Improvements in the Manufacture of Sulphate of Alumina.
Year: 1891

page_text: Date of Application, 20th Jan., 1891
Complete Specification Left, 20th Oct., 1891-Accepted, 21st Nov., 1891
PROVISIONAL SPECIFICATION.
Improvements in the Manufacture of Sulphate of Alumina.
I JOSIAH WYCKLIFFE KYNASTON of the Sutton Alkali Works of St. Helens
in the County of Lancaster, Manufacturing Chemist do hereby declare the nature
of this invention to be as follows:-
Sulphate of alumina, produced by the action of sulphuric acid on clays, bauxites
and other aluminous minerals, and subsequent treatment of the solutions by well
known processes for the removal of iron and other impurities, is, especially when
bauxite is the mineral used, of a yellowish or greenish colour, due to the presence
of a trace of chromium. Of all the aluminous minerals available for this manu-
facture, bauxite is the best and the cheapest. But the product obtained from
bauxite is comparatively unsaleable for the reason that it is always more or less
discoloured, on account of the presence of a trace of chromium. The extremely
small quantity of chromium contained in the sulphate of alumina does not affect the
purposes to which it is applied, but the faint discolouration is objected to by some
buyers.
The purpose of this invention is the prevention of this discolouration, and it is
carried out in the manner now to be described.
If the chromium is present in the condition of yellow chromic acid or a chromate,
it must first be reduced to the green sesquioxide of chromium by the addition, to
the solution, whilst being concentrated to the point of solidification when allowed
to cool, of the necessary quantity of a deoxidising agent, such as a sulphite, a hypo-
sulphite, a nitrite or arsenious oxide. To the green solution, either pre-existing or
produced as above, is now added a minute quantity of a solution of a red colouring
matter, or of a colouring matter which becomes red when mixed with an acid
solution or the solution of an acid salt. When the exact quantity necessary has
been added, the result is that the green colouration is completely destroyed and
the product of concentration is perfectly white. The colouring matters especially
suitable are the substances known as methyl orange and tropooline OO, an
extremely minute quantity of which is required. A watery solution of litmus also
perfectly answers the purpose.
Dated this 19th day of January 1891.
WM. P. THOMPSON & Co.,
Of 6, Lord Street, Liverpool, Patent Agents for the Applicant.
COMPLETE SPECIFICATION.
Improvements in the Manufacture of Sulphate of Alumina.
I, JOSIAH WYCKLIFFE KYNASTON of 149 Kensington, Liverpool in the County
of Lancaster, Analytical Chemist, 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:-
Sulphate of alumina, produced by the action of sulphuric acid on clays, bauxites
and other aluminous minerals and subsequent treatment of the solutions by well
known processes for the removal of iron and other objectionable impurities, is
usually of a yellow or greenish colour. This colouration is due to the presence in
the mineral used of a minute quantity of chromium.
The extremely small quantity of chromium contained in the sulphate of alumina
so produced has no injurious effect in any of the technical applications of the

page_text: aluminous salt, but the faint discolouration is objected to by some purchasers of the
material.
Of the minerals available for this manufacture, China clay contains the least
chromium and yields the whitest sulphate of alumina. But China clay or Kaolin
is probably the most costly of all the materials which can be used for the purpose;
firstly, by reason of the necessity to calcine it; secondly, for the reason that the
alumina contained in it is, as compared with other minerals, so difficult of solution;
and, thirdly, because of the very large proportion of insoluble silica which it
contains and which, with the undissolved clay, requires to be settled out of the
solution of sulphate of alumina and pressed and washed at very considerable cost.
The alumina contained in bauxite is, as compared with that in China clay, very
readily soluble in sulphuric acid, and the insoluble residues which require to be
treated are insignificant in quantity as compared with those from China clay.
Bauxite is, therefore, a more economical source of alumina for this purpose than
China clay. But bauxites contain more chromium than China clay and, conse-
quently, sulphate of alumina produced from bauxite, after the complete removal
therefrom of iron and other impurities, possesses either a yellowish colour or a
faintly green tint. By some processes of purification from iron, the chromium is
converted into chromic acid (CrO,) in which case the sulphate of alumina
obtained is coloured yellowish; by other processes, the chromium remains in the
condition of chromic oxide (Cr,O,) and the sulphate of alumina produced has a
greenish tint.
Now, the purpose of this invention is the production of white sulphate of alumina
from solutions of this salt containing also chromium in sufficient quantity to give
a yellow or greenish tint to the finished product.
1 accomplish this by the following mode of treatment :-
The sulphate of alumina solution, purified and ready for concentration, is run to
a leaden pan, in which it is to be boiled up to the required strength. If the
chromium present exist in the green condition of a chromic salt, the liquor is at
once boiled up to from 100 to 110 degrees Twaddle, tested whilst boiling hot. I
now add to the boiling solution so much as has been found, by experiment, to be
necessary of a solution of a red colouring matter or of a colouring matter which
becomes red when mixed with an acid solution or the solution of an acid salt. The
solution of sulphate of alumina is then allowed to boil up to the desired strength
and run off to solidify. The effect produced by the addition of the red colouring
matter is that the green colouration of the sulphate of alumina is completely
obliterated and the product of concentration is perfectly white. If the chromium
in the liquor to be treated exists in the condition of yellow chromic acid or a
chromate, must first be reduced to green chromic oxide or a salt thereof by the
addition of the necessary quantity of a suitable de-oxidising agent, such as an
alkaline sulphite, or hyposulphite, a nitrite or arsenious oxide. The subsequent
addition of the red colouring matter in just sufficient quantity entirely destroys the
green, and the finished product is perfectly white.
The substances known as methyl orange and tropaoline O O, both of which give
an intense red or pink colour in acid solutions, are perfectly suitable for the
purpose. Commercial methyl orange, which I prefer to use, differs much in
quality. Of the best quality I have met with, one part will obliterate the green
colour of 1250 parts of dissolved oxide of chromium, producing a neutral grey tint ;
and of the worst quality, one part has neutralised the green of only 600 to 700 parts
of dissolved oxide of chromium. It is necessary, therefore when commencing to
use a fresh supply of methyl orange, to determine its power by the use of a freshly
prepared standard solution of green chromic sulphate. The quantity of methyl
orange required to be used to treat liquors made from Irish bauxite may vary from 6
to 12 grains per ton of sulphate of alumina produced. The product from French
bauxite requires about half as much. The quantity of tropocoline OO required to
be used is much greater than of methyl orange, one part of this tropecoline
destroying the green colour of about 350 parts of dissolved chromic oxide. Litmus

page_text: solution is still less effective, one part of litmus obliterating the green colour of
only about 30 parts of chromic oxide.
The addition of a very minute quantity of a solution of a yellow colouring
matter, such as picric acid, in the proportion of only one or two grains to a ton of
sulphate of alumina usually further improves the colour of the finished product.
This addition may be made by adding it to the solution of red colouring matter or
separately.
I prefer to add the colouring matter in very dilute solution to the sulphate of
alumina liquor, whilst boiling as before mentioned, by means of a watering can
provided with a fine rose, so as to distribute it as evenly as possible over the
contents of the pan. A few minutes' boiling then diffuses the colour through the
sulphate of alumina liquor.
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 improvement in the manufacture of sulphate of alumina consisting in the
production of white sulphate of alumina from solutions of this salt containing
chromium in quantity sufficient to give a yellow or greenish tint to the product by
the addition to such solutions of a red colouring matter or of a colouring matter
which becomes red when mixed with an acid solution or the solution of an acid
salt substantially as described.
Dated this 19th day of October 1891.
WM. P. THOMPSON & Co.,
Of Liverpool, Manchester, Nottingham, and London, Patent Agents.