Roles of Sulfuric Acid in Elemental Mercury Removal by Activated Carbon and Sulfur-Impregnated Activated Carbon

摘要

This work addresses the discrepancy in the literature regarding the effects of sulfuric acid (H_2SO_4) on elemental Hg uptake by activated carbon (AC). H_2SO_4 in AC substantially increased Hg uptake by absorption particularly in the presence of oxygen. Hg uptake increased with acid amount and temperature exceeding 500 mg-Hg/g-AC after 3 days at 200 ℃ with AC treated with 20% H_2SO_4. In the absence of other strong oxidizers, oxygen was able to oxidize Hg. Upon oxidation, Hg was more readily soluble in the acid, greatly enhancing its uptake by acid-treated AC. Without O_2, S(VI) in H_2SO_4 was able to oxidize Hg, thus making it soluble in H_2SO_4. Consequently, the presence of a bulk H_2SO_4 phase within AC pores resulted in an orders of magnitude increase in Hg uptake capacity. However, the bulk H_2SO_4 phase lowered the AC pore volume and could block the access to the active surface sites and potentially hinder Hg uptake kinetics. AC treated with SO_2 at 700 ℃ exhibited a much faster rate of Hg uptake attributed to sulfur functional groups enhancing adsorption kinetics. SO_2-treated carbon maintained its fast uptake kinetics even after impregnation by 20% H_2SO_4.