CHAPTER XXVII PRODUCTION OF MAGNESIUM BY ELECTROLYSIS OF ITS OXIDE AND OF MAGNESIUM ALLOYS WITH OTHER METALS

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP82-00039R000100230042-0
• Release Decision: RIPPUB
• Original Classification: K
• Document Page Count: 9
• Document Creation Date: December 22, 2016
• Document Release Date: May 10, 2012
• Sequence Number: 42
• Publication Date: March 14, 1952
• Content Type: REPORT

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CHAPTER XXVII
PRODUCTION OF MAGNESIUM BY ELECTRQLYSTS OF ITS OXIDE AND
OF MAGNESIUM ALLOYS WITH OTHER METALS
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STAT
STAT
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PRODUCTION OF 1VIAGNESIUM BY ELECTROLYSIS OF ITS OXIDE
AND OF MAGNESIUM ALLOYS WITH OTHER METALS
103 Production of Ma
nesium bar Electrolysis of Magnesium Oxide.
Production of Magnesium by electrolysis of its oxide (the so-called
Oxide method) has been studied by a number of researchers. Reason for
interest in this method is a desire to avoid the very complex and
costly process of obtaining anhydrous chloride salts for their subsequent
electrolysis.
Success in producing aluminum by the electrolysis of alumina
(aluminium oxide) in fused fluorine salts, naturally led to the idea
of applying an analogous process to magnesium oxide,
however, during the development of the process of direct electro-
lysis of magnesium oxide in fused agents, certain difficulties were
encountered which have, as yet, not been solved for industrial application.
The basic difficulties usually connected with this process are:
(l) the very low solubility of magnesium oxide (tenths of a percent)
in compounds suitable as smelting agents for the electrolytic production
of pure magnesium; this results in frequent anodic complications that
interrupt the process of electrolysis; (2) high melting temperatures of
these agents (950 -1000 degrees foentigradeJ) resulting in considerable
loss of magnesium during the electrolysis process (evaporation, reoxidation);
(3) high (as compared with metalc magnesium) specific gravity of the
molten electrolyte, thus complicating the creating of an efficient electro-'
lyser so as to prevent considerable loss of the separated metal,
Should these shortcomings be eliminated, the oxide method, on account
of its simplicity, may present advantages as compared with existing
methods of producing magnesium by the electrolysis of fused chlorides.
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STAT
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PRODUCTION OF MAGNESIUM BY ELECTROLYSIS OF ITS OXIDE
AND OF MAGNESIUM ALLOYS WITH OTHER METALS
103 - Production of Magnesium by Electrolysis of Magnesium Oxide.
Production of Magnesium by electrolysis of its oxide (the so-called
Oxide method) has been studied by a number of researchers. Reason for
interest in this method is a desire to avoid the very complex and
costly process of obtaining anhydrous chloride salts for their subsequent
electrolysis.
Success in producing aluminum by the electrolysis of alumina
(aluminium oxide) in fused fluorine salts, naturally led to the idea
of applying an analogous process to magnesium oxide.
Eowever, during the development of the process of direct electro-
lysis of magnesium oxide in fused agents, certain difficulties were
encountered which have, as yet, not been solved for industrial application.
The basic difficulties usually connected with this process are;
(1) the very low solubility of magnesium oxide (tenths of a percent)
in compounds suitable as smelting agents for the electrolytic production
of pure magnesium; this results in frequent anodic complications that
interrupt the process of electrolysis; (2) high melting temperatures of
these agents (950 -1000 degrees foentigrade/) resulting in considerable
loss of magnesium during the electrolysis process (evaporation, reoxidation);
(3) high (as compared with metal, c magnesium) specific gravity of the
molten electrolyte, thus complicating the creating of an efficient electro-
lyser So as to prevent considerable loss of the separated metal.
Should these shortcomings be eliminated, the oxide method, on account
of its simplicity, may present advantages as compared with existing
methods of producing magnesium by the electrolysis of fused chlorides.
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and faci
the electrol~rte ? The metal collects on the surface under the crust of
the cathodes and is periodically ladled
the frozen electrolyte above
from the bath.
? dad to the electrolyte near the anpdes.
Magnesium oxa.de ~. S ad l xtent
of MgO in such an electrolyte is only O.pe.
Since the solub~.l~ty stating
first subject to electrolysis, while the sep
it appears that. MgF2 ~. s o1 e
t
sium oxide suspended in the electr y.
fluoride reacts with magna and 9-10 volts.
s described worked at 9000/13000 amperes
The electrolyser
. the rise of the segregated magnesium to the surface of
1 tats s
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In the production of Magnesium by electrolysis of Magnesium Oxide,
KF and BaF2 is usually used as a solvent.
a fused compound of MgF2, NaF, e
decomposition of MgO in such an electrolyt
Theoretical voltage of
~. is 2.45 volts with a platinum anode and 1.34
at 950 degrees /entigrade]
volts with a carbon anode. (M? Thomson, Trans. of the Elektr?ch. Sacs
1935,165).
The first important plant to produce Magnesium by electrolysis of
Magnesium Oxide in fused fluorides was installed by the American Magnesium
Company at Niagara Falls(~.arvey' Chem. metal Eng., 32,573,1925). Fro
was however, suspended after a yearts operation.
duction -
The , electrolyser (figure 198, Harvey Eleetrolyzer) used in this case
shell devoid of any heat insulation or lining.
consists of an iron
The latter is formed by solidification of the electrolyte on the
era 15-25 centimeters thick, serving simultar
bottom and side walls in lay
neously as heat and electric insulation. The iron cathodes pass under
neath through the shell of the bath. Two rows of carbon anodes immersed
re sus ended overhead. The anode and cathode areas
in the electrolyte a p
formed by a layer of solidified electrr
are separated by two diaphragms,
water. As an electrolyte, a melt of equal parts
lyte on pipes cooled by
addition of a suitable quantity of NaF to melt
of MgF2 and Ba.F2 with an
The resents of BaF2 increases the
approximately 950 degrees, is used p
3.2 rams per cubic centimeter
density of the molten electrolyte up to C
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In view of the high temperature of the electrolyte and frequent anodal
effects, electric current efficiency did not exceed 50 percent, while
energy efficiency was only 10 percent,
The metal produced contained
99 percent Magnesium with irons silicon, aluminum and traces of barium
as impurities. Subsequent resmelting produced metal of 99.9 percent
purity. Thanks to the non-hygroscopicity of the electrolyte, magnesium
thus produced is very corrosion resistant.
Considerable research on the subject of producing magnesium by
electrolysis of MgO dissolved in fused fluoride salts, was conducted by
Grube and his associates (1927-1930). (Z. F. Elektroch. 1927, XXXIII, 48i
ibid 1930, xxxiv.) These researchers studied the ternary fusion '
y sion diagrams
NaF -IgF2 - BaF2
NaF - MgF2 - CaF2
Determining the solubility of MgO in these systems revealed that
the solubility of MgO is determined, primarily by the presence of NaF
in the melt; the more NaF the higher the solubility of magnesium oxide.
Table 81 shows the results of Grebe's experiments in the electro-
lysis of MgO in melts of different compositions.
RESULTS OF EXPERIMENTS IN THE ELECTROLYSIS
OF MgO IN FLUORIDES
(BY GRUBS)
- - - - - - - - - - - - w - - a - r - r r - - - - - - - -
No. of Melt
Composition of electrolyte, %
Temperature
Current
--------------..-
during
yieldin
M F2
BaF2
NaF
process
of Mg
1
18
50
32
800
4
2
21
71
8
850
25
3
35
256
8
900
50
4
40
40
11
950
40
of MgO (about 1 percent), practically produces nothing but sodium. The
low fusion temperature (750 degrees) and comparatively high solubility
From table 81 it follows that electrolyte No 1, in spite of the
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The eleotrolysis of melt No 2 with a fusion temperature of 600 degrees
resulted in a 25 percent electric current yield of Magnesium due to the
simultaneous segregation on the cathode, of magnesium and sodium, the
latter b'rning on the surface. On the contrary melt No 3, in spite of
its low solubility of MgO (0.25 percent) segregates primarily metallic
magnesium (current yield 50 percent).
The reason for this phenomenon is that in the combination NaFs'-N F2
(figure 199)(Fusion Diagram for the System NaF, MgF2); this fusion has
great importance in the possibility of segregating magnesium from fused
fluoride salts at acceptable and practical current yields.
If free sodium fluoride is present in a given concentration of
components in a melt in accordance with the fusion diagram, primary
separation will be metallic sodium. If, however, sodium fluoride,
contained in the melt, is combined with magnesium fluoride in the form
of MgF2, NaF and, in addition there is a further abundance of Magnesium
Fluoride, then the cathode product is pure Magnesium.
However, the drawback in this case is the low solubility of MgO
in melts, resulting in frequent disruption of the process through anodic
effects.
I
The French researcher F. Ran... (1931-1932)(Chemie et nd. No 6,
1931, V. 26, 1261-1270; ibia, January 19$2, V. 27, 31-40) published
results of his experiments on the electrolysis of MgO, based on data of
prior researchers. He analyzed electrolytes composed of various com-
binations of MgF2~ CaF2, BaF2 and NaF with small additions of MgO.
Ran... confirmed by his own experiments conclusions of earlier researchers
that when the electrolyte contains a considerable quantity of NaF the
main product of electrolysis is Sodium.
To combat anodic effects, Ran... recommends a lowered anodic current
density (below 20 amperes per square inch) and use of anodes with the least
possible porosity.
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Several Institutes in the USSR (Gini~vetmet, Mvetmetzoloto,
MosVAMI) have repeatedly experimented with the process of producing
Magnesium by electrolysis of MgO in fused fluorides.
These experiments have confirme that in principle, it is possible
to obtain magnesium by this method. At the same time they also demon-
strated that for a practical application of this method further research
is necessary to find melts with a lower melting temperature, a larger
solubility vis a vis MgO and with a relatively small content of NaF.
Experiments of MosVAMI, showed, among other things, that an addition
of KF to the electrolyte is quite beneficial.
Ye
Thus, according to . I. Hazano, (Soviet Authors, Certificate
a
i\o 47447 dated 30 June 19??) an electrolyte composed of three molecules
MgF2 and diverse molecular quantities of KF, NaF and BaF2, fuses at a
temperature of approximately 900 degrees and is the most acceptable for
the electrolysis of MgO. Up to 3 percent MgO dissolves in this electrolyte.
Current yield of Magnesium during the electrolysis process attained
80 percent at a 940 degree working temperature of the electrolyte.
This process may be accomplished in an electrolyser, lined with magnesiue,
characterized by high stability and absence of anodic effects due to
considerable solubility of MgO in the electrolyte.
104 - Production of Magnesium Alloys by Electrolysis
Under existing methods of obtaining metallic Magnesium, the latter
being lighter than the molten electrolyte, rises to the surface. This
fact complicates the construction of a bath, requiring separate anode
and cathode areas and is also a reason for the loss of metal due to
oxidation on contact with air.
Numerous suggestions have been made on how to isolate the magnesium
on a molten metallic cathode, heavier than magnesium, such as aluminum,
lead, zinc, copper and others. In that case it would be possible to conduct
the electrolysis process in an electrolyser of a standard type, without
a diaphragm, and obtain a magnesium alloy heavier than the electrolyte,
K melt thus produced may be used directly as an
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a
30 amperes) showed that the best electrolyte for this process is magnesium
hid. Japan No 10, 1935) experimenting on a small scale (at approximately
Japanese researchers I. Namari and T. Ishiko (The Journ. of the Chem.
13-15 kilowatt hours per 1 kilogram magnesium.
surface was possible up to 9091 percent Magnesium. Power consumption was
Saturation of the melt with Magnesium without its rising to the
centimeter.
Temperature 600650 degrees and density of current 1.5 amperes per square
a liquid aliminum cathode. The process was performed at 50-120 amperes.
38, 232, 1932, who managed to electrolyze fused magnesium chloride on
electrolysis was originally conducted by R. Weiner (z. F. Ele ktroch,
Systematic research for direct production of magnesium alloys by
Let us describe a few of the more interesting ones:
feasible.
at times on a large scale, prove that in principle this process is
Nevertheless a number of experiments undertaken along this line,
disrupts the process.
cathode, considerably increases its electrical resistance and thus
of sludge in the bath. The sludge settles on top of the liquid metallic
any industrial acceptance. The main reason for this is the formation
Unfortunately up to this time, these suggestions have not received
very pure f orm,
alloy in the production of magnesium alloys or the magnesium may be
extracted by one method or another (for example by volatization) in
chloride with a small addition (5-10 percent) of NaCL; this permits the
process to be conducted at a temperature of approximately 670 degrees
with an average current yield of 94 percent. Alloys obtained by these
researchers contained approximately 50 percent aluminum and 50 percent
magnesium.
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Y
Here in USSR, B. Popoff' (Report VAMI, No 461, 1935) conducted
research on the production of magnesium aluminum alloys by electrolysis
of carnallite on liquid aluminum cathodes. He conducted the electrolysis
in an electrolyser at 300 amperes, a current density of 1.5.2 amperes
per square centimeter and a temperature of 660 degrees.
'. L'..skov S
Finally V. and H. StradetA (Metallurgist)No 10, 1936)
studied the process by electrolysis of magnesium and zinc alloys.
Carnallite was used as the electrolyser and at optimum conditions were
found as follows: Temperature within a range of 660680 degrees and
cathode current density of 1.1-1.2 amperes per square centimeter. Under
these conditions magnesium concentration in a magnesium zinc melt reached
8083 percent at a current yield of magnesium above 90 percent. Average
s gy'rt
power consumption 15 kilowatt hour for 1 kilowraagnesium.
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