A sodium metaaluminate doped calcium-aluminum-phosphorus defluorination material based on eggshell and acetic acid, and a preparation method and application thereof

Abstract

The application relates to an acetic acid-regulated sodium metaaluminate-doped calcium-aluminum-phosphorus defluorination material based on eggshell, a preparation method and application thereof, and belongs to the technical field of defluorination water treatment. The method is as follows: eggshell powder, a phosphorus source and sodium metaaluminate are added into a mixed solvent composed of acetic acid and water, mixed and dispersed to form a uniform reaction system; the pH of the reaction system is adjusted to be alkaline; the adjusted reaction system is transferred into a closed reaction container to perform a solvothermal reaction; after the reaction is completed, the obtained solid product is separated and washed; and the washed product is dried. In the application, acetic acid is used for regulating the dissolution and conversion of the eggshell calcium source and the material crystallization process, sodium metaaluminate is used for introducing aluminum components and adjusting the material structure, so as to construct an Al-Ca-P synergistic defluorination system. The obtained material can be used for removing fluorine ions in fluorine-containing water bodies. The application has the dual characteristics of resource utilization of waste eggshells and preparation of defluorination functional materials, and has the advantages of simple process, easily-obtained raw materials and high application value.

Description

Technical Field

[0001] This invention belongs to the field of water treatment defluoridation materials technology, specifically relating to an acetic acid-regulated sodium aluminate-doped eggshell-based calcium aluminum phosphorus defluoridation material, its preparation method, and its application. Background Technology

[0002] Fluorine is one of the trace elements needed by the human body, but excessive fluoride content in water can have adverse effects on human health and the ecological environment. Long-term consumption of high-fluoride water can easily lead to endemic fluorosis diseases such as dental fluorosis and skeletal fluorosis. Therefore, developing efficient, economical, and stable fluoride removal materials and their preparation methods is of great significance.

[0003] Currently, the main methods for treating fluoride-containing water include chemical precipitation, membrane separation, ion exchange, and adsorption. Among these, adsorption has received widespread attention due to its relatively simple process, wide applicability, and low operating cost. Existing defluoridation adsorption materials mainly include activated alumina, hydroxyapatite, metal oxides, and their composite materials. Although these materials have a certain application foundation in the field of defluoridation, they generally suffer from problems such as high raw material costs, complex preparation processes, limited structural control capabilities, insufficient distribution of active sites, and low resource utilization, which affect their further promotion and application.

[0004] Eggshells are a type of abundant and inexpensive biomass solid waste, with calcium carbonate as its main component, possessing the potential to be used as a calcium source for preparing calcium-based functional materials. Applying eggshells to the preparation of defluorination materials not only helps reduce material costs but also facilitates the resource utilization of solid waste, possessing significant economic and environmental value. However, when eggshells are directly used as raw materials in the construction of functional materials, the following problems still exist: First, the release and transformation process of the calcium source in eggshells in the reaction system is difficult to control, easily leading to incomplete raw material transformation; second, the composition and structure of the resulting products have poor uniformity, which is not conducive to forming a stable and efficient defluorination active structure; third, the functional components of single eggshell-based materials or single calcium-based or calcium-phosphorus-based materials are relatively limited, making it difficult to fully meet the requirements of efficient defluorination for material composition and structure.

[0005] In existing technologies, eggshells are mostly used to prepare single calcium-based materials or calcium-phosphorus materials. Although these materials can remove fluoride ions to a certain extent, they lack effective control over key processes such as the dissolution, transformation, crystallization of the calcium source, and the formation of composite structures, resulting in insufficient controllability in material structure design. Furthermore, most existing eggshell-based defluorination materials focus on single-component or simple composite systems, with limited research and utilization on the synergistic construction of multi-component systems and their impact on defluorination performance.

[0006] On the other hand, aluminum-based components have a good foundation for application in the field of fluoride removal materials. Introducing aluminum components helps to increase the active sites in the material and improve its composition and structural characteristics, thereby enhancing the material's ability to remove fluoride ions. However, in the preparation of eggshell-based materials, how to achieve the synergistic introduction of aluminum and phosphorus components while converting the calcium source from the eggshell, and further construct a stable calcium-aluminum-phosphorus composite structure, is still an effective and simple approach in the existing technology.

[0007] Furthermore, the reaction medium has a significant impact on the dissolution-conversion behavior of calcium sources from eggshells, the formation of product crystal phases, and the construction of composite structures. In existing technologies, conventional reaction systems often employ single-phase aqueous systems, strong acid direct dissolution systems, strong base activation systems, or simple organic solvent-assisted systems. When using a single-phase aqueous system, the release rate of calcium sources from eggshells is usually slow, easily leading to incomplete conversion of raw materials and poor uniformity in the composition and structure of the resulting products. While strong acid direct dissolution systems can promote calcium source release, they can also cause excessively rapid dissolution of calcium components, hindering the gentle control of the reaction process and the gradual formation of stable composite structures. Strong base activation systems, although able to alter the surface state of raw materials to some extent, often fail to simultaneously achieve orderly calcium source conversion and synergistic construction of multiple components, and are prone to causing damage to the material surface structure or increasing side reactions. Simple organic solvent-assisted systems often suffer from insufficient dispersion of inorganic components, limited control of the reaction interface, or incomplete formation of composite phases. The conventional systems described above generally suffer from defects in the preparation of eggshell-based defluorination materials, such as insufficient eggshell conversion, uneven distribution of functional components, inadequate crystal phase control, or limited composite structure formation, thus affecting the defluorination performance of the final material. Therefore, developing a preparation method that can regulate the calcium source conversion process of eggshells and simultaneously introduce aluminum and phosphorus components to construct a calcium-aluminum-phosphorus composite structure in situ is of great significance for improving the structural controllability and application performance of eggshell-based defluorination materials. Therefore, there is an urgent need to provide a new eggshell-based composite defluorination material and its preparation method to solve the problems of insufficient structural control, limited composite degree, and the need to improve defluorination performance in existing eggshell-based defluorination materials. Summary of the Invention

[0008] Technical problems solved: Addressing the issues of uncontrollable calcium source conversion process, relatively simple material composition, insufficient composite structure construction, and need for improved defluorination performance in existing eggshell-based defluorination materials, this invention provides an acetic acid-regulated sodium aluminate-doped eggshell-based calcium-aluminum-phosphorus defluorination material, its preparation method, and its application. By regulating the reaction system with acetic acid, phosphorus and aluminum components are simultaneously introduced during the calcium source conversion process, achieving in-situ conversion of the calcium source and synergistic construction of calcium, aluminum, and phosphorus components. This results in a relatively stable, rationally composed eggshell-based composite material suitable for defluorination treatment of fluoride-containing water.

[0009] Technical solution: The first objective of this invention is to provide a method for preparing an acetic acid-controlled sodium aluminate-doped eggshell-based calcium aluminum phosphorus defluorination material, comprising the following steps:

[0010] Step 1: Add eggshell powder, phosphorus source and sodium aluminate to a mixed solvent composed of acetic acid and water, mix and disperse to form a uniform reaction system;

[0011] Step two, adjust the pH of the reaction system to be alkaline;

[0012] Step 3: The adjusted reaction system is transferred to a closed reaction vessel for solvothermal reaction, causing the calcium source from the eggshell to dissolve and transform, and a composite material containing calcium, aluminum and phosphorus components is constructed in situ.

[0013] Step four: After the reaction is complete, the resulting solid product is separated and washed.

[0014] Step 5: Dry the washed product to obtain acetic acid-regulated sodium aluminate-doped eggshell-based calcium aluminum phosphorus defluorination material.

[0015] Preferably, in step one, the eggshell powder is used after being washed, dried, crushed, and sieved; the phosphorus source is a soluble phosphate, which includes at least one of sodium dihydrogen phosphate, disodium hydrogen phosphate, potassium dihydrogen phosphate, and dipotassium hydrogen phosphate.

[0016] Preferably, in step one, the mass ratio of eggshell powder, phosphorus source, and sodium aluminate is 1:(0.5-1.5):(0.5-1.5).

[0017] Preferably, in step one, the volume ratio of acetic acid to water in the mixed solvent is 1:5-5:1, and the ratio of the total mass of eggshell powder, phosphorus source and sodium aluminate to the mixed solvent is 1 g:(4:6) mL.

[0018] Preferably, in step two, the pH of the reaction system is adjusted to 8-11. More preferably, the pH is 9-10.

[0019] Preferably, in step three, the temperature of the solvothermal reaction is 150-200℃ and the reaction time is 400-600 min.

[0020] Preferably, in step four, the washing includes first washing with an organic solvent, and then washing with water until neutral. The organic solvent includes at least one of ethanol, methanol, and isopropanol. Preferably, the organic solvent is ethanol.

[0021] Preferably, in step five, the drying temperature is 40-80℃, and the drying is carried out overnight.

[0022] The second objective of this invention is to provide an acetic acid-regulated sodium aluminate-doped eggshell-based calcium-aluminum-phosphorus fluoride removal material prepared by the above-described method. The material is a composite material containing calcium, aluminum, and phosphorus components, formed by in-situ conversion of eggshell calcium source. It comprises a calcium-phosphorus phase and an aluminum-containing component. The calcium, aluminum, and phosphorus components form a synergistic structure within the material to enhance its ability to remove fluoride ions from fluoride-containing water.

[0023] The third objective of this invention is to provide the application of the above-mentioned acetic acid-regulated sodium aluminate-doped eggshell-based calcium aluminum phosphorus defluoridation material in the defluorination of fluoride-containing water bodies.

[0024] Beneficial effects: Compared with existing technologies, this invention uses eggshells as a calcium source, enabling the resource utilization of biomass waste, and has the advantages of wide availability of raw materials and low cost. This invention regulates the dissolution-conversion process of the eggshell calcium source through a reaction system composed of acetic acid and water, which is beneficial to improving the controllability of the material preparation process and promoting the formation of composite structures. Simultaneously, by introducing sodium aluminate as an aluminum component source, the synergistic construction of calcium, aluminum, and phosphorus components is achieved, which is beneficial to improving the composition and structural characteristics of the material. The material obtained by this invention can be used to remove fluoride ions from fluoride-containing water bodies, and the preparation method is simple, possessing good resource utilization value and application prospects. Attached Figure Description

[0025] Figure 1 The following are characterization diagrams of the adsorption and regeneration performance of the material prepared in Example 6 of the present invention. Among them, (a) is an adsorption isotherm diagram under different temperature conditions, (b) is a fitting diagram of diffusion kinetics within particles, (c) is a fitting diagram of the relationship between lnK and 1 / T, and (d) is a diagram of the change in defluorination rate during the regeneration cycle. Detailed Implementation

[0026] The present invention will be further described in detail below with reference to specific embodiments.

[0027] It should be noted that these embodiments are only used to illustrate the present invention and are not intended to limit the present invention. Simple improvements to the method under the premise of the present invention are all within the scope of protection claimed by the present invention.

[0028] Unless otherwise specified, the raw materials used in the embodiments of this specification are all from common commercially available products. Among them, the eggshell powder is obtained by washing, removing the inner membrane, drying, crushing and sieving eggshells.

[0029] Example 1

[0030] This embodiment provides a method for preparing an acetic acid-controlled sodium aluminate-doped eggshell-based calcium aluminum phosphorus defluorination material, which specifically includes the following steps:

[0031] Step 1: Weigh 2 g of eggshell powder (particle size < 0.178 mm), add 1.87 g of NaH2PO4·2H2O as a phosphorus source, add 2.0 g of sodium aluminate as an aluminum source, and place in a beaker;

[0032] Step 2: Add 15 mL of acetic acid and 15 mL of deionized water to the above system, wherein the volume ratio of acetic acid to deionized water is 1:1, and stir magnetically for 10 min to form a homogeneous reaction system.

[0033] Step 3: Adjust the pH of the reaction system to 9-10 using NaOH solution;

[0034] Step 4: Transfer the reaction system into a polytetrafluoroethylene-lined stainless steel reactor and carry out a solvothermal reaction at 180°C for 450 min.

[0035] Step 5: After the reaction is complete, allow it to cool naturally to room temperature. After centrifugation, discard the supernatant.

[0036] Step 6: The obtained solid is first washed with ethanol once, and then washed with deionized water in a circulating cycle until neutral;

[0037] Step 7: Dry the washed sample overnight at 60°C;

[0038] Step 8: Grind the dried sample and pass it through an 80-mesh sieve to obtain an acetic acid-regulated sodium aluminate-doped eggshell-based calcium aluminum phosphorus defluorination material, denoted as ACP-1.

[0039] The application of the above-mentioned acetic acid-regulated sodium aluminate-doped eggshell-based calcium aluminum phosphorus fluoride removal material (adsorbent) in water treatment defluorination: The above-mentioned ACP-1 sample was subjected to adsorption conditions of initial fluoride ion concentration of 10 mg / L, adsorbent dosage of 1 g / L, solution pH of 6, temperature of 25 ℃, and adsorption time of 24 h. The results showed that the fluoride removal rate of this material reached 94.74%, and the experimental adsorption capacity was 9.63 mg / g, exhibiting good fluoride removal performance.

[0040] Example 2

[0041] This embodiment provides a method for preparing an acetic acid-controlled sodium aluminate-doped eggshell-based calcium aluminum phosphorus defluorination material, which specifically includes the following steps:

[0042] Step 1: Weigh 2 g of eggshell powder (particle size < 0.178 mm), add 1.87 g of NaH2PO4·2H2O as a phosphorus source, add 2.0 g of sodium aluminate as an aluminum source, and place in a beaker;

[0043] Step 2: Add 10 mL of acetic acid and 20 mL of deionized water to the above system, wherein the volume ratio of acetic acid to deionized water is 1:2, and stir magnetically for 10 min to form a homogeneous reaction system.

[0044] Step 3: Adjust the pH of the reaction system to 9-10 using NaOH solution;

[0045] Step 4: Transfer the reaction system into a polytetrafluoroethylene-lined stainless steel reactor and carry out a solvothermal reaction at 180°C for 450 min.

[0046] Step 5: After the reaction is complete, allow it to cool naturally to room temperature. After centrifugation, discard the supernatant.

[0047] Step 6: The obtained solid is first washed with ethanol once, and then washed with deionized water in a circulating cycle until neutral;

[0048] Step 7: Dry the washed sample overnight at 60°C;

[0049] Step 8: Grind the dried sample and pass it through an 80-mesh sieve to obtain an acetic acid-controlled sodium aluminate-doped eggshell-based calcium aluminum phosphorus defluorination material, denoted as ACP-2.

[0050] The application of the above-mentioned acetic acid-regulated sodium aluminate-doped eggshell-based calcium aluminum phosphorus fluoride removal material (adsorbent) in water treatment defluorination: The ACP-2 sample was subjected to adsorption conditions of an initial fluoride ion concentration of 10 mg / L, an adsorbent dosage of 1 g / L, a solution pH of 6, a temperature of 25 ℃, and an adsorption time of 24 h. The results showed that the material achieved a fluoride removal rate of 94.76% and an adsorption capacity of 9.63 mg / g, demonstrating excellent defluorination performance.

[0051] Example 3

[0052] This embodiment provides a method for preparing an acetic acid-controlled sodium aluminate-doped eggshell-based calcium aluminum phosphorus defluorination material, which specifically includes the following steps:

[0053] Step 1: Weigh 2 g of eggshell powder (particle size < 0.178 mm), add 1.87 g of NaH2PO4·2H2O as a phosphorus source, add 1.5 g of sodium aluminate as an aluminum source, and place in a beaker;

[0054] Step 2: Add 15 mL of acetic acid and 15 mL of deionized water to the above system, wherein the volume ratio of acetic acid to deionized water is 1:1, and stir magnetically for 10 min to form a homogeneous reaction system.

[0055] Step 3: Adjust the pH of the reaction system to 9-10 using NaOH solution;

[0056] Step 4: Transfer the reaction system into a polytetrafluoroethylene-lined stainless steel reactor and carry out a solvothermal reaction at 180°C for 450 min.

[0057] Step 5: After the reaction is complete, allow it to cool naturally to room temperature. After centrifugation, discard the supernatant.

[0058] Step 6: The obtained solid is first washed with ethanol once, and then washed with deionized water in a circulating cycle until neutral;

[0059] Step 7: Dry the washed sample overnight at 60°C;

[0060] Step 8: Grind the dried sample and pass it through an 80-mesh sieve to obtain an acetic acid-controlled sodium aluminate-doped eggshell-based calcium aluminum phosphorus defluorination material, denoted as ACP-3.

[0061] The application of the above-mentioned acetic acid-regulated sodium aluminate-doped eggshell-based calcium aluminum phosphorus fluoride removal material (adsorbent) in water treatment defluorination: The ACP-3 sample was subjected to adsorption conditions of an initial fluoride ion concentration of 10 mg / L, an adsorbent dosage of 1 g / L, a solution pH of 6, a temperature of 25 ℃, and an adsorption time of 24 h. The results showed that the material achieved a defluorination rate of 94.30% and an adsorption capacity of 9.58 mg / g, demonstrating excellent defluorination performance.

[0062] Example 4

[0063] This embodiment provides a method for preparing an acetic acid-controlled sodium aluminate-doped eggshell-based calcium aluminum phosphorus defluorination material, which specifically includes the following steps:

[0064] Step 1: Weigh 2 g of eggshell powder (particle size < 0.178 mm), add 1.87 g of NaH2PO4·2H2O as a phosphorus source, add 2.0 g of sodium aluminate as an aluminum source, and place in a beaker;

[0065] Step 2: Add 15 mL of acetic acid and 15 mL of deionized water to the above system, wherein the volume ratio of acetic acid to deionized water is 1:1, and stir magnetically for 10 min to form a homogeneous reaction system.

[0066] Step 3: Adjust the pH of the reaction system to 8 using NaOH solution;

[0067] Step 4: Transfer the reaction system into a polytetrafluoroethylene-lined stainless steel reactor and carry out a solvothermal reaction at 180°C for 450 min.

[0068] Step 5: After the reaction is complete, allow it to cool naturally to room temperature. After centrifugation, discard the supernatant.

[0069] Step 6: The obtained solid is first washed with ethanol once, and then washed with deionized water in a circulating cycle until neutral;

[0070] Step 7: Dry the washed sample overnight at 60°C;

[0071] Step 8: Grind the dried sample and pass it through an 80-mesh sieve to obtain an acetic acid-controlled sodium aluminate-doped eggshell-based calcium aluminum phosphorus defluorination material, denoted as ACP-4.

[0072] The application of the above-mentioned acetic acid-regulated sodium aluminate-doped eggshell-based calcium aluminum phosphorus fluoride removal material (adsorbent) in water treatment defluorination: The ACP-4 sample was subjected to adsorption conditions of an initial fluoride ion concentration of 10 mg / L, an adsorbent dosage of 1 g / L, a solution pH of 6, a temperature of 25 ℃, and an adsorption time of 24 h. The results showed that the material achieved a fluoride removal rate of 93.33% and an adsorption capacity of 9.48 mg / g, demonstrating excellent defluorination performance.

[0073] Example 5

[0074] This embodiment provides a method for preparing an acetic acid-controlled sodium aluminate-doped eggshell-based calcium aluminum phosphorus defluorination material, which specifically includes the following steps:

[0075] Step 1: Weigh 2 g of eggshell powder (particle size < 0.178 mm), add 1.87 g of NaH2PO4·2H2O as a phosphorus source, add 2.0 g of sodium aluminate as an aluminum source, and place in a beaker;

[0076] Step 2: Add 15 mL of acetic acid and 15 mL of deionized water to the above system, wherein the volume ratio of acetic acid to deionized water is 1:1, and stir magnetically for 10 min to form a homogeneous reaction system.

[0077] Step 3: Adjust the pH of the reaction system to 9-10 using NaOH solution;

[0078] Step 4: Transfer the reaction system into a polytetrafluoroethylene-lined stainless steel reactor and carry out a solvothermal reaction at 160°C for 450 min.

[0079] Step 5: After the reaction is complete, allow it to cool naturally to room temperature. After centrifugation, discard the supernatant.

[0080] Step 6: The obtained solid is first washed with ethanol once, and then washed with deionized water in a circulating cycle until neutral;

[0081] Step 7: Dry the washed sample overnight at 60°C;

[0082] Step 8: Grind the dried sample and pass it through an 80-mesh sieve to obtain an acetic acid-controlled sodium aluminate-doped eggshell-based calcium aluminum phosphorus defluorination material, denoted as ACP-5.

[0083] The application of the above-mentioned acetic acid-regulated sodium aluminate-doped eggshell-based calcium aluminum phosphorus fluoride removal material (adsorbent) in water treatment defluorination: The above-mentioned ACP-5 sample was subjected to adsorption conditions of initial fluoride ion concentration of 10 mg / L, adsorbent dosage of 1 g / L, solution pH of 6, temperature of 25 ℃, and adsorption time of 24 h. The results showed that the fluoride removal rate of this material reached 91.05%, and the experimental adsorption capacity was 9.25 mg / g, exhibiting good fluoride removal performance.

[0084] Example 6

[0085] This embodiment provides a method for preparing an acetic acid-controlled sodium aluminate-doped eggshell-based calcium aluminum phosphorus defluorination material, which specifically includes the following steps:

[0086] Step 1: Weigh 2 g of eggshell powder (particle size < 0.178 mm), add 1.87 g of NaH2PO4·2H2O as a phosphorus source, add 2.0 g of sodium aluminate as an aluminum source, and place in a beaker;

[0087] Step 2: Add 15 mL of acetic acid and 15 mL of deionized water to the above system, wherein the volume ratio of acetic acid to deionized water is 1:1, and stir magnetically for 10 min to form a homogeneous reaction system.

[0088] Step 3: Adjust the pH of the reaction system to 9-10 using NaOH solution;

[0089] Step 4: Transfer the reaction system into a polytetrafluoroethylene-lined stainless steel reactor and carry out a solvothermal reaction at 180°C for 600 min.

[0090] Step 5: After the reaction is complete, allow it to cool naturally to room temperature. After centrifugation, discard the supernatant.

[0091] Step 6: The obtained solid is first washed with ethanol once, and then washed with deionized water in a circulating cycle until neutral;

[0092] Step 7: Dry the washed sample overnight at 60°C;

[0093] Step 8: Grind the dried sample and pass it through an 80-mesh sieve to obtain an acetic acid-regulated sodium aluminate-doped eggshell-based calcium aluminum phosphorus defluorination material, denoted as ACP-6.

[0094] The application of the above-mentioned acetic acid-regulated sodium aluminate-doped eggshell-based calcium aluminum phosphorus fluoride removal material (adsorbent) in water treatment defluorination: The ACP-6 sample was subjected to adsorption conditions of an initial fluoride ion concentration of 10 mg / L, an adsorbent dosage of 1 g / L, a solution pH of 6, a temperature of 25 ℃, and an adsorption time of 24 h. The results showed that the material achieved a fluoride removal rate of 95.16% and an adsorption capacity of 9.67 mg / g, demonstrating excellent defluorination performance.

[0095] Example 7 (pH=3 extreme conditions)

[0096] Same as Example 1, except that the adsorption conditions are set to pH=3.

[0097] Results: The fluoride removal rate was 90.18%, and the adsorption capacity was 9.16 mg / g.

[0098] Example 8 (pH=9 extreme conditions)

[0099] Same as Example 1, but with the adsorption condition set to pH=9.

[0100] Results: fluoride removal rate was 91.50%, and adsorption capacity was 9.30 mg / g.

[0101] Example 9 (Cl) - Interference experiment)

[0102] The adsorption solution contains 1000 mg / L Cl - The rest is the same as in Example 1.

[0103] Results: The fluoride removal rate was 92.57% (a decrease of 2.59%), and the adsorption capacity was 9.41 mg / g.

[0104] Example 10 (SO4) 2- Interference experiment)

[0105] The adsorption solution contains 400 mg / L SO4 2- The rest is the same as in Example 1.

[0106] Results: The fluoride removal rate was 89.99% (a decrease of 5.17%), and the adsorption capacity was 9.14 mg / g.

[0107] Comparative Example 1

[0108] This comparative example provides a method for preparing an eggshell-based calcium-phosphorus defluorination material, which specifically includes the following steps:

[0109] Step 1: Weigh 2 g of eggshell powder (particle size < 0.178 mm), add 1.87 g of NaH2PO4·2H2O as a phosphorus source, place in a beaker, do not add sodium aluminate;

[0110] Step 2: Add 15 mL of acetic acid and 15 mL of deionized water to the above system, wherein the volume ratio of acetic acid to deionized water is 1:1, and stir magnetically for 10 min to form a homogeneous reaction system.

[0111] Step 3: Adjust the pH of the reaction system to 9-10 using NaOH solution;

[0112] Step 4: Transfer the reaction system into a polytetrafluoroethylene-lined stainless steel reactor and carry out a solvothermal reaction at 180°C for 450 min.

[0113] Step 5: After the reaction is complete, allow it to cool naturally to room temperature. After centrifugation, discard the supernatant.

[0114] Step 6: The obtained solid is first washed with ethanol once, and then washed with deionized water in a circulating cycle until neutral;

[0115] Step 7: Dry the washed sample overnight at 60°C;

[0116] Step 8: Grind the dried sample and pass it through an 80-mesh sieve to obtain an eggshell-based calcium-phosphorus defluorination material that does not contain sodium aluminate, denoted as CP-1.

[0117] The above-mentioned CP-1 sample was tested for defluorination performance under the adsorption conditions in Example 1. The defluorination rate was 55.38% and the adsorption amount was 5.62 mg / g. This was used to compare the effect of sodium aluminate introduction on the defluorination performance of the material.

[0118] Comparative Example 2

[0119] This comparative example provides a method for preparing a sodium aluminate-doped eggshell-based calcium aluminum phosphorus defluorination material, which specifically includes the following steps:

[0120] Step 1: Weigh 2 g of eggshell powder (particle size < 0.178 mm), add 1.87 g of NaH2PO4·2H2O as a phosphorus source, add 2.0 g of sodium aluminate as an aluminum source, and place in a beaker;

[0121] Step 2: Add 30 mL of deionized water to the above system, without adding acetic acid, and stir magnetically for 10 min to form a homogeneous reaction system;

[0122] Step 3: Adjust the pH of the reaction system to 9-10 using NaOH solution;

[0123] Step 4: Transfer the reaction system into a polytetrafluoroethylene-lined stainless steel reactor and carry out a solvothermal reaction at 180°C for 450 min.

[0124] Step 5: After the reaction is complete, allow it to cool naturally to room temperature. After centrifugation, discard the supernatant.

[0125] Step 6: The obtained solid is first washed with ethanol once, and then washed with deionized water in a circulating cycle until neutral;

[0126] Step 7: Dry the washed sample overnight at 60°C;

[0127] Step 8: Grind the dried sample and pass it through an 80-mesh sieve to obtain an eggshell-based calcium aluminum phosphorus defluorination material without acetic acid control system, denoted as ACP-C1.

[0128] The above-mentioned ACP-C1 sample was tested for defluorination performance under the adsorption conditions in Example 1. The defluorination rate was 55.03% and the adsorption capacity was 5.60 mg / g. This was used to compare the effect of acetic acid regulation on the defluorination performance of the material.

[0129] Comparative Example 3

[0130] This comparative example provides a method for preparing an acetic acid-controlled sodium aluminate-doped eggshell-based calcium aluminum phosphorus defluorination material, which specifically includes the following steps:

[0131] Step 1: Weigh 2 g of eggshell powder (particle size < 0.178 mm), add 1.87 g of NaH2PO4·2H2O as a phosphorus source, add 2.0 g of sodium aluminate as an aluminum source, and place in a beaker;

[0132] Step 2: Add 15 mL of acetic acid and 15 mL of deionized water to the above system, wherein the volume ratio of acetic acid to deionized water is 1:1, and stir magnetically for 10 min to form a homogeneous reaction system.

[0133] Step 3: Do not adjust the pH of the reaction system;

[0134] Step 4: Transfer the reaction system into a polytetrafluoroethylene-lined stainless steel reactor and carry out a solvothermal reaction at 180°C for 450 min.

[0135] Step 5: After the reaction is complete, allow it to cool naturally to room temperature. After centrifugation, discard the supernatant.

[0136] Step 6: The obtained solid is first washed with ethanol once, and then washed with deionized water in a circulating cycle until neutral;

[0137] Step 7: Dry the washed sample overnight at 60°C;

[0138] Step 8: Grind the dried sample and pass it through an 80-mesh sieve to obtain an unpH-adjusted eggshell-based calcium aluminum phosphorus defluorination material, denoted as ACP-C2.

[0139] The above-mentioned ACP-C2 sample was tested for defluorination performance under the adsorption conditions in Example 1. The defluorination rate was 58.02% and the adsorption amount was 5.90 mg / g. This was used to compare the effect of pH control on the defluorination performance of the material.

[0140] Comparative Example 4

[0141] This comparative example provides a method for preparing other acid-controlled eggshell-based calcium aluminum phosphorus defluorination materials, specifically including the following steps:

[0142] Step 1: Weigh 2 g of eggshell powder (particle size < 0.178 mm), add 1.87 g of NaH2PO4·2H2O as a phosphorus source, add 2.0 g of sodium aluminate as an aluminum source, and place in a beaker;

[0143] Step 2: Add 15 mL of hydrochloric acid solution and 15 mL of deionized water to the above system, replacing acetic acid with hydrochloric acid, and stir magnetically for 10 min to form a homogeneous reaction system.

[0144] Step 3: Adjust the pH of the reaction system to 9-10 using NaOH solution;

[0145] Step 4: Transfer the reaction system into a polytetrafluoroethylene-lined stainless steel reactor and carry out a solvothermal reaction at 180 °C for 450 min.

[0146] Step 5: After the reaction is complete, allow it to cool naturally to room temperature. After centrifugation, discard the supernatant.

[0147] Step 6: The obtained solid is first washed with ethanol once, and then washed with deionized water in a circulating cycle until neutral;

[0148] Step 7: Dry the washed sample overnight at 60 °C;

[0149] Step 8: Grind the dried sample and pass it through an 80-mesh sieve to obtain an acid-controlled eggshell-based calcium aluminum phosphorus defluorination material, denoted as ACP-C3.

[0150] The above-mentioned ACP-C3 sample was tested for defluorination performance under the adsorption conditions in Example 1. Its defluorination rate was 36.35% and its adsorption capacity was 3.69 mg / g. This was used to compare the effects of different acidic media on the defluorination performance of the material.

[0151] Comparative Example 5

[0152] This comparative example provides a method for preparing an eggshell-based calcium aluminum phosphorus defluorination material under low acetic acid addition conditions, specifically including the following steps:

[0153] Step 1: Weigh 2 g of eggshell powder (particle size < 0.178 mm), add 1.87 g of NaH2PO4·2H2O as a phosphorus source, add 2.0 g of sodium aluminate as an aluminum source, and place in a beaker;

[0154] Step 2: Add 5 mL of acetic acid and 25 mL of deionized water to the above system, wherein the volume ratio of acetic acid to deionized water is 1:5, and stir magnetically for 10 min to form a homogeneous reaction system.

[0155] Step 3: Adjust the pH of the reaction system to 9-10 using NaOH solution;

[0156] Step 4: Transfer the reaction system into a polytetrafluoroethylene-lined stainless steel reactor and carry out a solvothermal reaction at 180 °C for 450 min.

[0157] Step 5: After the reaction is complete, allow it to cool naturally to room temperature. After centrifugation, discard the supernatant.

[0158] Step 6: The obtained solid is first washed with ethanol once, and then washed with deionized water in a circulating cycle until neutral;

[0159] Step 7: Dry the washed sample overnight at 60 °C;

[0160] Step 8: Grind the dried sample and pass it through an 80-mesh sieve to obtain an eggshell-based calcium aluminum phosphorus defluorination material prepared under low acetic acid addition conditions, denoted as ACP-C4.

[0161] The above-mentioned ACP-C4 sample was tested for defluorination performance under the adsorption conditions in Example 1. Its defluorination rate was 60.60% and its adsorption capacity was 5.84 mg / g. This was used to compare the effect of too low acetic acid addition on the defluorination performance of the material.

[0162] Comparative Example 6

[0163] This comparative example provides a method for preparing an eggshell-based calcium aluminum phosphorus defluorination material using other aluminum sources, specifically including the following steps:

[0164] Step 1: Weigh 2 g of eggshell powder (particle size < 0.178 mm), add 1.87 g of NaH2PO4·2H2O as a phosphorus source, and add aluminum nitrate equivalent to the molar amount of aluminum in 2.0 g of sodium aluminate as an aluminum source, and place them in a beaker;

[0165] Step 2: Add 15 mL of acetic acid and 15 mL of deionized water to the above system, wherein the volume ratio of acetic acid to deionized water is 1:1, and stir magnetically for 10 min to form a homogeneous reaction system.

[0166] Step 3: Adjust the pH of the reaction system to 9-10 using NaOH solution;

[0167] Step 4: Transfer the reaction system into a polytetrafluoroethylene-lined stainless steel reactor and carry out a solvothermal reaction at 180 °C for 450 min.

[0168] Step 5: After the reaction is complete, allow it to cool naturally to room temperature. After centrifugation, discard the supernatant.

[0169] Step 6: The obtained solid is first washed with ethanol once, and then washed with deionized water in a circulating cycle until neutral;

[0170] Step 7: Dry the washed sample overnight at 60 °C;

[0171] Step 8: Grind the dried sample and pass it through an 80-mesh sieve to obtain an eggshell-based calcium aluminum phosphorus defluorination material prepared with the participation of other aluminum sources, denoted as ACP-C5.

[0172] The above-mentioned ACP-C5 sample was tested for defluorination performance under the adsorption conditions in Example 1. Its defluorination rate was 55.76% and its adsorption capacity was 5.38 mg / g. This was used to compare the effects of different aluminum sources on the defluorination performance of the material.

[0173] As can be seen from Examples 1-10, different preparation and application conditions have a significant impact on the defluorination performance of the obtained materials. Factors such as the volume ratio of acetic acid to water, the amount of sodium aluminate introduced, the pH of the reaction system, and the solvothermal reaction temperature and time all affect the dissolution-conversion process of the eggshell calcium source, the degree of composite structure formation, and the final defluorination effect of the material. The results of all examples indicate that, within the conditions described in this invention, using appropriate acetic acid / water ratios, sodium aluminate dosages, and alkaline reaction conditions is beneficial for promoting the in-situ conversion of the eggshell calcium source and the formation of the calcium, aluminum, and phosphorus composite structure, thereby improving the defluorination performance of the material. Among these, the sample prepared in Example 6 showed superior overall performance, indicating that appropriately extending the solvothermal reaction time is beneficial for further improving the material structure and enhancing the defluorination effect. Furthermore, the results of Examples 7-10 also show that the material obtained in this invention maintains good defluorination performance under different adsorption pH conditions and in the presence of common coexisting ions, indicating that the material has certain environmental adaptability and application stability.

[0174] Furthermore, compared with the comparative examples, the acetic acid-controlled solvothermal in-situ conversion method for sodium aluminate doping used in this invention has significant advantages in both material formation and defluorination performance. The comparative results show that when sodium aluminate, acetic acid control, or pH adjustment is lacking, or when other acidic media, other aluminum sources, or unsuitable acetic acid addition ratios are used, the defluorination performance of the obtained materials is significantly reduced. This indicates that the acetic acid control system, the introduction of sodium aluminate, and the control of alkaline conditions all play important roles in the conversion of eggshell calcium source, the formation of the composite structure, and performance improvement. This invention regulates the dissolution-conversion process of eggshell calcium source through a reaction system composed of acetic acid and water, and achieves the synergistic construction of calcium, aluminum, and phosphorus components with the participation of sodium aluminate, thereby obtaining a relatively stable and rationally composed eggshell-based calcium-aluminum-phosphorus composite defluorination material. Compared with the comparative examples, the material obtained by this invention can still maintain good defluorination effect under low dosage and near-neutral conditions, indicating that it has good comprehensive application performance.

[0175] The performance of the ACP-6 sample prepared in Example 6 was tested, as follows:

[0176] (a) Adsorption isotherm experiment

[0177] Weigh 0.04 g of sample and add it to 40 mL of NaF solution with different concentrations: 10, 20, 40, 60, 80, 100, 120, 160 and 200 mg / L. Adjust the pH of the system to 6. Then, shake the solution at 25 ℃, 35 ℃ and 45 ℃ in a constant temperature shaker at 140 rpm for 24 h. After the reaction is completed, measure the concentration of residual fluoride ions in the solution and calculate the adsorption equilibrium amount.

[0178] (b) Adsorption kinetics experiment

[0179] Weigh 1.5 g of sample and add it to 1.5 L of NaF solution with an initial concentration of 10 mg / L. Adjust the pH of the system to 6 and stir magnetically at room temperature. Take samples at 5, 10, 15, 20, 25, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 150, 180, 210, 240, 270, 300, 360, 420, 480, 540, 600, 720, 840, 1440, 1620, and 1800 min, filter, and immediately measure the fluoride ion concentration and calculate the adsorption amount at different times.

[0180] (c) Adsorption thermodynamics experiment

[0181] Weigh 0.04 g of sample and add it to 40 mL of NaF solution with different initial concentrations of 10, 20, 40, 60, 80, 100, 120, 160 and 200 mg / L, and adjust the pH of the system to 6. Then, shake in a constant temperature shaker at 140 rpm for 24 h at 25 ℃, 35 ℃ and 45 ℃, respectively. After the reaction is completed, measure the concentration of residual fluoride ions in the solution and calculate the relevant thermodynamic parameters.

[0182] (d) Regeneration cycle experiment

[0183] The sample was added to a fluorine-containing solution (fluoride ion concentration of 10 mg / L) at a dosage of 1 g / L and adsorbed for 24 h at pH 6 and a temperature of 25 °C. After adsorption, the adsorbent was separated and placed in a 2 M NaOH solution for desorption in a 60 °C water bath for 1 h. The sample was then washed with deionized water until neutral and dried at 60 °C. The dried sample was then used for the next round of adsorption experiments, and the above process was repeated to examine the regeneration performance of the material. A control group was used without desorption (desorption in 2 M NaOH solution at 60 °C for 1 h).

[0184] The results are as follows Figure 1 As shown in Figure a, the material prepared in Example 6 exhibits good adsorption capacity for fluoride ions, and the adsorption amount gradually increases with increasing equilibrium concentration. As the temperature increases from 25 °C to 35 °C and then to 45 °C, the isotherms shift upwards overall, indicating that increasing the temperature is beneficial for the adsorption and fixation of fluoride ions by the material. Combined with the fitting results, it can be seen that the fluoride removal process of this material simultaneously possesses certain surface adsorption characteristics and non-uniform surface interaction characteristics.

[0185] Figure b shows that the intraparticle diffusion fitting curve of the material prepared in Example 6 exhibits multi-stage linear characteristics, indicating that the removal process of fluoride ions undergoes a continuous process from rapid surface adsorption to diffusion into the particle interior and finally tends to equilibrium. The fitting lines for each stage do not pass through the origin, indicating that intraparticle diffusion is not the only rate-controlling step, and liquid film diffusion and interfacial reactions also participate in the overall fluoride removal process.

[0186] In Figure c, lnK and 1 / T show a good linear relationship, and the fitted equation is y = -912.082x + 3.166, R0 2 =0.977, indicating that the system has good thermodynamic fitting characteristics within the investigated temperature range. Combined with the increase in adsorption after heating in Figure a, it can be seen that the material of this invention has certain endothermic characteristics in the removal of fluoride ions, and heating is beneficial to the adsorption and fixation processes.

[0187] Figure d shows that the material prepared in Example 6, after regeneration with 2 M NaOH at 60 °C, maintained a high defluorination rate in the first few cycles, indicating that the material has a certain recyclability. As the number of cycles increased, the defluorination rate gradually decreased, suggesting that some active sites may have been irreversibly occupied, or that the material structure was affected during the regeneration process. Overall, this material possesses both good initial defluorination performance and certain recycling potential.

[0188] The process steps of this invention are clear, the reaction conditions are relatively mild, and it does not require high-temperature calcination or complex equipment, thus possessing considerable potential for scale-up applications. This method uses waste eggshells as raw material, combining water defluoridation with resource utilization, and has good application value.

[0189] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described with reference to preferred embodiments, those skilled in the art should understand that various changes in form and detail can be made without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A method for preparing an acetic acid-controlled sodium aluminate-doped eggshell-based calcium aluminum phosphorus defluorination material, characterized in that, Includes the following steps: Step 1: Add eggshell powder, phosphorus source and sodium aluminate to a mixed solvent composed of acetic acid and water, mix and disperse to form a uniform reaction system; Step two, adjust the pH of the reaction system to be alkaline; Step 3: The adjusted reaction system is transferred to a closed reaction vessel for solvothermal reaction, causing the calcium source from the eggshell to dissolve and transform, and a composite material containing calcium, aluminum and phosphorus components is constructed in situ. Step four: After the reaction is complete, the resulting solid product is separated and washed. Step 5: Dry the washed product to obtain acetic acid-regulated sodium aluminate-doped eggshell-based calcium aluminum phosphorus defluorination material.

2. The preparation method of an acetic acid-regulated sodium aluminate-doped eggshell-based calcium aluminum phosphorus defluorination material according to claim 1, characterized in that, In step one, the eggshell powder is used after being washed, dried, crushed and sieved; the phosphorus source is a soluble phosphate, which includes at least one of sodium dihydrogen phosphate, disodium hydrogen phosphate, potassium dihydrogen phosphate and dipotassium hydrogen phosphate.

3. The preparation method of an acetic acid-regulated sodium aluminate-doped eggshell-based calcium aluminum phosphorus defluorination material according to claim 1, characterized in that, In step one, the mass ratio of eggshell powder, phosphorus source, and sodium aluminate is 1:(0.5-1.5):(0.5-1.5).

4. The preparation method of an acetic acid-controlled sodium aluminate-doped eggshell-based calcium aluminum phosphorus defluorination material according to claim 1, characterized in that, In step one, the volume ratio of acetic acid to water in the mixed solvent is 1:5-5:1, and the ratio of the total mass of eggshell powder, phosphorus source and sodium aluminate to the mixed solvent is 1 g:(4-6) mL.

5. The preparation method of an acetic acid-regulated sodium aluminate-doped eggshell-based calcium aluminum phosphorus defluorination material according to claim 1, characterized in that, In step two, the pH of the reaction system is adjusted to 8-11.

6. The preparation method of an acetic acid-controlled sodium aluminate-doped eggshell-based calcium aluminum phosphorus defluorination material according to claim 1, characterized in that, In step three, the temperature of the solvothermal reaction is 150-200℃, and the reaction time is 400-600 min.

7. The preparation method of an acetic acid-controlled sodium aluminate-doped eggshell-based calcium aluminum phosphorus defluorination material according to claim 1, characterized in that, In step four, the washing process includes first washing with an organic solvent, and then washing with water until neutral. The organic solvent includes at least one of ethanol, methanol, and isopropanol.

8. The preparation method of an acetic acid-regulated sodium aluminate-doped eggshell-based calcium aluminum phosphorus defluorination material according to claim 1, characterized in that, In step five, the drying temperature is 40-80℃, and the drying is carried out overnight.

9. The acetic acid-regulated sodium aluminate-doped eggshell-based calcium aluminum phosphorus defluorination material prepared by the method according to any one of claims 1-8.

10. The application of the acetic acid-controlled sodium aluminate-doped eggshell-based calcium aluminum phosphorus defluorination material according to claim 9 in the defluorination of fluoride-containing water bodies.

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