Dry separation for rare earth by vacuum distillation of Di and Triiodide mixture

A basic study on dry separation process for rare earth element by vacuum distillation combined with selective reduction of iodides has been carried out. A possibility for vacuum distillation of di and triiodide mixture is demonstrated. The process is based on large differences in the redox potential of the rare earth iodides and in the vapor pressure of rare earth di and triiodides. Experimental proof of the vacuum distillation is provided for binary iodide systems, neodymium-samarium and samarium-dysprosium. The apparent separation factors, calculated from the compositions of diiodide-enriched and triiodide-enriched deposits, are β_Sm/Nd > 890 and β_Sm/Dy = 2300, respectively. These values are large enough to produce commercial pure metals used in the rare earth magnets. Thermodynamic consideration of the process is made on the basis of data reported in the literature and some thermodynamic assumptions.