Analysis of Some Rare-Earth Ores by the Isotachophoresis-Particle Induced X-Ray Emission Method

Abstract

Rare-earth ores (monazite, ion-adsorption type and xenotime) were analyzed using a coupled analytical method, isotachophoresis-particle induced X-ray emission (ITP-PIXE). The detection limit for each minor rare-earth element in the ores was ca. 0.01 mass% of the total rare-earth elements (TREE), when 200 µg of monazite was analyzed. Since yttrium was the major component in ion-adsorption type and xenotime ores, the use of a leading electrolyte containing a-hydroxyisobutyric acid and tartaric acid as complexing agents was effective for the separation of yttrium ion from lanthanide ions. KeywordsRare-earth element, isotachophoresis, particle induced X-ray emission (PIXE), isotachophoresis-PIXE The analysis of rare-earth ores, which include fourteen lanthanide elements and yttrium with very different abundances, is one of the difficult problems for any analytical method. Especially when the minor components in the ores are analyzed, an accurate analysis may be disturbed by inherent disadvantages of the employed method, for example, spectrum interference in atomic emission spectroscopy, isotope interference in mass spectroscopy and a matrix effect in X-ray analysis.In such instances chromatographic analysis may be useful. However, since the separation column used for analytical chromatography is easily overloaded, a large amount of sample can not be applied. Therefore, the detection method should be sufficiently sensitive to analyze minor components in the applied sample. As long as conventional detection methods are used, however, the necessary sensitivity is not always available. A coupled analytical method for rare-earth ores, HPLC-ICP-AES, as reported by Yoshida and Haraguchi', is one possible solution, where ICP-AES plays the role of an HPLC detector with high sensitivity and discriminating ability.On the basis of the same strategy, we have developed isotachophoresis-particle induced X-ray emission (ITP-P1XE). Ionic components in a sample solution are first preconcentrated and separated by ITP, and zones of the separated components are fractionated utilizing the counterflow of a leading electrolyte. Dropwise fractions are then analyzed off-line by PIXE. By using this coupled method, a crude rare-earth chloride from monazite ore2 and a model solution of high-level waste from the nuclear fuel cycle3,4 were analyzed with high accuracy.The leading electrolyte used contained a-hydroxyisobutyric acid (HIB) as the complex-forming agent. The separation of fourteen lanthanide ions using the electrolyte is one of the typical applications of ITP.5,6 However, since Y and Dy could not be separated by using the electrolyte, ITP was not useful for analyzing rareearth ores containing both Y and Dy. In order to improve this defect we have recently developed a new leading electrolyte by adding tartaric acid to the previous leading electrolyte as a helping complexing agent.' This paper aims to confirm the utility of the abovementioned electrolyte system in the analysis of rare-earth ores containing Y as one of the major component...

One‐dimensional simulation of lanthanide isotachophoresis using COMSOL

“…One strategy for rare earth metal separation is through electrokinetic techniques such as capillary zone electrophoresis (CZE) and isotachophoresis (ITP). Both CZE [] and ITP [] have been used for rare earth metal separations; they take only a matter of minutes to separate many different analytes []. The method chosen for investigation in this paper is ITP because of its ability to concentrate analytes.…”

“…Many different ligands have been used in the literature for complexation with Ln including HIBA [], citric acid [], ethylenediaminetetraacetic acid [], lactic acid [], or a combination of multiple complexing agents []. For this study, HIBA has been selected as the primary binding ligand due to the variety of literature examples using HIBA and because the β for the reactions between HIBA and the individual Ln are given through the National Institutes of Standards and Technology as log( β ) values [].…”