Potentially valuable microelements in coal balance reserves of JSC SUEK mining units

Abstract

There are no coal deposits whose content of potentially valuable microelements (PVE), except for uranium (U), is high enough to ensure economically viable production of commercial PVE compounds. This process should be based on by-products which are generated as a result of conventional use of coals – combustion, coking, gasification, etc., which concentrate PVEs. By-products which accumulate certain PVEs are called primary concentrates. These can then be used to produce commercial compounds or industrial PVE concentrates. The PVE content in coals from various deposits or different areas (seams) of the same deposit is considerably variable. For example, there are some deposits where the PVE content is several scores of times higher than their percentage abundance in coals. Coals of this type are called metal-bearing and serve as the main raw material for production of commercial PVE compounds. JSC SUEK is striving for integrated development of coal deposits. Areas containing metal-bearing coals have been identified in deposits which are operated by JSC SUEK in the Russian Far East, Kuzbass, Kansk-Achinsky coal basin, Zabaikalye and other basins where concentrations of some PVEs are several scores of times higher than their average content in coal. To date, we have acquired extensive information on patterns of formation and location of metal-bearing coals and their PVE compounds within coal-bearing structures in these basins. For instance, it has been determined that a major part of gold contained within brown coals of Borodinsky-1 and Borodinsky-2 seams occurs as micro and nanoparticles of solid solutions of Au-Cu-Zn, Au-Cu-Ag, and Au-Cu-Zn-Pb whose gold content is over 50% by mass. We have also conducted preliminary studies of distribution of various PVEs in washed products, products of combustion, gasification and hydrogenation of coals as well as studies of the most advanced technologies for generating certain PVEs. We have discovered that industrial-scale combustion of coals and coal-bearing products has the highest potential in terms of producing primary PVE concentrates. Certain PVEs (Ge, Mo, W, Ag, Au, Zn, Re, Se, and possibly Ga and Rb) which form gaseous compounds within the high temperature zone, condense on fly ash particles once the gas flow cools down. This gas flow carries PVEs out of the furnace, thus the captured fly ash becomes the primary concentrate. For other PVEs (rare-earth elements, strontium, Nb, Hf, Zr) the primary concentrate is a mixture of fly ash and slag. Primary concentrates of both types, especially the fly ash one demonstrate much higher PVE content than the burnt fuel. Additional increase in the PVE content in primary concentrates can be achieved through preliminary processing of coals before combustion and through separation of fly ash either based on the particle size or various magnetic parameters.