The interactions in FeSO4 . H2O(MhFS)/BaO2 mixtures at molar ratios 0.5, 1,2,4 under oxidizing atmosphere and dynamic heating have been investigated with thermal, diffractometric and Mossbauer methods. The influence of temperature and partial pressure of the gaseous components on the rate of the process has been determined, as well as the formation of reaction intermediates such as FeOHSO4 and Fe2O(SO4)(2). Process mechanisms are suggested for different molar ratios of the starting mixtures.