Effect of thermal and acid treatments on properties of Argentinean low rank coals

The chemical, structural, and textural-morphological features of low rank coals, subbituminous and high volatile bituminous, from Argentinean minefields were examined. Features modifications arising from thermal treatment and mineral matter removal were analyzed and related to chars reacrivity for CO2 gasification. For this purpose, proximate, ultimate, and ash analyses, X-ray diffraction, mercury intrusion porosimetry, adsorption of CO2 (298 K), and scanning electronic microscopy were performed on the original coals as well as on the raw and demineralized char samples. Thermal treatment increased the coals structural ordering and affected pores of any size, leading to bimodal macro-meso-pore size distributions and to a pronounced development of micropores. Disarrangement of the structures took place as a result of mineral matter removal altering mainly macro- and mesopores, thus producing unimodal distributions. Structural changes occasioned by thermal treatment and demineralization were also reflected in modifications of the surface fractal dimensions estimated from mercury porosimetry data. Reactivity of chars for gasification was significantly affected by demineralization not only due to removal of metals, likely responsible for catalytic effects, but also induced by the structural modifications.