Production
The production of the metals itself is difficult due to their reactivity. The formation of oxides, nitrides and carbides must be avoided to yield workable metals, this is normally achieved by the Kroll process. The oxides (MO2) are reacted with coal and chlorine to form the chlorides (MCl4).The chlorides of the metals are then reacted with magnesium, yielding magnesium chloride and the metals.
Further purification is done by a chemical transport reaction developed by Anton Eduard van Arkel and Jan Hendrik de Boer. In a closed vessel, the metal reacts with iodine at temperatures of above 500 °C forming metal(IV) iodide; at a tungsten filament of nearly 2000 °C the reverse reaction happens and the iodine and metal are set free. The metal forms a solid coating at the tungsten filament and the iodine can react with additional metal resulting in a steady turn over.
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- M + 2 I2 (low temp.) → MI4
- MI4 (high temp.) → M + 2 I2
Read more about this topic: Group 4 Element
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