Internal surface area and porosity of kaolinitic glaebules

Abstract

Specific surface areas, cation exchange capacities and pore size distributions have been determined on sieved fractions of a sandy loam from Merredin, W.A., certain horizons of which contain significant proportions of kaolinitic glaebules. The sand-sized glaebules are resistant to breakdown by normal dispersion techniques, and so remain in the sand fraction during particle size analysis. However, certain of their physicochemical characteristics are consistent with those of soil colloids. For instance, the 250-500 µm fraction of the 155-190 cm horizon has a specific surface area of 16.3 m2/g, an average pore size of some 6 nm plate separation and a surface charge density of 3.8 x 104 esu/cm2. In soils containing significant proportions of such glaebules, the physicochemical properties will differ markedly from those inferred from particle size analysis.