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 hydrometallurgical 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 degrees C. (2) Cobalt, manganese and magnesium extraction over nickel by Cyanex 272 at pH: 5.5, T: 40 degrees C, with 20% extractant concentration and stripping of the loaded organic phase at T: 40 degrees C with diluted H(2)SO(4) (4 M). (3) Nickel concentration by solvent extraction using Cyanex 272 at pH: 7.5, T: 40 degrees C, with 10% extractant concentration and stripping of the loaded organic phase by nickel spent electrolyte (55.45 g/L Ni) at T: 40 degrees 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 degrees 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 degrees C, with 20% extractant concentration and stripping of the loaded organic phase at T: 40 degrees 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 degrees C. (C) 2009 Elsevier Ltd. All rights reserved.