DETERMINATION OF COMPONENTS OF CASSITERITE SURFACE FREE-ENERGY FROM CONTACT-ANGLE MEASUREMENTS

Measurements of contact angle for water, glycerol, formamide, diiodomethane, and bromoform on cassiterite surface with different initial treatments were conducted. Using the values of contact angle, the total surface free energy of cassiterite, and its components resulting from different kinds of intermolecular interactions were calculated. For this purpose, various approaches to the solid-liquid interfacial free energy have been considered. Next, the usefulness of these approaches for the determination of the cassiterite-water interfacial free energy and of the work of adhesion of water to the cassiterite surface were tested. Thus, it was found that the surface free energy of cassiterite previously dried at 110°C and not treated with HNO3 is mainly the result of dispersion intermolecular interactions and this energy strongly depends on the amount of OH groups and/or coordinated and physisorbed water molecules on its surface. The presence of OH groups and/or water molecules gives rise to the acid-base components of the cassiterite free energy. It was also found that all the approaches tested for a given sample gave, in many cases, near the same value of the total cassiterite surface free energy; however, their usefulness to predict the cassiterite-water interfacial free energy and the work of adhesion of water to the cassiterite surface was not the same. Using the values of the Lifshitz-van der Waals, electron-acceptor and electron-donor components of the surface free energy for both cassiterite and water, the free energy of interaction between two particles of cassiterite in water was calculated and related with observations of the aggregation process of cassiterite and it was stated that if the energy of interaction is negative the aggregation process of cassiterite particles takes place. © 1993 by Academic Press, Inc.