Tests were carried out to determine pyrite dissolution, present in coal, in aqueous sulfuric acid and oxygen as an oxidant. The main objective is the evaluation of oxidative treatment in acidic media focused on the elimination of pyrite from coal. The influence of several parameters such as temperature, acid, and oxygen pressure concentrations were investigated. It was found that the dissolution curves for pyritic sulfur follow the kinetic model of the shrinking core model, with diffusion through the solid product of the reaction as the controlling stage. Additional tests show a preferential release of iron from pyrite leaving a “polysulfide” or “metal deficient” layer. Results also indicate that in aqueous solutions of 0.5 M of H₂SO₄ at 150°C and with increase in the oxygen pressure, pyrite dissolution increases around 50%.