Influence of Mineral Matter on Carbon Dissolution from Metallurgical Coke into Molten Iron: Interfacial Phenomena

Identifying key factors governing the rate of carburisation of liquid iron is important for sustainable developments in blast furnace ironmaking. This study investigated the influence of mineral matter on carburisation rate 'K' for two different cokes: coke 1 (K=14.7x10(-3) s(-1)) and coke 2 (K=1.1 x 10(-3) s(-1)). The sessile drop technique was used to investigate carbon dissolution from coke into molten iron (1450 degrees C, 1550 degrees C) and the nature of interfacial products formed. Examination of the underside of the iron droplets showed the iron/coke interface was markedly different in appearance and composition between the two cokes. The interfacial product formed with coke 2 had a mesh like structure that seemed to wet the iron droplet much better than the interfacial product formed with coke 1. In contrast, Fe globules and discrete interfacial products were observed in coke 1. Interfacial products containing calcium sulfide (CaS) and manganese sulfide (MnS), were observed for both cokes. The presence of MnS could reduce the overall viscosity of the interfacial layer as it's known to lower the liquidus temperature. Electron dispersive X-ray analyses of coke I identified iron to be in close association with sulfur. These Fe/S species have atomic ratio similar to pyrrhotite (Fe1-xS) or troilite (FeS). Pyrrhotite in coke can decompose to release gaseous sulfur and metallic iron, which can be carburised to form Fe-C particles. Carburisation of liquid iron can thus occur via Fe-C particles. These factors can have a significant influence on the kinetics of carbon dissolution.