A surface lanthanum-rich oxyhydroxide modified shaped zirconium fumarate metal organic framework fluoride removal agent, a preparation method and application thereof

Abstract

This invention discloses a molten zirconium fumarate metal-organic framework (MOF) defluorinating agent modified with lanthanum oxyhydroxylate on its surface, its preparation method, and its application. It relates to the field of defluorination technology and aims to solve the problems of difficult engineering loading of existing MOF powder defluorinating agents, complex processes for some bimetallic co-coordinated MOFs, and insufficient adaptability for continuous operation. The defluorinating agent is a molten particle comprising a zirconium fumarate metal-organic framework, an inorganic binder phase, and a lanthanum oxyhydroxylate active phase loaded on the surface of the molten particle and the inner surface of the pores. The defluorinating agent of this invention combines the structural stability of the zirconium-based metal-organic framework, the high affinity of the surface lanthanum active sites for fluoride ions, and the engineering application advantages of low pressure drop, easy loading, and easy regeneration of the molten particle. It is suitable for deep defluorination treatment of semiconductor wastewater, photovoltaic wastewater, lithium battery production and recycling wastewater, metallurgical wastewater, and high-fluoride groundwater.

Description

Technical Field

[0001] This invention relates to a molten zirconium fumarate metal-organic framework defluorinating agent with a surface-modified lanthanum oxyhydroxylide, its preparation method, and its application, belonging to the field of defluorination technology. Background Technology

[0002] Fluoride-containing wastewater originates widely from semiconductor, photovoltaic, lithium battery production and recycling, glass etching, metallurgy, chemical, and groundwater environments. For water bodies with low to medium concentrations of fluoride, adsorption methods show promising application prospects due to their simple process and ease of deep purification.

[0003] Zirconium-based metal-organic frameworks (MOFs) have attracted attention in the field of defluorination due to their high water stability and strong affinity for fluoride ions. However, existing Zrconium-based MOF defluorination materials still face some practical application obstacles: First, the fine particle size of the powder materials makes them prone to pressure drop fluctuations, leakage, or difficulties in solid-liquid separation when used directly in engineering devices; second, some schemes improve recyclability through magnetic composites or organic polymer carrier composites, but these may result in complex structures, insufficient exposure of active sites, or complex scale-up processes; third, while some bimetallic co-coordinated MOF schemes improve defluorination activity, they may also lead to problems such as high rare earth element consumption, reliance on organic solvents in the synthesis system, difficulties in molding, or the need for further optimization of regeneration stability.

[0004] Fixed-bed adsorption is one of the more engineering-valuable methods for continuous industrial defluorination. Compared with powder adsorption, fixed-bed processes place greater emphasis on the particle strength, pressure drop control, packing performance, regeneration performance, and metal leaching control of the adsorbent.

[0005] Therefore, it is necessary to develop a molded defluorinating agent that is suitable for fixed-bed use, has a stable structure, a greener preparation process, and combines the stability of the zirconium-based framework with the fluorinophilicity of the lanthanum active sites. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a molten zirconium fumarate metal-organic framework defluorinating agent with surface-modified lanthanum oxyhydroxylide, its preparation method, and its application, so as to solve the problems of difficult engineering filling of existing MOF powder defluorinating agents, complex process of some bimetallic co-coordinated MOFs, and insufficient adaptability for continuous operation.

[0007] To achieve the above objectives, the present invention is implemented using the following technical solution: In a first aspect, the present invention provides a method for preparing a molten zirconate fumarate metal-organic framework defluorinating agent modified with lanthanum oxide hydroxylate on its surface, comprising: Zirconic fumarate metal-organic framework powder was prepared in a water-organic acid system. Zirconium fumarate metal-organic framework powder is mixed with inorganic binder and deionized water, then molded and dried to obtain a molding precursor. The molding precursor is immersed in a lanthanum salt aqueous solution to form a lanthanum oxide hydroxylate active phase in situ on the surface of the molding precursor. After washing and drying, a molten zirconium fumarate metal-organic framework defluorinating agent with a surface rich in lanthanum oxide hydroxylate is obtained.

[0008] Furthermore, the preparation of zirconium fumarate metal-organic framework powder in a water-organic acid system includes: Zirconium oxychloride octahydrate and fumaric acid were added to a water-organic acid solution, stirred, heated and crystallized, and then filtered, washed and dried to obtain zirconium fumaric acid metal-organic framework powder.

[0009] Furthermore, the molar ratio of zirconium oxychloride octahydrate to fumaric acid ranges from 5:1 to 25; And / or, the organic acid in the water-organic acid solution is a monocarboxylic acid, and the molar ratio of the organic acid in the water-organic acid solution to the metallic zirconium in zirconium oxychloride octahydrate is 10~200:1.

[0010] Furthermore, the conditions for the thermal crystallization include reacting at 90~100℃ for 8~10h; And / or, the drying temperature range is 70~100℃.

[0011] Furthermore, the inorganic binder includes one or more of boehmite, silica sol, and starch; And / or, the molding method includes granulation molding or extrusion molding.

[0012] Furthermore, when the inorganic binder is boehmite, the amount of boehmite added is 5-10% of the mass of the zirconium fumarate metal-organic framework powder; When the inorganic binder is silica sol, the amount of silica sol added is 0.3-1% of the mass of the zirconium fumarate metal-organic framework powder; When the inorganic binder is starch, the amount of starch added is 10-20% of the mass of the zirconium fumarate metal-organic framework powder.

[0013] Furthermore, the lanthanum salt aqueous solution is an aqueous solution containing lanthanum nitrate and urea; And / or, the molar ratio of the molding precursor to lanthanum nitrate and urea is in the range of 1:0.1~10:1~100; And / or, the in-situ formation of the lanthanum oxyhydroxyl active phase on the surface of the molding precursor is achieved by uniform hydrolysis-reduction deposition, wherein the uniform hydrolysis-reduction deposition includes immersion at room temperature for 0.5-1.5 h followed by heating to 80-90 °C and holding at that temperature for 2-4 h.

[0014] Secondly, the present invention also provides a molten zirconium fumarate metal-organic framework defluorinator with a surface-enriched lanthanum oxyhydroxylide modified structure, which is prepared by the preparation method of the molten zirconium fumarate metal-organic framework defluorinator with a surface-enriched lanthanum oxyhydroxylide modified structure as described in any one of the first aspects, comprising a zirconium fumarate metal-organic framework, wherein the surface layer and the inner surface of the pores of the zirconium fumarate metal-organic framework are provided with a lanthanum oxyhydroxylide active phase.

[0015] Furthermore, the defluorinating agent is in granular form, the average particle size of the particles ranges from 0.3 to 2.0 mm, and the shape of the particles is one or more of spherical, cylindrical, annular, or multi-leaf shapes; And / or, the lanthanum oxyhydroxylide active phase is enriched in a region of 0.1 to 100 micrometers inward from the outer surface of the particles.

[0016] Thirdly, the present invention also provides an application of the surface-modified lanthanum oxide-rich shaped zirconium fumarate metal-organic framework defluorinating agent prepared by the method described in any one of the first aspects, including its use in fixed-bed defluorination, wherein the fixed-bed defluorination step includes: A molten zirconium fumarate metal-organic framework defluorinating agent modified with lanthanum oxyhydroxylate on the surface is filled into the adsorption column in the fixed bed process to obtain a packed bed. Fluoride-containing water is continuously passed through the packed bed to achieve continuous removal of fluoride ions from the water.

[0017] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: This invention employs a configuration of "zirconium fumarate metal-organic framework host + surface lanthanum oxyhydroxylate active phase". The lanthanum oxyhydroxylate active phase is formed on the surface of the incubator particles by post-deposition, rather than directly introducing lanthanum into the zirconium-based metal-organic framework lattice to form a bimetallic co-coordinated framework. This is beneficial to introduce highly fluoride-loving active sites on the surface while maintaining the stability of the zirconium fumarate framework. Furthermore, the zirconium fumarate metal-organic framework is prepared using a water-organic acid system, and the surface active phase is formed by post-deposition of lanthanum salt aqueous solution. The overall process is relatively green and suitable for further scale-up. This invention obtains fixed-bed suitable particles through a route of first forming and then surface enrichment with lanthanum. Compared with directly using powder materials, this is more conducive to controlling bed pressure drop, improving filling stability and reducing the risk of particle loss. The use of an inorganic binder phase for forming avoids the swelling or aging problems that may occur in organic polymer carriers during long-term water treatment, making it more suitable for continuous flow processes. Attached Figure Description

[0018] Figure 1This is a scanning electron microscope (SEM) image of the molten zirconium fumarate metal-organic framework defluorinating agent with surface-rich lanthanum oxyhydroxylide modified by Example 1 of the present invention, magnified to 10 micrometers. Figure 2 This is a scanning electron microscope (SEM) image of the molten zirconium fumarate metal-organic framework defluorinating agent with surface-rich lanthanum oxyhydroxylated modified zirconium fumarate prepared in Example 1 of the present invention, magnified to 200 nm. Detailed Implementation

[0019] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention. Example 1

[0020] This invention provides a method for preparing a molten zirconium fumarate metal-organic framework defluorinating agent modified with lanthanum oxide hydroxylate on its surface, comprising the following steps: S1. Preparation of zirconium fumarate metal-organic framework powder Weigh 3.22 g of zirconium oxychloride octahydrate and 1.16 g of fumaric acid, add them to a mixed solution of 80 mL of deionized water and 20 mL of formic acid, stir for 30 min, then transfer to a polytetrafluoroethylene-lined reactor and place in an oven at 95 °C for 8 h. After the reaction is complete, allow to cool naturally, filter and collect the solid, wash with deionized water until pH is neutral, then wash twice with ethanol to ensure thorough removal of impurities and unreacted substances, and dry at 80 °C to obtain zirconium fumarate metal-organic framework powder.

[0021] S2. Preparation of molding precursor Weigh 10.0g of the above zirconium fumarate metal-organic framework powder, 0.8g of pseudoboehmite, 2.0g of silica sol with a solid content of 30wt%, and 1.0g of starch. Add an appropriate amount of deionized water and knead until a uniform wet material is formed. Use rolling granulation to obtain granules, and then dry at 85℃ for 10h to obtain the molding precursor.

[0022] S3. Constructing a surface-rich lanthanum oxide hydroxylide active phase. 10.0 g of the molding precursor was added to 400 mL of an aqueous solution containing 4 g of lanthanum nitrate and 3 g of urea. After soaking at room temperature for 1 h, the temperature was raised to 85 °C and held for 3 h to allow the lanthanum salt to undergo uniform hydrolysis and deposition on the surface of the particles and the inner surface of the pores. In this embodiment, the molar ratio of the molding precursor to lanthanum nitrate and urea is in the range of 1:1.68:6.8 (ideally).

[0023] After the reaction was completed, the particles were removed, washed with deionized water until nearly neutral, and dried at 75°C for 8 h to obtain a shaped zirconium fumarate metal-organic framework defluorinating agent with surface-rich lanthanum oxyhydroxylide modification.

[0024] A scanning electron microscope (SEM) schematic diagram of the surface-modified zirconium fumarate metal-organic framework defluorinating agent prepared in this embodiment is shown below. Figure 1 and Figure 2 As shown in the figure, the surface of the defluorinating agent is uniformly covered with a coating layer composed of tiny particles ranging from a few nanometers to tens of nanometers. The particle boundaries are blurred, and the overall structure appears flocculent or spongy. This is a typical characteristic of LaOOH / La(OH)3 with low crystallinity or amorphous structure. This structure, despite its numerous defects and high activity, does not form a dense crystalline layer that blocks the pores, perfectly verifying the superiority of "controlled uniform hydrolysis." This explains why an 83% fluoride removal rate can be achieved within 30 minutes after modification.

[0025] Even magnified to 200 nm, the intergranular pores within the lanthanum hydroxylate deposition layer, as well as the intrinsic macroporous channels of the MOF particles that are not completely covered, are still clearly visible. The open hierarchical porous structure allows fluoride ions to diffuse smoothly to the internal zirconium sites even after the surface lanthanum layer is saturated, achieving a synergistic effect of "rapid capture of lanthanum on the outside and continued adsorption of zirconium on the inside". Example 2

[0026] The only difference between this embodiment and Example 1 is that the amount of lanthanum nitrate added in step S3 is adjusted to 1.3g, and the amount of urea added is adjusted to 0.96g. In this embodiment, the molar ratio of the molding precursor to lanthanum nitrate and urea is 1:0.55:2.18 (ideally). Example 3

[0027] This embodiment provides a method for preparing a molten zirconium fumarate metal-organic framework defluorinating agent with a surface-modified lanthanum oxide hydroxylide, comprising the following steps: S1. Preparation of zirconium fumarate metal-organic framework powder Weigh 3.22 g of zirconium oxychloride octahydrate and 1.16 g of fumaric acid, add them to a mixed solution of 80 mL of deionized water and 20 mL of acetic acid, stir for 30 min, then transfer to a polytetrafluoroethylene-lined reactor and place in an oven at 95 °C for 8 h. After the reaction is complete, allow to cool naturally, filter and collect the solid, wash with deionized water until pH is neutral, then wash twice with ethanol to ensure thorough removal of impurities and unreacted substances, and dry at 80 °C to obtain zirconium fumarate metal-organic framework powder.

[0028] S2. Preparation of molding precursor Weigh 10.0g of the above zirconium fumarate metal-organic framework powder, 0.8g of pseudoboehmite and 2.0g of silica sol with a solid content of 30 wt%, add an appropriate amount of deionized water and knead until a uniform wet material is formed. Roll granulation is used to obtain particles, which are then dried at 85℃ for 10h to obtain the molding precursor.

[0029] S3. Constructing a surface-rich lanthanum oxide hydroxylide active phase. Measure 400 mL of deionized water into a clean beaker. Accurately weigh 4.8 g of lanthanum chloride (LaCl3·6H2O, calculated at 12 g / L; if anhydrous, the weight needs to be converted) and add it to the water. Stir at room temperature until completely dissolved to obtain a clear 12 g / L lanthanum chloride solution.

[0030] Slowly add 10.0 g of the molding precursor to the above solution. Let stand or stir very slowly at room temperature (approximately 25°C) for 1 hour to ensure La… 3+ Ions diffuse fully and are uniformly adsorbed on the particle surface and within the pores.

[0031] After soaking for 1 hour, add 1 mol / L ammonium bicarbonate solution dropwise to the lanthanum chloride impregnation solution (containing particles) with slow stirring. Monitor the pH of the system in real time using a precision pH meter. Continue adding dropwise until the solution pH slowly rises to 8, then stop adding. The addition process should be slow to avoid localized high pH, ​​which could lead to rapid and uneven deposition. After reaching the desired pH, continue stirring at a very slow speed or allow to stand for 1 hour to ensure complete deposition. Remove the particles and soak or rinse them with plenty of deionized water. Repeat the washing process 3-5 times, maintaining a near-neutral pH. Drain the water and spread them evenly on a petri dish or tray.

[0032] Place in an oven and dry at 75°C for 8 hours (or until constant weight). Allow to cool naturally to room temperature to obtain the molded zirconium fumarate defluorinating agent modified with lanthanum oxyhydroxylate on the surface.

[0033] Comparative Example 1: This comparative example provides a defluorinating agent, the preparation method of which differs from that of Example 1 only in that steps S1 and S2 are performed, and the resulting molding precursor is used as the defluorinating agent.

[0034] Comparative Example 2: This comparative example provides a defluorinating agent, the preparation method of which differs from that of Example 1 only in that step S1 is performed, and the resulting zirconium fumarate metal-organic framework powder is used as the defluorinating agent.

[0035] Comparative Example 3: This comparative example provides a defluorinating agent, the preparation method of which includes the following steps: The shaped precursor obtained in step S2 of Example 1 was added to a 400 mL aqueous solution containing 4 g of lanthanum nitrate for simple physical impregnation and adsorption.

[0036] Simple physical impregnation and adsorption specifically include: Continuously stir magnetically (approximately 175 rpm) or intermittently oscillate at room temperature (around 25°C) to ensure full contact between the particles and the solution. The soaking time can be set to 4 hours to ensure adsorption equilibrium is reached. Separate the solid particles by filtration (or centrifugation) using a Buchner funnel. Quickly rinse the particle surface twice with approximately 20 mL of deionized water to remove free, unadsorbed lanthanum ions and prevent enrichment and crystallization during subsequent drying.

[0037] The wet particles were transferred to a petri dish and dried in an oven at 80°C for 6 hours until constant weight was achieved. After removal, they were placed in a desiccator and cooled to room temperature to obtain lanthanum-impregnated modified MOF particles, which were then used as a defluorinating agent.

[0038] Comparative Example 4: This comparative example provides a defluorinating agent, the only difference from Example 1 being that the amount of lanthanum nitrate added in step S3 is adjusted to 9g, and the amount of urea added is adjusted to 6g. In this comparative example, the molar ratio of the molding precursor to lanthanum nitrate and urea is in the range of 1:2.84:13.6 (ideally).

[0039] The performance of the defluorinating agents prepared in Examples 1-3 and Comparative Examples 1-4 was tested and analyzed below.

[0040] First, static adsorption defluorination tests were conducted on the defluorinating agents prepared in Examples 1-3 and Comparative Examples 1-4.

[0041] Test method: Measure 200 mL of a 20 mg / L fluoride ion working solution and transfer it to a 250 mL polyethylene conical flask. Accurately weigh 0.10 g of the defluorinating agent using an analytical balance, carefully add it to the conical flask, and gently shake to evenly disperse the adsorbent in the solution to obtain a suspension.

[0042] At room temperature, adjust the pH of the suspension to 6.0 with 0.1 mol / L HCl or NaOH solution and record the actual pH value.

[0043] Tightly stopper the conical flask and quickly place it in a thermostatic shaker. Set the temperature to 25℃ and the rotation speed to 180 rpm, and start timing. At 30 min and 120 min of shaking, respectively, use a syringe to draw approximately 5 mL of the suspension and immediately filter it through a 0.45 μm filter membrane into a clean, dry sample tube, then seal it for testing.

[0044] The residual fluoride ion concentration (mg / L) in the filtrate was determined using the fluoride ion selective electrode method. After adding an equal volume of total ionic strength adjustment buffer (TISAB), the potential value was measured, and the concentration was calculated by referring to the standard curve.

[0045] The theoretical maximum adsorption capacity is 40 mg / g.

[0046] The static adsorption capacity is calculated using the following expression: q e = (C0 - C e ) × V / m Where, q e The equilibrium adsorption capacity is expressed in mg / g, where C0 represents the initial fluoride ion concentration. e The value represents the fluoride ion concentration after equilibrium, in mg / L; V represents the solution volume, in L; and m represents the amount of defluorinating agent used, in g.

[0047] The removal rate η is calculated using the following expression: η = (C0 - C e ) / C0× 100% Where C0 represents the initial fluoride ion concentration, C e This indicates the fluoride ion concentration after equilibrium is reached, expressed in mg / L.

[0048] The results of the static adsorption defluorination test are shown in Table 1.

[0049] Table 1: Static adsorption defluorination test results of the defluorinating agents prepared in Examples 1-3 and Comparative Examples 1-4

[0050] As shown in Table 1, the removal rates of Example 1 at 30 min and 120 min were 83% and 96%, respectively, corresponding to adsorption capacities of 33.2 mg / g and 38.4 mg / g, both higher than those of unmodified granules and unformed powder. This indicates that the structural design of "formed zirconium fumarate MOF host + lanthanum-rich hydroxylate active phase on the surface" is beneficial to improving fluoride ion adsorption efficiency and site utilization. The formed particles have micron-level interconnected stacking pores and MOF intrinsic pores, allowing fluoride ions to diffuse rapidly to the inner and outer surfaces of the particles. Compared with the easily agglomerated unformed powder, the formed particles effectively avoid the embedding of active sites, significantly shortening the diffusion path and enabling a large number of sites to be reached within 30 min, thus exhibiting a rapid removal rate of 83%. The lanthanum hydroxylate (LaOOH / La(OH)3) layer grown in situ on the surface does not severely block the zirconium fumarate MOF channels, allowing the internal Zr-oxo clusters to still participate in adsorption, ensuring the continuous increase of subsequent adsorption capacity (reaching 96% at 120 min).

[0051] Comparing Examples 1, 2, and 4, it is shown that the amount of lanthanum nitrate and urea added does not necessarily improve adsorption performance with higher or lower amounts. Furthermore, compared to Example 3, lanthanum chloride and acetic acid also exhibited good adsorption performance, but lower than Example 1. In addition, Comparative Example 3 showed some adsorption effect through simple physical adsorption, but the adsorption performance was not high. Therefore, the uniform hydrolysis-reduction deposition method of Example 1 is superior to simple physical impregnation adsorption.

[0052] Through controlled homogeneous hydrolysis of urea and lanthanum nitrate, a highly dispersed and low-crystallinity lanthanum-rich hydroxyl compound thin layer was formed on the surface of MOF particles. The lanthanum sites exhibit strong Lewis acid-base interactions and ligand exchange capabilities with F⁻ (La–OH + F⁻ → La–F + OH⁻), and the positively charged surface generated after protonation of the hydroxyl groups further enhances electrostatic attraction. This active layer directly exposes a large number of high-energy lanthanum sites to the liquid-solid interface, preventing them from being buried deep within the micropores, significantly improving the effective site density and utilization rate. Therefore, the equilibrium adsorption capacity of the modified molded particles is much higher than that of unmodified molded particles and unformed powders.

[0053] The Zr6O4(OH)4 cluster in the zirconium fumarate MOF framework can adsorb fluorine via coordination with hydroxyl groups, but its quantity and accessibility are limited. After the surface lanthanum hydroxylate rapidly captures most of the fluoride ions as the main adsorption phase, the internal zirconium sites continue to drive deep removal, forming a relay-style synergistic mechanism of "external lanthanum rapid capture - internal zirconium continued adsorption". This structural design not only improves the initial adsorption rate (surface lanthanum dominant) but also maximizes the total site utilization, thereby achieving a higher adsorption capacity in the same time.

[0054] Next, the defluorinating agents prepared in Example 1 and Comparative Examples 1-3 were subjected to coexisting anions and dissolution tests, as well as average crushing strength tests.

[0055] The coexisting anions and dissolution test methods are as follows: Measure 200 mL containing SO4 2- Transfer 200 mg / L of 10 mg / L fluoride ion working solution into a clean 250 mL polyethylene conical flask.

[0056] Measure 200 mL containing HCO3 - Transfer 200 mg / L of 10 mg / L fluoride ion working solution into a clean 250 mL polyethylene conical flask.

[0057] Accurately weigh 0.10g of defluorinating agent using an analytical balance, carefully add it to the two conical flasks mentioned above, and gently shake to evenly disperse the defluorinating agent in the solution to obtain a suspension.

[0058] Adjust the pH of the suspension to 6.5 ± 0.2 using 0.1 mol / L HCl or NaOH solution, and record the actual pH value.

[0059] Tighten the stopper and place the bottle in a thermostatic shaker. Parameter settings: temperature 25±1℃, rotation speed 180 rpm (or according to the equipment's standard settings), start timing. Shake continuously for 60 minutes. At the end of 60 minutes of shaking, immediately use a syringe to draw approximately 5 mL of the suspension and filter it through a 0.45 μm filter membrane into a clean sample tube.

[0060] For the solutions in the two conical flasks, the residual fluoride concentration (mg / L) in the filtrate was determined using the fluoride ion selective electrode method. Then, 10-15 mL of the supernatant from the same batch of filtration was taken and placed into a clean polyethylene centrifuge tube. The concentrations of La and Zr in the filtrate (mg / L) were determined using ICP-OES.

[0061] The test results are shown in Table 2.

[0062] Table 2: Results of coexisting anions and dissolution tests of the defluorinating agents prepared in Examples 1 and Comparative Examples 1-3

[0063] As shown in Table 2, even in the presence of sulfate and bicarbonate ions, Example 1 maintained a high defluorination efficiency, with La and Zr dissolution concentrations in the supernatant after adsorption being only 0.011 mg / L and 0.001 mg / L, respectively, demonstrating good resistance to interference from coexisting anions and structural stability. In contrast, the defluorination effects of the molding precursor of Comparative Example 1, the zirconium fumarate metal-organic framework powder of Comparative Example 2, and the simple physical adsorption of lanthanum solution in Comparative Example 3 were all significantly worse than those of Example 1.

[0064] Then, the defluorinating agents prepared in Example 1 and Comparative Example 1 were subjected to fixed-bed breakthrough tests.

[0065] The testing method is as follows: The polyethylene adsorption column is vertically fixed to the iron frame, with a 200-mesh nylon screen laid flat at the bottom to prevent adsorbent leakage. Weigh 10.0g of defluorinating agent and slowly pour it into the column in batches (approximately 3g each time), gently tapping the column wall after each addition to ensure a uniform and compact bed. After filling, place another nylon screen on top to prevent water flow from causing the adsorbent to float and leak out.

[0066] A peristaltic pump introduces deionized water from bottom to top at a very low flow rate to slowly wet the bed and expel air bubbles. Once the bed is fully wetted and no obvious air bubbles remain, the flow rate is switched to bottom to gradually increase to 3.14 mL / min, and the bed is compacted after 30 minutes. The final bed height is measured and recorded (it should be approximately 200 mm). If there is any deviation, the actual height should be recorded.

[0067] A 10 mg / L fluoride ion working solution, adjusted to pH 6.5 ± 0.2, was placed in the inlet water tank. An initial water sample was collected and stored for CO detection; three measurements were taken, and the average value was recorded. The peristaltic pump was turned on, and the flow rate was adjusted to 3.14 mL / min (EBCT = 5 min). Timing was started at the adsorption column outlet and recorded as t = 0. The fluoride-containing simulated water sample was continuously introduced, and the temperature was maintained at a constant 25 ± 1 °C.

[0068] Manual sampling was performed at time intervals: samples were taken every 150 minutes for the first 500 BV, every 100 minutes for 500-700 BV, and every 50 minutes after 7000 BV. Each sample was collected in approximately 5-10 mL and immediately sealed for analysis. The cumulative effluent volume V and running time corresponding to the sampling time were recorded.

[0069] Sampling continued until the effluent fluoride concentration met the following standard: C t When / C0 is greater than or equal to 0.90, the adsorption column is considered saturated and water intake can be stopped.

[0070] The dynamic capacity exceeding 10% of the fixed bed capacity is calculated using the integral method, and the expression is: qB = (Q / m) × ∫(C0 - C t )dt Where qB represents 10% breakthrough dynamic capacity, Q represents volumetric flow rate, m represents the mass of adsorbent packed, C0 represents the influent fluoride ion concentration, and C t This represents the concentration of fluoride ions in the effluent at time t.

[0071] The test results are shown in Table 3.

[0072] Table 3: Fixed-bed breakthrough test results of the defluorinating agents prepared in Example 1 and Comparative Example 1

[0073] Referring to Table 3, the 10% breakthrough volume, 50% breakthrough volume, and 90% saturation volume of Example 1 were 1147 BV, 1473 BV, and 1581 BV, respectively, which were significantly higher than those of Comparative Example 1. This effectively demonstrates that the defluorinating agent prepared in Example 1 has better engineering adaptability in continuous flow deep defluorination.

[0074] Finally, the defluorinating agent prepared in Example 1 was subjected to a cycle regeneration test. The test method is as follows: Weigh 4g of sodium hydroxide and slowly dissolve it in approximately 800mL of deionized water. Stir, cool, add 11.69g of sodium chloride and stir to dissolve. Transfer to a 1000mL volumetric flask, dilute to volume with deionized water, and shake well.

[0075] Switch the peristaltic pump of the saturated defluorination column in either direction to achieve counter-current regeneration from bottom to top. Maintain the regeneration solution flow rate at the same rate as the adsorption flow rate, and control the regeneration time to 60 minutes. After 60 minutes, wash with deionized water counter-currently or co-currently until nearly neutral. After washing, proceed to the next breakthrough experiment. Repeat this adsorption-regeneration cycle multiple times, recording data five times.

[0076] The test results are shown in Table 4.

[0077] Table 4: Results of Cyclic Regeneration Tests of the Defluorinating Agent Prepared in Example 1

[0078] As can be seen from the data in Table 4, after five fixed-bed adsorption-regeneration cycles, the 10% breakthrough volume of the defluorinating agent prepared in Example 1 remained at 76.50% of the initial value, and the leaching concentrations of La and Zr after regeneration were maintained at a low level, indicating that the defluorinating agent of the present invention has good regeneration stability and continuous operation potential.

[0079] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a molten zirconium fumarate metal-organic framework defluorinating agent with a surface-modified lanthanum oxyhydroxylide, characterized in that, include: Zirconic fumarate metal-organic framework powder was prepared in a water-organic acid system. Zirconium fumarate metal-organic framework powder is mixed with inorganic binder and deionized water, then molded and dried to obtain a molding precursor. The molding precursor is immersed in a lanthanum salt aqueous solution to form a lanthanum oxide hydroxylate active phase in situ on the surface of the molding precursor. After washing and drying, a molten zirconium fumarate metal-organic framework defluorinating agent with a surface rich in lanthanum oxide hydroxylate is obtained.

2. The method for preparing the surface-modified lanthanum-rich oxyhydroxylate-modified shaped zirconic acid metal-organic framework defluorinating agent according to claim 1, characterized in that, The preparation of zirconate fumarate metal-organic framework powder in a water-organic acid system includes: Zirconium oxychloride octahydrate and fumaric acid were added to a water-organic acid solution, stirred, heated and crystallized, and then filtered, washed and dried to obtain zirconium fumaric acid metal-organic framework powder.

3. The method for preparing the surface-modified lanthanum-rich oxyhydroxylate-modified shaped zirconic acid metal-organic framework defluorinating agent according to claim 2, characterized in that, The molar ratio of zirconium oxychloride octahydrate to fumaric acid is in the range of 5:1 to 25. And / or, the organic acid in the water-organic acid solution is a monocarboxylic acid, and the molar ratio of the organic acid in the water-organic acid solution to the metallic zirconium in zirconium oxychloride octahydrate is 10~200:

1.

4. The method for preparing the surface-modified lanthanum-rich oxyhydroxylate-modified shaped zirconic acid metal-organic framework defluorinating agent according to claim 2, characterized in that, The conditions for the thermal crystallization include reacting at 90-100°C for 8-10 hours; And / or, the drying temperature range is 70~100℃.

5. The method for preparing the surface-modified lanthanum-rich oxyhydroxylate-modified shaped zirconic acid metal-organic framework defluorinating agent according to claim 1, characterized in that, The inorganic binder includes one or more of boehmite, silica sol, and starch; And / or, the molding method includes granulation molding or extrusion molding.

6. The method for preparing the surface-modified lanthanum-rich oxyhydroxylate-modified shaped zirconic acid metal-organic framework defluorinating agent according to claim 5, characterized in that, When the inorganic binder is boehmite, the amount of boehmite added is 5-10% of the mass of the zirconium fumarate metal-organic framework powder; When the inorganic binder is silica sol, the amount of silica sol added is 0.3-1% of the mass of the zirconium fumarate metal-organic framework powder; When the inorganic binder is starch, the amount of starch added is 10-20% of the mass of the zirconium fumarate metal-organic framework powder.

7. The method for preparing the surface-modified lanthanum-rich oxyhydroxylate-modified shaped zirconic acid metal-organic framework defluorinating agent according to claim 1, characterized in that, The lanthanum salt aqueous solution is an aqueous solution containing lanthanum nitrate and urea; And / or, the molar ratio of the molding precursor to lanthanum nitrate and urea is in the range of 1:0.1~10:1~100; And / or, the in-situ formation of the lanthanum oxyhydroxyl active phase on the surface of the molding precursor is achieved by uniform hydrolysis-reduction deposition, wherein the uniform hydrolysis-reduction deposition includes immersion at room temperature for 0.5-1.5 h followed by heating to 80-90 °C and holding at that temperature for 2-4 h.

8. A molten zirconic acid metal-organic framework defluorinating agent with a surface-modified lanthanum oxide hydroxylide, characterized in that, The fluoride remover is prepared by the method described in any one of claims 1 to 7, which is a molten zirconium fumarate metal-organic framework modified with lanthanum oxyhydroxylate on the surface. The molten zirconium fumarate metal-organic framework has a lanthanum oxyhydroxylate active phase on the surface and the inner surface of the pores of the molten zirconium fumarate metal-organic framework.

9. The surface-modified lanthanum oxide-rich molded zirconium fumarate metal-organic framework defluorinating agent according to claim 8, characterized in that, The defluorinating agent is in granular form, with an average particle size ranging from 0.3 to 2.0 mm, and the particle shape is one or more of spherical, cylindrical, annular, or multi-leaf shapes. And / or, the lanthanum oxyhydroxylide active phase is enriched in a region of 0.1 to 100 micrometers inward from the outer surface of the particles.

10. The application of a surface-modified lanthanum oxide-rich molten zirconium fumarate metal-organic framework defluorinating agent prepared by the method described in any one of claims 1 to 7, characterized in that, Includes a method for defluorination of a fixed bed, wherein the steps of the fixed bed defluorination include: A molten zirconium fumarate metal-organic framework defluorinating agent modified with lanthanum oxyhydroxylate on the surface is filled into the adsorption column in the fixed bed process to obtain a packed bed. Fluoride-containing water is continuously passed through the packed bed to achieve continuous removal of fluoride ions from the water.

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