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A closed loop process for selective metal recovery from spent lithium iron phosphate batteries through mechanochemical activation Yongxia Yang, Xiaohong Zheng, Chunlong Zhao, Xiao Lin, Hongbin Cao, Pengge Ning, Yi Zhang, Wei Jin, and Zhi H.I. Sun ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b01914 • Publication Date (Web): 29 Sep 2017 Downloaded from http://pubs.acs.org on October 1, 2017

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ACS Sustainable Chemistry & Engineering

1

A closed loop process for selective metal recovery from spent lithium iron

2

phosphate batteries through mechanochemical activation

3

Yongxia Yanga,b, Xiaohong Zhengb,c, Hongbin Caob, Chunlong Zhaob,d, Xiao Linb, Pengge Ningb,

4

Yi Zhanga,b, Wei Jinb, Zhi Sunb*

5 6 7 8 9

a

School of Materials Science and Engineering, Northeastern University, Shenyang, Liaoning 110819, China b Beijing Engineering Research Center of Process Pollution Control, Division of Environment Technology and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China c

10 11

d

University of Chinese Academy of Sciences, Beijing 100190, China

State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing, Beijing 100083, China

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*Corresponding author: Zhi Sun ([email protected])

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National Engineering Laboratory for Hydrometallurgical Cleaner Production Technology

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Institute of Process Engineering, Chinese Academy of Sciences

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Tel: +86 10 82544844

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Fax: +86 10 82544845

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No. 1 Beierjie, Zhongguancun, Beijing, China

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ACS Paragon Plus Environment


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32

ABSTRACT

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With the increasing consumption of lithium ion batteries (LIBs) in electric and electronic products,

34

the recycling of spent LIBs has drawn significant attention due to their high potential of

35

environmental impacts and waste of valuable resources. Among different types of spent LIBs, the

36

difficulties for recycling spent LiFePO4 batteries rest on their relatively low extraction efficiency

37

and recycling selectivity in which secondary waste is frequently generated. In this research,

38

mechanochemical activation was developed to selectively recycle Fe and Li from cathode scrap of

39

spent LiFePO4 batteries. By mechanochemical activation pre-treatment and the diluted H3PO4

40

leaching solution, the leaching efficiency of Fe and Li can be significantly improved to be 97.67%

41

and 94.29%, respectively. In order to understand the Fe and Li extraction process and the

42

mechanochemical activation mechanisms, the effects of various parameters during Fe and Li

43

recovery were comprehensively investigated, including activation time, cathode powder to

44

additive mass ratio, acid concentration, the liquid-to-solid ratio and leaching time. Subsequently,

45

the metal ions after leaching can be recovered by selective precipitation. In the whole process,

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about 93.05% Fe and 82.55% Li could be recovered as FePO4·2H2O and Li3PO4, achieving

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selective recycling of metals for efficient use of resources from spent lithium ion batteries.

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KEYWORDS：： Spent LiFePO4; Mechanochemical activation; Lithium recovery; Leaching

49

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With the rapid development of electric vehicles (EVs), it has been forecasted that the global

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consumption of lithium-ion batteries for vehicles is expected to total $221 billion from 2015 to

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2024.1, 2 Since it was first reported in 1997, lithium iron phosphate (LiFePO4) for lithium-ion

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batteries has been recognized as one of the excellent cathode materials for applications in large

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vehicles or facilities because of its superior thermal safety, relatively high theoretical capacity, and

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theoretical energy density (580 Wh·kg-1), acceptable operating voltage (3.45 vs. Li+/Li), low

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material cost, nontoxicity and high reversibility.3 Commercial LiFePO4 batteries have been used in

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electric vehicles by improving poor intrinsic electronic conductivity and the low diffusion

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coefficient of Li+ with carbon coating and reduction to the particle size.4 The more reliance on

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lithium ion batteries (LIBs) in electronic equipment and electric vehicles, the more spent LIBs will

60

be generated due to their limited life spans and the wastes from the production process.5,

INTRODUCTION


6

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Although LiFePO4 material is considered to be relatively environmental friendly, the

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corresponding spent LIBs may still cause environmental problems (from the electrolyte) and waste

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of valuable resources such as lithium for the increasing accumulation of quantity and the improper

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disposal with a discarding manner. As a lithium-containing secondary resource, the necessity to

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develop an efficient and cost-effective route to recycle spent LiFePO4 cathode materials is

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significant.

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The treatment technology of spent LiFePO4 batteries mainly includes two categories: direct

68

regeneration of cathode materials and recycling as individual compounds. Chen et al.7 reported a

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small scale model line to direct regenerate cathode materials from spent LiFePO4 batteries. The

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recycled cathode powder exhibited almost the same discharge capacities and specific energy

71

densities as the fresh cathode material at high discharge current densities by heat-treatment for

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650°С under an Ar/H2 flow. Song et al.8 developed a process by adding new LiFePO4 approach to

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regenerate spent cathode materials. In the course of this process, the cathode scrap was soaked in

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DMAC solvent to separate the cathode materials and Al foil at optimal conditions of 30 min at

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30°С and solid to liquid ratio of 50g/L, the separate cathode materials were directly regenerated

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with addition of new LiFePO4 by solid phase sintering method, in which battery capacities can

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reach 144mAh/g at 0.1C when adding ratio of 3:7 for new and spent materials at 700°С. On the

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other hand, Fe and Li can be recovered as individual compounds. Bian et al.9 introduced

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phosphoric acid (H3PO4) as the leaching reagents to treat the cathode material which was already

80

separated from Al foil by using NaOH aqueous solution with ultrasound-assistance. The Fe and Li

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are recovered as FePO4·2H2O by aging and LiH2PO4 from the filtrate by ethanol solvent extraction.

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Zheng et al.10 utilized sulfuric acid to leach spent cathode materials after its separation from the

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current collector at 600°С annealing. The Fe can be recovered as FePO4 by adjusting pH value of

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the solution to 2, and the Li was recovered as Li2CO3 by adding saturated sodium carbonate.

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Huang et al.11 designed leaching-flotation-precipitation process to separate and recover Li/Fe/Mn

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from the mixed types of cathode materials (hybrid waste of LiFePO4 and LiMn2O4). The purity for

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obtained Li3PO4, FeCl3, MnO2/MnO3 is 99.32 ± 0.07%, 97.91 ± 0.05% and 98.73 ± 0.05%,

88

respectively. For the spent LiFePO4 batteries, direct regeneration is not suitable for cathode scrap

89

with a high amount of impurities. Olivine structured lithium iron phosphate is fairly stable that

90

effective extraction of lithium and iron has to rely on strong acid/alkaline or much larger amount



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91

of leachate than the stoichiometric requirement. Pre-treatment with high temperature roasting is

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often used in order to improve the leaching recovery. In these case, secondary pollution is

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inevitable and the excess acid/alkaline needs to be treated which can increase the process cost

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significantly.12

95

In recent years, the possibility of metal extraction selectively from a highly complex industrial

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information and communication technology (ICT)waste by using a hydrometallurgical method has

97

been presented.13

98

Mechanochemical activation begins with prehistoric times, when reactions could be initiated

99

during grinding and rubbing accidentally.14, 15 With the aid of high-energy ball-milling of materials,

100

the mechanically induced changes subsequently influence their physical and chemical properties.16

101

Takacs reported that mechanically activated self-sustaining high-temperature reactions (MSRs)

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represented a class of self-propagating high-temperature synthesis in the preparation of

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nanocrystalline materials, amorphous alloys, and metastable crystalline alloys.17-19 Sepelak

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reported on the single-step synthesis nanocrystalline Ca2SnO4 and Fe2SiO4 by mechanochemical

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activation.20 It demonstrates that mechanically induced reactions provide novel opportunities for

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the non-thermal manipulation of materials and the tailoring of their properties. Balaz introduced

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the mechanochemical route to synthesize well-crystallized ZnS, CdS and PbS nanoparticles and

108

discussed the suitability of mechanochemistry application in chalcogenide synthesis.21 Although

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Mechanochemical activation achieves good results in material preparation, it can also be used for

110

the recovery of wastes. In recent years, mechanochemical activation method has been increasingly

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applied in metal recycling from wastes, for example, recycling indium, lead, cobalt, lithium,

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tungsten, gold, and the REEs.22 The reduction in particle size, the increase in specific surface area,

113

point defects and dislocations in crystalline structures, polymorphic transformations, bond

114

breakage or even chemical reaction identified as the main processes occurring during the

115

mechanochemical activation.23 These physical and chemical changes indicate a decrease in

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activation energy and an increase in reaction activity after mechanochemical activation, which is

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expected to help on relieving the aforementioned problems during the recycling of spent LiFePO4

118

batteries22,

119

electrochemical insertion of Li in mechanochemically prepared Zn2SnO4.25 Sepelak prepared

120

nano-sized LiFe5O8 by the mechanochemical method.26 All of the previous findings show that it is

24

. For lithium-based systems, James and co-workers had been studied the


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possible to in-situ enhance/manipulate ion diffusion through mechanical activation. In this

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research, this technology was investigated to recover metals (Fe and Li) from an industrially

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provided cathode scrap. The aims are to reduce the acid consumption with less strong acidic

124

leachate, improve the recovery selectivity of lithium and decrease the emission of secondary

125

pollution, which finally to develop a closed-loop recycling process for spent LiFePO4 batteries. To

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fulfil the objectives, this work focuses on identifying the effect of mechanochemical activation

127

behaviour of spent cathode powder and the potential to recover lithium selectively. The examined

128

parameters including activation time, cathode powder to additive mass ratio, acidic concentration,

129

the liquid-to-solid ratio and leaching time were systematically discussed.

130

EXPERIMENTAL SECTION

131

Materials

132

The spent LiFePO4 batteries were supplied by Brunp Recycling Co. Ltd in China and were

133

dismantled using a manual procedure after discharging. The plastic cases of the batteries were first

134

removed which was followed by removing steel case mechanically. Anode and cathode uncurled

135

manually, and copper and aluminium foils were collected for recycling separately. The cathode

136

materials in the form of powder were separated from Al foil by ultrasonic-assisted and mechanical

137

enhancement technique in water after 1 h. The obtained powder was dried and stored for further

138

investigation. Table 1 presents the composition of the powder separated from cathode scrap. The

139

X-ray diffraction of the cathode powder (Figure 1) shows that the presence of LiFePO4 as the only

140

phase in the cathode powder. All chemical reagents used in this work were of analytical grade and

141

all solutions were prepared with ultrapure water (Milli-Q, Millipore).

142 143

Table 1 Main element composition of the cathode scrap powder Elements

Fe

Li

P

Al

Composition (wt.%)

31.25

4.08

18.94

0.16


10

20

30

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40

50

60

(223) (413)

(331) (430) (620)

(022) (131) (222) (412) (610)

(121)

(311)

LiFePO4 (JCPDS:01-081-1173 )

(410) (401) (112)

(301)

(111)

(101) (210)

(011)

(200)

Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(211)


70

80

90

2θ (degree)

144 145

Figure 1. XRD pattern of the cathode powder

146

Mechanochemical activation of cathode powder

147

The

148

powder/EDTA-2Na mass ratio from 6:1 to 1:1) and mechanochemical activation using a planetary

149

ball mill (QMQX2, Nanjing University Instrument Plant, China) with four symmetrical pots of

150

250mL. The rotation speed of the pot is twice that of the disk. Approximately 5 g cathode powder

151

and one of the additive were mixed with 120g Φ5mm zirconia beads. The planetary ball mill was

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operated at 550 rpm for 0.5~6h under ambient atmosphere. During activation, an interval of 15

153

min was set after each milling run of 15 min, to avoid the accumulation of heat. Activated samples

154

were further leached with diluted phosphoric acid.

155

Acidic leaching

156

The leaching experiments were performed in a series of 100 mL conical flasks conducted at room

157

temperature by magnetic stirring. For each run, a fixed amount of the cathode powder (∼2.0g) was

158

precisely measured and a known concentration of phosphoric acid was prepared as leaching

159

reagents. They were simultaneously added to the flask under continuous stirring. After a certain

160

time, the flask was taken down and filtered immediately by vacuum filtration using a cellulose

161

acetate membrane (pore size 0.45µm). The residues were washed several times with ultrapure

162

water and dried at 60°С for 24h in air. The concentrations of metals in the leachate were

163

determined by induction coupled plasma-optical emission spectrometry (ICP-OES, iCAP 6300

164

Radial, Thermo Scientific). The leaching efficiency of metals from the cathode powder were

165

calculated by

separated

cathode

powder

and

additive

were

mixed


proportionally

(cathode

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LEM =

166

CM ,tV CM , f V + W f

167

where LEM is the metal leaching efficiency; CM,t, CM,f, V, Wf refer to the concentration of metal

168

ions in the leachate at time t (g/L), metal contents in the final solution (g/L), leachate volume (L),

169

Wf is the metal contents in the final residue after leaching, respectively.

170

Materials Recovery

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The precipitation experiments were conducted to determine the optimum recovery of lithium and

172

possibly iron. The leachate was refluxed for 9 h at 90 °С in a 250 mL three-necked flask with a

173

vapour condenser. The precipitate was collected by filtering, washing at least three times with

174

ultrapure water, and drying at 60°С for 24 h in air. The precipitation efficiency PM can be

175

calculated by

 CV  PM = 1 − 1 1  × 100%  C2V2 

176

177

where PM is the metal precipitation efficiency; C1and C2 are the concentrations of metals in the

178

solution before and after precipitation (g/L), respectively; V1 and V2 refer to the volumes of the

179

liquor before and after precipitation (L), respectively.

180

Characterization

181

The separated cathode powder, mechanochemical activation powder and precipitated products

182

were analysed by X-ray diffraction spectrometer (X’pert PRO, PANalytical) with Cu Kα radiation.

183

The data was collected by step scanning with a scanning speed of 10°/min and a scanning angle

184

(2θ) of 5~90°. The morphology of the solid samples was characterized with scanning electron

185

microscope (SEM, JEOL JSM-7610F), the samples were deposited by a gold film to enhance

186

electric conductivity. Liquid samples were diluted and prepared for analyzing by ICP-OES.

187

188

Metal recovery from cathode powder through mechanochemical activation

189

Effect of mechanochemical activation

190

The EDTA-2Na is considered to be an excellent metal chelating reagent, which has been widely

191

used for the removal of metals from industrial waste, such as alkali metals, rare-earth elements or

RESULTS AND DISCUSSION


(1)

(2)


192

metals of spent LiCoO2 batteries.27, 28 As can be seen in Figure 2, around 60% of lithium and less

193

than 40% of iron could be leached out with direct acid leaching. However, 94.29% of Fe and

194

92.04% of Li were recovered when mechanochemical activation was applied with EDTA-2Na

195

being co-grinded with LiFePO4 cathode powder, indicating that mechanochemical activation

196

significantly accelerated the process of acid leaching for the extraction of metal. This behaviour

197

could be explained by the fact that mechanical forces such as shearing, impact and squeezing

198

exerted by ball milling, will transmit energy to powder, diminish powder particles and destroy the

199

crystal structures.22 Figure S1 demonstrates the effect of acidic type on the leaching of spent

200

LiFePO4 powder. It is clear that strong acids are possibly leaching both lithium and iron while

201

mild phosphate acid shows less effectiveness on the leaching. These leaching priority behaviors

202

can be explained based on hard-soft-acid-base (HSAB) interaction theory.29 By introducing

203

mechanical activation, it facilitates effective metal recovery from spent LiFePO4 when mild acidic

204

solution (H3PO4) is used. 100

Leaching efficiency (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Fe Li

80 60 40 20 0

Without mechanochemical Mechanochemical activation activation

205 206 207 208 209

Figure 2. Leaching efficiency of Fe and Li from different samples (Cathode powder with EDTA=3:1; Mechanochemical activation sample: activation time =5h, mass ratio of cathode powder to EDTA-2Na =3:1; Leaching parameters: H3PO4=0.5M, S/L ratio=40g/L, leaching time =60min).

210

Effect of activation time

211

The effect of activation time on Fe and Li extraction from LiFePO4 cathode powder were carried

212

out at the solution concentration of 0.5M H3PO4, solid/liquid ratio (g/L) of 40. There was a

213

significant increase in the leaching efficiency of Fe and Li with a prolonged activation time

214

especially in the first two hours. As given in Figure 3, the leaching efficiency of Fe and Li reached


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215

from 37.81% to 95.96% for Fe and 61.73~91.84% for Li, respectively. Considering the energy

216

consumption and recovery rates, it is recommended that 2h is the optimum milling time. 100


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80 Fe Li

60 40 20 0

217 218 219

0

1

2

3

4

5

Activation time (h) Figure 3. Effect of activation time on Fe and Li leaching efficiency (mass ratio of cathode powder

to EDTA-2Na =3:1; Leaching parameters: H3PO4=0.5M, S/L ratio=40g/L, leaching time =60min).

220 221

Generally, small particles tend to dissolve more rapidly compared with large particles because of

222

large specific surface areas.30 Amorphous materials have a larger fraction of highly energetic sites

223

such as dislocations and defects. Therefore, if milling the sample for a longer time, the particle

224

size will be smaller and the crystal structure may be destroyed continuously, so the leaching

225

efficiency will be improved. This is consistent well with Fe and Li leaching efficiency after

226

milling for different times. Meantime, small particles will be reunited with the increase in the

227

activation time, thus the leaching platform appeared in the leaching curves of activated samples.

228

Effect of mass ratio of cathode powder to activation additive

229

The mass ratio is another key parameter in the mechanochemical activation, since the chelating

230

efficiency of EDTA-2Na with ions in the cathode powder can be influenced. As shown in Figure 4,

231

the Fe or Li leaching efficiency increases sharply with the decrease of mass ratio of cathode

232

powder to EDTA-2Na that 52.46% for Fe and 72.14% for Li can be leached out at mass ratio of

233

6:1, while 95.96% of Fe and 91.84% of Li at mass ratio of 3:1. Then leaching efficiency almost

234

unchanged when the mass ratio is further decreased. The above results indicate that 3:1 can be the

235

appropriate mass ratio for mechanochemical activation process. This is consistent with a previous

236

report that EDTA generally coordinates with metal ions at the molar ratio of 1:1.28 In this research,



237

it indicates the mass ratio of LiFePO4 to EDTA-2Na shall be theoretically 2.4:1. This is calculated

238

by considering a perfect LiFePO4 crystal structure and the spent cathode material needs less

239

EDTA-2Na for full chelation. However, taking economic feasibility into account, we used a small

240

amount of EDTA-2Na to recover spent LiFePO4 in which mass ratios of cathode powder to

241

EDTA-2Na is 3:1 (as given in Figure S5 the recovery efficiencies show minor difference).

100


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80 Fe Li

60 40 20 0

6:1

5:1

4:1

3:1

2:1

1:1

Mass ratio 242 243 244

Figure 4. Effect of cathode powder to additive mass ratio on Fe and Li leaching efficiency (activation time=2h; Leaching parameters: H3PO4=0.5M, S/L ratio=40g/L, leaching time =60min)

245

Effect of acid concentration

246

After mechanochemical activation, leaching of Fe and Li was investigated at varying H3PO4

247

concentration in the range of 0.2~0.7M while maintaining all other parameters unchanged. As

248

shown in Figure 5, the leaching efficiency of Fe and Li was increased from 51.59% to 99.75% for

249

Fe and from 64.33 to 94.75% for Li, respectively, with increasing the H3PO4 concentration from

250

0.2 M to 0.7M. It was observed that the dissolution efficiency of Fe and Li kept constant when the

251

H3PO4 concentration was larger than 0.6M. The reason is most likely related to the

252

thermodynamic interaction between phosphate ionization and leaching reaction of LiFePO4. In an

253

aqueous solution, ionization of phosphate is under thermodynamic equilibrium at a certain

254

temperature (K1 and K2 are constant) as shown by Eqs. (3), (4) and (5).31 It can be concluded that

255

further increase of the phosphoric acid concentration may not be able to further increase the

256

activation of H+. Therefore, all further experiments were carried out using 0.6M H3PO4.


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H 3 PO 4 =H 2 PO 4- +H+

257

-

2-

H 2 PO 4 =HPO 4 +H

258

H 2 PO 4-  H+  K 1=  [ H 3 PO 4 ]

(3)

 HPO42-   H+  K 2=  H 2 PO 4- 

+

(4) 3

259

HPO 4 =PO 4 +H

 PO 43-  H+   PO 43-  H+  K 3=  = HPO 4 2-  [ H 3 PO 4 ] K 1 K 2

(5)

260

4LiFePO 4 + 4H + +O 2 = 4Fe 3+ +4Li + +4PO 4 3- +2H 2 O

(6)

2-

3-

+

100


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


80 Fe Li

60 40 20 0

0.2

0.3

0.4

0.5

0.6

0.7

261 262 263 264

Acid concentration (M) Figure 5. Effect of acid concentration on Fe and Li leaching efficiency (S/L ratio=40g/L, leaching time =60min; activation parameters: activation time=2h mass ratio of cathode powder to EDTA-2Na=3:1)

265

Effect of S/L ratio

266

The leaching of Fe and Li in the function of S/L ratio in the range of 40~100 (g/L) was studied, in

267

which other parameters were kept constant. Results given in Figure 6 clearly show that the

268

leaching efficiency decreases from 99.86% to 76.17% for Fe and 95.4~72.29% for Li, respectively,

269

with increasing S/L ratio of 50g/L to 100g/L, which indicated that the lower solid to liquid ratio

270

could enlarge the contact areas of activation powder and phosphate solution to accelerate the

271

leaching reaction. Generally speaking, both the increasing acid concentration and decreasing S/L

272

ratio facilitate the leaching rates of metals because of the increase of reagent in the reaction

273

system.32, 33 However, low solid to liquid ratio would lead to the increase of leach solution volume

274

which is not favorable for following metal separation and recovery.34, 35 Hence 50g/L can be taken

275

as the optimum value for rest of the experiments.




100

80 Fe Li

60

40

20 40

50

60

70

80

90

100

-1

S/L ratio (g• L )

276 277 278

Figure 6. Effect of S/L ratio on Fe and Li leaching efficiency (H3PO4=0.6M, leaching time =60min; activation parameters: activation time=2h, mass ratio of cathode powder to additive =3:1)

279

Effect of leaching time

280

The effect of time (0~60 min) on the leaching efficiency of metals was examined using 0.6M

281

H3PO4 and solid to liquid ratio of 50 g/L at room temperature after mechanochemical activation. It

282

is apparent that the dissolution of Fe and Li progressed well (Figure 7) with increasing in leaching

283

time. No further increased leaching efficiencies were observed after 97.67% Fe and 94.29% Li

284

being recovered at reaction duration over 30 min. This can be attributed to the residue hinders the

285

diffusion of H+ from the solution to the interface of residual materials. 100


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80 Fe Li

60 40 20 0

0

10

20

30

40

50

60

Time (min)

286 287 288

Figure 7. Effect of leaching time on Fe and Li leaching efficiency (H3PO4=0.6M, S/L ratio=50g/L; activation parameters: activation time=2h mass ratio of cathode powder to EDTA-2Na =3:1)

289

Mechanochemical activation mechanisms

290

To elucidate the mechanochemical activation mechanisms in details, physicochemical changes


Page 13 of 25

291

were also investigated. According to X-ray diffraction (XRD) patterns presented in Figure 8 a), the

292

intensity of characteristic diffraction peaks (the position can be found in Figure 1) decreased with

293

an increase in milling time, specifically, the X-ray diffraction intensities of (101), (111), (211) and

294

(311) lattice planes decrease as the milling time increases (Figure 9). However, the

295

mechanochemical activation powder (311) crystal plane intensity decreased faster than (101),

296

(111), (211). The FTIR patterns indicate that P-O/PO4 bond/tetrahedra is probably the structure

297

destroyed during mechanochemical activation. Meanwhile, as shown in Figure 10, the full width

298

at half maximum (FWHM) of peaks also broadened with simultaneous increase of milling time

299

and FWHM of the cathode powder (311) crystal plane is wider than other lattice planes. These

300

results indicate that (311) plane of cathode powder can be easily destroyed in accordance to

301

mechanochemical activation. During mechanochemical activation, it is easier to destroy the

302

atomic bonds with longer lengths which is the diagonal of an orthorhombic crystal cell. This is

303

reflected by (311) or (211) planes in the XRD patterns since the crystal constant of a-axis is the

304

longest for LiFePO4 crystal. The SEM micrographs of samples were presented in Figure S4.

305

Although the particle size is not significantly changed, agglomeration of particles is observed. It

306

may come from reactions between the agglomeration additive materials and the cathode powder.

307

With the mechanochemical activation proceeding, lithium and iron were chelated and subsequent

308

leaching using a diluted leachate solution can be facilitated.

15000 LiFePO4

2h

12000

Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


9000

1h

6000 0h 3000 0 10

309

20

30

40

50

60

70

2θ (degree)


80

90


310 311 312

Figure 8. Cathode powder for mechanochemical activation at different milling time a) XRD patterns; b) FTIR patterns 7000

Intensity(a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

6000

5000

4000

313 314

(101) (111) (211) (311)

0.0

0.5

1.0

1.5

2.0

Milling time(h)

Figure 9. The X-ray diffraction intensity of lattice faces with milling time

315


Page 14 of 25

Page 15 of 25

0.4

0.3

FWHM (rad)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.2 (101) (111) (211) (311)

0.1

0.0

0.0

0.5

1.0

1.5

2.0

Milling time(h)

316 317

Figure 10. The FWHM of lattice faces with milling time (All data were calculated by Jade6.5

318

software)

319

Recovery of iron

320

After mechanochemical activation leaching, a leachate with pH of 1.5 was obtained for materials

321

recovery. As can be seen in the E-pH diagrams in Figure S2, the FePO4 phase is

322

thermodynamically stable under acidic conditions. All diagrams were made using HSC 6.0

323

chemistry software. Accordingly, crystalline iron phosphate precipitation can be obtained by

324

refluxing air for 9 hours at 90°C in a 250 mL three-necked flask with a vapour condenser. Iron (II)

325

can be oxidized into iron (III) which can be further precipitated out from the solution. The main

326

reaction is shown as

327

Fe3+ + PO 4 3- +2H 2 O = FePO 4 ⋅ 2H 2 O ↓

328

The XRD pattern of the obtained iron phosphate precipitation is shown in Figure 11 and it agrees

329

well with the standard pattern peaks. To accurately calculate the quality of iron phosphate, the

330

precipitated iron phosphate was dissolved by 0.1M hydrochloric acids and its mass fraction of

331

components was tested by ICP-OES (Table 2). From Table 2, the P/Fe molar ratio of the

332

precipitate is 1.01, even a small amount of Al remaining in iron phosphate, which doped in the

333

cathode materials, was found to increase the rate performance and cycle stability of LiFePO4/C,

334

indicating the high quality of FePO4·2H2O was recovered.36

335 336


(7)


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 25

337 Table 2 Quality analysis of the recovered iron phosphate

338

Content

Fe (wt.%)

Li (wt.%)

P (wt.%)

Al (wt.%)

P/Fe (molar ratio)

Composition

30.31

0.04

16.97

0.13

1.01

339

340 341

Figure 11. XRD pattern of the recycled iron phosphate sample

342

The SEM images of the precipitated FePO4·2H2O are illustrated in Figure 12. It can be noticed

343

that the precipitated FePO4·2H2O is multistage structure of the spherical, the surface assembled by

344

nanosheets of iron phosphate, which can be used for the synthesis of catalyst and LiFePO4 cathode

345

material.37

346 347

Figure 12. SEM images of the recycled FePO4·2H2O. Insert: a microstructure of FePO4·2H2O


Page 17 of 25

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


348

Recovery of lithium

349

After iron was recovered, the residual solution consisting mainly Li and phosphate ions was used

350

for recovery lithium. In order to study the extraction behaviour of Li in complicated Li+ solution,

351

the thermodynamic aspects particularly the stability regions of different phases of lithium in the

352

aqueous solutions were calculated by HSC 6.0 software. The E-pH diagram of Li-P-H2O system is

353

shown in Figure S3. It can be seen that the stable domain of Li3PO4 phase is within the stability

354

region of water in neutral and alkaline region. Hence, the Li+ solution can be easily precipitated

355

into lithium phosphate by adjusting pH with 5M sodium hydroxide solution. The XRD pattern of

356

the obtained lithium phosphate is shown in Figure 13, and it agrees well with the standard pattern

357

peaks. The excessive amount of H3PO4 and Li+ should also be recycled or reused for the sake of

358

comprehensive recovery of metals and waste minimization.

359

As shown in Table 3, the purity of the obtained product (Li3PO4) is 96.51% based on the analytical

360

results of ICP-OES analysis by dissolving in 3M nitric acid and diluting into a suitable

361

concentration.

362

Due to the presence of EDTA-2Na complexing reagent in the solution, impurity iron and

363

aluminum especially at low concentrations, are potentially to form complexes and become

364

difficult to be completely removed (lgKFeY=25.1>lgKAlY=16.3> lgKLiY=2.79, Y is EDTA).38, 39

365

Even though, a residual solution containing mainly sodium phosphate and EDTA-2Na can be

366

obtained. The SEM image of the precipitated Li3PO4 is illustrated in Figure 14. It can be noticed

367

that the precipitated Li3PO4 was presented as massive agglomerates of numerous rhombic sheets.

368

The recovered Li3PO4 can be used for synthesis of dental material, catalyst and LiFePO4 cathode

369

material.



Li3PO4 (JCPDS: 00-025-1030 )

Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 25

10

20

30

40

50

60

70

80

90

2θ (degree)

370

Figure 13. XRD pattern of the recycled lithium phosphate

371 372 373 374 375

Table 3. The mass fraction of metals in the precipitated lithium phosphate Content

Al2O3

Fe2O3

Na2O

Li3PO4

others

Composition (wt.%)

0.05

0.64

0.87

96.51

1.93

376

377 378

Figure 14. SEM image of the recycled lithium phosphate


Page 19 of 25

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


379

Development of a new process for spent LiFePO4 batteries recovery

380 381

Figure 15. Development of a mechanochemical activation process for spent LiFePO4 batteries

382

recycling

383 384

Table 4. Global recovery rates of different metals from the cathode powder in this Research

Element

Leaching

Precipitation

Total recovery

Main

efficiency (%)

efficiency (%)

rate (%)

products

Fe

97.67%

96.95%

93.05%

FePO4·2H2O

Li

94.29%

87.89%

82.55%

Li3PO4

385

On the basis of the above theoretical and experimental results, a process to recover metals from

386

spent LiFePO4 batteries can be proposed. A schematic design of the process is plotted in Figure 15.

387

The spent LiFePO4 cathode powder with EDTA-2Na is treated by mechanochemical activation.

388

The Fe and Li leaching efficiency can reach more than 94%. FePO4·2H2O precipitates are recycled

389

without regulating pH value of the leaching solution. Lithium is recovered in the form of Li3PO4

390

by adjusting the filtrate pH to 8.0 which is obtained after collecting the FePO4·2H2O precipitates.

391

After recovery Li3PO4, the solution consists mainly of sodium ions, phosphate ions and

392

EDTA-2Na (Table S1). EDTA-2Na is possibly recovered by recrystallization while the remaining



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

393

solution with sodium phosphate can be used for softener and detergent, boiler scale inhibitor,

394

dyeing and finishing agent. Detailed research on how to recover the activation additive will be

395

provided in our subsequent research.

396

As shown in Table 4, the global recovery rates of Fe and Li are found to be 93.05%, 82.55%,

397

respectively. In the course of recovering Fe as FePO4·2H2O, without adjusting pH, it was found

398

that about 4.03% Fe was lost in leaching residue and 2.89% Fe into the Li solution. During the

399

lithium recovery process, the lithium loss of leaching process takes 5.72%, recovery Fe 0.35%,

400

precipitation Li3PO4 11.36%. During the precipitation process, the loss of lithium mainly resulted

401

from the complexation with EDTA-2Na and water rinsing in order to get high purity products. It is

402

obvious that the value loss of lithium tops all others in precipitation process due to the chelation of

403

EDTA to lithium ions. For this process, the iron and lithium can be effectively recovered without

404

secondary waste, which contributes significantly to the recycling of metals from waste lithium-ion

405

batteries.

406

407

The effect of mechanochemical activation process on metals recovery from industrial waste

408

LiFePO4 batteries was investigated in phosphoric acid solution. Then, about 93.05% Fe and 82.55%

409

Li could be recovered as FePO4·2H2O and Li3PO4. With a systematic understanding of this novel

410

process, the metal recovery can be optimized and following conclusions can be drawn:

CONCLUSIONS

411

(1) Mechanochemical activation. An innovative process for Fe and Li recovery from spent

412

LiFePO4 batteries through mechanochemical activation is proposed. After mechanochemical

413

activation, about 97.67% Fe and 94.29% Li are recovered under the optimized conditions of

414

activation time (2h), mass ratio of cathode powder to EDTA-2Na =3:1, 0.6M H3PO4, S/L

415

ratio (50g/L), leaching time (20min). According to the mechanochemical activation

416

mechanism, (311) face of cathode powder is more readily destroyed and transformed to

417

disordered states, leading to the significant increase of leaching efficiency.

418

(2) Material Recovery: The thermodynamic diagrams particularly the stable regions of lithium

419

and iron components in the aqueous solutions were calculated. As a result, about 93.05% Fe

420

and 82.55% Li could be recycled in the selective precipitation process via the proton activity

421

modulation.


Page 20 of 25

Page 21 of 25

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


422

On the basis of the results, the advantages of the process are: less amount of dilute acid, high

423

selectivity recovery rate, high purity of product and no secondary waste emission, which reaches

424

a closed-loop process. This research is to provide a technology for selective and effective

425

recycling valuable metals from spent lithium iron phosphate batteries.

426

ASSOCIATED CONTENT

427

Supporting information

428

The Supporting Information is available free of charge on the ACS Publications website at DOI:

429

Profiles of leaching efficiencies with different acidic solutions. The corresponding E-pH diagram

430

of Li-Fe-P-O-H. SEM images of the cathode materials with different leaching time. The

431

composition of residual solution prior to re-circulation.

432

433

The authors acknowledge the financial support on this research from CAS Pioneer Hundred

434

Talents Program (Z.S.), National Natural Science Foundation of China under Grant Nos.

435

51425405 and L1624051 and the National Science–technology Support Plan Projects

436

(2015BAB02B05).

437

438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455

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

ACKNOWLEDGEMENT

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552

TOC/Abstract Art

553

For Table of Contents Use Only

554 555 556 557 558

Synopsis:

559

A closed loop process is demonstrated for selective Fe and Li recovery from spent lithium iron

560

phosphate batteries through mechanochemical activation

561


A Closed-Loop Process for Selective Metal ... - ACS Publications

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