Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray solid which bears a close physical resemblance to the other five elements in the second column (group 2, or alkaline earth metals) of the periodic table: all group 2 elements have the same electron configuration in the outer electron shell and a similar crystal structure.
Magnesium is the ninth most abundant element in the universe.Magnesium is the eighth most abundant element in the Earth’s crust and the fourth most common element in the Earth (after iron, oxygen and silicon), making up 13% of the planet’s mass and a large fraction of the planet’s mantle. It is the third most abundant element dissolved in seawater, after sodium and chlorine. Magnesium occurs naturally only in combination with other elements, where it invariably has a +2 oxidation state. The free element (metal) can be produced artificially, and is highly reactive (though in the atmosphere, it is soon coated in a thin layer of oxide that partly inhibits reactivity – see passivation). The free metal burns with a characteristic brilliant-white light. The metal is now obtained mainly by electrolysis of magnesium salts obtained from brine, and is used primarily as a component in aluminium-magnesium alloys, sometimes called magnalium or magnelium. Magnesium is less dense than aluminium, and the alloy is prized for its combination of lightness and strength.
Magnesium is found in solution in sea-water (about 1.3 kg m-3 magnesium) and in natural brines. It is also found extensively in the ores magnesite (MgCO3) and dolomite (MgCO3.CaCO3). Both of the two types of resources can be used as raw materials to manufacture magnesium metal. The electrolytic process
Used to treat magnesite, serpentine, seawater magnesia and brines from carnallite and lake waters.
The process involves two stages:
i) production of pure magnesium chloride from sea water or brine
ii) electrolysis of fused magnesium chloride
(i) Production of pure magnesium chloride from sea water or brine
Where sea-water is the raw material, it is treated with dolomite which has been converted to mixed oxides by heating to a high temperature. Magnesium hydroxide precipitates, while calcium hydroxide remains in solution. Magnesium hydroxide is filtered off and on heating readily forms the pure the oxide.