The role of volatile species in the softening of blast furnace burden.

Considerable controversy exists concerning the mechanism involved in the softening of the burden within the iron blast furnace and in particular the role played by volatile species in this process. This laboratory investigation was undertaken in order to develop a better understanding of the fundamental processes involved in the softening of the iron bearing components of the blast furnace burden and in particular the contribution of sulphur and alkali metal vapours in this process. The experimental technique developed involved the encapsulation of the test material inside a sealed silica tube containing a gas phase of known composition. The test material was moulded into the form of a Seger cone and the behaviour of the cone at elevated temperatures was used to monitor the softening of the material. This technique was used to study the effect of sulphur and alkali metals on the softening behaviour of both chemical reagents and a commercial iron ore. High temperature observation of the cones was supplemented by optical and scanning electron microscopy after testing. The results showed that the softening behaviour of the ferrous constituents of the blast furnace burden was influenced by the mass, fraction of liquid formed within the sample and by the viscosity of this liquid. Vapour borne sulphur plays an important role in the softening process in the blast furnace through the formation of ferrous sulphide which melts and acts as a lubricant between the solid particles and the more viscous liquid oxide mixtures formed. Alkalis play a less important role in the chemistry of softening in the blast furnace and they may delay softening at low oxygen potentials.