Electrochemical and Spectroscopic Study of EuIII and EuII Coordination in the 1-Ethyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide Ionic Liquid.

Separation processes based on room temperature ionic liquids (RTIL) and electrochemical refining are promising strategies for the recovery of lanthanides from primary ores and electronic waste. However, they require the speciation of dissolved elements to be known with accuracy. In the present study, Eu coordination and EuIII /EuII electrochemical behavior as a function of water content in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIm][NTf2 ]) was investigated using UV-visible spectrophotometry, time-resolved laser fluorescence spectroscopy, electrochemistry, and X-ray absorption spectroscopy. In situ measurements were performed in spectroelectrochemical cells. Under anhydrous conditions, EuIII and EuII were complexed by NTf2 , forming Eu-O and Eu-(N,O) bonds with the anion sulfoxide function and N atoms, respectively. This complexation resulted in a greater stability of EuII , and in quasi-reversible oxidation-reduction with an E0 ' potential of 0.18 V versus the ferrocenium/ferrocene (Fc+ /Fc) couple. Upon increasing water content, progressive incorporation of water in the EuIII coordination sphere occurred. This led to reversible oxidation-reduction reactions, but also to a decrease in stability of the +II oxidation state (E0 '=-0.45 V vs. Fc+ /Fc in RTIL containing 1300 mm water).

Aqueous solutions of uranium(VI) as studied by time-resolved emission spectroscopy: a round-robin test.

Results of an inter-laboratory round-robin study of the application of time-resolved emission spectroscopy (TRES) to the speciation of uranium(VI) in aqueous media are presented. The round-robin study involved 13 independent laboratories, using various instrumentation and data analysis methods. Samples were prepared based on appropriate speciation diagrams and, in general, were found to be chemically stable for at least six months. Four different types of aqueous uranyl solutions were studied: (1) acidic medium where UO2(2+)aq is the single emitting species, (2) uranyl in the presence of fluoride ions, (3) uranyl in the presence of sulfate ions, and (4) uranyl in aqueous solutions at different pH, promoting the formation of hydrolyzed species. Results between the laboratories are compared in terms of the number of decay components, luminescence lifetimes, and spectral band positions. The successes and limitations of TRES in uranyl analysis and speciation in aqueous solutions are discussed.