Elisa Pinto da Rocha

Characterization and three-dimensional reconstruction of pores of self-reducing pellets done by EAF dust

This work focused on the characterization physical and microstructural of the self-reducing pellet made of Electric Arc Furnace (EAF) dust using different low cost techniques. The serial sectioning technique was used to evaluate detailed measurements of pore connections, tortuositiy of pores and porosity distribution. The chemical analysis using Inductively Coupled Plasma Atomic Emission Spectroscopy (ICPAES), Scanning Electron Microscopy (SEM), Optical Microscopy (OM) and X-ray diffraction were carried out to identify the common phases presented in EAF dust agglomerate. It was observed that the pellet phase composition is formed by iron as magnetite, metallic iron, wustite, and zinc ferrite. The visualization of the reconstructed 3D microstructure provided average qualitative and quantitative analysis of the porosity (41.61%), a consistent result and in accordance with that obtained by pycnometry technique (41.53%). As expected, these results are more precise when compared with the result obtained by two-dimensional technique (23.41%). In addition, it was calculated the value of the tortuosity parameter (0.84) that suggested a morphological structure closest to cylindrical shape.

Kinetic of Self-Reducing Mixtures of Iron Ore and Biomass of Elephant Grass

In this work, kinetic runs of self-reducing mixtures composed by pellet feed, BOF dust and biomass of elephant grass were performed using TGA-DSC method, for the temperatures, 900, 950, 1000, 1050 and 1100°C, and carbon percentages (15, 20 and 30% of carbon). The converted fraction versus time was calculated, and the different regions of the reactions progress were selected to analyze the reactions kinetics that occur in the mixture (devolatilization of biomass, Boudouard and sequence of reduction reactions). The kinetic behavior for the different steps showed good agreement with the first-order kinetic law. Using Arrhenius plot, was possible to estimate the apparent activation energy values obtained for the reaction mechanisms corresponding to Fe3O4→FeO and FeO→Fe. The kinetic constants for the 1100°C temperature and mixture containing 30% of carbon were the higher values: 0.0037 s-1 for the reaction Fe3O4 → FeO and 0.0258 s-1 for the mechanism FeO →Fe.

Characterization of BOF Dust for Pellets Production Used in Blast Furnace

In order to minimize the incorrect disposal of dust generated in the basic oxygen furnace (BOF) converter and to generate a new application for this solid residue, a simple characterization route was proposed. The powder residue is used to produce self-reducing pellets and can be used in the blast furnace process. The chemical analysis of the dust was carried out using Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES), and some elements as Fe, Si, P, Al and Ca were detected in high amount, as the iron which achieved about 65% concentration. Moreover, the X-ray diffraction analysis indicated that the iron was found in the phases, mainly, as magnetite (Fe3O4) and hematite (Fe2O3) while quartz (SiO2) and calcite (CaCO3) were the major impurities. The spectrometry dispersive energy (SDE) analysis confirmed the presence of such elements and the images obtained by SEM allowed visualizing the morphology of the particles. The average of particle size distribution of the dust was 0.053 mm which is suitable for self-agglomerates pellets.

Kinetic Behavior of Self-Reducing Pellets Containing Coal of Elephant Grass

Aiming to reducing the gas emissions in the steel mill, in the present study the kinetic behavior of self-reducing pellets containing elephant grass coal and iron ore was investigated through kinetic isotherms for different temperatures. The pellets were isothermally treated in different time intervals for X-Ray diffraction and SEM analyzes. The results obtained by XRD showed that the higher mass of iron in the sample was achieved until the first 24 min. The SEM analysis allowed visualizing the presence of a metallic porous structure closer to edge and whiskers in the center of sample.

Three-Dimensional Reconstruction of the Porosity of Pellets of Iron Oxide and Coal Powders by Serial Sectioning

The self-reducing agglomerates produced from powders generated within the electric arc furnace and LD converters is of special interest in process of recycling due to the amount of iron and other metals of high economical value. However, the reducibility and inner pore structures play important role on the processing technology of these materials. Aiming at investigating the influence of the agglomerate structure, some two-dimensional metallographic techniques have been used to evaluate the porosity in clusters with inaccurate results, essentially due its three-dimensional features. From the processing technological point of view, the shape and distribution of inner porosity of the powders agglomerates are of fundamental importance due to their effects on the reaction rates involving the present phases taking place into the reduction stage. In this study a 3D serial sectioning imaging reconstruction is proposed to determine local inner porosities and detailed measurements of parameters of pores connections and tortuosities. The averaged porosities results are discussed and compared with traditional measurements based on pycnometry method.