Removal of mineral matter from coal by alkali treatment

Abstract The removal of mineral matter from coal was attempted by caustic digestion followed by acid washing. A mild treatment at 460 K was found to be sufficient to remove most minerals and yet to avoid any substantial loss of heating value. The reaction products were identified by X-ray diffraction. Mass balance of each element was also clarified. The removal of major components, quartz and kaolinite, was rather easy, whereas the removal of Ca and Fe compounds strongly depended on the type of mineral matter.