Adsorption characteristics of Ag⁺ on sphalerite surface: a combined experimental and first-principle study

The rapid development of industrial society is also accompanied by the generation of a large amount of heavy metal wastewater, which has caused serious harm to the ecological environment and human society. Natural sphalerite has an important value in the environmental field due to its own semiconducting properties. In order to effectively remove Ag⁺ from wastewater containing silver, this study develops a natural mineral-based Ag⁺ adsorbent material (sphalerite) based on elemental affinity qualities and mineralization principles. The results of batch experiments showed that the initial Ag⁺ concentration of 50 mg/L reduced to 0.094 mg/L with a reaction duration of 15 min, a sphalerite dose of 5 g/L, an initial particle size of -400 mesh (38 μm), a reaction temperature of 25 °C, and a pH of 5. The highest adsorption capacity is 19.77 mg/g, and the adsorption behavior is consistent with the Freundlich isotherm model and pseudo-second-order adsorption kinetics. The results of solution chemical analysis indicate that the presence of Ag⁺ is primarily influenced by the presence of S^2-. Further analysis using SEM-EDS, FTIR, and XPS techniques reveals that Ag⁺ is chemically adsorb onto the mineral surface, resulting in the formation of Ag₂S. DFT calculations further confirm the overlap between the Ag 4d orbitals and the S 3p orbitals on the surface of sphalerite, further confirming its chemical adsorption. Mulliken populations suggest that charge transfer occurs between Ag⁺ and S atoms in the sphalerite surface. This research systematically reveals the Ag⁺ adsorption mechanism on sphalerite surface and expands research ideas for treating heavy metal wastewater.