Mineral matter in coal has an environmentally negative effect, as it is responsible for the generation of soot and slag. Technically, the mineral matter causes corrosion of equipment and reduces the combustion rate of coal, as well as influencing the sizing of equipment. Therefore, removal of this unwanted portion of the carbon matrix would reduce the need for importing high-quality coals and minimize transportation costs. This work aims to study the effects of the removal of mineral matter on the structure of southern Brazilian coal at the temperature of gasification and considering the kinetic parameters of the oxy-fuel combustion reaction. The demineralization process was conducted using solutions of HF, HCl, and HNO3 with concentrations of 20% (v/v). The samples were characterized by elemental analysis, proximate analysis, SEM, FT-IR spectroscopy, petrographic analysis, XRD, and XRF. The removal of the mineral portion introduced major changes in the structure of coal, reflecting an increase in the start temperature of the Boudouard reaction to 160 K. The oxy-fuel reaction was performed at temperatures of 873, 973, 1073, and 1173 K with O-2/CO2 concentration ratios ranging from 10% to 30% (v/v). Before the demineralization process, the activation energy for the oxy-fuel reaction was 10.8 kJ.mol(-1). The value obtained with demineralized char was 56.46 kJ.mol(-1).