The aim was to investigate the chemical composition of refinery slag obtained during silicon production in order to identify approaches to its further recycling. Research samples were collected from the slag remained after oxidation refining at the JSC Silicon (AO Kremny), RUSAL (Shelekhov, Irkutsk Oblast). The methods of X-ray phase, X-ray fluorescence, metallographic and scanning electron microscopy were employed to investigate the chemical composition of the samples. It was found that the refinery slag under study includes such basic components as elemental silicon, its carbide and oxide, as well as elemental carbon. It was shown that silicon carbide is the product of incomplete reduction, resulting from melting silica-containing ores in a smelting furnace. According to the conducted X-ray fluorescent analysis, the samples also contain (wt %): Ca - 7.40; Al - 3.80; Fe - 0.30; Ba - 0.19; K - 0.14; Na - 0.09; Sr - 0.09; Mg - 0.08; Ti - 0.05; S - 0.02. Calcium and aluminium are present in the slag mostly in the form of oxides. Complex oxides of an anor-thite type were also found: CaO Al2O3 2SiO2. The refinery slag under study also features insignificant amounts of other metal oxides, which are released from the furnace slag forming during the smelting process. The slag produced by oxidation refining during crystalline silicon production is a technogenic raw material containing valuable components. Due to the significant content of silicon in the refinery slag (from 42% to 65%), the existing methods applied to recycle such an industrial material were analysed in terms of additional silicon extraction or production of commercial silicon-containing products, which are in demand in various industries.

Metallurgical processes in Me-O-C systems cannot be studied and controlled using conventional analytical and physicochemical techniques. This is due to the complex physical and chemical interactions occurring in high-temperature metallurgical systems with the formation of various compounds. To study such processes, mathematical (thermodynamic) simulation and other techniques are widely used, among which graphical diagrams illustrating the equilibrium between individual phases or their systems occupy a special place. Diagrams have been proposed that are more common, informative, and herewith universal to study pyrometallurgical processes. The main research objective was to determine the equilibrium composition of the Me-O-C system, i.e., the amount or ratio of its various compounds such as carbides, oxides, pure substances, and, possibly, ternary compounds. The equilibrium compositions of the system were obtained to plot diagrams from not only experimental studies but also the chemical equilibria mathematical simulation results using the Selector software package. The diagrams proposed herein allow establishing a quantitative relationship between the temperature, the ratio of independent components (metal, oxygen, and carbon), on the one hand, and the complete equilibrium composition of the system, which implies data on the amount and type of condensed and gas phases in the system and their ratios, on the other hand. This mechanism is a new tool to study chemical conversions in complex metallurgical processes, which will be very useful for metallurgists, chemists, and technologists.