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

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Diagram of a zinc-lead blast furnace system showing ore and coke entering through charge hoppers, with labeled furnace, air preheater, blower, taphole for slag and lead bullion, and a connected lead-splash condenser using rotors to separate and cool lead and zinc, with pathways for molten metals and off-gas. — metallurgy A zinc-lead blast furnace and lead-splash condenser. This technology is utilized mainly for producing zinc while managing both lead and zinc from raw materials, a technique that was highly influential in 20th-century smelting.

In the Kroll process, magnesium serves as a reducing agent to convert titanium tetrachloride ( ${TiCl}_{4}$ ) into metallic titanium.12

The reaction is conducted in large, sealed steel vessels at temperatures between 800 and 1,000 °C (1,500 to 1,800 °F) within an inert argon atmosphere to prevent contamination from air or moisture. During this process, molten magnesium reacts with ${TiCl}_{4}$ , resulting in the formation of a highly porous material known as titanium sponge, along with magnesium chloride ( ${MgCl}_{2}$ ) as a byproduct.13

Once the reaction is complete, the titanium sponge is separated from the entrapped magnesium chloride and any excess magnesium through either a dilute acid leach or high-temperature vacuum distillation. The resulting magnesium salts are typically recycled through electrolytic cells to recover magnesium for reuse in the reduction process, ensuring an efficient industrial cycle.13