Abstract
The removal of mineral matter from four coals was attempted by using caustic digestion followed by acid washing. A mild treatment at 460 K was found enough to remove most minerals without losing heating value of coal. X-ray diffraction measurements of low temperature-and high temperature-ashes of both raw and treated coals revealed the chemical form of minerals which were difficult to be removed. The reduction of Si and Al content was proportional to the ash reduction, but the removal of Fe and Ca components strongly depended on the type of minerals. The degree of desulfurization was also determined. It was found that pyritic sulfur was easily removed but other type of sulfur seemed to be almost unaffected by the present treatment.
