| The solubilty products of La₂O₃ and Ce₂O₃ were measured by the potentiometric titration method in molten KCl-LiCl eutectic at 743K. Measured titration curves clearly showed formation of soluble intermediate oxychloride complex ions, LaOCl_x^(x-1)- and CeOCl_x^(x-1)-, before in situ precipitation of those rare earth oxides. Oxides thus formed seemed to be far more reactive than ordinary oxides, thereby explaining the discrepencies between measured and calculated solubility products. The equilibrium formation constants for the intermediate oxychloride complex ions, LaOCl_x^(x-1)- and CeOCl_x^(x-1)- were 10^(-5.09) and 10^(-6.39), respectively. The solubility products for La₂O₃ and, Ce₂O₃ were also determined, being 10^(-13.72) and 10^(-18.25), respectively. From those results the potential-pO^(2-) diagrams for La and Ce were constructed and new methods for the separation of the rare earth oxides have been suggested. |
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