Sulfurization of rare-earth oxides with CS₂

In the scheme of spent fuel reprocessing by using sulfides, selective sulfurization of rare-earths in the fuel is considered followed by either magnetic separation or selective leaching of rare-earth sulfides from uranium oxides such as UO₂. In this paper, sulfurization behavior of rare-earth oxides was investigated by XRD and TG methods in the presence of CS₂. From the results of thermogravimetric study the sulfurization of europium proceeds as follows; sulfurization from Eu₂O₃ to Eu₃S₄ occurs at ca. 400 °C, then the Eu₃S₄ decomposes to EuS via non-stoichiometric sulfides at temperatures between 450 and 700 °C. From the results of thermogravimetry for Nd₂O₃, it was found that the weight curve showed monotonic increase from ca. 600 to 1000 °C. At 1000 °C, the value of weight increase was close to that for the formation of Nd₂S₃ from Nd₂O₃. The XRD result of the 1000 °C product showed a formation of a single phase of Nd₂S₃ which is compared with the thermogravimetric result as well as our previous results. The selective sulfurization of rare-earths in the mixture of rare-earth and uranium oxides was discussed by both experimental results and thermodynamical consideration.