Tian Xiao, Zhao Lei
College of Geoscience and Survey Engineering, China University of Mining and Technology (Beijing), Beijing, 100083, China.
College of Geoscience and Survey Engineering, China University of Mining and Technology (Beijing), Beijing, 100083, China; State Key Laboratory for Fine Exploration and Intelligent Development of Coal Resources, Beijing, 100083, China.
Talanta. 2024 Jan 1;266(Pt 1):124919. doi: 10.1016/j.talanta.2023.124919. Epub 2023 Jul 10.
Concentrations of trace elements in coal and coal combustion products are commonly analyzed by inductively coupled plasma-mass spectrometry (ICP-MS) due to large number of elements detected and the relatively the low detection limits of this technique. Like other geological samples, complete dissolution of coal and coal combustion products is also essential for accurate ICP-MS results. In this study, Sr and Ba in coal and coal combustion products (fly and bottom ashes) from two coal-combustion power plants from North China analyzed by XRF and ICP-MS were comparatively studied. The concentrations of Sr and Ba analyzed by ICP-MS, when a mixture of acids (2 ml HF + 5 ml HNO for each 50 mg coal sample and 5 ml HF + 2 ml HNO for each 50 mg ash sample) was used for microwave-assisted digestion, do not fit well with the their relative XRF results. This is most probably due to the formation of the fluorides during microwave digestion, and this assumption is supported by the presence of various fluoride compounds, NaMgAl(F, OH)·HO, NHMgAlF, AlF, and KSiF, in the residues of all the coal and ash samples in our sequential extraction experiment. Cations of Sr and Ba were probably trapped into the divalent cation sites of the fluorides. Concentrations of Sr and Ba analyzed by ICP-MS using increased HF and HF/HNO ratio (7 ml HF and 2 ml HNO for each 50 mg coal/ash sample) are in better agreement with the XRF results. Our results indicate that excess amount of HF probably has led to the suppression of these elements due to fluoride precipitation. The results indicate that the modified digestion method is capable of achieving complete digestion of coal samples and results in a reliable analysis of Sr and Ba concentrations in coal samples and most fly ashes by ICP-MS. However, the formation of insoluble fluorides is probably not completely suppressed for some bottom ash samples, which can result in underestimation of Sr and Ba concentrations. Nevertheless, XRF analysis can serve as a reliable cross-check method to assist in the evaluation of the accuracy of ICP-MS results.
由于电感耦合等离子体质谱法（ICP-MS）能够检测大量元素且检测限相对较低，因此常用于分析煤和煤燃烧产物中的微量元素浓度。与其他地质样品一样，煤和煤燃烧产物的完全溶解对于获得准确的ICP-MS结果也至关重要。在本研究中，对华北地区两家燃煤电厂的煤和煤燃烧产物（飞灰和底灰）中的锶（Sr）和钡（Ba）进行了对比研究，分析方法采用X射线荧光光谱法（XRF）和ICP-MS。当使用混合酸（每50mg煤样加入2ml氢氟酸（HF）+5ml硝酸（HNO₃），每50mg灰样加入5ml HF+2ml HNO₃）进行微波辅助消解时，通过ICP-MS分析得到的Sr和Ba浓度与XRF相对结果不太吻合。这很可能是由于微波消解过程中形成了氟化物，我们的连续萃取实验中所有煤和灰样的残渣中存在各种氟化物化合物，如NaMgAl(F, OH)·H₂O、NH₄MgAlF₆、AlF₃和K₂SiF₆，这一假设得到了支持。Sr和Ba的阳离子可能被困在了氟化物的二价阳离子位点中。使用增加HF和HF/HNO₃比例（每50mg煤/灰样加入7ml HF和2ml HNO₃）的方法通过ICP-MS分析得到的Sr和Ba浓度与XRF结果更吻合。我们的结果表明，过量的HF可能由于氟化物沉淀导致这些元素被抑制。结果表明，改进后的消解方法能够实现煤样的完全消解，并通过ICP-MS对煤样和大多数飞灰中的Sr和Ba浓度进行可靠分析。然而，对于一些底灰样品，不溶性氟化物的形成可能没有被完全抑制，这可能导致Sr和Ba浓度被低估。尽管如此，XRF分析可以作为一种可靠的交叉检验方法，有助于评估ICP-MS结果的准确性。
