Electrokinetic Phenomena in Colloidal Clays

Abstract

While the variations of the physical properties of colloidal suspensions of bentonite clays under various conditions of contamination have been the subject of extensive investigations, the role of the associated electrical phenomena in the impartation of these physical properties is virtually undefined. Successful techniques for the measurement of the electrical phenomena have been reported previously but they are applicable only to very dilute clay suspensions in which negligible electrical interference between clay particles exists. Apparatus and techniques applicable to concentrations of colloidal material normally used in bentonite oil-well drilling fluids were developed and are discussed.Measurement of electrokinetic phenomena in concentrated suspensions was effected by application of the principle of electroosmosis by suitable modification of existing apparatus. The distinguishing modification was replacement of the conventional, consolidated diaphragm with a diaphragm of colloidal material supported by thin membranes.The applicability of the apparatus and techniques is demonstrated by qualitative comparison with data of previous investigations wherein the comparable depression of the electro-kinetic potential by the addition of various contaminating ions is shown. In addition, the relation between the measured electrokinetic potential and the filtration rate is shown to be linear and independent of the valence or type of contaminant for a major portion of the investigated concentration range. This suggests that for ions which appreciably repress the electrokinetic potential the fluid-loss may be used as a means of approximating the changes of the electrokinetic potential.