AbstractThe following paper revolves around the research work conducted in collaboration during Professor Iwase's brief visits to the Materials Process Science Division at Royal Institute of Technology, Stockholm. The paper focuses on the thermodynamic aspects of CaO–FeO–SiO2 and CaO–FeO–SiO2–MnO slag oxidation in air and sulfur transport through CaO–Al2O3–SiO2 slag. Thermodynamics of slag oxidation in air opens potential new areas in terms of focus on effective recovery of iron oxide from slag. The slag transport studies are of fundamental nature and focuses on a novel technique to calculate the diffusion of species through slag by analyzing its corresponding concentration in the metal phase.