Lk. Koopal et al., ANALYTICAL ISOTHERM EQUATIONS FOR MULTICOMPONENT ADSORPTION TO HETEROGENEOUS SURFACES, Journal of colloid and interface science, 166(1), 1994, pp. 51-60
Adsorption on heterogeneous surfaces may be influenced not only by the
heterogeneity but also by lateral interactions. For multicomponent so
lutions competition increases the complexity even further. In practice
such complex systems frequently occur and to investigate the behavior
of these systems it is rather useful to have analytical equations ava
ilable which can describe the adsorption. Existing analytical mono- an
d multicomponent binding equations for heterogeneous surfaces are brie
fly reviewed. These equations are based on a high degree of ideality w
ith respect to both the local isotherm and the affinity distribution f
or the different components. A new more generally valid analytical com
petitive binding equation is derived, using a nonideal local isotherm
equation. In this local isotherm all component-specific nonideality is
incorporated; i.e., it includes both lateral interactions and compone
nt-specific heterogeneity contributions. Under these conditions the re
maining adsorbate-surface interactions can be characterized by an ''in
trinsic'' affinity distribution that applies for all components. The f
eatures of the new equation are discussed and illustrated on the basis
of some model calculations. The model is tested in practice using cad
mium ion binding to fulvic acid at various pH values (data of Saar and
Weber, Can. J. Chem. 57, 1263, 1979). These data cannot be modeled sa
tisfactorily with the classical equation for multicomponent adsorption
on heterogeneous surfaces. The newly derived equation gives excellent
results. (C) 1994 Academic Press, Inc.