Journal of Power Sources 157 (2006) 600–604 Recycling of nickel–cadmium batteries using coal as reducing agent Denise Crocce Romano Espinosa, Jorge Alberto Soares Ten´ orio ∗ Polytechnic School, University of S˜ ao Paulo, Department of Metallurgical and Materials Engineering, Av. Prof. Mello Moraes, 2463 S˜ ao Paulo-SP, CEP 05508-900, Brazil Received 30 June 2005; received in revised form 21 July 2005; accepted 22 July 2005 Available online 21 September 2005 Abstract The objective of this work is to study the recycling of sealed nickel–cadmium batteries through cadmium distillation using a carbonaceous material as reducing agent. In spite of the existence of some industrial processes for nickel–cadmium batteries recycling, there are few fundamental studies about this subject. For the study of the reducing process, coal was added to the material of electrodes. Reduction process was performed from 700 to 1000 ◦ C with different quantities of reducing added to the load. Results showed that cadmium purity is of approximately 99.92% and the main impurity found was zinc at around 200 ppm. A Ni–Co alloy containing 100 ppm cadmium was also obtained. © 2005 Elsevier B.V. All rights reserved. Keywords: Nickel–cadmium Batteries; Recycling; Coal 1. Introduction Jungner developed nickel–cadmium alkaline cell technol- ogy in 1899. The materials to produce the batteries were scarce and expensive at that time, thus limiting the use of such batteries to very special situations, in which price was not a determining factor. In 1932 Shlecht and Ackermann invented porous nickel electrodes where the active materials of the batteries were deposited. This increased the contact area of the electrodes, allowing a higher velocity in the reac- tions of charge and discharge. This advance on the material of the electrodes was significant for the development of sealed batteries [1]. In 1947 Neumann succeeded in re-combining gases from the reaction of batteries, thus allowing the creation of sealed nickel–cadmium batteries. Up to then, vented (open) batteries were used to allow the exhausting of gases that were formed in the reaction. These advances allowed the evolution of this type of battery to their present state [1]. ∗ Corresponding author. Tel.: +55 11 3091 5546; fax: +55 11 3091 5243. E-mail addresses: espinosa@usp.br (D.C.R. Espinosa), jtenorio@usp.br (J.A.S. Ten´ orio). Nickel–cadmium batteries have a cadmium cathode which transforms to Cd(OH) 2 , and a NiOOH anode which trans- forms to Ni(OH) 2 . Charge and discharge reactions could thus be described in a simplified way [2–4]: positive electrode : Ni(OH) 2 + OH - charge ⇋ discharge NiOOH + H 2 O + e - negative electrode : Cd(OH) 2 + 2e - charge ⇋ discharge Cd + 2OH - global reaction : Cd(OH) 2 + 2Ni(OH) 2 charge ⇋ discharge Cd + 2NiOOH + 2H 2 O This reaction can be reverted by passing an electric current in the system, during the charging period of the battery. Nickel–cadmium batteries can be classified in two types: vented (open) and sealed. Vented batteries are normally used for industrial applications. Industrial batteries need high rates of charge and discharge and may eventually need electrolyte or water reposition. 0378-7753/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jpowsour.2005.07.061