Mechanism and sequence of the metal reduction in the lattice of chromospinelides

The solid-phase carbothermic reduction of metals in the crystal lattice of ferrichrompicotite from massive chromium ore is experimentally studied. The reduction is found to develop according to an electrochemical mechanism. The metals precipitate both on the surface and in the volume of an ore grain. The electron transfer from a reducing agent to cations takes place through anion vacancies, which form during the interaction of the reducing agent with an oxide. An iron-chromium metallic alloy is the primary product of reduction, and iron and chromium are reduced simultaneously but at different and variable rates, which depend on their concentrations in a local oxide volume. The formation of carbides on the surface of an ore grain as a result of the interaction of the reduced metals with carbon causes the metal atom flux from the volume to the surface of the grain, the appearance of cation vacancies in the oxide, the dissolution of the metallic phase, and the termination of reduction. The decomposition of silicon carbides with the formation of silicocarbides restores the extraction of oxygen anions from the oxide lattice, which facilitates the resumption of reduction.