Copper and nickel recovery from acidic polymetallic aqueous solutions I. Giannopoulou, D. Panias * National Technical University of Athens, School of Mining and Metallurgical Engineering, Laboratory of Metallurgy, 15780 Zografou, Athens, Greece Received 21 December 2006; accepted 23 February 2007 Available online 5 April 2007 Abstract Acidic polymetallic wastewaters are generated during the pyrometallurgical treatment of chalcopyrite for the production of primary copper. The most important wastewater streams originate from the copper refining and the electrolyte regeneration stages, as well as the sulphuric acid and the precious metals plants. These wastewaters are characterized by medium to high concentration of residual sulphuric acid and heavy metals such Cu, Ni, Pb, Zn, Fe, As, Sb, Bi, etc. Taking into account that the outflows of these industrial streams are usually high, a large amount of valuable metals such as copper and nickel are potentially lost. Thus, it is of great importance to treat properly the wastewaters so that the contained valuable metals to be recovered. This paper is dealing with the treatment of synthetic solutions simulating industrial wastewaters from the copper pyrometallurgical plant in Bor, Serbia. The basic concept includes copper electrorecovery followed by nickel precipitation through neutralization. The feasibility of this treatment was proved theoretically with the thermodynamic analysis of electrochemical and precipitation reactions in this system, as well as experimentally under various conditions. The main conclusion is that copper can be recovered electrolytically followed by bismuth and the two metalloids arsenic and antimony that exhibits almost the same electronegativity with copper. The other high electropositive metals Ni, Pb, Zn, Fe remain, as it was expected, in the solution from which nickel can be recovered with neutralization, contaminated with Cu, Fe, Zn and traces of bismuth, arsenic and antimony. The proposed treatment technology has innovative character because it can mitigate environmental impacts and eliminate solid waste generation while at the same time can recover valuable metals. Ó 2007 Published by Elsevier Ltd. Keywords: Copper recovery; Nickel recovery; Electrochemistry; Neutralization; Polymetallic wastewater; Thermodynamic modeling 1. Introduction Copper is the 25th most abundant element in the earth’s crust. It is found in earth mainly in the form of chalcopyrite (CuFeS 2 ) associated with other sulphides, such as pyrite (FeS 2 ), arsenopyrite (FeAsS), sphaelerite (ZnS), galena (PbS) and forming the complex sulphide ore deposits. The copper content in the relevant ore deposits is very low varying normally between 0.4% and 1%. Copper extraction from sulphide ores follows normally a five step treatment (Lossin, 2005; Moore, 1993). After crushing, ore is concentrated by froth-flotation giving a copper con- centrate with 15–25% Cu. Then, copper concentrate is partially roasted by air in order to reduce sulfur content. The produced calcine contains part of iron as FeS and all copper as Cu 2 S. The calcine product is smelted with an acid slag and a copper matte is produced containing precious metals (Au, Ag), as well as other impurity sulphides that were not oxidized in the previous steps. Arsenic and anti- mony, if present, form a liquid speiss layer. Air is blown through the liquid copper matte causing a partial oxidation of copper and a total oxidation of iron. Then, the air is turned off and copper oxides and sulphides are self-reduced producing blister copper. Blister copper is refined by elec- trolysis using a H 2 SO 4 /CuSO 4 solution as electrolyte. The major environmental problem of primary copper metallurgy is related with the emission of sulphur dioxide to air from the roasting and smelting of sulphide concen- trates (IPPC, 2001). The normal way to manage this 0892-6875/$ - see front matter Ó 2007 Published by Elsevier Ltd. doi:10.1016/j.mineng.2007.02.009 * Corresponding author. Tel.: +30 2107722276; fax: +30 2107722168. E-mail address: panias@metal.ntua.gr (D. Panias). This article is also available online at: www.elsevier.com/locate/mineng Minerals Engineering 20 (2007) 753–760