The microstructure of humic acid montmorillonite composites

An organo-clay composite was prepared by contacting Na-montmorillonite and humic acid in aqueous solution which was of variable pH. After freeze-drying the precipitate of the solution, the derailed structure of the humic acid-montmorillonite composite was observed. Transmission electron micrographs and electron diffraction patterns indicate that the composite which was formed under acidic conditions has a characteristic microstructure. Humic acid, a large organic molecule, is combined with bent or curled thin foils of montmorillonite to form a spherical aggregate. The X-ray diffraction pattern supports this observation and suggests that the montmorillonite is cleaved into thin flakes as a silicate layer. The composite formed under alkaline conditions was in the form of a thin plate or lath and had a similar morphology to that of montmorillonite. The difference in the microstructure of the composite is reasonably attributed to the chemical flexibility of humic acid, i.e., conformation changes depending on the pH of the solution.