ABSTRACT
Natural colloids are mixtures of aluminosilicates, hydrous oxides, and humus. The surface reactivity of these particles is conditioned on the aqueous environment in which they reside and by the molecular structure of the colloid/aqueous solution interface. The chapter reviews surface complexation as a mechanism of adsorption. It discusses the consideration of the experimental characterization of a prototypical case, the adsorption of ions by members of the 2:1 layer aluminosilicate group, smectite. The siloxane surface of a smectite is characterized by a distorted hexagonal symmetry among the constituent oxygen ions, and the reactive functional group associated with the siloxane surface is a roughly hexagonal cavity. Electron spin resonance spectroscopy combined with x-ray diffraction has proven to be a useful method for determining the speciation of Cu2+ on smectite surfaces. The prototypical example of Cu(II) complexes on smectites illustrates most of the general characteristics of the experimental detection of surface species on natural colloids.
