Journal
of Chemical
Technology
Metallurgy,
1, 2015
Journal
of Chemical
Technology
andand
Metallurgy,
50,50,
1, 2015,
26-34
INVESTIGATION OF NITRIC ACID BENEFICIATION
OF LOW GRADE PHOSPHORITES FROM CENTRAL KYZYLKUM
Bokhodir E. Sultonov, Shafoat S. Namazov, Bakhtiyar S. Zakirov
Institute of General and Inorganic Chemistry ,
Academy of Sciences of Uzbekistan
77a, st. Mirzo-Ulugbek, 100170, Tashkent, Uzbekistan
E -mail: [email protected]
Received 03 September 2014
Accepted 05 December 2014
ABSTRACT
With the purpose of obtaining chemical concentrated phosphates, suitable for quality fertilizers manufacture, a
process of chemical beneficiation of poor phosphorites from Central Kyzylkum was investigated. The influence of
norm of nitric acid on dressability phosphorites is studied and рН media are defined in which a passage of Р2О5 was
excluded in liquid phase. Optimum concentrations for the repulping solution of Ca(NO3)2 at which the concentration
of the received solution will be over, were defined. Influence of the quantity and temperature of washing water on
the extent of removal of Ca(NO3)2 from the phosphorus concentrates were investigated and the optimum quantity
and temperature of washing water where content of Ca(NO3)2 in phosphorus concentrates will be minimum was
defined. The possibility for obtaining of chemical beneficiation of phosphorus concentrates by interaction of Central
Kyzylkum phosphorites with aquafortis was shown. The chemical beneficiation phosphorus concentrates meets the
requirements for sulfuric acid extraction with obtaining of extraction phosphoric acid and phosphorous containing
fertilizers on its base.
Keywords: poor phosphorites, nitric acid, phosphorus concentrate, calcium module, degree of calcinations,
extent of removal.
INTRODUCTION
In Uzbekistan the phosphorites of Central Kyzylkum became the basic raw materials for production of
phosphorus containing fertilizers. These phosphorites
are with poorest content of the basic component - phosphorus (16.2 % Р2О5). In the world practice is known,
that the phosphate raw materials, applicable for sulfur
acid extraction should be with content of P2O5 not less
than 24.5 %, CO2 should be not more than 8 %, (R2O3 :
P2O5).100 can not be more than 12 %, (MgO : P2O5).100
can not be more than 7 - 8 %. The recommended value
of the calcium module (СаО : P2O5) is 1.6 and chlorine
is not more than 0.04 % in the raw materials. Therefore
the poor raw material has to be enriched.
The most accepted method for enrichment is flotation. However, the Kyzylkum phosphate rock, due
26
to along the close mutual germination of phosphate
minerals and calcite, the attempt to enrich them through
flotation did not lead to positive results. The value of
the calcium module (СаО:P2O5) is 2.85. The content of
chlorine reaches 0.10 - 0.25 %, that leads to intensive
corrosion of the equipment [1].
So, the Kyzylkum phosphorite plant developed the
manufacture of enriched phosphorites by their washing
out of chlorine and burning in fluidized process [2, 3].
During the proximate years an expanding production of washed and burned concentrate to 716 thousand
tons per year with the content of P2O5 not less than 26
% is provided.
The main drawbacks of the existing technology of
enrichment are the following:
The high value of the calcium module (2.0 - 2.1) in
the washed and burned concentrate, as removal of the
Bokhodir E. Sultonov, Shafoat S. Namazov, Bakhtiyar S. Zakirov
free CaO formed at decomposing of lime carbonate, is
not provided. A considerable amount of out of balance
ores the so-called “mineral masses” is dropped out in the
ore’s sorting and screening operations, having phosphate
with initial content of Р2О5 less than 16 % and fraction of
+5 mm. Annually more than 300 thousand tons mineral
masses is piled up. Currently we have more than 6 million tons mineral mass, which is not used in production
of mineral fertilizers.
Losses of phosphate anhydride reach 15-25 % in the
tails of the flush of ore out of chlorine from the initial
mass of the concentrate [4]. These slime phosphorites
also are not used in any way.
The process of enrichment is highly energy intensitive.
In [5 - 7] processes of chemical enrichment of phosphorites from Central Kyzylkum with dilute solutions
of nitric, sulfuric and hydrochloric acids, and as well
as with nitric acid solutions of calcium and magnesium
nitrates, were considered. The main drawbacks of the developed technologies are the following: plentiful foaming, process duration, low filtration rate of the nitric acid
phosphate suspension, formation of an enormous amount
of acid solutions, which create some technological difficulties at processing. In [8] the chemical beneficiation of
Kyzylkum’s phosphorites with organic acids was investigated. Under the optimum conditions of beneficiation
of phosphorites, containing 16.33 % Р2О5, 17.23 % СО2
and 47.13 % СаО, phosphorus concentrate with content
24.52 - 25.78 % Р2О5, which is suitable for sulfuric acid
extraction was obtained. The main drawbacks of the
developed technology were plentiful foaming, using
huge equipment for embodiment of the beneficiation
process and requirement of expensive sulfuric acid for
the regeneration of organic acids. In [9] a technology
for chemical beneficiation of high calcareous contents
of Kyzylkum’s phosphorites, which included processing
of phosphate raw material (PRM), containing 17-18 %
Р2О5, with nitric acid of concentration 45-60 % taken
in amount of 90-110 % from stoichiometry to СаСО3,
with following repulpation of the recycled solution,
containing 5-25 % Са(NO3)2, at mass ratio of phosphate
raw material to Са(NO3)2 solution equal to 1:(2.0 -3.5),
sedimentation of the formed nitrophosphate suspension
for 5 - 10 min, as well as wet cake washing with water
and product drying, was developed. The weaknesses of
this method are the low yield of Р2О5 (56 -60 %), greater
passage of Р2О5 into the liquid phase, heavy filtration
of the nitrophosphate suspension and the formation of
a huge volume of diluted solution, which demands an
enormous heating for its processing into nitrogen phosphate calcium fertilizers.
The above presented investigation of the more acceptable methods for beneficiation of high calcareous
Kyzylkum’s phosphorites is quite actual problem at
present.
Previously we studied the chemical enrichment
of the mineral mass, which is the waste of thermal
beneficiation of phosphorites of Kyzylkum [10] with
nitric acid and obtained data concerning the possible
producion of phosphorus concentrate for acid processing. Subsequent systematic research we conducted also
on nitric acid beneficiation of low grade phosphorites
and obtaining chemical phosphorus concentrate fully
suitable for wet-processing of phosphoric acid and new
types of highly concentrated unary and complex fertilizers based on it [10 -13].
EXPERIMENTAL
Materials
For the experiments a low grade phosphorite, containing (mass %): 17.52 - Р2О5, 47.53 - СаО; 15.23 - СО2,
2.00 - SO3; 1.98 - F; 1.75 - MgO; 0.97 - Al2O3; 0.56 Fe2O3; СаО:Р2О5 = 2.71, 58.78 % of nitric acid and different concentrations of Ca(NO3)2 solutions were used.
Formulas for calculations
The mass of nitric acid for its various norms, based
on the CaO in the initial phosphorite we determined by
the formula:
(1)
where
rite;
is the mass of the initial phospho-
is the mass fraction of CaO in the initial
phosphorite;
is the norm of HNO3 and 58.78 is the concentration of HNO3;
2.25 is the ratio of the molar mass of HNO3 and CaO
in the reaction:
CaO+2HNO3=Ca (NO3)2 + H2O
(2)
The norm of nitric acid from stoichiometry to CaO
was varied in a range from 40 tо 60 %.
27
Journal of Chemical Technology and Metallurgy, 50, 1, 2015
The degree of decarbonization was calculated by
the formula:
(3)
where
is the mass of the samples of phosphorusconcentrates,
is the initial mass of phosphorite,
is the mass fraction of CO2 in the samples of
obtained phosphorus concentrates and
is the
mass fraction of CO2 in the source of phosphorus.
The washing degree of phosphorus-concentrates was
calculated according to:
where
concentrate;
(4)
is a sample’s mass of phosphorusis the mass of the initial phosphorite;
is the mass fraction of CaO in the initial
phosphorite;
is the mass aqua form of CaO in the of
phosphorus concentrate;
is the norm of HNO3;
is the mass of NH3;
4.82 is the ratio of the molar masses of Са(NO3)2 and
NH3 in the reaction:
Ca(H2PO4)2 + Ca(NO3)2 + 2NH3 = 2CaHPO4 + 2NH4NO3
(5)
2.93 is the ratio of molar masses of Са(NO3)2 and CaO.
Experimental procedure
The interaction of the phosphate raw material with
nitric acid was performed at 35-40°C in a glass reactor, equipped with a stirrer. The reactor was charged
with nitric acid and a suitable amount (25 g) of PRM.
The latter was fed in portions within 3-4 min. Partial
decomposition and decarbonization of the phosphate
raw materials, occurred in the reactor. After 20 minutes
the resulting pulp was treated with gaseous ammonia
under pH control (pH 3) to avoid P2O5 transition into a
liquid phase. The differently concentrated solutions of
calcium nitrate stayed at vigorous stirring in the reactor. The mass ratio of phosphorus to the calcium nitrate
solution was in the range of 1:(2.0 - 3.0). The resultant
slurry was separated by filtration under vacuum. The
28
wet phosphorite concentrate was washed with water in
a mass ratio of PRM:H2O = 1:1.5. The wet phosphorus
concentrates were dried at 100 - 105°C.
However, in our investigation the influence of
nitrate calcium concentration in the repulpating solution on the phosphorus concentrate quality and on the
obtaining of more concentrated solution of Ca(NO3)2,
the concentration repulpating solution was varied in a
range from 5 tо 25 %. The influence of the water quantity
on the phosphorus concentrate quality was studied by
changing the mass ratio of PRM:Н2О from 1:1 tо 2:1.
For investigation of the water temperature influence on
phosphorus concentrate quality, the wet phosphorus
concentrate was washed one-fold by water at different
temperatures with mass ratio of PRM : Н2О = 1:1.5. The
wet phosphorus-concentrate was dried at 100 - 1050С.
Methods for analysis
The dried precipitate and the filtrate were subjected
to chemical analyses as follows: all forms of P2O5 [total
(t), acceptable by citric acid (ac.c.a.) and acceptable by
EDTA (ac. EDTA)] were determined by the calorimetric
method on calorimeter CPhC-3 ((l 440 nm) in the form
of an yellow phosphoro-vanadio-molybdenum complex
compound [14]. The total (t) and water solubile (w.s.)
forms of CaO were determined by the volume complexometric titration with 0,02 N EDTA in the presence of
indicator fluorene or chrome navy-blue [14]. The form
of N total (t) was determined by the Kjeldahl’s method
[15]. The СО2 total (t) was determined by dissolution
of carbonates with hydrochloric acid (10 % HCl).
The volume of СО2t. was calculated by the difference
between the total amount of CO2 and the volume of air
which has remained after the absorption of the CO2 by
40 % solution of potassium hydroxide [16]. The pH of
the nitrophosphate suspension was controlled with a
pH-150MI (Russian Federation, 2013).
RESULTS AND DISCUSSION
Influence of the norm of nitric acid and pH of the
medium on the phosphorus concentrate quality [10]
The norm of nitric acid was taken according to CaO
45, 50 and 60 %. The acid nitric calcium phosphate
solution was treated with gaseous ammonia under pH
control 2.5; 3.0; 3.5; 4.0 and then it was carried out on
the basis of experiments. The laboratory tests results are
shown in Table 1.
Bokhodir E. Sultonov, Shafoat S. Namazov, Bakhtiyar S. Zakirov
СО2t
СаО:
Р2О5
Degree of Р2О5
passege into
liquid phase
The extent of
removal of
Са(NO3)2
from phosph.concen.,%
1.64
2.15
93.46
1:3,0
3.0
3.5
4.0
2.50
2.52
2.55
2.43
2.45
2.48
2.52
1.66
1.67
1.70
1.62
1.60
1.63
1.64
3.02
-
93.71
93.87
94.01
94.53
94.78
94.89
95.02
CaOtotal
CaOw.s.
2.46
0.87
0.91
0.93
0.86
0.80
0.83
0.85
CaO ac.c.a
0.94
7.14
40.89
18.49
1.75
7.06
41.01
18.50
1.61
6.93
41.09
18.49
1.52
7.16
38.86
17.91
1.72
7.53
40.52
18.41
1.61
7.25
41.06
18.55
1.50
7.18
41.12
18.55
1.40
Norm of HNO3 for СаО = 50%
P2O5ac.EDTA
7.04
10.92
10.84
10.66
10.82
11.36
11.15
11.04
P2O5ac.c.a
10.81
24.67
24.56
24.22
23.99
25.36
25.19
25.01
P2O5t.
24.03
3.0
3.5
4.0
2.5
pH
2.5
1:2.5
Ratios PRM:
solution
Са(NO3)2
Nt.
Table 1. Influence of pH on the composition of the phosphorus concentrate obtained at various norms of HNO3 and
ratios of PRM:solution of Са(NO3)2.
Norm of HNO3 for СаО = 45%
2.5
39.41
3.0
3.5
4.0
2.5
25.48
26.25
26.10
26.07
25.58
11.65
11.88
11.78
11.73
11.66
7.83
7.99
7.92
7.88
7.82
0.97
0.92
0.96
1.01
0.94
2.25
2.32
2.36
2.41
2.21
1.52
1.52
1.54
1.56
1.49
3.25
4.05
94.27
94.41
94.62
94.71
94.59
1:3,0
3.0
3.5
4.0
26.50
26.41
26.36
12.06
11.99
11.94
8.07
39.62
18.56
1.71
0.85
8.00
39.88
18.64
1.62
0.91
7.95
40.33
18.81
1.50
0.90
Norm of HNO3 for СаО = 60%
2.27
2.31
2.35
1.50
1.51
1.53
-
94.97
95.05
95.21
2.5
3.0
3.5
4.0
2.5
25.50
26.70
26.61
26.52
25.41
26.96
26.87
26.74
11.66
12.18
12.10
12.03
11.64
12.32
12.25
12.15
7.84
8.18
8.12
8.06
7.84
8.29
8.23
8,16
2.15
2.18
2.21
2.24
2.09
2.11
2.14
2.17
1.47
1.48
1.49
1.50
1.44
1.45
1.46
1.47
4.35
5.07
-
93.44
93.76
93.85
94.03
94.14
94.51
94.67
94.78
1:3,0
3.0
3.5
4.0
37.48
39.56
39.65
39.78
36.59
39.22
39.26
39.31
It is seen that under pH control (pH 2.5 of pulp),
Р2О5 is passed into liquid phase. In addition its value is
increased with raising the norm of nitric acid and with
raising the ratio of PRM: Са(NO3)2 solution. This fact
shows that under pH 2.5 monocalcium phosphate has not
changed into dicalcium phosphate in above mentioned
reaction (2) yet. For pH of pulp 3,0 and more, there
is not Р2О5 in the liquid phase, which is evidenced on
finishing the interaction amongst Ca(H2PO4)2, Ca(NO3)2
and NH3. With increasing of pH from 2.5 tо 3.0 the
content of Р2О5 increases from 0.64 tо 1.55 % in the
phosphorus concentrate, depending on the conditions
of experiments. With further increasing of pH from
3.0 tо 4.0, the content of Р2О5 decreases slightly in the
phosphorus concentrate. Increasing of some contents of
Р2О5 and decreasing the value of the calcium module
18.09
18.50
18.62
18.76
17.90
1.87
1:2,5
1:2,5
38.77
39.81
40.19
40.67
38.11
18.13
17.61
18.54
18.52
18.52
17.29
18.47
18.42
18.40
1.91
1.86
1.82
1.75
1.83
2.30
2.19
2.08
2.00
2.17
1.97
1.81
1.73
1.22
1.08
1.05
1.01
1.16
0.98
0.93
0.92
(СаО:Р2О5) in the phosphorus concentrate samples at
the same HNO3 norm and pH of the pulp with raising
the ratio of PRM:solution of Са(NO3)2 is also observed.
This is explained, in all probability, with increasing of
the extent of removal of Са(NO3)2 from the phosphorus
concentrate. The increasing of the norm of НNO3 from
45 to 60 % contributes raising of Р2О5 content in the
phosphorus concentrate from 24.67 tо 26.70 % and from
25.36 tо 26.96 %, respectively, under рН 3.0 and ratio of
PRM:solution of Са(NO3)2 1:2.5 and 1:3.0. The value of
the calcium module, which is important, indicates that
the phosphorus concentrate quality mainly depends on
the norm of НNO3. The dependence of the Р2О5 contents
in the phosphorus concentrate and the value of the calcium module from the norm of НNO3 at the investigated
ratios of PRM:solution of Са(NO3)2, is presented in Fig.
29
Journal of Chemical Technology and Metallurgy, 50, 1, 2015
2.71
2.71
1.66
1.66
2
Content of Р2О5,%
26.67
1.62
26.96
1.60
26.70
26.50
26.17
1.60
1.58
1
1.56
26.25
1.54
25.67
25.17
1.52
25.36
1.50
1.52
1.50
3
1.48
24.67
4
24.67
45
50
Norm of HNO3, %
1.48
1.46
1.45
17.52
0
Ratio of СаО:Р2О5
27.7
1.44
60
Fig. 1. Change of the Р2О5 content and the value of the calcium module in the phosphorus concentrate in dependence of the norm of НNO3 at рН 3; 1,3- ratio of PRM:solution of Са(NO3)2 = 1:2.5; 2,4- ratio of PRM:solution of
Са(NO3)2 = 1:3.0.
1. It should be noted that the content of dissolved calcium
is also a quality index of the phosphorus concentrate.
The content of CaOw.s. in the phosphorus concentrate
does not have to be more than 1.5 %, in recalculation
of Са(NO3)2 4.4. This creats some technological difficulties in acid processing of phosphorus concentrate
for fertilizers, because at Са(NO3)2 more than 4.4 % it
starts to cake because of its high hygroscopicity. It can
be seen from the Table 1, that at the studied conditions,
the content of CaOw.s. is varied in the range 1.4 - 2.3 %.
The concentration of Са(NO3)2 obtained in the solution is
13.32 - 20.41 %, which demands an enormous quantity
of heat for processing of diluted nitrate calcium solution
for NСа-fertilizers.
In order to find the optimal conditions for separating
the calcium nitrate from the calcium nitrophosphate solution and limit it in the phosphorus concentrate, where the
content of CaOw.s. should be < 1.5 %, and obtain a concentrated by-product - solution of calcium nitrate, we studied
the influence of the concentration of the repulped solution,
as well as the amount and temperature of the washing
water for obtaining high quality phosphorus concentrate.
Influence of the repulped solution on the quality
phosphorus concentrate [11]
The laboratory tests results of this investigation are
shown in Table 2.
30
It is seen that lower concentration of the calcium
nitrate solution leads to higher extent of removal of the
calcium nitrate from phosphorus concentrate. It is determined also that the calcium nitrate is very water-soluble.
However, the problem of utilization of the diluted
solution formed at leaching of the acid pulp appeared.
That is why we needed an optimal concentration of
the calcium nitrate for leaching of acid pulp, which as
phosphorus concentrate would be the best and formed
more concentrated solution of Са(NО3)2. At leaching of
the acid pulp with 5 % solution of calcium nitrate with
a ratio of PRM:solution of Са(NO3)2 = 1:(2.0-2.5), the
extent of removal of calcium nitrate is 91.65 - 94.10 %
(at norm of HNO3 - 45 %). At norm of HNO3 50 % the
extent of removal of calcium nitrate from the phosphorus
concentrate is 92.75 - 94.93 %.
Under these conditions the best phosphorus concentrate is obtained. The content of Р2О5 is 24.55 - 26.40 %
and the value of the calcium module equals 1.51 - 1.68.
For leaching the acid pulp with a 10 % solution of calcium nitrate with a ratio of PRM:solution of Са(NO3)2 =
1:(2.0-2.5), the extent of removal of the calcium nitrate
is 91.34 - 93.71 % (at norm of HNO3 - 45 %). At norm
of HNO3 50 % the removal of calcium nitrate from the
phosphorus concentrate is somewhat increased and
varies in a range 92.00 - 94.41 %, the content of Р2О5
is 25.63 - 26.25 %, the value of the calcium module
Bokhodir E. Sultonov, Shafoat S. Namazov, Bakhtiyar S. Zakirov
equals 1.52 - 1.58. Further increase of the concentration
of Са(NО3)2 (15 and 20 %) solution leads to decrease of
the extent of removal of calcium nitrate from phosphorus concentrate, raising of the calcium module and for
reduction of the Р2О5 content in the latter.
The data in Table 2 show, that at norm of НNО3
50 %, the content of P2O5 is increased notably and the
calcium module is decreased.
In spite of the increase of the СаОw.s. content in the
phosphorus concentrates the rising of the extent of
removal of nitrate calcium is observed since the total
mass of calcium nitrate is less in these phosphorus concentrates than in the phosphorus concentrates, obtained
with a norm of НNО3 45 %.
Fig. 2 shows the Са(NО3)2 concentration in the
mixed liquid phases I and II as depending on the concentration of the repulping solutions of Са(NО3)2. It is seen,
that with an increase of the concentration of repulping
solutions of Са(NО3)2, its concentration is raised. From
the data in Table 2 and Fig. 2 it is seen that the optimum
concentration of repulping solutions of Са(NО3)2 is 10 %
and ratio of PRM:solution of Са(NO3)2 = 1:2.5 at norm of
HNO3 50 %. At that is obtained phosphorus concentrate
containing (mass %): Р2О5t. 26.25; P2O5 ac.c.a. 11.88; P2O5
EDTA 7.99; СаОt. 39.81; СаОac.c.a. 18.50; СаОw.s. 1.86;
ac.
СО2 2.32; N 0.92; СаО: P2O5 1.52. The single drawback
for the obtained phosphorus concentrate is the increased
content of СаОw.s.- 1.86 %, in recalculation to Са(NО3)2
- 5.45 %. It was specified above that the content СаОw.s.
not be more than 1.5 %, (in recalculation for Са(NO3)2
> 4.4). Therefore in our further research we studied the
influence of the quantity and the temperature of the
washing water which lead to a minimum of Са(NO3)2
content in the phosphorus concentrates.
Influence of the quantity and temperature of the
water on the quality parameters of phosphorus concentrates [12,13]
In order to obtain a phosphorus concentrate with a
minimal content of Са(NO3)2, we studied the influence
quantity and temperature of water on the quality parameters of the phosphorus concentrates. The obtained
data are presented by a volumetric graph (Fig. 3). It is
seen that with increase of the ratio of PRM:solution of
Са(NO3)2 from 1:2.0 to 1:3.0, the content of СаОw.s. is
decreased notably in the phosphorus concentrates. The
amount water contributes also to decreasing of the latter.
The more is the water, the less is the content of СаОw.s.
in phosphorus concentrates. Thus, with increasing of
the amount of water, the calcium nitrate content will
be reduced, i.e. the extent of removal of calcium nitrate
from phosphorus concentrate is raised and the calcium
15
20
Extent of
removal of
Са(NO3)2
%
CaO ac.c.a
11.59
11.87
11.55
11.88
11.15
11.33
11.09
11.27
CaOtotal
25.85
26.40
25.63
26.25
24.70
25.00
24.51
24.82
P2O5ac.EDTA
1:2.0
1:2.5
1:2.0
1:2.5
1:2.0
1:2.5
1:2.0
1:2.5
Norm of HNO3, 45 %
6.79
41.25 17.72
6.98
40.80 17.87
6.97
41.35 18.62
7.14
40.89 18.49
6.57
41.35 18.82
6.86
41.10 19.05
6.58
41.81 20.16
6.86
41.65 20.39
Norm of HNO3, 50 %
7.54
40.50
18.02
7.77
39.80
18.13
7.54
40.53 18.32
7.99
39.81 18.50
7.33
40.83 19.85
7.62
40.23 19.81
7.33
40.95 20.15
7.64
40.65 20.27
СаО:
Р2О5
10
10.66
10.91
10.73
10.92
10.21
10.43
10.17
10.37
СО2t
5
24.55
24.81
24.35
24.67
23.15
23.53
23.02
23.34
Nt.
20
1:2.0
1:2.5
1:2.0
1:2.5
1:2.0
1:2.5
1:2.0
1:2.5
CaOw.s.
15
P2O5ac.c.a
10
P2O5t.
5
Ratio of PRM
: solution of
Са(NO3)2
Concentration
solution of
Са(NO3)2, %
Table 2. Chemical composition phosphorus-concentrates.
2.26
1.66
2.37
1.75
2.59
2.27
3.01
2.67
1.12
0.82
1.18
0.87
1.25
1.21
1.35
1.29
2.70
2.63
2.64
2.50
2.45
2.32
2.41
2.27
1.68
1.64
1.70
1.66
1.79
1.75
1.82
1.78
91.65
94.10
91.34
93.71
89.23
90.92
87.27
89.03
2.40
1.70
2.52
1.86
2.84
2.51
3.15
2.96
1.19
0.86
1.25
0.92
1.32
1.24
1.52
1.33
2.49
2.36
2.45
2.32
2.31
2.19
2.18
2.10
1.57
1.51
1.58
1.52
1.65
1.61
1.67
1.64
92.75
94.93
92.00
94.41
90.21
91.66
89.02
90.01
31
Journal of Chemical Technology and Metallurgy, 50, 1, 2015
22
• 21.73
• 20.96
• 20.80
21
8
20.15•
Concentration of Са(NO3)2 in mixes, %
20
00
00
19
00
000
00
18
00
•
2
• 20.15
•
19.47
19.60
18.89 •
•
18.80
•
18.24
00
00
17
0
1
•
•
17.45
17.19
2
1
15.96
16
16.84•
•
•
16.16
15.70 •
1
1
15
15
10
5
Concentration of repulping Са(NО3)2 solutions, %
20
Fig. 2. Change of the concentration of Са(NO3)2 depending on the concentration of the repulping solutions of Са(NО3)2.
1,11- norm of НNO3 45 % in ratio of PRM:solution of Са(NO3)2 = 1:2.0 and 1:2.5, respectively; 2,21- norm of НNO3 50
% in ratio of PRM:solution of Са(NO3)2 = 1:2.0 and 1:2.5, respectively.
The content СаОw.s. in phosph.-concen., %
2.9
2.87 •
2.8
2
2.7
2.61
2.6 •
2.52
•
2.5
2.4
2.35
•
1.88• 1.9
•
2.3
2.37
1.8
•1.72
1.7
2.2
2.1
1.6
•
2.0
1.5
2,02
1.9
2.4
2.3
•2.25
1.71 2.2
•
1.62
• 2.1
•2.04
2.0
1.69
•
•
1,62
1,7
1.6
•1.58
•1.52
1.5
1.9
1
1.8
1.8
1.7
1.7
1.6
1.6
1.5
1.5
1:3.0
1:2.5
PRM : solution of Са(NO3)2
1:2,0
1:1.0
1:1.5
1:2.0
PRM: Н2О
Fig. 3. Dependence of the content of СаОw.s. in the phosphorus concentrates on the ratio PRM:Н2О and the ratio PRM:solution
of Са(NO3)2. The norm of НNO3 is :1 - 45 %; 2 – 50 %.
module will be decreased.
It should be mentioned that at the above ratios of
PRM:Н2О we could not fully separate the wet phosphorus concentrate from the calcium nitrate. Therefore,
we should not increase higher the amount of water as
with that, the water drain is diluted violently on calcium
nitrate. On this basis we believe that at washing of the
wet phosphorus concentrate it is necessary to control the
32
water amount. In our case the ratio PRM:Н2О = 1:1.5,
at ratio of PRM:solution of Са(NO3)2 = 1: (2.5-3.0) is
better since the by-product - solution of calcium nitrate
will be obtained comparatively more concentrated. It
is known that in washing of wet phosphorus concentrate
besides the water amount, its temperature also has an important function. In addition, the solubility of the calcium
nitrate in water depends considerably on temperature.
Bokhodir E. Sultonov, Shafoat S. Namazov, Bakhtiyar S. Zakirov
1:2.0
1:2.5
24.86
25.24
11.17
11.39
1:2.0
1:2.5
25,15
25,77
11,32
11,65
1:2.0
1:2.5
25.63
26.25
11.55
11.88
1:2.0
1:2.5
25.89
26.75
11.68
12.12
1:2.0
1:2.5
26.23
27.04
11.85
12.26
1:2.0
1:2.5
26.28
27.10
11.89
12.28
1:2.0
1:2.5
26.33
27.14
11.90
12.30
For example, at 200С its solubility equals 128.8 g, at
300С - 149.4 g, at 400С - 189 g, at 600С - 359 g and at
1000С - 363 g [17].
Following these data the influence of washing water
temperature on the quality of phosphorus concentrates
was studied. The laboratory tests results are shown in
Table 3.
It is seen that with increasing washing water
temperature from 20 to 800oС at ratio PRM: solution
of Са(NO3)2 = 1:2.0, the content of P2O5t. increases
from 24.86 tо 26.33 %, but the calcium module of the
phosphorus concentrate is decreased from 1.69 tо 1.52,
the extent of removal of Са(NO3)2 from the phosphorus
concentrate changes from 89.34 tо 93.59 %.
The contents of СаОt. and СаОw.s. go down from
41.89 to 40.05 % and from 3.05 tо 2.15 %, respectively.
At ratio of PRM:Н2О = 1:2, increase of washing water
temperature from 20 tо 800oС������������������������
to contributes to raising of the P2O5t. content from 25.24 tо 27.15 % in the
samples of phosphorus concentrates, but the calcium
module decreases from 1.61 tо 1.44. In addition, the
extent of removal of Са(NO3)2 goes up from 92.51 tо
95.97 %, as well.
СаО:
Р2О5
Extent of
removal of
Са(NO3)2
%
Тemperature of washing water = 200С
7.28
41.89
18.85
3.05
1.53
7.65
40,68
18.57
2.25
1.13
Тemperature of washing water = 300С
7.38
41.05
18.52
2.84
1.42
7.83
40.26
18.44
2.01
1.01
Тemperature of washing water = 400С
7.54
40,53
18,32
2,52
1,25
7.99
39,81
18,50
1,86
0,92
Тemperature of washing water = 500С
7.62
40.31
18.24
2.37
1.18
8.16
39.56
18.43
1.65
0.82
Тemperature of washing water = 600С
7.73
40.18
18.20
2.24
1.12
8.25
39.21
18.27
1.54
0.77
Тemperature of washing water = 700С
7.76
40.10
18,20
2.18
1,09
8.29
39.10
18.24
1.48
0.74
Тemperature of washing water = 800С
7.78
40.05
18.18
2.15
1.07
8.31
39.06
18.24
1.45
0.72
СО2t.
Nt.
CaOw.s.
CaO ac.c.a
CaOtotal
P2O5ac.EDTA
P2O5ac.c.a
P2O5t.
Ratio of
PRM:
solution of
Са(NO3)2
Table 3. Chemical composition of the phosphorus concentrates.
2.39
2.31
1.69
1.61
89.34
92.51
2.42
2.34
1.63
1.56
90.54
93.65
2,45
2,32
1,58
1,52
92,00
94,41
2.47
2.36
1.56
1.48
92.66
95.24
2.48
2.38
1.53
1.45
93.26
95.68
2.48
2.39
1.52
1.44
93.47
95.88
2.48
2.39
1.52
1.44
93.59
95.97
The contents of СаОt. and СаОw.s. change from 40.68
tо 39.06 % and from 2.25 to 1.45 %, respectively. So,
the quality of phosphorus concentrate is significantly
improved. It should be noted that for temperatures of
washing water above 600oС, independently of the ratio
of PRM:solution of Са(NO3)2, the quality of the phosphorus concentrate is not changed. It is connected with
an unimportant variation of the calcium nitrate solubility in the range of 60 - 800oС. When temperatures of
washing water are lower than 500oС, a plentiful amount
of Са(NO3)2 is precipitated. So, preferably the washing
of the wet cake should be carried out at temperatures
between 60oС and 70oС.
CONCLUSIONS
From the results obtained the following should be
noted:
● The influence of nitric acid on the enrichment of
phosphorite was studied and the pH of the medium was
determined, at which the passage of P2O5 into liquid
phase was excluded.
● The optimal concentration for the repulping solution of Са(NO3)2 was defined.
33
Journal of Chemical Technology and Metallurgy, 50, 1, 2015
● The influence of the quantity and temperature of
the washing water on the extent of removal of Са(NO3)2
from the phosphorus concentrate were studied.
● The possibility for obtaining of chemical phosphorus concentrate by interaction of phosphorite of Central
Kyzylkum with nitric acid was shown. The chemical
composition of the phosphorus concentrate is suitable for
sulfur acid extraction for wet-processing of phosphoric
acid and phosphorus-containing fertilizers on its base.
Acknowledgements
We thank Dr. U.K. Alimov, senior staff scientist of
the Laboratory of Phosphoric Fertilizers, for translation and the most valuable advice for the preparation
of the manuscript.
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