Gradient utilization process of ammonium phosphate slurry

Abstract

The invention discloses a gradient utilization process of ammonium phosphate slurry, and relates to the technical field of ammonium phosphate production. According to the method, the comprehensive utilization rate of phosphorus is increased, products are graded more finely, the graded products meet the requirements of different industries, meanwhile, the graded products at least reach or exceed the national standard, the content of ammonium dihydrogen phosphate in industrial grade monoammonium phosphate reaches 99.8%, the content of water-insoluble substances is as low as 0.04%, and the content of phosphorus in the industrial grade monoammonium phosphate reaches 99.8%. The water-soluble phosphorus content of the liquid agricultural monoammonium phosphate reaches 83.9%, the water-soluble phosphorus content of the fire-fighting monoammonium phosphate reaches 97.5%, the water-insoluble substance content is as low as 2.49%, and the three products have high economic values.

Description

Technical Field

[0001] The present invention relates to the technical field of ammonium phosphate production, and particularly relates to a process for cascaded utilization of ammonium phosphate slurry. Background Art

[0002] Many domestic companies use the slurry method to produce monoammonium phosphate (also known as ammonium dihydrogen phosphate, NH4H2PO4, available in granular and powdered forms) combined with dilute phosphoric acid to produce industrial-grade monoammonium phosphate. The products are sold in grades according to different nutrient contents and the levels of water-soluble phosphorus. In order to improve the comprehensive utilization rate of phosphorus, the products are further refined into grades to meet the requirements of different industries.

[0003] The cascaded utilization of ammonium phosphate slurry has been widely applied in ammonium phosphate production. Monoammonium phosphate can be classified into agricultural grade (mass fraction of NH4H2PO4 ≥ 74.6%), industrial grade, food grade, etc. according to its purity. According to the standard HG / T 4133—2021 (Industrial Ammonium Dihydrogen Phosphate), the mass fractions of NH4H2PO4 in industrial-grade ammonium dihydrogen phosphate products of types I, II, and III are ≥ 99%, ≥ 98.5%, and ≥ 98.0% respectively. The water-insoluble matter in industrial ammonium dihydrogen phosphate does not exceed 0.2%.

[0004] It is necessary to simultaneously produce: ① industrial-grade monoammonium phosphate (12-61.1-Type I ammonium dihydrogen phosphate HG / T4133-2021), ② monoammonium phosphate for fire protection, and ③ then produce agricultural compound fertilizers from the sludge. During the production process, the water-insoluble matter in industrial-grade monoammonium phosphate is unstable, sometimes exceeding 0.6%, which does not meet the requirement of item 6 in clause 6.2 of HG / T4133-2021 (Ammonium Dihydrogen Phosphate) that the water-insoluble matter ≤ 0.1%, nor does it meet the standard requirement of item 4 in table 1 of clause 4.2 of HG / T5048-2016 (Water-Soluble Monoammonium Phosphate) that the water-insoluble matter ≤ 0.5%, thus failing to reach the national standard. The monoammonium phosphate for fire protection requires a water-soluble phosphorus content > 97% and a water-insoluble matter content ≤ 3%, but the products obtained in actual production often have unqualified water-soluble phosphorus content and water-insoluble matter content, resulting in unstable product qualification rates. The common agricultural powdered binary fertilizers generally do not meet the national standards and customer requirements (i.e., water-soluble phosphorus content > 75%), and can only be sold at a negotiated price, resulting in economic benefits not reaching the expected value. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides a process for cascaded utilization of ammonium phosphate slurry, which can simultaneously produce three products: industrial-grade monoammonium phosphate, monoammonium phosphate for fire protection, and agricultural monoammonium phosphate, and all three products meet the national standards.

[0006] To achieve this technical purpose, the present invention adopts the following scheme: The process for cascaded utilization of ammonium phosphate slurry includes the following steps: S1. Desulfurize the finished phosphoric acid to make the SO3 content in the reaction mixture 1.7 - 1.8 wt%, then perform three - stage sedimentation. The sedimented solution is the first phosphoric acid solution, and the concentration of the first phosphoric acid ≥ 23.5 wt%. S2. Prepare industrial monoammonium phosphate: Neutralize the first phosphoric acid solution for the first time, add hydrogen peroxide for premixing after neutralization, then send it to the first clarifying tank and add citric acid aqueous solution for the first ripening; After ripening, the liquid is neutralized for the second time, and after the second neutralization, it is sent to the second clarifying tank for the second ripening; After the second ripening, it is filtered by pressure, flash - evaporated in the second effect, heated in the first effect, flash - evaporated in the first effect, crystallized, centrifuged, and dried to obtain industrial monoammonium phosphate. S3. Prepare monoammonium phosphate for fire - fighting: Divide the centrifuged product in S2. One part is used for drying to obtain industrial monoammonium phosphate, and the other part is concentrated to make the solution specific gravity reach 1.42 - 1.43 g / cm 3 , and then it is sent to the ammonium powder tower through a high - pressure pump to obtain monoammonium phosphate for fire - fighting. S4. Prepare monoammonium phosphate for agriculture: Mix the sludge from the first clarifying tank, the second clarifying tank and the filter cake obtained by pressure filtration to get a sludge mixture, add the first phosphoric acid solution to the sludge mixture for treatment, react with citric acid aqueous solution in the treated mixture, then add a phosphorus conversion agent to continue the reaction, and finally transport it to the monoammonium phosphate production line for agriculture.

[0007] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention improves the comprehensive utilization rate of phosphorus, classifies the products more finely, and makes the classified products meet the needs of different industries. At the same time, the classified products at least reach or exceed the standards formulated by the state. Among them, the content of ammonium dihydrogen phosphate in industrial monoammonium phosphate reaches 99.8%, the content of water - insoluble substances is as low as 0.04%, the water - soluble phosphorus content of liquid monoammonium phosphate for agriculture reaches 83.9%, the water - soluble phosphorus content of monoammonium phosphate for fire - fighting reaches 97.5%, and the content of water - insoluble substances is as low as 2.49%. All three products have high economic value.

[0008] Further, use phosphate ore pulp and finished phosphoric acid to stir and mix in a desulfurization tank. The temperature in the desulfurization tank is 75℃ - 80℃, the desulfurization time is 2 h, and the SO3 content in the mixed liquid drops to 1.7 - 1.8 wt%. The time for three - stage sedimentation is 4.5 - 5 h.

[0009] Further, the content of phosphate ore solid particles in the phosphate ore pulp is 73 - 75%, the particle size of phosphate ore solid particles is ≥ 90% of - 100 mesh, and the content of P2O5 in the phosphate ore solid particles is 30 - 32 wt%.

[0010] Further, both the first neutralization and the second neutralization are carried out by adding ammonia gas. The degree of neutralization in the first neutralization is controlled at 0.8 - 0.85, and the degree of neutralization in the second neutralization is controlled at 0.98 - 1.05.

[0011] Further, the concentration of the citric acid aqueous solution added in the first - stage clarifier is 10 wt%, and the dosage is 0.5% of the total volume of the mixture in the first - stage clarifier.

[0012] Further, the temperature of the first aging is 85°C and the time is 6 h; the temperature of the second aging is 90°C and the time is 6 h.

[0013] Further, when performing two - effect flash evaporation, an EDTA solution accounting for 0.3% of the total volume of the two - effect flash evaporation reactants is added, and the concentration of the EDTA solution is 20 wt%.

[0014] Further, the dosage ratio of the sludge mixture to the first phosphoric acid solution in S4 is (0.5 - 0.8):1.

[0015] Further, the concentration of the citric acid aqueous solution added in S4 is 10 wt%, and the dosage is 0.3% of the total volume of the first phosphoric acid solution and the sludge mixture; after adding the citric acid aqueous solution, the reaction is carried out at 60°C - 65°C for 8 h.

[0016] Further, the phosphorus - converting agent is an ammonium molybdate solution with a mass concentration of 10 wt%, the dosage is 0.1% of the total volume of the reactants, the reaction temperature is 60°C, and the reaction time is 4 h. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a flow chart of the process for cascaded utilization of phosphoric - ammonium slurry. DETAILED DESCRIPTION OF THE INVENTION

[0018] To fully understand the purpose, features and effects of the present invention, the present invention will be described in detail through the following specific embodiments, but the present invention is not limited thereto.

[0019] The degree of neutralization refers to the degree of neutralization of phosphoric acid by ammonia, that is, the molar ratio of ammonia to phosphoric acid. EXAMPLE

[0020] As Figure 1 shown, a process for cascaded utilization of phosphoric - ammonium slurry provided by the present invention comprises the following steps: S1. Desulfurize the finished dilute phosphoric acid to make the content of SO3 in the reaction mixture be 1.7 - 1.8 wt%, and then perform three - stage sedimentation. The solution after sedimentation is the first phosphoric acid solution, and the phosphoric acid concentration in the first phosphoric acid solution is ≥23.5 wt%; the solid phase substances sedimented in the three - stage sedimentation are returned to the extraction tank.

[0021] Furthermore, the concentration of the finished phosphoric acid is 22.5 wt%. The desulfurization is carried out by stirring the phosphate rock pulp and the finished phosphoric acid in a desulfurization tank. The temperature in the desulfurization tank is 75°C - 80°C, the desulfurization time is 2 h, and the desulfurization operation is completed when the SO3 content in the mixture in the desulfurization tank drops to 1.7 - 1.8 wt%. Then, three-stage sedimentation is carried out, and the time for three-stage sedimentation is 4.5 - 5 h.

[0022] Preferably, the content of phosphate rock solid particles in the phosphate rock pulp is 73% - 75%, the particle size of the phosphate rock solid particles is such that the content of -100 mesh is ≥90%, and the content of P2O5 in the phosphate rock solid particles is 30 - 32 wt%.

[0023] S2. Preparation of industrial monoammonium phosphate: S2-1. Perform the first neutralization on the desulfurized first phosphoric acid solution. Add gaseous ammonia for the first neutralization. The addition amount of gaseous ammonia is based on ensuring that the first neutralization degree is controlled at 0.8 - 0.85. After the first neutralization is completed, transfer the reactants to a premixer, add hydrogen peroxide to the premixer for thorough mixing to prevent and partially prevent the conversion of water-soluble phosphorus in the primary neutralization slurry into water-insoluble phosphorus and citrate-soluble phosphorus; then transfer the mixture in the premixer to a primary clarifying tank, and add a citric acid aqueous solution to the primary clarifying tank to carry out the first ripening reaction under normal pressure. The mass concentration of hydrogen peroxide is 25%, and the addition amount is 1% of the total volume of the reactants after the first neutralization. The concentration of the citric acid aqueous solution is 10 wt%, the addition amount of the citric acid aqueous solution is 0.5% of the total volume of the liquid in the primary clarifying tank, the first ripening temperature is 85°C, and the time is 6 h.

[0024] S2-2. Perform the second neutralization on the solution after the first ripening. Also add gaseous ammonia for the second neutralization. The usage amount of gaseous ammonia is based on controlling the neutralization degree of the second neutralization at 0.98 - 1.05. The reactants after neutralization are transferred to a secondary clarifying tank for the second ripening at 90°C under normal pressure, and the time for the second ripening is 6 h.

[0025] The slurry after the second neutralization is filtered by a filter press, and the obtained filtrate enters a second-effect flash evaporation chamber for flash evaporation. Add an EDTA aqueous solution to the second-effect flash evaporation chamber. The mass concentration of the EDTA aqueous solution is 20%, and the addition amount is 3.5% of the total volume of the filtrate. The purpose is to prevent the formation of divalent iron during the concentration process and reduce the water-soluble phosphorus in the product. Then it enters a first-effect heater and a first-effect flash evaporation chamber for treatment, and finally crystallizes and centrifuges. A part of the liquid after centrifugation is dried to obtain industrial monoammonium phosphate, and another part of the liquid after centrifugation is used to prepare monoammonium phosphate for fire protection.

[0026] S3. Preparation of monoammonium phosphate for agricultural use: The sludge discharged from the first-stage clarifier and the second-stage clarifier and the filter cake pressed out by the filter press enter the sludge tank. At the same time, 23.5 wt% dilute phosphoric acid (i.e., the first phosphoric acid solution obtained in S1) is added and mixed and stirred. The volume ratio of the mixture in the sludge tank to the dilute phosphoric acid is (0.5 - 0.8):1. To feed into the sludge tank later, a 10% citric acid aqueous solution by mass concentration is added to the sludge tank, and the dosage of the citric acid aqueous solution is 0.3% of the total volume of the mixture in the sludge tank. At normal pressure and 60°C - 65°C, the reaction is carried out for 8 h to prevent the regeneration of water-insoluble phosphorus and citrate-soluble phosphorus during the subsequent high-temperature concentration and drying processes of monoammonium phosphate for agricultural use. The mixture after mixing and stirring in the sludge tank enters the metering tank.

[0027] In the metering tank, a phosphorus conversion agent (the phosphorus conversion agent is ammonium molybdate with a mass concentration of 5%) is added, and the dosage of ammonium molybdate is 0.1% of the total volume of the reactants in the metering tank. The product obtained in the metering tank is liquid monoammonium phosphate for agricultural use, which enters the monoammonium phosphate for agricultural use production line, and granular or powdered monoammonium phosphate for agricultural use is prepared according to the needs of the final product.

[0028] S4. Preparation of monoammonium phosphate for fire protection: After centrifugation, part of the liquid enters the concentration equipment, and the liquid specific gravity is controlled at 1.42 - 1.43 g / cm 3 , and the concentrated liquid is sprayed into the ammonium powder tower through a high-pressure piston pump, and heat exchange with hot air in the tower to obtain the monoammonium phosphate for fire protection product. The high-pressure piston pump is pressurized to 10 - 12 Mpa.

[0029] Comparative Example 1 It is basically the same as the steps and dosages of the example, the difference is only that: hydrogen peroxide is not added in the pre-mixer before the first-stage clarifier.

[0030] Comparative Example 2 It is basically the same as the steps and dosages of the example, the difference is only that: an EDTA solution is not added to the second-effect flash chamber.

[0031] Comparative Example 3 It is basically the same as the steps and dosages of the example, the difference is only that: a phosphorus conversion agent is not added in the metering tank.

[0032] The three products obtained in the example and Comparative Examples 1 - 3 are respectively detected according to the HG / T 4133—2021 (industrial diammonium hydrogen phosphate) standard. Among them, the nitrogen content of all products meets the requirements, and the data are not listed in the table.

[0033]

[0034] The cascade utilization of ammonium phosphate slurry makes the total nutrient and water-soluble phosphorus indexes of each stage of products meet the national standards, industry standards and customer requirements by adjusting the neutralization degree process indexes at each stage and adding hydrogen peroxide, citric acid, EDTA and phosphorus conversion agent at different stages, different positions and different dosages.

[0035] Finally, it should be noted that the above-listed are only the preferred embodiments of the present invention. Of course, those skilled in the art can make changes and modifications to the present invention. If these modifications and variations fall within the scope of the claims of the present invention and its equivalent technologies, they should be regarded as within the protection scope of the present invention.

Claims

1. A cascade utilization process of ammonium phosphate slurry, characterized in that: The steps include: S1. Desulfurization treatment is performed on the finished phosphoric acid to make the content of SO3 in the reaction mixture 1.7-1.8wt%, followed by three-stage sedimentation. The solution after sedimentation is the first phosphoric acid solution, and the concentration of the first phosphoric acid is ≥23.5wt%; S2, preparing industrial-grade monoammonium phosphate: neutralizing the first phosphoric acid solution for the first time, adding hydrogen peroxide premix after neutralization, and then sending it to a primary clarification tank and adding citric acid aqueous solution for the first aging; after aging, the liquid is neutralized for the second time, and after the second neutralization, it is sent to a secondary clarification tank for the second aging; after the second aging, filter pressing, second-effect flash evaporation, first-effect heating, first-effect flash evaporation, crystallization, centrifugation, and drying to obtain industrial-grade monoammonium phosphate; S3, preparation of monoammonium phosphate for fire fighting: the centrifugal product of S2 is split, one part is used for drying to obtain industrial-grade monoammonium phosphate, and the other part is concentrated to make the solution specific gravity reach 1.42~1.43 g / cm 3 , and then it is pumped to the ammonium powder tower through a high-pressure pump to obtain monoammonium phosphate for fire fighting; S4. Preparation of agricultural monoammonium phosphate: mixing the sludge from the primary clarifier and the secondary clarifier with the filter cake obtained by filter pressing to obtain a sludge mixture, and adding the first phosphoric acid solution to the sludge mixture for treatment, adding citric acid aqueous solution to the treated mixture for reaction, and then adding a phosphorus conversion agent to continue the reaction, and finally transporting it to the agricultural monoammonium phosphate production line.

2. The cascade utilization process of ammonium phosphate slurry according to claim 1, characterized in that: The desulfurization treatment steps are as follows: phosphate ore slurry and finished phosphoric acid are stirred and mixed in a desulfurization tank. The temperature in the desulfurization tank is 75℃~80℃. The desulfurization time is 2h. The SO3 content in the mixed liquid drops to 1.7~1.8wt%; the time for the tertiary sedimentation is 4.5~5h.

3. The cascade utilization process of ammonium phosphate slurry according to claim 2, characterized in that: The content of phosphate rock solid particles in the phosphate rock slurry is 73~75%, the particle size of the phosphate rock solid particles is -100 mesh ≥90%, and the content of P2O5 in the phosphate rock solid particles is 30~32wt%.

4. The cascade utilization process of ammonium phosphate slurry according to claim 1, characterized in that: Both the first neutralization and the second neutralization are performed by adding ammonia gas. The neutralization degree of the first neutralization is controlled at 0.8-0.85, and the neutralization degree of the second neutralization is controlled at 0.98-1.

05.

5. The cascade utilization process of ammonium phosphate slurry according to claim 1, characterized in that: The concentration of the citric acid aqueous solution added to the primary clarifier is 10wt%, and the amount used is 0.5% of the total mixture in the primary clarifier.

6. The cascade utilization process of ammonium phosphate slurry according to claim 1, characterized in that: The first aging temperature is 85°C and the time is 6 hours; the second aging temperature is 90°C and the time is 6 hours.

7. The cascade utilization process of ammonium phosphate slurry according to claim 1, characterized in that: During the second-effect flash evaporation, EDTA solution accounting for 0.3% of the total volume of the second-effect flash evaporation reactants is added, and the concentration of the EDTA solution is 20wt%.

8. The cascade utilization process of ammonium phosphate slurry according to claim 1, characterized in that: The dosage ratio of the sludge mixture to the first phosphoric acid solution in S4 is (0.5~0.8):

1.

9. The cascade utilization process of ammonium phosphate slurry according to claim 1, characterized in that: The concentration of the citric acid aqueous solution added to S4 is 10 wt %, and the amount used is 0.3% of the total volume of the first phosphoric acid solution and the sludge mixture; after adding the citric acid aqueous solution, the temperature is kept at 60° C. to 65° C. for 8 hours to react.

10. The cascade utilization process of ammonium phosphate slurry according to claim 1, characterized in that: The phosphorus conversion agent is an ammonium molybdate solution with a mass concentration of 10wt%, the dosage is 0.1% of the total reactant volume, the reaction temperature is 60°C, and the reaction time is 4h.

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