APPLICATION OF SOLVENT EXTRACTION IN METAL RECOVERY FROM SPENT NICKEL-METAL HYDRIDE BATTERIES

摘要

Sulphuric acid leaching of spent nickel-metal hydride secondary batteries yields an acidic solution containing high levels of metal values such as nickel, cobalt and rare earths, together with an appreciable amount of metal impurities such as iron, aluminium, zinc and manganese. In the present work, solvent extraction has been used for separation and recovery of nickel, cobalt and rare earths from this leach liquor. A mixed rare earth oxide of over 99.8% purity was obtained by the use of an extraction circuit with 25 vol.% bis(2-ethylhexyl) phosphoric acid in kerosene, followed by precipitation with oxalic acid, and calcination of the precipitate. The total yield of rare earths approached 93.6%. The cobalt and nickel in the raffinate are separated efficiently by selective extraction of cobalt with 20 vol.% bis-(2,4,4-tri-methylpentyl)phosphinic acid in kerosene. Subsequently the cobalt and nickel are recovered as oxalates by the addition of oxalic acid. The purities of cobalt and nickel oxalates were close to 99.6% and 99.8%, respectively. The overall recoveries were found to be over 96% for both cobalt and nickel.