271
THE CURRENT STATUS OF RESEARCH ON THE METHODS USED TO
OBTAIN MONOPOTASSIUM AND MONOCALCIUM PHOSPHATE.
1
Shaymardanova M.A.,
2
Toshmamatov O.A.,
3
Khodjamkulov S.Z
4
Nomozov A.K
5
Boltaboyev O. E,
6
Eshkoraev S. S
1,2,3,4,5,6
Department of Chemical Engineering, Termez State University of Engineering
and Agrotechnologies. Termez, 190111 Uzbekistan
.
Abstract.
The need to provide food and drinking water to the world's population is developing
urgently due to the planet's rapidly expanding population and the loss of arable and irrigated land.
At the start of the twenty-first century, this issue is still unsolved despite the tremendous
advancements in agriculture and cattle farming. Increasing the productivity of livestock, poultry,
and fish farming as well as the production of agricultural products is one of the best strategies to
address this issue. The production and variety of potassium and NPK fertilizers without chlorine,
as well as feed calcium phosphates, are on the rise in practically all industrialized nations
worldwide.
Keywords:
Central Kyzylkum, monocalcium, monopotasium phosphate, NPK fertilizers.
Analysis of existing methods for the production of potassium phosphates
The main methods for producing potassium dihydrogen phosphate are the interaction of
phosphoric acid with calcium-containing compounds, ion exchange and conversion
methods.
When phosphoric acid reacts with salts and potassium hydroxide, the following reactions
occur:
H
3
PO
4
+ K
2
CO
3
= 2KH
2
PO
4
+ CO
2
+ H
2
O
H
3
PO
4
+ KCl = KH
2
PO
4
+ HCl
H
3
PO
4
+ KOH = KH
2
PO
4
+ H
2
O
Modern production of phosphorus salts, as a rule, is based on multi-stage processes,
including the production of phosphoric acid, its neutralization to the corresponding
hydrogen phosphates, their isolation, drying and dehydration [59]. Commonly used are
potash or potassium hydroxide and phosphoric acid. As a result, the fertilizer is expensive
272
and the scale of its production is small. Even the agricultural need for fertilizers for
greenhouses is not met[60].
Currently, the production of feed, food and reactive salts of phosphoric acid is based on
the use of thermal phosphoric acid, obtained by electrothermal method at a temperature
of 1600-1800°C [61]. These industries are energy-intensive, which, in light of the
continuous rise in energy prices, leads to an increasing decrease in their profitability.
To obtain pure salts of potassium dihydrogen phosphate, thermal phosphorus, purified
EPA is used or the process is carried out in an environment of organic reagents [62].
There is a known method for producing potassium dihydrogen phosphate by reacting TPA
with potassium hydroxide, in which potassium hydroxide is preliminarily purified from
insoluble impurities, poured into a crystallizer and, with stirring, TPA is introduced to pH
5.8-6, the solution is cooled to a temperature of 15-20°C and dihydrogen phosphate
crystals are separated potassium [63].
Purification of EPA from accompanying impurities is a complex and relatively expensive
method for producing acid. Purification of EPA can be carried out by evaporation and
stripping with superheated steam, precipitation in the form of poorly soluble compounds,
ion exchange, sorption methods, using organic solvents [64].
Therefore, the most promising methods for producing potassium dihydrogen phosphate
are methods based on the use of EPA without preliminary purification.
A method has been developed for the production of potassium dihydrogen phosphate by
the interaction of EPA with potassium chloride in an aqueous-alcoholic medium [65]. A
method for producing potassium dihydrogen phosphate is described, including the
interaction of EPA and potassium chloride in a molar ratio of 2:1 at a temperature of 70-
145°C, grinding the resulting mass, extraction of excess acid with a boiling organic
solvent and subsequent drying at a temperature of 80-100°C. Aminol, acetone, and N-
butanol are used as organic solvents. There are methods for producing potassium
dihydrogen phosphate using crude EPA [66]. The essence of the method is the
neutralization of EPA with potassium carbonate (potash) at a stoichiometric rate to pH
3.5-4.5 at a temperature of 80-90°C, separation of the resulting mixture at a temperature
of 70-80°C and crystallization of potassium dihydrogen phosphate from a solution at a
temperature of 15 -20°C.
A method has been developed in which EPA is used together with TPA, which involves
mixing 52-54% phosphoric acid with potassium chloride at a mass ratio of 2:1 and heating
to 265°C [67]. The resulting mixture is dissolved in water until a saturated solution is
273
obtained, water-insoluble impurities are separated by filtration and potassium dihydrogen
phosphate is crystallized.
There is a known method for producing chlorine-free monopotassium phosphate, which
includes neutralization of EPA with a solution of potassium carbonate to pH 3.8-4.5 at a
temperature of 70-78°C, separation of the resulting mixture by filtration, subsequent
crystallization and separation of the finished product upon cooling [68]. The mother liquor
is returned to the potassium carbonate dissolution stage.
The ion exchange method for producing potassium dihydrogen phosphate consists of a
heterogeneous reaction between a solid phase cation and a liquid phase cation exchanger
in columns filled with a cation exchanger [69]. When treating a cation resin with
phosphoric acid in the columns, the interaction occurs according to the following scheme:
H
3
PO
4
+ RK = RK + KH
2
PO
4
with the formation of potassium dihydrogen phosphate. To restore the cation exchanger,
a solution of potassium chloride is passed through the column according to the scheme
RH + KCl = RK + HCl.
The resulting solution is evaporated at the first stage, the potassium dihydrogen phosphate
crystals are separated while cooling and dried.
This method of producing potassium dihydrogen phosphate has not found widespread use,
although it is quite simple technologically due to the production of dilute solutions of
potassium dihydrogen phosphate, the use of TPA and the need to dispose of hydrochloric
acid solutions.
Condensation methods are based on the interaction of purified solutions of phosphoric
acid salts and calcium-containing compounds, mainly potassium chloride. Ammonium
phosphates are most widely used as phosphate salts, the interaction of which with
potassium chloride proceeds through the following reactions:
NH
4
H
2
PO
4
+ KCl → KH
2
PO
4
+ NH
4
Cl
(NH
4
)
2
HPO
4
+ KCl → K
2
HPO
4
+ 2NH
4
Cl
When using sodium dihydrogen phosphate, the process is carried out according to the
reaction:
NaH
2
PO
4
+ KCl → KH
2
PO
4
+ NaCl
These reactions are reversible and depend significantly on the solubility of the salts used.
The solubility of potassium dihydrogen phosphate in water is significantly lower than the
solubility of ammonium and sodium dihydrogen phosphates, and when they are present
274
together in saturated solutions at high temperatures upon cooling, potassium dihydrogen
phosphate will precipitate first.
There is a known method for producing potassium dihydrogen phosphate, which involves
the interaction of a solution of ammonium phosphate containing 16-20% P
2
O
5
, obtained
by leaching ammophos from apatite concentrate, with potassium chloride at a molar ratio
of K
+
:NH4
+
at 95°C equal to (0.75-1):1 ) until complete dissolution, followed by filtration,
cooling to 20°C and separation of crystals [70]
There is a known method for producing a complex fertilizer by the interaction of
potassium chloride and solutions of ammonium phosphate at a molar ratio (1.0-1.3): 1 and
a temperature of 35-85 ° C, followed by crystallization of monosubstituted potassium and
ammonium phosphates at a temperature from 0 to -5 ° C [71].
There is a known method for producing complex fertilizer by reacting a solution of
ammonium phosphate with a concentration of 16-20% P2O5, obtained by leaching
ammophos with water at a temperature of 20-60°C and potassium chloride at a ratio of
K
+
:NH
4
+
= (0.75-1):1 [72]. Crystallization is carried out at a temperature of 10-20°C, the
resulting precipitate is washed with a solution of ammonium phosphate with a
concentration of 16-20% P
2
O
5
.
It has been established that the interaction of ammonium phosphate and potassium
chloride in aqueous solutions results in the formation of mixed crystals of potassium
ammonium phosphates [73]. Potassium ammonium phosphate is obtained on the basis of
evaporated apatite EPA and ammophos, by leaching with water. Precipitates of potassium
ammonium phosphate have high humidity, which varies from 11.5 to 25.9% and is a
saturated mother solution. Since the saturated solution contains chlorine and undesirable
impurities, they pass into the product during the drying process, contaminating it.
Conclusions
From a critical analysis of literary sources it is clear that there are a large number of
methods for purifying products to obtain especially pure inorganic substances. Often, the
use of one or another method is limited to its selective purification from certain impurities.
The most effective among the described methods, which allows deep and complete
purification of various substances, both from anions and cations, is the recrystallization
method. A generalization of literature data related to the production of feed and purer
calcium orthophosphates from phosphate raw materials from various deposits indicates
275
the need to purify the resulting solutions from accompanying impurities of phosphorites
and especially from fluorine.
The production of calcium salts is based on the acid decomposition of phosphate raw
materials and subsequent processing of nitric acid solutions and EPA. Methods for
purifying EPA with organic solvents have become the most widespread, and precipitation
purification methods are gaining momentum. Purification of EPA by sedimentation of
existing impurities is safer and can be easily accomplished using existing equipment.
Mineral feed additives play a huge role in the development of livestock, poultry and fish
farming. The global range of basic mineral supplements includes more than 10 items.
Calcium, ammonium, and sodium phosphates are most widely used. The most valuable
are calcium phosphates. In feeds where there is a significant amount of calcium and
insufficient phosphorus, sodium phosphorus additives are used. To compensate for the
lack of protein in the diets of cattle and sheep, non-protein nitrogen-containing compounds
– ammonium phosphates – are used.
Neither potassium dihydrogen phosphate nor defluorinated monocalcium phosphate are
produced in the Republic. In connection with the above, the organization of production of
fertilizer chlorine-free potassium dihydrogen phosphate and feed grade monocalcium
phosphate from CC phosphorites is a problem that needs to be solved.
Acknowledgment
Authors thanks to
Termez State University of Engineering and Agrotechnologies for
support this research work.
Authors’ Declaration
-
Conflicts of Interest: None.
-
Conflicts of Interest: None.
-
We hereby confirm that all the Figures and Tables in the manuscript are ours.
-
No human studies are present in the manuscript.
-
Ethical Clearance: The project was approved by the local ethical committee at the
Termez Institute of Engineering and Technology and Termez State University.
276
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