Journal of Hazardous Materials 143 (2007) 328–334 Leaching and separation of zinc from the black paste of spent MnO 2 -Zn dry cell batteries Y.A. El-Nadi, J.A. Daoud ∗ , H.F. Aly Hot Laboratories Centre, Atomic Energy Authority, Post Code 13759, Cairo, Egypt Received 30 April 2006; received in revised form 8 September 2006; accepted 11 September 2006 Available online 15 September 2006 Abstract 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 MnO 2 -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 MnO 2 -Zn dry cell black paste show the efficiency of the process, where the extraction and stripping of Zn(II) are 98% and 99%, respectively. © 2006 Elsevier B.V. All rights reserved. Keywords: MnO 2 -Zn dry cells; Zinc; CYANEX 301; Liquid–liquid extraction 1. Introduction Spent batteries represent a serious pollutant in terms of heavy metals content when discarded in an inappropriate way. Among these, MnO 2 -Zn cell batteries represent a major amount of the spent batteries waste. During the last decade, the pro- ducers of batteries were engaged trying to find substitutes for toxic substances still used in batteries, to match environmental requirements, although, the basic systems of the batteries and its composition remains more or less the same (steel, plastic, zinc, manganese dioxide, etc.). Most of these materials recov- ered by means of mechanical and chemical treatments show some advantages as they can be used as raw materials for bat- teries production. Several methods to recover metal values from spent batteries are given in the literature but industrial routes are generally based on pyrometallurgical [1–4] and/or hydrometallurgical [5–7] operations. Hydrometallurgical routes commonly found ∗ Corresponding author. Tel.: +20 2 6352474; fax: +20 2 6352474. E-mail address: jadaoud@yahoo.com (J.A. Daoud). are more economical and efficient than pyrometallurgical ones. Metal separation routes based on hydrometallurgical operations are characterised by lower energy consumption, higher metal selectivity and low air pollution, as there are no particles produced. Veloso et al. [8] proposed a method for selective separation of zinc and manganese from spent alkaline batteries. Their recycling route comprises the dismantling of the batteries to separate the spent batteries dust from other components and grinding the batteries dust to produce a black homogeneous powder. The powder was then leached in two sequential steps, “neutral leaching with water” to separate potassium and produce a KOH solution, followed by an “acidic leaching with sulfuric acid” to remove zinc and manganese from the powder. This was followed by selective precipitation of zinc and manganese using the KOH solution (pH around 11) produced in the neutral leaching step. In a modified ZINCEX process, as an example of hydrometallurgical route, zinc extraction from the leached liquor (pH 2) was performed with di-(2-ethylhexyl) phosphoric acid (D2EHPA) as extractant, leaving manganese in the raffinate while other metals such as copper, cadmium, nickel and mercury were cemented [6]. 0304-3894/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2006.09.027