Method of calcium fluoride crystallization system based on functional quartz sand coupled fluidized bed

Abstract

The invention discloses a method of a calcium fluoride crystallization system based on a functional quartz sand coupled fluidized bed, which comprises the following steps: S1, pretreating quartz sand by using sodium hydroxide, and reacting silicon hydroxyl with silicon dioxide in the quartz sand by using KH550 as a silane coupling agent; and step S2, grafting a high-molecular organic monomer 2-acrylamido-2-methylpropanesulfonic acid on the KH550 in the step S1, and carrying out negative charge electricity modification. The fluorine ions in the fluorine-containing wastewater form calcium fluoride crystals through the fluidized bed, calcium fluoride is captured in situ through functional quartz sand, heterogeneous crystallization of calcium fluoride is enhanced, the filterability of precipitation particles is improved, calcium fluoride is captured in a resource mode while deep fluorine removal is achieved, the removal efficiency of the fluorine ions can be improved, and the method is suitable for industrial production. The fluorine concentration of the discharged water is reduced, the problem that follow-up agent adding is needed due to high turbidity of the discharged water of a traditional fluidized bed crystallizer is solved, the sludge yield is reduced, and the economical efficiency and sustainability of wastewater treatment are improved.

Description

Technical Field

[0001] The invention relates to the technical field of calcium fluoride crystallization, and in particular to a method of a calcium fluoride crystallization system based on functionalized quartz sand coupled fluidized bed. Background Art

[0002] In recent years, semiconductor manufacturing and the photovoltaic industry, as the two core pillars to promote scientific and technological progress and energy transformation, are experiencing rapid development. From chip design, lithography, etching to packaging and testing in the semiconductor manufacturing process, to silicon wafer cleaning, texturing and cell coating 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, change the chemical properties of the soil, and thus affect the growth of crops. If it seeps into underground aquifers, it will lead to groundwater pollution and threaten human drinking water safety.

[0003] At present, the treatment of fluoride-containing wastewater includes chemical precipitation, adsorption, membrane separation, etc. In particular, chemical precipitation, as a traditional low-cost treatment method, promotes the conversion of fluoride ions into insoluble fluoride precipitates by adding precipitants such as calcium salts and magnesium salts to the wastewater, such as calcium chloride reacting with fluoride ions to form calcium fluoride precipitates. This method is simple to operate, low in cost, and has a significant effect on the treatment of high-concentration fluoride-containing wastewater, but it has shortcomings such as large amount of precipitants, high sludge production, and poor treatment of low-concentration wastewater. Unlike the chemical precipitation method for treating fluoride-containing wastewater, fluidized bed induced crystallization technology can solve the problem of fluoride-containing sludge disposal, recover fluorine resources, and produce low-water content, high-value fluorite products. Patent No. CN201010272000.9 discloses a method and device for treating fluorine-containing wastewater, which uses a fluidized bed as a crystallization reactor, adds calcium fluoride seeds, and feeds fluorine-containing wastewater and calcium-containing precipitants into the fluidized bed according to a ratio. Fluoride ions are precipitated on the seeds, and the generated sandy calcium fluoride precipitation sludge is recovered. The primary treated water is discharged after coagulation and sedimentation to meet the standards. However, the fluidized bed induced crystallization technology currently used to treat fluorine-containing wastewater can only control the fluorine concentration of the effluent to about 10-20 mg / L. Patent No. CN202210399549.7 introduces a fluidized bed deep defluorination device and process, which contains outer, middle and inner cylinders, and integrates multiple process units such as deep defluorination and flocculation to achieve integration. However, the treatment process is complicated, and the effluent from the fluidized bed with high turbidity still needs to be further treated in depth. Therefore, it is of great significance to design a fluidized bed crystallization system and functionalized seeds to directly achieve low fluoride ion and low turbidity effluent in one step.

[0004] As mentioned above, we have designed a method of calcium fluoride crystallization system based on functionalized quartz sand coupled fluidized bed to solve the above problems. Summary of the invention

[0005] The purpose of the present invention is to solve the shortcomings of the prior art and to propose a method for a calcium fluoride crystallization system based on a functionalized quartz sand coupled fluidized bed.

[0006] In order 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 fluidized bed comprises the following steps:

[0008] Step S1, taking quartz sand, adding sodium hydroxide solution thereto, stirring at a high speed in a constant temperature water bath, and washing the quartz sand filtrate with ultrapure water until it is neutral; then adding KH550 as a silane coupling agent to the quartz sand to achieve a reaction between silanol and silicon dioxide in the quartz sand;

[0009] Step S2, grafting a high molecular organic monomer 2-acrylamide-2-methylpropanesulfonic acid onto the KH550 in step S1 for negative charge modification, by using the amino group on the KH550 as the head end of the C=C polymerization chain reaction, grafting 2-acrylamide-2-methylpropanesulfonic acid on the surface of the microsphere, and preparing a functionalized quartz sand seed for capturing calcium fluoride crystals;

[0010] Step S3, adding functionalized quartz sand seed crystals into a fluidized bed crystallizer, wherein the filling amount and density of the added quartz sand seed crystals are 20% and 1.5 g / cm3 respectively; the fluoride-containing wastewater 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 the water flow, the functionalized quartz sand is in a fluidized state in the bed, and the calcium fluoride crystals generated by the reaction of fluoride ions in the wastewater and the precipitant are attached to the surface of the seed crystals by the sulfonate ions on the functionalized quartz sand and grow, thereby 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 chip manufacturing, electroplating, and photovoltaic industries.

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

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

[0014] Preferably, in the steps S1-S2, 5wt%-25wt% of 2-acrylamido-2-methylpropanesulfonic acid is added in an anaerobic environment, and the mixture is stirred for 2-10h in a water bath at 30-80°C, and the white suspension is finally obtained and recovered by filtration.

[0015] Preferably, in step S3, the amount of calcium precipitation salt added is controlled at a calcium-fluoride 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 present invention has the following beneficial effects: 1. The present invention realizes the formation of calcium fluoride crystals from fluoride ions in fluoride-containing wastewater through a fluidized bed, and in-situ captures calcium fluoride through functionalized quartz sand, thereby enhancing the heterogeneous crystallization of calcium fluoride and improving the filterability of precipitated particles, achieving deep fluoride removal and resource-based capture of calcium fluoride, thereby improving the removal efficiency of fluoride ions and reducing the fluoride concentration in effluent water.

[0019] 2. The present invention is simple and easy to operate, and solves the problem that the traditional fluidized bed crystallizer needs subsequent addition of reagents due to high effluent turbidity, reduces sludge production, and improves the economy and sustainability of wastewater treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram of the structure of the calcium fluoride crystallization system of functionalized quartz sand coupled with fluidized bed proposed by the present invention;

[0021] Figure 2 This is a functionalized quartz sand display diagram of a method of a calcium fluoride crystallization system based on functionalized quartz sand coupled with a fluidized bed proposed in Example 3 of the present invention;

[0022] Figure 3 This is a diagram showing calcium fluoride crystals of a method of a calcium fluoride crystallization system based on functionalized quartz sand coupled with a fluidized bed proposed in Example 3 of the present invention.

[0023] In the figure: 1 fluoride-containing wastewater, 2 quartz sand seed crystals, 3 calcium fluoride crystals. DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0025] Reference Figure 1-Figure 3 , a method for a calcium fluoride crystallization system based on functionalized quartz sand coupled with a fluidized bed, comprising the following steps:

[0026] Step S1, taking quartz sand, adding sodium hydroxide solution thereto, stirring at a high speed in a constant temperature water bath, and washing the quartz sand filtrate with ultrapure water until it is neutral; then adding KH550 as a silane coupling agent to the quartz sand to achieve a reaction between silanol and silicon dioxide in the quartz sand;

[0027] Step S2, grafting a high molecular organic monomer 2-acrylamide-2-methylpropanesulfonic acid onto the KH550 in step S1 for negative charge modification, and using the amino group on the KH550 as the head end of the C=C polymerization chain reaction to graft 2-acrylamide-2-methylpropanesulfonic acid onto the surface of the microsphere to prepare a functionalized quartz sand seed 2 for capturing the calcium fluoride crystal 3;

[0028] In which, the fluorine-containing wastewater 1 in step S1 can be derived 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, 5wt%-25wt% of 2-acrylamido-2-methylpropanesulfonic acid is added in an anaerobic environment, and the mixture is stirred for 2-10h under heating conditions at 30-80°C in a water bath, and finally a white suspension is obtained and filtered and recovered.

[0029] Step S3, adding functionalized quartz sand seed crystals 2 into a fluidized bed crystallizer, wherein the filling amount and density of the added quartz sand seed crystals are 20% and 1.5 g / cm3 respectively; the fluoride-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 the water flow, the functionalized quartz sand is in a fluidized state in the bed, and the calcium fluoride crystals generated by the reaction of the fluoride ions in the wastewater and the precipitant are attached to the surface of the seed crystals by the sulfonate ions on the functionalized quartz sand and grow, thereby promoting the deep removal of fluoride ions and the heterogeneous crystallization of calcium fluoride.

[0030] Wherein, in the step S3, the amount of calcium precipitation salt added is controlled according to a calcium-fluoride molar ratio of 0.2-1.0, the calcium salt added in the step S3 is calcium chloride, quicklime or calcium hydroxide, and in the step S3, the experiment is stopped when the fluoride ion concentration in the fluoride-containing wastewater 1 is lower than 8 mg / L.

[0031] The following are specific embodiments of the present invention:

[0032] Example 1

[0033] Step S1: soak 10 g of quartz sand in 500 mL of 0.5 wt % sodium hydroxide solution, stir at 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 1 wt % of KH550 as a silane coupling agent to the quartz sand to achieve a reaction between silanol and silica in the quartz sand.

[0034] Step S2: taking the quartz sand after the reaction with KH550, adding a 5 wt% concentration of 2-acrylamide-2-methylpropanesulfonic acid solution thereto, stirring at a speed of 200 rpm for 2 h for negative charge modification, and preparing functionalized quartz sand seeds 2 for capturing calcium fluoride crystals 3.

[0035] Step S3: Add functionalized quartz sand seed crystals 2 to the 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 at a flow rate of 0.1 L / h through the inlets on both sides of the bottom of the crystallizer, respectively, and the calcium-fluoride molar ratio is 0.2. Under the action of water flow, the functionalized quartz sand is in a fluidized state in the bed, and the calcium fluoride crystals generated by the reaction of fluoride ions in the wastewater with the calcium chloride solution are attached to the surface of the seed crystals by the sulfonate ions on the functionalized quartz sand and grow, which promotes the deep removal of fluoride ions and the heterogeneous crystallization of calcium fluoride, so that the fluoride ion concentration in the water is 540 mg / L and the turbidity is 225 NTU. After the experiment, the yield of calcium fluoride is 21.3% and the purity is 97.4%.

[0036] Example 2

[0037] Step S1: Step S1: Soak 10 g of quartz sand in 500 mL of 5 wt % sodium hydroxide solution, stir at 200 rpm in a constant temperature water bath at 80°C for 2 h, and wash the quartz sand filtrate with ultrapure water until neutral; then add 5 wt % of KH550 as a silane coupling agent to the quartz sand to achieve the reaction of silanol with silica in the quartz sand.

[0038] Step S2: taking the quartz sand after the reaction with KH550, adding a 15 wt% 2-acrylamide-2-methylpropanesulfonic acid solution thereto, stirring at a speed of 200 rpm for 2 h for negative charge modification, and preparing functionalized quartz sand seeds 2 for capturing calcium fluoride crystals 3.

[0039] Step S3: Add the functionalized quartz sand seed 2 to the 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 at a flow rate of 0.1L / h through the inlets on both sides of the bottom of the crystallizer, respectively, and the calcium-fluoride molar ratio is 0.5. Under the action of water flow, the functionalized quartz sand is in a fluidized state in the bed, and the calcium fluoride crystals generated by the reaction of fluoride ions in the wastewater with the calcium chloride solution are attached to the surface of the seed by the sulfonate ions on the functionalized quartz sand and grow, which promotes the deep removal of fluoride ions and the heterogeneous crystallization of calcium fluoride, so that the fluoride ion concentration in the water is 60 mg / L and the turbidity is 57NTU. After the experiment, the yield of calcium fluoride is 89.7% and the purity is 98.2%.

[0040] Example 3

[0041] Step S1: soak 10 g of quartz sand in 500 mL of 10 wt % sodium hydroxide solution, stir at 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 10 wt % of KH550 as a silane coupling agent to the quartz sand to achieve a reaction between silanol and silica in the quartz sand.

[0042] Step S2, taking the quartz sand after the reaction with KH550, adding 20wt% 2-acrylamide-2-methylpropanesulfonic acid solution thereto, stirring at 200 rpm for 2h for negative charge modification, and preparing functionalized quartz sand seeds 2 for capturing calcium fluoride crystals 3.

[0043] Step S3: Add functionalized quartz sand seed crystals 2 to the 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 at a flow rate of 0.1L / h through the inlets on both sides of the bottom of the crystallizer, respectively, and the calcium-fluoride molar ratio is 0.8. Under the action of water flow, the functionalized quartz sand is in a fluidized state in the bed, and the calcium fluoride crystals generated by the reaction of fluoride ions in the wastewater and the calcium chloride solution are attached to the surface of the seed crystals by the sulfonate ions on the functionalized quartz sand and grow, which promotes the deep removal of fluoride ions and the heterogeneous crystallization of calcium fluoride, so that the fluoride ion concentration in the water is 7.6 mg / L and the turbidity is 32NTU. After the experiment, the yield of calcium fluoride is 97.6% and the purity is 98.3%.

[0044] It can be seen that the quartz sand in Example 3 is fully negatively charged by further increasing the concentration of 2-acrylamido-2-methylpropanesulfonic acid to 20wt%, effectively inducing heterogeneous crystallization of calcium fluoride on its surface. In addition, by increasing the calcium-fluoride ratio to 0.8, the fluoride ion concentration in the water body can be further reduced by enhancing the common ion effect, thereby increasing the calcium fluoride yield.

[0045] The basic principles, main features and advantages of the present invention are shown and described above. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention. The scope of the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for calcium fluoride crystallization system based on functionalized quartz sand coupled fluidized bed, characterized in that: The following steps are involved: Step S1, taking quartz sand, adding sodium hydroxide solution thereto, stirring at a high speed in a constant temperature water bath, and washing the quartz sand filtrate with ultrapure water until it is neutral; then adding KH550 as a silane coupling agent to the quartz sand to achieve a reaction between silanol and silicon dioxide in the quartz sand; Step S2, grafting a high molecular weight organic monomer 2-acrylamide-2-methylpropanesulfonic acid onto the KH550 in step S1 for negative charge modification, using the amino group on the KH550 as the head end of the C=C polymerization chain reaction to graft 2-acrylamide-2-methylpropanesulfonic acid onto the surface of the microsphere, thereby preparing a functionalized quartz sand seed (2) for capturing the calcium fluoride crystal (3); Step S3, adding the functionalized quartz sand seed crystals (2) into the fluidized bed crystallizer; the fluoride-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 the water flow, the functionalized quartz sand is in a fluidized state in the bed, and the calcium fluoride crystals (3) generated by the reaction of fluoride ions in the wastewater and the precipitant are attached to the surface of the seed crystals by the sulfonate ions on the functionalized quartz sand and grow, thereby 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: The fluorine-containing wastewater (1) in step S1 is derived from one or more of the chip manufacturing, electroplating and photovoltaic industries.

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

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 the steps S1-S2, the mass fraction of the silane coupling agent KH550 is 1wt%-10wt%.

5. The method of a calcium fluoride crystallization system based on functionalized quartz sand coupled fluidized bed according to claim 1, characterized in that: In the steps S1-S2, 5wt%-25wt% of 2-acrylamido-2-methylpropanesulfonic acid is added in an anaerobic environment, and the mixture is stirred for 2-10h in a water bath heated at 30-80°C, and finally the obtained white suspension is filtered and recovered.

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, the amount of calcium precipitation salt added is controlled according to a calcium-fluorine molar ratio of 0.2-1.

0.

7. The method of 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. 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, the experiment is stopped when the fluoride ion concentration in the fluoride-containing wastewater (1) is lower than 8 mg / L.

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