Study on mercury adsorption mechanism of iron-modified biomass char in coal-fired flue gas based on density functional theory

As a new type of porous adsorbent, iron-modified biomass char (Fe10%-BC) may efficiently remove Hg0 from flue gas. However, the lack of in-depth research on the mercury adsorption mechanism of biomass char limits the development of this technology. The reaction path of mercury adsorption was quantitatively revealed by DFT (Density Functional Theory). The effects of oxygen-containing groups and adsorption atmosphere on Hg0 adsorption were analyzed. The results show that Hg0 adsorption by Fe10%-BC includes two stages, that is adsorption and oxidation. The modified biochar utilized the strong oxygen release/storage capacity of iron oxides, reacting with Hg0 by Lewis acid-base reaction. Oxygen-containing groups regulated molecular orbital energy level and surface charge distribution of iron-modified biomass char, affecting the adsorption capacity of Fe10%-BC. Aldehyde, ketone and carboxyl group promoted Hg0 adsorption performance of Fe10%-BC, and the effect from strong to weak was aldehyde group > ketone group > carboxyl group. Hydroxyl group inhibited mercury adsorption by Fe%10-BC. The adsorption atmosphere CO2，O2 and HCl promoted the mercury adsorption performance of the iron-based modified biomass char by forming new adsorption sites with the modified biomass char. SO2 consumed the high valence metal and lattice oxygen, forming competitive adsorption with Hg0. Hg0 adsorption efficiency of the modified biomass char decreased to 58%.