Determination of Clay Surface Potential: A More Reliable Approach

Surface electrical potential is an important parameter in soil electrochemistry. Currently there are several methods that can be used to estimate the surface potential, but they all have their limitations. Thus a noninvasive, more reliable, and widely applicable method is needed. In this research, a new method for the determination of surface potential was developed. The new method not only provides a more reliable determination for the surface potential, but also can be widely applied to any charged materials under any conditions of pH, temperature, and electrolyte concentration. The new method was used to determine the surface potentials of 36 different montmorillonites. Results showed that the average surface potential obtained by the new method was 5.4 times higher than the average zeta potential from electrophoresis experiments. Under the same experimental conditions, the estimated swelling pressures based on the surface potentials from the new method matched the experimental data very well for the montmorillonite/aqueous solutions, while the predicted values based on the zeta potential deviated from the experimental data, indicating that the new approach provides a more reliable prediction of surface potential than the zeta potential approach.