Electrochemical Formation of Dy–Fe Alloys in Molten LiF–CaF2–DyF3

Abstract

We conducted a fundamental study on the recycling of Dy and Nd from Dy-doped Nd–Fe–B magnet scraps by investigating the electrochemical Dy alloying behavior of Fe in molten LiF–CaF2–DyF3 (0.3 or 0.5 mol%) at 1123 K. Using open-circuit potentiometry with a Mo electrode, the equilibrium potential of Dy3+/Dy was determined to be 0.16 V (vs Li+/Li). The formation of multiple phases in the Dy–Fe alloys was suggested by cyclic voltammetry and open-circuit potentiometry. The deposition of Dy metal and formation of the solid DyFe2 alloy were confirmed by potentiostatic electrolysis at 0.10 V. The solid alloys of DyFe2, DyFe3, Dy6Fe23, and Dy2Fe17 were formed by two-step potentiostatic electrolysis in which the potential was changed to 0.22, 0.27, 0.29, and 0.34 V, after the initial electrolysis at 0.10 V, respectively. The equilibrium potentials of the coexistence states of DyFe2 + DyFe3, DyFe3 + Dy6Fe23, Dy6Fe23 + Dy2Fe17, and Dy2Fe17 + Fe were determined to be 0.25, 0.28, 0.31, and 0.36 V, respectively, and these values closely approximated those calculated from previously reported thermodynamic data.