SITE ENERGY-DISTRIBUTION ANALYSIS OF PRELOADED ADSORBENTS

A methodology relating changes in the isotherm parameters for sorption of one solute by a heterogeneous sorbent to changes in the site energy distributions of that sorbent caused by prior irreversible sorption (preloading) of other solutes is proposed. Approximate site energy distributions underlying three isotherm models commonly used to describe sorption of organic solutes from aqueous solutions are developed using the theory of heterogeneous surf:aces. It is demonstrated that, regardless of the type of initial site energy distribution assumed, preloading by a non-desorbable solute results in a loss of surface heterogeneity. The loss occurs preferentially across sites having the highest energies, with the number of sites in the lowest energy ranges actually increasing in some cases. Activated carbon is used to demonstrate the methodology, but the approach is generally applicable to other heterogeneous;adsorbents in both natural and engineered systems.