Experimental and computational study on the adsorption mechanism of silver ions on galena surface

Abstract

With the increased use of silver in industry, a lot of wastewater containing silver is produced. If this wastewater is not treated, it will seriously impact both the ecological environment and human life. In order to effectively remove Ag+ from silver-containing wastewater, this study innovatively developed a natural mineral-based adsorption material (galena). The effects of reaction time, galena dosage, starting concentration, initial particle size, temperature, and solution pH on Ag+ removal were first studied using batch studies. The outcomes demonstrated that the initial Ag+ concentration of 50 mg/L reduced to 0.086 mg/L with the reaction duration of 15 min, the galena dose of 5 g/L, the initial particle size of −400 mesh (38 μm), the reaction temperature of 25 °C, and the pH of 5. The adsorption results show that the removal behavior of Ag+ by galena is consistent with the pseudo-second-order adsorption kinetic model and the Freundlich isothermal adsorption model, with the maximum adsorption amount of 18.78 mg/g. Solution chemical analysis shows that in the Ag+-NO32−-Pb2+-S2− system, Ag+ mainly reacts with S2− and forms a precipitate at pH = 5–6. SEM-EDS, FT-IR, and XPS analysis also showed that S2− and Ag+ are bound together as Ag2S in the galena surface. Orbital hybridization of the 4d orbitals of Ag+ with the S2− 3p orbitals occurs during the adsorption process according to density functional theory (DFT) calculations. During the adsorption process, Ag+ undergo charge transfer with S2− in the surface of galena.