A process of treating high sulfur coal to reduce sulfur dioxide emission when the high sulfur coal is burned comprising placing coal in pressure tank (16) of reduced pressure sufficient to fracture a portion of the coal by withdrawing ambient fluids trapped within the coal. The fractured coal is contacted with an aqueous silica colloid composition supersaturated with calcium carbonate via conduit (21), and the majority of the aqueous composition is then removed from contact with the coal. The aqueous composition-treated coal is pressurized in pressure tank (16) under a carbon dioxide atmosphere for a period of time sufficient for the calcium carbonate to enter fractures in the coal produced in the first step.