X射线荧光光谱法测定地质样品中铌和钽的探讨

采用粉末压片制样,利用X射线荧光光谱仪(XRF)对地质样品中铌、钽的X射线荧光强度与含量关系进行了讨论。对低含量铌、钽的测量条件进行了优化,铌的检出限为1.0μg/g,钽的检出限为3.1μg/g;对水系沉积物标准样品GBW07311进行精密度考察,铌、钽测定结果的相对标准偏差(RSD,n=10)小于2.0%;对地质样品进行分析,测定值与电感耦合等离子体质谱法的结果相一致。当地质样品中铌含量高时,铌的谱线强度在峰值处下降,呈凹状,这是因为铌的含量过高使光管计数率达到上限溢出,从而引起元素本身出现自吸现象。实验通过选择低管电压和管电流(40kV-40mA)解决了自吸现象,此条件适用于大批样品的测试;而使用常规管电压和管电流(50kV-60mA),以Nb-Kβ(Ⅰ)作为分析线,则适用于少量样品的多种元素同时测定;对高含量铌、钽样品进行分析,测定值与重量法测定值一致。实验方法满足了地质样品中不同含量铌、钽的测试要求。

Discussion on the determination of niobium and tantalum in geological samples by X-ray fluorescence spectrometry

The sample was prepared with powder pressed pellet method. The relationship between fluorescence intensity and content of niobium and tantalum in geological samples during the determination by X-ray fluorescence spectrometry (XRF) was discussed. The determination conditions of low content niobium and tantalum were optimized. The detection limit of niobium and tantalum was 1.0 μg/g and 3.1 μg/g, respectively. The precision test was conducted by standard sample of stream sediment (GBW07311). The relative standard deviations (RSD, n=10) of determination results of niobium and tantalum were less than2.0%. The proposed method was applied to the analysis of geological samples, and the found results were consistent with those obtained by inductively coupled plasma mass spectrometry (ICP-MS). When the content of niobium in geological sample was high, the spectral intensity of niobium decreased at peak value with concavity, which was due to the overflow of counting rate caused by the excessive content of niobium. As a result, the element showed self-absorption phenomenon. This problem was solved in experiments by selecting low tube voltage and tube current (40 kV-40 mA). This condition was applicable for the test of large amount samples. If the conventional tube voltage and tube current (50 kV-60 mA) were used, the method was applicable for the simultaneous determination of multiple elements in few amount of samples using Nb-Kβ(I) as analytical line. For the analysis of high content niobium and tantalum, the found results were consistent with those obtained by gravimetric method. The proposed method could meet the analysis requirements of niobium and tantalum in geological samples with different contents.