Heterogeneity and electrolyte adsorption: intrinsic and electrostatic effects.

Abstract

Adsorption of electrolytes in natural systems is an important phenomenon. Natural systems contain sorbents with a predominantly constant surface charge, such as clay minerals, as well as a complex mixture of mainly variable charge sorbents like organic matter, both in the dissolved and in the soil solid phase, and metal oxides. The effect of a combination of an intrinsic-affinity distribution (both discrete and continuous) and a variable surface potential on adsorption behaviour of protons is discussed both for random and patchwise heterogeneity. It is shown that the variable charge (potential) or intrinsically homogeneous metal oxides and organic model colloids leads to an apparent heterogeneity of binding sites. This effect is quantified with simulated data and condensation approximation. For heterogeneous charged sorbents, where the apparent affinity represents both chemical heterogeneity and electrostatic interactions, very wide apparent-affinity distributions will be found. The apparent-affinity distribution is in general only a poor representation of the intrinsic-affinity distribution. (Abstract retrieved from CAB Abstracts by CABI’s permission)