Effect of hydration and hydroxylation on the adsorption of metal ions on quartz surfaces: DFT study

Quartz is one of the most abundant minerals on planet earth. Quartz activation plays a crucial role in the flotation and separation of a wide range of minerals. However, the microscopic mechanism of quartz activation remains unclear and the activating component in quartz activation via metal ions has been controversial. In this paper, the activation mechanism of Ca2+, Fe3+, Cu2+ and Pb2+ on quartz surface is studied using density functional theory (DFT) for the first time. The results show that hydration of metal ions significantly influences their adsorption on quartz surface; the hydrated metal complexes are unable to adsorb on quartz surface. Hydroxylation of metal ions facilitates their adsorption on quartz surface. During adsorption, the bond breaks between the metal ion and the hydroxyl group of the metal hydroxy complex. The freed hydroxyl group combines with the surface hydrogen atom to form a free water molecule while the exposed metal ion bonds to the surface oxygen atom. This establishes a theoretical foundation that hydroxylation of metal ions is a prerequisite for their adsorption on quartz surface. This research sheds new light on the mechanism of quartz activation via metal ions and helps the design of novel activators.