Graded ultrasonic induction calcium fluoride crystallization process and equipment used by same

Abstract

The invention discloses a grading ultrasonic induction calcium fluoride crystallization process and equipment used in the grading ultrasonic induction calcium fluoride crystallization process, and the equipment comprises a wastewater adjusting tank, a lime solution blending tank, an ultrasonic induction crystal nucleus generator, an ultrasonic induction crystal grower, a crystal collecting tank, a dehydration system, a comprehensive wastewater defluorination system, a dosing pump, a wastewater lifting pump and a control system, part of the high-concentration acidic fluorine-containing wastewater and the lime solution are crystallized in the ultrasonic induced crystal nucleus generator to form crystal nucleuses; the crystal nucleus enters an ultrasonic induction crystal grower along with the effluent, crystals generated by reaction of the residual high-concentration acidic fluorine-containing wastewater and the lime solution in the ultrasonic induction crystal grower grow on the surface of the crystal nucleus, and large-particle calcium fluoride crystals are dehydrated to form a calcium fluoride crystal product; according to the method, the dissolution and use efficiency of lime can be improved, the purity of calcium fluoride can be improved, the nucleation and growth process of calcium fluoride can be controlled, and therefore the particle size of calcium fluoride crystals can be effectively controlled.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of wastewater treatment, and particularly relates to a hierarchical ultrasonic induction calcium fluoride crystallization process. BACKGROUND

[0002] Fluorine is an important strategic resource and is widely used in key fields such as rare earth industry and semiconductor manufacturing, and has irreplaceability in modern industry and technology. In nature, fluorine mainly exists in the form of fluorine-containing minerals (such as fluorite), and it is reported that the global proven fluorite reserves are about 460 million tons. High-grade fluorite is the most ideal raw material in industry, but its reserves only account for 20%-30% of the total global fluorite reserves. In recent years, photovoltaic cells and semiconductor chips have developed rapidly, and a large amount of hydrofluoric acid is required in the production process, accompanied by the discharge of high-concentration acidic fluorine-containing wastewater. Such wastewater is usually treated by the lime method and fluorine is recovered.

[0003] There are currently two ways to recover fluorine by the lime method. One is through stirring reaction and precipitation, that is, high-concentration acidic fluorine-containing wastewater is added into a stirring tank, and lime solution is added at the same time, the pH is controlled in a certain range, the calcium fluoride precipitate generated by reaction is separated into a slurry in a sedimentation tank, and fluorine-containing calcium sludge is obtained. This process has the advantages of short process flow and simple operation, but also has obvious disadvantages:

[0004] (1) Because of the low solubility of lime, extensive stirring is carried out in the stirring reaction tank, which is easy to cause local insufficient reaction due to the lime particles that cannot be dissolved in time, and finally the lime particles are wrapped, resulting in low sludge purity (below 80%) and reducing the resource value;

[0005] (2) The calcium fluoride precipitate formed belongs to sludge, and the particle size is low (10 μm and below), and the too small particle size causes dusting and blockage of the device in the production of hydrofluoric acid, and cannot be effectively reused.

[0006] The other way is to use a crystallization fluidized bed to recover calcium fluoride particles by inducing crystallization, which greatly improves the particle size of the crystalline particles, but also has the problem of lime particle wrapping due to insufficient dispersion of lime. First, the utilization efficiency of lime and the purity of calcium fluoride are reduced, and the amount of lime is increased. Second, due to the high fluorine concentration of the influent, the local supersaturation degree is too high, which easily causes the problem of crystal explosion, resulting in a wide particle size distribution range and difficulty in controlling the particle size of calcium fluoride crystals, which to some extent affects the stability of the quality of calcium fluoride crystals. Third, the crystallization fluidized bed needs to continuously supplement small particle seeds into the system to ensure the effect of induced crystallization, which also leads to the increase of cost. SUMMARY

[0007] In order to overcome the above defects, the application provides a hierarchical ultrasonic induction calcium fluoride crystallization process and equipment thereof, which can effectively control the purity and crystal particle size of calcium fluoride extracted in the recovery process of high-concentration acidic fluorine-containing wastewater.

[0008] The application adopts the technical scheme that a hierarchical ultrasonic induction calcium fluoride crystallization process comprises the following steps:

[0009] Step one: part of the high-concentration acidic fluorine-containing wastewater is sent into an ultrasonic induction crystal nucleus generator;

[0010] Step two: a lime solution is sent into the ultrasonic induction crystal nucleus generator at a calcium fluoride molar ratio of 0.45-0.55;

[0011] Step three: the lime solution and the hydrofluoric acid in the high-concentration acidic fluorine-containing wastewater react in the ultrasonic induction crystal nucleus generator to form small-particle crystal nuclei, and the ultrasonic power of the ultrasonic transducer in the ultrasonic induction crystal nucleus generator is controlled to realize the sufficient mixing and dispersion of the lime solution and the hydrofluoric acid and the generation amount of the crystal nuclei;

[0012] Step four: the crystal nuclei formed in the ultrasonic induction crystal nucleus generator enter an ultrasonic induction crystal growth generator with water;

[0013] Step five: the remaining high-concentration acidic fluorine-containing wastewater is sent into the ultrasonic induction crystal growth generator, and a lime solution is sent into the ultrasonic induction crystal growth generator at a calcium fluoride molar ratio of 0.45-0.55;

[0014] Step six: the lime solution and the hydrofluoric acid in the high-concentration acidic fluorine-containing wastewater react in the ultrasonic induction crystal nucleus generator to form calcium fluoride, and the calcium fluoride grows on the surface of the crystal nuclei to form calcium fluoride crystal particles, and the ultrasonic power of the ultrasonic transducer in the ultrasonic induction crystal growth generator is controlled to realize the sufficient mixing and dispersion of the lime solution and the hydrofluoric acid and the growth particle size of the crystal;

[0015] Step seven: when the crystal in the ultrasonic induction crystal growth generator reaches a certain particle size range, the crystal is discharged through a crystal discharge port at the bottom of the ultrasonic induction crystal growth generator, and after dehydration treatment, high-purity calcium fluoride crystals with a water content of less than 30% are obtained, and the water outlet of the ultrasonic induction crystal growth generator enters a subsequent comprehensive wastewater defluorination system for standard treatment.

[0016] As a further improvement of the present application, the ultrasonic induced crystal growth device is at least one stage, and the stages are connected in sequence, the calcium fluoride crystal particles generated in the former stage are transferred into the next stage with the water, the high concentration acidic fluorine-containing wastewater and the lime solution are respectively fed into the ultrasonic induced crystal growth device at a calcium fluoride molar ratio of 0.45-0.55, the calcium fluoride generated by the reaction of the lime solution and the hydrofluoric acid in the ultrasonic induced crystal growth device grows on the surface of the calcium fluoride crystal particles, until the particle size of the calcium fluoride crystal particles reaches the design standard, and the calcium fluoride crystal particles with the standard particle size in the last stage are discharged and subjected to dehydration treatment.

[0017] As a further improvement of the present application, the amount of the high concentration acidic fluorine-containing wastewater fed into the ultrasonic induced crystal nucleus generator accounts for 1%-10% of the total amount of the high concentration acidic fluorine-containing wastewater.

[0018] As a further improvement of the present application, the concentration of the lime solution is controlled at 5%-10%.

[0019] As a further improvement of the present application, a crystal collection tank is further provided, the calcium fluoride crystal particles with the standard particle size are discharged from the ultrasonic induced crystal growth device into the crystal collection tank for collection, and the mixture of the calcium fluoride crystal particles and water in the crystal collection tank is stirred by a stirrer, and the mixture in the crystal collection tank is periodically sent to a dehydration system for dehydration treatment.

[0020] As a further improvement of the present application, the power of the stirrer in the crystal collection tank is 100-300W / m3.

[0021] As a further improvement of the present application, the filtrate generated by the dehydration treatment is simultaneously returned into the ultrasonic induced crystal nucleus generator.

[0022] As a further improvement of the present application, the ultrasonic power of the ultrasonic transducer in the ultrasonic induced crystal nucleus generator is controlled at 50-100W / m 3 , and the ultrasonic power of the ultrasonic transducer in the ultrasonic induced crystal growth device is controlled at 30-75W / m 3 .

[0023] The application discloses a hierarchical ultrasonic induction calcium fluoride crystallization device, which comprises a wastewater adjusting tank, a lime solution preparation tank, an ultrasonic induction crystal nucleus generator, ultrasonic induction crystal growth devices, a crystal collecting tank, a dehydration system, a comprehensive wastewater fluorine removal system, a dosing pump, a wastewater lifting pump and a control system, the ultrasonic induction crystal nucleus generator and at least one ultrasonic induction crystal growth device are sequentially communicated, the water outlet of the ultrasonic induction crystal nucleus generator is communicated with the water inlet of the first ultrasonic induction crystal growth device through a pipeline, the water outlet of the front-stage ultrasonic induction crystal growth device is communicated with the water inlet of the rear-stage ultrasonic induction crystal growth device in the multiple-stage ultrasonic induction crystal growth devices, the high-concentration acidic fluorine-containing wastewater in the wastewater adjusting tank is respectively punched into the ultrasonic induction crystal nucleus generator and the ultrasonic induction crystal growth devices in proportion through the wastewater lifting pump, the lime solution in the lime solution preparation tank is respectively punched into the ultrasonic induction crystal nucleus generator and the ultrasonic induction crystal growth devices in proportion through the dosing pump, the ultrasonic induction crystal nucleus generator and the ultrasonic induction crystal growth devices are both provided with ultrasonic transducers, the ultrasonic transducers can generate high-frequency ultrasonic waves, the bottom of the last-stage ultrasonic induction crystal growth device is provided with a crystal discharge port, the crystal discharge port is communicated with the crystal collecting tank so that the large calcium fluoride crystal particles deposited at the bottom of the last-stage ultrasonic induction crystal growth device are discharged into the crystal collecting tank, the crystal collecting tank is provided with a stirrer, the stirrer can stir the mixture of the large calcium fluoride crystal particles and water in the crystal collecting tank, the crystal collecting tank is communicated with the inlet of the dehydration system through a crystal conveying device, the crystal conveying device can convey the large calcium fluoride crystal particles in the crystal collecting tank into the dehydration system, the dehydration system can perform dehydration treatment on the large calcium fluoride crystal particles, the water outlet of the last-stage ultrasonic induction crystal growth device is communicated with the water inlet of the comprehensive wastewater fluorine removal system through a pipeline, the comprehensive wastewater fluorine removal system can perform standard treatment on the wastewater entering the system, and the control system can control the power of the ultrasonic transducers in the ultrasonic induction crystal nucleus generator and the ultrasonic induction crystal growth devices, the power of the stirrer and the operation of the dehydration system, the dosing pump and the wastewater lifting pump.

[0024] As a further improvement of the application, a filtrate collecting tank is further arranged for collecting the filtrate generated by the dehydration system during the dehydration treatment of the large calcium fluoride crystal particles, a backflow pump is further arranged for punching the filtrate in the filtrate collecting tank into the ultrasonic induction crystal nucleus generator, a plurality of water outlets are further arranged, each of the water outlets can punch the mixed solution in the ultrasonic induction crystal nucleus generator into the first ultrasonic induction crystal growth device, the mixed solution in the front-stage ultrasonic induction crystal growth device is punched into the rear-stage ultrasonic induction crystal growth device, and the control system can control the operation of the backflow pump and the water outlets.

[0025] The beneficial effects of the present application are: in the process of reaction crystallization of hydrofluoric acid in high-concentration acidic fluorine-containing wastewater and lime solution, by introducing an ultrasonic transducer and a control system in the crystallization bed reactor, high-frequency ultrasonic waves are emitted by the ultrasonic transducer, and the cavitation effect and mechanical vibration effect generated by the high-frequency ultrasonic waves in the liquid optimize the mixing and dispersion effect of the lime solution and the high-concentration acidic fluorine-containing wastewater, improve the lime dissolution and use efficiency, thereby improving the purity of calcium fluoride. At the same time, the present application also sets an ultrasonic induced crystal nucleus generator and at least one ultrasonic induced crystal growth device, realizes gradient crystallization of calcium fluoride, effectively controls the nucleation and growth process of calcium fluoride, and effectively controls the particle size of calcium fluoride crystals. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The present application is a schematic diagram of the structural principle. DETAILED DESCRIPTION

[0027] Embodiment: A hierarchical ultrasonic induced calcium fluoride crystallization process, characterized by comprising the following steps:

[0028] Step one: part of the high-concentration acidic fluorine-containing wastewater is sent into the ultrasonic induced crystal nucleus generator 3;

[0029] Step two: the lime solution is sent into the ultrasonic induced crystal nucleus generator 3 at a calcium fluoride molar ratio of 0.45-0.55, and the concentration of the lime solution is controlled at 5%-10%;

[0030] Step three: the lime solution and the hydrofluoric acid in the high-concentration acidic fluorine-containing wastewater react in the ultrasonic induced crystal nucleus generator 3 to form small-particle crystal nuclei, and the ultrasonic power of the ultrasonic transducer in the ultrasonic induced crystal nucleus generator 3 is controlled during the reaction process to realize the sufficient mixing and dispersion of the lime solution and the hydrofluoric acid and the crystal nucleus generation amount;

[0031] Step four: the crystal nuclei formed in the ultrasonic induced crystal nucleus generator 3 enter the ultrasonic induced crystal growth device 4 with the water outlet;

[0032] Step five: the remaining high-concentration acidic fluorine-containing wastewater is sent into the ultrasonic induced crystal growth device 4, and the lime solution is sent into the ultrasonic induced crystal growth device 4 at a calcium fluoride molar ratio of 0.45-0.55;

[0033] Step six: the lime solution and the hydrofluoric acid in the high-concentration acidic fluorine-containing wastewater react in the ultrasonic induced crystal nucleus generator 3 to form calcium fluoride, and the calcium fluoride grows on the surface of the crystal nuclei to form calcium fluoride crystal particles, and the ultrasonic power of the ultrasonic transducer in the ultrasonic induced crystal growth device 4 is controlled during the reaction process to realize the sufficient mixing and dispersion of the lime solution and the hydrofluoric acid and the growth particle size of the crystal;

[0034] Step 7: After the crystals in the ultrasonic induced crystal grower 4 reach a certain particle size range (30-50 μm), they are discharged through the crystal discharge port at the bottom of the ultrasonic induced crystal grower 4 and dehydrated to obtain high-purity calcium fluoride crystals with a moisture content of less than 30%. The effluent from the ultrasonic induced crystal grower 4 enters the subsequent comprehensive wastewater defluorination system 7 for treatment to meet the standards.

[0035] The high-concentration acidic fluorine-containing wastewater to be treated is transported to the ultrasonic induced crystal nucleation generator 3 and the ultrasonic induced crystal growth device 4 through pipelines, and the prepared lime solution is transported to the ultrasonic induced crystal nucleation generator and the ultrasonic induced crystal growth device 4 through pipelines. The calcium hydroxide in the lime solution reacts with the hydrofluoric acid in the high-concentration acidic fluorine-containing wastewater to generate calcium fluoride. The ultrasonic induced crystal nucleation generator 3 is started first, and the calcium hydroxide and hydrofluoric acid are fully mixed and dispersed by using the dispersion effect of high-frequency ultrasound (the cavitation effect and mechanical vibration effect generated by high-frequency ultrasound in the liquid, the instantaneous high-pressure shock wave and shear force break the particle agglomeration structure). The ultrasonic power is adjusted to control the amount of crystal nuclei generated. A large number of small-particle calcium fluoride crystal nuclei are formed in the ultrasonic-induced crystal nucleus generator 3. These crystal nuclei enter the ultrasonic-induced crystal grower 4 along with the water discharged from the ultrasonic-induced crystal nucleus generator 3. After the ultrasonic-induced crystal grower 4 is started, the calcium fluoride generated by the reaction of calcium hydroxide and hydrofluoric acid therein adheres to the surface of the crystal nuclei and grows to form large-particle calcium fluoride crystals. Similarly, the dispersion effect of high-frequency ultrasonic waves is utilized to control the sufficient mixing and dispersion of calcium hydroxide and hydrofluoric acid. The growth of the crystals is controlled by adjusting the power of the high-frequency ultrasonic waves. At the same time, the high-frequency ultrasonic waves are prevented from being broken due to excessive power. As the ultrasonic-induced crystal grower 4 is started, the calcium fluoride generated by the reaction of calcium hydroxide and hydrofluoric acid is attached to the surface of the crystal nuclei and grows to form large-particle calcium fluoride crystals. The nucleus generator 3 continuously forms crystal nuclei and discharges them into the ultrasonic induced crystal grower 4, thereby realizing the continuous replenishment of the crystal nuclei in the ultrasonic induced crystal grower 4. The calcium hydroxide in the lime solution continuously entering the ultrasonic induced crystal grower 4 and the hydrofluoric acid in the high-concentration acidic fluoride-containing wastewater continuously react to generate calcium fluoride, and the calcium fluoride continuously adheres to the surface of the replenished crystal nuclei, thereby continuously generating large-particle calcium fluoride crystals. Due to the presence of high-frequency ultrasonic waves in the ultrasonic induced crystal grower 4, on the one hand, the lime solution and the high-concentration acidic fluoride-containing wastewater are fully mixed, thereby ensuring sufficient reaction. At the same time, the particle size of the generated large-particle calcium fluoride crystals can be controlled, so that the final formed The large calcium fluoride crystals produced have substantially the same particle size. The large calcium fluoride crystals sink in the ultrasonically induced crystal grower 4 and are regularly discharged from a crystal discharge port at the bottom of the ultrasonically induced crystal grower 4. The discharged large calcium fluoride crystals are mixed with a portion of wastewater and enter a dehydration system 6 for dehydration treatment. Ultimately, high-purity calcium fluoride crystals with a moisture content below 30% are obtained. These high-purity calcium fluoride crystals can be recycled as industrial raw materials. Meanwhile, the final effluent from the ultrasonically induced crystal grower 4 enters a subsequent comprehensive wastewater defluorination system 7. After further treatment such as defluorination and SS removal by the continued addition of reagents, the qualified water is discharged or reused.

[0036] The process described above forms the ultrasonic induced crystal nucleus generator 3 and the ultrasonic induced crystal growth device 4 by setting the ultrasonic generating device in the reactor, and realizes the sufficient mixing and dispersion of the lime solution and the high-concentration acidic fluorine-containing wastewater by controlling the power of the high-frequency ultrasonic wave, ensures the sufficient reaction of the calcium hydroxide in the lime solution and the hydrofluoric acid in the high-concentration acidic fluorine-containing wastewater, at the same time, controls the particle size of the calcium fluoride crystals generated in the ultrasonic induced crystal nucleus generator 3 and the ultrasonic induced crystal growth device 4, the ultrasonic induced crystal nucleus generator 3 is used to generate small-particle calcium fluoride crystal nucleus, which is supplied to the ultrasonic induced crystal growth device 4, the calcium fluoride generated by reaction in the ultrasonic induced crystal growth device 4 grows on the surface of the crystal nucleus to form large-particle calcium fluoride crystal, this gradient crystallization mode controlled by ultrasonic wave can effectively control the particle size of the calcium fluoride crystal in a certain range (30 μm-50 μm), at the same time, ensures that the hydrofluoric acid in the wastewater and the lime solution can be fully dispersed, can effectively control the reaction supersaturation, prevents the crystal explosion phenomenon in the reaction process, and can greatly improve the utilization rate of lime, maximally avoids the problem of lime particle wrapping, can improve the purity of calcium fluoride to more than 93%, and the water content is controlled to be less than 30%, ensures the stability of the calcium fluoride crystal product, and the process does not need to provide calcium fluoride crystal seeds externally, saves the cost of crystal seeds.

[0037] The ultrasonic induced crystal growth device 4 is at least one stage, and the multi-stage ultrasonic induced crystal growth device 4 is sequentially connected, the calcium fluoride crystal particles generated in the front-stage ultrasonic induced crystal growth device 4 enter the next-stage ultrasonic induced crystal growth device 4 with water, the high-concentration acidic fluorine-containing wastewater and the lime solution are respectively punched into each stage of the ultrasonic induced crystal growth device 4 at a calcium fluoride molar ratio of 0.45-0.55, the calcium fluoride generated by the reaction of the lime solution and the hydrofluoric acid in each stage of the ultrasonic induced crystal growth device 4 grows on the surface of the calcium fluoride crystal particles, until the particle size of the calcium fluoride crystal particles reaches the design standard, the calcium fluoride crystal with the standard particle size in the last-stage ultrasonic induced crystal growth device 4 is discharged and subjected to dehydration treatment, by setting the ultrasonic induced crystal growth device 4 as a multi-stage series structure, the growth of the calcium fluoride crystal particle size can be better controlled, and the calcium fluoride crystal growth speed and particle size consistency are improved.

[0038] The amount of the high-concentration acidic fluorine-containing wastewater sent into the ultrasonic induced crystal nucleus generator 3 accounts for 1%-10% of the total amount of the high-concentration acidic fluorine-containing wastewater. The amount of the high-concentration acidic fluorine-containing wastewater and the lime solution sent into the ultrasonic induced crystal nucleus generator 3 and the ultrasonic induced crystal growth device 4 can be controlled by the flow rate of the respective wastewater lifting pump and the dosing pump, to ensure that the amount of the crystal nucleus sent into the ultrasonic induced crystal growth device 4 matches the calcium fluoride generated in the ultrasonic induced crystal growth device 4, and finally all form large-particle calcium fluoride crystals with the required particle size.

[0039] The crystal collection tank 5 is also provided, and the calcium fluoride crystal particles meeting the particle size standard are discharged from the ultrasonic induced crystal growth device 4 into the crystal collection tank 5 for collection. The mixture of the calcium fluoride crystal particles and water in the crystal collection tank 5 is stirred by the stirrer, the power of the stirrer in the crystal collection tank 5 is 100-300 W / m3, and the mixture of the calcium fluoride crystal particles and water in the crystal collection tank 5 is periodically sent to the dehydration system 6 for dehydration treatment. The large calcium fluoride crystal particles discharged from the ultrasonic induced crystal growth device 4 are uniformly collected by the crystal collection tank 5, and the mixture of the calcium fluoride crystal particles and water is continuously stirred to keep the calcium fluoride crystal particles dispersed and suspended in the water, and then the mixture is sent to the dehydration system 6 for dehydration. The consistency of the calcium fluoride crystal product is high, and the dehydration system 6 can be a filter pressing device.

[0040] The filtrate generated by the dehydration treatment is simultaneously returned to the ultrasonic induced crystal nucleus generator 3. The return of the dehydration filtrate is mainly to improve the solubility of lime in the ultrasonic induced crystal nucleus generator 3, and at the same time, to reduce the supersaturation in the ultrasonic induced crystal nucleus generator 3, and further prevent the occurrence of crystal explosion.

[0041] The ultrasonic power of the ultrasonic transducer in the ultrasonic induced crystal nucleus generator 3 is controlled at 50-100 W / m 3 The ultrasonic power of the ultrasonic transducer in the ultrasonic induced crystal growth device 4 is controlled at 30-75 W / m 3 .

[0042] The application relates to a hierarchical ultrasonic induction calcium fluoride crystallization device, which comprises a wastewater conditioning tank 1, a lime solution preparation tank 2, an ultrasonic induction crystal nucleus generator 3, an ultrasonic induction crystal growth device 4, a crystal collecting tank 5, a dehydration system 6, a comprehensive wastewater fluorine removal system 7, a dosing pump, a wastewater lifting pump and a control system 8; the ultrasonic induction crystal nucleus generator 3 and at least one stage of the ultrasonic induction crystal growth device 4 are sequentially communicated; the water outlet of the ultrasonic induction crystal nucleus generator 3 is communicated with the water inlet of the first stage of the ultrasonic induction crystal growth device 4 through a pipeline; the water outlet of the former stage of the ultrasonic induction crystal growth device 4 is communicated with the water inlet of the latter stage of the ultrasonic induction crystal growth device 4; the high-concentration acidic fluorine-containing wastewater in the wastewater conditioning tank 1 is pumped into the ultrasonic induction crystal nucleus generator 3 and each stage of the ultrasonic induction crystal growth device 4 through the wastewater lifting pump in proportion; the lime solution in the lime solution preparation tank 2 is pumped into the ultrasonic induction crystal nucleus generator 3 and each stage of the ultrasonic induction crystal growth device 4 through the dosing pump in proportion; the ultrasonic induction crystal nucleus generator 3 and the ultrasonic induction crystal growth device 4 are both provided with ultrasonic transducers which can generate high-frequency ultrasonic waves (cavitation effect and mechanical vibration effect of high-frequency ultrasonic waves in liquid); the bottom of the last stage of the ultrasonic induction crystal growth device 4 is provided with a crystal discharge port which is communicated with the crystal collecting tank 5 so that the large-particle calcium fluoride crystal particles deposited at the bottom of the last stage of the ultrasonic induction crystal growth device 4 are discharged into the crystal collecting tank 5; the crystal collecting tank 5 is provided with a stirrer which can stir the mixture of the large-particle calcium fluoride crystal and water in the crystal collecting tank 5; the crystal collecting tank 5 is communicated with the inlet of the dehydration system 6 through a crystal conveying device; the crystal conveying device can convey the large-particle calcium fluoride crystal in the crystal collecting tank 5 into the dehydration system 6; the dehydration system 6 can perform dehydration treatment on the large-particle calcium fluoride crystal; the water outlet of the last stage of the ultrasonic induction crystal growth device 4 is communicated with the water inlet of the comprehensive wastewater fluorine removal system 7 through a pipeline; the comprehensive wastewater fluorine removal system 7 can perform standard treatment on the wastewater entering the system; and the control system 8 can control the power of the ultrasonic transducers in the ultrasonic induction crystal nucleus generator 3 and the ultrasonic induction crystal growth device 4, the power of the stirrer and the operation of the dehydration system 6, the dosing pump and the wastewater lifting pump.

[0043] The application further comprises a filtrate collecting tank 9 and a reflux pump; the filtrate collecting tank 9 is used for collecting the filtrate generated by the dehydration system 6 during the dehydration treatment on the large-particle calcium fluoride crystal; the reflux pump can pump the filtrate in the filtrate collecting tank 9 into the ultrasonic induction crystal nucleus generator 3; a plurality of water outlets are further arranged; each water outlet can pump the mixture in the ultrasonic induction crystal nucleus generator 3 into the first stage of the ultrasonic induction crystal growth device 4; the first stage can pump the mixture in the former stage of the ultrasonic induction crystal growth device 4 into the latter stage of the ultrasonic induction crystal growth device 4; and the control system 8 can control the operation of the reflux pump and the water outlets.

Claims

1. A process for the crystallization of calcium fluoride by graded ultrasonic induction, characterized in that: The steps include: Step 1: Send part of the high-concentration acidic fluoride-containing wastewater into the ultrasonic induced crystal nucleation generator; Step 2: feeding lime solution into an ultrasonic induced crystal nucleation generator at a calcium to fluorine molar ratio of 0.45-0.55; Step 3: The lime solution and the hydrofluoric acid in the high-concentration acidic fluoride-containing wastewater react in an ultrasonically induced crystal nucleation generator to form small-particle crystal nuclei. During the reaction, the ultrasonic power of the ultrasonic transducer in the ultrasonically induced crystal nucleation generator is controlled to achieve sufficient mixing and dispersion of the lime solution and the hydrofluoric acid and the amount of crystal nuclei generated; Step 4: The crystal nuclei formed in the ultrasonic induced crystal nucleus generator enter the ultrasonic induced crystal growth device along with the outlet water; Step 5: feeding the remaining high-concentration acidic fluoride-containing wastewater into an ultrasonic induced crystal grower, and feeding lime solution into the ultrasonic induced crystal grower at a calcium-fluoride molar ratio of 0.45-0.55; Step 6: The lime solution and the hydrofluoric acid in the high-concentration acidic fluoride-containing wastewater react in an ultrasonically induced crystal nucleation generator to form calcium fluoride, which grows on the surface of the crystal nucleus to form calcium fluoride crystal particles. During the reaction, the ultrasonic power of the ultrasonic transducer in the ultrasonically induced crystal growth device is controlled to achieve sufficient mixing and dispersion of the lime solution and the hydrofluoric acid, and to achieve the growth of the crystal particle size; Step 7: After the crystals in the ultrasonic induced crystal grower reach a certain particle size range, they are discharged through the crystal discharge port at the bottom of the ultrasonic induced crystal grower and dehydrated to obtain high-purity calcium fluoride crystals with a moisture content of less than 30%. The effluent from the ultrasonic induced crystal grower enters the subsequent comprehensive wastewater defluorination system for treatment to meet the standards.

2. The process for crystallizing calcium fluoride by graded ultrasound induction according to claim 1, characterized in that: The ultrasonic induced crystal grower comprises at least one stage, and the multiple stages are sequentially connected. Calcium fluoride crystal particles generated in the ultrasonic induced crystal grower of the previous stage enter the ultrasonic induced crystal grower of the next stage along with the effluent water. High-concentration acidic fluoride-containing wastewater and lime solution are respectively injected into the ultrasonic induced crystal growers of each stage at a calcium-fluoride molar ratio of 0.45-0.

55. Calcium fluoride generated by the reaction of the lime solution with hydrofluoric acid in the ultrasonic induced crystal growers of each stage grows on the surface of the calcium fluoride crystal particles until the particle size of the calcium fluoride crystal particles reaches the design standard. The calcium fluoride crystals with the particle size reaching the standard in the last stage ultrasonic induced crystal grower are discharged and dehydrated.

3. The process for crystallizing calcium fluoride by graded ultrasound induction according to claim 1, characterized in that: The amount of high-concentration acidic fluorine-containing wastewater fed into the ultrasonic induced crystal nucleus generator accounts for 1%-10% of the total amount of high-concentration acidic fluorine-containing wastewater.

4. The process for crystallizing calcium fluoride by graded ultrasound induction according to claim 1, characterized in that: The concentration of lime solution is controlled at 5%-10%.

5. The process for crystallizing calcium fluoride by graded ultrasound induction according to claim 1, characterized in that: A crystal collection pool is also provided. Calcium fluoride crystal particles that meet the particle size standards are discharged from the ultrasonic induced crystal grower and collected in the crystal collection pool. The mixture of calcium fluoride crystal particles and water entering the crystal collection pool is stirred by a stirrer. The mixture of calcium fluoride crystal particles and water in the crystal collection pool is regularly sent to the dehydration system for dehydration treatment.

6. The process for crystallizing calcium fluoride by graded ultrasound induction according to claim 5, characterized in that: The power of the agitator in the crystal collection pool is 100-300W / m3.

7. The process for crystallizing calcium fluoride by graded ultrasound induction according to claim 1 or 5, characterized in that: The filtrate produced by the dehydration treatment is synchronously refluxed into the ultrasonic induced crystal nucleation generator.

8. The process for crystallizing calcium fluoride by graded ultrasound induction according to claim 1, characterized in that: The ultrasonic power of the ultrasonic transducer in the ultrasonic induced crystal nucleation generator is controlled at 50-100W / m 3 The ultrasonic power of the ultrasonic transducer in the ultrasonic induced crystal grower is controlled at 30-75W / m 3 .

9. A device for the crystallization of calcium fluoride by graded ultrasonic induction used in the process for the crystallization of calcium fluoride by graded ultrasonic induction according to any one of claims 1 to 8, characterized in that: The invention comprises a wastewater regulating tank (1), a lime solution mixing tank (2), an ultrasonically induced crystal nucleus generator (3), an ultrasonically induced crystal grower (4), a crystal collecting tank (5), a dehydration system (6), a comprehensive wastewater defluorination system (7), a dosing pump, a wastewater lifting pump and a control system (8). The ultrasonically induced crystal nucleus generator and at least one stage of ultrasonic induced crystal grower are sequentially connected. The water outlet of the ultrasonically induced crystal nucleus generator is connected to the water inlet of the first stage of ultrasonic induced crystal grower through a pipeline. The water outlet of the first stage of ultrasonic induced crystal grower in the multi-stage ultrasonic induced crystal grower is connected to the water inlet of the next stage of ultrasonic induced crystal grower. High-concentration acidic fluoride-containing wastewater in the wastewater regulating tank is respectively pumped into the ultrasonically induced crystal nucleus generator and each stage of ultrasonic induced crystal grower in proportion through the wastewater lifting pump. The lime solution in the lime solution mixing tank is respectively pumped into the ultrasonically induced crystal nucleus generator and each stage of ultrasonic induced crystal grower in proportion through the dosing pump. The ultrasonically induced crystal nucleus generator and the ultrasonically induced crystal grower are both provided with ultrasonic transducers. The ultrasonic transducer can generate high-frequency ultrasonic waves. A crystal discharge port is provided at the bottom of the last-stage ultrasonic induced crystal grower. The crystal discharge port is connected to the crystal collection pool so that the large-particle calcium fluoride crystal particles deposited at the bottom of the last-stage ultrasonic induced crystal grower are discharged into the crystal collection pool. A stirrer is provided in the crystal collection pool. The stirrer can stir the mixture of large-particle calcium fluoride crystals and water in the crystal collection pool. The crystal collection pool is connected to the inlet of the dehydration system through a crystal conveying device. The crystal conveying device can convey the large-particle calcium fluoride crystals in the crystal collection pool into the dehydration system. The dehydration system can dehydrate the large-particle calcium fluoride crystals. The water outlet of the last-stage ultrasonic induced crystal grower is connected to the water inlet of the comprehensive wastewater defluorination system through a pipeline. The comprehensive wastewater defluorination system can treat the wastewater entering it to meet the standards. The control system can control the power of the ultrasonic induced crystal nucleus generator and the ultrasonic transducer in the ultrasonic induced crystal grower, the power of the stirrer, and the operation of the dehydration system, the dosing pump and the wastewater lifting pump.

10. The stepwise ultrasonic-induced calcium fluoride crystallization device according to claim 9, characterized in that: A filtrate collecting tank (9) and a reflux pump are also provided. The filtrate collecting tank is used to collect filtrate generated by the dehydration system when dehydrating large-particle calcium fluoride crystals. The reflux pump can pump the filtrate in the filtrate collecting tank into the ultrasonic induced crystal nucleation generator. A plurality of water outlet pumps are also provided. Each water outlet pump can pump the mixed liquid in the ultrasonic induced crystal nucleation generator into the first ultrasonic induced crystal growth device, and each water outlet pump can pump the mixed liquid in the previous ultrasonic induced crystal growth device into the next ultrasonic induced crystal growth device. The control system can control the operation of the reflux pump and the water outlet pump.

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