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

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

Determination of Sulfur in Different Types of Geochemical Samples by ICP-OES with Acid Dissolution and Combustion-Infrared Absorption Spectrometry

BACKGROUND： Inductively coupled plasma-optical emission spectrometry (ICP-OES) and combustion-infrared absorption spectrometry are the most widely used methods to measure sulfur content in geological samples. The ICP-OES method has high sensitivity and good stability, but it is greatly affected by sample pretreatment and matrix interference. Combustion-infrared absorption spectrometry is convenient and efficient, but due to the interference of crystal water infrared absorption, the analysis of samples with low sulfur content has poor stability. OBJECTIVES： To study the application scope of the two methods in geological sample analysis. METHODS: The sulfur content of samples was determined by ICP-OES and combustion-infrared absorption spectrometry. The detection limit, detection range, precision, accuracy and analysis efficiency of the two methods was compared in order to study and understand the performance of the two methods in sulfur measurement of geological samples. RESULTS: The best test condition of combustion-infrared absorption spectrometry was determined thus: optimal sample weight of 0.0500g, combustion time of 25s, analysis time of 40s and oxygen analysis flow rate of 4.0L/min. The detection limit of combustion-infrared absorption spectrometry was 10×10-6 and the detection range was 10×10-6-470000×10-6. The accuracy relative standard deviation (RSD) of the method was less than 6% (n=12) and the absolute value of relative error was less than 8%. CONCLUSIONS: For the analysis of low-sulfur samples, ICP-OES method can be used to analyze or compare, and multi-element simultaneous measurement can be determined. Batch samples or samples with a complex matrix can be analyzed by combustion-infrared absorption spectrometry, which is more convenient and efficient

Determination of Iodine in Geochemical Samples by ICP-MS with Sodium Carbonate-Zinc Oxide Semi-melting

BACKGROUND： The determination of iodine in geochemical samples by inductively coupled plasma-mass spectrometry (ICP-MS) is treated mainly by closed sample melting, mixed acid solution, alkali fusion and semi-melting method. However, due to the complex existent morphology of iodine in soil and sediment samples, including periodate, iodate and iodide ions, and the first ionization energy of iodine being high as a halogen group element, there are problems such as incomplete dissolution, strong memory effect and poor precision during sample processing and measurement. OBJECTIVES： To improve the determination of iodine in geochemical samples by ICP-MS. METHODS: The samples were treated by sodium carbonate-zinc oxide semi-melting method, extracted with boiling water-ethanol, and separated by 732 cation exchange resin. Following this, iodine in the solution was determined by ICP-MS using an internal standard method. RESULTS: The optimized detection limit of iodine was 0.045μg/g, the lower limit of detection was 0.15μg/g. The precision (RSD, n=12) and the accuracy (△logC) of the method were ≤5.93% and ≤0.01, respectively, which satisfied the analysis standards of geochemical survey sample. CONCLUSIONS: This method meets the requirements of sample analysis for geochemical investigation, and can be used for the analysis of iodine in large quantities of soil and sediment samples

Catalysts for conversion of synthesis gas

A more comprehensive exploitation of biosources could be assured by the conversion of biofuels to valuable chemicals. The syngas, obtained by hydrocarbons reforming process, represents the most important reactants mixture for other processes devoted to the production of methanol, higher hydrocarbons (Fischer-Tropsch synthesis), and ammonia.The first two processes are very similar, since they involved main components of syngas in exothermic processes in which a more complex compound is achieved; they are promoted at high pressure and low temperature, for which anyway other side reactions occur (mainly methanation), and each reaction could be considered side-reaction for the other. Such observation remarks the relevance of the catalytic system that should enable desired reactions in the selected operating system. In particular, the Fischer-Tropsch synthesis is widely carried out on cobalt-based catalysts at low temperature, achieving long-chain hydrocarbons as main products; conversely, if low chain is preferred, iron-based catalyst could be employed. Methanol catalysts were effectively developed in the 1960s, in which Cu-ZnO-based formulations appeared very promising both in terms of activity and selectivity.Ammonia synthesis utilized hydrogen obtained by syngas purification (WGS, PROX, and PSA), reducing nitrogen to NH3: such process is thermodynamically promoted at low temperature and high pressure. Iron catalysts are currently used in industrial plants. For all these processes, the very high operating pressure was reflected in a limited catalyst lifetime, so nowadays, studies are focusing in the ability to enlarge catalyst lifetime, by doping active phases or supports.Globally, the exothermic nature of these processes suggests to investigate the effect of highly thermal conductive structured carrier, in order to have a better thermal management in the catalytic volume that could reduce hot spot risks and in turn assure a more stable behavior