Minerals Beneficiation - A Chemical Interpretation of Surface Phenomena in Silicate Minerals

Further information on the surface characteristics of the silicate minerals was obtained by experimentally correlating the oxygen-silicon ratio of the silicates with their electrokinetic properties. Specifically, the behavior of the minerals in an electric field was investigated using zero point of charge as a parameter. A modified electrophoresis cell was used for the determination of electrophoretic mobilities. It was shown that there is an increase in the zero point of charge with increasing oxygen-silicon ratio in the silicates. Finally, a chemical interpretation was presented to describe the surface phenomena observed in the experiments. In recent years great interest in surface chemistry has produced a number of methods to study the surfaces of minerals and to observe the phenomena occurring at their interfaces. One such method is discussed in this paper. A rather complete review of the surface characteristics of the oxide minerals has been undertaken by parks,' but, a similar study has not been made for the silicate minerals. Two previous papers by the authors2'3 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 least for the quartz and greatest for the olivines. A hypothesis was then set forth explaining 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. This results in the exposure of unsatisfied oxygen sites on one hand and active, exchangeable cations on the other. These active sites on the fractured surfaces are then available for reaction with the hydrogen ions in acidified aqueous solution. Thus, an increase in degree of adsorption of hydrogen ions occurs as the oxygen-silicon ratio increases due to the presence of a larger number of active sites on such minerals. A correlation between oxygen-silicon ratio and electrokinetic properties will be further pursued in this paper from both the theoretical and experimental points of view. Efforts will then be made to present a chemical interpretation of surface phenomena observed in the experiments. It is believed that this study may supply pertinent information on the behavior of silicate minerals in froth flotation systems. ELECTROKINETIC STUDIES Equipment: In a previous paper,2 Deju and Bhappu described a simple method for determing the zero point of charge using a potential across a cata-phoresis cell and observing particle movement by means of a Rayoscope* optical system. This setup is simple in design and operation and extremely reliable. With care, reproducible results within 1.5% accuracy may be obtained. A new setup has been developed, based partly on the design by Zeta-Meter Corp.4 and partly on previous cells used at the New Mexico Bureau of Mines. This new, modified cell is shown in Fig. 1. Although