Role of activated carbon structural properties and surface chemistry in mercury adsorption

In this work the performance of activated carbons prepared from raw and demineralised lignite for gas-phase Hg° removal was evaluated. A two-stage activation procedure was used for the production of the activated samples. In order to study the effect of mineral matter on pore structure development and surface functionality of the activated carbons, a demineralisation procedure involving a three-stage acid treatment of coals, was used, prior to activation. Hg° adsorption tests were realized in laboratory-scale unit consisted of a fixed-bed reactor charged with the tested activated samples. The examined adsorbent properties that may affect removal capacity were the pore structure, the surface chemistry and the presence of sulphur on the surface of activated carbons. The obtained results revealed that activated carbons produced from demineralised lignite posses a high-developed micropore structure with increased total pore volume and BET surface area. These samples exhibit enhanced Hg° adsorptive capacity. In all cases, mercury removal efficiency increased by sulphur addition. Finally, the starting material properties and activation conditions affect the concentration and the type of the oxygen groups on activated carbon surface, that have been determined with TPD-MS experiments.

ganic matter from the raw lignite were proven to be highly microporous and more efficient to capture Hg°. On the contrary, the mesoporous activated carbons produced from raw lignite exhibit faster rate of Hg° uptake. For all samples tested, sulphur addition increased Hg° adsorption capacity due to chemisorption that takes place. The Activated carbons with different pore structure characteristics have been produced from Ptolemais lignite by a two-stage activation procedure (pyrolysis followed by CO2 activation). Samples prepared after the removal of the inor- number of oxygen groups is higher for activated carbons produced from demineralised lignite and is decreased as activation time is prolonged. The removal of inorganic matter released lactones that favour Hg° adsorption.