# Preparation of Metallic Zr from ZrO2 via Carbothermal and Electrochemical Reduction in Molten Salts

## TL;DR

This paper presents a new method to produce high-purity zirconium metal using vacuum reduction and molten-salt electrolysis, offering a shorter and more efficient process than traditional methods.

## Contribution

A novel short-flow process for zirconium metal production using vacuum reduction and electrolysis of zirconium oxycarbide is proposed.

## Key findings

- ZrCxOy was successfully produced from ZrO2 under vacuum at 1750 °C with good electrical conductivity.
- Electrochemical tests showed reversible redox behavior of ZrCxOy, enabling zirconium metal production via electrolysis.
- High-purity β-zirconium metal (99.2 ± 0.3 wt.%) was obtained meeting ASTM B551-12 standards.

## Abstract

Zirconium, a critical rare metal with exceptional corrosion resistance and nuclear applications, is conventionally produced via the energy-intensive Kroll process. The electrolysis of ZrCxOy soluble anodes has been extensively investigated due to its advantages in having a short process flow and resulting in high-quality products. In particular, during the electrolysis of zirconium oxycarbide with a C:O molar ratio of 1:1, gaseous CO can be released, and no residual anodes are generated, which is extremely appealing. In this regard, this paper explores the feasibility of preparing zirconium metal through high-temperature vacuum reduction to produce zirconium oxycarbide using ZrO2 as the raw material, followed by direct molten-salt electrolysis. Firstly, the reduction products were characterized using an X-ray diffractometer (XRD) and a scanning electron microscope (SEM). The results showed that under a vacuum of <10 Pa at 1750 °C, the reduction products mainly consisted of ZrCxOy and a small amount of ZrO2, and they exhibited good electrical conductivity (0.0169 Ω·cm). Subsequently, the cyclic voltammetry test results of the reduction products revealed the reversible redox behavior of ZrCxOy. There were characteristic oxidation peaks at −0.53 V and −0.01 V (vs. Pt), corresponding to the formation of Zr2+ and Zr4+, respectively, and a reduction peak at −1.51 V, indicating the conversion from Zr2+ to Zr. Finally, β-zirconium metal with a purity of 99.2 ± 0.3 wt.% was obtained through potentiostatic electrolysis, and its quality met the R60704 grade specified in ASTM B551-12 (2021). This study offers a novel approach for the short-flow preparation of zirconium metal, which is conducive to expanding its applications.