Correlation between Surface Free Energy Parameters of Solids and Separation Efficiency in Mineral Beneficiation

Knowledge of surface free energies (and its components) between two entities is important. They dictate not only the strength of the interaction, but also control the processes such as the stability of aqueous colloidal suspensions, the dynamics of molecular self-assembly, wetting, spreading, deinking and adhesion (1-4). Many of the mineral processing techniques, e.g. froth flotation, selective flocculation, filtration and thickening are also controlled by the interfacial energies of the solid and the liquid involved. Therefore, characterization of the surface properties, especially the surface free energy components is important for understanding the mechanisms of the various surface-based phenomena. The standard approach used for determining the surface free energies of solids and the interfacial surface free energies between two interacting surfaces has been through wetting experiments. Specifically, the contact angle method has been widely used to characterize the surface properties of solids (5-10). The most commonly used measure of surface hydrophobicity is the water contact angle (11-15). The higher the contact angle value is, the more hydrophobic the solid surface becomes. The value of the water contact angles can also be used to determine the surface free energies. In principle, the higher the contact angle, the lower the surface free energy (γ S) of a solid surface (16-19). Besides direct contact angle measurements, microcalorimetric measurements give valuable information regarding the surface properties of powdered solids such as surface hydrophobicity-hydrophilicity and acidity-basicity characteristics. The interactions between various reagents and the solid surfaces in aqueous or non-aqueous media can also be studied by using a microcalorimeter. Microcalorimetric studies should also be useful in explaining the physico-chemical aspects of mineral separation techniques such as flotation and selective flocculation.