Leaching kinetics of spent nickel-cadmium battery in sulphuric acid

- Leaching kinetics of spent Ni-Cd battery powder in sulfuric acid medium was studied.
- Cadmium leaching was very fast giving rise to 99.5% recovery within 2 min.
- Ni recovery was only ~ 23% due to passivation of metallic nickel in sulfuric acid.
- Addition of hydrogen peroxide highly enhanced the nickel recovery.
- Kinetics followed shrinking core model; rate depended on surface chemical reactions.

Acid leaching process for recovering nickel and cadmium from spent Ni-Cd batteries consumes concentrated acid solution and operate at quite high temperature. The present paper reports improved nickel and cadmium recoveries in sulphuric acid leaching of Ni-Cd battery powder at relatively lower temperatures. The spent Ni-Cd battery powder containing about 69% Ni, 15% Cd and 0.94% Fe was leached in sulphuric acid varying the parameters viz., acid concentration, time, temperature and hydrogen peroxide addition. Dissolution of various nickel and cadmium phases present in Ni-Cd battery powder was investigated by XRD analysis. The kinetics data conformed well to the shrinking core model and the dissolution rate was found to be controlled by surface chemical reaction. The leaching mechanism was further established by characterizing the leach residues for phase composition and morphology. The novelty of the present study was high recovery of nickel (96%) and cadmium (99.5%) by leaching of spent Ni-Cd batteries using dilute sulfuric acid (10 vol.%) at moderate temperature (328 K) showing potential for scale up trails. The leach liquor obtained in present study contained about 6-7 g/dm3 Cd2+, 26-28 g/dm3 Ni2+ and up to 0.34 g/dm3 Fe3+, and can be subjected to suitable purification and separation technique to recover pure cadmium and nickel metals/compounds.