Leaching and separation of zinc from the black paste of spent MnO2-Zn dry cell batteries

Spent batteries represent a source of hazardous materials when discarded without appropriate treatment. Investigations on the recovery of zinc from the black paste of spent MnO2-Zn cell batteries were carried out. Leaching of zinc and manganese from the black paste of spent batteries using sulfuric or hydrochloric acid solutions was studied. It was found that leaching with sulfuric acid solution is more efficient than with HCl solution. Different parameters affecting the leaching of Zn(II) and Mn(II) with sulfuric acid were further studied. Extraction of Zn(II) and Mn(II) from the leaching sulfate medium by bis(2,4,4-trimethylpentyl) dithiophosphinic acid (CYANEX 301) diluted with kerosene was investigated. The factors affecting the extraction process, separately studied, include the effect of contact time, sulfuric acid concentration, CYANEX 301 concentration, phase ratio as well as temperature. The results indicated that, from sulfate medium, Zn(II) is more extracted than Mn(II). Selective stripping of Zn(II) was obtained using 5 M HCl. Application of the method on the leaching sulfate solution of the spent MnO2-Zn dry cell black paste show the efficiency of the process, where the extraction and stripping of Zn(II) are 98% and 99%, respectively.