What is the role of a flux in the metallurgical process?

In metallurgy, a flux is a substance added to the ore during smelting to remove impurities (gangue) from the molten metal. The flux reacts with the non-fusible impurities to form a fusible product called slag, which is lighter than the molten metal and floats on its surface, making it easy to separate. For example, in the extraction of iron, limestone (CaCO3) is used as a flux. It decomposes to CaO, which then reacts with silica (SiO2, an acidic impurity) to form calcium silicate (CaSiO3) slag.