Characterization of residue generated during medium temperature leaching of chalcopyrite concentrate under CESL conditions

The typical copper recovery from medium temperature pressure leaching of chalcopyrite concentrates, such as from the CESL process, is 95–99%. In order to examine the modes of copper loss to residue, a variety of CESL process residue samples were examined by chemical analysis, Quantitative X-Ray Diffraction (QXRD), Scanning Electron Microscopy/Energy Dispersive X-Ray Spectroscopy (SEM/EDX) and Electron microprobe analysis. The SEM and QXRD analyses indicated the presence of hematite and elemental sulfur as the major phases in the residue samples. Other phases present in minor to significant quantity were jarosite, pyrite, gypsum and anhydrite. Poor agreement between total chemical analyses of the residues by ICP-MS and those calculated from QXRD indicated the presence of an amorphous phase (ferrihydrite) in the residues. The amount of ferrihydrite and crystalline iron oxyhydroxide, and association of copper with these phases were determined by a sequential extraction method. There was a five-fold increase in the amount of copper associated with amorphous iron phases as compared to the crystalline phases.