It is established that firing samples (granules) in a layer of fluxed magnetite iron ore concentrates are accompanied by complex physicochemical processes related to the oxidation of magnetite and the decomposition of carbonates. When they are heated, along with heat exchange processes, mass transfer processes also occur. These processes are interrelated and affect each other, as well as the degree of completion of the processes of oxidation and decarbonization in the layer. The oxidation mechanism of the samples containing magnetite is considered. A model of the mass transfer process for the period of decomposition of carbonates is refined. An equation is proposed that describes the kinetics of magnetite oxidation in samples upon heating for a more general form of boundary conditions. An equation is presented that makes it possible to determine the rate constant of the oxidation process depending on the characteristics of the heat-carrier gas and the properties of the material. A calculation procedure is developed to determine the diffusion coefficient of oxygen in the combustion products of various fuels. Experiments are carried out to study the kinetics of oxidation and decarbonization processes in a layer of granules on an experimental setup, which make it possible to simulate these processes in relation to different periods of their heat treatment in thermal plants and determine the mass transfer coefficients. This will make it possible to determine the degree of completion of processes by the height of the layer at the given values of the temperature and duration of firing.