How are the impurities removed from the blast furnace?
The mix in a blast furnace going in is Haematite (Iron ore mainly Fe2O3) limestone CaCO3, and coke (source of C) The most annoying impurities for an iron maker are silicon, phosphorus, and carbon (in high levels) The limestone removes the silica (and phoshorus) as calcium silicate (and phosphate) which is called slag. This is molten (at temp of furnace) and less dense than molten iron so floats on top. This has the advantage of preventing reoxidation at the iron surface. The slag is tapped off periodically, and run off the surface of the iron. The amount of carbon impurities in the iron is controlled by adding more or less coke at the top, but also controlling the length of the blast of air coming through at the bottom. The air will `burn` off the excess C Equations (Main ones) CaCO3 ===> CaO + CO2 SiO2 + Ca O ==> CaSiO3 C + O2 ===> CO2 C + CO2 ===> CO Fe2O3 + 3CO ===> Fe (l) + 3CO2 Hope that helps!
