The work is devoted to research of chemical-metallurgical decarbonization process in iron ore pellets, taking into account thermal and technological operation features of roasting conveyor-type machines. Calcination of pelletized iron ore raw material was experimentally examined, using the samples that save their initial structure within the temperature and heating rate ranges of the existing roasting conveyor-type machines. Appearance of essential temperature gradients in the examined samples was proved experimentally; it was connected with non-stationary heating conditions and thermal effects of carbonates dissociation reaction. These conditions and effects restrict possibility of use of the existing non-isothermal kinetic methods for determination of kind and parameters of kinetic equations. The relationship among heterogeneous endothermic transformations and thermal physical calcination conditions was revealed.