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土壤和岩石矿物中氟元素分析测试技术研究进展

A Review of Research Progress on Analysis and Testing Technology of Fluorine in Soil and Rock Minerals

  • 摘要: 准确测定土壤和岩石矿物中氟元素含量,对于评估区域性地球化学行为和预防人类氟相关病症具有重要的意义。本文阐述了近年来土壤和岩石矿物中氟元素分析测试技术研究进展,重点对样品前处理方法、试剂和流程进行了归纳总结,对不同检测方法的基体校正、干扰控制、性能及应用现状等进行评述,分析了不同测试技术的特点与不足,展望了其未来发展方向。目前常用的前处理方法主要有粉末压片法、熔片法、水蒸气蒸馏法、高温燃烧水解法、碱熔法和酸溶法等,常用的测定方法主要有离子选择电极法、离子色谱法、X射线荧光光谱法(XRF)、分光光度法、比色法和液相色谱法等。其中碱熔-离子选择电极法和粉末压片XRF法经分析测试工作者不断探究和改进,已是土壤和岩石矿物中氟元素分析广泛应用的测试技术。但碱熔法存在试剂消耗量大、流程长,步骤繁琐以及阳离子干扰等缺点,优化测试技术方法还需要进一步研究和实践;粉末压片法为无损进样,简单快速环保,具有潜在的研究价值,使用XRF法能够实现多元素联测,在稳定性和精密度方面具有显著的优势,降低方法检出限、消除粒度效应和矿物效应将是未来XRF法测定氟的研究趋势之一;其他前处理方法因步骤繁琐、前处理设备昂贵以及只能处理特定类型样品等因素的制约,或因测试方法的局限性制约其发展,暂不作推荐。由于氟属于轻元素以及赋存形式复杂多样等特殊性,需要针对样品类型的特点选择相适应的分析测试技术。本文认为,对于土壤和岩石矿物中氟含量分析测试技术,样品无损分析、安全环保、快速等是前处理方法研究的主要方向,同时能够建立多元素联测、检出限低以及稳定性好的测试方法是测试技术研究的主要方向,综合来说粉末压片-XRF法测定土壤和岩石矿物中氟具有重要的研究价值。

     

    Abstract: Fluoride is one of the important trace elements of human life and health. A proper amount of fluoride is beneficial to health. Excessive intake of fluoride will lead to dental fluorosis, bone fluorosis and urolithiasis, and serious excessive intake will affect the human central nervous system, endocrine hormone levels and reproductive system. The same lack of fluorine can also cause dental caries, Kaschin-beck disease signs and osteoporosis symptoms and cause hematopoietic dysfunction. Due to the chemical characteristics of fluorine, the forms of fluorine in the natural environment are very complex, and the transformation between different forms needs further study. How to quickly and accurately determine the content of fluorine in soil, rocks and minerals is of great significance for evaluating regional geochemical behavior and preventing fluorine-related diseases in humans.In this paper, the research progress of fluorine analysis and testing technology in soil, rocks and minerals in recent years is described. The methods, reagents and processes of sample pretreatment are summarized. The matrix correction, interference control, performance and application status of different testing methods are reviewed. In order to ensure the accuracy and reliability of the test results, it is necessary to eliminate the interference of metal cation, matrix effect and particle size validity, select the appropriate pretreatment and detection technology, reduce the detection limit, and constantly improve the accuracy and precision of the test.At present, the commonly used pretreatment methods mainly include pressed powder pellet, fusion, steam distillation, high temperature combustion hydrolysis, alkali fusion and acid dissolution. Among them, the pressed powder pellet method is simple, employs nondestructive analysis, has high sample preparation efficiency, and can meet the requirements of pretreatment of fluorine in large quantities of soil. The fusion method can effectively reduce the particle size effect and mineral effect, but different matrix samples need to use different oxidants, the preparation process is complicated, and requires high experience of the sample maker. Steam distillation and high temperature combustion hydrolysis are mainly used in rock sample treatment. The interference of metal ions can be effectively reduced by steam distillation or high temperature combustion hydrolysis. The test results of the samples treated by the alkali fusion method are stable and widely used, but there is metal ion interference, which leads to low fluorine test results. The acid dissolution method is used mainly for the decomposition of some specific ore samples, such as phosphate ore, and is rarely used at present.The commonly used determination methods include the ion selective electrode method, ion chromatography, XRF method, spectrophotometry, colorimetric method and liquid chromatography. Among them, the ion selective electrode method is mature and widely used because of its high accuracy and good stability. The detection limit of ion chromatography is low, but the test efficiency is low. X-ray fluorescence spectrometry uses lossless injection, simple environmental protection and can measure multiple elements at the same time. The colorimetric method is not accurate enough, the stability of the method is poor, the analysis steps are more complicated, and it is not suitable for the analysis of daily samples. Liquid chromatography is rarely used at present because of the expensive pretreatment equipment. At present, the alkali fusion method (accounting for 26%) is widely used as the most important pretreatment means, but it has many shortcomings, such as large reagent consumption, long process, complicated steps and cationic interference. Further research and practice are needed to optimize testing techniques and methods. The high temperature combustion hydrolysis method (accounting for 13%) and steam distillation method (accounting for 18%) can reduce cationic interference, but their cumbersome steps and special expensive equipment are currently used less. The ion selective electrode method accounted for more than one third of the test methods. Currently, the pre-treatment method using alkali fusion-ion selective electrode method is one of the most effective test technologies for the determination of fluorine content in soil, rocks and minerals.Pressed powder pellet method (accounting for 17%) has potential research value because of its unique non-destructive injection, simple, fast and environmental protection, and the matching XRF method (accounting for 29%) can realize multi-element combined measurement, which has significant advantages in stability and precision. The future research direction of fluorine determination by X-ray fluorescence spectrometry will be how to reduce the detection limit of the method and eliminate the particle size effect and mineral effect. Other analysis and testing techniques are not recommended because of cumbersome procedures, expensive pre-treatment equipment, only certain types of samples can be processed, and limitations of testing methods.As fluorine is a light element and its occurrence forms are complex and diverse, it is necessary to select appropriate analysis and testing techniques according to the characteristics of sample types.The main research directions of fluorine analysis and testing technology in soil, rocks and minerals and pretreatment methods are focused on non-destructive analysis of samples, safety and environmental protection, rapid and other aspects, and the main research directions of testing technology are focused on the establishment of multi-element simultaneous determination. In conclusion, the determination of fluorine in soil, rocks and minerals by pressed powder pellet-X-ray fluorescence spectrometry has important research value.

     

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