Simultaneous Determination of Fluorite, Barite and Celestite in Rare Earth Ores by X-Ray Fluorescence Spectrometry after Fusion Sample Preparation

A method for simultaneous determination of contents of fluorite, barite and celestite in rare earth ores was established by X-ray fluorescence spectrometry (XRFS) after fusion sample preparation. The sample powder was prepared through DZ/T 0130.2-2006, and calcium sulfate in the sample was dissolved by 150 mL water with magnetic stirring. After standing still, part of the supernatant was discarded, the remaining solution volume was about 30 mL. The same volume of acetic acid solution containing calcium and strontium as the remaining solution was added and kept boiling slightly for 5 min on the electric hot plate, the same volume of ethanol as the remaining solution was added, and the mixed solution was kept steady condition and filtered, thus to remove the interference from calcium carbonate, barium carbonate and strontium carbonate. The filter paper together with precipitate was transferred into a Pt-Au crucible and dried. The crucible was placed into a muffle furnace for ashing at 800 ℃, and silica was added until the ash mass reached 0.800 0 g. Mixed flux (8.000 0 g) composed of lithium tetraborate and lithium metaborate with mass ratio of 12:22 and 0.1 g release agent of ammonium iodide were added for melting at 1 100 ℃ for 620 s, and the glassy slice of sample was analyzed under the optimal XRFS instrument working conditions. The series of standard samples by mixing pure substances and standard substances were prepared to make calibration curves, matrix effect was calibrated with the basic parameter method, and the contents of calcium oxide, barium oxide and strontium oxide were calculated and converted to those of calcium fluoride, barium sulfate and strontium sulfate to characterize the content of fluorite, barite and celestile. The results showed that correlation coefficients of standard curves were above 0.999 5; the proposed method was used for the analysis of self-made samples and actual samples, with the determined values basically consistent with the known values of the self-made samples and RSDs (n=6) of the determined values of the actual samples not more than 2.0%.