Dissolution and Electrochemical Reduction of Rare Earth Oxides in Fluoride Electrolytes

Dissolution and Electrochemical Reduction of Rare Earth Oxides in Fluoride Electrolytes

Guo, X. (TU Delft Team Yongxiang Yang)

Yang, Y. (promotor)
Sietsma, J. (promotor)

Delft University of Technology

2021-04-30

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.

rare earth metals
oxide-fluoride electrolysis
solubility
dissolution kinetics
electrochemical reduction

https://doi.org/10.4233/uuid:79a1f6f1-52d1-48a9-a0df-03c1b1ce0ac6

Institutional Repository

doctoral thesis

© 2021 X. Guo