Note: Descriptions are shown in the official language in which they were submitted.
CA 02892542 2015-05-22
1
TITLE OF THE INVENTION
Method and system for sonic-assisted production of fertilizers
FIELD OF THE INVENTION
[0001] The present invention relates to fertilizers. More
specifically, the present
invention is concerned with a method and a system for sonic-assisted
production of fertilizers.
BACKGROUND OF THE INVENTION
[0002] Potassium is an essential component in fertilizers. The most
abundant source
of potassium is potassium chloride (KCI), sometimes referred to as potash.
However in the case of
intensive cultures, which typically require repeated applications of
fertilizers, potassium chloride as
such cannot be used because of the associate chloride that can sterilize the
soil if present in too
large amounts. In those circumstances, potassium sulfate (K2SO4) rather than
potassium chloride
(KCI) is used.
[0003] Magnesium is also an element required by some cultures, such as
tobacco,
potatoes or corn for example. With such crops, it has been found useful to use
a naturally occurring
mixed sulfate of potassium and magnesium such as langbeinite (K2SO4 . 2MgSO4),
known as SOPM.
However, the increased uses of SOPM, along with the depletion of natural
sources of this naturally
occurring mineral, have led to using a synthetic potassium sulfate mixed with
magnesium sulfate so
as to duplicate the naturally occurring SOPM.
[0004] Another important agronomic element is phosphorus. A source of
phosphorus
is a fluorophosphate of calcium (Ca5(PO4)3F) referred to as apatite, which
cannot be used as a
fertilizer because of its insolubility. However, treatment with sulfuric acid
removes some calcium from
the apatite and the resulting mixture of calcium monobasic phosphate,
Ca(H2PO4)2 and gypsum is
then a convenient source of agronomic phosphorus, referred to as
superphosphate. More refined
sources of phosphorus can be obtained with pure phosphoric acid. However, this
acid is very costly
because of the complexity of its preparation, either from acid treatment of
apatite or via the reduction
CA 02892542 2015-05-22
2
of apatite to elemental phosphorus, followed by oxidation to P205 and
hydrolysis. Potassium salts of
phosphoric acid can be prepared using phosphoric acid and a source of
potassium such as potash
(KCI). But the reaction is difficult and generates mixtures of hydrochloric
and hydrofluoric acids along
with other undesirable substances. For these reasons as well as due to the
high priced phosphoric
acid, the end product is too costly for agronomic uses.
[0005] There is still a need in the art for a method for producing
fertilizers.
SUMMARY OF THE INVENTION
[0006] More specifically, in accordance with the present invention,
there is provided a
method for the production of a potassium-based fertilizer, comprising reacting
a source of
magnesium or phosphorus with potassium acid sulfate in a slurry submitted to
sonication.
[0007] There is further provided a method for the production of mono-
or di-
potassium phosphate by reacting, under sonication, apatite with potassium acid
sulfate in a slurry.
[0008] There is further provided a method for the production of
sulfate of potassium
and magnesium by reacting, under sonication, magnesium silicate with potassium
acid sulfate
solution in a slurry.
_
[0009] There is further provided a method for the production of
potassium ammonium
phosphate, comprising reacting a source of phosphorus with potassium acid
sulfate in a slurry
submitted to sonication, yielding monopotassium phosphate, and reacting the
resulting
monopotassium phosphate with ammonia.
[0010] There is further provided a method, comprising: a) producing
potassium acid
sulfate by reacting potash with sulfuric acid; b) recovering hydrochloric acid
produced during step a);
and c) reacting a source of magnesium or phosphorus with the potassium acid
sulfate in a slurry
submitted to sonication, thereby producing a potassium-based fertilizer.
CA 02892542 2015-05-22
3
[0011] Other objects, advantages and features of the present invention
will become
more apparent upon reading of the following non-restrictive description of
specific embodiments
thereof, given by way of example only with reference to the accompanying
drawings.
DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0012] The present invention is illustrated in further details by the
following non-
limiting examples.
[0013] Potassium acid sulfate (KHSO4) is produced by the treatment of
potash (KCI)
with sulfuric acid (H2SO4), according to reaction 1 below, by substitution of
the first hydrogen of
sulfuric acid (H2SO4) with potassium, yielding potassium acid sulfate (KHSO4),
at a temperature
comprised within the range between 120 and 130 C. Interestingly, hydrochloric
acid (NCI) is also
produced, which may be recovered as a secondary sellable product.
[0014] KCI + H2SO4 --- KHSO4 + HCI (1)
[0015] Potassium acid sulfate (KHSO4) is then used for producing
fertlisers such as
monobasic potassium phosphate and SOPM, according to reactions (2) and (3)
below.
[0016] Reaction 2 below describes the reaction of potassium acid sulfate
(KHSO4)
with apatite:
[0017] 3KHSO4 + 2H2504 + Ca5(PO4)3F + 10H20 ¨> 3KH2PO4 + 5CaSO4.2H20 + HF
(2)
[0018] Reaction 3 below describes the reaction of potassium acid sulfate
(KHSO4)
with magnesium silicate:
CA 02892542 2015-05-22
4
[0019] 2KHSO4 + 2(3Mg0.2Si02.2H20) + H2SO4¨ 4(MgO.Si02) +
K2SO4.2MgSO4 +
6H20 (3)
[0020] These reactions were performed at near ambient temperature,
i.e. at a
temperature comprised in a range between 1000 and 50 C, under atmospheric
pressure and with a
content of solid mineral in the slurry of mixed potassium acid sulfate and
sulfuric acid (KHSO4/H2SO4)
comprised in a range between 10 and 40% w/w. By submitting the reactants to
sonication during the
reactions, yields of the order of 95 to 99% of desired products, i.e.
monobasic potassium phosphate
and SOPM respectively, after contact times as short as one minute, were
obtained.
[0021] Sonication of the reactants during the reactions can be
achieved by using
ultrasonic piezogenerators or mechanically by hydrodynamic cavitation. Both
methods were tested
successfully, to generate micro-bubbles in the reacting slurry either by
immersing a sonic probe or by
generating cavitation in the reacting slurry. The resulting soluble
fertilizing elements, i.e. monobasic
potassium phosphate (KH2PO4) in the case of reaction 2 and SOPM (K2SO4.2MgSO4)
in the case of
reaction 3, can be isolated by filtration and separation from residual
insoluble products reactions 2
and 3 respectively, i.e. gypsum and magnesium silicate respectively.
[0022] Crystallization allows obtaining pure monobasic potassium
phosphate and
pure SOPM respectively. In some cases, the produced monobasic potassium
phosphate and SOPM
are used as concentrated solutions rather than solids.
[0023] In the case of monobasic potassium phosphate (KH2PO4), the
second proton
on the phosphate group can be combined with ammonia (NH3) to produce potassium
ammonium
phosphate as described by reaction 4 below:
[0024] KH2PO4 + NH3¨* K(NI-14)HPO4 (4)
[0025] Dibasic
potassium phosphate (K2HPO4) may be obtained with sonic treatment
CA 02892542 2015-05-22
of apatite using a larger amount of potassium acid sulfate as described by
reaction 5 below:
[0026] 6KHSO4 + 1,5 Ca(OH)2 + Ca5(PO4)3F + 9H20 --3K2HPO4 +
6CaSO4.2H20 +
0.5CaF2 (5)
[0027] The results of the reactions of potassium acid sulfate (KHSO4)
with
magnesium silicate and with apatite were unexpected. Indeed, standard methods
use concentrated
sulfuric acid (H2SO4) and conditions of high temperature and/or pressure.
Potassium acid sulfate
(KHSO4) being a relatively very weak acid when compared to sulfuric acid
(H2SO4), it was not an acid
that was contemplated in the art.
[0028] As known in the art, due to the significant difference between
the ionization
constants K1 and K2 of the two hydrogens of sulfuric acid (H2SO4), with Ki. 4
X 10-1 and K2= 1.2 X 10-
2, involving the second hydrogen of sulfuric acid (H2SO4) in a combination
with potassium to yield
potassium sulfate (K2SO4) from potash (KCI) is more difficult. Thus potassium
sulfate (K2SO4) is
produced under severe conditions, mainly using the Mannheim process, which is
the reaction of
potassium chloride with concentrated sulfuric acid at high temperatures,
typically of at least 500 C.
[0029] Similarly, in the reaction between sulfuric acid (H2SO4) and
magnesium silicate
(3Mg0.2Si02.2H20) to yield magnesium sulfate (Mg504), obtaining a full
substitution of both
hydrogens of sulfuric acid (H2SO4) by magnesium typically requires pressure
leaching of the silicates
at a temperature of at least 200 C.
[0030] Sulfatation of apatite (Ca5(PO4)3F) with sulfuric acid (H2SO4)
also requires high
temperatures.
[0031] Since potassium acid sulfate (KHSO4) is a relatively very weak
acid when
compared to sulfuric acid (H2SO4), considering that conditions of high
temperature and/or pressure
are required for reacting a mineral such as magnesium silicate or apatite with
sulfuric acid (H2SO4)
CA 02892542 2015-05-22
6
as described hereinabove, it was not expected that substituting potassium acid
sulfate (KHSO4) to
sulfuric acid (H2SO4) in these reactions would facilitate these reactions.
[0032] The present invention provides a method for producing chloride-
free fertilisers,
comprising reacting potassium acid sulfate with a source of magnesium or
phosphorus in a slurry
submitted to sonication during a time of the order of the minute, i.e.
comprised in a range between
30s and 2 minutes.
[0033] By blending of the products of reactions 2-5 above, namely,
monobasic
potassium phosphate, SOPM, potassium ammonium phosphate and dibasic potassium
phosphate,
all obtained under very mild conditions and fast rates as described
hereinabove, fertilizers adapted to
the nature of the corps and the properties of the soils, free of undesirable
elements such as chlorine
and non-soluble product such as gypsum, are produced, at lower costs than
existing methods.
[0034] Without limitation to the scope of the method, the following
examples illustrate
the implementation of the present invention.
[0035] First, potassium acid sulfate may be produced as per reaction 1
hereinabove.
One mole of potassium chloride (74.56 g) was placed in a one-liter reaction
flask and one mole of 98
`)/0 sulfuric acid (100.0 g) was added to it in the flask over a period of
half an hour, There was an
evolution of hydrochloric acid, which was cooled in a condenser and adsorbed
in 200 ml of water
cooled to a temperature in a range between 0 and 2 C. After addition of the
sulfuric acid, the
temperature of the reaction flask was raised to a temperature in a range
between 120 and 130 C in a
sand bath and was maintained in this temperature range while 100 ml of water
was added slowly, i.e.
over a period of two hours, to the system in the reaction flask. The
distillate resulting from this water
addition was then combined to the 200 ml of cold water and the HCI content was
determined by
titration, 35.9 g of HCI or 98.4 % of the expected acid being thus recovered.
The residual solid in the
reactor was potassium acid sulfate, 136.5 g.
Example 1: production of SOPM (reaction 3)
CA 02892542 2015-05-22
7
[0036] To a solution of 0.2 mole of potassium acid sulfate KHSO4 (27.2
g), 0.1 mole
of sulfuric acid (10.0 g of H2SO4, 98 %) in 200 ml of water in a 300 ml
beaker, was added 100 g of
hydrated magnesium silicate (serpentine: 3Mg0.2S102.2H20) 100 % minus 60 mesh.
This slurry was
stirred at a temperature in a range between 25 and 5000 while being submitted
to a sonic treatment
at 24 KHz for a period of 15 minutes, using a Hielscher apparatus, model 400S
with a 7 mm titanium
probe, 75 % power setting. The reaction mixture was then filtered, washed with
water and the
combined washing and filtrate was evaporated and recrystallized in water. The
solid 40.9 g was
submitted to elemental analysis and corresponds to the formulation
K2SO4.2MgSO4, a mixed sulfate
of potassium and magnesium known as langbeinite or SOPM. The potassium
recovery in the form of
langbeinite was 98.5 %.
Example 2: preparation of potassium phosphates (reactions 2, 4, 5)
[0037] Potassium acid sulfate, 0.3 mole, 40.8 g, was dissolved in 200
ml of water
along with 0.2 mole, 20 g, of 98 % sulfuric acid. In this solution, in a 300
ml beaker, 50.4 g of apatite
(0.1 mole) was slurried by stirring at 25-50 C. Then sonication was applied,
using the Hielscher
equipment described in Example 2. After a 15-minutes contact under sonication,
the mixture was
filtered, and the solid was rinsed with water. The solution was submitted to
elemental analysis for
potassium, phosphates and sulfates. The results indicated that reaction had
involved 13 % of the
potassium as K2HPO4, 84.4 % of the potassium as KH2PO4 and only 2.6 % as non-
reacted KHSO4.
Therefore, this conversion of potassium acid sulfate to potassium phosphates
is 97.4 %. A 100 ml
solution of mono potassium phosphates (13.6 g, 0.1 mole) treated with 0.5 mole
of ammonium
hydroxide (17 g NH4OH) in 150 ml of water. Upon evaporation, the residual
solid, 14.9 g, indicated a
near-complete (97 %) transformation of KH2PO4 into K(NH4)HP0.4 as per the
elemental analysis.
Example 3: production of SOPM (reaction 3)
[0038] In a solution of 272.3 g of KHSO4 and 100.0 of H2SO4 in 3 I of
water, 554.22 g
of magnesium silicate (serpentine, 3Mg0.2Si02.2H20) was slurried at 50 C while
being submitted to
sonication by hydrodynamic cavitation (RAPS Technology System). Sampling at
five minutes periods
CA 02892542 2015-05-22
8
indicated that the reaction was completed after less than 5 minutes.
[0039] A one-liter aliquot of the treated material was
filtered and the filtrate
evaporated to dryness. The elemental analysis for K, Mg, and S indicated the
presence of the
expected product, K2504.2MgSO4, 137.0 g or 99 % yield. Upon recrystallization,
leonite
(K2SO4.MgSO4) was obtained.
Example 4: production of phosphate of potassium (reaction 2)
[0040] In a solution of 408.5 g of KHSO4 (3 moles) and 200 g
of H2SO4 98 % (2
moles) in 3 liters of water was slurried 504.3 g of apatite (Ca5(PO4)3F, one
mole) at 45 C while being
submitted to sonication by hydrodynamic cavitation (RAPS Technology System).
Samplings after 2
minutes periods indicated that the reaction was completed after about one
minute; in fact, after 30
seconds 90% of the phosphorus was already in solution to give monobasic
potassium phosphate
(KH2PO4) with a slight excess of free phosphoric acid.
[0041] It was thus shown that by using sonic treatment,
potassium acid sulfate could
be reacted very rapidly at low temperature with near quantitative yield with
magnesium silicate and
apatite, to give the corresponding potassium magnesium sulfate or potassium di-
hydrogen
= phosphate respectively.
[0042] There is thus provided a method for producing
potassium salts, either sulfate
= (see reaction 3 above) or phosphate (see reactions 2, 4, 5 above), that
can incorporate one or more
other agronomic elements such as phosphorus, nitrogen, magnesium and sulfur,
these potassium
salts being deprived of adverse elements such as chloride, or insoluble
components such as
gypsum. There is thus provided a method for producing useful fertilizers,
fairly soluble in water as
required by intensive cultures such as aquaculture or drop watering.
[0043] There is provided a method for producing a chlorine-
free mixed sulfate of
CA 02892542 2015-05-22
9
potassium and magnesium (see reaction 3 above) or a phosphate of potassium
(see reactions 2, 4, 5
above) free of insoluble material, by using potassium acid sulfate as the
source of potassium. The
method comprises reacting, under sonic treatment, potassium acid sulfate with
a source of
magnesium, such as magnesium silicate for example, or with a source of
phosphorus, such as
apatite for example, to obtain a mixed sulfate of potassium and magnesium
(K2SO4.2MgSO4) or
potassium phosphate (KH2PO4) respectively. Under sonic treatment during the
reactions, potassium
acid sulfate yields fast and complete reaction with these minerals, at near
ambient temperature and
under atmospheric pressure, opening a new and much simplified access to mixed
sulfate of
potassium and magnesium, or phosphate of potassium.
[0044] There is thus provided a method for production of potassium-
based fertilizers
by a sonication-assisted reaction of potassium acid sulfate with a source of
magnesium or
phosphorus.
[0045] The source of magnesium may be a finely ground magnesium
silicate, i.e.
ground to 40-100 mesh, for example to 50 mesh.
[0046] The source of phosphorus may be a finely ground, i.e. ground to
40-100
mesh, for example to 50 mesh, phosphate of calcium, i.e. apatite.
[0047] The sonic assistance may be provided using an ultrasonic
piezogenerator or
by hydrodynamic cavitation.
[0048] The reaction is conducted in a temperature range comprised
between 10 and
50 C, under atmospheric pressure, in a water slurry.
[0049] There is provided a method for the production of mono or
dipotassium
phosphate by reacting, under sonic treatment, a potassium acid sulfate
solution with apatite slurried
in the acidic solution. There is further provided a method for the production
of potassium ammonium
CA 02892542 2015-05-22
phosphate by reaction of the produced monopotassium phosphate with ammonia.
[0050] There is provided a method the production of SOPM by reacting,
under sonic
conditions, a potassium acid sulfate solution with magnesium silicate slurried
in the acidic solution
[0051] The scope of the claims should not be limited by the
embodiments set forth in
the examples, but should be given the broadest interpretation consistent with
the description as a
whole.
