Recovery of REEs, Ni and Co from spent NiMH battery – purification and process flowchart

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In this manuscript, we propose a hydrometallurgical flowchart for recycling spent NiMH batteries by evaluating successive stages of REEs precipitation, ozonation, Al and Fe removal, selective separation of Zn and Y, and separation of Ni and Co. NiMH batteries are important for hybrid vehicles, complementing the use of Li-ion batteries in electric vehicles to contribute to the energy transition in transport. REEs were precipitated as double sulfates (above 99% purity) using Na 2 CO 3 at pH 1.0, 25°C, and 60min. Ozonation enabled the selective oxidation and removal of Mn at pH 1.0 and 25°C after 240 min. Al and Fe were removed by Na 2 CO 3 precipitation at pH 3.5, 80°C, and 120min. The selective extraction of Y and Zn was carried out using 20% Cyanex 272 at 25°C, pH 3.5, an aqueous/organic (A/O) ratio of 1/1, and 15 min of contact time. The separation of Co and Ni was achieved through two solvent extraction contacts with Cyanex 272, followed by selective precipitation with Na 2 CO 3 and C 2 H 2 O 4 , resulting in basic Ni carbonate and Co oxalate with purities of 97% and 99%, respectively. The proposed process demonstrates how different hydrometallurgical techniques can be integrated into a single purification flowsheet, enabling the sequential removal of impurities and the recovery of high-purity REE, Ni, and Co products. Although developed for spent NiMH batteries, the proposed downstream purification strategy may also provide a basis for adapting similar hydrometallurgical flowsheets to other battery recycling systems.