The effect of pH and metal binding on the transport properties of humic acids

The molecular weight, shape and size of fractionated humic acids and their metal complexes were determined from sedimentation and diffusion measurements made at various pH values. For all the species studied, the molecular weight and size decreased as the pH became more alkaline. However, the shape of the molecule (approximately spherical) was unaffected by pH. The molecular weight and size of the metal humates depended not only on the type of cation but also on the degree of dissociation ofthe humic acid and the hydrolysis ofthe metal ion.