1. Extraction from Dolomite CaMg(CO3)2 and Magnesite Ore MgCO3.
MAGNESIUM
Extraction from Dolomite CaMg(CO3)2 and Magnesite Ore MgCO3.
Electrochemical processes are used to extract the metal from dolomite and magnesite ore.
When dolomite is crushed, roasted and mixed with seawater in large tanks, magnesium hydroxide settles to the bottom.
Heating, mixing in coke, and reacting with chlorine, then produces molten magnesium chloride. This can be electrolyzed, releasing magnesium, which floats to the surface.

2. Extraction from Sea Salt
Magnesium is also extracted from salt brines, which contains about 10 percent magnesium chloride. The magnesium chloride at these sources still contains significant amounts of water and must be dried in order to make the magnesium chloride anhydrous, before it can be electrolyzed to produce metal.
Salt water can also have a high magnesium content. The first magnesium metal extracted from sea-water was produced by Dow Chemicals at their Freeport, Texas plant in 1948.
The Freeport facility operated until 1998, but, presently, the only remaining salt water magnesium producer is the Dead Sea Magnesium Ltd. (Israel); A joint venture between Israel Chemicals Ltd. and Volkswagen AG.

3. 1-When sea-water is the raw material, it is treated with dolomite which has been converted to mixed oxides by heating to a high temperature.  
2-Magnesium hydroxide precipitates, while calcium hydroxide remains in solution.
3-Magnesium hydroxide is filtered off and on heating readily forms the pure the oxide2,825 °C. 4-Conversion to magnesium chloride is achieved by heating the oxide, mixed with carbon, in a stream of chlorine at a high temperature in an electric furnace.
5-The resulting anhydrous magnesium chloride is fed continuously into electrolytic cells which are hot enough to melt it.
6-On electrolysis, magnesium and chlorine are produced. The molten metal is removed and cast into ingots.  The chlorine gas can be further recycled.

5. Electrolysis of molten magnesium oxide, MgO
In this process, reduction of magnesium oxide dissolved in fluoride- based electrolytes (MgF2-CaF2-MgO) is carried out by passing electric current at 1150 to 1300 oC .Som process year 2001
Electrodes: Carbon rods (Graphite)
Electrolyte: Molten magnesium oxide
Ions present in electrolyte: Magnesium ions (Mg2+)Oxygen ions (O2−)
Reaction at the CATHODE: Mg2+ (l) + 2e−→ Mg (s)
Reaction at the ANODE: O2− (l) → O2(g) + 4e−