A method for recovering fluorine by using flash cooling coupled with cyclone in wet-process phosphoric acid process

Abstract

The present invention provides a method for recovering fluorine in a wet-process phosphoric acid production process using flash evaporation and cooling coupled with cyclone flow. The method comprises: subjecting a slurry obtained from the acid hydrolysis of phosphate rock to flash evaporation and cooling for crystallization to obtain a flashed slurry; and subjecting the obtained flashed slurry to cyclone separation to recover fluorosilicate particles. The method, provided herein, utilizes flash evaporation and cooling coupled with cyclone separation to separate and recover fluorine from the acid hydrolysis of phosphate rock into large-particle fluorosilicates. The process is simple and easy to operate, and without the need for the addition of any chemical reagents, the method achieves excellent fluorine recovery, with a recovery rate exceeding 32.4%. This method can effectively reduce the fluorine content in phosphogypsum and phosphoric acid produced during the wet-process phosphoric acid production process and facilitates the subsequent recycling of fluorine resources.

Description

Technical Field

[0001] The present invention belongs to the technical field of wet-process phosphoric acid and relates to a method for recovering fluorine in a wet-process phosphoric acid process, and in particular to a method for recovering fluorine in a wet-process phosphoric acid process by utilizing flash cooling coupled with cyclone flow. Background Art

[0002] The wet-process phosphoric acid process uses inorganic acids to decompose phosphate rock to produce phosphoric acid. The main steps in the wet-process phosphoric acid production process include: acid hydrolysis of phosphate rock with acids (including sulfuric acid, nitric acid, and hydrochloric acid), filtration of the reaction slurry after acid hydrolysis to produce a gypsum filter cake and low-concentration phosphoric acid, and concentration of this low-concentration phosphoric acid to produce the phosphoric acid product. Phosphate rock contains fluorine impurities. During the acid hydrolysis process, fluorine reacts with the acid to form hydrofluoric acid. Hydrofluoric acid reacts with silicon oxide or silicates in the phosphate rock to form fluorosilicic acid. This fluorine enters the wet-process phosphoric acid process, affecting the purity of the phosphoric acid product. Therefore, defluorination and purification of the wet-process phosphoric acid process are of great significance.

[0003] With the development of phosphate rock resources, the resource utilization of medium- and low-grade phosphate rock has become an urgent need in the phosphate chemical industry. Low- and medium-grade phosphate rock has a high impurity content. During the acid hydrolysis process, large amounts of impurities such as sodium, potassium, and silicon are released, which combine with fluorine to form sodium and potassium fluorosilicates. As impurities continue to accumulate, they can easily reach a supersaturated state. During the vacuum filtration process, the supersaturated sodium and potassium fluorosilicates cool and easily precipitate out and become mixed with the phosphogypsum, resulting in a high fluorine content in the phosphogypsum and a significant waste of fluorine resources. During the aging and refining of phosphoric acid, sodium and potassium fluorosilicates are easily converted into low-value fluorine-containing slag, making resource utilization difficult.

[0004] At present, the defluorination methods of wet-process phosphoric acid process mainly include chemical precipitation method, vacuum concentration method and steam stripping method. The chemical precipitation method is to add alkali metal salt as a defluorinating agent to generate fluorosilicate precipitate for filtration. The vacuum concentration method is to add active SiO2 to convert fluorine into fluorosilicic acid, and then convert the fluorine into gas by heating and concentrating. The steam stripping method is to heat the acid in the concentrated phosphoric acid with high-pressure supersaturated steam to vaporize and escape the fluorine. For example, CN117699760A, CN114314539A, CN110467167A, etc. disclose methods for defluorination of wet-process phosphoric acid, and the above-mentioned defluorination methods are all for defluorination and purification of the produced phosphoric acid while concentrating to obtain phosphoric acid product. It is difficult to remove and purify the fluorine impurities in the wet-process phosphoric acid process, and the defluorination effect in the wet-process phosphoric acid process cannot be guaranteed, thereby affecting the purity of the phosphogypsum product and wasting fluorine resources.

[0005] Therefore, it is necessary to provide a method for enhancing fluorine resource recovery in the acid decomposition process of phosphate rock in the wet process phosphoric acid. Summary of the Invention

[0006] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a method for recovering fluorine in the wet-process phosphoric acid process by using flash cooling coupled with cyclone flow. In order to solve the problem of fluorine-containing impurities and fluorine resource waste caused by the acid hydrolysis process releasing a large amount of sodium, potassium, silicon and fluorine impurities to form fluorosilicates in the wet-process phosphoric acid process of medium and low-grade phosphate rock, the fluorosilicates can be recovered in the acid hydrolysis process.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] The present invention provides a method for recovering fluorine by utilizing flash cooling coupled with cyclone flow in a wet-process phosphoric acid process, the method comprising the following steps:

[0009] (1) flash evaporation and cooling crystallization of the phosphate rock acid-decomposed slurry to obtain a flash evaporation slurry;

[0010] (2) subjecting the flash evaporation slurry obtained in step (1) to cyclone separation to recover the fluorosilicate particles.

[0011] During the acid hydrolysis process, medium and low-grade phosphate rock releases a large amount of impurities such as sodium, potassium, silicon and fluorine, forming sodium fluorosilicate and potassium fluorosilicate. Sodium fluorosilicate and potassium fluorosilicate continue to accumulate to supersaturation and enter the subsequent phosphogypsum products.

[0012] The method provided by the present invention targets the sources of sodium fluorosilicate and potassium fluorosilicate. After the acid hydrolysis process of phosphate rock, the method utilizes the characteristics of sodium fluorosilicate and potassium fluorosilicate that they have high solubility under high temperature conditions and low solubility under low temperature conditions. A flash evaporation method is used to achieve rapid vaporization of liquid in the slurry and absorb a large amount of heat, thereby increasing the supersaturation of fluorosilicate in the slurry and simultaneously reducing the slurry temperature. The supersaturated fluorosilicate is then rapidly crystallized and grown into large particles of millimeter to centimeter size. The fluorosilicate particles then continue to grow in the slurry system. Cyclone separation is then used to quickly and cost-effectively recover the large fluorosilicate particles in the slurry, thereby achieving fluorine precipitation recovery in the wet-process phosphoric acid process, facilitating the subsequent resource utilization of fluorine resources, and reducing the entry of fluorine impurities into subsequent processes.

[0013] The process of acid decomposition of phosphate rock includes reacting phosphate rock with sulfuric acid.

[0014] Preferably, the composition of the phosphate rock includes: P2O5 content of 20-30wt%, F content of 2-4wt%, SiO2 content of 6-12wt%, Al2O3 content of 2-6wt%, K2O content of 0.5-2wt%, and Na2O content of 0.1-1wt%.

[0015] The F content is 2-4wt%, for example, 2wt%, 2.5wt%, 3wt%, 3.5wt% or 4wt%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0016] The SiO2 content is 6-12wt%, for example, it can be 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt% or 12wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0017] The content of K2O is 0.5-2wt%, for example, 0.5wt%, 1wt%, 1.5wt% or 2wt%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0018] The Na2O content is 0.1-1wt%, for example, it can be 0.1wt%, 0.3wt%, 0.5wt%, 0.8wt% or 1wt%, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0019] Preferably, the composition of the slurry obtained by acid hydrolysis of phosphate rock includes: 30-35 wt% phosphogypsum, 25-35 wt% P2O5, 1-5 wt% sulfuric acid, and 0.1-2 wt% hydrofluoric acid.

[0020] Among them, the content of phosphogypsum is 30-35wt%, for example, it can be 30wt%, 31wt%, 32wt%, 33wt%, 34wt% or 35wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0021] The content of P2O5 is 25-35wt%, for example, it can be 25wt%, 28wt%, 30wt%, 32wt% or 35wt%, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0022] The content of sulfuric acid is 1-5wt%, for example, 1wt%, 2wt%, 3wt%, 4wt% or 5wt%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0023] The content of hydrofluoric acid is 0.1-2 wt%, for example, 0.1 wt%, 0.5 wt%, 1 wt%, 1.5 wt% or 2 wt%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0024] Preferably, the solid content of the phosphate rock acid hydrolysis slurry is 25-38%, for example, it can be 25%, 26%, 28%, 30%, 32%, 34%, 35%, 36% or 38%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0025] Preferably, the D50 particle size distribution of the solid phase in the phosphate rock acid-hydrolyzed slurry is 70-100 μm, for example, it can be 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm or 100 μm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0026] Preferably, the total content of sodium and potassium in the liquid phase of the phosphate rock acid hydrolysis slurry is 0.4-0.8%, for example, it can be 0.4%, 0.5%, 0.6%, 0.7% or 0.8%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0027] Preferably, the P2O5 content of the liquid phase in the slurry of the acid hydrolysis of the phosphate rock is 25-35%, for example, it can be 25%, 26%, 28%, 30%, 32%, 34% or 35%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0028] Preferably, in the slurry of the acid hydrolysis of the phosphate rock, the F content of the liquid phase is 0.5-2.0%, for example, it can be 0.5%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.5%, 1.6%, 1.8% or 2.0%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0029] Preferably, the temperature of the phosphate rock acid hydrolysis slurry is 70-80°C, for example, it can be 70°C, 71°C, 72°C, 73°C, 74°C, 75°C, 76°C, 77°C, 78°C, 79°C or 80°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0030] Preferably, the vacuum degree of the flash cooling crystallization is 65-85 kPa, for example, it can be 65 kPa, 68 kPa, 70 kPa, 72 kPa, 75 kPa, 78 kPa, 80 kPa, 82 kPa or 85 kPa, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0031] Preferably, the temperature difference between the feed and discharge of the flash crystallization is 4-8°C, for example, 4°C, 5°C, 6°C, 7°C or 8°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0032] In the present invention, the flash evaporation and cooling crystallization is achieved by a conventional flash evaporation device in the art, and the present invention does not limit its structure.

[0033] Preferably, the temperature of the slurry after flash evaporation is controlled to be 70-80°C, for example, 70°C, 72°C, 75°C, 78°C or 80°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0034] Preferably, the temperature of the slurry after flash evaporation is controlled to be kept warm for 2-3 hours, for example, it can be 2 hours, 2.2 hours, 2.4 hours, 2.5 hours, 2.6 hours, 2.8 hours or 3 hours, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0035] In the present invention, the slurry temperature after flash evaporation is regulated and the holding time is increased. Since impurities such as fluorine and silicon / potassium / sodium are still dissolved in large quantities during the holding process, the system is still in an oversaturated state, and the crystallized fluorosilicate particles will further grow, thereby achieving recovery through subsequent cyclone separation.

[0036] Preferably, the feed pressure for the cyclone separation is 0.08-0.16 MPa, for example, it can be 0.08 MPa, 0.09 MPa, 0.10 MPa, 0.11 MPa, 0.12 MPa, 0.13 MPa, 0.14 MPa, 0.15 MPa or 0.16 MPa, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0037] Preferably, the feed flow rate for the cyclone separation is 3.0-6.0 m / s, for example, 3.0 m / s, 4.0 m / s, 5.0 m / s or 6.0 m / s, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0038] Preferably, the cyclone separation is performed using a cyclone separation device.

[0039] In the present invention, the cyclone separation device can be a conventional cyclone separation device in the art, and the present invention does not limit its specific structure.

[0040] Preferably, the inner diameter of the cyclone tube of the cyclone separation device is 250-300 mm, for example, it can be 250 mm, 260 mm, 270 mm, 280 mm, 290 mm or 300 mm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0041] Preferably, the inner diameter of the sand settling port of the cyclone separation device is 50-70 mm, for example, it can be 50 mm, 55 mm, 60 mm, 65 mm or 70 mm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0042] Preferably, the cyclone separation device comprises 3-5 cyclone tubes arranged in parallel, for example, 3, 4 or 5 cyclone tubes.

[0043] Preferably, the D50 particle size distribution of the fluorosilicate particles is 1-8 mm, for example, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm or 8 mm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0044] As a preferred technical solution of the method for recovering fluorine by using flash cooling coupled with cyclone in the wet-process phosphoric acid process provided by the present invention, the method comprises the following steps:

[0045] (1) subjecting the acid-hydrolyzed phosphate rock slurry at a temperature of 70-80° C. to flash cooling crystallization, wherein the solid content of the acid-hydrolyzed phosphate rock slurry is 25-38%, the D50 particle size distribution of the solid phase in the acid-hydrolyzed phosphate rock slurry is 70-100 μm, the P2O5 content of the liquid phase in the acid-hydrolyzed phosphate rock slurry is 25-35%, the total content of sodium and potassium in the liquid phase is 0.4-0.8%, and the F content in the liquid phase is 0.5-2.0%; the vacuum degree of the flash cooling crystallization is 65-85 kPa, the temperature difference between the feed and discharge of the flash cooling crystallization is 4-8° C., and after the flash cooling crystallization is completed, the temperature of the flash-evaporated slurry is controlled to 70-80° C. and kept warm for 2-3 hours;

[0046] (2) The slurry after flash evaporation is subjected to cyclone separation, the feed pressure of the cyclone separation is 0.08-0.16 MPa, the feed flow rate of the cyclone separation is 3.0-6.0 m / s, and the fluorosilicate particles are recovered after cyclone separation. The D50 particle size distribution of the fluorosilicate particles is 3-8 mm.

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] The method provided by the present invention uses flash cooling coupled with cyclone separation to separate and recover fluorine from the acid hydrolysis of phosphate rock into large-particle fluorosilicate. The process is simple and easy to operate, and no chemical reagents need to be added. The fluorine recovery effect is good, with a recovery rate of more than 32.4%. The method can effectively reduce the fluorine content of subsequent phosphogypsum and phosphoric acid in the wet-process phosphoric acid process, and is conducive to the subsequent resource utilization of fluorine resources. DETAILED DESCRIPTION

[0049] The technical solution of the present invention is further illustrated below through specific implementation methods.

[0050] Example 1

[0051] This embodiment provides a method for recovering fluorine by using flash cooling coupled with cyclone flow in a wet-process phosphoric acid process.

[0052] The composition of the phosphate rock acid hydrolysis slurry used includes: 33wt% phosphogypsum, 25wt% P2O5, 2.5wt% sulfuric acid, and 1.1wt% hydrofluoric acid, wherein the solid content is 33%, the D50 particle size distribution of the solid phase is 88μm, the total content of sodium and potassium in the liquid phase is 0.6%, the P2O5 content of the liquid phase is 25%, and the F content of the liquid phase is 1.1%.

[0053] The method comprises the following steps:

[0054] (1) The 80°C phosphate rock acid-dissolved slurry is passed through a flash evaporator for cooling and crystallization. The vacuum degree of the flash evaporator is 65 kPa, the temperature difference between the inlet and outlet materials is 7°C, and the slurry is output at 73°C. The slurry temperature is adjusted to 75°C and kept warm for 2.5 hours.

[0055] (2) The slurry is subjected to cyclone separation. The feed pressure of the cyclone separation is 0.13 MPa, the feed flow rate is 4.5 m / s, the inner diameter of the cyclone tube of the cyclone separation device used is 350 mm, the inner diameter of the sand settling port is 60 mm, and the number of cyclone tubes is 4 and arranged in parallel to recover large fluorosilicate particles in the slurry.

[0056] Example 2

[0057] This embodiment provides a method for recovering fluorine by using flash cooling coupled with cyclone flow in a wet-process phosphoric acid process.

[0058] The composition of the phosphate rock acid hydrolysis slurry used includes: 30wt% phosphogypsum, 35wt% P2O5, 1wt% sulfuric acid, and 2wt% hydrofluoric acid, wherein the solid content is 38%, the D50 particle size distribution of the solid phase is 70μm, the total content of sodium and potassium in the liquid phase is 0.4%, the P2O5 content of the liquid phase is 35%, and the F content of the liquid phase is 2.0%.

[0059] The method comprises the following steps:

[0060] (1) The slurry of phosphate rock acid hydrolysis at 70°C is passed through a flash evaporation device for cooling and crystallization. The vacuum degree of the flash evaporation device is 85kPa, the temperature difference between the inlet and outlet materials is 4°C, and the slurry at 66°C is output. The slurry temperature is adjusted to 70°C and kept warm for 3 hours;

[0061] (2) The slurry is subjected to cyclone separation. The feed pressure of the cyclone separation is 0.08 MPa, the feed flow rate is 6.0 m / s, the inner diameter of the cyclone tube of the cyclone separation device used is 250 mm, the inner diameter of the sand settling port is 50 mm, and the number of cyclone tubes is 5 and arranged in parallel to recover large fluorosilicate particles in the slurry.

[0062] Example 3

[0063] This embodiment provides a method for recovering fluorine by using flash cooling coupled with cyclone flow in a wet-process phosphoric acid process.

[0064] The composition of the phosphate rock acid hydrolysis slurry used includes: 35wt% phosphogypsum, 30wt% P2O5, 5wt% sulfuric acid, and 0.1wt% hydrofluoric acid, wherein the solid content is 25%, the D50 particle size distribution of the solid phase is 100μm, the total content of sodium and potassium in the liquid phase is 0.8%, the P2O5 content of the liquid phase is 30%, and the F content of the liquid phase is 0.5%.

[0065] The method comprises the following steps:

[0066] (1) The slurry of phosphate rock acid hydrolysis at 78°C was passed through a flash evaporation device for cooling and crystallization. The vacuum degree of the flash evaporation device was 70 kPa, the temperature difference between the inlet and outlet materials was 8°C, and the slurry at 70°C was output. The slurry temperature was adjusted to 73°C and 80°C in sequence, and kept warm for 1 hour respectively, for a total of 2 hours;

[0067] (2) The slurry is subjected to cyclone separation. The feed pressure of the cyclone separation is 0.16 MPa, the feed flow rate is 3.0 m / s, the inner diameter of the cyclone tube of the cyclone separation device used is 300 mm, the inner diameter of the sand settling port is 70 mm, and the number of cyclone tubes is 3 and arranged in parallel to recover large fluorosilicate particles in the slurry.

[0068] Example 4

[0069] This embodiment provides a method for recovering fluorine by flash cooling coupled with cyclone in a wet-process phosphoric acid process. Compared with Example 1, the temperature difference between the feed and discharge of the flash cooling crystallization in step (1) is controlled to be 2°C. The rest is the same as Example 1.

[0070] Example 5

[0071] This embodiment provides a method for recovering fluorine by flash cooling coupled with cyclone in a wet-process phosphoric acid process. Compared with Example 1, the temperature difference between the feed and discharge of the flash cooling crystallization in step (1) is controlled to be 10°C. The rest is the same as Example 1.

[0072] Example 6

[0073] This embodiment provides a method for recovering fluorine by using flash cooling coupled with cyclone in a wet-process phosphoric acid process. Compared with Example 1, the vacuum degree of the flash cooling crystallization in step (1) is controlled to be 50 kPa, and the rest is the same as Example 1.

[0074] Example 7

[0075] This embodiment provides a method for recovering fluorine by using flash cooling coupled with cyclone flow in a wet-process phosphoric acid process. Compared with Example 1, the vacuum degree of the flash cooling crystallization in step (1) is controlled to be 95 kPa, and the rest is the same as Example 1.

[0076] Example 8

[0077] This embodiment provides a method for recovering fluorine by using flash cooling coupled with cyclone flow in a wet-process phosphoric acid process. Compared with Example 1, the temperature is not adjusted or kept warm after the flash cooling crystallization in step (1). The rest is the same as Example 1.

[0078] Comparative Example 1

[0079] This comparative example provides a method for recovering fluorine in a wet-process phosphoric acid process. Compared with Example 1, step (2) of cyclone separation is not performed, and the rest is the same as Example 1.

[0080] Comparative Example 2

[0081] This comparative example provides a method for recovering fluorine in a wet-process phosphoric acid process. Compared with Example 1, step (1) of flash evaporation and cooling crystallization is not performed, and the rest is the same as Example 1.

[0082] Performance Characterization

[0083] The slurry after cyclone separation in the examples and comparative examples was filtered to obtain filter cake phosphogypsum and filtrate wet-process phosphoric acid. The fluorine content therein was determined and the fluorine recovery rate was calculated. The results are listed in Table 1.

[0084] The fluorine content in the acid solution was measured using the method of "GB / T 21057-2007 General method for determination of fluorine content in inorganic chemical products - Ion selective electrode method".

[0085] The fluorine content in phosphate rock and phosphogypsum was detected by X-ray fluorescence spectrometer.

[0086] The D50 particle size distribution of the fluorosilicate particles was detected using a fully automatic BET specific surface (area) analyzer.

[0087] The calculation formula of fluorine recovery rate is as follows:

[0088] Fluorine recovery rate = (mass of phosphate rock * fluorine content of phosphate rock - mass of phosphogypsum * fluorine content in phosphogypsum - mass of phosphoric acid * fluorine content in phosphoric acid) / (mass of phosphate rock * fluorine content of phosphate rock) × 100%.

[0089] Table 1

[0090]

[0091]

[0092] As can be seen from Table 1, the fluorine recovery method provided by the present invention converts the fluorine in the slurry into large-particle fluorosilicate by flash evaporation and cooling crystallization, and then recovers it by cyclone separation. In Examples 1-3, large particles with a D50 particle size of 5.9 mm or more can be recovered, fluorine impurities can be effectively separated and recovered, and the fluorine content in the phosphogypsum can be reduced to below 0.18%.

[0093] Compared with Example 1, in Example 4, when the inlet and outlet temperature difference of the flash cooling crystallization is too small, the amount of water removed by vacuum flash evaporation is small, the supersaturation of fluorosilicate in the slurry is low, the fluorosilicate particle size generated is small, and it is difficult to carry out cyclone separation and recovery, resulting in low fluorine recovery rate and high fluorine content in phosphogypsum; in Example 5, when the inlet and outlet temperature difference of the flash cooling crystallization is too large, the amount of water removed by vacuum flash evaporation is large, the slurry temperature is reduced too much, the crystallization temperature is low, the fluorosilicate crystal growth rate in the slurry is slow, the fluorosilicate particle size generated is small, and it is difficult to carry out cyclone separation and recovery, resulting in low fluorine recovery rate and high fluorine content in phosphogypsum; in Example 6, the vacuum degree of the flash cooling crystallization is too low, the vacuum flash dehydration rate is slow, the amount of water removed by vacuum flash evaporation is also small, the supersaturation of fluorosilicate in the slurry is low, and the fluorosilicate crystals are difficult to be recovered. The rapid growth results in a small particle size of the generated fluorosilicate, which is difficult to be recovered by cyclone separation, resulting in a low fluorine recovery rate and a high fluorine content in the phosphogypsum; in Example 7, the vacuum degree of the flash cooling crystallization is too high, the vacuum flash dehydration rate is too fast, a large number of small crystal nuclei are formed in the fluorosilicate in the slurry, and the fluorosilicate crystals cannot grow larger, resulting in a small particle size of the fluorosilicate, which is difficult to be recovered by cyclone separation, resulting in a low fluorine recovery rate and a high fluorine content in the phosphogypsum; in Example 8, the slurry temperature is not adjusted or kept warm, the fluorosilicate particles obtained after flash evaporation are small, and there is a lack of a process for the particles to continue to grow, resulting in a small size of the obtained fluorosilicate particles, and a large amount of fluorosilicate is still present in the slurry, thereby affecting the subsequent cyclone separation, resulting in a low fluorine recovery rate, and a large amount of fluorosilicate still remains in the phosphogypsum, resulting in a high fluorine content in the phosphogypsum.

[0094] In Comparative Example 1, no cyclone separation is performed, and the large-particle fluorosilicate generated enters the phosphogypsum and cannot be separated, resulting in a fluorine recovery rate of 0 and an extremely high fluorine content in the phosphogypsum; in Comparative Example 2, no flash cooling crystallization is performed, and the fluorosilicate in the slurry cannot grow rapidly to generate large-particle fluorosilicate, and can only generate a small amount of fine-particle fluorosilicate. Only a small amount of fine-particle fluorosilicate can be separated by cyclone, resulting in a low fluorine recovery rate, and a large amount of fluorosilicate still remains in the phosphogypsum, resulting in a high fluorine content in the phosphogypsum.

[0095] In summary, the method provided by the present invention separates and recovers the fluorine from the acid hydrolysis of phosphate rock into large-particle fluorosilicates through flash cooling coupled with cyclone separation. The process is simple and easy to operate, and does not require the addition of any chemical reagents. The fluorine recovery effect is good, with a recovery rate of more than 32.4%. It can effectively reduce the fluorine content of subsequent phosphogypsum and phosphoric acid in the wet-process phosphoric acid process, and is conducive to the subsequent resource utilization of fluorine resources.

[0096] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for recovering fluorine by using flash cooling coupled with cyclone flow in a wet-process phosphoric acid process, characterized in that: The method comprises the following steps: (1) flash evaporation and cooling crystallization of the phosphate rock acid-hydrolyzed slurry to obtain a flash evaporation slurry; wherein the phosphate rock acid-hydrolyzed slurry has a liquid phase P2O5 content of 25-35%, a liquid phase sodium and potassium total content of 0.4-0.8%, and a liquid phase F content of 0.5-2.0%; (2) subjecting the flash evaporation slurry obtained in step (1) to cyclone separation to recover the fluorosilicate particles.

2. The method according to claim 1, characterized in that The solid content of the phosphate rock acid-decomposed slurry is 25-38%; The D50 particle size distribution of the solid phase in the phosphate rock acid-hydrolyzed slurry is 70-100 μm.

3. The method according to claim 1, characterized in that The temperature of the phosphate rock acid-decomposed slurry is 70-80°C.

4. The method according to claim 1, wherein The vacuum degree of the flash cooling crystallization is 65-85 kPa.

5. The method according to claim 1, characterized in that The temperature difference between the feed and discharge of the flash cooling crystallization is 4-8°C.

6. The method according to claim 1, characterized in that After the flash evaporation and cooling crystallization, the temperature of the slurry after the flash evaporation is adjusted to 70-80° C. and kept warm for 2-3 hours.

7. The method according to claim 1, characterized in that The feed pressure of the cyclone separation is 0.08-0.16MPa; The feed flow rate of the cyclone separation is 3.0-6.0 m / s.

8. The method according to claim 1, characterized in that The D50 particle size distribution of the fluorosilicate particles is 1-8 mm.

9. The method according to claim 1, characterized in that The method comprises the following steps: (1) subjecting the acid-hydrolyzed phosphate rock slurry at a temperature of 70-80° C. to flash cooling crystallization, wherein the solid content of the acid-hydrolyzed phosphate rock slurry is 25-38%, the D50 particle size distribution of the solid phase in the acid-hydrolyzed phosphate rock slurry is 70-100 μm, the P2O5 content of the liquid phase in the acid-hydrolyzed phosphate rock slurry is 25-35%, the total content of sodium and potassium in the liquid phase is 0.4-0.8%, and the F content in the liquid phase is 0.5-2.0%; the vacuum degree of the flash cooling crystallization is 65-85 kPa, the temperature difference between the feed and discharge of the flash cooling crystallization is 4-8° C., and after the flash cooling crystallization is completed, the temperature of the flash-evaporated slurry is adjusted to 70-80° C. and kept warm for 2-3 hours; (2) The slurry after flash evaporation is subjected to cyclone separation, the feed pressure of the cyclone separation is 0.08-0.16 MPa, the feed flow rate of the cyclone separation is 3.0-6.0 m / s, and the fluorosilicate particles are recovered after cyclone separation. The D50 particle size distribution of the fluorosilicate particles is 3-8 mm.

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