Extraction of Zirconium from Its Oxide during Electrolysis of the KF–AlF3–Al2O3–ZrO2 Melts

Zirconium is one of the widely demanded materials, while the existing methods of its production are multistage and energy-intensive. The paper proposes a method for extracting zirconium from its oxide by electrolysis of low-temperature oxide-fluoride melt KF–AlF₃–Al₂O₃–ZrO₂ with a temperature of 750°C. For this purpose, the potentials for the electroreduction of zirconium and aluminum ions on a glassy carbon electrode have been determined by means of voltammetric methods. It was shown that the electroreduction of aluminum ions in the KF–AlF₃–Al₂O₃ melt occurs at a potential more negative than –0.05 V relative to the aluminum electrode with the formation of a cathode peak in the potential range from –0.18 to –0.2 V. With the addition of 1 wt % of ZrO₂, cathode current on the voltammogram begins at a potential more negative 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 the addition of ZrO₂ by means of square-wave voltammetry. It has been suggested that, because of the lower bond energy, 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. At a graphite cathode potential of –0.1 and –0.3 V relative to the aluminum electrode, the electrolysis of the KF–AlF₃–Al₂O₃–ZrO₂ melt was carried out, and the elemental and phase composition of the obtained deposits was determined by X-ray phase analysis, scanning electron microscopy, and energy dispersive microanalysis. It was shown that, at a potential of –0.1 V, a deposit with 98.5–99.5 wt % zirconium can be obtained. This indicates a reliable possibility of selective extraction of zirconium by the proposed method.