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PURIFICATION OF PHOSPHORIC ACID BASED ON
PHOSPHORITES OF CENTRAL KYZYL KUM IN THE
PROCESS OF EXTRACTION WITH CALCIUM CARBONATE
AND OBTAINING FROM A SINGLE PHOSPHORUS
FERTILIZER
Abdulkhayev Yaxhoxon
Student of Namangan State Technical University
Ulashov Shakhbos
Student of Namangan State Technical University
Najmiddinov Rikhsitilla
Head of the Department of “Chemical Engineering”
of Namangan State Technical University, PhD
Tel:+99(894) 150 5891
e-mail: najmiddinov9191@gmail.com
https://doi.org/10.5281/zenodo.15558822
ARTICLE INFO
ABSTRACT
Qabul qilindi: 25-May 2025 yil
Ma’qullandi: 28-May 2025 yil
Nashr qilindi: 31-May 2025 yil
The work describes the processes of purification of
phosphoric acid based on phosphorites of the Central
Kyzylkum from impurities of fluorine and sulfates in the
process of extraction with calcium carbonate and the
production of single phosphorus fertilizer by
neutralizing the purified acid with calcium carbonate.
KEY WORDS
phosphoric
acid,
extraction
phosphoric
acid,
fertilizers,
mineral fertilizers, phosphorus
fertilizers, calcium carbonate,
monocalcium
phosphate,
dicalcium
phosphate,
double
superphosphate.
Introduction.
Fluorine compounds have a great harmful effect on the surrounding
environment. Studies show that fluorine not only has a negative effect on plants but also
causes various serious diseases in humans and other living organisms [1, 2].
Many plants have the ability to absorb large amounts of fluoride. For example, 57 to
1370 mg of fluorine is absorbed in 1 kg of tea and up to 4500 mg in cotton [2, 55 p.]. In this
case, fluorine accumulates in the cotton seed, and most of it passes into the cottonseed oil.
Studies show that when fluorine falls on the soil, including mineral fertilizers, the amount of
fluorine in the crop also increases [3, S. 10–18]. In the presence of nitrogen-phosphorus-
potassium fertilizers, the amount of fluorine absorbed by plants increases [4, S. 131–136].
Main part.
Phosphorous fertilizers are the main source of fluorine entering the soil. For example,
apatite and phosphorites contain an average of 3.0 and 2.7% fluorine, respectively.
Extractable phosphoric acid (WPPA) produced on the basis of Central Kyzylkum phosphorites
contains about 1.2% fluorine. The method of deposition from acid using alkali metals in the
form of silicon fluorides is not very effective, because the amount of silicon compounds
soluble in acid in EFK is practically very small [5, S. 34-40].
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During the processing of natural phosphates, the fluorine contained in them is
distributed between gas, liquid (WPPA) and solid (phosphogypsum) phases. 80-85% of the
raw materials (apatite and phosphorite) are converted into hydrofluoric acid during the
production of phosphoric acid according to the dihydric scheme, and during its further
processing, it becomes part of fertilizers.
In order to fully satisfy the demand for fertilizers in agriculture, the increase in the
production of phosphorus, especially complex fertilizers, creates a risk of fluorine saturation
of soil, plants and water bodies [6, P. 55]. The negative effects of fluorine compounds that fall
into the atmosphere and open water bodies and accumulate in living organisms and flora have
been sufficiently studied [3, S. 10-18; 4, S. 131-136; 7, S.42-47].
Sodium and potassium sulfates, chlorides, phosphates, carbonates, and hydroxides are
used to precipitate fluorine from WPPA in the form of silicon fluoride compounds of poorly
soluble alkali metals [8, S.191-206]. These methods are based on the chemical interaction of
the above salts with the fluorinated acid contained in WPPA. The level of fluoride removal
reaches 90%. According to this method, the level of fluorine removal in WPPA obtained from
Central Kyzylkum phosphorites does not exceed 38-40%.
The process of purifying WPPA based on Central Kyzylkum phosphorites with alkali
metal salts is sufficiently presented in literature sources. It is suggested to clean WPPA first
from sulfates and then from fluorine [9, S.2-4]. The process of defluoridation of WPPA based
on Central Kyzylkum phosphorites with sodium sulfate, dihydrophosphate, metasilicate was
thoroughly studied by the authors and it was shown that the level of fluorination can be
increased from 38-40% to 80-85%, and the technology of WPPA defluorination was created
[10; S. 16-19, 11; S. 8-11; 12; P.41-45].
Fluorinated WPPA can be made from unenriched raw materials of Central Kyzylkum [13,
B.32-39], calcium carbonate and oxide, washed enriched phosphorites [14; 156 p., 15-18]
with desulfation materials are also available. A patent was obtained for the method of
obtaining a nutrient precipitate by purifying WPPA from fluorine compounds and sulfates
[19]. However, there are no materials for simultaneous purification of the extraction slurry
from fluorine and sulfates in obtaining WPPA from Central Kyzylkum phosphorites.
Currently, the demand for phosphate raw materials in the world is 190 million tons or
43 million tons of Р
2
О
5
per year. The demand for phosphate raw materials is expected to grow
by 1.3 million tons by 2020 and by 2 million tons by 2030. By 2050, the demand for raw
materials will reach 220 million t of phosphate raw materials or 70 million t of Р
2
О
5
[20].
As a result of the increase in the demand for phosphorous fertilizers in agriculture and
the decrease of their stock from year to year as a result of the processing of phosphate raw
materials into phosphorous fertilizers, it is one of the urgent tasks of the present time to
include other types of raw materials in the production of phosphorous fertilizers along with
phosphate raw materials. Neutralization of extractable phosphoric acid (WPPA) produced
during the production of phosphorous fertilizers with natural carbonate raw materials gives
the opportunity to increase the volume of the product by 4-5%.
In addition, manufactured phosphorus fertilizers contain a large amount (up to 4%) of
fluorine. This has a negative impact on the ecological efficiency of fertilizers. In this regard, a
number of studies have been conducted on the treatment of fluorine from the received WPPA.
Defluorination of WPPA is carried out by three different methods [8, 19]: defluorination by
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acid evaporation; conversion of fluorine compounds in acid into water-insoluble compounds
and separation of these compounds from WPPA; separation of fluorine compounds in acid
using organic reagents. Purification of WPPA by these methods requires additional reagents
and bulky equipment, as well as significant capital costs.
That's why research aimed at researching the methods of simultaneously cleaning
WPPA from fluorine and sulfates is of great importance.
The purpose of this research work is to reduce the amount of fluorine and sulfates in the
extracted phosphoric acid by cleaning the extractive porridge (EB) with the help of calcium
raw materials - calcium carbonate before filtering, and to obtain high-quality phosphoric
fertilizers containing calcium and magnesium based on it.
For this, in the composition, og. in %: P
2
O
5
= 26,85; CO
2
= 3,14; CaO = 52,64; MgO = 1,03;
R
2
O
3
= 1,16; SO
3
= 2,31; F = 3,09; e.g. (insoluble residue) = 1,89 incinerated phosphate
concentrate was used.
Precipitation of fluorine and sulfates from extraction porridge was carried out with
calcium carbonate (c.t.) at the rate of 60-150% compared to the rate of formation of calcium
fluoride from calcium oxide and 80-100% compared to the rate of binding of SO
3
in the form
of calcium sulfate. The process of extraction of phosphoric acid with sulfuric acid was carried
out in the dihydrate mode, before filtering the resulting extraction slurry, fluorine and free
sulfuric acid were precipitated with calcium carbonate (k.t.).
The experiments were carried out in a continuous laboratory unit consisting of a two-
section extractor made of EI-943 steel, shielded and equipped with an electric heater layer.
Acid and phosphorite enter the device through the moderators. The working volume of the
device is 2.5 liters, and its productivity is 150 g of phosphate raw materials.
Phosphorite digestion was carried out in the dihydrate mode with sulfate and circulating
phosphoric acid. Before starting the work, both sections of the extractor were filled with the
extraction porridge obtained in advance from the standard raw materials under the
conditions of the dihydrate regime. The mixing speed was 120-140 rpm in the first section of
the reactor, and 80-100 rpm in the second section, and the duration of the process was 3
hours. The ratio of liquid and solid phases was 2.5, the excess amount of sulfate ions in the
liquid phase was 3.3-3.5 g/100 ml based on SO
3
. Filtration of porridge in a Buchner funnel
through a filter cloth 400 mm sim.set. carried out under vacuum conditions. The time of the
extraction porridge in the first section of the reactor is 3 hours, and in the second section it is
30 minutes, because in the second section of the reactor, fluorine and sulfate additives in the
extraction porridge are precipitated with the help of calcium carbonate.
Chemical analyzes of raw materials, intermediates and finished products were
performed according to known methods [21-24].
The obtained results are presented in Tables 1 and 2.
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Table 1
The effect of calcium carbonate (c.t.) rate on the chemical composition of WPPA,
the rate of fluorine transfer to the gas phase and phosphogypsum
Naming of indicators
Ratio of calcium carbonate to calcium oxide to
bind free fluorine relative to stoichiometry, %
- 60
80
100
120
140
150
Rate
of
calcium
carbonate to bind free H
2
SO
4
relative to stoichiometry, %
- 80
100
100
100
100
100
Chemical composition of WPPA in weight %
P
2
O
5
17,23 17,28 17,25 17,19 17,10 16,98
16,90
CaO
0,32
0,39
0,54
0,88
1,40
2,21
2,73
MgO
0,66
0,72
0,71
0,68
0,68
0,67
0,67
SO
3
1,21
0,47
0,28
0,26
0,25
0,25
0,24
R
2
O
3
0,71
0,70
0,68
0,67
0,67
0,65
0,65
F
1,18
0,62
0,46
0,29
0,24
0,23
0,22
suspended particle
0,29
0,31
0,27
0,24
0,21
0,18
0,15
Fluoride pass rate, in %
To phosphogypsum
41,3
69,1
74,5
81,8
84,9
85,2
85,4
and gaseous phase
5,1
5,1
4,9
4,4
4,2
4,1
4,0
Ҳаммаси
46,4
74,2
79,4
86,2
89,1
89,3
89,4
Degree of fluoridation of
WPPA
- 47,6
61,1
75,4
79,5
80,2
81,0
The degree of desulfation of
WPPA
- 61,3
76,9
78,5
79,2
79,2
79,3
It can be seen from Table 1 that when WPPA is obtained without adding calcium
carbonate, 5.1% of the total fluorine in phosphorite goes to the gas phase, 41.3% to
phosphogypsum, and 53.6% of fluorine remains in WPPA. The following reactions may occur
when calcium carbonate is added to the extraction slurry:
CaCO
3
+ H
2
SO
4
= CaSO
4
+ CO
2
+ H
2
O
CaCO
3
+ H
3
PO
4
= Ca(H
2
PO
4
)
2
+ CO
2
+ H
2
O
2Ca(H
2
PO
4
)
2
+ H
2
SO
4
+ 2HF = CaSO
4
+ CaF
2
+ 4H
3
PO
4
Table 2
Technological indicators of production of fluorinated and desulfurized extractive
phosphoric acid
Naming of indicators
Total ratio of calcium carbonate to bind fluorine and
free H
2
SO
4
relative to stoichiometry, %
-
140
180
200
220
240
250
Kparch.. %
99,1
99,0
98,.9
98,9
98,9
98,8
98,8
Kajr., %
96,3
96,2
96,2
96,1
96,1
96,1
96,1
Cuvil., %
99,0
99,1
99,1
99,2
99,2
99,2
99,2
Day, %
95,3
95,3
95,3
95,3
95,3
95,3
95,3
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Porridge
density
(r),
g/cm3, at 25°C
1,24
1,24
1,24
1,24
1,25
1,25
1,25
Porridge viscosity (η), spz,
at 25°С
3,10
3,42
3,52
3,61
3,68
3,72
3,73
Filtering rate of extractive
porridge, kg/m
2
•s
815,4
812,6 811,7 810,6 809,5 808,3 807,6
The size of crystalline
phosphogypsum, μm
100x24, 120x20, 220x20, many 560x80, 400x80,
360x28 and partially 100x16, 80x60, 60x20
The amount of magnesium in WPPA remains unchanged, its amount is 0.66-0.72% in
purified acids (Table 1). When calcium carbonate is added and calcium fluoride is formed, the
amount of fluorine released into the gas phase decreases from 5.1 to 4.0%, indicating that the
main amount is released early in the process. When 100-150% of CaCO
3
is introduced into the
decomposition process, the total rate of fluorine transfer to the gas phase and
phosphogypsum is 86.2-89.4%. In this case, the amount of fluorine in WPPA is 0.22-0.29%,
which is 4.1-5.3 times less than when calcium carbonate is not added. The degree of
fluorination of the extractable phosphoric acid product produced by fluoridation of extractive
porridge with the help of 100-150% stoichiometric calcium carbonate is 75.4-81.0%.
During the extraction of phosphoric acid and the precipitation of fluorine and sulfates in
the resulting extraction slurry with calcium carbonate, when the rate of CaO in the form of
CaCO
3
is 100-120%, the degree of fluorine transition to phosphogypsum is 81.8-84.9%, and
the degree of transition to the gas phase is 4.4-4.2%. , the degree of fluorination of the product
WPPA is 75.4-79.5%, and the degree of sulfation is 78.5-79.2%. When adding more than
120% normal calcium carbonate compared to the amount of fluorine and sulfates present in
the acid, fluoridation and desulfation change to a very low degree, that is, to 80.2-81.0% and
79.2-79.3%, respectively. The amount of fluorine remaining in WPPA is 11.3-14.7% compared
to the total amount of fluorine in the initial phosphorite. When the ratio of calcium carbonate
to available fluorine in phosphorite varies from 60 to 100%, it is observed that the additional
transfer of fluorine to phosphogypsum is 27.8-40.5%. When the rate of calcium carbonate is
increased by 120-150%, it increases the transfer of fluorine to the solid phase by only 3.1-
3.6%. The excess calcium carbonate during the precipitation of fluorine in EB is spent on the
formation of calcium sulfate due to the presence of excess sulfuric acid, and due to its reaction
with phosphoric acid, monocalcium phosphate is formed.
From the data in Table 1, it can be seen that the amount of SO3 decreases from 1.21% to
0.24-0.26%, while the amount of calcium oxide increases from 0.32% to 2.73%. In this case,
the decomposition, separation, leaching and productivity coefficients are from 60 to 150% to
bind fluorine, from 80 to 100% to neutralize excess sulfuric acid, corresponding to 98.8-
99.1%, 96.1-96.3% for standard calcium carbonate. , is 99.0-99.2% and 95.3% (Table 2). Due
to the formation of crystals of phosphogypsum 100x24, 120x20, 220x20, most 560x80,
400x80, 360x28 and partially 100x16, 80x60, 60x20, the filtration rate is relatively high and is
807.6-812.6 kg/m
2
•s based on dry residue. is enough.
The conducted studies showed that simultaneous defluoridation and desulfurization of
WPPA based on Central Kyzylkum phosphorites by adding calcium carbonate (k.t.) to the
extraction slurry is possible in principle. The optimal rate of calcium carbonate is 100-120%
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of CaO for the formation of calcium fluoride and 100% of CaO for the formation of calcium
sulfate. In this case, the amount of sulfates decreases from 1.21% to 0.25-0.26%, fluorine from
1.18% to 0.24-0.29%, the rate of fluorine transition to the gas phase during extraction
increases from 5.1% to 4.2- decreases to 4.4%, and the rate of conversion to phosphogypsum
increases from 41.3% to 81.8-84.9%. The degree of fluorination of WPPA obtained as a
product is 75.4-79.5%, and the degree of sulfation is 78.5-79.2%.
In order to obtain a high-quality defluorinated phosphorous fertilizer containing calcium
and magnesium phosphates, the WPPA product purified from fluorine and sulfates using
calcium carbonate during the extraction process and the process of neutralization of the
concentrated acid obtained from its evaporation with calcium carbonate (c.t.) were studied.
During the extraction of phosphoric acid, the product acid purified from fluorine and
sulfate additives and the concentrated acid obtained by evaporating it were neutralized with
stoichiometric СaСO
3
to pH = 2.8-3.5, corresponding to the formation of calcium and
magnesium monophosphates. The resulting slurry was evaporated to 30-35% Н
2
О (when
unconcentrated WPPA was used) and dried at 100-105
О
С.
The technological parameters of the neutralization process, the chemical composition of
the obtained intermediate and finished products are presented in Tables 3 and 4.
At the stage of phosphoric acid extraction, the amount of sulfates (SO
3
) in the phosphate
slurry obtained as a result of the neutralization of WPPA, which is not purified from fluorine
and sulfates with calcium carbonate, is 1.15%, the amount of fluorine is 1.06%, and the level
of defluoridation is 43.70% compared to the initial phosphorite raw material. is enough.
Table 3
Technological indicators of neutralization of WPPA with calcium carbonate
(k.t) raw materials and the chemical composition of the obtained intermediate and
finished products
Т/
р
Indicators
Chemical composition, %
Phosphate porridges
Dried calcium-
magnesium phosphate
fertilizers
1. Stoichiometric rate of СаСО
3
by
СаО, %:
on F during the extraction step
-
100
120
-
100
120
on SO
3
during the extraction step
-
100
100
-
100
100
for WPPA in the neutralization
phase
100
100
100
100
100
100
2. Р
2
О
5
general
16,35
17,18
17,24 48,56 52,94 53,41
3. Р
2
О
5
absorbed
16,26
16,94
17,20 48,29 52,73 53,26
4. Р
2
О
5
water soluble
14,82
15,89
16,15 44,06 49,03 50,08
5. СаО general
7,77
6,18
6,11
23,08 19,04 18,93
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6. MgO general
0,63
0,68
0,69
1,87
2,09
2,14
7. R
2
О
3
general
0,67
0,67
0,68
1,99
2,06
2,11
8. SO
3
general
1,15
0,27
0,25
3,42
0,82
0,77
9. F general
1,06
0,28
0,24
2,99
0,85
0,74
10. H
2
O
66,97
68,65
68,76
1,89
3,39
3,21
11.
(Р
2
О
5own
.:Р
2
О
5total.
)х100, %
99,45 98,60 99,77 99,44 99,60 99,72
12.
(Р
2
О
5
s.e
.:Р
2
О
5total.
)х100, %
90,64 92,49 93,68 90,73 92,61 93,77
Table 4
Concentrated WPPA is carbonated raw materials - с.t. Technological parameters of the
neutralization process with CaCO
3
and the chemical composition of the obtained
intermediate and finished products
Т/р
Indicators
Chemical composition, %
Phosphate porridge
Dried calcium-
magnesium phosphate
fertilizer
1.
Р
2
О
5
general
32,94
53,90
2.
Р
2
О
5
absorbed
32,88
53,81
3.
Р
2
О
5
water soluble
30,98
50,74
4.
СаО general
11,24
18,39
5.
MgO general
1,30
2,13
6.
R
2
О
3
general
1,29
2,11
7.
SO
3
general
0,48
0,79
8.
F general
0,15
0,23
9.
H
2
O
40,20
2,15
10. (Р
2
О
5own
.:Р
2
О
5total.
)х100, %
99,82
99,83
11. (Р
2
О
5s.e
.:Р
2
О
5total.
)х100, %
94,05
94,14
12. Degree of defluoridation, %
96,06
96,34
The amount of SO
3
in the porridge formed when the extractive porridge is neutralized
with 100% and 120% stoichiometric calcium carbonate to form monocalcium and
monomagnesium phosphates with 100% and 120% stoichiometric calcium carbonate is
0.25% and 0.27, respectively. %, and the amount of F is 0.28% and 0.24% (Table 3). The ratio
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of (Р
2
О
5own
.:Р
2
О
5total.
)х100 in porridge is 98.60-99.77%, and the ratio of (Р
2
О
5s.e
.:Р
2
О
5total.
)х100
is 92.49-93.68%.
The pulps were steamed until 30-35% Н
2
O remained, granulated and dried at 100-
105
O
C, compared to the product obtained from untreated WPPA, the amount of sulfates was
from 3.42% to 0.77-0.82%, and the amount of fluorine was from 1.06% to 0.74 Total Р
2
O
5
in
products obtained on the basis of WPPA purified from fluorine and sulfates due to reduction
to -0.85%. amount from 48.56% to 52.94-53.41%, P
2
O
5
own. amount from 48.23% to 52.73-
53.26%, amount of Р
2
O
5
s.e.. increases from 44.06% to 49.03-50.08%. As a result, the degree of
defluoridation of the product reaches 73.9-77.5%. The amount of calcium in the obtained
products is 18.93-19.04%, and the amount of magnesium is 2.09-2.14%,
(Р
2
О
5own
.:Р
2
О
5total.
)х100 ratio is 92.61-93.77%. The degree of fluoridation of calcium and
magnesium phosphate products compared to phosphate raw materials used in the extraction
stage is 86.1-87.9%.
In order to further reduce the amount of fluorine in the products, to reduce the thermal
energy costs of evaporating the solutions and suspensions generated during production,
carbonated raw materials are purified from fluorine and sulfate additives in an optimal ratio
(to bind fluorine - 120%, to bind free H
2
SO
4
) and contain (fat .%): P
2
O
5
= 17,10; CaO = 1,40;
MgO = 0,68; SO
3
= 0,25; R
2
O
3
= 0,67; F = 0,24 by evaporating the acid contained in it (ugh.%):
P
2
O
5
= 35,25; CaO = 2,25; MgO = 1,39; SO
3
= 0,51; R
2
O
3
= 1,38; F = 0,17 concentrated WPPA
was formed. In this case, the degree of defluoridation of extractable phosphoric acid reaches
93.0%.
When concentrated WPPA is neutralized with 100% stoichiometric raw calcium
carbonate to form monocalcium and monomagnesium phosphates, the amount of SO
3
in the
porridge is 0.48%, and the amount of F is 0.15% (Table 4). The ratio of
(Р
2
О
5own
.:Р
2
О
5total
.)x100 in porridge is 99.82%, and the ratio of (Р
2
О
5s.e
.: Р
2
О
5total
.)x100 is
94.05%.
Р
2
О
5general
in the product when the porridge is granulated and dried at a temperature of
100-105
O
C. amount up to 53.90%, Р
2
О
5
own. amount up to 53.81%, Р
2
О
5s.e.
amount up to
50.74%. As a result, the degree of defluoridation of the obtained calcium and magnesium
phosphate products compared to the phosphate raw materials used in the extraction stage is
96.34%. The amount of calcium in the obtained products is 18.39%, and the amount of
magnesium is 2.13%, (Р
2
О
5own
.:Р
2
О
5general.
)х100 ratio 99,83% the, (Р
2
О
5s.e
.:Р
2
О
5general.
)х100 and
the ratio is 94.14%. Evaporation of extracted phosphoric acid to 35% Р
2
О
5
before
neutralization with carbonate raw materials, processing of evaporated acid into phosphorus
fertilizers containing calcium and magnesium phosphates, firstly, saves energy resources
compared to suspension evaporation costs, and secondly, reduces the amount of fluorine in
the product.
Figure 1 shows the material flow block diagram for the production of high-quality
phosphorus fertilizer from Central Kyzylkum's washed-burnt phosphate concentrate (WCPC).
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Figure 1. Material flow block diagram for the production of high-quality
phosphorus fertilizer from the washed-burned phosphate concentrate (WCPC) of
Central Kyzylkum.
Conclusion.
Thus, during the extraction process of phosphoric acid, by adding a reagent (calcium
carbonate) containing 100% calcium for sulfates and 120% for fluorine to the sulfate-
phosphate slurry in the stoichiometric ratio, simultaneous defluoridation and desulfation of
extractable phosphoric acid based on Central Kyzylkum phosphorites showed that it is
possible. By neutralization with 100% stoichiometric calcium carbonate (c.t.) raw materials to
form WPPA monocalcium and monomagnesium phosphates, purified from fluorine and
sulfates, it is possible to obtain high-quality concentrated phosphorous simple fertilizers, the
composition of which is similar to double superphosphate. Evaporation of extracted
phosphoric acid to 35% Р
2
О
5
before neutralization with carbonated raw materials and
processing of evaporated acid into phosphorus fertilizers containing calcium and magnesium
phosphates, firstly, saves energy resources compared to suspension evaporation costs, and
secondly, reduces the amount of fluorine in the product.
EXTRACTOR
PRECIPITATOR
VACUUM FILTER
REACTOR
REFRIGERATIO
N
DRUM-GRANULATOR
DRYER
REFRIGERATOR
H
2
SO
4
WСPC
Circulating
solution
Calcium
carbonate or
WСPC
Phosphogyp
sum
СО
2
Steam-gas
mixture
Dolomite or
limestone
H
2
O, HF
Final product
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