Use of mild organic acid reagents to recover the Co and Li from spent Li-ion batteries

Highlights

• New organic acid mixtures have been investigated for the recovery of metal ions.

• Complete dissolution occurred in IDA and MA in presence of ascorbic acid at 80 °C.

• Formation of Co(III)- to Co(II)-L in presence of AA is evident from UV–Vis spectra.

• Selective precipitation of Co as Co(II)-oxalate and Li as LiF occurred.

• UV spectra of Co(III)- and Co(II)-L is useful from coordination chemistry viewpoint.

Abstract

New organic acid mixtures have been investigated to recover the valuable metal ions from the cathode material of spent Li-ion batteries. The cathodic active material (LiCoO₂) collected from spent Li-ion batteries (LIBs) is dissolved in mild organic acids, iminodiacetic acid (IDA) and maleic acid (MA), to recover the metals. Almost complete dissolution occurred in slightly excess (than the stoichiometric requirement) of IDA or MA at 80 °C for 6 h, based on the Co and Li released. The reducing agent, ascorbic acid (AA), converts the dissolved Co(III)- to Co(II)-L (L = IDA or MA) thereby selective recovery of Co as Co(II)-oxalate is possible. The formation of Co(III)- and Co(II)-L is evident from the UV–Vis spectra of the dissolved solution as a function of dissolution time. Thus, the reductive-complexing dissolution mechanism is proposed here. These mild organic acids are environmentally benign unlike the mineral acids.

Introduction

Li-ion batteries (LIBs) have been the power source for portable electronic devices viz., mobile phones, personal computers, cameras and recently in electric vehicles due to their favorable characteristics such as high energy density, high voltage, long storage life, low self discharge rate and wide temperature range of use (Chagnes and Pospiech, 2013, Thyabat et al., 2011, Gonclaves et al., 2015). The production of LIBs will be increased further in the upcoming years as the large numbers of electric vehicles are entering the market (Scrosati and Garche, 2010). Such an wide spread use of these portable energy storage devices by billions of people around the world, large number of spent LIBs are accumulated day-by-day (Jha et al., 2013a, Jha et al., 2013b). The active cathode material in most of the LIB is LiCoO₂ due to its good performance, although new materials such as LiMn₂O₄ and LiFePO₄ are being developed. Such lithium cobalt oxide must be treated properly considering the environmental toxicity of Co and at the same time the scarcity of Li. Furthermore, Co is a rare and precious metal, and is a relatively expensive (Li et al., 2010b, Hayashi et al., 2009, Yang et al., 2011). Lithium is also vitally important for many industrial applications. Hence, recovery of these valuable metals by a suitable method would greatly benefit the society and environment. Thus, recycling of these spent LIBs is appropriate for at least two significant reasons: it often pays to recover valuable materials, especially if their supply is limited; and now it is necessary to recycle LIBs according to government regulations for the sake of sustainability and safety hazards associated with the disposal of spent LIBs (Chagnes and Pospiech, 2013). Therefore, spent LIB must be properly recycled through pyrometallurgical or hydrometallurgical processes (Maschler et al., 2012, Ziemann et al., 2012, Li et al., 2010a, Chen et al., 2011). The technologies existing for LIBs recycling can be categorized into physical (electrostatic, magnetic, gravity separations) and chemical (electrolysis, solvent extraction, bioleaching, leaching, precipitation) separations. Among these, hydrometallurgical process is advantageous from environmental conservation viewpoint (Freitas et al., 2010).

There are several studies on dissolution of LiCoO₂ from spent LIBs by strong acids like H₂SO₄ (Chen et al., 2011, Daniel et al., 2009, Kang et al., 2010), HCl (Wang et al., 2009), and HNO₃ (Freitas et al., 2010, Ivano et al., 2009) with the addition H₂O₂ as reducing agents (Dorella and Mansur, 2007, Swain et al., 2007) with more than 95% recovery of Co and Li. However these strong acids are high cost, difficult to handle in large scale and are not environment friendly as they emit toxic gases. So it is important and essential to develop simple, cost-effective and environmentally benign recycling processes to recover these valuable metals from spent LIBs. Recently few studies have reported on mild organic acid with H₂O₂ as reducing agent viz., citric acid (Li et al., 2010c, Li et al., 2013), malic acid, aspartic acid (Li et al., 2013), oxalic acid (Sun and Qiu, 2012) and ascorbic acid (Li et al., 2012). In our previous study (Nayaka et al., 2015), we have used citric acid and ascorbic acid as reducing agent because it was proved to dissolve even the sintered metal oxides like Cr-substituted hematites (Manjanna et al., 2001). All of these reagents have not shown almost complete dissolution of Co and Li. In order to investigate the efficient dissolution media among various mild organic acids, this study is focused on the iminodiacetic acid (IDA) and maleic acid (MA) in presence of ascorbic acid. There are no reports on these reagents, which are soluble in aqueous medium and environmentally benign.