Effects of Slag Composition on H2 Generation and Magnetic Precipitation from Molten Steelmaking Slag–Steam Reaction

Abstract

In this paper, the effects of slag composition (slag basicity CaO/SiO2 and FeO concentration) on the amounts of H2 gas generated and the magnetic spinel phase precipitated as a result of the reaction between synthetic steelmaking slag and steam at 1873 K (1600 °C) were studied by thermodynamic simulation (using Thermodynamic Package FactSage 7.0) and laboratory experiments. The thermodynamic calculation showed that, upon increasing slag basicity (CaO/SiO2) from 1.0 to 2.5, for the reaction of 100 g of slags with 100 g of H2O gas, the accumulated amount of the produced H2 gas increased from 0.17 to 0.27 g, while the amount of magnetic spinel phase first increased and then decreased, with the maximum precipitation of 16.71 g at the basicity of 1.5. When the FeO concentration increased from 15 to 30 pct for the slag with basicity of 2.0, the accumulated amount of the produced H2 gas increased from 0.17 to 0.28 g, and the amount of magnetic spinel phase increased from 5.88 to 10.59 g. The laboratory experiments were conducted in confocal laser scanning microscope to verify the reaction between 0.2 g of slag and 3.75 L of H2O-Ar gas $$ \left( {P_{{{\text{H}}_{2} {\text{O}}}} \, = 0.2\,{\text{atm}}} \right) $$ . The results indicated that, for 100 g of slags, upon increasing slag basicity (CaO/SiO2) from 1.0 to 2.5, both the produced H2 gas and magnetic spinel phase first increased and then decreased, with the maximum amounts being 0.09 g of gas and 37.00 g of magnetic spinel phase at the slag basicity of 1.50. For the FeO concentration increasing from 15 to 30 pct, the amounts of both the produced H2 gas and magnetic spinel phase increased from 0.04 to 0.10 g and from 18.00 to 27.00 g, respectively. The reaction rate between the molten CaO-SiO2-FeO-MnO-Al2O3-MgO slag and the moisture $$ \left( {P_{{{\text{H}}_{2} {\text{O}}}} \, = 0.2\,{\text{atm}}} \right) $$ increased with the increasing FeO activity in the slag. The dependence of the reaction rate (mol/cm2/s) on FeO content can be expressed as $$ r \, = (7.67\left( {a_{\text{FeO}} } \right) - 2.99) \times 10^{ - 7} $$ .