Raman and Electrochemical Study of Zirconium in LiCl-KCl-LiF-ZrCl₄

Abstract

In this work, Raman measurements were performed with quenched LiCl-KCl-LiF-ZrCl 4 /ZrF 4 /K 2 ZrF 6 salt mixtures for deciphering the coordination chemistry of zirconium(IV) in the presence of fluoride ion in the melt. The occurrence of ZrCl 6 2− , ZrCl 4 F 2 2− , ZrF 6 2− , ZrF 7 3− and ZrF 8 4− in melt at different F/Zr molar ratios was confirmed by Raman spectra. The electrochemical redox behaviors of zirconium in LiCl-KCl-LiF-ZrCl 4 were also examined at 773 K. Transient methods such as cyclic voltammetry and square wave voltammetry were used. In LiCl-KCl-LiF-ZrCl 4 with LiF concentration less than 1.27 wt% (molar ratio F/Zr < 9.1), the reduction behavior was found to be largely dependent on the formed Zr(I) species; In LiCl-KCl-8.0 wt% LiF (F/Zr > 101), the reduction of Zr(IV) followed a two-step mechanism of Zr(IV)/Zr(III) and Zr(III)/Zr(0) at the potentials of about −0.85 and −1.40 V versus Pt, respectively.

Optical monitoring of the anodic dissolution of zirconium and the agglomeration of potassium hexachlorozirconate during transpassive dissolution in molten LiCl–KCl salt

“…They assigned those peaks to the octahedral ZrCl 6 2− structure with two Raman-active vibration modes (T 2g and A 1g ). 44…”

“…Yao et al 44 observed Raman peaks at similar wavenumbers (163 cm −1 and 332 cm −1 ) in the spectrum of Raman-active vibration modes (T 2g and A 1g ). 44 Previous studies 42,[45][46][47][48][49] peaks in the O4 agglomerate relative to the background noise (zone A in Fig. 9) were noticeably greater than those of ZrCl 4 (5.0 wt%)-LiCl-KCl.…”

Competitive Coordination of Chloride and Fluoride Anions Towards Trivalent Lanthanide Cations (La3+ and Nd3+) in Molten Salts

“…Consequently, the Ln−F interaction was anticipated to be less strong than others. Furthermore, for M n+ with high polarizing power, [MF x ] n−x (x=6‐8) species were determined with the addition of fluoride in molten chloride salts, which indicated the complete substitution of F − for Cl − in the first coordination sphere [5a,c,g,h,13] . Since ionic bonding model also gave the best interpretation of M−F interaction, [21] the remarkable difference between Ln and M species in molten chloride‐fluoride salts should be attributed to the discrepancy in polarizing power.…”

Quantitative Studies on the Structure of Zirconium Fluoride Anions in Molten LiF and FLiBe

“…Due to its excellent corrosion-resistance and extremely low neutron-adsorption cross-section, zirconium has been widely used in nuclear industry. [3] In FLiBe-ZrF 4 -UF 4 or LiF-ZrF 4 -ThF 4 , ZrF 4 is used for stabilizing the uranium/thorium species against the oxygenation by complexing with oxygen. [4] In addition, Zr(IV) can be used as a substitute for Th(IV) in routine research to avoid the radioactivity based on their chemical similarities.…”

“…[9] Based on the results of previous studies by means of spectroscopic techniques, zirconium fluoride anions were considered probably to exist in the form of these three types ZrF 6 2À , ZrF 7 3À and ZrF 8 4À in fluorine molten salt and chlorine molten salt with K 2 ZrF 6 and/or LiF as fluorine source at proper F/Zr molar ratios. [3,8] In order to investigate the energy and structural properties, vibrational frequencies of ZrF n (nÀ 4)À anions were determined with ab initio and density functional theory (DFT) calculations. [10] In addition, the quantitative analysis has also been performed on the structure of ZrF 4 in molten alkali fluorides with EXAFS and MD.…”