Method of producing metallic magnesium, magnesium oxide or a ref

Details Method of producing metallic magnesium, magnesium oxide or a ref Method of producing metallic magnesium, magnesium oxide or a ref

1995-07-13

1998-09-08

Andrews, Melvyn

Specialized metallurgical processes, compositions for use therei

Processes

Electrothermic processes

75 1063, 75419, 75599, 420129, 423346, 423350, 423636, C22B 2622

Patent

active

058039473

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to methods of processing a starting material selected from the group consisting of magnesium oxide containing minor amounts of oxides of Fe, Si, Ca and Al; natural and industrially produced magnesium silicate minerals; and mixtures thereof, e.g. olivine, by carbothermal reduction and methods of producing metallic magnesium, pure magnesium oxide (MgO) and refractory masses consisting of MgO, Mg.sub.2 SiO.sub.4 and SiC by carbothermal reduction of starting materials selected from the above-mentioned group.


REVIEW OF PRIOR ART

In general metallic magnesium is produced by electrolytic and by thermal processes. By the thermal processes two groups of minerals/rocks are used as starting materials.
The first group in which magnesium oxide is bound to carbon dioxide, includes i.a. the minerals magnesite and dolomite.
The second group in which magnesium oxide is bound to silicon dioxide, includes i.a. the mineral olivine.
Although the minerals in the second group, such as olivine, occur in large deposits and exhibit a high magnesium content, the industry has mainly been employing magnesite and dolomite, i.e. starting materials from the first group for the production of magnesium.
This is due to the fact that it has been found more easy to remove and separate CO.sub.2 from the members of the first group than to remove and separate SiO.sub.2 from the members of the second group.
In general two classes of methods have been suggested for removing and separating SiO.sub.2 from the second group: The wet methods wherein the ores are treated with strong mineral acids, and the direct reduction methods wherein the magnesium oxide component of the ores is reduced to and withdrawn as gaseous Mg.
The direct methods may be classified in two groups.
In the first group of direct reduction methods, which have only been suggested in connection with reduction of metal oxides, i.e. not metal silicates, reducing agents are employed forming gaseous oxygen containing reaction products, for example reduction of MgO with carbon as reducing agent forming Mg and CO as gaseous oxygen-containing reaction product at atmospheric pressure and a temperature about 1850.degree. C., or other carbothermal reduction methods, vide e.g. U.S. Pat. No. 2,268,779 (SEIFERT), and U.S. Pat. Nos. 2,582,119 and 2,582,120 (HANSGIRG).
When a mixture of magnesium silicate, e.g. olivine (Mg.sub.2-x Fe.sub.x SiO.sub.4 ; x:0-1), and carbon is heated to a temperature in the interval from about 1300.degree. C. to about 2200.degree. C., the following reactions occur: ##EQU1## (1') Mg.sub.2 SiO.sub.4 (s)+3 C(s).rarw..fwdarw.2 MgO(s)+SiC(s)+2 CO(g) (1") Mg.sub.2 SiO.sub.4 (s)+3 C(s).rarw..fwdarw.2 Mg(g)+SiO(g)+3 CO(g) respectively.
These equilibria, except equilibrium (4), are all shifted to the right by increasing temperature and decreasing pressure.
Similar reactions occur by carbothermal reduction of MgO containing impurities such as oxides of Fe, Si, Ca and Al, in the following referred to as "crude MgO".
Due to the formation of the gaseous components Mg(g) and SiO(g) transport of Mg and SiO may occur within the reaction mixture and Mg and SiO may even be removed therefrom by evaporation.
Thus, solid Mg may be collected by condensation of evaporated metallic Mg in a separate condensation zone, i.e. in a condenser positioned at a distance from the reaction mixture.
A problem inherently associated with the first group of direct methods consists in the possibility of back-reaction, vide equation (2), between magnesium and the gaseous oxygen containing reaction product whereby magnesium is oxidized to magnesium oxide.
This problem has been solved in the second group of direct methods by using reducing agents which form non-gaseous reaction products, for example reduction of magnesium ores with silicon, aluminium, calcium carbide or silicon carbide.
Methods belonging to the second group of direct reduction methods have been described in a number of patent specifications, e.g. U.S. Pat. Nos. 2,372,571, 2,379,576, 2,527,722, 2,527,724 and 2,570

REFERENCES:
patent: 2257910 (1941-10-01), Kirk
patent: 2268779 (1942-01-01), Seifert
patent: 2372571 (1945-03-01), Hansgirg
patent: 2379576 (1945-07-01), Hansgirg
patent: 2527722 (1950-10-01), Hansgirg
patent: 2527724 (1950-10-01), Hansgirg
patent: 2570232 (1951-10-01), Hansgirg
patent: 2582119 (1952-01-01), Hansgirg
patent: 2582120 (1952-01-01), Hansgirg
patent: 4147534 (1979-04-01), Hori
patent: 4200264 (1980-04-01), Hori
patent: 4437886 (1984-03-01), Miura et al.
patent: 4545975 (1985-10-01), Kobayashi et al.
patent: 5383953 (1995-01-01), Christini

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