Treatment of spent Ni-Cd batteries by acid lixiviation

This work reports on the results of laboratory experiences for the treatment of spent Ni-Cd batteries, using a hydro metallurgical process. The stages of mechanical preparation, lixiviation and extraction with organic solvents are described. The mechanical separation involving a sequence of shearing, drying, crushing and magnetic separation, resulted in the separation into a fine fraction of more than 95% of the cadmium and nickel in the spent batteries, leaving a big fraction of almost all iron and non metallic materials. Lixiviation trials were performed with the fine fraction and modifying the variables of temperature, acidity, reaction time and degree of oxidation of the solution. The incidence of the medium used was evaluated depending on whether it was sulfuric acid or chlorhydric acid solution. Under some conditions more than 90% of the cadmium and nickel could be dissolved, in short periods of no more than 2 hours and it was observed that in the concentrations studied, the chlorhydric acid solutions are more effective than the sulfuric acid ones. DEPHA (Di(2-ethylhexyl) phosphoric acid) extractants from the sulfuric solutions and TBP (tributyl phosphate) for the chlorhydrics were used for the extractions using organic solvents. Both extractants are effective in separating the cadmium and nickel contents in the lixiviation solutions but when using the TBPS solution, less steps are needed in the extraction as well as in the re-extraction. The results obtained from these studies show that this method can be used for recycling spent Ni-Cd batteries (CW)