Kroll process

The Kroll process is a method for making metal from ore. It is the main way that people make titanium and zirconium metal.^[1]

The process makes the ore into a volatile tetrachloride salt, uses distillation to separate the salt from other chemicals in the ore, and then reduces the salt using magnesium to make very pure metal.^{[2][better source needed]} The process can reuse many of its byproducts, but uses large amounts of energy.

Steps

First, the ore needs to be purified of other metals to avoid byproducts. The most common ore of titanium is ilmenite, which also contains iron. The Becher process is the main way that iron is removed from ilmenite.

Next, the purified titanium ore is treated with carbon and chlorine. This reaction makes metal chloride salts and carbon monoxide:^[2]

TiO₂ + 2 C + 2 Cl₂ → TiCl₄ + 2 CO

The metal chlorides are volatile, meaning they become a gas easily through sublimation. Distillation separates the gas from other compounds in the ore. Once the gas is separated, it is treated with magnesium, reducing the compound to make the pure metal and magnesium chloride:

TiCl₄ + 2 Mg → Ti + 2 MgCl₂

Finally, the magnesium chloride is electrolysed to restore the magnesium metal and chlorine used earlier in the process:

MgCl₂ → Mg + Cl₂