Phosphate ore are a complex combination of chemical substances in natural minerals. The complicated physicochemical process of heating phosphorites includes a set of heat and mass exchange processes, endothermic reactions of carbonates dissociation, and processes of structural transformations during solid- and liquid-state sintering. The temperature-concentration and temperature-time dependences of the heat capacity of phosphate ore samples on the thermal conditions of the carbonates dissociation reaction in the samples, under structural modifications, as a result of a change in the chemical composition of the samples were experimentally investigated. The influence of the structural changes in the samples in the range of the raw material roasting temperatures and of the heating rates on the heat capacity of the phosphorites was evaluated. Scientific justification was provided for the occurrence of significant temperature gradients in the samples due to transient heating conditions and to the action of the thermal effects of the carbonates dissociation reaction, which limits the applicability of conventional methods to determine the true and effective heat capacities of the samples. The relationship between the heterogeneous endothermic structural transformations and the thermophysical conditions of the endothermic reaction of carbonates dissociation was established, which allows increasing the energy efficiency of the thermal treatment of the phosphate raw material during beneficiation on roasting conveyor and sintering machines. Analysis of the experimental data reveals a significant effect of thermal dissociation of carbonates and of the internal heat exchange on the heat capacity of the phosphorites. The error of the found heat capacity is determined by the technique of thermoanalytical experiments, the dimensions of the samples, the thermal effect of the carbonates dissociation reaction, and the reacting phase concentration. The error increases with an increase in the sample heating rate, i.e., with growth of the factors increasing the steepness of the temperature gradient field in the samples. The chemical and energy technological features of the thermal treatment of the phosphate raw materials are determined by the dependence of their heat capacity on the endothermic reaction of carbonates dissociation during heating in a wide range of heating rates in a moving dense multilayer of pellets on the grate of operating roasting conveyor machines, which allows optimizing energy-saving roasting modes.