RU2234485C1 - Method for preparing complex fertilizer - Google Patents

Abstract

FIELD: agriculture, fertilizers.

SUBSTANCE: invention relates to methods for preparing complex nitrophosphate fertilizers with prolonged effect that are used widely in agriculture. Method involves decomposition of apatite concentrate with nitric acid, isolation of calcium nitrate by crystallization, separation of nitric acid-phosphoric acid solution, its neutralization with ammonia to pH = 0.6-1.2, decomposition of low-grade raw with the neutralized nitric acid-phosphoric acid solution for two stages, additional ammonization of prepared suspension to pH = 4.5-5.5, evaporation, mixing evaporated pulp with ammonium nitrate melt and potassium salt, granulation and drying the ready product. Fluorine compound is added to pulp before additional ammonization to provide the ratio of fluorine and R₂O₃ containing in the pulp liquid phase obtained after the second stage of decomposition of low-grade phosphate raw = (2.5-3.5):1, respectively. Ammonium of alkaline metal fluorides are used as fluorine compounds. Method provides enhancing content of water-soluble forms in fertilizers and to simplify the technological process.

EFFECT: improved preparing method.

2 cl, 3 ex

Description

The invention relates to methods for producing long-acting complex nitrophosphate fertilizers widely used in agriculture.

A known method for producing complex fertilizers, including the decomposition of apatite concentrate with nitric acid, the separation of calcium nitrate by crystallization, the decomposition of low-grade phosphate raw materials with a pre-neutralized solution containing nitric and phosphoric acid, a residue, mixing with a mixture of ammonium nitrate and potassium salt, granulation and drying of the product.

In this method, the apatite concentrate is decomposed with nitric acid for 1 hour at 60 ° C. Calcium nitrate tetrahydrate is isolated from the obtained nitrogen phosphate extract at a temperature of -10 ° C. The nitrogen-phosphate extract is neutralized with ammonia to a pH of 5-5.5 and evaporated, then mixed with low-grade phosphate raw materials (for example, Vyatka-Kama phosphorite, Egorievsky phosphorite, Kingisepp flotation concentrate). In this case, decomposition of low-grade phosphate feedstock occurs. The ratio of apatite to low-grade raw materials is 0.05-0.8: 1. Then, the decomposition product is mixed with potassium salt (potassium chloride) and ammonium nitrate melt, granulation and drying of the finished product are carried out (RF Patent No. 2145316, С 05 В 11/06, 2000).

The disadvantage of this method is that when low-grade phosphate feed is introduced into the process, a product is obtained containing a reduced amount of P ₂ O ₅ in an assimilable form, which is caused by incomplete decomposition of the phosphate feed.

The closest to the described technical essence and the achieved result is a known method for producing complex fertilizers, including decomposition of apatite concentrate with nitric acid, separation of calcium nitrate by crystallization, separation of nitric phosphate solution, its neutralization with ammonia to pH 0.6-1.2, decomposition of low-grade raw materials with neutralized nitric phosphate solution in two stages, additionally ammoniating the resulting suspension to a pH of 4.5-5.5, evaporation, mixing one stripped off pulp with a melt of ammonium nitrate and potassium oh salt, granulation and drying of the final product.

In this method, the apatite concentrate is decomposed with nitric acid. From the resulting suspension at T = -10 ° C, calcium nitrate is isolated. Nitrogen-phosphate extract (AFV) is neutralized with ammonia to a pH of 0.6-1.2. This partially neutralized extract is sent to the decomposition of low-grade phosphate raw materials (for example, Upper Kama phosphorite flour - VKFM). In the first stage of decomposition, low-grade phosphate raw materials are decomposed at W: T = 0.8-1.2: 1 at a temperature of 60 ° C.

In this case, up to 80% of carbon dioxide is removed into the gas phase. Further, phosphorite is further decomposed with either the remaining amount of antipyretic acid or a mixture of it with nitric acid with a ratio of НNО ₃ : Н ₃ РО ₄ equal to (0.8-2.5) :( 1.5-3) - the second stage of decomposition, after which they are neutralized ammonia. Post-ammonization is carried out to a pH of 4.5-5.5. Then the resulting pulp is evaporated, mixed with a mixture of ammonium nitrate and potassium salt, granulated and dried the finished product (RF Patent No. 2167843, class C 05 11/04, 2000).

The disadvantages of this method are the low content of water-soluble forms in the finished product, as well as complications in the process by reducing the fluidity of the pulp obtained after the second stage of decomposition of phosphate raw materials during ammonization, which is accompanied by its thickening, and therefore leads to clogging of the equipment and lower productivity process. To restore the mobility of the pulp, it is necessary to supply water for its dilution.

We set the task to create a method for producing complex fertilizers by nitric acid decomposition of phosphate raw materials with the involvement of a sufficiently large amount of low-grade phosphate raw materials, devoid of the above disadvantages.

The proposed method includes the decomposition of apatite concentrate with nitric acid, the separation of calcium nitrate by crystallization, the separation of nitric phosphate solution, its neutralization with ammonia to a pH of 0.6-1.2, the decomposition of low-grade raw materials with a neutralized nitric phosphate solution in two stages, the ammoniation of the resulting suspension to a pH of 4.5- 5.5, evaporation, mixing one stripped off pulp with a melt of ammonium nitrate and potassium salt, granulation and drying of the finished product.

According to this method, prior to ammonization, fluorine compounds are added to the pulp in such an amount that its ratio from the content of R ₂ O ₃ in the liquid phase of the pulp obtained after the second stage of decomposition of low-grade phosphate feedstock is (2.5-3.5): 1. As fluorine compounds, fluoride salts of ammonium or alkali metals are used.

The essence of the method is as follows. The main distinguishing feature of the proposed method is an additional amount of fluorine (since fluorine is also present in the feed). Fluorine is added in an active water-soluble form. The following reactions occur:

(Fe, Al) ₃ NH ₄ H ₈ (PO ₄ ) ₆ · 6H ₂ O + 6NH ₄ F → 3 (Fe, Al) NH ₄ HPO ₄ F ₂ +

+ 2NH ₄ H ₂ PO ₄ + (NH ₄ ) ₂ HPO ₄ + 6H ₂ O

Due to this, there is an increase in the proportion of water-soluble phosphates in the ammoniated NP-pulp due to the conversion of part of the phosphates of complex R ₂ O ₃ compounds to the water-soluble form of MAF and DAP, as well as an increase in the fluidity (decrease in effective viscosity) of the reaction pulp as a result of the release of crystallization water (6 moles H ₂ O) in a crystalline state. Thickening of NP-pulps does not occur during their neutralization with ammonia; additional water input is not required. Ultimately, the introduction of an additional amount of fluoride ions makes it possible to obtain ammonized NP pulps of lower (24-27%) moisture, which favorably affects the energy consumption at the stage of drying the granules of the finished product.

It is very important at what stage of the process to introduce fluoride compounds, since it is possible to cause the formation of sparingly soluble calcium salts (CaF ₂ , CaSiF ₆ , etc.). Therefore, fluoride compounds are fed into the pulp obtained after the second stage of decomposition of low-grade phosphate raw materials, before its ammoniation. Fluoride compounds are introduced with short-term vigorous stirring to achieve uniform distribution of fluoride ions in the volume of NP-pulp. In this case, at the stage of de-neutralization, fluorine ions will actively interact with Fe ³⁺ , Al ^{3+ cations} with the formation of stable complex compounds (To _{random order} 10 ^-8 -10 ^-6 ). The removal of fluoride ions in the form of complexes with R ₂ O ₃ from the reaction sphere creates unfavorable conditions for the formation of fluorapatite, so that deep digestion of the assimilated forms of phosphates does not occur during ammonization.

The amount of introduced fluorine ions depends on various conditions: but, mainly, on the quantity and quality of low-grade phosphate raw materials containing different amounts of R ₂ O ₃ , and accordingly different degrees of extraction of R ₂ O ₃ into the liquid phase of the pulp obtained before the pre-ammonization stage. Therefore, only the limits declared by us in each case allow us to obtain the best effect.

Using the proposed method will increase in the finished product P ₂ O _{5 aq} by 6-8%, P ₂ O _{5 assimilation} by 10-12% compared with the prototype. In addition, the process becomes more technologically advanced, there is no thickening of the pulp despite a decrease in its moisture, and therefore, productivity increases and energy consumption for drying decreases.

The method is illustrated by the following examples.

Example 1

1000 kg of apatite concentrate containing 39% P ₂ O ₅ , 52% CaO, 3.2% F, 0.3% Fe ₂ O ₃ , 0.85% Al ₂ O ₃ , 1.4% insoluble residue, decompose 2574 kg of nitric acid concentration of 50% with an excess of 10% in excess of stoichiometry. Calcium nitrate tetrahydrate in the amount of 1643.6 kg (α = 75%) is isolated from the resulting suspension at t = -10 ° C.

The filtrate or nitric phosphoric acid extract (AFV) in an amount of 1930.4 kg, containing 527.5 kg of H ₃ PO ₄ , 212.7 kg of HNO ₃ , 380.7 Ca (NO ₃ ) ₂ , 30.72 kg of F in the form of HF and H ₂ SiF ₆ pre-neutralize 55.3 kg of NH ₃ to a pH of 0.6.

Partially neutralized APV is directed to the decomposition of low-grade phosphate (Verkhnekamsk phosphorite flour - VKFM is shown in the examples) of the composition 22.6% P ₂ O ₅ , 38.5% CaO, 4.9% CO ₂ , 4.6% Fe ₂ O ₃ , 3.1% Al ₂ O ₃ , 2.6% F, 14.7% n.a. in the amount of 15.3% by weight of apatite concentrate (in terms of P ₂ O ₅ phosphates), namely 304.5 kg VKFM.

In the first stage, phosphorite is decomposed at T: L = 0.8 and t = 60 ° C for 30 min in order to decarbonize the phosphate feed. The consumption of partially neutralized AFV is 43.6 kg, respectively. At the same time, 80% of VKFM carbon dioxide, namely 11.94 kg of CO _2, is removed into the gas phase. Further, phosphorite is further decomposed with the remaining amount of antipyretic agent, while the remaining amount of carbon dioxide - 2.88 kg - is released into the gas phase.

To improve the rheological properties of the pulp and reduce the loss of phosphates in an unapproachable form, an additional amount of fluoride ions in the form of ammonia fluoride NH ₄ F in the amount of 4.93 kg is introduced into the decomposition pulp. The mass ratio F: R ₂ O ₃ in the decomposition pulp rises from 2.3: 1 to 3: 1.

The pulp is neutralized to pH 5.2 by the addition of 113.34 kg of NH ₃ . The pulp has a moisture content of 26.17%. After evaporation to a moisture content of 15%, it is mixed with a melt of ammonium nitrate (98% of the main substance) in an amount of 417.0 kg.

Upon receipt of the brand N: P ₂ O ₅ : K ₂ O = 1: 1: 1, potassium chloride in the amount of 754.34 kg (59.5% K ₂ O) is introduced into the pulp. The pulp in front of the granulation and drying unit of the product has a moisture content of 10.08% H ₂ O.

The finished product with a moisture content of 1% contains 15.28% P ₂ O _{5 total.} ; 14.94% P ₂ O _{5 equ.} ; 8.22% P ₂ O _{5 aq.} (55% of P ₂ O _{5 assim.} ); 15.19% K ₂ O; 15.36% N _total ; 1.38% F.

Example 2

Obtaining nitrogen phosphate extract and crystallization of calcium nitrate tetrahydrate is carried out analogously to example 1.

Nitrogen-phosphoric acid extract (AFV) in an amount of 1930.4 kg is preliminarily neutralized to a pH of 0.95 with ammonia in an amount of 59.04 kg of NH ₃ .

The partially neutralized extract is sent to the processing of Verkhnekamsk phosphorite flour of the composition specified in example 1, taken in an amount corresponding to 25% P ₂ O ₅ phosphorite by weight of P ₂ O ₅ apatite concentrate in the composition of AFV, namely 563.7 kg of phosphorite. W: T at the stage of decarbonization is 0.8: 1, that is, 450.96 kg of APV with a pH of 0.95 is fed to the first stage. At the same time, 70% of CO ₂ phosmicum - 19.33 kg - is released into the gas phase. The decomposition pulp in the amount of 2525.52 kg contains 44.64 kg F in the form of HF and H ₂ SiF ₆ .

Further, phosphorite is further decomposed with the remaining amount of antiphospholipid for 30 minutes also at 60 ° C. In this case, 8.29 kg of CO ₂ is removed in the gas phase.

In order to reduce losses of P ₂ O _{5 ass.} during ammonization and preservation of fluidity without dilution with water from the outside, sodium fluoride in the amount of 96.15 kg is introduced into the pulp to a mass ratio of F: R ₂ O ₃ to 3.5: 1.

After this, the decomposition pulp is neutralized to pH 4.9 with ammonia in an amount of 168.57 kg of NH ₃ and evaporated from a moisture content of 23.51% to a moisture content of 14% of the mass. One stripped off pulp in an amount of 2481.69 kg is mixed with a melt of ammonium nitrate (98% AC) in an amount of 387.99 kg and with potassium chloride in an amount of 424.64 kg KCl (60% K ₂ O) to obtain nitroammophosphate grade N: P ₂ O ₅ : K ₂ O = 1: 1: 0.5.

Pulp NPK in an amount of 3294.32 kg with a moisture content of 10.91% is supplied to granulation and drying in a BGS apparatus.

The finished product in an amount of 2964.56 kg with a moisture content of 1% contains: 17.19% P ₂ O _{5 total.} ; 15.72% P ₂ O _{5 equ.} ; 7.05% P ₂ O _{5 aq.} ; 17.07% N _total ; 8.57% K ₂ O; 2.97% F (excluding fluorine losses during the drying phase).

Example 3

Obtaining nitrogen phosphate extract and crystallization of calcium nitrate tetrahydrate is carried out analogously to example 1.

Nitrogen-phosphoric acid extract (AFV) in an amount of 1930.4 kg is preliminarily neutralized to a pH of 1.15 with ammonia in an amount of 64.19 kg.

Partially neutralized extract is sent to the processing of Verkhnekamsk phosphorite flour composition: 21.8% P ₂ O ₅ , 35.31% CaO, 4.5% CO ₂ , 3.85% Fe ₂ O ₃ , 2.97% Al ₂ O ₃ , 1.49% F, 13.02% n.a. in the amount of 438.27 kg, which corresponds to a ratio of P ₂ O ₅ apatite to P ₂ O ₅ phosphorite as 80:20.

In the first stage, phosphorite is decomposed for 30 min at t = 60 ° C of partially neutralized AFV in the amount of 438.3 kg, that is, at T: W equal to 1: 1.

In this case, 75% of CO ₂ phosphorite, or 14.79 kg, is released into the gas phase. Then phosphorite is further degraded with the remaining amount of antiphospholipid for 60 minutes. In this case, the remaining amount of carbon dioxide - 4.93 kg - is released into the gas phase. The decomposition pulp in the amount of 2413.14 kg contains: 36.92 kg F in the form of HF and H ₂ SiF ₆ .

To maintain the mobility of the pulp during its subsequent neutralization with ammonia, to prevent its thickening, and also to reduce the losses of digestible forms of phosphates due to their retrograde, ammonium bifluoride in the amount of 9.42 kg of NH ₄ HF ₂ is introduced into the pulp to increase the mass ratio F: R ₂ O ₃ from 2.125: 1 to 2.5: 1.

The pulp is then neutralized to pH 4.7 with ammonia in an amount of 158.83 kg.

Ammonized pulp with a mass of 2581.39 kg is evaporated from a moisture content of 26.08% to 15% H ₂ O. In this case, 336.49 kg of H ₂ O are released into the gas phase.

One stripped off pulp (2240.90 kg) is balanced by nitrogen (N) by adding 365.74 kg of ammonium nitrate melt with a content of 98% of the basic substance. The resulting pulp in an amount of 2610.64 kg to obtain complex NPK fertilizer brand N: P ₂ O ₅ : K ₂ O = 1: 1: 1 is mixed with potassium chloride in an amount of 796.18 kg (60% K ₂ O).

The NPK pulp is fed to granulation and drying to the nozzle of the BGS apparatus in the amount of 3406.82 kg with a moisture content of 10.33%.

The finished balanced product - nitroammophosk - in the amount of 3085.76 kg with a moisture content of 1% contains 15.48% P ₂ O _{5 total.} ; 14.60% P ₂ O _{5 equ.} ; 7.09% P ₂ O _{5 aq.} ; 15.46% N _total ; 15.47% K ₂ O; 1.40% F _total . The ratio of P ₂ O _5suv to P ₂ O _5total is 94.31 rel.%; the proportion of P ₂ O _{5 aq} from P ₂ O _{5 is} 48.54%.

Claims (2)

1. A method of producing complex fertilizers, including the decomposition of apatite concentrate with nitric acid, the separation of calcium nitrate by crystallization, the separation of nitric phosphate solution, its neutralization with ammonia to pH 0.6-1.2, the decomposition of low-grade raw materials with a neutralized nitric phosphate solution in two stages, additionally ammoniating the resulting suspension to a pH of 4.5-5.5 evaporation, mixing one stripped off pulp with a mixture of ammonium nitrate and potassium salt, granulation and drying of the finished product, characterized in that before adding to the ammonia in the pulp fluorine compounds are added in such an amount that the ratio of fluorine to R ₂ O ₃ contained in the liquid phase of the pulp obtained after the second stage of decomposition of low-grade phosphate feed is (2.5-3.5): 1. 2. The method according to claim 1, characterized in that the fluorine compounds use fluoride salts of ammonium or alkali metals.