By Allan Robinson
Updated Aug 30, 2022
Magnesium chloride (MgCl₂) is a versatile inorganic salt used across industries—from construction materials to food supplements. While the pure compound is MgCl₂, commercial products often contain its hydrated forms, MgCl₂·xH₂O. The salt is sourced primarily from seawater, where it is recovered either by mining or through extraction processes.
Precipitate magnesium hydroxide from seawater. By adding slaked lime (Ca(OH)₂) to seawater, magnesium ions (Mg²⁺) form insoluble magnesium hydroxide (Mg(OH)₂). The reaction is: Mg²⁺ + Ca(OH)₂ → Mg(OH)₂ + Ca²⁺.
Convert the precipitated magnesium hydroxide into magnesium chloride hydrates using hydrochloric acid. This conversion—known as the Dow Process—is widely employed on a commercial scale: Mg(OH)₂ + 2 HCl → MgCl₂ + 2 H₂O.
Transform magnesium carbonate (MgCO₃), a naturally occurring mineral, into magnesium chloride. The reaction proceeds as follows: MgCO₃ + 2 HCl → MgCl₂ + CO₂ + H₂O. This route is valuable when MgCO₃ is available in commercial quantities.
Generate magnesium chloride in a laboratory setting by reacting magnesium metal with hydrochloric acid. Though straightforward, the reaction—Mg + 2 HCl → MgCl₂ + H₂—is inefficient for large‑scale production.
Prepare magnesium chloride from magnesium sulfate (MgSO₄) and table salt (NaCl). Heating a concentrated solution of these reagents and then cooling it rapidly drives the following reaction: MgSO₄ + 2 NaCl → MgCl₂ + Na₂SO₄.
