Abstract
Leaching treatment of electrode materials has been studied to recover valuable metals in a used nickel-metal hydride rechargeable battery by a hydrometallugical process on the effects of sulfuric acid concentration, temperature, leaching duration and oxidizing agents (air, O2 gas, H2O2 solution). The positive electrode materials were identified to be Ni(OH)2 (active material) and Ni (current collector) by XRD analysis, and the active material of negative electrode to be LaNi5. Leaching behavior was investigated by using positive electrode materials, active material of negative electrode, and reagents such as Ni(OH)2 and Ni. The nickel hydroxide ,Ni(OH)2, reagent was easily leached with diluted sulfuric acid, but leaching of the Ni reagent was difficult. Oxidizing agents were however effective in leaching metal Ni. The nickel hydroxide particles in positive electrode materials and the active material of negative electrode could be leached in 0.5 kmol·m-3 of sulfuric acid solution, dispite no leaching of the current collector in positive electrode materials. The current collector was easily leached by adding oxidizing agents. Both O2 gas and H2O2 solution were found to be effective. A practical process was tested to separate electrode materials from a used battery. The process contained the following treatments; cutting, heat treatment, magnetic separation and screening. NiO which is a product of heating treatment of Ni(OH) 2 could be leached at a higher sulfuric acid concentration or higher temperature.
