Formation of Spinel Phases in Oxidized BOF Slag under Different Cooling Conditions.

To enhance utilization of wastes generated from steelmaking, a BOF slag sample from Ning Steel group in China is treated by oxidizing at 1500 °C for 30 min and then cooled by different methods. The treated samples are characterized, in combination with calculations using FactSage 6.4. XRD results show that iron oxides in BOF slag are converted largely by the oxidation to spinel phases, Fe₃O₄ and MgFe₂O₄, which also eliminates free CaO and MgO. EDS analyses show Fe element existing in di-calcium silicate and glass phase, which are Fe³⁺ ions formed by oxidation. An incorporation of Fe³⁺ ions into crystal structures has stabilized high temperature polymorph of C₂S, β-C₂S, and α'-C₂S, in the treated slag samples. Fe³⁺ ions may also act as a network former to facilitate glass formation. This may make it possible for the glass and α'-C₂S phase to complement each other, leading to a higher hydraulicity, while the BOF slag, after the spinel separation, is blended in cements. Some suggestions are proposed, based on the present and early studies, to enhance hydraulicity for the BOF slag, as well as grain sizes of spinel phases, which may result in economic and environmental benefits for steel and cement industries. [ABSTRACT FROM AUTHOR]