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

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 (0 0 1) 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 (0 0 1) 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.