Abstract. 1 The article presents results of thermodynamic modeling of Fe-Si-Al complex containing alloy of the silica clay (77.8 % Al 2 O 3 , 11.6 % Al 2 O 3 ). The modeling is based on the principle of minimum Gibbs energy and fulfilled by means of software complex HSC-5.1. It was found that the joint reduction of silicon and aluminum from an amorphous SiO 2 and Al 2 O 3 is characterized by higher thermodynamic probability than from a mixture of a crystalline SiO 2 and Al 2 O 3 . At the silicon reduction there is the undesirable formation of a gaseous SiO; the transition degree of silicon in SiO can be reduced by means of decrease in temperature and increase in carbon content.
At flotation concentration of copper ores the tailings are formed, which contain both nonferrous metals and a significant amount of silicon and iron. The nonferrous metals from the tailings can be taken by flotation or leaching; but the silicon and iron is used irrationally as a backfilling material in mined-out space. The work purpose was the development of a complex technology of processing the Balkhash concentrating factory's tailings (Kazakhstan) with production of a collective polymetallic concentrate and ferroalloys. The research has been fulfilled by a method of thermodynamic modelling using the software package HSC-5.
<p>This article contains the research results of the equilibrium interaction of iron carbide (Fe<sub>3</sub>C) with silicon carbide (SiC) in a temperature interval of 700-2000 K with the formation of iron silicides (Fe<sub>3</sub>Si, Fe<sub>5</sub>Si<sub>3</sub>, FeSi, FeSi<sub>2</sub>), by using the program of the Finnish metallurgical company Outokumpy HSC Chemistryj-5.1 for Windows with regard to the electrothermal production of ferrosilicium from siliceous and carboncontaining raw materials. On the basis of the received regression equations connecting the Gibbs energy change with the temperature and the silicon content in a ferroalloy, the response surfaces (change of the Gibbs free energy - ∆G<sub>T</sub><sup>0</sup>) and their horizontal sections for three groups of ferroalloys were constructed with the program Mathcad. The silicon content in the first group of alloys is 14.3-23%, in the second group of alloys – 23-33.3% and in the third group of alloys – 33.3-42.8%. It was established, that the reactions between Fe<sub>3</sub>C and SiC with the formation of iron silicides in the range of temperatures 700-2000 K are possible, and the probability of these reactions increases with increasing the mole ratio Fe<sub>3</sub>C/SiC from 0.166 to 1.0. As a result of the reactions the low-silicon ferrosilicium can be obtained, answering to a grade FS20 with Si content from 19 to 27 % and consisting of a mixture of Fe<sub>3</sub>Si and Fe<sub>5</sub>Si<sub>3</sub>, and also the ferrosilicium corresponding to a grade FS25 with a Si content from 23 to 29% and consisting of a mixture of Fe<sub>5</sub>Si<sub>3</sub> and FeSi. It was found, that at the technological temperature of 1900-2000 K the maximum Si content in the received ferrosilicium can’t be more than 37.7 - 38.8%. Production of the medium-silicon and the high-silicon ferrosilicium answering to grades FS45- FS90 from the Fe<sub>3</sub>C-SiC mixture is impossible from a thermodynamic point of view. The received information extends our knowledge about the iron silicides formation during the electrothermal production of ferrosilicium with a silicon content in the alloy from 19 to 90%.</p>
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