Abstract
With the growing industrialization, there is a constant increase in the world demand for steel, causing an increase on extraction of low-grade iron ores, which bear high levels of impurities. A feasible alternative is the use of residues from steel rolling processes (steelmaking mill scale) generated in the steel industry, which are composed of iron oxides consisting mainly of wustite (FeO), hematite (Fe2O3) and magnetite (Fe3O4). In line with the recycling of wastes, the application of heating by microwave energy in ironmaking processes consists in a promising new method developed in recent decades and is considered a cleaner technique. Therefore, this study aims to evaluate the self-reduction of mixtures composed of iron ore and steelmaking mill scale as iron source, together with coke fines as carbon source, heated using microwave energy. Through the rotational central composite design technique, it was possible to evaluate the best conditions for the use of steelmaking scale residue as well as the effect of the applied microwave energy power. The results indicated that the developed process has relevant utility with up to 41.48% of reduction obtained. The outcomes contribute to a better understanding of iron recovery from steelmaking residues in reduction processes using microwave energy for heating, providing significant insight for the development of new clean technologies.
Highlights
An integrated steel mill can generate 500 to 700 kg of waste per ton of steel produced
Haque et al.[11] presented a review on the application of microwaves in the field of mineral engineering, where he stated that the rapid heating of ore particles that occurred through the application of microwave energy in ores with a transparent matrix generates thermal stress of sufficient magnitude to create micro-cracks along the grain boundaries of minerals
In order to evaluate the profile of the reduction of iron oxides contained in the iron ore and steelmaking mill scale, as well as the advantages inherent to the process of heating by microwave energy, a statistical modeling was elaborated, evaluating the best conditions for the reduction of self-reducing mixtures containing coke as reducing agent
Summary
An integrated steel mill can generate 500 to 700 kg of waste per ton of steel produced. Such residues can vary in composition and are generally recycled during the process itself, undergoing various types of treatment, so that they can be left in contact with the soil in a safe manner, to meet environmental regulatory standards. Pollution caused by steelmaking processes can be harmful to the air, water and soil. Air pollution occurs in the processing of ore (sintering), in the coke oven, in the blast furnace and, to a lesser extent, in the areas of manufacture of semi-finished products, due to the fuels and the process of burning in the furnaces.
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