Washability curves for the lower coal seams in Candiota Mine — Brazil

In Brazil, the largest coal reserve is located in Candiota Coalfield, in the State of Rio Grande do Sul, currently mined by CRM — Companhia Riograndense de Mineração. The lower coal seams in this coalfield correspond to 30% of the entire coal reserve, but they are not mined. For the purpose of this paper, only the seams I1, I2 and I4 will be discussed. These seams have as yet not been characterized for beneficiation purposes. Therefore, washability curves were generated based on sink-and-float tests to evaluate the main characteristics of such coals for a future gravimetric beneficiation study. From these curves, the average curves were plotted, representing more closely the characteristics of each seam. Based on this, a comparative study was carried out for both selective and simultaneous gravimetric beneficiation of these three seams, without taking into consideration the process efficiency. For an ash content of 42%, the mass theoretical yield obtained was of 33% (selective beneficiation) and 31% (simultaneous beneficiation) for the coarse size fraction, and 76% (selective beneficiation) and 74% (simultaneous beneficiation) for the fine size fraction.