Improved Process of Purifying the Anhydrous Double Chloride Compounds of Aluminium.
Year: 1889

page_text: Date of Application, 12th Nov., 1889
Complete Specification Left, 11th Aug., 1890—Accepted, 13th Sept., 1890
DDAVIYUTAN AL
NATION
PROY
Improved Process of Purifying the Anhydrous Double Chloride
Compounds of Aluminium.
I, HAMILTON YOUNG CASTNER of 115 Cannon Street in the City of London, Managing
Director of The Aluminium Company Limited, do hereby declare the nature of this
invention to be as follows :-
The object of this invention is to purify the anhydrous double chloride compounds
of aluminium, such as the double chloride of aluminium and sodium and others.
In the production of metallic aluminium from the double chloride by the action of
sodium or otherwise, it is of great importance that this compound should be pure.
It is however ordinarily contaminated with iron which renders the aluminium also
impure.
My present invention relates to a method of purifying these double chlorides by
decomposing the chlorides of iron which they contain, by the use of the electric
current, the apparatus and the quantity of current used being so arranged as to
decompose the ferrous and ferric chlorides and to deposit the iron in the form of metallic
iron, leaving the double chloride pure.
To do this by my invention it is necessary to melt the impure anhydrous double
chloride of aluminium and pass through it an electric current of proper magnitude,
taking care that the molten crude chloride is kept in motion between the electrodes,
and further that the current which operates on the double chloride is diminished
from time to time, so that it may just be sufficient to cause the iron to be deposited,
but not to deposit any substantial portion of aluminium with it. This may be effected
in a single bath if the current be diminished from time to time, or it may be carried
out by causing the molten crude chloride to pass through a series of baths in which it
is exposed to a series of electric currents of decreasing quantity suitable to produce
the above effect, it being kept in motion throughout the process. In this arrange-
ment it is not necessary to vary the quantity of the current in each bath as the required
object is attained by using a series of baths.
The quantity of the current at each stage will depend upon the amount of iron
remaining to be deposited.
1000
PHILIP M. JUSTICE,
55 & 56, Chancery Lane, London, Applicant's Agent.
COMPLETE SPECIFICATION.
Improved Process of Purifying the Anhydrous Double Chloride
Compounds of Aluminium.
I, HAMILTON YOUNG CASTNER of 115 Cannon Street in the City of London,
Managing Director of The Aluminium Company Limited, 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 object of this invention is to purify the anhydrous double chloride compounds of
aluminium.
Although reference is only made herein to the double chloride of aluminium and
sodium it will be evident that the process is equally applicable to other double chloride
compounds of aluminium-such for instance as the double chloride of aluminium and
potassium.
In the production of metallic aluminium from the double chloride (by the

page_text: action of sodium or otherwise) it is of great importance that this compound should
be pure.
The double chloride of aluminium and sodium is now generally manufactured by
passing chlorine gas over or through a highly heated mixture of alumina carbon
and salt contained in fire clay retorts. The double chloride formed by reaction being
distilled and condensed in receivers attached to the said retorts through which the
vapours are made to pass.
In manufacturing the double chloride in this manner it becomes much contaminated
with ferrous and ferric chloride produced by the action of the chlorine gas and carbon
monoxide upon the iron contained in the materials composing the charge and also
contained in the fire clay of which the retorts are composed.
In the subsequent treatment of this impure double chloride with sodium for the
production of aluminium both the chlorides of aluminium and iron are reduced to the
metallic state yielding an aluminium of inferior quality due to the presence of iron,
the proportion of the same in the aluminium produced depending upon the quantity
of iron contained in the crude chloride employed.
My present invention relates to a method of purifying the anhydrous double chlorides
by the use of an electric current the apparatus being so arranged and the quantity of
current being so regulated and applied in such a manner as will only decompose the
ferrous and ferric chlorides causing metallic iron to be deposited and leaving the
double chloride of aluminium and sodium pure.
In order that my invention may be clearly understood I take the following as an
example of how my invention may be practically employed.
Let it be assumed that I desire to treat an impure double chloride of aluminium and
sodium containing 5 (one half of one) per cent. of iron in the form of ferrous and
ferric chlorides and have a current of 1000 amperes with which to carry out the
purification. One thousand amperes of current passed into molten crude chloride
will decompose and precipitate about 700 grammes of iron per hour from the
equivalent amount of ferric chloride which is about the amount of iron contained in
310 pounds of crude chloride containing 5 (one half of one) per cent. of iron.
My experiments have proven that if the 1000 amperes were continuously passed
through the crude double chloride in a single bath and no means were taken to keep
the electrolyte in motion there would be a greater or lesser deposit of metallic
aluminium with and among the iron deposited on the negative electrodes, and to
prevent this and to accomplish the separation with little or no waste of either
inaterial or current I propose to purify the crude chloride gradually by treating
it while in motion, in a series of baths to a series of electric currents of decreasing
quantity.
A convenient arrangement of apparatus for this purpose is indicated in the
accompanying drawings in which Figure 1 is a view in section, Figure 2 is a
perspective view of one of the metal plates used as a negative electrode alternately in
the decomposing cells with the plate as shown in Figure 3 also as a negative electrode.
The vessel A serves for melting the crude chloride (being set in brickwork over a small
fireplace) and is provided with a tap B, by means of which the quantity of molten
chloride flowing into tank C' can be regulated. Tank C¹ is a long narrow iron vessel
(preferably porcelain lined) fitted with a series of electrodes so arranged that the
molten chloride will flow in a regular manner between the plates forming these
electrodes. This end may be attained by arranging the plates as follows:-
The anodes E (which are preferably of carbon) are of such a size that when fixed
in place they do not either extend to the bottom or sides of the bath. The cathodes H
(which are of metal, preferably of sheet aluminium about 1" or "thick) are
of the shape shown in Figures 2 and 3. These plates are of the same width as the
bath and when placed in position between the carbon anodes, cause the chloride flowing
from A to take the direction shown by the arrows. The tank C2 and C³ are similarly
fitted and are each provided with overflow or discharge pipes F, the last named
discharging into the receptacle D for the purified material. The vessel A and
tank C³, C and are sufficiently heated to keep the chloride just melted so that it

page_text: may run freely. The anodes and cathodes in each bath are so connected with the
poles of the dynamo that the 1000 amperes of current used are divided so that, say
about 600 pass through the moving electrolyte in tank C¹ per hour, 300 through that
in C per hour, and 100 through that in C3 per hour. If therefore the tap B is set
so that the 310 lbs. of impure chloride are passed from vessel A to tank C¹ per hour
and there submitted to a current of 600 amperes, 420 grammes of iron out of the 700
contained therein, will be deposited on the cathodes together with a quantity of
salt (Na Cl) from the double chloride. In passing through the tank C² the partially
purified chloride is submitted to a further current of 300 amperes, a further quantity
of 210 grammes of iron being in like manner deposited, while in flowing through
tank Cs the remaining 70 grammes will be eliminated by the 100 amperes of current,
and the material flowing into receptacle D will be found to be practically pure. If
therefore the vessel A be kept duly charged with the impure chloride containing 5
(one half of one) per cent. of iron and the tap B be set to allow a flow of 310 lbs. to
pass into tank C₁ hourly, and submitting it to the action of the current as mentioned
during its passage to D, a continuous process of purification will be obtained, it being
only necessary to remove the cathodes from time to time and substitute clean ones
while those removed are cleansed from the adhering iron and salt together with a little
double chloride and with a very small amount of metallic aluminium which has been
deposited owing to a small proportion of the double chloride of aluminium and sodium
having been decomposed. The anodes if made of carbon are of course gradually
disintegrated by the chlorine and require to be removed from time to time and new
ones substituted.
I do not of course confine my process to the treatment of double chlorides con-
taining 5 (one half of one) per cent. of iron, or to a current of 1000 amperes as these
quantities have simply been assumed for the purpose of illustration nor do I confine
myself to the particular form or number of baths as the operation might be conducted
in a single bath if due care were taken to diminish the current at successive stages of
the operation in the manner indicated herein the molten crude or partially purified
double chloride being kept in motion throughout the operation.
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
1. The process of purifying the anhydrous double chloride compounds of
aluminium containing iron which consists in treating such compounds when in
motion and in a fused condition to the action of an electric current substantially
as set forth.
2. The process of purifying the anhydrous double chloride compounds of
aluminium containing iron, which consists in first inelting the crude material and
then causing it to pass through a series of receptacles in which it is subjected while
in motion to the action of electric currents substantially as set forth by which the iron
chlorides are decomposed and the metallic iron deposited.
3. The process of purifying the anhydrous double chloride compounds of
aluminium containing iron, which consists in treating the crude material when in
motion and in a fused condition to an electric current of gradually decreasing quantity
proportioned to the gradually decreasing quantity of iron contained in the material
substantially as and for the purpose set forth.
Dated this 11th day of August 1890.
PHILIP M. JUSTICE,
55 & 56, Chancery Lane, London, Applicant's Agent.