Combined process of magnesium oxide precipitation-extraction for efficient recovery of cobalt and nickel from extraction slag of spent Li-ion batteries

Abstract

The recovery of valuable metals such as cobalt (Co) and nickel (Ni) from spent Li-ion batteries (LIBs) is crucial steps for resource sustainability and environmental protection. In this study, sulfuric acid was used for selective leaching valuable metals from extraction slag of spent LIBs in presence of hydrogen peroxide as a reducing agent, and then a magnesium oxide (MgO) precipitation strategy to separate the Co and Ni from sulfate leach liquor was proposed. 98.7% for Co and 99.1% for Ni was precipitated by MgO, and the mixed precipitate demonstrated the presence of primary Co(OH)₂ and Ni(OH)₂, except for MgO and Mg(OH)₂, which could be recycled using dissolved CO₂ to form Mg(HCO₃)₂. Subsequently, nine stages extraction was conducted for recovery of a high-purity CoSO₄ using 0.5 mol L^-1 Cyanex 272 at pH 2.5, followed by seven stages extraction for separation of Mg and Ni. Finally, a NiCO₃ purity of 98.5% was obtained by 0.2 mol L^-1 NH₄HCO₃. In this process, Co and Ni can be recovered in the form of high-purity sulfate and carbonate, respectively, along with the recovery of Mg as its sulfate.

Keywords: Cobalt and nickel; Extraction slag; MgO precipitation; Recovery; Solvent extraction.