A Systematic Approach to Zeta Potential Testing and Clay Dispersivity

ABSTRACT Zeta potential, an indicator of surface charge on clay particles, significantly influences geotechnical properties such as dispersivity, swelling, electrokinetic behavior, and electric double layer characteristics. Despite various proposed methods, establishing a reliable and systematic procedure to correlate clay behavior with zeta potential has been challenging. This study develops a systematic procedure for estimating the zeta potential of clays by examining the forces that affect the mechanical stability of solute particles in a colloidal suspension. The accuracy of the procedure is evaluated on three different soils in their natural state and after treatment with hydroxide salts of various monovalent cations, which are known to alter zeta potential and other geotechnical properties. The method’s precision was verified using “zeta deviations,” which indicate the uniformity of the zeta potential distribution. A low value of zeta deviations was observed for soil suspensions filtered through 0.45 μm, indicating uniformity in the zeta potential values within the distribution. To empirically validate the procedure, zeta potential values were correlated with the modified free swell index and dispersivity measured through the double hydrometer method for various soils. A linear relationship between zeta potential and double hydrometer dispersivity was established with a regression coefficient of 0.95, suggesting a faster and convenient method for classifying clays based on their dispersivity values. This systematic procedure demonstrates better reproducibility and efficiency, allowing for the classification of clays into dispersivity grades based on zeta potential values, enhancing the geotechnical assessments.