Abstract The aim of this study was to determine the kinetic parameters of the oxy-fuel combustion of char from a Brazilian bituminous coal with a high ash content. The char, with a particle diameter of 715 μm, was prepared in a N2 atmosphere at 1173 K. The oxy-fuel combustion assays were performed using a thermobalance at different temperatures and O2/CO2 gas mixtures of different concentrations. According to the unreacted core model, the process is determined by chemical reaction at low temperatures, with an activation energy of 56.7 kJ.kmol-1, a reaction order of 0.5 at 973 K and a reaction order of 0.7 overall. The use of the continuous reaction model did not provide a good fit for the experimental data because the consumption of the particles during the reaction was not constant, as predicted by the model. According to the Langmuir-Hinshelwood model, the activation energy for the first step was 37.3 kJ.kmol-1.

Chromium used in leather manufacturing can be oxidized from the trivalent to the hexavalent state, causing environmental concerns. In this study, the influence of Cr(III) from tanning, deacidification pH, fatliquors, chrome retanning and vegetable retanning on the formation of Cr(VI) in leather was analyzed by comparing natural and aged samples. In wet-blue leather, even after aging and in fatliquored leathers that did not suffer the aging process, the presence of Cr(VI) was always below the detection limit of 3 mg/kg. Considering the presence of Cr(VI), the supply of chromium during the retanning step had a more significant effect than during the tanning. In the fatliquoring process with sulfites, fish and synthetic fatliquor leather samples contained Cr(VI) when aged, and the highest concentration detected was 26.7 mg/kg. The evaluation of Cr(VI) formation led to recommendations for regulation in the leather industry.