Adsorption of Si(OH)4 and Al(OH)4 onto arsenopyrite surface: Exploring the sealing feasibility of geopolymer to arsenopyrite

Abstract

As a common arsenic-bearing mineral, arsenopyrite is highly abundant in most nonferrous metal tailings. Therefore, arsenic is leached into the environment from the stacking of tailings by rainwater and natural weathering. Using a geopolymer method to backfill tailings is a promising method to prevent leaching of arsenic from these tailings. Whether a geopolymer can effectively seal arsenopyrite is the key to preventing arsenic from entering the environment. Using Si(OH)4 and Al(OH)4 as geopolymer monomers, the adsorption energies, geometries, charge transfer, and density of states (DOS) of Si(OH)4 and Al(OH)4 on arsenopyrite crystal (001) surface were studied. The results indicated that the adsorption sites of Si(OH)4 were mainly H atoms, mostly by means of physical adsorption. Si(OH)4 was more easily adsorbed onto the S2 atom site. The Al(OH)4 molecule used the H atom and O atoms as the adsorption sites. The H atom as the adsorption site was characterized as physical adsorption, whereas the O atom as the adsorption site was characterized as chemical adsorption. Based on the DOS and population analysis results, there was a strong tendency for orbital hybridization and bonding between the oxygen atoms in Al(OH)4 molecules and the As and Fe atoms on the (001) surface. Compared to Si(OH)4, Al(OH)4 had a stronger affinity for the crystal surface. These results suggest that it is theoretically feasible to use a geopolymer method to seal and backfill arsenopyrite.