Effect of coexistence of potassium and sulphur on abnormal swelling during reduction of hematite pellets.

Abstract

In order to elucidate the effect of coexistence of potassium and sulphur on abnormal swelling during reduction of iron oxides, hematite pellets containing potassium carbonate have been reduced with sulphur bearing hydrogen base gas under the condition of gas starvation in the temperatures of 800 to 1 000°C.The addition of 0.12.0 mol% K2CO3 shows that normal swelling amounts to below 40% with macro- and microscopic cracks and that abnormal swelling reaches 300% at 800°C with coarse iron whiskers. This abnormal swelling due to only potassium takes place considerably regardless of any reduction history.The abnormal swelling due to gaseous sulphur is observed in range of 10-21 as sulphur activity of gas (aS) relative to Fe/FeS equilibrium. The maximum swelling is 500% with fine iron whiskers in aS of 0.1 at 900°C. It is found that sulphur has stronger abilities for the swelling than potassium.The largest swelling is 600% and it is observed under coexistence of potassium and sulphur without the formation of liquid phase at 800°C.Actions of both additives during metallization is discussed in the light of authors' previous researches dealing with the effect of sulphur on reduction of wustite.