Production method for improving quality of washed phosphogypsum

Abstract

The invention relates to the technical field of ardealite resource utilization, in particular to a production method for improving the quality of washed ardealite, which comprises the following steps: S1, forced dissolution of gypsum, S2, induced crystallization and crystal phase oriented conversion, and S3, separation and recovery. By controlling proper conditions, the dissolving speed of fine crystals in the fresh phosphogypsum is increased, intergranular phosphorus is quickly released and converted into water-soluble phosphorus to enter a liquid phase, the composite crystallizing agent is added into the crystallizing tank, the dissolved crystals are directionally crystallized, newly generated crystals are coarse, large and neat, intergranular phosphorus and fluorine are reduced, washing is easy, and the method is suitable for industrial production. The total phosphorus of the purified phosphogypsum is reduced, and the water-soluble phosphorus and the water-soluble fluorine of the washed gypsum are further reduced.

Description

Technical Field

[0001] This invention relates to the field of phosphogypsum resource utilization technology, and in particular to a production method for improving the quality of water-washed phosphogypsum. Background Technology

[0003] As a byproduct of wet-process phosphoric acid production, phosphogypsum has a calcium sulfate content close to that of natural gypsum and can be used as a gypsum resource. However, due to the presence of impurities of varying amounts, especially the high content of intercrystalline phosphates, water-soluble phosphorus, and fluorine in gypsum, its application is limited. After purification and impurity removal, its application can be expanded, the amount of stockpiling can be reduced, and land occupation can be reduced.

[0004] The main methods for pretreatment of phosphogypsum are: Storage and aging; Water washing and purification; Lime neutralization treatment, etc.

[0005] While previous water washing treatments have improved the quality of gypsum, the key performance indicators of the gypsum are still not ideal and require further improvement. Therefore, this treatment process still needs to be optimized to further enhance the quality of gypsum and broaden its application areas. Summary of the Invention

[0006] The purpose of this invention is to provide a production method for improving the quality of water-washed phosphogypsum, and to solve the problems of difficulty in reducing intercrystalline phosphorus and poor washing effect in existing water-washed phosphogypsum.

[0007] The solution of the present invention is: A production method for improving the quality of water-washed phosphogypsum includes the following steps: S1. Forced dissolution of gypsum: The phosphogypsum discharged from the phosphoric acid production filter is mixed with the returned wash water and sent to the dissolution reactor. Hot water and a co-solvent are added to form a slurry. At the same time, the ultrasonic generator is turned on to use the cavitation effect of ultrasound to destroy the original crystals of phosphogypsum, causing the soluble phosphorus wrapped in the crystal lattice to be released into the liquid phase. The wash water is the wash water after washing the phosphogypsum. The cavitation effect is achieved by using its cavitation effect to violently act on the slurry, which rapidly destroys the original crystals of phosphogypsum and forces the soluble phosphorus wrapped in the gypsum crystal lattice to be released into the liquid phase. S2. Induced crystallization and directional transformation of crystal phase: The slurry obtained in step S1 overflows into the induced crystallizer, and a suitable temperature is controlled and a composite crystallizing agent is added. Under stirring conditions, the dissolved gypsum undergoes directional crystallization and crystal growth. S3. Separation and recovery: The slurry after recrystallization in step S2 is subjected to solid-liquid separation. The solid phase is washed to obtain gypsum for building materials. The wash water generated after washing is returned to step S1 for recycling. The separated filtrate is returned to the phosphoric acid production unit to recover phosphorus (rich in phosphorus) and fluorine.

[0008] As a preferred technical solution, the phosphogypsum in step S1 is fresh phosphogypsum, and the temperature of the hot water is controlled at 45-52℃.

[0009] As a preferred technical solution, the mass ratio of the liquid phase to the dry phosphogypsum in step S1 is 2.8 to 3.5:1.

[0010] As a preferred technical solution, the co-solvent in step S1 is one of citric acid, citrate, or sulfuric acid; when the co-solvent is citric acid or citrate, the co-solvent accounts for 1 to 2‰ of the dry basis mass of the phosphogypsum slurry in step S1; when the co-solvent is sulfuric acid, the co-solvent accounts for 0.5 to 0.8‰ of the dry basis mass of the phosphogypsum slurry in step S1.

[0011] As a preferred technical solution, the dissolution reactor in step S1 is equipped with an ultrasonic transducer of an ultrasonic generator; the ultrasonic working frequency is 20-40kHz and the power is 400-600W.

[0012] As a preferred technical solution, the ultrasonic transducer of the ultrasonic generator is installed in a built-in, insertable manner on the side wall and / or bottom of the dissolution tank of the dissolution reactor, with its radiating surface submerged in the slurry. The transducer is made of a corrosion-resistant metal material (such as 316L). The number of ultrasonic transducers is determined according to the reactor volume, ideally to form a uniform and powerful ultrasonic field within the reaction zone. Alternatively, the ultrasonic generator can be located outside the dissolution reactor and connected to the ultrasonic transducers via a cable.

[0013] As a preferred technical solution, the temperature of the recrystallization slurry in step S2 is controlled at 42-48℃.

[0014] As a preferred technical solution, the stirring paddle used in step S2 is a frame-type stirring paddle, and the stirring speed is controlled at 80-100 r / min.

[0015] As a preferred technical solution, the composite crystallizer in step S2 accounts for 0.8 to 1‰ of the total mass of the slurry in step S2. The composite crystallizer includes sodium dodecyl sulfate, triethylenetriaminepentamethylene phosphoric acid and surfactant TX-10, with a mass ratio of 15:2:1.5.

[0016] As a preferred technical solution, the residence time of the material in the crystallization tank of the induced crystallizer in step S2 is 40 to 60 minutes.

[0017] Working principle: Fresh phosphogypsum crystals are in a metastable state, with a small average particle size and a high proportion of fine crystals. By controlling suitable conditions for recrystallization and adding a co-solvent, along with the synergistic effect of ultrasound enhancement, the small and unstable crystals in the gypsum can be rapidly dissolved. The intercrystalline phosphorus and fluorine in the gypsum crystals also dissolve into the liquid phase. After dissolution, the slurry enters a crystallization tank, where a composite crystallizing agent is added. The dissolved gypsum undergoes directional crystallization, promoting crystal growth and uniformity. During recrystallization, the phosphorus and fluorine dissolved in the liquid phase no longer participate in crystallization and remain in the liquid phase, thus improving the recovery rate of phosphorus and fluorine. Therefore, the gypsum filtered after phosphoric acid production is directly discharged into the tank for re-slurrying. A co-solvent is added, and an ultrasonic device is activated to enhance dissolution. The appropriate temperature, liquid-to-solid ratio, and residence time of the slurry are controlled to rapidly dissolve the small and unstable gypsum crystals. At the same time as the small crystals dissolve, the intercrystalline phosphates also dissolve, reducing the intercrystalline phosphorus content in the gypsum. The dissolved phosphorus and fluorine enter the liquid phase. The dissolved gypsum slurry overflows into the crystallization tank, where a prepared composite crystallizing agent is added to induce directional crystallization of the dissolved gypsum, resulting in large and uniform crystals. A frame-type stirring paddle with low shear force is selected, and the stirring speed is controlled at 80-100 r / min to prevent the large crystals from being damaged. Finally, the phosphogypsum crystals after filtration and dehydration are large and easy to wash to remove impurities.

[0018] The use of ultrasonic devices can accelerate the dissolution of fine gypsum crystals, significantly shorten the gypsum dissolution time, and effectively reduce the volume of the dissolution tank.

[0019] The composite crystallizer is composed of crystallizing inducing agents, impurity complexing / masking agents, and surfactants. Each component works synergistically to address the problem from different angles, ultimately achieving a synergistic effect greater than the sum of its parts (1+1>2). This allows the fine crystals dissolved in the dissolving tank to further grow directionally on the well-organized gypsum crystals in the slurry, forming larger, more uniform crystals, thereby improving filtration and washing performance. The composite crystallizer is environmentally friendly; the selected materials are harmless to the environment and do not affect the post-processing of phosphoric acid or the comprehensive utilization of phosphogypsum.

[0020] The beneficial effects of this invention are: Under ultrasonic enhancement and with appropriate conditions, the fine crystals in fresh phosphogypsum dissolve faster, causing intercrystalline phosphorus to be rapidly released and converted into water-soluble phosphorus, which then enters the liquid phase. A composite crystallizing agent is added to the crystallization tank, causing the dissolved crystals to crystallize in a directional manner. The newly formed crystals are large and uniform, reducing intercrystalline phosphorus and fluoride levels, and making them easier to wash. The total phosphorus content in the purified phosphogypsum is reduced, and the water-soluble phosphorus and fluoride content in the washed gypsum is further reduced. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0022] Figure 1 This is a flowchart illustrating the principle of the production method for improving the quality of water-washed phosphogypsum according to the present invention. Detailed Implementation

[0023] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific embodiments.

[0024] Example 1 (only slurry is added, without dissolving and recrystallizing the gypsum) After filtration by the phosphoric acid production turntable, the gypsum is discharged into the phosphogypsum slag hopper via a screw conveyor. The phosphogypsum is then flushed into the phosphogypsum re-slurry tank using the wash water (wash water temperature 52℃) after washing the gypsum. Hot water is added to adjust the slurry while stirring. The stirring speed is 65 r / min, the solid content of the slurry is controlled at 24%, and the slurry stays in the re-slurry tank for more than 60 minutes.

[0025] The slurry is sent to a filter press for filtration and dewatering, and then washed twice in countercurrent to dry it. The dried gypsum is then sent to a gypsum storage silo.

[0026] The average particle size of the gypsum after re-slurrying remains basically unchanged, but increases by 2-3 μm compared to the average particle size before treatment. The eutectic phosphorus content of the gypsum decreases from 0.46% in fresh phosphogypsum to 0.43%, a reduction of 6.5%, which is a slight improvement. The water-soluble phosphorus content of the gypsum after washing is 0.13%, and the water-soluble fluoride content is 0.1%.

[0027] Example 2 (dissolving and recrystallizing gypsum without activating the ultrasonic device) After filtration at the phosphoric acid production turntable, the gypsum is discharged via a screw conveyor into the phosphogypsum slag hopper. The phosphogypsum is then flushed into the phosphogypsum slag tank using the wash water (wash water temperature 52℃) from the gypsum washing process. Hot water is continuously added to adjust the slurry while stirring at a speed of 65 r / min. The solid content of the slurry is controlled at 24%. Sulfuric acid is added at a ratio of 0.7‰ of the gypsum mass, and the slurry residence time is 25 min.

[0028] The dissolved slurry overflows from the dissolving tank to the induced crystallizer. A frame agitator is used with a rotation speed of 85 r / min. The ratio of the composite crystallizer added is 0.8‰ of the slurry volume. The slurry stays in the re-slurry tank for more than 45 minutes.

[0029] The recrystallized slurry is sent to a filter press for filtration and dewatering, and then washed twice in countercurrent to absorb the water. The dried gypsum is then sent to a gypsum storage silo.

[0030] After recrystallization treatment, the average particle size of the gypsum increased by 8-15 μm compared to before treatment. The eutectic phosphorus content of the gypsum decreased from 0.45% in fresh phosphogypsum to 0.38%, a reduction of 15.6%, indicating improved quality. The water-soluble phosphorus content of the washed gypsum was 0.09%, and the water-soluble fluoride content was 0.08%, showing a significant improvement in the quality of the washed gypsum.

[0031] Example 3 The gypsum filtered from the phosphoric acid production turntable is discharged into the phosphogypsum slag hopper via a screw conveyor. The phosphogypsum is then flushed into the phosphogypsum slag hopper using wash water (wash water temperature 52℃) after washing the gypsum. Hot water is continuously added to adjust the slurry while stirring at a speed of 65 r / min, maintaining the slurry solids content at 24%. Simultaneously, sulfuric acid is added at a ratio of 0.7‰ of the gypsum mass. An ultrasonic device is activated at a frequency of 25 kHz and an ultrasonic power of 450 W. The slurry temperature in the dissolving tank is 48℃, and the slurry residence time is 25 min.

[0032] The dissolved slurry overflows from the dissolving tank to the induced crystallizer. A frame agitator is used with a rotation speed of 85 r / min. The ratio of the composite crystallizer added is 0.8‰ of the slurry volume. The slurry stays in the re-slurry tank for more than 45 minutes.

[0033] The recrystallized slurry is sent to a filter press for filtration and dewatering, and then washed twice in countercurrent to absorb the water. The dried gypsum is then sent to a gypsum storage silo.

[0034] After recrystallization treatment, the average particle size of the gypsum increased by 30-40 μm compared to before treatment. The eutectic phosphorus content of the gypsum decreased from 0.45% in fresh phosphogypsum to 0.25%, a reduction of 44.4%, which is a significant effect. The water-soluble phosphorus content of the washed gypsum was 0.06%, and the water-soluble fluoride content was less than 0.04%, indicating a significant improvement in the quality of the washed gypsum.

[0035] Example 4 The gypsum filtered from the phosphoric acid production turntable is discharged into the phosphogypsum slag hopper via a screw conveyor. The phosphogypsum is then flushed into the phosphogypsum slag tank using wash water (wash water temperature 53℃) after washing the gypsum. Hot water is continuously added to adjust the slurry while stirring at a speed of 65 r / min, maintaining the slurry solids content at 25%. Simultaneously, sulfuric acid is added at a ratio of 0.75‰ of the gypsum mass. An ultrasonic device is activated at a frequency of 30kHz and an ultrasonic power of 500W. The slurry temperature in the dissolving tank is 49℃, and the slurry residence time is 25 min.

[0036] The dissolved slurry overflows from the dissolving tank to the induced crystallizer. A frame agitator is used with a rotation speed of 86 r / min. The ratio of the composite crystallizer added is 0.7‰ of the slurry volume. The slurry stays in the re-slurry tank for more than 45 minutes.

[0037] The recrystallized slurry is sent to a filter press for filtration and dewatering, and then washed twice in countercurrent to absorb the water. The dried gypsum is then sent to a gypsum storage silo.

[0038] After recrystallization treatment, the average particle size of the gypsum increased by 32-40 μm compared to before treatment. The eutectic phosphorus content of the gypsum decreased from 0.46% in fresh phosphogypsum to 0.25%, a reduction of 46.7%, showing a significant effect. The water-soluble phosphorus content of the washed gypsum was 0.058%, and the water-soluble fluoride content was less than 0.042%, indicating a significant improvement in the quality of the washed gypsum.

[0039] Example 5 After filtration at the phosphoric acid production turntable, the gypsum is discharged via a screw conveyor into the phosphogypsum slag hopper. The phosphogypsum is then flushed into the phosphogypsum slag tank using wash water (55℃) from the gypsum washing process. Hot water is continuously added to adjust the slurry while stirring at 65 rpm, maintaining a solids content of 25%. Simultaneously, sulfuric acid is added at a ratio of 0.75‰ of the gypsum mass. An ultrasonic device is activated at a frequency of 32 kHz and an ultrasonic power of 550 W. The slurry temperature in the dissolving tank is 49℃, and the slurry residence time is 25 minutes.

[0040] The dissolved slurry overflows from the dissolving tank to the induced crystallizer. A frame agitator is used with a rotation speed of 92 r / min. The ratio of the composite crystallizing agent added is 0.9‰ of the slurry volume. The slurry stays in the re-slurry tank for more than 50 minutes.

[0041] The recrystallized slurry is sent to a filter press for filtration and dewatering, and then washed twice in countercurrent to absorb the water. The dried gypsum is then sent to a gypsum storage silo.

[0042] After recrystallization treatment, the average particle size of the gypsum increased by 33-41 μm compared to before treatment. The eutectic phosphorus content of the gypsum decreased from 0.48% in fresh phosphogypsum to 0.27%, a reduction of 43.8%, which is a significant effect. The water-soluble phosphorus content of the washed gypsum was 0.06%, and the water-soluble fluoride content was less than 0.04%, indicating a significant improvement in the quality of the washed gypsum.

[0043] Example 6 The gypsum filtered from the phosphoric acid production turntable is discharged into the phosphogypsum slag hopper via a screw conveyor. The phosphogypsum is then flushed into the phosphogypsum slag hopper using wash water (55℃) from the gypsum washing process. Hot water (45℃) is added continuously while stirring to adjust the slurry. The stirring speed is 65 r / min, and the solids content of the slurry is controlled at 26.32%. Simultaneously, citric acid is added at a ratio of 2‰ of the gypsum mass. The ultrasonic device is activated at a frequency of 40kHz and an ultrasonic power of 600W, with the slurry residence time set at 30 minutes.

[0044] The dissolved slurry overflows from the dissolving tank to the induced crystallizer. A frame agitator is used at a speed of 80 r / min and a temperature of 42℃. The ratio of the composite crystallizing agent added is 0.8‰ of the slurry volume. The slurry stays in the re-slurry tank for 40 minutes.

[0045] The recrystallized slurry is sent to a filter press for filtration and dewatering, and then washed twice in countercurrent to absorb the water. The dried gypsum is then sent to a gypsum storage silo.

[0046] After recrystallization treatment, the average particle size of the gypsum increased compared to before treatment, the eutectic phosphorus content of the gypsum decreased significantly, and the quality of the washed gypsum was significantly improved.

[0047] Example 7 The gypsum filtered from the phosphoric acid production turntable is discharged into the phosphogypsum slag hopper via a screw conveyor. The phosphogypsum is then flushed into the phosphogypsum slag hopper using wash water (55℃) from the gypsum washing process. Hot water (52℃) is added continuously while stirring to adjust the slurry. The stirring speed is 65 r / min, and the solids content of the slurry is controlled at 22.22%. Simultaneously, citric acid is added at a ratio of 2‰ of the gypsum mass. The ultrasonic device is activated at a frequency of 40kHz and an ultrasonic power of 600W, with the slurry residence time set at 30 minutes.

[0048] The dissolved slurry overflows from the dissolving tank to the induced crystallizer. A frame agitator is used at a speed of 100 r / min and a temperature of 48℃. The ratio of the composite crystallizing agent added is 1‰ of the slurry volume. The slurry stays in the re-slurry tank for 60 minutes.

[0049] The recrystallized slurry is sent to a filter press for filtration and dewatering, and then washed twice in countercurrent to absorb the water. The dried gypsum is then sent to a gypsum storage silo.

[0050] After recrystallization treatment, the average particle size of the gypsum increased compared to before treatment, the eutectic phosphorus content of the gypsum decreased significantly, and the quality of the washed gypsum was significantly improved.

[0051] Example 8 The gypsum filtered from the phosphoric acid production turntable is discharged into the phosphogypsum slag hopper via a screw conveyor. The phosphogypsum is then flushed into the phosphogypsum slag hopper using wash water (55℃) from the gypsum washing process. Hot water (50℃) is added continuously while stirring to adjust the slurry. The stirring speed is 65 r / min, and the solids content of the slurry is controlled at 25%. Simultaneously, citrate is added at a ratio of 1.5‰ of the gypsum mass. The ultrasonic device is activated at a frequency of 30kHz and an ultrasonic power of 4500W, with a slurry residence time of 25 minutes.

[0052] The dissolved slurry overflows from the dissolving tank to the induced crystallizer. A frame agitator is used at a speed of 92 r / min and a temperature of 45℃. The ratio of the composite crystallizing agent added is 0.9‰ of the slurry volume. The slurry stays in the re-slurry tank for 50 minutes.

[0053] The recrystallized slurry is sent to a filter press for filtration and dewatering, and then washed twice in countercurrent to absorb the water. The dried gypsum is then sent to a gypsum storage silo.

[0054] After recrystallization treatment, the average particle size of the gypsum increased compared to before treatment, the eutectic phosphorus content of the gypsum decreased significantly, and the quality of the washed gypsum was significantly improved.

[0055] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A production method for improving the quality of water-washed phosphogypsum, characterized in that, Includes the following steps: S1. Forced dissolution of gypsum: The phosphogypsum unloaded from the phosphoric acid production filter is mixed with the returned wash water and sent to the dissolution reactor. Hot water is added to adjust the slurry and a co-solvent is added to form a slurry. At the same time, the ultrasonic generator is turned on to use the cavitation effect of ultrasound to destroy the original crystals of phosphogypsum, so that the soluble phosphorus wrapped in its crystal lattice is released into the liquid phase. The wash water is the wash water after washing the phosphogypsum. S2. Induced crystallization and directional transformation of crystal phase: The slurry obtained in step S1 overflows into the induced crystallizer, and a suitable temperature is controlled and a composite crystallizing agent is added. Under stirring conditions, the dissolved gypsum undergoes directional crystallization and crystal growth. S3. Separation and recovery: The slurry after recrystallization in step S2 is subjected to solid-liquid separation. The solid phase is washed to obtain gypsum for building materials. The wash water generated after washing is returned to step S1 for recycling. The separated filtrate is returned to the phosphoric acid production unit to recover phosphorus and fluorine.

2. The production method for improving the quality of water-washed phosphogypsum as described in claim 1, characterized in that: In step S1, the phosphogypsum is fresh phosphogypsum, and the temperature of the hot water is controlled at 45-52℃.

3. The production method for improving the quality of water-washed phosphogypsum as described in claim 1, characterized in that: In step S1, the mass ratio of the liquid phase to the dry phosphogypsum is 2.8 to 3.5:

1.

4. The production method for improving the quality of water-washed phosphogypsum as described in claim 1, characterized in that: In step S1, the co-solvent is one of citric acid, citrate, or sulfuric acid; when the co-solvent is citric acid or citrate, the co-solvent accounts for 1 to 2‰ of the dry weight of phosphogypsum in step S1; when the co-solvent is sulfuric acid, the co-solvent accounts for 0.5 to 0.8‰ of the dry weight of phosphogypsum in step S1.

5. The production method for improving the quality of water-washed phosphogypsum as described in claim 1, characterized in that: The dissolution reactor in step S1 is equipped with an ultrasonic transducer of an ultrasonic generator; the ultrasonic working frequency is 20-40kHz and the power is 400-600W.

6. The production method for improving the quality of water-washed phosphogypsum as described in claim 1, characterized in that: In step S2, the temperature of the recrystallization slurry is controlled at 42–48°C.

7. The production method for improving the quality of water-washed phosphogypsum as described in claim 1, characterized in that: In step S2, the agitator used for mixing is a frame agitator, and the mixing speed is controlled at 80-100 r / min.

8. The production method for improving the quality of water-washed phosphogypsum as described in claim 1, characterized in that: The composite crystallizer in step S2 accounts for 0.8 to 1‰ of the total mass of the slurry in step S2. The composite crystallizer includes sodium dodecyl sulfate, triethylenetriaminepentamethylenephosphoric acid and surfactant TX-10, with a mass ratio of 15:2:1.

5.

9. A production method for improving the quality of water-washed phosphogypsum as described in claim 1, characterized in that: In step S2, the residence time of the material in the crystallization tank of the induced crystallizer is 40 to 60 minutes.

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