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

A clear understanding of the anodic dissolution behavior of zirconium in molten LiCl-KCl salt plays an essential role in developing the electrometallurgical recycling of spent nuclear-fuel cladding. In this study, we utilized a real-time optical monitoring system designed for molten salt systems to investigate the passive and transpassive dissolution behavior of zirconium in molten LiCl-KCl eutectic salt. Constant-potential dissolution experiments were performed at the potential at which passive or transpassive dissolution of zirconium occurs. The formation of a thin film layer on the zirconium electrode was observed during passive anodic dissolution. We discovered the unique phenomenon that a white-colored agglomerate is formed on the zirconium-electrode surface during transpassive anodic dissolution (0.00 V vs. Ag|AgCl 10 wt%). The chemical analysis results showed that the agglomerate consists of potassium hexachlorozirconate (K 2 ZrCl 6 ) and LiCl-KCl. The formation of the K 2 ZrCl 6 agglomerate on the zirconium electrode is due to the solubility limit of tetravalent zirconium in molten LiCl-KCl salt. We studied the passivation and transpassivation behavior of Zr. Optical monitoring revealed the formation of a white-colored agglomerate during transpassivation.