IMPROVEMENTS IN THE MANUFACTURE OF ALUMINA
Year: 1884

page_text: Í, ĠUSTAV ROSENTHAL doctor of philosophy of 3 Moorgate Street Buildings in
the City of London, Chemist do hereby declare the nature of my invention for
IMPROVEMENTS IN THE MANUFACTURE OF ALUMINA to be as follows:-
The object of my invention is: The manufacture from Sulphate of Alumina,
of Alumina which is suitable for the manufacture of Aluminium therefrom and for
all purposes for which hitherto Hydrate of Alumina or Alumina obtained by
heating such Hydrate has been employed. My process also embraces the manu-
facture of Oxide or Oxides of Iron which are used in the arts as colours or
pigments.
My process is based upon the observation, that Sulphate of Alumina is readily
decomposed by Magnesium Chloride when heated with it, in this way that
anhydrous Alumina, free Hydrochloric Acid and Sulphate of Magnesia are formed,
and this decomposition is not affected by Oxide of iron however large its quantity
that may be present in the Sulphate of Alumina as an impurity except that such
Sulphate of iron behaves in a manner quite analogous to the Sulphate of Alumina,
the only difference being in the case of iron the more easy conversion of the
Sulphate into the Oxide under particular working conditions I employ the said
substances intended to act upon one another so as to render the decomposition
complete, in the proportion of three equivalents of anhydrous Magnesium Chloride
to every one equivalent of Alumina combined with Sulphuric Acid or one equi-
valent of anhydrous Magnesium Chloride to every one equivalent of Sulphuric
Acid present in the Sulphate of Alumina.
When the quantity of Oxide of iron in the Sulphate of Alumina is large, the
proportion of the Magnesium Chloride has to be modified, so that for every one
equivalent of Oxide of iron Fе, O, in solution three equivalents of Magnesium
Chloride are used as in the case of Alumina and for every one equivalent of
Protoxide of iron Fe O one equivalent of Magnesium Chloride.
I employ the said substances either solid or as solutions, but the latter will in
practice be usually made use of, because the complete boiling down of the
Alumina solution before the adding thereto of the Magnesium Chloride is obviated
and because it is not necessary for the Magnesium Chloride to be pure. When the
said substances are heated together in suitable vessels, a large quantity of water is
TDA77

page_text: set free before the evolution of Hydrochloric acid begins, but after most of the
water is driven off, the proportion of Hydrochloric acid escaping with the steam
increases, until finally strong Hydrochloric acid distills over which may be
condensed and collected.
In the dry mass now remaining in the vessel the whole of the Alumina is
rendered insoluble, but is still retains a considerable proportion of Sulphuric acid
chemically combined with it, whereas the Oxides of iron are found to have parted
with the whole of their Sulphuric acid. Such proportion of Sulphuric acid varies
from four to seven per cent of the total originally in combination with Alumina,
the other 96 to 93 per cent having combined with Magnesia. In order to
separate this remaining portion of Sulphuric acid from the Alumina, superheated
steam is passed through the mixture in suitable apparatus which can be heated
from the outside in addition thereto. Before the final transfer of the mass into
the vessel in which steam is to pass through it, a small quantity of caustic line
say to of the quantity that would be required to chemically combine with all
the Sulphuric acid still in combination with Alumina, should be added to facilitate
the completion of the process. When the steam having passed through the mass
does not carry off any more Hydrochloric acid, the mixture now left in the
decomposing vessel or vessels consists of Alumina and Oxide of iron and Sulphate
of Magnesia. The Sulphate of Magnesia is separated by lixiviation. To render
the Alumina suitable for the manufacture of Aluminium, the Oxides of iron mixed
with it as Peroxide or Protoxide or a combination of both these commonly called
magnetic Oxide must be separated therefrom and this I effect by either mechanical
or chemical methods. Elutriation can be resorted to by which I mean a mode of
separation which is founded on the difference of the specific gravity of Alumina
and of Oxide of iron respectively, or magnetic action consisting in the application
of a magnet or electromagnet which attracts the iron and is without any action
upon the Alumina. Any of these methods can be used separately or in combination
successively.
The chemical methods which I employ for the said separation are based upon the
observation that Alumina as manufactured in the manner already described readily
takes up water forming a Hydrate of Alumina. It is enabled thereby to form
compounds with alcalis and alcaline earths with much greater facility and con-
sequently at a lower cost than native Alumina.
1
.

page_text: I GUSTAV ROSENTHAL, doctor of philosophy of 3 Moorgate Street Buildings in
the City of London, Chemist do hereby declare the nature of my invention for
IMPROVEMENTS IN THE MANUFACTURE OF ALUMINA and in what manner the same
is to be performed, to be particularly described and ascertained in and by the
following statement :-
The object of my invention is the manufacture from Sulphate of Alumina of
Alumina which is suitable for the manufacture of Aluminium therefrom and for all
purposes for which hitherto Hydrate of Alumina or Alumina obtained by heating
such Hydrate has been employed. My process also embraces the manufacture of
Oxides of Iron which are used in the arts as colours or pigments among other
purposes, and as a secondary product that of Hydrochloric Acid To obtain
Alumina, it has been the practice hitherto to precipitate Hydrate of Alumina from
its solutions in acids or alcalis. The solutions in acids as a rule contain more or
less of the impurities notably Oxides of iron that are mixed with Alumina in its
native ores and in the minerals from which it is industrially extracted by treatment
with acids. Oxide of iron is found in the Hydrate of Alumina after precipitation
from these solutions unless previously separated. On the other hand where alcalis
or basic substances are employed for the extraction of the Alumina, the process for
recovering the alcali is complicated and expensive. By my process Alumina is first
obtained as anhydrous Alumina but in a state which admits an easy purification
and conversion if required into the Hydrate. The process is founded upon the
observation that Sulphate of Alumina is readily decomposed by Chloride of Magne-
sium, when heated with it, in this way that anhydrous Alumina, free Hydrochloric
acid and Sulphate of Magnesia are formed. Any Sulphate of iron that may be
present is acted upon by the Magnesium Chloride in a manner analogous to the
Alumina salt. The chemical reaction which takes place can be expressed by the
formula:
Al, O, 8 SO, + 3 Mg C₁₂ + 3 H₂ 0 = Al, 0, +3 Mg SO, + 6 H CL
The relative quantities in which the said substances are to be employed so as to
completely effect their decomposition are three equivalents of Magnesium Chloride
to every equivalent of Alumina combined with Sulphuric acid or one equivalent of
Magnesium Chloride to every one equivalent of Sulphuric acid. Similarly for
every equivalent of Peroxide of iron Fe, O, three equivalents of Magnesium Chloride
are required as for Alumina, but if iron is present in the state of Protoxide Fe O,
the equivalent proportions of Protoxide and Magnesium Chloride are one to one.
I employ the said substances either as solids or in solutions, but the latter will in
practice be usually made use of, because the complete boiling down of the Alumina
solution before the adding thereto of the Magnesium Chloride is dispensed with
and also, because strong solutions of Magnesium Chloride are readily obtainable as
residual liquors from Potash works. When Aluminium Sulphate and Magnesium
Chloride are heated together in suitable vessels, a large quantity of water is set

page_text: free before the evolution of Hydrochloric acid begins, but after the greater portion
of the water is driven off, the proportion of Hydrochloric acid escaping with the
steam increases until finally strong acid distills over which is condensed and
collected by well known methods. In order to prevent the mass from caking and
adhering to the bottom of the vessel, it has to be stirred vigorously, and care has
to be taken not to let it become dry so as to stop the chemical action. The
temperature should be kept low. When the liberation of Hydrochloric acid ceases,
the whole of the Alumina is rendered insoluble, but it still retains a considerable
proportion of Sulphuric acid chemically combined with it, whereas the Oxide of
iron is found to have parted with the whole of its Sulphuric acid. That proportion
of Sulphuric acid varies from 4 to 7 per cent of the total originally in combination
with Alumina, the other 96 to 93 per cent having combined with Magnesia. In
order to separate this remaining portion of Sulphuric acid from the Alumina,
superheated steam is passed through the mixture in suitable apparatus such as
cylinders, retorts or muffles which can be heated in addition thereto from the
outside. Before the final transfer of the mass into the vessel in which superheated
steam is to pass through it, a small quantity of caustic lime say to of the
quantity that would be required to combine with the whole of the Sulphuric acid
still in combination with Alumina, should be added to facilitate the completion of
the process.
When the steam does not carry off any more-Hydrochloric acid,-the-
mixture now left in the vessel consists of Alumina and Oxide of iron and Sulphate
of magnesia. I separate the Sulphate of Magnesia by lixiviation. The iron
which is present as Peroxide or Protoxide or a combination of both commonly
called Magnetic Oxide, is to be separated by either mechanical or chemical methods.
Elutriation can be resorted to, by which I mean a mode of separation which is
founded on the difference of the specific gravity of Alumina and the Oxides of iron
respectively, or magnetic action consisting in the application of a magnet or
electromagnet which attracts the iron but not the Alumina. The chemical methods
which I make use of for the said separation are based upon the fact that Alumina
manufactured by the process above described readily takes up water, so forming
Hydrate of Alumina. It is enabled thereby to enter into chemical combination
with some acids and with alcalis and alcaline earths with much greater facility
and consequently at a smaller cost than native Alumina
Having now particularly described and ascertained the nature of my said
Invention and in what manner the same is to be performed, I declare that what
I claim is
1. The process for the manufacture of Alomina by the action of Magnesium
Chloride upon Sulphate of Alumina.
2. The process for the manufacture of Oxides of Iron by the decomposition of
Sulphates of Iron with Magnesium Chloride.
3. The manufacture of Hydrochloric Acid and Sulphate of Magnesia as bye-
products of the process by which Alumina and the Oxides of Iron are prepared in
the manner herein described.
Dated this 19th day of December 1881.