Experiment and simulation research on the effect of lattice defect-Fe3+ on the quartz surface wettability

Abstract

The hydration characteristic of quartz surface is the key of quartz deep flotation purification. In this study, molecular dynamics (MD) simulation and experimental methods were used to study the effect of lattice Fe³⁺ impurities on quartz surface hydration properties. Quartz samples with different lattice Fe³⁺ content were obtained by roasting H₂SO₄-HCl-HF mixed acid with NH₄Cl. The changes in the lattice Fe³⁺ content of the prepared quartz samples were characterized and validated using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). The accuracy of the hydration simulation calculations was validated using contact angle measurements and wettability test results. The results indicate that as Fe³⁺ doping increases, Na⁺ ions diffuse into the water layer during adsorption on the Fe³⁺-doped quartz (0 0 1) surface and form hydrated complexes with H₂O molecules, reaching an equilibrium state. As the doping concentration increases, the interaction between water molecules and the Fe³⁺-doped α-quartz (0 0 1) surface strengthens, accompanied by an increase in interfacial hydrogen bonds. In the contact angle simulation, the contact angle of the undoped quartz surface is about 4° higher than that of the Fe³⁺ doped surface. When the Fe³⁺ content in the quartz sample increased from 39.4 ppm to 80 ppm, the contact angle decreased by about 3.2°, consistent with the simulated trend. Wettability tests show that with increasing levels of Fe³⁺ there is a further increase in surface hydrophilicity in the order: NH₄Cl(0 %)-Q-H⁺<NH₄Cl(1 %)-Q-H⁺<NH₄Cl(5 %)-Q-H⁺. It can be concluded that higher Fe³⁺ impurity levels in the quartz lattice significantly enhance the surface hydration characteristics. These results provide a theoretical basis for the selective separation and deep purification of quartz minerals.