Pxrf土壤重金属检测的影响因素、模式与校正方法

针对便携式X射线荧光光谱（Pxrf）法测定土壤重金属检测精度不足的问题，提出一种以Pxrf测定值及场地参数的特性关系为基础的通用建模方法和流程，用以构建适用于各场地特性的Pxrf校正模型，以提高Pxrf的测量准确度.以北京某典型矿区污染场地为例开展研究，选取土壤中Pb、Sr、Cu、Fe、Mn、Zn 6种重金属，通过潜在相关因子（土壤有机质含量、含水率、实际污染物含量）及其不同数学变换形式（指数、对数、幂函数的数学变换）与Pxrf测定值的相关分析，识别显著影响Pxrf测定值的影响变量、影响程度及影响形式；基于影响因子识别结果，建立其与Pxrf的数学模型表达式，实现Pxrf测定值校正，准确值提高的目的.结果表明：Pb、Cu、Zn 3种重金属的Pxrf测量值与实际浓度呈现显著相关，相关系数值为0.75~0.82；重金属Sr、Fe、Mn相关系数值为0.25~0.52，其相关性稍差.含水率对Pxrf检测影响程度从小到大排列依次为Sr、Mn、Cu、Pb、Zn，相关系数值范围为0.1~0.7.所有重金属的Pxrf测量值受土壤有机质含量影响弱，相关系数均低于0.5.经模式变换后，重金属Zn、Pb、Cu的Pxrf测量值与实际浓度相关性呈增大趋势（增大了4%~13%）；其他重金属无显著变化.模型校验结果显示，Pb、Zn、Cu、Mn四种重金属的模型可用来提高该场地Pxrf法检测精度.相较于原始Pxrf测量值，可用模型中经校正后的Pxrf值的相对误差从32.4%~56.6%降至4%~29.9%.

Influence factors,correction mode and method of heavy metal detection in Pxrf soil

In view of the problem that the portable X-ray fluorescence (pxrf) method is not accurate enough for the determination of heavy metals in soil, a general modeling method and process based on the relationship between the measured value of Pxrf and the characteristics of the site parameters are proposed, which is used to build a Pxrf correction model suitable for the characteristics of each site, so as to improve the measurement accuracy of Pxrf. Taking a typical mining area in Beijing as an example, By analyzing the correlation of potentially related factors (i.e., soil organic matter content, water content, and actual pollutant content) and different mathematical transformations of these factors (i.e., index, logarithm, and power function) with the measured values of Pxrf, we identified the influencing variables, influence degrees, and influence forms that significantly affect the measured values of Pxrf. Based on the identification of influencing factors, we established the mathematical model of Pxrf to achieve the purpose of correcting the measured value of pxrf and improving the accurate value. The results showed that the measured values of Pb, Cu and Zn were significantly correlated with the actual concentrations, and the correlation coefficients were 0.75~0.82; the correlation coefficients of Sr, Fe and Mn were 0.25~0.52, with slightly poor correlation. The influence of water content on the detection of Pxrf was in order of Sr, Mn, Cu, Pb, Zn, the correlation coefficient range was 0.1~0.7. The Pxrf of all heavy metals is weakly affected by the content of soil organic matter, and the correlation coefficient was lower than 0.5. After the model transformation, the correlation between the Pxrf of heavy metals Zn, Pb, Cu and the actual concentration increases (increased by 4%~13%); other heavy metals had no significant change. The model verification results showed that the correlation between the Pxrf of four heavy metals Pb, Zn, Cu, Mn Compared with the original Pxrf measurement, the relative error of the corrected Pxrf value in the model could be reduced from 32.4%~56.6% to 4%~29.9%.