Improvements in Processes for Reducing Aluminium.
Year: 1894

page_text: Date of Application, 27th Oct., 1894-Accepted, 1st Dec., 1894
COMPLETE SPECIFICATION.
Improvements in Processes for Reducing Aluminium.
A communication from abroad by FRANK A. GOOCH, of the City and County of
New Haven, in the State of Connecticut, United States of America, and
LEONARD WALDO, of Bridgeport, Fairfield County, in the State of
Connecticut, United States of America.
1, JOHN CORRY FELL, of the Firm of Fell and Wilding, of. 1 Queen Victoria
Street, in the City of London, Chartered Patent Agent 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:-
The invention described herein relates to processes for the reduction of aluminium
from its compounds by the electrolysis of a suitable fused mass containing such
compounds, and in general terms comprises an improved process for reducing
aluminium from its compounds which consists in passing an electric current through
a suitable fused mass containing a suitable compound of aluminium, thereby
electrolyzing the bath, and in introducing into the fused mass hydrogen in
combination in a suitable solid compound.
The compound of aluminium used should be one which will fuse at a
temperature and under conditions which shall be practically attainable. More
especially this invention relates to the reduction of aluminium from a suitable
halogen compound thereof. In practice, I find that the halogen compounds of
aluminium, which are most suitable and best adapted to be used in this process,
are the chloride of aluminium and the fluoride of aluminium. The specific form
of this invention, so far as it relates to such last named reduction, consists, in
general terms, in passing an electric current through a suitable fused bath,
containing a suitable halogen compound of aluminium, thereby electrolyzing the
bath, and in introducing into such bath hydrogen in combination in a suitable solid
compound.
For convenience, I describe this invention with special reference to the reduction
of aluminium from its chloride, it being understood, however, that this invention is
also applicable to other compounds of aluminium. I find it convenient, in this
improved process, to employ hydrogen in combination in suitable hydrous salts or
salts containing combined water, either as water of crystallization or as water of
constitution or both. I preferably employ those salts into whose composition
water enters in a considerable degree. It is also desirable not to use any salt,
which, upon surrendering its water to the bath, will add any deleterious element
to the bath. While this invention is applicable to a large class of substances, I
shall for convenience describe it with reference to the use of a hydrous chloride of
aluminium. I find the hydrous crystalline chloride of aluminium, (represented by
the formula Al,Cl, 12 H₂O) a very excellent salt for our purpose, inasmuch as
it is one of the best known and most easily obtainable of the hydrous chlorides of
aluminium, admits of being handled freely without special precautions, and contains
a large proportion of water in its composition. The hydrous chlorides of aluminium,
besides being otherwise suitable for use in this process, have the great advantage
that the chloride of aluminium contained in the salt replenishes the bath, while the
combined water in the salt, when decomposed, furnishes the hydrogen necessary in
our process. It is to be understood, however, that our description is in substance
applicable to the use of all other suitable solid substances containing combined
water, either of crystallization, of constitution, or both.
In the accompanying drawings, which are hereby made a part of this
Specification, is shown one form of apparatus suitable to the practice of our
.

page_text: invention. I do not, however, limit ourselves to the apparatus shown, since any
other suitable apparatus would answer equally well for the practice of this
invention.
Figure 1 represents a sectional diagrammatic view of the apparatus employed
by me.
Figure 2 represents a sectional view of a modified form of apparatus-employed
by me.
Similar letters refer to similar parts throughout the drawings.
F is a furnace having a fire box f, and opening f1 in the top of the furnace,
into which is set a tapering crucible A, the same being supported by the sides of the
opening. The construction of the crucible and the arrangement of the electrodes
and conductors are fully described hereafter, are binding posts for the
conductors N, P. B is the bath contained in the crucible A, through which the
electric current is passed.
In the practice of this invention, so far as it relates to the reduction of
aluminium from its chloride, I preferably prepare a bath by fusing in a suitable
tank or crucible A, and in proper proportions, the chloride of aluminium and the
chloride of an alkaline metal, preferably sodium, or of an alkaline earth metal
with the fluoride of aluminium and the fluoride of sodium. A convenient way to
form a suitable bath is to combine the double chloride of aluminium and sodium
(represented by the formula 2 NaCIAL,C) with the mineral cryolite. I find it
of advantage to add to the combination just named an additional amount of
chloride of sodium in excess of the amount necessary to form the double chloride.
These ingredients are preferably mingled together in the following proportions:
15 parts
The double chloride of aluminium and scdium
Cryolite -
Sodium chloride
-
55 parts.
-
30 parts.
But these proportions are variable serviceably within wide limits, without
materially affecting the operation or function of the bath, as, in fact, any
proportions which may be found suitable may be employed.
The reason for employing cryolite or the fluorides of aluminium and sodium in
the bath is the well known fact that, when they are present and electrolysis takes
place, the aluminium melts and flows to globules, while, when the bath contains
only the chlorides named, the aluminium is obtained in the form of a powder, which
has to be further treated before it can be made commercially available. The object
of adding the excess of sodium chloride to the bath is to make the bath more liquid.
It is also advantageous in diluting the cryolite. In place of the excess of the sodium
chloride or of a part of the same, I may employ a certain proportion of chloride of
potassium or of some other of the alkaline metals or of some one of the alkaline
earth metals, as of magnesium. In case of any such substitution in the ingredients
of the bath, the proportions of all the ingredients used are suitably re-adjusted, if
necessary.
For example, if the chloride of potassium be used, the ingredients are preferably
mingled together in the following proportions:
Cryolite -
Chloride of aluminium
Chloride of sodium
Chloride of potassium
55 parts
-
12 parts
-
19 parts
14.parts.
But these proportions are variable serviceably within considerable limits, without

page_text: a detached carbon electrode partly immersed in the bath B and connected in the
following manner with the source of electricity. We preferably suspend the
anode C from an iron bar D raised above the crucible and resting on wooden
supports E E. The bar D is connected by the conductor P to the positive pole ot
the source of electricity. If desired, the cathode may also be formed of a detached
carbon suspended in a similar way to that just described for the anode, or otherwise
supported, and partially immersed in the bath. If desired, a number of separate
carbons may be used to form the electrodes as shown in Figure 2, where C, C₁, C³,
C&C, all suspended from the bar D, collectively form the anode, the relative
superficial areas of the electrodes in any particular case being adjusted so as to
secure the greatest economy in action. In place of a carbon anode, an anode of
any other suitable material, as of platinum, may be used. The bath may be fused
and the fusion may be maintained by the application of heat from any suitable
source, as externally from a furnace F. The temperature required to fuse the baths
suggested above is that of a dull red heat. We may also fuse the ingredients of the
bath in a separate apparatus, and introduce the same in a molten condition into the
tank at the beginning of the process, the fusion being thereafter maintained in any
suitable way.
When the electric current is passed through the bath and electro-
lysis takes place, aluminium is deposited at the cathode, and the halogens (chiefly
chlorine) are liberated at the anode. It is well known that these gases, in a free
state, are highly noxious to health. On this account, and for the further reason
that they attack and quickly destroy the positive electrode in the apparatus used in
any process similar to the one described, their escape in a free state would render
such process commercially useless. To obviate these difficulties, and to accomplish
other desirable results, we add to the bath from time to time suitable quantities of
hydrous crystalline chloride of aluminium (Al,Cl, 12 H,O) or other substance
used. The said substance being decomposed in the bath, hydrogen from the
combined water contained in the substance is supplied to the bath in a substantially
continuous manner, and unites with the halogen elements liberated by the electro-
lysis, which then escape at the anode in the form of hydrochloric or hydrofluoric
acid. These gases are easily controlled and disposed of, without injury to
apparatus or workmen by appropriate means external to the bath, as by the
use of a flue K, having a strong draught and provided with a hood J projecting
over the crucible A; or cloths saturated with water may be suspended over the
crucible, the escaping gases being taken up by the water, whose extraordinary
power of acting as a solvent for hydrochloric and hydrofluoric acids is well known.
In the practical operation of this invention, where I use any of the baths
suggested above, I find that I obtain at the anode hydrochloric acid almost
exclusively, with very little trace of fluorine. This indicates that the aluminium
deposited at the cathode is derived chiefly from the chloride of aluminium in the
bath. I have found that by the addition from time to time of the chloride of
aluminium contained in the hydrous. chloride of aluminium employed in the process,
the bath will be replenished, and the process will be a substantially continuous one
through a considerable period of time. 1 preferably add the hydrous chloride of
aluminium to the bath in quantities sufficient to prevent the escape of these free
halogens, but a moderate excess of the same does no harm. I have spoken of
fluorine being set free, but I am aware that it is considered very difficult to isolate
this element. I, however, use the word " Aluorine merely for convenience,
meaning thereby to include not only free fluorine, if any be liberated, but also any
compound thereof which might be set free at the anode if hydrogen were not
supplied to the bath during the process.
"
As before stated, the aluminium is deposited at the cathode, where it melts,
forming globules, which (when either of the suggested baths, whose proportions
are herein given, is used) gather at the bottom of the bath, the aluminium having a
higher specific gravity than the fused bath. The aluminium may then be removed
in any suitable or convenient manner, as for example by means of a ladle lined and
covered with carbon, or by drawing it off through a suitable opening at the bottom.

page_text: In case a bath should be used whose specific gravity is higher than that of
aluminium, the aluminium would of course rise to the top, where it could be easily
removed.
In the process herein described, we use an electric current of suitably low
electro-motive force, usually of from four to ten volts, but the voltage of the
current required will depend on the size and form of the electrodes, as well as on
the composition of the bath, it being only necessary to have a voltage sufficient to
decompose electrolytically the compounds of aluminium in the bath, under all the
existing conditions of resistance, and of chemical construction. The electric
current which we employ in our process, and which is herein referred to as being
passed through the bath, is employed solely for purposes of electrolysis. The salt
or other compound from the decomposition of which the hydrogen is obtained for
our process may, in the first instance, be introduced into the bath before or after
the electric current is passed through the same, or simultaneously therewith, the
order of operations being unimportant.
It being possible to form a large number of different baths, to which this
invention would be applicable, I do not limit myself to the use of any particular
bath which has been described herein.
Where the solid substance from which the hydrogen is derived contains water in
combination, there is likely to be some oxydation of the anode, if the material of
the anode is oxydizable; but, unless such material is very easily oxydizable, the
waste of the anode will usually be much less than would be the case if the anode
were exposed to the action of the free halogens.
Having now particularly described and ascertained the nature of this said
invention and in what manner the same is to be performed, I declare that what I
claim is
1. As an improvement in the art of manufacturing aluminium by reduction from
its compounds, the herein described process which consists in passing an electric
current through a suitable fused bath containing a suitable halogen compound of
aluminium, thereby electrolyzing the same, and in introducing into the bath
hydrogen in combination in a suitable solid compound, substantially as and for the
purposes set forth.
2. As an improvement in the art of manufacturing aluminium by reduction from
its compounds, the herein described process which consists in passing an electric
current through a suitable fused bath containing a suitable halogen compound of
aluminium, thereby electrolyzing the same, and in adding to the bath a suitable
solid compound containing water in combination, substantially as and for the
purposes set forth.
3. As an improvement in the art of manufacturing aluminium, the herein
described process which consists in passing an electric current through a suitable
fused bath, containing the chloride of aluminium, thereby electrolyzing the same,
and in adding to the bath a suitable salt containing water in combination
substantially as and for the purposes set forth.
4. As an improvement in the art of manufacturing aluminium, the herein
described process, which consists in passing an electric current through a suitable
fused bath containing the chloride of aluminium and the chloride of an alkaline
metal, thereby electrolyzing the same, and in adding to the bath a suitable salt
containing water in combination, substantially as and for the purposes set forth.
5. As an improvement in the art of manufacturing aluminium, the herein
described process which consists in forming a bath by fusing the chloride of
aluminium and the chloride of an alkaline metal with the fluoride of aluminium
and the fluoride of sodium, passing an electric current through the fused mass,
thereby electrolyzing the same, and in adding to the bath a suitable salt containing
water in combination, substantially as and for the purposes set forth.
6. As an improvement in the art of manufacturing aluminium, the herein
.described process which consists in forming a bath by fusing the chloride of

page_text: aluminium and the chloride of sodiun with the fluoride of aluminium and the
Huoride of sodium, passing an electric current through the fused mass. thereby
electrolyzing the same, and in adding to the bath a suitable salt containing water
in combination, substantially as and for the purposes set forth.
7. As an improvement in the art of manufacturing aluminium, the herein
described process which consists in fusing together the chlorides of aluminium,
sodium and potassium, and the fluorides of aluminium and sodium, passing an
electric current through the fused mass, thereby electrolyzing the same, and in
adding to the bath a suitable salt containing water in combination, substantially as
and for the purposes, set forth.
8. As an improvement in the art of manufacturing aluminium, the herein
described process which consists in forming a bath by fusing the chloride of
aluminium and the chloride of an alkaline metal with the fluoride of aluminium
and the fluoride of sodium, passing au electric current through the fused mas³,
thereby electrolyzing the saine, and in adding to the bath a suitable salt containing
water of crystallization, substantially as and for the purposes set forth.
9. As an improvement in the art of manufacturing aluminium, the herein
described process which consists in forming a bath by fusing the chloride of
aluminium and the chloride of an alkaline earth metal with the fluoride of
alumiuium and the fluoride of sodium, passing an electric current through the
fused mass, .and. adding to the bath a suitable solid compound containing water
in combination, substantially as and for the purposes set forth.
10. As an improvement in the art of manufacturing aluminium, the herein
described process, which consists in forming a bath by fusing the chloride of
aluminium and the chloride of magnesium with the fluoride of aluminium and
the fluoride of sodium, passing an electric current through the fused mass, and
adding to the bath a suitable solid compound containing water in combination,
substantially as and for the purposes set forth.
11. As an improvement in the art of manufacturing aluminium, the herein
described process which consists in forming a bath by fusing together the
chloride of aluminium the chloride of an alkaline earth metal and the chloride
of sodium with the fluorides of aluminium and sodium, passing an electric current
through the fused mass, and adding to the bath a suitable solid compound
containing water in combination, substantially as and for the purposes set forth.
12. As an improvement in the art of manufacturing aluminium, the herein
described process, which consists in forming a bath by fusing the chloride of
aluminium and the chloride of an alkaline earth metal with the fluoride of sodium,
passing an electric current through the fused mass, and adding to the bath a
suitable salt containing water of crystallization, substantially as and for the
purposes set forth.
13. As an improvement in the art of manufacturing aluminium, the herein
described process, which consists in forming a bath by fusing the chloride of
aluminium and the chloride of magnesium, with the fluoride of aluminium and
the fluoride of sodium, passing an electric current through the fused mass, and
adding to the bath a suitable salt containing water of crystallization, substantially
as and for the purposes set forth.
14. As an improvement in the art of manufacturing aluminium, the herein
described process, which consists in passing an electric current through a suitable
fused bath containing the chloride of aluminium, and adding to the bath a hydrous
chloride of aluminium, substantially as and for the purposes set forth.
15. As an improvement in the art of manufacturing aluminium, the herein
described continuous process, which consists in forming a bath by fusing the
chloride of aluminium and the chloride of an alkaline metal with the fluoride of
aluminium and the fluoride of sodium, passing an electric current through the
fused mass, and in adding to the bath from time to time suitable quantities of a
hydrous chloride of aluminium, substantially as and for the purposes set forth.
16. As an improvement in the art of manufacturing aluminium, the herein

page_text: described continuous process, which consists in forming a bath by fusing the
chloride of aluminium and the chloride of an alkaline metal with the fluoride of
aluminium and the fluoride of sodium, passing an electric current through the
fused mass, and in adding to the bath from time to time suitable quantities of
the bydrous crystalline chloride of aluminium, substantially as and for the purposes
set forth.
17. As an improvement in the art of manufacturing aluminium, the herein
described continuous process, which consists in forming a bath by fusing
the chloride of aluminium and the chloride of sodium with the fluoride of
aluminium and the fluoride of sodium passing an electric current through the
fused mass, and in adding to the bath from time to time suitable quantities of
the hydrous crystalline chloride of aluminium, substantially as and for the purposes
set forth.
18. As an improvement in the art of manufacturing aluminium, the herein
described continuous process which consists in fusing together the chlorides of
aluminium, sodium and potassium, and the fluorides of aluminium and sodium,
passing an electric current through the fused mass, and in adding to the bath
from time to time suitable quantities of the hydrous crystalline chloride of
aluminium, substantially as and for the purposes set forth.
Dated this 27th day of October 1894.
FELL & WILDING,
Agents for the Applicant.