The production of electrolytic zinc front sulphide ores consists mainly of four stages: roasting, acid leaching, purification and electrolysis. The roasting step plays an important role in zinc extraction due to the transformation from sulphide to oxide structure which provides more reactivity in presence of acid solutions. Incomplete particle roasting and presence of highly stable zinc ferrite (ZnFe2O4) formed in the pyrometallurgical step are the two major obstacles in the hydrometallurgical extraction of zinc. The objective of this study is to detect problems observed in an industrial electrolytic zinc circuit. For this purpose, X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF) and scanning electron microscopy (SEM/EDS) techniques were used to characterize sulphide and roasted concentrate samples. Microscopic investigations of cross-sectional particles revealed incomplete roasting in some particle sizes and the presence of ferrite clusters inside the roasted ores. (c) 2007 Elsevier Ltd. All rights reserved.