In the process of making iron, limestone is added to:

Limestone is added to the blast furnace as a flux to help remove impurities from the iron ore during the smelting process. When limestone is heated in the presence of iron ore, it reacts with the silica and other impurities to form a slag, which is a molten material that can float on top of the molten iron. This separation is crucial because it allows for the collection of high-quality pig iron while the slag can be removed and discarded or further processed.

This process enhances the overall efficiency of iron production by ensuring that the resulting pig iron is not contaminated with undesirable materials. The formation of slag is a critical step in metallurgy, especially in the conversion of raw ore into usable iron. Thus, the addition of limestone directly contributes to both the quality of the iron produced and the efficacy of the smelting process.