At present, carnallite cell feed for magnesium production is used only in the CIS. Carnallite (MgCl2 • KCl • 6H2 O) is obtained as a natural mineral or as a byproduct in the processing of potassium chloride from complex salt deposits. Dehydration of carnallite is simpler than that of aqueous magnesium chloride because hydrolysis is weaker.
Impurities in the carnallite must not exceed the following levels: CaSO4 0.06%, B 0.001 %, Fe 0.01 %, and SiO2 0.01 %. The sodium chloride content may be 5-7%.
Carnallite is dehydrated in two stages. The first stage is performed in a fluidized bed at 160-200 oC to give a water content of 3.7-4.8%. The second stage, which yields molten dehydrated carnallite, is performed in a chlorinator at 700-750 oC. The chlorinator combines melting, chlorination, and settling-mixing in a single unit. The final product contains 49-51% magnesium chloride and 0.6-1% magnesium oxide. Efforts are being made to reduce the degree of hydrolysis during dehydration. Also there are plans to replace the chlorination stage by hydrogen chloride treatment in a fluidized bed. |
