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

Abstract

Arsenic (As) pollutants are highly toxic and using Ca-based minerals to adsorb As2O3 is effective for emission control. In this study, a fixed-bed experimental system was used to study the adsorption of As2O3 by the mixture of CaO, SiO2, and Al2O3 at 1200 °C. The amount of As adsorbed by multiple minerals was higher than that by single minerals, indicating enhanced adsorption of As2O3 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:(SiO2 +Al2O3) and SiO2:Al2O3 ratios. Adsorbed As was mainly enriched in Ca-Si-Al mineral, including Ca2Al2SiO7. Density Functional Theory calculation was conducted to study the As2O3 adsorption on the Ca2Al2SiO7 (0 0 1) surface. The analysis of Mulliken charge and density of states showed that As2O3 molecules formed Al-O, O-As, and Ca-O bonds with the Al, O, and Ca sites. Si and Al in Ca2Al2SiO7 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.