Process for Obtaining Alkali-phosphates from Neutral or Acid Alkali-sulphates.
Year: 1892

page_text: Date of Application, 8th Feb., 1892
Complete Specification Left, 14th Sept., 1892-Accepted, 15th Oct., 1892
PROVISIONAL SPECIFICATION.
[Communicated from abroad by the firm of H. & E. ALBERT, Manufacturers, of
Biebrich on the Rhine, Germany.]
Process for Obtaining Alkali-phosphates from Neutral or Acid
Alkali-sulphates.
I, JASPER WETTER, Patent Agent, of 433, Strand, in the County of London,
do hereby declare the nature of this invention to be as follows:-
Phosphates of alkalies, especially those of potash and of ammonia, have attained
a constantly increasing importance as a manure for modern agriculture.
Hitherto the said phosphates have been produced by saturating alkali carbonates
with phosphoric acid, and are therefore expensive, without satisfying all reasonable
requirements, such as the complete solubility of the phosphoric acid in water.
The present invention has for its object, to obtain all alkali-phosphates from
cheap sulphates by a simple method and therefore at a reduced cost.
My correspondents decompose the alkali-sulphate in dilute solution by means of
phosphoric acid in the presence of calcium carbonate, and in proportions indicated
by the following equation, potash being taken as an example.
The actual process is not, however, so simple, as would appear from this
hypothetical equation, because the phosphoric acid is not able to drive the
sulphuric acid immediately out of the alkali-sulphates, nor will the carbonate of
lime abstract the sulphuric acid from the neutral sulphate. On the contrary, it is
well-known, that an equal number of molecules of neutral sulphate and of
phosphoric acid produce by their interaction, acid sulphate and acid phosphate
(biphosphate) as described in the "Zeitschrift für angewandte Chemie" 1891,
page 478. The former, however, yields one half of its sulphuric acid to the lime
of the calcium carbonate and forms again neutral sulphate, which subsequently
reacts with a fresh quantity of free phosphoric acid, and so on.
The actual process
may therefore be represented by the following equations
0
2 K₂SO + 3 H₂РO + CaCO3
=
4
2 KHSO + 2 KHРO + HPO + CaCO¸
=
CaSO + K₂SO + 2 KHРO + HPO + H₂CO₂ =
4
CaSO + KHSO + 3 кHРО + H₂CO₂.
Now, if we take, instead of 2 K,SO, 4 molecules, 7 molecules of H.PO, will
5 interact with 3 molecules of CaCO3; in the same manner 8 K₂SO, would correspond
to 15 H₂PO, and 7 CaCO₂, and it is very easy to see, therefore, that by further
doubling the molecules of sulphate to be employed, we approach more and more
the proportion:

page_text: My correspondents therefore proceed as follows:
A tank lined with lead and provided with an agitator, is partly filled with a
measured volume of a solution of phosphoric acid of known strength or specific
gravity, the said acid having been obtained by the decomposition of phosphates
with dilute sulphuric acid, in the manner described in the British Patent No. 2614
of 1872, "Manufacture of phosphoric acid, phosphoric manure etc." It has a
density or weight of 9-24° Be. and contains from 6 to 19 per cent. of P₂O.
2
In this liquid, they first dissolve the corresponding quantity of potassium-(or
ammonium or sodium) sulphate, then add the calculated quantity of the finely
pulverised material containing calcium carbonate, while constantly stirring. The
use of heat is not necessary. A phosphate containing a high percentage of lime,
such as
occurs in large quantities in Northern France, Belgium and other
localities, will be found most advantageous, because the high percentage of lime
renders the utilisation of the phosphoric acid for other purposes difficult, and the
said mineral can therefore be obtained at a low price.
By this process, the chalk of the phosphate is converted partly into gypsum, and
its insoluble phosphoric acid may now be rendered soluble with a less quantity of
sulphuric acid. Consequently, the mineral thus treated is more valuable and may
be employed for the manufacture of super-phosphates of potash or of ammonia,
without requiring the previous removal, by washing, of any alkali-phosphate that
may still adhere to it; or it may be used for obtaining the phosphoric acid
necessary for our process, by extraction with sulphuric acid, in which case the
small quantities of alkali-phosphate are again introduced into the process; the same
is the case with the small quantities of phosphoric acid, which, owing to the
presence of iron- and alumina-compounds, form with the same an insoluble deposit.
By thus avoiding the further washing and the. boiling down of the liquid thus
obtained, and this without any loss of material, the described process represents a
decided advantage.
As soon as the chemical reaction is completed, the solution of phosphate is
separated from the residue by means of filter presses, centrifugal machines etc.,
and boiled down to the consistency of syrup. By subsequent drying, the salt is
obtained as a hard solid body, which can be pulverised by disintegrators.
The concentration of the liquid may be performed in open wooden vessels lined
with lead, by means of steam, but, of course, vacuum evaporators are more
economical.
The product contains about 35 per cent. of P₂O, soluble in water, 26-30 per cent.
of K,O respectively about 12 per cent. of NH, and generally also from 2-4 per
cent. of SO, which will not interfere with its application as a manure.
If a purer product is required, the contents of sulphuric acid may be further
reduced by taking for the decomposition a slight excess of phosphoric acid and
subsequently adding to the filtered solution a corresponding quantity of alkali-
carbonate (or ammonia-water).
Where an acid alkali sulphate is at disposal, it may also be employed, because
it always occurs as an intermediate product in the course of the process.
As may be seen from the above chemical equations, we obtain the alkali-phosphates
as di-acid salts.
The product is completely soluble in water, highly concentrated, and, apart from
small admixtures of lime and sulphuric acid, it is free from foreign matter.
Dated this 8th day of February 1892.

page_text: COMPLETE SPECIFICATION.
Process for Obtaining Alkali-phosphates from Neutral or Acid
Alkali-sulphates.
I, JASPER WETTER, Patent Agent, of 433, Strand, in the County of London,
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:-
Phosphates of alkalies, especially those of potash and of ammonia, have attained.
a constantly increasing importance as a manure for modern agriculture.
Hitherto the said phosphates have been produced by saturating alkali carbonates
with phosphoric acid, and are therefore expensive, without satisfying all reasonable
requirements, such as the complete solubility of the phosphoric acid in water.
The present invention has for its object, to obtain all alkali phosphates from
cheap sulphates by a simple method and therefore at a reduced cost.
I decompose the alkali sulphate in dilute solution by means of phosphoric acid
in the presence of calcium carbonate, and in proportions indicated by the following
equation, potash being taken as an example.

page_text: with dilute sulphuric acid, in the manner described in the British Patent No. 2614
of 1872 (Manufacture of phosphoric acid, phosphoric manure etc.). It has a density
or weight of 9-24° Bé. and contains from 6 to 19 per cent. of P₂O5.
In this liquid, I first dissolve the corresponding quantity of sulphate of potassium
(or of ammonium or sodium), then add the calculated quantity of the finely
pulverised material containing calcium carbonate, while constantly stirring. The
use of heat is not necessary. A phosphate containing a high percentage of lime,
such as occurs in large quantities in Northern France, Belgium and other localities,
will be found most advantageous, because the high percentage of lime renders the
utilization of the phosphoric acid for other purposes difficult, and the said mineral
can therefore be obtained at a low price.
By this process, the chalk of the phosphate is converted partly into gypsum, and
its insoluble phosphoric acid may now be rendered soluble with a less quantity of
sulphuric acid. Consequently, the mineral thus treated is more reliable and may
be employed for the manufacture of superphosphates of potash or of ammonia,
without requiring the previous removal, by washing, of any alkali phosphate that
may still adhere to it, or it may be used for obtaining the phosphoric acid necessary
for the new process, by extraction with sulphuric acid, in which case the small
quantities of alkali phosphate are again introduced into the process; the same is
the case with the small quantities of phosphoric acid, which, owing to the presence
of iron and alumina compounds, form with the same an insoluble deposit.
By avoiding in this manner the further washing and the boiling down of the
liquid thus obtained, and this without any loss of material, the described process
represents a decided advantage.
As soon as the chemical reaction is completed, the solution of phosphate is
separated from the residue by means of filter presses, centrifugal machines etc. and
boiled down to the consistency of pap. By subsequent drying, the salt is obtained
as a hard solid body, which can be pulverised by disintegrators.
The concentration of the liquid may be performed by means of steam in open
wooden vessels lined with lead, but, of course, vacuum evaporators are more
economical.
The product contains about 35 per cent. of P₂O, soluble in water, 26-30 per cent.
of K,O or about 12 per cent. of NH, and generally also from 2-4 per cent. of SO3,
which will not interfere with its application as a manure.
If a purer product is required, the contents of sulphuric acid may be further
reduced by taking for the decomposition a slight excess of phosphoric acid and
subsequently adding to the filtered solution a corresponding quantity of alkali
carbonate (or ammonia water).
Where an acid alkali sulphate is at disposal, it may also be employed, because it
always occurs as an intermediate product in the course of the process.
As may be seen from the above chemical equations, I obtain the alkali phosphates
as di-acid salts.
The product is completely soluble in water, highly concentrated, and, apart from
small admixtures of lime and sulphuric acid, it is free from foreign matter.
Having now particularly described and ascertained the nature of the said inven-
tion, and in what manner the same is to be performed, I declare that what I
claim is :-
1. The process for obtaining phosphates of alkalies, which consists in treating
an alkali sulphate with phosphoric acid in the presence of calcium carbonate,
substantially as described.
2. The process for obtaining phosphates of alkalies, which consists in first
dissolving an alkali sulphate in diluted phosphoric acid, then adding calcium
carbonate, separating the solid residues from the resulting solution of alkali
phosphate, and finally evaporating the latter to dryness, substantially as set forth.
3. The process for obtaining alkali phosphates, which consists in first dissolving
an alkali sulphate in diluted phosphoric acid, then adding calcareous phosphate,

page_text: separating the solid residues from the resulting solution of alkali phosphate, and
finally evaporating the latter to dryness, substantially as set forth.
4. The process for obtaining alkali phosphates, which consists in first dissolving
an alkali sulphate in diluted phosphoric acid, then adding a compound that contains
calcium carbonate, separating the solid residue from the resulting alkali phosphate
solution, and finally evaporating the latter to dryness, substantially as set forth.
Dated this 14th day of September 1892.
FAIRFAX & WETTER,
433, Strand, London, Agents.