Circular 97—A mathematical and experimental model of the electrical properties of silicate minerals

By R. A. Deju and R. B. Bhappu, 1968, 7 pp., 1 table, 6 figs.

Reprinted from Materials Technology-"An Inter-American Approach", published by The American Society of Mechanical Engineers. Describes development of a model of a mineral particle and its surrounding electric layers, studies of electric layers surrounding a mineral particle in suspension, and construction of a model of potential as a function of distance and presents the results obtained from these experiments. The electrical phenomena occurring at the water-solid interface have been the subject of almost constant investigation for the past two centuries. The first breakthrough was accomplished by Reuss who found that if a potential is applied across a porous plug of wet clay, separating two portions of water, then a flow of water occurs from one side of the plug to the other. This phenomenon has been termed electro-osmosis.

In this paper, the authors show the results of a new, modified model of the water-solid interface. The terminology that will be used in describing the electrical layers that extend between the solid particle's surface and the bulk of the water has been modernized. The model is then tested by experimental means and its electrical properties are related to other properties of the water-solid system.

When a potential differential is externally applied to a liquid containing charged particles, it causes a migration of the particles to the pole having a charge opposite to that of the particles. If the particles are ions, the phenomenon is called ionic conduction; in the case of mineral particles, it is called electrophoresis. Here, the authors are concerned only with electrophoresis and other electrical properties of a colloidal suspension of a mineral. Generally, a mineral particle in suspension has a charge on its surface. This surface charge, together with the ions in solution near the surface to maintain electroneutrality, forms a series of electrical layers around the mineral particle. The ions responsible for the surface charge are termed surface-charge ions. Some of the ions near the surface of the mineral are anchored within a layer directly adjacent to the surface. These ions, which are said to be in the Stern layer, are strongly held to the surface. The remaining ions are loosely held by electrostatic forces and constitute the diffuse layer of counter ions that extends deep into the solution. The surface layer and the Stern layer are grouped into what we call the dipole layer.