Magnesium Extraction by Magnola Process

Magnola Process use Serpentine as Raw Material as fig 1:

Fig. 1. Sepentine

 

A magnesium chloride-rich solution (27%) is poured into the spray dryer. In this installation,with the aid of hot gases, by burning of natural gas, the magnesium chloride is dried to MgCl2*2H2O, Eqs. (1) and (2), as in the hydro magnesium drying process.

 

MgCl2*6H2O = MgCl2*4H2O + 2H2O(g)             T = 117oC    (1)

MgCl2*4H2O = MgCl2*2H2O + 2H2O(g)             T = 185oC    (2)

 

The main difference lies in the fact that in the magnola process drying is carried out in one stage (see Fig. 2). The “price” is the relatively high percentage of hydrolysis,which causes a concentration of magnesium oxide of up to about 2%. During the second stage the material is transferred to a unique chlorinator called “super chlorinator”. The melting process is carried out as follows: an electrolyte low in magnesium chloride is pumped from the electrolysis cell to the chlorinator where it assists in the melting of  magnesium chloride hydrate; this electrolyte returns to the electrolysis cell richer in magnesium chloride in the overflow. The reason for the melting in the electrolyte is the relatively high melting temperature of pure magnesium chloride; melting in the electrolyte enables the melting temperature to be decreased 200–300°C. The electrolyte temperature is about 650°C, and this is also the temperature at which the material is returned to the electrolysis cell,with the assistance of heating by the graphite electrodes.

 

The chlorinator is fed with dry, gaseous HCl, which is produced from all the chlorine manufactured in the electrolysis cells.Feeding is carried out with the assistance of a number of graphite mixers, which are introduced from the chlorinator ceiling. These mixers assist in dispersing the HCl and improve the efficiency of the following reaction:

 

MgO + 2HCl(g)  = MgCl2(l) + H2O(g) (2.21)

The high concentration of HCl in the melt and above the melt prevents the back hydrolysis reaction between the water vapors to the magnesium chloride. The concentration of magnesium oxide in the electrolyte returning to the electrolysis cell is about 0.05%.

 

The HCl discharged from the two drying stages is received in watery solutions and transferred back to the extraction process, according to Fig. 2, thus closing the process circle for the production of magnesium from raw material that does not contain chlorine.

 

Fig. 2. Magnola Process