Electrochemical Extraction of Cerium by Forming Ce-Zn Alloys in LiCl-KCl Eutectic on W and Liquid Zn Electrodes

Abstract

The electrochemical formation of Ce-Zn alloys in LiCl-KCl eutectic was systematically investigated by cyclic voltammetry (CV), square wave voltammetry (SWV) and open circuit chronopotentiometry (OCP). Due to the decrease of Ce activity in the metal phase of formed Ce-Zn alloys, the deposition potential of Ce(III) at a liquid Zn electrode was found to be 0.64 V more positive than that on an inert W electrode. The co-reduction behaviors of Ce(III) and Zn(II) ions were also studied in LiCl-KCl eutectic. Signals associated with six and nine Ce x Zn y intermetallic compounds were detected by CV and OCP techniques, respectively. In addition, potentiostatic electrolyses were carried out to extract Ce at a liquid Zn electrode in LiCl-KCl-CeCl 3 melt and on a W electrode in LiCl-KCl-CeCl 3 -ZnCl 2 melt, respectively. Deposited samples were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS). The results showed that intermetallic compound CeZn 11 was prepared on both the inert W electrode and liquid Zn electrode. Pyrochemical reprocessing of spent nuclear fuels is now considered to be one of the most promising options in nuclear fuel cycles due to their outstanding properties such as high thermal and radiation stability which allows a shorter cooling time of fuels before reprocessing, compactness, high actinide content and inherent proliferation resistance.1-4 The aim of the traditional pyrochemical processing technology is to achieve a group-selective separation of all actinides (Ans) for recycling or transmutation, generating the minimum of ultimate waste flows with an acceptable decontamination of fission products. A typical process in pyrochemical reprocessing is the electrorefining, [5][6][7][8][9][10] in which lanthanides (Lns) and Ans in spent fuels are dissolved into molten chloride salt by anodic dissolution. Subsequently, Ans (e.g. U) are selectively deposited on the stainless steel cathode or liquid cadmium cathode with respect to their different redox potentials in melt. In contrast, most fission products (FPs) still remain in the electrolyte.8 Actually, Lns are the major and most awkward FPs and are difficult to be separated from Ans due to their similar chemical properties. On the other hand, Lns are well known to possess large neutron capture cross sections, which can spoil the neutron economy of reactor cores in the transmutation operation. Therefore, though quite challenging, it is still imperative to efficiently separate Ans from Lns.In recent years, liquid-liquid reductive extraction has attracted considerable interest as a promising technique for the separation of minor actinides (MAs) from Lns.11-15 During a typical separation process, the solute cations in molten salt are recovered into the liquid metal phase via direct electrolysis or reductive extraction, due to the low activity coefficients of their corresponding metal phases in liquid metals. Since the operation of liquid metals plays an important role in the pyrochem...

Selective morphological analysis of cerium metal in electrodeposit recovered from molten LiCl-KCl eutectic by radiography and computed tomography

“…1a. The well-known reduction peak of cerium(III) was observed at −2.02 V 21 . Concentration of cerium(III) in all the experiments was adjusted to be 1.0 ± 0.2 wt%.…”

Electrochemical properties of yttrium on W and Pb electrodes in LiCl–KCl eutectic melts

“…For example, the electrode area is changeless, and the diffusion of deposited metal into the liquid metal is easier. 6,7 Thus, liquid Ga, [7][8][9][10][11] Bi, [12][13][14][15] Cd, 13,16 Zn, [17][18][19][20][21][22][23][24] Sn 25 were selected as cathode to separate REs from molten salts. The melting point of Pb metal is 600 K and boiling point is 1798 K, it is easy to melt but doesn't evaporate at 723-823 K. Thus, Pb metal seems to be a good candidate as the cathode material in separation and extraction of REs by molten salt electrolysis.…”

Electrochemical Coreduction of Gd(III) with Pb(II) and Recovery of Gd from LiCl-KCl Eutectic Assisted by Pb Metal

“…14 Thus, liquid cathode is paid more attention because of its complete physical separation between the metal product and electrolyte, constant electrode area, and easy diffusion of deposited metal into liquid metal. Low melting metal and alloy, for example, Bi, [30][31][32] Sn, 33,34 Cd, 35,36 Pb, [37][38][39] Ga, 40,41 Zn 14,[42][43][44] metals and Al-Ga alloy [45][46][47] were explored as a liquid cathode. The feasibility of liquid metals (Sb, Bi, Pb, Sn, Ga) as cathode was systematically investigated in molten fluorides, Gibilaro et al found that the electroactivity domains and reactivity of liquid metals are Bi > Pb > Sn > Sb > Ga. 48 Lebedev 49 evaluated the separation factor between actinides and lanthanides on various cathodes in molten chlorides, and found that the separation order is Al > Ga > Pb > Zn > Bi > Sn > In > Cd > Tl.…”