Scandium (Sc) geochemistry in coals (Siberia, Russian Far East, Mongolia, Kazakhstan, and Iran)

• The work examines the coals of Northern Asia:
• concentration, distribution, and accumulation of scandium in coals
• reasons of Sc variations in coals of different age
• origin of Sc in the coals in the studied regions.

This research discusses new original data on the geochemistry of scandium (Sc) in the coals of the Asian region of Russia, Mongolia, Kazakhstan, and Iran. In general, the studied coals are enriched in Sc compared with the mean value for coals throughout the world. In different regions of the studied territory, coal deposits with anomalous Sc concentrations (up to commercially important concentrations) were found and the factors that control the Sc contents in those coals were revealed. The composition of the rock types that surround the coal-forming basins and the hydro-geochemical conditions of these basins and deposits determine the levels of Sc accumulation in the coals. It was found that Sc was redistributed and partially lost from the seams during coal metamorphism. Studies of the modes of Sc occurrence in the coals showed the predominance of an organic mode. In addition, the peculiarities of the Sc distribution in the deposits and coal seams indicate a predominantly hydrogenous mechanism for the accumulation of anomalous Sc concentrations in coal and peat. Scandium in coal and peat accumulates by leaching from coal-bearing strata and re-deposition in coal (peat) beds with the participation of soil and ground water enriched with organic acids. Specific conditions for the formation of coal containing Sc-enriched rocks and for the Sc leaching and transportation into coal seams are necessary for the accumulation of high Sc concentrations in the coals. Such conditions that occur in the contemporary mire ecosystems of Western Siberia could also have occurred in ancient basins of peat (coal) accumulation.