Improvements in the Manufacture of Alumina.
Year: 1891

page_text: Date of Application, 20th Oct., 1891-Accepted, 28th Nov., 1891
Improvements in the Manufacture of Alumina.
A communication by JOSEPH ALBERT BRADBURN and JOHN DOWNER PENNOCK,
both of Syracuse, in the County of Onondaga and State of New York, United
States of America, Practical Chemists.
I, WILLIAM PHILLIPS THOMPSON F.C.S., M.I.M.E. of the Agency for
Foreign Patent Solicitors, 6 Lord Street, Liverpool, and 6, Bank Street,
Manchester, both in the County of Lancaster, and 323 High Holborn in the
County of Middlesex, Civil Engineer, do hereby declare the nature of this inven-
tion 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 the extraction of alumina from the mineral earths in
which, in nature, it is associated with various other acids.
The object of the invention is to produce a commercially pure alumina, Al,O,
from minerals, or that class of minerals, which allow part or all of their hydrated
alumina to be dissolved out by the use of a caustic soda solution, as the disinte-
grating agent, and separating the alumina from the caustic liquor by precipitation,
gathering it, and rendering it anhydrous by calcining.
This invention consists in the process hereinafter described, and which is
specifically set forth in the claims hereunto annexed.
Mineral bauxite in its hydrated condition is taken, in which the iron present is in
its highest state of oxidisation, namely, Fe,O,; and which accordingly is wholly,
or nearly, free from organic matters.
In case the bauxite does contain organic matters, or its iron in the ferrous con-
dition, these substances are oxidised by mixing the ground mineral with a solution
of a hypo-chlorite, such as bleaching powder, and then carbonic acid gas is passed
in and the liberated chlorine oxidises the iron and organic matter.
The process will first be described as applied to red bauxite, in which the iron is
already fully oxidised.
It is first ground, hydrated as it comes from the earth; then treated with a
solution of caustic soda containing about 150 grammes Na,O per litre in a digester
for about five hours, with agitation to prevent the mineral from packing together,
and to better expose the mineral to the action of the solution, during the heating
therein.
The grinding can be dispensed with in case the mineral is not too hard or
lumpy.
By this digestion, the mineral is disintegrated, and the bulk of the alumina existing
as hydrate therein goes into solution.
The contents of the digester are then filtered, and the liquor drawn through.
Then the mineral is taken from the filter, and mixed with carbonate of soda in
the proportion of about two and one-half to three parts to each two parts of
alumina present.
This mixture is then heated to a red heat for about five hours, and is then placed
in tanks, and lixiviated with the liquor made in the digester.
In this instance, the liquor is of a red, turbid appearance, which arises from the
action of the caustic liquor upon the ferric oxide in the mineral, which liberates
the oxide in such an extremely fine state of division that, in suspension, it is carried
through a filter or filter press, still turbid and red, and the red particles remain in
suspension even after the liquor has stood several days.
After this lixiviation of the furnaced mixture of mineral and soda, the liquor is
clarified by being treated with precipitated hydrated alumina, which, being
voluminous, flocculent and more or less gelatinous, collects, and picks up or encloses
these suspended particles, and carries them down by precipitation.

page_text: This precipitation of the hydrated alumina is effected within the liquid itself,
by using any known precipitant of alumina, such as carbonic acid or milk of lime
with agitation.
The precipitant is added continuously until the liquid begins to become cloudy
from the separation of the alumina, when the addition of precipitant is stopped.
This liquid is then filtered. In this mauner, the liquor is purified from iron oxide.
Bicarbonate of soda is now added in sufficient quantity to precipitate all of the
remaining alumina, the liquor being heated and agitated."
The liquor is then filtered out and the alumina washed with water.
The reaction with the bicarbonate may be represented as follows:
to ten per cent. of its weight in alkali, and this soda can only be washed out by long
and protracted washing.
Accordingly, after washing with a reasonable amount of water, this alumina is
heated in a solution of ammonium chloride, which changes the soda into common
'salt, without acting upon the alumina.
This salt can then be easily washed out and the resulting pure alumina is taken
from the filter and calcined to render it anhydrous.
This treatment with ammonium chloride is also applicable to alumina, pre-
cipitated by carbonic acid gas.
The process has been described above as applied to red bauxite, in which the
iron is fully oxidised; and to bauxite containing unoxidised matter and foreign
matter; but it is evident that there are many other kinds of bauxite, when their
component materials are considered, which will require, in their treatment to
separate and obtain the alumina, variations in and departures from the process
above described, some of such variations consisting in preliminary treatment, and
some in intermediate steps, sandwiched into the above process, and this invention
is not, therefore, limited to the process and the precise steps above given.
It will be seen that, after the iron, etcetera, in the bauxite is oxidised, the greater
part of the alumina is extracted in the wet state and before the mineral is dried,
and that the alumina obtained in this way is exceedingly pure, and that, by the
remaining steps, the remainder, existing as Al,O,, is extracted.
It will be seen also that some bauxite will be so perfectly oxidised naturally
that, by the first step, all of the alumina can be obtained, or so much thereof that
further treatment of the residue would be unprofitable.
Having now particularly described and ascertained the nature of the said inven-
tion, and in what manner the same is to be performed, as communicated to me
by my foreign correspondents, I declare that what I claim is :-
1. The process of obtaining alumina from bauxite consisting in treating it with
a caustic soda solution, and precipitating the hydrate of aluminium, filtering out
the liquor, and then calcining the alumina, substantially as set forth.
2. In the art of obtaining alumina from ferrous bauxite, the process of oxidising
the iron and organic matter therein, consisting in mixing the ground mineral
with a solution of a hypo-chlorite, and then passing carbonic acid gas into the
solution.
3. The process of obtaining alumina from bauxite consisting in oxidising the
iron and organic matter therein, by treatment substantially as described with a
hypo-chlorite and carbonic acid gas, and then treating the oxidised bauxite with a
caustic soda solution, filtering out the liquor, precipitating the hydrate of
aluminium, and calcining it, substantially as set forth.
This 90th
of Ontahan 1001
WM. P. THOMPSON & Co.,
Agents for the Applicant.