Research on the adsorption mechanism of As by Fe-bearing minerals in coal during high-temperature combustion

Abstract

As can be retained by Fe components in coal during high-temperature combustion, which is beneficial for reducing As emissions. In this study, high-temperature As adsorption experiments were carried out in a fixed-bed experimental system with As model compound and minerals. The adsorption amount of As was much higher when Fe2O3, SiO2, and Al2O3 acted together than when they acted alone. As was mainly distributed in the Fe-Si-Al minerals generated by the reaction of the three oxides, for which the Fe2O3:SiO2:Al2O3 mass ratio of 1:1:1 was the most favorable, and the maximum adsorption amount of As was 18.2 mg·g−1. Density functional theory calculations were carried out for the adsorption of As2O3 by Fe2O3, SiO2, Al2O3, and Fe2Al4Si5O18. Fe2Al4Si5O18 had the highest adsorption energy for As2O3, indicating the most stable adsorption. As2O3 was adsorbed on the Fe and Si sites. The adsorption ability of the Fe site was strengthened in Fe2Al4Si5O18 relative to that in Fe2O3. The formation of Fe-O-Si and Fe-O-Al in the mineral promoted electron transfer from the adsorbent to As2O3 molecule, thereby strengthening adsorption. These results can guide the optimization of coal blending methods and the modification of adsorbents to control As emissions in coal-fired systems.