SOME COLLOIDAL PROPERTIES OF BENTONITE SUSPENSIONS

Abstract

A study of the swelling and gelling properties of bentonite dispersions has been made in connection with the increasing use of this mineral for drilling oil wells. It is shown that the emulsoid type of colloids present responds to changes in the pH of the dispersion medium with respect to rate of settling, viscosity and swelling, thus behaving as a typical hydrophilic colloid. The curve for percent of solid matter settled in a definite time as ordinate against the pH shows a maximum at the isoelectric point, with minima on each side of this point, corresponding to the points of maximum adsorption. As the pH is further increased or decreased flocculation begins with increased rate of settling. The viscosity curve is closely related to the rate of settling curve, showing maxima and minima corresponding to the electro‐viscous effect. Maximum swelling occurs at approximately the point of maximum viscosity. Methods are given for controlling the swelling of bentonites. Relaxation curves are given for bentonite suspensions and utilized to explain the suspension qualities of these sols for heavy mineral dispersions, such as barytes or amorphous silica. A few applications of bentonite sols to the drilling of oil wells are given.