Effect of molten caustic leaching on the combustion characteristics of anthracite

Changes in structure and combustion characteristics of anthracite after demineralization using molten caustic leaching (MCL) were investigated. The peak temperature of the treated anthracite during thermogravimetric analysis was lower (by similar to 150 K) than that of raw coal, so that the combustion region of the treated anthracite became similar to that of bituminous coal (350-600 degrees C). The effect of caustic treatment was so marked for anthracite that the maximum reactivity increased about four times above that of the raw coal, whereas the increase in reactivity of bituminous coal was marginal. Analytical investigation showed that coals experience carbonization during MCL treatment, with disruption of reactive hydrocarbons, and that the micro-defects formed by changes in functional groups affect the combustion temperature and reactivity. The effect on surface area and particle size was marginal for the anthracite, but very pronounced for the bituminous coal. (C) 1997 Elsevier Science Ltd.