Process for improving crystallization rate of calcium nitrate in freezing-method nitrophosphate fertilizer production process

Abstract

The invention aims to provide a process for improving the crystallization rate of calcium nitrate in a freezing-method nitrophosphate fertilizer production process, and belongs to the technical field of nitrophosphate fertilizer production. Based on the existing freezing-method nitrophosphate fertilizer production process, an acidolysis solution premixing process is added after an acid insoluble substance filtering process; the acidolysis solution obtained through the acid insoluble substance separation process is mixed with the crystallization enhancer, so that the solubility of calcium nitrate in the acidolysis mother solution is reduced, the crystallization rate of calcium nitrate in the freezing crystallization process is increased, and calcium nitrate is separated out in the form of soluble calcium nitrate; therefore, while generation and accumulation of insoluble calcium salt are avoided, effective utilization of resources and zero emission are achieved, viscosity of neutralized slurry is reduced, P2O5 is prevented from being combined with calcium in the neutralization process to generate insoluble phosphate to affect the content of water-soluble phosphorus in a product, and finally the purposes of improving freezing crystallization of the process and neutralizing the mother liquor are achieved. The adaptability of the freezing-method nitrophosphate fertilizer process to low-grade phosphorite is improved, and the phosphorus content and the water solubility in the product are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of nitrophosphate fertilizer production, and in particular relates to a process for improving the crystallization rate of calcium nitrate in the process of producing nitrophosphate fertilizer by a freezing method. Background Art

[0002] The freezing process of nitrophosphate fertilizer is the earliest, most widely used and largest production method of nitrophosphate fertilizer in the world. The main processes include: decomposition of phosphate rock with nitric acid, separation of acid-insoluble matter, freezing crystallization of acid hydrolyzate to remove calcium, filtration of calcium nitrate, neutralization of mother liquor with ammonia, evaporation concentration and granulation (Jing Hongjian, Chen Mingliang, Chen Jingyu, etc. Freezing process of nitrophosphate fertilizer production technology [M]. Beijing: Chemical Industry Press, 2002). Compared with other phosphate fertilizer production processes, it has the following advantages: ① The frozen nitric acid phosphate fertilizer process uses nitric acid to decompose phosphate rock, which not only uses the chemical energy of nitric acid to decompose phosphate rock, but also preserves nitrate ions as a nitrogen source in the product, playing the role of nitrogen carrying phosphorus; ② In the production process of this process, nitric acid is used instead of sulfuric acid to decompose phosphate rock, which not only saves sulfur resources, but also provides a new production idea for countries such as my country that are short of sulfur resources, and improves the decomposition rate of phosphate rock, making its decomposition rate reach more than 99%; ③ In this process, the acid hydrolysis mother liquor is indirectly frozen to remove calcium (the calcium removal rate is more than 70%), which can convert the removed calcium nitrate into calcium ammonium nitrate, so that the nitrate nitrogen required by plants and Ca 2+ The residues are retained in the product, thus avoiding the discharge of waste residues. Therefore, this process has attracted more and more attention since it was developed and introduced into China.

[0003] However, this process has high requirements on the grade of raw phosphate ore (generally P 2 O 5 Around 32%, MgO <1.0%, acid insoluble matter <10%), while more than 93% of phosphate rock in my country is difficult to select medium and low-grade phosphate rock, which makes the grade of phosphate rock, the main raw material of frozen nitric acid phosphate fertilizer process, continuously reduce, and phosphate compound fertilizer enterprises have to face the dilemma of using low-grade phosphate rock to organize production. In this process, with the fluctuation of impurity content in phosphate rock, the calcium removal rate of calcium nitrate crystallization process dropped from more than 75% in the original design to between 60-70%. This phenomenon not only leads to the formation of monocalcium phosphate and dicalcium phosphate in the neutralization process, which in turn affects the change of slurry viscosity value, but also causes some P in the neutralization process to 2 O 5 It combines with calcium to form insoluble phosphates (tricalcium phosphate and calcium fluorophosphate), causing some soluble phosphorus products to degenerate into insoluble phosphates, thus affecting the water solubility of phosphorus in the final product and the utilization rate of phosphorus in the process. At the same time, the degraded phosphorus is difficult to be absorbed by plants, ultimately resulting in a certain amount of resource waste.

[0004] At present, the solutions mainly include: 1. Using chemical precipitation method to deeply remove calcium ions, that is, adding sulfate to the mother liquor to make the Ca 2+ ions to generate calcium sulfate dihydrate precipitation. This method will result in the production of phosphogypsum, a byproduct that is difficult to recycle; 2. Use physical adsorption to deeply remove calcium ions, that is, remove Ca in the solution by using resins, activated carbon and other substances to adsorb calcium ions. 2+ ions, but due to the presence of Ca 2+ The ion content is high, the adaptability of this method is poor, and there are problems such as poor adsorbent regeneration and circulation, poor stability in strong acidic solutions; 3. Use new technologies and methods such as secondary crystallization, vacuum low-temperature concentration crystallization or low back pressure supersonic nozzle direct freezing crystallization to improve the removal rate of calcium ions, but it faces the disadvantages of high energy consumption, high equipment requirements and poor stable operation in a strong acidic environment; Therefore, in order to make this process adapt to medium and low-grade phosphate ores, we urgently need to find a new type of frozen nitric phosphate fertilizer production process that can effectively improve the crystallization rate of calcium nitrate in the frozen crystallization process and increase the phosphorus content in the slurry, so as to achieve the adaptation of the frozen nitric phosphate fertilizer process to low-grade phosphate ores and improve the phosphorus content and water solubility in the product. Summary of the invention

[0005] In order to solve the problem that the existing freezing method nitrophosphate fertilizer production process is not suitable for medium and low-grade phosphate ore, the present invention provides a process for improving the crystallization rate of calcium nitrate in the freezing method nitrophosphate fertilizer production process.

[0006] To achieve the above object, the present invention adopts the following technical solution: A process for improving the crystallization rate of calcium nitrate in the production process of nitrophosphate fertilizer by freezing method, the process comprising the following steps in sequence: acidification of phosphate rock with nitric acid, precipitation and separation of acid insoluble matter, freezing and crystallization of calcium nitrate, separation of calcium nitrate, evaporation of mother liquor, neutralization of mother liquor, evaporation, granulation, drying and cooling; Among them, after the acid-insoluble matter precipitation and separation process, an acid hydrolysis solution premixing process is added, and the acid hydrolysis solution obtained by the acid-insoluble matter precipitation and separation process is mixed with the crystallization enhancer from the enhancer storage tank in the premixing tank, thereby reducing the solubility of calcium nitrate in the acid hydrolysis mother liquor and improving the crystallization rate of calcium nitrate in the freeze crystallization process, and finally achieving an increase in the crystallization rate of calcium nitrate in the freeze crystallization process and an increase in the phosphorus content in the product.

[0007] Furthermore, the phosphate ore is a medium-low grade phosphate ore, wherein P 2 O 5 The content is less than 30%.

[0008] Furthermore, the crystallization enhancer includes one or more of ferric nitrate nonahydrate, aluminum nitrate nonahydrate, magnesium nitrate hexahydrate, and ammonium nitrate.

[0009] Furthermore, the added amount of the crystallization enhancer relative to the mass fraction of the acidolysis solution is: ferric nitrate nonahydrate is 10-17%, aluminum nitrate nonahydrate is 4-8%, magnesium nitrate hexahydrate is 1-5%, and ammonium nitrate is 1-4%. The crystallization enhancer is evenly mixed in a powder mixer and then enters the acidolysis solution premixing process.

[0010] Furthermore, the size of the premixing tank is: Φ4300-5000 mm×4300-5000 mm, and a turbine agitator is installed in the premixing tank, and the blade diameter of the agitator is 1300-1400 mm.

[0011] Furthermore, the volume of the powder mixer is 23-48m 3 .

[0012] Furthermore, the premixing temperature of the acid hydrolysis solution premixing process is 50-60°C, the premixing time is 2-3h, and the end point linear speed of the paddle stirring is 5-6 m / s.

[0013] The beneficial effects of the present invention are as follows: 1. The crystallization enhancer used in the present invention is an effective component in the fertilizer obtained by the original process. Therefore, this method not only does not introduce impurities, but also increases the fertilizer efficiency of the fertilizer. More importantly, it reduces the solubility of calcium nitrate in the acid hydrolysis mother liquor and improves the crystallization rate of calcium nitrate in the freezing crystallization process, thereby achieving the purpose of modifying the freezing crystallization process and the mother liquor neutralization process, and improving the adaptability of the freezing method nitric acid phosphate fertilizer production process to the grade of phosphate ore. It is low in cost and simple to operate.

[0014] 2. The acid hydrolyzate premixing process adopted in the present invention is simple, relatively independent and self-contained, and does not require additional equipment. It can be directly used to implement technical transformation on the existing freezing method nitrophosphate fertilizer device.

[0015] 3. The process adopted by the present invention is a physical process, which simply utilizes the change in the solubility of calcium nitrate to improve the calcium removal rate, avoids the generation and accumulation of insoluble calcium salts, and achieves effective resource utilization and zero emissions; at the same time, the water-soluble phosphorus content in the obtained product is significantly improved, the scope of application is widened, and the use and economy are higher.

[0016] 4. The present invention can optimize the nitrogen-phosphorus ratio in nitrophosphate fertilizer by adding different proportions of crystallization enhancers, which meets the requirements of the country in recent years for nitrophosphate fertilizer factories to adjust their product structure and reduce weight and increase efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0018] The technical solution of the present invention is described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] Example 1 The quality index of the phosphate rock powder in this embodiment is: 2 O 5 28.9wt%, CaO 42.05wt%, F 2.59wt%, AI18.71wt%, Fe 2 O 3 1.14wt%,Al 2 O 3 1.26wt%, MgO 0.74wt%; the concentration of nitric acid is 58 wt%.

[0020] Nitric acid and phosphate rock powder are added to the acidolysis tank in a chemical ratio of 1.2:1 for acidolysis reaction. The acid insoluble matter in the acidolysis solution is separated by precipitation separation, and then the acidolysis solution with separated acid insoluble matter enters the acidolysis solution premixing process and is premixed with a crystallization enhancer. The crystallization enhancer is aluminum nitrate nonahydrate, and the amount added is 5.2% of the mass of the acidolysis solution obtained after separation of the acid insoluble matter. This crystallization enhancer enters the acidolysis solution premixing process through a powder mixer. In the acidolysis solution premixing process, the acidolysis solution is mixed with the acidolysis solution at 60°C and a paddle stirring end point linear velocity of 5.4 m / s for 2 h and then enters the freezing crystallization. After freezing crystallization, calcium nitrate is precipitated from the acidolysis solution and enters the calcium nitrate filtration for solid-liquid separation. The obtained solid is the calcium nitrate precipitate, and the obtained liquid is the mother liquor. The calcium nitrate precipitate goes to the calcium nitrate conversion process, and the mother liquor goes to the mother liquor for neutralization, and reacts with the added ammonium nitrate and ammonia. After the reaction is completed, the neutralized mother liquor is evaporated, granulated, dried, and cooled by slurry to obtain nitrophosphate fertilizer. During this process, we calculated the calcium removal rate, neutralization slurry viscosity, and the water-soluble phosphorus content and nitrogen-phosphorus ratio of the final product.

[0021] Comparative Example 1-1 The quality index of the phosphate rock powder in this comparative example is: 2 O 5 28.9wt%, CaO 42.05wt%, F 2.59wt%, AI18.71wt%, Fe 2 O 3 1.14wt%,Al 2 O 3 1.26wt%, MgO 0.74wt%; the concentration of nitric acid is 58 wt%. The process adopts the existing freezing method nitrophosphate fertilizer production process.

[0022] 58% nitric acid and phosphate rock powder are added to the acid hydrolysis tank at a chemical ratio of 1.2:1 for acid hydrolysis reaction. The acid insoluble matter in the acid hydrolysis solution is separated by precipitation separation, and then the acid hydrolysis solution with separated acid insoluble matter directly enters freezing crystallization. After freezing crystallization, calcium nitrate precipitates from the acid hydrolysis solution and enters calcium nitrate filtration for solid-liquid separation. The obtained solid is calcium nitrate precipitate, and the obtained liquid is mother liquor. Among them, the calcium nitrate precipitate enters the calcium nitrate conversion process and is converted into ammonium nitrate, and returns to the mother liquor neutralization process to adjust the viscosity of the neutralized material and the nitrogen-phosphorus ratio of the mother liquor; the mother liquor goes to the mother liquor for neutralization, and reacts with the added ammonium nitrate and ammonia gas. After the reaction is completed, the neutralized mother liquor is evaporated, granulated, dried, and cooled by slurry to obtain nitrophosphate fertilizer. In this process, we measured the calcium removal rate, the viscosity of the neutralized slurry, and the water-soluble phosphorus content and nitrogen-phosphorus ratio of the final product.

[0023] Example 2 The quality index of the phosphate rock powder in this embodiment is: 2 O 5 28.9wt%, CaO 42.05wt%, F 2.59wt%, AI18.71wt%, Fe 2 O 3 1.14wt%,Al 2 O 3 1.26wt%, MgO 0.74wt%; the concentration of nitric acid is 58 wt%.

[0024] Nitric acid and phosphate rock powder are added to the acidolysis tank in a chemical ratio of 1.2:1 for acidolysis reaction. The acid insoluble matter in the acidolysis solution is separated by precipitation separation, and then the acidolysis solution with separated acid insoluble matter enters the acidolysis solution premixing process and is premixed with a crystallization enhancer. The crystallization enhancers are aluminum nitrate nonahydrate and iron nitrate nonahydrate, wherein the amount of aluminum nitrate nonahydrate added is 6.4% of the mass of the acidolysis solution obtained after separation of the acid insoluble matter, and the amount of iron nitrate nonahydrate added is 14.5% of the mass of the acidolysis solution obtained after separation of the acid insoluble matter. This crystallization enhancer enters the acidolysis solution premixing process through a powder mixer. In the acidolysis solution premixing process, the acidolysis solution is mixed with the acidolysis solution at 60°C and a paddle stirring end point linear velocity of 5.4 m / s for 2 h, and then enters into frozen crystallization. After frozen crystallization, calcium nitrate precipitates from the acidolysis solution and enters into calcium nitrate filtration for solid-liquid separation. The obtained solid is calcium nitrate precipitate, and the obtained liquid is the mother liquor. The calcium nitrate precipitate goes to the calcium nitrate conversion process, and the mother liquor goes to the mother liquor neutralization process, where it reacts with the added ammonium nitrate and ammonia. After the reaction is completed, the neutralized mother liquor is evaporated, granulated, dried, and cooled to obtain nitrophosphate fertilizer. During this process, we measured the calcium removal rate, the viscosity of the neutralized slurry, and the water-soluble phosphorus content and nitrogen-phosphorus ratio of the final product.

[0025] Example 3 The quality index of the phosphate rock powder in this embodiment is: 2 O 5 28.9wt%, CaO 42.05wt%, F 2.59wt%, AI18.71wt%, Fe 2 O 3 1.14wt%,Al 2 O 3 1.26wt%, MgO 0.74wt%; the concentration of nitric acid is 58 wt%.

[0026] Nitric acid and phosphate rock powder are added to the acidolysis tank according to the chemical dosage of 1.2:1 for acidolysis reaction. The acid insoluble matter in the acidolysis solution is separated by precipitation separation, and then the acidolysis solution with separated acid insoluble matter enters the acidolysis solution premixing process and is premixed with the crystallization enhancer. The crystallization enhancer is aluminum nitrate nonahydrate, iron nitrate nonahydrate and magnesium nitrate hexahydrate. The amount of aluminum nitrate nonahydrate added is 6.8% of the mass of the acidolysis solution obtained after separation of the acid insoluble matter, the amount of iron nitrate nonahydrate added is 15% of the mass of the acidolysis solution obtained after separation of the acid insoluble matter, and the amount of magnesium nitrate hexahydrate added is 2.7% of the mass of the acidolysis solution obtained after separation of the acid insoluble matter. This crystallization enhancer enters the acidolysis solution premixing process through a powder mixer. In the acidolysis solution premixing process, the acidolysis solution is mixed with the acidolysis solution at 60°C and the end point linear speed of the paddle stirring is 5.4 m / s for 2 h, and then enters the freezing crystallization. After freezing crystallization, calcium nitrate precipitates from the acidolysis solution and enters the calcium nitrate filtration for solid-liquid separation. The obtained solid is the calcium nitrate precipitate, and the obtained liquid is the mother liquor. The calcium nitrate precipitate goes to the calcium nitrate conversion process, and the mother liquor goes to the mother liquor neutralization process, where it reacts with the added ammonium nitrate and ammonia. After the reaction is completed, the neutralized mother liquor is evaporated, granulated, dried, and cooled to obtain nitrophosphate fertilizer. During this process, we measured the calcium removal rate, the viscosity of the neutralized slurry, and the water-soluble phosphorus content and nitrogen-phosphorus ratio of the final product.

[0027] Example 4 The quality index of the phosphate rock powder in this embodiment is: 2 O 5 28.9wt%, CaO 42.05wt%, F 2.59wt%, AI18.71wt%, Fe 2 O 3 1.14wt%,Al 2 O 3 1.26wt%, MgO 0.74wt%; the concentration of nitric acid is 58 wt%.

[0028] Nitric acid and phosphate rock powder are added to the acidolysis tank according to the chemical measurement of 1.2:1 for acidolysis reaction, and the acid insoluble matter in the acidolysis solution is separated by precipitation separation, and then the acidolysis solution from which the acid insoluble matter is separated enters the acidolysis solution premixing process for premixing with the crystallization enhancer. The crystallization enhancer is aluminum nitrate nonahydrate, iron nitrate nonahydrate, magnesium nitrate hexahydrate and ammonium nitrate, wherein the amount of aluminum nitrate nonahydrate added is 6.9% of the mass of the acidolysis solution obtained after separation of the acid insoluble matter, the amount of iron nitrate nonahydrate added is 15.2% of the mass of the acidolysis solution obtained after separation of the acid insoluble matter, the amount of magnesium nitrate hexahydrate added is 2.7% of the mass of the acidolysis solution obtained after separation of the acid insoluble matter, and the amount of ammonium nitrate added is 2.3% of the mass of the acidolysis solution obtained after separation of the acid insoluble matter. The crystallization enhancer enters the acidolysis solution premixing process through a powder mixer. In the acid hydrolysis solution premixing process, the acid hydrolysis solution is mixed with the acid hydrolysis solution at 60°C and the end point linear speed of the blade stirring is 5.4m / s for 2 hours, and then enters the freezing crystallization. After freezing crystallization, calcium nitrate is precipitated from the acid hydrolysis solution and enters the calcium nitrate filtration for solid-liquid separation. The obtained solid is the calcium nitrate precipitate, and the obtained liquid is the mother liquor. The calcium nitrate precipitate goes to the calcium nitrate conversion process, and the mother liquor goes to the mother liquor for neutralization, and reacts with the added ammonium nitrate and ammonia. After the reaction is completed, the neutralized mother liquor is evaporated, granulated, dried, and cooled by slurry to obtain nitrophosphate fertilizer. In this process, we measured the calcium removal rate, the viscosity of the neutralized slurry, and the water-soluble phosphorus content and nitrogen-phosphorus ratio of the final product.

[0029] Table 1 Changes in calcium removal rate, neutralization slurry viscosity, final water-soluble phosphorus content and nitrogen-phosphorus ratio in each embodiment and comparative example It can be seen from the above table that: compared with the existing frozen nitrophosphate fertilizer production process (Comparative Example 1-1), the implementation of the process designed by the patent of the present invention can effectively improve the removal rate of calcium nitrate in the process acid hydrolyzate, reduce the viscosity of the neutralization slurry, increase the water-soluble phosphorus content in the product, adjust the nitrogen-phosphorus ratio in the product, and achieve the purpose of improving the process freezing crystallization and mother liquor neutralization procedures, so that the adaptability of the frozen nitrophosphate fertilizer process to low-grade phosphate ore is improved, and the phosphorus content and water solubility in the product are improved.

[0030] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A process for improving the crystallization rate of calcium nitrate in the production process of nitrophosphate fertilizer by freezing method, the process comprising the following steps in sequence: acidification of phosphate rock with nitric acid, precipitation and separation of acid insoluble matter, freezing and crystallization of calcium nitrate, separation of calcium nitrate, evaporation of mother liquor, neutralization of mother liquor, evaporation, granulation, drying and cooling; Features: After the acid-insoluble matter precipitation and separation process, an acid hydrolysis solution premixing process is added, and the acid hydrolysis solution obtained by the acid-insoluble matter precipitation and separation process is mixed with the crystallization enhancer from the enhancer storage tank in the premixing tank, thereby reducing the solubility of calcium nitrate in the acid hydrolysis mother liquor and improving the crystallization rate of calcium nitrate in the freeze crystallization process, and finally achieving an increase in the crystallization rate of calcium nitrate in the freeze crystallization process and an increase in the phosphorus content in the product.

2. A process for improving the crystallization rate of calcium nitrate in the freezing nitrophosphate fertilizer production process according to claim 1, characterized in that: The phosphate ore is of medium-low grade, and the content of P2O5 in the medium-low grade phosphate ore is less than 30%.

3. A process for improving the crystallization rate of calcium nitrate in the freezing nitrophosphate fertilizer production process according to claim 1, characterized in that: The crystal strengthening agent includes one or more of ferric nitrate nonahydrate, aluminum nitrate nonahydrate, magnesium nitrate hexahydrate, and ammonium nitrate.

4. A process for improving the crystallization rate of calcium nitrate in the production process of nitrophosphate fertilizer by freezing method according to claim 3, characterized in that: The added amounts of the crystallization enhancers relative to the mass fraction of the acidolysis solution are: 10-17% of ferric nitrate nonahydrate, 4-8% of aluminum nitrate nonahydrate, 1-5% of magnesium nitrate hexahydrate, and 1-4% of ammonium nitrate. The crystallization enhancers are mixed evenly in a powder mixer and then enter the acidolysis solution premixing process.

5. A process for improving the crystallization rate of calcium nitrate in the production process of nitrophosphate fertilizer by freezing method according to claim 1, characterized in that: The size of the premixing tank is Φ4300-5000 mm×4300-5000 mm. A turbine stirring paddle is installed in the premixing tank, and the diameter of the paddle of the stirring paddle is 1300-1400 mm.

6. A process for improving the crystallization rate of calcium nitrate in the production process of nitrophosphate fertilizer by freezing method according to claim 4, characterized in that: The volume of the powder mixer is 23-48m 3 .

7. A process for improving the crystallization rate of calcium nitrate in the production process of nitrophosphate fertilizer by freezing method according to claim 1, characterized in that: The premixing temperature of the acid hydrolyzate premixing process is 50-60° C., the premixing time is 2-3 hours, and the end point linear speed of the paddle stirring is 5-6 m / s.

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