Valorization of waste NiMH battery through recovery of critical rare earth metal: A simple recycling process for the circular economy.

The process flowsheet consists of three main circuits, i.e., metal extraction by acid leaching, critical rare earth metal (REM) recovery from leach liquor and pure Co/Ni recovery by solvent extraction. Quantitative metal extraction using 1 M H2SO4, pulp density of 25 g/L at 90 °C from waste NiMH battery was achieved. From leach liquor using 10 M NaOH, at pH 1.8, more than 99% REM was precipitated out and isolated through calcination at 600 °C. Undesired metals like Mn, Al, Zn, and Fe were scrubbed out from the leach liquor using 0. 7 M D2EPHA at the equilibrium pH of 2.30. From the scrubbed raffinate Co and Ni was separated using 0.5 M Cyanex 272 at pH 4.70 through solvent extraction. At pH 4.70 Co was completely extracted from solution leaving Ni in solution, which can be recovered completely. From Co loaded Cyanex 272, the Co was stripped by 1 M H2SO4 and regenerated Cyanex 272 can be reused and close the loop. Similarly, the undesired metal loaded D2EPHA can be regenerated and reused and close the loop. As the process is close-loop process recovers critical REMs, Co, and Ni, the valorization process efficiently addresses the circular economy and recycling challenges associated with waste NiMH battery.