Recovery of nickel, cobalt and some salts from spent Ni-MH batteries

This work provides a method to help recover nickel, cobalt metals and some of their salts having market value from spent nickel-metal hydride batteries (SNiB). The methodology used benefits the solubility of the battery electrode materials in sulfuric or hydrochloric acids. The results obtained showed that sulfuric acid was slightly less powerful in leaching SNiB compared to HCl acid. Despite that, sulfuric acid was extremely applied on economic basis. The highest level of solubility attained 93.5% using 3 N sulfuric acid at 90 °C for 3 h. The addition of hydrogen peroxide to the reacting acid solution improved the level of solubility and enhanced the process in a shorter time. The maximum recovery of nickel and cobalt metals was 99.9% and 99.4%, respectively. Results were explained in the light of a model assuming that solubility was a first order reaction. It involved a multi-step sequence, the first step of which was the rate determining step of the overall solubility. Nickel salts such as hydroxide, chloride, hexamminenickel chloride, hexamminenickel nitrate, oxalate and nickel oleate were prepared. With cobalt, basic carbonate, chloride, nitrate, citrate, oleate and acetate salts were prepared from cobalt hydroxide Cost estimates showed that the prices of the end products were nearly 30% lower compared to the prices of the same chemicals prepared from primary resources.