Results of a kinetic study on sphalerite leaching in ammonia using Cu(II) as an oxidation catalyst are presented. The effect of oxygen partial pressure, temperature, particle size, pH, NH3 and Cu(II) concentration was studied. Kinetic analysis of the experimental data was made both by differential approach (initial rate method) and integral approach (Shrinking Core Model). Rate controlling step was found to be surface reaction. Apparent activation energy was estimated to be 48.3 kJ/mol and apparent reaction orders of 0.2, 0.3 and 0.3 were obtained with respect to P-O2, [NH3] and Cu(II) concentration, respectively. Catalytic action of Cu(II) was attributed to redox couple Cu(II)/Cu(I), where cupric ammine [Cu(NH3)(4)(2+)] oxidizes sphalerite and the reduced state cuprous ammine [Cu(NH3)(2)(+)] is subsequently oxidized by dissolved oxygen. (C) 2003 Elsevier Science B.V. All rights reserved.