Determination of calcium fluoride in low-grade fluorite tailings by ion chromatography after alkali fusion
The accurate determination of calcium fluoride content in low-grade fluorite tailings is of great significance for the evaluation and improvement of comprehensive recycling process.The semi-quantitative component analysis of low-grade fluorite tailings sample was first conducted by wavelength dispersion X-ray fluorescence spectrophotometer(WDXRF)and X-ray diffractometer(XRD).It was found that fluorine mainly existed in the form of calcium fluoride,and the sample mainly contained silicon,aluminum,iron,calcium,magnesium,potassium,sodium,sulfur and manganese.4.0 g of potassium hydroxide and 0.35 g of potassium nitrate were used as flux.The sample was melted at 650 ℃ for 8 min and then leached with hot water.IC-Na pretreatment column was used to separate alkaline earth and transition metal cations such as aluminum,iron,calcium,magnesium and manganese.Thus,a method for determination of calcium flu-oride in low-grade fluorite tailings was established by alkali fusion-ion chromatography.The results showed that the mass concentrations of cations such as aluminum,iron,calcium,magnesium and manga-nese in test solution were all lower than 0.1 μg/mL after separation with IC-Na pretreatment column.Therefore,the interference of these elements with the determination could be ignored.The calibration curve was drawn with the mass concentration of fluorine ion as x-axis and its corresponding peak area re-sponse as y-axis.The results indicated that its correlation coefficient was 0.999 6 with calcium fluoride in range of 1-30 μg/mL.Two fluorite tailings samples and one reference material of fluorite ore were deter-mined according to the proposed method.Meanwhile,different amounts of high-grade fluorite ore certified reference material were added for recovery tests.The recoveries were between 96％and 104％.The pro-posed method was applied for determination of calcium fluoride in low-grade fluorite tailings samples and fluorite ore reference materials.The relative standard deviations(RSD,n=7)were between 0.54％and 1.5％.The results were consistent with those obtained by ion selective electrode method or the standard values.The proposed method was applicable for determination of calcium fluoride in low-grade fluorite tailings samples with mass fraction in range of 5％-60％.
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