South Ural State University (Chelyabinsk, Russia):

V. E. Roshchin, Dr. Eng., Prof., Dept. "Pyrometallurgical processes", e-mail: roshchinve@susu.ru
A. V. Roshchin, Dr. Eng., Associate Prof., Senior Researcher, Dept. "Pyrometallurgical processes"

Current interpretations of the solid-phase iron reduction theory are atom-molecule based. They view the reduction process as an exchange between oxide molecules and deoxidizer, i.e. oxygen atoms. However, there are neither atoms nor molecules in solid oxides or metals; there are just ions and electrons that bind the former. Thus, the oxidation-reduction reaction is not an exchange of atoms but that of electrons. Therefore, when viewing it in atom/molecule terms, formulating a consistent theory of processes that develop at a different — i.e. electron — level does not appear to be feasible. The electronic theory of reduction furthered by the authors describes electro- and mass transfer in gaseous and condensed phases, exchange of electrons between deoxidizer and oxide, redistribution of electrons between the cations and anions in the oxide lattice and transformation of the oxide lattice into a metal lattice, as well as the effect of pressure and temperature on the above processes. According to the theory, the extraction of one oxygen anion from the crystal lattice at the surface of an oxide would result in the creation of an anion vacancy and two free electrons bound to it. In complex and low-grade ores, vacancies and electrons tend to disperse across the oxide, build up and merge together near the cations the Fermi energy of which is below the chemical potential of electrons in the vacancies. The results obtained through experimental and real-life production of pig iron and ferroalloys were attributed to the charged particles of low-temperature plasma that are involved in redox reactions in the solid reagents layer. Plasma is formed as a result of the thermionic emission from the deoxidizer surface and the thermal ionization of gases. It is shown that the carbothermal reduction of active metals and iron from solid complex oxides can only be achieved with solid carbon. Through plasma, carbon is transferred to the oxide surface, and oxides — to the carbon surface. As a result, carbide shells form at the surface of both. Carbides contaminate the surface, they slow down and stop the reduction process. Melting and flowing of the shells switches the reduction process to a kinetic mode thus ensuring its efficient realization.

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