In situ electrochemical investigation of the reaction progress between Zr and a CuCl-SnCl2 mixture in a LiCl-KCl molten salt

The electrochemical behaviors of CuCl, SnCl₂ and a CuCl-SnCl₂ mixture were investigated by cyclic voltammetry (CV) and square wave voltammetry (SWV). The reduction potentials of Cu(i) and Sn(ii) on CV curves are -0.49 and -0.36 V, respectively, while the reduction potentials of Cu(i)-Sn(ii) in the CuCl-SnCl₂ mixture almost overlap. The co-chlorination reaction progress between CuCl-SnCl₂ and Zr was also studied by monitoring the concentration changes of Cu(i), Sn(ii) and Zr(iv) ions in situ by CV, SWV and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) analyses. The results indicate that during the reaction, the concentration of Zr(iv) ions increases gradually, while those of Cu(i) and Sn(ii) decrease rapidly until they disappear. When the molar ratios of Cu(i) to Sn(ii) are 1 : 1 and 1 : 0.5, the reaction between Cu(i) and Zr is faster but cannot exceed twice that of Sn(ii) and Zr in a short time. When the theoretical product of ZrCl₄ is a constant, and with the proportion of CuCl to SnCl₂ decreasing from 1 : 0 to 0 : 1, the chlorination reaction time periods increase from 40 to 170 min. Chloride products such as Cu _x Sn _y , Sn _x Zr _y , and Cu _x Zr _y , are formed with different molar ratios. The coupling effect caused by the formation of alloys will promote the chlorination reaction when the ratios of CuCl to SnCl₂ are 0.66 : 0.17 and 0.5 : 0.25. The results provide a theoretical basis for the electrolytic refinement of zirconium.

Anodic behaviour of Cu, Zr and Cu-Zr alloy in molten LiCl-KCl eutectic

The anodic dissolution behaviours of Cu, Zr and Cu-Zr alloy were analysed in LiCl-KCl at 500°C by anode polarization curve and potentiostatic polarization curve. The results show that the initial and fast-dissolving potentials of Cu are -0.50 and -0.29 V, and Zr are -1.0 and -0.88 V, respectively. But, in the Cu-Zr alloy, the initial and fast-dissolving potentials of Cu are -0.52 and -0.41 V, and Zr are -0.96 and -0.92 V, respectively. The potentials satisfy the selection dissolution principle that Zr in the alloy dissolves first, while Cu is left in the anode and is not oxidized. The passivation phenomenon of Zr is observed in the quick dissolution of Zr, while it is not observed in the Cu-Zr alloy. Moreover, from the above anodic dissolution results, potentiostatic electrolysis of Cu-Zr alloy was carried out at -0.8 V for 40 min, and the anodic dissolution mechanism and kinetics of Zr in Cu-Zr alloy were also discussed. In the initial stage, Zr dissolves as Zr4+ ions from the alloy surface and enters into the molten salt, leaving a Cu layer called 'dissolving layer' on the surface of the alloy. After that, another layer between the matrix and 'dissolving layer' called 'diffusion-dissolution layer' appears. Zr diffuses in the alloy matrix and dissolves as Zr4+ ions on the surface of the 'diffusion-dissolution layer' continuously, and Zr4+ ions diffuse through the 'dissolving layer' and enter into the molten salt finally. In addition, the factors affecting the dissolution of Cu-Zr alloy, such as time and potential, were also investigated. The dissolution loss increases with the increasing dissolution potential and time, while the dissolution rate increases with the increasing dissolution potential and declines with the prolonging dissolution time.