IMPROVEMENTS IN THE MANUFACTURE OF SULPHATE OF POTASH
Year: 1879

page_text: LETTERS PATENT to August Dupré, of Westminster Hospital, in the County of
Middlesex, for the Invention of "IMPROVEMENTS IN THE MANUFACTURE OF
SULPHATE OF POTASH." A communication from abroad by Friedrich Dupré
and Cecil Hake, both of Stassfurt, in the Empire of Germany.
PROVISIONAL SPECIFICATION left by the said August Dupré at the Office
of the Commissioners of Patents on the 18th October 1879.
AUGUST DUPRÉ, of Westminster Hospital, in the County of Middlesex.
"IMPROVEMENTS IN THE MANUFACTURE OF SULPHATE OF POTASH." A communi-
cation from abroad by Friedrich Dupré and Cecil Hake, both of Stassfurt, in the
Empire of Germany.
The Invention relates, first, to the manufacture of sulphate of potash direct from
schönit by means of lime, and consists in mixing finely ground schönit with caustic
lime or with slaked lime, and in moistening the said substances while mixing them
in order to obtain a more complete mixture, the most advantageous proportions
being found to be 100 parts of schönit to 14 parts of lime corresponding to the
equation:-
K2SO4 + Mg SO4 + (6 aq) + Ca O =
K2SO4 + Ca SO4 + Mg O + 6 aq.
This mixture of schönit and lime is at first nearly dry, but gradually becomes
plastic owing to the water of the crystals being set free. The so obtained product
is now either to be calcined or left to itself for some days, the result being in both
cases a hard mass which can be lexiviated without difficulty. By repeatedly using
the so obtained lyes (after precipitation of the sulphate of potash dissolved by heat)
for further extractions the quantity of water required is reduced to a minimum, the
solubility of the gypsum much reduced, and any sulphate of magnesia contained in
the lye at once removed. The Invention relates further to the manufacture of
schönit from kainit, and consists in adding a concentrated solution of sulphate of
magnesia to ground kainit, such as is supplied by the mines, whereby chloride
of magnesium and also chloride of sodium are completely removed and pure schönit
remains. This process can be carried out either hot or cold; in the former case
kainit is completely dissolved in a hot and nearly saturated solution of sulphate of
magnesia. By cooling slowly a crystalline deposit of the salt K2 SO* + Mg SO* +
6 H2O is formed in. the lye. In the latter case a cold solution of sulphate of
magnesia is added to finely ground kainit and the mixture well stirred, by which
process chloride of magnesium and chloride of sodium are extracted, so as to leave
a residue which contains the salt K2 SO* Mg SO' as a crystalline powder mixed
with more or less sulphate of magnesia.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said August Dupré in the Great Seal Patent Office on the 15th April
1880.
AUGUST DUPRÉ, of Westminster Hospital, in the County of Middlesex.
"IMPROVEMENTS IN THE MANUFACTURE OF SULPHATE OF POTASH." A communi-
cation from abroad by Friedrich Dupré and Cecil Hake, both of Stassfurt, in the
Empire of Germany.
The Invention relates to the manufacture of potassium sulphate from kainit or
from schönit, and consists in the following consecutive processes:-
First. In adding a more or less concentrated solution of magnesium sulphate
(kieserit epsoms) to ground kainit or the reverse, whereby the chlorides of
magnesium and sodium-go into solution, and can be separated from the residue by
decantation. This process can be carried out either hot or cold; in the former case
kainit is completely dissolved in a hot and nearly saturated solution of magnesium
sulphate and the solution allowed to cool slowly, whereby a crystalline deposit of
the salt K2SO4 + Mg SO4 + (6 aq), commonly called schönit, is formed in the lye.
In the latter case a cold solution of magnesium sulphate is added to finely ground
kainit and the mixture well stirred, by which process the chlorides of magnesium
and sodium go into solution, and may afterwards be removed by decantation, and
a residue is left which contains the salt K2SO4 + Mg SO* + (6 aq) as a crystal-
line powder mixed with more or less magnesium sulphate.
In the second process schönit obtained as described, or in any other way, in a
fine state of division is mixed with finely ground lime, baryta, or strontia, or the
carbonates, of these substances, the said substances being preferably moistened while
mixing them in order to obtain a more complete mixture. When lime is used the
most advantageous proportions are 100 parts of uncalcined or 73% parts of calcined
schönit to 14 parts of lime, more or less corresponding to the equation, K² SO* +
Mg SO + (6 aq) + Ca O = K2SO4 + Ca SO* + Mg O + (6 aq).
This mixture of schönit and lime is, when uncalcined schönit has been taken, at
first nearly dry but gradually becomes plastic.
The so obtained product is now either to be calcined more or less strongly or left
to itself for some days, the result being in both cases a hard mass, from which the
potassium sulphate can be extracted by lixiviation without difficulty.
When baryta or strontia salts are used an equivalent proportion of such salts is
to be taken.
By repeatedly using the so obtained lyes for further extraction of potassium
sulphate the quantity of water is reduced to a minimum, the solubility of the
gypsum much reduced, and any sulphate of magnesia contained in the lye at once
removed, so that the lye contains potassium sulphate with only a small proportion
of impurities.
CLAIMS.
1. The process of manufacturing schönit from kainit, substantially as and for
the purpose described.
2. The process of manufacturing potassium sulphate from schönit, substantially
as described.
In witness whereof. I. the said August Dunré have hereunto set my band