Note: Descriptions are shown in the official language in which they were submitted.
~7~27
PROC~SS FOR PRODUCING AND DECOMPOSING SYNGE~ITE,
FOR PRODUCING K3~(SO4)2 CRYSTALS AND
POT~SSIUM SULFATE CRYSTALS, AND FOR
PRODUCING POTASSIUM NITRATE
BACKGROUND OF THE INVENTION
Potassium chloride, the major form in which potassium
is used in fertilizers, has been known for many years to
have agronomic disadvantages when compared with certain
other potassium salts. Thus, currently the sulphate and
nitrate are widely used on crops such as tobacco, tomatoes,
and potatoes, especially for those to be used in the production
of potato chips (crisps).
The chloride ion, if allowed to build to sufficiently
high levels, is toxic to most plant species, and its elimination
is a desirable aim for the fertilizer industry. In arid
areas, totally dependent upon irrigation for their water,
for example, the build-up OL chloride ions in the soil can
become a major factor in producing a reduced crop yield. At
such times, major quantities of water are required to flush
out the chloride. Such flushin~ not only wastes large
quantities of valuable water, but, at the same time, flushes
out necessary fertilizer constituents in the soil.
The major, if not the sole, factor which has
caused the continued use of potassium chloride under these
circumstances, is the ready availability and consequently
low cost of the chloride as compared with other potassium
salts.
The most common substitute for potassium chloride
is potassiu~ sulphate. This salt exists in various mineral
~orms in a number of places, but its separation, usually by
crystallization techniques, is more complex and more expensive
than that for the chloride. It is produced directly as a
double sulphate salt along with magnesium sulphate in the
Western UoS~A~ but such material, although not expensive,
per se, is low in potassium concentration and hence more
costly to transport and store.
For many years, the ch]oride sal~ of potassium has
been converted into the sulphate by high temperature reaction
with sulfuric acid, and considerable quantities are manu-
factured in this way, particularly in Belgium. U.S. Patent
4,342,737 discloses one such process. The major factors
restricting further production by this method are threefold:
1. The high energy requirement.
2. The highly corrosive nature of the reactants
and the by-product hydrogen chloride.
3. The need for a local market for the hydrogen
chloride produced - otherwise, it must be neutralized at
considerable cost before it can be discarded.
For many years, varying routes have been described
to convert the chloride using calcium sulphate or sodium
sulphate, but none has been used commercially up to the
present.
Many of the routes proposed produce glaserite, a
double salt of potassium and sodium sulphate, Na2SO4 3K2SO4,
as an intermediate and subsequently react with excess potassium
chloride to convert the sodium sulphate to potassium sulphate.
The product may be recovered, for example, by evaporation
and recrystallization. U.S. Patent 4,215,100 is directed to
such a process. Other routes produce the calcium double
salt, syngenite, CaSO4 K2SO4 H2O as intermediary. This may
be decomposed by water at elevated temperature and pressure,
as disclosed in British Patent 435,772, or by concentrated
ammonia at low temperature, as disclosed in French Patent
787,713. In British Patent 2,068,918, sylvinite, a double
salt of potassium and sodium chloride of variable composition,
and calcium sulphate are reacted with aqueous ammonia to
produce the potassium sulphate, sodium sulphate double salt;
the double salt is reacted with sylvinite or additional
sylvinite in aqueous ammonia to produce potassium sulphate
crystals.
All such routes are complexl costly, major energy
users and may require operation under undesirable conditions.
Thus, a need has continued to exist for a process of producing
K2S04 using readily available raw materials of low cost,
said process being relatively uncomplicated, highly energy
efficient, and requiring no substantial equipment cost
outlay.
Potassium nitrate is largely produced by one of
two processes. In the first, which is the only one currently
practiced in the U.S.A., potassium chloride is reacted with
nitric acid at a high temperature to produce potassium
nitrate and chlorine, utilizing the following reactions:
3 > 3KNo3 + C12 + NOCL + 2H20
2NOCl + 4HN03 ---~ 6N02 + Cl + 2H O
4N2 + 2 ~ 2H2 4HNo3
The corrosive nature of the various reagents with
consequent design and maintenance problems and the need to
dispose of the by-product chlorine have prevented wider usP
of the process.
In recent years, an increasing tonnage of potassium
nitrate has been imported into the U.S. A major source is
Israel where a process is operating whereby nitric acid and
potassium chloride are reacted in solution-and the co-
product hydrogen chloride is removed from the solution by
solvent extraction. The viability of such a process is
depen~-~ent upon the economic disposal of the hydrogen chloride
for which no major demand exists in many parts of the world.
Thus, a need has continued to exist for a process
of producing XN03 by an alternative method without either
the maintenance and construction, or by-product disposal
problems.
Q2~
SUMMARY OF THE INVENTION
.
It is an object of this invention to produce an
agronomically acceptable form o~ potassium.
It is a further object of this invention to produce
potassium in the form of potassium sulphate or potassium
nitrate.
It is another object of this invention to produce
potassium sulphate or potassium nitrate by a process which
is relatively uncomplicated and highly energy efficient to
operate.
It is still another object of this invention to
produce potassium sulphate or potassium nitrate from syngenite.
It is yet another object of this invention to
produce potassium sulphate utilizing a process wherein
various of the process by-products are returned to the
production cycle.
These and other objects of the invention, as will
hereinafter become more readily apparent, have been accomplished
by a simple process which produces, and then decomposes,
syngenite to yield potassium sulphate or potassium nitrate.
In reaction stage 1, potassium chloride and a
sulphate are a~itated with a calcium sulphate or penta salt
suspension which may be recycled from a subsequent decomposition,
stage 2, to produce sodium chloride and syngenite in suspension
according to the equation:
2KCl + Na2S4 + CaS04 + H ~ CaSO K SO H O + 2NaCl
or
8KCl + 4Na2S04 + 5CaS04 K2S04 H2 2
~ 5(CaS04~K2S04-H20) + 8NaCl
After separation, the syngenite is fed to reaction
stage 2 where it is reacted with a suitable acid containing
solution such as a hot sulphuric acid containing solution
-- 4
~1 ~ ~fll'r3
and thereby decomposed into calcium sulphate or penta salt
and potassium sulphate, depending on reaction conditions.
The stoichiometry is as follows:
2 o4 CaS04 K2S04 H20----~CaS04 + 2KHS04 + H20
or
4H2S04 + 5(CaS04 K2S4 H2 ) 5CaS04 K2S04 H20
+ 8KHS04 ~ 4H20
The suspension so produced is separated at the
reaction temperature, and the calcium sulphate or penta salt
removed may be recycled to stage 1 for further syngenite
synthesis. The resultant hot solution containing potassium,
sulphate, and bisulphate ions, at appropriate concentrations,
is cooled to crystallize K3H(S04)2, a double salt of potassium
sulphate and bilsuphate. This is removed by filtration or
other suitable means and the mother liquor recovered may be
reheated and recycled to sta~e 2 to decompose further
syngenite.
Crystallization of an aqueous solution of the
double salt, K3H(S04)2, yields crystals of potassium sulphate,
the desired product, and a mother liquor containing potassium
bisulphate and free sulphuric acid which may be separated
and recycled to stage 2 to decompose further syngenite.
In the case of decomposing syngenite with nitric
acid rather than sulphuric acid, potassium, hydrogen, bi-
sulphate and nitrate ions remain in solution, after removal
of calcium sulphate.
CaS04-K2S04 H20 + 2H + 2N03 > CaS04~ +
HS04 + 2K + 2N03 + H+ + H20
To maximize decomposition using nitric acid,
therefore, the nitric acid content in solution must be
sufficient to convert all the potassium sulphate into potassium
bisulphate solutions.
-- 5 --
. .
7~
The addition of lime or calcium carbonate, in
appropriate amounts, to such a solution results in the
precipitation of further calcium sulphate leaving a solution
containing effectively potassium and nitrate ions, from
which potassium nitrate may be crystallized.
2K + HS04 ~ H + 2N03 + CaC03 3
4~ + 2~ ~ 2No3 + H20 + C02 ~
The presence of excess nitric acid may be advantageous as
this lowers the solubility of the potassium nitrate and
results in a lower potassium recycle. Alternatively, calcium
nitrate may be added to the solution to precipitate calcium
sulphate and after crystallization and removal of potassium
nitrate, the nitric acid solution remaining, containing some
potassium nitrate, may be recycled to the syngenite decomposition
stage.
2X + HS04 ~ H + ~N03 + Câ + 2No3 >
CaS04 + 2K + 4N03 + 2H+
2K+ + 4N0 + 2H+ Crystallize_ 2KNo + 2N0 ~ + 2H+
While developing the above processes using nitric
acid, it became clear that any process, which reduces the
sulphate level in reactant solutions to a level below that
which is in equilibrium with syngenite, will result in the
liberation of potassium ions from the syngenite even in the
absence of hydrogen ions.
Thus, the addition of calcium ions to such a
solution does, in fact, result in the precipitation of
calcium sulphate and liberation of potassium ions.
4 2 4 2 + Ca __~ 2Cas04~ + 2K~ + H20
The addition of calcium ions in the form of calcium nitrate,
which may be produced "in situ" from nitric acid and calcium
carbonate or hydroxide, results in the production of a
-
Q2~
potassium nitrate solution from which solid KN03 may be
crystallized, i.e.,
4 2 4 2 Ca N03 --~ 2CaS04 ~+ 2K + 2N03 + H20 .
This may be interpreted as:
4 ~ 4 2 + Ca(N03)2-~ 2CaS04 ~ + 2KNo ~ H O
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a flow diagram of the process of this
invention wherein sylvinite is converted to potassium sulphate.
Figure 2 is a process flow diagram representing
one embodiment wherein syngenite is decomposed with HN03 and
additional sulphate ion precipit~ted by addition of calcium
in the form of calcium carbonate, calcium hydroxide or
calcium nitrate, fol-lowed by recovery of crystalline KN03.
Figure 3 is a process flow diagram representing
another embodiment wherein syngenite is decomposed by addition
of calcium ion in the form of calcium nitrate, followed by
recovery of crystalline KN03.
DESCRIPTION OF THE PREFERRED E~BODIMENT
.
Much of the potassium chloride mined in the world
is in the form of sylvinite, a double salt of sodium and
potassium chloride of variable composition. The method used
to prepare syngenite from potassium chloride can be readily
modified to use sylvinite as starting material. In fact, an
advantage exists in using sylvinite in that the sodium
chloride generated by the syngenite synthesis can be discarded
along with the sodium chloride in the sylvinite without
separate segregation or evaporation.
The data presented by Hill, A.E., J. Am. Chem.
Soc. 56, 1071-8 (1934) ibid. 59 2242-4 (1937) and Bodaleva,
N.V. and Lepeshkov, I.N., Zh. Neorgan. Khim 1, 995-1007
(1956) shows that the stability of syngenite decreases as
the temperature increases from 40C to 100C. This shows
that syngenite is best synthesized at lower temperatures and
decomposed into calcium and potassium sulphate at higher
temperatures.
This same data further indicates that in order to
produce stable syngenite, the concentration of potassium
sulphate in the solution must be in excess of about 4~ w/w
at 40C increasing to about 11% w/w at 100C.
Any process synthesizir.g syngenite from potassium
sulphate solutions must then operate within these parameters.
We have shown that it is possible with solid calcium sulphate
to obtain syngenite from solutions containing potassium
ions, added as potassium chloride, and sulphate ions, added
as sodium sulphate, ammonium sulphate, or other soluble
sulphates, in concentrations which satisfy the solubility
product for syngenite at the reaction temperature.
Further, we have shown, based on data of Cornec,
E. and Krombach, H., Compt. Rend. 194, 714-6 (1932) that
satisfactory concentrations of potassium chloride can be
obtained directly from sylvinite by taking advantage of the
mutual solubilities of sodium and potassium chloride.
The compositions of solutions in equilibrium with
both sodium and potassium chloride at various temperatures
can be plotted from the Cornec et al data. Thus, a solution
in equilibrium at 20C when heated to 80C and used to leach
sylvinite, will dissolve potassium chloride and discard
solid sodium chloride until it attains equilibrium with both
sodium and potassium chloride.
If such a solution at 80C is now contacted with
the appropriate amou.,t of calcium sulphate and an amount of
~2~7(~7
sodium sulphate equivalent to the calcium sulphate is added
to the solution, which is allowed to cool to 20C, syngenite
is formed.
The concentration of potassium chloride can be
reduced to that at the invariant or equilibrium point at
20C by choosing the appropriate amounts of calcium and
sodium sulphate. The sodium chloride produced by the reaction
CaS04 + 2KCl + Na2S04 ~ H2 ~~~ 4 2 4 2
is in excess of that solution at the 20C invariant so that
the excess will precipitate along with the syngenite while
the remainder will stay in solution at the invariant or
equilibrium point at 20C. After separation of the precipitated
solids, the solution may be heated to ~0C and recycled to
leach sylvinite and dissolve resh potassium chloride while
rejecting the remainder of the sodium chloride generated by
the syngenite synthesis step. This sodium chloride is then
discarded along with that remaining after solution of the
potassium chloride from the sylvinite. Alternatively,
potassium chloride alone may be added to the solution at
80C, where it will dissolve until equilibrium is reached,
and sodium chloride will be precipitated and can be removed.
Phase considerations also restrict the conditions
for the decomposition of the syngenite and for separation of
the potassium sulphate so produced. The phase diagram for
K2SO4-H2SO4 in water can be plotted from data of D'Ans,
J.z., Anorg. Chem. 63, 225-9 (1909), Stortenbecker, W., Rec.
Trav. Chem. 21, 407 (1909), and Babaewa, A.W., Trans. Inst.
Pure Chem. Reagents (Moscow) llI 114 (1931).
Our studies have shown that in the presence of
hydrogen ion at elevated temperature ( >60C), syngenite
decomposes into either calcium sulphate or penta salt
(5CaSO4 K2SO4 H2O), dependent upon conditions. ~he mechanism
~2~'7~
appears to depend upon the conversion of sulphate ion in
solution into bisulphate ion with consequent dissolution of
K2S04 from the syngenite to try to restore the sulphate
concentration in solution.
If sufficient hydrogen ion is present in the form
of sulphuric acid, or other acid with a dissociation constant
greater than the second dissociation constant of sulphuric
acid, 1.2 x 10 2, the syngenite will totally decompose into
solid CaSO4 and potassium and bisulphate ions in solution.
To maximize decomposition using sulphuric acid,
therefore, the sulphuric acid content in solution must be
sufficient to convert all the potassium sulphate, both any
in solution originally and that liberated from the syngenite,
into potassium bisulphate solutions.
Solutions, a~ter syngenite decomposition, with
compositions with a K:SO4 sulphate molar ratio greater than
1:1 containing excess potassium sulphate compared with a
solution of potassium bisulphate, will be technically feasible
but economically unsatisfactory r since the amount of potassium
sulphate liberated from the syngenite is directly equivalent
to the amount of free sulphuric acid available in the
decomposition solutiont since it is the hydrogen ions which
convert sulphate to bisulphate ions.
The data of D Ans, Stortenbecker and Babaewa shows
that even solutions containing free sulphuric acid in excess
of that required to form bisulphate upon cooling will, under
appropriate conditions, yield crystals, not of potassium
bisulphate, but of the double salt X3H(SO4)2. However, at
low starting temperatures ( >30~C), bisulphate composition
solutions will, in fact, yield potassium sulphate on cooling.
The mother liquor will contain free acid and may be recycled
to decompose fresh syngenite.
The data of D'Ans, Stortenbecker and Babaewa also
shows that t at any given temperature t with sulphuric acid
-- 10 --
~17C~7
concentrations lower than that at the invariant point (i.e.,
where the solid double salt K3H(SO4)2 along with solid
potassium sulphate are in equilibrium with the solution) the
solid phase in equilibrium is potassium sulphate. Thus, for
example, at 30CC the addition of double salt to solutions
containing less than 20 grams of H2SO4 per 100 grams water
will result in the crystallization of potassium sulphate
until such additions bring the sulphuric acid concentration
in the mother liquor to 20 grams per 100 grams water. After
separation of the solid potassium sulphate, such mother
liquor may be recycled to syngenite decomposition after
suitable concentratlon by evaporation. At higher temperatures,
up to the boiling point of the solution, a similar result is
obtained, but with h:.gher concentration solutions being
recycled. This reduces the amount of evaporation required.
Although such isothermal crystallization of
potassium sulphate is preferred, the double salt, K3H(SO4)2,
may be dissolved in hot water. Such solution, upon cooling,
will yield potassium sulphate as the solid phase, and the
acid rich mother liquor may be recycled to syngenite
decomposition.
The preferred temperature for this solution step
is at, or near, the boiling point. Typically, a solution
containing 46.5% K3H(SO4)2 on a weight to weight basis (87.5
grams of K3H(SO~)2/100 grams of water) at 95C will, when
cooled to 0C, precipitate K2SO4 crystals [68.5 grams of
K2SO4 - 187.5 grams original solution].
In order to operate the process in its most
financially economical way, it is desirable to minimize
plant equipment size, which means operating at conditions
which will give maximum through-put for a given unit size.
For this reason, it is clearly best to leach
sylvinite at the highest feasible temperature, about 100C,
thereby extracting the maximum amount of potassium chloride
and obtainin~ the invariant solution of highest concentration.
Assuming tha~ we wish to maintain the potassium chloride
concentration, after synthesis, greater than 3.5%, this
defines the amount of KCl which can be reacted and hence the
amount of NaCl produced. It is clear that at this portion
of the solubility curve, temperature is unimportant.
The lowest potassium concentration quoted above is
derived from examination of the data presented by Hill and
Bodaleva et al discussed above, which defines the lowest
K2S04 concentration in equilibrium with syngenite at 40C as
about 4 grams per 100 grams solution which is equivalent in
potassium concentration to 3.5 grams KCl per 100 grams
solution. In practice, we have shown that at 20C, KCl
concentrations as low as 2.9 grams per 100 grams are satis-
factory. The data presented by Hill and Bodaleva et al also
shows that the stability range of syngenite is greater at
lower temperatures, which defines the most useful synthesis
temperature range as being below 60C, probably below 40C,
which has, in fact, been confirmed by experiment.
As already mentioned, the data of D'Ans, Stortenbecker
and Babaewa shows that the most efficient syngenite decompo-
sition conditions are ones where the composition of the
solution, after decomposition, corresponds to a K:S04 molar
ratio of 1:1. These compositions should also yield the
double salt, K3H(S04)2, upon cooling, and the highest concen-
tration solution meeting these criteria is that at a concen-
tration of about 31.6 grams K2S04 and 17.8 grams H2S04 per
100 grams solution which, upon cooling to 0C, yields a
solution at a concentration of about 12 grams K2S04 and 18.5
grams H2S04 per 100 grams solution. The cooling, therefore,
crystallizes out double salt containing the equivalent of
22.86 grams K2S04, along with 4.3 grams H~S04 per 100 grams
of initial solution. No other composition of solution has
- 12 -
~L2~
such a favorable yield of K2S04 with as good a K2S04/H2S04
ratio.
The invention may best be described by reference
to Figure 1. A potassium chloride salt, such as sylvinite
or KCl, and recycle solution A, to be described below, are
contacted, in leach system 1, wherein potassium chloride is
dissolved and solid sodium chloride precipitated. The
sodium chloride is discarded. The preferred temperatures
for this step are in the range between about ambient and the
boiling point of the solution. Eighty degrees centigrade
(80C) to the boiling point is the most preferred temperature
range.
The leach solution B is now fed to the syngenite
preparation unit 2, wherein it is allowed to cool while
reacting with a calcium sulphate salt and additional sulphate.
Suitable additional sulphate sources include, but are not
limited to, (NH4)2S04 and alkali metal sulphates. Suitable
calcium sulphate salts include, but are not limited to,
CaS04 and the penta salt, 5CaS04 K2S04 H20. At least a part
of this addition may come from the by-product recovery of
the subsequent syngenite decomposition. The syngenite
slurry, D, so produced, is separated by, for example, filtra-
tion and washed to remove sodium chloride in unit 3. The
mother liquor and washings, E, may be concentrated to remove
the wash water in concentrator 4 and recycled to the leach
stage as the concentrate A.
Solid syngenite, F, is fed to the syngenite
decomposition vessel 5, maintained at elevated temperature,
along with a mineral acid. The mineral acid may be supplied
in the recycled liquor, G and H, from later stages in the
process. "Gypsum" slurry, J, is separated by filtration in
separation unit, 6, and the solid "gypsum", I, washed in 7
with water. This "gypsum" may be recycled to syngenite
preparation, 2, as C.
13
7C~
Suitable temperatures for the acid decomposition
of syngenite are in the range of ambient to boiling, with
temperatures above about 70C preferred. Eighty degrees
centigrade (80C) or above are the most preferred tempera-
tures. The reaction goes to completion at atmospheric
pressure, usually re~uiring a time of about 30 minutes to 2
hours. Appropriate concentrations for proceeding to the
next step are 31.6~ w/w K2SO4 and 17.8% w/w X2SO4.
The mother liquor, K, from 6, containing K~SO4,
is cooled to 0C in crystallizer 8 to precipitate K3HSO4
crystal slurry L which is separated by, for example,
filtration in 9. It is preferred that the solution containing
KHSO4 be cooled to a temperature in the range of about 0C
to 45C, preferably in the range of about 0C to 30C. The
most preferred range is about 0C to 20C. The mother
liquor Q may be recycled to syngenite decomposition in 5.
The double salt K3H(SO4)2 obtained from the
cooling step above is slurried at 100C in the wash liquors
N and O in crystallizer 10. Wash liquor N is recycled from
the gypsum wash 7, while wash liquor O is recycled from a
subsequent potassium sulphate wash.
Potassium sulphate crystals so produced, P, are
separated in 11 and the mother liquor, Q, after concentration
in evaporator 12, is recycled to syngenite decomposition 5.
The crude potassium sulphate crystals R are washed in 13
with saturated potassium sulphate solution S before being
passed as wet potassium sulphate T to the drier 1~, from
which the product X2SO4 is obtained~
Referring now to Figure 2, syngenite 136, recycle
solution 1~8 and the appropriate amount of fresh nitric acid
137 are reacted in syngenite decomposition vessel 138.
Suitable temperatures for the acid decomposition of syngenite
are in the range of ambient to boiling, with temperatures
above 70C preferred. Eighty degrees centrigrade (80C) or
- 14 -
7C~7
above are the most preferred temperatures. The reaction
goes to completion at atmospheric pressure, usually requiring
a time of about 5 minutes to 2 hours.
The slurry of calcium sulphate 140 so produced is
separated, for example, by filtration, in first stage
separator 142. The calcium sulphat~ solids 144 are washed
at 132 with water 134 and the washings 139, recycled through
evaporator 146 as part of solution 148 to vessel 138. The
washed calcium sulphate 130 is discarded to recycled to
syngenite synthesis, as appropriate.
The solution 143 separated in 142 is reacted in
the second stage calcium sulphate precipitator 152 with the
appropriate amounts of calcium carbonate, calcium hydroxide,
or calcium nitrate 150. The slurry of calcium sulphate 154
so produced is separated, for example, by filtration, in
second stage separator 156. The calcium sulphate 158 is
washed at 150 with water 162 and discarded, or recycled to
syngenite preparation as appropriate at 164. The wash
liquor 161 is recycled through evaporator 146 as part of
solution 148 to syngenite decomposition vessel 138.
The separated solution 180 is cooled in crystallizer
182 to crystallize solid potassium nitrate which is separated
from the mother liquor in the slurry 184 in separator 186.
The solution 180 is typically cooled in crystallizer 182 to
a temperature in the range of about 0C to 45C, more
typically in the range of about 0C to 30C. The preferred
range is about 0C to 20C. The filtrate 198 is recycled
through evaporator 146 as part of solution 148 to syngenite
decomposition.
In Figure 3~ syngenite 236 and recycle solution
248 are reacted at the same temperatures as in Figure 1 with
the equivalent amount of calcium nitrate 237 in syngenite
decomposer 238. The slurry of calcium sulphate 240 so
produced is fed to separator 242 where the calcium sulphate
- 15 ~
~ \
244 is removed and washed with water 234 at 232 before being
discarded or recycled, for example, to syngenite preparation
230.
The wash liquor 239 is fed to evaporator 246 and
thence as part of recycle solution 248 recycled to 238.
The solution 254 separated from the calcium
sulphate is now cooled in crystallizer 282 to crystallize
potassium nitrate. The crystallizer 282 is operated at the
same temperatures as the crystallizer 182 in Figure 1. The
slurry of potassium nitrate 284 so p~oduced is separated in
separator 286. The mother liquor 298 is fed to evaporator
246 before being recycled as part of solution 248 to syngenite
decomposition 238. The potassium nitrate produced is washed
and dried as appropriate to yield KNO3 crystals 296.
Having generally described the invention, a better
understanding can be obtained by reference to certain specific
preliminary examples, which are provided herein for purposes
of illustration only and are not intended to be limiting
unless otherwise specified.
Example 1
This example shows that potassium chloride and
sodium sulphate can be used to prepare syngenite.
A saturated solution of potassium chloride was
prepared by dissolving 859 grams of potassium chloride in
2500 grams water at 23C. To this solution was added 115
grams potassium chloride, 216.5 grams sodium sulphate and
186 grams anhydrous calcium sulphate. This mixture was
reacted at 23C for two hours. The slurry was filtered, and
the product washer and dried. The product contained 22.3%
potassium and 60.43~ sulphate. The 414.2 grams of dried
product represents a yield of 92.3~ based on the calcium
sulphate.
~ 16 -
7()~7
E _ ple 2
This example demonstrates that ammonium sulphate
can be used for the preparation of syngenite by reaction
with potassium chloride and calcium sulphate.
A calcium sulphate slurry was prepared by adding
77 grams of calcium hydroxide to 730 grams of water and
reacting this mixture with 101.6 grams of concentrated
sulphuric acid (97~) and cooling to 10C.
Syngenite was prepared from the above mixture by
adding 149.1 grams potassium chloride, 132 grams ammonium
sulphate and 520 grams additional water. This mixture was
stirred for one hour at 10C, filtered, and the product
washed with approximately 600 grams water.
The washed product, after drying, weighed 266.9
grams (81% yield), and had potassium, sulphate, calcium,
ammonium (as nitrogen) and chloride ion contents of 18.46~,
62.65%, 14.17~, 0.0% and 0.07%, respectively. This represents
100% conversion based on potassium, allowing for the potassium
sulphate remaining in the solution and washings, in equilibrium,
with the syngenite.
Example 3
This example illustrates that syngenite can be
prepared from a sylvinite leach liquor mutually saturated
with potassium and sodium chloride, containing potassium
chloride, sodium chloride and water contents of 20%, 17.5%
and 62.5%, respectively.
One kilogram of the above clear solution at 80C
was placed in a reactor and to it was added, in order, 71
grams sodium sulphate and 6~ grams calcium sulphate~ The
mixture was reacted at 80C for 30 minutes, then cooled to
23C. The total reaction time was about two hours~ The
reaction slurry was filtered, washed and dried. The dried
product, 140.7 grams, contained 22.3% potassium, 59.1%
7~7
sulphate and 0% chloride ion. The 140.7 grams of product
represents a 96% yield based on the calcium sulphate.
Example 4
This e~ample shows that syngenite can be effectively
decomposed with sulphuric acid.
Filtrate solution, 476 grams, from a prior decomposition
containing 29.2% potassium sulphate and 14.7% sulphuric acid
was reacted with 47.9 grams sulphuric acid (97%) and 140
grams syngenite for 2 hours at lOO~C, the resultant slurry
was filtered hot (90C). The residue was washed and dried
to yield 43.2 grams of calcium sulphate solids containing
2.6% potassium, 64.2% sulphate and 0% chloride. The decomposition
efficiency, when adjusted for 5.9 grams of potassium sulphate
that was contained in the solution held by the wet gypsum
residue before drying, was about 100%.
r
Example_5
This example shows that nitric acid will also
decompose syngenite. 241 grams of syngenite was reacted
with 500 grams of a 1.51 molar HNO3 acid solution containing
48.3 grams of HNO3 for 2 hours at 60C.
The resultant slurry was -filtered, the 166 grams
wet solids were washed and dried. The 116.8 grams of dry
solids contained 9.5~ potassium and 63.9% sulphate. The
decomposition efficiency to calcium sulphate under these
conditions was 81% based on the potassium remaining in the
decomposition residues, and, to the penta salt, 95%.
Example 6
This example demonstrates the crystallization of
double salt, K3H(SO4)2, from solutions with a sulphuric acid
to potassium sulphate molar ratio of 1 to 1/ equivalent to
potassium bisulphate. 300 grams of potassium sulphate and
~7~
180.9 grams of sulphuric acid (94%) were dissolved in 519.1
grams water at 50C. The solution was cooled to 0C and the
solids which crystallized were removed by filtration to
yield 283.6 grams wet solids, which, on drying, yielded
260.8 grams dry crystals of the double salt, analyzing K,
40.1%, and SO4, 61.8~. (K3H(SO4)2 required K, 37.7%; SO4
61.9%). Yield based on potassium sulphate, 77.8%.
Example 7
This example illustrates the isothermal crystalliza-
tion of K2SO4 from K3H(SO4)2 solution at 30C. K3H(SO4)2,
250 grams, is added to water, 200 grams, at 30C and the
slurry so produced agitated for 2 hours. At the end of this
time, the solids were removed by filtration and dried, to
yield, after water washing, 148.9 grams dry solids analyzing
K, 44.4%, SO4 54.7%. (K2SO4 requires K, 44.8%; SO4, 55.2%).
The mother liquor contained K 8.4%, and SO4 19.9%, corresponding
to 26.2 grams K2SO4/100 grams H2O and 13.7 grams H2SO4/100
grams H2O.
Example 8
This demonstrates the separation of potassium
sulphate crystals from solutions of the double salt, K3H(SO4)2.
225 grams of the double salt produced in Example 6
were dissolved in 250 grams of water at approximately 100C.
When cooled to 0C, the solution yielded 152.4 grams wet
potassium sulphate crystals which gave a dry weight of 144.3
grams of material analyzing K, 44.9% and SO4, 54.9%. (K2SO4
requires K, 44.8%; SO4 55.2%). Yield based on potassium
sulphate, 72.0%.
-- 19 --
.
Example 9
This example demonstrates that a solution from a
prior syngenite preparation can be regenerated b~ leaching a
sylvini~e-type ore composite, prior to reuse.
845.~ grams of a solution containing 6% potassium,
0.91% sulphate and 17.2~ chloride or approximately 11.5~ KCl
and 20% NaCl was mixed with 175 grams potassium chloride,
and 132 grams of sodium chloride at 80C for 1 hour. The
slurry was filtered yielding 253.3 grams wet solid and 831.9
grams of solution. The wet solid was dried to 244 grams and
contained 21.8% potassium, 2.11% sulphate and 55.0% chloride.
The resultant leach solution contain2d 10.2~ potassium,
19.5% chloride and 0.8% sulphate or 19.4% KCl and 16.9%
NaCl.
This solution composition, as shown in Example 3,
is satisfactory for syngenite preparation.
Example 10
This example shows the use of nitric acid and
calcium carbonate.
Syngenite, 256g., containing 67g. K was agitated
at 100C for two hours in a solution of nitric acid containing
155g of 69% HNO3 nitric acid and 345g. water. The calcium
sulphate produced was removed by filtration and, after
washing with water and drying, weighed 113g. (the washings
were discarded). The mother liquor, 535g., was neutralized
with stirring, to pH 7, by the addition of calcium carbonate
at 50C. Filtration of the slurry so produced yielded 89g.
of dry, washed calcium sulphate and 306g. of filtrate ~the
washings were discarded), which on cooling to 0C yielded
67g. wet potassium nitrate crystals, which dried to 61.5g.
of product analyzing K, 38.23% (KNO3 required K, 38.67%).
-- 20 -
Example 11
This example shows the use of nltric acid and
calcium nitrate. Syngenite, 149g., was agitated at 100C
for two hours with a solution of nitric acid, 137g., at 69%
in 458g. water. The calcium sulphate so produced was removed
by filtration and after washing and drying, weighed 52g.
(the washings were discarded). Mother liquor, 593g., was
agitated for thirty minutes with 147.5g. of Ca(NO3)2 4H2O
(calcium nitrate tetrahydrate) at 50C. Filtration of the
slurry so produced yielded 54g. of dry, washed calcium
sulphate and 574g. of filtrate ~the washings were discarded).
On cooling to 0C, the solution yielded 70g. of wet potassium
nitrate crystals, which dried to 38.5g. product analyzing K,
38.5~ IKNO3 requires K, 38.67%).
Example 12
This example shows the direct decomposition of
syngenite using calcium nitrate.
Syngenite, 149g., was agitated at 100C for two
hours with a solution of calcium nitrate tetrahydrate,
147.5g., in 500g. water.
The calcium sulphate produced was removed by
filtration and, after washing with water and drying, weighed
122g. The washings were discarded. After coolin~ to 0C,
the filtrate, 426g., yielded 33.7g. of wet crystals which,
on drying, yielded 25.2g. of potassium nitrate, analyzing K,
38.1%.
Having now fully described the invention, it will
be apparent to one of ordinary skill in the art that many
changes and modifications can be made without departing from
the spirit and scope of the invention as set forth herein.
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