Theoretical Investigation of Arsenic and Selenium Species Adsorption Behavior on Different Mineral Adsorbents

CaO and Fe2O3 are effective mineral sorbents to inhibit the damage of arsenic and selenium release into the atmospheric environment. Density functional theory was applied to explore the adsorption mechanism of different arsenic and selenium species (atom, hydride, oxide, and chloride) on CaO and Fe2O3 surfaces. The effect of the As4O6 cluster on the adsorption behavior of CaO and Fe2O3 surfaces was also examined. The results show that the O top sites serve as the active sites for arsenic and selenium atom adsorption on the CaO(001) surface. For the Fe2O3(001) surface, the adsorption energy of the As atom at the Fe top and O bridge site can reach -381.38 and -439.55 kJ/mol, respectively. The results show that the Fe top site and O bridge site are both effective chemical adsorption sites. CaO and Fe2O3 also exhibit a good performance to adsorb atomic arsenic and selenium under the condition of multicoverage. In addition, the interactions between two adsorbents and complex arsenic/selenium species are weakened in different degrees, but still belong to chemical adsorption. The adsorption of the As4O6 cluster on the CaO surface is mainly attributed to the interaction between As atoms and O atoms on the CaO surface. The As4O6 adsorption on the Fe2O3 surface depends on the interaction between O atoms of As4O6 and Fe atoms on the Fe2O3 surface. However, the interactions can both lead to the formation of more stable arsenate, which contributes to the reduction of detrimental arsenic release.