Hydrometallurgical process for the separation and recovery of nickel from sulphate heap leach liquor of nickeliferrous laterite ores S. Agatzini-Leonardou, P.E. Tsakiridis * , P. Oustadakis, T. Karidakis, A. Katsiapi Department of Mining and Metallurgical Engineering, Laboratory of Metallurgy, National Technical University of Athens, 9, Iroon Polytechniou Street, 157 80 Zografou, Athens, Greece article info Article history: Received 6 April 2009 Accepted 18 June 2009 Keywords: Laterite leach liquor Hydrometallurgical process Nickel recovery abstract The Laboratory of Metallurgy of the National Technical University of Athens has developed and patented a novel integrated hydrometallurgical method, suitable to treat low-grade nickel oxide ores efficiently and economically. It involves heap leaching of the ore by dilute sulphuric acid at ambient temperature, purification of the leach liquor and recovery of nickel and cobalt by electrowinning. A typical composition of the pregnant solution produced from heap leaching is the following: Ni 2+ = 5 g/L, Co 2+ = 0.3 g/L, Fe 3+ = 23.0 g/L, Al 3+ = 6.0 g/L, Cr 3+ = 1.0 g/L, Mn 2+ = 1 g/L and Mg 2+ = 8 g/L. The proposed hydrometallurgi- cal process for nickel recovery from real sulphate heap leach liquors consists of the following six (6) unit operations: (1) Removal of iron, aluminium and chromium, as easily filterable crystalline basic sulphate salts of the jarosite–alunite type, at atmospheric pressure, by chemical precipitation at pH: 3.5 and 95 °C. (2) Cobalt, manganese and magnesium extraction over nickel by Cyanex 272 at pH: 5.5, T: 40 °C, with 20% extractant concentration and stripping of the loaded organic phase at T: 40 °C with diluted H 2 SO 4 (4 M). (3) Nickel concentration by solvent extraction using Cyanex 272 at pH: 7.5, T: 40 °C, with 10% extract- ant concentration and stripping of the loaded organic phase by nickel spent electrolyte (55.45 g/L Ni) at T: 40 °C with diluted H 2 SO 4 (2 M). (4) Nickel electrowinning from sulphate solutions, using stainless steel as cathode and Pb–8%Sb as anode. The pH of the electrolyte (10 g/L H 3 BO 3 , 75.95 g/L Ni 2+ and 130 g/L Na 2 SO 4 ) was adjusted at 3.5 and at 60 °C, while the current density was kept constant at 20 mA/cm 2 . (5) Cobalt and manganese extraction over magnesium by Cyanex 302 at pH: (5.0), T: 40 °C, with 20% extractant concentration and stripping of the loaded organic phase at T: 40 °C with diluted H 2 SO 4 (1 M). (6) Removal of magnesium by chemical precipitation (as brucite), using Ca(OH) 2 as neutralizing agent, at atmospheric pressure, pH = 10 and 25 °C. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction About 60% of the current worldwide production of nickel is de- rived from sulphide ores and the rest comes from nickel laterites (Sudol, 2005). However, about 70% of the nickel reserves are pres- ent in laterite deposits (Dalvi et al., 2004). As a result, there is growing interest in improving the technology for extraction of nickel (and cobalt) from laterites, as the demand for stainless steel continues to grow and the sulphide deposits become depleted (McDonald and Whittington, 2008). Nickel laterite ores can be broadly characterised as dry-land (e.g. deposits found in Greece, Albania, Western Australia) or tropical (e.g. deposits found in Cuba, New Caledonia, Brazil) (Whittington and Muir, 2000; Krause et al., 1997). Typically the dry-land laterites are less weathered than tropical laterites and contain more clay minerals and less goethite. Since laterite type ores naturally occur close to surface, economical open pit mining techniques are employed to recover the ore after removal of the overburden (Moskalyk and Alfantazi, 2002). Laterite deposits typ- ically occur in layers, ranging from zero to 40 m in depth below the surface. Greece is the only EU country with extensive but low-grade nickel laterites. They mainly occur as limonitic laterites and, to a 0892-6875/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.mineng.2009.06.006 * Corresponding author. Tel.: +30 210 7721761; fax: +30 210 7722218. E-mail address: ptsakiri@central.ntua.gr (P.E. Tsakiridis). Minerals Engineering 22 (2009) 1181–1192 Contents lists available at ScienceDirect Minerals Engineering journal homepage: www.elsevier.com/locate/mineng