Year: 1887

page_text: Date of Application, 21st Oct., 1887
Complete Specification Left, 18th July, 1888
Complete Specification Accepted, 24th Aug., 1888
I, LUDWIG GRABAU, of 41 Schiffgraben, Hanover, in the Empire of Germany
Civil Engineer, do hereby declare the nature of this invention to be as follows:-
This invention relates to a process of separating fluoride of aluminium from
cryolite, and simultaneously transforming the fluoride of an alkali, combined with
fluoride of aluminium in the cryolite, into fluoride of aluminium.
For the purpose of preparing aluminium from fluoride of aluminium by means of
an alkaline metal, the quantitative proportions are preferablys uch, that the by-product
obtained besides aluminium has the composition of cryolite. The utilization of this
cryolite by-product, by isolating the fluoride of aluminium therefrom, and transforming
the fluoride of sodium of this cryolite at the same time into fluoride of aluminium, is
accordingly of great importance and high value for the manufacture of aluminium from
fluoride of aluminium.
Up to the present time an advantageous process has not been known for this
purpose.
According to the present process the isolation of fluoride of aluminium, and the
simultaneous transformation of the fluoride of an alkali from the cryolite into fluoride
of aluminium is effected by means of sulphate of aluminium. The latter can be used
as such or in compounds, as an alum or as an aluminium fluorine sulphate. From this
results substantially the following two modifications.
1. A solution of sulphate of aluminium, or of alum, is mixed with as much natural
or artificial cryolite as corresponds with the anhydrous sulphate of alumina contained
in the solution, according to the combining weights. The transformation is then
effected according to the formula.

page_text: The clear solution is evaporated, and the residue from the evaporation containing
fluoride of aluminium and sulphate of an alkali is heated, and the sulphate of an
alkali is removed from the same by washing out with water.
2. In order to save cryolite, or to obtain greater quantities of fluoride of aluminium
when using smaller quantities of cryolite, the solution of sulphate of aluminium can
first be treated with fluor-spar, in order to transform the sulphate of aluminium for the
most part with fluoride of aluminium. For this purpose a solution is employed which
contains about ten per cent. of Al (SO)³, it being immaterial whether a solution is
used which contains only sulphate of aluminium or one that also contains alkaline
salts. This solution is mixed with the equivalent quantity of pulverized fluor-spar,
and heated up to about 90 degrees Centigrade. The transformation is effected
according to the formula :-
==
Al² F* SO + 2 (Ca SO) + Ca F².
Al² (SO4)3 + 3 (Ca F³)
According to the duration of the action, the heating, quantity and condition of the fluor-
spar powder, from two thirds to three-quarters of the entire sulphate of aluminium are
transformed into fluoride of aluminium. The solution of aluminium fluorine sulphate
thus obtained is separated by filtering and pressing from the gypsum produced and from
the fluor-spar which has not been decomposed. In order to transform the remainder of the
alumina combined with sulphuric acid also into fluoride of aluminium, this solution
of aluminium fluorine sulphate is likewise mixed with cryolite, the following process
then taking place :-

page_text: COMPLETE SPECIFICATION.
Improvements relating to the Production of Fluoride of Aluminium.
I, LUDWIG GRABAU, of 41 Schiffgraben, Hanover, 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 :-
:~
This invention relates to a process of separating fluoride of aluminium from cryolite,
simultaneously transforming the fluoride of an alkali combined with fluoride of
aluminium in the cryolite into fluoride of aluminium.
For the purpose of preparing aluminium from fluoride of aluminium by means of
an alkaline metal, the quantitative proportions are preferably such, that the by-product
obtained, besides aluminium has the composition of cryolite. The utilization of this
cryolite by-product, by isolating the fluoride of aluminium therefrom, and trans-
forming the fluoride of sodium of this cryolite at the same time into fluoride of
aluminium is accordingly of great importance and high value for the manufacture of
aluminium from fluoride of aluminium.
Up to the present time an advantageous process has not been known for this
purpose.
According to the present process the isolation of fluoride of aluminium, and the
simultaneous transformation of the fluoride of an alkali from the cryolite into fluoride
of aluminium is effected by means of sulphate of aluminium. The latter can be
used as such or in compounds, as an alum or as an aluminium fluorine sulphate. From
this results substantially the following two modifications.
1. A solution of sulphate of aluminium, or of alum, is mixed with as much natural
or artificial cryolite as corresponds with the anhydrous sulphate of alumina contained
in the solution, according to the combining weights. The transformation is then
effected according to the formula
The cryolite is already in part dissolved at the ordinary temperature, and completely,
on heating the liquid. Any impurities of the cryolite, such as silicic acid and the like,
remain undissolved.
The clear solution is evaporated and the residue from the evaporation containing
fluoride of aluminium and sulphate of an alkali is heated, and the sulphate of an alkali
is removed from the same by washing out with water.
2. In order to save cryolite or to obtain greater quantities of fluoride of aluminium
when using smaller quantities of cryolite, the solution of sulphate of aluminium
can first be treated with fluor-spar in order to transform the sulphate of aluminium
for the most part into fluoride of aluminium. For this purpose a solution is employed
which contains about ten per cent. of Al² (SO) it being immaterial whether a
solution is used which contains only sulphate of aluminium or one that also contains

page_text: alkaline salts. This solution is mixed with the equivalent quantity of pulverized
fluor-spar, and heated up to about 90 degrees centigrade. The transformation is
effected according to the formula.
AP (SO4)3 + 3 (Ca F²) = Al² F¹ SO¹ + 2 (Ca SO¹) + Ca F³.
According to the duration of the action, the heating, quantity and condition of the
fluor-spar powder, from two-thirds to three quarters of the entire sulphate of aluminium
are transformed into fluoride of aluminium. The solution of aluminium fluorine
sulphate thus obtained is separated by filtering and pressing from the gypsum
produced and from the fluor-spar which has not been decomposed.
In order to transform the remainder of the alumina combined with sulphuric acid
also into fluoride of aluminium this solution of aluminium fluorine sulphate is likewise
mixed with cryolite, the following process then taking place.
גדד
By evaporating the solution produced, and heating and laxiviating the residue
fluoride of aluminium is obtained.
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 preparation of fluoride of aluminium by treating a solution of sulphate of
aluminium or alum, or aluminium fluorine sulphate with sodium cryoline or potassium
cryolite, evaporating the solution, glowing and lixiviating the residue.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C.,
Agents for the Applicant.