Deep fluorine removal agent and application thereof in wastewater of photovoltaic industry

Abstract

The invention discloses a deep fluorine removal agent and application thereof in wastewater in the photovoltaic industry, and belongs to the technical field of fluorine-containing wastewater treatment.The deep fluorine removal agent is obtained by conducting coordination on cross-linked hybrid chitosan microspheres and lanthanum ions to obtain composite microspheres and then synthesizing zirconium-based MOF on the composite microspheres through a hydrothermal synthesis method. The pore channels of the MOF facilitate the passing of fluorine ions but not the passing of sulfate ions, play a certain barrier role, facilitate the enrichment of the fluorine ions on the surfaces of the composite microspheres and the selective adsorption of the lanthanum ions on the fluorine ions, so that the fluorine ions are fixed, and the combination stability of the fluorine ions and the lanthanum ions is greater than that of the sulfate ions. The sulfate ions are in disadvantage when competitive adsorption with the fluorine ions, the selectivity of the deep fluorine removal agent to the fluorine ions is improved, the magnesium ions can be combined with the fluorine ions to generate complexes and can be combined with the sulfate ions to generate soluble magnesium sulfate, and interference of the sulfate ions is reduced through cooperation of the magnesium ions and the sulfate ions.

Description

Technical Field

[0001] The present invention belongs to the technical field of fluoride-containing wastewater treatment, and specifically relates to a deep defluorinating agent and its application in photovoltaic industrial wastewater. Background Art

[0002] At present, effective methods for removing fluoride ions from wastewater include ion exchange method, membrane method, adsorption method, chemical reagent method, etc. The ion exchange method is suitable for small-volume and low-concentration wastewater, but when treating large-volume and high-concentration fluoride-containing wastewater, it has no advantages in terms of treatment cost and operation efficiency; membrane technologies such as nanofiltration, reverse osmosis, and electrodialysis, although having good treatment effects, have high costs and require high operation and management experience, and problems may often occur during operation, and the biggest problem is that the produced concentrated water also needs to be treated; the adsorption method uses high specific surface area adsorbents such as activated carbon and clay, which is only applicable to low-concentration fluoride-containing wastewater and is also not economical and operable for large-volume and high-concentration wastewater; currently, the treatment effects of chemical reagents on the market such as activated alumina, aluminum sulfate, and silicic acid hydrogel are not satisfactory, and the effluent effect cannot be stable while the dosage is large.

[0003] The Chinese patent application with the publication number CN116062941B discloses a method for synergistic defluorination and dechlorination of high-fluoride and high-chloride wastewater in the photovoltaic industry. By adding manganese element to the iron-containing sludge after Fenton reaction for conditioning, the iron element in the iron-containing sludge exists in the form of amorphous FeOOH, which has redox characteristics and certain electron transfer ability. The iron and manganese elements are reduced to low valence states during the carbonization process, the electron migration and transformation ability is enhanced, and the surface functional groups of the carbon material are enriched and the conductivity of the carbon material is improved, which promotes the removal of chloride ions by capacitive deionization technology; in addition, divalent iron directionally catalyzes potassium permanganate, a strong oxidant, to destroy the structure of the organic matter mainly composed of highly polymerized extracellular polymers in the iron sludge, disperse the sludge particles, and form a porous high specific surface area structure during the drying and carbonization process, improving the physical and chemical adsorption ability.

[0004] In the above treatment process, the iron-manganese doped sludge carbon material electrode can remove chloride ions and fluoride ions through redox reactions, but cannot effectively remove sulfate ions in the wastewater. The content of sulfate ions in photovoltaic wastewater is relatively high. High-concentration sulfate ions may compete for adsorption sites with fluoride ions, reducing the defluorination efficiency. Moreover, sulfate and calcium ions will form calcium sulfate precipitation, covering the active components of the defluorinating agent and affecting the efficiency of deep defluorination. Summary of the Invention

[0005] The object of the present invention is to provide a deep defluorinating agent and its application in photovoltaic industrial wastewater. By loading lanthanum ions on the surface of cross-linked hybrid chitosan microspheres and generating zirconium-based MOF, the high selectivity of the deep defluorinating agent for fluoride ions in photovoltaic industrial wastewater is improved.

[0006] The object of the present invention can be achieved by the following technical solutions:

[0007] A deep defluorinating agent is prepared by the following steps:

[0008] Step 1: Hybrid chitosan powder and magnesium citrate hydrate are compounded to obtain magnesium-loaded hybrid chitosan microspheres, and formaldehyde, glutaraldehyde and magnesium-loaded hybrid chitosan microspheres are cross-linked together through chemical cross-linking to obtain cross-linked hybrid chitosan microspheres.

[0009] Step 2: Lanthanum nitrate is loaded on the cross-linked hybrid chitosan microspheres by ion coordination to obtain composite microspheres, and zirconium-based MOF is generated on the composite microspheres by hydrothermal synthesis to obtain the deep defluorinating agent.

[0010] Further, the cross-linked hybrid chitosan microspheres are prepared by the following steps:

[0011] The magnesium-loaded hybrid chitosan microspheres and acetic acid solution with a concentration of 2 wt% are added to a reaction kettle, stirred at 40 - 45 °C and 300 - 500 r / min for 30 - 40 min, liquid paraffin and Span-80 are added, stirred at 60 - 65 °C and 400 - 500 r / min for 40 - 50 min, a formaldehyde solution with a concentration of 37 vol% is dropped in, reacted at 35 - 40 °C for 60 - 70 min, then a glutaraldehyde solution with a concentration of 50 vol% is dropped in, reacted at 50 - 60 °C for 4 - 5 h, the pH value is adjusted to 9 with sodium hydroxide solution, reacted for 30 - 40 min, purified, suction filtered, washed, and dried to obtain the cross-linked hybrid chitosan microspheres.

[0012] Further, the dosage ratio of the magnesium-loaded hybrid chitosan microspheres, acetic acid, liquid paraffin, Span-80, formaldehyde solution and glutaraldehyde solution is 10 - 15 g : 500 - 700 mL : 700 - 800 mL : 50 - 60 mL : 70 - 75 mL : 4 - 5 mL.

[0013] Further, the magnesium-loaded hybrid chitosan microspheres are prepared by the following steps:

[0014] The hybrid chitosan powder, magnesium citrate hydrate and acetic acid solution with a concentration of 2 vol% are mixed evenly and then dropped into a sodium hydroxide solution with a concentration of 1 mol / L at 20 - 25 °C and 200 - 300 r / min, reacted for 4 - 5 h, filtered, washed to obtain the magnesium-loaded hybrid chitosan microspheres.

[0015] Furthermore, the dosage ratio of the hybrid chitosan powder, magnesium citrate hydrate, acetic acid solution and sodium hydroxide solution is 10 - 20 g : 5 - 10 g : 1 - 2 L : 5 - 10 L.

[0016] Furthermore, the hybrid chitosan powder is prepared by the following steps:

[0017] Add chitosan, acetic acid solution, sodium phosphate and deionized water into a reaction kettle, add tetraethyl orthosilicate into the reaction kettle under the condition of 500 - 600 r / min, react for 18 - 20 h under the conditions of 50 - 70 °C and 500 - 600 r / min, filter, wash, dry and grind to obtain the hybrid chitosan powder.

[0018] Furthermore, the dosage ratio of chitosan, acetic acid solution, sodium phosphate, deionized water and tetraethyl orthosilicate is 18 - 20 g : 1.2 - 1.5 L : 240 - 250 g : 1.5 - 2 L : 150 g - 160 g.

[0019] Furthermore, the composite microspheres are prepared by the following steps:

[0020] Add the crosslinked hybrid chitosan microspheres and lanthanum nitrate solution with a concentration of 0.02 mol / L into a reaction kettle, react for 3 - 4 h under the conditions of 40 - 45 °C and 300 - 500 r / min, filter, wash, dry to obtain the composite microspheres.

[0021] Furthermore, the dosage ratio of the crosslinked hybrid chitosan microspheres and lanthanum nitrate solution is 8 - 12 g : 1 - 1.2 L.

[0022] Furthermore, the deep defluorination agent is prepared by the following steps:.

[0023] Add zirconium chloride, composite microspheres and N,N - dimethylformamide into a reaction kettle, ultrasonically disperse for 30 - 40 min, mix terephthalic acid and N,N - dimethylformamide evenly and then add them into the reaction kettle, ultrasonically disperse for 30 - 40 min, react for 24 - 26 h under the condition of 100 - 110 °C, cool to room temperature, filter, wash, dry to obtain the deep defluorination agent.

[0024] Furthermore, the dosage ratio of zirconium chloride, composite microspheres, terephthalic acid and N,N - dimethylformamide is 12 - 16 g : 8 - 12 g : 12 - 15 g : 0.95 - 1.06 L.

[0025] Application of a deep defluorination agent in photovoltaic industrial wastewater.

[0026] Advantages of the present invention:

[0027] 1. In the present invention, the deep defluorination agent is obtained by coordinating cross-linked hybrid chitosan microspheres with lanthanum ions to obtain composite microspheres, and then synthesizing zirconium-based MOF on the composite microspheres through a hydrothermal synthesis method. The pores of the MOF facilitate the passage of fluoride ions but not sulfate ions, playing a certain blocking role, which is conducive to the enrichment of fluoride ions on the surface of the composite microspheres. Lanthanum ions selectively adsorb fluoride ions, thereby fixing the fluoride ions. The stability of the combination of fluoride ions and lanthanum ions is greater than that of sulfate ions. Sulfate ions are at a disadvantage in competing for adsorption with fluoride ions. The highly selective adsorption of lanthanum ions improves the selectivity of the deep defluorination agent for fluoride ions. Magnesium ions can combine with fluoride ions to form complexes and combine with sulfate ions to form soluble magnesium sulfate. The two work together to reduce the interference of sulfate ions and form a structure for gradient defluorination. At the same time, the bond energy of the Zr-F bond is relatively large and can also combine with fluoride ions. In the photovoltaic industry wastewater, it reduces the interference of sulfate ions and improves the selectivity for fluoride ions, playing an efficient defluorination role.

[0028] 2. In the present invention, first, tetraethyl orthosilicate is used as a silicon source to synthesize silica, which is hybridized with chitosan. The silanol groups of silica and the amino groups of chitosan form hydrogen bonds, which can not only increase the porosity but also enhance the mechanical strength of the hybrid chitosan powder. Then, a phase inversion method is used to prepare magnesium-loaded hybrid chitosan microspheres to maintain the integrity of the shell structure of the magnesium-loaded hybrid chitosan microspheres and prevent the microspheres from swelling and collapsing under acidic conditions. Then, it is cross-linked with formaldehyde and glutaraldehyde to form a Schiff base cross-linked network to obtain cross-linked hybrid chitosan microspheres, further inhibiting the protonation swelling of the cross-linked hybrid chitosan microspheres under acidic conditions, ensuring the integrity of the structure, making the deep defluorination agent applicable in a relatively wide pH range and facilitating reclamation.

[0029] 3. In the present invention, silica is doped into chitosan to form magnesium-loaded hybrid chitosan microspheres. Compared with pure chitosan, its specific surface area is increased. Then, cross-linking is carried out to obtain cross-linked hybrid chitosan microspheres, increasing the roughness of the surface of the cross-linked hybrid chitosan microspheres. Then, lanthanum ions are loaded on the cross-linked hybrid chitosan microspheres. The increased specific surface area can improve the loading rate of lanthanum ions and also provide more sites for the subsequent synthesis of zirconium-based MOF, thereby making the defluorination efficiency of the deep defluorination agent higher, and the components play a synergistic role. Detailed implementation manners

[0030] Next, specific embodiments of the present invention will be combined to clearly and completely describe the technical solutions 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. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0031] Example 1: This example provides a deep defluorination agent, which is prepared through the following steps:

[0032] S1: Add 19 g of chitosan and 1.35 L of acetic acid solution into a reaction kettle, then add 245 g of sodium phosphate and 1.75 L of deionized water. Add 155 g of tetraethyl orthosilicate into the reaction kettle under the condition of 550 r / min. React at 60 °C and 550 r / min for 19 h, filter, and wash the precipitate alternately with ethanol and distilled water until it is neutral. Dry to constant weight, grind, and obtain hybrid chitosan powder.

[0033] S2: Mix 15 g of hybrid chitosan powder, 7.5 g of magnesium citrate hydrate, and 1.5 L of acetic acid solution with a concentration of 2 vol% evenly, and then drop the mixture into 7.5 L of sodium hydroxide solution with a concentration of 1 mol / L under the conditions of 22 °C and 250 r / min. React for 4.5 h, and prepare magnesium-loaded hybrid chitosan microspheres by the phase inversion method. Centrifuge and filter, and wash the precipitate with deionized water until it is neutral to obtain magnesium-loaded hybrid chitosan microspheres.

[0034] S3: Add 12.5 g of magnesium-loaded hybrid chitosan microspheres and 600 mL of acetic acid solution with a concentration of 2 wt% into a reaction kettle, stir at 42 °C and 400 r / min for 35 min, add 750 mL of liquid paraffin and 55 mL of Span-80 as an emulsifier, stir at 62 °C and 450 r / min for 45 min, drop in 72.5 mL of formaldehyde solution with a concentration of 37 vol%, react at 37 °C for 65 min, then drop in 4.5 mL of glutaraldehyde solution with a concentration of 50 vol%, react at 55 °C for 4.5 h, adjust the pH value to 9 with sodium hydroxide solution, and react for 35 min. The amino groups on the magnesium-loaded hybrid chitosan microspheres react with the aldehyde groups on formaldehyde and glutaraldehyde to undergo Schiff base reaction and crosslinking. Extract with acetone in a Soxhlet extractor for 1 h, filter by suction, wash with acetone 4 times, and vacuum dry at 85 °C to constant weight to obtain crosslinked hybrid chitosan microspheres.

[0035] S4: Add 10 g of crosslinked hybrid chitosan microspheres and 1.1 L of lanthanum nitrate solution with a concentration of 0.02 mol / L into a reaction kettle, react at 42 °C and 400 r / min for 3.5 h. The hydroxyl groups on the crosslinked hybrid chitosan microspheres react with lanthanum ions to undergo a coordination reaction. Centrifuge and filter, wash with deionized water until it is neutral, and vacuum freeze-dry to obtain composite microspheres.

[0036] S5: Add 14 g of zirconium chloride, 10 g of composite microspheres, and 950 mL of N,N-dimethylformamide into a reaction kettle, ultrasonically disperse for 35 min. After mixing 13.5 g of terephthalic acid and 55 mL of N,N-dimethylformamide evenly, add them into the reaction kettle and ultrasonically disperse for 35 min. React at 105 °C for 25 h. Use the hydrothermal synthesis method to generate zirconium-based MOF on the composite microspheres. Cool to room temperature, filter, wash 4 times with N,N-dimethylformamide and absolute ethanol respectively, and dry at 82 °C for 12 h to obtain a deep defluorination agent.

[0037] Example 2: This example provides a deep defluorination agent, which is prepared through the following steps:

[0038] S1: Add 18 g of chitosan and 1.2 L of acetic acid solution into a reaction kettle, then add 240 g of sodium phosphate and 1.5 L of deionized water. Add 150 g of tetraethyl orthosilicate into the reaction kettle under the condition of 500 r / min. React at 50 °C and 500 r / min for 18 h. Filter, and wash the precipitate alternately with ethanol and distilled water until it is neutral. Dry to constant weight and grind to obtain hybrid chitosan powder.

[0039] S2: After mixing 10 g of hybrid chitosan powder, 5 g of magnesium citrate hydrate, and 1 L of acetic acid solution with a concentration of 2 vol% evenly, drop them into 5 L of sodium hydroxide solution with a concentration of 1 mol / L under the conditions of 20 °C and 200 r / min, and react for 4 h. Use the phase inversion method to prepare magnesium-loaded hybrid chitosan microspheres. Centrifuge and filter, and wash the precipitate with deionized water until it is neutral to obtain magnesium-loaded hybrid chitosan microspheres.

[0040] S3: Add 10 g of magnesium-loaded hybrid chitosan microspheres and 500 mL of acetic acid solution with a concentration of 2 wt% into a reaction kettle, stir at 40 °C and 300 r / min for 30 min. Add 700 mL of liquid paraffin and 50 mL of Span-80 as an emulsifier, stir at 60 °C and 400 r / min for 40 min, drop 70 mL of formaldehyde solution with a concentration of 37 vol%, react at 35 °C for 60 min, then drop 4 mL of glutaraldehyde solution with a concentration of 50 vol%, react at 50 °C for 4 h, adjust the pH value to 9 with sodium hydroxide solution, and react for 30 min. The amino groups on the magnesium-loaded hybrid chitosan microspheres react with the aldehyde groups on formaldehyde and glutaraldehyde to undergo a Schiff base reaction and crosslink. Extract with acetone in a Soxhlet extractor for 1 h, filter by suction, wash 3 times with acetone, and vacuum dry to constant weight at 80 °C to obtain crosslinked hybrid chitosan microspheres.

[0041] S4: Add 8 g of cross-linked hybrid chitosan microspheres and 1 L of lanthanum nitrate solution with a concentration of 0.02 mol / L into a reaction kettle, react for 3 h under the conditions of 40 °C and 300 r / min. The hydroxyl groups on the cross-linked hybrid chitosan microspheres undergo a coordination reaction with lanthanum ions. Then, centrifuge and filter, wash with deionized water until neutral, and vacuum freeze-dry to obtain composite microspheres.

[0042] S5: Add 12 g of zirconium chloride, 8 g of composite microspheres and 900 mL of N,N-dimethylformamide into a reaction kettle, ultrasonically disperse for 30 min. After mixing 12 g of terephthalic acid and 50 mL of N,N-dimethylformamide evenly, add them into the reaction kettle and ultrasonically disperse for 30 min. React at 100 °C for 24 h. Use the hydrothermal synthesis method to generate zirconium-based MOF on the composite microspheres. Cool to room temperature, filter, wash 3 times with N,N-dimethylformamide and absolute ethanol respectively, and dry at 80 °C for 12 h to obtain a deep defluorination agent.

[0043] Example 3: This example provides a deep defluorination agent, which is prepared through the following steps:

[0044] S1: Add 20 g of chitosan and 1.5 L of acetic acid solution into a reaction kettle, then add 250 g of sodium phosphate and 2 L of deionized water. Add 160 g of tetraethyl orthosilicate into the reaction kettle under the condition of 600 r / min, and react at 70 °C and 600 r / min for 20 h. Filter, and wash the precipitate alternately with ethanol and distilled water until neutral, dry to constant weight, and grind to obtain hybrid chitosan powder.

[0045] S2: Mix 20 g of hybrid chitosan powder, 10 g of magnesium citrate hydrate and 2 L of acetic acid solution with a concentration of 2 vol% evenly, and then dropwise add them into 10 L of sodium hydroxide solution with a concentration of 1 mol / L at 25 °C and 300 r / min. React for 5 h, use the phase inversion method to prepare magnesium-loaded hybrid chitosan microspheres, centrifuge and filter, and wash the precipitate with deionized water until neutral to obtain magnesium-loaded hybrid chitosan microspheres.

[0046] S3: Add 15 g of magnesium-loaded hybrid chitosan microspheres and 700 mL of acetic acid solution with a concentration of 2 wt% into a reaction kettle, stir for 40 min under the conditions of 45 °C and 500 r / min, add 800 mL of liquid paraffin and 60 mL of Span-80 as an emulsifier, stir for 50 min under the conditions of 65 °C and 500 r / min, dropwise add 75 mL of formaldehyde solution with a concentration of 37 vol%, react for 70 min under the condition of 40 °C, then dropwise add 5 mL of glutaraldehyde solution with a concentration of 50 vol%, react for 5 h under the condition of 60 °C, adjust the pH value to 9 with sodium hydroxide solution, react for 40 min, the amino groups on the magnesium-loaded hybrid chitosan microspheres react with the aldehyde groups on formaldehyde and glutaraldehyde to undergo Schiff base reaction and crosslinking, extract with acetone in a Soxhlet extractor for 1 h, filter by suction, wash with acetone 5 times, and vacuum dry at 90 °C until constant weight to obtain crosslinked hybrid chitosan microspheres.

[0047] S4: Add 12 g of crosslinked hybrid chitosan microspheres and 1.2 L of lanthanum nitrate solution with a concentration of 0.02 mol / L into a reaction kettle, react for 4 h under the conditions of 45 °C and 500 r / min, the hydroxyl groups on the crosslinked hybrid chitosan microspheres react with lanthanum ions to undergo coordination reaction, centrifuge and filter, wash with deionized water until neutral, and vacuum freeze-dry to obtain composite microspheres.

[0048] S5: Add 16 g of zirconium chloride, 12 g of composite microspheres and 1000 mL of N,N-dimethylformamide into a reaction kettle, ultrasonically disperse for 40 min, mix 15 g of terephthalic acid and 60 mL of N,N-dimethylformamide evenly and then add them into the reaction kettle, ultrasonically disperse for 40 min, react for 26 h under the condition of 110 °C, use hydrothermal synthesis method to generate zirconium-based MOF on the composite microspheres, cool to room temperature, filter, wash 5 times with N,N-dimethylformamide and absolute ethanol respectively, and dry at 85 °C for 12 h to obtain a deep defluorination agent.

[0049] Comparative Example 1: On the basis of Example 1, use chitosan powder to replace the magnesium-loaded hybrid chitosan microspheres in step S3, and keep the rest of the steps unchanged to prepare a deep defluorination agent.

[0050] Comparative Example 2: On the basis of Example 1, use the magnesium-loaded hybrid chitosan microspheres prepared in step S2 to replace the crosslinked hybrid chitosan microspheres in step S4, and keep the rest of the steps unchanged to prepare a deep defluorination agent.

[0051] Comparative Example 3: On the basis of Example 1, use the magnesium-loaded hybrid chitosan microspheres prepared in step S2 to replace the composite microspheres in step S5, and keep the rest of the steps unchanged to prepare a deep defluorination agent.

[0052] Comparative Example 4: On the basis of Example 1, without going through step S5, the composite microspheres prepared in step S4 are the deep defluorination agent.

[0053] The performance tests were carried out on the deep defluorination agents prepared in Examples 1 - 3 and Comparative Examples 1 - 3:

[0054] Defluorination performance test: The method for determining the fluoride ion concentration was to use a fluoride ion selective electrode method to measure the fluoride ion concentration in the wastewater:

[0055] (1) Prepare the total ion strength adjustment buffer (TISAB): Weigh 58.8 g of sodium citrate dihydrate and 85 g of sodium nitrate and place them in a beaker. Stir well to dissolve, adjust the pH value to 5 - 6, and make up the volume to 1000 mL.

[0056] (2) Prepare the fluoride ion standard solution: Take 10 mL of sodium fluoride and place it in a 100 mL volumetric flask. Add 10 mL of the total ion strength buffer to prepare a sodium fluoride solution with a concentration of 100 mg / L. Similarly, prepare sodium fluoride solutions with concentrations of 1 mg / L, 10 mg / L, 50 mg / L, 500 mg / L, and 1000 mg / L respectively.

[0057] (3) Measure the concentration: Install the fluoride ion selective electrode and the 232 - 01 type calomel reference electrode on the ion meter. Place the above sodium fluoride solutions with different concentrations on a supporting stirrer, add a rotor, measure each group of solutions three times, and take the average value.

[0058] The test experimental steps are as follows:

[0059] 1. At room temperature, add 500 mL of photovoltaic wastewater treated with lime (fluoride ion concentration is 30.5 mg / L, sulfate ion concentration is 101.2 mg / L) to a 2 L plexiglass cup, and measure the fluoride ion concentration in the initial photovoltaic wastewater;

[0060] 2. Add 20% sodium hydroxide and 10% hydrochloric acid solution to adjust the pH of the water sample;

[0061] 3. Respectively add the deep defluorination agents prepared in Examples 1 - 3 and Comparative Examples 1 - 3 with a dosage of 4 g / L, and stir at a speed of 180 r / min for 10 min;

[0062] 4. Add the coagulant PAM and stir rapidly at 250 r / min for 1 min; stir at 250 r / min for 5 min; adjust the speed to 50 r / min and stir slowly for 15 min. After standing for 1 h, take the supernatant and filter it with a 0.45 μm membrane to measure the fluoride ion concentration after treatment. The calculation formula for the defluorination rate (η) is as follows: η = (C o - C e ) / C o ×100%, where: C o is the initial fluoride ion concentration; C eis the fluoride ion concentration after adsorption equilibrium.

[0063] Regeneration performance: For the deep defluorination agent saturated in the fluoride ion solution with a concentration of 10 mg / L -1 the regenerated deep defluorination agent is obtained by stirring and soaking in 0.5 mol / L -1 sodium hydroxide solution for 6 h, followed by washing and drying, and the test is repeated 10 times.

[0064] Table 1 Summary of performance tests

[0065]

[0066] As can be seen from Table 1, in Comparative Examples 1 - 4, chitosan powder was used instead of magnesium-loaded hybrid chitosan microspheres in step S3 of Comparative Example 1, magnesium-loaded hybrid chitosan microspheres prepared in step S2 were used instead of crosslinked hybrid chitosan microspheres in step S4 of Comparative Example 2, magnesium-loaded hybrid chitosan microspheres prepared in step S2 were used instead of composite microspheres in step S5 of Comparative Example 3, and Comparative Example 4 did not go through step S5, and the composite microspheres prepared in step S4 were used as the deep defluorination agent. This shows that the magnesium ions in the magnesium-loaded hybrid chitosan microspheres can play a role in adsorbing fluoride ions, and the crosslinked hybrid chitosan microspheres after crosslinking hybridization have a higher removal rate of fluoride ions. This may be because the surface roughness of the crosslinked hybrid chitosan microspheres is higher, which improves the loading rate and thus affects the removal rate of fluoride ions. The coordination of lanthanum ions and zirconium-based MOF jointly improve the selectivity of the deep defluorination agent for fluoride ions, resulting in higher defluorination efficiency.

[0067] When the pH value is 9, the defluorination rate of Comparative Example 2 is not much different from that of Examples 1 - 3. When the pH value is 5, the defluorination rate of Comparative Example 2 is less than that of Examples 1 - 3. In step S4 of Comparative Example 2, magnesium-loaded hybrid chitosan microspheres prepared in step S2 were used instead of crosslinked hybrid chitosan microspheres, indicating that the crosslinked hybrid chitosan microspheres after hybridization are more stable under acidic conditions.

[0068] The adsorption capacity of the deep defluorination agents in Examples 1 - 3 is equivalent after being used 10 times and after being used 1 time. However, the adsorption capacity of Comparative Examples 1 - 3 is less after being used 10 times than after being used 1 time. In step S3 of Comparative Example 1, chitosan powder was used instead of magnesium-loaded hybrid chitosan microspheres, in step S4 of Comparative Example 2, magnesium-loaded hybrid chitosan microspheres prepared in step S2 were used instead of crosslinked hybrid chitosan microspheres, and in step S5 of Comparative Example 3, magnesium-loaded hybrid chitosan microspheres prepared in step S2 were used instead of composite microspheres. This may be because the silanol groups of silica and the amino groups of chitosan form hydrogen bonds, improving the mechanical strength. The crosslinked hybrid chitosan microspheres crosslinked with formaldehyde and glutaraldehyde have better integrity, and the two cooperate to improve the integrity of the composite microspheres, enabling repeated use.

[0069] It should be noted that, in this document, terms such as "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not explicitly listed, or further includes elements inherent to such process, method, article or device.

[0070] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention.

Claims

1. A deep defluorination agent, characterized in that, It is prepared through the following steps: Step 1: Hybrid chitosan powder and magnesium citrate hydrate are compounded to obtain magnesium-loaded hybrid chitosan microspheres, and formaldehyde, glutaraldehyde and the magnesium-loaded hybrid chitosan microspheres are cross-linked together through chemical cross-linking to obtain cross-linked hybrid chitosan microspheres; Step 2: Lanthanum nitrate is loaded on the cross-linked hybrid chitosan microspheres through ion coordination to obtain composite microspheres, and zirconium-based MOF is generated on the composite microspheres through hydrothermal synthesis to obtain a deep defluorination agent.

2. The deep defluorinating agent according to claim 1, characterized in that, The cross-linked hybrid chitosan microspheres described in Step 1 are prepared through the following steps: The magnesium-loaded hybrid chitosan microspheres and acetic acid solution with a concentration of 2 wt% are added to a reaction kettle, stirred at 40 - 45 °C and 300 - 500 r / min for 30 - 40 min, liquid paraffin and Span-80 are added, stirred at 60 - 65 °C and 400 - 500 r / min for 40 - 50 min, a formaldehyde solution with a concentration of 37 vol% is dropped in, reacted at 35 - 40 °C for 60 - 70 min, then a glutaraldehyde solution with a concentration of 50 vol% is dropped in, reacted at 50 - 60 °C for 4 - 5 h, the pH value is adjusted to 9 with sodium hydroxide solution, reacted for 30 - 40 min, purified, filtered, washed, and dried to obtain cross-linked hybrid chitosan microspheres.

3. The deep defluorinating agent according to claim 2, characterized in that, The dosage ratio of the magnesium-loaded hybrid chitosan microspheres, acetic acid, liquid paraffin, Span-80, formaldehyde solution and glutaraldehyde solution is 10 - 15 g : 500 - 700 mL : 700 - 800 mL : 50 - 60 mL : 70 - 75 mL : 4 - 5 mL.

4. The deep defluorinating agent according to claim 3, characterized in that, The magnesium-loaded hybrid chitosan microspheres are prepared through the following steps: The hybrid chitosan powder, magnesium citrate hydrate and acetic acid solution with a concentration of 2 vol% are mixed evenly, and then dropped into a sodium hydroxide solution with a concentration of 1 mol / L at 20 - 25 °C and 200 - 300 r / min, reacted for 4 - 5 h, filtered, and washed to obtain magnesium-loaded hybrid chitosan microspheres.

5. The deep defluorinating agent according to claim 4, characterized in that, The dosage ratio of the hybrid chitosan powder, magnesium citrate hydrate, acetic acid solution and sodium hydroxide solution is 10 - 20 g : 5 - 10 g : 1 - 2 L : 5 - 10 L.

6. The deep defluorinating agent according to claim 5, characterized in that, The hybrid chitosan powder is prepared through the following steps: Chitosan, acetic acid solution, sodium phosphate and deionized water are added to a reaction kettle, tetraethyl orthosilicate is added to the reaction kettle at 500 - 600 r / min, reacted at 50 - 70 °C and 500 - 600 r / min for 18 - 20 h, filtered, washed, dried, and ground to obtain hybrid chitosan powder.

7. The deep defluorinating agent according to claim 6, characterized in that, The dosage ratio of chitosan, acetic acid solution, sodium phosphate, deionized water and tetraethyl orthosilicate is 18 - 20 g : 1.2 - 1.5 L : 240 - 250 g : 1.5 - 2 L : 150 g - 160 g.

8. The deep defluorinating agent according to claim 1, wherein, The composite microspheres described in Step 2 are prepared through the following steps: The cross-linked hybrid chitosan microspheres and lanthanum nitrate solution with a concentration of 0.02 mol / L are added to a reaction kettle, reacted at 40 - 45 °C and 300 - 500 r / min for 3 - 4 h, filtered, washed, and dried to obtain composite microspheres; The dosage ratio of the cross-linked hybrid chitosan microspheres to the lanthanum nitrate solution is 8-12 g: 1-1.2 L.

9. The deep defluorinating agent according to claim 1, characterized in that, The deep defluorination agent described in step two is prepared by the following steps: Add zirconium chloride, composite microspheres and N,N-dimethylformamide into a reaction kettle, ultrasonically disperse for 30-40 min, add terephthalic acid and N,N-dimethylformamide after mixing evenly into the reaction kettle, ultrasonically disperse for 30-40 min, react at 100-110 °C for 24-26 h, cool to room temperature, filter, wash, and dry to obtain the deep defluorination agent; The dosage ratio of the zirconium chloride, composite microspheres, terephthalic acid and N,N-dimethylformamide is 12-16 g: 8-12 g: 12-15 g: 0.95-1.06 L.

10. Application of a deep defluorination agent according to any one of claims 1-9 in photovoltaic industrial wastewater.

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