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Why is chlorine formed during the production of magnesium metal from magnesium chloride?

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A labeled diagram of the chlorine element from the periodic table shows its atomic number 17, symbol Cl, electron configuration, and atomic weight range. The box is shaded green to indicate chlorine is a halogen, with icons for orthorhombic crystal structure, gas state at room temperature, and strong acidity. A key explains the icons and colors used. — chlorine Properties of chlorine.

Chlorine is formed during the production of magnesium metal from magnesium chloride because the process utilizes electrolysis to dissociate the compound.1

In this industrial method, magnesium chloride is dissolved in a molten salt electrolyte within an electrolytic cell equipped with steel cathodes and graphite anodes. When an electric current is applied, the magnesium chloride undergoes chemical dissociation: the magnesium ions are reduced to molten magnesium metal at the cathodes, while chlorine gas is generated at the graphite anodes. This byproduct is often captured and reused in the dehydration stages of the production process.1