Determination of mineral matter in Brazilian coals by thermal treatments

Information about the mineral and organic fractions of coal is essential for its sustainable use. However, most analytical characterization techniques used could be affected by the presence of organic matter in the matrix. The Brazilian coal contains high levels of sulfur ash (up to 50%), being usually classified as low-rank. In this study, the mineral matter (MM) content in Brazilian coals was obtained from the ash content of samples calcined at moderate (300 °C, 400 °C and 370 °C) and low (< 200 °C) temperatures with oxygen plasma (LTA). The isolate MM could be analyzed without the interference caused by organic matter. The best results for estimating the MM content from thermal treatments at moderate temperatures were obtained at 300 °C (MTAC300 °C). Residual organic and inorganic carbon contents in the ash are recommended for a more accurate MM estimation. LTA analysis indicated MM of 45% to 62% content, similar to values obtained with MTAC300 °C analysis (errors < 9%). In addition, it is possible to estimate the mineral matter content with proposed empirical equations based on easily determined parameters (HTA) with mean relative errors < 10%.