Electric arc furnace dust (EAFD) is a solid waste generated in the collection of particulate material during steelmaking process in electric arc furnace. The aim of this work is to carry out a chemical and structural characterization of two EAFD samples with different Zn contents. Optical emission spectroscopy via inductively coupled plasma (ICP), X ray diffractometry (XRD) and Mössbauer spectroscopy analysis were carried out in such EAFD samples. From XRD measurements, the samples exhibits the following phases: ZnFe2O4, Fe3O4, MgFe2O4, FeCr2O4, Ca0.15Fe2.85O4, MgO, Mn3O4, SiO2 and ZnO. The phases detected by Mössbauer spectroscopy were: ZnFe2O4, Fe3O4, Ca0.15Fe2.85O4 and FeCr2O4. Magnesium ferrite (MgFe2O4), observed in the XRD patterns as overlapped peaks, was not identified in the Mössbauer spectroscopy analysis

For about 10 years the steel industry in Brazil has used pulverized coal injection (PCI) technology in the blast furnaces based on imported coals. In order to decrease the dependence on imported coals, Brazilian coal, which has limited use due to high ash content, was suggested to be mixed with imported coal and charcoal. The aim was to examine the reactivity of the samples. The charcoal use in the steel industry contributes to the CO 2 emission reduction, since it represents a renewable source of energy. The reactivity of the coals, charcoal and mixtures was evaluated through simultaneous thermal analyses. Results of this study are presented and discussed.

Pulverized Coal Injection (PCI) is an important standard technology replacing coke partially by pulverized coal into the blast furnace that allows a significant reduction of hot metal costs and environmental impact, contributing to a decrease of coke requirements for ironmaking. Coals typically used in this process in Brazil are, at current time, exclusively imported from many countries, although economic important coal-measures occur in the southern part of the country. The Brazilian coals have a low rank, higher contents of inert components, proportioning nocoking properties and an expected high reactivity. Due to these caractheristics, these coals could be used for injection in the blast furnaces in order to decrease the dependency on high cost imported coals. The efficiency in the combustion and the coal reactivity are considered important parameters in the blast furnace, since a larger amount of char (unburned coal) causes severe problems to the furnace operation. The aim of the present work is to compare the reactivity of a south Brazilian coal, obtained from Faxinal mine, with two imported coals and the blends of the Brazilian coal with the imported ones. The reactivity of these coals and their blends were evaluated in a thermogravimetric analyzer. In the experiments, various mass ratios of Faxinal coal and the imported coals were used to compose the blends. The gasification reaction with pure CO2 was conducted under isothermal conditions at 1050 °C and atmospheric pressure. The experimental results show the greater reactivity of the Faxinal coal. The additive behavior was confirmed. The blends with a composition of up to 50% Faxinal coal have parameters according to the usual limits used for PCI

A thermodynamic study was carried out to evaluate the contents of Al, Ca, S and O at which liquid or partially liquid inclusions are formed to optimize the castability of SAE 8620 steel. Samples of steel secondary treatment (Ladle) and continuous‐casting billets (Tundish) were obtained from an electric steel mill. Entry data for this study were obtained in heats carried out in the steel plant. Furthermore, analyses were performed with a Scanning Electron Microscope (SEM) and an Energy‐Dispersive Spectrometer (EDS), as well as chemical analysis of both steel and total oxygen. In the Ladle sample, after calcium addition, inclusions had concentrations between 30 and 45% CaO and consisted mainly of calcium‐aluminates with MgO content of 10%. In the Tundish sample, inclusions contained a high percentage of alumina. Combining the characterization of inclusions with a computational thermodynamics model, the obtained results showed that the ideal range of calcium may vary between 10 and 14 ppm to form liquid inclusions with a minimum CaS content for the O, S and Al levels from SAE 8620 in this process stage. An analysis of Mg influence on the formation of calcium‐aluminates was also carried out. For contents of Mg found in aluminium‐killed steels treated with Ca, Mg does not significantly influence the formation of calcium‐aluminates inclusions. Higher calcium contents can be taken into account, depending on both the process type in steel production and the demanded product properties. The present study shows that the combined application of both inclusions characterization techniques and computational thermodynamics can drastically reduce the empiricism regarding the development of processes for the control of non‐metallic inclusions in steels. Thus, this research can contribute to increase the efficiency of manufacturing processes, improve the quality of existent products and make possible the economic development of new ones.

ResumoEm aciarias elétricas, o consumo dos insumos tem impacto importante na composição do custo final do aço, dos quais se destaca o consumo de energéticos utilizados no forno elétrico a arco, que pode representar até 30% do custo operacional de uma aciaria. Para quantificar o aporte desses diferentes tipos de energia é utilizado o indicador de consumo de energia total FEA + FP, que associa fatores de equivalência a cada tipo de energético de forma a transformar sua unidade de medida para a unidade base de kWh/t. Nesse trabalho foi realizado um teste no formato de projeto de experimentos, variando-se as vazões de gás natural e/ou oxigênio em um dos modos de queimador e em três modos de lança a fim de modificar suas proporções O 2 /GN e avaliar o impacto no consumo de energia total. Palavras-chave: Energia total; Eficiência energética; Injeção de gases; Processo de FEA.

Steel production process generates waste, among which is the electric arc furnace dust (EAFD). This waste has varying amounts of zinc, which is principally contained in the minerals zincite (ZnO) and franklinite (Fe 2 ZnO 4 ). The presence of Zn is capable of economically motivating the recycling of this residue and facilitating the co-processing of the remaining material. The zinc content in EAFD and the presence of zincite, however, have significant influence on the application of hydrometallurgical recovery processes (economic alternatives to the Waelz process). In this study, based on the computational thermodynamic tool FactSage, theoretical considerations are made on the conditions for the formation of zinc-containing minerals found in EAFD. Through thermodynamic analysis, the best conditions for obtaining a high fraction of ZnO were analyzed, which favor the hydrometallurgical processes for EAFD treatment. A classification of dust depending on the phases present in the EAFD is suggested as a guide for the feasibility analysis for the use of a hydrometallurgical process.

ResumoA produção siderúrgica em usinas semi-integradas gera vários tipos de resíduos dentre os quais as carepas. No presente trabalho estuda-se o comportamento físico-químico em altas temperaturas de briquetes autorredutores elaborados com carepa e finos de carvão vegetal produzidos no Rio Grande do Sul, objetivando sua introdução no processo produtivo de aciaria elétrica. Ensaios realizados em laboratório com briquetes industriais confeccionados com estes resíduos demonstraram a potencialidade de utilização destes briquetes autorredutores em processos siderúrgicos via forno elétrico a arco (FEA). Palavras-chave: Carepa; Finos carvão vegetal; Briquetes autorredutores. SELF-REDUCING BRIQUETTES FROM STEELMAKING MILL SCALE FOR USE IN ELECTRIC ARC FURNACE AbstractThe steelmaking industry in semi-integrated plants generates several wastes, among which mill scale. In this paper it was studied self-reducing briquettes made with mill scale and charcoal fines produced in Rio Grande do Sul State and its physicochemical behavior at high temperatures. The objective is its reintroduction in electric steelmaking process. Laboratory tests with industrial briquettes made with these residues had demonstrated the potential use of these briquettes in steelmaking processes through electric arc furnace (EAF).

Secondary refining slag samples with different chemical compositions (45-54 % CaO, 7-13 % Al 2 O 3 , 20-29 % SiO 2 , 9-16 % MgO, 0-5 % CaF 2) were investigated to verify the influence of their effective viscosity on inclusion cleanliness of DIN 38MnS6 in a steelmaking plant. The steel samples were collected during the production process for analysis of inclusions. Using the commercial software FactSage 6.4, thermodynamic calculations were performed to determine the effective viscosity, solid fraction, liquid fraction and MgO saturation point of these slags at 1560ºC. The results showed that all the slags were saturated in MgO, revealing a better protection of the ladle refractory. The addition of 2 to 5 % of CaF 2 reduced the effective viscosity values for the analyzed slags from 0.45 Pa•s to 0.10 Pa•s , in comparison to the slags without the addition of CaF 2 , with an effective viscosity of 0.40 Pa•s, 0.27 Pa•s and 0.22 Pa•s, decreasing the level of non-metallic inclusions for some of the analysed heats. However, it was detected during the manufacturing process that high slag fluidity and re-oxidation events continue to be a challenge associated with reducing the level of non-metallic inclusions.