Method for recycling fluorine in white fertilizer and preparing slow-release nitro fertilizer simultaneously

Abstract

This invention discloses a method for recovering fluoride from white fertilizer while simultaneously preparing slow-release nitro fertilizer, belonging to the field of clean processing and utilization technology of phosphorus resources. This invention uses nitric acid to perform staged acid hydrolysis of white fertilizer. The phosphorus-containing filtrate after preliminary acid hydrolysis has a low impurity content and can be used to prepare water-soluble ammonium phosphate. The remaining acid hydrolysis residue undergoes complete acid hydrolysis to completely leach phosphorus and fluoride elements, followed by defluorination. Fluorine precipitates as fluorosilicates, which can be further separated to obtain fluorosilicate products. The defluorinated liquid is neutralized and dried to obtain the slow-release nitro fertilizer product. This method comprehensively utilizes the phosphorus and fluoride resources in white fertilizer, achieving clean processing and utilization of phosphorus resources. The overall process of the method described in this invention is simple to implement, has low production costs, and fully utilizes the phosphorus and fluoride resources in white fertilizer.

Description

Technical Field

[0001] This invention belongs to the field of clean processing and utilization technology of phosphorus resources, specifically relating to a method for recovering fluoride from white fertilizer while preparing slow-release nitro fertilizer. Background Technology

[0002] In the wet-process phosphoric acid production of industrial monoammonium phosphate (MAP), after the ammonia neutralization reaction, impurity ions in the slurry will generate a large amount of insoluble complex compounds—white fertilizer—with a yield 0.5 to 1.0 times that of industrial MAP. White fertilizer has a high phosphorus content, with P2O5 content around 30% to 40%, mostly existing in the form of citrate-soluble available phosphorus. Simultaneously, white fertilizer enriches most of the fluorine and iron, calcium, aluminum, and magnesium ions from the wet-process phosphoric acid. Comprehensive recycling and utilization of industrial MAP white fertilizer remains a challenge for enterprises.

[0003] Several existing studies have reported technical routes for treating white fertilizer, primarily utilizing it by pulping and integrating it into other equipment for compound fertilizer production, or directly producing slow-release phosphate fertilizer. While these methods reduce the presence of white fertilizer to some extent, they do not recover and utilize the fluorine element within it. Existing technology one involves directly adding white fertilizer to fertilizer production equipment to utilize its available phosphorus and sulfur elements to produce magnesium ammonium sulfate and sulfur-based ammonium phosphate products. However, this method sometimes requires equipment modification, resulting in high production costs, and it does not fully utilize the elements in the white fertilizer. Existing technology two involves mixing white fertilizer and mother liquor to form a slurry, adding nitrogen and potassium sources, and then spray-drying and granulating to obtain nitrate phosphate fertilizer. However, the quality of the obtained product is unstable. Existing technology three designs a treatment process involving washing, acid hydrolysis, defluorination, extraction, back-extraction, and neutralization to obtain ammonium phosphate, sodium fluorosilicate, and magnesium ammonium sulfate, achieving the recovery of phosphorus, fluorine, nitrogen, and magnesium. However, this process is lengthy, and the extraction agent recovery effect is poor, making industrialization difficult. Existing technology involves adding citric acid solution to white fertilizer to chelate it and obtain liquid fertilizer, but this method does not fully utilize the fluorine resources in white fertilizer. Summary of the Invention

[0004] In view of the above-mentioned prior art, the present invention provides a method for recovering fluorine from white fertilizer and preparing slow-release nitro fertilizer at the same time. By graded acid hydrolysis, defluorination and neutralization of white fertilizer to prepare slow-release nitro fertilizer, not only can the high-value utilization of phosphorus in white fertilizer be realized, but also the fluorine resources in white fertilizer can be effectively recovered.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is to provide a method for simultaneously recovering fluoride from white fertilizer and preparing slow-release nitro fertilizer, which includes the following steps:

[0006] (1) Slurry preparation: Mix water and white fertilizer at a liquid-solid ratio of 1.5 to 3.5 to obtain slurry;

[0007] (2) First step acid hydrolysis: Heat the slurry to 30~70℃, then add nitric acid until the pH of the system is 1.0~3.0, and then keep it at the temperature for 0.5~2h; then filter to obtain phosphorus-containing filtrate and residual acid hydrolysis residue;

[0008] (3) Second step acid hydrolysis: Add nitric acid and water to the remaining acid hydrolysis residue to make the mass fraction of nitric acid in the resulting system 18%~25%, then keep the reaction at 30~70℃ for 0.5~2h, and then filter;

[0009] (4) Defluorination: Add a defluorinating agent (potassium nitrate, or sodium nitrate, potassium carbonate or sodium carbonate, etc.) to the filtrate obtained in step (3), then keep it at 20~60℃ for 50~70 min, then filter to obtain fluorosilicate and defluorinated filtrate.

[0010] (5) Neutralization: Ammonia is passed into the defluorinated filtrate and reacted at 60~70℃ for 0.5~1h, then dried to obtain slow-release nitro fertilizer.

[0011] This invention utilizes nitric acid to fractionally acid-hydrolyze white fertilizer. The phosphorus-containing filtrate after the initial acid-hydrolysis has a low impurity content and can be sent to the ammonium phosphate mother liquor for the production of industrial monoammonium phosphate. The remaining acid-hydrolysis residue undergoes further complete acid-hydrolysis to completely leach phosphorus and fluorine, followed by defluorination. Fluorine precipitates as fluorosilicates, which can be further separated to obtain fluorosilicate products. The defluorinated solution is neutralized and dried to obtain a slow-release nitro fertilizer product. This method comprehensively utilizes the phosphorus and fluorine resources in white fertilizer, achieving clean processing and utilization of phosphorus resources.

[0012] This invention utilizes controlled pH in the first acidolysis reaction to preliminarily recover phosphorus from white fertilizer, yielding a phosphorus-containing filtrate with a MER value of 0.01–0.1. The main reactions occurring in the first acidolysis process are as follows:

[0013] NH4H2PO4 + HNO3 = NH4NO3 + H3PO4

[0014] The main reactions that occur in the second step of acid hydrolysis are as follows:

[0015] AlPO4 + 3HNO3 = Al(NO3)3 + H3PO4

[0016] Mg3(PO4)2+6HNO3=3Mg(NO3)2+2H3PO4

[0017] Ca2Mg(PO4)2+6HNO3=2Ca(NO3)2+2H3PO4+Mg(NO3)2

[0018] FeNH4HF2PO4+4HNO3=Fe(NO3)3+NH4NO3+2HF+H3PO4

[0019] Fe3(PO4)2+12HNO3=3Fe(NO3)3+2H3PO4+3NO2+6H2O

[0020] This invention utilizes a two-stage acid hydrolysis process to not only achieve high-value utilization of phosphorus in white fertilizer, but also effectively recover fluorine resources from white fertilizer.

[0021] Based on the above technical solution, the present invention can be further improved as follows.

[0022] Furthermore, in step (2), the mass fraction of nitric acid is 65-70%; nitric acid is added until the pH of the system is 2.5; the reaction temperature of the first acid hydrolysis step is 50℃ and the acid hydrolysis time is 0.5h.

[0023] Furthermore, in step (3), the mass fraction of nitric acid is 65-70%; the reaction temperature of the second acid hydrolysis step is 40-50℃, and the acid hydrolysis time is 1h.

[0024] Furthermore, the defluorinating agent is potassium nitrate, and the amount of potassium nitrate added is based on a molar ratio of F to K of 3 in the system.

[0025] Furthermore, diatomaceous earth was added along with potassium nitrate; the amount of diatomaceous earth added was based on a molar ratio of F to Si of 6 in the system; the fluorosilicate was potassium fluorosilicate.

[0026] Furthermore, the temperature of the defluorination reaction in step (4) is 40°C and the defluorination time is 60 min.

[0027] Furthermore, in step (5), the ammonia is introduced into the defluorinated filtrate by passing ammonia gas or adding ammonia water, and the pH of the system after the ammonia is introduced is 4~5; the neutralization reaction temperature is 65℃ and the reaction time is 1h; the drying temperature is 60℃ and the drying time is 12h.

[0028] The beneficial effects of this invention are:

[0029] 1. Unlike sulfuric acid acid hydrolysis, this method uses nitric acid acid hydrolysis, which does not produce gypsum and greatly reduces the amount of residue.

[0030] 2. Unlike the one-step acid hydrolysis method, this method uses staged acid hydrolysis to achieve staged recovery and utilization of phosphorus. Water-soluble phosphorus is recovered in the form of phosphorus-containing filtrate, and citrate-soluble phosphorus is recovered in the form of slow-release nitro fertilizer, which improves the recovery value of phosphorus.

[0031] 3. In this invention, the fluorine in the white fertilizer is enriched in the second-step acid hydrolysis solution during the process. After the defluorination reaction, most of the fluorine enters the potassium fluorosilicate. Potassium nitrate is used as the defluorinating agent, which avoids the introduction of sulfate ions, an impurity in the potassium fluorosilicate product, and helps to ensure the purity of potassium fluorosilicate, thus realizing the recovery and utilization of fluorine.

[0032] 4. The method of the present invention has a simple overall process, low production cost, and makes full use of phosphorus and fluorine resources in white fertilizer. Attached Figure Description

[0033] Figure 1 A flowchart illustrating the process of simultaneously recovering fluorine from white fertilizer and preparing slow-release nitro fertilizer;

[0034] Figure 2 The XRD patterns of the white fertilizer used in Examples 1-5 and Comparative Example 2;

[0035] Figure 3 The image shows the XRD pattern of the white fertilizer used in Comparative Example 1. Detailed Implementation

[0036] The specific embodiments of the present invention will be described in detail below with reference to examples.

[0037] Example 1

[0038] A method for simultaneously recovering fluoride from white fertilizer and preparing slow-release nitro fertilizer, the process flow is as follows: Figure 1 As shown, the specific steps include:

[0039] (1) Mix water and white fertilizer to make slurry, and control the liquid-solid ratio to 1.5 to obtain slurry; the white fertilizer used comes from Company 1, and its composition is shown in the table below:

[0040]

[0041] (2) Heat the slurry to 50°C, add 68% nitric acid, control the reaction pH to 2.5, and keep the reaction at this temperature for 0.5 h; then filter and separate to obtain phosphorus-containing filtrate and residual acid hydrolysis residue. The phosphorus-containing filtrate contains 10.52% P2O5, 0.09% F, and MER value of 0.076; 98.03% of the F in the white fertilizer enters the residual acid hydrolysis residue.

[0042] (3) Mix the remaining acid hydrolysis residue with water at a mass ratio of 2:1, and then add 68% HNO3 by mass to the mixture. The dry basis mass ratio of the added HNO3 to the remaining acid hydrolysis residue is 1.0, so that the mass fraction of nitric acid in the resulting system is 20%. Then react at 50°C for 1 hour, and filter and separate after the reaction.

[0043] (4) Add potassium nitrate to the filtrate obtained in step (3) to remove fluoride. The amount of potassium nitrate added is based on a molar ratio of F to K of 3 in the system. Diatomaceous earth is added as a silicon supplement. The amount of diatomaceous earth added is based on a molar ratio of F to Si of 6 in the system. Then react at 40°C for 60 min. After the reaction, filter and separate. The filter residue is potassium fluorosilicate. The fluoride content in the filtrate is 0.92%.

[0044] (5) Neutralize the filtrate obtained in step (4) by passing ammonia through it (neutralization by passing ammonia through it by adding 25% ammonia water by volume to the filtrate). The neutralization endpoint pH is 4.5. Then react at 65℃ for 60 min and dry in an oven at 60℃ for 12 h to obtain the slow-release nitro fertilizer.

[0045] The total nutrient content (N+P2O5+K2O) of the obtained slow-release nitro fertilizer product was 34.08%. During the process of preparing slow-release nitro fertilizer by acid hydrolysis of white fertilizer, 52.86% of the fluorine was recovered in the form of potassium fluorosilicate, of which 38.60% of the phosphorus was recovered in the form of phosphorus-containing filtrate for subsequent use, and 59.77% of the phosphorus was recovered in the form of slow-release nitro fertilizer.

[0046] Example 2

[0047] A method for simultaneously recovering fluoride from white fertilizer and preparing slow-release nitro fertilizer, the process flow is as follows: Figure 1 As shown, the specific steps include:

[0048] (1) Mix water and white fertilizer to make slurry, and control the liquid-solid ratio to 1.5 to obtain slurry; the white fertilizer used comes from Company 1, and its composition is shown in the table below:

[0049]

[0050] (2) Heat the slurry to 50°C, add 68% nitric acid, control the reaction pH to 3.0, and keep the reaction at this temperature for 0.5 h; then filter and separate to obtain phosphorus-containing filtrate and residual acid hydrolysis residue. The phosphorus-containing filtrate contains 10.13% P2O5, 0.07% F, and has a MER value of 0.0516; 99.3% of the F in the white fertilizer enters the residual acid hydrolysis residue.

[0051] (3) Mix the remaining acid hydrolysis residue with water at a mass ratio of 2:1, and then add 68% HNO3 by mass to the mixture. The dry basis mass ratio of the added HNO3 to the remaining acid hydrolysis residue is 1.2, so that the mass fraction of nitric acid in the resulting system is 25%. Then react at 50°C for 1 hour, and filter and separate after the reaction.

[0052] (4) Add an appropriate amount of potassium nitrate to the filtrate obtained in step (3) to make the F / K molar ratio in the system 3, and perform defluorination. Add an appropriate amount of diatomaceous earth as a silicon supplement to ensure that the F / Si molar ratio in the system is 6. Then react at 40℃ for 60 min. After the reaction, filter and separate. The obtained filter residue is potassium fluorosilicate, and the fluorine content in the obtained filtrate is 0.86%.

[0053] (5) Neutralize the filtrate obtained in step (4) by passing ammonia through it (neutralization by passing ammonia through it by adding 25% ammonia water by volume to the filtrate). The neutralization endpoint pH is 4.5. Then react at 65℃ for 60 min and dry in an oven at 60℃ for 12 h to obtain the slow-release nitro fertilizer.

[0054] The total nutrient content (N+P2O5+K2O) of the obtained slow-release nitro fertilizer product was 39.93%. During the process of preparing slow-release nitro fertilizer by acid hydrolysis of white fertilizer, 60.77% of the fluorine was recovered in the form of potassium fluorosilicate, of which 36.32% of the phosphorus was recovered in the form of phosphorus-containing filtrate for subsequent use, and 61.57% of the phosphorus was recovered in the form of slow-release nitro fertilizer.

[0055] Example 3

[0056] A method for simultaneously recovering fluoride from white fertilizer and preparing slow-release nitro fertilizer, the process flow is as follows: Figure 1 As shown, the specific steps include:

[0057] (1) Mix water and white fertilizer to make slurry, and control the liquid-solid ratio to 1.5 to obtain slurry; the white fertilizer used comes from Company 1, and its composition is shown in the table below:

[0058]

[0059] (2) Heat the slurry to 50°C, add 68% nitric acid, control the reaction pH to 3.0, and keep the reaction at this temperature for 0.5 h; then filter and separate to obtain phosphorus-containing filtrate and residual acid hydrolysis residue. The phosphorus-containing filtrate contains 10.13% P2O5, 0.07% F, and has a MER value of 0.0516; 99.3% of the F in the white fertilizer enters the residual acid hydrolysis residue.

[0060] (3) Mix the remaining acid hydrolysis residue with water at a mass ratio of 2:1, and then add 68% HNO3 by mass to the mixture. The dry mass ratio of the added HNO3 to the remaining acid hydrolysis residue is 0.8, so that the mass fraction of nitric acid in the resulting system is 18%. Then react at 50°C for 1 hour, and filter and separate after the reaction.

[0061] (4) Add an appropriate amount of potassium nitrate to the filtrate obtained in step (3) to make the F / K molar ratio in the system 3, and perform defluorination. Add an appropriate amount of diatomaceous earth as a silicon supplement to ensure that the F / Si molar ratio in the system is 6. Then react at 40℃ for 60 min. After the reaction, filter and separate. The obtained filter residue is potassium fluorosilicate, and the fluorine content in the obtained filtrate is 0.87%.

[0062] (5) Neutralize the filtrate obtained in step (4) by passing ammonia through it (neutralization by passing ammonia through it by adding 25% ammonia water by volume to the filtrate). The neutralization endpoint pH is 4.5. Then react at 65℃ for 60 min and dry in an oven at 60℃ for 12 h to obtain the slow-release nitro fertilizer.

[0063] The total nutrient content (N+P2O5+K2O) of the obtained slow-release nitro fertilizer product was 44.5%. During the process of preparing slow-release nitro fertilizer by acid hydrolysis of white fertilizer, 53.40% of the fluorine was recovered in the form of potassium fluorosilicate, of which 33.09% of the phosphorus was recovered in the form of phosphorus-containing filtrate for subsequent use, and 40.21% of the phosphorus was recovered in the form of slow-release nitro fertilizer.

[0064] Example 4

[0065] A method for simultaneously recovering fluoride from white fertilizer and preparing slow-release nitro fertilizer, the process flow is as follows: Figure 1 As shown, the specific steps include:

[0066] (1) Mix water and white fertilizer to make slurry, and control the liquid-solid ratio to 1.5 to obtain slurry; the white fertilizer used comes from Company 1, and its composition is shown in the table below:

[0067]

[0068] (2) The slurry was heated to 50°C, and 68% nitric acid was added. The pH of the reaction was controlled at 1.0, and the reaction was kept at this temperature for 0.5 h. Then, the mixture was filtered to separate the phosphorus-containing filtrate and the remaining acid hydrolysis residue. The phosphorus-containing filtrate contained 11.28% P2O5, 1.06% F, and a MER value of 0.112, indicating a high content of metal impurities. 56.65% of the F in the white fertilizer entered the remaining acid hydrolysis residue.

[0069] (3) Mix the remaining acid hydrolysis residue with water at a mass ratio of 2:1, and then add 68% HNO3 by mass to the mixture. The dry basis mass ratio of the added HNO3 to the remaining acid hydrolysis residue is 1.2, so that the mass fraction of nitric acid in the resulting system is 25%. Then react at 50°C for 1 hour, and filter and separate after the reaction.

[0070] (4) Add an appropriate amount of potassium nitrate to the filtrate obtained in step (3) to make the F / K molar ratio in the system 3, and perform defluorination. Add an appropriate amount of diatomaceous earth as a silicon supplement to ensure that the F / Si molar ratio in the system is 6. Then react at 40℃ for 60 min. After the reaction, filter and separate. The obtained filter residue is potassium fluorosilicate, and the fluorine content in the obtained filtrate is 0.91%.

[0071] (5) Neutralize the filtrate obtained in step (4) by passing ammonia through it (neutralization by passing ammonia through it by adding 25% ammonia water by volume to the filtrate). The neutralization endpoint pH is 4.5. Then react at 65℃ for 60 min and dry in an oven at 60℃ for 12 h to obtain the slow-release nitro fertilizer.

[0072] The total nutrient content (N+P2O5+K2O) of the obtained slow-release nitro fertilizer product was 33.25%. During the process of acid hydrolysis of white fertilizer to prepare slow-release nitro fertilizer, 25.25% of the fluorine was recovered in the form of potassium fluorosilicate, of which 64.28% of the phosphorus was recovered in the form of phosphorus-containing filtrate for subsequent use, and 34.71% of the phosphorus was recovered in the form of slow-release nitro fertilizer.

[0073] Example 5

[0074] A method for simultaneously recovering fluoride from white fertilizer and preparing slow-release nitro fertilizer, the process flow is as follows: Figure 1 As shown, the specific steps include:

[0075] (1) Mix water and white fertilizer to make slurry, and control the liquid-solid ratio to 1.5 to obtain slurry; the white fertilizer used comes from Company 1, and its composition is shown in the table below:

[0076]

[0077] (2) Heat the slurry to 50°C, add 68% nitric acid, control the reaction pH to 1.0, and keep the reaction at this temperature for 0.5 h; then filter and separate to obtain phosphorus-containing filtrate and residual acid hydrolysis residue. The phosphorus-containing filtrate contains 11.28% P2O5, 1.06% F, and has a MER value of 0.112; 56.65% of the F in the white fertilizer enters the residual acid hydrolysis residue.

[0078] (3) Mix the remaining acid hydrolysis residue with water at a mass ratio of 1:1, and then add 68% HNO3 by mass to the mixture. The dry mass ratio of the added HNO3 to the remaining acid hydrolysis residue is 0.6, so that the mass fraction of nitric acid in the resulting system is 18%. Then react at 50°C for 1 hour, and filter to separate after the reaction.

[0079] (4) Add an appropriate amount of potassium nitrate to the filtrate obtained in step (3) to make the F / K molar ratio in the system 3, and perform defluorination. Add an appropriate amount of diatomaceous earth as a silicon supplement to ensure that the F / Si molar ratio in the system is 6. Then react at 40℃ for 60 min. After the reaction, filter and separate. The obtained filter residue is potassium fluorosilicate, and the fluorine content in the obtained filtrate is 0.94%.

[0080] (5) Neutralize the filtrate obtained in step (4) by passing ammonia through it (neutralization by passing ammonia through it by adding 25% ammonia water by volume to the filtrate). The neutralization endpoint pH is 4.5. Then react at 65℃ for 60 min and dry in an oven at 60℃ for 12 h to obtain the slow-release nitro fertilizer.

[0081] The total nutrient content (N+P2O5+K2O) of the obtained slow-release nitro fertilizer product was 36.44%. During the process of acid hydrolysis of white fertilizer to prepare slow-release nitro fertilizer, 18.11% of the fluorine was recovered in the form of potassium fluorosilicate, of which 64.28% of the phosphorus was recovered in the form of phosphorus-containing filtrate for subsequent use, and 20.83% of the phosphorus was recovered in the form of slow-release nitro fertilizer.

[0082] As can be seen from Examples 2 and 4, a decrease in pH during the initial acid hydrolysis will increase the phosphorus content entering the initial acid hydrolysis solution, but it will also lead to an increase in the content of metal impurities in the initial acid hydrolysis solution, affecting the subsequent utilization of the leachate. As can be seen from Examples 3 and 5, when the amount of acid used in the complete acid hydrolysis step is low, the total phosphorus utilization rate will be reduced.

[0083] Comparative Example 1

[0084] A method for simultaneously recovering fluoride from white fertilizer and preparing slow-release nitro fertilizer, the process flow is as follows: Figure 1 As shown, the specific steps include:

[0085] (1) Mix water and white fertilizer to make slurry, and control the liquid-solid ratio to 1.5 to obtain slurry; the white fertilizer used comes from enterprise 2, and its composition is shown in the table below:

[0086]

[0087] (2) Heat the slurry to 50°C, add 68% nitric acid, control the reaction pH to 2.5, and keep the reaction at this temperature for 0.5 h; then filter and separate to obtain phosphorus-containing filtrate and residual acid hydrolysis residue. The phosphorus-containing filtrate contains 12.85% P2O5, 0.08% F, and has a MER value of 0.14; 90.46% of the F in the white fertilizer enters the residual acid hydrolysis residue.

[0088] (3) Mix the remaining acid hydrolysis residue with water at a mass ratio of 1:1, and then add 68% HNO3 by mass to the mixture. The dry mass ratio of the added HNO3 to the remaining acid hydrolysis residue is 1.0. Then react at 50°C for 1 hour, and filter to separate after the reaction.

[0089] (4) Add an appropriate amount of potassium nitrate to the filtrate obtained in step (3) to make the F / K molar ratio in the system 3, and perform defluorination. Add an appropriate amount of diatomaceous earth as a silicon supplement to ensure that the F / Si molar ratio in the system is 6. Then react at 40℃ for 60 min. After the reaction, filter and separate. The obtained filter residue is potassium fluorosilicate, and the fluorine content in the obtained filtrate is 0.85%.

[0090] (5) Neutralize the filtrate obtained in step (4) by passing ammonia through it (neutralization by passing ammonia through it by adding 25% ammonia water by volume to the filtrate). The neutralization endpoint pH is 4.5. Then react at 65℃ for 60 min and dry in an oven at 60℃ for 12 h to obtain the slow-release nitro fertilizer.

[0091] The total nutrient content (N+P2O5+K2O) of the obtained slow-release nitro fertilizer product was 50.86%. During the process of preparing slow-release nitro fertilizer by acid hydrolysis of white fertilizer, 49.10% of the fluorine was recovered in the form of potassium fluorosilicate, of which 51.30% of the phosphorus was recovered in the form of phosphorus-containing filtrate for subsequent use, and 47.99% of the phosphorus was recovered in the form of slow-release nitro fertilizer.

[0092] The XRD patterns of the white fertilizer used in Examples 1-5 are as follows: Figure 2 As shown, the XRD pattern of the white fertilizer used in Comparative Example 1 is as follows: Figure 3 As shown; from Figure 2 and Figure 3 As can be seen, the different phosphate rock raw materials and industrial-grade monoammonium phosphate preparation processes of different enterprises will result in different compositions of white fertilizer. Combining Example 1 and Comparative Example 1, it can be seen that the graded acid hydrolysis process in the examples has a good phosphorus and fluorine recovery rate for white fertilizers with different compositions.

[0093] Comparative Example 2

[0094] A method for simultaneously recovering fluoride from white fertilizer and preparing slow-release nitro fertilizer includes the following steps:

[0095] (1) Mix water and white fertilizer to make slurry, and control the liquid-solid ratio to 1.5 to obtain slurry; the white fertilizer used comes from Company 1, and its composition is shown in the table below:

[0096]

[0097] (2) The slurry was mixed with HNO3 with a mass fraction of 68% and the dry basis mass ratio of HNO3 to white fertilizer was 0.8; the mixture was reacted at 50℃ for 0.5h and then filtered to separate the slurry; 91.74% of the fluorine in the white fertilizer was leached into the filtrate.

[0098] (3) Add an appropriate amount of potassium nitrate to the filtrate obtained in step (2) to make the F / K molar ratio in the system 3, and perform defluorination. Add an appropriate amount of diatomaceous earth as a silicon supplement to ensure that the F / Si molar ratio in the system is 6. Then react at 40℃ for 60 min. After the reaction, filter and separate. The obtained filter residue is potassium fluorosilicate, and the fluorine content in the obtained filtrate is 0.63%.

[0099] (4) Neutralize the filtrate obtained in step (4) by passing ammonia through it (neutralization by passing ammonia through it means adding 25% ammonia water by volume to the filtrate). The neutralization endpoint pH is 4.5. Then react at 65℃ for 60 min and dry in an oven at 60℃ for 12 h to obtain the slow-release nitro fertilizer.

[0100] The total nutrient content (N+P2O5+K2O) of the obtained slow-release nitro fertilizer product was 47.85%; during the acid hydrolysis of white fertilizer to prepare slow-release nitro fertilizer, 56.87% of the fluorine was recovered in the form of potassium fluorosilicate, of which 88.34% of the phosphorus was recovered in the form of slow-release nitro fertilizer.

[0101] Comparing Example 1 and Comparative Example 2, it can be seen that, under the same nitric acid dosage, the staged acid hydrolysis method (Example 1) has better phosphorus and fluorine recovery rates than the one-step acid hydrolysis method (Comparative Example 2). Compared with Example 1, the phosphorus recovery rate in Comparative Example 2 decreased by 10.03%, and the amount of white fertilizer treated decreased by 8.16%.

[0102] Although specific embodiments of the present invention have been described in detail with reference to examples, they should not be construed as limiting the scope of protection of this patent. Various modifications and variations that can be made by those skilled in the art without inventive effort within the scope described in the claims are still within the scope of protection of this patent.

Claims

1. A method for simultaneously recovering fluoride from white fertilizer and preparing slow-release nitro fertilizer, characterized in that, Includes the following steps: (1) Slurry preparation: Mix water and white fertilizer at a liquid-solid ratio of 1.5 to 3.5 to obtain slurry; (2) First step acid hydrolysis: Heat the slurry to 30~70℃, then add nitric acid until the pH of the system is 2.5~3.0, and then keep it at the temperature for 0.5~2h; then filter to obtain phosphorus-containing filtrate and residual acid hydrolysis residue; water-soluble phosphorus is recovered in the form of phosphorus-containing filtrate; (3) Second step acid hydrolysis: Add nitric acid and water to the remaining acid hydrolysis residue to make the mass fraction of nitric acid in the resulting system 18%~25%, then keep the reaction at 30~70℃ for 0.5~2h, and then filter; (4) Defluorination: Add a defluorinating agent to the filtrate obtained in step (3), then keep it at 20~60℃ for 50~70 min, and then filter to obtain fluorosilicate and defluorinated filtrate; the defluorinating agent is potassium nitrate; The amount of potassium nitrate added is based on a molar ratio of F to K of 3 in the system; diatomaceous earth is also added at the same time as potassium nitrate; the amount of diatomaceous earth added is based on a molar ratio of F to Si of 6 in the system; the fluorosilicate is potassium fluorosilicate; (5) Neutralization: Ammonia is passed into the defluorination filtrate and reacted at 60~70℃ for 0.5~1h. Then it is dried to obtain slow-release nitro fertilizer. Citrate-soluble phosphorus is recovered in the form of slow-release nitro fertilizer.

2. The method for simultaneously preparing slow-release nitro fertilizer while recovering fluoride from white fertilizer according to claim 1, characterized in that: The mass fraction of nitric acid in step (2) is 65-70%; the reaction temperature of the first acid hydrolysis step is 50℃ and the acid hydrolysis time is 0.5h.

3. The method for simultaneously preparing slow-release nitro fertilizer while recovering fluoride from white fertilizer according to claim 1, characterized in that: The mass fraction of nitric acid in step (3) is 65-70%; the reaction temperature of the second acid hydrolysis step is 40-50℃, and the acid hydrolysis time is 1h.

4. The method for simultaneously preparing slow-release nitro fertilizer while recovering fluoride from white fertilizer according to claim 1, characterized in that: In step (4), the defluorination reaction temperature is 40℃ and the defluorination time is 60min.

5. The method for simultaneously preparing slow-release nitro fertilizer while recovering fluoride from white fertilizer according to claim 1, characterized in that: In step (5), ammonia is introduced until the pH of the system is 4-5; the neutralization reaction temperature is 65℃ and the reaction time is 1h.

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