Determination of calcium fluoride in fluorite by X-ray fluorescence spectrometry with fusion sample preparation after separation by calcium-containing acetic acid
YUAN Yonghai, YANG Feng, WU Jie, LI Bo, FANG Guicong, WEN Meilan
Guangxi Key Laboratory of Hidden Metal Mineral Exploration,Guilin University of Technology,Guilin 541006,China
Abstract：The main component of fluorite is calcium fluoride, and its content is the main index to determine the grade of ore. During the determination of calcium fluoride by X-ray fluorescence spectrometry (XRF), calcium carbonate and other fluorides in fluorite will have interference, thus influencing the determination results. The fluorite sample was dissolved with calcium-containing acetic acid(containing 0.02 mol/L Ca2+). The residue was retained after filtration and then calcined to constant weight. The acid dissolution reduction was corrected by mass correction coefficient method. Consequently, a method for determination of calcium fluoride in fluorite by XRF was established with calcium spectral line as the analytical line. The results showed that the prepared fuse pellet were uniform and transparent under the following conditions: the mixture of lithium tetraborate and lithium metaborate (mLi2B4O7∶mLiBO2=7∶3) was used as the flux; the dilution ratio of flux to sample was controlled as 20∶1; ammonium bromide solution was selected as the release agent; the sample was pre-oxidized at 650 ℃ for 5 min, and then fused with shaking at 1 100 ℃ for 8 min. The certified reference materials of fluorite and artificially synthesized calibration samples were used to prepare the calibration curve with calcium fluoride content in range of 12.17%-94.91%(mass fraction, the same below) and correlation coefficient of 0.999 8. The limit of detection of method was 0.21%. The contents of calcium fluoride in certified reference materials and actual samples of fluorite were determined according to the proposed method. The relative standard deviations (RSD, n=6) were all less than 1.0%. The contents of calcium fluoride in eight fluorite samples were determined according to the proposed method and EDTA titration method specified in GB/T 5195.1-2017, and the determination results were consistent.
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