Chemical cleaning of low grade coals through alkali-acid leaching employing mild conditions under ambient pressure

The washability of low grade coals using physical means is sometimes poor and this warrants the use of chemical means. Cleaning such coal using dilute aqueous NaOH solution under mild conditions at atmospheric pressure followed by acid leaching results in a 75 wt% demineralization of the coal. The alkali and acids used can be recovered for re-use. This affords a convenient method for coal demineralization. The use of dilute HCl or dilute H2SO4 alone can also lead to an appreciable degree of demineralization.