Waste Management 38 (2015) 349–356
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Waste Management journal homepage: www.elsevier.com/locate/wasman
Hydrometallurgical recovery of metal values from sulfuric acid leaching liquor of spent lithium-ion batteries Xiangping Chen, Yongbin Chen, Tao Zhou ⇑, Depei Liu, Hang Hu, Shaoyun Fan Key Laboratory of Resources Chemistry of Nonferrous Metals, College of Chemistry and Chemical Engineering, Central South University, Changsha 410083, China
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Article history: Received 21 November 2014 Accepted 20 December 2014 Available online 22 January 2015 Keywords: Hydrometallurgical process Recovery Metal value Selective precipitation Solvent extraction
a b s t r a c t Environmentally hazardous substances contained in spent Li-ion batteries, such as heavy metals and nocuous organics, will pose a threat to the environment and human health. On the other hand, the sustainable recycling of spent lithium-ion batteries may bring about environmental and economic benefits. In this study, a hydrometallurgical process was adopted for the comprehensive recovery of nickel, manganese, cobalt and lithium from sulfuric acid leaching liquor from waste cathode materials of spent lithiumion batteries. First, nickel ions were selectively precipitated and recovered using dimethylglyoxime reagent. Recycled dimethylglyoxime could be re-used as precipitant for nickel and revealed similar precipitation performance compared with fresh dimethylglyoxime. Then the separation of manganese and cobalt was conducted by solvent extraction method using cobalt loaded D2EHPA. And McCabe–Thiele isotherm was employed for the prediction of the degree of separation and the number of extraction stages needed at specific experimental conditions. Finally, cobalt and lithium were sequentially precipitated and recovered as CoC2O42H2O and Li2CO3 using ammonium oxalate solution and saturated sodium carbonate solution, respectively. Recovery efficiencies could be attained as follows: 98.7% for Ni; 97.1% for Mn, 98.2% for Co and 81.0% for Li under optimized experimental conditions. This hydrometallurgical process may promise a candidate for the effective separation and recovery of metal values from the sulfuric acid leaching liquor. Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction Lithium-ion batteries (LIBs) have been widely used in portable equipment, such as mobile devices (e.g. iPad, iPhone), personal computers and video cameras, but also in hybrid and electric vehicles and other modern-life appliances. Their desirable characteristics such as modest size and weight, high cell voltage, low selfdischarge rate and high energy density may make LIBs an alternative to reduce the currently heavy dependence on fossil fuel resources (Castillo et al., 2002; Contestabile et al., 1999; Zhang et al., 1998). The drastic growth of their usage in nomadic technology market has greatly stimulated the production and consumption of LIBs. However, the consequence of the expansion of LIBs usage and the reduced life of LIBs would be an increasing demand for the disposal of spent LIBs in the forthcoming years (Contestabile et al., 1999; Zhang et al., 1998; Lupi et al., 2003; Lain, 2001). Lithium-ion batteries recently present an active research field and numerous research works are focused on the substitution ⇑ Corresponding author. Tel.: +86 731 8876605. E-mail address:
[email protected] (T. Zhou). http://dx.doi.org/10.1016/j.wasman.2014.12.023 0956-053X/Ó 2015 Elsevier Ltd. All rights reserved.
products to LiCoO2 cathode material, mainly for the consideration of cost and safety. Lower valued transition metals, such as nickel, manganese and iron, were employed to substitute partially or totally for cobalt and a series of newly developed cathode materials have sprung up like mushrooms recently, such as LiFePO4, LiNi1/3Co1/3Mn1/3O2, LiNi0.8Co0.15Al0.05O2 and LiMnO2 (Ellis et al., 2010). However, these emerging materials will lead to a more complicated waste material stream (e.g. mixed waste cathode materials of LiCoO2, LiMnO2, LiNiO2, LiNi1/3Co1/3Mn1/3O2) and an increasing difficulty in the separation and recovery metal values. Spent LIBs are usually comprised of metal values (e.g. Ni, Co, Li), organic chemicals and plastics, varying from different manufacturers and different types of batteries (Chagnes and Pospiech, 2013). However, irresponsible discarding of these untreated spent LIBs may lead to environmental contamination, which cannot meet the requirement of sustainable utilization of valuable materials. This study was particularly focused on the sustainable separation and recovery of metal values from leaching liquor of spent lithium-ion batteries, regardless of battery types. Currently, pyrometallurgical and hydrometallurgical processes are the two common routes used in valuable metals recovery from
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Table 1 Separation and recovery techniques investigated by some previous references. Recovery method
References
Sample
Additive
Solvent extraction
Lupi et al. (2003) Kang et al. (2010) Shen et al. (2008) Pranolo et al. (2010) Provazi et al. (2011) Zhao et al. (2011)
LiCoxNi1xO2 – LiCoO2 LiCoO2 Mixed types of batteries LiCoO2
Cyanex272 Cyanex272 AcorgaM5640, etc. PC-88A Cyanex272, etc. Cyanex272 and EDTA
Selective precipitation
Castillo et al. (2002) Contestabile et al. (2001) Kang et al. (2010) Wang et al. (2009) Dorella and Mansur (2007) Li et al. (2009) Chen et al. (2011)
LiCoO2 & LiMnO2 LiCoO2 LiCoxNi1xO2 LiCoO2, LiMnO2 & LiNiO2 LiCoO2 LiCoO2 LiCoO2
NaOH NaOH NaOH Dimethylglyoxime & KMnO4, etc. NH4OH NaOH H2C2O4
Electrochemical method
Armstrong et al. (1997) Lupi et al. (2005)
– LiCoO2 & LiCoxNi1xO2
–
Resin-ion exchange
Badawy et al. (2014)
LiCoO2
Polyamidoxime resin
Bio-hydrometallurgy
Mishra et al. (2008)
LiCoO2
Acidithiobacillus ferrooxidans
spent lithium-ion batteries (Georgi-Maschler et al., 2012; Cheret and Santen, 2005; Al-Thyabat et al., 2013). The pyrometallurgical processes, however, involve some disadvantages such as materials loss, hazardous gases release, dust emission and high energy consumption. Moreover, a hydrometallurgical process is usually needed to refine the residues into purer forms (such as salts, hydroxides and metals). Conversely, hydrometallurgical process may present an alternative and an opportunity to turn spent batteries into pure metals or metal salts with low energy requirement but produce salts as by-products. Table 1 shows the relevant recovery and separation techniques investigated by some previous references. Sustainable recycling of spent lithium-ion batteries exhibits a promising research field for both environmental protection and valuable materials re-utilization. Present study is, therefore, focused on the separation and recovery of metal values from sulfuric acid leaching liquor of mixed types of waste cathode materials (mixture of LiCoO2, LiMnO2, LiNiO2, LiNi1/3Co1/3Mn1/3O2 in this case) after the pre-treatment of spent LIBs as reported in our previous study (Chen and Zhou, 2014). First, nickel was selectively precipitated by dimethylglyoxime reagent at optimized precipitation conditions after removing of iron ions. Then manganese was selectively extracted from the leaching liquor using cobalt loaded D2EHPA (Co-D2EHPA) (Cole, 2002; Hossain et al., 2011). Finally, cobalt and lithium were sequentially precipitated and separated using ammonium oxalate solution and saturated sodium carbonate solutions (Tang et al., 2014; Wang et al., 2009), respectively. It is expected that this study can provide an effective recycling route for Ni, Co, Mn and Li recovery from leaching liquor of waste cathode materials. 2. Materials and methods 2.1. Materials and reagents In this study, the leaching liquor used was obtained from real leaching liquor of waste cathode materials (reductive leaching of mixed powders contained LiNi1/3Co1/3Mn1/3O2, LiCoO2 and LiMnO2 on conditions as follows: 2 mol L1 H2SO4 + 2 vol.% H2O2, liquid/ solid ratio of 20 ml g1, reaction temperature of 80 °C and reaction time of 60 min). Organic extraction reagents, di-(2-ethylhexly) phosphoric acid (D2EHPA, 95.7% in purity), tri-butyl phosphate
(TBP, 96.8% in purity) and sulfonated kerosene employed were kindly supplied by Luoyang Aoda Chemical Co., Ltd. (Luoyang, China). All other chemical reagents used during the experiments were of analytical grade and all the solutions at specified concentrations were prepared or diluted using deionized water. 2.2. Purification Before the separation and recovery process, iron ions were removed by adjusting pH value of the leaching liquor using 2 mol L1 sodium hydroxide solution. A pH meter (PHS-3D, 2000) was applied for pH monitoring and regulating of the leaching liquor during the purification operation. Afterwards, the pulp was filtered using vacuum suction filter machine and the residue was washed with deionized water to wash off as much valuable metals as possible. The concentrations of metal ions before and after purification were determined by ICP–OES to calculate the precipitation efficiencies of different metals. A small amount of the leaching liquor sample (2 ml) was drawn out and diluted to appropriate concentration. Then contents of different metals in the sample were detected and analyzed using an Induced Coupled Plasma Optical Emission Spectrometer (Agilent Technologies 700 Series ICP–OES). 2.3. Selective precipitation The recovery of nickel, cobalt and lithium was carried out by selective precipitation method. First, nickel was selectively precipitated by adding 0.05 mol L1 dimethylglyoxime reagent (DMG, C4H8N2O2) to the leaching liquor (Wang et al., 2009). Then manganese was extracted by Co-D2EHPA. After the separation of nickel and manganese, cobalt and lithium were sequentially precipitated using 0.5 mol L1 ammonium oxalate solution [(NH4)2C2O4] and hot saturated sodium carbonate solution (Na2CO3, 95 °C), respectively. Experimental conditions, such as equilibrium pH and molar ratio of dimethylglyoxime and nickel, were optimized to obtain the appropriate precipitation conditions. Then the nickel–DMG chelating precipitate was dissolved in 1 mol L1 hydrochloric acid solution to re-generate dimethylglyoxime. The recycled DMG will be re-used as precipitant for nickel. The precipitation and the dissolution reactions can be expressed as follows:
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Cobalt was selectively precipitated using 0.5 mol L1 (NH4)2C2O4 and recovered as CoC2O42H2O after filtration and drying. Finally, lithium was treated with hot saturated sodium carbonate (prepared at 95 °C) and recovered as Li2CO3. All precipitation reactions and dissolution reaction were carried out in a 250 mL three-necked flask placed into an oil bath to control the reaction temperature. The leaching liquor was stirred at 300 rpm by an electromagnetic stirrer, and a vapor condenser was employed to prevent water evaporation. The precipitation efficiency can be calculated according to Eq. (1):
P¼
C 0 V 0 CV 100% C0V 0
ð1Þ
where P is the metal precipitation efficiency; C0 and C are the concentrations of different metals in the solution before and after precipitation, respectively; V0 and V are the volumes of the leach liquor before and after precipitation, respectively. 2.4. Solvent extraction First, di-(2-ethylhexly) phosphoric acid (D2EHPA) was 70–75% saponified using concentrated sodium hydroxide solution (10 mol L1) and then followed by pre-loading of cobalt ions into the organic (Cole, 2002; Hossain et al., 2011). Cobalt ions were pre-loaded to D2EHPA and formed a new extraction reagent, which was carried out by mixing cobalt contained solution (leaching liquor from waste LiCoO2 cathodes after removing the impurity ions such as Fe and Al) with 30 vol.% D2EHPA and 5 vol.% TBP in sulfonated kerosene. The pH values of the aqueous phase were changed from 3.0 to 6.0 with an interval of 0.5 to determine the maximum loading capacity of cobalt in the organic. And the maximum loading of cobalt was attained at pH 5.0 under conditions as follows: 30 vol.% D2EHPA and 5 vol.% TBP in sulfonated kerosene, A:O = 2:1 and mixing time of 300 s. Then the mixture was separated in a centrifugal machine to obtain Co-D2EHPA. After the stripping of manganese, the barren organic of D2EHPA will be pre-loaded with cobalt before it is re-used for manganese extraction. The content of pre-loaded cobalt in the organic was precisely measured using ICP–OES for the calculation of extraction efficiency of cobalt. All the extraction and stripping experiments were conducted in a programmable air bath shaker (Innova-43 Incubator Shaker from New Brunswick Scientific) for the control of reaction temperature, reaction time and stirring rate of the mixture. The stirring speed was maintained at 300 rpm with a stirring time varied at a range from 1 min to 30 min to obtain the optimal extraction time. Unless otherwise stated, all other experiments were carried out at room temperature (25 °C). A series of experimental conditions, including extraction time, equilibrium pH, volume ratio of the organic and aqueous phase (O:A), and volume content of the organic, were investigated to determine the optimal extraction conditions. Besides, extraction isotherm (McCabe–Thiele diagram) was studied to predict the
degree of separation and the number of extraction stages required at specific extraction conditions. The extraction efficiency of different metals can be calculated according to Eq. (2):
E¼
C1V 1 C2V 2 100% C1V 1
ð2Þ
where E is the extraction efficiencies of different metals; C1 and C2 are the concentrations of different metals in the aqueous phase before and after extraction, respectively; V1 and V2 are the volumes of aqueous phase before and after extraction, respectively. 2.5. Analytical methods The concentrations of different metals were measured by an Induced Coupled Plasma Optical Emission Spectrometer (Agilent Technologies 700 Series ICP–OES). Concentrations of metals in the organic phase were computed from the differences between initial concentrations of different metals in aqueous phase and the concentrations of different metals in raffinate. The pH meter (PHS-3D, 2000) was employed for pH monitoring and regulating. IR spectra (Thermo Scientific Nicolet iS10 FR-IR Spectrometer) were employed to identify the relevant vibrational characteristic bands of the loaded organic and predict the detailed mechanism of the extraction reaction. XRD (Rigaku, Cu Ka) was employed for phase analysis and structure determination of different precipitates (nickel–DMG chelating precipitate and CoC2O42H2O). To avoid random errors, three parallel experiments were performed during the whole selective precipitation and solvent extraction operations and the mean values of precipitation or extraction efficiencies would be treated as the final experimental results. 3. Results and discussion 3.1. Purification The main elements in the sulfuric acid leachate were Fe, Ni, Co, Mn and Li and their contents were 0.59, 6.89, 6.45, 6.31 and 1.60 g L1, respectively. Table 2 shows the effect of pH value on the precipitation of different metals between 3.0 and 7.0. The result shows that nearly all Fe ions could be removed at a low pH of 3.1. And higher pH will result in obvious loss of other metal values (e.g. 51.9% and 38.4% for Ni and Co, respectively at pH of
Table 2 Removal of iron ions by adjusting the pH of the leaching liquor (25 °C). pH
Contents of different metals (mg/L) Fe
Ni
Co
Mn
Li
3.1 4.2 5.5 6.8
2.1
