Dissolution kinetics of CaO·2Al₂O₃ (CA₂) particles in a synthetic CaO–Al₂O₃–SiO₂ steelmaking slag system have been investigated using the high-temperature confocal laser scanning microscope. Effects of temperature (i.e., 1500, 1550, and 1600 °C) and slag composition on the dissolution time of CA2 particles are investigated, along with the time dependency of the projection area of the particle during the dissolution process. It is found that the dissolution rate was enhanced by either an increase in temperature or a decrease in slag viscosity. Moreover, a higher ratio of CaO/Al₂O₃ (C/A) leads to an increased dissolution rate of CA₂ particle at 1600 °C. Thermodynamic calculations suggested the dissolution product, i.e., melilite, formed on the surface of the CA₂ particle during dissolution in slag with a C/A ratio of 3.8 at 1550 °C. Scanning electron microscopy equipped with energy dispersive X-ray spectrometry analysis of as-quenched samples confirmed the dissolution path of CA₂ particles in slags with C/A ratios of 1.8 and 3.8 as well as the melilite formed on the surface of CA₂ particle. The formation of this layer during the dissolution process was identified as a hindrance, impeding the dissolution of CA₂ particle. A valuable reference for designing or/and choosing the composition of top slag for clean steel production is provided, especially using calcium treatment during the secondary refining process.

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In the pre-reduction cyclone of the HIsarna process, both thermal decomposition and gas reduction of the injected iron ores occur simultaneously at gas temperatures of 1723–1773 K. In this study, the kinetics of the thermal decomposition of three iron ores (namely OreA, OreB and OreC) for HIsarna ironmaking were analysed as an isolated process with a symmetrical thermogravimetric analyser (TGA) under an inert atmosphere. Using various methods, the chemical and mineralogical composition, particle size distribution, morphology and phase distribution of the ores were analysed. The ores differ in their mineralogy and morphology, where OreA only contains hematite as iron-bearing phase and OreB and OreC include goethite and hematite. To obtain the kinetic parameters in non-isothermal conditions, the Coats–Redfern Integral Method was applied for heating rates of 1, 2 and 5 K/min and a maximum temperature of 1773 K. The TGA results indicate that goethite and hematite decomposition occur as a two-stage process in an inert atmosphere of Ar. The proposed reaction mechanism for the first stage of goethite decomposition is chemical reaction with an activation energy ranging from 46.55 to 60.38 kJ/mol for OreB and from 69.90 to 134.47 kJ/mol for OreC. The proposed reaction mechanism for the second stage of goethite decomposition is diffusion, showing an activation energy ranging between 24.43 and 44.76 kJ/mol for OreB and between 3.32 and 23.29 kJ/mol for OreC. In terms of hematite decomposition, only the first stage was analysed. The proposed reaction mechanism is chemical reaction control. OreA shows an activation energy of 545.47 to 670.50 kJ/mol, OreB one of 587.68 to 831.54 kJ/mol and OreC one of 424.31 to 592.32 kJ/mol.@en

In this study, different existing methods to remove alloyed and coated copper from steel are summarized, compared, and discussed. None of these methods have been scaled up industrially so far. Characterization of industrial steel scrap will indicate in which forms and quantities copper is present. Based on environment, economics and process efficiency, the most promising techniques will be selected for further investigation. The study will then focus on ways to bring the process efficiency to the level required for industrial application, by better understanding of thermodynamic limits and the reaction kinetics. Possible removal of other undesired elements from the scrap will be taken into account as well.

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