Recycling of Spent Nickel-Cadmium Batteries

A technique for recycling spent nickel-cadmium batteries, which makes separaion of cadmium and nickel possible, is developed by laboratory-scale experiments. NH₃-H₂CO₃ aqueous solution was used in this leaching technique. Since neutralization and/or solvent extraction were not required in the separation procedure of nickel and cadmium, the closed systemizaion of the process becomes possible. Experimental results show that, (1) if the NH₃ concentraion of leaching solution is sufficiently high and the ratio of H₂CO₃ to NH₃ is properly adjusted, both Ni(OH)₂ and Cd(OH)₂ react with NH, and quickly dissolve into leaching solution, and (2) Ni(OH)₂ can be converted into insoluble NiO by calcination at 500℃, and CdO from Cd(OH)₂ by calcination maintains good solubility in NH₃-H₂CO₃ aqueous solution. As a conclusion, the recycling technique characterized by two step leaching can be developed based on such changes in dissolution behavior by calcination. Meanwhile, the yields of 99.8% for nickel and 97.6% for cadmium are obtained, and the purities of recovered nickel and cadmium are 99.9% and 98.6%, respectively.