Processing of sulfide concentrates with high iron content in the hydrometallurgy of zinc increases the amount of obtained cakes containing 15-20% Zn and 25-30% Fe. The main reason for this undesirable process is the presence of a part of the zinc as insoluble ZnF2O4. In this regard, 6 zinc concentrates of different origins were investigated using Mossbauer spectroscopy as well as chemical, XRD, DTA and TGA analyses. The relation between the phase content and the received TG and DTA curves, as well as the behavior of the main phases in the concentrates during their oxidation was established. On the basis of the Mossbauer spectra, the iron containing phases and their influence on the oxidation process were determined. The results are used to choose the charge of concentrates for optimal oxidative roasting in fluidized bed furnace and for minimizing ferrite formation. (C) 2014 Elsevier B.V. All rights reserved.