Arsenic removal from coal-fired flue gas by metal oxides modified wood chips coke: Experimental and DFT study

Abstract

Coal-fired power plant is one of the main anthropogenic arsenic emission sources, where gaseous As2O3 is the main form in the flue gas to the atmosphere. In this work, a series of metal salt impregnated wood chips coke (Me-BC) were developed for As2O3 removal from flue gas, which selected BC with low cost and high arsenic removal potential as the carrier and modified by metal nitrate through impregnation and pyrolysis to load active components. The results indicate that As2O3 removal performance of the Me-BC obeys Fe-BC-0.15 > BC > Al-BC-0.15 > Ca-BC-0.15 > K-BC-0.15 under the basic flue gas composition (N2 + O2 + CO2) at 150℃, with the highest As2O3 removal capacity (141.5 μg/g) and efficiency (92.9%) for Fe-BC-0.15 compared to 92.4 μg/g, 60.7% of the BC. The arsenic removal ability of Fe-BC firstly increases and then decreases as Fe(NO3)3 impregnation concentration increases with its maximum value at 0.15 mol/L. Generally, the NO has a significant inhibitory effect on the arsenic removal of Fe-BC-0.15 due to consumption of surface active oxygen species by or the competitive adsorption between NO and As2O3. Low-concentration SO2 complete with As2O3 for the adsorption on active sites while high-concentration SO2 will promote SO3 and Oβ formation which benefits for As2O3 capture. Overall, Oɑ and Oβ and C-O play an important promoting role in the arsenic removal by adsorbents. DFT calculations indicates that C-O have strongest adsorption energy for As2O3 among oxygen-containing functional groups. The adsorption of SO2 and NO on naked BC and BC-O is easier than As2O3. Both Fe2O3 and BC play an important role in the arsenic removal process by Fe-BC-0.15.