The steel industry produces large amounts of slag coming from different stages during the steelmaking process every year. Currently, there are numerous attempts to recycle it or to use it in some other industry sectors and to preserve the environment. The characteristics of the slag depends on the steelmaking process and it is crucial to have it before any attempt of recycling. In this work, slag sample produced in the ladle furnace from SIDERPERU steel plant were collected and analyzed by using energy dispersion X-ray (EDX), X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), SQUID magnetometer and Mössbauer spectroscopy. The chemical analysis obtained by EDX and XRF indicate that the main elemental composition of the material is Fe, Ca, Si and Cr. XRD identifies that these elements are in the phases: FeO, Fe3O4, α-Fe2O3, Ca2SiO4, and Ca2,32Mn0,68SiO7. Magnetometry measurements suggest the Verwey transition for magnetite and the Morin transition for hematite are screened by the presence of superparamagnetic phases. The Mössbauer spectrum shows two doublets related to Fe2+ and Fe3+ ions with hyperfine parameters belonging to that of non-stoichiometric wustite. Also, the presence of hyperfine fields characteristic of the Fe3O4 and Fe2O3 phase identified at room temperature verifies the magnetometry analysis. The analysis of the sample used in this work reveals details connected with the steel fabrication processes and are helpful for posterior recycling attempts.
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The metallurgical slag is a by-product material generated during the steelmaking process. Large amounts of slags are produced in the steel industry and increase every year generating pollution and affecting the environment [
Steel slags are formed during the melting of iron ore or iron scrap and subsequently discharged as waste [
In this work, we present the characterization of the slags produced during the second step process of steel in a ladle furnace from SIDERPERU in order to facilitate the recycling of the steel in Peru.
The samples were collected from SIDERPERU steel plant, Chimbote, Peru. The steelmaking process in this steel plant consists of three different stages: A melting process in an Electric Arc Furnace (EAF), the forming of chemical equilibrium between Fe, Ca and other components in a Ladle Furnace (LF), and the solidification through continuous casting. During the second stage, some melted steel remains stuck at the internal walls of the LF, which are discarded after the melting steel reaches its chemical equilibrium and dried to room temperature. Tons of this slag are produced every week and they are crushed for recycling. Several kilograms of this material were collected during this work and named as ‘remanent’ sample, as listed in Table Difference between slag samples collected after treatment in the ladle furnace at SIDERPERU Sample Source Factory treatment Remanent Melted steel stuck in the internal walls of the ladle furnace Dried in normal conditions Demetallized Crushed remanent sample Magnetically separated
The collected samples were powdered and sieved down to 72 μm for better performance analysis in order to increase the accuracy of measurements. The obtained powders were stored in two Eppendorf (each containing one sample), from which they supplied for each characterization technique. The morphology of the samples was inspected through a scanning electron microscope (SEM, Philipps XL30) with a resolution of 10 nm at 30 kV, voltage range: 0.5 V to 30 kV and magnification of 300,000× adapted with an energy dispersive X-ray (EDX) spectrometer OXFORD Xplorer. An XRF-720 Shimadzu equipment was used to register the elemental composition of the sample, which counts with an advantage algorithm that allows analyzing a variety of types of matrices. The X-ray diffraction (XRD) measurements were performed in a Rigaku brand diffractometer using a cobalt target (λKα = 1.79026 Å) with 10° ≤ 2θ ≤ 90°, step width 0.02° and speed of 4 s/step. The Co-target was used for XRD since, in contrast to other targets, it increases the diffraction signal of iron-containing minerals. The magnetic measurements were carried out using a DC-MPMS-SQUID magnetometer (Quantum Design Inc.) in zero field cooling (ZFC) and field cooling (FC) modes. The magnetization response as a function of temperature was collected from 5 to 400 K and applying external magnetic fields of 500 Oe and 10 kOe. The applied field response of the magnetization was also measured in the range ± 10 kOe at 5, 300 and 400 K. The Mössbauer spectroscopy of the sieved samples were performed at room temperature (RT) using a Mössbauer spectrometer in transmission geometry with a radioactive source of 57Co (Rh) with 50 mCi current activity with a constant acceleration function. The data were registered in a multichannel analyzer with counting data stored in 1024 channels platform. For the calibration measurement, a thin α-Fe foil was used. The fitting process was carried out considering Lorentzian profiles using the WinNormos software.
Figure Elemental Composition of remanent and demetallized slag generated in the ladle furnace from SIDERPERU steel plant Sample EDX Remanent Element Fe Ca Si Zn Cr wt (%) 46.98 30.22 12.2 2.2 1.49 XRF Element Fe Ca Si Cr Ti K Sr Nb Zr Mass % 47.2 29.3 17.6 3.49 1.217 0.359 0.311 0.122 0.064 Element Zn Rb Mass % 0.051 0.017 Demetallized EDX Element Fe Ca Si Mn wt (%) 26.8 53.45 9.12 10.13 XRF Element Fe Ca Si Mn Cr Ti Sr Nb Zr Mass % 35.54 32.89 9.62 8.047 2.616 0.359 0.46 0.043 0.076 Element Cu Mass % 0.065
Figure X-ray diffractogram of metallurgical slag produced in a ladle furnace during steelmaking process in SIDERPERU plants.
Figures Magnetization response as a function of the temperature for the remanent (
The Mössbauer spectra for both samples at room temperature are shown in Fig. Mössbauer spectra at RT of a slag produced in a ladle furnace during steelmaking process in SIDERPERU plant Hyperfine Mössbauer parameters of the slags produced in the ladle furnace from SIDERPERU steel plant during steelmaking process Sample Site IS (mm/s) QS (mm/s) Bhf (T) W (mm/s) Area (%) Remanent Fe1-xO (Fe2+) 0.99(2) 1.01(1) – 0.64(3) 53.3 Fe1-xO (Fe3+) 0.36(2) 0.71(1) – 0.34(3) 8.0 Magnetite (Fe2+/Fe3+) 0.47(3) −0.02(2) 45.2(1) 0.85(5) 22.9 Magnetite (Fe3+) 0.33(2) −.0.02 48.8(4) 0.6(2) 13.9 Hematite (Fe3+) 0.41(2) −0.21(2) 52.2(0) 0.14(3) 1.9 Demetallized Doublet 1 (Fe2+) 0.90(1) 1.00(2) – 0.50(3) 33.5 Doublet 2 (Fe3+) 0.46(1) 0.52(1) – 0.42(3) 7.3 CaFeSiO4 (Fe2+) 0.87(1) 1.89(1) – 0.63(1) 11.1 Magnetite (Fe3+) 0.26(5) – 49.2(5) 0.51(1) 10.6 Magnetite (Fe2+/Fe3+) 0.34(1) 46.6(1) 0.70(2) 21.5 Ca2Fe2O5 (Td) 0.70(2) −1.4(1) 43.9(2) 0.63(1) 11.5 Ca2Fe2O5 (Oh) 0.77(3) 1.36(1) 50.85(2) 0.55(2) 4.5
The information provided in the present work would be very useful for posterior attempts to recycle these types of steel slags. As a matter of fact, recently our research group has reported the reduction of the slags produced in SIDERPERU plant [
Remanent and demetallized slag produced in the ladle furnace from SIDERPERU steel plant were characterized by different techniques. The samples are hard sponge stones and dark grey in color. Fe, Ca, Si and Mn are the main elements detected by both EDX and XRF analysis. The common iron oxide phases detected by XRD were magnetite and wustite. Larnite, ankerite manganese and hematite were also found in remanent slag. Kirschteinite, srebrodolskite and ankerite manganese are the mineralogical phases found in the demetallized slag. The magnetic measurements suggest the presence of a superparamagnetic phase screening the Verwey transition signal of magnetite and the Morin transition of hematite in both samples. The Mössbauer spectroscopy analysis reveals that magnetite and wustite are not in stoichiometric state and that the wustite contributes with paramagnetic doublets in the spectra. The remanent and demetallized slag produced in the ladle furnace in SIDERPERU steel plant are promising materials for recycling in the steelmaking industry due to their high iron content minerals.
This work was supported by the CONCYTEC – World Bank – FONDECYT program “
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