High pressure oxidative acid leaching (HPOXAL) was employed to extract valuable metals from nickel converter slag. Parameters such as sulfuric acid concentration, temperature, liquid/solid (L/S) ratio, leaching time, oxygen partial pressure and particle size were investigated to optimize the solubility of metal values and improve the solid-liquid separation characteristics of the leaching slurry. A highly selective leaching of valuable metals with extraction of >97% for cobalt and nickel, >95% for copper and <0.4% for iron was successfully achieved under the conditions of -150 + 74 mu m particle size, 0.3 mol/L sulfuric acid concentration, 7 mL/g liquid/solid (L/S) ratio and 600 kPa oxygen partial pressure at 200 degrees C for 80 min. Under the conditions, less than 2% silicon was dissolved, and the leaching slurry performed a good solid-liquid separation characteristics with a filtration rate of 433.73 L/m(2) h. The residue containing hematite, silica and <0.1% bases metals was suitable for further disposal. (C) 2015 Elsevier B.V. All rights reserved.