Abstract
The interfacial tension and the conductivity of humic acid solutions were measured and the aggregate formation was suggested. The concentration at which aggregation begins is in good accordance with that determined by other methods.
The effect of metal cations on the conductivity, viscosity, interfacial tension, and potentiometric titration of humic acid solutions was also examined. The added metal cations form complexes with marine humic acid, the order of complexing ability of metal cations is as follows :
Na+; K+<Mg2+<Ca2+<Ba2+<Cu2+
The metal ions are thought to be mainly bound to the carboxyl ions of the humic acid. No substantial difference was observed between marine humic acid and commercially obtained Aldrich humic acid in the effect of cations on solution properties.
The marine humic acid samples fractionated by molecular weight were used to study the molecular size effect on the solution properties. It is confirmed that the smaller molecule shows the lower humification degree and the higher acidity.
