Solubility and dissolution behavior of ZrO2 in KF–AlF3 molten salts

The fluorine salt system is a potential electrolyte for the preparation of metals and alloys from metal oxides via molten salt electrolysis. The solubility of ZrO 2 in KF–AlF 3 –Al 2 O 3 molten salts (KF/AlF 3 molar ratio = 2.1–2.8, Al 2 O 3 content = 0–9 wt%) was measured using the isothermal saturation method in this study. The influence of temperature and electrolyte composition on ZrO 2 solubility was analyzed. The dissolution mechanism of ZrO 2 was then determined based on the analysis of X–ray diffraction and Raman spectroscopy results. The experimental results show that the solubility of ZrO 2 in the 2.4KF–AlF 3 molten salt at 1233 K could reach up to 6.62 wt%. Besides, the solubility of ZrO 2 increase with the increase of temperature, the decrease of KF/AlF 3 molar ratio and Al 2 O 3 content. X-ray diffraction and Raman spectroscopy analyses show that the dissolved ZrO 2 in KF–AlF 3 molten salts existed in the form of [Zr 2 O 2 F 6 ] 2− and [ZrF 6 ] 2− complex ions under melting and cooling conditions, respectively. And the dissolution process of ZrO 2 in KF–AlF 3 molten salts can be described using a mass transfer control model.