Recovery of Ni, Co and rare earths from spent Ni–metal hydride batteries and preparation of spherical Ni(OH) 2

Abstract

A hydrometallurgical procedure has been developed for the separation and recovery of nickel, cobalt and rare earths (RE) from spent Ni–MH batteries. In the process of separation and recovery, the positive and negative electrode materials were merged and leached with 3 M H 2SO 4 at 95 °C. In this stage, about 94.8% of rare earths were separated from other metals due to the low solubility of RESO 4 at relatively high temperature. Then iron, zinc and manganese (together with the remaining 5.2% rare earths) were almost completely separated from nickel and cobalt by solvent extraction with 20% P204. Rare earths in the organic phase were recovered by stripping with 2 M HCl after scrubbing Zn and Mn. Most rare earth sulphates remaining in the leach residue were transformed to RE(OH) 3 by treatment with NaOH and then redissolved from the filter cake as RECl 3 by using the rare earth strip liquor and additional HCl. Cobalt was easily separated from nickel by solvent extraction with 20% Cyanex 272 and pure cobalt and nickel sulphates were recovered from evaporation of the strip liquor and raffinate respectively. Finally, spherical nickel hydroxide powder was synthesized from the pure nickel sulphate, which is an important starting material for Ni–MH batteries. The overall recovery efficiency for rare earths, cobalt and nickel exceeded 98%.