The correct answer is D. All of the above.
Slag is a byproduct of the iron and steel making process. It is a molten mixture of impurities that floats on top of the molten iron and is skimmed off. The composition of slag varies depending on the type of iron ore being used and the type of furnace being used. However, it typically contains lime (CaO), silica (SiO2), alumina (Al2O3), and other impurities such as MgO, CaSO4, KMnO2, and FeO.
Lime is added to the iron ore to remove impurities such as silica and alumina. Silica and alumina are both acidic oxides, and lime is a basic oxide. When these two oxides react, they form a slag that is less dense than the molten iron and floats to the surface.
The slag is then skimmed off and disposed of. It can be used as a road base, as a filler in concrete, or as a flux in the steel making process.
The following are the functions of slag in the iron and steel making process:
- To remove impurities from the molten iron
- To act as a flux, which helps to lower the melting point of the iron ore
- To protect the molten iron from oxidation
- To improve the quality of the iron or steel produced