Critical Surface Tension of Wetting and Flotation Separation of Hydrophobic Solids

Wetting characteristics of a number of minerals including layer-type hydrophobic minerals as well as common sulfides were investigated. For the majority of the minerals, the critical surface tension of wetting, γc determined using Zisman's technique was in the range of 40 to 45 mN/m. Surface pressures of water, IIe, on molybdenite and coal samples were determined from adsorption isotherms. The dispersion component of the surface-free energy, γs d, for molybdenite was estimated to be 113 ± 3 mJ/m2 as compared to the γs d value for graphite, 109 mJ/m2. The wettability data of aqueous methanol solutions, presented in the form of adhesion tension diagrams, yielded significantly lower γc values. Flotation behavior of common sulfides, which was similar to that of inherently hydrophobic polymers and minerals, was attributed to elemental sulfur formation. The relevance of critical surface tension of wetting to selective flotation and separation of hydrophobic solids is discussed.