Sulfur-containing calcium polyphosphate ammonium fertilizer and preparation method thereof

Abstract

The application discloses a kind of sulphur-containing calcium polyphosphate ammonium fertilizer and preparation method thereof, belong to polymer fertilizer technical field.Preparation method includes: after phosphorite is ground pretreatment, join the mixed acid system consisting of fuming sulfuric acid and concentrated sulfuric acid, carry out self-heating defluorination reaction in airtight reactor, do not separate phosphogypsum, do not exogenous heating, rely on reaction self-heating and maintain system temperature 200~280 DEG C, and the defluorination rate is greater than or equal to 80%;Subsequently, urea is added to the defluorination slurry, and the system temperature is maintained at 140~200 DEG C using the defluorination residual heat, in-situ polymerization to obtain a sulphur-containing calcium polyphosphate ammonium crude product, and the product is obtained by post-treatment with a degree of polymerization of 1~9 distribution fertilizer product.The application realizes defluorination and polymerization integration, without exogenous heating, simplifying process, reducing energy consumption and cost;The product contains sulfur and calcium nutrients, has low fluorine content, good water solubility and slow release, and can be used in the field of slow-release fertilizer for agriculture, and is suitable for large-scale industrial production.

Description

Technical Field

[0001] This invention belongs to the field of polymer fertilizer technology, specifically relating to a sulfur-containing calcium polyphosphate ammonium fertilizer and its preparation method. Background Technology

[0002] Ammonium polyphosphate (APP) is a multifunctional material that combines flame retardancy with plant nutrition. Among them, oligomeric ammonium polyphosphate (degree of polymerization 1-9) has broad application prospects in the field of agricultural slow-release fertilizers due to its good water solubility and excellent slow-release properties. Sulfur- and calcium-containing oligomeric ammonium polyphosphate can simultaneously provide the phosphorus, nitrogen, sulfur, and calcium nutrients required for crop growth, solving the problem of single nutrient content in traditional polyphosphates and improving fertilizer utilization and crop quality.

[0003] Currently, the preparation of ammonium polyphosphate fertilizer mainly adopts the phosphoric acid-urea high-temperature polycondensation method. This method requires a large amount of additional heat energy to maintain the polymerization temperature (140~200℃), resulting in high energy consumption (ZL202110285470.7). At the same time, the raw material phosphoric acid is mostly derived from the acid hydrolysis of phosphate rock, and the fluorine element contained in phosphate rock will cause the fluorine content of the product to exceed the standard, affecting the safety of product application. Therefore, an additional defluorination process is required, which leads to a complex process route and increased equipment investment.

[0004] Existing phosphate rock defluorination processes mostly employ wet phosphoric acid defluorination, which suffers from low defluorination rates (only 65-75%), the need for external heating, and cumbersome processes (ZL202311040411.9). Furthermore, the ammonium polyphosphate polymerization process is independent of the phosphate rock defluorination process, requiring two separate steps, which not only increases the number of process steps but also wastes heat. In addition, existing technologies for preparing sulfur-containing calcium polyphosphate require the addition of additional sulfur and calcium sources, further increasing production costs and making it difficult to achieve effective bonding between sulfur, calcium, and ammonium polyphosphate, resulting in unstable product performance (ZL202411260694.2).

[0005] Therefore, developing a method that can integrate phosphate rock defluorination and ammonium polyphosphate polymerization and stably prepare sulfur-containing calcium polyphosphate fertilizer with a degree of polymerization distribution of 1 to 9 has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] In view of the above-mentioned prior art, the present invention provides a sulfur-containing calcium polyphosphate ammonium fertilizer and its preparation method. A method has been developed that can realize the integration of phosphate rock defluorination and polyphosphate ammonium polymerization, and can stably prepare sulfur-containing calcium polyphosphate ammonium fertilizer with a degree of polymerization distribution of 1 to 9.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is to provide a method for preparing sulfur-containing calcium polyphosphate ammonium fertilizer, comprising the following steps: S1: The phosphate rock is crushed into powder to obtain dry-based phosphate rock powder; the dry-based phosphate rock powder contains the following components by mass fraction: P2O5 28~32%, SiO2 6~12%, F 1~2%, MgO≤1.2%, CaO 40~48%, Al2O3+Fe2O3≤3%; S2: Add mixed acid to dry phosphate rock powder, with a mass ratio of dry phosphate rock powder to mixed acid of 1:0.6~1; use the heat released by the reaction to maintain the temperature of the reaction system at 200~280℃, and maintain this temperature for 0.5~3h to obtain defluorination slurry; the mixed acid is composed of fuming sulfuric acid and concentrated sulfuric acid, the fuming sulfuric acid is fuming sulfuric acid with a free SO3 content of 20~30wt%, the concentrated sulfuric acid has a mass concentration of 98%, and the mass proportion of fuming sulfuric acid in the mixed acid is 25~40%; negative pressure extraction or inert gas purging is performed during the reaction; S3: Add urea to the defluorination slurry. After adding urea, the nitrogen-phosphorus molar ratio in the system is 1.5~2.5:1. Use the residual heat of the defluorination slurry to maintain the system temperature at 140~200℃ and keep the polymerization reaction at this temperature for 0.5~2.5h to obtain crude sulfur-containing calcium polyphosphate ammonium. S4: Cool the crude sulfur-containing calcium polyphosphate to room temperature, crush and sieve it to obtain sulfur-containing calcium polyphosphate fertilizer.

[0008] Based on the above technical solution, the present invention can be further improved as follows.

[0009] Furthermore, the particle size of the dry-based phosphate rock powder is 50-400 mesh.

[0010] Furthermore, the urea should be added within 10-20 minutes.

[0011] The present invention also discloses a sulfur-containing calcium polyphosphate ammonium fertilizer, which is prepared by the above-described preparation method.

[0012] Furthermore, the prepared sulfur-containing calcium polyphosphate ammonium fertilizer exhibits a degree of polymerization distribution of 1-9, with 3-7 polymers accounting for ≥50%; P2O5 content is 10-20%, N content is 5-10%, fluorine content is ≤0.1%, and SO4 content is the most abundant. 2- The effective sulfur content is 3-10% and the effective calcium content (calculated as CaO) is 3-10%.

[0013] The beneficial effects of this invention are: 1. Achieve integrated defluorination and polymerization, simplifying the process: This invention integrates the defluorination of phosphate rock with the polymerization of ammonium polyphosphate, eliminating the need for additional defluorination and polymerization heating processes, thus simplifying the process route, reducing equipment investment, and lowering operational difficulty; 2. No external heating required, extremely low energy consumption: Utilizing the exothermic reaction of phosphate rock acidolysis and the exothermic hydration of free SO3 in fuming sulfuric acid, self-heating is achieved to maintain defluorination and polymerization, completely eliminating dependence on external heat sources, significantly reducing energy consumption, and conforming to the industrial trend of energy conservation and consumption reduction. 3. High defluorination rate and good product safety: Through finer mineral powder particle size, higher proportion of fuming sulfuric acid, higher self-heating temperature and gas phase enhanced removal measures, the fluoride removal rate is ≥80%, and can reach more than 95%. The residual fluoride content of the product is ≤0.1%, which meets the application requirements of agricultural fertilizers and other fields. 4. Excellent product performance and comprehensive nutrition: No additional sulfur or calcium source is required. It utilizes the calcium element contained in the phosphate rock itself and the sulfur element in the mixed acid system to achieve in-situ combination of sulfur, calcium and ammonium polyphosphate. The degree of polymerization of the product is stable at 1~9. It combines water solubility and slow release, and can provide four nutrients: phosphorus, nitrogen, sulfur and calcium at the same time, improving fertilizer utilization and crop quality. 5. Low cost and high practicality: The raw materials are conventional phosphate rock, fuming sulfuric acid and urea, which are widely available and inexpensive; the process does not require the addition of additional auxiliary materials, and there is no large amount of wastewater or waste residue discharge. Moreover, the reaction conditions are mild and easy to control, making it suitable for large-scale industrial production. Attached Figure Description

[0014] Figure 1 The XRD patterns of the dry phosphate rock powder and defluorinated slurry dried powder in Example 1 are shown below. Figure 2 The ion chromatography analysis of the sulfur-containing calcium polyphosphate ammonium fertilizers obtained in Examples 1-3 shows that the peaks P1-P9 represent orthophosphate to nonapolyphosphate. Detailed Implementation

[0015] The specific embodiments of the present invention will be described in detail below with reference to examples.

[0016] Example 1

[0017] A sulfur-containing calcium polyphosphate ammonium fertilizer is prepared through the following steps: S1: The phosphate rock is crushed to 200 mesh to obtain dry-basis phosphate rock powder; the dry-basis mass fraction of this phosphate rock powder is: P2O5:32%, SiO2:12%, F:2%, MgO:0.6%, CaO:40%, Al2O3+Fe2O3:1.5%; S2: 100 kg of the above-mentioned dry-based phosphate rock powder was added to a closed reactor with an insulation layer. A mixed acid system was added at a uniform rate. The mixed acid system consisted of 32 kg of fuming sulfuric acid with a free SO3 content of 30 wt% and 48 kg of concentrated sulfuric acid with a mass concentration of 98% (fuming sulfuric acid accounted for 40% of the total mass of the mixed acid system). The mixture was stirred rapidly to ensure full contact between the dry-based phosphate rock powder and the mixed acid. The autothermal defluorination reaction was then initiated. The system temperature was maintained at around 280 ℃ by the exothermic reaction of the acid hydrolysis of the phosphate rock and the hydration of free SO3 in the fuming sulfuric acid. During the autothermal defluorination reaction, a negative pressure of -0.05 MPa was used to continuously remove the SiF4, HF and other gases generated in the reaction. The phosphogypsum was not separated and no external heating was used. The system temperature was maintained by the autothermal reaction. The reaction was kept at this temperature for 2.2 h to obtain a defluorinated slurry. The fluoride removal rate was found to be 94.8%. S3: After the defluorination reaction is completed, keep the closed reactor under heat preservation and add urea to the defluorination slurry at a uniform rate until the nitrogen-phosphorus molar ratio in the system is 2:1. The urea is added within 15 minutes. Continue stirring to make the urea completely melt and mix evenly with the slurry. The added room temperature urea lowers the system temperature, and the residual heat of defluorination is used to maintain the system temperature at about 200 °C. The polymerization reaction is carried out for 1 hour to obtain sulfur-containing calcium polyphosphate crude product. S4: Cool the crude sulfur-containing calcium polyphosphate to room temperature, crush it, and then sieve it through a 100-mesh sieve to obtain the sulfur-containing calcium polyphosphate fertilizer product.

[0018] Example 2

[0019] A sulfur-containing calcium polyphosphate ammonium fertilizer is prepared through the following steps: S1: The phosphate rock is crushed to 200 mesh to obtain dry-basis phosphate rock powder; the dry-basis mass fraction of this phosphate rock powder is: P2O5:28%, SiO2:6%, F:1%, MgO:1%, CaO:48%, Al2O3+Fe2O3:2.8%; S2: Add 100 kg of the above-mentioned dry-based phosphate rock powder to a sealed reactor with an insulation layer, and uniformly add a mixed acid system. The mixed acid system consists of 20 kg of fuming sulfuric acid with a free SO3 content of 20 wt% and 60 kg of concentrated sulfuric acid with a mass concentration of 98% (fuming sulfuric acid accounts for 25% of the total mass of the mixed acid system). Stir rapidly to ensure full contact between the dry-based phosphate rock powder and the mixed acid, and then start the autothermal defluorination reaction. The system temperature is maintained at around 200 ℃ by the exothermic reaction of the acidolysis of the phosphate rock and the hydration release of free SO3 in the fuming sulfuric acid. During the autothermal defluorination reaction, nitrogen is used for purging (purging rate 0.5 m). 3The reaction continuously removes SiF4, HF, and other gases generated during the reaction, without separating phosphogypsum or external heating. The system temperature is maintained by the self-heating of the reaction, and the reaction is kept at this temperature for 3 hours to obtain a defluorinated slurry. The fluorine removal rate was found to be 85.6%. S3: After the defluorination reaction is completed, keep the closed reactor under heat preservation and add urea to the defluorination slurry at a uniform rate until the nitrogen-phosphorus molar ratio in the system is 1.5:1. The urea is added within 10 minutes. Continue stirring to make the urea completely melt and mix evenly with the slurry. The added room temperature urea lowers the system temperature, and the residual heat of defluorination is used to maintain the system temperature at about 140 °C. The polymerization reaction is carried out for 2.5 h to obtain sulfur-containing calcium polyphosphate crude product. S4: Cool the crude sulfur-containing calcium polyphosphate to room temperature, crush it, and then sieve it through a 90-mesh sieve to obtain the sulfur-containing calcium polyphosphate fertilizer product.

[0020] Example 3

[0021] A sulfur-containing calcium polyphosphate ammonium fertilizer is prepared through the following steps: S1: The phosphate rock is crushed to 200 mesh to obtain dry-basis phosphate rock powder; the dry-basis mass fraction of this phosphate rock powder is: P2O5:30%, SiO2:9%, F:1.5%, MgO:0.8%, CaO:45%, Al2O3+Fe2O3:2.2%; S2: 100 kg of the above-mentioned dry-based phosphate rock powder was added to a closed reactor with an insulation layer. A mixed acid system was added at a uniform rate. The mixed acid system consisted of 32 kg of fuming sulfuric acid with a free SO3 content of 30 wt% and 48 kg of concentrated sulfuric acid with a mass concentration of 98% (fuming sulfuric acid accounted for 40% of the total mass of the mixed acid system). The mixture was stirred rapidly to ensure full contact between the dry-based phosphate rock powder and the mixed acid. The autothermal defluorination reaction was then initiated. The system temperature was maintained at around 280 ℃ by the exothermic reaction of the acid hydrolysis of the phosphate rock and the hydration of free SO3 in the fuming sulfuric acid. During the autothermal defluorination reaction, a negative pressure of -0.05 MPa was used to continuously remove the SiF4, HF and other gases generated in the reaction. The phosphogypsum was not separated and no external heating was used. The system temperature was maintained by the autothermal reaction. The reaction was kept at this temperature for 2.2 h to obtain a defluorinated slurry. The fluoride removal rate was found to be 88.7%. S3: After the defluorination reaction is completed, keep the closed reactor under heat preservation and add urea to the defluorination slurry at a uniform rate until the nitrogen-phosphorus molar ratio in the system is 2.5:1. The urea is added within 20 minutes. Continue stirring to make the urea completely melt and mix evenly with the slurry. The added room temperature urea lowers the system temperature, and the residual heat of defluorination is used to maintain the system temperature at about 200 °C. The polymerization reaction is carried out for 1 hour to obtain crude sulfur-containing calcium polyphosphate ammonium. S4: Cool the crude sulfur-containing calcium polyphosphate to room temperature, crush it, and then sieve it through a 100-mesh sieve to obtain the sulfur-containing calcium polyphosphate fertilizer product.

[0022] Comparative Example 1 A sulfur-containing calcium polyphosphate ammonium fertilizer is prepared through the following steps: S1: The phosphate rock is crushed to 200 mesh to obtain dry-basis phosphate rock powder; the dry-basis mass fraction of this phosphate rock powder is: P2O5:32%, SiO2:12%, F:2%, MgO:0.6%, CaO:40%, Al2O3+Fe2O3:1.5%; S2: Add 100 kg of the above-mentioned dry-based phosphate rock powder to a reactor with an insulation layer, and add 160 kg of 50% sulfuric acid at a uniform rate. Stir rapidly to ensure full contact between the dry-based phosphate rock powder and sulfuric acid. Then, use an external heat source to raise the temperature to 80°C and maintain the temperature for defluorination for 3 hours to obtain a defluorinated slurry. The fluoride removal rate was found to be 62.3%. S3: After the defluorination reaction is completed, keep the reactor in a warm state and add urea to the defluorination slurry at a uniform rate until the nitrogen-phosphorus molar ratio in the system is 2:1. The urea is added within 20 minutes. Continue stirring to make the urea completely melt and mix evenly with the slurry. Use an external heat source to raise the temperature to about 170 °C and carry out the polymerization reaction for 1 hour to obtain sulfur-containing calcium polyphosphate crude product. S4: Cool the crude sulfur-containing calcium polyphosphate to room temperature, crush it, and then sieve it through a 100-mesh sieve to obtain the sulfur-containing calcium polyphosphate fertilizer product.

[0023] Experimental Example To investigate the defluorination effect of the mixed acid treatment process in this invention on phosphate rock powder, Example 1 was used as an example to compare the metallographic structures of dry-based phosphate rock powder and defluorination slurry dried powder (dried using conventional drying processes). The X-ray diffraction (XRD) patterns of both are shown below. Figure 1 As shown. From Figure 1 As can be seen from the defluorination slurry drying process, the phosphate rock crystal phase disappears, indicating that the defluorination process effectively removes fluorine from the phosphate rock powder.

[0024] In addition, the degree of polymerization and composition of the sulfur-containing calcium polyphosphate ammonium fertilizer products obtained in Examples 1-3 and Comparative Example 1 were tested. The degree of polymerization of the products obtained in Examples 1-3 are as follows: Figure 2 As shown. The results show that the degree of polymerization of the product in Example 1 is 1-9, of which 3-7 account for 68%, P2O5 content is 18%, N content is 7%, fluorine content is 0.06%, and effective sulfur content (as SO4) is... 2-The product in Example 2 has a polymerization degree distribution of 1-9, with 3-7 polymers accounting for 61%, P2O5 content of 15%, N content of 6%, fluorine content of 0.08%, and effective sulfur content (calculated as SO42-4). The effective calcium content (calculated as CaO) is 4.8%, and the effective calcium content (calculated as CaO) is 3.2%, exhibiting a balanced water solubility and sustained-release performance. 2- The product in Example 3 has a degree of polymerization distribution of 1-9, with 3-7 polymers accounting for 56%, P2O5 content of 16%, N content of 5%, fluorine content of 0.09%, and effective calcium content (calculated as CaO) of 3.5%, and a balanced water solubility and sustained-release performance. 2- The effective calcium content (calculated as CaO) was 6.2%, with a balanced water solubility and sustained-release properties. The product in Comparative Example 1 had a degree of polymerization distribution of 1-6, with 3-6 polymers accounting for 34%, P2O5 content of 16%, N content of 7%, fluorine content of 0.38%, and effective sulfur content (calculated as SO42-42-42-42-6). 2- The effective calcium content (calculated as CaO) is 3.8%, the process energy consumption is 1.8 times that of the present invention, and the fertilizer fluorine residue is 6 times that of Example 1.

[0025] 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 preparing a sulfur-containing calcium polyphosphate ammonium fertilizer, characterized in that, Includes the following steps: S1: The phosphate rock is crushed into powder to obtain dry-based phosphate rock powder; the dry-based phosphate rock powder contains the following components by mass fraction: P2O5 28~32%, SiO2 6~12%, F 1~2%, MgO≤1.2%, CaO 40~48%, Al2O3+Fe2O3≤3%; S2: Add a mixed acid to dry-based phosphate rock powder, wherein the mass ratio of dry-based phosphate rock powder to mixed acid is 1:0.6~1; use the heat released by the reaction to maintain the temperature of the reaction system at 200~280℃, and maintain this temperature for 0.5~3 hours to obtain a defluorinated slurry; the mixed acid is composed of fuming sulfuric acid and concentrated sulfuric acid, wherein the fuming sulfuric acid has a free SO3 content of 20~30wt%, the concentrated sulfuric acid has a mass concentration of 98%, and the mass percentage of fuming sulfuric acid in the mixed acid is 25~40%; negative pressure evacuation or inert gas purging is performed during the reaction; S3: Add urea to the defluorination slurry. After adding urea, the nitrogen-phosphorus molar ratio in the system is 1.5~2.5:

1. Use the residual heat of the defluorination slurry to maintain the system temperature at 140~200℃ and keep the polymerization reaction at this temperature for 0.5~2.5h to obtain crude sulfur-containing calcium polyphosphate ammonium. S4: Cool the crude sulfur-containing calcium polyphosphate to room temperature, crush and sieve it to obtain sulfur-containing calcium polyphosphate fertilizer.

2. The preparation method according to claim 1, characterized in that: The particle size of the dry-based phosphate rock powder is 50-400 mesh.

3. The preparation method according to claim 1, characterized in that: The urea should be added within 10-20 minutes.

4. A sulfur-containing calcium polyphosphate ammonium fertilizer, characterized in that: It is prepared by the preparation method according to any one of claims 1 to 3.

5. The sulfur-containing calcium polyphosphate ammonium fertilizer according to claim 4, characterized in that: The sulfur-containing calcium polyphosphate ammonium fertilizer has a degree of polymerization distribution of 1-9, with 3-7 polymers accounting for ≥50%; P2O5 content is 10-20%, N content is 5-10%, fluorine content is ≤0.1%, and SO4 content is the main component. 2- The effective sulfur content is 3-10% and the effective calcium content (calculated as CaO) is 3-10%.

Images