Electrochemical behavior of Sm(III)/Sm(II) and extraction of Sm on reactive electrode from molten LiF-BeF2

Evaluation of noble metals as reactive electrodes for separation of lanthanides from molten LiF-BeF2

“…29,30 The reductions of Eu( iii ) and Sm( iii ) involved a two-step reduction mechanism. 10,11,20,26,31 The reduction mechanism of Nd( iii ) in fluoride molten salts seems to be more complicated. Hamel et al reported a mono-step 3-electron transfer mechanism for the reduction of Nd( iii ) in 1083 K LiF-CaF 2 melts, 32 while a multi-step mechanism was reported in a high-temperature (1373 K) LiF-NdF 3 system by Kwon et al 33 Since the thermodynamic data of NdF 2 was not available from the database of the HSC6.0 software and the temperature (873 K) of our evaluation is closer to the temperature of a mono-step process, the reduction mechanism of Nd( iii ) in FLiBe melts was assumed to be one step for the calculation of the reduction potential of Nd.LnF 3 + 1.5Be = Ln + 1.5BeF 2 (Ln = Pr,Gd,Nd)LnF 2 + Be = Ln + BeF 2 (Ln = Eu,Sm)…”

“…The Gibbs free energy data of EuF 2 and SmF 2 was obtained from our recent studies. 10,11 Other fluoride data from the HSC6.0 database was employed for the calculations shown in eqn (1)–(4) and the calculated standard potentials are shown in Table 1. The results indicate that the reduction potential of a multi-step reaction is much lower than that of a mono-step reaction.…”

“…Pt wire (Sinopharm, ∅ 1 mm, purity 99.5%) is used as a pseudo reference electrode (RE) (Pt/PtO x /O 2− ) in all electrochemical tests. 28 For convenience, to compare the electrochemical behavior in FLiBe and FLiBe-LnF 3 systems, a hypothesis Be reference electrode is used in the data handling by taking the equilibrium potential of Be on W or Ag to be 0 V. 10,11 A high-purity graphite crucible (Tokai) is used as a container for the molten salts and is taken as auxiliary electrode (AE) in the electrochemical tests. The deposition products on the electrodes are identified by X-ray diffraction (XRD, X'Pert Powder III, Panaco), scanning electronic microscopy and energy dispersive X-Ray spectroscopy (SEM-EDS, LEO 1530VP).…”

“…9 Due to the reduction potential of Be being higher than that of lanthanide elements, they are difficult to separate directly from the LiF-BeF 2 melt. 10,11…”

“…Our recent work indicated that Sm could be reduced and extracted on an Al reactive electrode from FLiBe melt. 11…”