Thermodynamics of reduction of sintered dolomite

The thermodynamic data are determined, and the variations in the standard values of the Gibbs energy (Δ G 0 ) are evaluated for three groups of reactions (selected among 32) of the silicothermic reduction of roasted dolomite, which differ in oxygen content in the reduction products and in the characteristics of the processes with a limited oxygen access (retort method), and of the vacuum silicothermic reduction both with the addition of dolomite and without it. It is established that the reduction reactions of roasted dolomite to Fe 2 SiO 4 , Ca 2 SiO 4 , and CaMg(SiO 3 ) 2 in the retort method, which are presented in classic works, have a positive or close-to-zero negative value of Δ G 0 and, consequently, are low-probable in practice. The reactions with the formation of a complex calcium-magnesium silicate Ca 3 Mg(SiO 4 ) are more preferable thermodynamically. For the vacuum silicothermic reduction with the introduction of carbon and without it with the formation of Ca 2 SiO 4 at 1200–1350 K, the negative value of Δ G 0 is larger by a factor of 4–8 by the absolute magnitude. The optimal temperature and kinetic parameters of these processes are found experimentally. It is shown that the use of carbon as an additional reducing agent stably increases the yield of Mg by 20–30%. In this case, the FeSi consumption decreases by a factor of 3 compared with the retort method and by a factor of 2 compared with the vacuum process without carbon. Our data served as the basis for the project task of designing an installation for the vacuum-silicothermic reduction of magnesium from roasted dolomites.