Improvements in the Manufacture of Aluminium.
Year: 1888

page_text: RESE
Date of Application, 25th May, 1888
Complete Specification Left, 7th Sept., 1888
Complete Specification Accepted, 12th Oct., 1888
PROVISIONAL SPECIFICATION.
Improvements in the Manufacture of Aluminium.
I, WILLIAM GEORGE FORSTER, of Lonesome Chemical Works, Streatham Common,
in the County of Surrey, Chemist, do hereby declare the nature of this invention
to be as follows:-
Aluminium is now commonly made from a mineral called cryolite which is a double
fluoride of soda and alumina-the slag produced in the process is at present
wasted.
According to my invention I regenerate, (if it may be so termed) the slag and
employ it again for the manufacture of aluminium. The slag consists mainly of
fluoride of soda mixed with the flux which has been employed-In carrying out my
invention I add to a solution of the slag a solution of hydro-fluorate of alumina which
I produce by treating hydrate of alumina with hydro-Huoric acid-1 then wash, press
and dry the precipitate and afterwards treat it in the same way as cryolite for the
extraction of aluminium-Or I add to the powdered slag hydro-fluorate of alumina or
fluoride of aluminium-Or I add to a solution of the slag a solution of chloride of
aluminium and then wash press and dry the precipitato.

page_text: Improvements in the Manufacture of Aluminium.
I, WILLIAM GEORGE FORSTER, of Lonesome Chemical Works, Streatham Common,
in the County of Surrey, Chemist, do hereby declare the nature of this invention
and in what manner the same is be performed, to be particularly described and
ascertained in and by the following statement :-
If aluminium is prepared by means of sodium from the mineral cryolite which is
a double salt of aluminium and sodium fluoride, the remaining scoria or slag consists
chiefly of fluoride of sodium mixed with the flux which was employed in the
operation.
As neither the flux nor the fluoride of sodium are of much commercial value, the
scorice or slag has heretofore usually been regarded as worthless.
According to my invention I regenerate the said scoriae or slag, that is to say, I use
the same for the production of a new double salt either of fluorine, sodium and
aluminium, or of fluorine, chlorine, sodium and aluminium, either of these compounds
being adapted for the reduction of the aluminium they contain by means of metallic
sodium.
In carrying my invention into practice I first prepare an aqueous solution of fluoride
of sodium by lixiviating the scoriæ or slag with water.
If I wish to produce the double salt of fluoride of sodium and fluoride of aluminium,
I add to the solution of fluoride of sodium an aqueous solution of hydrofluoride of
aluminium.
The latter, is prepared by treating hydrate of alumina with hydrofluoric acid.
Upon bringing together the solution of fluoride of sodium (got by lixiviation of the
scoriae) with the solution of the hydrofluoride of aluminium, a white precipitate of the
double compound of fluoride of sodium and aluminium is formed.
This precipitate is allowed to settle, is washed, pressed, dried, and subsequently
treated for the extraction of aluminium in the same way as the natural cryolite.
The scoriae resulting from this latter operation will be regenerated again and so on
ad infinitum; the resulting scoria of each reducing operation consisting chiefly of
fluoride of sodium, the addition of fresh fluoride of aluminium gives rise to the
formation of the required double salt of sodium and aluminium.
However for the extraction of aluminium by means of metallic sodium it is not
indispensable to have the double salt mentioned, a compound of chloride of aluminium
and of fluoride of sodium answering the purpose as well.
To produce the latter I prepare a solution of hydrous aluminium chloride and add
this to the aqueous solution of sodium fluoride as obtained by the lixiviation of the
scorim by water as hereinbefore mentioned.
The resulting precipitate is collected, washed, pressed, dried and then treated in the
same way as cryolite for the extraction of aluminium.
It may be mentioned here that in the lixiviation of the scoriæ there is a residue
consisting of undecomposed cryolite.

page_text: An important feature of my invention is that I obtain for further use any such
cryolite remaining in the slag which has escaped decomposition during the reducing
process for obtaining metallic aluminium by means of sodium or other alkaline
metal.
The slag after lixiviation may either be treated separately or it may be added to
fresh cryolito or to the artificial compounds above mentioned and treated by any
suitable process for the manufacture of aluminium.
In some cases I, instead of lixiviating, treat the scorico with water and stir up tho
mixture without drawing off the fluid. I then add the solution of hydrofluoride or
hydrochloride of aluminium. The resulting precipitato mixes with the solid residuo
of the scorico or slag and the two together are treated for the production of aluminium
as above described.
As the scoriæ used for the production of the secondary aluminium compound costs
nothing, the expenses incurred relate only to the hydro-fluoride or hydrochloride of
aluminium, and the cost of production is low enough to allow the artificial product to
compete successfully with natural cryolite.
It is obvious that if desired this process may be applied when natural cryolite is not
used as the basis of the process. For instance artificial cryolite or similar aluminium
producing compound may be produced by adding a solution of artificially prepared
sodium fluoride to either a solution of hydrofluoride or hydrochloride of aluminium
and by treating the precipitate as above described.
It is obvious that other alkaline metals, such as potassium, may be used in place of
sodium in the processos above described, and I regard such processes as my invention
whether sodium or other reducing metal be employed.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed I declaro that what I
claim is :-
First. The production of an artificial double compound of fluoride of aluminium
and fluoride of sodium by the addition of aluminium fluoride to an aqueous solution of
the scoria or slag produced in the reduction of cryolite by means of sodium, substan-
tially as described.
Second. The production of an artificial double compound of chlorine and fluorine
on the one hand and aluminium and sodium on the other hand by the addition of
hydrous aluminium chloride to an aqueous solution of the scorice or slag produced in
the reduction of cryolite by means of sodium, substantially as described.
Third. The production of an artificial double salt of aluminium and sodium mixed
with the solid residue of the scoria or slag, substantially as described.
Fourth. The production of an artificial double compound of fluorine, aluminium and
sodium by mixing a solution of sodium fluoride with a solution of hydrofluoride of
aluminium, substantially as described.
Fifth. The production of an artificial double compound of aluminium chloride and
sodium on the one hand and chlorine and fluorine on the other hand by mixing a
solution of sodium fluoride with a solution of hydrochloride of aluminium.
Sixth. In the process above described the utilization of the residual cryolite.
W. G. FORSTER.
Haseltine, Lake & Co.,
45, Southampton Buildings, London, W.C.,
Agents for the Applicant.