Abstract: By Ferric Ion Treatment of crushed and/or pulverized coal, the ash content of a coal can be significantly and efficiently reduced. This treatment of coal, preferably in an acidic medium, creates an increase in osmotic pressure inside the pores and crevices of the coal matrix until they open up, allowing the ash-forming mineral matter to be released from the coal. Also, the ferric ions preferentially attack the sessile bonds of the coal molecule and help open up the pores. The liberated mineral matter is then separated from the coal to obtain a clean coal. A flow-through reactor, utilizing working, reference and counter electrodes, and a loosely-packed coal bed through which the electrolyte flows, is particularly effective in facilitating the Ferric Ion Treatment.