Electrolytic reduction of magnesium chloride
Iron cell 2. Magnesium 3. Graphite anode 4. Porcelain hood 5. Iron cathode 6. Coal gas 7. Chlorine 8. Coal gas 9. Molten electrolyte
In this step anhydrous MgCl2 is mixed with NaCl and KCl. Addition of NaCl and KCl will lower the melting point of MgCl2 and also increase the conductivity of the electrolyte.
The electrolysis is carried out in an iron pot which acts as cathode. A graphite rod enclosed in a porcelain tube is dipped into the electrolyte and acts as anode. The iron vessel is maintained at 700o C by external heating. The porcelain tube has an outlet for letting off chlorine gas. During electrolysis the following reactions take place.
Chlorine gas liberated at anode escapes through the porcelain tube. Magnesium formed at cathode floats on the electrolyte as its density is less. Magnesium is susceptible to oxidation by air. Therefore a stream of coal gas is passed over floating magnesium to prevent oxidation. Floating magnesium is removed at regular intervals. The magnesium thus obtained will be 99.9% pure.