Impurities in Iron Ores

There are certain impurities that lower the value of iron ores or may even make them valueless. Sulphur in the ore goes partly into the iron and steel and makes them brittle.

While it is possible by roasting the ore and by other means to remove the sulphur, the presence of any considerable amount is objectionable. Phosphorus in steel makes it brittle. For steel-making the limit for phosphorus is one hundredth of one per cent for ten per cent of iron in the ore; this is the so-called Bessemer limit. A Bessemer ore carrying 52% of iron must not have more than .052% of phosphorus and the sulphur should not exceed .04%. But since the presence of phosphorus in pig iron increases the fluidity and tends to make sound castings, ores high in phosphorus are used in making foundry pig iron. Titanium is objected to by users of iron ores, because it is said to make a pasty slag and to interfere in other ways with the smooth running of the blast furnace. At present, ores containing more than 5% or 6% of titanic acid (TiO2) are not saleable.