Circular 89—A chemical interpretation of surface phenomena in silicate minerals

By R. A. Deju and R. B. Bhappu, 1966, 13 pp., 1 table, 3 figs.

In this report, the oxygen-silicon ratio for a representative series of silicate minerals is correlated to the degree of adsorption on the surface of the mineral when it is immersed in water. Experiments are conducted to prove that there is a corresponding increase in adsorption with increasing oxygen-silicon ratio. The behavior of the minerals in an electric field is investigated using zero point of charge as a parameter. Equipment for these zero point of charge experiments consists of a moving boundary cell, a mass transport cell, two cataphoresis cells, and a streaming potential cell. Finally, a theoretical model is developed to explain the increase in zero point of charge with increasing oxygen-silicon ratio. A comprehensive bibliography on electrokinetic properties of silicates has been included at the end of the paper.

In recent years great interest in surface chemistry has produced a number of methods to study the surface of minerals and to observe the phenomena occurring at their interfaces. Several such methods are discussed in this paper. A rather complete study of the surface chemistry of the oxide minerals has been undertaken by Parks. However, a similar study had not been made for the silicate minerals. Two previous papers by the authors attempted to remedy this situation. In these papers it was demonstrated that the reaction between the silicate mineral particles and acidic water involves mainly an exchange of metal ions for hydrogen ions on the surface of the solid, leading to an increase in pH of the aqueous phase. Also, the degree of reaction was found to depend on the oxygen-silicon ratio of the silicate structure, being greatest for the olivines. It was then theorized that upon the fracturing of a silicate mineral, the oxygen-metal bond, which is almost entirely ionic in character, will break more easily than the stronger oxygen-silicon bond, resulting in a greater number of unsatisfied negative forces on the surface. Thus, an increase in the degree of adsorption of hydrogen ions occurs as the oxygen-silicon ratio increases.

A correlation between oxygen-silicon ratio and other electrophoretic properties will be further pursued in this paper from both the theoretical and experimental points of view. It is believed that this study may supply pertinent information on the behavior of silicate minerals in froth flotation systems.