Treatment Solid-liquid ratio * Time

ABSTRACT: Since digestion of imogolite or allophane in 5 ~ NazCO3 at 95 ~ for periods of 2-100 h leads to solid products different in structure and composition from the starting materials, the procedure is unsuitable for selective dissolution of reactive silica-alumina gels from complex clay mixtures. Cold 5 ~ Na2COa does not alter these clays, but effects partial solution, the extent of which depends on the degree of dispersion of the clay and the ratio of solids to solution. A sequence of alkaline dissolution procedures of increasing severity are commonly applied to soil clays to dissolve out, and so to estimate, their content of poorly ordered and amorphous hydrated gels incorporating silica and alumina (Jackson, 1956; Hashimoto & Jackson, 1960; Follett et al., 1965; Mitchell et al., 1968). It is generally presumed that each reagent will attack and dissolve gels of up to a certain degree of reactivity, and TABLE 1. Dissolution of imogolite and allophane by alkaline digestion. SiO2 and AIzOa dissolved as percentage of air-dry samples. imogolite Allophan