A Process for the Extraction of Aluminium from its Fluorides by Electrolysis.
Year: 1887

page_text: Communicatou
тоц
1, Boulevard Saint-Denis, Paris, France, Gentlemen.]
A Process for the Extraction of Aluminium from its Fluorides by
Electrolysis.
1, ERNEST DE PASS, of 68 Fleet Street in the City of London, Fellow of the
Institute of Patent Agents, do hereby declare the nature of this Invention to be as
follows:-
It is well known that the salts of aluminium, like all chemical compounds, which
have a saline function can be electrolysed. In order, however, that the electric
current may act in an efficient manner, certain arrangements must be made, in
accordance with the nature of the aluminium salts to be electrolysed. Among the
latter, some are very slightly fusible, while others are volatile, and, in order that an
electrolytic action may be produced it is essential that the salt to be electrolysed,
should be in a particular state of liquefaction which is very difficult to be obtained
with aluminium salts. Thus, the chloride of aluminium is too volatile, while the
fluoride of aluminium is not fusible enough.
It has already been proposed, as regards the first, to combine it with the salt of
another metal, and to thus form a double salt, which imparts to it a little more fixity,
and allows it to be subjected, at a relatively low temperature, to the action of the
current, in order to extract the aluminium therefrom. But the double salt thus
formed that is to say, the double chloride of aluminium and of sodium, is an exceedingly
unstable body, which is handled with difficulty, and it gives rise to extremely noxious
vapors, hence it cannot be used industrially for the extraction of aluminium therefrom
by electrolysis; in all cases, great losses are occasioned.
It has been sought to render it still more fixed, by mixing it with small quantities
of chloride of sodium, and even of cryolite (double fluoride of aluminium and of
sodium); this latter body being then adopted solely as a flux.
Now, experiment shews, that if the current be passed through a
posed of :-
Double chloride of aluminium and of sodium,
Chloride of sodium,
bath com-
Double fluoride of aluminium and of sodium (cryolite) the double chloride is
volatilized to a great extent, and the fluoride of aluminium which is more fixed than
the former is decomposed by the currents.

page_text: We have, therefore, formed a bath in which the fluoride of aluminium is contained
in larger proportions, either in the form of a single salt, or in the form of a double
salt, the fluoride not being employed by us as a flux, but being used as the principal
electrolyte which will be subjected to the action of the current. Experiment shews,
moreover, that the yield in aluminium increases with the proportion of fluoride of
aluminium contained in the bath. It reaches its maximum when the fluoride of
aluminium is found in a melted state, without being mixed with any other salt.
Very good results are obtained with the following proportions:
0
100
100
It is to be understood, that we can employ, as electrolytes in the bath, mixtures or
compounds of fluorides of sodium and of aluminium in different proportions to those in
which they are found in cryolite, for instance :
Fluoride of Aluminium
Fluoride of Sodium
35
10
Chloride of Sodium (or other flux)
55
GG

page_text: COMPLETE SPECIFICATION.
·
A Process for the Extraction of Aluminium from its Fluorides by
Electrolysis.
I, ERNEST DE PASS, of 68 Fleet Street, in the City of London, Fellow of the
Institute of Patent Agents, do hereby declare the nature of this invention, and in
what manner the same is to be performed, to be particularly described and ascertained
in and by the following statement (reference being had to the accompanying drawings,
and to the letters and figures marked thereon) that is to say :-
It is well known that the salts of aluminium, like all chemical compounds which
have a saline function, can be electrolysed. In order, however, that the electric
current may act in an efficient manner, certain arrangements must be made in
accordance with the nature of the aluminium salts to be electrolysed.
Among the latter, some are very slightly fusible, while others are volatile, and in
order that an electrolytic action may be produced, it is essential that the salt to be
electrolysed should be in a particular state of liquefaction which is very difficult to
be obtained with aluminium salts. Thus the chloride of aluminium is too volatile,
while the fluoride of aluminium is not fusible enough.
It has already been proposed, as regards the first, to combine it with the salt of
another metal, and to thus form a double salt which imparts to it a little more fixity,
and allows it to be subjected at a relatively low temperature, to the action of the
current, in order to extract the aluminium therefrom. But the double salt thus
formed, that is to say the double chloride of aluminium and of sodium, is an
exceedingly unstable body which is handled with difficulty, and it gives rise to
extremely noxious vapors, hence it cannot be used commercially for the extraction of
aluminium therefrom by electrolysis; in all cases, great losses are occasioned.
It has been sought to render it still more fixed by mixing it with small quantities
of chloride of sodium and even of cryolite (double fluoride of aluminium and of
sodium); this latter body being then adopted solely as a flux.
Now, experiment shews that if the current be passed through a bath com-
posed of
Double chloride of aluminium and of sodium,
Chloride of sodium,
Double fluoride of aluminium and of sodium (cryolite), the double chloride is
volatilized to a great extent, and the fluoride of aluminium, which is more fixed than
the former, is decomposed by the current.
A bath has therefore been formed in which the fluoride of aluminium is contained
in larger proportions either in the form of a single salt, or in the form of a double salt,
the fluoride not being employed, according to this invention, as a flux, but being
used as the principal electrolyte which will be subjected to the action of the current.
Experiment shows, moreover, that the yield in aluminium increases with the
proportion of fluoride of aluminium contained in the bath. It reaches its maximum

page_text: when the fluoride of aluminium is found in a melted state without being mixed with
any other salt. Very good results are obtained with the following proportions :-
Fluoride of aluminium
Chloride of Sodium
-
40
60
A double salt of sodium and of aluminium, such as natural or artificial cryolite may
even be used, not as a flux, but as an electrolyte in the following proportions :-
14
100 100
• It must be understood that there can be employed as electrolytes in the bath,
mixtures or compounds of fluorides of sodium and of aluminium in different pro-
portions to those in which they are found in cryolite, for instance:
Fluoride of aluminium
Fluoride of sodium
Chloride of Sodium (or other flux)
35
10
-
55
ALUMINIUM BRONZE.
Anode (red copper or carbon).
Cathode (copper or carbon).
FERRO-ALUMINIUM.
Anode (Iron or carbon).
Cathode (Iron or carbon).
In short, metal or graphite may be employed without distinction as electrodes.
The crucible may be of refractory earth, of plumbago, or of metal (iron, cast iron,
red copper, platinum and the like), and in cases where an alloy is required the
crucible itself may serve as the cathode, or as the anode.
Besides platinum, which is unalterable but costly, the other metals are attacked by
the bath (mixture of chloride of sodium and of fluoride of sodium) and have still a
further defect, that is to say when they are subjected to the direct action of the flame,
or to too high a temperature, they allow the bath to filter through, hence a considerable
loss results.
With the arrangements hereinafter described, with reference to the accompanying
drawings, such defects are obviated.
Figs. 1 and 2 of the drawing shew a general view of the tanks arranged in such
a manner that the bath cannot filter through. It is sufficient for this purpose to
provide the metallic tank a, b, outwardly with a thin brick wall. The bath is
prevented from becoming dirty in consequence of the metal of the tank being
attacked. by means of two entirely different arrangements according as it is desired to
obtain an alloy of aluminium, or pure aluminium alone.

page_text: FIRST ARRANGEMENT, FIG. 1. FORMATION OF ALUMINIUM ALLOYS.
The tank is made of the metal which forms a component part of such alloys. A, A,
re the carbon anodes; a, b, is the metallic tank serving as a cathode. At the
eginning of the operation, and as fast as aluminium is produced by electrolysis,
here is formed on the inner surface of the tank a layer a of the aluminium alloy to
e obtained. When this alloy is sufficiently rich in aluminium, the metal formed
new electrolytically runs to the bottom of the tank. As shewn in fig. 1, the
ottom of the said tank is slightly inclined, and is provided with a tap hole T which
llows after a lapse of time, determined by means of experiments, the withdrawal of
he fused aluminium containing smaller or greater portions of the metal forming the
ank, which is not a defect, as the object to be attained was the formation of an alloy.
SECOND ARRANGEMENT, FIG. 2. FORMATION OF PURE ALUMINIUM.
Let A be the anode or anodes, and
C the cathode, or cathodes.
The cathode C is arranged in a small crucible d, placed upon a plate e, these two
apparatus being formed of fused alumina, or fluoride of calcium, or of carbon blocks.
a, b, is the metallic tank arranged in derivation with the cathode.
The resistance interposed between the cathode and the metal tank is sufficiently
great so that the derived current in the tank represents only a small portion of the
whole current (5 to 10 %). It serves to form upon the inner surface of the tank an
alloy of aluminium and of the metal forming the said tank, which alloy protects the
latter and is only feebly acted upon by the bath. The metal which is deposited in the
crucible d in this arrangement is nearly pure.
Having now particularly described and ascertained the nature of my said,
invention, and in what manner the same is to be performed, I declare that what'
I claim is :-
The herein-before described process for the extraction, upon a large scale of
aluminium by electrolysis, and comprising the extraction of pure or alloyed aluminium,
the characteristic features of said process being
:-
1. The electrolysis of a melted bath where fluoride of aluminium (in the state of a
single or a double salt) is used, not as a flux, but as the main electrolyte being
subjected to the influence of the current.
2. The use of a brick covering for the metallic tank so as to avoid the filtration of
the bath.
3. The use of the tank as a cathode for the production of an alloy of aluminium,
or at least of aluminium destined to form an alloy with the metal constituting the
tank.
4. The use of a derived current on the tank when it is required to obtain pure
aluminium.
5. The use of fused alumina and of fluoride of calcium (or carbon blocks) for the
formation of plates and of the crucible serving for the production of pure aluminium.
Dated this 4th day of January 1888.
ERNEST DE PASS,
68, Fleet Street, London, E.C.