of phosphate from wastewater Yushi Tian, Weihua He, Xiuping Zhu, Wulin Yang, Nanqi Ren, and Bruce E. Logan ACS Sustainable Chem. Eng., Just Accepted Manuscript • Publication Date (Web): 01 Nov 2016 Downloaded from http://pubs.acs.org on November 1, 2016

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ACS Sustainable Chemistry & Engineering

1

Hollow aluminum particle in eddy current separation of

2

recovering waste toner cartridges

3 4

Jie Zhenga, Jujun Ruan a∗, Lipeng Donga , Tao Zhanga, Mingzhi Huang*b, Zhenming

5

Xuc

6 7 8 9 10 11 12

a. School of Environmental Science and Engineering, Sun Yat-Sen University, 135 Xingang Xi Road,Guangzhou,510275, People's Republic of China b. School of geography and planning, Sun Yat-Sen University, 135 Xingang Xi Road, Guangzhou, 510275, People's Republic of China c. School of Environmental Science and Engineering, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, People’s Republic of China

13 14

Abstract

15

Abundant waste toner cartridges were generated from the using of printer.

It

16

contained aluminum, plastic, steel, and toner. Waste toner cartridges will pollute

17

environment if they are not properly treated. An environment-friendly recovery line of

18

waste toner cartridges had been constructed in our previous work. Eddy current

19

separation was employed to separate aluminum particles from plastic particles of

20

crushed waste toner cartridges. However, hollow aluminum particles were existed in

21

crushed waste toner cartridges and they have a rather low separation rate from plastic

22

particles. There was little information about hollow aluminum particles in eddy

23

current separation. For improve the efficiency of eddy current separation, models of

Corresponding author: Jujun, Ruan Tel:+86 20 84113620; Fax:+86 20 84113620; E-mail: [email protected]. 1

ACS Paragon Plus Environment


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24

eddy current force and movement behaviors of hollow aluminum particles in eddy

25

current separation were established. Compared horizontal throw of hollow aluminum

26

particle to solid aluminum particle, we found hollow characters greatly decreased

27

horizontal throw (reduced about 0.03 m) of aluminum particles and destroyed the

28

separation rate. Therefore, a new compactor was designed to eliminate hollow

29

aluminum particles in crushed waste toner cartridges. This paper provided models of

30

eddy current force and movement behavior of hollow nonferrous metallic particle in

31

eddy current separation and contributed to improve the efficiency of recovery line of

32

waste toner cartridges.

33 34

Key words: Recovery, Eddy current force, Trajectory models, Improve efficiency

35 36 37

Introduction

38

Abundant e-waste has been generated from the using of electrical and electronic

39

equipment (1) in the world. Developing and undeveloped countries have been the

40

dump of e-waste, not only self-produced but also imported from developed countries

41

(2). These countries bear principal responsibility for treating e-waste. High-purity

42

precious metals, nonferrous metals, and high-quality plastics are contained in e-waste

43

(3). Recovering e-waste not only can obtain sustainable, renewable resources of

44

metals and plastics but also save the costs of energy and environment for producing

45

them. Meanwhile, vast hazardous materials (polyvinyl chloride, dechlorane plus, et al.) 2


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46

are also existed in e-waste (4, 5). If e-waste was not properly treated, heavy metals

47

and hazardous materials would expose to environment. Due to employ crude

48

technologies, heavy metals and organic pollutants had polluted the local environment

49

and human bodies (6, 7). Therefore, recovering e-waste is a crucial work of resource

50

conservation, energy renewal, and environmental protection (8-10).

51 52

Chemical methods are always considered as the preferable methods in

53

environmental remediation and resource recovery (11-13). Physical technologies are

54

the suitable treatment method of recovering e-waste (14, 15). Eddy current separation

55

is a physical technology of separating nonferrous metallic particles from others (16,

56

17). In eddy current separation, alternating eddy current is induced in nonferrous

57

metallic particle when meeting variable magnetic field. The alternating eddy current

58

causes a new magnetic field in nonferrous metallic particle. Repulsive force between

59

the two magnetic fields changes the movement of nonferrous metallic particle and

60

separates them from others. No pollutions are generated. Eddy current separation was

61

employed in mineral processing in past years (18, 19). It was also encouraged to

62

recover nonferrous metallic particles from crushed e-waste (20). In our constructed

63

environmental-friendly production line of recovering waste toner cartridges, eddy

64

current separation was employed to separate aluminum particles from crushed waste

65

toner cartridges (Figure 1a) (21).

3



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66 67 68 69

Figure 1. (a) environmental-friendly production line of recovering waste toner cartridges, (b) the structure of employed eddy current separator

70

However, nonferrous metallic particles in e-waste have great differences in size,

71

shape, and purity than minerals. Traditional eddy current separator offered low

72

separation rate. For improving separation rate, models of eddy current force and

73

movement behavior of nonferrous metallic particle in eddy current separation had

74

been established to research the influencing factors (22, 23). In the production line of

75

recovery waste toner cartridges, many hollow aluminum particles were existed in

76

crushed waste toner cartridges. The reason was that coarse crushing was employed to

77

crush waste toner cartridges and aluminum in toner cartridges had the shape of tubular.

78

These hollow aluminum particles had rather low separation rate from plastic particles.

79

Additionally, irregular movement behaviors of hollow aluminum particles also

80

destroyed the separation rate of other solid aluminum particles by impacting and

81

changing their movement in eddy current separation. How to improve the separation

82

rate of hollow aluminum particles has been the critical problem of enhancing the

83

efficiency of the production line. The eddy current force and movement behavior of 4


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84

aluminum particle in eddy current separation need to be investigated for researching

85

the influencing factors of separation rate. We found there was little information about

86

the model of eddy current force of hollow nonferrous metallic particles in eddy

87

current separation. This study provided the models of eddy current force and

88

movement behavior of hollow aluminum particles in eddy current separation of

89

recovering waste toner cartridges. Then, a compactor was designed to eliminate

90

hollow aluminum particles in crushed waste toner cartridges. This study contributes to

91

improve the efficiency of eddy current separation in the production line of recovering

92

waste toner cartridges.

93 94

Materials and methods

95

Hollow aluminum particles

96

Aluminum particles employed in this study were collected from crushed waste

97

toner cartridges. Different shapes of aluminum particles were obtained. Besides circle,

98

rectangle, and triangle flake aluminums (reported in previous work) (23), triangle

99

hollow aluminum (T0) and rectangle hollow aluminums (R0) (in Figure 2) were

100

existed in crushed aluminum material. Their sizes ranged from 15 mm to 40 mm.

101

Their physical characters were presented in Table 1. For investigating the influencing

102

of hollow of aluminum particles on separation rate, T0 and R0 were compressed to

103

solid particles (T1 and R1 in Figure 2). Physical characters of T1 and R1 were also

104

presented in Figure 2.

5



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105 106

Figure 2. Hollow and solid aluminum particles collected from crushed waste toner cartridges

107 Table 1. Characteristics of the employed aluminum particles Particles Se (cm2) V (cm3) M (g) d (cm) δ γ (S/m) T0 T1 R0 R1

2.86 4.51 3.45 5.75

0.87 0.87 1.05 1.05

2.35 2.35 2.82 2.82

0.08 0.08 0.08 0.08

0.35

6.67x105

0.2

108 109

Eddy current separator

110

The employed eddy current separator was presented in Figure 1b and Figure 1c.

111

Physical characters of eddy current separator were presented in Table 2. The separator

112

was comprised of feeding conveyor and magnetic drum. Magnetic flux of surface of

113

magnetic drum was 0.3 T, and magnetic drum was comprised of 4 pair of magnetic

114

poles. The radius of the magnetic drum was 0.096 m. Thickness of magnetic field of

115

separator was measured by teslameter and the value was 0.05m.

116 6


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Table 2. physical characters of eddy current separator Bm 0.3 T Rd 0.096 m µ0 4π×10-7 N/A2 H 0.9 m k 4 pairs η 0.05 m 117

Distribution of magnetic field flux of the eddy current separator was simulated by the

118

software of COMSOL 5.1. The simulated result was presented as Figure 3. The

119

magnetic flux density decreased as the distance increasing from magnet surface. Since

120

the weak magnetic permeability of air, gradient of magnetic flux density was very

121

great and the strong magnetic flux density mainly assembled in a small distance near

122

the separator surface. Figure 3 also showed density distribution of magnetic field was

123

different at the same latitude of the side view of magnetic drum. It showed low

124

rotation speed will provide aluminum particles longer time of weaker magnetic field

125

and will decrease the eddy current force. Thus, the rotation speed of magnetic drum

126

should be as high as possible in separation process.

127 128 129

Figure 3. (a) Side view of magnetic field distribution of magnetic drum; (b) 3-D view of magnetic field distribution of magnetic drum.

130 131 7



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132

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Results and discussion

133

In eddy current separation, the aluminum particle subjected to gravity force,

134

eddy current force, air frication, and impact force from other particles. Air frication

135

force will play a big role in determining the horizontal throw of aluminum particle in

136

eddy current separation. However, because aluminum particle kept rolling in eddy

137

current separation, air frication force was difficult to be calculated. But, it will be the

138

important work in our future. Impact force from other particles will also influence the

139

trajectory of aluminum particle. This influence also will be the future work in our

140

research.

141

Eddy current force of hollow aluminum particles in eddy current separation

142

Alternating magnetic field will be produced around the magnetic drum by the

143

rotation of eddy current separator. The magnetic flux density of the field yields to the

144

following formulas (24):

145

Br = ∑ bn ( r / R) − (2 n +1) k −1 sin(2n + 1)k (α − ωmt )

∞

(1)

n =0

146

The values of parameter R and k of the eddy current separator are 0.096m and 4 pair.

147

Since the big gaps of size and rotation speed between the particle and the magnetic

148

separator in eddy current separation, alternating magnetic flux can be supposed as

149

crossing over the aluminum flake vertically when the flake gets close to magnet. Thus,

150

the value of (α-ωmt) can be supposed as 90°. Fourier coefficient (bn) can be obtained

151

by measuring the magnetic flux density and the corresponding value of radial distance

152

(r).

153

Eddy current was induced in aluminum particle when it meeting time-depended 8


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154

magnetic field. Then, an induced time-depended magnetic field is also produced in

155

aluminum particle immediately. The induced magnetic field in the metal has the same

156

vector orientation of magnetic flux to the inducing magnet. Eddy current force will

157

generate between aluminum particle and magnets because of the same vector of

158

magnetic flux. The direction of eddy current force is determined by the position of

159

aluminum particle in magnetic field. When vertical component of eddy current force

160

is greater than gravity force, the flake will leave from the belt and levitate to be

161

accelerated forward acted by the horizontal component of eddy current force. Eddy

162

current force makes the flake detach from the conveyor belt and determine the

163

movement behavior.

164

In case I of Figure 2, aluminum particle was folded and there was a hollow in the

165

particle. From the lateral view of case I, when the magnetic flux crossed the solid part

166

of the particle, magnetic flux was called effective magnetic flux. When the magnetic

167

flux crossed the hollow part of the particle, the magnetic flux was called invalid

168

magnetic flux. The reason was that the hollow part of particle was a closing surfaces

169

and the total magnetic flux was 0. In case II of Figure 2, there was no hollow in

170

aluminum particle. Thus, all over the magnetic flux crossed the particle was effective

171

magnetic flux. In case III of Figure 2, the whole aluminum particle was became a

172

closed surface, and all the magnetic flux crossed the particle was invalid and the

173

magnetic flux was 0. Thus, the completely hollow aluminum particle will have the

174

same trajectory with plastic particle in eddy current separation.

175

As aluminum particle moving near to rotating magnetic drum, the applied 9



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176

alternating magnetic flux is supposed to cross the aluminum particle vertically since

177

the big gaps of size and speed between aluminum particle and magnetic drum.

178

Therefore, the effective crossing area (Se) of aluminum particle in case I, case II, and

179

case III were Sp-S0, Sp, and 0 respectively.

180

According to the previous constructed models of eddy current force (20), eddy current

181

force of hollow triangle aluminum particle in case I yielded to:

182

 B k (ωm R − v)γ dSe 2 S m Bmδ Tτ  FT = r 16π 2 R3   δ T = 0.35  1 τ = 2  ( sec β − 1)

183

Eddy current force of hollow rectangle aluminum particle in case I was given as:

184

 B k (ωm R − v)γ dS e 2 Sm Bmδ Rτ  FR = r 16π 2 R 3   δ R = 0.2  1 τ = 2  ( sec β − 1)

185

Due to no hollow in aluminum particle, models of eddy current force for aluminum

186

particles in case II were the same as the previous work. Eddy current force of solid

187

triangle aluminum particle was presented as:

188

 B k (ωm R − v)γ VS p Sm Bmδ Tτ  FT = r 16π 2 R 3   δ T = 0.35  1 τ = 2  ( sec β − 1)

189

Eddy current force of solid rectangle aluminum particle was expressed as:

(2)

(3)

(4)

10


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190

 B k (ωm R − v)γ VS p S m Bmδ Rτ  FR = r 16π 2 R3   δ R = 0.2  1 τ = 2  ( sec β − 1)

191

Due to no effective magnetic flux, hollow aluminum particle of case III subjected to

192

no eddy current force in eddy current separation. It meant aluminum particle of case

193

III cannot be separated from other particles in eddy current separation.

(5)

194 195

Verification of models of eddy current force of hollow aluminum particles

196

The constructed models for computing eddy current force of hollow aluminum

197

particle were tested by calculation and measure of horizontal throws of aluminum

198

particles in eddy current separation. Movement behavior of aluminum particle in eddy

199

current separation was divided into three stages: (I) entering magnetic field, (II)

200

detaching from conveyor belt surface, (II) exiting from magnetic field (see Figure 1c).

201

At the beginning of stage (I), eddy current force increased as aluminum particle got

202

close to magnetic drum. Horizontal component of eddy current force was

203

counteracted by friction force of conveyor belt and no horizontal relative motion

204

happened between aluminum particle and belt. As eddy current force increasing,

205

vertical component would be greater than gravity force (G), and aluminum particle

206

will have a vertical-upward acceleration and move upward.

207

G = cos β × F

(6)

208

Meanwhile, eddy current force decreased with the upward movement of

209

aluminum particle due to the decline of magnetic flux. When vertical component was 11



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210

equal to gravity force, aluminum particle will be suspended and keep constant radial

211

distance to the axis (O) of separator. Position (x, y) was called detachment point and β

212

was detachment angle.

213

Coordinate of detachment point (x, y) of aluminum particle can be calculated by:

214

x1 = Rtg β

(7)

215

y1 =

R cos β

(8)

216

Meanwhile, point (x1, y1) is supposed as the symmetry point of (x, y) at the right of

217

Y-axis (Figure 1c). The movement of aluminum particle from point (x, y) to point (x1,

218

y1) was considered as rectilinear motion. At this rectilinear movement, magnetic

219

fluxes of aluminum particle and magnetic drum was considered to be parallel,

220

horizontal component of eddy current force can be neglected, and eddy current force

221

was supposed as equal to gravity force. Once aluminum particle passes over point (x1,

222

y1), vertical component of eddy current force was less than gravity force. Horizontal

223

component of repulsive force can no longer be neglected because the directions of the

224

two magnetic fluxes were not parallel. Horizontal component will accelerate

225

aluminum particle in horizontal direction until it passes through magnetic field

226

boundary. Point (x2, y2) was supposed as exiting position. As passing through point (x2,

227

y2), aluminum particle only subjected to gravity force and the movement was

228

considered as horizontal projectile motion. Horizontal throw (D) of aluminum particle

229

in eddy current separation is comprised of two parts: one is the horizontal distance

230

from Y-axis to existing point (x2, y2); the other is the horizontal distance from point (x2,

231

y2) to the collection position. Abscissa of point (x2, y2) can be calculated by the 12


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232

following equations (9) and the results were placed in Figure 4 (25).

233

2  2       ( x − Rtg β ) +  v  − v  + R  y = −(2 g − g cos β )  g sin β g sin β  cos β  g sin β        x2 + y 2 = ( R + η )2    

(9)

234

Horizontal distance from point (x2, y2) to collection position is determined by the

235

horizontal muzzle velocity (vx) of aluminum particle after leaving magnetic field and

236

the vertical height (H) from collection position to conveyor. Horizontal and vertical

237

muzzle velocities (vx and vy) of aluminum particle when leaving magnetic field can be

238

presented as:

239

 g sin β vx = v + 2     v = g  2 − cos β   y 2  

4 y2 − y1

g ( 2 − sin β ) (10) 4 y2 − y1    g ( 2 − sin β )

240 241 242

Figure 4. (a) Calculation of abscissa of point (x2, y2) of T0 and T1 in eddy current separation; (b) calculation of abscissa of point (x2, y2) of R0 and R1 in eddy current separation

243

Movement of aluminum particle from point (x2, y2) to the collection position can be

244

considered as horizontal projectile motion. Thus, horizontal throw (D) of aluminum 13



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245

particle in eddy current separation can be computed by:

246

D = vx

247

The horizontal throws of T0 and R0 in the three cases were computed and measured.

248

The results were placed in Table 3. Compared the calculation horizontal throws to

249

measure horizontal throws, the constructed models of eddy current force of hollow

250

aluminum particles can accurately describe the repulsive force of the particle in eddy

251

current separation.

2 ( H − y2 g

) + v

2

 vy   − + x2 g g y

(11)

252

The horizontal throw (D′) of plastic particle is determined by feeding speed and

253

the vertical height (H) from the collection position to conveyor. Trajectory equation of

254

plastic particle in eddy current separation was expressed as:

255

D′ = v

256

For separating aluminum particle from plastic particles, the critical separation

257

distance should satisfy equation (13):

258

d = D − D > Lmax ( metal ) + Lmax ( plastic )

259

Where Lmax(metal) is maximum size of aluminum particle, Lmax(plastic) is maximum size

260

of plastic particles. In crushed waste refrigerator, Horizontal throws and separation

261

distances between aluminum particles and plastic particles were computed, measured

262

and placed in Table 3.

2H g

(12)

(13)

263

In order to investigate the influencing of hollow on separation rate, T0 and R0

264

were compressed into solid aluminum particles (T1 and R1 in Figure 2). Then,

265

horizontal throws of T1 and R1 were computed and measured at the same operation 14


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266

parameters of eddy current separator. Table 3 indicated that the horizontal throw of T1

267

was greater than T0 about 0.031 m. horizontal throw of R1 was greater than R0 about

268

0.033 m. Size of plastic particles in crushed toner cartridges ranged from 0.05 m to

269

0.08 m. the value of Lmax(metal)+ Lmax(nonmetal) was about 0.12 m. According to Table 3,

270

T0 and R0 could not be separated from plastic particles, but T1 and R1 were

271

successfully separated. Thus, compressing hollow aluminum particles to solid

272

particles can greatly improve separation rate of aluminum particle from plastic

273

particles.

274 Table 3. Calculation of horizontal throws of aluminum particles and plastic particle with v: 0.4 m/s and ω: 800 r/min in eddy current separation Calculation results Al

β (deg)

T0

11.08

T1

14.97

R0

10.62

R1

14.51

(x1, y1)

(x2, y2)

(0.0188,

(0.1391,

0.0979 )

-0.0439)

(0.0256,

(0.1441,

0.0994)

-0.0233)

(0.0180,

(0.1385,

0.0977)

-0.0453)

(0.0248,

(0.1434,

0.0992)

-0.0241)

D (m) vx

vy

(m/s)

(m/s)

0.568

Cal.

Exp.

0.893

0.291

0.289

0.614

0.859

0.322

0.318

0.562

0.893

0.287

0.286

0.609

0.858

0.320

0.316

D ‘(m)

d (m)

Cal.

Exp.

Cal.

Exp.

0.172

0.167

0.119

0.122

0.15

0.151

0.115

0.119

0.148

0.149

275 276

The designed compactor for changing hollow aluminum particle to solid particle

277

According to the calculations of horizontal throws of hollow aluminum particles

278

and solid aluminum particles, we found the character of hollow greatly destroyed the

279

separation rate of eddy current separation. Therefore, a compactor was designed to

280

eliminate hollow aluminum particles in the crushed waste toner cartridges. The

281

structure of compactor was given in Figure 5. When the aluminum particles came out 15



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282

from the crusher, they were conveyed to storage tank. When the storage tank was full

283

of aluminum particles, sliding plate of the tank was opened, and aluminum particles

284

were fed into the compactor. Vibration layer of compactor caused aluminum particles

285

paved in compactor monolayer. Then, hydraumatic stick made the pressing plate

286

squeezing the hollow aluminum particles to solid aluminum particles. After squeezing

287

process, one leg of compactor lift and the supporting body of compactor will incline

288

for transporting the solid aluminum particles from the support body of compactor to

289

vibration feeding system of eddy current separation. The compressing process will

290

eliminate hollow aluminum particles in crushed waste toner cartridges and improve

291

the separation rate of aluminum particles from plastics.

292 293

Figure 5. Structure of the designed compactor

294 295 296 297 298 16


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299

Conclusion

300

This paper discussed the eddy current force of hollow aluminum particle in eddy

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current separation and constructed the computing models. Horizontal throws of

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hollow aluminum particles and solid aluminum particles were computed and

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measured. The comparison results of their horizontal throws indicated that hollow

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character greatly decreased the horizontal throws of aluminum particles and destroyed

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the separation rate of eddy current separation. Then, a new compactor was designed to

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change hollow aluminum particles in to solid particles. This paper contributed to

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guide the eddy current separation of hollow nonferrous metallic particles and improve

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the efficiency of the recovering line of waste toner cartridges.

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310 311 312

Supporting information Nomenclatures of the manuscript were placed in Supporting Information. These materials are available free of charge via the internet at http:// pubs.acs.org.

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314 315

Acknowledgment This work was supported by National Natural Science Foundation of China

316

(51308488),

Guangdong

Provincial

Scientific

and

317

(2015B020237005, 2016A020221014), Natural Science Foundation of Jiangsu

318

province (BK20130449), Guangdong Provincial Natural Science Foundation

319

(2016A030306033). The authors are grateful to the reviewers who help us improve

320

the paper by many pertinent comments and suggestions. 17


Technological

Projects


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Title: Hollow aluminum particle in eddy current separation

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of recovering waste toner cartridges

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Jie Zhenga, Jujun Ruan a∗, Lipeng Donga , Tao Zhanga, Mingzhi Huang*b, Zhenming Xuc

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Synopsis

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Recovery resource from e-waste is a meaningful work in the area of sustainable

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development of the world

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TOC GRAPHIC

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Corresponding author: Jujun, Ruan Tel:+86 20 84113620; Fax:+86 20 84113620; E-mail: [email protected]. 21


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