Influence of amorphous silica and iron hydroxide on interparticle action and soil surface properties

Abstract

The study of the physicochemical properties of pure amorphous materials (complexes) consisting of Fe2O3 and SiO2 in various proportions indicates that the amorphous complexes will exhibit different properties and characteristics depending on the proportions of Fe2O3 and SiO2. Addition of the amorphous complexes with illitic clay studied shows that the properties of the clay admixture will also vary according to the properties of the amorphous complex, albeit to a lesser degree. The properties and behaviour observed for the amorphous complexes and the clay admixtures can be linked directly to the large specific surface area and high surface charge of the amorphous complexes. The contribution of amorphous complexes to the clay – amorphous complex mixtures (clay admixtures) is twofold: firstly, by the amount of amorphous complex in the clay admixture, and secondly by the composition of the amorphous complex used. The contribution from the amorphous complex is in two forms: water-holding capacity and bonding action. The presence of pH-dependent surface charges associated with the amorphous complexes makes the physicochemical properties and behaviour of the clay admixtures (e.g., liquid limits and zeta potential) sensitive to the pH environment. Coating of amorphous colloids onto clay particle surfaces, shown by scanning electron microscopy, appears to, be enhanced by a decrease in pH of the system, indicating that the enhancement is likely due to the increased electrostatic attraction resulting from the increased amounts of positive charges on the amorphous colloids. Key words : amorphous materials, mass ratio, zeta potential, Bingham yield stress, clay admixtures, hydrogen bonding, specific surface area, cation exchange capacity, anion exchange capacity, fabric and soil structure.