IONIC FACTORS AFFECTING THE FORMATION OF SHORT-RANGE ORDERED ALUMINOSILICATES

The formation of short-range ordered aluminosilicates is substantially influenced by organic and inorganic ligands, metallic cations, and montmorillonite. Chemical composition, size, number, and nature of the functional groups, and concentrations of non-humified organic acids play a vital role in perturbing the formation of allophanes and imogolite. Humic substances also substantially perturb the interactions of hydroxy-Al ions with orthosilicic acid and thus inhibit the formation of these aluminosilicates. Inorganic ligands such as phosphates and sulfates vary in their ability to impede the formation of these aluminosilicates. Iron has a stronger inhibiting effect than Mn on imogolite formation, resulting in the formation of poorly ordered mineral colloids. Adsorption of hydroxy-aluminosilicate (HAS) in the interlayers of montmorillonite results in an expanded structure. The transformation of HAS ions to noncrystalline aluminosilicates can, therefore, be affected by naturally occurring expansible layer silicates such as montmorillonite. These ionic factors perturb the genesis of allophane and imogolite to various extents, resulting in the formation of ill-defined aluminosilicate complexes, HAS-interlayered expansible layer silicates, and/or precipitated hydroxy-Al-organic or -inorganic complexes. Organic and inorganic ligands with a strong affinity for Al significantly modify the nature of the soluble products, which range from proto-imogolite sol complexed with organic or inorganic ligands to hydroxy-Al-organic or -inorganic complexes.