Fractional precipitation of Ni and Co double salts from lithium-ion battery leachates†

Abstract

Alternative sourcing of critical metals from lithium-ion batteries (LIBs) is necessary to secure the future supplies of Li, Ni, and Co. Most recovery processes of LIBs utilize pyrometallurgical and hydrometallurgical methodologies; however, these processes to recycle LIB cathode/anode materials can require several steps to isolate the desired metals. We have developed a facile isolation of the valued metals, where Ni and Co will co-crystallize as a sulfate double salt, called Tutton's salt [(NH₄)₂Ni/Co(SO₄)₂·6H₂O]. Thermodynamic modelling of these Ni(II)/Co(II) sulfate double salts shows that Ni is less soluble than Co which could enhance the separation of Ni and Co from electrochemical (EC) leachates. This calculated difference between Ni and Co can be controlled further by temperature and ammonium sulfate concentration. Here, Ni-rich sulfate double salts were achieved at 30–45 °C while Co-rich sulfate double salts were formed at 2–9 °C, where 99% Ni and 89% Co were recovered from the EC-leach solution. Further tests with the leachate solution show that crystallization occurs above pH 2 which allows for higher pulp density leachates. Chemical analyses and single crystal X-ray characterization confirm that the Ni-rich sulfate double salts contain Ni and Co. However, the Co-rich sulfate double salts have ∼30% Mn(II) in the crystal lattice with ∼37% of Ni. As a result, this process reduces the total number of steps to isolate the desired metals while also reducing chemical waste generation and without employing organic solvents.