Comparision of Different Reductants in Leaching of Spent Lithium Ion Batteries

Abstract

The present work focuses on the processing of cathode active material of spent lithium ion batteries to improve the recovery of constituent metals using reducing agents. Reductants enhance the solubility of metals, which hitherto have been solubilised to a lesser extent u sing only acid as leaching agent. Thus, we have investigated sulfuric acid leaching in the presence of sodium bisulfite comparing its efficiency with hydrogen peroxide. By simple acid leaching using 1 M H2SO4 at 368 Kand 50 g/L pulp density, 93.4% Li, 66.2% Co, 96.3% Ni and 50.2% Mn were recovered in 240 min. In the presence of 5% H2O2 as a reducing agent at 368 K with 1 M H2SO4 and 50 g/L pulp density, the leaching of cobalt (79.2%) and manganese (84.6%) were significantly improved in 240 min. With the addition of0.075 M NaHSO3 as a reducing agent, ~ 96.7% Li, 91.6% Co, 96.4% Ni and 87.9% Mn were recovered under similar conditions. Sodium bisulfite addition results in better recovery of cobalt and manganese by reducing them to their lower oxidation states. The HSC evaluation of thermodynamic feasibility vis-à-vis x-ray diffraction and scanning electron microscopy characterization of residues generated by leaching with hydrogen peroxide and sodium bisulfite substantiates the governing mechanism.