The electrochemical behavior of Dy(III) and its co-reduction process with Zn(II) on a tungsten electrode were studied in eutectic NaCl-KCl melts at 700 °C by using a series of electrochemical techniques. The results indicate that the reduction of Dy(III) to Dy(0) is a diffusion controlled quasi-reversible process through a one-step reaction of exchanging three electrons. The diffusion coefficient of Dy(III) was calculated to be 1.7 × 10-5 cm2 s-1. Furthermore, the co-reduction of Dy(III) and Zn(II) on the tungsten electrode makes Dy(III) be reduced at more positive potentials due to the formation of various Dy-Zn intermetallic compounds. The electromotive force measurements were performed to determine the thermodynamic properties of the Dy-Zn intermetallic compounds, including the activities and relative partial molar Gibbs free energies of dysprosium in the two-phase coexisting state, as well as the standard formation Gibbs energies of Dy-Zn intermetallic compounds. Finally, potentiostatic electrolysis at -2.0 V was carried out in molten NaCl-KCl-DyCl3(1.0 mol%)-ZnCl2(1.0 mol%) at 700 °C for 11 h to prepare Dy-Zn alloy. X-ray diffraction and scan electron micrograph - energy dispersive spectrometry analyses showed that the obtained Dy-Zn alloy mainly comprised of DyZn2, as well as the minor phases of Dy2Zn17, DyZn3 and DyZn.

Waste aluminate phosphor is a valuable secondary resource of rare earth elements (REEs). However, Ce and Tb in aluminate green phosphor can hardly be extracted by direct leaching in an inorganic acid. Therefore, Na₂CO₃ assisted roasting is adopted to decompose the stable spinel structure of Ce_0.67Tb_0.33MgAl₁₁O₁₉ in the present work and to achieve the transformation of REEs to simple oxides. Based on the thermodynamic calculations, systematic experiments of thermal decomposition have been conducted. The thermal decomposition behavior, phase evolution, valence state change, variations in micro and macro morphology of the green phosphor during Na₂CO₃ assisted roasting were examined by using TG-DSC/MS, XRD, XPS, SEM/EDS analyses. The results indicated that the green phosphor began to react with solid Na₂CO₃ at 800 °C, and the reaction was dramatically accelerated with temperature rising above 851 °C. At about 1000 °C, Ce_0.67Tb_0.33MgAl₁₁O₁₉ could completely decomposed into CeO₂, Tb₂O₃ and MgO by roasting in an equivalent mass of Na₂CO₃ for 2 h, while α-Al₂O₃ was hardly attacked in roasting. The decomposition mechanism of Ce_0.67Tb_0.33MgAl₁₁O₁₉ in molten Na₂CO₃ could be depicted by the unreacted shrinking core model, and the reaction rate constant was estimated at approximately nanometers per second. The synergistic effect of cation-oxoanion ensures the successful extraction of CeO₂ and Tb₂O₃ from the green phosphor via Na₂CO₃ assisted roasting method. The converted CeO₂ and Tb₂O₃ can be extracted by using chlorination roasting and separated from non-REE residues. According to these investigations, a new efficient process technology is proposed for sustainable recycling of waste phosphor.