Improvements relating to the Manufacture of Aluminium Fluoride.
Year: 1892

page_text: Date of Aplication, 20th Aug., 1892
Complete Specification Left. 19th May, 1893-Accepted, 24th June, 1893
PROVISIONAL SPECIFICATION.
Improvements relating to the Manufacture of Aluminium Fluoride.
I, LUDWIG GRABAU, of Grabau's Aluminium Works, Trotha, near Halle on
the Saale, in the Empire of Germany, do hereby declare the nature of this
invention to be as follows:-
For the manufacture of perfectly pure aluminium it is essential to employ pure
aluminium materials, such as pure aluminium fluoride especially free from silicon
and iron. In order to obtain for the pure aluminium an extensive industrial use
corresponding to its advantageous properties endeavours are made to cheapen the
manufacture of the same for which purpose the cheap supply of sufficiently pure
aluminium materials is a necessity.
Now my said invention has for its object to supply such an aluminium material,
namely aluminium fluoride, in a sufficiently pure state free from iron and silicon at
a cheap rate which enables it to be advantageously employed for the manufacture
of aluminium.
For this purpose I produce according to the present invention pure aluminium
fluoride as free as possible from iron and silicon and, with employment of hydro-
fluoric acid or hydrofluosilicic acid, use the aluminium material which occurs most
generally, that is to say clay, from which it has heretofore not been possible to
produce an aluminium fluoride free from iron and silicon.
Accordingly the process forming the subject of my invention may be carried into
practice as follows.
cent.
Pulverized calcined clay or kaolin as poor in iron as possible is introduced, while
continually stirring, into dilute crude hydrofluoric acid, preferably about 12
hydrofluoric acid, or into hydrofluosilicic acid of corresponding strength.
реда
When using hydrofluoric acid the reaction generally takes place more or less
violently with a considerable increase of temperature, and must be mitigated by
cooling to a maximum temperature of 95 degrees centigrade or at all events
sufficiently to prevent boiling.
In case hydrofluosilicic acid is employed which produces only a gentle action, the
latter must be increased by heating.
The reaction is terminated in a short time, even in a few minutes, and the mass
neutralized so that a drop of the same forms with tropaolin a purely yellow colour.
Owing to such a neutralization the solution of aluminium fluoride obtained will be
free from silicic acid, for as long as the mass is acid it contains hydrofluosilicic acid,
and the complete separation of silicic acid takes place only in a neutral or slightly
basic solution.
With uncalcined clay or kaolin it is not possible to obtain a neutral solution, not
even after long heating of the mixture, so that the solution of aluminium fluoride
will always contain silicic acid. Moreover a large portion of the aluminium fluoride
(up to about 50 per cent.) passes over to the insoluble residue, which implies as
great a loss of aluminium fluoride.
The neutral hot mixture is somewhat cooled and rapidly filtered. The residue
which consists of hydrated silicic acid and undecomposed clay is washed with hot
water. This water may be used for washing fresh quantities of the aforesaid
residue from the filtration, evaporated to the concentration of the main solution,
and then added to the latter. This solution contains, when using 12 per cent.
hydrofluoric acid, from about 15 to 16 per cent. of aluminium fluoride (Al,Fl¸),
and may contain metals, such as lead, arsenic, which can be precipitated with
sulphuretted hydrogen, and also dissolved iron oxide as ferric fluoride. For this

page_text: reason it is expedient to add sulphuretted hydrogen to the filtrate whereby the said
metals are precipitated and the ferric fluoride corresponding to the iron oxide is
converted into the ferrous fluoride corresponding to the iron protoxide. After the
filtration of this liquid smelling like sulphuretted hydrogen the liquid is acidified a
little, say by adding hydrochloric acid, so that a sample is just colored red with
tropaolin as otherwise the neutral liquid containing sulphuretted hydrogen would
always allow some iron sulphide to precipitate. It is expedient to energetically
cool this slightly acid liquid, while stirring, in a receptacle which may be made of
aluminium metal.
In this manner I separate crystalline alumiinium fluoride (Al,Fl. 18 H₂O) which
is as clear as water, and which is free both from silicon and iron, as the latter is
present, not as a fluoride corresponding to the iron oxide which easily precipitates
with it, but as a fluoride corresponding to the iron protoxide in consequence of the
reduction. The crystallization may be caused to commence and promoted by adding
some crystallized aluminium fluoride to the cooled liquid.
This liquid is also cooled during the crystallization by which a disengagement of
heat is caused. When the temperature has decreased to zero the crystallization is
generally terminated.
The crystal paste thus obtained is separated from the adhering mother liquor in
a suitable manner, for instance by a sucking or centrifugal action, and completely
freed from the same by means of water which is preferably as cold as ice. The
mother liquor containing all the iron is removed, whilst the water can be used for
the above described lixiviation of the kaolin residues.
From the aluminium fluoride crystals, in which will be found 95 per cent. of the
fluorine used in the hydrofluoric acid or in the hydrofluosilicic acid, the water may
be readily removed by heating.
Dated this 20th day of August 1892.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, Agents for the Applicant.
COMPLETE SPECIFICATION.
Improvements relating to the Manufacture of Aluminium Fluoride.
I, LUDWIG GRABAU, of Grabau's Aluminium Works, Trotha, near Halle on the
Saale, in the Empire of Germany, 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:-
For the manufacture of perfectly pure aluminium it is essential to employ pure
aluminium materials, such as pure aluminium fluoride especially free from silicon
and iron. In order to obtain for the pure aluminium an extensive industrial use
corresponding to its advantageous properties, endeavours have been made to
cheapen the manufacture of the same, for which purpose the cheap supply of
sufficiently pure aluminium materials is a necessity.
Now my said invention has for its object to supply such an aluminium material,
namely aluminium fluoride, in a sufficiently pure state free from iron and silicon at
a cheap rate which enables it to be advantageously employed for the manufacture
of aluminium.
For this purpose I produce, according to the present invention, pure aluminium
fluoride as free as possible from iron and silicon, and, with employment of hydro-
fluoric acid or hydrofluosilicic acid, may use the aluminium material which occurs
most generally, that is to say clay from which it has heretofore not been possible
to produce an aluminium fluoride free from iron and silicon.
Accordingly the process forming the subject of iny invention may be carried into
practice as follows:
Pulverized, calcined clay or kaolin as poor in iron as possible is introduced

page_text: slightly in excess, while continually stirring, into dilute crude hydrofluoric acid,
preferably about 12 per cent. hydrofluoric acid, or into hydrofluosilicic acid of
corresponding strength.
When using hydrofluoric acid the reaction generally takes place more or less
violently with a considerable increase of temperature, and must therefore, in most
cases, be mitigated by cooling to a maximum temperature of 95 degrees centigrade,
or at all events sufficiently to prevent boiling.
In case hydrofluosilicic acid is employed, which produces only a gentle action,
the latter must in most cases be increased by heating.
In a short time, even in a few minutes the reaction is terminated and the mass
has become neutral which may be seen by a drop of the same forming with
tropaolin a purely yellow colour.
The result of this neutrality will be that the solution of aluminium fluoride
obtained is free from silicic acid; for as long as the mass is acid it contains hydro-
fluosilicic acid and the complete separation of the hydrated silicic acid formed takes
place only in a neutral or slightly basic solution.
With uncalcined clay or kaolin it is not possible to obtain a neutral solution, not
even after a prolonged heating of the mixture, so that the solution of aluminium
fluoride will always contain silicic acid. Moreover a large portion of the
aluminium fluoride (up to about 50 per cent.) passes over to the insoluble residue
and is therefore not utilized, which implies as great a loss of aluminium fluoride.
In order to utilize the clay as completely as practicable, that is to say, dissolving
as much aluminium of the same as possible the calcination or the burning of the
clay must not be too gentle nor too fierce. The proper calcining temperature is
advantageously ascertained by small preliminary trials in such a manner that a
sample of the calcined clay is treated in the described manner with hydrofluoric
acid so as to determine whether it becomes neutral.
The neutral hot reaction mixture is cooled to a mean temperature and rapidly
filtered. The solid residue which consists of hydrated silicic acid and undecomposed
clay, is washed with hot water. This water may be used for washing fresh
residues, then evaporated to the concentration of the main solution, and like the
latter treated further. In general about 95 per cent. of the hydrofluoric acid
employed may be regained in the form of dissolved alumininm fluoride. The main
solution contains, when using 12 per cent. hydrofluoric acid, from about
15 to 16 per cent. of aluminium fluoride (Al,Fl₁) and is suitably treated with
sulphuretted hydrogen, in order
(1) To remove dissolved metals which can be precipitated with sulphuretted
hydrogen, such as lead, arsenic and the like,
(2) To convert existing iron oxide or compounds corresponding to the same
(such as ferric fluoride) into protoxide or compounds corresponding to the protoxide
(such as ferrous fluoride).
Of course this reduction of the iron oxide or this transformation of compounds
corresponding to the iron oxide into iron compounds corresponding to the protoxide
may also be effected by other reducing agents (such as sulphurous acid, hypo-
sulphurous acid, nascent hydrogen). After the filtration of this liquid which smells
like sulphuretted hydrogen the liquid is acidified a little, say by adding hydro-
chloric acid, so that a sample is just coloured red with tropaolin as otherwise the
neutral liquid containing sulphuretted hydrogen would always allow some iron
sulphide to precipitate. It is expedient to energetically cool this slightly acid
liquid, while stirring in a receptacle which may be made of aluminium metal.
In this case crystalline aluminium fluoride (Al, Fl, 18 H₂O) which contains water
separates in most cases of itself, and it is free both from silicon and iron, as the
latter is present, not as a fluoride corresponding to the iron oxide which
easily precipitates with it, but as a fluoride corresponding to the iron protoxide in
consequence of the reduction. The crystallization may be caused to commence
and be promoted by adding some crystallized aluminium fluoride to the cooled
liquid.

page_text: This liquid is also cooled during the crystallisation by which a disengagement of
heat is caused. When the temperature has decreased to zero the crystallization is
generally terminated.
The crystal paste thus obtained is separated from the adhering mother liquor in
a suitable manner, for instance by a sucking or centrifugal action and completely
freed from the same by means of water which is preferably as cold as ice. The
mother liquor containing all the iron is removed, whilst the water can be used for
the above described lixiviation of the kaolin residues.
The sufficiently washed aluminium fluoride crystals are free from iron, but if
prior to the crystallization the iron contained in the solution was not transformed
into protoxide or into iron compounds corresponding to the protoxide considerable
quantities of the same enter the crystals as ferric fluoride. In this manner I may
obtain from any solution of aluminium fluoride of any desired origin which contains
iron, aluminium fluoride which is free from iron.
From the aluminium fluoride crystals the water may be readily removed.
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. A process of manufacturing a solution of aluminium fluoride free from silicic
acid by producing it in a neutral state, hydrofluoric acid or hydrofluosilicic acid
being brought together with an excess of calcined clay or calcined kaolin and these
substances allowed to act upon each other.
2. A process of manufacturing hydrous aluminium fluoride destitute of silicon
and iron from a solution of aluminium fluoride containing iron, more especially that
obtained according to the first claim, by converting iron, so far as it is contained
therein as a compound corresponding to the oxide, such as ferric fluoride, by a
reducing agent into a compound corresponding to the protoxide, such as ferrous
fluoride, then causing the solution to crystallize by cooling whereupon the crystal
paste formed is separated from the adhering mother liquor containing iron and can
be completely freed from this liquor by washing with water.
Dated this 18th day of May 1893.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicant.