Magnesium Extraction By Dow Process

This process use Dolomite (see fig. 1) as Raw Material:

 

Fig. 1. One of Dolomite Minerals

 

Dolomite is composed mainly of the double salts of magnesium and calcium carbonate, and contains low concentrations of iron and manganese as impurities. Dolomite is usually colorless and looks like small diamond-shaped crystals. Dolomite is formed as a result of calcite transformations in the presence of magnesium ions.

Dolomite rock is useful in the chemical industry for the preparation of magnesium and serves as construction and decoration stone.Common deposits can be found in England, Germany, Brazil,Norway and Mexico. The magnesium concentration in dolomite by weight is 28.8%.

The process developed at Dow (see Fig. 2) is unique, due to the fact that the material fed into the electrolysis cells still contains a significant amount of water – about 27%. A solution of magnesium chloride is introduced directly into the spray dryer and comes into direct contact with burning gases, predominantly natural gas. During this process only reactions (1) and (2) take place.

MgCl2*6H2O = MgCl2*4H2O + 2H2O(g)        T = 117oC          (1)
MgCl2*4H2O = MgCl2*2H2O + 2H2O(g)        T = 185oC          (2)
The products of this stage are granules of MgCl2*2H2O. The additional dehydratation is, in fact, carried out in the electrolysis cell, by the chlorine,which is created in the cell and the graphite anodes,which are used up at a fast rate.

 

Fig. 2. Dow Process