GB499302A - Improvement in iron desulphurization - Google Patents

Abstract

In the desulphurization of molten pig iron, outside the blast furnace, with a basic slag in the presence of a reducing agent, the process is carried out with the positive exclusion of air and other oxidizing substances and under an oxygen activity substantially lower than that of the equilibrium of the reaction between carbon and oxygen to form carbon monoxide at the temperature of the pig iron and at atmospheric pressure. The process may be carried out in the presence of carbon at a pressure less than atmospheric, e.g. below 380 or even 150 mm. or in the presence of a metallic reducing agent such aluminium, magnesium or calcium or in the presence of carbon during the initial stage and in the presence of the metallic agent at a subsequent stage. The pig iron treated may have a sulphur content greater than 0,1 per cent and air may be excluded by a gas having an oxygen activity of the kind stated above. The slag used may be an alkaline oxide slag such as a soda slag with or without additions of alkaline earth oxides or may contain more than 30 per cent of alkaline earth oxides and sufficient fluorspar to make it flow above 1200 DEG C. The slag used may be blast furnace slag alone or mixed with 5-50 per cent of fluorspar and optionally also lime. The process may be carried out in a vessel with a carbon or magnesite lining and having gas tight walls except a conduit for applying vacuum or reduced pressure, and the contents of the vessel may be agitated. The iron may be treated with a slag which has been previously used and then treated with a slag which has not been previously used. After desulphurization a protecting gas free from oxygen, carbon dioxide, carbon monoxide and water vapour, e.g. nitrogen, is admitted at about atmospheric pressure into the desulphurizing vessel and maintained there until the slag and iron have been separated. The slag may be revivified as described in Specification 477,083. The total weight of the slag used is not more than 8 per cent of the iron desulphurizer.