Indirect determination of lanthanum in a mixture of rare earth oxide

Lanthanum in a mixture of rare earth oxide, consisting of the elements of cerium and yttrium groups, was determined indirectly by using a combination of gravimetric, volumetric and colorimetric procedures. The two groups were separated from each other by the double sulfate method, and the rare earth elements of the cerium group were determined by weighing the oxide. In addition to lanthanum and cerium, the cerium group contained praseodymium, neodymium and samarium, which were determined colorimetrically by utilizing their sharp absorptions at 444.5 nm, 521.8 nm and 401.5 nm, respectively. Cerium was determined volumetrically by the method of JIS 8404 without group separation. The lanthanum content was calculated by the equationLa2O3(%) =Cerium group rare earth oxide (%)-CeO2(%)-Pr6O11(%)-Nd2O3(%)-Sm2O3(%).The results obtained showed good precision, and were in fairly good agreement with those by the X-ray fluorescence method. It suggests that at the stage of the group separation the lanthanum and cerium in the sample were completely precipitated as their double sulfates and all the yttrium group elements were removed from the precipitate.The method reported here is expected to be generally applicable to the determination of lanthanum in a mixture of rare earth oxide which consists mainly of cerium group elements.