Physico-chemical properties lime-ammonium nitrate based on chalk, nitrate and ammonium sulphate

. For the granulation of nitrate-sulfate-carbonate melt, the prilling method is applied using a granulation tower. The composition and properties of new types of fertilizers were studied. It is shown that with the ratio NH 4 NO 3 : СаСО 3 : (NH 4 ) 2 SO 4 = 100: 24: 1 the product contains 28,03% - N, 0,50% - SO 3 , 10% - СаО and has a granule strength of 6.03 MPa, which is much higher than the strength of pure NH 4 NO 3 granules (1.32 MPa). The absorption of pure AN granules is 4.82 g. With an increase in the proportion of chalk and ammonium sulfate to the NH 4 NO 3 : СаСО 3 : (NH 4 ) 2 SO 4 = 100: 24: 1 ratio, the absorbency of the LAN granules is 2.57g.


Introduction
Ammonium nitrate is the world's most widespread and effective nitrogen fertilizer. In 2007, its global production capacity amounted to 43 million tons per year [1].
It is used in agriculture for all types of crops and on all types of soil. But it has one very serious drawbackexplosiveness [3].
The explosion of ammonium nitrate at a warehouse of a chemical enterprise in Toulouse (France) in 2001, a series of terrorist attacks in Southeast Asia, Russia, Uzbekistan, and other countries using ammonium nitrate as explosive put consumers and producers of fertilizers in a difficult position. Several countries -China, the Philippines, Colombia, Ireland, and Algeria, have banned the use of ammonium nitrate in agriculture. In this regard, the requirements for the quality of ammonium nitrate and its storage conditions were tightened. And the manufacturers have been tasked with ensuring the transition to the production of fertilizers based on ammonium nitrate, which retains agrochemical efficiency, with significantly greater resistance to external influences and, accordingly, less explosiveness.
The following substances are used as additives that reduce the level of the potential hazard of ammonium nitrate: carbonate-containing compounds of natural and technogenic origin (chalk, calcium carbonate, dolomite); potassium-containing substances (chloride and potassium sulfate); substances containing the cation of the same name -ammonium (ammonium sulfate, ortho-, and ammonium polyphosphates); other ballast substances that do not carry a payload, but determine only the mechanical dilution of ammonium nitrate (gypsum, phosphogypsum, etc.) [10].
The most widespread are the additives of the first group in producing the so-called limeammonium nitrate [11][12][13].
In Europe, it is produced by 31 firms, in Russia -by five industrial enterprises. Earlier [14][15][16], we studied the composition and properties of LAN obtained based on ammonium nitrate (NH 4 NO 3 ) (34.96% N) and limestone flour (CaCO 3 ), "Karmana," "Zhamansay," "Ovkhona," "Forish" and "Karnab" deposits of Uzbekistan. It is shown that depending on the mass ratio NH 4 NO 3 : CaCO 3 = 100: (5-80), the nitrogen content in the products obtained varies within the range of 33.3-18.8%. When the Karmaninskaya limestone flour is added to the AN melt at the ratio NH 4 NO 3 : CaCO 3 = 100 : (5-80), the strength of the granules is 3.52-8.45 MPa, and for Zhamansai, Ovkhoninskaya, Forishskaya, and Karnabskaya flours 2.32-6.41, 2.76-9.57, 3.02-7.77 and 2.83-7.31 MPa, respectively. With the studied NH 4 NO 3 : CaCO 3 ratios, the caking of finished products based on Karmaninsky limestone is in the range of 2.34-3.58 kg / sm 2 , which is 1.3-2 times less than the caking of standard nitrate with the addition of 0.28% MgO (4.67 kg/sm 2 ). The proposed mechanism of action of limestone additives, which increase the strength of AN granules and at the same time reduce its caking, is based on the creation of many crystallization centers, which accelerates the crystallization process and causes the formation of small crystals that make the granules denser and stronger.
This work aims to expand the field of application of carbonate compounds and improve the quality, increase the thermal stability of the LAN and increase the content of the fourth nutrient, sulfur, in the fertilizer.

Materials and methods
In laboratory conditions, we used NH 4 NO 3 grade "pure" (34.96% N) as starting raw materials, as well as powdered chalk with the composition (wt%): CaO 52.23; MgO 1.11; CO 2 41.5. To obtain samples of chalk-containing LAN, the experiments were carried out as follows: a weighed portion of NH 4 NO 3 was melted in a metal cup by electric heating. Then (NH 4 ) 2 SO 4 and chalk were introduced into the melt at the mass ratios NH 4 NO 3 : CaCO 3 : (NH 4 ) 2 SO 4 = 100 : (2-58): (0.5-2.0). Then, the nitrate-carbonate-sulfate melt was kept at 175-180℃ for 1-1.5 minutes. Then it was poured into a laboratory granulator, which is a metal beaker with a perforated bottom, the diameter of the holes in which was 1.2 mm. The pump created pressure in the upper part of the glass, and the melt was sprayed from a height of 35 m onto a plastic film lying on the ground. The resulting granules were sieved by particle size. Particles 2-3 mm in size were tested for strength according to GOST 21560.2-82. Then the products were crushed and analyzed according to known methods [17].
The pH value of 10% aqueous suspensions of the studied samples was measured on an I-130M laboratory ionometer with an electrode system of ESL 63-07, EVL-1M3.1, and TKA-7 electrodes with an accuracy of 0.05 pH units.
The accumulation of fertilizers was determined using the express method [18]. Sagging (X -kg/cm 2 ) was calculated using formula: X = P / S where, P -breaking force, Н (kgf); S is the cross-sectional area of the sample, sm 2 .
The absorbency of the granules about liquid fuel (diesel oil) was determined according to the procedure provided by TU 6-03-372-74 for granular porous AN grade "P." This indicator is expressed in the number of grams that 100 g of granules (g/100g) can absorb.
The temperature of the onset of decomposition of the obtained fertilizers was determined using a NETSCH STA 409 PC / PG device (Germany) in aluminum crucibles at a sample heating rate of 2 deg/min, a sample weight of 10-16 mg. The thermal stability of granules to repeated heating-cooling cycles in the range of 20-60℃ was determined according to the method described in [19].
The rate of dissolution of sample granules in water was determined as follows. The fertilizer granule was dipped into a glass with 100 ml of distilled water, in which its complete dissolution was visually observed and recorded. Room temperature tests five times. Granular samples of NH 4

Results and Discussions
In terms of its physiological role in plant nutrition, sulfur should be ranked fourth after nitrogen, phosphorus, and potassium [20]. And the calcium in importance for plant nutrition is in fifth place after nitrogen, phosphorus, potassium, and sulfur. If it is introduced into the soil in a form assimilable for plants, it will significantly increase yield [21]. Thus, we can say that the composition of the AN is additionally enriched with two macroelementssulfur and calcium. This suggests that when the NO 3  anion is bound by alkaline cations (Ca +) of chalk, the pH value rises to a value that approaches the aqueous suspensions of chalk. It can be assumed that the carbonate raw material neutralizes the acidity of the AN.
The discovered property of the samples can provide a decrease in soil "acidification" after application of the AN. The main properties (strength, temperature of the onset of decomposition, dissolution rate, caking, porosity, and adsorption absorption of liquid fuel granules) of ammonium sulfate LAN are studied in the figure. It was found that the addition of any amount of (NH 4 ) 2 SO 4 and chalk sharply reduces caking, porosity, absorbency, increases the strength and temperature of the onset of decomposition of nitrate granules. If the strength of the granules of the industrial AN is 1.58 MPa, then at NH 4 (Fig., a). All this indicates a decrease in the tendency of the fertilizer to detonate, which is explained by a decrease in the size of the crystals, providing them with a denser packing and the presence of chalk and ammonium sulfate in the mixture, which interrupt the homogeneity of the properties of the AN and the zone of propagation of the detonation wave.
It follows from Fig., b that the addition of any amount of (NH 4 ) 2 SO 4 significantly reduces the caking of the AN (from 2.41 to 0.33 kg/sm 2 ), which is 2-14 times less than the caking of standard nitrate with the addition of 0.28% MgO (4.67 kg/sm 2 ).
Another indicator characterizing the quality of a thermostable speaker is the adsorption capacity of granules for liquid fuel. The lower the porosity of the granules, the lower their absorbency should be. As the data in Fig. c., such a provision is indeed linked. Depending on the weight ratio of the initial components, the absorbency of granules of ammonium sulfate LAN ranges from 1.75-3.24 g of fuel to 100 g of the product. It is 4.82 g for granular NH 4 NO 3 .
With an increase in the mass fraction of chalk and ammonium sulfate in the NH 4 NO 3 melt from 100 : 2 : 0.5 to 100 : 58 : 2, the decomposition start temperature increases from 210℃ for pure NH 4 NO 3 to 232.9-266.2℃ in the finished product (Fig. d). This means that the higher the strength and temperature of the beginning of the decomposition of the granules, the less diesel fuel gets inside the granules. As a result, the less the detonation ability of nitrate ammonium. As the data in Fig. e, the presence of chalk and ammonium sulfate in the composition of nitrate affects the dissolution rate of the latter's granules. With an increase in the amount of CaCO 3 and (NH 4 ) 2 SO 4 in the NH 4 NO 3 melt, the time for the complete dissolution of the finished product granules in water increases. The complete dissolution of granules of pure NH 4 NO 3 and AN with a magnesian additive (0.28% MgO) in water is 44.6 sec on average and 46.8 sec, accordingly, and with the addition of chalk and ammonium sulfate in an amount from 2 and 0.5 to 58 and 2g, slows down the dissolution rate of product granules from 83 to 116.2 sec. This means that AN granules containing chalk and ammonium sulfate dissolve much more slowly in the soil solution. Therefore, the presence of chalk and ammonium sulfate in the nitrate promotes the gradual release of nitrogen from the granule.
In addition, the addition of chalk and ammonium sulfate to the NH 4 NO 3 melt increases the pH of a 10% solution of the latter from 5.17 to 7.05-7.33 (Fig. f), and this is most effective in neutral and acidic soils.

Conclusion
Research has been carried out to obtain sulfur-containing lime-ammonium nitrate based on ammonium nitrate and powdered chalk, and ammonium sulfate. It was found that the more powdered ammonium sulfate and chalk are introduced into the ammonium nitrate melt, the lower the N content and the higher the S and CaO content in the product. It was also shown that the greater the amount of ammonium sulfate and chalk, the lower the caking and absorbency of diesel oil, and the higher the strength, thermal stability, water solubility, and decomposition temperature of nitrate granules. Thus, the samples of sulfur-containing limeammonium nitrate have improved physicochemical, agrochemical, and lower detonation properties.