Recovery of metals from spent nickel-cadmium (Ni-Cd) battery by leaching-electrowining process

Growing demand of Nickel-Cadmium (Ni-Cd) batteries in the railway locomotives, mines, armored vehicles, aircraft engines, etc. have been demanding more output from the conventional resources of nickel and cadmium. Mining and processing of metals like cadmium and nickel have always been accompanied with their hazardous effects on the environment. In addition, end of life Ni-Cd batteries have also been viewed as threat to the environment owing to their heavy metal contents, which may contaminate the surrounding atmosphere if discarded inappropriately. To alleviate the problems associated with spent batteries and also to minimize the environmental burden while producing above metals from ores, spent Ni-Cd batteries have been processed through appropriate techniques to recover metal values and recycling. In this connection, a process based on sulphuric acid leaching of spent Ni-Cd battery powder followed by electrowining has been investigated and presented in this paper. Several parameters namely, acid concentration, time, temperature, oxidizing agent, pulp density etc were varied. About 95% Cd and 25% Ni recoveries were achieved with 10% sulphuric acid in 5h and 5% (w/v) pulp density at 35 oC. Increase in temperature to 45 oC enhanced cadmium recovery 99% to but not affected the nickel recovery. Hydrogen peroxide as oxidation agent addition during leaching enhanced the Ni recovery to about 93%. The Ni and Cd metals were recovered from the leach liquor by electrowining at current density of 400 A/m2. The recovery of Ni and Cd in the electrowining was 98% and 99.5% respectively.