An electron microscopic examination of fulvic acid

Abstract

An electron microscopic examination of fulvic acid shows that the crystallinity, shapes, dimensions and extent of aggregation vary with pH. At pH 2.5, three types of particles can be observed: small spheroids (15–20 Å in diameter), aggregates of spheroids (200–300 Å in diameter) and an amorphous material of low contrast, perforated by voids, 500–1,100 Å in diameter. spheroidal aggregates tend to form elongated, irregularly shaped structures, 20,000–30,000 Å long. At pH 3.5, which is the natural pH of a dilute fulvic acid solution, electron micrographs show a sponge-like structure of variable thickness (100–300 Å), punctured by voids, 200–1,000 Å in diameter. At pH 4.5 and higher, electron micrographs show flat sheet-like lamellae of very low contrast, perforated by voids, 200–2,000 Å in diameter. Electron diffraction patterns show crystallinity in fulvic acid aggregates formed at pH 2.5 only but not in those formed at pH 3.5. The electron microscopic data are in harmony with X-ray, chemical and spectroscopic data on the same fulvic acid, and point to a relatively “openlrd structure, perforated by voids of varying dimensions which can trap or fix organic and inorganic compounds that fit into the voids, provided that the charges are complementary.