Recovery of energy values from high-ash content washery tailings using waste oils by oil agglomeration

Froth flotation is widely used worldwide, but its efficiency drastically reduces, for recovery of fine coal particles containing high clay content, oxidized and low-rank coal. Under these circumstances, oil agglomeration has proven to be efficient in terms of beneficiated product with lesser ash content and high recovery. In present work, oil agglomeration was used to recover coal fines from washery tailings with ash content of 52.74%. The effect of operational parameters such as solid concentration, oil dosage, type of oil, and agglomeration time were analyzed. The process was evaluated on the basis of % ash rejection (% AR) and % combustible matter recovery (% CMR). For optimization purpose, 4-variable 3-level Response Surface Methodology Box-Behnken Design was used. From ANOVA, solid concentration found to be the most significant parameter for the recovery of coal fines from washery tailings. The closeness between R-2 and Adj. R-2 (for % AR, 0.9906 and 0.9891; for % CMR 0.9821 and 0.9776) ascertains the significance of the proposed model. The ash rejection found to be in the range of 58.03-74.63% and combustible matter recovery found to be 54.76-87.09%. The optimal condition found to be solid concentration 3.5%, oil dosage 15% and agglomeration time 14 min.