Thermodynamics of Phosphorus and Sulphur Removal during Basic Oxygen Steelmaking



Removal of impurity elements from hot metal is essential in basic oxygen steelmaking. Oxidation of phosphorus from hot metal has been studied by several authors since the early days of steelmaking. Influence of different parameters on the distribution of phosphorus, seen during the recent work of the authors, differs somewhat from that reported earlier. On the other hand, removal of sulphur during steelmaking has drawn much less attention. This may be due to the magnitude of desulphurisation in oxygen steelmaking being relatively low and desulphurisation during hot metal pre-treatment or in the ladle furnace offering better commercial viability. Further, it is normally accepted that sulphur is removed to steelmaking slag in the form of sulphide only. However, recent investigations have indicated that a significant amount of sulphur removed during basic oxygen steelmaking can exist in the form of sulphate in the slag under oxidising conditions. The distribution of sulphur during steelmaking becomes more important in the event of carry-over of sulphur-rich blast-furnace slag, which increases sulphur load in the BOF. The chemical nature of sulphur in this slag undergoes a gradual transition from sulphide to sulphate as the oxidative refining progresses.