Impurities that do not produce gaseous oxides, such as silicon and phosphorus, lime (CaO) is added to the furnace.
The basic
oxide of calcium react with the impurities forming a ‘slag,’ just
as it does in the blast furnace when extracting iron from its ore.
–CaO(s) + SiO2(s) ® CaSiO3(l)
The slag of course
floats on top of the molten iron.
The molten iron is
poured off by tilting the furnace.
Controlled
amounts of carbon and other elements are added to make different
types of steel.
The large majority of iron from the blast furnace is made into steel
for construction, steel contains 0.1% to 1.5%
carbon.