Improvements in the Reduction of Aluminium by Electrolysis.
Year: 1899

page_text: Date of Application, 15th Aug., 1899-Accepted, 16th Sept., 1899
COMPLETE SPECIFICATION.
Improvements in the Reduction of Aluminium by Electrolysis.
I, FRANK AUSTIN GOOCH, of 164, Edwards Street, New Haven, Connecticut,
United States of America, Professor of Chemistry, 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 and by the following statement:-
This invention relates to processes for the reduction of aluminium from its
compounds by electrolysis of a suitable fused mass containing such compounds.
In general terms, the invention comprises an improved process for reducing
aluminium from its compounds, which consists in forming a bath by fusing
together a suitable compound of aluminium and a suitable halogen compound of
a metal more electro-positive with reference to sulphur than is aluminium, adding
to the bath a suitable compound of sulphur, together with alumina, and then
passing an electric current of suitably low voltage through the fused mass, thereby
electrolyzing the same.
More particularly my invention relates to processes for reducing aluminium
from its sulphide by electrolysis.
I am aware that processes have been described for the electrolysis of almuinium
sulphide, where the sulphide is formed without the bath, and then added to
the bath, or formed from aluminium oxide suspended in the bath.
My invention is intended to facilitate the formation of a suitable sulphide
bath by forming the aluminium sulphide from the oxide dissolved or combined in
the bath. The halogen compounds of the metals more electro-positive with
reference to sulphur than is aluminium, which are to be employed, should be such
as when fused are capable of dissolving the aluminium sulphide after it is formed
in the bath. The compound of aluminium employed should be one which, with the
other constituents of the bath, will unite to form a bath capable of dissolving
alumina. In practice, I find that the best results are obtainable from baths
composed of fluorides of the alkali metals, with the addition of a halogen com-
pound of aluminium. The compound of sulphur should be one which is capable
of acting upon alumina in the bath, so as to substitute sulphur for the oxygen
in the alumina.
For convenience, I describe my invention with special reference to the use of
carbon bisulphide (C S₂), it being understood, however, that my invention is also
applicable to other compounds of sulphur, as for example, hydrogen sul-
phide (H, S). I also select for convenience a bath composed of sodium fluoride
and aluminium chloride fused, it being understood that I do not confine myself
to the bath so constituted since any bath composed of a suitable halogen com-
pound of the metals hereinbefore mentioned will answer the purpose. I prefer-
ably employ the ingredients named in the proportion of three parts of sodiumi
fluoride to two parts of aluminium chloride. A moderate excess of either of these
ingredients does no harm.
In the accompanying drawings is shewn an apparatus suitable to the practice of
my invention. I do not, however, limit myself to the apparatus shewn, since any
other suitable apparatus will answer equally well for the practice of my invention.

page_text: Fig. 1 represents a sectional diagrammatic view of the apparatus, and Fig. 2
a plan view of a portion of the apparatus from above. Similar letters refer
to similar parts throughout the drawings.
I prepare a bath by fusing, in suitable tank or crucible T, sodium fluoride
and aluminium chloride. The crucible preferably consists of a tank of iron O,
provided with sleeves S, St, for the insertion of the anodes C¹ C³, and lined on
the bottom and half way up on the sides with compact carbon L. The remainder
of the tank and the sleeves are lined with compact alumina I, which serves to
keep the anodes from electrical contact with the tank and casing. The
anodes C C are detached carbon electrodes partly immersed in the bath B,
connected by copper rods, with the metal bar K in any suitable way, as by
the screw clamps w, w, and perforated longitudinally. The metal bar K is
preferably supported by wooden supports f f The carbon lining L serves as
the cathode. The conductors P, N, are connected with the positive and negative
poles respectively of the source of electricity E; conductor P is also connected
with the anodes C, C through the bar K and the rods r, r, by a binding post m,
and the conductor N is connected in a similar manner with the cathode L by
the binding post ml. F' is a furnace over the fire box of which the crucible T is
supported. The carbon bisulphide or other compound of sulphur is introduced
into the bath through the pipes G, G¹, which form tight joints with the
anodes C C³, so that the pipes are continuous with the perforations in the anodes.
The gaseous products which escape from the bath pass through the bell J, which
may be made of boiler iron plate and lined with compact carbon or other suitable
material, the gases passing through the pipe R at the outlet j. The bell J is
supported by a wooden support T, which is adjustably attached to the metal bar K
by screw clamp y or other suitable means. When the bath is in operation, the
bell J is lowered below the surface of the bath, and the space between the rim
of the bell J and the interior surface of the tank T is covered with powdered
carbon p, sprinkled thickly upon the surface of the bath. Through this space
when desired, alumina is introduced into the bath B in quantities required. A
moderate excess of alumina does no harm. In the bath described, the alumina
will be dissolved.
When the carbon bisulphide is introduced, it acts upon the dissolved alumina
to convert that oxide to aluminium sulphide, while carbon oxysulphide or carbon
monoxide is formed at the same time. Then an electric current of suitable low
voltage (which will vary according to the constitution of the bath and the size of
the electrodes) is passed through the bath thereby electrolyzing the aluminium
sulphide. Aluminium is deposited at the cathode, and may be removed by ladle
or siphon or other convenient means, while sulphur is liberated at the anode, and
passes off through the pipe J and the outlet j. By supplying alumina to the
bath and maintaining the current of carbon bisulphide, the production of
aluminium sulphide will go on continuously, and, if properly regulated, will keep
pace with the elctrolysis.
One great advantage in the process thus described is the low voltage of the
current required to reduce the aluminium, this being about 0.9 volt. I therefore
employ a current of just sufficient voltage to overcome the resistance of the bath
and other resistances under the conditions of the process, together with the added
voltage, of 09 required to electrolyze aluminium sulphide. Such a current
would, of course, have no effect in electrolyzing alumina, dissolved in the bath.
I have found in practice that similar results are obtained when, instead of
introducing carbon bisulphide directly into the bath, sulphur is introduced into
a bath covered with charcoal. In such a case, aluminium sulphide is formed and
aluminium is precipitated when the current is passed. Preferably, however, the
crude carbon bisulphide, either directly from the generator in which it is made
or after condensation, is passed through the crucible T, and the carbon bisulphide
and sulphur which escape from the crucible through the pipe J are condensed
and again sent through the generator and into the crucible. From the carbon

page_text: oxysulphide which escapes from the condenser, the sulphur may be recovered in
any known manner, or the carbon oxysulphide may be burned to form sulphur
dioxide and carbon dioxide, the former of which being a by-product of value may
be absorbed by suitable re-agents, while the carbon dioxide will ordinarily be
permitted to escape.
I have described a form of my process in which the bath is composed of a
halogen compound of an alkali metal and of a halogen compound of aluminium,
which bath is capable when fused, of dissolving alumina. I find also, that
excellent results are obtained from the use of baths composed of aluminium
fluoride and fluorides of alkali metals, particularly the sodium fluoride. As is
well known, when alumina is introduced into the last named bath, it dissolves.
When the compound of sulphur is introduced into such a bath, the sulphide of
aluminium is rapidly formed in solution, and on passing a current of the
voltage above specified, electrolysis takes place and aluminium is produced at
the cathode.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, I declare that what I
claim is:
1. The herein described process of reducing aluminium by electrolysis by
fusing together a suitable compound of aluminium and a suitable halogen com-
pound of a metal more electro-positive with reference to sulphur than is
aluminium, adding to the bath a suitable compound of sulphur, together with
alumina, and then passing an electric current of suitably low voltage through the
fused mass.
2. The herein described process of reducing aluminium by electrolysis by
fusing together a halogen compound of aluminium and a suitable halogen com-
pound of a metal more electro-positive with reference to sulphur than is aluminium,
adding to the bath a suitable compound of sulphur, together with alumina, and
then passing an electric current of suitably low voltage through the fused mass.
3. The herein described process of reducing aluminium by electrolysis by
fusing together a halogen compound of aluminium and suitable halogen com-
pounds of metals which are more electro-positive with reference to sulphur than
is aluminium, adding to the bath in suitable quantity carbon bisulphide together
with alumina, and then passing an electric current of suitably low voltage through
the fused mass.
4. The herein described process of reducing aluminium by electrolysis by
fusing together fluorides of aluminium and of metals more electro-positive with
reference to sulphur than is aluminium, adding to the bath in suitable quantity
carbon bisulphide together with alumina, and then passing an electric current
of suitably low voltage through the fused mass.
5. The herein described process of reducing aluminium by electrolysis by
fusing together fluorides of aluminium and of an alkali metal, adding to the bath
in suitable quantity carbon bisulphide together with alumina, and then passing
an electric current of suitably low voltage through the fused mass.
6. The herein described process of reducing aluminium by electrolysis by
fusing fluoride of aluminium and fluoride of sodium, adding to the bath in suit-
able quantity carbon bisulphide and alumina, and then passing an electric current
through the fused mass.