Dissolution and Electrochemical Reduction of Rare Earth Oxides in Fluoride Electrolytes

Doctoral thesis (2021)

Authors

X. Guo Team Yongxiang Yang - Mechanical, Maritime and Materials Engineering
Research Group
Team Yongxiang Yang (Mechanical, Maritime and Materials Engineering) (TU Delft)
Copyright: © 2021 X. Guo
DOI: https://doi.org/10.4233/uuid:79a1f6f1-52d1-48a9-a0df-03c1b1ce0ac6
Solubility Rare earth metals Oxide-fluoride electrolysis Dissolution kinetics Electrochemical reduction
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Published Date

2021

Language

English

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Faculty

Mechanical, Maritime and Materials Engineering

Department

Materials Science and Engineering

Research Group

Team Yongxiang Yang

Abstract

Rare earth elements (REEs) are a group of 17 metallic elements, including 15 lanthanides, scandium and yttrium, which have remarkably similar chemical and physical properties. Nowadays, rare earth metals are widely used in such fields as electronics, petroleum, and metallurgy. Rare earth elements are considered as vitamin to modern industry and critical resources to many countries.

Neodymium is a light lanthanide, and its demand has been substantially boosted due to the broad application of NdFeB permanent magnets in electronics and new energy industries.

Oxide-fluoride electrolysis is the main commercial method to produce rare earth metals and their alloys, especially light lanthanides, in both primary and secondary production. The oxide-fluoride electrolysis process involves first the dissolution of rare earth oxide(s) (REO(s)) in a molten fluoride, which serves as both a solvent and an electrolyte. During an electrochemical process, rare earth cations are reduced at the cathode and the respective metal is formed. Even though this method was adopted from laboratory to industrial production about 50 years ago, the exact mechanism of the process is not fully clarified. A deeper understanding of the process from both physicochemical and electrochemical points of view is crucial for process optimization, improving its current efficiency and power consumption. Maintaining enough REOs in the electrolyte and having a fast dissolution are crucial factors for good industrial practice. Identifying the electrochemical reactions involved during the electrolysis is vitally important for promoting target reactions and restricting side reactions, which are linked directly to the economic indicators of the process.

Therefore, this thesis focuses on the solubility of REOs in molten fluorides, developing a semi-empirical model for the estimation of REO solubility, dissolution behavior of Nd2O3 in molten fluoride, and electrochemical behavior of Nd(III) in fluoride melt.