Zohidbek
Hamrakulov,
Mamuraand
Askarova,
Saidahral
Tukhtaev
Journal
of Chemical
Technology
Metallurgy,
50, 1, 2015,
65-70
PREPARATION OF CALCIUM-MAGNESIUM CHLORATE
DEFOLIANT FROM DOLOMITE
Zohidbek Hamrakulov, Mamura Askarova, Saidahral Tukhtaev
Institute of General and Inorganic Chemistry,
Academy of Sciences of Uzbekistan,
77a, st. Mirzo-Ulugbek, 100170, Tashkent, Uzbekistan.
E-mail: [email protected]
Received 15 May 2014
Accepted 05 November 2014
ABSTRACT
The paper provides results for the kinetics of a process for conversion of calcium and magnesium chloride solution,
obtained as a result of decomposition of dolomite with hydrochloric acid, with sodium chlorate with and without its
evaporation.
The process activation energy, order and conversion reaction rate constant are defined. The expediency of conducting of the
conversion is installed at temperature 363 К with evaporation. The equation of Arrenius for processes of conversion with and
without evaporation is fitted empirically. On the basis of these equations the reaction rate constants of conversion for various
temperatures in the interval 32-363 К through 10 К and the temperature factor for the speed of conversion are determined.
The temperature factor of the speed of conversion at increase of temperature by 10 К in the interval 323-363 К is 1,171-1,355
times higher for a case of conversion without evaporation, and for a case with evaporation is raised 1,211-1,578 times.
Keywords: dolomite, calcium chloride, sodium chlorate, defoliants, conversion, degree of conversion, activation energy.
INTRODUCTION
In terms of cotton production and harvest Uzbekistan
holds the fifth positionin the world. The natural maturation process of the cotton crop, especially in Central
Asia, one of the most northern cotton growing regions
of the world, and cotton production may take several
weeks. Therefore, it is necessary to accelerate the process
of crop ripening and plants’ leaves pulling-down. This
problem can be solved by applying defoliants.
The existing assortment of the defoliants recommended for application does not fully meet modern
requirements of agriculture and of healthcare organizations for chemical protections of crops. In terms of production and application, chlorate containing defoliants
are considered to be the most low-toxic and inexpensive
chemicals.
Widely used in agriculture in Uzbekistan, the mag-
nesium chlorate defoliant contains in its composition 36
% of active ingredients [1]. However, for the production
of magnesium chlorate as a 50 % raw material, magnesium chloride (bischofite) is imported abroad, being
expensive for local industry. This leads to attraction of
local defoliant production based on local raw materials. In this regard, development of chlorate containing
chemicals with increasing of efficiency, and reducing
of the “stiffness” of the defoliants effect on cotton, are
an urgent problems of the cotton growing industry.
This urgent problem can be solved by using decomposition products appearing in the process of hydrochloric acid effect treatment of natural local dolomite taken
as a raw material, instead of the imported bischofite.
Earlier [2, 3] we investigated the process foaming of
the dolomite dissolution by hydrochloric acid, the product of which is the feed stock for production of chlorate
calcium-magnesium defoliants. The process dissolution
65
Journal of Chemical Technology and Metallurgy, 50, 1, 2015
of Nigerian dolomites with hydrochloric acid were also
studied and optimum parameters of dissolution were
defined by Nigerian scientists [4].
The aim of this research is to obtain a mixed
calcium-magnesium chlorate defoliant by converting of
the calcium-magnesium chlorides solution, obtained by
decomposition of dolomite from of Fergana’s “Shorsu”
deposit by hydrochloric acid [5], with sodium chlorate.
A solution of calcium and magnesium chlorides,
containing on average: 21.49 % СaCl2, 15.50 % MgCl2,
1.20 % NaCl и 61.81 % H2O and sodium chlorate
manufactured by JSC «Ferganaazot» was employed
for the work.
For the purpose of obtaining calcium-magnesium
chlorate defoliant, the conversion process of chlorides
of calcium and magnesium with sodium chlorate, depending on the temperature and duration of the process,
was studied. The conversion was carried out at 323, 348
and 363 K and duration of the experiments 30, 60, 90
and 120 minutes without evaporation and with solution
evaporation.
RESULTS AND DISCUSSION
The process of the conversion was studied in a round
bottom flask with 250 cm3 capacity, equipped with a
stirrer. For the study, it was filled with 100 g of a solution of calcium and magnesium chlorides, derived from
dolomite taken at “Shorsu” deposit, and an equivalent
amount of sodium chlorate. The flask was placed in a
thermostat at a predetermined temperature and its content was intensively stirred. After a certain time interval,
the liquid phase was separated from the sediment and
the corresponding chemical analysis of the sediment, for
the content of chlorine, chlorate-ions, and sodium was
conducted. The content of chlorate and chloride-ions was
determined with the volumetric permanganatometric and
argentometry methods [6, 7], and the amount of sodium,
calcium and magnesium was determined with an atomic
absorption spectrophotometry [8]. After the first filtration step, the liquid phase was cooled down to 293 K,
wherein the crystals of unreached portions of sodium
chlorate fell as a sediment. A second filtering step was
conducted to separate the liquid phase from the crystals
of sodium chlorate. The liquid phase was analyzed after
the second filtration for the content of ClO3-, Cl-, Ca+2,
Mg+2 and Na+ ions (Table 1).
66
The experimental data in Table 1 indicate that the
degree of formation of calcium and magnesium chlorate from calcium and magnesium chlorides during the
process without solution evaporation after 60 minutes
at 323, 348 and 363 K are 18.67, 30.26 and 42.11 %,
respectively, and after 90 minutes, 28.31, 41.11 and
55.68 %, respectively. By increasing the duration of the
conversion process up to 120 minutes, the increase of the
degree of conversion varies slightly and at the temperatures mentioned above, the degrees of conversion were
32.12, 45.62 and 58.93 %, respectively. The amounts of
calcium and magnesium chlorates in the solution after
conversion under the above mentioned temperatures and
process duration of 60, 90 and 120 minutes were 7.20,
11.66, 16.23 %; 10.91, 15.84, 21.46 % and 12.38, 17.58,
22.71 %, resepectively.
Studies on conversion of calcium and magnesium
chlorides with sodium chlorate conducted without solution evaporation showed that the maximum degree of
conversion at 363 K for 120 minutes achieved was only
58.93 %, which was not high enough. To increase the
degree of conversion, studies of calcium and magnesium
chlorides conversion with sodium chlorate carried at
solution evaporation were performed.
In carrying out the conversion with evaporation,
the intensity of the process considerably accelerates,
as demonstrated by the data in Table 1. Thus, at 323 K
after 60, 90 and 120 minutes the degree of conversion
increases by 1.30, 1.24 and 1.18 times.
As a result of an increase in the temperature, the
conversion process accelerates and the degree of the
water removal increases. After the duration of the process of 60, 90 and 120 minutes at 348 K, the degree of
conversion is increased by 1.51, 1.47 and 1.45 times,
respectively, and at 363 K after 60, 90 and 120 minutes
the degree of conversion reaches a maximum value,
being is increased 1.43, 1.36 and 1.35 times. The maximum degree of conversion of 79.27 % is achieved at
temperature of 363 K for 120 minutes. The conversion
product contains: 40.5 % Σ calcium and magnesium
chlorate; 7.5 % Σ calcium and magnesium chloride; 1.3
% sodium chloride, the remaining being water.
For the conversion process, the order of reaction for
kinetic equation (1) was determined [9]:
=
K
2.303
⋅ lg
Co
(1)
τ
(Co − Cτ )
with Со и Сτ, respectively being the concentration of
Zohidbek Hamrakulov, Mamura Askarova, Saidahral Tukhtaev
Table 1. Dependence of the degree of calcium and magnesium chlorides interaction with sodium
chlorate on the temperature and the duration of the process for conversion with and without
evaporation.
Temperature,
К
1/Т·10-3
323
3.10
348
2.90
363
2.75
323
3.10
348
2.90
363
2.75
Time
(τ), min
30
60
90
120
30
60
90
120
30
60
90
120
30
60
90
120
30
60
90
120
30
60
90
120
Σ Calcium and
Degree
magnesium chlorate
of conversion
content in the liquid
Ск, %
phase, %
for conversion without evaporation
3.85
9.98
7.20
18.67
10.91
28.31
12.38
32.12
5.83
15.12
11.66
30.26
15.84
41.11
17.58
45.62
8.16
21.18
16.23
42.11
21.46
55.68
22.71
58.93
for conversion with evaporation
6.42
12.10
12.90
24.31
18.64
35.13
20.17
38.02
12.26
23.10
24.32
45.83
31.98
60.27
35.18
66.31
18.95
35.72
31.88
60.08
40.03
75.45
42.06
79.27
calcium and magnesium chlorides in the initial stage of
the conversion and after the time interval (τ); K is the
constant of the conversion.
According to the data achieved, the process of calcium and magnesium chlorides conversion with sodium
chlorate is of the first order. Evidence of this is that the
constant of the conversion rate, calculated with eq. (1)
a)
The activation
energy, (Еа·103)
kJ/mol)
lg(Co- Cτ)
(average)
1.474
22.503
1.407
1.317
1.582
29.325
1.411
1.254
based on experimental data, remains practically the
same for each temperature within the first 120 minutes
(Table 2).
In addition, the rectilinear dependence of lg (Co-Сτ)
on τ attests for the first order reaction of the conversion of calcium and magnesium chlorides with sodium
chlorate (Fig. 1).
b)
Fig. 1. Dependence of lg (Co-Сτ) on τ at 323, 348 and 363 K in a conversion without evaporation (a) and with evaporation (b).
67
Journal of Chemical Technology and Metallurgy, 50, 1, 2015
Table 2. Constant of the rate of interaction of calcium and magnesium chlorides
with sodium chlorate in conversion without and with evaporation.
Time (τ), minute
Constant of the speed, (К⋅10-2, τ-1)
323 К
348 К
363 К
30
0.3504969
0.5462018
0.7922551
60
0.3443341
0.5998822
0.9100100
90
0.3693834
0.5874486
0.9029255
120
0.3225369
0.5069342
0.7403862
average
0.3466878
0.5601167
0.8363942
30
0.4299601
0.8759620
1.4730412
60
0.4643367
1.0220732
1.5308858
90
0.4809594
1.0258499
1.5604688
120
0.3986173
0.9066137
1.3115096
average
0.4434683
0.9576247
1.4689763
conversion without evaporation
conversion with evaporation
The reaction rate’s constant increases when increasing temperature (Tables 1 and 2) and its change dependence on temperature is subject to the Arrhenius law that
is confirmed by the rectilinear graph dependence of lg
K on 1/T (Fig. 2).
To set the value of the constant of the conversion
velocity for different temperatures, a preexponential
factor, (Ко), was calculated for the Arrhenius equation
from the obtained data:
K = Kî ⋅ e
−
E
R⋅T
(2)
and the dependence equation of lg K on 1/T was inferred.
Fig. 2. Dependence of lg K on 1/T in the conversion without evaporation (a) and with evaporation (b).
68
Zohidbek Hamrakulov, Mamura Askarova, Saidahral Tukhtaev
When the more complex functions are transformed
into linear, for the logarithmic eq. (2) we obtain:
E
1
lg K =
lg K o −
⋅
2.303 ⋅1.987 T
(3)
For the purpose of brevity, we introduce the new nota
tion:
lg=
K η ;lg K
=
a=
;b
o
E
E
1
=
;= ξ
2.303 ⋅1.987 4.576 T
The result is the following:
η= а–b∙ζ
By making up the relation:
b2.1 =
(4)
1
T
(7)
Value of the apparent activation energy (Еа) calculated using the formula Е=4.576∙b was 5.375766208·103
kcal/mol or 22.50295735·103 kJ/mol. Substituting the
calculated value of «а» in lg Ко = a, we get: lg Ко = 3.372988681, from where Ко = 0.423654·10-3.
According to the obtained data, the empirical Arrhenius equation for the observed process of conversion
without evaporation, takes the form:
1
T
5375.766208
=
K 0.423654 ⋅10−3 ⋅ exp(
)
T
lg K =
−3.372988681 − 1174.774084 ⋅
η −η2
η − η1
η 2 − η1
; b3.2 = 3
; b3.3 = 3
ξ1 − ξ 2
ξ2 − ξ3
ξ1 − ξ 3
and performing calculations of the individual values
of ​​«b» from the experimental data (Tables 1 and 2) the
mean value of b is determined.
Calculation of mean values​​is carried out according
to the following formula:
a = ∑η + b ⋅ ∑
lg K =
−3.372988681 − 1174.774084 ⋅
ξ
(5)
3
Substituting the calculated values ​​of a and b in
equation (4) we get:
η = −3.372988681 − 1174.774084 ⋅ ξ
(6)
and
(8)
For conversion with evaporation, after the calculations, the following equation is derived:
1
(9)
lg K =
−1.752790061 − 1530.933618 ⋅
T
The value of the apparent activation energy (Еа), calculated using the formula Е=4.576∙b was 7.005552236·103
kcal / mol or 29.32524166·103 kJ / mol. Substituting the
calculated value of «а» in lg Ко = a we will have:
lg Ко = - 1.752790061, from it Ко = 17.668917·10-3
When the values of Ко and E are substituted, the
empirical Arrhenius equation (2) transforms in:
Table 3. Reaction velocity constant and temperature coefficient of conversion at different temperatures.
Temperature,
Constant of the conversion velocity,
The temperature coefficient
К
-2
of conversion velocity (γ)
-1
К ּ◌10 min
for conversion without evaporation
323
0.346
-
333
0.469
1.355
343
0.592
1.262
353
0.714
1.206
363
0.836
1.171
for conversion with evaporation
323
0.443
-
333
0.699
1.578
343
0.956
1.368
353
1.213
1.269
363
1.469
1.211
69
Journal of Chemical Technology and Metallurgy, 50, 1, 2015
7005.552236
)
(10)
T
On the basis of equations (7 and 9) and (8 and 10),
the constants of the reaction rate of conversion for various temperatures in the range 323-363 K, withn every 10
K, as well as the temperature coefficient of the conversion velocity are calculated (Table 3).
According to the obtained data, the temperature coefficient of conversion velocity increases 1.171 - 1.355
times when temperature is increased by 10 K step in a
range of 323-363 K for conversion without evaporation, and for conversion with evaporation, it increases
1.211-1.578 times.
=
K 17.668917 ⋅10−3 ⋅ exp(
CONCLUSIONS
The parameters of the mixed calcium and magnesium chlorate preparation are the following: the conversion of chlorides of calcium and magnesium with sodium
chlorate at molar ratio at 1:2, duration 120 minutes and
363 K temperature, with solution evaporation.
REFERENCES
1.Specifications, TR (Technical Requirements) 88.1634, Liquid magnesium chlorate defoliant, 2010,
Tashkent, Uzbekistan standard agency’s publishing
house, p. 10, (in Russian).
70
2.Z.A. Hamrakulov, Study of the process of foaming dolomite at the dissolution by hydrochloric acid, Uzbek
Chemical Journal, 5, 2011, 16-20, (in Russian).
3.Z.A. Hamrakulov, S. Tukhtaev, C.M. Tadjiev, M.K.
Askarova, Investigations the process of foaming at the
decomposing dolomite by hydrochloric acid, Journal
of Chemistry and Chemical Technology, Tashkent, 1,
2012, 7-9, (in Russian).
4. A.A. Baba, A.O. Omipidan, F.A. Adekola,
Obalowu Job, Abdul G.F. Alabi, A. Baral, R. Samal,
Optimization study of Nigerian dolomite ore dissolution by hydrochloric acid, J. Chem. Technol. Metall.,
49, 3, 2014, 280-287.
5.Z.A. Hamrakulov, M.K. Askarova, S. Tukhtaev,
Obtaining of solution of calcium magnesium chloride
from dolomite, Journal of Chemical Industry, SanktPetersburg, 2, 2013, 70-78, (in Russian).
6.State standard 12257-77, Sodium chlorate, Moscow,
Standard agency’s publishing house, 1987, p. 19, (in
Russian).
7.E.N. Dorokhova, G.V. Prokhorova, Analytical
chemistry: Physical-chemical methods of analysis,
Moscow, 1991, (in Russian).
8.I. Khavezov, D. Salev, Atomic Absorption Analysis,
Sofia, 1980, (in Bulgarian).
9.J.C. Ospanov, Physico-chemical basis of selective
dissolution of minerals, Moscow, 1993, (in Russian).