The carbothermic route to magnesium has been recognized as a low energy, yet high productivity path to magnesium extraction. The chemistry is as follow:
The reaction between magnesia and carbon produces a magnesium and carbon monoxide vapour. A disadvantage of this method is that slow cooling the vapour can cause the reaction to quickly revert back. To prevent this from happening, the magnesium can be dissolved directly in a suitable metal solvent before reversion starts happening. Rapid quenching of the vapour can also be performed to prevent reversion.
The Bolzano process is very similar to the Pidgeon process. The difference between the Pidgeon process and the Bolzano process is that the heating process is done through electric heating conductors, and retorts are placed vertically into large blocks in the Bolzano process. A complete reaction takes about 20–24 hours. The Pidgeon method is less technologically complex and because of distillation/vapour deposition conditions, a high purity product is easily achievable.
Besides the Pigeon process, the second most used process for magnesium production is electrolysis. This is a two step process. The first step is to prepare feedstock containing magnesium chloride and the second step is to dissociate the compound in electrolytic cells as magnesium metal and chlorine gas. The basic reaction is as follows:
The magnesium chloride can be obtained using the Dow process, a process that mixes sea water and dolomite in a flocculator or by dehydration of magnesium chloride brines. The electrolytic cells are partially submerged in a molten salt electrolyte to which the produced magnesium chloride is added in concentrations between 6-18%. The temperatures at which this reaction is operated is between 680 and 750 degrees Celsius. This process does have its fair share of disadvantages including production of harmful chlorine gas and the overall reaction being very energy intensive, creating environmental risks. The Pidgeon process is more advantageous regarding its simplicity, shorter construction period, low power consumption and overall good magnesium quality compared to the electrolysis method.