RU2223933C1 - Method for preparing complex fertilizer - Google Patents

Abstract

FIELD: chemical technology, fertilizers. SUBSTANCE: invention relates to methods for preparing complex nitrate-phosphate fertilizers with the prolonged effect used widely in agriculture. Method involves decomposition of apatite concentrate with nitric acid, isolation of calcium nitrate by crystallization, treatment of carbonate-containing low-grade phosphate raw for two stages. Method involves using nitratephosphate solution neutralized with ammonia preliminary, additional ammonization of the prepared suspension, its evaporation, mixing evaporated pulp with ammonium nitrate melt and potassium salt and drying the ready product. On the first stage for decomposition of carbonate-containing low-grade phosphorus raw preliminary neutralized solution is fed in the amount to provide the ratio liquid : solid at this stage = (2.5-3.5):1. Remained part of nitrate-phosphate solution is fed to the second treatment stage and process is carried out in dispersing nitric acid-containing liquid reagent in the amount 5-7% as measured for HNO₃ of stoichiometry for apatite CaO. Preliminary neutralization of part of nitrate-phosphate solution with ammonia is carried out to pH 0.6-2.5. Nitric acid or part of nitrate-phosphate solution is used as liquid reagent fed for dispersing. Method provides reducing foam formation in the process, to enhance utilization coefficient of equipment volume and to retain quality of product. EFFECT: improved preparing method. 2 cl, 4 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 one embodiment of this method, the apatite concentrate is decomposed with nitric acid for 1 h 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 pH 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 (calcium chloride) and melt of ammonium nitrate, granulation and drying of the finished product are carried out (RF Patent 2145316, С 05 В 11/06, 2000).

The disadvantage of this method is that when low-grade phosphate feed is introduced into the processing 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. In addition, the process is characterized by a significant release of stable foam, which complicates the process, makes it unstable, leads to the loss of phosphate raw materials.

 According to this method, the preliminary neutralization of the solution containing nitric and phosphoric acids with ammonia is carried out to a pH of 0.6-1.2, and the decomposition of low-grade carbonate-containing phosphate raw materials is carried out in two stages, while the first neutralized solution in the amount necessary for achievements in the pulp W: T equal to 0.8-1.2: 1, and the remaining portion of the solution neutralized to pH 0.6-1.2 is introduced into the second.

Two versions of the method are possible depending on the specific conditions. For preliminary neutralization with ammonia, either a nitrogen-phosphate extract obtained by decomposition of the apatite concentrate is fed, or nitric acid is added to it. As low-grade phosphate raw materials, raw materials with a high content of CO ₂ (carbonate-containing raw materials) are used. Boron-containing compounds are added to the process in the second stage of processing low-grade phosphate feed. The method allows to involve in the production of cheap phosphate raw materials and to obtain a fertilizer of prolonged action with improved physical and mechanical properties (RF Patent 2167843, C 05 11/04, 2001).

The disadvantage of this method is that in connection with the processing of carbonate-containing phosphate raw materials, increased foaming occurs, which leads to losses of P ₂ O ₅ , disruption of the technological regime, as well as a decrease in the productivity of the equipment. The technology of the known method, although it helps to reduce foaming, however, does not allow to eliminate it to fully acceptable in large-tonnage production.

 We have set the task to significantly reduce the release of foam in the production process while maintaining the productivity of the process and the quality of the finished product.

The problem was solved in the proposed method for producing complex fertilizers, including the decomposition of apatite concentrate with nitric acid, the separation of calcium nitrate by crystallization, the processing of carbonate-containing low-grade phosphate raw materials in two stages, using a nitrogen-phosphate solution previously neutralized with ammonia, and the ammoniation of the resulting suspension with a mixture of it melt of ammonium nitrate and potassium salt, granulation and drying of the finished product. According to the proposed method, a pre-neutralized solution is supplied to the first stage of the decomposition of carbonate-containing low-grade phosphorus feedstock in the amount necessary to obtain a W: T ratio of 2.5-3.5: 1 at this stage, the remaining part of the nitric phosphate solution is fed to the second stage processing, and the process is conducted when dispersing a liquid reagent containing nitric acid in an amount of 5-7% based on HNO ₃ from stoichiometry on CaO of apatite. Preliminary neutralization of part of the nitric phosphate solution with ammonia is carried out to a pH of 0.6-2.5, and either the nitric acid or part of the nitric phosphate solution is used as the liquid reagent supplied for dispersion.

 At the second stage of processing low-grade phosphate raw materials, it is possible to add boron-containing components in amounts and ratios proposed in the prototype method.

The essence of the method is as follows. The proposed method uses a combination of two methods of defoaming - mechanical and chemical. In this process, the foam released is a three-phase system (gas-liquid-solid) having an elastic framework formed by a liquid phase (decomposition solution). Foam bubbles are modified into multifaceted cells, separated by liquid films. The gas phase of the cells consists of carbon dioxide, fluoride gases, nitrogen oxides and water vapor. The stability of the foam during the acid decomposition of phosphorites by the presence of organic impurities, a finely divided fraction of phosphate. The method proposes to disperse a liquid reagent into a foam layer. For spraying, spraying devices are used that operate under the pressure of compressed air, i.e. there is a mechanical suppression of the foam. On the other hand, a liquid component is sprayed containing a strong chemical oxidizing agent - nitric acid, either in pure form or contained in an un-neutralized nitric phosphoric acid solution taken from the decomposition stage of apatite raw materials. Nitric acid interacts with organic impurities and with highly dispersed fractions of phosphate raw materials. The dispersed solution should contain a strictly defined amount of nitric acid - 5-7% calculated on HNO ₃ from stoichiometry on CaO of apatite. Reducing this norm will not allow to achieve the desired result, and increasing it is an acidic finished product.

 It is known that the process of processing carbonate-containing phosphate raw materials should be carried out in two stages, the first of which decomposes the carbonate part, and then the phosphate part. In the first stage serves pre-neutralized nitric phosphate solution. Its amount is selected so that the ratio W: T at this stage is 2.5-3.5: 1, since when the content of the liquid phase is present, the suspension has a rather viscous structure in which the interaction is determined by diffusion, which accordingly leads to an increase in the interaction time reagents. An increase in the content of the liquid phase above 3.5: 1 will lead to unjustified energy expenditures at the stage of pulp evaporation.

 The foam released at the first stage of processing low-grade phosphate raw materials is intensively absorbed in the second stage due to dispersion of a liquid reagent into it, since at the first stage of processing, due to the created conditions, intensive and quite complete decomposition of the carbonate part of the phosphate raw material occurs, the second stage is aimed at its additional decomposition with phosphate parts. In this regard, it is advisable to apply to it a non-neutralized nitric phosphate solution taken from the decomposition stage of apatite. This will speed up the process of its decomposition.

 Carrying out the first stage of processing low-grade phosphate raw materials at these parameters led to a change in the pH limits of the pre-neutralized solution. Depending on the specific W: T in the first stage, the pH of the previously neutralized solution is also selected.

Using the proposed method will allow you to create a technological process for the production of complex fertilizers based on the decomposition of phosphates by nitric acid, involving cheap phosphate raw materials in the production, and to obtain a finished product containing P ₂ O ₅ practically in an assimilable form (water-soluble and citrate-soluble), i.e. long-acting fertilizer with improved physical and mechanical properties.

 At the same time, the foam release process is significantly reduced, which leads to an increase in the utilization rate of the reaction volume of equipment to 0.75-0.85 (in the prototype method, the utilization rate of reaction equipment is 0.55-0.65).

Example 1
1000 kg of Apatite concentrate containing 39.0% P ₂ O ₅ ; 52.0% CaO; 3.2% F; 0.3% Fe ₂ O ₃ ; 0.85% Al ₂ O ₃ ; 1.5% of the insoluble residue decompose 2340.0 kg of 55% nitric acid, taken with an excess of 10% in excess of the stoichiometric norm, at a temperature of 60 ^o C for 90 minutes From the resulting suspension at a temperature of -5 ^{° C.} , a precipitate of calcium nitrate tetrahydrate is isolated in an amount of 1687.4 kg (α = 77%).

Nitrogen-phosphate solution (AFR) after separation of calcium nitrate weighing 1652.6 kg, including 527.5 kg of H ₃ PO ₄ ; 117.0 kg of HNO ₃ and 319.8 kg of Ca (NO ₃ ) ₂ are sent to the decomposition of low-quality carbonate-containing phosphate raw materials in order to obtain a prolonged action fertilizer. The ratio of P ₂ O ₅ apatite and P ₂ O ₅ low-grade phosphate is 85:15. As the latter in the examples, Verkhnekamsk phosphorite flour (VKFM) of the composition is used: 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% insoluble residue. The mass of fosmuki is 304.5 kg of VKFM. The decomposition of fosmuki using AFR is carried out in two stages.

In the first stage, phosphate is treated with a portion of AFR, neutralized to a pH of 0.6, in a ratio of W: T = 2.5: 1. Why 762.5 kg of AFR neutralize 25.7 kg of ammonia. The resulting suspension is sent to the processing of fosmuki. At the same time, 40% of carbon dioxide VKFM is released into the gas phase, which is 5.98 kg of CO ₂ .

In the second stage, phosphorite is further degraded by the remaining initial PRA in the amount of 890.1 kg. Under these conditions, the degree of decomposition of the phosphate part of the feed is 98.5%, the remaining amount of carbon dioxide - 8.97 kg of CO ₂ is released into the gas phase.

 When re-decomposing VKFM in order to suppress intense foaming (destruction of the resulting foam), nitric acid is dispersed in the foam layer at a concentration of 55% in an amount of 5% of the stoichiometric norm on CaO of apatite concentrate, which is 10.64 kg.

The resulting pulp decomposition VKFM in the amount of 1978.99 kg is further neutralized with gaseous ammonia in the amount of 116.6 kg of NH ₃ to a pH of 4.7.

The neutralized nitrophosphate pulp is evaporated to a moisture content of 14%, balanced by the nitrogen component by introducing melt of ammonium nitrate in an amount of 729.2 kg (98% of the basic substance) and mixed with potassium chloride in an amount of 748.8 kg of KCl (60% K) to obtain tripartite fertilizer ₂ O).

The finished product - nitroammophosk - contains at a moisture content of 1%: 14.85% P ₂ O ₅ total; 14.25% P ₂ O ₅ assimilation; 5.92% P ₂ O ₅ aq; 14.83% N _total ; 14.84% K ₂ O.

 Example 2

 The stages of decomposition of apatite concentrate and freezing of calcium nitrate, as well as the consumption of VKFM are similar to example 1.

A portion of the obtained AFR taken in the amount of _AFR : T _VKFM = 3: 1, which is 915 kg, is preliminarily neutralized with ammonia in the amount of 34.8 kg to a pH of 1.75.

The decomposition of phosphate raw materials is carried out under the previously specified conditions. At the same time, at the first stage of the VKFM treatment with partially neutralized AFR, 32% of the carbon dioxide of VKFM, namely 4.78 kg of CO _{2, are} released into the gas phase.

In the second stage, phosphorite is additionally decomposed with the remaining amount of the initial APP in the amount of 737.6 kg The degree of decomposition of phosphate raw materials in this case is 97.9%. The remaining amount of carbon dioxide -10.17 kg of CO ₂ is released into the gas phase.

 In order to suppress foaming, a concentration of 50% nitric acid is dispersed in the foam layer in an amount of 6% of the stoichiometric norm on CaO of apatite concentrate, which is 14.04 kg.

The resulting decomposition pulp is neutralized to pH 5.0 with gaseous ammonia in an amount of 93.8 kg of NH ₃ .

To obtain complex fertilizers of the brand N: P ₂ O ₅ : K ₂ O = 1: 1: 0.5 evaporated to a moisture content of 12% NP-pulp is mixed with 98% melt of ammonium nitrate in an amount of 818.5 kg and potassium chloride in the amount of 384.4 kg KCl (60% K ₂ O).

The finished product - nitroammophosk - contains at a moisture content of 1%: 16.32% P ₂ O ₅ total; 16.44% P ₂ O ₅ equ; 6.46% P ₂ O ₅ aq; 16.35% Ntotal; 8.20% K ₂ O.

Example 3
The stages of decomposition of apatite concentrate and freezing of calcium nitrate, as well as the consumption of VKFM are similar to the data of examples 1-2.

A portion of the obtained APR taken in the amount of _AFR : T _VKFM = 3.5: 1, which is 1067.5 kg, is preliminarily neutralized to a pH of 2.5 with ammonia in an amount of 50.4 kg.

The decomposition of low-grade carbonate-containing raw materials is carried out under the previously specified conditions. At the first stage of phosphorite treatment with partially neutralized AFR with a pH of 2.5, 26% of VKFM carbon dioxide, namely, 3.88 kg of CO _{2, are} released into the gas phase.

 In the second stage, phosphorite is further degraded by the remaining initial PRA in the amount of 585.1 kg. The degree of decomposition of phosphate raw materials is 97.4%. The carbon dioxide component of phosphorite in the amount of 11.06 kg is released into the gas phase.

 In order to suppress intense foaming, 55% nitric acid is sprayed into the foam layer in the amount of 7% of the stoichiometric norm for CaO of apatite concentrate, namely 14.89 kg.

The resulting decomposition pulp is neutralized to pH 4.5 with gaseous ammonia in an amount of 78.3 kg of NH ₃ .

In order to obtain N: P ₂ O ₅ = 1: 1 nitroammophosphate, the neutralized NP pulp was previously evaporated to a moisture content of 14%, after which it was equilibrated with nitrogen by the addition of ammonium nitrate melt (98% of the basic substance) in an amount of 791.2 kg NH ₄ NO ₃ .

The finished product - nitroammophosk - contains at a moisture content of 1%, respectively, of the brand N: P ₂ O ₅ total = 1: 1: 19.28% P ₂ O ₅ total; 18.63% P ₂ O ₅ equ; 8.13% P ₂ O ₅ aq; 19.25% N _total

Example 4
The stages of decomposition of apatite concentrate and freezing of calcium nitrate, as well as the consumption of VKFM are similar to the data of examples 1-3.

A part of the obtained APR taken in the amount of _AFR : T _VKFM = 3: 1, i.e. 915 kg, is preliminarily neutralized to pH 2.0 with ammonia in an amount of 41.8 kg NH ₃ .

The decomposition of low-grade carbonate-containing raw materials is carried out under the above conditions. In the first stage, phosphorite is treated with partially neutralized AFR with a pH of 2.0, 28% of the carbon dioxide of phosphorus, namely 4.18 kg of CO ₂ , is released into the gas phase.

In the second stage, phosphorite is further degraded by the remaining amount of AFR, namely 712.5 kg. The degree of decomposition of phosphate raw materials is 97.6%. In this case, 10.76 kg of CO _{2 are} released into the gas phase.

 In this embodiment, foaming is suppressed by feeding into the foam layer the initial AFR in atomized form in the amount of 6% of the stoichiometric norm of free hydrogen ions AFR on CaO of apatite concentrate, which is 25.1 kg AFR.

The resulting pulp decomposition VKFM is neutralized to pH 4.75 with gaseous ammonia in the amount of 83.6 kg of NH ₃ .

In order to obtain balanced fertilizer - nitroammophoski grade N: P ₂ O ₅ : K ₂ O = 1: 1: 1 - 98% ammonium nitrate in the amount of 804.2 kg of NH ₄ NO ₃ is introduced into pre-evaporated NP pulp and potassium chloride in an amount of 752.4 kg KCl (60% K ₂ O).

The finished NPK product contains at a moisture content of 1%: 14.55% P ₂ O ₅ total; 14.06% P ₂ O ₅ equ; 5.98% P ₂ O ₅ aq; 14.52% Ntotal; 14.57% K ₂ O.

Claims (2)

1. A method for producing complex fertilizers, including the decomposition of apatite concentrate with nitric acid, the separation of calcium nitrate by crystallization, the processing of carbonate-containing low-grade phosphate raw materials in two stages using a nitrogen-phosphate solution previously neutralized with ammonia, the ammoniation of the resulting suspension, its evaporation, and the evaporation of evaporated pulp with mixed ammonia saltpeter and potassium salt, granulation and drying of the finished product, characterized in that the first stage of decomposition of carbonate-containing of low-grade phosphorus feedstock, a pre-neutralized solution is supplied in an amount necessary to obtain a W: T ratio of 2.5-3.5: 1 at this stage, the remainder of the nitric phosphate solution is fed to the second processing stage, the process being carried out at dispersing a liquid reagent containing nitric acid in an amount of 5-7% based on HNO ₃ from stoichiometry on CaO of apatite. 2. The method according to claim 1, characterized in that the preliminary neutralization of part of the nitric phosphate solution with ammonia is carried out to a pH of 0.6-2.5, and either nitric acid or part of nitric acid is used as the liquid reagent supplied for dispersion phosphoric acid solution.