Magnesium is commercially extracted from sea water via Dow's process, which concludes with the elect — Metallurgy and Isolation of Elements Chemistry Question
Question
Magnesium is commercially extracted from sea water via Dow's process, which concludes with the electrolysis of fused Carnallite. Dehydrating hydrated Carnallite ($KCl \cdot MgCl_2 \cdot 6H_2O$) in normal air leads to the formation of an unwanted basic compound ($MgO \cdot MgCl_2$) due to hydrolysis. How is this prevented industrially?
💡 Solution & Explanation
Heating hydrated magnesium chloride in air causes it to hydrolyze with its own water of crystallization, yielding $MgO$. To obtain pure anhydrous $MgCl_2$ suitable for fused salt electrolysis, the crystals must be heated (calcined) in an atmosphere of dry $HCl$ gas, which suppresses the hydrolysis equilibrium.