The dissolution of chalcopyrite in acidic potassium dichromate solution has been investigated with respect to the effects of sulphuric acid and potassium dichromate concentrations, by changing stirring speed, leaching temperature and particle size. It was determined that dissolution rate increased with increasing sulphuric acid concentration, potassium dichromate concentration and temperature. A particle size below 75 mu m was required to leach > 80% copper in 150 min at 90 degrees C. The kinetic study showed that the dissolution of chalcopyrite is represented by shrinking core model with diffusion through a porous product layer of sulphur. The activation energy (E-a) for the dissolution reaction was calculated as 24 kJ/mol. Pyrite dissolution from the concentrate was significant in potassium dichromate solutions because of its high oxidation potential. (c) 2005 Elsevier B.V. All rights reserved.