Adsorption mechanism of As2O3 by Ca-Si-Al mineral: An experimental and DFT study

Arsenic (As) pollutants are highly toxic and using Ca-based minerals to adsorb As 2 O 3 is effective for emission control. In this study, a fixed-bed experimental system was used to study the adsorption of As 2 O 3 by the mixture of CaO, SiO 2 , and Al 2 O 3 at 1200 °C. The amount of As adsorbed by multiple minerals was higher than that by single minerals, indicating enhanced adsorption of As 2 O 3 under the coupling effects of Ca, Si, and Al. The adsorption amount of As first increased and then decreased with an increase in the CaO:(SiO 2 +Al 2 O 3 ) and SiO 2 :Al 2 O 3 ratios. Adsorbed As was mainly enriched in Ca-Si-Al mineral, including Ca 2 Al 2 SiO 7 . Density Functional Theory calculation was conducted to study the As 2 O 3 adsorption on the Ca 2 Al 2 SiO 7 (0 0 1) surface. The analysis of Mulliken charge and density of states showed that As 2 O 3 molecules formed Al-O, O-As, and Ca-O bonds with the Al, O, and Ca sites. Si and Al in Ca 2 Al 2 SiO 7 enhanced the adsorption ability of Ca sites by promoting electron transfer . Si/Al ratio close to 1:1 is conducive to the formation of Si-O-Al structures, thus further enhancing the adsorption. The results can help optimize coal blending strategies and modify adsorbents to further reduce As emissions during coal combustion .