RU2471756C1 - Method of reducing caking of ammonium phosphate-based fertiliser - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to agriculture. The method of reducing caking of ammonium phosphate-based fertiliser, obtained by neutralising wet-process phosphoric acid with ammonia with granulation of the end product, while adding a magnesium-containing additive into the process, the magnesium-containing additive being added at the neutralisation step and taken in an amount necessary to maintain the ratio F:MgO=1:(0.15-0.75) in the end product.

EFFECT: invention increases strength of granules and reduces caking of fertiliser.

2 tbl, 5 ex

Description

The invention relates to the production of mineral fertilizers, in particular to fertilizers based on ammonium phosphates, for example ammophos, diammonium phosphate and others, and is aimed at reducing their caking, one of the main criteria that determine their quality.

In the practice of fertilizer production, two directions are used to reduce their caking.

The first is the numerous methods for conditioning finished granular fertilizers by coating the surface of the granules with films, for example, coatings comprising wax, oil, resin and surfactants (patent No. 2291847, 2007, class C05G 3/10), or applying to the surface of the granules dispersed particles neutralized to a pH of 5-8, Petrov’s contact (patent No. 2085550, 1997, CL C05G 3/00) and others.

Many of the known methods cannot be applied to granules of phosphorus-containing fertilizers obtained in drum-type granulators (BGS, AG), since the latter have a finely porous structure and lose their strength during storage and transportation.

In addition, recently due to the extensive sale of fertilizers abroad and, consequently, their long transportation and storage, as well as increased requirements for them not only at the time of receipt (strength, dust, caking), but also the preservation of these qualities over time , the question arose about the creation of new technologies that would allow not only to receive dust-free, non-caking, durable fertilizers, but also to preserve all these qualities in time.

The most promising are methods for conditioning granular phosphorus-containing fertilizers with industrial oils (Technology of phosphorus and complex fertilizers. M: “Chemistry”, under the editorship of S. D. Evenchik, A. A. Brodsky, 1987, pp. 260-261).

However, this treatment of porous granules can significantly reduce the dust content, but with further transportation and storage, the dust content was resumed, and the strength fell.

This effect was especially observed on fertilizers obtained using weak phosphoric acid.

The second direction, which reduces the caking of fertilizers, is the introduction of additives to the product, which structure the granules and strengthen them. Studies have been conducted on the change in hygroscopicity and caking of samples structured with magnesium, aluminum and iron salts, which stimulate the granulation process. Additives were introduced at the granulation stage of nitroammophoski. The introduction of additives allowed to obtain a denser structure of the granules, which, of course, significantly reduces the caking of fertilizers (“Mineral fertilizers and salts. Properties and methods for improving them.” I.M. Kuvshinnikov. M.: “Chemistry”, 1987, p.211- 212). This indicates stronger bonds between the structural elements during granulation of the charge and a higher density of the structure compared to samples without additives. Depending on the amount of additive, there is a significant increase in strength, a decrease in the coefficient of hygroscopicity and caking. Based on the studies, methods have been developed to obtain various fertilizers with the introduction of these additives into the process.

The closest to the proposed technical essence and the achieved result is a known method for producing granular fertilizers based on ammonium phosphates, which can significantly increase the strength of the granules (up to 98-120 kg / cm ² ) and, accordingly, reduce the caking of fertilizers (by 10-15%).

According to this method, the finished ammonium phosphate, which is obtained by neutralizing the extraction of phosphoric acid with ammonia, is mixed with magnesium orthophosphate and granulated. The aim of the known method was, first of all, to obtain a fertilizer of prolonged action, which indicates the amount of introduced magnesium orthophosphate. The disadvantage of this method is the production of fertilizers whose caking does not meet modern requirements, as well as the high price of magnesium orthophosphate, which is not applicable in large-tonnage production.

The present invention solves the problem of reducing the caking of fertilizers based on ammonium phosphates, while fertilizers can be obtained not only using one stripped off phosphoric acid, but, which is especially important at the present time, and one stripped off acid or a mixture thereof. Replacing part or all of the acid with unpaired will significantly reduce energy costs for the process of evaporation of the acid and reduce fluoride emissions. Unpaired extraction phosphoric acid, as you know, contains a large amount of fluorine, which leads to poor granulation, dustiness increases, the surface of the granules from glossy becomes dull, and caking of the product increases.

The proposed method for the production of ammonium phosphates, consisting of the stages of neutralization of extraction phosphoric acid with ammonia with granulation of the finished product and the introduction of a magnesium-containing additive, is characterized in that the additive is introduced into the neutralization stage, and it is introduced in an amount necessary to maintain an F: MgO ratio of 1 : (0.15-0.75) in the finished product.

As a magnesium-containing additive, magnesite, brucite, and inorganic magnesium salts are used.

The proposed solution is aimed at the possibility of changing the structure of the obtained fertilizer in order to strengthen the granules and reduce caking of the finished product during storage and transportation. High caking of mineral fertilizers is associated with the mobility of the structural elements of the salt system and, accordingly, with the low strength of the structure of defective crystalline blocks.

When neutralizing extraction phosphoric acid with a high fluorine content, the latter forms amorphous gel-like compounds, as a result of which viscous pulps form, which in a certain way affect the granulation processes and the structure of the granules formed. The resulting amorphous gel-like compounds contribute to the formation of point substitutional defects in the surface layer of crystalline blocks and their interaction with dislocations emerging on the surface of the granule (crystal). As a result, the structural strength of the defective crystalline blocks decreases, the granular structure softens and the strength decreases.

It was noted that ammonium phosphate samples obtained from acids with a high fluorine content were characterized by a decrease in strength and an increase in caking. Moreover, an increase in the fluorine content leads to a significant decrease in strength; obviously, fluorine softens the structure of the granules, making it less dense.

The introduction of inorganic additives significantly changes the properties: increases the strength and density of the granules, reduces hygroscopicity and caking.

In the proposed method, the magnesium-containing additive was introduced into the stage of neutralizing the acid with ammonia. Maintaining a magnesium-containing additive at the stage of neutralization allows to reduce the caking of fertilizers obtained using unpaired phosphoric acid or a mixture of stripped and unboiled acids.

By the method of X-ray phase analysis of fertilizer samples based on ammonium phosphates using unpaired acid, it was found that the introduction of a small amount of MgO (0.4-0.6%) leads to a significant change in the input structure of the insoluble sediments that make up the product.

It was found that magnesium enters the structure of the precipitate in the form of ammoxidized phosphate of the Mg (NH ₂ ) ₂ (НРО ₄ ) ₂ · 4H ₂ O type. Magnesium enters the structure of Fe and Al fluorophosphate precipitates, strengthening and structuring the precipitate, while binding more fluoride.

The formation of such a crystalline hydrate with a high content of structurally bound water can inhibit the hydration of gel-like SiO ₂ and can also bind surface moisture under adverse conditions: relatively high humidity, humidification, etc.

Table 1 shows the phase composition of ammonium phosphate without the addition of MgO and with the addition of MgO.

Table 1 Phase composition of ammonium phosphate samples Connections MgO free With MgO (NH ₄ ) ₂ HPO ₄ 74 74 NH ₄ H ₂ PO ₄ 8.3 8.3 (NH ₄ ) ₂ SO ₄ 8.5 8.3 CaHPO ₄ 3.0 - CaF ₂ - 1.95 SiO ₂ (gel) 1,0 1,0 NH ₄ ALHPO ₄ F ₂ 1,6 - NH ₄ FeHPO ₄ F ₂ 1.8 - Mg (NH ₄ ) ₂ (HPO ₄ ) ₂ · 4H ₂ O - 1.8 Mg (Al, Fe) NH ₄ (HPO ₄ ) ₂ F ₂ · nH ₂ O - 3.6 NH ₄ F 0.6 - Total 98.8 98.95

From the data of table 1 it follows that, in contrast to the usual product modified with magnesite additives:

1) does not contain ammonium fluoride NH ₄ F - a very hygroscopic compound (hygroscopicity coefficient - 8.1 mol H ₂ O / kg · h. Instead, fluorine binds to calcium in the form of CaF ₃ and into a complex water-insoluble complex Mg (Al, Fe) NH ₄ (HPO ₄ ) ₂ F ₂ · nH ₂ O;

2) contains magnesium ammonium phosphates - compounds that form crystals of hydrates of various double and triple salts, which positively affect the properties of fertilizers in which they are included.

All these differences in the properties of magnesium-modified ammonium phosphates improve the properties of fertilizers, reduce caking, and so on.

Magnesia additive is introduced into the process of producing ammonium phosphates in a strictly defined ratio, namely F: MgO = 1: (0.15-0.75). The influence of the ratio F: MgO in the finished product on the physicochemical properties of ammonium phosphates is given in table 2.

table 2 The dependence of the strength and caking of ammonium phosphates on the content of Mg and F No. p / p Content in prod.,% The ratio of F: MgO The strength of the granules, MPa Traceability *), kPa F MgO one 2.2 0 - 2,8 180 2 3.4 0 - 2.2 220 3 1.65 0.25 1: 0.15 4.85 28.2 four 3.2 0.46 1: 0.14 4.10 32,0 5 1.86 0.37 1: 0.20 5.3 15.3 6 1.95 0.60 1: 0.31 5,6 7.0 7 2.25 1.12 1: 0.50 5.8 3,5 8 2.20 1.30 1: 0.60 6.1 0.75 9 2.0 1.51 1: 0.75 6.9 0 10 2.05 1,62 1: 0.79 7.1 0 *) Deterrability was determined by wetting all samples to a moisture content of 1.5-1.6% H ₂ O

As can be seen from the data in table 2, with an increase in the ratio F: MgO in the product, the magnesium content and the strength of the granules increase, and caking decreases.

The higher the fluorine content in the product, the higher the F: MgO ratio should be. The optimal ratio for the fluorine content of 1.6-2.25% should be considered the ratio F: MgO in the range 1: 0.15-1: 0.75. With a ratio of F: MgO = 1: 0.15, the product is obtained with low strength and high caking.

The ratio of F: MgO of more than 1: 0.75 is impractical because this gives a product with higher strength, which prevents the rapid dissolution of the product and the slow digestibility of nutrient components. In addition, this increases the consumption of magnesium raw materials, which leads to higher prices for products.

The method is illustrated by the following examples.

Example 1

In 200.0 g of EPA with a concentration of 36.5% P ₂ O ₅ with a content of F = 1.5%, 0.46 g of magnesite with a content of 86.0% MgO is added. The resulting mixture was neutralized with gaseous ammonia to a molar ratio of 1.08. The resulting mixture is dried to a moisture content of 0.4-0.5%. Receive 140.0 g of ammonium phosphate composition: 1.9% F; 52% P ₂ O ₅ ; 12% N; 0.25% MgO. The ratio of F: MgO = 1: 0.15; granule strength - 4.85 MPa; caking - 28.2 kPa.

Example 2

In 200.0 g of EPA with a concentration of 36.5% P ₂ O ₅ with a content of F = 1.5%, magnesite is added in an amount of 1.07 g. The mixture is neutralized with ammonia to a molar ratio of 1.73. The pulp is dried to a moisture content of 0.5% H ₂ O. The ratio of F: MgO = 1: 0.21. Get the product 48.5% P ₂ O ₅ ; 18.1% N; 0.58% MgO; 1.92% F. The strength of the granules is 6.2 MPa; caking - 5.65 kPa.

Example 3

In 200.0 g of EPA with a concentration of 35.8% P ₂ O, with a content of F = 1.8%, an addition of brucite (MgO = 60%) is introduced in an amount of 29.95 g, neutralized to a molar ratio of 1.7. Get a product with a content of 47.8% P ₂ O ₅ ; 18.0% N; 1.12% MgO; 2.25% F. F: MgO ratio = 1: 0.5. The strength of the granules is 5.3 MPa, caking - 3.5 kPa.

Example 4

2.9 g of magnesium sulfate are added to 200.0 g of extraction phosphoric acid with a content of 36.5% P ₂ O ₅ , neutralized with ammonia to a molar ratio of 1: 1.71, and 30 g of KCl are added. The resulting mixture is dried. Get a product with a content of 10% N: 27% P ₂ O ₅ ; 10% K ₂ O, 0.5% MgO; 1.7% F. F: MgO ratio = 0.29. The strength of the granules is 5.0 MPa, caking - 5.1 kPa.

Example 5

In a mixture of acids 300 g (unpaired with P ₂ O ₅ = 40.8% and 30% one stripped off EPA) with a content of 1.8% F, magnesite was introduced to bind F in the ratio F: MgO = 1: 0.75 in an amount 4.3 g. The mixture was neutralized to a molar ratio of 1.73; 210 g of product of the composition obtained: 48% P ₂ O ₅ ; 18% N; 1.49% MgO; 1.98% F, ratio F: MgO = 1: 0.75. The strength of the granules is 7.11 MPa, caking is 0 (the sample has not caked for more than 3 months).

Claims (2)

1. A method of reducing the caking of fertilizers based on ammonium phosphates obtained by neutralizing extraction phosphoric acid with ammonia and granulating the finished product when a magnesium-containing additive is introduced into the process, characterized in that the magnesium-containing additive is introduced into the neutralization stage and is taken in an amount necessary to maintain the ratio in the finished product F: MgO = 1: (0.15-0.75). 2. The method according to claim 1, characterized in that magnesite, brucite or other inorganic salts of magnesium are used as a magnesium-containing additive.