The Influencing Factors for Volume Stability of Ladle Slag

The purpose of this study was to investigate the mechanism causing the unsoundness of ladle slag. Calcination temperature may have an impact on the level of reactivity of f-CaO. When CaO was produced at a higher temperature, the reactivity of CaO was lower. For example, dead burnt CaO (DCaO) was produced at higher temperatures than light burnt CaO (LCaO); therefore, DCaO had less reactivity than LCaO. In a hydration test, DCaO (1500 °C) showed 62 times lower reactivity than LCaO (900 °C), which meant that DCaO would result in the delay of hydration of CaO easily. Additionally, DCaO would cause unsoundness more easily than LCaO when adding the same number of cementitious materials. For this reason, using ASTM C114-18 (Standard Test Methods for Chemical Analysis of Hydraulic Cement) to quantify DCaO content may underestimate DCaO content by up to 20%. Conversely, this method was more suitable for f-CaO since it had high reactivity. Moreover, this study demonstrated that ladle slag would cause unsoundness when added into the cementitious material because it was produced from a higher temperature process (over 1500 °C), which generates the DCaO. Therefore, when reusing ladle slag, the problem of low reactivity of DCaO should be considered.

Leaching and Geochemical Modelling of an Electric Arc Furnace (EAF) and Ladle Slag Heap

Old metallurgical dumps across Europe represent a loss of valuable land and a potential threat to the environment, especially to groundwater (GW). The Javornik electric arc furnace (EAF) and ladle slag heap, situated in Slovenia, was investigated in this study. The environmental impact of the slag heap was evaluated by combining leaching characterization tests of landfill samples and geochemical modelling. It was shown that throughout the landfill the same minerals and sorptive phases control the leaching of elements of potential concern, despite variations in chemical composition. Although carbonation of the disposed steel slags occurred (molar ratio CO3/(Ca+Mg) = 0.53) relative to fresh slag, it had a limited effect on the leaching behaviour of elements of potential concern. The leaching from the slag heaps had also a limited effect on the quality of the GW. A site-specific case, however, was that leachates from the slag heap were strongly diluted, since a rapid flow of GW fed from the nearby Sava River was observed in the landfill area. The sampling and testing approach applied provides a basis for assessing the long-term impact of release and is a good starting point for evaluating future management options, including beneficial uses for this type of slag.

Treatment and utilization of artificial aggregate in the production of cement composites

The aim of the work is to find a suitable way of treatment of steel ladle slag for subsequent use as a partial replacement of the binder component in cement composites. The goal is based on the raw materials policy of the Czech Republic. Within this work is solved the issue of possible use of steel slag as the largest by-product of steel production. The work is focused on a specific ladle slag from ladle furnaces, by which are equipped the modern steel plants. Ladle slag is similar in chemical composition to Portland cement. However, its mineralogical composition should be taken into account in relation to its expansion reactions and lower hydraulic activity. One of the goals is the research of effect of particle size in cement-slag mixtures. The slag was ground for research on two different specific surfaces - coarsely in a vibrating mill and finely in a ball mill. The research within the experimental part of the work verified the positive influence of ladle slag on the properties of fresh and hardened mortar mixtures. Tensile bending strengths and compressive strengths are for some mixtures with ladle slag even higher than the strengths of the reference mixtures.

Effect of White Mud Addition on Desulfurization Rate of Molten Steel

Fluorspar (CaF2) is commonly used to control the fluidity of slag in ladle-refining of steel. However, because it is desirable to reduce CaF2 consumption because of its environmental impacts, the industrial waste material such as white mud (WM) was investigated as a potential substitute for fluorspar. Steel sample (Fe-0.3C-0.9Mn-0.3Si-0.03Al-0.05S, mass pct) was melted in a high-frequency induction furnace, followed by additions of ladle slag (CaO-Al2O3-SiO2-5MgO-xCaF2, CaO/Al2O3=3, x = 0 to 10 mass pct) and fluxing agent (WM) at 1823 K (1550 °C). The desulfurization experiments were carried out by reducing CaF2 content in the ladle slag and increasing the addition of WM. Ladle slag with added WM showed an overall mass transfer coefficient of sulfur (kO) equivalent to or higher than that of conventional 10 mass pct CaF2-containing ladle slag. In a slag melting experiment based on DIN 51730 standard, the melting rate of mixed slag increased with the amount of WM added, which is considered to have a positive effect on the initial desulfurization rate. In addition, adding WM provided sulfide capacity of the slag equivalent to that of CaF2-containing slag. Consequently, the use of WM yielded slag having $$k_{{\text{O}}}$$ k O equivalent to or higher than that of conventional ladle slag with 10 pct CaF2, and thus, WM shows promise as a partial replacement for fluorspar.

Effect of TiO2 content in slag on Ti content in molten steel

A calculation model of activity for CaO–SiO2–MgO–Al2O3–TiO2 slag is established according to molecular-ion coexistence theory of slag structure to calculate the activities of Al2O3, SiO2, and TiO2 in the slag. The possibility of TiO2 reduction in the slag during refining is analyzed by thermodynamics and verified by laboratory and industrial experiments. Both theoretical analysis and laboratory experimental results show that the content of TiO2 in the ladle slag significantly influences the Ti content in molten steel. When the content of the dissolved aluminum in molten steel is 0.030–0.050%, the TiO2 content in the ladle slag should be controlled below 0.3% to prevent TiO2 reduction. The critical content of TiO2 decreases with an increasing amount of the dissolved aluminum in molten steel. In addition, silicon should be used as a deoxidizer during diffused deoxidization because aluminum as a deoxidizer would lead to the reduction of TiO2. The industrial experiments confirm the results of the laboratory experiments and thermodynamics analysis.