Method for producing powdered high-concentration monoammonium phosphate by two-stage neutralization of high-impurity raffinate acid

Abstract

The method for producing powdery high-concentration monoammonium phosphate by two-stage neutralization of high-impurity raffinate acid is as follows: the by-product raffinate acid generated in the production process of wet purified phosphoric acid is preheated to 65-75 DEG C, ammonia gas is first introduced to perform a first-stage neutralization reaction, the pre-stable impurity neutralization slurry is obtained after constant temperature ripening, ammonia gas is introduced to perform a second-stage neutralization reaction on the pre-stable impurity neutralization slurry, the qualified monoammonium phosphate slurry is obtained after constant temperature ripening, the qualified monoammonium phosphate slurry is continuously subjected to grading concentration, drying is performed after the slurry solid content is concentrated to 70-75%, and the powdery high-concentration monoammonium phosphate product is prepared. The present application takes the by-product high-impurity raffinate acid generated in the production process of wet purified phosphoric acid as the only phosphorus source, realizes full-value utilization of the raffinate acid, the process is green and environmentally friendly, and is suitable for industrialized continuous production.

Description

Technical Field

[0001] This invention belongs to the field of resource utilization of phosphorus chemical by-products and fertilizer production technology, specifically relating to a method for producing powdered high-concentration monoammonium phosphate using high-impurity raffinate residue produced as a by-product in the wet purification process of phosphoric acid production. Background Technology

[0002] The wet purification process for phosphoric acid production produces a large amount of residual acid as a byproduct. This material has a high P2O5 content, but it is enriched with most of the impurities such as iron, aluminum, magnesium, and fluorine from the raw phosphate rock. It is a typical difficult-to-treat byproduct in the phosphoric chemical industry, and its resource utilization is extremely difficult.

[0003] In existing technologies, the mainstream utilization of residual acid is for the production of fertilizer-grade monoammonium phosphate. However, the production process suffers from many insurmountable technical defects, mainly: 1. Significant loss of nutrients and water-soluble phosphorus. When high-impurity raffinate is directly neutralized, iron, aluminum, and magnesium impurities easily react with phosphate ions to form amorphous colloidal precipitates. These precipitates not only encapsulate phosphate ions, leading to a significant decrease in the proportion of water-soluble P2O5, but also make it difficult for the effective nutrients in the product to meet the high-concentration superior grade standard in GB 10205-2009. Most products can only reach the qualified grade or low-concentration grade, resulting in extremely low added value.

[0004] 2. Low phosphorus yield and serious resource waste. Existing two-stage neutralization processes are mostly based on "slag removal and purification". Impurities are precipitated and removed by filtration through staged neutralization. Although this can improve product purity, the filtration process causes more than 15% of phosphorus to be lost with the filter residue. The phosphorus yield is generally less than 85%. At the same time, the storage and treatment of filter residue brings high costs and environmental pressure.

[0005] 3. Poor slurry rheological properties and insufficient production continuity. The large amount of amorphous colloids generated by the traditional neutralization process leads to a sharp increase in slurry viscosity. During subsequent concentration, severe scaling occurs in the equipment, evaporation efficiency decreases significantly, energy consumption increases significantly, and long-term continuous production cannot be achieved.

[0006] 4. Poor raw material compatibility and high cost. To alleviate interference from impurities, some processes use the addition of large amounts of modifiers such as fluorides and complexing agents, or mix with high-quality wet-process phosphoric acid to dilute the impurity concentration. The former significantly increases the raw material cost, while the latter cannot achieve full high-value utilization of raffinate, and both are difficult to adapt to raffinate raw materials with ultra-high iron, aluminum and magnesium content (the combined content of Fe2O3, Al2O3 and MgO exceeds 9%). Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to solve the core problems in the production of monoammonium phosphate from high-impurity raffinate acid, such as large loss of water-soluble phosphorus, low phosphorus yield, high slurry viscosity, high energy consumption for concentration, and substandard product nutrient content. It provides a two-stage neutralization in-situ impurity stabilization process that requires no filtration or slag removal, no acid dilution, and no additional modifiers. This process enables the full and high-value utilization of ultra-high-impurity raffinate acid, and the stable production of high-concentration, high-grade powdered monoammonium phosphate.

[0008] The technical solution adopted in this invention is as follows: A method for producing powdered high-concentration monoammonium phosphate through two-stage neutralization of high-impurity raffinate acid includes the following steps: S1. Raw material pretreatment: The residual acid, a byproduct generated during the wet purification process of phosphoric acid production, is preheated to 65-75°C. The residual acid contains 37.0%-38.5% P2O5, 4.5%-5.0% Fe2O3, 2.5%-3.0% Al2O3, 1.7%-2.0% MgO, 1.2%-1.4% F, and 0.4%-0.5% SO3 by mass fraction. Preheating to 65-75°C in this step promotes the dissociation of fluorosilicic acid in the residual acid, releasing sufficient free fluoride ions to provide a fluorine source for subsequent complexation and stabilization. Simultaneously, it reduces the viscosity of the residual acid, improves the uniformity of transport and stirring, and avoids localized temperature and pH fluctuations during the neutralization reaction. S2. First-stage neutralization and in-situ pre-stabilization of impurities: Ammonia gas is continuously introduced into the preheated residual raffinate to carry out a first-stage neutralization reaction. After the reaction is completed, the mixture is aged at a constant temperature to complete the in-situ pre-stabilization of impurities and obtain a pre-stabilized neutralized slurry. S3. Two-stage neutralization and deep impurity stabilization: Ammonia gas is continuously introduced into the pre-stabilized and neutralized slurry to carry out a two-stage neutralization reaction. After the reaction is completed, constant temperature aging is continued to complete the deep impurity stabilization and obtain a qualified monoammonium phosphate slurry. S4. Slurry classification and concentration: The qualified monoammonium phosphate slurry is classified and concentrated until the slurry solid content is 70-75% to obtain concentrated slurry; S5. Preparation of powdered products: The concentrated slurry is dried to prepare a powdered high-concentration monoammonium phosphate product with a total nutrient content (N+P2O5) ≥58%, a water-soluble P2O5 content of ≥85% of the effective P2O5, and a moisture content ≤2.0%.

[0009] Furthermore, in step S2, the control conditions for the neutralization reaction are as follows: reaction temperature 85~95℃, final pH value 2.2~2.8, degree of neutralization 0.4~0.6, stirring during the reaction, and reaction time 20~40min; the isothermal ripening conditions are as follows: the isothermal ripening temperature is the same as the reaction temperature, and the ripening time is 30~60min. The high temperature of 85~95℃ can significantly increase the complexation reaction rate of iron, aluminum and fluoride ions, ensuring that iron and aluminum impurities are completely stabilized within the reaction residence time; the low pH window of 2.2~2.8 can prevent iron and aluminum from combining with phosphate to form precipitates, ensuring that the complexation reaction proceeds preferentially, and eliminating the loss of water-soluble phosphorus from the source.

[0010] Further, in step S3, the control conditions for the two-stage neutralization reaction are: reaction temperature 70~80℃, final pH value 4.2~4.6, degree of neutralization 0.95~1.05, stirring during the reaction, and reaction time 15~30min; the isothermal ripening conditions are: the isothermal ripening temperature is the same as the reaction temperature, and the ripening time is 20~40min. Cooling to 70~80℃ can directionally regulate the formation of complete crystalline magnesium ammonium phosphate crystals from magnesium impurities, preventing the formation of amorphous colloids and avoiding an increase in slurry viscosity; at the same time, it can reduce ammonia volatilization loss, accurately control the degree of neutralization, ensure that the main product is monoammonium phosphate, and avoid the dissociation of stabilized iron and aluminum complexes.

[0011] Further, in step S4, the specific process of graded concentration is as follows: the first-effect evaporation is controlled at a temperature of 90~100℃ and a vacuum degree of -0.04~-0.06MPa, and the slurry solid content is concentrated to 55~60%; the second-effect evaporation is controlled at a temperature of 70~80℃ and a vacuum degree of -0.07~-0.09MPa, and the slurry solid content is concentrated to 70~75%.

[0012] Furthermore, in step S5, a spray granulation dryer or a pressure spray dryer is used to dry the concentrated slurry.

[0013] The main technical principles of the method of this invention are as follows: The in-situ pre-stabilization process in this invention differs from the existing "precipitation and impurity removal" logic. It transforms active impurity ions such as iron, aluminum, and magnesium in the raffinate—which easily lead to the loss of water-soluble phosphorus and increased slurry viscosity—into stable states that do not combine with phosphate ions, do not form amorphous colloids, and do not lose effective nutrients. The entire process is free of precipitation filtration and phosphorus loss, achieving the harmlessness and resource utilization of impurities. This invention uses the fluorine inherent in the raffinate as a complexing agent. Through a first-stage low-pH, high-temperature pre-stabilization, iron and aluminum impurities are directionally converted into stable, soluble fluoride complexes, fundamentally preventing them from forming water-insoluble precipitates with phosphate ions. Further, a second-stage precise pH, low-temperature deep stabilization regulates the formation of fully crystalline, citrate-soluble magnesium ammonium phosphate crystals from magnesium impurities, completely eliminating the formation of amorphous colloids. Combined with raw material preheating and gradient temperature control processes, the stabilization reaction is ensured to be complete and the system stable, ultimately achieving the complete preparation of high-concentration, high-grade monoammonium phosphate from high-impurity raffinate.

[0014] The present invention has the following significant advantages: 1. This invention pioneers a two-stage neutralization and in-situ impurity stabilization technology, overturning the core logic of the existing two-stage neutralization process of "segmented precipitation - filtration and slag removal." It focuses on "in-situ impurity stabilization - morphology control," eliminating the need for filtration and slag removal throughout the entire process. Through a low-pH pre-stabilization stage, the fluorine element inherent in the residual acid is used to directionally convert iron and aluminum impurities into stable fluorine complexes, preventing them from combining with phosphate ions to form water-insoluble phosphates during subsequent neutralization. Through two stages of precise neutralization and deep impurity stabilization, magnesium impurities are controlled to form crystalline, citrate-soluble magnesium ammonium phosphate, eliminating the formation of amorphous colloids.

[0015] 2. The method of this invention significantly improves the utilization rate of phosphorus resources and reduces production costs significantly. All phosphorus in the residual acid enters the product, with no phosphorus loss in the filter residue, and the phosphorus recovery rate is ≥98%, which is far higher than the phosphorus recovery rate of less than 85% in existing filtration and slag removal processes.

[0016] 3. The method of the present invention does not require the addition of additional fluorides, complexing agents or other modifiers, and only utilizes the fluorine element inherent in the raw materials to stabilize impurities.

[0017] 4. The residual acid does not need to be mixed with high-quality wet-process phosphoric acid, achieving 100% full utilization of ultra-high impurity residual acid, which greatly reduces raw material costs and environmental treatment costs.

[0018] 5. This invention effectively solves the problem of the extreme difficulty in resource utilization of residual raffinate with ultra-high impurity content (Fe2O3, Al2O3, and MgO total content exceeding 9%). Moreover, the monoammonium phosphate product produced is of stable quality and meets the standards. It can stably prepare high-grade powdered monoammonium phosphate with a total nutrient content (N+P2O5) ≥ 58%. The proportion of water-soluble P2O5 in the product is ≥ 85% of the effective P2O5, and the moisture content is ≤ 2.0%, which fully meets the GB 10205-2009 high-grade standard. The added value of residual raffinate is greatly improved.

[0019] 6. The method of the present invention is green and environmentally friendly, with no secondary pollution and no filter residue generated, thus avoiding the environmental pressure caused by the storage and treatment of filter residue.

[0020] 7. The equipment required for the method of the present invention is simple, the process is easy to control, it is highly practical, easy to industrialize, and has good application prospects. Detailed Implementation

[0021] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments. Example 1

[0022] A method for producing powdered high-concentration monoammonium phosphate through two-stage neutralization of high-impurity raffinate acid, the steps of which are as follows: S1. Raw Material Pretreatment: The residual acid, a byproduct generated during the wet purification process of phosphoric acid production, is preheated to 70°C. The residual acid contains 37.61% P₂O₅, 4.72% Fe₂O₃, 2.75% Al₂O₃, 1.88% MgO, 1.29% F, and 0.47% SO₃ by mass. The preheating heat source utilizes the waste heat from subsequent concentration and drying processes, achieving energy conservation and consumption reduction.

[0023] S2. First-stage neutralization and in-situ pre-stabilization: The preheated residual acid is fed into the first continuous neutralization reactor. Ammonia gas is continuously introduced into the first continuous neutralization reactor, and the reaction temperature is controlled at 90℃. The final pH value is 2.5, and the degree of neutralization is 0.5. After stirring for 30 minutes, the slurry is sent to a maturation tank and matured at a constant temperature for 45 minutes to complete the in-situ pre-stabilization of impurities, obtaining a pre-stabilized neutralized slurry. The core chemical reaction in this step is as follows: (1) Neutralization of the main reaction: H3PO4 + NH3 = NH4H2PO4; (2) In-situ pre-stabilized heterostructure reaction: Fe ³+ + 6F - = [FeF6] 3- ; Al 3+ + 6F - = [AlF6]3- ; S3. Two-stage neutralization and deep impurity stabilization: The pre-stabilized and neutralized slurry is fed into the second continuous neutralization reactor. Ammonia gas is continuously introduced into the second continuous neutralization reactor to carry out the two-stage neutralization reaction. The reaction temperature is controlled at 75℃, the final pH value is 4.4, and the degree of neutralization is 1.0. After stirring for 20 minutes, the mixture is aged at 75℃ for 30 minutes to complete the deep impurity stabilization and obtain a qualified monoammonium phosphate slurry. The core chemical reaction in this step is as follows: (1) Neutralization of the main reaction: H3PO4 + NH3 = NH4H2PO4; (2) Deeply stable crystallization reaction: Mg 2+ + NH4 + + PO4 - + 6H2O = MgNH4PO4·6H2O; S4. Slurry Classification and Concentration: The qualified monoammonium phosphate slurry is fed into a double-effect falling film evaporator for classification and concentration. The first-effect evaporation is controlled at a temperature of 95℃ and a vacuum degree of -0.05MPa, and the slurry is concentrated to a solid content of 58%. The second-effect evaporation is controlled at a temperature of 75℃ and a vacuum degree of -0.08MPa, and the slurry is concentrated to a solid content of 72%, thus obtaining a concentrated slurry.

[0024] S5. Preparation of powdered products: The concentrated slurry is fed into a pressure spray dryer, and the inlet air temperature is controlled at 320℃ and the outlet air temperature at 105℃ to prepare a powdered high-concentration monoammonium phosphate product.

[0025] Test results of monoammonium phosphate product: Total nutrients (N+P2O5) 58.32%, of which N content 11.25%, available P2O5 content 47.07%, water-soluble P2O5 accounts for 87.2% of available P2O5, moisture 1.85%, pH value (1% aqueous solution) 4.38, fully meeting the GB 10205-2009 standard for superior grade monoammonium phosphate; phosphorus yield 98.42%. Example 2

[0026] A method for producing powdered high-concentration monoammonium phosphate through two-stage neutralization of high-impurity raffinate acid, wherein the raffinate acid contains 38.5% P2O5, 5.0% Fe2O3, 3.0% Al2O3, 2.0% MgO, 1.4% F, and 0.5% SO3 by mass fraction. The production steps are as follows: S1. Raw material pretreatment: The residual acid, a byproduct generated during the wet purification process of phosphoric acid production, is preheated to 65°C.

[0027] S2. First-stage neutralization and in-situ pre-stabilization of impurities: The preheated residual acid is fed into the first continuous neutralization reactor, and ammonia gas is continuously introduced into the first continuous neutralization reactor. The reaction temperature is controlled at 85℃, the final pH value is 2.2, and the degree of neutralization is 0.4. After stirring for 40 minutes, the slurry is sent to the maturation tank and maturated at 85℃ for 60 minutes to complete the in-situ pre-stabilization of impurities and obtain the pre-stabilized neutralized slurry.

[0028] S3. Two-stage neutralization and deep impurity stabilization: The pre-stabilized and neutralized slurry is fed into the second continuous neutralization reactor. Ammonia gas is continuously introduced into the second continuous neutralization reactor to carry out the two-stage neutralization reaction. The reaction temperature is controlled at 70℃, the final pH value is 4.2, and the degree of neutralization is 0.95. After stirring for 30 minutes, the mixture is aged at 70℃ for 40 minutes to complete the deep impurity stabilization and obtain a qualified monoammonium phosphate slurry.

[0029] S4. Slurry Classification and Concentration: The qualified monoammonium phosphate slurry is fed into a double-effect falling film evaporator for classification and concentration. The first-effect evaporation is controlled at a temperature of 90℃ and a vacuum degree of -0.06MPa, and the slurry is concentrated to a solid content of 55%. The second-effect evaporation is controlled at a temperature of 70℃ and a vacuum degree of -0.09MPa, and the slurry is concentrated to a solid content of 70%, thus obtaining a concentrated slurry.

[0030] S5. Preparation of powdered products: The concentrated slurry is fed into a spray granulation dryer. The hot air inlet temperature of the spray granulation dryer is controlled at 300℃ and the tail gas outlet temperature is controlled at 95℃. After granulation, the powdered high-concentration monoammonium phosphate product is obtained by sieving.

[0031] Test results of monoammonium phosphate product: Total nutrients (N+P2O5) 58.17%, of which N content is 11.18%, available P2O5 content is 46.99%, water-soluble P2O5 accounts for 86.5% of available P2O5, moisture is 1.92%, pH value (1% aqueous solution) is 4.32, which meets the GB10205-2009 standard for superior grade monoammonium phosphate; phosphorus yield is 98.67%. Example 3

[0032] A method for producing powdered high-concentration monoammonium phosphate through two-stage neutralization of high-impurity raffinate acid. The raffinate acid used contains 37% P2O5, 4.5% Fe2O3, 2.5% Al2O3, 1.8% MgO, 1.2% F, and 0.4% SO3 by mass. The production steps are as follows: S1. Raw material pretreatment: The residual acid, a byproduct generated during the wet purification process of phosphoric acid production, is preheated to 75°C.

[0033] S2. First-stage neutralization and in-situ pre-stabilization of impurities: The preheated residual acid is fed into the first continuous neutralization reactor, and ammonia gas is continuously introduced into the first continuous neutralization reactor. The reaction temperature is controlled at 95℃, the final pH value is 2.8, and the degree of neutralization is 0.6. After stirring for 20 minutes, the slurry is sent to the maturation tank and maturated at a constant temperature of 95℃ for 30 minutes to complete the in-situ pre-stabilization of impurities and obtain the pre-stabilized neutralized slurry.

[0034] S3. Two-stage neutralization and deep impurity stabilization: The pre-stabilized and neutralized slurry is fed into the second continuous neutralization reactor, and ammonia gas is continuously introduced into the second continuous neutralization reactor to carry out the two-stage neutralization reaction. The reaction temperature is controlled at 80℃, the final pH value is 4.6, and the degree of neutralization is 1.05. After stirring for 15 minutes, the mixture is aged at 80℃ for 20 minutes to complete the deep impurity stabilization and obtain a qualified monoammonium phosphate slurry.

[0035] S4. Slurry Classification and Concentration: The qualified monoammonium phosphate slurry is fed into a double-effect falling film evaporator for classification and concentration. The first-effect evaporation is controlled at 100℃ and vacuum degree -0.04MPa, and the slurry solid content is concentrated to 60%. The second-effect evaporation is controlled at 80℃ and vacuum degree -0.07MPa, and the slurry solid content is concentrated to 75%, thus obtaining concentrated slurry.

[0036] S5. Preparation of powdered product: The concentrated slurry is fed into a pressure spray dryer, and the inlet air temperature of the pressure spray dryer is controlled at 330℃ and the outlet air temperature at 110℃ to prepare a powdered high-concentration monoammonium phosphate product.

[0037] Test results of monoammonium phosphate product: Total nutrients (N+P2O5) 58.41%, of which N content is 11.32%, available P2O5 content is 47.09%, water-soluble P2O5 accounts for 85.8% of available P2O5, moisture is 1.76%, pH value (1% aqueous solution) is 4.45, which meets the GB10205-2009 standard for superior grade monoammonium phosphate; phosphorus yield is 98.29%. Example 4

[0038] A method for producing powdered high-concentration monoammonium phosphate through two-stage neutralization of high-impurity raffinate acid. The raffinate acid used contains 37.8% P2O5, 4.7% Fe2O3, 2.6% Al2O3, 1.7% MgO, 1.25% F, and 0.46% SO3 by mass. The production steps are as follows: S1. Raw material pretreatment: The residual acid, a byproduct generated during the wet purification process of phosphoric acid production, is preheated to 70°C.

[0039] S2. First-stage neutralization and in-situ pre-stabilization of impurities: The preheated residual acid is fed into the first continuous neutralization reactor, and ammonia gas is continuously introduced into the first continuous neutralization reactor. The reaction temperature is controlled at 90℃, the final pH value is 2.6, and the degree of neutralization is 0.5. After stirring for 25 minutes, the slurry is sent to the maturation tank and maturated at a constant temperature of 90℃ for 35 minutes to complete the in-situ pre-stabilization of impurities and obtain the pre-stabilized neutralized slurry.

[0040] S3. Two-stage neutralization and deep impurity stabilization: The pre-stabilized and neutralized slurry is fed into the second continuous neutralization reactor. Ammonia gas is continuously introduced into the second continuous neutralization reactor to carry out the two-stage neutralization reaction. The reaction temperature is controlled at 80℃, the final pH value is 4.5, and the degree of neutralization is 1.0. After stirring for 25 minutes, the mixture is aged at 80℃ for 25 minutes to complete the deep impurity stabilization and obtain a qualified monoammonium phosphate slurry.

[0041] S4. Slurry Classification and Concentration: The qualified monoammonium phosphate slurry is fed into a double-effect falling film evaporator for classification and concentration. The first-effect evaporation is controlled at a temperature of 95℃ and a vacuum degree of -0.05MPa, and the slurry is concentrated to a solid content of 58%. The second-effect evaporation is controlled at a temperature of 75℃ and a vacuum degree of -0.08MPa, and the slurry is concentrated to a solid content of 75%, thus obtaining a concentrated slurry.

[0042] S5. Preparation of powdered product: The concentrated slurry is fed into a pressure spray dryer, and the inlet air temperature of the pressure spray dryer is controlled at 330℃ and the outlet air temperature at 110℃ to prepare a powdered high-concentration monoammonium phosphate product.

[0043] The test results of the monoammonium phosphate product meet the superior grade indicators of monoammonium phosphate in GB 10205-2009; the phosphorus yield is 98.31%.

[0044] Unless otherwise stated, all percentages mentioned in this invention are mass percentages.

[0045] This invention uses high-impurity raffinate acid, a byproduct of wet purification of phosphoric acid, as the sole phosphorus source to prepare high-concentration monoammonium phosphate. The entire production process requires no pre-removal of impurities, dilution of mixed acid, or filtration to remove slag. The phosphorus yield is ≥98%, and it can stably produce high-quality powdered monoammonium phosphate with a total nutrient content ≥58%. This invention solves the industry problems of low nutrient content, high viscosity, high energy consumption, and significant phosphorus loss during the utilization of high-impurity raffinate acid, achieving full and high-value utilization of the raffinate acid. The process is green and environmentally friendly, suitable for continuous industrial production.

[0046] The equipment used in the method of this invention, such as the first continuous neutralization reactor and the second continuous neutralization reactor, are all prior art reactors. The ripening tank, double-effect falling film evaporator, pressure spray dryer, and spray granulation dryer are also prior art devices and equipment. The production equipment is all commonly used in the fertilizer production field, with low equipment investment, easy-to-control production processes, and easy to achieve industrial-scale production of high-concentration monoammonium phosphate.

Claims

1. A method for producing powdered high-concentration monoammonium phosphate through two-stage neutralization of high-impurity raffinate acid, characterized in that, Includes the following steps: S1. Raw material pretreatment: The by-product raffinate generated during the wet purification process of phosphoric acid production is preheated to 65~75℃. The raffinate contains 37.0%~38.5% P2O5, 4.5%~5.0% Fe2O3, 2.5%~3.0% Al2O3, 1.7%~2.0% MgO, 1.2%~1.4% F, and 0.4%~0.5% SO3 by mass fraction. S2. First-stage neutralization and in-situ pre-stabilization of impurities: Ammonia gas is continuously introduced into the preheated residual raffinate to carry out a first-stage neutralization reaction. After the reaction is completed, the mixture is aged at a constant temperature to complete the in-situ pre-stabilization of impurities and obtain a pre-stabilized neutralized slurry. S3. Two-stage neutralization and deep impurity stabilization: Ammonia gas is continuously introduced into the pre-stabilized and neutralized slurry to carry out a two-stage neutralization reaction. After the reaction is completed, constant temperature aging is continued to complete the deep impurity stabilization and obtain a qualified monoammonium phosphate slurry. S4. Slurry classification and concentration: The qualified monoammonium phosphate slurry is classified and concentrated until the slurry solid content is 70-75% to obtain concentrated slurry; S5. Preparation of powdered products: The concentrated slurry is dried to prepare a powdered high-concentration monoammonium phosphate product with a total nutrient content (N+P2O5) ≥58%, a water-soluble P2O5 content of ≥85% of the effective P2O5, and a moisture content ≤2.0%.

2. The method for producing powdered high-concentration monoammonium phosphate by two-stage neutralization of high-impurity raffinate acid according to claim 1, characterized in that, In step S2, the control conditions for the neutralization reaction are: reaction temperature 85~95℃, reaction endpoint pH value 2.2~2.8, neutralization degree 0.4~0.6, stirring during the reaction, and reaction time 20~40min; the constant temperature ripening conditions are: the constant temperature ripening temperature is the same as the reaction temperature, and the ripening time is 30~60min.

3. The method for producing powdered high-concentration monoammonium phosphate by two-stage neutralization of high-impurity raffinate acid according to claim 1, characterized in that, In step S3, the control conditions for the two-stage neutralization reaction are: reaction temperature 70~80℃, reaction endpoint pH value 4.2~4.6, degree of neutralization 0.95~1.05, stirring during the reaction, and reaction time 15~30min; The constant temperature curing conditions are: the constant temperature curing temperature is the same as the reaction temperature, and the curing time is 20~40 min.

4. The method for producing powdered high-concentration monoammonium phosphate by two-stage neutralization of high-impurity raffinate acid according to claim 1, characterized in that, In step S4, the specific process of graded concentration is as follows: the first-effect evaporation is controlled at a temperature of 90~100℃ and a vacuum degree of -0.04~-0.06MPa, and the slurry solid content is concentrated to 55~60%; the second-effect evaporation is controlled at a temperature of 70~80℃ and a vacuum degree of -0.07~-0.09MPa, and the slurry solid content is concentrated to 70~75%.

5. The method for producing powdered high-concentration monoammonium phosphate by two-stage neutralization of high-impurity raffinate acid according to claim 1, characterized in that, In step S5, a spray granulation dryer or a pressure spray dryer is used to dry the concentrated slurry.