IMPROVEMENTS IN THE MANUFACTURE AND IN THE PURIFICATION OF SULPHATE OF ALUMINA AND 'ALUMINOUS CAKES.
Year: 1879

page_text: LETTERS PATENT to William Chadwick, Thomas Chadwick, and James
Chadwick, all of Manchester, in the County of Lancaster, and Josiah
Wickliffe Kynaston, of Liverpool, in the saine County, for the Invention of
"IMPROVEMENTS IN THE MANUFACTURE AND IN THE PURIFICATION OF
SULPHATE OF ALUMINA AND 'ALUMINOUS CAKES.'”
Sealed the 23rd March 1880, and dated the 9th October 1879.
PROVISIONAL SPECIFICATION left by the said William Chadwick, Thomas
Chadwick, James Chadwick, and Josiah Wickliffe Kynaston at the Office of
the Commissioners of Patents on the 9th October 1879.
WILLIAM CHADWICK, THOMAS CHADWICK, and JAMES CHADWICK, all of Man-
chester, in the County of Lancaster, and JOSIAH WICKLIFFE KYNASTON, of
Liverpool, in the same County. "IMPROVEMENTS IN THE MANUFACTURE AND IN
THE PURIFICATION OF SULPHATE OF ALUMINA AND ALUMINOUS CAKES."
·
735
The object of our Invention is the production of sulphate of alumina neutral, and
either absolutely free from iron or containing only an extremely small proportion
of this element, and free from other impurity or admixture.
In carrying out this Invention we take bauxite or other aluminous mineral
reduced to a state of exceedingly fine powder, and mix it intimately with a pro-
portion of arsenious acid (common white arsenic) also finely powdered, varying
from 3 to 5 per cent. of the weight of the bauxite according to the proportion of
iron contained in the bauxite. We now take sulphuric acid of from 90 to 100
degreees Twaddle (specific gravity 1-450 to 1.500), and having first heated it in a
leaden pan of large capacity, we add to it the mixture of bauxite and arsenic in
sufficient quantity to produce a neutral solution. We continuously agitate the
mixture, and to moderate the violence of the reaction we run in from time to time
sufficient cold water, but so as not to dilute the mixture unnecessarily. We
continue the agitation until the reaction is complete, and then add sufficient hot
water to reduce the mixture to about 40 degrees Twaddle (specific gravity 1.200).
We now add to the mixture finely powdered chalk or other carbonate of lime in
small portions at a time so long as it continues to produce a brown or brownish

page_text: red colouration. This point is determined by taking from time to time a portion
of the liquid and filtering or allowing it to deposit, and then adding to the clear
or slightly turbid solution a little more carbonate of lime.
When no further deepening of the colour of the liquid is produced, sufficient
carbonate of lime has been added. If the operation has been properly conducted
and a neutral or basic solution obtained, it will be found that by far the larger
proportion of the oxide of iron present will be in an insoluble form in union with
arsenic, previous to the addition of carbonate of lime, and if the solution is allowed
to stand at rest it will fall out of the solution as a brown layer superincumbent on
the heavier deposit of undecomposed bauxite.
The addition of carbonate of lime in small proportion now determines the
separation of nearly the whole of the remaining soluble iron. If the solution
obtained is not neutral, but contains more or less free acid, a larger proportion
of carbonate of lime is required, the first portions added being consumed in
neutralizing the free acid, but when a sufficient quantity of carbonate of lime is
added the separation of the iron is as complete as when a neutral solution has been
obtained in the first instance.
After the addition of the necessary quantity of carbonate of lime the mixture
is thoroughly agitated, and then transferred to settling tanks of lead, where it is
allowed to stand for from ten to fourteen days to allow the insoluble matters to
deposit. The supernatant liquid is then drawn off, passed through a filter if not
quite clear, and then by any suitable means treated with sulphuretted hydrogen
gas until the excess of arsenic is rendered insoluble; it is then allowed to stand for
twenty four hours, or until the sulphide of arsenic has completely deposited, and
the clear liquid is run into a leaden pan and boiled down to a degree sufficient to
allow of its solidifying when cold.
There is thus obtained a sulphate of alumina of a higher degree of purity than
we believe has ever yet been obtained, and fit for use extensively in the arts and
manufactures. We find that our process yields almost as satisfactory results if
instead of mixing the bauxite with the arsenic, as before described, arsenic is first
dissolved in the sulphuric acid, or the arsenic may be dissolved in the solution
obtained by heating bauxite and sulphuric acid alone. In either case the
subsequent addition of carbonate of lime determines the separation of iron in the
insoluble state. We find also that the process is equally applicable for the
separation of iron from ordinary commercial ferruginous sulphates of alumina,
either prepared from bauxite or other aluminous minerals.
To obtain sulphate of alumina perfectly free from all traces of iron we take the
clear solution, obtained as before described by settling after the addition of
carbonate of lime, and to this solution (before the reinoval of the excess of arsenic)
we add a solution of ferrocyanide of calcium exactly in sufficient quantity to
precipitate the whole of the iron. We allow the mixture to stand at rest for two
or three days when the blue precipitate settles perfectly down, leaving a clear
bright solution. We draw off this solution, remove the arsenic by means of
sulphuretted hydrogen, and concentrate the clear solution till it solidifies on cooling
as before mentioned. The result is a sulphate of alumina free from all impurity,
which may be used for any purpose for which the crystallized potash or ammonia
alums are now requisite. We take the precipitate of ferrocyanide of iron or
Prussian blue obtained as before described, and after washing it slightly with water
we add to it milk of lime in sufficient quantity to entirely destroy the blue colour.
We boil the mixture well with steam, and allow it to deposit the insoluble matter,
and then draw off the clear solution. We thus again obtain the ferrocyanide of
calcium required for the precipitation of iron as before described.
When the use of white arsenic is objected to we vary the process in the following
manner: We take bauxite in a state of extremely fine powder, and mix it to a
thick cream with a solution of oxalic acid containing from 5 to 10% of the weight
of the bauxite, and about the same proportion of hydrochloric acid, the latter being
used to prevent the formation of insoluble oxalate should any lime be present in

page_text: the bauxite. We allow the mixture to stand at rest or with occasional stirring
for a week or ten days; we then add five or six times as much water as the bulk
of the mixture, thoroughly agitate, and allow to stand till the bauxite is deposited.
The latter is again repeatedly washed until quite free from oxalic acid. We make
of this purified bauxite sulphate of alumina or aluminous cake by the well known
process in common use, and we obtain a product containing not more than from
0.10 to 0.20 per cent of iron. We take the strongly acid solution of oxalate of
iron (containing also some alumina) obtained in this process of purification, and
add to it milk of lime considerably more than equivalent to the oxalic acid present,
but still leaving the mixture strongly acid. After standing two or three days the
oxalic acid is thus almost perfectly precipitated as oxalate of lime. This
precipitate is well washed and then boiled with its equivalent of sulphuric acid.
The sulphate of lime produced is allowed to settle out, and a clear solution of
oxalic acid is again obtained for the purification of a second portion of bauxite, as
before described.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said William Chadwick, Thomas Chadwick, James Chadwick, and Josiah
Wickliffe Kynaston in the Great Seal Patent Office on the 9th April 1880.
WILLIAM CHADWICK, THOMAS CHADWICK, and JAMES CHADWICK, all of Man-
chester, in the County of Lancaster, and JOSIAH WICKLIFFE KYNASTON, of
Liverpool, in the same County. "IMPROVEMENTS IN THE MANUFACTURE AND IN
THE PURIFICATION OF SULPHATE OF ALUMINA AND‘ÅLUMINOUS CAKES.'
.
"
The object of our Invention is the production of sulphate of alumina neutral,
and either practically free from iron or containing only an extremely small pro-
portion of this element, and free from other objectionable impurity or admixture.
In carrying out this Invention we take bauxite (or other mineral soluble in
sulphuric acid, and rich in alumina, but not in iron), and reduce it to a state of
exceedingly fine powder, and mix it intimately with a proportion of arsenious acid
(common white arsenic), also finely powdered, varying from three to five per cent.
of the weight of the bauxite according to the proportion of iron contained in the
bauxite. We now take sulphuric acid of from ninety to one hundred degrees
Twaddle (specific gravity 1.45 to 1.50), and having first heated it in a leaden pan
of large capacity, we add to it the mixture of bauxite and arsenic in sufficient
quantity to produce a neutral solution. We continuously agitate the mixture, and
to moderate the violence of the re-action we run in from time to time sufficient
cold water, but so as not to dilute the mixture unnecessarily. We continue the
agitation until the re-action is complete, and then sufficient hot water to reduce the
mixture to about forty degrees Twaddle (specific gravity 1·200). We now add to
the mixture finely powdered chalk or other carbonate of lime in small portions at
a time so long as it continues to produce a brown or brownish red colouration.
This point is determined by taking from time to time a portion of the liquid and
filtering or allowing it to deposit, and then adding to the clear or slightly turbid
solution a little more carbonate of lime. When no further deepening of the colour
of the liquid is produced sufficient carbonate of lime has been added. If the
operation has been properly conducted and a neutral or basic solution obtained, it
will be found that by far the larger proportion of the oxide of iron present will be
in an insoluble form in union with arsenic previous to the addition of carbonate of
lime, and if the solution is allowed to stand at rest it will fall out of the solution as
a brown layer superincumbent on the heavier deposit of undecomposed bauxite.
The addition of carbonate of lime in small proportion now determines the separation
of nearly the whole of the remaining soluble iron. If the solution obtained is not
neutral, but contains more or less free acid, a larger proportion of carbonate of lime
is required, the firet portion added being consumed in neutralizing the free acid, but
when a sufficient quantity of carbonate of lime is added the separation of the iron
is as complete as when a neutral solution has been obtained in the first instance.
After the addition of the necessary quantity of carbonate of lime the mixture is
thoroughly agitated, and then transferred to settling tanks of lead, where it is
allowed to stand for from ten to fourteen days to allow the insoluble matters to
deposit. The supernatant liquid is then drawn off, passed through a filter if not
quite clear, and then by any suitable means treated with sulphuretted hydrogen
gas or other sulphide decomposable by the aluminous solution until the excess of
arsenic is rendered insoluble. It is then allowed to stand for twenty four hours, or
until the sulphide of arsenic has completely deposited, and the clear liquid is run
into a leaden pan and boiled down to a degree sufficient to allow of its solidifying
when cold. There is thus obtained a sulphate of alumina of a higher degree of
purity than we believe has ever yet been obtained, and fit for use extensively in
the arts and manufactures.
We find that our process yields almost as satisfactory results if instead of mixing
the bauxite with the arsenic, as before described, arsenic is first dissolved in the

page_text: sulphuric acid, or the arsenic may be dissolved in the solution obtained by heating
bauxite and sulphuric acid alone. In either case the subsequent addition of
carbonate of lime determines the separation of iron in the insoluble state. We find
also that the process is equally applicable for the separation of iron from ordinary
commercial ferruginous sulphatos of alumina, either prepared from bauxite or other
aluminous minerals.
To obtain sulphate of alumina practically free from iron we take the clear
solution, obtained as before described by settling aftor the addition of carbonate of
line, and to this solution (before the removal of the excess of arsenic) we add a
solution of ferrocyanide of calcium exactly in sufficient quantity to precipitate tho
whole of the iron. We allow the mixture to stand at rest for two or three days,
when the blue precipitate settles perfectly down, leaving a clear bright blue
solution. We draw off this solution, remove the arsenic and remaining blue colour
by means of sulphuretted hydrogen, or other sulphide decomposable by the
aluminous solution, and concentrate the clear solution until it solidifies on cooling
as before mentioned. The result is a hydrated sulphate of alumina almost
chemically pure, which may be used for almost any purpose for which the
crystallized potash or ammonia alumns are now requisite. We take the precipitato
of ferrocyanide of iron or Prussian blue obtained as before described, and after
washing it with water we add to it milk of lime in sufficient quantity to entirely
destroy the blue colour, We boil the mixture well with steain, and allow it to
deposit the insoluble matter, and then draw off the clear solution. We thus again
obtain the ferrocyanide of calcium required for the precipitation of iron as before
described.
That ferrocyanide of potassium will precipitato iron from its solutions has long
been known, but this re-action has been hitherto considered impracticable for com-
mercial purposes on the following grounds:-First, owing to its costliness it could
not be commercially applied when any large amount of iron was required to be
separated; and, second, there was no available means known for precipitating or
getting rid of the blue colour left in solution or in fine suspension in the solution,
and consequently the resulting alum cake had a blue colour greatly detracting from
its value. By our process however we find that as we first extract most of the
iron by means of arsenic and carbonate of lime, (and therefore so very small a pro-
portion of ferrocyanide is required), and regenerate the calcium ferrocyanide for
further use, and as the remaining blue ferrocyanide is precipitated undecomposed
with the arsenic when treated with sulphuretted hydrogen, we find this process
very economical.
When the use of white arsenic is objected to, we vary the process in the
following manner :-
We take bauxite in a state of extremely fine powder and mix it to a thick
cream with a solution of oxalic acid and hydrochloric acid in the proportion of one
hundred bauxite to from five to ten of oxalic acid, and from five to ten of
hydrochloric acid. The exact quantities depend upon the impurities; if there be
much iron much oxalic acid will be required; if much lime the hydrochloric acid must
be increased sufficient to hold it in solution, and prevent the formation of solid oxalate
of lime. We allow the mixture to stand at rest, or with occasional stirring, for a
week or ten days. We then add five or six times as much water as the bulk of
the mixture, thoroughly agitate, and allow to stand till the purified bauxite is
deposited. The latter is again repeatedly washed until quite free from oxalic acid.
We make of this purified bauxite sulphate of alumina or aluminous cake by the
well known process in common use, and we obtain a product containing not more
than from 0.10 to 0.20 per cent. of iron.
We take the strongly acid solution of oxalate of iron (containing also some
lumina) obtained in this process of purification, and add to it milk of lime con-
siderably more than equivalent to the oxalic acid present, but still] leaving the
mixture strongly acid. After standing two or three days the oxalic acid is thus
most perfectly precipitated as oxalate of lime. This precipitate is well washed,

page_text: and then boiled with its equivalent of sulphuric acid. The sulphate of lime pro-
duced is allowed to settle out, and a clear solution of oxalic acid is again obtained
for the purification of a second portion of bauxite, as before described.
Having now described our Invention and the best mode known to us of carrying
it into effect, we wish it to be understood that what we believe to be new and
desire to protect under the herein before in part recited Letters Patent is,-
First. The process for making sulphate of alumina or alum cake commercially
pure, namely, treating bauxite or other alumina or hydrate of alumina soluble in
sulphuric acid with sulphuric acid and arsenious acid, neutralizing with carbonate
of lime until the iron is precipitated, and then separating the arsenic in the form
of sulphide.
Second. The mode of separating iron from alum or sulphate of alumina in
solution by treating the solution with 'arsenious acid, neutralizing with carbonate of
lime until the iron is precipitated, and then precipitating the remaining arsenic as
a sulphide.
Third. The process of making pure sulphate of alumina or alum cake by treating
bauxite or other alumina or hydrate of alumina soluble in sulphuric acid with
sulphuric acid and arsenious acid, neutralizing with carbonate of lime until most
of the iron is precipitated, and then treating with ferrocyanide of calcium and
sulphuretted hydrogen or other sulphide decomposable by the aluminous salt
successively.
Fourth. In the purification of alum or sulphate of alumina from iron treating
the aluminous solution with arsenious acid, carbonate of lime, ferrocyanide of
calcium, and sulphuretted hydrogen successively, substantially as described.
Fifth. In the manufacture or purification of sulphate of alumina, alum cake, or
alum, the use of arsenious acid and carbonate of lime conjointly for the precipitation
of iron.
Sixth. The purification of bauxite, hydrated alumina, and other aluminous
minerals used for the manufacture of sulphate of alumina or alum by means of
oxalic acid, and sufficient hydrochloric acid to hold the lime in solution for the
purpose of making sulphate of alumina or alum.
In witness whereof, I, the said Josiah Wickliffe Kynaston, for and on
behalf of myself and the said William Chadwick, Thomas Chadwick, and
James Chadwick, have hereunto set my hand and seal, this Eighth day
of April, in the year of our Lord One thousand eight hundred and eighty.
Witness,
J. OWDEN O'BRIEN,
Clerk to W. P. Thompson & Co.,
Patent Agents,
6, Lord St, Liverpool, &
323, High Holborn, London.
J. W. KYNASTON. (L.S.)