Enhanced adsorption of gaseous mercury on activated carbon by a novel clean modification method

Abstract

Activated carbon is the most widely used gaseous mercury adsorbent. However, lack of active sites on its surface leads to its poor mercury adsorption ability. Various modification methods, including acid-alkali, sulfide, halogenide, metallic oxides, etc., are used to modify activated carbon to enhance its adsorption ability, but there are still secondary pollution or/and solid waste problems. This article tried to use a clean ultraviolet (UV)/H2O2 advanced oxidation process (AOP) to modify activated carbon by generating hydroxyl radicals for enhancing adsorption of Hg0 on activated carbon. The activated carbon modification parameters, main influencing factors, mechanism and kinetics of mercury removal were studied. Studies indicate that UV/H2O2 AOP modification could substantively enhance the Hg0 adsorption over activated carbon. The optimum H2O2 modification concentration is 9%, and the optimum reaction temperature for Hg0 adsorption is 120 °C. The optimized Hg0 adsorption capacity reaches 3636.43 μg/g. Characterization measurement (e.g., BET, SEM, FTIR, XPS, etc.) demonstrates that UV/H2O2 AOP modification has slight destructive effect on pore structure of activated carbon, but significantly raises the contents of oxygen-containing functional groups (e.g., -OH, CO and CO). It is found that Hg0 adsorption is enhanced by O2 and NO in gas stream, while is inhibited by H2O and SO2 in gas stream. The whole process of Hg0 adsorption is mainly dominated via chemical adsorption step, and the oxygen-containing functional groups (e.g., -OH, CO and CO) and the chemisorbed oxygen (O*) are the main active sites to realize the oxidative removal of Hg0 on the modified activated carbon surface.