Chlorination of samarium sesquioxide

Samarium as either a metal or a compound has become very popular in the last years, mainly due to the applications of the metal or the fluorides as precursors in permanent magnets, the use of the oxychlorides in optics and those of the oxide in many applications such as catalysis and fuel cells. But samarium does not occur in nature as a metal due to its strong affinity for oxygen and sulfur. Therefore, its extraction from minerals becomes difficult because of both the high stability of the oxides and the well known chemical similarities among them. Chlorination using Cl-2 (g) has been proposed as a useful method to separate Sm2O3 from the other lanthanide oxides. Despite its potential application as a separation method, no kinetic data related to the interactions of this oxide and chlorine is known. This fact, related to the scientific field and the possibility of using this method in extractive metallurgy at industrial scale aimed the elaboration of this work. The chlorination of samarium sesquioxide with gaseous chlorine was studied by thermogravimetry. The effects of both the total gas flow rate between 2.1 and 7.91 h(-1) (NTP) and temperature between 200 and 950 degrees C on the reaction rate were analyzed. Apparent activation energy values of 20-40, 129 +/- 1 and 12 +/- 7 kJ mol(-1) corresponding to the 200-270, 270-350 and 350-950 degrees C temperature ranges were found. SmOCl (s) and O-2 (g) were the reaction products. Solids involved on the reaction were analyzed by X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). The microstructure was observed by scanning electron microscopy (SEM). (c) 2005 Elsevier B.V. All rights reserved.