Hygroscopic Water Content As an Indicator of Soil Dispersity: Thermodynamic Basis and Experimental Verification

Abstract

The adsorption properties of dispersed systems are determined by their surface energy, therefore the parameters of hygroscopy (adsorbed water content) and dispersity (specific surface area of the solid phase) of soils and sediments are in close mutual correlation. This well-known empirical fact has received a new fundamental interpretation based on the theory of disjoining water pressure according to Derjaguin should be in the form of a thermodynamic equation that connects the specific surface area, hygroscopic water content of soil samples, and relative air humidity in the laboratory room. The theoretical equation enables us to substantiate the methodology of quantifying the hydrophilic specific surface area of soil samples based on widespread data on their hygroscopy. Comparison of the new method with the standard BET analysis of the specific surface area, as well as with the previously proposed physically based method for its determining by the slope of thermodynamic water retention curves, shows their statistically reliable agreement in a wide range of the estimated specific surface area from 5 to 340 m² g^–1 for soil samples of different genesis and texture.