Behavior of UO2 in a room-temperature ionic liquid in the presence of AlCl3

Abstract

A study was made of interaction between AlCl 3 and room-temperature ionic liquid (RTIL) [C 8 H 15 N 2 ][N(SO 2 CF 3 ) 2 ], or BuEtIm!Tf 2 N, and of anodic dissolution in RTIL of UO 2 and of a simulated oxide fuel at 297!302 K, depending on the AlCl 3 concentration. It was shown that anodic dissolution of UO 2 pellets and a UO 2 !Al mixture in RTIL yields soluble uranium species. Potentiostatic electrolysis of the resulting solutions can yield uranium compounds at the cathode, though with low current efficiencies. The role of AlCl 3 in these processes was suggested. A heterophase reaction between UO 2 and AlCl 3 was studied, depending on the content of AlCl 3 in solution. It was found that the exchange reaction products, soluble uranium species, are accumulated in solution only at the molar ratio AlCl 3 /Tf 2 N > 1. Implementation of both pyrochemical and conventional aqueous methods of nuclear material processing involves certain problems. These include high operation costs, high corrosivity of structural materials, abundant waste, risk of accidents, etc.Low-temperature solvents such as room-temperature ionic liquids (RTILs) eliminate or, at least, significantly reduce some of the above-mentioned drawbacks. It is known [1!9] that RTILs are incombustible and virtually nonvolatile at process temperatures of up to 573 K; they exceed aqueous media in radiation resistance and exhibit a high selectivity with respect to the components being separated.It was of interest to study separation and purification of nuclear materials using such new process media as room-temperature ionic liquids, in particular, to study the possibility of utilization of uranium from the pressed mixture of 90 wt % Al with 10 wt % UO 2 , simulating the irradiated oxide fuel. To this end, we studied interaction of AlCl 3 and anodic dissolution of UO 2 and of the pressed Al!UO 2 mixture, as well as the exchange reaction between UO 2 and AlCl 3 in an RTIL of the composition [C 8 H 15 N 2 ][N(SO 2 CF 3 ) 2 ], or BuEtIm!Tf 2 N, at 297!302 K, depending on the AlCl 3 concentration. EXPERIMENTALWe studied the chemical and electrochemical behavior of UO 2 and Al!UO 2 mixture in BuEtIm!NTf 2 RTIL by linear and cyclic voltammetry and zerocurrent chronopotentiometry. Also, we carried out electrolysis of ionic liquids of different compositions, followed by the chemical and X-ray phase analyses of the solid and liquid phases.All manipulations, including assembling the electrochemical cells, were carried out in a dry glove box in an argon atmosphere. Argon was permanently freed from oxygen-containing impurities by forced circulation through a column packed with metallic Zr chips and heated to 1000 K. Argon circulation was effected by a membrane pump placed directly inside the glove box.As solvent we used RTIL of the composition BuEtIm!Tf 2 N, synthesized at the Los Alamos National Laboratory (the United States). Before use, the RTIL was additionally freed from oxygen-containing impurities by keeping at a residual pressure of 10 33 atm for 12 h.Electrochemical s...

Electrochemistry of rare earth oxy ions REO+ (RE=Ce, La, Nd) in molten MgCl2–NaCl–KCl eutectic

“…Our results showing the presence of rare earth oxychlorides in MgCl 2 -NaCl-KCl eutectic are also substantiated by the XPS of cerium oxychloride [10] [19,20]. The formation of CeOCl and NdOCl has also been reported by Ogawa and Minato [24] and Smolenskii et al [25,26].…”

Redox behaviour of cerium oxychloride in molten MgCl2–NaCl–KCl eutectic

“…The electron transfer process at the glassy carbon electrode is similar to what has been observed by Smolenskii et al [6]:…”

“…Smolenskii et al [6] have also reported that the probability of formation of cerium oxo ions in alkaline earth chloride based melts is higher compared to that in alkali chloride based melts. Therefore, the formation of CeOCl should be more probable in MgCl 2 -NaCl-KCl eutectic in Cl 2 /O 2 atmosphere which is in line with our observations.…”

“…Smolenskii et al [6] have reported a single anodic peak for the dissolution of a solid solution of cerium and uranium oxides in NaCl-KCl eutectic. In the present study, there are two separate oxidation peaks for cerium oxo and uranyl ions.…”

“…Smolenskii et al [6] have carried out electrochemical studies of UO 2 Cl 2 -CeCl 3 in NaCl-KCl melt under Cl 2 /Ar atmosphere to explore the feasibility of co-deposition of these ions. They reported two cathodic peaks at −0.8 and −1.6 V (probably versus Cl 2 /Cl − reference electrode) which they attributed to reduction of UO 2 2+ and CeO + ions, respectively, and an anodic peak at −0.65 V to the dissolution of a solid solution deposit UO 2+x .CeO 2 from the cathode.…”