Abstract
This study was carried out to examine the removal of rare earth (RE) elements by electrodeposition for the purification and reuse of LiCl-KCl salt after electrorefining and electrowinning. The electrochemical behavior of RE elements (Dy and Gd) in LiCl-KCl-DyCl3-GdCl3 at 500°C was investigated using the cyclic voltammetry (CV) technique using Mo and Mg electrodes. It was observed that the reduction potential of the RE elements shifted at the Mg electrode owing to the alloy formation with Mg (RE-Mg alloy). Subsequently, a series of potentiostatic electrolysis tests were conducted to remove the RE elements in the salt and check the formation of deposits at the Mg and Mo electrodes. The scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM/EDS) technique was used to confirm that the reduced RE metals were deposited on the surface of the Mg electrode. However, no significant deposit on the Mo electrode was observed, and a mud-like deposit was found on the bottom of the electrochemical cell. The salt analysis performed by employing the inductively coupled plasma-optical emission spectrometry (ICP-OES) indicated that the removal efficiency of Dy3+ and Gd3+ through electrodeposition was 83.5∼95.2 and 91.6∼95.2%, respectively.
Highlights
Pyroprocessing is an option which enables to recover the useful nuclear elements from spent fuel and to recycle them for fast reactors [1, 2]
At a scan rate of 3 mV/s, low height of two peaks were found at −1.88 and −1.94 V, which were assumed to be the formation of Dy-Mg alloy and Gd-Mg alloy, respectively [22]. e phase diagram shows that one Dy-Mg alloy (DyMg) and four Gd-Mg alloys (GdMg, GdMg2, GdMg3, and GdMg5) can exist at 500°C
The redox peak heights of Dy3+ and Gd3+ clearly decreased after the run 1. Another anodic peak appeared at −1.82 V, likely, because of the presence of Mg2+ in the salt, which was contributed by the Mg electrode
Summary
Pyroprocessing is an option which enables to recover the useful nuclear elements from spent fuel and to recycle them for fast reactors [1, 2]. En, the reduced spent fuel is transferred into an electrorefiner which contains a eutectic LiCl-KCl melt with some portion of UCl3 at 500°C. Uranium is recovered using solid cathode (i.e., electrorefining) [5,6,7] and uranium and transuranic elements are recovered using liquid cathode (i.e., electrowinning) [8,9,10]. After both of the recovery steps such as electrorefining and electrowinning, there are abundant amounts of rare earth (RE) elements in the salt. RE elements are key elements in industries and often used as additives to improve properties of alloy such as thermal and mechanical properties and corrosion resistance [11]
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