Effect of aqueous phase properties on clay particle zeta potential and electro-osmotic permeability: Implications for electro-kinetic soil remediation processes

Abstract

The influence of aqueous phase properties (pH, ionic strength and divalent metal ion concentration) on clay particle zeta potential and packed-bed electro-osmotic permeability was quantified. Although pH strongly altered the zeta potential of a Georgia kaolinite, it did not significantly change that of a Wyoming bentonite. The zeta potential for the kaolinite ranged from +0.7 mV at pH = 2 to −54 mV at pH = 10 (0.01 M KCl) while the bentonite zeta potential changed by only 5 mV (−31 to −36 mV) over the same pH range. For both clays, ionic strength was found to have a weak effect while divalent cations made the zeta potential markedly more positive. Charge reversal was observed for kaolinite at 100 ppm Pb 2+ (pH = 5) with a background ionic strength of 0.01 M KCl and only 10 ppm Pb 2+ with a background of 5 × 10 −4 M KCl. A theoretical relationship between the electro-osmotic permeability coefficient for packed clay beds and particle zeta potential was developed and experimentally verified for kaolinite. For example, both the electro-osmotic permeability coefficient and particle zeta potential were found to be three times greater at pH = 5 than at pH = 3. As a result, rapid zeta potential analyses can be used to predict electro-osmotic performance for expected site conditions as well as to select electrolyte control strategies to optimize an electro-kinetic soil remediation process.