How is magnesium used in the Kroll process for making titanium?

In the Kroll process, magnesium serves as the reducing agent used to extract metallic titanium from titanium tetrachloride (${\text{TiCl}}_4$).12

The process is conducted in a sealed steel vessel under an inert argon atmosphere to prevent contamination from air or moisture. The reaction occurs at approximately 800 to 1,000 °C, where molten magnesium reacts with ${\text{TiCl}}_4$ to produce metallic titanium in the form of a highly porous material known as "sponge".12

Following the reaction, the resulting mixture contains the titanium sponge along with entrapped magnesium chloride (${\text{MgCl}}_2$) and excess magnesium. These impurities are subsequently removed through either a dilute acid leach or high-temperature vacuum distillation. The magnesium chloride byproduct is often recycled through electrolytic cells to recover magnesium for reuse in the reduction process.12