Determination of Rare-Earth and Accompanying Elements in Niobium−Rare-Earth Ores by Inductively Coupled Plasma Atomic Emission Spectrometry Using Model Calibration and a Mathematical Approach for Resolving Spectral Interferences

Abstract

A procedure is developed for the direct determination of all rare-earth and a number of accompanying elements in niobium−rare-earth ores by inductively coupled plasma atomic emission spectrometry after sample decomposition by fusion and further disolution. Because of the complex elemental composition of the samples, numerous mutual overlapping of spectral lines of matrix and rare-earth elements were observed, which required corrections in the calculations of concentrations. The procedure is based on a calibration, modeling spectral and matrix interferences; compilation of the set (mathematical matrix) of mutual interference coefficients; and use of the matrix obtained and the results of sample measurement for the computation of element concentrations. A precise method is used to solve a system of linear equations; it implies the resolution of interferences for all lines. Software utilizing a regularization algorithm ensuring stable solutions of the system of linear equations and also a method of evaluation of the uncertainty of the results of measurements are developed. The method ensures correct results and is rather stable to changes in the composition of the analyzed sample. This was confirmed by the results of analyses of certified reference materials (CRMs) of the composition of rare-earth ores of different origin.