熔融制样-X射线荧光光谱法测定萤石中氟化钙和二氧化硅

萤石广泛应用于钢铁工业,作为炼铁、炼钢的助剂,对萤石质量进行评价的主要指标是氟化钙和二氧化硅的含量。采用熔融制样-X射线荧光光谱法(XRF)测定萤石中氟化钙常采用氟谱线法和钙谱线法两种方法,若采用氟谱线法测定,会因无法消除萤石可能含有的氟化镁干扰,存在测定结果偏高的问题;若采用钙谱线测定,因测定得到的是钙的总量,还需再减去碳酸钙中钙量,方法较为繁琐。依据萤石中的碳酸钙可被稀乙酸溶解而氟化钙和二氧化硅不会被溶解的原理,采用10%(V/V)乙酸溶解样品后过滤,保留滤渣,实现了对样品中碳酸钙的分离。将残渣和滤纸灰化,将其与四硼酸锂-偏硼酸锂-氟化锂混合熔剂(m∶m∶m=65∶25∶10)、溴化钾混合熔融制成玻璃样片,实现了X射线荧光光谱法对萤石中氟化钙和二氧化硅测定。实验结果表明,氟化钙和二氧化硅校准曲线的线性相关系数达到0.997以上,方法中二氧化硅的检出限为0.089%。对萤石样品进行精密度考察,氟化钙和二氧化硅测定结果的相对标准偏差(RSD,n=12)分别不大于0.12%和0.92%。按照实验方法测定萤石标准样品和实际样品,标准样品中氟化钙和二氧化硅的测定值与标准值一致;实际样品中氟化钙的测定值与标准方法GB/T 5195.1—2017中EDTA滴定法测定值一致性较好,二氧化硅测定值与标准方法GB/T 5195.8—2017中硅钼蓝分光光度法测定值一致性较好。

Determination of calcium fluoride and silicon dioxide in fluorite by X-ray fluorescence spectrometry with fusion sample preparation

Fluorite is widely used in iron and steel industry as an auxiliary for iron and steel making. The main index to evaluate the quality of fluorite is the content of CaF₂ and SiO₂. The determination of calcium fluoride in fluorite by X-ray fluorescence spectrometry (XRF) with fusion sample preparation usually adopts two methods, i.e., fluorine spectrum method and calcium spectrum method. If the fluorine spectrum method is used, the determination results are usually higher due to the interference of magnesium fluoride which possibly existed in fluorite. If the calcium spectrum method was used, the determination result is the total amount of calcium, and the component of calcium carbonate should be subtracted, so the method is relatively complicated. Since calcium carbonate in fluorite can be dissolved by dilute acetic acid, while calcium fluoride and silicon dioxide cannot be dissolved, the sample was treated with 10% acetic acid in experiments. The residue was reserved after filtration, realizing the separation of calcium carbonate from the sample. The residue and filter paper were ashed and then fused with lithium tetraborate-lithium metaborate-lithium fluoride (m∶m∶m=65∶25∶10) mixed flux and potassium bromide for sample preparation. The determination of calcium fluoride and silicon dioxide in fluorite by XRF was realized. The experiment results showed that the linear correlation coefficients of calibration curves for calcium fluoride and silicon dioxide were above 0.997. The limit of detection of silicon dioxide of method was 0.089%. The precision of fluorite samples was investigated, and the relative standard deviations (RSD, n=12) of the determination results of calcium fluoride and silicon dioxide were not more than 0.12% and 0.92% respectively. The standard samples and actual samples of fluorite were determined according to the experimental method. The measured results of calcium fluoride and silicon dioxide in standard sample were consistent with the standard values. The measured results of calcium fluoride in actual sample were in good agreement with that obtained by EDTA titration in standard method GB/T 5195.1-2017, and the measured results of silicon dioxide were in good agreement with that obtained by silicon molybdenum blue spectrophotometry in standard method GB/T 5195.8-2017.