Determination of rare earth elements in phosphate minerals by inductively coupled plasma atomic emission spectrometry

Abstract

Inductively coupled plasma atomic emission spectro-metry(ICPAES) was applied to the determination of rare earth elements (REEs) in phosphate rare earth minerals such as xenotime and monazite. The ICPAES operating conditions were 1.0~l.5kW RF power, 0.45~0.49 1/min carrier gas, 14 1/min coolant gas, and 1.0 1/min plasma gas. The detection limits of REEs were in the range from ca. 1 ppb to 40 ppb. The relative standard deviation(10 replicates) for 1 ppm of REE were ca. 1~5 %. There was no influence of the inorganic acids in the concentration range from 10-2 M to 2 X 10 -1 M, but signal suppression was observed at concentrations above 1 M of these acids. No significant change in intensities of REEs was observed for sodium ion in the concentration range between 10 and 10 3 ppm. Determination of several REEs in phosphate mineral solutions necessitated corrections of spectral interferences from coexiting REEs. The corrections were easily made from the contents of coexisting elements which were already known. Phosphate minerals were dissolved with hot concentrated sulfuric acid. After insoluble residue was filtrated, the solutions were diluted with water to give concentrations in the range 10~500µg/ml. These sample solutions were directly injected into the plasma. REEs contents in the phosphate minerals were measured by calibration curve method. The contents of REEs(Dy, Yb, Sm, Tb, Eu) obtained ICPAES were in good agreement with those obtained by atomic absorption spectrometry or fluorometry. It was found that REEs distribute in xenotime and monazite following the Oddo and Harkins law. © 1985, The Japan Society for Analytical Chemistry. All rights reserved.