EPR Investigation on a Quantitative Analysis of Eu(II) and Eu(III) in LiCl/KCl Eutectic Molten Salt

Abstract

EPR spectroscopic technique was applied for a quantitative analysis of Eu(II) for a speciation of europium in a LiCl-KCl eutectic melt. By adopting the first absorption line of each isotopes ( 151 Eu and 153 Eu), a calibration plot was obtained. The calibration of the EPR intensity shows a good linearity according to the amount of Eu(II). The EPR intensity was identified to increase proportionally with a decrease of the attenuation parameter for EPR microwave power. The fluorescence technique was used qualitatively to find whether either of Eu(II) or Eu(III) ions exists in a molten salt sample. The ICP-AES technique was also adopted to determine the total concentration of europium in the sample, since EPR is only sensitive for detecting the Eu(II) ion. The extent of the reduction of Eu(III) in the LiCl-KCl eutectic melt at 723 K was determined by using this technique.

Reduction of Trivalent Europium in Molten LiCl-KCl Eutectic Observed by In-Situ Laser Spectroscopic Techniques

“…[10][11][12]18,19 Eu(III) is reduced to Eu(II) immediately after adding them into the molten chloride salt. The redox reaction can be simply described as follows: 8,10 2EuCl 3 ↔ 2EuCl 2 + Cl 2 [1] Fig.…”

“…This divergent result requires the reliable technique for in situ quantitative analysis of reduction of trivalent europium. Recently, several groups have measured the fluorescence spectrum of Eu(II) in LiCl-KCl eutectic at various temperatures, [11][12][13] whereas the fluorescence spectrum of Eu(III) have not been observed in high-temperature LiCl-KCl eutectic. The fluorescence intensity of Eu(II) did not obey linear relationship against the concentrations, so that the quantitative analysis of redox behavior of Eu(III) have not been performed based on the results from fluorescence measurements in high-temperature molten salt.…”

“…[3][4][5][6][7][8] The qualitative and quantitative analysis of reduction of europium from Eu(III) to Eu(II) has been performed in molten alkali chloride salts by electrochemical method, 9,10 absorption spectroscopy, 10 and electron paramagnetic resonance (EPR) technique. 11 Nevertheless, there has been still a relatively large discrepancy of the reducing capacity of europium in chloride molten salts reported in literatures. Kim et al 10 reported that around 20% of Eu(III) was reduced to Eu(II) at 5.4 × 10 −4 M by absorption spectroscopy and electrochemical analysis in high temperature, and Park et al 11 observed that approximately 50% of Eu(III) was reduced to Eu(II) measured by EPR technique at room temperature after solidification of molten salt samples.…”

“…11 Nevertheless, there has been still a relatively large discrepancy of the reducing capacity of europium in chloride molten salts reported in literatures. Kim et al 10 reported that around 20% of Eu(III) was reduced to Eu(II) at 5.4 × 10 −4 M by absorption spectroscopy and electrochemical analysis in high temperature, and Park et al 11 observed that approximately 50% of Eu(III) was reduced to Eu(II) measured by EPR technique at room temperature after solidification of molten salt samples. This divergent result requires the reliable technique for in situ quantitative analysis of reduction of trivalent europium.…”

“…The fluorescence intensity of Eu(II) did not obey linear relationship against the concentrations, so that the quantitative analysis of redox behavior of Eu(III) have not been performed based on the results from fluorescence measurements in high-temperature molten salt. 11 To our knowledge, this paper is highlighted as the first dealing with the ways in which redox behaviors of Eu(II) and Eu(III) in hightemperature LiCl-KCl eutectic have been characterized by TRLFS in simultaneous combination of UV-Vis absorption measurements.…”