The rate of desulfurization of liquid iron in an alumina crucible by CaO40%-SiO₂40%-Al₂O₃20% slag was studied at about 1550°C. At the same time, the change of interfacial tension during desulfurization was examined by the X-ray photography.
The rate of desulfurization incereased in order of pure iron, iron containing silicon, and iron saturated with carbon. From the analysis of experimental results by the rate equation of the mixed-controlled reaction model, it was found that the partitioning of sulfur between liquid iron and slag at the interface reached its equilibrium one in the case of liquid iron without carbon and not in the case of liquid iron containing carbon. This indicates that the rate controlling step is the mass transfer in the former and the chemical reaction in the latter.
The overall rate constants ranged from 9.2×10^-6 to 4.9×10^-4 cm/sec.
The interfacial tension incereased monotonously with the progress of desulfurization and showed no abnormal change. It decreased remarkably with increase of the activity of sulfur in liquid iron.