ACID TREATMENT OF LIGNITE AND ITS EFFECT ON ACTIVATION

Coal specimens with different contents of inorganic constituents were produced from Greek lignite under various acid treatment conditions. Activated carbons were produced with heat treatment of the raw and acid-treated lignites at 900-degrees-C. Characterization of the activated carbons was accomplished by adsorption of N2 at 77 K and CO2 at 298 K. Adsorption isotherms were analysed by the Dubinin-Radushkevich method to give an assessment of the micropore volumes. The ash content of the lignites depended upon the type of the acid used and the treatment stages. Removal of the catalytically active inorganic constituents brought about a lowering in the reactivity of the acid-treated coals. Complete demineralization resulted in activated carbons with a highly developed microporosity and very large pore volumes. However, activated carbons from lignites with medium ash content presented values of pore volume lower than the respective values of the above samples, yet exceeded the corresponding volumes of carbons from untreated lignite.