Obtaining absolute ligand complexation kinetics for metal ions in both the aqueous and organic phases is essential for a quantitative understanding of large-scale nuclear waste reprocessing efforts involving solvent extraction. In this work we have focused on quantifying the complex formation kinetics for the ligand DTPA reacting with lanthanide ions in acidic aqueous media. Previously, these rate constants were measured using metal-dye complex displacement techniques, but we have found this approach to significantly underestimate rate constants due to the slow kinetics of dye decomplexation. However, by using the change in europium luminescence upon its binding to DTPA, an exact, absolute, rate constant can be measured. Establishing this value allowed determination of the formation constants for other lanthanides by observing competitive complexation. We have also determined the exchange rate between different complexed lanthanide ions. The combination of exchange rates and competitive complexation were determined in three separate experiments; pre-loaded luminescent, competitive and pre-loaded non-luminescent. Exchange rates depended strongly on temperature, pH, and buffer concentrations. The order of loading of the complexing ligand was also important, giving insight into the preferential nature of the complexation of these lanthanide ions.

Investigating formation and competitive exchange kinetics for DTPA complexed Eu ions in aqueous solution

255th National Meeting (2018)

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