Resource recovery of critically-rare metals by hydrometallurgical recycling of spent lithium ion batteries

The increasing demand for critical metals and mounting pressure on the environmental impact of solid waste disposal have widely attracted the recycling of spent lithium ion batteries (LIBs). Although the hydrometallurgical recycling of LiCoO2 cathode materials from spent LIBs has been commonly investigated, the studies on LiNixCoyMnzO2 type cathode materials are infrequent. Hence, the present work is focused on sulfuric acid leaching of LiNixCoyMnzO2 cathode material for resource recovery of all the critical and rare metals from spent LIBs. The process parameters viz., pulp density, acid concentration, the dosage of reducing agent (i.e., H2O2), time, and temperature have been optimized for leaching of cathode powder (of weight composition: 7.6% lithium, 20.48% cobalt, 19.47% manganese, and 19.35% nickel). The maximum 92% lithium and nickel, 68% cobalt, and 34.8% manganese could be leached while leaching a 5% pulp density in 3.0 M H2SO4 without H2O2 at 90 °C. Leaching efficiencies of metals were found to be increased within 30 min and reaching to >98% by adding 4 vol% H2O2 even at a lower temperature, 50 °C. Thereafter selective precipitations of manganese and nickel were carried out from leach liquor using KMnO4 and C4H8N2O2 as suitable precipitants, respectively. Subsequently, a 2-stage solvent extraction using 0.64 M Cyanex 272 (50% saponified) at equilibrium pH 5.0 and O:A of 1:1 was employed for recovery of a highly pure solution of CoSO4. Finally, lithium could be precipitated at Li+:Na2CO3 of 1.2:1.0 and a process flow-sheet has been proposed for the recycling of spent LIBs.