A method for preparing a fluorine adsorbent, a fluorine adsorbent obtained by the preparation method and its application

Abstract

The present invention provides a method for preparing a fluorine adsorbent, which uses tungsten trioxide, ammonium metatungstate, and water glass as raw materials, obtains a granular substrate after granulation and sintering, then performs a primary modification with a phosphoric acid solution, and after drying, performs a secondary modification with an aluminum chloride aqueous solution, and obtains a fluorine adsorbent after washing and drying. The present invention also provides the use of the adsorbent obtained by the above preparation method in removing fluoride ions from water. The present invention utilizes Al4(PO4) x (OH) 12‑3x The material's rapid adsorption capacity for fluoride ions enables it to quickly capture fluoride ions in water, ensuring that the fluoride ion concentration in the produced water meets the standard. It has the ability to adsorb fluoride ions in large capacity, which can reduce the number of regenerations and increase the adsorption capacity and water treatment volume of the adsorbent per unit volume.

Description

Technical Field

[0001] The present invention relates to a fluorine adsorbent, in particular to a method for preparing a novel fluorine adsorbent, and also to the fluorine adsorbent obtained by the preparation method and application of the fluorine adsorbent in treating fluoride ions in water. Background Art

[0002] Fluoride is widely present in surface water. According to my country's "Standard for Drinking Water Quality" (GB5749-2006), the fluoride concentration limit in drinking water cannot exceed 1.0 mg L -1 Existing methods for removing fluoride from water include precipitation, ion exchange, electrodialysis, membrane separation, adsorption, and in-situ methods. Among them, adsorption is a method that uses porous materials to adsorb fluoride on the surface of solids to achieve the purpose of fluoride removal. It is a common method for removing fluoride from water and can reduce the fluoride concentration in water to 1 mg L -1 The following methods meet drinking water standards and are economical and easy to operate. However, existing fluorine adsorbents generally suffer from technical drawbacks such as poor stability, low fluorine adsorption efficiency, and low adsorption capacity. For example, Chinese invention patent application CN 117816116A provides a method for preparing a defluorination adsorbent by modifying coal-based solid waste. The method comprises ball-milling the coal-based solid waste and a portion of a defluorination active substance, adding an active coupling agent for reaction, and then adding the defluorination active substance for reaction. However, the defluorination material has a low adsorption capacity of only about 0.49 mg / g.

[0003] Chinese invention patent application CN 117732420A provides a method for preparing a rare earth-based defluorination adsorbent. This method utilizes a complex precipitation method to complex lanthanum and cerium ions in a liquid phase with a complexing agent to produce a sheet-like porous defluorination adsorbent. However, the high cost of lanthanum and cerium raw materials makes the industrial application of this defluorination adsorbent expensive. Similarly, Chinese invention patent application CN 117563557A provides a defluorination adsorbent, its preparation method, and a method for defluoridating lithium battery recovered fluid. However, the synthesis process of this method uses a large amount of toxic and hazardous organic raw materials or solvents, which is unfriendly to workers and the environment, making it difficult to promote.

[0004] In their paper "Preparation of Nano-spherical LaAlO3 and Its Fluoride Removal Performance under Acidic Conditions," Liu Jingdu et al. used a co-precipitation-hydrothermal method to prepare nano-spherical perovskite LaAlO3. At an initial fluoride concentration of 200 mg / L, the LaAlO3 adsorption capacity reached 53.8 mg / g after 8 minutes, and the equilibrium adsorption capacity reached 66.5 mg / g after 4 hours. Using alum as a desorbent, the LaAlO3 retained over 90% of its original fluoride removal performance after four cycles, demonstrating excellent regeneration and practical utility. However, this defluoride adsorbent requires use in an acidic environment, limiting its application.

[0005] Through analysis of existing technologies, it was found that existing fluorine removal adsorbents generally have the disadvantages of low adsorption capacity and susceptibility to interference from coexisting ions, or are difficult to apply industrially due to problems such as limited pH range and low regeneration efficiency. Summary of the Invention

[0006] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a fluorine adsorbent with stable physical and chemical structure, high adsorption capacity, wide application range, high regeneration efficiency and long service life.

[0007] The idea of ​​the present invention is to load Al4(PO4) on WO3 pellets. x (OH) 12-3x WO3 is used as the substrate to obtain the function of removing fluoride ions, and Al4(PO4) is used x (OH) 12-3x The powder has stable physical and chemical structure to increase the adsorption capacity of the substrate, broaden the scope of application and improve the regeneration efficiency.

[0008] Based on this, the present invention provides a method for preparing a fluorine adsorbent, the method comprising the following steps:

[0009] (1) Preparation of substrate

[0010] Tungsten trioxide and ammonium metatungstate are weighed at a tungsten ion molar ratio of 1:2 to 1:5, and the tungsten trioxide, ammonium metatungstate and water glass are placed in a molding device for granulation to obtain a granular wet material with a diameter of 0.5 to 3 mm. The obtained wet material is sintered at 600°C to 900°C to obtain a granular substrate, wherein the amount of water glass is 10 to 20 times the total weight of tungsten trioxide and ammonium metatungstate;

[0011] (2) One-time modification

[0012] A phosphoric acid solution having a molar concentration of 1 to 3 mol / L is prepared, and a sodium hydroxide solution is added until the pH value is adjusted to 13 to 14 to obtain a mixed solution, and then the granular substrate obtained in step (1) is fully immersed in the mixed solution, taken out and dried to obtain primary modified particles;

[0013] (3) Secondary modification

[0014] The primary modified particles obtained in step (2) are fully immersed in an aluminum chloride aqueous solution with a mass concentration of 20% to 60%, taken out and dried to obtain secondary modified particles;

[0015] (4) Post-processing

[0016] The obtained secondary modified particles are washed with water and dried to obtain a fluorine adsorbent.

[0017] In the present invention, the molding equipment in step (1) is a rotary disk molding machine. A rotary disk molding machine refers to a molding machine in which the working part or molding piece of the machine rotates to plastically deform the material to obtain the desired shape and size. For example, a rotary granulator manufactured and sold by Changzhou Lima Drying Technology Co., Ltd. is used to add tungsten trioxide, ammonium metatungstate, and water glass to the material inlet to obtain granular wet material.

[0018] Water glass (commonly known as sodium silicate) is a soluble alkali metal silicate material composed of alkali metal oxides and silicon dioxide. The molecular formula of sodium water glass is Na2O·nSiO2, and the molecular formula of potassium water glass is K2O·nSiO2. It is usually in liquid form. According to a preferred embodiment, the modulus of the water glass in step (1) is 2.5 to 3.6, and the specific gravity of the water glass is 1.318 to 1.599 g / cm 3 The Baume degree of the water glass is preferably 34.98 to 54.32°Bé.

[0019] In the present invention, controlling the amount of water glass to 10 to 20 times the combined weight of tungsten trioxide and ammonium metatungstate ensures that the resulting fluorine adsorbent has a sufficiently high adsorption capacity and good strength. When the amount of water glass is too high, exceeding 20 times the combined weight of tungsten trioxide and ammonium metatungstate, the proportion of WO3 in the substrate is too low, resulting in a decrease in the adsorption capacity of the adsorbent. When the amount of water glass is too low, less than 10 times the combined weight of tungsten trioxide and ammonium metatungstate, the resulting granular wet material contains too little viscous material, and the resulting adsorbent, after subsequent processing of the substrate, is too weak and easily cracked or shattered during use.

[0020] As a preferred embodiment, the molar concentration of the sodium hydroxide solution in step (2) is 2 to 4 mol / L.

[0021] In the present invention, the full immersion in step (2) means that the solid phase material is completely immersed in the liquid phase. Generally, the volume of the solution should be no less than 1.5 times, preferably 1.5 to 3 times, of the granular substrate, and the immersion time is 8 to 24 hours to ensure that the sodium phosphate and disodium hydrogen phosphate are fully attached to the surface of the granular substrate. Similarly, the full immersion in step (3) means that the volume of the solution should be no less than 1.2 times, preferably 1.2 to 1.5 times, of the granular substrate, and the immersion time is 12 to 24 hours to ensure that the material is fully in contact with the aluminum chloride aqueous solution.

[0022] Preferably, the drying temperature in step (2) is 100-150°C, and the drying temperature in step (3) is 150-200°C. In step (2), since a mixture of sodium phosphate and disodium hydrogen phosphate adheres to the surface of the granular substrate, the drying temperature in step (2) should be kept relatively low to prevent disodium hydrogen phosphate from forming sodium pyrophosphate at high temperatures. In step (3), a higher temperature can be used to achieve rapid drying of the material.

[0023] The drying in step (4) is carried out at a constant temperature of 40 to 150° C. for 2 to 24 hours.

[0024] Al4(PO4) on the defluorination adsorbent obtained by the above method x (OH) 12-3x The free fluoride ions in the water are quickly captured, and the fluoride ions further diffuse on the WO3 substrate, thereby increasing the adsorption rate of the defluorination adsorbent.

[0025] Furthermore, the present invention also provides the use of the fluorine adsorbent obtained by the above preparation method in removing fluoride ions from water, which is particularly beneficial when the concentration of fluoride ions in water is less than 100 mg / L.

[0026] The present invention utilizes the good adsorption capacity of WO3 for fluoride ions, and using it as a substrate can greatly improve the adsorption capacity of the defluorination adsorbent for fluoride ions.

[0027] On the other hand, Al4(PO4) obtained by double modification x (OH) 12-3x The powder has a stable physical and chemical structure, high adsorption capacity, a wide pH range, and high regeneration efficiency. Al4(PO4) with rapid adsorption capacity for fluoride ions is loaded on the porous WO3 substrate. x (OH) 12-3x The material can quickly capture fluoride ions in water, increase the adsorption rate, and increase the amount of water treated per unit time.

[0028] The present invention utilizes Al4(PO4) x (OH) 12-3x The material has a rapid adsorption capacity for fluoride ions, first quickly capturing the fluoride ions in the water and gathering them in Al4(PO4) x (OH) 12-3x / WO3 pores, and then the base material WO3 is used to adsorb fluoride ions in large capacity. This coupling effect can achieve Al4(PO4) x (OH) 12-3x / WO3 can not only quickly capture fluoride ions to make the fluoride ion concentration of produced water meet the standard, but also adsorb fluoride ions in large capacity, reduce the number of regeneration times, and increase the adsorption capacity of the adsorbent per unit volume and the amount of water treated. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The physical image and surface scanning electron microscope image of sample 1 of Example 1;

[0030] Figure 2 is the adsorption capacity of sample 1 of Example 1;

[0031] Figure 3 The physical image and surface scanning electron microscope image of Sample 2 of Example 2;

[0032] Figure 4 is the adsorption performance of sample 2 of Example 2;

[0033] Figure 5 The physical image and surface scanning electron microscope image of Sample 3 of Example 3;

[0034] Figure 6 This is the adsorption performance of sample 3 in Example 3. DETAILED DESCRIPTION

[0035] The following examples are used to illustrate the technical solutions of the present invention in a non-limiting manner.

[0036] In the present invention, unless otherwise specified, “%” used to describe concentrations refers to percentage by weight, and “:” refers to ratio by weight.

[0037] Example 1

[0038] 7.3 kg of water glass, 23 kg of tungsten trioxide, and 50 kg of ammonium metatungstate were added to the rotating disk of a granulator for granulation. The granulator had a diameter of 1.0 m, a horizontal inclination angle of 45°, and a speed of 30 rpm. After sintering at 650°C, a substrate with a diameter of 0.5 mm was obtained. The granular substrate was immersed in a mixed solution of sodium hydroxide and phosphoric acid with a pH of 13 for 8 hours, removed, and dried.

[0039] The obtained material was immersed in 100 L of 20% aluminum chloride aqueous solution for 12 hours, taken out and dried at 150° C. The dried granular material was washed with water and dried conventionally to obtain fluorine adsorbent sample 1.

[0040] The physical image and surface scanning electron microscope image of sample 1 are as follows: Figure 1 As shown, it can be seen that the adsorbent particles are relatively uniform and the particle surface is irregular.

[0041] Sample 1 was put into concentrated hydrochloric acid. The Al element and PO4 in the solution were tested by inductively coupled plasma spectrometer and ion chromatography. 3- The content of elements is shown in Table 1.

[0042] The test results in Table 1 confirm that the Al4(PO4) x (OH) 12-3x The chemical formula is Al4(PO4)3(OH)3.

[0043] An adsorption column was constructed by loading the adsorbent into a glass column. Adsorption was performed using a flow-through method at a flow rate of 20 BV / h with a 20 mg / L (fluoride ion) fluoride-containing test solution. The fluoride ion concentration in the test solution was recorded before and after adsorption, and the adsorption capacity per unit mass of the adsorbent was calculated. After saturation of the adsorption capacity, the adsorbent was regenerated with a 2 mol / L sodium hydroxide solution at a flow rate of 8 BV / h for 1 hour. After regeneration, the adsorption test was repeated. This cycle was repeated 20 times.

[0044] The existing fluorine removal adsorbents on the market were used as controls.

[0045] The results are as follows Figure 2 As shown, the test confirmed that the saturated adsorption capacity of the adsorbent of the present invention for fluoride ions is 76 mg / g, which is significantly higher than the 31 mg / g of Ti-SiO2 defluorination adsorbent purchased on the market. This proves that the defluorination adsorbent of the present invention has the performance advantage of high adsorption capacity.

[0046] Table 1 Chemical formula and adsorption capacity analysis of defluorination adsorbents

[0047]

[0048] It can be seen that the adsorbent of the present invention has a high adsorption capacity at this flow rate and good product stability.

[0049] Example 2

[0050] 7.5 kg of water glass, 23 kg of tungsten trioxide, and 87 kg of ammonium metatungstate were added to the rotating disk of a granulator with a diameter of 1.2 m, a horizontal inclination angle of 50°, and a rotation speed of 50 r / min for granulation. After sintering at 750°C, granular seeds with a diameter of 2.0 mm were obtained. The granular seeds were soaked in a mixed solution of sodium hydroxide and phosphoric acid with a pH of 14 for 12 hours, removed, and dried at 120°C. The pellets were then soaked in 150 L of a 40% aluminum chloride aqueous solution for 16 hours, removed, and dried at 170°C. The dried pellets were then washed with water and dried to obtain fluoride removal adsorbent sample 2.

[0051] Figure 3 This is a physical picture of the defluorination adsorbent pellet product and a surface scanning electron microscope picture. The defluorination adsorbent particles are relatively uniform. From the electron microscope photo, it can be seen that they have a cubic structure with a diameter of about 0.5 to 1 μm.

[0052] The Al4(PO4) of sample 2 was confirmed by the same method as in Example 1. x (OH) 12-3x The chemical formula is Al4(PO4) 3.6 (OH) 1.2 .

[0053] The saturated adsorption capacity of the adsorbent of this embodiment for fluoride ions was tested to be 84 mg / g, which is much higher than the 31 mg / g of commercially available defluoridation adsorbents, demonstrating that the defluoridation adsorbent of the present invention has the performance advantage of high adsorption capacity.

[0054] Table 2 Chemical formula and adsorption capacity analysis of defluorination adsorbents

[0055]

[0056]

[0057] The same method as in Example 1 was used, except that the flow rate of the test liquid was adjusted to 30 BV / h, the fluoride ion concentration in the test liquid was about 100 mg / L, and after adsorption by the defluorination adsorbent, the results were as follows: Figure 4 As shown in the figure, during the 30-day continuous operation test, the produced water concentration was always less than 1 mg / L, meeting the national emission standards.

[0058] Example 3

[0059] 7 kg of water glass, 23 kg of tungsten trioxide, and 120 kg of ammonium metatungstate were added to the rotating disk of a granulator for granulation. The granulator had a diameter of 2.0 mm, a horizontal inclination angle of 40°, and a rotation speed of 20 r / min. After sintering at 850°C, granular seeds with a diameter of 3.0 mm were obtained. The granular seeds were soaked in a mixed solution of sodium hydroxide and phosphoric acid with a pH of 14 for 22 hours, removed, and dried at 150°C. The pellets were then soaked in 200 L of a 60% aluminum chloride aqueous solution for 24 hours, removed, and dried at 200°C. The dried pellets were washed with water and dried to obtain defluorination adsorbent sample 3.

[0060] Figure 5 This is a physical picture of the defluorination adsorbent pellet product and a surface scanning electron microscope picture. The defluorination adsorbent particles are relatively uniform. From the electron microscope photo, it can be seen that they have a cubic structure with a diameter of about 0.2 to 0.5 μm.

[0061] The Al4(PO4) of sample 3 was confirmed by the same method as in Example 1. x (OH) 12-3x The chemical formula is Al4(PO4) 3.8 (OH) 0.6The same test as in Example 1 confirmed that the sample of this example had a saturated adsorption capacity of 81 mg / g for fluoride ions, which is much higher than the 31 mg / g of commercially available defluorination adsorbents. This demonstrates that the defluorination adsorbent of the present invention has the performance advantage of high adsorption capacity.

[0062] Table 3 Chemical formula and adsorption capacity analysis of defluorination adsorbents

[0063]

[0064] The same method as in Example 1 was used, except that the flow rate of the test solution was adjusted to 50 BV / h, the fluoride ion concentration in the test solution was about 50-60 mg / L, and after adsorption by the defluorination adsorbent, the results were as follows: Figure 6 As shown in the figure, during the 30-day test, the produced water concentration was less than 1 mg / L, meeting the national emission standards.

[0065] Comparative Example

[0066] Comparative Example 1: 7 kg of water glass, 23 kg of tungsten trioxide, and 120 kg of ammonium metatungstate were added to the turntable of a granulator for granulation. The diameter of the granulator was 2.0 mm, the horizontal inclination angle of the granulator was 40°, the speed of the granulator was 20 r / min, and after sintering at 850°C, a WO3 defluorination adsorbent with a diameter of 3.0 mm was obtained.

[0067] Comparative Example 2: 7 kg of water glass, 23 kg of tungsten trioxide, and 120 kg of ammonium metatungstate were added to a granulator rotary disc for granulation. The granulator had a diameter of 2.0 mm, a horizontal inclination angle of 40°, and a granulator speed of 20 rpm. After sintering at 850°C, granular seeds with a diameter of 5.0 mm were obtained. The granular seeds were soaked in a mixed solution of sodium hydroxide and phosphoric acid at a pH of 14 for 22 hours, removed, and dried at 150°C. The pellets were then soaked in 200 L of a 60% aluminum chloride aqueous solution for 24 hours, removed, and dried at 200°C. The dried pellets were washed with water and dried to obtain a defluorination adsorbent.

[0068] Comparative Example 3: 7 kg of water glass, 25 kg of tungsten trioxide, and 25 kg of ammonium metatungstate were added to a granulator rotary disc for granulation. The granulator had a diameter of 2.0 mm, a horizontal inclination angle of 40°, and a granulator speed of 20 r / min. After sintering at 850°C, granular seeds with a diameter of 3.0 mm were obtained. The granular seeds were soaked in a mixed solution of sodium hydroxide and phosphoric acid at a pH of 14 for 22 hours, removed, and dried at 150°C. The pellets were then soaked in 200 L of a 60% aluminum chloride aqueous solution for 24 hours, removed, and dried at 200°C. The dried pellets were washed with water and dried to obtain a defluorination adsorbent.

[0069] The saturated adsorption capacity of each sample for fluoride ions was confirmed by the same test as in Example 1, as shown in Table 4:

[0070] Table 4 Adsorption performance of comparative examples

[0071] Saturated adsorption capacity (mg / g) Comparative Example 1 17 Comparative Example 2 31 Comparative Example 3 39

[0072] It can be seen that the Al4(PO4) x (OH) 12-3x / WO3 pellet-type defluorination adsorbent, Al4(PO4) loaded on WO3 pellets x (OH) 12-3x WO3 as the base material itself has the function of removing fluoride ions, Al4(PO4) x (OH) 12-3x The powder has a stable physical and chemical structure, high adsorption capacity, a wide pH range, and high regeneration efficiency. x (OH) 12-3x / WO3 greatly improves the adsorption capacity, adsorption stability and service life of the adsorbent.

Claims

1. A method for preparing a fluorine adsorbent, comprising the following steps: (1) Preparation of substrate Tungsten trioxide and ammonium metatungstate are weighed at a tungsten ion molar ratio of 1:2 to 1:5, and the tungsten trioxide, ammonium metatungstate and water glass are placed in a molding device for granulation to obtain a granular wet material with a diameter of 0.5 to 3 mm. The obtained wet material is sintered at 600°C to 900°C to obtain a granular substrate, wherein the amount of water glass is 10 to 20 times the total weight of tungsten trioxide and ammonium metatungstate; (2) One-time modification A phosphoric acid solution having a molar concentration of 1 to 3 mol / L is prepared, and a sodium hydroxide solution is added to adjust the pH value to 13 to 14 to obtain a mixed solution, and then the granular substrate obtained in step (1) is fully immersed in the mixed solution, taken out and dried to obtain primary modified particles; (3) Secondary modification The primary modified substrate obtained in step (2) is fully immersed in an aluminum chloride aqueous solution with a mass concentration of 20% to 60%, taken out and dried to obtain secondary modified particles; (4) Post-processing The obtained secondary modified particles are washed with water and dried to obtain a fluorine adsorbent.

2. The method for preparing a fluorine adsorbent according to claim 1, characterized in that The molding equipment of step (1) is a turntable molding machine.

3. The method for preparing a fluorine adsorbent according to claim 1, characterized in that The modulus of the water glass in step (1) is 2.5 to 3.6, the specific gravity of the water glass is 1.318 to 1.599 g / cm3, and the Baume degree of the water glass is 34.98 to 54.32°Bé.

4. The method for preparing a fluorine adsorbent according to claim 1, characterized in that The molar concentration of the sodium hydroxide solution in step (2) is 2 to 4 mol / L.

5. The method for preparing a fluorine adsorbent according to claim 1, characterized in that The step (2) of fully soaking means that the volume of the solution is not less than 1.5 times that of the granular substrate, and the soaking time is 8 to 24 hours.

6. The method for preparing a fluorine adsorbent according to claim 1, characterized in that The drying temperature of step (2) is 100-150°C.

7. The method for preparing a fluorine adsorbent according to claim 1, characterized in that The sufficient soaking in step (3) means that the volume of the solution should be no less than 1.2 times of the primary modified substrate, and the soaking time is 12 to 24 hours.

8. The method for preparing a fluorine adsorbent according to claim 1, characterized in that The drying temperature of step (3) is 150-200°C.

9. Use of the fluorine adsorbent obtained by the preparation method according to any one of claims 1 to 8 in removing fluoride ions from water.

10. The use according to claim 9, characterized in that The concentration of fluoride ions in water is less than 100 mg / L.

Images