Partitioning of mineralogical and inorganic geochemical components of coals from Santa Catarina, Brazil, by industrial beneficiation processes

Abstract

Comparative studies of the mineral matter and trace elements in 12 pairs of run-of-mine (ROM) and clean-coal products from beneficiation plants in Santa Catarina, southern Brazil, have been carried out using low-temperature oxygen-plasma ashing, X-ray diffraction and chemical analysis techniques with the aim of evaluating the effect of coal preparation on the mineralogy and chemical composition of the final coal products. The results show that substantial reductions in mineral matter and ash percentages are associated with beneficiation of coals mined from the different deposits. These reductions are accompanied by changes in the percentages of Fe2O3 in the respective coal ashes, due to the reduction in the proportion of pyrite in the mineral matter, and also by a reduction in the percentage of Na2O, possibly due to ion exchange within the clay minerals. The relative proportions of quartz, clay minerals, and minor phases such as calcite and feldspar (mainly albite) within the mineral matter are not, however, significantly changed by the beneficiation processes.The concentrations of most trace elements in the beneficiation products are similar to the respective concentrations in the relevant ROM materials, or are reduced to an extent similar to that of the total mineral matter percentage for the respective coal samples. This suggests an association mainly with the clay-rich mineral matter. The concentrations of As and Pb, however, are reduced to a greater extent for most samples by the beneficiation processes, consistent with a pyrite association. Concentrations of Ge, U and Zr are higher in many of the clean coals than in the respective run-of-mine materials, suggesting the possibility of preferential association, at least for some deposits, with the organic-rich fractions of the coals concerned.