A method for a calcium fluoride crystallization system based on functionalized quartz sand coupled fluidized bed

Abstract

The present invention discloses a method for a calcium fluoride crystallization system based on functionalized quartz sand coupled with a fluidized bed, comprising the following steps: Step S1, pretreat the quartz sand with sodium hydroxide, and then use KH550 as a silane coupling agent to enable the reaction of silanol groups with silicon dioxide in the quartz sand; Step S2, graft the polymer organic monomer 2-acrylamido-2-methylpropanesulfonic acid onto KH550 in Step S1 for negatively charged modification. The present invention realizes the formation of calcium fluoride crystals from fluoride ions in fluorine-containing wastewater through a fluidized bed, and in-situ captures calcium fluoride through functionalized quartz sand, enhances the heterogeneous crystallization of calcium fluoride, improves the filterability of precipitation particles, realizes resource capture of calcium fluoride while achieving deep fluorine removal, can improve the removal efficiency of fluoride ions, reduce the fluorine concentration in the effluent, solves the problem that subsequent chemical agents need to be added due to high effluent turbidity in a traditional fluidized bed crystallizer, reduces sludge production, and improves the economy and sustainability of wastewater treatment.

Description

Technical Field

[0001] The present invention relates to the technical field of calcium fluoride crystallization, and particularly relates to a method for a calcium fluoride crystallization system based on functional quartz sand coupled with a fluidized bed. Background Art

[0002] In recent years, the semiconductor manufacturing and photovoltaic industries, as two core pillars driving technological progress and energy transformation, have been experiencing rapid development. From the design, lithography, etching to packaging and testing of chips in the semiconductor manufacturing process, to the wafer cleaning, texturing and coating of battery wafers in the photovoltaic industry, a large number of fluorine-containing compounds are widely used. If directly discharged without proper treatment, fluoride ions can combine with metal ions in the soil, changing the chemical properties of the soil and thus affecting the growth of crops. If it seeps into the underground aquifer, it will cause pollution of groundwater and threaten the safety of human drinking water.

[0003] Currently, the treatment of fluorine-containing wastewater includes chemical precipitation, adsorption, membrane separation, etc. In particular, chemical precipitation, as a traditional low-cost treatment method, adds precipitants such as calcium salts and magnesium salts to the wastewater to promote the conversion of fluoride ions into poorly soluble fluoride precipitates. For example, calcium chloride reacts with fluoride ions to form calcium fluoride precipitate. This method is simple to operate, low in cost, and has a significant treatment effect on high-concentration fluorine-containing wastewater, but it has deficiencies such as a large amount of precipitant consumption, a large amount of sludge production, and poor treatment of low-concentration wastewater. Different from the treatment of fluorine-containing wastewater by chemical precipitation, the fluidized bed induced crystallization technology can solve the problem of disposal of fluorine-containing sludge, recover fluorine resources, and produce fluorite products with low water content and high value. Patent No. CN201010272000.9 discloses a method and device for treating fluorine-containing wastewater, using a fluidized bed as a crystallization reactor, adding calcium fluoride crystal seeds, and feeding the fluorine-containing wastewater and a calcium-containing precipitant into it according to a ratio. The fluoride ions precipitate on the crystal seeds, and the generated sand-like calcium fluoride precipitate sludge is recovered. The primary treated water is then coagulated and settled to meet the standards before being discharged. However, currently, the fluidized bed induced crystallization technology used to treat fluorine-containing wastewater can only control the fluorine concentration in the effluent at about 10 - 20 mg / L. Patent No. CN202210399549.7 introduces a fluidized bed deep defluorination device and process, including outer, middle, and inner cylinders, integrating multiple process units such as deep defluorination and flocculation to achieve integration. However, the treatment process is complex, and the high-turbidity fluidized bed effluent still needs to be further treated deeply. Therefore, how to design a fluidized bed crystallization system and functional crystal seeds to directly achieve low-fluoride ion and low-turbidity effluent in one step is of great significance.

[0004] As described above, for this reason, we have designed a method for a calcium fluoride crystallization system based on functional quartz sand coupled with a fluidized bed to solve the above problems. Summary of the Invention

[0005] The object of the present invention is to solve the drawbacks existing in the prior art, and a method for a calcium fluoride crystallization system based on functionalized quartz sand coupled with a fluidized bed is proposed.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for a calcium fluoride crystallization system based on functionalized quartz sand coupled with a fluidized bed, comprising the following steps:

[0008] Step S1: Take quartz sand, add sodium hydroxide solution thereto, stir at a constant speed in a constant temperature water bath, and wash the quartz sand filtrate with ultrapure water until neutral; then add KH550 as a silane coupling agent to the quartz sand to realize the reaction of silanol groups with silicon dioxide in the quartz sand;

[0009] Step S2: Graft the polymer organic monomer 2-acrylamido-2-methylpropanesulfonic acid onto KH550 in Step S1 for negatively charged modification. The amino group on KH550 can be used as the starting end of the C=C polymerization chain reaction, and 2-acrylamido-2-methylpropanesulfonic acid is grafted onto the surface of the microspheres to obtain functionalized quartz sand seeds for calcium fluoride crystal capture;

[0010] Step S3: Add the functionalized quartz sand seeds to a fluidized bed crystallizer. The filling amount and density of the added quartz sand seeds are 20% and 1.5 g / cm3 respectively; the fluorine-containing wastewater and the calcium precipitant enter the fluidized bed crystallizer through the inlets on both sides of the bottom of the crystallizer; under the action of water flow, the functionalized quartz sand is in a fluidized state in the bed, and the calcium fluoride crystals formed by the reaction of fluoride ions in the wastewater with the precipitant are attached to the surface of the seeds by sulfonate ions on the functionalized quartz sand and grow, promoting the deep removal of fluoride ions and the heterogeneous crystallization of calcium fluoride.

[0011] Preferably, the fluorine-containing wastewater in Step S1 comes from one or more of the chip manufacturing, electroplating, and photovoltaic industries.

[0012] Preferably, the concentration of sodium hydroxide in Step S1 is 0.5 wt% - 10 wt%.

[0013] Preferably, the mass fraction of the silane coupling agent KH550 in Steps S1 - S2 is 1 wt% - 10 wt%.

[0014] Preferably, in Steps S1 - S2, in an anaerobic environment, 2-acrylamido-2-methylpropanesulfonic acid with a total mass of 5 wt% - 25 wt% is added, and stirred for 2 - 10 h under the condition of water bath heating at 30 - 80 °C, and finally a white suspension is obtained and filtered for recovery.

[0015] Preferably, in Step S3, the dosage of the calcium precipitating salt is controlled according to the calcium-fluorine molar ratio of 0.2 - 1.0.

[0016] Preferably, the calcium salt added in step S3 is one of calcium chloride, quicklime or calcium hydroxide.

[0017] Preferably, in step S3, the experiment is stopped when the fluoride ion concentration in the fluoride-containing wastewater is lower than 8 mg / L.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] 1. In the present invention, a fluidized bed is used to form calcium fluoride crystals from fluoride ions in fluoride-containing wastewater, and functional quartz sand is used to in-situ capture calcium fluoride, enhancing the heterogeneous crystallization of calcium fluoride, improving the filterability of precipitate particles, achieving deep fluoride removal while resourcefully capturing calcium fluoride, which can improve the removal efficiency of fluoride ions and reduce the fluoride concentration in the effluent.

[0020] 2. The operation of the present invention is simple and easy to implement, solving the problem that the traditional fluidized bed crystallizer requires subsequent chemical dosing due to high effluent turbidity, reducing sludge production, and improving the economy and sustainability of wastewater treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a schematic structural diagram of a calcium fluoride crystallization system coupling a fluidized bed with functional quartz sand proposed by the present invention;

[0022] Figure 2 is a display diagram of functional quartz sand of a method of a calcium fluoride crystallization system coupling a fluidized bed with functional quartz sand proposed in Example 3 of the present invention;

[0023] Figure 3 is a display diagram of calcium fluoride crystals of a method of a calcium fluoride crystallization system coupling a fluidized bed with functional quartz sand proposed in Example 3 of the present invention.

[0024] In the figure: 1 fluoride-containing wastewater, 2 quartz sand seed crystal, 3 calcium fluoride crystal. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0026] Referring to Figures 1 - 3 , a method of a calcium fluoride crystallization system coupling a fluidized bed with functional quartz sand includes the following steps:

[0027] Step S1: Take quartz sand, add sodium hydroxide solution thereto, stir at a constant speed in a thermostatic water bath, and wash the quartz sand filtrate with ultrapure water until it is neutral; then add KH550 as a silane coupling agent to the quartz sand to react the silanol groups with silicon dioxide in the quartz sand;

[0028] Step S2: Graft the polymer organic monomer 2-acrylamido-2-methylpropanesulfonic acid onto KH550 in Step S1 for negatively charged modification. The amino group on KH550 can be used as the starting end of the C=C polymerization chain reaction, and grafting 2-acrylamido-2-methylpropanesulfonic acid to prepare the functionalized quartz sand seed crystal 2 for calcium fluoride crystal 3 capture on the surface of the microspheres;

[0029] Among them, the fluorine-containing wastewater 1 in Step S1 can be from one or more of the chip manufacturing, electroplating, and photovoltaic industries. The concentration of sodium hydroxide in Step S1 is 0.5wt%-10wt%. The mass fraction of the silane coupling agent KH550 in Steps S1-S2 is 1wt%-10wt%. In Steps S1-S2, in an anaerobic environment, 2-acrylamido-2-methylpropanesulfonic acid with a total mass of 5wt%-25wt% is added, and stirred for 2-10h under the condition of water bath heating at 30-80°C, and finally a white suspension is filtered and recovered.

[0030] Step S3: Add the functionalized quartz sand seed crystal 2 into the fluidized bed crystallizer. The filling amount and density of the added quartz sand seed crystal are 20% and 1.5g / cm3 respectively; the fluorine-containing wastewater 1 and the calcium-containing precipitant enter the fluidized bed crystallizer through the inlets on both sides of the bottom of the crystallizer respectively; under the action of water flow, the functionalized quartz sand is in a fluidized state in the bed, and the calcium fluoride crystals formed by the reaction of fluoride ions in the wastewater with the precipitant are attached to the surface of the seed crystal by the sulfonate ions on the functionalized quartz sand and grow, promoting the deep removal of fluoride ions and the heterogeneous crystallization of calcium fluoride.

[0031] Among them, in Step S3, the dosage of the calcium precipitating salt is controlled according to the calcium-fluorine molar ratio of 0.2-1.0. The calcium salt added in Step S3 is calcium chloride, quicklime or calcium hydroxide. In Step S3, the experiment is stopped when the fluoride ion concentration in the fluorine-containing wastewater 1 is lower than 8mg / L.

[0032] The following are the specific embodiments of the present invention:

[0033] Example 1

[0034] Step S1: Immerse 10g of quartz sand in 500mL of 0.5wt% sodium hydroxide solution, stir at a speed of 200rpm in a constant temperature water bath at 80°C for 2h, and wash the quartz sand filtrate with ultrapure water until neutral; then add 1wt% of KH550 as a silane coupling agent to the quartz sand to realize the reaction of silanol groups with silicon dioxide in the quartz sand.

[0035] Step S2: Take the quartz sand reacted with KH550, add a 2-acrylamido-2-methylpropanesulfonic acid solution with a concentration of 5 wt% thereto, and stir at a rotation speed of 200 rpm for 2 h for negatively charged modification to obtain a functionalized quartz sand seed crystal 2 for the capture of calcium fluoride crystals 3.

[0036] Step S3: Add the functionalized quartz sand seed crystal 2 into a fluidized bed crystallizer. A fluorine-containing wastewater 1 with a fluorine ion concentration of 800 mg / L and a calcium chloride solution respectively enter the fluidized bed crystallizer through the inlets on both sides at the bottom of the crystallizer at a flow rate of 0.1 L / h, and the calcium-fluorine molar ratio is 0.2. Under the action of the water flow, the functionalized quartz sand is in a fluidized state in the bed, and the calcium fluoride crystals formed by the reaction of the fluorine ions in the wastewater with the calcium chloride solution are attached to the surface of the seed crystal by the sulfonate ions on the functionalized quartz sand and grow, promoting the deep removal of fluorine ions and the heterogeneous crystallization of calcium fluoride, so that the fluorine ion concentration in the effluent is 540 mg / L and the turbidity is 225 NTU. After the experiment, the calcium fluoride recovery rate is 21.3% and the purity is 97.4%.

[0037] Example 2

[0038] Step S1: Soak 10 g of quartz sand with 500 mL of a 5 wt% sodium hydroxide solution, stir at a rotation speed of 200 rpm in a constant temperature water bath at 80 °C for 2 h, and wash the quartz sand filtrate with ultrapure water until it is neutral; then add 5 wt% of KH550 to the quartz sand as a silane coupling agent to achieve the reaction of silanol groups with silicon dioxide in the quartz sand.

[0039] Step S2: Take the quartz sand reacted with KH550, add a 2-acrylamido-2-methylpropanesulfonic acid solution with a concentration of 15 wt% thereto, and stir at a rotation speed of 200 rpm for 2 h for negatively charged modification to obtain a functionalized quartz sand seed crystal 2 for the capture of calcium fluoride crystals 3.

[0040] Step S3: Add the functionalized quartz sand seed crystal 2 into a fluidized bed crystallizer. A fluorine-containing wastewater 1 with a fluorine ion concentration of 800 mg / L and a calcium chloride solution respectively enter the fluidized bed crystallizer through the inlets on both sides at the bottom of the crystallizer at a flow rate of 0.1 L / h, and the calcium-fluorine molar ratio is 0.5. Under the action of the water flow, the functionalized quartz sand is in a fluidized state in the bed, and the calcium fluoride crystals formed by the reaction of the fluorine ions in the wastewater with the calcium chloride solution are attached to the surface of the seed crystal by the sulfonate ions on the functionalized quartz sand and grow, promoting the deep removal of fluorine ions and the heterogeneous crystallization of calcium fluoride, so that the fluorine ion concentration in the effluent is 60 mg / L and the turbidity is 57 NTU. After the experiment, the calcium fluoride recovery rate is 89.7% and the purity is 98.2%.

[0041] Example 3

[0042] Step S1: Immerse 10 g of quartz sand in 500 mL of 10 wt% sodium hydroxide solution, stir at 200 rpm in an 80°C constant temperature water bath for 2 h, and wash the quartz sand filtrate with ultrapure water until neutral. Then add 10 wt% KH550 as a silane coupling agent to the quartz sand to react the silanol groups with the silicon dioxide in the quartz sand.

[0043] Step S2: Take the quartz sand reacted with KH550, add a 20 wt% solution of 2-acrylamido-2-methylpropanesulfonic acid to it, stir at 200 rpm for 2 h for negatively charged modification to obtain functionalized quartz sand seeds 2 for the capture of calcium fluoride crystals 3.

[0044] Step S3: Add the functionalized quartz sand seeds 2 into a fluidized bed crystallizer. Fluoride-containing wastewater 1 with a fluoride ion concentration of 800 mg / L and calcium chloride solution enter the fluidized bed crystallizer through the inlets on both sides of the bottom of the crystallizer at a flow rate of 0.1 L / h, and the calcium-to-fluoride molar ratio is 0.8. Under the action of the water flow, the functionalized quartz sand is in a fluidized state in the bed, and calcium fluoride crystals formed by the reaction of fluoride ions in the wastewater with the calcium chloride solution are attached to the surface of the seeds by sulfonate ions on the functionalized quartz sand and grow, promoting the deep removal of fluoride ions and the heterogeneous crystallization of calcium fluoride, so that the fluoride ion concentration in the effluent is 7.6 mg / L and the turbidity is 32 NTU. After the experiment, the calcium fluoride recovery rate is 97.6% and the purity is 98.3%.

[0045] It can be seen that in Example 3, the quartz sand is fully negatively charged modified by further increasing the concentration of 2-acrylamido-2-methylpropanesulfonic acid to 20 wt%, effectively inducing heterogeneous crystallization of calcium fluoride on its surface. In addition, by increasing the calcium-to-fluoride ratio to 0.8, the concentration of fluoride ions in the water body can be further reduced and the calcium fluoride recovery rate can be increased by enhancing the common ion effect.

[0046] The above shows and describes 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 by the above embodiments, and without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope claimed by the present invention. The scope claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for a calcium fluoride crystallization system based on functionalized quartz sand coupled with a fluidized bed, characterized in that, It includes the following steps: Step S1: Take quartz sand, add sodium hydroxide solution thereto, stir at a constant speed in a constant temperature water bath, and wash the quartz sand filtrate with ultrapure water until it is neutral; then add KH550 as a silane coupling agent to the quartz sand to react the silicon hydroxyl group with silicon dioxide in the quartz sand; Step S2: Graft the polymer organic monomer 2-acrylamido-2-methylpropanesulfonic acid onto KH550 in Step S1 for negatively charged modification. By taking the amino group on KH550 as the starting end of the C=C polymerization chain reaction, graft 2-acrylamido-2-methylpropanesulfonic acid on the surface of the microspheres to obtain the functionalized quartz sand seed crystal (2) for capturing calcium fluoride crystals (3); Step S3: Add the functionalized quartz sand seed crystal (2) into a fluidized bed crystallizer; the fluorine-containing wastewater (1) and the calcium-containing precipitant enter the fluidized bed crystallizer through the inlets on both sides at the bottom of the crystallizer respectively; under the action of water flow, the functionalized quartz sand is in a fluidized state in the bed, and the calcium fluoride crystals (3) formed by the reaction of fluoride ions in the wastewater with the precipitant are attached to the surface of the seed crystal by the sulfonate ions on the functionalized quartz sand and grow, promoting the deep removal of fluoride ions and the heterogeneous crystallization of calcium fluoride.

2. The method of a calcium fluoride crystallization system based on functionalized quartz sand coupled fluidized bed according to claim 1, characterized in that, In Step S1, the fluorine-containing wastewater (1) comes from one or more of the chip manufacturing, electroplating, and photovoltaic industries.

3. A method for a calcium fluoride crystallization system based on functionalized quartz sand coupled fluidized bed according to claim 1, characterized in that, In Step S1, the concentration of sodium hydroxide is 0.5 wt% - 10 wt%.

4. The method of a calcium fluoride crystallization system based on functionalized quartz sand coupled fluidized bed according to claim 1, characterized in that, In Steps S1 - S2, the mass fraction of the silane coupling agent KH550 is 1 wt% - 10 wt%.

5. A method for a calcium fluoride crystallization system based on functionalized quartz sand coupled fluidized bed according to claim 1, characterized in that, In Steps S1 - S2, in an anaerobic environment, add 2-acrylamido-2-methylpropanesulfonic acid with a total mass of 5 wt% - 25 wt%, stir for 2 - 10 h under the condition of water bath heating at 30 - 80 °C, and finally obtain a white suspension for filtration and recovery.

6. The method of a calcium fluoride crystallization system based on functionalized quartz sand coupled fluidized bed according to claim 1, characterized in that, In Step S3, control the dosage of the calcium precipitating salt according to the calcium-fluorine molar ratio of 0.2 - 1.

0.

7. A method for a calcium fluoride crystallization system based on functionalized quartz sand coupled fluidized bed according to claim 1, characterized in that, The calcium salt added in Step S3 is one of calcium chloride, quicklime, or calcium hydroxide.

8. A method for a calcium fluoride crystallization system based on functionalized quartz sand coupled fluidized bed according to claim 1, characterized in that, In Step S3, stop the experiment when the fluoride ion concentration in the fluorine-containing wastewater (1) is lower than 8 mg / L.

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