Exploitation of spent nickel-metal hydride (Ni-MH) batteries as a source of value-added products

Spent Nickel-metal hydride batteries can be sources of valuable metals such as nickel, cobalt, manganese, rare earths and toxic chemicals. The recycling of these materials is necessary from both economic and environmental points of view. In this study the nickel is leached in acid solution followed by precipitation and thermal decomposition or by cementation. The affecting parameters such as acid type and concentration, time, temperature and solid/liquid ratio were investigated. The maximum of leached nickel could be obtained in 3M sulfuric acid at 65 degrees C for 60 min with solid-to-liquid ratio of 30 g L-1. The liquid film is a more suitable model for demonstrating the kinetics of the nickel leaching. Thermal decomposition of the precipitated nickel dimethyl-glyoxime was employed in preparation of nickel oxide. Nickel was separated from aqueous solution by cementation on zinc. The cementation process follows pseudo first-order kinetics and diffusion controlling steps. The yield was 91% of the original nickel content.