Recovery of nickel, cobalt and rare-earth elements from spent nickel–metal-hydride battery: Laboratory tests and pilot trials

Abstract

The recycling of nickel, cobalt and rare earths from spent nickel–metal-hydride batteries was investigated. Nickel and cobalt were recovered as a nickel–cobalt mixed sulfide, which can be used as an intermediate raw material in existing nickel refineries. Rare earths were recovered as double sulfates, which can be recycled into industrial materials. In the recovery of rare earths, yttrium, a heavy rare earth, could be precipitated and recovered by co-precipitation with a light rare-earth double sulfate, which was considered impossible by the double-sulfate precipitation method because of high solubility of yttrium double sulfate. On the other hand, the coprecipitation behavior of yttrium was found to be unstable at the pilot scale because the stirring force was weaker than that in the laboratory experiments. In this study, the optimum conditions for leaching, double-sulfate precipitation, and sulfide precipitation reactions were determined in a laboratory test and the good performance was demonstrated in a pilot test. Based on the results, the estimated metal yields were 87% nickel, 90% cobalt, 54% yttrium, 99% lanthanum and 99% cerium. The nickel and cobalt impurities in the double sulfate that were recovered by this process were 0.04% and 0.005%, respectively, and the rare-earth impurities in the nickel–cobalt mixed sulfide were low at 0.049% yttrium, 0.007% lanthanum and 0.003% cerium. This process combined with a precipitation method showed a high separation performance.