Abstract This study investigated the phase equilibria in the Mg–Fe–Tb ternary system as a basis for developing a new energy-efficient production process for metallic terbium that integrates molten salt electrolysis, liquid metal extraction, and vacuum distillation. An 88 mass% Tb–12 mass% Fe eutectic alloy was reacted with varying amounts of Mg and held at 973 and 1273 K under an Ar atmosphere, resulting in its separation into a Tb–Mg-based liquid phase and an Fe-rich solid phase. SEM–EDX and ICP–OES analyses revealed that increasing the Mg content reduced the activity of Tb in the liquid phase and changed the equilibrium of the solid phases. Thermodynamic equilibrium was confirmed at both temperatures, and the obtained results were used to construct the ternary phase diagrams. The Fe concentration in the liquid phase increased with increasing temperature and Tb concentration. Subsequent vacuum distillation of the Tb–Mg-based liquid phase successfully removed Mg, recovering metallic Tb with up to 99.5 mass% purity and containing only trace amounts of Fe. These results demonstrate the effectiveness of the proposed process for Tb recovery and show that the constructed phase diagrams are useful for optimizing extraction and purification conditions. Graphical Abstract
Murata et al. (Fri,) studied this question.