Recovery of Metal Values from Spent Nickel-cadmium Rechargeable Batteries by Solvent Extraction Route

Spent Nickel cadmium batteries are classified as hazardous waste due to the presence of toxic cadmium in high concentration. Recycling of metal value by environmentally friendly process is the best option to obtain economical advantage and prevent environmental pollution. In the present investigation, a metal separation scheme is proposed for recovery of cadmium, nickel and cobalt from the leach solution of Ni-Cd battery electrode materials. After removal of the external case, the electrodes were washed with water to remove adhered alkali and dissolve in sulphuric acid in presence of a suitable additive. The iron from the leach solution was removed by selective precipitation and the iron free leach solution of composition: Ni:18.63 g/L, Cd:17.24 g/L, and Co:1.89 g/L was subjected to solvent extraction for separation of cadmium, cobalt nickel using phosphoric acid based extractants. Initially di-(2-ethyl hexyl) phosphoric acid (D2EHPA) and cyanex 302 were used to extract cadmium selectively, followed by cobalt and nickel separation using PC 88A, Cyanex 272 of suitable composition. Effect of different parameters such as equilibration time, pH aqueous feed, solvent concentration, organic to aqueous phase ratio were studied to determine the optimum conditions for extraction, scrubbing and stripping of cadmium, cobalt and nickel. Requirement of number of stages were determined from Mc-Cabe-Thiele plot for complete extraction and stripping of specific metal and subsequently validated by counter current simulation study.