Sorption hysteresis on soils and sediments: Using single‐point desorption isotherms to obtain characteristic free energy values

Abstract

Sorption-desorption hysteresis (SDH) may control distributions of chemicals across diverse environmental phases, including soils and sediments. Formation of metastable states caused by pore deformation or inelastic swelling of a sorbent and their persistence during desorption have been considered in the literature as one reason for "true" SDH. Such metastable states may lead to the lack of closure of the sorption-desorption loop at non-zero sorbate concentrations, a phenomenon often noted in soil and environmental literature. SDH has often been characterized using single-point desorption isotherms (DIs) that combine sorbed states reached during single desorption steps started from different points along a sorption isotherm (SI). This work aimed to demonstrate how single-point DIs could be used to characterize SDH in the liquid phase in terms of the Gibbs free energy accumulated in some non-relaxed sorbed states belonging to a DI, as compared with the states of the same composition (sorbed Highlights • Desorption from soils and sediments to solutions may be hysteretic due to formed metastable states