Two stage leaching process for selective

In this study, a closed loop two-stage leaching process has been experimentally and theoretically established for the selective dissolution of metals from electrode material of spent Ni-MH batteries. In the first step, baking parameters, such as temperature, acid concentration, and duration were optimized as 300 °C, 2 mL H2SO4 for 1.5 g of cathode powder, and 90 min. The thermodynamic feasibility of the process ascertained the spontaneous formation of water-soluble sulfates of nickel, zinc, and rare earth elements during the acid baking. Post-baking, a two-stage leaching was performed for leaching of different metals from the baked material, achieving significant metal recovery. Results indicated that the initial leaching stage dissolved 91-94% of nickel, zinc, and rare earth elements with low levels of cobalt and manganese extracted. The second stage showed that 55% cobalt and 74% manganese were reductively leached using sodium bisulfite with sulfuric acid. Overall, the leaching efficiency reached up to 98.2% for nickel, 91.4% for cobalt, 98% for zinc, and 97.8% for manganese, while the rare earth element recoveries ranged from 80.4% for lanthanum to 99.2% for samarium.