A polygonal diagram of the state of the CaO-SiO2-MgO ternary system was constructed in the entire range of concentrations of solid and liquid initial components, which increases the informativeness of polygonal diagrams of the state of metallurgical systems. The obtained results of the SCS analysis of the silicate and silicide phases of the duplex system SiO2–MgO–CaO : Si–Mg–Ca are the scientific basis for the optimization of blast furnace iron refining processes with smelting slags and magnesium alloys. Keywords: polygonal diagram, magnesium slag, silicate and silicide phases of calcium, physicochemical, technological and quantum-mechanical parameters.

The classification and structuring of oxide and metallic phases of binary duplex systems of silicates-silicides of alkaline earth metals are carried out in the work. This will determine the optimal composition of alkaline earth metal alloys based on silicon in the refining of ferrocarbon melts and modification of non-metallic inclusions. The ionic-molecular complexes of magnesium, oxygen and silicon are constructed in the work, which determine the mechanism of formation of non-metallic inclusions (magnesium silicates) in steel when using silicomagnesium alloys for refining. The parameters of chemical bonding for oxides with ionic bond type, for liquid silicomagnesium alloys having a metallic type of chemical bonding and for hard alloys with metal-covalent bond are determined. The presented results of structural and chemical analysis of the duplex system MgO–SIO2–Mg–Si allow to reveal the mechanisms of desulfurization processes and to develop technologies of blast furnace desulfurization in smelting and ladle treatment with furnace slag, magnesium and its alloys with silicon. Keywords: polygonal diagram, magnesium oxides, alkaline earth metal silicides, quantum mechanical parameters, classification and structuring.

The mechanism of cast iron desulfurization through structural and chemical reactions in smelting slags corresponding to the composition of the main mineral phases is presented: monticellite (MT, SiO2MgOCaO) → mervinite (MP, 2SiO2MgO3CaO) → ockermannite (OK, 2SiO2MgO2CaO) →diopside (DP, 2SiO2MgOCaO) → rankinite (pH, 2SiO23CaO) and eutectic slags (E, 3SiO2MgO4CaO). A sequential series of adsorption capacity of slag phases with respect to sulfur (АС, mas. %) and the depth of metal desulfurization – Δ(S), ppm was determined: Е (3.54/36) → MR (4.8/49) → OK (5, 7/59) → DP (7.14/74) → MT (9.8/103) → RN (20/222). In factory conditions, the efficiency of smelting slags of eutectic composition and diopside for ladle processing of cast iron was tested. The expediency of using such blast furnace slags for ladle processing of cast iron has been established, which at a consumption of 5-10 kg/t provide a desulfurization depth of 200-400 ppm. The consumption of slag is significantly reduced with the additional deoxidation of smelting slags with carbon during the release of melt in the ditch of the foundry and in the pig iron ladle.