THE ROLE OF LOW-MOLECULAR-WEIGHT NATURAL ORGANICS IN METAL HUMATE INTERACTIONS

The possibility of mixed ligand complex formation, resulting from the interaction of europium with mixtures of high and low molecular weight naturally occurring organic acids has been investigated. Three system s were studied containing europium with humic acid in the presence of (i) acetic acid, (ii) oxalic acid, and (iii) citric acid. The various mixtures were analysed using both high performance size exclusion chro matography (HPSEC) and ion exchange (I. Ex). To facilitate the measure ments C-14 labelled low molecular weight acids and Eu-152 were used. T he observed amounts of complexation in the mixed systems were compared with predicted amounts. Predictions were based both on the complexati on parameters derived from analyses of the individual ligand systems a nd on modelling experiments using MINTEQA2. The agreement of the obser ved and predicted results was taken as evidence that mixed ligand comp lexes were absent under the conditions employed.