Extraction of zirconium from its oxide during the electrolysis of KF–AlF₃ –Al₂O₃ –ZrO₂ melts

Abstract

   Zirconium is one of the most commonly used materials, while the existing methods of its production are multi-stage and energy-intensive. The paper proposes a method for extracting zirconium from its oxide by KF–AlF3 –Al2O3 –ZrO2 low-temperature oxide-flu-oride melt electrolysis with a temperature of 750 °C. For this purpose, voltammetric methods were used to determine potentials of the electrochemical reduction of zirconium and aluminum ions on a glassy carbon electrode. It was shown that the electrochemical reduction of aluminum ions in the KF–AlF3 –Al2O3 melt occurs at a more negative potential than –0.05 V relative to the aluminum electrode with the cathode peak formation in the potential range from –0.18 to –0.2 V. With the addition of 1 wt.% of ZrO2 , cathode current growth on the voltammogram begins at a more negative potential than 0 V, and the cathode peak is formed at a potential of about –0.1 V. Similar results were observed in the study of the cathode process in the KF–AlF3 –Al2O3 melt with and without ZrO2 added by means of square wave voltammetry. It was suggested that zirconium-containing electroactive ions are discharged at a potential that is 0.05–0.08 V more positive than the discharge potential of aluminum-containing ions due to the lower bond energy. At a graphite cathode potential of –0.1 and –0.3 V relative to the aluminum electrode, the KF–AlF3 –Al2O3 –ZrO2  melt electrolysis was carried out, and the elemental and phase composition of deposits obtained was determined by X-ray phase analysis, scanning electron microscopy and energy dispersive microanalysis. It was shown that the 98.5 –99.5 wt. % zirconium deposit was obtained at a potential of –0.1 V. This indicates a reliable possibility of selective zirconium extraction using the proposed method.