How is magnesium used to remove sulfur and oxygen from blast-furnace iron?

Magnesium is used in the treatment of liquid blast-furnace iron primarily through the injection of particulate magnesium blended with lime or other fillers.1

Because magnesium is a strong reactant that forms stable compounds with sulfur and oxygen, it serves as an effective agent for refining the metal. When injected into the liquid iron, magnesium acts as a desulfurizer by combining with sulfur and as a deoxidizer by combining locally with dissolved oxygen. This process improves the mechanical properties of the resulting steel by removing these impurities. The addition of lime in the mixture serves a dual purpose: it assists in the desulfurization process and helps prevent the low-melting magnesium powder from melting prematurely inside the injection lance.213