Some Problems on the Structure of Surfaces of Clay Minerals and Clay/Aqueous Electrolyte Interfaces

Abstract

Three open reseach problems are briefly reviewed, solutionsto which problems are indispensable for understanding properties of clay mineral/aqueous electrolyte systems.
The first problem is to elucidate the distribution pattarn of excessive negative charge generated by isomorphous substitution in tetrahedral and octahesral sheets of layer silicate minerals. This problem is closely related to predicting swelling properties of smectite and vermiculite from a given chemical composition.
The second one is to quantify surface hydroxyl groups of metal oxides and hydroxides which are responsible for development of negative and positive surface charge. Without the knowledge on the number of the reactive hydroxyl groups, verification of chemical models describing ion adsorption, e. g., surface complexation models, is difficult.
The third one is the determination of the structure of surface complexes formed at oxide/ aqueous electrolyte interfaces. Despite the success of widely accepted surface complexation models, the structure of the surface complexes adopted in them are only hypothetical, the presence of which has not been proven on a physico-chemical basis.