Improvements in the Manufacture of Artificial Cryolite.
Year: 1899

page_text: PROVISIONAL SPECIFICATION.
Improvements in the Manufacture of Artificial Cryolite.
We, DONALD MATTHEWS, of 9, Victoria Street, Westminster, Chemist, and
THE BRITISH ALUMINIUM COMPANY, LIMITED, of the same address, do hereby
declare the nature of this invention to be as follows;-
The present invention has reference to a process and apparatus for producing
cryolite artificially.
This product is obtained by treating hydrofluoric acid with a solution of
sodium chloride in the presence of alumina.
In carrying out the present invention, fluor spar is placed in a lead-still with
a suitable quantity of sulphuric acid.
The still is first heated by means of a steam jacket to a temperature of about
100° C. The temperature is then raised for a number of hours, during which
time the mixture is kept stirred by means of a current of air Hydrofluroric acid
is given off in the still, and passes over into a purifier by means of a lead pipe
nearly reaching the bottom of the latter. This purifier contains water with
potassium fluoride in solution. The water absorbs part of the hydrofluoric acid;
a portion is however carried over into a precipitating tank by a current of air
blown into the purifier.
When the reaction in the still is complete, the purifier is disconnected from the
still, and steam blown into the jacket of the former. Pure hydrofluoric acid
distils over into the ebonite-lined precipitating tank already mentioned, the
impurities, which are chiefly sulphuric and hydrofluosilicic acid, being retained
by the potassium fluoride in the purifier, in the form of sulphate and silico
fluoride of potassium. If much sulphurous acid is found to be present, it may be
oxidised by adding a small quantity of sodium peroxide or other suitable oxidis-
ing agent to the liquid in the purifier, but this is not absolutely necessary.
When the whole of the hydrofluoric acid has distilled over into the precipitating
tank, the amount of liquor is measured, and a sample taken. The amount of
hydrofluoric acid is determined, volumetrically, and the calculated amount of
hydrate of alumina added. When solution is complete, the calculated amount of
filtered sodium chloride solution is run into the precipitating tank, and the whole
well stirred by a current of air. The cryolite separates out at once in a gelatinous
state, and is allowed to settle. The upper layer of hydrochloric acid is run off.
and the cryolite is then allowed to run into a washing tank which is also lined
with ebonite. It is washed here by decantation, and then filtered off in a vulcanite
filter press, and washed till free from chloride. From the filter press, the cryolite
is taken to the drying floor, where it is heated till free from moisture. It is now
in the form of a white powder ready for packing.
Dated this 8th day of June 1800

page_text: We. DONALD MATTHEWS, of 9, Victoria Street, Westminster, Chemist, and
THE BRITISH ALUMINIUM COMPANY, LIMITED, of the same address, 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 present invention has reference to a process and apparatus for producing
cryolite artificially.
This product is obtained by treating hydrofluoric acid with a solution of
sodium chloride in the presence of alumina.
In carrying out the invention, we proceed as follows, making use of an
apparatus which is diagramatically illustrated in the accompanying sheet of
drawings.
Fluor spar is placed in a lead still a, with a suitable quantity of sulphuric acid.
The still a is first heated, by means of a steam jacket b, to a temperature of about
100° C. The temperature is then raised for a number of hours, during which
time the mixture is kept stirred by means of a current of air.
Hydrofluoric acid is given off in the still , and passes over into a purifier e by
means of a lead pipe d, nearly reaching the bottom of the latter. This purifier c
contains water with potassium fluoride in solution. The water absorbs part of the
hydrofluoric acid; a portion is, however, carried over into a precipitating tank e
by a current of air blown into the purifier.
When the reaction in the still a is complete, the purifier c is disconnected from
the still, and steam blown into the jacket f of the former. Pure hydrofluoric
acid distils over into the ebonite-lined precipitating tank e already mentioned, the
impurities, which are chiefly sulphuric and hydrofluosilicic acid,-being retained
by the potassium fluoride in the purifier c, in the form of sulphate and silico-
fluoride of potassium. If much sulphurous acid is found to be present, it may be
oxidized by adding a small quantity of sodium peroxide or other suitable oxydiz-
ing agent, to the liquid in the purifier, but this is not absolutely necessary.
When the whole of the hydrofluoric acid has distilled over into the precipitating
tank e, the amount of liquid is measured and a sample taken. The amount of
hydrofluoric acid is determined volumetrically, and the calculated amount of
hydrate of alumina added to combine with half the hydrofluoric acid present,
according to the equation.
A₁₂С¸ — 3H₂O + 6HF
=
Al₂F + 6H₂O.
that is, for 1 pound of hydrofluoric acid present, 0425 pounds of alumina in the
form of hydrate will be required.
When solution is complete, the calculated amount of filtered sodium chloride
solution, equivalent to the amount of free hydrofluoric acid remaining, that is,
for every pound of hydrofluoric acid originally found, 146 pounds of sodium
chloride is run from the tank into the precipitating tank e, and the whole well
stirred by a current of air. The cryolite separates out at once in a gelatinous
state, and is allowed to settle. The upper layer of hydrochloric acid. is run off.
and the cryolite is then allowed to run into a washing tank h, which is also lined
with ebonite.
It is washed here by decantation, and then filtered off in a vulcanite filter
press i, and washed till free from chloride.
From the filter-press, the cryolite is taken to a drying floor, where it is heated
till free from moisture. It is now in the form of a white powder ready for packing.

page_text: The boiler for supplying steam. to the jackets of the still a and purifier c is
not shewn in the diagram, but 1 is the steam supply pipe, having branches 2 and 3
respectively connected to the jackets 6 and f. 4, 5, and 6, are air supply pipes,
leading into the still a, purifier c, and precipitating tank e, from a suitable blower,
not shown.
is a funnel supply pipe for the purifier c, fitted with a cock c³. e¹ is a similar
pipe for the tank e.
We may obtain the potassium fluoride, for use in the purifier c, by intercepting
the hydrofluoric acid fumes which escape during the distillation of the purified
acid.
Accordingly, on the escape pipe of the precipitating tank e, we arrange closed
traps, wherein is contained carbonate of potash, which forms, with the hydro-
fluoric acid fumes, potassium fluoride.
Having now particularly described and ascertained the nature of our said
invention and in what manner the same is to be performed, we declare that what
we claim is:-
The process of and apparatus for producing artificial cryolite substantially as
described with reference to the accompanying drawing.
Dated this 8th day of March 1900