Estimation of the distribution of surface sites and contact angles on coal particles from film flotation data

Because of their heterogeneity, coal particles may vary widely in composition and, consequently, each particle may have its own unique set of surface properties. The distribution of surface wettabilities of coal particles can be determined by a film flotation technique, using a series of aqueous methanol solutions to vary the surface tension of the liquid. This paper shows how such measurements of the critical wetting surface tension can be used to quantify the contact angle of the particles and the distribution of hydrophobic sites on the surface of the particles. The mean contact angles of particles calculated from film flotation for sulfur, graphite, and a number of different coals are in reasonable agreement with the values reported in the literature for bulk material