Kinetic Studies of Colloidal Metal Complex Species Relevant to Natural Waters

Abstract

The dissociation reactions of colloidal complexes of Fe(III), Al(III), and Cu(II) formed by binding of the metals to naturally occurring organic ligands and by their inclusion in hydrous oxide colloids are studied by treatment with an excess of a ligand suitable for sensitive spectrophotometric detection under solution conditions favorable to formation of the complex with the color former. A range of rates varying with metal to ligand ratio are found which emphasize the importance of the extension to kinetics of the mixture polyelectrolyte approach which has gained acceptance in discussion of the equilibrium properties of similar complexes. Results do show interpretable relationships to the kinetic behavior of the better studied mononuclear chelate species and some aspects point to a role for mass transport. The ground is prepared for inorganic kineticists to enter this problem area which probably encompasses the subject of bioavailability of metal ion nutrients and toxicants.