A cleaner and energy-saving technology of vacuum step-by-step reduction for recovering cobalt and nickel from spent lithium-ion batteries

Abstract

Waste power banks (a kind of lithium-ion battery) are widely generated along with the growing widespread use of mobile phone. Vacuum carbon reduction is encouraged to recover cobalt and nickel from spent lithium-ion battery. However, the mixed nickel and cobalt particles are difficult to be further separated. Recovering cobalt and nickel respectively from the electrode powders is important to improve the recovery value of spent lithium-ion battery. According to the analysis of Gibbs free energy of the reduction process of Ni2+ and Co2+, we proposed a cleaner technology of step-by-step vacuum carbon reduction to recover nickel and cobalt in sequence from the electrode powder of spent lithium-ion batteries. The Ni2+ and Co2+ in the spent lithium-ion battery are reduced into nickel and cobalt in vacuum tubular furnace at the temperatures of 691 °C and 873 °C respectively. Nickel and cobalt can be separated in sequence by magnetic separation at the reduction products of different temperatures. Additionally, for energy saving and accurate reduction, we analyzed the heat transfer in the vacuum reduction process and constructed the models for computing the true temperature of electrode powder in crucible. The models are used to compute the accurate reduction temperatures for Co2+ and Ni2+. It will greatly reduce the energy cost in the reduction process which be attributed to sustainable development. The models also can guide the structure design of vacuum tubular furnace for improving the efficiency of heat transfer.