Magnesium is one of the most abundant elements on Earth and is found in various geological formations and minerals. It is the eighth most abundant element in the Earth's crust, comprising about 2.1% by weight.
The primary minerals containing magnesium include dolomite (a calcium magnesium carbonate), magnesite (a magnesium carbonate), and brucite (a magnesium hydroxide). These minerals are typically found in sedimentary rocks. Seawater also contains large amounts of magnesium, which are dissolved in seawater as ions. Each liter of seawater contains 35 grams of salt, 90% is sodium chloride and the remaining 10% is dominated by magnesium chloride.
Production of magnesium elementary substance
The production of magnesium involves several processes, with the most common method being the electrolytic reduction of the melting magnesium chloride.
Magnesium Chloride Crystals
The mined minerals are then converted into magnesium chloride by reacting them with hydrochloric acid. This time the solution contains magnesium and calcium ions. Calcium oxide is added to turn the magnesium ions into water-insoluble magnesium hydroxide. Hydrochloric acid is used to convert the precipitate to magnesium chloride solution again. The solution was evaporated to obtain magnesium chloride crystals.
CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g)
MgCO₃(s) + 2HCl(aq) → MgCl₂(aq) + H₂O(l) + CO₂(g)
Mg²⁺(aq) + CaO(s) + H₂O(l) → Mg(OH)₂(s) + Ca²⁺(aq)
Mg(OH)₂(s) + 2HCl(aq) → MgCl₂(aq) + 2H₂O(l)
Magnesium Chloride Electrolysis
Electric current passes through the melting magnesium chloride crystals to break down it into magnesium metal and chlorine gas. The magnesium metal is deposited on the cathode (negative electrode), while chlorine gas is evolved at the anode (positive electrode).
Mg²⁺ + 2e⁻ → Mg
Cl²⁻ - 2e⁻ → Cl₂
It's important to note that the extraction of magnesium is energy-intensive due to the high temperatures required for the electrolytic reduction process. As a result, the cost of magnesium production can be relatively high compared to other metals.
Magnesium is also Produced from sea water
Seawater is rich in magnesium ions. Adding calcium oxide turns the magnesium ions into a precipitate. The precipitate is then extracted and hydrochloric acid is added to convert it into a magnesium chloride solution. Other steps are similar to the above.