Improvements in the Process of and Apparatus for Purifying Double Carbonate of Potassium and Magnesium.
Year: 1890

page_text: Date of Application, 30th June, 1890
Complete Specification Left, 3rd Mar., 1891-Accepted, 25th Apr., 1891
PROVISIONAL SPECIFICATION.
Improvements in the Process of and Apparatus for Purifying Double
Carbonate of Potassium and Magnesium.
I, HEINRICH PRECHT, of Loederburg, near Stassfurt, in the Empire of Germany,
Doctor of Philosophy, do hereby declare the nature of this invention to be as
follows:-
My invention relates to the purification of double carbonate of potassium and
magnesium and to apparatus therefor.
The double salt of carbonate of potassium and magnesium (Mg CO, KH CO,
4H₂O), produced by the process of Charles Rodolphe Engel, of Paris, which
consists, as is well known, in producing a double salt (carbonate) of potassium and
magnesium by the action of carbonic acid on carbonate of magnesium and a
solution of salts of potash (preferably a solution of chloride of potassium) in an
air-tight vessel is, after being separated from the liquid in which it was formed
always mixed with the salts dissolved in the lye. The double salt thus produced
contains about three per cent. of chlorine in the form of chloride of potassium and
chloride of magnesium.
To obtain pure carbonate of potassium from the above double salt it is most
essential that the double salt should be as pure as possible, because impurities such
as chloride of potassium and chloride of magnesium cannot well be separated from
the finished carbonate of potassium.
According to my invention the carbonate of potassium and magnesium con-
taining chlorine is before its decomposition treated with water or preferably with a
solution of carbonate of magnesium in water charged with carbonic acid gas because
the latter liquid has the advantage of decomposing the double-salt to a much less
degree than plain water.
The solution of carbonate of magnesium in aërated water is prepared from
magnesia or native hydrate of magnesia or carbonate of magnesium by treating the
same with carbonic acid under pressure in a cylindrical vessel.
The double salt to be purified is then put together with a lye prepared in the
said vessel or with water into an agitator in which it is stirred.
By using a solution of carbonate of magnesium for treating the double salt the
latter becomes scarcely at all decomposed and the product obtained does not
possess more than 0.2 to 0.3 per cent. of impure salts.
The purified double salt is separated from the lye by filtration and the lye is
collected in a suitable vessel. The lye can be utilized by pumping it into a second
agitator where it is then saturated with chloride of potassium and afterwards stirred
up with magnesia, hydrate of magnesia or carbonate of magnesium. The mixture
is then treated with carbonic acid whereby a double salt of carbonate of potassium
and magnesium is produced.
In this manner not only the chloride of potassium resulting from the wash of the
double salt but also the carbonate of magnesium present in the solution are com-
pletely exhausted.
G. F. REDFERN & Co.,
4, South Street, Finsbury, London, Agents for the Applicant.

page_text: COMPLETE SPECIFICATION.
Improvements in the Process of and Apparatus for Purifying Double
Carbonate of Potassium and Magnesium.
I, HEINRICH PRECHT, of Loederburg, near Stassfurt, in the Empire of Germany,
Doctor of Philosophy, 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 :-
My invention relates to the purification of double carbonate of potassium and
magnesium and to apparatus therefor.
The double salt of carbonate of potassium and magnesium (Mg CO KH CO,
4H2O) produced by the process of Charles Rodolphe Engel of Paris, which consists,
as is well known, in producing a double salt (carbonate) of potassium and magnesium
by the action of carbonic acid on carbonate of magnesium and a solution of salts of
potash (preferably a solution of chloride of potassium) in an air-tight vessel is,
after being separated from the liquid in which it was formed always mixed with the
salts dissolved in the lye. The double salt thus produced contains about three per
cent. of chlorine in the form of chloride of potassium and chloride of magnesium.
To obtain pure carbonate of potassium from the above double salt it is most
essential that the double salt should be as pure as possible, because impurities such
as chloride of potassium and chloride of magnesium cannot well be separated from
the finished carbonate of potassium.
In the accompanying drawing,―
Figure 1 is an elevation; and,
Figure 2 is a plan of apparatus suitable for purifying double carbonate of
potassium and magnesium by my improved process.
According to my invention the carbonate of potassium and magnesium con-
taining chlorine is, before its decomposition, treated with water, or preferably with
a solution of carbonate of magnesium in water charged with carbonic acid gas,
because the latter liquid has the advantage of decomposing the double salt to a
much less degree than plain water.
The solution of carbonate of magnesium in aërated water (that is to say, water
containing carbonic acid) is prepared from magnesia or native hydrate of magnesia
or carbonate of magnesium by treating the same with carbonic acid, under pressure,
in a cylindrical vessel A. The double salt to be purified is then put together with
a lye prepared in the vessel A or with water into an agitator B in which it is
stirred.
By using a solution of carbonate of magnesium for treating the double salt the
latter becomes scarcely at all decomposed and the product obtained does not possess
more than 0.2 to 0.3 per cent. of impure salts.
The purified double salt is separated from the lye by filtration in a vessel C and
the lye is collected in a vessel D. The lye can be utilized by pumping it into a
second agitator E where it is then saturated with chloride of potassium and after-
wards stirred up with magnesia, hydrate of magnesia or carbonate of magnesium.
The mixture is then treated with carbonic acid whereby a double salt of carbonate
of potassium and magnesium is produced.
In this manner not only the chloride of potassium resulting from the wash of
the double salt, but also the carbonate of magnesium present in the solution, are
completely exhausted.
The apparatus shewn in the drawing for illustrating the process can be of
different construction or arrangement.
When the purifying process is to be carried out under pressure the open stirring
apparatus B must be replaced by a closed one so as to withstand the pressure.

page_text: 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:-
1. The process of purifying the double carbonate of potassium and magnesium
by treatment with a solution of carbonate of magnesium in water containing
carbonic acid under ordinary or high pressure, substantially as hereinbefore
described.
2. The process of completely utilizing the lye resulting from the purification of
the double salt by treatment with water or with the solution referred to in Claim 1
in such a manner that it can be used for mixing with magnesia, hydrate of magnesia
or carbonate of magnesium and for dissolving chloride of potassium for the purpose
of producing the double carbonate of potassium and magnesium preferably according
to Engel's process, the latter consisting in treating carbonate of magnesium and a
solution of a potash-salt (preferably chloride of potassium solution) in closed
vessels with carbonic acid, substantially as hereinbefore described.
Dated the 2nd day of March 1891.
G. F. REDFERN & Co.,
4, South Street, Finsbury, London, Agents for the Applicant.