波长色散X射线荧光光谱法测定高铬土壤中Cr含量及Cr形态的影响研究

Wavelength-Dispersive XRF Analysis of Total Cr and the Effects of Cr Speciation in High-Chromium Soils

  • 摘要: 随着铬在工业领域使用量激增及污染排放持续加剧,众多区域土壤中铬(Cr)含量显著升高。X射线荧光光谱法(XRF)具有前处理简单、多元素同时测定、测量元素含量范围宽等特点,但该方法在测定 Cr 污染土壤时,存在的标准物质浓度梯度不足、矿物效应、粒度效应以及吸收增强效应等问题,均会影响Cr及多元素测定的准确度。本文以国家土壤标准物质(GBW系列)作为基础基质,通过添加K2Cr2O4 (Cr6+)和CrCl3·6H2O (Cr3+)配制24个梯度浓度的人工标样,将人工标样与国家土壤标准物质结合用于校准曲线制作,有效弥补了现有标准物质浓度梯度不足的问题,使校准范围更契合高 Cr 污染土壤的检测需求。本文通过实验论证了三价铬(Cr3+)和六价铬(Cr6+)在测量角度、分辨率、灵敏度等方面对分析结果的影响。结果表明Cr3+和Cr6+的测量角度存在微小差异,同一件样品在Cr3+和Cr6+特征峰角度下测量,计数率相差很小,可以忽略;两者的分辨率和灵敏度无明显差异。使用该方法测定标准物质,其相对误差小于10%,相对标准偏差(RSD)小于5%,并分析了某铬渣场及其周边区域实际土壤样品,Cr测定结果与ICP-OES法测试结果的相对误差在10%以下。采用波长色散XRF分析,发现Cr3+和Cr6+的峰位角度存在明显差异,对应能量漂移约0.39 eV,且Cr6+的峰位能量低于Cr3+,与文献报道的能量位移值相符,揭示本方法具有土壤中Cr形态分析的理论基础。本方法不仅能够准确测定土壤中的总铬含量,还能同步分析 Na、Mg、Al、Si 等主次量元素,拓展了土壤金属元素检测范围,适用于各类土壤样品多元素定量分析,尤其适用于高 Cr 污染土壤中的多元素准确定量分析,为高铬土壤环境下多元素精确测定构建了更完备的方法体系。

     

    Abstract: With the surge in industrial use of chromium (Cr) and continuous intensification of pollution emission, Cr levels in soils across numerous regions have risen significantly. X-ray fluorescence spectrometry (XRF) offers advantages including simple sample preparation, simultaneous multi-element determination, and a broad analytical concentration range. However, when determining Cr-polluted soils, this method faces multiple challenges such as insufficient concentration gradients in certified reference materials (CRMs), mineral effects, particle size effects, and absorption-enhancement effects, all of which can impact the accuracy of Cr and multi-element determinations. These limitations are addressed by preparing 24 artificial standard samples across gradient concentrations via spiking low-Cr soil CRMs (GBW series) with K2Cr2O7 (Cr6+) and CrCl3·6H2O (Cr3+). Integrating these artificial standards with national soil CRMs for calibration curve development effectively compensates for the inadequate concentration coverage of existing CRMs, making the calibration range more suitable for the detection needs of high Cr-polluted soils. Experimental verification demonstrates the influence of trivalent chromium (Cr3+) and hexavalent chromium (Cr6+) on analytical results in terms of measurement angle, resolution, and sensitivity. There are slight differences in the measurement angles for Cr3+ and Cr6+, but the count difference for the same sample measured at their respective characteristic peak angles is negligible. No significant differences are observed in resolution and sensitivity. When applying this method to determine CRMs, the relative error (RE) is less than 10%, and the relative standard deviation (RSD) is less than 5%. Furthermore, analysis of actual soil samples from a Cr residue site and its surrounding areas in China shows that the RE of the Cr determination results are within 10% compared to those obtained by ICP-OES. Wavelength-dispersive XRF (WDXRF) analysis reveals a distinct difference in the peak angles between Cr3+and Cr6+, corresponding to an energy shift of approximately 0.39 eV, with the peak energy of Cr6+ being lower than that of Cr3+. This is consistent with the energy shift values reported in the literature, demonstrating the potential of this method for Cr speciation analysis in soils. The proposed method not only accurately determines the total Cr content in soil but also simultaneously analyzes major and minor elements such as Na, Mg, Al, and Si, thereby expanding the detection scope of soil metal elements. It is suitable for the quantitative multi-element analysis of various soil samples, especially for the accurate quantification of multiple elements in highly Cr-contaminated soils, establishing a more comprehensive methodological system for the precise multi-element determination in high-Cr soil environments. The BRIEF REPORT is available for this paper at http://www.ykcs.ac.cn/en/article/doi/10.15898/j.ykcs.202504010075.

     

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