Demineralization of low grade coal – A review

World over large reserves of low grade coals are available. The use of low-grade coal in various industries like power plants, metallurgical plants, cement units, etc. creates environmental pollution because of generation of large amount of solid and gaseous pollutants. Therefore, it is of paramount importance to clean the coal before its utilization. A number of upgrading technologies are being followed to produce clean coal. The current paper reviews demineralization/desulfurization of coals containing high ash and/or sulfur by physical, microwave, bio- and chemical beneficiation methods. Physical beneficiation of coal is not very effective in separation of the finely dispersed minerals, whereas microwave processing requires lesser time but is not favoured energetically. Bio-processing is mainly used for the desulfurization of high sulfur coal, although it is usually slow and requires long incubation period. Chemical beneficiation uses expensive reagents and leads to the generation of large amount of wastewater which is to be purified before discharge. Thus, a combined approach consisting of physical beneficiation followed by chemical cleaning of coal appears to have a potential for significant reduction of ash with less investment while generating less amount of wastewater.