A new method for obtaining homogeneous samples for XRF analysis

A method for obtaining homogeneous samples of solid mineral fuel for X-ray fluorescence analysis. Sample preparation for XRF.

General information

Contacts

General information

Developer: Saint Petersburg Mining University

Industry

Chemistry, Ecology

Project Research Team

Head: Ivan Pavlovich Sverchkov Scientific Team: Yuri Dmitrievich Smirnov, Maria Alekseevna Chukaeva

Scientific novelty

A method for preparing solid mineral fuel samples for X-ray fluorescence analysis is disclosed, involving heating a mixture of the sample and flux in a crucible made of noble metals or their alloys; the resulting melt is molded with cooling to room temperature, wherein solid mineral fuel is used as the sample, which is ground to a size of less than 100 μm and placed in a crucible, at the bottom of which flux is pre-placed, using a mixture of lithium tetraborate and lithium metaborate in a ratio of 1:5 to 1:3 as the flux, then a non-wetting additive of lithium bromide is additionally introduced in an amount of 0.5% of the total mass of the solid mineral fuel sample and flux, after which the crucible is heated at a temperature of 800 to 830 °C in an oxidizing atmosphere with a heating rate of 10 to 20 °C/min and held until complete carbon oxidation, then additionally heated from 1000 to 1100 °C with a hold of 2 to 5 min and constant stirring, after which the melt is poured into platinum molds and cooled to room temperature

Advantages

The invention provides for obtaining samples for X-ray fluorescence analysis that are uniform in composition and reduces the preparation time for solid mineral fuel samples. Currently, the literature considers several methods for preparing samples with known concentrations, which consist of: 1. grinding and mixing pure oxides or other solid compounds of the elements to be determined; 2. adding pure solid compounds to standard samples. Such methods are well-suited for preparing artificial standard samples for major oxides when the content of the elements to be determined exceeds 1%. However, for elements with low content, this method is quite difficult to implement due to the small sample mass. For example, when obtaining a fused disk with a diameter of 40 mm and a sample/flux ratio of 1:10, 1 g of sample is required; to obtain a component content of 1%, 10 mg of pure substance must be taken. Such a weight is too small for most laboratory scales, and the weighing error is likely to be high; 3. preparing standard samples by mixing 2 or more solid standard samples in different proportions to obtain the required concentration of the elements to be determined; however, this method does not allow for obtaining samples with a concentration higher than the maximum concentration in one of the samples. In this case, the concentration of only one of the elements can be controlled; 4. sequential fusion, where a standard sample and pure compounds of the elements to be determined are fused separately with flux, then the fused samples are ground, mixed in the required ratio, and fused again. This method allows for obtaining artificial standard samples with concentrations higher than in the original standard samples, but it is long and labor-intensive. Also, with this preparation method for fused disks, the risk of sample contamination with foreign impurities increases due to a series of sequential fusion and grinding operations. For this reason, to expand the measurement range and refine calibration dependencies, it was decided to prepare multi-component standard samples by adding solutions with a known concentration of elements to standard samples. This work proposes a procedure for preparing standard samples for X-ray fluorescence analysis with the required element content. To evaluate the feasibility of using this method for preparing modified standard samples, a temperature program was selected and the metrological characteristics of the resulting artificial standard samples were evaluated.

Commercial implementation

The main region for the implementation of the development is universally in X-ray fluorescence analysis laboratories. Atomic absorption spectrometry, inductively coupled plasma atomic emission spectrometry, and inductively coupled plasma mass spectrometry are also used to analyze major, minor, and trace elements in rocks; however, these instrumental methods require long preliminary sample preparation associated with their conversion into solution, which can cause changes in the elemental composition of the sample. In addition, reagents toxic to the analyst are used to convert rock samples into solution. Given this, X-ray fluorescence analysis has numerous advantages, including simple and rapid sample preparation, no environmental pollution, and simultaneous analysis of a wide range of elements. Moreover, XRF spectrometers possess long-term stability, allowing for the analysis of samples with high precision and reproducibility over a long period of time. To take full advantage of this method, special attention must be paid to the sample preparation process and the construction of calibration dependencies. The content of the elements to be determined in the analyzed samples does not always fall within the concentration range provided by standard samples and goes beyond the boundaries of the calibration curve. One possible way to solve this problem is the preparation of modified standard samples. Sample preparation consisting of obtaining fused sample disks with fluxes allows for obtaining homogeneous samples compared to powder samples. Fused glass disks are suitable for both major and minor element determination, as such sample preparation reduces matrix effects, eliminates the influence of particle size on measurement results, and ensures sample uniformity.