Physicochemical approach for analyzing equilibrium volume of clay sediments in salt solutions

Equilibrium sediment volume (ESV) is used as an important parameter for understanding the expansive nature of the bentonites and natural clay soils, for assessing a given bentonite for engineering applications, and for the determination of the type of dominant clay mineral present in a given soil. The ESV is often estimated using different salt solutions to understand the compatibility of given clay soil for long-term engineering application such as landfills. A theoretical approach based on physicochemical behavior of clays was proposed in this paper for the estimation of equilibrium sediment volume of bentonites in the presence of salt solutions. A simple analytical expression relating equilibrium sediment volume with different influencing physicochemical parameters such as clay surface and pore-fluid parameters was presented using the diffuse double layer theory. A quantitative estimation of ESV by the proposed theory was validated on the measured data. A very good agreement between the theoretical and measured data was observed for the commercial bentonite. The theory was in good agreement with the measurements in the concentration range of 0.01 M ≤ n < 1 M for Kutch bentonite while the concentration range was 0.001 M ≤ n < 1 M for Barmer bentonite in NaCl solutions. The influence of different exchangeable cations and the presence of non-clay content on the prediction were analyzed with a great detail using theory and by comparing the ESV data of studied bentonites with the homoionic sodium clay. The parallel plate assumption made in the theory overestimated the ESV data in CaCl2 solution. The proposed analytical model is very useful for understanding the influencing parameters on the bentonite behavior.