Basic oxygen furnace (BOF) slag contains a significant amount of iron-containing species, which is considered to be iron resources and therefore need to be recovered. In this work, the oxidation behaviour of BOF slag under air (at selected oxidation temperatures and holding time) was investigated to explore the potential of transforming non-magnetic wustite in the BOF slag into magnetic spinel, which may subsequently be recovered by magnetic separation. The experimental results show that the iron-containing spices in the BOF slag can be oxidised into magnetic spinel phases in the investigated temperature range of 1000–1150°C and thereafter be recovered by magnetic separation. The formation of these phases is closely related to the oxidation temperatures and holding time: a higher oxidation temperature and longer holding time lead to a larger amount of formed magnetic species; however, the amount of formed magnetic species decreases at elevated temperature (>1050°C) and with extended holding time (>40 min).

Although steel slag exhibits cementitious properties, the addition of steel slag in cement is still limited due to both the presence of excess iron oxides and instability of free lime and periclase. This paper proposes a method for oxidizing molten slag in air, aiming at extraction of superfluous wustite and stabilization of free lime and periclase. Mineralogical characteristics of raw slag and modified products were examined using X-ray diffraction (XRD), scanning electron microscopy equipped with backscattered electron imaging (SEM-BEI), energy dispersive spectrometry (EDS) and thermogravimetric analysis (TGA) with differential scanning calorimetry (DSC). Thermodynamic calculations were performed to aid to discuss the experimental results. The results indicate that non-magnetic wustite and periclase are transformed into magnetic spinel (magnetite/magnesioferrite) after oxidation. Temperature has a significant effect on the formation of spinel. The mass fraction of free lime decreases from 3.54 wt.% to 0.96 wt.% as a result of the conversion from free lime to calcium ferrite.

An investigation of mineralogical phases in industrial slag transferred from non-magnetic to magnetic substances was carried out in this study, aiming at extraction of superfluous wustite and stabilization of free lime and free periclase. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were employed to investigate the mineralogy and phase distribution. Wet magnetic separation was conducted to determine the recovery rate of iron. The thermodynamic and kine-tic calculations for the oxidation of steel slag in a CaO-SiO2-FeO-MgO system were also performed, and the results were compared with a CaO-SiO2-FeO system. XRD analysis and SEM-EDS observation confirmed the conversion from non-magnetic wustite to magnetite spinel (magnetite/magnesioferrite) after oxidation. Magnetic separation experiment indicated that the optimal oxidation temperature is 1 100℃, which coincided well with the thermodynamic calculations. The addition of periclase had a significant influence on the formation of spinel and leaded to the presence of spinel under a partial pressure of oxygen range log10(PO2)=4.3 (correspon-ding to air). The oxidation process of steel slag could be divided into three steps: initial incubation, chemical reaction and diffusion. 

A steel slag has been treated by air granulation, in order to enhance cementitious properties of the slag. Two samples with sizes ranged 1.68-2.38mm and 212-297μm and coded as Slag A and Slag B, respectively, were chosen from the granulated slag for investigations. A sample of the original steel slag was also studied. XRD analyses indicated the formations of α-C₂S, β-C₂S, C₂F, C₂MS₂, f-MgO and α-C₂S, C₂F, f-MgO in Slag A and Slag B, respectively. The phases in the two slag samples were quite different from the phases found in steel slag. The SEM results show a reduction of C₂S sizes from 10-20μm for the steel slag to nano-scales by air quenching for Slag B. This treatment of air quenching has increased the cumulative heat of hydration to 105.35J/g measured for Slag B, almost two times greater than that of the steel slag. The study results demonstrate a high potential for utilizations of the steel slag in cement and concrete applications after the slag treatment by air quenching. The treatment may thus lead to an environmental friendly and cost-effective recycling for the steel slag. This can also contribute to the sustainable developments in the steel and cement/concrete industries.

In this work, the effectiveness of using briquettes made from chromite ore, mill scale, and petroleum coke for direct chromium alloying is tested by induction furnace trials carried out in three different scales. The experimental results show that steel scrap can be alloyed with chromium by the chromite ore in the briquettes and the Cr yield from the chromite ore increases with the increase in mill scale addition to the briquettes: the more mill scale is added to the briquettes, the lower the mass ratio of Cr to (Cr+Fe) would be, leading to a higher Cr yield from the chromite ore. Specifically, the maximum Cr yield from the chromite ore is 99.9% when the mass ratio of Cr to (Cr+Fe) in the briquettes is 0.05, and being 93.0% when the ratio is 0.10. However, when the ratio of Cr to (Cr+Fe) in the briquettes reaches 0.20, the maximum Cr yield is only 67.1%. The reduction of chromite ore under the present experimental conditions is promoted by a solid-state reduction mechanism

Recycling of iron oxide from BOF slagshas always been a difficult issue in metallurgy. The core of this study was transforming the iron oxide into ferromagnetic phase MgFe₂O₄ by modifying industrial BOF slag appropriately first, and then recycling the iron resources by magnetic separation. The effect of basicity and calcination temperature on the formation of MgFe₂O₄ in synthetic BOF slags was investigated first, and then the industrial BOF slag was modified. Various experiments and analyses such as XRD, SEM-EDS, Factsage thermodynamic simulation and chemical analyses were conducted.The results show that the optimal basicity was 2, and the optimal calcination temperatures were 1 250 and 1 300℃. Moreover, MgFe₂O₄ was formed in modified BOF slag by mixing the industrial BOF slag with 6% SiO₂ first, and then cooling the modified BOF slag from 1 400 to 1 270℃ at a rate of 1℃/min. After magnetic separation, the total Fe content in magnetic slag increased by 15.80%, to 37.00%, compared with that in the industrial BOF slag. This is better than the direct magnetic separation of iron oxide without any treatment

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.

In this paper, the Fe-containing phases in BOF slag were identified before and after oxidized with atmospheric air. XRD and SEM with EDS results showed that The element Fe existed in slag in the form of calcium ferrite, wustite solid solution and hematite. Mg solid solute in wustite. After oxidized, magnetite became the major mineral phase in slag and Mg⁺ replace the Fe²⁺ of magnetite crystal to form spinel

Efficient recycling of iron oxide from industrial BOF (basic oxygen furnace) slags has always been an issue in metallurgy. In this study, a new method was developed for the efficient recycling of iron oxide: It was transformed into magnesioferrite spinel (MgFe₂O₄) by mixing the industrial BOF slag with 6.00% SiO₂ first, and then the modified slag got cooled down from 1400 °C to 1270 °C at a rate of 1 °C/min. Finally, the Fe resources were recycled by magnetic separation. Various experiments and analyses such as XRD, SEM–EDS analyses, Factsage thermodynamic simulation, magnetization characterization, dry magnetic separation, and chemical analysis were carried out. The results show that the obtained MgFe₂O₄ has a high melting point (1716.76 °C in theory) and ferromagnetism (specific magnetic susceptibility of (8.03–206.84) × 10⁻⁵ m³/kg). Therefore, it could be separated from the weakly magnetic industrial BOF slag (specific magnetic susceptibility of (0.024–0.136) × 10⁻⁵ m³/kg). Furthermore, this new method could be applied to different BOF slags. The yield of MgFe₂O₄ increased to above 80% when the content of Fe₂O₃ was in the range 25.81–46.90%. After the modification and magnetic separation, the total Fe content increased by 15.80%, from 21.20% in the industrial BOF slag to 37.00% in the magnetic slag. This is better than the direct magnetic separation of iron oxide without any treatment. The magnetic slag could be reused as either a sintering or slag splashing material. The nonmagnetic slag can be used to produce high value-added building materials. Hence, this new method can be used to recycle the iron oxide from industrial BOF slags, achieving the sustainable development of the iron and steel industry.

The production of belite-calcium sulfoaluminate-ferrite (BCSAF) cement with the addition of industrial wastes as feedstock has been studied for many years. The preparation of clinkers is essential in cement production, in which all raw materials react with each other to generate key phases in cement under some specified conditions. The objective of this study was to investigate the sintering characteristics of BCSAF cement clinkers. Four BCSAF clinkers with different compositions were examined. High-temperature microscopy, quantitative x-ray powder diffraction analysis and scanning electron microscopy were used to analyse sintering features and phase composition. The results show that the use of wastes from the production of manganese and magnesium metals, which were added to the raw materials to make clinker pellets, can significantly reduce the firing temperature of BCSAF clinker. The firing temperatures of clinkers with added wastes were below 1300°C, much lower than the temperature used for conventional Portland cement (1450°C). The ferrite phase was always found to inter-grow with the C4A3S¯">C 4 A 3 S ¯  C4A3S¯ phase or C₂AS phase, just like the interstitial phase. The ferrite phase acted as a solid solution during cement sintering. A small quantity of iron oxide can make the clinker more porous, leading to energy savings in subsequent grinding processes.