Novel concept of steam modification towards energy and iron recovery from steel slag : Oxidation mechanism and process evaluation

The motivation of this work is driven by the feasible hydrogen production, through the reaction between iron-bearing phases, i.e. RO phase, metallic Fe in steel slag and steam. The RO phase can be regarded as (Mn,Mg,Ca)xFe1-xO wüstite that divalent iron is partially substituted by foreign cations of magnesium, manganese and calcium. The reaction behavior in terms of hydrogen generation variation in the temperature range of 500–1000 °C has been studied. It was found that the hydrogen production rate was strongly temperature dependent. Under isothermal conditions, the steel slag-steam reaction proceeded rapidly during the first 2000s. Beyond this, the rate of the reaction decreased significantly due to the formation of (Mg,Mn,Ca)yFe3-yO4 ferrite layer. The theoretical hydrogen generation capacity for steel slag was found to be proportional to the substitution level of foreign cations, i.e. Mg, Mn, Ca in wüstite. The underlying phase transitions, as well as the structural changes were discussed in detail by combing the XRD, SEM-EDS, XPS and VSM analysis. The kinetics analysis showed that the slag-steam reaction agreed well with the three-dimensional diffusion (D3) model and the corresponding activation energy for diffusion was estimated as 105.76 kJ/mol. Moreover, it was noticed that the magnetic properties of steel slag after steam oxidation was greatly enhanced, and the maximum specific magnetic susceptibility was 1.8E-4 m3/kg at 800 °C. This demonstrated steam oxidation could significantly improve the magnetism of steel slag and provide the possibility of iron recovering through magnetic separation. Based on the findings, the novel concept of the steam modification process towards highly efficient utilization of steel slag along its cooling path was proposed. It allowed us to envision the potentials that implementing management of energy production, iron recovery, and volumetric stabilization.
QC 20200322