Determination of Major Components in Rock Salt by X-ray Fluorescence Spectrometry with Sample Fusion
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摘要: 以XRF分析岩盐,需解决标准物质缺乏和Cl在分析过程中的损失问题,选择合适的前处理方法以保证结果重现性。经实验发现用于粉末压片法的人工标准物质中氯化钠、硫酸钙等组分经X射线照射后呈现向样片表面扩散的趋势,其中氯化钠进一步分解,难以建立稳定的工作曲线;熔融制样则不存在这一问题,具备定量基础。本文选择熔融制样作为前处理方法,将光谱纯盐类、氧化物与土壤、水系沉积物国家标准物质以不同比例混合,配制人工标准物质建立工作曲线。熔融制样条件为:取样量0.6000 g,四硼酸锂+偏硼酸锂(12:22)混合熔剂10.000 g,熔融温度1000℃,预熔时间300 s,熔样时间300 s,静置时间30 s,所得样片平整通透,因样品中所含Cl具有脱模效果无需补充脱模剂。本方法测定主量元素的精密度(RSD)均小于1.5%,与经典方法相比减少了分析时间与试剂消耗,可作为岩盐主量成分分析的备选方法。Abstract: The lack of reference materials, and chlorine loss are two of the problems that need to be solved in order to aid the determination of major components in rock salt by X-ray Fluorescence Spectrometry. It is important to select an appropriate sample pretreatment method to ensure reproducibility and it has been demonstrated that sodium chloride, calcium sulfate and other components in synthetic calibration materials for the pressed pellets method show a tendency of diffusion towards the pellet surface when samples are exposed to X-ray irradiation. Moreover, the decomposition of sodium chloride makes it difficult to obtain a stable calibration curve. The fusion bead method, however, does not exhibit these problems. In the study documented in this paper, samples were prepared by the fusion method. Synthetic calibration materials used for standard curve establishment were prepared by mixing spectrum pure salts/oxides with sediment/soil reference materials. 0.6 g of sample was fused by 10 g of mixing flux of lithium tetraborate and lithium metaborate (12:22) at 1000℃ for 300 s pre-fusion and for another 300 s fusion, followed by 30 s standing. The resulting glass disk was flat and transparent. No extra release agent was added because the samples contained chlorine. Analytical results of the major components in salt rock yielded a precision of less than 1.5% (relative standard deviation). This method shortens the analysis time and reduces the reagent consumption compared with the traditional method, which is an alternative method for analyzing major components in salt rock.
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表 1 XRF仪器测量条件
Table 1. Measurement parameters of XRF instrument
通道 谱线 晶体 准直器(μm) 探测器 管电压(kV) 管电流(mA) 2θ(°) 背景(°) PHD LL UL Na Kα PX1 700 Flow 25 144 27.75 25.96 29.56 20 75 Mg Kα PX1 700 Flow 30 120 22.96 20.88 25.09 25 75 Ca Kα LiF200 300 Flow 40 90 113.13 115.30 - 30 70 K Kα LiF200 300 Flow 40 90 136.71 140.41 - 30 70 S Kα Ge111 300 Flow 25 144 110.68 108.16 - 30 70 Cl Kα Ge111 300 Flow 25 144 92.83 91.04 - 30 70 Si Kα PE002 300 Flow 30 120 109.10 111.02 - 20 75 Al Kα PE002 300 Flow 30 120 144.92 143.55 - 22 78 Fe Kα LiF200 300 HiperScint 40 90 57.51 58.38 - 15 78 注： Na、Mg设置两点背景，其余元素设置单点背景。 
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表 2 人工标准物质元素含量范围
Table 2. Concentration ranges of components in synthetic calibration materials
组分 含量(%) 组分 含量(%) Na 6.599~20.130 Cl 10.110~30.330 Mg 0.125~6.620 SiO2 9.950~27.630 K 0.786~15.300 Al2O3 1.823~3.687 Ca 1.191~17.796 Fe2O3 0.487~1.463 SO4 9.188~35.119
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表 3 本方法与岩盐经典分析方法的比较
Table 3. Comparison of analytical results of salt rock samples obtained by this method and traditonal methods
实际样品编号 Na含量(%) Mg含量(%) K含量(%) Ca含量(%) Cl含量(%) SO4含量(%) XRF FAAS XRF FAAS XRF FAAS XRF EDTA容量法 XRF 硝酸银容量法 XRF 重量法 1 33.23 31.22 0.12 0.066 0.01 0.032 4.64 4.52 50.88 48.85 10.52 9.77 2 37.8 41.86 0.06 0.018 0.07 0.085 1.29 1.30 57.55 55.11 3.13 2.62 3 27.17 26.85 0.39 0.26 0.04 0.033 8.89 8.81 41.7 40.34 19.15 19.12 4 28.53 28.92 0.29 0.20 0.06 0.04 7.48 7.69 43.2 42.25 17.22 17.53 5 38.86 38.00 0.05 0.01 0.02 0.038 0.37 0.37 59.38 57.63 0.86 0.94
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