Adsorption and reaction mechanism of arsenic vapors over γ-Al2O3 in the simulated flue gas containing acid gases.

Arsenic emission from fuel combustion and metal smelting flue gas causes serious pollution. Addition of sorbents is a promising way for the arsenic capture from high temperature flue gas. However, it is difficult to remove arsenic from SO2/HCl-rich flue gas due to the competitive reaction of the sorbents with arsenic and these acid gases. To solve this problem, arsenic adsorption over γ-Al2O3 was studied in this work to evaluate its adsorption mechanism, resistance to acid gases as well as regeneration behavior. The results show that γ-Al2O3 had good resistance to acid gases and the arsenic adsorption by γ-Al2O3 could be effectively carried out at a wide temperature range between 573 and 1023 K. Nevertheless, adsorption at higher-temperature (like 1173 K) leaded to the decrease of surface area and the rearrangement of crystal structure of γ-Al2O3, reducing the active sites for arsenic adsorption. The adsorption of arsenic was confirmed to occur at different active sites in γ-Al2O3 by forming various adsorbed species. Increasing temperature facilitated arsenic transformation into more stable chemisorbed As3+ and As5+ which were difficult to remove through thermal treatment regeneration. Fortunately, the regeneration of spent γ-Al2O3 could be well performed using NaOH solution.