An Insight into the Speciation and Extraction Behavior of Eu(III) with Dinonyl Phenyl Phosphoric Acid and Di(2-ethylhexyl) Phosphoric Acid: Solvent Extraction and Fluorescence Studies

Abstract

The speciation of Eu(III) with dinonyl phenyl phosphoric acid (DNPPA) and di(2-ethylhexyl) phosphoric acid (D2EHPA) extracted from nitric acid medium were investigated using time resolved fluorescence spectroscopy (TRFS) technique. The fluorescence life time measurements on both the systems indicated that the Eu(III)-DNPPA complex contains 2H₂O molecules in the inner coordination sphere while Eu(III)-D2EHPA complex does not contain any H₂O molecule. These studies indicated the formation of Eu(HA₂)₃ · 2H₂O species in the organic phase using DNPPA and Eu(HA₂)₃ using D2EHPA as extractants (HA: DNPPA/D2EHPA). No change in fluorescence lifetimes and spectra with increased nitric acid and extractant concentration indicated the presence of identical species. However, the presence of neutral donors such as tri-n-butyl phosphate (TBP), Cyanex 923 (a mixture of four trialkyl phosphine oxides viz. R₃PO, R₂R′PO, RR′₂PO and R′₃PO where R: n-octyl and R′: n-hexyl chain) showed spectral changes for both the extractants. There was an increase in fluorescence life time from ∼400 µs to ∼1500 μs for Eu(III)-DNPPA system in the presence of neutral donors indicating complete dehydration of the extracted species. By contrast, no change in fluorescence life time was observed in the case of Eu(III)-D2EHPA system after the addition of neutral donors.

Keywords:

• complexation
• D2EHPA
• DNPPA
• Eu(III)
• fluorescence
• neutral donors