A negative pressure enhanced acidolysis process for phosphate rock

Abstract

This invention provides a negative pressure-enhanced acidolysis process for phosphate rock, comprising the following steps: S1: Acidolysis enhancer is mixed evenly with dilute phosphoric acid and added to phosphate rock for reaction; S2: After heating to 75-85℃, the reactor is subjected to negative pressure to -55--75 kPa, while concentrated sulfuric acid is added dropwise to the reactor to maintain the slurry in a slightly boiling state for reaction; S3: Throughout the reaction process, the tail gas is washed by a water washing device, and the washing liquid is the fluorosilicic acid product; S4: After the reaction is completed, the slurry is filtered to obtain phosphogypsum and phosphoric acid with low fluorine content. This invention is applicable to the wet process of producing phosphoric acid from low-grade phosphate rock, with a simple process flow, easy operation, and easy industrial application.

Description

Technical Field

[0001] This invention belongs to the field of wet-process phosphoric acid production technology, specifically relating to a process for the synergistic recovery of phosphorus and fluorine resources through acid hydrolysis of phosphate rock under negative pressure. Background Technology

[0002] Traditional wet-process phosphoric acid production uses atmospheric pressure acid hydrolysis, which suffers from problems such as high reaction temperature, fine gypsum crystals encapsulating mineral particles, low phosphorus leaching rate, emission of fluorine-containing tail gas, high acid consumption, and poor filtration performance. Low- and medium-grade phosphate rock, due to its high levels of silicon, magnesium, iron, and aluminum impurities, undergoes incomplete acid hydrolysis under atmospheric pressure, resulting in high residual phosphorus in phosphogypsum. This restricts the long-term stable operation of the plant, hindering its ability to achieve its intended benefits.

[0003] Patent CN115608002A proposes an apparatus and method for enhancing the extraction of phosphate rock acid hydrolysis slurry. By setting a fluidized mixing section in the tower and introducing microbubbles into the extractant to form a multiphase flow, it is beneficial to enhance the dispersion and mixing of phosphate rock acid hydrolysis slurry and extractant in the fluidized mixing section, thus achieving efficient extraction of phosphate rock acid hydrolysis slurry. However, this technology introduces organic impurities and has a complex process. Patent CN115611260A proposes a microbubble-enhanced phosphate rock acid hydrolysis liquid extraction method. It introduces microbubbles and regulators into the slurry extraction process to improve the dispersion and mixing performance of phosphate rock acid hydrolysis liquid and extractant, achieving rapid extraction and separation of impurities and crystal growth of phosphogypsum. However, this technology has difficulties in separating the two phases of the raffinate, has a long back-extraction process, increases process costs, and is not conducive to widespread application. CN118637589B proposes a method for in-situ extraction, separation, and recovery of fluorine during the acidolysis of phosphate rock. The method involves mixing phosphate rock, phosphoric acid, and an extractant, and then applying an external field to enhance the reaction extraction, yielding a slurry and a fluorine-loaded organic phase. The obtained fluorine-loaded organic phase is then back-extracted to obtain a fluorine solution. The resulting slurry is then subjected to an acidolysis reaction, followed by solid-liquid separation to obtain phosphoric acid and phosphogypsum. However, this technology suffers from difficulties in back-extracting the fluorine-loaded organic phase and significant extractant loss, making it uneconomical.

[0004] Therefore, there is a need to provide a simple and feasible method for enhancing the acidolysis process of phosphate rock. Summary of the Invention

[0005] To address the problems and deficiencies of the existing technology, the technical solution of this invention is: a high-efficiency fluorine recovery process associated with phosphate rock, comprising the following steps:

[0006] S1: Mix the acid hydrolysis enhancer with dilute phosphoric acid evenly, and then add it to the phosphate rock to react; S2: After heating to 70~80℃, the reactor is evacuated to -55~-80kPa, and concentrated sulfuric acid is added dropwise to the reactor to keep the slurry in a boiling state for reaction. S3: Throughout the entire reaction process, the exhaust gas is washed by a water washing device, and the washing liquid is the fluorosilicic acid product. S4: After the reaction is complete, filter the slurry. The phosphogypsum contains low levels of fluorine and phosphorus, and the phosphoric acid contains low levels of fluorine.

[0007] The acidolysis enhancer comprises at least one of dialkylphosphonic acid and trifluoropropylsiloxane oligomers.

[0008] The reinforcing agent is a dialkylphosphino acid and a trifluoropropylsiloxane oligomer (degree of polymerization 20-30), with a mass ratio of 1-5:1, and the total amount used is 0.01% to 0.08% of the mass of phosphate rock.

[0009] The phosphate rock has a P2O5 content of 20%~28% and a CaO content of 38%-45%.

[0010] The reaction temperature of the phosphate rock with dilute phosphoric acid is 20℃-30℃, and the reaction time is 5-10 min.

[0011] The dilute phosphoric acid contains 15% to 20% P2O5 and is used in amounts that are 2.5 to 4.0 times the mass of phosphate rock.

[0012] The reaction time under the aforementioned simmering state is 2-3 hours.

[0013] The concentrated sulfuric acid has a mass fraction of 98%, and the amount of concentrated phosphoric acid used is 0.6 to 0.9 times the mass of the phosphate rock.

[0014] Principle of this invention: The P–OH group in the dialkylphosphinoic acid structure can dissociate to release H. + It coordinates with metal ions, and its tetrahedral steric hindrance allows for selective coordination of small-radius metal ions (such as K+). + Na + Mg 2+ Al 3+ In the trifluoropropylsiloxane oligomer structure, the Si–O–Si can undergo interfacial adsorption with HF in phosphoric acid, inhibiting HF gas escape, reducing fluorine loss due to complexation and precipitation with metal ions, promoting the conversion of HF to SiF4, and improving fluorine yield. Acidolysis of phosphate rock slurry with sulfuric acid under negative pressure, combined with enhancing agents, selectively complexes Mg. 2+ Fe 3+ Al 3+ It releases phosphorus fixed by impurities, promotes the stable release of fluorine in the form of SiF4, reduces fluorine entrainment in gypsum, effectively inhibits phosphate rock encapsulation, improves phosphate rock decomposition rate and phosphorus yield, and makes phosphogypsum crystals more likely to form regular crystal forms, thus improving filtration effect.

[0015] Beneficial effects: This invention can improve the decomposition rate of phosphate rock in wet process phosphoric acid production, increase phosphorus and fluorine yield, and is green and efficient, suitable for industrial promotion. Detailed Implementation

[0016] The present invention will be further described below with reference to specific embodiments.

[0017] Example 1 0.2g of dialkylphosphine and 0.2g of trifluoropropylsiloxane oligomer were mixed evenly with 3000g of dilute phosphoric acid with a P2O5 content of 20%. 1000g of phosphate rock with a phosphorus content of 27% was added and reacted for 10 minutes. After heating to 80℃, the reactor was evacuated to a negative pressure of -55kPa. At the same time, 700g of concentrated sulfuric acid (mass fraction of 98%) was slowly added dropwise to the reactor. The slurry was kept in a slightly boiling state for acid hydrolysis reaction for 2 hours. The tail gas generated during the reaction was washed by a water washing device. The washing liquid was the fluorosilicic acid product. After the reaction was completed, the slurry was filtered to obtain low-fluorine finished phosphoric acid and phosphogypsum with low fluorine and phosphorus content.

[0018] Example 2 The steps are the same as in Example 1, except that the reactor is evacuated to a negative pressure of -70 kPa.

[0019] Example 3 The steps are the same as in Example 1, except that the reactor is evacuated to a negative pressure of -80 kPa.

[0020] Example 4 The steps are the same as in Example 1, except that the reaction is carried out in the reactor under normal pressure.

[0021] Example 5 The steps are the same as in Example 3, except that the acid hydrolysis reinforcing agent does not contain trifluoropropylsiloxane oligomers. Specifically, 0.2g of dialkylphosphine acid is mixed evenly with 3000g of dilute phosphoric acid with a P2O5 content of 20%, and 1000g of phosphate rock with a phosphorus content of 27% is added and reacted for 10 minutes. After heating to 80°C, the reactor is evacuated to a negative pressure of -80kPa, and 700g of concentrated sulfuric acid is slowly added dropwise to the reactor. The reaction is carried out for 2 hours, and the tail gas is washed by a water washing device. The washing liquid is the fluorosilicic acid product. After the reaction is completed, the slurry is filtered to obtain phosphogypsum with low fluorine and phosphorus content.

[0022] Example 6 The steps are the same as in Example 3, except that the acid hydrolysis reinforcing agent does not contain dialkylphosphine. 0.2g of trifluoropropylsiloxane oligomer is mixed evenly with 3000g of dilute phosphoric acid with a P2O5 content of 20%. 1000g of phosphate rock with a phosphorus content of 27% is added and reacted for 10 minutes. After heating to 80°C, the reactor is evacuated to a negative pressure of -80kPa. Simultaneously, 700g of concentrated sulfuric acid is slowly added dropwise to the reactor. The reaction is carried out for 2 hours. The exhaust gas is washed with a water washing device, and the washing liquid is the fluorosilicic acid product. After the reaction is complete, the slurry is filtered to obtain phosphogypsum with low fluorine and phosphorus content.

[0023] The statistical results of the case analysis are shown in Table 1 below: Table 1. Analysis results of phosphoric acid and phosphogypsum (unit: %)

Claims

1. A negative pressure-enhanced acidolysis process for phosphate rock, characterized in that, Includes the following steps: S1: Mix the acid hydrolysis enhancer with dilute phosphoric acid evenly, and add it to phosphate rock to react; S2: After heating to the preset temperature, the reactor is evacuated to the preset negative pressure range, and concentrated sulfuric acid is added dropwise into the reactor while keeping the slurry in a slightly boiling state to carry out the acid hydrolysis reaction. S3: During the entire reaction process, the generated tail gas is washed and absorbed to obtain fluorosilicic acid product; S4: After the reaction is complete, filter the slurry to obtain phosphogypsum and phosphoric acid with reduced fluorine content.

2. The process according to claim 1, characterized in that, The acidolysis enhancer comprises at least one of dialkylphosphonic acid and trifluoropropylsiloxane oligomers.

3. The process according to claim 2, characterized in that, The acid hydrolysis reinforcing agent is a combination of dialkylphosphino acid and trifluoropropylsiloxane oligomer, with a mass ratio of 1-5:1, and the total amount used is 0.01% to 0.08% of the mass of phosphate rock.

4. The process according to claim 1, characterized in that, The phosphate rock contains 20% to 28% P2O5 and 38% to 45% CaO.

5. The process according to claim 1, characterized in that, The reaction temperature of the phosphate rock and dilute phosphoric acid described in S1 is 20℃~30℃, and the reaction time is 5~10 minutes.

6. The process according to claim 1, characterized in that, The dilute phosphoric acid contains 15% to 20% P2O5, and its dosage is 2.5 to 4.0 times the mass of phosphate rock.

7. The process according to claim 1, characterized in that, The preset temperature for heating in S2 is 70~85℃; the preset negative pressure range is -55kPa ~ -80kPa; and the acidolysis reaction time under the slight boiling state is 2~3 hours.

8. The process according to claim 1, characterized in that, The concentrated sulfuric acid has a mass fraction of 98%, and its dosage is 0.6 to 0.9 times the mass of the phosphate rock.

9. The process according to claim 1, characterized in that, The exhaust gas described in S3 is washed and absorbed by a water washing device, and the washing liquid is directly used as a fluorosilicic acid product.

10. The process according to claim 1, characterized in that, The fluorine content in the phosphoric acid obtained by filtration described in S4 is reduced, and the total P2O5 content and total fluorine content in phosphogypsum are also reduced.

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