IMPROVEMENTS IN THE MANUFACTURE OF POTASH ALUM FROM ALUMINOUS ROCKS, EARTHS, OR SUBSTANCES
Year: 1876

page_text: LETTERS PATENT to Thomas Henry Cobley, of Dunstable, in the County of
Bedford, but at present residing at Glasgow, in the County of Lanark, North
Britain, for the Invention of "IMPROVEMENTS IN THE MANUFACTURE OF
POTASH ALUM FROM ALUMINOUS ROCKS, EARTHS, OR SUBSTANCES."
Sealed the 16th March 1877, and dated the 22nd December 1876.
PROVISIONAL SPECIFICATION left by the said Thomas Henry Cobley at the
Office of the Commissioners of Patents on the 22nd December 1876.
THOMAS HENRY COBLEY, of Dunstable, in the County of Bedford, but at present
"IMPROVEMENTS IN
residing at Glasgow, in the County of Lanark, North Britain.
THE MANUFACTURE OF POTASH ALUM FROM ALUMINOUS ROCKS, EARTHS, OR
SUBSTANCES."
This Invention, which relates to improvements in the manufacture of potash
alum, consists as follows:-
In the case of alunite, which is composed generally of one equivalent of sulphate
of potash, one equivalent of sulphate of alumina, and two and one half equivalents
of hydrate of alumina, mixed more or less with gangu or other foreign substances,
my process of treatment consists in bringing together an admixture of about two
parts alunite in a powdered state with about one part of chloride of potassium and
about three parts of sulphuric acid of 100° Twaddle, or the equivalent of a more
concentrated acid.
The alunite and chloride of potassium are placed first in the decomposer or pot of
a sulphate of soda furnace, and the acid run in upon the mixture, as in the ordinary
manner of converting common salt into sulphate of soda; this mixture is boiled
until all the aqueous vapours are driven off, which is complete in about one and a
half hours; it is then run out upon the hearth of a furnace, and left there until it
begins to cake (the furnace being kept at a dull red heat), when it is drawn off, dis-
solved by any convenient means, and run off to crystallize; or it may run (without
furnacing) when sufficiently boiled and whilst still in a liquid state direct into
water, and the alum crystallized out.
The hydrochloric acid fumes are condensed in towers in the ordinary manner, and
may be converted into bleaching powder or sold as hydrochloric acid.
Again, it may be desirable in some varieties of mineral to vary the process and
proceed in this way, namely, to add only sufficient sulphuric acid necessary to

page_text: decompose the chloride of potassium in the mixture, and to add the further quantity
of acid in the melting up of the cake or inass formed by boiling in the decomposer,
with furnacing or not as the case may be.
The same process with the foregoing modification is applicable to all schists, shales,
rocks, or earths containing a workable amount of alumina.
Where sulphate of potash is obtainable, and it is found advantageous to work
with it in preference to chloride of potassium, I proceed in like manner, only
reducing the quantity of sulphuric acid, that is to say, omitting that portion of sul-
phuric acid which in the process with chloride of potassium would be used for the
conversion of the chloride of potassium into sulphate of potash on on the basis of the
above mixture reducing the quantity of sulphuric acid one third.
For removing the iron I blow in compressed air, or throw a nitrate into the coolers
while the solution is still hot.
SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Thomas Henry Cobley in the Great Soal Patent Office on the 20th
June 1877.
THOMAS HENRY COBLEY, of Dunstable, in the County of Bedford, but at present
residing at Glasgow, in the County of Lanark, North Britain. "IMPROVEMENTS IN
THE MANUFACTURE OF POTASH ALUM FROM ALUMINOUS ROCKS, EARTHS, OR
SUBSTANCES."
My said Invention relates to improvements in the manufacture of potash alum
from schists, shales, rocks, or earths containing alumina, either with or without sul-
phuric acid or potash co-existing with the alumina in the mineral.
In the case of alunite (which is a native basic alum composed generally of one
equivalent of sulphate of potash, one equivalent of sulphate of alumina, and two and
one half equivalents of hydrate of alumina, mixed more or less with gangue or other
foreign substances), my process of treatment consists in bringing together into
intimate admixture about two parts by weight of raw or uncalcined alunite in a
powdered state with about one part of chloride of potassium and about three parts
of sulphuric acid of 100° Twaddle, or the corresponding equivalent of a more con-
centrated acid.
The alunite and chloride of potassium are placed first in a decomposing vessel or
pot similar to that of a sulphate of soda furnace, and the acid is run in upon the
mixture as in the ordinary manner of converting common salt into sulphate of soda;
this mixture is boiled in the said decomposing vessel until all the aqueous vapours
are driven off, which operation is complete in about one and a half hours. The
material is then run out upon the hearth of a furnace, and left there until it begins
to cake (the furnace being kept at a dull red heat), when it is drawn off, dissolved
with the aid of heat, and preferably dry heat, in any convenient manner (an iron
steam-jacketed vessel lined with lead and heated by steam introduced into the jacket,
or an ordinary dissolving vessel surrounded inside by coils of steam piping being
best), and run off to crystallize.
It must be observed that in the application of heat for the purpose of boiling and
furnaceing the material, the heat must be regulated so that the greatest heat must
be applied to the decomposing pot, and a diminished heat employed during the fur-
naceing, in order that SOS be not driven off, and the alum formed partially
decomposed.
The object and principle of boiling the alunite with chloride of potassium and
sulphuric acid is to dehydrate the alumina, which is effected by the combined action
of the affinity of the chlorine existing in the chloride of potassium for water, and
the affinity of the sulphuric acid for the potash, the play of these affinities being
promoted by a sufficiently high temperature; but care must be taken that the tem-
perature be not allowed to become so high as to drive off any of the sulphuric acid

page_text: along with the hydrochloric acid. To guard against this, samples of the hydro-
chloric acid may from time to time be drawn from the condensing tower, herein-after
mentioned, during the process, and tested to ascertain the presence or absence of
sulphuric acid coming off along with it.
Instead of boiling raw alunite and then furnaceing it, the alunite in a state of
powder may be first calcined at a dull red heat until fumes of sulphurous acid begin
to come off. Usually a couple of hours furnaceing will suffice for its complete dehy-
dration. In this state it is then inixed with chloride of potassium and sulphuric
acid, and boiled as before to drive off the hydrochloric and form potash alum.
By this mode of operation the necessity of furnaceing after boiling is dispensed
with.
Another modification of the process is to boil the raw alunite as above described,
but for a longer time, so as to complete the two operations of dehydrating and fur-
naceing in the same vessel, the temperature during the two stages being regulated
as herein-before directed. The material may then be run (without after-furnaceing)
when sufficiently boiled and whilst still in a liquid state direct into water, and the
alum crystallized out.
The hydrochloric acid fumes are condensed in towers in the ordinary manner, and
may be converted into bleaching powder or sold as hydrochloric acid.
My object in drawing off the hydrochloric acid is to obtain mother liquors free
from hydrochloric acid, and capable of being wrought up so as to get out practically
the whole alum contained in them which is at present lost, a large portion of alum
being, according to the present modes of working, necessarily left in the mothers,
on account of the pressure of hydrochloric acid and compounds of chlorine in the
same.
Again, it may be desirable to vary the above-mentioned process in any of its
before-mentioned modifications in this way, viz., to add at first only the quantity
of sulphuric acid necessary or sufficient to decompose the chloride of potassium in
the mixture, and to add the further quantity of acid which is necessary to convert
the alumina into sulphate of alumina during the melting up of the cake (if the
material has been furnaced) or mass (if only boiled).
The same process, either with or without the foregoing modifications, is applicable to
all schists, shales, rocks, or earths containing a workable amount of alumina; but where
carbonaceous matter is present in the mineral I prefer to calcine it in the first place
in order to remove the carbon, and where the mineral is destitute of or deficient in
the requisito proportion of potash or of SO³ requisite to form alum, these wants
must be supplied or the proportions supplemented; or with such a mineral as
leucite, which contains no sulphuric acid, but just the proper amount of potash and
alumina for formning alum, sulphuric acid alone will be added. Where any sulphuret;
such as pyrites, is present in the native mineral, the mineral must be calcined in the
first place.
Where sulphate of potash is obtainable, and circumstances render it necessary, or
it may be advantageous to work with it instead of chloride of potassium, I proceed
in like manner, but with the following alterations, vizt:-If the aluminous material
is employed in an uncalcined state, then the sulphuric acid must be of greater
strength (1.45 Twaddle at least) and the time of digestion prolonged, and the vessel
must be covered to the exclusion of air; if it is calcined, ordinary chamber acid
may be employed. In either case the quantity of SOS will require to be reduced by
omitting that portion of sulphuric acid which in the process with chloride of
potassium would be used for the conversion of the chloride of potassium into sul-
phate of potash.
It may not be desirable under certain circumstances to use any extraneous potash
salt in order to convert the whole of the alumina or the alunite into potash alum;
but merely to extract from it the potash alum it contains naturally (or the elements
of which it contains naturally). In such case the cost of extracting the potash alum
may be greatly reduced by converting the surplus hydrate of alumina into sulphate
of alumina at thesame time and in the course of the same process by which thì

page_text: natural potash alum is extracted. For this purpose the alunite is first freed from
iron by washing the raw alunite in a powdered state with dilute hydrochloric acid,
or a mixture of dilute sulphuric and hydrochloric acids, and is afterwards dried and
calcined;
then add the proportion of sulphuric acid (chamber acid), about 100 parts
acid to 100 parts alunite, and boil the whole until the mixture is sufficiently dis-
solved. The liquor is then allowed to settle and clear, and the natural potash alum
to crystallize out. The mother liquor is then boiled down to as stiff a condition as
possible, and the mass is pressed through a felt press, such as is used for pressing the
inoisture out of clays, and it is then dried on fire-clay tiles or plaster slabs in a
warmed room.
Native basic alums, such as alunite, after being calcined, and roasted aluminous
schists, shales, and earths, all admixed with the necessary equivalent of potash salt,
may, instead of being treated with sulphuric acid, be treated with sulphurous acid
generated from sulphur or any convenient sulphuret, and for this purpose an appa-
ratus and process similar to that used by Mr. Hargreaves for converting common salt
into sulphate of soda may be employed.
It will be preferable to grind up and calcine the potash salt along with the alu-
minous material, which will produce a mass more permeable by the sulphurous acid
gas; but in treating leucite, which is a native silicate of alumina and potash, or
leucitic lava, rocks, or sands, I prefer to pass the sulphurous fumes into a receptacle
containing powdered leucitic material in the raw or calcined state covered with
water, and so contrived that the fumes of sulphurous acid are introduced into the
liquor and other contents of the vessel from the bottom, and what portion of the
sulphurous acid is not taken up passes on to a second receptacle containing leucitic
material and water, and so on through a sufficient number of receptacles. By this
means a double sulphite of alumina and potash in solution is formed, which may be
drawn off from time to time and oxidised by blowing in oxygenated or compressed
air, or by adding a certain portion of any suitable nitrate (as nitrate of potash), and
the potash alum is afterwards crystallized out; or the nitrate may be added to the
receptacles through which the SO is passed, in which case alum would be formed
in the receptacle.
In order to obtain the alum free from iron, and that in one crystallization without
the necessity of the repeated recrystallizations at present used to effect that object,
I add a nitrate to the solution of alum to be crystallized, and that either in the dis-
solving vessel or in the settling vat, or even (tho' this is not so convenient) in the
crystallizer. The nitrates which I employ are, in the order of preference, as
follows: Nitrate of potash, nitrate of alumina, nitrate of soda, or nitrate of mag-
nesia. I have found it most advantageous to add these nitrates in the form of a
saturated solution, but the nitrate may be added in any other convenient way.
Even nitric acid may be used for this purpose instead of a nitrate. About two per
cent. of nitrate of potash, reckoned on the amount of ordinary alunite used to form
the solution, has been found to answer sufficiently, but the proportion required of
course depends on the amount of iron present. The temperature after the addition
of the nitrate should be kept up to at least 180° till the liquor clears (except where
it is added to the crystallizer, in which case to keep up the heat would prevent
crystallization). I also use, in place of nitrate, aluminates, and especially and pre-
ferably aluminate of potash. I also employ for the same purpose insufflation of air
(preferably of oxygenated or compressed air) into the alum solutions, and after oxy-
genation in this way I sometimes add precipitated alumina.
In order to obtain the crystallized alum in masses of convenient size and of a form
suitable for conveyance without waiting the length of time necessary to obtain large
crystals in the ordinary way, I agitate the mass of liquor under crystallization by a
more or less constant and gentle movement, kept up in it by any convenient means,
in order to hasten the crystallization and obtain the crystals in a finely granulated
condition. The crystals thus obtained I wash and then press them together into
blocks; allowing them to remain under the pressure, they agglomerate into a solid
or coherent mass.

page_text: The mothers left after crystallization in cases where chlorate of potassium has
been used, and which contain sulphate of alumina and potash, free hydrochloric
acid, and nitrates (where a nitrate or nitric acid has been used), as also chlorides of
iron and other bases, I neutralise with caustic lime or caustic potash in order to
render them suitable for using over again without injury to the plant employed,
and also in order to free them from iron and other impurities. The mothers being
thus treated, the precipitated iron is then removed, the mothers are boiled down
to crystallizing point, and crystallized; or without boiling they may be used for
redissolving a fresh quantity of the prepared material or cake herein-before
described.
Having now described and particularly ascertained the nature of my said Inven-
tion, and the system, mode, or manner in or under which the same is or may be
used or practically carried into effect, I desire to observe that what I claim as the
Invention secured to me by the herein-before in part recited Letters Patent is,―
First. The manufacture of potash alum by the process or alternative processes
herein-before described.
Second. The simultaneous use, in manner herein-before described or in any
manner substantially the same, of aluminous material, sulphuric acid, and potash
salt in preparing by the process or alternative processes herein-before described, or
any equivalent or substantially similar process, the mass or cake herein-before
described, from the solution of which alum is to be crystallized.
Third. The use of sulphurous acid instead of sulphuric acid in the manufacture of
alum, in manner herein-before described, and the process of manufacturing alum
with sulphurous acid herein-before described.
Fourth. The application of dry heat instead of immited steam in dissolving the
cake or mass, as herein-before described.
Fifth. The use of leucite and leucitic minerals for the manufacture of alum, and
the process herein-before described for manufacturing alum therefrom.
Sixth. The clearing of the alum solutions and alum from iron by the means
herein-before described.
Seventh. The process, berein-before described, for obtaining the so-called natural
alum from alunite, and at the same time obtaining sulphate of alumina as a bye-
product.
Eighth. The granulation and pressure of alum crystals into block, as herein-before
described.
Ninth. The utilization of the mother liquors, in manner herein-before described.
In witness whereof, I, the said Thomas Henry Cobley, have to this my Speci-
fication set my hand and seal, this Twelfth day of June, One thousand
eight hundred and seventy-seven.
TMAS HENRY CODT EV
THOMAS HENRY COBLEY
(L.S.)