Fig. 1. Graphic and schematic representation of States S, D, , and for the calculation of the Thermodynamic Index of Irreversibility (TII). The identical sorbent particles are transferred from the sorption bath at solute concentration C = C^S to one of the desorption baths at C^D, C, or C. Irreversibility is symbolized by the distorted shape of the particle in State D. State S (C^S/sorbed concentration q = q^S) is the sorption state from which desorption is initiated. State D is the experimental desorption state (C^D/q^D). States (C/q) and (C/q) are hypothetical reversible desorption states.