Improving the processing of steelmaking waste. Part 1. Thermodynamic analysis
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New approaches are required in the industrial processing of tailings slag from steelmaking. It has been shown in recent years that slag may be processed to obtain not only construction materials but also metal suitable for industrial use. In the present work, we study the expediency of reducing steelmaking slags as to obtain metallic and oxide phases for use in steelmaking and the construction industry. In particular, we consider slag from the tailings at Zlatoust Metallurgical Plant. FactSage software (version 6.4) is used for thermodynamic modeling of high-temperature slag reduction. Three slag compositions are considered, with 5, 10, and 15 wt % FeO. Modeling is undertaken for temperatures at intervals of 5°C in the range 750–1650°C, at a gas pressure of 0.1 MPa. We assume that a known excess of carbon (graphite) is introduced in the system. For convenience of analysis, the basic calculation results are presented as temperature dependences of the masses of the components and the composition of the phases considered. Modeling shows that, beyond 1340°C, practically all the iron is reduced and passes to the melt. Nickel and copper behave analogously. However, the results indicate that complete extraction of manganese in the metallic melt on reduction by carbon should not be expected. Even with maximum manganese extraction in the metallic melt, its presence in the slag and gas phases remains pronounced. The volume of gas phases formed in reduction at different temperatures is estimated. Modeling convincingly shows that, over the whole temperature range considered, carbon monoxide predominates in the gas phase. Information regarding the enthalpy of the system as a function of the temperature permits estimation of the thermal energy that must be expended to bring the system to a state at which the required reduction processes are possible.
Keywordsthermodynamic analysis steelmaking slag high-temperature reduction slag melts
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