CHAPTER XXIX THERMAL PROCESSES FOR THE REDUCTION OF MAGNESIUM

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP82-00039R000100230044-8
• Release Decision: RIPPUB
• Original Classification: R
• Document Page Count: 9
• Document Creation Date: December 22, 2016
• Document Release Date: May 10, 2012
• Sequence Number: 44
• Publication Date: March 14, 1952
• Content Type: REPORT

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CHAPTER XXZX
THERMAL PROCESSES FOR THE REDUCTION OF MAGNESIUM
Source; Metallurgiya legkikh Metallov, Metallurgizdat,
Hp 515-522 (ch. XXIX).
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STAT'?
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CHAPTER XXIX
THERMAL PROCESSES FOR THE REDUCTION OF MAGNESIUI4
In view of the difficulty of producing anhydrous magnesium chloride
and due to the high electrical-power consumption in its electrolysis, the
cost of metallic magnesium is comparatively high. Therefore, scientific-
technical thought has long been concerned with simpler and cheaper methods
~e for obtaining this metal from abundant magnesium ores (magnesiue
In the 1930's these efforts met with complete success and at the
present time one may refer to the importance and industrial significance
of producing magnesium by thermal reduction.
In 1942, approximately 30 percent of the magnesium produced in the
United !States of America was obtained by the thermal reduction process.
Reduction of magnesium oxide to the metal, zr~ay be achieved by two
processes: Carbon and non-carbon, both methods having industrial appli-
cation. (M
108. Carbon Reduction of Magnesium Oxide
First effort to reduce magnesium oxide by carbon, even though un-
successful, were made by Walter in 1$84. Satisfactory production of
metallic magnesium by carbon reduction of MgO was only recently possible
and was based on an exact knowledge of the`physico--chemical nature of this
reaction. Numerous' efforts during the previous 50 years to achieve this
result had invariably led to, negative; results. The point is that the re--
action
Mg0 C7. `. CO
is normally reversible Sight to, lef 7 and' only with an increase in temper-
ature moves from left to ? right. A temperature of over 2000 degrees LCenti-
grade ; is required to shift the reaction completely ? to the right. Under
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STAT
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these temperature conditions, the products of reaction are CO and vaporized
magnesium.
However, while cooling the products of reaction for the purpose of
condensing the magnesium vapours, equilibrium is shifted back to the
left - magnesium reacting with CO to return the MgO and carbon. This
situation was long the main reason for failing to obtain metallic mag-
nesium by carbon reduction of. MgO.
Subsequent research showed that in order to prevent the back reaction
of MgO LMil and CO during the condensation of vaporized magnesium, the hot
gas mixture must be shock-cooled (chemical chilling) to a temperature, at
which the back reaction is supressed. This may be achieved by spraying
liquid hydrogen and mineral oil or hydrocarbons on the gaseous products
of reaction (Report, Bureau of Mines No 3635, May 1942). As a result
powdered magnesium (blue powder) with a small quantity of MgO is formed.
The above described process is the basis of the electro-thermal method
of obtaining magnesium by carbon reduction of MgO, developed by the Austrian-
American Corporation wit. This process, tested in a pilot plant in
Radenthein (Austria) is now used on an industrial scale in a number of
countries (w.L. Landis, Met. Tnd? (L), 1937, 51 No 17, p. 403)?
A general flow-sheet of the process is illustrated in Figure 201.
Figure 201. TEC} OLOGIPAL FLOW-SHEET OF THE PRODUCTION OF MA ESIUM
BY REDUCTION OF MAGNESIJE BY CARBON
1.
Electric furnace
5?
Filter
2.
Cooler
6.
Cyclone
3.
Distilling Pipe
7.
Filter
4,
Oil
~.
High pressure washer
Well-calcined magnesite, if possibLe free of impurities, is used as
raw material. The magnesite is mixed with anthracite or ashfree coke
(approximately 3 parts by weight of 92 percent magnesiue and 1 part re-
ducing agent) and the charge loaded between the electrodes of a hermetically
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sealed three phase electric furnace (Figure 202). Pressure in the furnace
reached approximately 100 millimeters of mercury.
The gaseous products of the reaction (Co, Mg vapors) on passing from
the furnace to the condenser (Figure 203) are shock-cooled with a blast of
liquid hydrogen.
.As a result, the temperature of the gas mixture drops from 2200/2300
150/200 degrees entigrad 7 and the magnesium vapors condense into powder.
To achieve this 40-50 volumes of hydrogen are required for each volume
of vaporized magnesium.
Fi
re 202.
Electric Furnance For the Reducti
f M
on o
agnesiue at
the Radenthein 1Nbrks
Fi
20 3.
Condenser for Magnesium Vapors at the H
d
th
a
en
ein Works
Magnesium powder thus produced is continually removed from the con-
denser, while the separating gases (C0, C02, and H2) are purified of all
suspended particles by filtering. The magnesium powder consists of 60-
70 percent pure magnesium and 15-22 percent MgO, the balance being impurities
from the magnesite and the reducing agent which also volatilize during the
high temperatures of the reduction process. The recovery of magnesium from
the magnesiue present in the magnesium powder is 80-90 percent.
In view of the fact that the latter is highly inflammable, it is mixed
with oil before being transported, preparatory to distilling out the pure
magnesium.
Magnesium powder is then briquetted under a hydrogen atmosphere and the
briquettes are automatically transferred to the distilling furnace.
The distilling furnace is a hermetically sealed installation with a
residual pressure of 20 millimeters of mercury. The furnace is heated by
internal electric resistance up to a temperature of 750-950 degrees
1Centi-
grad.
From the distilling furnace the vaporized magnesium is fed into the con-
denser, where the magnesium vapors condense as spherical drops varying '
in
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KILOWATT HOURS
Reduction
Distilling
Remelting
Auxiliary Operations
18.0
Hydrogen used for each 1 kilogram of magnesium is about 0.25 cubic
meters and may be returned into the process after removal of CO. To this
end, the gas mixture, remaining after separation from the magnesium powder,
is treated by steam in a contact chamber where CO is converted into C02?
The CO2 is then absorbed by the water and the pure hydrogen returned into
the process. .
109. Reduction of Ma esium oxide b Non.-carbon Reducing Agents
Reduction of magnesium oxide by non-carton reducing agents is simpler
than by carbon. In this case solid rather than gaseous products result from
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size from small pellets to balls over 1 centimeter in diameter. Drops
of condensed magnesium fall into an oil filled collector. Magnesium is
then filtered from the oil, melted in an electric furnace and poured in-
to ingots. The oil is returned to the collector.
Non-volatile residue after the distillation of magnesium, mostly MgO,
is removed from the distillery furnace by mechanical means and returned
for reduction.
Magnesium recovery of magnesium in the powder after the second dis-
tillation reaches 98 percent so that total recovery of magnesium from
calcined magnesiuo is over 80 percent.
The metal obtained after additional distilling and remelting is of a
very high purity.
Electrical energy consumed in individual stages of the reduction by
the electro-thermal process per 1 kilogram of metal in ingots is bxken
down as follows:
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oxidation-reduction and this makes it possible to produce comMercial metal
in one operation.
As reducing agents for non-carbon reduction of MgO one could use for
example, aluminium, silicon, silico-aluminium and ferrosilicon?
Reduction of MgO by non-carbon reducing agents goes virtually to
completion and is comparatively simple in its technical aspect.
The drawback of this process is however the comparatively high cost
of the reducing agents, which clinker completely.
of special interest are methods for the reduction of magnesiue or
dolomite with the aid of silicon, usually used in the form of ferrosilicon.
This process (in a furnace with carbon electrodes) was first introduced
by Blecker and Ivrrison in 1915? At the present time, technical methods
have been developed for the reduction of magnesite (dolomite) by silicon
(ferrosilicon), which are the basis for a number of operating industrial
installations.
The reaction in the reduction of calcined dolomite with silicon
follows the equation:
2Mg0 ? Ca0 -4- Si 2 CaO ' 5i02 + 2Mg
Thus, calcium oxide present in calcined dolomite is changed into
calcium orthosilicate; magnesium oxide from the calcined dolomite is re-
duced practically completely to a metal.
Besides, this process does not require temperatures as high as those
for the reaction in the reduction of MgO by carbon (above 2000 degrees), but
is conducted at a satisfactory rate at 12001400 degrees. As an example of
how the technological problem of reducing dolomite by ferrosilicon is solved
let us examine the process of producing magnesium at the H? Ford plant . (G.E.
Stedman. Chem.a? Met. Eng. September 1942, 134-137)?
The technological flow chart is represented by Figure 204.
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To dumping grounds
.
ical Flow Chart - for producing magnesium
Fi ;~.e 20 . dolomite
through the reduction of
ferrosilicon at the H. Ford Plant
by
basic stages: Conditioning the dolomite,
The process cons?sts of 2
Raw dolomite from Michigan quarries
ro cess of reduction (smelting) ?
he
and t p
t undergoes calcination (roasting) and
is delivered to the plant, where i
grinding. anon the dolomite loses, in the f?~ grinding. As a result of calc' ~.n ,
ximatel~ 50 percent of its original weight.
carbon dioxide, appro ~
Calcined dolomite arid ground 75 percent ferrosilicon (in the pro?
~t directly into large circular mills, which
portion 6:1) is measured o tti
ctians of grinding and mixing the materials.
perform simultaneously the fun
A mixture of calcined dolomite and f e rro sili con flows into bunkers,
ans orted to the reduction depart.
from where, as necessity arises it is tr p
charge is briquetted before going into the furnace.
meat. Here the furnace reduction of dolomite (Figure 205) are arranged in
Furnaces. for the
is 5?'7 meters high, .1~.$ meters wide and 5~4
several rows' Each furnace
meters long.
,
e
c
of chr~m-n
Eleven pipes
are laid
the lower and five in the upper row -?
l,
furnace. The reduction process takes place in
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Raw dolomite
Re coon in the Furnace
in. two
l steel
k
i
horizontal rows - six in
in the middle 0f . each
these retorts'
Da.ameter 0?Z5 or 0.30 meter;
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zone and 0.7 meters extend outside the walls on each side of the furnace.
The retorts rest on a crown of refractory brick in the center of the furnace.
Cylinders of sheet steel are inserted into the protruding ends of each
retort and serve for the condensation and crystallization of magnesium
(Figure 206).
F, re 20 . General View of Furnances for the Reduction of lEblomite
surface of the steel cylinders. After several experiments with water
cooling, it was determined that the natural contact of cool air with the
flanges of the retorts was sufficient for the normal solidification of
The process of reduction is conducted in a vacuum. For this purpose,
each retort is connected at both ends to a vacuum line by means of a 1.5
inch pipe. Each furnace is served by four vacuum pumps of 2800 liters per
minute capacity. To obtain a high vacuum the retorts are sealed on both
sides by tight fitting covers.
Before being loaded into the retorts, the briquettes are heated in
the upper part of the furnace by exhaust gases directed into the pipe. A
single charge for each retort is approximately 175 kilograms of briquettes.
After charging with the briquettes, condensing cylinders are inserted, the
covers securely screwed on and the vacuum pumps turned on.
Each furnace is equipped with several generator gas burners in order
to maintain the required internal temperature.
The process of reduction for each charge of dolomite continues for
eight hours. Magnesium vapors (under influence of reduced pressure) flow
towards the ends of the retort, where magnesium solidifies on the inner
magnesium.
After eight hours of heating, the cylinders with the deposited mag-
nesium are removed from the retort, the two halves opened and druses of
crystalized magnesium removed from the surface.
Theoretically the recovery of metallic magnesium should represent
20 percent of the weight of the briquettes. This represents approximately
35 kilograms of metal for each retort.
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After removing the cylinders containing the condensed magnesium, the
retorts are scraped free of slag formed during the process. This slag,
having a high lime content, may be used in agriculture.
At another magnesium plant in the province of tario (Canada)
also using the ferrosilicon process of dolomite reduction operating since
1942, the retorts are heated electrically by means of sillimaniterous
(Engineer and Mining Jour. 1943, Vol 144, No 5, 56-61). s )? The latter are
grouped, strictly in accordance with their power of resistance. Inasmuch
as the resistance of the silimanite rods varies with wear, a system of
transformers, regulating the voltage, is provided to compensate for the
changing resistance of the bars. This makes it possible to maintain a con-
stant temperature.
At the magnesium producing plants in Murex (?) Great Britian and
Broken Hill, Australia, metallic magnesium is obtained by reducing g calcined
rnagnesite by calcium carbide (Canter A A Electrometallurgy Eng. Min. J.
1942, Vol 143, No 2, 13). To this end finely crushed ma nesite is
g briquetted
with crushed Ca02; the briquettes are heated in steel retorts at a tempe~
ature of 1100-1200 degrees. The reduction process is conducted in a vacuum
and magnesium solidifies in the upper regions of the retort on the surface
of the condensers, is cooled by water, and forms a solid ring of c
nrystalie
metal of high purity (99.85 percent Mg). The heating cycle takes 24-36
hours depending on the size of the retort. .wring the reduction process
the briquettes should not be subject to melting. A solid residue of a
mixture of lime and coal remains after the process.
Production of metallic magnesium by the thermal reduction process,
during the past years, particularly over the war period, has become hi
aly
developed in various countries.
There is reason to believe that ultimately, due to the simple techno-
to gical technique, safety, compact installation an l lower .power consumption,
production by this process will exceed that by the electrolytic process.
t. EAi O
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