IMPROVEMENTS IN THE TREATMENT OF MINERAL PHOSPHATES CONTAINING ALUMINA AND OXIDE OF IRON, OR EITHER OF THEM, FOR THE PRODUCTION OF PHOSPHORIC ACID AND SALTS OF ALUMINA AND IRON."
Year: 1880

page_text: LETTERS PATENT to John James Knight, of Widnes, in the County of
Lancaster, for an Invention of "IMPROVEMENTS IN THE TREATMENT OF
MINERAL PHOSPHATES CONTAINING ALUMINA AND OXIDE OF IRON, OR EITHER
OF THEM, FOR THE PRODUCTION OF PHOSPHORIC ACID AND SALTS OF
ALUMINA AND IRON."
PROVISIONAL SPECIFICATION left by the said John James Knight at the
Office of the Commissioners of Patents on the 22nd December 1880.
JOHN JAMES KNIGHT, of Widnes, in the County of Lancaster.
"IMPROVEMENTS
IN THE TREATMENT OF MINERAL PHOSPHATES CONTAINING ALUMINA AND OXIDE
OF IRON, OR EITHER OF THEM, FOR THE PRODUCTION OF PHOSPHORIC ACID AND
SALTS OF ALUMINA AND IRON."
The nature and object of my Invention consist principally in the treatment of
mineral phosphates containing alumina and oxides of iron (which are comparatively
useless at present) with an excess of sulphuric acid or oil of vitriol of a specific
gravity of one hundred and forty degrees (Twaddle) and upwards, by means of
which the sulphates of alumina and iron produced are rendered insoluble in the
sulphuric acid, whilst the phosphoric acid is converted into the soluble state, and
mixes with the excess of sulphuric acid used, from which the phosphoric acid may
be separated, if desired, by distillation, and the sulphuric acid used over again.
This solution of phosphoric and sulphuric acids may be used direct for the
manufacture of superphosphates, or it may be used over again in treating
fresh mineral phosphates, instead of using fresh sulphuric acid, which increases
considerably the percentage of phosphoric acid in the solution, and enables the
artificial manure manufacturer to make a superior quality of superphosphates,
containing a higher percentage of soluble phosphates.
The phosphoric acid itself, or that mixed with sulphuric acid, may also be used
for the manufacture of alkalies and their phosphates by the decomposition of their
muriates or sulphates.
The insoluble residue left after extracting the phosphoric acid consists of
sulphates of alumina and iron mixed with silica and other ingredients, and may be
dried and sold as alumino-ferric cake, or it may be used for the manufacture of
alum or other salts of alumina.
Or the sulphuric acid which it contains may be recovered, if desired, by simply
calcining it at a strong heat in a furnace, and condensing the sulphuric fumes in a
vitriol chamber or condenser.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent, and of
an Order of the Lord Chancellor, filed by the said John James Knight in the
Great Seal Patent Office on the 5th July 1881.
JOHN JAMES KNIGHT, of Widnes, in the County of Lancaster.
"
IMPROVEMENTS
IN THE TREATMENT OF MINERAL PHOSPHATES CONTAINING ALUMINA AND OXIDE
OF IRON, OR EITHER OF THEM, FOR THE PRODUCTION OF PHOSPHORIC ACID AND
SALTS OF ALUMINA AND IRON."
Mineral phosphates containing alumina and oxides of iron, such as rodonda, alta
vela, and other similar ores, are comparatively useless at present for the manu-
facture of manures or alumina salts until the phosphoric acid in them is separated
from the alumina and oxides of iron, and the separation of these is the object of
my said Invention.
My Invention consists principally in the treatment of such mineral phosphates
with an excess of sulphuric acid of the specific gravity of one hundred and forty
degrees of Twaddle's hydrometer (equal to 1.70) and upwards in the manner herein-
after described, by means of which the sulphates of alumina and iron produced are
rendered insoluble in the excess of sulphuric acid, whilst the phosphoric acid is
rendered soluble and mixes with the sulphuric acid.
I take any of the above named class of mineral phosphates (say) for example,
redonda phosphate, which contains about thirty seven per cent. of phosphoric acid,
equal to about eighty per cent. of tribasic phosphate of lime, twenty per cent. of
alumina, and ten per cent. of peroxide of iron, and calcine it in kilns by any of
the well known methods. By this means the water of combination is driven off,
and the mineral rendered easier for the operation of grinding it to a fine powder.
I then heat it with an excess (say three or four times its weight) of sulphuric acid
of a specific gravity of one hundred and forty degrees to one hundred and forty
five degrees (Twaddle) for about an hour until the mixture gets thick and of a
grey colour. I may mention here that if the ground raw redonda phosphate is
used the sulphuric acid should not be of less strength than one hundred and fifty
degrees Twaddle, as the combined water in the mineral weakens the acid. The
mixture is run on to a filter composed of asbestos, sand, or other substance which
will withstand the action of the strong acids, placed in a vessel of any convenient
size and shape, and the filtratration assisted by means of a vacuum pump.
The filtrate is a mixture containing practically free phosphoric and sulphuric
acids, and from this solution the sulphuric acid can (if desired) be driven off by
distillation in the ordinary way, condensed, and used over again for treating more
mineral phosphates.
The phosphoric acid left in the retort is then suitable for the manufacture of
phosphorus, and also for the manufacture of alkalies and their phosphates in the
decomposition of their muriates or sulphates.
The filtrate itself may also be used direct for the decomposition of the alkaline
sulphates.
The filtrate may also be used in the manufacture of manures and superphosphates
of lime in the manner well known to manure manufacturers by treating it in the
mixing machine with commercial phosphates of lime, thus making a superphosphate
of superior quality, the free phosphoric acid acting on the phosphate of lime and
rendering it soluble in the same way that sulphuric acid acts. The percentage of
phosphoric acid in this filtrate may be increased (if desired) by treating another
batch of the redonda phosphate with it, and the addition of enough sulphuric acid
to combine with the alumina and oxides of iron, instead of using fresh sulphuric
acid, and this will give a higher percentage of soluble phosphate in the super-
phosphate made from it.

page_text: The residue on the filter, which is insoluble in the sulphuric acid, is then washed
with sulphuric acid of one hundred and forty degrees (Twaddle) and upwards, and
the washings after filtration are used in the treatment of fresh redonda phosphate
in the same manner as above described. The residue consists of a mixture of
sulphate of alumina, sulphate of iron, silica, and free sulphuric acid, and this I
treat by either of the following methods, namely:-
Firstly. I distil the mixture at a temperature sufficient to expel the excess of
sulphuric acid only, which is condensed and used over again, if desired, leaving as
residue the sulphates of alumina and iron, which may then be utilized in the
manufacture of alum and sulphate of alumina for the purification of sewage and
for other industrial purposes.
Or, Secondly. I calcine the mixture in a furnace or retort at a strong red heat,
and condense the sulphuric acid fumes given off in a suitable chamber or condenser.
By this means the greater part of the sulphuric acid is recovered, and may be used
over again.
Having now described the nature and object of my said Invention, together
with the manner in which the same is to be or may be performed or carried into
practical effect, I wish it to be understood that I claim as my Invention, the
treatment of mineral phosphates containing alumina and oxides of iron, or either of
them, with sulphuric acid in the manner hereinbefore described, for the separation
of the phosphoric acid from the alumina and oxides of iron contained in them.
In witness whereof, I, the said John James Knight, have hereunto set my
hand and seal, this Second day of July, in the year of our Lord One
thousand eight hundred and eighty one.
JNO. JAS. KNIGHT. (L.S.)