Selective recovery of Zn and Fe from spent pickling solutions by the combination of anion exchange and membrane electrowinning techniques Ga ´bor Csicsovszki, Tama ´s Ke ´kesi T , Tama ´s I. Tfrfk Department of Nonferrous Metallurgy, University of Miskolc, Egyetemvaros, Miskolc 3515, Hungary Received 27 May 2004; received in revised form 6 September 2004; accepted 10 October 2004 Abstract Although the environmental industry has developed many modern techniques to treat spent pickling liquors, including also the membrane separation, still neither of them can be applied alone for the efficient treatment of HCl containing spent pickling solutions originating from hot dip zinc galvanizing plants. In this area, the most frequently applied treatment is still the common precipitation–filtration process. However, this technique generates large amounts of hazardous waste to be deposited at high costs and does not recover the acid. Our novel approach to treat such spent liquors consists of an ion-exchange separation and a membrane electrolysis step to recover HCl, Fe and ZnCl 2 as saleable products. The experimental part of this paper concentrates on the anion-exchange separation of the components in the raw liquor and the cathodic deposition of iron at varied pH, temperature and cathode materials by using potentiodynamic testing technique. As a result, a direct anion-exchange with a strongly basic resin can separate the main components (Fe and Zn) of the raw solution loaded at a moderate flow rate into the column. The recommended conditions for the electrolytic deposition of iron are pH N1 and nickel cathode. D 2005 Elsevier B.V. All rights reserved. Keywords: Spent pickling liquor; Recovery of Fe and Zn; Hydrochloric acid; Anion-exchange separation; Potentiodynamic examination; Cathode process; Polarization curves 1. Introduction Membrane separation techniques are becoming more and more mature for the purpose of treating industrial effluents like spent acidic liquors originat- ing from the metals industries. Common grade low carbon steels, for example, are surface treated in aqueous solutions (de-scaling, pickling, polishing, etc.) in huge quantities all over the word. In addition to the traditional procedures of neutralization of the acids and precipitation of the metal cations in the form of sparingly soluble hydroxides or sulphides, the use of electro-membrane processes based on ion- exchange membranes is of increasing interest and 0304-386X/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.hydromet.2004.10.020 T Corresponding author. Fax: +36 46 565119. E-mail address: tkekesi@uni-miskolc.hu (T. Ke ´kesi). Hydrometallurgy 77 (2005) 19 – 28 www.elsevier.com/locate/hydromet