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Recovery of cobalt from spent lithium-ion batteries using supercritical carbon dioxide extraction
Waste Management xxx (2016) xxx–xxx
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Recovery of cobalt from spent lithium-ion batteries using supercritical carbon dioxide extraction Daniel A. Bertuol ⇑, Caroline M. Machado, Mariana L. Silva, Camila O. Calgaro, Guilherme L. Dotto, Eduardo H. Tanabe Environmental Processes Laboratory (LAPAM), Chemical Engineering Department, Universidade Federal de Santa Maria – UFSM, Avenida Roraima 1000, 97105-900 Santa Maria, RS, Brazil
a r t i c l e
i n f o
Article history: Received 30 September 2015 Revised 3 March 2016 Accepted 4 March 2016 Available online xxxx Keywords: Recycling Lithium ion batteries Fast extraction Supercritical fluids Cobalt
a b s t r a c t Continuing technological development decreases the useful lifetime of electronic equipment, resulting in the generation of waste and the need for new and more efficient recycling processes. The objective of this work is to study the effectiveness of supercritical fluids for the leaching of cobalt contained in lithium-ion batteries (LIBs). For comparative purposes, leaching tests are performed with supercritical CO2 and cosolvents, as well as under conventional conditions. In both cases, sulfuric acid and H2O2 are used as reagents. The solution obtained from the supercritical leaching is processed using electrowinning in order to recover the cobalt. The results show that at atmospheric pressure, cobalt leaching is favored by increasing the amount of H2O2 (from 0 to 8% v/v). The use of supercritical conditions enable extraction of more than 95 wt% of the cobalt, with reduction of the reaction time from 60 min (the time employed in leaching at atmospheric pressure) to 5 min, and a reduction in the concentration of H2O2 required from 8 to 4% (v/v). Electrowinning using a leach solution achieve a current efficiency of 96% and a deposit with cobalt concentration of 99.5 wt%. Ó 2016 Elsevier Ltd. All rights reserved.
1. Introduction The useful lifespans of electronic products, especially portable devices such as cell phones and laptops, have decreased due to the constant introduction of new technologies. This has resulted in the generation of large quantities of waste electrical and electronic equipment (WEEE), including spent lithium-ion batteries (LIBs) (M.K. Jha et al., 2013; Shin et al., 2005). The inappropriate disposal of these batteries can cause serious environmental problems due to their hazardous constituents, such as heavy metals and electrolytes. However, some of these materials, for example cobalt and lithium, are strategic and valuable metals and must therefore be recycled (Zhu et al., 2012). In addition to protecting the environment, the recycling of LIBs improves the use of natural resources and can contribute to decreasing the cost of battery production. These wastes are an important secondary source of metals; in some cases, the concentrations of metals present in batteries are higher than in ores (A.K. Jha et al., 2013; Dorella and Mansur, 2007). Moreover, the price of cobalt has increased significantly in recent years, making it economically feasible to recycle this metal (L. Li et al., 2013). In ⇑ Corresponding author.
2007, approximately 25% of global demand for cobalt was for battery applications (Dewulf et al., 2010). The widespread use of LIBs is mainly due to their high energy density, low weight, high cell voltage, low self-discharge rate, and wide operating temperature range, when compared to nickel-cadmium or nickel-metal hydride batteries used in mobile phones and other electronic devices (Swain et al., 2007; Bertuol et al., 2015a). LIBs consist of an anode, a cathode, electrolytes, a separator, and an outer shell (Bertuol et al., 2015a; Bernardes et al., 2004; Ferreira et al., 2009). The anode is composed of a copper foil covered by a layer of powdered graphitic carbon, while the cathode consists of an aluminum foil coated with a layer of metal oxide such as LiCoO2 powder (L. Li et al., 2013). This compound is most widely employed as the cathode in LIBs, due to its good electrochemical performance. However, disadvantages are its high cost, limited cobalt resources, and toxicity (Bertuol et al., 2015a; Li et al., 2010). The separators are made of polymeric materials, and the external case is usually constructed of steel or aluminum (Wu et al., 2000; Bertuol et al., 2015b). The typical composition of these batteries is 5–20 wt% Co, 5–10 wt% Ni, 5–7 wt% Li, 15 wt % organics, and 7 wt% plastics (Bertuol et al., 2015b; Kang et al., 2010). The composition varies slightly, depending on the manufacturing process.
E-mail address: [email protected] (D.A. Bertuol). http://dx.doi.org/10.1016/j.wasman.2016.03.009 0956-053X/Ó 2016 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Bertuol, D.A., et al. Recovery of cobalt from spent lithium-ion batteries using supercritical carbon dioxide extraction. Waste Management (2016), http://dx.doi.org/10.1016/j.wasman.2016.03.009
99
95
98
97
93
70 96.3 80
80 60 50 2M Sun and Qiu (2011)
5%
85 120 100 4M Chen et al. (2011)
10%
60 60 100 2M Kang et al. (2010)
6%
40 60 33.33 0.75 M Ferreira et al. (2009)
1%
2M Swain et al. (2007)
5%
100
30
75
Leaching of the anode and cathode, with sizes of 4 mm LiCoO2 leaching assisted by ultrasound Manual dismantling, simultaneous leaching of cathode and anode Leaching of LiCoO2 waste generated during the manufacture of lithium-ion batteries Cathode leaching in two steps: first with NaOH to selectively leach of Al, then acid leaching to extract cobalt and lithium Discharge, dehydration, drying, and grinding of the battery as a physical pretreatment, followed by leaching of 16-mesh powder Manual battery disassembly followed by leaching of the anode and cathode Pretreatment by vacuum pyrolysis followed by acid leaching of the LiCoO2
Method Temperature (°C)
75 60 65 60 120 60
Reaction time (min) Solid-liquid ratio (g/L)
100 33 33.33 5% 2% 1% 2M 2M 6% (v/v) M.K. Jha et al. (2013) Zhu et al. (2012) Dorella and Mansur (2007)
H2O2 (v/v) H2SO4 Reference
Different technologies based on pyrometallurgical or hydrometallurgical processes can be used for the recycling of LIBs (Freitas et al., 2010). Pyrometallurgical processes are commonly used in industry for the recovery of valuable metals, providing high productivity and efficiency, but drawbacks are high energy consumption and the emission of hazardous gases (Joulié et al., 2014). Hydrometallurgical processes involve the dissolution of metals in alkaline or acid medium (Birloaga et al., 2013). Hydrometallurgical processes are more benign from an environmental point of view and usually involve mechanical separation processes for battery dismantling, followed by dissolution of the electrodes in concentrated acids (Bertuol et al., 2015a, 2015b). After the leaching step, the resulting solution containing the metallic ions is usually submitted to precipitation, extraction, and electrowinning processes in order to recover the desired metals (Bertuol et al., 2015a; Freitas et al., 2010). The recovery of valuable metals from spent LIBs usually employs acid leaching in the presence of a reducing agent that converts the metals to a more soluble oxidation state. H2O2 in sulfuric acid solution acts as an effective reducing agent, which enhance the percentage leaching of metals (M.K. Jha et al., 2013). The metals in solution can then be readily separated by techniques such as electrowinning or precipitation (L. Li et al., 2013). The literature reports several studies that have evaluated the recovery of cobalt after leaching with H2SO4 (Table 1). In most of the studies, reaction times longer than 60 min were required. The present work evaluates a more efficient method for cobalt recovery, with faster reaction kinetics, using supercritical CO2 modified with co-solvents. The use of supercritical fluids is an attractive option, due to the interesting properties of these solvents and the fact that they can be recycled and reused, hence providing environmental benefits (Herrero et al., 2010). Among the various fluids used for extraction, CO2 stands out because of its low cost, good chemical stability, relatively low critical point (Tc = 31.1 °C, Pc = 7.38 MPa), high diffusivity, low viscosity, wide range of applications, and easy handling (Lin et al., 2014). Calgaro et al. (2015) developed an alternative method for recovery of Cu from the printed circuit boards (PCBs) of obsolete mobile phones, employing supercritical CO2 modified with sulfuric acid and hydrogen peroxide. They concluded that supercritical leaching with CO2 and co-solvents provided faster reaction kinetics for Cu recovery. The supercritical extraction was 9 times faster, compared to atmospheric pressure extraction. In addition, the use of supercritical CO2 using water as cosolvent, in order to de-laminate the PCB and separate its constituent materials by removing the polymers was studied (Sanyal et al., 2013). The use of water under supercritical conditions has also been employed for removal of the polymer fraction by the degradation of brominated epoxy resins, constituting a pretreatment step for recovery of the metals present (Xiu and Zhang, 2009; Xing and Zhang, 2013; Xiu et al., 2013). Supercritical fluids such as CO2, modified with complexing or chelating agents, have also been employed for the extraction of metal ions from various solid or liquid matrices (Herrero et al., 2010). Chelation or complexation is responsible for converting the metal species into soluble neutral complexes in the supercritical CO2 (Sunarso and Ismadji, 2009). For example, Cu was extracted from waste wood containing chromated copper arsenate using supercritical CO2 and Cyanex 302 as co-solvent (Wang and Chiu, 2008). In many environmental applications, water is often present in a supercritical fluids extraction system as a part of the original sample or added deliberately. Water in contact with carbon dioxide becomes acidic due to the formation and dissociation of carbonic acid (Toews et al., 1995):
Cobalt recovery (wt%)
D.A. Bertuol et al. / Waste Management xxx (2016) xxx–xxx
Table 1 Studies reported in the literature for cobalt recovery from LIBs by acid leaching.
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Please cite this article in press as: Bertuol, D.A., et al. Recovery of cobalt from spent lithium-ion batteries using supercritical carbon dioxide extraction. Waste Management (2016), http://dx.doi.org/10.1016/j.wasman.2016.03.009
D.A. Bertuol et al. / Waste Management xxx (2016) xxx–xxx
CO2 þ H2 O $ H2 CO3 $ Hþ þ HCO3
ð1Þ
It is therefore of interest to study the application of supercritical CO2 modified with co-solvents in the direct recovery of metals from solid wastes such as spent Li-ion batteries. Conversion of metals from their solid forms to soluble ionic forms can result in more efficient reaction kinetics for the leaching process involved. This study investigates cobalt recovery using acid leaching at atmospheric pressure, and using supercritical CO2 with cosolvents (H2SO4 and H2O2), followed by an electrowinning step. The obtained results demonstrate the efficiency of the process. The supercritical CO2 employment in the LIBs recycling is a promising alternative and the CO2 is environmentally acceptable and reusable. However, to the best of our knowledge, there have been no previous studies concerning the application of supercritical fluids in battery recycling. 1.1. Electronic waste management strategies Several studies related to the management of electronic waste have been reported in scientific literature, since this is both a local and global issue (Araújo et al., 2012; Kidee et al., 2013; Hong et al., 2015; J. Li et al., 2013; Niza et al., 2014; Song et al., 2012; Steubing et al., 2010; Wibowo and Deng, 2015). Kidee et al. (2013) performed a literature review and discussed the use of managerial tools such as Life Cycle Assessment (LCA), Material Flow Analysis (MFA) and Extended Producer Responsibility (EPR) to evaluate e-waste destination in develop countries. Song et al. (2012) used LCA to evaluate environmental impacts of TV sets in China. Steubing et al. (2010) used MFA method to assess the generation of electronic waste from desktops, laptops, CRT e LCD-monitors in Chile. In Brazil, the National Solid Waste Management Policy (Política Nacional de Resíduos Sólidos – PNRS) was approved in August 2010 (Brazil, Presidência da República, 2010), based on the concepts of shared product responsibility, product life cycle and the reverse logistics for several sectors, including electrical and electronic waste (Araújo et al., 2012). This policy, in general terms, establishes the shared responsibility between government, industry, commerce and end consumers in the management of the solid wastes. This policy also imposes reverse logistics, which requires manufacturers, importers, distributors and sellers of special waste (where the electronics products are included), to collect and give the best destination of its products once discarded by consumers. Thus, this new environmental policy will stimulate the implementation of industrial plants in Brazil, for the recycling of technological waste such as batteries (Brazil, Presidência da República, 2010).
3
were performed in triplicate. Results represent an average of 3 determinations. 2.2. Leaching at atmospheric pressure Leaching tests were conducted at atmospheric pressure in 500 mL three-neck round-bottom volumetric flasks, immersed in a bath heated at a controlled temperature of 75 °C. A condenser was used to avoid losses by evaporation, and the system was kept under magnetic stirring at 300 rpm. Initial tests to determine the best experimental conditions were conducted using hydrogen peroxide concentrations varying from 0 to 8% v/v, sulfuric acid (H2SO4) at a concentration of 2 M, a leaching time of 60 min, and a solid-liquid ratio of 1:20 (g:mL). These conditions were chosen to enable comparison with results reported in the literature. The extraction kinetics was determined for the H2O2 concentration that provided the highest cobalt recovery. At the end of the leaching processes, the solutions were filtered and analyzed by flame atomic absorption spectroscopy (FAAS) (240 FS AA series, Agilent Technologies). All results represent an average of 3 determinations. 2.3. Supercritical fluid extraction In order to improve the leaching process, shortening the extraction time and reducing the consumption of reagents, leaching tests were performed under supercritical conditions. All the tests, performed as a batch process, were done under CO2 pressure of 75 bar, at a temperature of 75 °C, using 2 M H2SO4 and H2O2 as co-solvents, with a solid:liquid ratio of 1:20 (g:mL). The selected pressure was close to the minimum required to achieve the critical pressure of the gas used (CO2), while the other parameters (including temperature) were the same as used in conventional leaching tests, for the purposes of comparison (Lin et al., 2014). Firstly, tests were performed with H2O2 concentrations of 1.3– 8% (v/v) and time of 5 min, in order to identify the best conditions for cobalt extraction. The reaction kinetics was then determined using the hydrogen peroxide concentration that provided highest cobalt recovery. Finally, the solutions were analyzed by FAAS. All results represent an average of 3 determinations. Fig. 1 shows the system used to perform the leaching tests under supercritical conditions. The material to be leached was placed together with the co-solvents in a stainless steel reactor (Extractor, Fig. 1) internally coated with Teflon and jacketed to
2. Materials and methods 2.1. LIBs characterization and dismantling A batch of 30 batteries of the same brand and model were manually opened and the different constituents were separated. Only the cathodic material was used in the cobalt recovery tests. This material was separated from the aluminum foil by scraping, mixed and then quartering prior to use in the characterization and leaching procedures. The batteries employed had an individual average weight of about 20 g, with about 8 g (40 wt%) corresponding to the cathode. The active cathodic material was a powder composed of LiCoO2, weighing about 6 g per battery. The powder was characterized by X-ray fluorescence (XRF) (S8 TIGER, Bruker), and X-ray powder diffractometry (XRD) (Miniflex 300, Rigaku). The XRF analyzes
Fig. 1. Scheme of the system employed in the leaching tests under supercritical conditions.
Please cite this article in press as: Bertuol, D.A., et al. Recovery of cobalt from spent lithium-ion batteries using supercritical carbon dioxide extraction. Waste Management (2016), http://dx.doi.org/10.1016/j.wasman.2016.03.009
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allow the reaction temperature to be controlled using an ultrathermostatic bath (Q214M2, Quimis). Pressurized CO2 (99.5%) was supplied to the system, with the pressure controlled by a syringe-type pump (model 500D, Teledyne Isco). At the end of the extraction, the gas was separated from the solution, which was collected in a flask (Extracted sample, Fig. 1), while the gas passed through a washing step with sodium hydroxide solution (Basic solution, Fig. 1) before being released to the atmosphere.
2.4. Electrowinning A cell with 500 mL capacity was used, consisting of two compartments separated by an anionic membrane (PC Acid 60, PCA GmbH) with dimensions of 7.0 9.0 cm. The use of a membrane increases the current efficiency by separating the cathodic and anodic reactions, and avoids rapid changes in pH (Bertuol et al., 2012). A stainless steel cathode (9 cm2) and a titanium anode coated with a platinum/iridium alloy (49 cm2) were used. The solutions were circulated through the system by two centrifugal pumps operated at a constant rate of 2 L min1. Leaching solution was employed as the cathodic solution and sodium sulfate (1 M) was used as the anodic solution. Fig. 2 shows the assembly of the cell used in the electrowinning tests. The anodic compartment consisted of the module 1. The cathodic compartment is composed of modules 2 and 3, connected with a seal ring, allowing the anolyte to circulate freely in both modules. The cathodic solution inlet was at the top of the cell in order to provide better mixing. The experiments were performed for 120 min at 60 °C and current density of 250 A m2, under constant agitation (200 rpm). The pH was maintained constant at pH 4 by the addition of concentrated sodium hydroxide and sulfuric acid solutions. The cathode was weighed before and after each experiment, with the mass difference corresponding to the deposited material. The current efficiency was then determined by dividing the theoretical current required to produce the deposit by the real current supplied (Bertuol et al., 2012). The metallic deposit was characterized by scanning electron microscopy (SEM) (Inspect S50, FEI).
3. Results and discussion 3.1. LIBs characterization Table 2 shows the elemental composition of the cathodic material, determined using XRF. Cobalt, a main component of LiCoO2, was present at the highest concentration. Phosphorus was derived from the LiPF6 electrolyte used in LiBs (Zhang et al., 2014). Aluminum contamination probably originated from the foil that was scraped to remove the cathodic material (Bertuol et al., 2015b). A sample of the cathodic powder was also analyzed by X-ray diffraction (XRD) to confirm the presence of LiCoO2. The resulting spectrum (Fig. 3) was similar to those reported elsewhere (Ferreira et al., 2009; Sun and Qiu, 2011; Ganesan et al., 2006). The XRD pattern of LiCoO2 is compared with standard JCPDS data (card # 50-0653).
3.2. Acid leaching 3.2.1. Influence of H2O2 concentration on the extraction Fig. 4a shows the results obtained using H2O2 at different ratios during a leaching time of 60 min. Acid leaching of lithium cobalt oxide is difficult due to the strong chemical bond between cobalt and oxygen. Higher recovery of cobalt was obtained when the amount of H2O2 was increased, as found previously under comparable conditions (Swain et al., 2007). In the absence of H2O2, cobalt recovery was around 69 wt%, while the value increased to 98 wt% with addition of 8% (v/v) H2O2. The positive effect of H2O2 addition can be explained by its decomposition during the leaching process, releasing oxygen, which then converts Co3+ in the solid species to Co2+ in the aqueous phase, helping dissolution of the metal (Shin et al., 2005; Ferreira et al., 2009; Lee and Rhee, 2002). The results showed that the use of H2O2 was essential in order to be able to recover almost all of the cobalt in the material.
Table 2 Cathode composition obtained by X-ray fluorescence (XRF). Composition (wt%) Element
Co
P
Al
Others
72.85 ± 0.5
0.58 ± 0.02
0.34 ± 0.15
1.07
Fig. 2. Assembly scheme of the two-compartment cell used in the electrowinning tests.
Please cite this article in press as: Bertuol, D.A., et al. Recovery of cobalt from spent lithium-ion batteries using supercritical carbon dioxide extraction. Waste Management (2016), http://dx.doi.org/10.1016/j.wasman.2016.03.009
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Fig. 5. Reaction kinetics for leaching tests using 2 M H2SO4, and solid-liquid ratio of 1:20 (g:mL) at 75 °C. (a) Atmospheric pressure, 8% (v/v) of H2O2. (b) Supercritical extraction, 4% (v/v) H2O2, 75 bar.
Fig. 3. X-ray diffractogram of the battery cathode.
constant at around 72 wt% after times of 10 and 20 min, while 98 wt% of cobalt was extracted after 60 min. In earlier work using conditions similar to those employed here, M.K. Jha et al. (2013) found that the reaction reached equilibrium after 60 min and that the cobalt extraction efficiency was low for times shorter than 20 min. 3.3. Supercritical extraction
Fig. 4. Cobalt extraction as a function of H2O2 concentration, using 2 M H2SO4 and a solid-liquid ratio of 1:20 (g:mL) at 75 °C. (a) Atmospheric pressure, reaction time of 60 min, (b) supercritical extraction, reaction time of 5 min at 75 bar.
The following reaction scheme was proposed by Ferreira et al. (2009) for the leaching of LiCoO2 in the presence of H2O2:
4LiCoO2ðsÞ þ 3H2 SO4 þ H2 O2 ! Co3 O4ðsÞ þ 2Li2 SO4ðaqÞ þ CoSO4ðaqÞ þ 4H2 O þ O2 Co3 O4 þ 3H2 SO4 þ H2 O2 ! 3CoSO4ðaqÞ þ 4H2 O þ O2
ð2Þ ð3Þ
The following global reaction was proposed by Swain et al. (2007):
4LiCoO2ðsÞ þ 6H2 SO4 þ 2H2 O2 ! 4CoSO4ðaqÞ þ 2Li2 SO4ðaqÞ þ 8H2 O þ 2O2
ð4Þ
The results reported here showed that the concentration of H2O2 was the most significant variable in the leaching of LiCoO2 from Li-ion batteries using H2SO4, in agreement with the literature describing the importance of H2O2 for cobalt leaching (Swain et al., 2007; Bertuol et al., 2015a; Bernardes et al., 2004; Ferreira et al., 2009). Although the lithium behavior was not studied in this work, it is expected that the lithium will be also solubilized by this method. In the study conducted by M.K. Jha et al. (2013), leaching with 2 M sulfuric acid with the addition of 5% H2O2 (v/v) at a pulp density of 100 g/L and 75 °C resulted in the recovery of 99.1% lithium and 70.0% cobalt in 60 min. 3.2.2. Influence of extraction time The effect of reaction time on extraction performed using 8% (v/ v) H2O2 is illustrated in Fig. 5a. The extraction efficiency remained
3.3.1. Influence of H2O2 concentration The extraction of cobalt using supercritical CO2 was achieved in a shorter time, compared to leaching at atmospheric pressure, as can be seen in Fig. 4. The dissolution of CO2 in water results in formation of carbonic acid with a decrease in pH, favoring the metals leaching (Jean et al., 2015). Under normal supercritical fluid extraction conditions, water in equilibrium with supercritical CO2 has a pH value in the range of 2.8–2.9, due to dissolution of CO2 and formation of carbonic acid in water (Wang et al., 2005; Beckman, 2004). The optimal H2O2 concentration was determined in tests performed over periods of 5 min, using different concentrations of this co-solvent. The results (Fig. 4b) showed that a higher H2O2 concentration had a positive effect on cobalt extraction, with maximum extraction of 95.5 wt% obtained with 4% (v/v) H2O2. However, when the H2O2 percentage was increased to 5.3 and 8% (v/v) H2O2 lower cobalt recoveries were obtained. The same behavior was observed by Calgaro et al. (2015), when employed CO2 in the leaching of copper from the printed circuit boards. 3.3.2. Influence of extraction time The extraction kinetics data showed that after 1 min of reaction, around 80 wt% of cobalt was extracted under the optimum conditions employing 4% (v/v) H2O2 (Fig. 5b). Maximum cobalt extraction (95.5 wt%) was achieved in a reaction time of 5 min. For times longer than 5 min, there was a decrease in extraction efficiency, as observed in the leaching tests at atmospheric pressure after 60 min of reaction. This could have been due to the consumption of H2O2, so that the maintenance of cobalt in a soluble form was not favored.
Table 3 Comparison of cobalt extraction efficiencies (wt%) obtained using supercritical and conventional leaching. % H2O2 (v/v)
Supercritical (5 min)
Conventional (60 min)
2.6 4 5.3
76.3 ± 2.2 95.5 ± 4.5 92.5 ± 1.9
72.6 ± 1.4 75.2 ± 0.9 86.7 ± 1.2
Please cite this article in press as: Bertuol, D.A., et al. Recovery of cobalt from spent lithium-ion batteries using supercritical carbon dioxide extraction. Waste Management (2016), http://dx.doi.org/10.1016/j.wasman.2016.03.009
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Fig. 6. (a) X-ray diffractogram of the deposit obtained in the electrowinning process. (b) Micrograph of the cobalt deposit obtained from electrowinning of a leaching solution at 250 A/m2, 60 °C.
This could be explained by the degradation of H2O2, hindering Co dissolution, because when extractions were performed in the absence of H2O2, a reduced amount of Co was leached (Fig. 4a). Furthermore, the degradation of H2O2 might result in the displacement of some of the Co from the complex with sulfate, due to reaction with more reactive metals present in the reaction medium, such as Li (Calgaro et al., 2015). The supercritical extraction method was able to improve the efficiency of cobalt extraction. When compared to conventional leaching, the amount of H2O2 required to achieve cobalt extraction exceeding 90% was reduced from 8 to 4% (v/v), and the time required for satisfactory extraction was significantly shorter (Table 3). The extraction efficiencies achieved in 5 min under supercritical conditions were superior to those obtained in 60 min of conventional leaching. Despite the power consumption required to maintain the CO2 in supercritical conditions, the major advantages of using supercritical technology for cobalt extraction were therefore that the process was significantly faster and required less consumption of reagents. It is believed that faster reaction kinetic for the cobalt extraction is result from the use of supercritical CO2, which significantly improves mass transfer process, through the disappearance of phase boundaries (Calgaro et al., 2015). 3.4. Electrowinning After leaching, the solutions were subjected to an electrowinning process, where a current efficiency of 96% was achieved. The deposit obtained was then analyzed by X-ray diffraction (Fig. 6a) in order to confirm the presence of cobalt (JCPDS data # 01-1278). The deposit was also examined using scanning electron microscopy. Fig. 6b shows the deposit surface, where it can be seen that the particle morphology consisted of fibrous crystallites (Pradhan et al., 2001). In addition, the deposit was dissolved in an acidic solution and analyzed by AAS to determine the concentrations of lithium and cobalt. The results confirmed that lithium and cobalt were present at concentrations of 0.4 wt% and 99.5 wt%, respectively. 4. Conclusions The findings showed that supercritical extraction of cobalt from spent lithium-ion batteries offers advantages over conventional
methods. Supercritical extraction enabled cobalt recovery of 95.5 wt% in a shorter reaction time and using a smaller amount of H2O2, compared to leaching at atmospheric pressure. In order to achieve an extraction efficiency of 98 wt%, the conventional method required the use of 8% (v/v) H2O2 and a reaction time of 60 min, whereas the supercritical method achieved a satisfactory extraction of 95.5 wt% in a reaction time of 5 min and using 4% (v/v) H2O2. Hence, in order to achieve a very similar degree of extraction, supercritical technology shortened the extraction time 12-fold and required only half the amount of H2O2 used in the conventional method. Furthermore, cobalt was efficiently recovered in metallic form by electrowinning, with a current efficiency of approximately 96%.
Acknowledgments The authors are grateful for the financial support provided by CAPES (Brazilian Agency for Improvement of Graduate Personnel), CNPq (National Council of Science and Technological Development), and FAPERGS (Rio Grande do Sul State Research Support Foundation).
References Araújo, M.G., Magrini, A., Mahler, C.F., Bilitewski, M., 2012. A model for estimation of potential generation of waste electrical and electronic equipment in Brazil. Waste Manage. 32, 335–342. Beckman, E., 2004. Supercritical and near-critical CO2 in green chemical synthesis and processing. J. Supercrit. Fluids 28, 121–191. Bernardes, A.M., Espinosa, D.C.R., Tenório, J.A.S., 2004. Recycling of batteries: a review of current processes and technologies. J. Power Sources 130, 291–298. Bertuol, D.A., Amado, F.D.R., Ferreira, J.Z., Bernardes, A.M., 2012. Recovery of nickel and cobalt from spent NiMH batteries by electrowinning. Chem. Eng. Technol. 35, 2084–2092. Bertuol, D.A., Foletto, E.L., Tanabe, E.H., Costa, A.J., 2015a. Lithium ion batteries. In: Veit, H.M., Moura Bernardes, A. (Eds.), Electronic Waste, Topics in Mining, Metallurgy and Materials Engineering. http://dx.doi.org/10.1007/978-3-31915714-6_10. Bertuol, D.A., Toniasso, C., Jimenez, B.M., Meili, L., Dotto, G.L., Tanabe, E.H., Aguiar, M.L., 2015b. Application of spouted bed elutriation in the recycling of lithium ion batteries. J. Power Sources 275, 627–632. Birloaga, I., Michelis, I., Farella, F., Buzatu, M., Vegliò, F., 2013. Study on the influence of various factors in the hydrometallurgical processing of waste printed circuit boards for copper and gold recovery. Waste Manage. 33, 935–941. Brazil, Presidência da República, 2010. National Solid Waste Policy (Politica Nacional de Resíduos Sólidos – Lei No. 12.305/2010) (in Portuguese). Calgaro, C.O., Schlemmer, D.F., Silva, M.D., Maziero, E.V., Tanabe, E.H., Bertuol, D.A., 2015. Fast copper extraction from printed circuit boards using supercritical carbon dioxide. Waste Manage. 45, 289–297.
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D.A. Bertuol et al. / Waste Management xxx (2016) xxx–xxx Chen, L., Tang, X., Zhang, Y., Li, L., Zeng, Z., Zhang, Y., 2011. Process for the recovery of cobalt oxalate from spent lithium-ion batteries. Hydrometallurgy 108, 80–86. Dewulf, J., Van der Vorst, G., Denturck, K., Langenhove, H.V., Ghyoot, W., Tytgat, J., Vandeputte, K., 2010. Recycling rechargeable lithium ion batteries: critical analysis of natural resource savings. Resour. Conserv. Recycl. 54, 229–234. Dorella, G., Mansur, M.B., 2007. A study of the separation of cobalt from spent Li-ion battery residues. J. Power Sources 170, 210–215. Ferreira, D.A., Prados, L.M.Z., Majuste, D., Mansur, M.B., 2009. Hydrometallurgical separation of aluminium, cobalt, copper and lithium from spent Li-ion batteries. J. Power Sources 187, 238–246. Freitas, M.B.J.G., Celante, V.G., Pietre, M.K., 2010. Electrochemical recovery of cobalt and copper from spent Li-ion batteries as multilayer deposits. J. Power Sources 195, 3309–3315. Ganesan, M., Sundararajan, S., Dhananjeyan, M.V.T., Sarangapani, K.B., Renganathan, N.G., 2006. Synthesis and characterization of tetravalent titanium (Ti4+) substituted LiCoO2 for lithium-ion batteries. Mater. Sci. Eng. B 131, 203–209. Herrero, M., Mendiola, J.A., Cifuentes, A., Ibáñez, E., 2010. Supercritical fluid extraction: recent advances and applications. J. Chromatogr. A 1217, 2495– 2511. Hong, J., Shi, W., Wang, Y., Chen, W., Xiangzhi, Li., 2015. Life cycle assessment of electronic waste treatment. Waste Manage. 38, 357–365. Jean, J.S., Wang, C.L., Hsiang, H.I., Li, Z., Yang, H.J., Jiang, W.T., Yang, K.M., Bundschuh, J., 2015. Experimental investigation of trace element dissolution in formation water in the presence of supercritical CO2 fluid for a potential geological storage site of CO2 in Taiwan. J. Nat. Gas Sci. Eng. 23, 304–314. Jha, A.K., Jha, M.K., Kumari, A., Sahu, S.K., Kumar, V., Pandey, B.D., 2013. Selective separation and recovery of cobalt from leach liquor of discarded Li-ion batteries using thiophosphinic extractant. Sep. Purif. Technol. 104, 160–166. Jha, M.K., Kumari, A., Jha, A.K., Kumar, V., Hait, J., Pandey, B.D., 2013. Recovery of lithium and cobalt from waste lithium ion batteries of mobile phone. Waste Manage. 33, 1890–1897. Joulié, M., Laucournet, R., Billy, E., 2014. Hydrometallurgical process for the recovery of high value metals from spent lithium nickel cobalt aluminum oxide based lithium-ion batteries. J. Power Sources 247, 551–555. Kang, J., Senanayake, G., Sohn, J., Shin, S.M., 2010. Recovery of cobalt sulfate from spent lithium ion batteries by reductive leaching and solvent extraction with Cyanex 272. Hydrometallurgy 100, 168–171. Kidee, P., Naidu, R., Wong, M.H., 2013. Electronic waste management approaches: an overview. Waste Manage. 33, 1237–1250. Lee, C.K., Rhee, K.I., 2002. Preparation of LiCoO2 from spent lithium-ion batteries. J. Power Sources 109, 17–21. Li, L., Ge, J., Chen, R., Wu, F., Chen, S., Zhang, X., 2010. Environmental friendly leaching reagent for cobalt and lithium recovery from spent lithium-ion batteries. Waste Manage. 30, 2615–2621. Li, L., Dunn, J.B., Zhang, X.X., Gaines, L., Chen, R.J., Wu, F., Amine, K., 2013. Recovery of metals from spent lithium-ion batteries with organic acids as leaching reagents and environmental assessment J. Power Sources 233, 180–189. Li, J., Lopez, B.N., Liu, L., Zhao, N., Yu, K., Zheng, L., 2013. Regional or global WEEE recycling. Where to go? Waste Manage. 33, 923–934. Lin, F., Liu, D., Das, S.M., Prempeh, N., Hua, Y., Lu, J., 2014. Recent progress in heavy metal extraction by supercritical CO2 fluids. Ind. Eng. Chem. Res. 53 (5), 1866– 1877.
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Niza, S., Santos, E., Costa, I., Ribeiro, P., Ferrão, P., 2014. Extended producer responsibility policy in Portugal: a strategy towards improving waste management performance. J. Clean. Prod. 64, 277–287. Pradhan, N., Singh, P., Tripathy, B.C., Das, S.C., 2001. Electrowinning of cobalt from acidic sulphate solutions—effect of chloride ion. Miner. Eng. 14, 775–783. Sanyal, S., Ke, Q., Zhang, Y., Ngo, T., Carrell, J., Zhang, H., Dai, L.L., 2013. Understanding and optimizing delamination/recycling of printed circuit boards using a supercritical carbon dioxide process. J. Clean. Prod. 41, 174–178. Shin, S.M., Kim, N.H., Sohn, J.S., Yang, D.H., Kim, Y.H., 2005. Development of a metal recovery process from Li-ion battery wastes. Hydrometallurgy 79, 172–181. Song, Q., Wang, Z., Li, J., Zeng, X., 2012. Life cycle assessment of TV sets in China: a case study of the impacts of CRT monitors. Waste Manage. 32, 1926–1936. Steubing, B., Boni, H., Schluep, M., Silva, U., Ludwig, C., 2010. Assessing computer waste generation in Chile using material flow analysis. Waste Manage. 30, 473– 482. Sun, L., Qiu, K., 2011. Vacuum pyrolysis and hydrometallurgical process for the recovery of valuable metals from spent lithium-ion batteries. J. Hazard. Mater. 194, 378–384. Sunarso, J., Ismadji, S., 2009. Decontamination of hazardous substances from solid matrices and liquids using supercritical fluids extraction: a review. J. Hazard. Mater. 161, 1–20. Swain, B., Jeong, J., Lee, J., Lee, G., Sohn, J., 2007. Hydrometallurgical process for recovery of cobalt from waste cathodic active material generated during manufacturing of lithium ion batteries. J. Power Sources 67, 536–544. Toews, K.L., Shroll, R.M., Wai, C.M., 1995. pH-defining equilibrium between water and supercritical CO2. Influence on SFE of organics and metal chelates. Anal. Chem. 67, 4040–4043. Wang, J.S., Chiu, K., 2008. Extraction of chromated copper arsenate from wood wastes using green solvent supercritical carbon dioxide. J. Hazard. Mater. 158, 384–391. Wang, J.S., Herman, J., Enokida, Y., Wai, C.M., 2005. Dissolution of organic acids in supercritical CO2 using a CO2-philic Lewis base carrier. J. Supercrit. Fluids 36, 98–105. Wibowo, S., Deng, H., 2015. Multi-criteria group making for evaluating the performance of e-waste recycling programs under uncertainty. Waste Manage. 40, 127–135. Wu, Q., Lu, W., Prakash, J., 2000. Characterization of a commercial size cylindrical Liion cell with a reference electrode. J. Power Sources 88, 237–242. Xing, M., Zhang, F.S., 2013. Degradation of brominated epoxy resin and metal recovery from waste printed circuit boards through batch sub/supercritical water treatments. Chem. Eng. J. 219, 131–136. Xiu, F.R., Zhang, F.S., 2009. Recovery of copper and lead from waste printed circuit boards by supercritical water oxidation combined with electrokinetic process. J. Hazard. Mater. 165, 1002–1007. Xiu, F.R., Qi, Y., Zhang, F.S., 2013. Recovery of metals from waste printed circuit boards by supercritical water pre-treatment combined with acid leaching process. Waste Manage. 33, 1251–1257. Zhang, T., He, Y., Wang, F., Li, H., Duan, C., Wu, C., 2014. Surface analysis of cobaltenriched crushed products of spent lithium-ion batteries by X-ray photoelectron spectroscopy. Sep. Purif. Technol. 138, 21–27. Zhu, S., He, W., Li, G., Zhou, X., Zhang, X., Huang, J., 2012. Recovery of Co and Li from spent lithium-ion batteries by combination method of acid leaching and chemical precipitation. Trans. Nonferrous Met. Soc. China 22, 2274–2281.
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Recovery of cobalt from spent lithium-ion batteries using supercritical carbon dioxide extraction Daniel A. Bertuol ⇑, Caroline M. Machado, Mariana L. Silva, Camila O. Calgaro, Guilherme L. Dotto, Eduardo H. Tanabe Environmental Processes Laboratory (LAPAM), Chemical Engineering Department, Universidade Federal de Santa Maria – UFSM, Avenida Roraima 1000, 97105-900 Santa Maria, RS, Brazil
a r t i c l e
i n f o
Article history: Received 30 September 2015 Revised 3 March 2016 Accepted 4 March 2016 Available online xxxx Keywords: Recycling Lithium ion batteries Fast extraction Supercritical fluids Cobalt
a b s t r a c t Continuing technological development decreases the useful lifetime of electronic equipment, resulting in the generation of waste and the need for new and more efficient recycling processes. The objective of this work is to study the effectiveness of supercritical fluids for the leaching of cobalt contained in lithium-ion batteries (LIBs). For comparative purposes, leaching tests are performed with supercritical CO2 and cosolvents, as well as under conventional conditions. In both cases, sulfuric acid and H2O2 are used as reagents. The solution obtained from the supercritical leaching is processed using electrowinning in order to recover the cobalt. The results show that at atmospheric pressure, cobalt leaching is favored by increasing the amount of H2O2 (from 0 to 8% v/v). The use of supercritical conditions enable extraction of more than 95 wt% of the cobalt, with reduction of the reaction time from 60 min (the time employed in leaching at atmospheric pressure) to 5 min, and a reduction in the concentration of H2O2 required from 8 to 4% (v/v). Electrowinning using a leach solution achieve a current efficiency of 96% and a deposit with cobalt concentration of 99.5 wt%. Ó 2016 Elsevier Ltd. All rights reserved.
1. Introduction The useful lifespans of electronic products, especially portable devices such as cell phones and laptops, have decreased due to the constant introduction of new technologies. This has resulted in the generation of large quantities of waste electrical and electronic equipment (WEEE), including spent lithium-ion batteries (LIBs) (M.K. Jha et al., 2013; Shin et al., 2005). The inappropriate disposal of these batteries can cause serious environmental problems due to their hazardous constituents, such as heavy metals and electrolytes. However, some of these materials, for example cobalt and lithium, are strategic and valuable metals and must therefore be recycled (Zhu et al., 2012). In addition to protecting the environment, the recycling of LIBs improves the use of natural resources and can contribute to decreasing the cost of battery production. These wastes are an important secondary source of metals; in some cases, the concentrations of metals present in batteries are higher than in ores (A.K. Jha et al., 2013; Dorella and Mansur, 2007). Moreover, the price of cobalt has increased significantly in recent years, making it economically feasible to recycle this metal (L. Li et al., 2013). In ⇑ Corresponding author.
2007, approximately 25% of global demand for cobalt was for battery applications (Dewulf et al., 2010). The widespread use of LIBs is mainly due to their high energy density, low weight, high cell voltage, low self-discharge rate, and wide operating temperature range, when compared to nickel-cadmium or nickel-metal hydride batteries used in mobile phones and other electronic devices (Swain et al., 2007; Bertuol et al., 2015a). LIBs consist of an anode, a cathode, electrolytes, a separator, and an outer shell (Bertuol et al., 2015a; Bernardes et al., 2004; Ferreira et al., 2009). The anode is composed of a copper foil covered by a layer of powdered graphitic carbon, while the cathode consists of an aluminum foil coated with a layer of metal oxide such as LiCoO2 powder (L. Li et al., 2013). This compound is most widely employed as the cathode in LIBs, due to its good electrochemical performance. However, disadvantages are its high cost, limited cobalt resources, and toxicity (Bertuol et al., 2015a; Li et al., 2010). The separators are made of polymeric materials, and the external case is usually constructed of steel or aluminum (Wu et al., 2000; Bertuol et al., 2015b). The typical composition of these batteries is 5–20 wt% Co, 5–10 wt% Ni, 5–7 wt% Li, 15 wt % organics, and 7 wt% plastics (Bertuol et al., 2015b; Kang et al., 2010). The composition varies slightly, depending on the manufacturing process.
E-mail address: [email protected] (D.A. Bertuol). http://dx.doi.org/10.1016/j.wasman.2016.03.009 0956-053X/Ó 2016 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Bertuol, D.A., et al. Recovery of cobalt from spent lithium-ion batteries using supercritical carbon dioxide extraction. Waste Management (2016), http://dx.doi.org/10.1016/j.wasman.2016.03.009
99
95
98
97
93
70 96.3 80
80 60 50 2M Sun and Qiu (2011)
5%
85 120 100 4M Chen et al. (2011)
10%
60 60 100 2M Kang et al. (2010)
6%
40 60 33.33 0.75 M Ferreira et al. (2009)
1%
2M Swain et al. (2007)
5%
100
30
75
Leaching of the anode and cathode, with sizes of 4 mm LiCoO2 leaching assisted by ultrasound Manual dismantling, simultaneous leaching of cathode and anode Leaching of LiCoO2 waste generated during the manufacture of lithium-ion batteries Cathode leaching in two steps: first with NaOH to selectively leach of Al, then acid leaching to extract cobalt and lithium Discharge, dehydration, drying, and grinding of the battery as a physical pretreatment, followed by leaching of 16-mesh powder Manual battery disassembly followed by leaching of the anode and cathode Pretreatment by vacuum pyrolysis followed by acid leaching of the LiCoO2
Method Temperature (°C)
75 60 65 60 120 60
Reaction time (min) Solid-liquid ratio (g/L)
100 33 33.33 5% 2% 1% 2M 2M 6% (v/v) M.K. Jha et al. (2013) Zhu et al. (2012) Dorella and Mansur (2007)
H2O2 (v/v) H2SO4 Reference
Different technologies based on pyrometallurgical or hydrometallurgical processes can be used for the recycling of LIBs (Freitas et al., 2010). Pyrometallurgical processes are commonly used in industry for the recovery of valuable metals, providing high productivity and efficiency, but drawbacks are high energy consumption and the emission of hazardous gases (Joulié et al., 2014). Hydrometallurgical processes involve the dissolution of metals in alkaline or acid medium (Birloaga et al., 2013). Hydrometallurgical processes are more benign from an environmental point of view and usually involve mechanical separation processes for battery dismantling, followed by dissolution of the electrodes in concentrated acids (Bertuol et al., 2015a, 2015b). After the leaching step, the resulting solution containing the metallic ions is usually submitted to precipitation, extraction, and electrowinning processes in order to recover the desired metals (Bertuol et al., 2015a; Freitas et al., 2010). The recovery of valuable metals from spent LIBs usually employs acid leaching in the presence of a reducing agent that converts the metals to a more soluble oxidation state. H2O2 in sulfuric acid solution acts as an effective reducing agent, which enhance the percentage leaching of metals (M.K. Jha et al., 2013). The metals in solution can then be readily separated by techniques such as electrowinning or precipitation (L. Li et al., 2013). The literature reports several studies that have evaluated the recovery of cobalt after leaching with H2SO4 (Table 1). In most of the studies, reaction times longer than 60 min were required. The present work evaluates a more efficient method for cobalt recovery, with faster reaction kinetics, using supercritical CO2 modified with co-solvents. The use of supercritical fluids is an attractive option, due to the interesting properties of these solvents and the fact that they can be recycled and reused, hence providing environmental benefits (Herrero et al., 2010). Among the various fluids used for extraction, CO2 stands out because of its low cost, good chemical stability, relatively low critical point (Tc = 31.1 °C, Pc = 7.38 MPa), high diffusivity, low viscosity, wide range of applications, and easy handling (Lin et al., 2014). Calgaro et al. (2015) developed an alternative method for recovery of Cu from the printed circuit boards (PCBs) of obsolete mobile phones, employing supercritical CO2 modified with sulfuric acid and hydrogen peroxide. They concluded that supercritical leaching with CO2 and co-solvents provided faster reaction kinetics for Cu recovery. The supercritical extraction was 9 times faster, compared to atmospheric pressure extraction. In addition, the use of supercritical CO2 using water as cosolvent, in order to de-laminate the PCB and separate its constituent materials by removing the polymers was studied (Sanyal et al., 2013). The use of water under supercritical conditions has also been employed for removal of the polymer fraction by the degradation of brominated epoxy resins, constituting a pretreatment step for recovery of the metals present (Xiu and Zhang, 2009; Xing and Zhang, 2013; Xiu et al., 2013). Supercritical fluids such as CO2, modified with complexing or chelating agents, have also been employed for the extraction of metal ions from various solid or liquid matrices (Herrero et al., 2010). Chelation or complexation is responsible for converting the metal species into soluble neutral complexes in the supercritical CO2 (Sunarso and Ismadji, 2009). For example, Cu was extracted from waste wood containing chromated copper arsenate using supercritical CO2 and Cyanex 302 as co-solvent (Wang and Chiu, 2008). In many environmental applications, water is often present in a supercritical fluids extraction system as a part of the original sample or added deliberately. Water in contact with carbon dioxide becomes acidic due to the formation and dissociation of carbonic acid (Toews et al., 1995):
Cobalt recovery (wt%)
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Table 1 Studies reported in the literature for cobalt recovery from LIBs by acid leaching.
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D.A. Bertuol et al. / Waste Management xxx (2016) xxx–xxx
CO2 þ H2 O $ H2 CO3 $ Hþ þ HCO3
ð1Þ
It is therefore of interest to study the application of supercritical CO2 modified with co-solvents in the direct recovery of metals from solid wastes such as spent Li-ion batteries. Conversion of metals from their solid forms to soluble ionic forms can result in more efficient reaction kinetics for the leaching process involved. This study investigates cobalt recovery using acid leaching at atmospheric pressure, and using supercritical CO2 with cosolvents (H2SO4 and H2O2), followed by an electrowinning step. The obtained results demonstrate the efficiency of the process. The supercritical CO2 employment in the LIBs recycling is a promising alternative and the CO2 is environmentally acceptable and reusable. However, to the best of our knowledge, there have been no previous studies concerning the application of supercritical fluids in battery recycling. 1.1. Electronic waste management strategies Several studies related to the management of electronic waste have been reported in scientific literature, since this is both a local and global issue (Araújo et al., 2012; Kidee et al., 2013; Hong et al., 2015; J. Li et al., 2013; Niza et al., 2014; Song et al., 2012; Steubing et al., 2010; Wibowo and Deng, 2015). Kidee et al. (2013) performed a literature review and discussed the use of managerial tools such as Life Cycle Assessment (LCA), Material Flow Analysis (MFA) and Extended Producer Responsibility (EPR) to evaluate e-waste destination in develop countries. Song et al. (2012) used LCA to evaluate environmental impacts of TV sets in China. Steubing et al. (2010) used MFA method to assess the generation of electronic waste from desktops, laptops, CRT e LCD-monitors in Chile. In Brazil, the National Solid Waste Management Policy (Política Nacional de Resíduos Sólidos – PNRS) was approved in August 2010 (Brazil, Presidência da República, 2010), based on the concepts of shared product responsibility, product life cycle and the reverse logistics for several sectors, including electrical and electronic waste (Araújo et al., 2012). This policy, in general terms, establishes the shared responsibility between government, industry, commerce and end consumers in the management of the solid wastes. This policy also imposes reverse logistics, which requires manufacturers, importers, distributors and sellers of special waste (where the electronics products are included), to collect and give the best destination of its products once discarded by consumers. Thus, this new environmental policy will stimulate the implementation of industrial plants in Brazil, for the recycling of technological waste such as batteries (Brazil, Presidência da República, 2010).
3
were performed in triplicate. Results represent an average of 3 determinations. 2.2. Leaching at atmospheric pressure Leaching tests were conducted at atmospheric pressure in 500 mL three-neck round-bottom volumetric flasks, immersed in a bath heated at a controlled temperature of 75 °C. A condenser was used to avoid losses by evaporation, and the system was kept under magnetic stirring at 300 rpm. Initial tests to determine the best experimental conditions were conducted using hydrogen peroxide concentrations varying from 0 to 8% v/v, sulfuric acid (H2SO4) at a concentration of 2 M, a leaching time of 60 min, and a solid-liquid ratio of 1:20 (g:mL). These conditions were chosen to enable comparison with results reported in the literature. The extraction kinetics was determined for the H2O2 concentration that provided the highest cobalt recovery. At the end of the leaching processes, the solutions were filtered and analyzed by flame atomic absorption spectroscopy (FAAS) (240 FS AA series, Agilent Technologies). All results represent an average of 3 determinations. 2.3. Supercritical fluid extraction In order to improve the leaching process, shortening the extraction time and reducing the consumption of reagents, leaching tests were performed under supercritical conditions. All the tests, performed as a batch process, were done under CO2 pressure of 75 bar, at a temperature of 75 °C, using 2 M H2SO4 and H2O2 as co-solvents, with a solid:liquid ratio of 1:20 (g:mL). The selected pressure was close to the minimum required to achieve the critical pressure of the gas used (CO2), while the other parameters (including temperature) were the same as used in conventional leaching tests, for the purposes of comparison (Lin et al., 2014). Firstly, tests were performed with H2O2 concentrations of 1.3– 8% (v/v) and time of 5 min, in order to identify the best conditions for cobalt extraction. The reaction kinetics was then determined using the hydrogen peroxide concentration that provided highest cobalt recovery. Finally, the solutions were analyzed by FAAS. All results represent an average of 3 determinations. Fig. 1 shows the system used to perform the leaching tests under supercritical conditions. The material to be leached was placed together with the co-solvents in a stainless steel reactor (Extractor, Fig. 1) internally coated with Teflon and jacketed to
2. Materials and methods 2.1. LIBs characterization and dismantling A batch of 30 batteries of the same brand and model were manually opened and the different constituents were separated. Only the cathodic material was used in the cobalt recovery tests. This material was separated from the aluminum foil by scraping, mixed and then quartering prior to use in the characterization and leaching procedures. The batteries employed had an individual average weight of about 20 g, with about 8 g (40 wt%) corresponding to the cathode. The active cathodic material was a powder composed of LiCoO2, weighing about 6 g per battery. The powder was characterized by X-ray fluorescence (XRF) (S8 TIGER, Bruker), and X-ray powder diffractometry (XRD) (Miniflex 300, Rigaku). The XRF analyzes
Fig. 1. Scheme of the system employed in the leaching tests under supercritical conditions.
Please cite this article in press as: Bertuol, D.A., et al. Recovery of cobalt from spent lithium-ion batteries using supercritical carbon dioxide extraction. Waste Management (2016), http://dx.doi.org/10.1016/j.wasman.2016.03.009
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allow the reaction temperature to be controlled using an ultrathermostatic bath (Q214M2, Quimis). Pressurized CO2 (99.5%) was supplied to the system, with the pressure controlled by a syringe-type pump (model 500D, Teledyne Isco). At the end of the extraction, the gas was separated from the solution, which was collected in a flask (Extracted sample, Fig. 1), while the gas passed through a washing step with sodium hydroxide solution (Basic solution, Fig. 1) before being released to the atmosphere.
2.4. Electrowinning A cell with 500 mL capacity was used, consisting of two compartments separated by an anionic membrane (PC Acid 60, PCA GmbH) with dimensions of 7.0 9.0 cm. The use of a membrane increases the current efficiency by separating the cathodic and anodic reactions, and avoids rapid changes in pH (Bertuol et al., 2012). A stainless steel cathode (9 cm2) and a titanium anode coated with a platinum/iridium alloy (49 cm2) were used. The solutions were circulated through the system by two centrifugal pumps operated at a constant rate of 2 L min1. Leaching solution was employed as the cathodic solution and sodium sulfate (1 M) was used as the anodic solution. Fig. 2 shows the assembly of the cell used in the electrowinning tests. The anodic compartment consisted of the module 1. The cathodic compartment is composed of modules 2 and 3, connected with a seal ring, allowing the anolyte to circulate freely in both modules. The cathodic solution inlet was at the top of the cell in order to provide better mixing. The experiments were performed for 120 min at 60 °C and current density of 250 A m2, under constant agitation (200 rpm). The pH was maintained constant at pH 4 by the addition of concentrated sodium hydroxide and sulfuric acid solutions. The cathode was weighed before and after each experiment, with the mass difference corresponding to the deposited material. The current efficiency was then determined by dividing the theoretical current required to produce the deposit by the real current supplied (Bertuol et al., 2012). The metallic deposit was characterized by scanning electron microscopy (SEM) (Inspect S50, FEI).
3. Results and discussion 3.1. LIBs characterization Table 2 shows the elemental composition of the cathodic material, determined using XRF. Cobalt, a main component of LiCoO2, was present at the highest concentration. Phosphorus was derived from the LiPF6 electrolyte used in LiBs (Zhang et al., 2014). Aluminum contamination probably originated from the foil that was scraped to remove the cathodic material (Bertuol et al., 2015b). A sample of the cathodic powder was also analyzed by X-ray diffraction (XRD) to confirm the presence of LiCoO2. The resulting spectrum (Fig. 3) was similar to those reported elsewhere (Ferreira et al., 2009; Sun and Qiu, 2011; Ganesan et al., 2006). The XRD pattern of LiCoO2 is compared with standard JCPDS data (card # 50-0653).
3.2. Acid leaching 3.2.1. Influence of H2O2 concentration on the extraction Fig. 4a shows the results obtained using H2O2 at different ratios during a leaching time of 60 min. Acid leaching of lithium cobalt oxide is difficult due to the strong chemical bond between cobalt and oxygen. Higher recovery of cobalt was obtained when the amount of H2O2 was increased, as found previously under comparable conditions (Swain et al., 2007). In the absence of H2O2, cobalt recovery was around 69 wt%, while the value increased to 98 wt% with addition of 8% (v/v) H2O2. The positive effect of H2O2 addition can be explained by its decomposition during the leaching process, releasing oxygen, which then converts Co3+ in the solid species to Co2+ in the aqueous phase, helping dissolution of the metal (Shin et al., 2005; Ferreira et al., 2009; Lee and Rhee, 2002). The results showed that the use of H2O2 was essential in order to be able to recover almost all of the cobalt in the material.
Table 2 Cathode composition obtained by X-ray fluorescence (XRF). Composition (wt%) Element
Co
P
Al
Others
72.85 ± 0.5
0.58 ± 0.02
0.34 ± 0.15
1.07
Fig. 2. Assembly scheme of the two-compartment cell used in the electrowinning tests.
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Fig. 5. Reaction kinetics for leaching tests using 2 M H2SO4, and solid-liquid ratio of 1:20 (g:mL) at 75 °C. (a) Atmospheric pressure, 8% (v/v) of H2O2. (b) Supercritical extraction, 4% (v/v) H2O2, 75 bar.
Fig. 3. X-ray diffractogram of the battery cathode.
constant at around 72 wt% after times of 10 and 20 min, while 98 wt% of cobalt was extracted after 60 min. In earlier work using conditions similar to those employed here, M.K. Jha et al. (2013) found that the reaction reached equilibrium after 60 min and that the cobalt extraction efficiency was low for times shorter than 20 min. 3.3. Supercritical extraction
Fig. 4. Cobalt extraction as a function of H2O2 concentration, using 2 M H2SO4 and a solid-liquid ratio of 1:20 (g:mL) at 75 °C. (a) Atmospheric pressure, reaction time of 60 min, (b) supercritical extraction, reaction time of 5 min at 75 bar.
The following reaction scheme was proposed by Ferreira et al. (2009) for the leaching of LiCoO2 in the presence of H2O2:
4LiCoO2ðsÞ þ 3H2 SO4 þ H2 O2 ! Co3 O4ðsÞ þ 2Li2 SO4ðaqÞ þ CoSO4ðaqÞ þ 4H2 O þ O2 Co3 O4 þ 3H2 SO4 þ H2 O2 ! 3CoSO4ðaqÞ þ 4H2 O þ O2
ð2Þ ð3Þ
The following global reaction was proposed by Swain et al. (2007):
4LiCoO2ðsÞ þ 6H2 SO4 þ 2H2 O2 ! 4CoSO4ðaqÞ þ 2Li2 SO4ðaqÞ þ 8H2 O þ 2O2
ð4Þ
The results reported here showed that the concentration of H2O2 was the most significant variable in the leaching of LiCoO2 from Li-ion batteries using H2SO4, in agreement with the literature describing the importance of H2O2 for cobalt leaching (Swain et al., 2007; Bertuol et al., 2015a; Bernardes et al., 2004; Ferreira et al., 2009). Although the lithium behavior was not studied in this work, it is expected that the lithium will be also solubilized by this method. In the study conducted by M.K. Jha et al. (2013), leaching with 2 M sulfuric acid with the addition of 5% H2O2 (v/v) at a pulp density of 100 g/L and 75 °C resulted in the recovery of 99.1% lithium and 70.0% cobalt in 60 min. 3.2.2. Influence of extraction time The effect of reaction time on extraction performed using 8% (v/ v) H2O2 is illustrated in Fig. 5a. The extraction efficiency remained
3.3.1. Influence of H2O2 concentration The extraction of cobalt using supercritical CO2 was achieved in a shorter time, compared to leaching at atmospheric pressure, as can be seen in Fig. 4. The dissolution of CO2 in water results in formation of carbonic acid with a decrease in pH, favoring the metals leaching (Jean et al., 2015). Under normal supercritical fluid extraction conditions, water in equilibrium with supercritical CO2 has a pH value in the range of 2.8–2.9, due to dissolution of CO2 and formation of carbonic acid in water (Wang et al., 2005; Beckman, 2004). The optimal H2O2 concentration was determined in tests performed over periods of 5 min, using different concentrations of this co-solvent. The results (Fig. 4b) showed that a higher H2O2 concentration had a positive effect on cobalt extraction, with maximum extraction of 95.5 wt% obtained with 4% (v/v) H2O2. However, when the H2O2 percentage was increased to 5.3 and 8% (v/v) H2O2 lower cobalt recoveries were obtained. The same behavior was observed by Calgaro et al. (2015), when employed CO2 in the leaching of copper from the printed circuit boards. 3.3.2. Influence of extraction time The extraction kinetics data showed that after 1 min of reaction, around 80 wt% of cobalt was extracted under the optimum conditions employing 4% (v/v) H2O2 (Fig. 5b). Maximum cobalt extraction (95.5 wt%) was achieved in a reaction time of 5 min. For times longer than 5 min, there was a decrease in extraction efficiency, as observed in the leaching tests at atmospheric pressure after 60 min of reaction. This could have been due to the consumption of H2O2, so that the maintenance of cobalt in a soluble form was not favored.
Table 3 Comparison of cobalt extraction efficiencies (wt%) obtained using supercritical and conventional leaching. % H2O2 (v/v)
Supercritical (5 min)
Conventional (60 min)
2.6 4 5.3
76.3 ± 2.2 95.5 ± 4.5 92.5 ± 1.9
72.6 ± 1.4 75.2 ± 0.9 86.7 ± 1.2
Please cite this article in press as: Bertuol, D.A., et al. Recovery of cobalt from spent lithium-ion batteries using supercritical carbon dioxide extraction. Waste Management (2016), http://dx.doi.org/10.1016/j.wasman.2016.03.009
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D.A. Bertuol et al. / Waste Management xxx (2016) xxx–xxx
Fig. 6. (a) X-ray diffractogram of the deposit obtained in the electrowinning process. (b) Micrograph of the cobalt deposit obtained from electrowinning of a leaching solution at 250 A/m2, 60 °C.
This could be explained by the degradation of H2O2, hindering Co dissolution, because when extractions were performed in the absence of H2O2, a reduced amount of Co was leached (Fig. 4a). Furthermore, the degradation of H2O2 might result in the displacement of some of the Co from the complex with sulfate, due to reaction with more reactive metals present in the reaction medium, such as Li (Calgaro et al., 2015). The supercritical extraction method was able to improve the efficiency of cobalt extraction. When compared to conventional leaching, the amount of H2O2 required to achieve cobalt extraction exceeding 90% was reduced from 8 to 4% (v/v), and the time required for satisfactory extraction was significantly shorter (Table 3). The extraction efficiencies achieved in 5 min under supercritical conditions were superior to those obtained in 60 min of conventional leaching. Despite the power consumption required to maintain the CO2 in supercritical conditions, the major advantages of using supercritical technology for cobalt extraction were therefore that the process was significantly faster and required less consumption of reagents. It is believed that faster reaction kinetic for the cobalt extraction is result from the use of supercritical CO2, which significantly improves mass transfer process, through the disappearance of phase boundaries (Calgaro et al., 2015). 3.4. Electrowinning After leaching, the solutions were subjected to an electrowinning process, where a current efficiency of 96% was achieved. The deposit obtained was then analyzed by X-ray diffraction (Fig. 6a) in order to confirm the presence of cobalt (JCPDS data # 01-1278). The deposit was also examined using scanning electron microscopy. Fig. 6b shows the deposit surface, where it can be seen that the particle morphology consisted of fibrous crystallites (Pradhan et al., 2001). In addition, the deposit was dissolved in an acidic solution and analyzed by AAS to determine the concentrations of lithium and cobalt. The results confirmed that lithium and cobalt were present at concentrations of 0.4 wt% and 99.5 wt%, respectively. 4. Conclusions The findings showed that supercritical extraction of cobalt from spent lithium-ion batteries offers advantages over conventional
methods. Supercritical extraction enabled cobalt recovery of 95.5 wt% in a shorter reaction time and using a smaller amount of H2O2, compared to leaching at atmospheric pressure. In order to achieve an extraction efficiency of 98 wt%, the conventional method required the use of 8% (v/v) H2O2 and a reaction time of 60 min, whereas the supercritical method achieved a satisfactory extraction of 95.5 wt% in a reaction time of 5 min and using 4% (v/v) H2O2. Hence, in order to achieve a very similar degree of extraction, supercritical technology shortened the extraction time 12-fold and required only half the amount of H2O2 used in the conventional method. Furthermore, cobalt was efficiently recovered in metallic form by electrowinning, with a current efficiency of approximately 96%.
Acknowledgments The authors are grateful for the financial support provided by CAPES (Brazilian Agency for Improvement of Graduate Personnel), CNPq (National Council of Science and Technological Development), and FAPERGS (Rio Grande do Sul State Research Support Foundation).
References Araújo, M.G., Magrini, A., Mahler, C.F., Bilitewski, M., 2012. A model for estimation of potential generation of waste electrical and electronic equipment in Brazil. Waste Manage. 32, 335–342. Beckman, E., 2004. Supercritical and near-critical CO2 in green chemical synthesis and processing. J. Supercrit. Fluids 28, 121–191. Bernardes, A.M., Espinosa, D.C.R., Tenório, J.A.S., 2004. Recycling of batteries: a review of current processes and technologies. J. Power Sources 130, 291–298. Bertuol, D.A., Amado, F.D.R., Ferreira, J.Z., Bernardes, A.M., 2012. Recovery of nickel and cobalt from spent NiMH batteries by electrowinning. Chem. Eng. Technol. 35, 2084–2092. Bertuol, D.A., Foletto, E.L., Tanabe, E.H., Costa, A.J., 2015a. Lithium ion batteries. In: Veit, H.M., Moura Bernardes, A. (Eds.), Electronic Waste, Topics in Mining, Metallurgy and Materials Engineering. http://dx.doi.org/10.1007/978-3-31915714-6_10. Bertuol, D.A., Toniasso, C., Jimenez, B.M., Meili, L., Dotto, G.L., Tanabe, E.H., Aguiar, M.L., 2015b. Application of spouted bed elutriation in the recycling of lithium ion batteries. J. Power Sources 275, 627–632. Birloaga, I., Michelis, I., Farella, F., Buzatu, M., Vegliò, F., 2013. Study on the influence of various factors in the hydrometallurgical processing of waste printed circuit boards for copper and gold recovery. Waste Manage. 33, 935–941. Brazil, Presidência da República, 2010. National Solid Waste Policy (Politica Nacional de Resíduos Sólidos – Lei No. 12.305/2010) (in Portuguese). Calgaro, C.O., Schlemmer, D.F., Silva, M.D., Maziero, E.V., Tanabe, E.H., Bertuol, D.A., 2015. Fast copper extraction from printed circuit boards using supercritical carbon dioxide. Waste Manage. 45, 289–297.
Please cite this article in press as: Bertuol, D.A., et al. Recovery of cobalt from spent lithium-ion batteries using supercritical carbon dioxide extraction. Waste Management (2016), http://dx.doi.org/10.1016/j.wasman.2016.03.009
D.A. Bertuol et al. / Waste Management xxx (2016) xxx–xxx Chen, L., Tang, X., Zhang, Y., Li, L., Zeng, Z., Zhang, Y., 2011. Process for the recovery of cobalt oxalate from spent lithium-ion batteries. Hydrometallurgy 108, 80–86. Dewulf, J., Van der Vorst, G., Denturck, K., Langenhove, H.V., Ghyoot, W., Tytgat, J., Vandeputte, K., 2010. Recycling rechargeable lithium ion batteries: critical analysis of natural resource savings. Resour. Conserv. Recycl. 54, 229–234. Dorella, G., Mansur, M.B., 2007. A study of the separation of cobalt from spent Li-ion battery residues. J. Power Sources 170, 210–215. Ferreira, D.A., Prados, L.M.Z., Majuste, D., Mansur, M.B., 2009. Hydrometallurgical separation of aluminium, cobalt, copper and lithium from spent Li-ion batteries. J. Power Sources 187, 238–246. Freitas, M.B.J.G., Celante, V.G., Pietre, M.K., 2010. Electrochemical recovery of cobalt and copper from spent Li-ion batteries as multilayer deposits. J. Power Sources 195, 3309–3315. Ganesan, M., Sundararajan, S., Dhananjeyan, M.V.T., Sarangapani, K.B., Renganathan, N.G., 2006. Synthesis and characterization of tetravalent titanium (Ti4+) substituted LiCoO2 for lithium-ion batteries. Mater. Sci. Eng. B 131, 203–209. Herrero, M., Mendiola, J.A., Cifuentes, A., Ibáñez, E., 2010. Supercritical fluid extraction: recent advances and applications. J. Chromatogr. A 1217, 2495– 2511. Hong, J., Shi, W., Wang, Y., Chen, W., Xiangzhi, Li., 2015. Life cycle assessment of electronic waste treatment. Waste Manage. 38, 357–365. Jean, J.S., Wang, C.L., Hsiang, H.I., Li, Z., Yang, H.J., Jiang, W.T., Yang, K.M., Bundschuh, J., 2015. Experimental investigation of trace element dissolution in formation water in the presence of supercritical CO2 fluid for a potential geological storage site of CO2 in Taiwan. J. Nat. Gas Sci. Eng. 23, 304–314. Jha, A.K., Jha, M.K., Kumari, A., Sahu, S.K., Kumar, V., Pandey, B.D., 2013. Selective separation and recovery of cobalt from leach liquor of discarded Li-ion batteries using thiophosphinic extractant. Sep. Purif. Technol. 104, 160–166. Jha, M.K., Kumari, A., Jha, A.K., Kumar, V., Hait, J., Pandey, B.D., 2013. Recovery of lithium and cobalt from waste lithium ion batteries of mobile phone. Waste Manage. 33, 1890–1897. Joulié, M., Laucournet, R., Billy, E., 2014. Hydrometallurgical process for the recovery of high value metals from spent lithium nickel cobalt aluminum oxide based lithium-ion batteries. J. Power Sources 247, 551–555. Kang, J., Senanayake, G., Sohn, J., Shin, S.M., 2010. Recovery of cobalt sulfate from spent lithium ion batteries by reductive leaching and solvent extraction with Cyanex 272. Hydrometallurgy 100, 168–171. Kidee, P., Naidu, R., Wong, M.H., 2013. Electronic waste management approaches: an overview. Waste Manage. 33, 1237–1250. Lee, C.K., Rhee, K.I., 2002. Preparation of LiCoO2 from spent lithium-ion batteries. J. Power Sources 109, 17–21. Li, L., Ge, J., Chen, R., Wu, F., Chen, S., Zhang, X., 2010. Environmental friendly leaching reagent for cobalt and lithium recovery from spent lithium-ion batteries. Waste Manage. 30, 2615–2621. Li, L., Dunn, J.B., Zhang, X.X., Gaines, L., Chen, R.J., Wu, F., Amine, K., 2013. Recovery of metals from spent lithium-ion batteries with organic acids as leaching reagents and environmental assessment J. Power Sources 233, 180–189. Li, J., Lopez, B.N., Liu, L., Zhao, N., Yu, K., Zheng, L., 2013. Regional or global WEEE recycling. Where to go? Waste Manage. 33, 923–934. Lin, F., Liu, D., Das, S.M., Prempeh, N., Hua, Y., Lu, J., 2014. Recent progress in heavy metal extraction by supercritical CO2 fluids. Ind. Eng. Chem. Res. 53 (5), 1866– 1877.
7
Niza, S., Santos, E., Costa, I., Ribeiro, P., Ferrão, P., 2014. Extended producer responsibility policy in Portugal: a strategy towards improving waste management performance. J. Clean. Prod. 64, 277–287. Pradhan, N., Singh, P., Tripathy, B.C., Das, S.C., 2001. Electrowinning of cobalt from acidic sulphate solutions—effect of chloride ion. Miner. Eng. 14, 775–783. Sanyal, S., Ke, Q., Zhang, Y., Ngo, T., Carrell, J., Zhang, H., Dai, L.L., 2013. Understanding and optimizing delamination/recycling of printed circuit boards using a supercritical carbon dioxide process. J. Clean. Prod. 41, 174–178. Shin, S.M., Kim, N.H., Sohn, J.S., Yang, D.H., Kim, Y.H., 2005. Development of a metal recovery process from Li-ion battery wastes. Hydrometallurgy 79, 172–181. Song, Q., Wang, Z., Li, J., Zeng, X., 2012. Life cycle assessment of TV sets in China: a case study of the impacts of CRT monitors. Waste Manage. 32, 1926–1936. Steubing, B., Boni, H., Schluep, M., Silva, U., Ludwig, C., 2010. Assessing computer waste generation in Chile using material flow analysis. Waste Manage. 30, 473– 482. Sun, L., Qiu, K., 2011. Vacuum pyrolysis and hydrometallurgical process for the recovery of valuable metals from spent lithium-ion batteries. J. Hazard. Mater. 194, 378–384. Sunarso, J., Ismadji, S., 2009. Decontamination of hazardous substances from solid matrices and liquids using supercritical fluids extraction: a review. J. Hazard. Mater. 161, 1–20. Swain, B., Jeong, J., Lee, J., Lee, G., Sohn, J., 2007. Hydrometallurgical process for recovery of cobalt from waste cathodic active material generated during manufacturing of lithium ion batteries. J. Power Sources 67, 536–544. Toews, K.L., Shroll, R.M., Wai, C.M., 1995. pH-defining equilibrium between water and supercritical CO2. Influence on SFE of organics and metal chelates. Anal. Chem. 67, 4040–4043. Wang, J.S., Chiu, K., 2008. Extraction of chromated copper arsenate from wood wastes using green solvent supercritical carbon dioxide. J. Hazard. Mater. 158, 384–391. Wang, J.S., Herman, J., Enokida, Y., Wai, C.M., 2005. Dissolution of organic acids in supercritical CO2 using a CO2-philic Lewis base carrier. J. Supercrit. Fluids 36, 98–105. Wibowo, S., Deng, H., 2015. Multi-criteria group making for evaluating the performance of e-waste recycling programs under uncertainty. Waste Manage. 40, 127–135. Wu, Q., Lu, W., Prakash, J., 2000. Characterization of a commercial size cylindrical Liion cell with a reference electrode. J. Power Sources 88, 237–242. Xing, M., Zhang, F.S., 2013. Degradation of brominated epoxy resin and metal recovery from waste printed circuit boards through batch sub/supercritical water treatments. Chem. Eng. J. 219, 131–136. Xiu, F.R., Zhang, F.S., 2009. Recovery of copper and lead from waste printed circuit boards by supercritical water oxidation combined with electrokinetic process. J. Hazard. Mater. 165, 1002–1007. Xiu, F.R., Qi, Y., Zhang, F.S., 2013. Recovery of metals from waste printed circuit boards by supercritical water pre-treatment combined with acid leaching process. Waste Manage. 33, 1251–1257. Zhang, T., He, Y., Wang, F., Li, H., Duan, C., Wu, C., 2014. Surface analysis of cobaltenriched crushed products of spent lithium-ion batteries by X-ray photoelectron spectroscopy. Sep. Purif. Technol. 138, 21–27. Zhu, S., He, W., Li, G., Zhou, X., Zhang, X., Huang, J., 2012. Recovery of Co and Li from spent lithium-ion batteries by combination method of acid leaching and chemical precipitation. Trans. Nonferrous Met. Soc. China 22, 2274–2281.
Please cite this article in press as: Bertuol, D.A., et al. Recovery of cobalt from spent lithium-ion batteries using supercritical carbon dioxide extraction. Waste Management (2016), http://dx.doi.org/10.1016/j.wasman.2016.03.009