Reactions Between Fulvic Acid, A Soil Humic Compound, and Montmorillonite

The magnitudes of d001 spacings of fulvic acid‐Na‐montmorillonite complexes were not affected by temperatures between 25 and 60°C. Slightly more than one half of the total amount of fulvic acid adsorbed by Na‐montmorillonite was in the interlamellar spaces, with the remainder on external surfaces. The d001 spacings and amounts of fulvic acid adsorbed in the interlamellar spaces of Pb++−, Mg++−, Co++− and Ni++− saturated montmorillonite decreased with increase in pH. The capacities of cation saturated clays to adsorb fulvic acid in interlamellar spaces decreased in the following order: Pb++ > Mg++ > Co++ > Ni++. The exotherm near 670°C in the DTA curve of the fulvic acid‐Na‐montmorillonite complex signalized the formation of an interlayer complex.