THE EFFECT OF DEMINERALIZATION ON LIGNITE ACTIVATION

Activated carbons were produced from raw and demineralized Greek lignites under various experimental conditions using CO2 as the oxidizing agent. Removal of inorganic impurities was accomplished by acid washing of raw lignite with HF and HCl acid solutions. For the characterization of the activated carbons produced, adsorption of N2 at 77 K and CO2 at 298 K was used. Resulting isotherms were analysed by the BET and Dubinin-Radushkevich methods to give an assessment of microporosity. Demineralization brought about a lowering in the reactivity of the acid-washed coal and an increase in the apparent activation energy for reaction. Removal of inorganic matter resulted in activated carbons with very large surface area values and a highly developed microporosity. Surface area values of activated carbons produced from demineralized lignite were up to five times greater than those of activated carbons from untreated lignite, especially at high burn-off. Activation temperature increased the reaction rate, but it did not affect the pore structure of the final products.