Crystal formation by low molecular weight fulvic and humic acids

Abstract

Fulvic and humic acid molecular weight fractions from a variety of origins such as natural waters, microbial cultures and soils, were investigated for their ability of crystal formation. It was found that low molecular weight fractions could be induced to crystallize by slowly lowering the dielectric constant of weak aqueous solutions of the material by means of the addition of small amounts of appropriate water-miscible organic solvents. Very well-defined micro-crystals could be obtained from fractions of fulvic and humic acids of different origin, with nominal molecular weights of up to 5 500 dalton. The form of the crystals changed with increasing molecular weight of the material from long needle-shaped, via leaf-shaped, to flakes. At molecular weights greater than 5 500 dalton, mostly flake-like forms; were noticed. Many of the fulvic acid flakes showed moire patterns, revealing a basic periodic structure in the specimens. Electron diffraction of the crystalline material indicated the presence of regions with either a hexagonal or a cubic structure. X-ray diffraction on the crystalline low molecular weight samples revealed spacings varying between 0,140 and 0,62 nm.