Determination of washability characteristics of anthracite coal by index of washability and near gravity material index - a case study

This paper summarizes the results of determination of the washability characteristics of anthracite coal from Vrska Cuka coal mine, Serbia. The effect of different coal size fractions has been studied through washability studies. In this study, float-sink experiments were carried out with the anthracite coal samples on (-19 + 9.5) mm, (-9.5 + 4.75) mm, (-4.75 + 2.36) mm, and (-2.36 + 0.6) mm size fractions. Two washability parameters, Index of Washability (IW) and Near Gravity Material Index (NGMI), were calculated and the results were compared. The IW and NGMI values indicated that the washability of different size fractions of anthracite coal was easy to relatively difficult to wash. The obtained values of IW showed that the order of coal washing ability by size fractions was as follows: (-9.5 + 4.75) mm, (-4.75 + 2.36) mm, (-2.36 + 0.6) mm, and (-19 + 9.5) mm. The NGMI values decreased with increasing specific gravity and decreasing particle size fractions. The minimum values of NGMI were achieved at density of 1650 kg/m(3) and these values were 0.1322, 0.0695, 0.0677, and 0.0240, respectively. The results presented in this study indicate that washability of the anthracite coal is relatively easy and should be washed at a specific density of 1650 kg/m(3).