Determination of Chromite by X-ray Fluorescence Spectrometry with Sample Preparation of a Lower-Dilution Fusion
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摘要: 铬铁矿属难熔矿物，目前对铬铁矿的分析以化学分析为主，方法成熟，但操作麻烦且步骤繁琐；而应用X射线荧光光谱法进行分析测定，一般都采用较高稀释比熔融制样，不利于低含量元素的测定。本文选用四硼酸锂+偏硼酸锂作为混合熔剂，与样品以20:1的稀释比熔融制样，利用波长色散X射线荧光光谱测定铬铁矿中多种元素(Cr、Si、Al、TFe、Mg、Ca、Mn)的方法。采用多种铬铁矿标准物质和人工配制标准物质制作工作曲线，理论α系数及康普顿散射内标法校正元素间的吸收-增强效应，方法精密度(RSD，n=10)为0.2%～5.3%。方法检出限低，如锰元素的检出限可低至60 μg/g；镁元素的检出限为225 μg/g，比文献采用高稀释比XRF测定的方法检出限(250 μg/g)要低。本方法通过选择有效的熔剂和较低的稀释比解决了铬铁矿的制样问题，熔剂的用量减少，称样量增加，提高了低含量元素分析的准确度，相应地降低了分析成本。Abstract: Chromite analysis is dominated by chemical analysis, which is a wel-established but complicated procedure. Chromite can also be analysed by X-ray Fluorescence Spectrometry (XRF), however, a high-dilution fusion is not conducive to low content elements. In this paper, a method is reported for the determination of multi-elements (Cr, Si, Al, TFe, Mg, Ca and Mn) in chromite by Wavelength Dispersive X-ray Fluorescence Spectrometry with a low-dilution fusion for Li2B4O7 and LiBO2-mixed flux (20:1 reagent to sample). Also discussed in this paper is the effective flux of molten chromite. The working curve was established by a variety of chromite standard substances and manual preparation of standard materials. The inter-element effect was corrected by using the theoretical alpha coefficient with Compton scattered radiation. The results are consistent with the certified values and RSD (n=10) range from 0.2% to 5.3%. The detection limit of Mn is 60 μg/g. The detection limit of Mn by this method is as low as 225 μg/g which is lower than the previous reported limit of 250 μg/g reported elsewhere. By selecting the effective flux and low dilution ratio, the problem of chromite sample preparation has been solved, which reduces the amount of flux, increases the sample weight, improves the analysis accuracy for low content elements and reduces the cost of analysis.
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Key words:
- chromite /
- X-ray Fluorescence Spectrometry /
- fusion sampling /
- 20: 1 of dilution ratio
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表 1 元素的测量条件
Table 1. Measuring condition of elements by XRF
元素 分析线 分析晶体 准直器
/μm探测器 电压
U/kV电流
i/mA2θ/(°) t/s PHA 峰值 背景 峰值 背景 LL UL Cr Kα LiF200 150 F-PC 60 60 69.389 70.509 20 10 15 69 Al Kα PE002 550 F-PC 30 120 145.079 140.504 26 12 22 78 Fe Kα LiF200 150 F-PC 60 60 57.501 55.501 20 10 15 72 Ca Kα LiF200 150 F-PC 30 120 113.149 112.148 30 10 30 73 Si Kα PE002 550 F-PC 30 120 109.202 111.365 30 14 24 78 Mn Kα LiF200 150 F-PC 60 60 62.979 64.638 30 10 15 72 Mg Kα PX1 550 F-PC 30 120 22.988 24.720 36 12 36 66 12.121 12 注：PHA为脉冲高度分析器，LL为下限，UL为上限。 
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表 2 校准曲线各元素的含量范围
Table 2. The content range of elements in calibration curves
元素 含量范围w/% Cr 3.44~39.55 Si 0.51~16.09 Al 0.71~7.08 TFe 5.50~17.58 Mg 5.92~21.78 Ca 0.093~1.19 Mn 0.078~0.22
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表 3 方法检出限
Table 3. Detection limits of the method
元素 检出限/(μg·g-1) 理论值 测定值 Cr2O3 182 1170 SiO2 231 510 Al2O3 186 420 TFe 55 240 MgO 175 225 CaO 166 210 MnO 78 60
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表 4 方法精密度
Table 4. Precision tests of the method
元素 GSB D33001.4-94 GBW 07819 GBW 07818 w/% RSD/% w/% RSD/% w/% RSD/% Cr 34.81 0.2 23.60 0.3 12.00 0.3 Si 1.64 1.1 5.69 1.0 9.49 1.0 Al 6.99 0.3 6.04 0.3 6.31 0.3 TFe 12.59 0.3 8.25 0.3 7.45 0.3 Mg 5.98 0.2 14.03 0.2 16.89 0.2 Ca 0.09 5.3 0.21 5.1 0.29 5.1 Mn 0.33 0.9 0.07 1.0 0.07 1.0 注：w为10次测量的平均值。
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表 5 方法准确度
Table 5. Accuracy tests of the method
元素 GBW 07201 GSB D33001.2-94 GBW 07818 标准值 测定值 标准值 测定值 标准值 测定值 Cr 33.83 33.80 26.55 26.49 12.04 11.97 Si 1.90 1.86 4.49 4.42 9.47 9.41 Al 6.41 6.43 6.76 6.78 6.28 6.33 TFe 11.44 11.49 17.58 17.53 7.40 7.45 Mg 9.40 9.45 7.75 7.79 16.87 16.91 Ca 0.26 0.23 0.54 0.56 0.31 0.30 Mn 0.22 0.21 - 0.12 0.09 0.08
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