The work in this paper examines the effect of schwertmannite on the ferric sulphate/sulphuric acid leaching of copper from chalcopyrite 'concentrates' at 60 degrees C. Pyrrhotite, which is present in the Cobar concentrate, is more reactive than the chalcopyrite and it releases iron and consumes significant acid. Most of the leached iron precipitates as schwertmannite, which coats the Cobar chalcopyrite and other minerals present in the residue. For the MIM concentrate, jarosite is the main iron-containing precipitate. Copper leaches more rapidly from the Cobar concentrate than the MIM concentrate, at a solids loading of 5.0% w/v. This occurs despite the significantly higher iron precipitate weight. Furthermore, similar copper extractions are obtained upon leaching the Cobar concentrate in the range 1.0-2.5% w/v, despite the schwertmannite concentrations ranging from similar to 6% to similar to 33%, respectively. These data suggest that schwertmannite does not hinder the rate at which copper leaches from chalcopyrite in ferric sulphate solutions. Crown Copyright (C) 2007 Published by Elsevier Ltd. All rights reserved.