Nickel Metal Hydride Battery Waste: Mechano-hydrometallurgical Experimental Study on Recycling Aspects

In this research, the recycling of industrially collected and crushed nickel metal hydride battery waste, rich in valuable metals such as Ni and rare earth elements (REE), was investigated. The crushed waste was characterized based on elemental distribution per particle size class and density. Although issues with sieving, such as agglomeration of shredded separator fibers, were observed, a good separation of Fe and plastics could be achieved by using a 1-mm sieve size. It was observed that, as the waste battery particles were washed with water, some organic compounds were dissolved. Acid consumption of 14 mol H⁺ ions per 1 kg of battery sample (sieve fraction—1 mm) was determined to be sufficient to achieve the desired final pH of < 1. Selectivity of the leaching at higher equilibrium pH was also investigated by using dilute H₂SO₄. Pregnant leach solution rich in Ni (46 g/L) and REEs (La: 9 g/L, Ce: 7.5 g/L, Pr: 1.4 g/L, Sm: 0.29 g/L, Y: 0.17 g/L) was obtained and REE precipitation was investigated as a function of dilute Na₂SO₄ solution concentration (0.01–0.5 M) at a temperature of 50 °C. The best precipitation efficiency was achieved with a Na:REE ratio of 9.1, which resulted in a > 99% precipitation efficiency for the REEs.