An Improved Process for the Electrolytic Production of Aluminium.
Year: 1891

page_text: Date of Application, 13th June, 1891
Complete Specification Left, 9th Mar., 1892--Accepted, 9th Apr., 1892
PROVISIONAL SPECIFICATION.
An Improved Process for the Electrolytic Production of Aluminium.
I, LUDWIG GRABAU, of 41, Schiffsgraben, Hanover, in the Empire of Germany,
Civil Engineer do hereby declare the nature of this invention to be as follows:-
My invention relates to a process for the direct separation of pure aluminium
from a molten mass by means of electrolysis.
The manufacture of aluminium has heretofore always presented the inconvenience
that the materials used for obtaining metallic aluminium regularly contain silicon
and iron, so that only a metallic aluminium has been obtained which is more or less
contaminated by these auxiliary ingredients and deteriorated in its properties.
According to the present invention the aforesaid inconvenience is obviated by
subjecting a mixture of aluminium fluoride with soda or other basic substances,
such as caustic soda, caustic potash, potash, which can all be easily produced free
from iron and silicon, to electrolysis in the manner hereinafter described.
Cryolite is fused in a receptacle through the agency of the electric current, and
into this fluid bath is introduced during the electrolysis a mixture of aluminium
fluoride and soda (which may be taken as an example) in definite proportions
according to the quantity of aluminium which is separated.
Of the electrodes used for this purpose at least the positive electrode consists
of carbon, whilst the negative electrode may consist of metal, such as aluminium.
By reason of the action of electric current metallic aluminium is in this case
separated at the negative pole, and carbonic acid is formed at the positive pole,
which acid is obtained partly from the soda and partly from the action. of the
molten mass upon the carbon of the electrode.
The proportion between aluminium fluoride and soda may be such that, besides
aluminium, chiefly sodium fluoride, or chiefly aluminium fluoride sodium fluoride
(cryolite Al,Fl, 6 NaFl) is formed. Any proportion lying between these two
extreme cases may be employed, which may be represented by the following
formulæ :
If, in lieu of soda, use is made of potash as a basic material potassium compounds
corresponding to the sodium compounds are of course produced.
The proportion between aluminium fluoride and basic material, such as sodium
carbonate, potassium carbonate, sodium protoxide, potassium protoxide, depends
therefore on whether either sodium fluoride or potassium fluoride or cryolite is to
be obtained as a by-product.
In this manner a pure metallic aluminium can be produced with certainty,
because, as above stated, the materials employed can be easily obtained quite free
from the usual aluminium impurities that is to say from silicon and iron. It is
important that in the improved process a valuable by product such as cryolite can
be obtained.
In this process it is moreover not at all needful to employ neutral aluminium
fluoride, as any basic products containing aluminium fluoride may be used.
Thus aluminium oxyfluoride (Al,OFI) which can be readily and advantageously
produced may be employed in like manner instead of aluminium fluoride, the pro-
portions being likewise selected with regard to whether chiefly sodium fluoride or
potassium fluoride or cryolite is to be obtained as a by-product. These two extreme

page_text: cases may be represented by the following formulæ, which enables the proportions
to be computed with facility.
(3) 2 AO̟OF] + 4 Na2CO3 + 3 C = 4 Al + 8 NaFl + 7 CO.
(4) 3 A₁₂OFI + 3 Na,CO, + 3 C = 4 Al + Al¸Fl¸ 6 NaFl + 6 CO¸
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, Agents for the Applicant.
COMPLETE SPECIFICATION.
An Improved Process for the Electrolytic Production of Aluminium.
1, LUDWIG GRABAU, of 41, Schiffsgraben, Hanover, in the Empire of Germany,
Civil Engineer, 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:-
My invention relates to a process for the direct separation of pure aluminium
from a molten mass by means of electrolysis.
The manufacture of aluminium has heretofore always presented the inconvenience
that the materials used for obtaining metallic aluminium regularly contain silicon
and iron, so that only a metallic aluminium has been obtained which is more or
less contaminated by these substances and which is deteriorated in its properties.
According to the present invention the aforesaid inconvenience is obviated by
subjecting a mixture of aluminium fluoride with soda or other basic substances such
as caustic soda, caustic potash, which can all be easily produced free from iron and
silicon, to electrolysis in the manner hereinafter described.
Cryolite is fused in a receptacle by means of an electric current, and into this
fluid bath is introduced, during the electrolysis, a mixture of aluminium fluoride
and soda (which may be taken as an example) to definite proportions according to
the quantity of aluminium which is separated.
Of the electrodes used for this purpose at least the positive electrode, consists of
carbon, whilst the negative electrode may consist of metal, such as aluminium.
By the action of an electric current metallic aluminium is in this case separated
at the negative pole, and carbonic acid is formed at the positive pole, which acid is
obtained partly from the soda and partly from the action of the molten mass upon
the carbon of the electrode.
The proportion between aluminium fluoride and soda may be such that, besides
aluminium, chiefly sodium fluoride or aluminium fluoride sodium fluoride (cryolite
Al,F], 6 NaFl) is formed. Any proportion lying between these two extreme cases
may be employed, which may be represented by the following formulæ :
(1) 2 AlFl¸ + 6 Na, CO, + 3 C=4 Al + 12 NaFl + 9 CO,.
(2) 4-Al,Fl, + 6 Na,CO, + 3 C = 4 Al + 2 (AlFl¸ 6 NaFl) + 9 CO,.
If in lieu of soda, use is made of potash as a basic material, potassium compounds
corresponding to the sodium compounds are of course produced.
'
The proportion between aluminium fluoride and basic material, such as soda,
potash, sodium protoxide, potassium protoxide, depends therefore on whether
either sodium fluoride or potassium fluoride or cryolite is to be obtained as a
by-product.
In this manner a pure metallic aluminium can be produced with certainty,
because, as above stated, the materials employed can be easily obtained quite free
from the usual aluminium impurities, that is to say from silicon and iron. It is
important that in the improved process a valuable by-product such as cryolite, can
be obtained.

page_text: In this process moreover it is not necessary to employ neutral aluminium fluoride,
as any basic products containing aluminium may be used.
Thus aluminium oxyfluoride (Al,OFI), which can be readily and advantageously
produced, may be employed in like manner instead of aluminium fluoride the pro-
portions being likewise selected with regard to whether chiefly sodium fluoride or
potassium fluoride or cryolite is to be obtained as a by-product. These two extreme
cases may be represented by the following formula, which enables the proportions
to be computed with facility.
(3) 2 ALOFI. + 4 Na„CO, + 3 C = 4 Al + 8 NâFl + 7 CO….
(4) 3 Al,OFI, +3 Na,CO, + 3 C = 4 Al + Al„Fl¸ 6 NaFl + 6 CO„.
(4) 3 Al,OFI + 3 Na,CO, + 3 C = 4 Al + Al„Fl¸ 6 NaFl + 6 CO„
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
The manufacture of aluminium with simultaneous production of an alkaline
fluoride or an alkaline fluoride aluminium fluoride (cryolite) by the electrolysis of a
mixture of aluminium fluoride, or compounds or substances containing aluminium
fluoride, and a basic substance such as an alkali or alkaline carbonate.
Dated this 9th day of March 1892.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicant.