Recycling of steel plant mill scale via iron ore pelletisation process

Abstract

Mill scale is an iron oxide waste generated during steelmaking, casting and rolling. Total generation of mill scale at JSWSL is around 150 t/day and contains 60–70%FeO and 30–35%Fe₂O₃. To recover the iron, the mill scale must be smelted in a blast furnace or other reduction furnace; however, it is usually too fine to use without previous agglomeration such as via pellet or sinter mix. JSWSL operates a 4·2 Mtpa pellet plant to produce pellets for Corex and BF ironmaking units. The aim of this study is to determine the effect of mill scale on pellet properties. Detailed laboratory basket trials were conducted using up to 40% of mill scale in the pellet mix. The addition of mill scale up to 10% is considered to provide the optimum balance of chemical, physical and metallurgical properties of the pellet.     

Application of artificial neural network model to predict reduction degradation index of iron oxide pellets

Abstract

The reduction degradation index (RDI) is an important metallurgical property of iron ore pellets used for the production of RDI from shaft furnace or for use in blast furnaces. In order to develop a control strategy, a neural network model has been developed to predict the RDI of pellets from 13 input variables, namely feedrate of green pellets, bed height, burn through temperature, firing temperature, specific corex gas consumption, bentonite, moisture and carbon content in green pellets and Al₂O₃, SiO₂, CaO, MgO and FeO in fired pellets. The RDI of pellets was more sensitive to variation in MgO, CaO, bentonite and green pellet carbon content. The predicted results were in good agreement with the actual data.     

Mineralogical evaluationof ladle slags at voestalpine Stahl GmbH

Abstract

A large number of steel grades are produced at voestalpine Stahl GmbH. The ladle slag must meet different requirements according to the specific steel grade. The mineralogical structure of ladle slag is highly dependent on its basicity. At a basicity of <0·8, spinels occur, and, at higher values, periclase or (Mg,Fe)-wüstite occurs, depending on the degree of slag deoxidation. At basicities between 0·6 and 1·6, calcium aluminates C₁₂A₁₇ and C₃A (C=CaO; A=Al₂O₃) are predominant. Calcium silicates C₂S and C₃S (S=SiO₂) occur throughout the basicity range, and CaO _free occurs at basicities >1·2, both depending on the SiO content. This enables the metallurgist to specifically adjust the ladle slag according to the steel grade requirements. Knowledge of the slag condition is essential in order to achieve certain metallurgical results, such as desulphurisation or degree of oxide purity.