Improvements in the Preparation of Aluminium Fluoride and Double Fluorides and in the Manufacture of Aluminium from Fluorides.
Year: 1890

page_text: Date of Application, 23rd Oct., 1890
Complete Specification Left, 23rd July, 1891-Accepted, 5th Sept., 1891
· PROVISIONAL SPECIFICATION.
Improvements in the Preparation of Aluminium Fluoride and
Double Fluorides and in the Manufacture of Aluminium from
Fluorides.
I, THOMAS STEVEN LINDSAY, Manager, White's Alkaline Metals Syndicate
of 31 Poultry, London E.C., do hereby declare the nature of this invention to be
as follows:
In the process hitherto used for the manufacture of aluminium the well known
method of "Deville" has been generally adopted as a basis and accordingly the
aluminium has been reduced from its chloride by means of metallic sodium. In
one process adopted, the double fluoride of aluminium and sodium known as
cryolite has been used as a solvent and alumina has been dissolved in the fused
salt and subjected to electrolytic decomposition whereby aluminium is deposited
in the metallic state.
In another process it has been attempted to reduce aluminium directly from
cryolite by metallic sodium but with limited success.
The object of this present invention is to apply fluorides and double fluorides to
the manufacture of aluminium in such manner as to overcome the difficulties
experienced in other processes.
In the known double fluorides of the alkaline metals and alkaline earth metals
the general formula is Al,F, 3 MF, where M represents a molecule of any of the
alkaline metals as Na₂, K, or the radicle 2 NH, and an atom of the alkaline earth
metals as Ca, Ba, or Sr, and such fluorides are not advantageously applicable to
the manufacture of aluminium by reduction with sodium.
In accordance with this.invention suitable double fluorides are prepared in the
following manner :- Alumina or its hydrate is treated with sufficient hydrofluoric
acid to dissolve it, and two equivalents of an alkali or alkaline earth added, which
alkali may be in the form of hydrate or carbonate; the solution is then heated
sufficiently and the whole of the aluminium is thrown down as a new double
fluoride having less alkaline fluoride than the usual salt. The general formula is
Al,FMF, where M represents the alkaline metal or alkaline earth metal.
Hydrates of potassium, sodium, and ammonium, calcium, barium, and strontium
used in this manner produce double fluorides of the respective metals Al₂F 2 KF,
ALF 2 NaF, Al₂F, 2 NH,F, Al,F CaF, Al,F,BaF, and Al,F,SrF. Carbonates
of potassium, sodium, ammonium, calcium, barium, and strontium produce the same
result. The same double fluoride may also be prepared by adding to the hydro-
fluoric acid solution of aluminium a haloid salt such as chloride or fluoride of the
alkaline metal or alkaline earth metal and heating as herein before described.
These double fluorides are also produced by mixing one equivalent (Al2O3) of
alumina or its hydrate with two equivalents of the alkaline or alkaline earth
hydrate, carbonate, or haloid salt and then adding the required amount of hydro-
fluoric acid and heating.
6
Those fluorides present very considerable advantages for use in the manufacture
of aluminium by the aid of sodium, partly because of the relatively large
proportion of (AF) aluminium fluoride which they contain. In the cases of
sodium and potassium double fluorides with aluminium, respectively AlF 2 NaF
and Al,F, 2 KF the salts are dried by heat without chemical change and are then
reduced with metallic sodium at a suitable temperature and with suitable furnace
arrangements when metallic aluminium is readily and advantageously produced.
When the double fluoride of aluminium and ammonium Al,F, 2 NHF is adopted,
the salt is so heated that the ammonium fluoride (NHF) is driven off and

page_text: collected for future use while pure aluminium fluoride is retained and is reduced
by heating with metallic sodium. Both methods present certain advantages over
existing processes and produce metallic aluminium with a considerably reduced
expenditure of sodium over previous fluoride processes and the economy of sodium
is greatest in the case of the adoption of pure aluminium fluoride.
In connection with the reduction of these fluorides with metallic sodium it should
be noted that the reductions take place best in each case when the proportions of
the salt and sodium used are such that the slag which is formed simultaneously
with the reduced aluminium is a sodium or potassium cryolite. Sodium or potassium
chloride is sometimes added to the mixture to lower the melting point of the slag.
The slag may be used for producing fresh quantities of hydrofluoric acid and
for this purpose it may be washed and heated in suitable retorts with sulphuric
acid. Sometimes it is preferable to add only acid sufficient to decompose the
alkaline-fluoride and then evaporate to dryness, aluminium fluoride remains and
the alkaline sulphate is washed out. Enough acid may also be added to decompose
four equivalents of the alkaline fluoride in the cryolite slag (Al,F,6 MF) and so,
on evaporation, the alkaline sulphate may be washed out and the double fluoride
(ALF 2 MF) remains.
The new double fluoride may be prepared in various ways such as have been
hereinbefore described without departing from the essential features of the inven-
tion, those essential features consisting principally in preparing the new double
fluoride having with aluminium fluoride only two equivalents of the alkaline
fluoride or one equivalent of the alkaline earth fluoride or by preparing pure
aluminium fluoride so that in both cases the aluminium produced is of a high
standard of purity in consequence of the purity of the fluorides prepared in
accordance with this invention.
Dated this 21st day of October 1890.
MARKS & CLERK,
5, Furnival's Inn, Holborn, London, E.C., Agents for Applicant.
COMPLETE SPECIFICATION.
Improvements in the Preparation of Aluminium Fluoride and
Double Fluorides and in the Manufacture of Aluminium from
Fluorides.
I, THOMAS STEVEN LINDSAY, Manager, White's Alkaline Metals Syndicate,
of 31 Poultry, London E.C. 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:—
In the process hitherto used for the manufacture of aluminium, the well known
method of Deville has been generally adopted as a basis, and accordingly the
aluminium has been reduced from its chloride by means of metallic sodium. In
one process adopted, the double fluoride of aluminium and sodium known as cryolite
has been used as a solvent, and alumina has been dissolved in the fused salt and
subjected to electrolytic decomposition whereby aluminium is deposited in the
metallic state. In another process it has been attempted to reduce aluminium
directly from cryolite by metallic sodium, but with limited success.
The object of this present invention is to apply fluorides. and double.fluorides to
the manufacture of aluminium in such manner as to overcome the difficulties
experienced in other processes.
In the known fluorides of the alkaline metals and alkaline earth metals the
general formula is Al,F, 3 MF2, where M represents a molecule of any of the
alkaline metals as Na, K, or the radicle 2 NH, and an atom of the alkaline earth
metals as Ca Ba or Sr; and such fluorides are not advantageously applicable to the
> manufacture of aluminium by reduction with sodium.

page_text: In accordance with this invention suitable double fluorides are prepared in the
following manner :-Alumina or its hydrate is treated with sufficient hydro-fluoric
acid to dissolve it, and two equivalents of an alkali or alkaline earth added, which
alkali may be in the form of hydrate or carbonate; the solution is then heated
sufficiently and the whole of the aluminium is thrown down as a new double fluoride
having less alkaline fluoride than the usual salt. The general formula is Al,FMF,
where M represents two atoms of the alkaline metal or one atom of the alkaline
earth metal. Hydrates of potassium, sodium, and ammonium, calcium, barium,
and strontium used in this manner, produce double fluorides of the respective
metals Al F2 KF; Al,F, 2 NaF; ALF 2 NHF; AF CaF, ALF BaF,;
and AlFr. Carbonates of potassium, sodium, ammonium, calcium, barium and
strontium produce the same result.
The same double fluoride may be prepared by adding to the hydro-fluoric acid
solution of aluminium, a haloid salt such as chloride or fluoride of the alkaline
metal or alkaline earth metal, and heating as hereinbefore described.
These double fluorides are also produced by mixing one equivalent (A₁₂O₂) of
alumina or its hydrate with two equivalents of the alkaline or alkaline earth
hydrate, carbonate, or haloid salt and then adding the required amount of hydro-
fluoric acid and heating.
These fluorides present very considerable advantages for use in the manufacture
of aluminium by the aid of sodium partly because of the relatively large pro-
portion of (Al,F) aluminium fluoride, which they contain. In the cases of sodium
and potassium, double fluorides with aluminium respectively, Al,F, 2 NaF, and
Al,F 2 KF, the salts are dried by heat without chemical change, and are then
reduced with metallic sodium at a suitable temperature and with suitable furnace
arrangements when metallic aluminium is readily and advantageously produced.
When the double fluoride of aluminium Al,F, 2 NHF is adopted, the salt is so
heated that the ammonium fluoride (NHF), is driven off and collected for future
use, while pure aluminium fluoride is retained and is reduced by heating with
metallic sodium. Both methods present certain advantages over existing processes
and produce metallic aluminium with a considerably reduced expenditure of sodium
over previous fluoride processes and the economy of sodium is greatest in the case
of the adoption of pure aluminium fluoride.
In connection with the reduction of these fluorides with metallic sodium, it should
be noted that the reductions take place best in each case, when the proportions of
the salt and sodium used are such that the slag which is formed simultaneously
with the reduced aluminium, is a sodium or potassium cryolite (Al,F, 6 NaF or
A₁₂F 6 KF).
Sodium or potassium chloride is sometimes added to the mixture to lower the
melting point of the slag.
The slag may be used for producing fresh quantities of hydro-fluoric acid and for
this purpose it may be washed and heated in suitable retorts with sulphuric acid.
Sometimes it is preferable to add only acid sufficient to decompose the alkaline
fluoride, and then evaporate to dryness; aluminium fluoride remains and the
alkaline sulphate is washed out. Enough acid may also be added to decompose
four equivalents of the alkaline fluoride in the cryolite slag (ALF, 6 NaF) and so,
on evaporation, the alkaline sulphate may be washed out and the double fluoride
(ALF 2 NaF) remains.
The new double fluoride may be prepared in various ways, such as have been
herein before described without departing from the essential features of the
invention, those essential features consisting principally in preparing the new
double fluoride, having with aluminium fluoride only two equivalents of the alkaline
fluoride, or one equivalent of the alkaline earth fluoride, or by preparing pure
aluminium fluoride so that in both cases the aluminium produced is of a high
standard of purity in cousequence of the purity of the fluorides prepared in
accordance with this invention.

page_text: 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 :-
(1) In the manufacture of metallic aluminium, the use of the new double
fluoride of the general formula Al,FMF2, where M represents one atom of a dyad
metal or two atoms of a monad metal, in whatever manner that fluoride may
be prepared or produced, substantially as and for the purposes hereinbefore
described.
(2) The method of preparing the new double fluoride by bringing together in
solution in the required proportions aluminium fluoride Al,F, and either of the
fluorides of sodium, potassium, ammonium, barium, strontium or calcium; evaporating
the solution sufficiently, and so throwing down the said double fluoride, substantially
as and for the purposes hereinbefore described.
(3)-The method of preparing the new double fluoride by the use of hydrates or
carbonates, or haloid salts of alkali or alkaline earth metals substantially as and for
the purposes hereinbefore described.
(4) The method of preparing the new double fluoride by the use of hydrate of
alumina, mixed with alkaline or alkaline carth hydrate, carbonate or haloid salt to
which hydro-fluoric acid is added substantially as and for the purposes hereinbefore
described.
(5)-In the manufacture of metallic aluminium, the use of aluminium fluoride
prepared by heating the new double fluoride of ammonium (Al,F, 2 NHF) to
volatilize the ammonium fluoride, the said double fluoride of ammonium being
prepared as set forth substantially as hereinbefore described.
(6)-In the manufacture of metallic aluminium, decomposing the fluoride slag
produced by sulphuric acid, either wholly to produce hydro-fluoric acid, or partially
to recover the new aluminium double fluoride by converting a portion of the
alkaline fluoride to sulphate, evaporating and washing out substantially as herein-
before described.
Tated this Wnd dav
1001
ated this Wnd
1001
FUST
MARKS & CLERK,
5, Furnival's Inn, Holborn, London, E.C., Agents for the Applicant.