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The zeta potential measurements in sandpacks saturated with monovalent electrolytes

Measurements of the zeta potential in sandpacks saturated with monovalent electrolytes at six different electrolyte concentrations have been reported. The values we record are classified into two groups based on the magnitude of the zeta potential: group 1 (samples S1 and S2) and group 2 (samples S3 and S4). The measured zeta potential in magnitude in group 1 is much smaller than that in group 2 and in literature at the same electrolyte concentration. The reason for a big variation of the zeta potential between group 1 and group 2 may be due to the difference in technique of making sand particles of different size leading to change of particle surface properties. Consequently, the zeta potential that depends on the surface properties would vary. The results show that there is a gradual decrease in the zeta potential with increase in monovalent electrolyte concentration (from 10−4 M to 10−2 M). Additionally, the empirical expressions between the zeta potential and electrolyte concentration are obtained in this work for both group 1 and group 2. The obtained expression for group 2 is in good agreement with those available in literature. From the experimental data in combination with a theoretical model, the binding constants for Na+ and K+ cations are obtained for the samples of group 2 and they are in the same range reported in literature for silica-based samples. 