Optimization of Process Conditions for Leaching of Middling Coal

In a typical coal washery, middlings are generated as a byproduct of a dense media cyclone having a size range of -13+0.5 mm and an ash content of 40–45%. Nearly 40% of the feed material is discharged as middlings. Middlings have good carbon values but embedded minerals in it and, hence, it is difficult to wash using conventional physical-cleaning techniques. Here in this article, the optimization of process variables from the lab scale to the pilot scale with a chemical-leaching technique is reported. Almost a 68% ash reduction could be achieved while maintaining the optimum process conditions. Higher reaction temperature, increased alkali concentration, and lesser reaction time favor the leaching process. Moreover, the alumina-to-silica ratio reduced from 0.53 to 0.25 and the phosphorus content significantly reduced by 90%.