GB477083A - Improvements in or relating to the desulphurization of pig iron - Google Patents

Abstract

Pig iron is produced in a coke blast furnace and the molten iron is treated under strict reducing conditions in a desulphurizing vessel, free from substantial additions of oxidizing substances and without substantial application of heat, with a basic desulphurizing slag containing not more than 55 per cent of lime, and silica and fluorspar in a total amount of 25 per cent or more, the remainder of the slag if any, (in addition to sulphur compounds, being basic such as alumina or soda, the treatment being carried out in the presence of carbon and a reducing atmosphere containing carbon monoxide and at a temperature of 1400 DEG C. or below. The slag is separated from the pig iron after treatment and revivified outside the desulphurizing vessel, the slag then being suitable for further desulphurizing of additional quantities of pig iron. The desulphurizing vessel may be lined with carbon or carbon may be introduced into the slag, and the reducing atmosphere may be under superatmospheric pressure. In an example, a slag contains 30-55 per cent of lime, 20-50 of fluorspar and 5-25 of silica to which 5 of alumina may be added, and may contain other alkaline earth oxides such as barium or strontium oxide. Other reducing agents besides carbon, such as calcium carbide, ferro-silicon or other ferro-alloys such as ferro-manganese may be added to the slag. The reducing atmosphere may consist of carbon monoxide or a mixture of carbon monoxide, carbon dioxide and nitrogen, the proportion of carbon monoxide being large compared with that of the carbon dioxide. The desulphurizing vessel consists of a ladle lined with carbon and mounted on wheels, which run on rails and provided with means for rocking and agitating charge. The charging opening of the ladle, after the pig iron charge has been run in, is tightly closed by a cover, and carbon monoxide or a gas containing the latter is introduced into the space above the slag. The ladle may also be provided with electrodes for the purpose of heating the charge if the temperature of the latter is too low. The slag removed after treatment may be revivified by treating with water and carbon dioxide, or with an oxidizing gas or by maintaining it in contact with a molten matte-forming metal such as copper. The revivified slag may be dried and calcined and then charged into the ladle at an elevated temperature. The pig iron may be treated with slags of progressively decreasing sulphur content, each slag being revivified when its sulphur content becomes too high to prevent efficient desulphurization.