KINETIC-STUDIES OF METAL-ION SPECIATION

The use of kinetics of metal ion transfer from naturally occurring colloidal ligand systems to complexes with spectrophotometrically favourable ligands as a means of study of speciation of metal ions in natural systems is described. The systems have a species distribution which is determined by the conditions of sample "equilibration", but kinetic analysis is conducted under conditions (pH, ionic strength) defined by the reagent solution. The resulting species distribution is that of the equilibration condition with relative lability characterized. Application of the approach to complexes of simple metal ions, Cu2+ and Ni2+, with humic colloids and hydrous ferric oxides and to ternary systems of iron(III) or aluminium(III) with humics and OH- are reviewed. The latter studies have been extended to application to natural waters. The conditions for extension of the study of simpler systems to actual natural samples are considered. A method based on laser thermal lensing is proposed.