Magnesium Extraction By Magnetherm Process

This technology was developed in the 1950s and 1960s by the large aluminum production company Pechiney. Later, it was also used by Northwest Alloys in the United States (see Fig. 1). The main characteristic of this technology is the heating and production furnace in which the heating takes place with electrodes using alternating current. Such heating requires liquid slag, which will conduct electricity, and therefore, in addition to Dolomite, which has undergone calcination and in addition to the reduction silicon, alumina is also added. Figure 2 describes the furnace and its components, schematically.

 

The furnace in the Magnetherm process operates within a temperature range of 1,300–1,700°C. This high temperature range stems from a number of reasons and variations in the process. The first reason is the difficulty in maintaining low pressures in the furnace with a large volume, and, therefore, as can be seen from reaction (1) :

 

2MgO*CaO(s) + Si (Fe)  =  2Mg(g) + Ca2SiO4(l) + Fe                            (1)

P = 1 at’ ; T = 1,700°C or P = 1 mm Hg ; T = 1,150–,200°C

 

it is necessary to work at higher temperatures. At times a certain quantity of magnesite,which has undergone calcination, is also added, to increase the reaction temperature.Another variation of the process that can also influence the temperature is the addition of metallic aluminum as an alternative to silicon. The use of aluminum in these processes will be detailed in the aluminothermic processes.

Production in a furnace with the Magnetherm process is in batch form and a complete cycle lasts normally 16–24 h. The magnesium fumes rise and accumulate in the cooled condenser in the liquid or solid state. The furnace usually produces between 3 and 8 t of magnesium a day, according to its size. As a rule, 7 t of raw material are required in order to produce 1 t of magnesium.

 

 

 

Fig. 1. Magnetherm Flow Chart Process

 

 

 

Fig. 2. The Magnetherm Production Facilities