The staff of the Frumkin Institute of Physical Chemistry and Electrochemistry of the Russian Academy of Sciences (IFHE RAS), together with colleagues from the Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry of the Russian Academy of Sciences (IGEM RAS) and the Mendeleev Moscow Art Technical University, have developed an innovative method for detecting low concentrations of rhenium in natural samples. This technique will make it possible to create express methods for the integral assessment of the rhenium content in new deposits.
New rhenium detection technique
Studies have shown that after laser ionization by the MALDI method of a rhenium-containing ore sample from the fumarole fields of Kudryavy volcano on Iturup Island (Russia), a mass spectrometric detector detected cluster formations of rhenium sulfides containing up to 10 metal atoms. The confirmed propensity of rhenium to form cluster compounds facilitates the assessment of its content using instrumental methods.
Rhenium is a unique metal with high refractoriness, hardness and ductility. It is indispensable in the aviation and aerospace industries, and is also used in alloys used at high temperatures and high loads. In addition, rhenium is used in catalysis, for example, for the production of high-octane gasoline. However, this rare chemical element is becoming more and more in demand.
Problems with rhenium deficiency
The rhenium deficiency is due to the fact that it does not form its own deposits. The metal is present as an impurity in molybdenum, tungsten-molybdenum, and copper-molybdenum ores, as well as in the fumarolic gases of volcanoes. Even in the richest ores, the rhenium content does not exceed 1 gram per ton.
Geologists often use laser ablation to determine the elemental composition of samples. This method allows you to vaporize a substance from the surface of a sample and transfer it to a plasma state for analysis using emission spectrometry or mass spectrometry. Although the method is very accurate, it does not allow us to draw conclusions about the integral content of a chemical element or about the form of its existence.
Advantages of the MALDI method
The MALDI method provides soft ionization, which makes it possible to determine the molecular shape of compounds. The mass spectrometric detector counts the number of ions with a certain charge-to-mass ratio and generates a mass spectrum. The peaks in the mass spectrum correspond to molecular ions, including clusters. The identification of compounds is carried out using a program developed at the Institute of Chemical Analysis of the Russian Academy of Sciences for the selection of probable gross formulas.
“We have created software to determine the correspondence of ions to peaks in the mass spectrum. This allows us to identify the composition of the molecule,” said Vyacheslav Lebedev, the author of the program.
Application prospects
Scientists are developing alternative methods for measuring the amount of rhenium in rocks for monitoring and calibrating MALDI mass spectrometric methods. Existing methods require the preliminary dissolution of poorly soluble compounds, which makes them time-consuming and expensive.
“Our goal is to create a library of mass spectra for inorganic compounds and refine the process so that dissolution is completely eliminated,” concluded Vyacheslav Lebedev.
The work was carried out with the financial support of the Ministry of Education and Science of Russia.