ИССЛЕДОВАНИЕ СИЛИКОТЕРМИЧЕСКОГО ВОССТАНОВЛЕНИЯ МАГНИЯ ИЗ ДОЛОМИТОВ УРАЛА

Abstract

This paper gives the results of studies of magnesium recovery by ferrosilicon (75%) from the calcined dolomite of Ural deposits (Boitsovskoe and Chernorechenskoe). Analysis of chemical composition of dolomite samples showed that their quality is rather high (there are almost no impurities of alkali and heavy metals), but they differ by high content of calcium carbonate, which determines the peculiarity of their use in magnesium production. It is established that the structure of dolomite samples is characterized by a grain size of calcium carbonate inclusions. The sample I is characterized by CaCO3 inclusions with the particle size of 10-20 μm (7%), and the sample II is larger - CaCOj inclusions with the particle size of 20-30 μm (12.5%). The paper presents the results of the rmodynamic modeling of multi-component system MgO - CaO - Si - Fe - Mg - Ca2SiO4 - Ca3SiO5, according to which the excess of calcium oxide in the mixture (CaO/Si = 2.2-2.5) makes possible to recover magnesium from its oxide with ferrosilicon with formation of Ca3SiO5 compound. This paper discusses the features and parameters of magnesium recovery process, which laboratory simulations were carried out using high-temperature setting consisting of electric furnace, high-alloy chromium-nickel steel retort, vacuum pump and vacuum gauge. During the experiments, the pressure and the temperature in the retort were maintained at 0.1 kPa and 1195 °C, while the temperature in the condenser was maintained at 475-500 °C. The mixture of calcined dolomite with ferrosilicon (FS 75 (φC 75)) was extruded at a pressure of 1000 kg/cm into cylindrical pellets (diameter, equal to 20, height, equal to 20-22 mm) weighing 12-13.5 g. During the experiment, there were identified the optimal parameters for magnesium recovery, which reached the output of metallic magnesium, equal to 81.2%. It is established that the increase of content of calcium oxide in the charge to CaO:MgO:Si = 2.5:2:1 leads to the reduction of magnesium output by 3% and increase the flow of charge by 9.5%. Allocated in the course of dolomite processing, magnesium condensate has a high quality (content of magnesium is 99.5%), so it can be recommended to use for alloy production without further refining. The formed retort residues containing 57-60% CaO, 20-24% SiO2, 6.0-6.5% MgO, 3.8-4.0% Fe, 1.3-1.7% A12O3, have similar composition with the Portland cement and, after the separation of metal component, they can be used as an additive in its production.