Influence of Ca²⁺ and Mg²⁺ Ions on the Surface Properties and Reagent Adsorption of Hemimorphite (Zn₄[Si₂O₇](OH)₂·H₂O): DFT and MD Study

Hemimorphite (Zn 4 [Si 2 O 7 ](OH) 2 ·H 2 O) is one of the sources of zinc metal, which is commonly recovered through flotation. The presence of Ca 2+ and Mg 2+ ions could inevitably impact the flotation process, yet the mechanism remains unclear. In this paper, the influence of the adsorption of [Ca(H 2 O) 6 ] 2+ and [Mg(H 2 O) 6 ] 2+ on the surface properties and reagent interactions of hemimorphite was investigated using density functional theory (DFT) calculations and molecular dynamics (MD) simulations. The results indicate that [Ca(H 2 O) 6 ] 2+ is chemically adsorbed through Ca‐O bonding under both acidic and alkaline conditions, while [Mg(H 2 O) 6 ] 2+ is physically adsorbed through hydrogen bonding under acidic conditions but chemically adsorbed under alkaline conditions. Based on the work function results, [Ca(H 2 O) 6 ] 2+ enhances surface stability under acidic conditions, depressing sodium oleate adsorption, whereas [Mg(H 2 O) 6 ] 2+ has minimal impact. Under alkaline conditions, [Mg(H 2 O) 6 ] 2+ is more effective than [Ca(H 2 O) 6 ] 2+ in promoting sodium oleate adsorption. Additionally, mean square displacement results reveal that [Ca(H 2 O) 6 ] 2+ increases surface hydrophobicity under both acidic and alkaline conditions. However, [Mg(H 2 O) 6 ] 2+ decreases surface hydrophobicity under acidic conditions, while the opposite occurs under alkaline conditions. These findings elucidate the differences in mechanisms by which Ca 2+ and Mg 2+ ions influence the direct flotation of hemimorphite, providing a microscopic perspective for the direct flotation of hemimorphite.