Anisotropy-Driven Wettability Heterogeneity of Smithsonite Surface: A Crystal Cleavage Perspective on Fine Mineral Flotation Limitations

The presence of fine-grained minerals with poor flotability in zinc oxide ores results in a notable loss of zinc resources. While previous studies have focused on macroscopic flotation parameters, the crystallographic origin of microfine mineral processing challenges remains unexplored. Indeed, the distinctive anisotropy of fine-grained mineral crystal surfaces exerts a profound influence on the wettability and flotability. In this study, a comprehensive examination of the anisotropy of typical smithsonite during grinding and cleavage was conducted. The methods employed included flotation experiments, X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, atomic force microscopy (AFM), contact angle measurements, and density functional theory (DFT) calculations. Results demonstrated that significant anisotropy was exhibited on the surface of smithsonite crystal during the grinding process. The reduced particle sizes correlated with the preferential exposure of the (012) cleavage surface and the diminished relative content of the (104) surface. This process was dominated by the surface energy, broken bond density, and strength of mineral crystals. Subsequent analysis revealed significantly weaker collector affinity for the (012) surface compared with the (104) surface, directly manifesting as severely compromised surface hydrophobicity during flotation. This phenomenon originated from the tendency of the (012) surface to form stable hydration layers that impeded collector interaction. The pronounced anisotropy of microfine smithsonite during grinding and cleavage represents a pivotal intrinsic factor contributing to the deterioration of flotation. This work can contribute to a more comprehensive understanding of fine-grained flotation from a novel microscopic perspective, taking into account the anisotropic effects of the mineral crystals themselves.