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Turdialiev Umid Muhtaralievich, Institute of General and Inorganic Chemistry Academy of Sciences of the Republic of Uzbekistan, senior scientific researcher, the Laboratory of Phosphate fertilizers E-mail: [email protected] Namazov Shafoat Sattarovich, nstitute of General and Inorganic Chemistry Academy of Sciences of the Republic of Uzbekistan, Doctor of Sciences, Professor
E-mail: [email protected] Reymov Ahmed Mambetkarimovich, Institute of General and Inorganic Chemistry Academy of Sciences of the Republic of Uzbekistan, Doctor of Science, Deputy of scientific study
E-mail: [email protected] Beglov Boris Mihaylovich, Institute of General and Inorganic Chemistry Academy of Sciences of the Republic of Uzbekistan, Academician E-mail: [email protected] Mirsalimova Saodat Rahmatjanovna, Fergana polytechnic institute, associate professor, department of chemical technology E-mail: [email protected]
Modificated ammonium nitrate based on its melt and bentonic clay
Abstract: The approaches of nonexplosive ammonium nitrate by mean introduction of different inorganic matter into ammonium nitrate's composition have been analyzed in the study. The results of thermostable ammonium nitrate obtain using Azkamarsk, Lagonsk, Kattakurgansk, and Navbahorsk bentonite from Uzbekistan as an additive, have been given. Composition and property (granule strength, modification transition temperature, thermal effect of modification transition, dimensions of granule's micropores and microcracks) of bentonite containing samples of ammonium nitrate depending on the weight ratio of initial components have been determined. The rheological properties of nitrogen-bentonite melt in the ranges of 160-185°C and weight ratio of ammonium nitrate to bentonite 100: (3-40), as well have been studied.
Keywords: ammonium nitrate, bentonite, rheological property, thermic analysis, modification transition, and electron microscope examination.
Introduction
Ammonium nitrate is the main widespread product in the world and an affective nitrogen fertilizer. In 2007 its production capacity was 43 mln. tons per year in the world [1]. In Uzbekistan the total capacity of three chemical industries, producing ammonium nitrate (AN) exceeds 1 mln. 700 thousand tons per year. It is used widely in agriculture for all kind of plants and any type of soils.
However, late tenth in the world market readable tendency of demand decrease has been traced for this kind of fertilizer. It is connected to high level potential risk of AN, which is explosive substance [2; 3]. In European countries and Russia great attention is payed attention to organization ofAN production with lower detonating behavior, in particular by addition of various inorganic
substances into AN solution or its melt. It was proved that highly explosive behaviors of AN decreased when reduction of nitrogen up to 26-28% by introduction its composition of different additives [1].
It is known that as additives, reducing level of potential danger ofAN can be followed: natural and anthropogenic calcareous containing (chalk, calcium carbonate, dolomite); potassium containing (potassium chloride, potassium sulphate); similarly ammonium-cation, such as ammonium sulphate, ammonium phosphate and polyphosphates; other ballast substances which are not useful load, but determine mechanic properties of AN (gypsum, phosphogypsum and others) [4].
Russian enterprise including "Angarskiy zavod minu-dobreniya", JSC "Dorogobuj", JSC "Nevinomisskiy Azot"
and Novomoskovskaya JC "Azot" begin to produce stabilized AN in form of calcareous AN with content of 32% nitrogen by introduction limestone into AN melt. Fraction of industrial capacity of calcareous AN in the world is about 7% [5]. All over the world 42 companies produce and supply calcareous AN with 32% nitrogen which of them 31 ones are in Europe [6].
The process of explosion-proof AN by introduction of crystalline potassium chloride into its melt is problematic. It depends while time of stay in the mixer before granulation in tower for granulation should not be exceeded more than one minute. Otherwise potassium nitrate resulting of potassium chloride conversion and can be formed "goat" in the mixer [7].
The results of conducted production experiments indicate that phosphate additives are the best ones which can decrease detonating behavior of AN. In fact, that phosphorus containing additives are allow to solve issue of increase explosion safety of AN and simultaneously to concentrate product by supplemental nutritious element, phosphorus. To problem of introduction of phosphates additives into AN composition devoted a lot of studies, some of them were implemented.
In 2002 JSC "Cherepoveskiy azot" developed the technology of complex nitrogen-phosphorus fertilizer contenting 32.3% N and 5.2% P205 by introduction liquid complex fertilizer composition 11% N and 37% P205 based on superphosphorus acid into AN solution. The addition reduced ability of AN to detonation. Production capacity was 400 thousand t. fertilizer per year [8; 9].
In 2001 the factories, developed industrial production of nitrogen-phosphorus fertilizer based on AN used wet process phosphoric acid or monoammonium phosphate' solution from the same acid as phosphates additive [10-12].
The additives were put into the nitric acid before an apparatus speed ammonizator- evaporator. The evaporation process of nitro-phosphate pulp was performed in the evaporator system and before evaporator one. In a case, ferrous, aluminum, magnesium and calcium phosphates which are in the wet process phosphorus acid and monoammonium phosphate obtained from the same acid, failed out as sediments on the heat exchange surfaces that lead to blocking and obliteration of the equipments.
At that numbers of stops increased in order to clean equipments that lead to system productivity decrease more than two times compare to AN process. Moreover, metal's strong corrosion was observed due to fluorine in the acid which was on interfacial phases of liquid-gas.
In order to elimination of the defects the new approach of nitrogen-phosphate fertilizer was implemented at JSC "Navoiazot" where phosphorite flour ofKyzylkum fed directly into AN melt before the granulation process in the granulation tower [13-18]. When the introduction of phosphorite flour as 0.5 to 5.0% P205 into AN melt, the nitrogen-phosphate fertilizer obtained, content of nitrogen from 25.24 to 33.70%. The results product with granule diameter 2-3 mm has from 3.2 to 7.8 MPa, against 1.6 MPa of straight AN.
It is known that when the introduction of natural gypsum or phosphogypsum into AN melt, less stabilized and explosive AN is formed [19-21].
So, thermic researches conducted shown, that products obtained have significant much higher thermic stability as compared to straight AN.
In [22] it was submitted that application of solid insoluble impurity into AN melt lead to formation of the granule with fine-crystalline structure, possessing large density and strength. The clay, various silicates, talc, precipitated silica gel and others are offered as above mentioned. Among many offer additives in the technical publications which are centre of crystallization, bentonite holds industrial application only.
The bentonite clay is natural polymineral composition changed depending on the formation condition and other factors. The quality of the bentonite is defined to montmorillonite content. The montmorillonite has a laminated crystalline structure, changed composition and corresponds to Si8Al4O20(OH)4nH2O. Where the silicon can be changed by different cations, such as K, Na, Ca, Mg, Al, Fe, Zn and etc.
Distinctive specifics of montmorillonite is high dispersion ability and ability to adsorption and base cation exchange capacity, as well as, absorb water capacity. These valuable substances of bentonite can be served for application them in various fields of manufactures including drilling technique, foundry engineering, potting and etc.
Bentonite is alkaline (sodium or calcium- sodium) and alkaline-earth (calcium, magnesium-calcium, and calcium-magnesium). The latter can be differed on properties and determined in presence interface intervals of crystalline lattice of montmorillonite with exchange cation of alkaline and alkaline-earth metals in various ratios. Alkaline bentonite swell in water, transfer in gel state and form stable suspension, alkaline-earth decayed on small, promptly falling particles.
Alkaline bentonite is found in a few fields, while alkaline widespread.
It is known that several papers are devoted on the use of bentonite to improve the quality of AN, mainly to eliminate its caking [23-26].
The effectiveness of application ofAN in the production that was granulated by bentonite of various fields can be completely different, due to the variability of the composition and properties of raw materials. Therefore, the suitability ofbentonite clay of a deposit for the above purposes should be verified experimentally.
In [23], the research results of the use effectiveness of the production of granular AN by bentonite were shown, having the following composition: 51.9% SiO2; 17.10% Al2O3; 7.92% Fe2O3; 1.53% CaO; 1.18% MgO; 0.38% SO3; 0.26% K2O; 0.21% Na2O; 0.81% TiO2; 8.7810.26% H2O.
Bentonite clay was introduced into the AN melt in powder containing humidity not more than 2% with a particle size less than 0.045 mm. AN melt granulation with the addition of bentonite was carried out on a special test bench installation. When the additive of 0.5-1.0% bentonite in the AN melt increases the crush strength of the granules as compared to the granules without the addition of nitrate is almost two times, and with addition of 2 and 3% bentonite pellet strength increases, respectively, in 3 and 4 times. Caking granules of AN starts to decrease when the content bentonite more than 0.5% in it. Addition of 1-3% bentonite reduces caking of AN approximately two times.
The mechanism of bentonite action as an additive that increases the granule strength of the AN and simultaneously reduces its caking, based on the creation of a plurality of nucleation sites, which speeds up the crystallization process and causes the formation of small crystals that make pellets more dense and strong. Moreover, high hydrophilicity ofbentonite suggests that its particles will rapidly absorb moisture contained in the saltpetre, and thus removes from granules of saturated mother solution which contributes to the destruction and granule caking during storage [24].
An approach [24] patented by author's certificate a process for preparing granular AN by mixing its melt with bentonite, with a fineness of 40 microns, and a moisture content of 1.5% at 172°C. Bentonite was introduced on the basis of the calculation of its content in the finished product to 2%. Granules of AN cooled to temperature 45 °C, treated with aqueous 40% solution of NF preheated to temperature 65 °C in an amount of 0.03 wt. % (in terms of dry substance). After application of the film
of the surfactant granules were dusted by vermiculite in an amount of 1 wt. %.
The main disadvantages of this method are the fol-lowings: multistage (mixing, granulating, spraying, dusting), fall ofvermiculite out of the surface of the granules during storage and transport, low strength pellets, as well as tendency of AN to thermal decomposition.
In [25] the effect of bentonite's additives on the strength of granules and AN's caking also studied. In experiments bentonite powders obtained from ben-tonite clays of Gumbrinsk and Askansk (Georgia), Kazakh and Azkamarsk (Uzbekistan), Cherkassy and Krivorojsk (Ukraine) were used. Before its use clay was ground in a ball mill, mashed in a porcelain mortar and dried at a temperature of 100-110 °C and bolt. The additive had particles size of 40 microns and moisture content was 1-2%. AN was fused in the reactor then when constant stirring introduced into melting bentonite powder at 170-175 °C. The resulting melt was granulated by prilling. It was obtained that samples of the granulated AN with addition of 0.5-3.0% based on different bentonite.
The results showed that the addition of bentonite in an amount of 1-3% increased considerably granule strength and resistance of AN to modification transformations III&IV, as well as to reduce caking one. Addition of the bentonite deposits from Cherkassy was the most effective. If the strength of the pellets AN without additives is 0.54 MPa, with 0.3% addition of the bentonite is 0.97 MPa, and then with 3% addition of will be 2.2 MPa. Caking nitrate without addition was 5.6 kg/cm2 and 3% addition - 2.53 kg/cm2.
Analysis of the above work clearly shows that the addition of bentonite is very perspective for the AN, suitable for bulk transportation and storage. However, there is not some information about the availability of thermostable AN with the addition of bentonite in the scientific literature.
Based on the mentioned above, we investigated to obtain the AN with lower explosive and improved physicochemical properties, using it Navbakhor and Azkamarsk bentonite deposits from Navoi, Lagonsk, Ferghana, and Kattakurgan, Samarkand.
Experimental procedure
Bentonite composition used is shown in Table 1. Before use of bentonite was ground to a particle size of 40 microns and dried. The dispersed composition is given in Table 2.
Table 1. - Chemical composition of bentonite
Grade of bentonite SiO2 Tio2 FeA MgO CaO Na2° K2° P2O5 S°3 Loss from roast H2° CO2
Navbahor (PPD) 46.06 0.39 8.78 3.00 4.33 12.20 0.75 1.05 0.77 1.39 20.90 6.0 9.35
Navbahor (PBG) 72.23 0.45 8.82 3.93 1.81 1.26 1.12 1.33 0.5 1.10 7.36 4.37 0.20
Lagon 42.86 0.73 18.90 4.29 8.33 5.60 4.04 4.82 0.10 0.41 12.0 4.43 8.1
Azkamarsk 50.34 0.73 15.21 5.67 2.30 4.76 2.31 2.36 0.13 1.48 15.89 5.42 3.41
Kattakurgan 50.44 0.66 16,23 5.64 2.21 4.9 0.75 4.2 0.17 1.72 14.49 3.71 4.84
Table 2. - Dispersed composition of bentonite
Class size, mm Yield of fraction, wt.%
Navbahor Lagon Azkamarsk Kattakurgan
Grade PPD Grade PBG
+0.5 0.2 0.35 1.85 0.7 1,95
-0.5+0.25 2.25 3.35 1.35 0.9 0,60
-0.25+0.16 5.55 11.6 3.4 4.45 2,45
-0.16+0.063 21.85 25.25 13.0 28.05 11,2
-0.063+0.05 43.75 22.8 55.6 54.35 51,15
-0.05 26.4 36.65 24.8 11.55 32,65
Initial weight 100 100 100 100 100
Laboratory experiments were conducted in the following way: Chemically pure AN melted on a hotplate. Bentonite was introduced stirring in AN melt at temperature 175°C. The weight ratio of AN melt to the bentonite (BN) was 100 (5-40) for Navbakhor, 100: (5-35) for Azkamarsk 100: (5-32) for Lagonsk, and 100: (5-40) for Kattakurgan, respectively. The temperature was kept constant by means of a contact thermometer TC-300 and electronic relay RT-230. The melt is held for 10-15 min, after which it was
Table 3. - The composition of fertilizers of ammonium nitrate of bentonite from
poured into a laboratory granulator, which is a metallic glass, stainless steel, with a perforated bottom, wherein the diameter of the holes equal 1.2 mm. With help pump on top of the cup are pressurized and the melt was sprayed from the tenth floor of a building on a polyethylene film, lying on the ground. Composition of AN samples were determined according to known techniques [27]. Pellet strength of AN 2-3 mm measured at MIP-10-1 [28]. The experimental results are given in Table 3-6.
obtained by introducing into the melt Navbakhor and strength of granule
The ratio of AN: BN N, % Moisture, % Granule strength
kg/granule kgf/cm 2 MPa
1 2 3 4 5 6
When using carbonate-palygorskite clay PPD
100: 5 32.97 0.26 2.38 47.98 4.70
100: 8 32.04 0.26 3.11 62.69 6.14
100:10 31.49 0.28 3.40 68.54 6.72
100:12 30.93 0.30 3.56 71.77 7.03
100:15 30.10 0.35 3.93 79.22 7.76
100:18 29.38 0.40 4.15 83.66 8.20
100:20 28.89 0.44 4.37 88.10 8.63
100:22 28.40 0.50 4.38 88.30 8.65
100:25 27.72 0.52 4.49 90.51 8.87
100:30 26.58 0.60 4.58 92.33 9.05
100:35 25.84 0.61 4.59 92.53 9.07
100:40 25.01 0.65 4.59 92.53 9.07
1 2 3 4 5 6
When using alkaline earth clay PBG
100: 5 32.94 0.25 2.25 45.36 4.44
100: 8 32.06 0.26 2.88 58.06 5.69
100:10 31.51 0.29 3.19 64.31 6.30
100:12 30.92 0.35 3.34 67.33 6.60
100:15 30.06 0.36 3.64 73.38 7.19
100:18 29.29 0.45 3.90 78.62 7.71
100:20 28.82 0.51 4.05 81.64 8.00
100:22 28.45 0.53 4.24 83.46 8.18
100:25 27.68 0.60 4.39 86.48 8.48
100:30 26.66 0.65 4.38 88.30 8.65
100:35 25.82 0.67 4.49 90.51 8.87
100:40 25.92 0.70 4.56 91.93 9.01
Table 4. - Fertilizer composition obtained by introducing bentonite from Azkamarsk into the melt of ammonium nitrate and strength of granule
The ratio of N, Moisture, Granule strength
AN: BN % % kg/granule kgf/cm 2 MPa
100: 5 32.81 0,25 1.73 34.71 3.52
100: 8 31.89 0,26 2.04 40.81 4.16
100:10 31.30 0,29 2.29 45.70 4.52
100:12 30.81 0,31 2.34 46.80 4.80
100:15 29.96 0,34 2.41 48.26 5.26
100:18 29.19 0,41 2.90 58.0 5.69
100:20 28.68 0,44 3.25 65.0 6.01
100:22 28.25 0,51 3.54 70.80 6.28
100:25 27.54 0,53 3.79 75.62 6.71
100:30 26.55 0,59 3.83 76.60 7.26
100:35 25.51 0,62 3.91 78.20 7.73
Table 5. - Fertilizer composition obtained by introducing bentonite from Lagonsk into the melt of ammonium nitrate and strength of granule
The ratio of N, Moisture, Granule strength
AN: BN % % kg/granule kgf/cm 2 MPa
100: 5 32.91 0.26 2.48 50.08 4.91
100: 7 32.30 0.26 3.11 62.63 6.14
100:10 31.42 0.28 3.43 69.16 6.78
100:12 30.83 0.30 3.56 71.71 7.03
100:15 30.07 0.35 3.97 79.97 7.84
100:18 29.37 0.40 4.19 84.46 8.28
100:20 28.80 0.44 4.38 88.33 8.66
100:22 28.32 0.50 4.49 90.47 8.87
100:25 27.70 0.52 4.52 91.09 8.93
100:28 26.97 0.60 4.56 91.90 9.01
100:30 26.58 0.61 4.58 92.31 9.05
100:32 26.18 0.65 4.59 92.51 9.07
Table 6. - Fertilizer composition obtained by introducing bentonite from Kattaurgansk into the melt of ammonium nitrate and strength of granule
The ratio of N, Moisture, Granule strength
AN: BN % % kg/granule kgf/cm 2 MPa
1 2 3 4 5 6
100: 5 32.95 0.26 2.25 45.36 4.25
1 2 3 4 5 6
100: 8 32.01 0.27 2.88 58.06 5.35
100:10 31.45 0.28 3.19 64.31 6.26
100: 12 30.89 0.36 3.34 67.33 6.61
100:15 30.01 0.37 3.64 73.38 7.04
100:18 29.23 0.46 3.90 78.62 7.57
100:20 28.84 0.50 4.05 81.64 7.88
100:22 28.41 0.54 1.14 83.46 8.04
100:25 27.60 0.59 4.29 86.48 8.28
100:30 26.61 0.64 4.38 88.30 8.56
100:35 25.75 0.65 4.49 90.51 8.75
100:40 24.87 0.70 4.56 91.93 8.80
Results and discussion
From these tables could be seen that with increasing the amount of bentonite's additive, nitrogen content is decreased. The granule strength is increased with increasing amounts of the additive independently of the type bentonite used.
When the change of the ratio of AN melt to bentonite, the granule strength is changed in the following way:
For carbonate- polygorskitov clay PPD at a ratio of AN: bentonite 100:5 granule strange is 4.70 MPa; 100: 10 is 6.72 MPa; 100: 15 is 7.76 MPa; 100: 20 is 8.63 MPa; 100: 25 is 8.87 MPa; 100: 30 is 9.05 MPa and 100: 40 is 9.07 MPa; for alkaline earth clay PBG: 100: 5 is 4.44 MPa; 100: 10 is 6.30 MPa; 100: 15 is 7.19 MPa; 100: 20 is 8.00 MPa; 100: 25 is 8.48 MPa; 100: 30 is 8.65 MPa; 100: 40 is 9.01 MPa; for Azkamarsk bentonite: 100: 5 is 3.52 MPa; 100: 10 is 4.52 MPa; 100: 15 is 5.26 MPa; 100: 20 is 6.01 MPa; 100: 25 is 6.71 MPa; 100: 35 is 7.73 MPa; for Lagonskogo bentonite: 100: 5 is 4.91 MPa; 100: 10 is 6.78 MPa; 100: 15 is 7.84 MPa; 100: 20 is 8.66 MPa; 100: 25 is 8.93 MPa; 100: 30 is 9.05 MPa; for Kattakurgan bentonite: 100: 5 is 4.25 MPa; 100 8 is 5.35 MPa; 100: 10 is 6.26 MPa; 100: 15 is 7.04 MPa; 100: 20 is 7.88 MPa; 100: 25 is 8.28 MPa; 100: 30 is 8.56 MPa; 100: 40 is 8.80 MPa.
The data above show that increasing the additive amount of bentonite clay from 5 to 25 g per 100 g of AN melt leads to increases the granule strength from 4.70 to 8.87; from 4.44 to 8.48; from 4.91 to 8.93, from 3.52 to 6.71 MPa, and from 4.25 to 8.28 MPa, respectively, for bentonite of Navbakhor brand PPD and PBG, Lagonsk, Azkamarsk, and Kattakurgan fields. In [1] it is indicated that the AN with a nitrogen content of 28% is already a non-explosive. Considering the above, we consider the optimal weight ratio of AN melt to bentonite for all the studied deposits is 100: 22. In this case, AN contains 28.40; 28.45; 28.32; 28.25 and 28.41% of N, and its granule strength is 8.65; 8.18; 8.87; 6.28 and 8.04 MPa,
respectively, for bentonite Navbakhor brand PPD, PBG, Lagonsk, Azkamarsk, and Kattakurgan fields. Pellet strength of the products obtained at the mentioned ratio of AN: BN as compared with the strength of pure nitrate depending on the type of bentonite increases approximately 3.9-5.5 times. The highest strength of AN's granule is obtained in the case of bentonite from Lagonsk. The higher the strength of granules, the lower the porosity, the lower diesel fuel fall within the granules, and the lesser extent nitrate will detonate.
When processing bentonit containing melt ofAN in granular fertilizer, their rheological properties play important role. In this connection, the density and the viscosity of the melt were tested at all weight ratios of AN: BN at temperature ranges 160-185 °C. The density was determined by pycnometric technique, and the viscosity with a viscometer grade of VPJ-2.
These experiments show that the density and the viscosity depend mainly on the temperature and mass fraction ofbentonite introduced into the melt ofAN. As the density and the viscosity decreases with increasing temperature and vice- versa increases with the amount of bentonite in the nitrate melt. With increasing amounts ofbentonite additives from 5 to 30 g per 100 g ofAN melt at temperature 170 °C leads to increase of the density and the viscosity of melt from 1.526 to 1.762 g/cm 3; from 6.01 to 19.11 cps; from 1.518 to 1.75 g/cm 3; from 12.94 to 591 cps; from 1.638 to 1.865 g/cm 3; from 9.98 to 43.28 cps; from 1.542 to 1.786 g/cm 3; from 6.22 to 18.96 cps; from 1,520 to 1.75 gf/m 3; from 5.99 to 19.00 cps, respectively, for bentonite of Navbakhor brand of PPD and PBG, Az-kamarsk, Lagonsk, and Kattakurgan fields.
A similar pattern is observed at other temperatures. When the ratio of AN: BN 100: 5; 100: 10; 100: 15; 100: 20; 100: 25, and 100: 30, increasing temperature from 170 to 185°C reduces the density and the viscosity from 1.526 to 1.501 g/cm 3; from 6.01 to 5.23 cps; from 1.596 to 1.564 g/cm 3; from 6.83 to 6.03 cps; from
1.660 to 1.613 g/cm 3; from 7.79 to 6.76 cps; from 1.701 to 1.646 g/cm 3; from 10.47 to 8.87 cps; 1.738 to 1.689 g/cm 3; from 15.37 to 13.21 cps; from 1.762 to 1.713 g/cm 3; from 19.11 to 16.33 cps, respectively, for the brand of PPD Navbakhor bentonite This same relationship can be seen in the case of using other bentonite.
When studied of weight ratios in the range of temperatures 170-185 ° C bentonite containing melt ofAN has sufficient fluidity, which creates favorable conditions for their granulation in the existing granulation tower without any technical difficulties.
The results of X-ray studies show that the phase composition of bentonite containing AN, obtained at different ratios of AN: BN, mainly consists of ammonium nitrate and bentonite.
Derivative graphic thermic analysis (DTA) studies were performed in the temperature ranges from 25 to 180 °C. DTA curves were recorded on NETSCH STA 409 PC/PG (made in Germany) in aluminum crucibles with a heating rate of fertilizer samples 2 deg/min, sample samples is 10-16 mg. The results are as shown in Table 7 below.
According to Table 7 can be seen that the transformation temperature of pure AN IV ^ III is 52.8 °C,
Table 7. - Temperatures of modification transformation
and bentonite additives promotes to increase transformation temperature for samples containing additive of bentonite from 15 to 35%, it is in the ranges 58.3-59, 2 °C. Temperatures transitions of III ^ II, II ^ I, and I ^ melt in bentonite containing AN are also varied, and make up 93.1-93.7; 134.3-134.7 and 164.1-168.4 °C, respectively, when the temperature of the transition to pure AN is 90.5; 133.3 and 174.7 °C. Analogous pattern is observed in the case of bentonite of Kattakur-gan. The results of DTA show that the introduction of bentonite additive reduces the temperature melting and crystallization of AN. During the cooling of nitrate's melt with the addition of bentonite transformations of melt ^ I; I ^ II and II ^ IV occur sequentially. III phase is formed during cooling melt. Thus, the addition of bentonite stabilizes modification of IV. When storing of nitrate bentonite containing temperature fluctuations within the 58.3-59.2 °C abrupt volumetric changes its crystal, related codification transitions will not occur. Temperature transitions of I ^ II and II ^ IV also increased from 123.6 to 125.3 and from 51.0 to 52.0 °C, from 124.6 to 125.4 and from 51.2 to 51.9 °C, respectively for the bentonite of Azkamarsk and Kat-takurgan.
of fertilizers, obtained based on AN melt and bentonite
Samples Moisture, % The values of the peak on the curve
rv^m IIM! IM I^melt MelM MI IMII IIMV IMV
Heating from 25 to 180 °C Cooling from 180 to 25 °C
When using bentonite from Azkamarsk
100:15 0.41 58.3 93.1 134.3 168.4 162.9 123.6 - - 51.0
100:20 0.46 58.5 93.4 134.4 167.4 160.2 124.1 - - 51.3
100:25 0.50 58.8 93.5 134.5 166.8 159.1 124.6 - - 51.5
100:30 0.53 59.1 93.5 134.6 165.2 156.7 125.0 - - 51.7
100:35 0.56 59.2 93.7 134.7 164.1 155.0 125.3 - - 52.0
When using bentonite from Kattakurgan
100:15 0.40 58.2 93.2 134.2 167.3 165.1 1246 - - 51.2
100:20 0.45 58.3 93.4 134.3 166.2 163.5 124.8 - - 51.4
100:25 0.49 58.7 93.6 134.5 163.6 160.8 124.9 - - 51.7
100:30 0.53 59.0 93.7 134.7 160.7 159.3 125.1 - - 51.8
100:35 0.57 59.2 93.9 134.9 159.1 158.5 125.4 - - 51.9
Pure ammonium nitrate without additives
100:0.0 0.23 52.8 90.5 133.3 174.7 168.1 122.1 - - 48.6
The thermal effects of modification transitions the studied samples, defined on the device NETSCH STA 409 PC/PG as shown in Table 8. From the table can be seen that the samples of bentonite containing nitrate, the heat of modification transitions is significantly lower than the heat of transitions of pure AN. It means that they occur with less thermal modifications. This indicates that the addition of bentonite has
an inhibiting effect on the modification transformations and at the transition points of transformation does not takes place till the end.
The sharp decline of heat of crystallization in the presence of the AN in presence additives can be explained by the fact that the insoluble components of the additive components being centers of crystallization facilitates the process of solidification of AN melt.
Table 8. - Thermal effects of modification transformation of AN melt with the bentonite addition
The weight ratio of AN: BN, g The values of t he peak on the curve, J/g
rv^m IIM! IM I^melt MelM MI IMII IIMV IMV
HEAT COOLING
When using bentonite from Azkamarsk
100:15 15.65 11.71 41.09 46.33 43.03 42.57 — — 17.02
100:20 14.94 11.29 38.42 43.09 36.11 39.80 — — 15.45
100:25 14.07 10.70 36.70 39.88 33.55 37.31 — — 14.80
100:30 11.09 10.06 33.21 37.81 31.99 32.65 — — 13.22
100:35 10.40 9.47 30.78 35.80 30.80 29.18 — — 11.58
When using bentonite from Kattakurgan
100:15 16.05 11.95 41.72 46.57 43.08 40.27 — — 16.90
100:20 15.30 11.28 39.63 44.82 40.12 39.04 — — 15.80
100:25 14.02 11.01 37.43 42.38 36.50 37.15 — — 13.58
100:30 12.23 10.15 35.26 41.42 32.95 32.72 — — 12.34
100:35 10.41 9.50 33.65 40.60 31.24 29.31 — — 11.10
Pure ammonium nitrate without additives
100:0.0 24.09 12.43 58.19 71.36 72.50 60.16 - - 30.20
On the basis of DTA studies we can conclude the following. Rising temperatures transition of IV ^ III and inverse transition of II ^ IV leads to the maintenance of high strength and reduction caking AN granule when transport and storage in hot climates.
The instrument NETSCH STA 409 PC/PG also measured the temperature of decomposition bentonite containing AN by thermogravimetry. The results show that the pure AN begins to lose weight at temperature about of 250 °C; the maximum value of the rate of weight loss is achieved at 250-262.8 °C. The progress
of the decomposition processes of pure AN starts with temperature of 210 °C, as it proves exothermic effect on the DTA curve. The thermograms of the samples of bentonite containing AN have endothermic effect at temperatures of 235, 240, 245 °C, respectively. Thermal decomposition correlates with the recorded on thermogravimetric TG curve at maximum diminution of weight. As the thermal image presented, bentonite additive increases the temperature of beginning of the exothermic decomposition of AN at 25-35 °C.
Fig. 1. AN: BN (Azkamarsk) = 100:10
Fig. 2. AN: BN (Azkamarsk) = 100:15
Fig. 3. АС: БГ (Azkamarsk) = 100:20
Microscopic examinations of samples were carried out using a scanning electron microscope REM-200. To review samples of pre-sprayed by silver in a vacuum post VDA-4K. It is shown that the surface of its granules there is large conglomerates ofplate shape crystal size from 40 to 140 microns in sample of pure AN (Fig. 5 a). The surface ofthe granule with a large amount offine pores (1 to 5 microns), and microcracks with width is 1-3 microns. The surface of the granules and their cut consists mainly of crystal conglomerates lamellar structure. However, the granule sections and its surface are micropores (1-3 microns) width has 1-5 microns. Photomicrograph
of initial bentonite in powder form indicates that the bentonite particles have dimensions from 7 to 30 microns.
Analysis of the micrographs of the initial components in a ratio of AN: BN (Navbakhor) = 100: 15 is observed as a more dense structure on the surface of granules and in its cut (Fig. 6a and 6b). On the surface of the granules both aggregated and individual particles of the bentonite additive are observed, but rather evenly distributed on the surface and the pore size of 2 to 10 microns. Moreover, pore with size of1 to 10 microns and bentonite particles sizes of 2 to 10 microns can be seen on the section.
Fig. 4. The pure AN
When investigation of sample surface structure at a ratio of AN: BN = 100:20, can be seen a rather homogeneous structure with uniformly distributed particles over the entire surface, more dense structure determined by increased content of BN (Fig. 7a and 7b). Thus, there is a reduction in the dimensions of the micropores and microcracks width of up to 1 micron.
The electron microscopic examination showed a certain influence of the additive of bentonite on the microstructure AN granules. These results indicate
(without additives)
that BN additive reduces the crystal size of AN, which is centers of crystallisation. Furthermore, the addition of BN is precipitated into the pores and micro cracks, filling them, thereby more perfect surface and internal structure of the AN granules. Such a structure is deprived of defects as nucleus of the future destruction. This fact also explains the reasons for the increase in pellet strength and reduces their porosity. The result it increases the stability of ammonium nitrate.
Fig. 5a. Electron microscope photography of the surface of pure ammonium nitrate
Fig. 5b. Electron microscope photography of pure ammonium nitrate cut
Fig. 6a. Electron microscope photography of fertilizer granule's AN:BN(PBG)=100:15
Fig. 7a. Electron microscope photography of fertilizer granule's AN:BN(PBG)=100:20
Conclusion
Thus, the results carried out laboratorial experiments showed that the addition of bentonite in an amount of 1-3% increased considerably granule strength and resistance of AN to modification transformations III&IV. The result can be seen that the strength of the pellets AN without additives is 0.54 MPa, with 0.3% addition of the bentonite is 0.97 MPa, and then with 3% addition ofwill be 2.2 MPa. Caking nitrate without addition was 5.6 kg/cm 2 and 3% addition — 2.53 kg/cm 2.
Fig. 6b. Electron microscope photography of fertilizer granule's cut AN:BN(PBG)=100:15
Fig. 7b. Electron microscope photography of fertilizer granule's cut AN:BN(PBG)=100:20
It was conducted studies in order to study rheological properties of bentonite containing melt of AN. It was found that all weight ratios investigated in the range of temperatures 170-185°C have sufficient fluidity, create favorable conditions for their granulation in the existing granulation tower without any technical difficulties.
DTA carried out shown that rising temperatures transition of IV ^ III and inverse transition of II ^ IV lead to retention of the high strength and reduction caking AN granule when transport and storage in hot climates.
The effect of a certain influence of the additive of bentonite on the microstructure AN granules was shown by electron microscopic examinations. These results indicate that BN additive reduces the crystal size of AN, is centers of crystallisation. In fact that the addition of BN is precipitated into the pores and micro cracks,
filling them, thereby more perfect surface and internal structure of the AN granules. The structure is deprived of defects as nucleus of the future destruction. This fact also explains the reasons for the increase in pellet strength and reduces their porosity. The result it increases the stability of ammonium nitrate.
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