Electric arc furnace (EAF) steelmaking is increasingly adopting sustainable carbon sources to improve slag foaming and reduce energy consumption. Among them, spent tire-derived carbon represents a viable alternative to coal, offering high volatile and carbon contents. However, its elevated sulfur level and modified slag chemistry can markedly affect foaming stability and desulfurization. This study elucidates the interactive effects of spent tire substitution (0-30 wt%) and slag basicity (CaO/SiO2 = 1.5-2.4) on foaming dynamics, bubble evolution, and sulfur behavior at 1,600 °C. Real-time imaging and quantitative analyses demonstrated that moderate substitution (10-20 wt%) enhanced initial foaming due to volatile-induced gas release, whereas excessive addition (30 wt%) caused unstable coalescence and premature collapse from sulfur-driven surface tension reduction. Lower basicity limited early foaming but improved long-term stability via increased viscosity, while higher basicity promoted rapid collapse and reduced sulfur retention. The optimal condition (CaO/SiO2 = 2.0) maintained stable foaming for over 40 min, achieving superior sulfur capture (about 24 %) and minimal refractory attack. Overall, these findings reveal the mechanistic coupling between carbon source, basicity, and interfacial properties, offering practical guidance for sustainable slag design and efficient sulfur control in EAF operations employing waste-derived carbonaceous materials.

To improve the initial strength and stability of lightweight-foamed concrete, which shows suitable sound absorption and insulation characteristics, the effect of CO2-reduced cement on the properties of the concrete was investigated. Various mixing ratios were applied by substituting a certain amount of slag and Calcium Sulfo Aluminate (CSA) in CO2-reduced Ordinary Portland Cement (OPC) and the physical properties of the samples were examined using the Korean Standard. The kiln temperatures of the CSA were 100–200°C ; these values are lower than those of OPC and can lead to energy saving. In addition, the low limestone content reduces greenhouse gas emissions by 20 %. Adding a small amount of CSA in OPC content activates Ca-Al-H2-based hydrates, and the initial compressive strength of the concrete is improved. As the CSA content increased, the thermal conductivity of the concrete decreased by up to 8% compared to plain concrete, thus indicating an improvement in its insulation. Therefore, the settlement stability was improved as the addition of CSA shortened the setting time.