IMPROVEMENTS IN THE MANUFACTURE OF CARBONATE OF POTASSIUM
Year: 1881

page_text: ETTERS PATENT to Edwin Powley Alexander, of 14, Southampton Buildings,
.
in the County of Middlesex, Consulting Engineer and British and Foreign
Patent Agent, for an Invention of "IMPROVEMENTS IN THE MANUFACTURE
OF CARBONATE OF POTASSIUM." A communication from abroad by Charles
Rodolphe Engel, of Paris, in the Republic of France.
ا.
PROVISIONAL SPECIFICATION left by the said Edwin Powley Alexander
at the Office of the Commissioners of Patents on the 14th January 1881.,
EDWIN POWLEY ALEXANDER, of 14, Southampton Buildings, in the County
of Middlesex, Consulting Engineer and British and Foreign Patent Agent.
"IMPROVEMENTS IN THE MANUFACTURE OF CARBONATE OF POTASSIUM." A com-
munication from abroad by Charles Rodolphe Engel, of Paris, in the Republic of
France.
This Invention has for its object the manufacture of carbonate of potassium by
the precipitation of a double carbonate by means of carbonate of magnesium,
carbonic acid, and a salt of potassium.
Heretofore the double salt in question, carbonate of magnesium and of potassium,
has only been obtained by causing the bi-carbonate of potassium in excess to act
upon a salt of magnesium, but my process is entirely different; it is based on the
formation of a double carbonate by the action of carbonate of magnesium upon a
salt of potassium (sulphate, chloride, carnallite, or other) in the presence of
carbonic acid.
The operation is effected in an apparatus consisting of hermetically closed vessels,
each vessel being provided with an agitator of any suitable construction actuated
by any convenient motor. Cocks or taps are also fitted to the said vessels to
admit of the introduction of the materials and their discharge at the completion
of the operation. Into one of such vessels there is introduced carbonate of
magnesium and an aqueous solution of salt of potassium; carbonic acid is then
introduced, either at or above the atmospheric pressure, the mass is agitated, and
the saturation and reaction are accomplished, resulting in the formation of small
crystals. The reaction terminates when the carbonic acid ceases to be absorbed.
After being allowed to rest for a time the liquid is run off into large basins, and
TDA71

page_text: after a while large crystals of the double carbonate are deposited. The addition
of magnesia or of oxycarbonate or of carbonate of magnesium with agitation
accelerates the deposit, which is then pulverulent. The precipitate formed in the
apparatus is separated from the mother liquors by the aid of a centrifugal machine,
filter-press, or other well known means. The double carbonate obtained from
these two sources is heated with or without water, and the decomposition of the
salt is effected; carbonate of magnesium and carbonate or bi-carbonate of
potassium (according to the temperature employed) being produced; the separation
is effected by water; the carbonate of potassium is then submitted to cold crys-
tallization or is brought to a dry state to obtain an anhydrous salt. The carbonate
of magnesium obtained can be re-employed for a fresh operation. The chloride of
magnesium is concentrated and decomposed by heat in presence of water.
Chlorhydric acid and oxyde of magnesium are the result; the first is condensed in
water, and the second is transformed into carbonate of magnesium in the vessels
before referred to, and serves for a fresh operation. The same quantity of magnesia
will thus serve indefinitely.
The ultimate products are carbonate of potassium and chlorhydric acid. The
carnallite may be employed direct. The respective quantities of materials to be
employed are indicated by the following formulæ, which take into account also the
reactions produced.
(1.) 3 Mg CO³ + 2 KCl + H³ O + CO² = Mg Cl² + 2 (CO² Mg CO³ HK).
(2.) Mg Cl2 + 2 H2O = Mg O³ H² + 2 HCl.
2 (COS Mg CO³ HK):
=
2 (CO® Mg) + CO® K° + H® 0 + CO or

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Edwin Powley Alexander in the Great Seal Patent Office on
the 9th July 1881.
"
EDWIN POWLEY ALEXANDER, of 14, Southampton Buildings, in the County
of Middlesex, Consulting Engineer and British and Foreign Patent Agent.
"IMPROVEMENTS IN THE MANUFACTURE OF CARBONATE OF POTASSIUM." A com-
munication from abroad by Charles Rodolphe Engel, of Paris, in the Republic of
France.
The said Invention consists in an entirely new method of manufacturing carbonate
of potash from any other soluble salt of potassium. It is based upon the discovery
of my correspondent that if either magnesia or a carbonate of magnesium be added
to an aqueous solution of a potassium salt, and the resulting mixture be then
treated by carbonic acid gas, there is formed a double carbonate of magnesium and
potassium, from which carbonate of potash may afterwards be separated, as will
hereinafter be set forth.
In describing how this Invention is to be carried into effect I will suppose that
the potassium salt from which carbonate of potash is to be manufactured is
potassium chloride. In such case an aqueous solution of potassium chloride and
carbonate of magnesium in a finely divided state are charged into a suitable vessel
furnished with a mechanical agitator, and the aperture by which these materials
were admitted is then closed by a suitable cock or otherwise. The agitator is then
set in motion, and there is then sent into the said vessel carbonic acid gas, either
at or above the atmospheric pressure. Absorption of carbonic acid takes place,
with formation on the one hand of small crystals of a double carbonate of
magnesium and potassium, and on the other hand of chloride of magnesium. When
carbonic acid ceases to be absorbed the reaction is terminated. The contents of
the vessel in which the reaction has been performed are now drawn off by a
suitable cock into another vessel, in which they are allowed to settle. The deposit
consists of small crystals of the aforesaid double carbonate of magnesium and
potassium mixed or not with any excess of carbonate of magnesium, which may
have been used, whilst the supernatant liquor is chiefly a solution of chloride of
magnesium, with any excess of chloride of potassium which may have been
employed. The supernatant liquor however contains also the elements of more
double carbonate, which it is capable of depositing on longer standing. It is
therefore drawn off into still another vessel, in which it is allowed to remain unti!
is has deposited as much further double carbonate as it will. It is found to do
this more rapidly if either magnesia or oxycarbonate of magnesium be added to it
with agitation. Both deposits are then separated as far as possible from the
mother liquor by means either of a centrifugal hydro-extractor, or a filter press, or
other suitable appliance, as will be well understood. The double carbonate of
potassium and magnesium is thus obtained practically free from mother-liquor, and
from all foreign solids except perhaps magnesia or carbonate of magnesium, or
both, and these are immaterial. It now remains to separate carbonate of potash
from the said double carbonate, and this may be done in either of two ways. If
the double carbonate be boiled with water it splits up into carbonic acid,
carbonate of magnesium, and carbonate of potash. The carbonic acid goes off
s gas, and can be used for the production of more double carbonate. There
emains a solution of carbonate of potash holding in suspension carbonate of

page_text: magnesium. This solution can be readily separated from the suspended carbonate
of magnesium by fitration, and from the filtered solution commercial carbonate
of potash can then be obtained either by evaporation to dryness or partial
evaporation followed by cooling and crystallization, as will be well understood.
Or the double carbonate may be decomposed by heating it in the dry way and
the product be treated by water, and the resulting solution of carbonate of
potash be then filtered from carbonate of magnesium and thereafter be dealt
with as already described. In either case the carbonate of magnesium filtered from
the solution of carbonate of potash should be used for the production of more
double carbonate. It is to be observed however that the quantity of carbonate of
magnesium thus separated by filtration from the solution of carbonate of potash
will not be so great as the quantity which was originally added to the solution of
chloride of potassium commenced with, since a portion of the carbonate of
magnesium commenced with has been converted into chloride of magnesium. If
the mother-liquor containing this chloride of magnesium be concentrated by
evaporation and be then further evaporated to dryness, and the residue calcined in
presence of vapour of water, the chloride of magnesium will be decomposed into
hydrochloric acid which can be condensed in the usual way, and magnesia, which
should be added together with the carbonate of magnesium filtered from the
solution of carbonate of potash to the solution of chloride of potassium used in the
next operation; if this be done each time the quantity of earbonate of magnesium
commenced with will serve indefinitely, except to the extent of any small mechanical
loss; if this be not done a quantity of fresh carbonate of magnesium must be
employed in each successive operation; equivalent to the quantity of carbonate of
potash obtained from the preceding operation; or instead of adding carbonate of
magnesium in the first operation, one may add free magnesia, since what first takes
place in that operation when free magnesia is present at the commencement of it is
simply the conversion of that free magnesia into magnesium carbonate.
The double carbonate produced as above described will usually consist of one
equivalent, or say eighty four parts by weight of normal carbonate of magnesium
or Mg CO₂, combined with one equivalent, or say one hundred parts by weight of
bicarbonate of potassium or HK CO,, but it may also under some circumstances
consist of one equivalent, or say eighty four parts by weight of normal carbonate of
magnesium or Mg CO, combined with one equivalent, or say one hundred and thirty
eight parts by weight of monocarbonate of potassium or K, CO,, or its constitution
may be intermediate between these two extremes. The maximum and most usual
quantity of carbonate of magnesium or of free magnesia to be employed in the
first operation above described is thus the quantity containing one equivalent, or
say twenty four parts by weight of metallic magnesium per one equivalent, or say
thirty nine parts by weight of metallic potassium contained in the double carbonate
produced. In some cases less than this proportion would suffice but the
employment of a larger quantity of carbonate of magnesium or of magnesia than
the quantity contained in the double carbonate produced will not be attended by
any serious disadvantage.
may
From this description of the manner in which the present Invention be
performed, when it is applied to the manufacture of carbonate of potash from
chloride of potassium, the manner of performing it when it is applied to the
manufacture of carbonate of potash from other salts of potassium will be fully
understood. All the operations are the same, whatever salt of potassium be
commenced with, except as regards the treatment of the inother-liquour from the
first operation. When, for example, the salt commenced with is sulphate of potassium,
the mother-liquour will contain sulphate of magnesium, which cannot be utilized in
the same manner as chloride of magnesium, but can be utilized in other ways, as will
be well understood by practical men.
It should be added that this Invention can
be applied to double salts of potassium and magnesium such as carnallite.
Having now described the nature of the said Invention and in what manner the

page_text: same may be performed, I claim as the Invention to be secured by the hereinbefore
in part recited Letters Patent,-
First. Obtaining a double carbonate of magnesium and potassium by treating
by carbonic acid gas a mixture of carbonate of magnesium or free magnesia
with an aqueous solution of a salt of potassium, substantially as herein before
described.
Secondly. Obtaining carbonate of potash from a double carbonate of magnesium
and potassium so produced, substantially as is hereinbefore set forth.
In witness whereof, I, the said Edwin Powley Alexander, have hereunto set
my hand and seal, this Ninth day of July, in the year of our Lord One
thousand eight hundred and eighty one.
EDWIN P. ALEXANDER. (LS)