Study on the adsorption behavior and adsorption mechanism of green depressant TA on the basal plane and edge surface of talc

Talc is a layered silicate mineral with pronounced crystal anisotropy, consisting of a basal (001) surface and an edge (100) surface, which complicates its separation from valuable minerals. In this study, tannic acid (TA) was used as a depressant, and its adsorption behaviors on the two representative surfaces of talc—silica (basal plane surface) and magnesium silicate (edge surface)—were systematically investigated using experimental methods and molecular simulations. TA addition reduced the contact angles of the talc basal and edge surfaces by 30.5° and 22.7°, respectively, indicating enhanced hydrophilicity. ToF-SIMS analysis revealed that TA physically adsorbs onto the silica surface, while both physical and chemical interactions occur on the magnesium silicate surface. AFM showed lumpy adsorbate on the silica surface and point-like adsorbate on the magnesium silicate surface, with a greater roughness change observed for the former. QCM-D measurements confirmed that TA formed a multilayer flexible adsorbate on the silica surface and a dense, rigid monolayer on the magnesium silicate surface. Molecular dynamics simulations further revealed that van der Waals interactions dominated TA adsorption on the (001) surface, while electrostatic interactions prevailed on the (100) surface. These findings provide insight into the selective depression mechanism of talc and offer guidance for the depression of other layered silicate minerals.