Features of determination of native carbon in carbon-containing rocks on the analyzer of carbon and water

Abstract

The largest deposits of graphite in the Russian Federation are located in the Middle and South Urals. However, several manifestations, e.g., «Opytnyi» sector, which have not yet been placed under production, require substantiation of the strategies for their integrated development, which, in turn, requires gaining the reliable data on the content of graphite in carbon-containing rocks. A method for simultaneous determination of organic and native carbon in carbon-containing rocks using an ELTRA CW MULTIPHASE carbon and water analyzer is proposed. The method is based on the combustion of organic carbon (coal, shale) in a stream of oxygen at 550°C and native carbon (graphite) in the temperature range 550 – 1000°C with subsequent IR-spectroscopic determination of the content of gaseous carbon dioxide. The interfering effect of magnesium carbonate and calcium carbonate on the determination of organic and native carbon was taken into account in the calculations. The carbonate content was determined using a separate sample in a nitrogen flow by decomposition of magnesium carbonate at 550°C and calcium carbonate within a temperature range of 550 – 1000°C. The content of chemically bound water in the composition of the minerals of carbon-containing rocks, was determined simultaneously with carbon. The only one type of carbon — graphite — was observed in the studied samples of the carbon-containing rock from «Opytnyi». The different combustion capacity of graphite was revealed: some of the crystals almost completely burn out at a temperature below 800°C and others above 800°C, which suggests the presence of cryptocrystalline and explicit crystalline graphite in the rocks. The developed method is rapid and corresponds in accuracy to the method for native carbon determination ±0.27 C % – 0.01 C % developed and approved by the Research Council for Analytical Methods of Research (NSAM).