Method for preparing aluminum-based anode slime-sodium alginate composite microspheres and adsorbing trace fluorine

Abstract

The present application relates to the technical field of fluorine removal in water bodies, and particularly relates to a method for preparing aluminum-based anode sludge-sodium alginate composite microspheres and adsorbing trace fluorine, wherein the aluminum-based anode sludge-sodium alginate composite microspheres are prepared by taking sodium alginate as a skeleton carrier, aluminum-based anode sludge as active adsorption sites, and calcium chloride as a crosslinking agent. The sodium alginate constructs a porous three-dimensional network, provides a large specific surface area and pores, and uniformly disperses the aluminum-based anode sludge in the sodium alginate, so as to avoid the sedimentation of the anode oxidation sludge in the fluorine-containing waste liquid. The aluminum-based anode sludge provides fluorine ion-specific adsorption active sites, and the aluminum-based anode sludge as inorganic steel filler doped in the sodium alginate organic network can effectively enhance the mechanical strength of the adsorbent. The present adsorbent combines the advantages of the aluminum-based anode sludge and the sodium alginate through compounding, and plays a synergistic effect. The prepared composite adsorbent has good formability, high mechanical strength, good hydrophilicity, easy adsorption of fluorine ions, and easy recovery.

Description

Technical Field

[0001] This invention relates to the field of fluoride removal technology in water, specifically to a method for preparing aluminum-based anode mud@sodium alginate composite microspheres and adsorbing trace amounts of fluoride. Background Technology

[0002] Aluminum-based anode sludge is an industrial solid waste generated during the anodizing process of aluminum and aluminum alloy surfaces. Its core characteristics include high aluminum content (aluminum content can reach over 30% by mass) and complex composition. Currently, the main methods for disposing of this type of solid waste are stockpiling or direct landfilling, which not only occupies a large amount of land resources and wastes aluminum resources but also poses significant environmental safety hazards. In addition, there are reports of using it as a raw material in ceramics, refractory materials, or cement, glass, and abrasive products for resource utilization, but these also involve complex processing procedures and risks of secondary pollution. Therefore, how to efficiently utilize aluminum-based anode sludge is a pressing technical challenge for the aluminum processing industry.

[0003] Meanwhile, my country's industrial wastewater discharge containing fluoride is enormous, involving numerous industries and exhibiting complex water quality. Existing fluoride wastewater treatment technologies mainly include chemical precipitation, coagulation sedimentation, membrane separation, and adsorption. Among these, adsorption, a common water treatment method, removes fluoride from water primarily through adsorption, ion exchange, or surface complexation, and is one of the most effective and reliable methods. Fluoride ion adsorbents are often metal oxides and hydroxides, with alumina and aluminum hydroxide adsorbents being the most widely used for fluoride removal. Chinese invention patent CN201611071502.9 discloses the application of modified activated alumina in wastewater defluorination. This invention modifies γ-alumina by adding a certain concentration of sodium hydroxide followed by a certain concentration of sulfuric acid, then filtering, drying, and calcining to obtain modified alumina, thereby improving its fluoride adsorption performance. However, this method suffers from high raw material costs and high energy consumption during preparation, posing significant challenges for large-scale industrial application. Chinese invention patent CN202411899536.1 discloses a coordination unsaturated alumina material, its preparation method, and its application. This invention involves adding glacial acetic acid to a solution containing aluminum salts, followed by the addition of urea, and conducting a hydrothermal reaction to obtain a solid product. The solid product is then heat-treated at 200-600℃ to obtain the coordination unsaturated alumina for adsorbing fluoride ions. However, the preparation process suffers from poor reproducibility of raw materials, unreliable yield, and significant waste generation, resulting in limited prospects for industrial application. Summary of the Invention

[0004] The purpose of this invention is to solve the problems of resource utilization of aluminum-based anode mud and high cost of preparation of defluorination adsorbents, and to provide a method for preparing aluminum-based anode mud@sodium alginate composite microspheres and adsorbing trace amounts of fluoride.

[0005] To achieve the above objectives, this invention discloses a method for preparing aluminum-based anode mud@sodium alginate composite microspheres, comprising the following steps:

[0006] S1, heat-treat aluminum-based anode mud, ball-mill it, and sieve it to collect the permeate;

[0007] S2, the aluminum-based anode mud treated in step S1 is thoroughly mixed with sodium alginate powder, deionized water is added and stirred thoroughly to form a composite hydrogel;

[0008] S3. The composite hydrogel obtained in step S2 is placed in a mold for shaping and then placed in a calcium chloride aqueous solution for cross-linking. After filtration, washing, and aging, aluminum-based anode mud@sodium alginate composite microspheres are obtained.

[0009] In step S1, the heating temperature is 60°C, the heating time is about 48 hours, and the sieve is an 80-mesh sieve.

[0010] In step S2, the mass ratio of aluminum-based anode mud is 30%, and the mass ratio of sodium alginate is 70%. The mass of deionized water added is 3.25 times the total mass of aluminum-based anode mud and sodium alginate.

[0011] In step S3, the diameter of the sphere made by the mold is 2-3 mm, the concentration of calcium chloride in the calcium chloride aqueous solution is 0.5 mol / L, and the crosslinking time is 4 h.

[0012] In step S3, the cleaning process involves washing with deionized water 2-3 times, and the aging time is 72 hours.

[0013] This invention also discloses aluminum-based anode mud@sodium alginate composite microspheres prepared by the above preparation method, and the application of such aluminum-based anode mud@sodium alginate composite microspheres in the adsorption of trace amounts of fluorine.

[0014] Adsorbing trace amounts of fluoride from wastewater specifically includes the following steps:

[0015] A1. Add dilute sulfuric acid solution and sodium hydroxide solution to fluoride-containing wastewater to adjust the pH;

[0016] A2, aluminum-based anode mud@sodium alginate composite microspheres are added to the fluoride-containing wastewater treated in step A1, and static adsorption is carried out after heating and stirring.

[0017] In step A1, the concentration of the dilute sulfuric acid solution is 0.5 mol / L, the concentration of the sodium hydroxide solution is 0.5 mol / L, and the pH of the fluoride-containing wastewater after pH adjustment is 4.

[0018] In step A2, the mass ratio of aluminum-based anode mud@sodium alginate composite microspheres to fluoride in fluoride-containing wastewater is 1000:1; the heating and stirring speed is 600 rpm; the adsorption temperature is 60℃; and the adsorption time is 2 hours.

[0019] This invention addresses the problem that sodium alginate gel alone has extremely weak adsorption capacity for fluoride ions and poor mechanical properties. Aluminum-based anode mud contains large amounts of alumina and aluminum hydroxide, but pure aluminum-based anode mud powder has a small specific surface area, making it prone to agglomeration and difficult to separate and recover. By combining sodium alginate with aluminum-based anode mud, the problems of molding, dispersion, and separation of aluminum-based anode mud are solved. Specifically, the aluminum-based anode mud imparts the core function of targeted fluoride removal to sodium alginate, while sodium alginate provides a stable three-dimensional framework to the aluminum-based anode mud. The result is a composite adsorbent material with good moldability, high mechanical strength, excellent hydrophilicity, high efficiency in adsorbing fluoride ions, and easy recovery. Finally, a method for preparing and applying aluminum-based anode mud@sodium alginate composite microspheres for treating wastewater containing trace amounts of fluoride is provided.

[0020] Given the high aluminum content of aluminum-based anode mud and the need for fluoride-containing wastewater treatment, the inventors of this invention, starting from the perspective of "treating waste with waste," have finally obtained this invention after a long period of research and practice. This invention uses aluminum-based anode mud as the main raw material, combined with the three-dimensional gel framework structure of sodium alginate, a natural polymer, to prepare sodium alginate-based composite microspheres through in-situ composite and ion cross-linking molding processes. This effectively solves the problems of low resource utilization rate, difficult disposal, and environmental pollution associated with aluminum-based anode mud, achieving high-value utilization of solid waste. It also overcomes the technical defects of traditional fluoride removal adsorbents, such as low capacity, poor selectivity, easy loss, difficult separation, and poor stability. Simultaneously, it achieves the resource utilization of industrial solid waste and the efficient and deep purification of fluoride-containing wastewater, possessing significant environmental and economic benefits.

[0021] Compared with existing technologies, the advantages of this invention are as follows: This invention uses adsorption technology to remove fluoride ions from wastewater and discloses a method for preparing aluminum-based anode mud@sodium alginate composite microspheres for treating fluoride-containing wastewater. It utilizes aluminum-based anode mud, a byproduct of aluminum and aluminum alloy oxidation surface treatment processes, and prepares aluminum-based anode mud@sodium alginate composite microspheres through a process of pretreatment of aluminum-based anode mud-proportional doping-crosslinking-aging. This not only simplifies the route for synthesizing the adsorbent but also solves the problems of complex preparation, high cost, and difficulty in recycling of common metal oxide and hydroxide type adsorbents. Furthermore, it explores the potential value of industrial byproducts, which is in line with the green chemistry concept of "treating waste with waste". Attached Figure Description

[0022] Figure 1The images show macroscopic images, electron microscope (EM) images, and energy dispersive spectroscopy (EDS) spectra of the adsorbent preparation process. (a) is a macroscopic image of the treated anodized sludge; (b) is a macroscopic image of the cross-linked adsorbent; (c) is a macroscopic image of the aged adsorbent; (d) and (e) are cross-sectional EMS images of the adsorbent; (f) is an EMS image after adsorption; (g) is a distribution map of O element in the adsorbent after adsorption; (h) is a distribution map of Al element in the adsorbent after adsorption; and (i) is a distribution map of F element in the adsorbent after adsorption.

[0023] Figure 2 The figure shows the change in the fluoride removal efficiency of the aluminum-based anode mud over time with different doping percentages in the adsorbent, namely 10%, 20%, 30%, 40%, 50%, 60%, and 70%.

[0024] Figure 3 The variation of the fluoride removal effect of the adsorbent over time under different solid-liquid mass ratios of dry material and deionized water in Example 3 is shown. The solid-liquid ratios are 1:3.5, 1:3.25, 1:3, 1:2.75, and 1:2.5.

[0025] Figure 4 The fluoride removal effect of the adsorbents prepared at different concentrations of crosslinking agent in Example 4 changes over time. The crosslinking agent concentrations are 0.01 mol / L, 0.05 mol / L, 0.1 mol / L, 0.5 mol / L, 1 mol / L, and 2 mol / L.

[0026] Figure 5 The fluoride removal effect of the adsorbent prepared under different crosslinking times in Example 5 is shown as a function of time, with crosslinking times of 3h, 4h, 5h, 6h, and 7h.

[0027] Figure 6 The fluoride removal effect of the adsorbent prepared in Example 6 varies with time under different aging times: 0h, 24h, 48h, 72h, and 96h.

[0028] Figure 7 The effect of the adsorbent on fluoride removal over time is shown in Example 7 under the influence of pH changes in the fluoride-containing waste liquid during adsorption. The pH values ​​are 3, 4, 5, 6, 7, 8, 9, and 10.

[0029] Figure 8 The effect of the adsorbent on fluoride removal during adsorption in Example 8 is shown as the temperature of the fluoride-containing waste liquid changes over time, with temperatures of 0℃, 20℃, 40℃, 60℃, and 80℃.

[0030] Figure 9 The effect of the adsorbent on fluoride removal over time is shown in Example 9 under the influence of different stirring speeds during adsorption. The stirring speeds are 150 rpm, 300 rpm, 450 rpm, 600 rpm, and 800 rpm.

[0031] Figure 10 The variation of the fluoride removal effect of the adsorbent over time is shown in Example 10 under different adsorbent addition amounts: 0.5g, 0.75g, 1g, 1.5g, and 2g.

[0032] Figure 11 The effect of fluoride removal by the adsorbent over time is shown in Comparative Example 1, where the particle size of the adsorbent varies with the adsorbent size of 1-2 mm, 2-3 mm, 3-4 mm, 4-5 mm, and 5-6 mm. Detailed Implementation

[0033] The above-mentioned and other technical features and advantages of the present invention will be described in more detail below with reference to the accompanying drawings.

[0034] Example 1

[0035] (1) Heat-treat aluminum-based anode mud at 60℃ for 48h, ball mill it and pass it through an 80-mesh sieve, and take the permeate;

[0036] (2) Add 70% of the treated aluminum-based anode mud to sodium alginate powder and mix thoroughly to obtain a mixture;

[0037] (3) Add deionized water with a solid-liquid mass ratio of 1:3.25 to the mixture of aluminum-based anode mud and sodium alginate and stir thoroughly to form a composite hydrogel;

[0038] (4) After shaping the composite hydrogel in a mold, it is placed in a 0.5 mol / L calcium chloride aqueous solution for cross-linking for 4 hours;

[0039] (5) After filtering the cross-linked composite hydrogel, wash it with deionized water 2-3 times and then age it for 72 hours to complete the preparation of the adsorbent;

[0040] (6) Add dilute sulfuric acid solution and sodium hydroxide solution to the simulated fluorine waste liquid to adjust the pH to about 4;

[0041] (7) Take 1g of adsorbent and add it to 50mL of simulated fluoride waste liquid with a concentration of 20mg / L;

[0042] (8) Add a magnetic stir bar and perform static adsorption at 600 rpm and 60°C for 2 hours.

[0043] like Figure 1 As shown in (a), the treated pure aluminum-based anode mud has a small particle size, making it difficult to separate and recover fluoride ions if used directly for adsorption in water. Furthermore, the aluminum-based anode mud contains a certain amount of water-soluble salts, which can easily cause secondary pollution of the water body if directly adsorbed.

[0044] like Figure 1As shown in (b), calcium chloride crosslinking agent can effectively help the adsorbent maintain its spherical shape after molding.

[0045] like Figure 1 As shown in (c), the prepared adsorbent effectively immobilizes the aluminum-based anode mud within the sodium alginate network gel structure, solving the problems of difficult recycling and secondary pollution caused by adsorption of pure aluminum-based anode mud. Furthermore, the adsorbent's uniform size and shape, along with numerous surface wrinkles, contribute to increasing its specific surface area, thus facilitating better adsorption of fluoride ions.

[0046] like Figure 1 As shown in (d)(e), the cross-section of the adsorbent shows that the adsorbent contains a large number of layered folds and irregular pores. This structure further increases the specific surface area of ​​the adsorbent and exposes more adsorption sites, which is beneficial to improving the adsorption effect of the adsorbent.

[0047] like Figure 1 As shown in (f), the aluminum oxide and aluminum hydroxide in the aluminum-based anode mud will rapidly hydrate on the surface when in water, forming a large number of surface hydroxyl groups, so that fluoride ions are well adsorbed on the adsorbent.

[0048] Figure 1 (g), (h), and (i) are the elemental distribution diagrams of oxygen, aluminum, and fluorine after adsorption by the adsorbent, respectively. As can be seen from the diagrams, oxygen, aluminum, and fluorine are evenly distributed in the adsorbent powder after adsorption, which further proves the adsorbent's ability to treat fluoride ions.

[0049] Example 2

[0050] The effect of the percentage content of aluminum-based anode slime on adsorption efficiency:

[0051] (1) Heat-treat aluminum-based anode mud at 60℃ for 48h, ball mill it and pass it through an 80-mesh sieve, and take the permeate;

[0052] (2) The aluminum-based anode mud treated with sodium alginate powder was doped into the powder at proportions of 110%, 20%, 30%, 40%, 50%, 60%, and 70% respectively and then thoroughly mixed to obtain a mixture.

[0053] (3) Add deionized water with a solid-liquid mass ratio of 1:3.25 to each group of aluminum-based anode mud and sodium alginate mixture and stir thoroughly to form a composite hydrogel;

[0054] (4) After the composite hydrogel is shaped in a mold, it is placed in a 0.5 mol / L calcium chloride aqueous solution for cross-linking for 4 h;

[0055] (5) After filtering the cross-linked composite hydrogel, wash it with deionized water 2-3 times and then age it for 72 hours to complete the preparation of the adsorbent;

[0056] (6) Add dilute sulfuric acid solution and sodium hydroxide solution to the simulated fluorine waste liquid to adjust the pH to about 4;

[0057] (7) Take 1g of adsorbent and add it to 50mL of simulated fluoride waste liquid with a concentration of 20mg / L;

[0058] (8) Add a magnetic stir bar and perform static adsorption at 600 rpm and 60°C for 2 hours.

[0059] like Figure 2 As shown, the adsorption effect of the adsorbent gradually increases with the increase of the doping percentage of aluminum-based anode mud from 10% to 70%. This is because sodium alginate mainly plays a role in fixing the aluminum-based anode mud and providing a three-dimensional framework, while the actual adsorption centers are mainly alumina and aluminum hydroxide in the aluminum-based anode mud. However, as the doping percentage increases, when the doping percentage of aluminum-based anode mud exceeds 70%, the stability of the adsorbent is compromised and it becomes difficult to shape. Therefore, a doping ratio of 70% is chosen after comprehensive consideration.

[0060] Example 3

[0061] The effect of solid-liquid mass ratio on adsorption effect:

[0062] (1) Heat-treat aluminum-based anode mud at 60℃ for 48h, ball mill it and pass it through an 80-mesh sieve, and take the permeate;

[0063] (2) Add 70% of the treated aluminum-based anode mud to sodium alginate powder and mix thoroughly to obtain a mixture;

[0064] (3) Add deionized water with solid-liquid mass ratios of 1:3.5, 1:3.25, 1:3, 1:2.75 and 1:2.5 respectively to the aluminum-based anode mud and sodium alginate mixture and stir thoroughly to form a composite hydrogel;

[0065] (4) After shaping each group of composite hydrogels in a mold, they were placed in a 0.5 mol / L calcium chloride aqueous solution for cross-linking for 4 h.

[0066] (5) After filtering the cross-linked composite hydrogel, wash it with deionized water 2-3 times and then age it for 72 hours to complete the preparation of the adsorbent.

[0067] (6) Add dilute sulfuric acid solution and sodium hydroxide solution to the simulated fluorine waste liquid to adjust the pH to about 4;

[0068] (7) Take 1g of adsorbent and add it to 50mL of simulated fluoride waste liquid with a concentration of 20mg / L;

[0069] (8) Add a magnetic stir bar and perform static adsorption at 600 rpm and 60°C for 2 hours.

[0070] Adding a certain amount of deionized water to the mixture affects not only further shaping but also the internal pore size of the shaped spheres. Too much deionized water will decrease the viscosity of the solid-liquid mixture, making further shaping difficult. Conversely, too little deionized water will reduce the internal pore size of the shaped spheres, thus decreasing the adsorption effect. Specific details are as follows... Figure 3 As shown in the figure, the optimal solid-liquid mass ratio is 1:3.25.

[0071] Example 4

[0072] The effect of crosslinking agent concentration on adsorption effect:

[0073] (1) Heat-treat aluminum-based anode mud at 60℃ for 48h, ball mill it and pass it through an 80-mesh sieve, and take the permeate;

[0074] (2) Add 70% of the treated aluminum-based anode mud to sodium alginate powder and mix thoroughly to obtain a mixture;

[0075] (3) Add deionized water with a solid-liquid mass ratio of 1:3.25 to the mixture of aluminum-based anode mud and sodium alginate and stir thoroughly to form a composite hydrogel;

[0076] (4) After the composite hydrogel is shaped in the mold, it is placed in calcium chloride aqueous solutions of 0.01 mol / L, 0.05 mol / L, 0.1 mol / L, 0.5 mol / L, 1 mol / L and 2 mol / L respectively for cross-linking for 4 h;

[0077] (5) After filtering the cross-linked composite hydrogel, wash it with deionized water 2-3 times and then age it for 72 hours to complete the preparation of the adsorbent.

[0078] (6) Add dilute sulfuric acid solution and sodium hydroxide solution to the simulated fluorine waste liquid to adjust the pH to about 4;

[0079] (7) Take 1g of adsorbent and add it to 50mL of simulated fluoride waste liquid with a concentration of 20mg / L;

[0080] (8) Add a magnetic stir bar and perform static adsorption at 600 rpm and 60°C for 2 hours.

[0081] like Figure 4 As shown, a low concentration of the crosslinking agent makes it difficult to form a stable three-dimensional network. The defluorination effect reaches its peak, exceeding 90%, when the crosslinking agent concentration increases from 0.01 mol / L to 0.5 mol / L. Subsequently, the adsorption effect decreases with further increases in crosslinking agent concentration. This may be because excessively high crosslinking agent concentrations cause calcium chloride to accumulate on and inside the adsorbent, clogging its pore structure and thus reducing the adsorption effect.

[0082] Example 5

[0083] The effect of calcium chloride crosslinking time on adsorption efficiency:

[0084] (1) Heat-treat aluminum-based anode mud at 60℃ for 48h, ball mill it and pass it through an 80-mesh sieve, and take the permeate;

[0085] (2) Add 70% of the treated aluminum-based anode mud to sodium alginate powder and mix thoroughly to obtain a mixture;

[0086] (3) Add deionized water with a solid-liquid mass ratio of 1:3.25 to the mixture of aluminum-based anode mud and sodium alginate and stir thoroughly to form a composite hydrogel;

[0087] (4) After the composite hydrogel is shaped in a mold, it is placed in a 0.5 mol / L calcium chloride aqueous solution for cross-linking for 3 h, 4 h, 5 h, 6 h, and 7 h.

[0088] (5) After filtering the cross-linked composite hydrogel, wash it with deionized water 2-3 times and then age it for 72 hours to complete the preparation of the adsorbent.

[0089] (6) Add dilute sulfuric acid solution and sodium hydroxide solution to the simulated fluorine waste liquid to adjust the pH to about 4;

[0090] (7) Take 1g of adsorbent and add it to 50mL of simulated fluoride waste liquid with a concentration of 20mg / L;

[0091] (8) Add a magnetic stir bar and perform static adsorption at 600 rpm and 60°C for 2 hours.

[0092] like Figure 5 As shown, the adsorption effect of calcium chloride gradually increases from 3h to 4h, but the adsorption effect decreases significantly after the cross-linking time increases from 4h. This is because excessive cross-linking time leads to over-cross-linking of the gel, shrinkage and densification of the structure, ultimately resulting in a decrease in adsorption performance.

[0093] Example 6

[0094] The effect of aging time on adsorption efficiency:

[0095] (1) Heat-treat aluminum-based anode mud at 60℃ for 48h, ball mill it and pass it through an 80-mesh sieve, and take the permeate;

[0096] (2) Add 70% of the treated aluminum-based anode mud to sodium alginate powder and mix thoroughly to obtain a mixture;

[0097] (3) Add deionized water with a solid-liquid mass ratio of 1:3.25 to the mixture of aluminum-based anode mud and sodium alginate and stir thoroughly to form a composite hydrogel;

[0098] (4) After shaping the composite hydrogel in a mold, it is placed in a 0.5 mol / L calcium chloride aqueous solution for cross-linking for 4 hours;

[0099] (5) After filtering the cross-linked composite hydrogel, wash it with deionized water 2-3 times and then age it for 0h, 24h, 48h, 72h and 96h to complete the preparation of the adsorbent.

[0100] (6) Add dilute sulfuric acid solution and sodium hydroxide solution to the simulated fluorine waste liquid to adjust the pH to about 4;

[0101] (7) Take 1g of adsorbent and add it to 50mL of simulated fluoride waste liquid with a concentration of 20mg / L;

[0102] (8) Add a magnetic stir bar and perform static adsorption at 600 rpm and 60°C for 2 hours.

[0103] like Figure 6 As shown, the defluorination effect gradually increases with aging time from 0h to 72h. This is because aging removes free water occupying the pores, making the diffusion channels for fluoride ions more unobstructed and reducing mass transfer resistance. Some physically adsorbed water on the surface of the aluminum-based anode mud is removed, exposing more active sites. The gel skeleton initially shrinks and stabilizes, preventing excessive swelling during adsorption. When the aging time exceeds 72h, the gel is completely dehydrated, and a large number of micropores close, preventing fluoride ions from entering the adsorbent, resulting in a sharp reduction in effective adsorption sites.

[0104] Example 7

[0105] The effect of pH on adsorption efficiency of waste liquid:

[0106] (1) Heat-treat aluminum-based anode mud at 60℃ for 48h, ball mill it and pass it through an 80-mesh sieve, and take the permeate;

[0107] (2) Add 70% of the treated aluminum-based anode mud to sodium alginate powder and mix thoroughly to obtain a mixture;

[0108] (3) Add deionized water with a solid-liquid mass ratio of 1:3.25 to the mixture of aluminum-based anode mud and sodium alginate and stir thoroughly to form a composite hydrogel;

[0109] (4) After shaping the composite hydrogel in a mold, it is placed in a 0.5 mol / L calcium chloride aqueous solution for cross-linking for 4 hours;

[0110] (5) After filtering the cross-linked composite hydrogel, wash it with deionized water 2-3 times and then age it for 72 hours to complete the preparation of the adsorbent.

[0111] (6) Add dilute sulfuric acid solution and sodium hydroxide solution to the simulated fluorine waste liquid to adjust the pH to about 3, 4, 5, 6, 7, 8, 9, 10;

[0112] (7) Take 1g of adsorbent and add it to 50mL of simulated fluoride waste liquid with a concentration of 20mg / L;

[0113] (8) Add a magnetic stir bar and perform static adsorption at 600 rpm and 60°C for 2 hours.

[0114] like Figure 7 As shown, the defluorination efficiency increases from pH 3 to 4, exceeding 90%, and remains around 90% from pH 4 to 6. However, the defluorination efficiency decreases significantly above pH 6, then slightly increases again at pH 9. The relationship between adsorption efficiency and pH exhibits an M-shaped curve trend. Considering all factors, pH 4 is selected as the optimal adsorption pH.

[0115] Example 8

[0116] The effect of stirring speed on adsorption effect:

[0117] (1) Heat-treat aluminum-based anode mud at 60℃ for 48h, ball mill it and pass it through an 80-mesh sieve, and take the permeate;

[0118] (2) Add 70% of the treated aluminum-based anode mud to sodium alginate powder and mix thoroughly to obtain a mixture;

[0119] (3) Add deionized water with a solid-liquid mass ratio of 1:3.25 to the mixture of aluminum-based anode mud and sodium alginate and stir thoroughly to form a composite hydrogel;

[0120] (4) After shaping the composite hydrogel in a mold, it is placed in a 0.5 mol / L calcium chloride aqueous solution for cross-linking for 4 hours;

[0121] (5) After filtering the cross-linked composite hydrogel, wash it with deionized water 2-3 times and then age it for 72 hours to complete the preparation of the adsorbent.

[0122] (6) Add dilute sulfuric acid solution and sodium hydroxide solution to the simulated fluorine waste liquid to adjust the pH to about 4;

[0123] (7) Take 1g of adsorbent and add it to 50mL of simulated fluoride waste liquid with a concentration of 20mg / L;

[0124] (8) Add a magnetic stir bar at 600 rpm and perform static adsorption at 0℃, 20℃, 40℃, 60℃ and 80℃ for 2 hours.

[0125] like Figure 8As shown, from 0℃ to 60℃, both the adsorption effect and the adsorption rate increase with increasing temperature. When the temperature exceeds 60℃ and reaches 80℃, the adsorption effect does not change significantly. With increasing temperature, the thermal motion of water molecules and fluoride ions intensifies, allowing fluoride ions to diffuse faster within the adsorbent and more easily reach the active adsorption sites in the aluminum-based anode mud.

[0126] Example 9

[0127] (1) Heat-treat aluminum-based anode mud at 60℃ for 48h, ball mill it and pass it through an 80-mesh sieve, and take the permeate;

[0128] (2) Add 70% of the treated aluminum-based anode mud to sodium alginate powder and mix thoroughly to obtain a mixture;

[0129] (3) Add deionized water with a solid-liquid mass ratio of 1:3.25 to the mixture of aluminum-based anode mud and sodium alginate and stir thoroughly to form a composite hydrogel;

[0130] (4) After shaping the composite hydrogel in a mold, it is placed in a 0.5 mol / L calcium chloride aqueous solution for cross-linking for 4 hours;

[0131] (5) After filtering the cross-linked composite hydrogel, wash it with deionized water 2-3 times and then age it for 72 hours to complete the preparation of the adsorbent.

[0132] (6) Add dilute sulfuric acid solution and sodium hydroxide solution to the simulated fluorine waste liquid to adjust the pH to about 4;

[0133] (7) Take 1g of adsorbent and add it to 50mL of simulated fluoride waste liquid with a concentration of 20mg / L;

[0134] (8) Add a magnetic stir bar at 150 rpm, 300 rpm, 450 rpm, 600 rpm and 800 rpm, and perform static adsorption at 60°C for 2 hours.

[0135] like Figure 9 As shown, when the rotation speed is below 300 rpm, the adsorption effect increases significantly with increasing rotation speed. This is because when the liquid turbulence is weak, the mass transfer resistance is large, and the adsorption effect is also poor. When the rotation speed is greater than 300 rpm, although the adsorption effect also increases with increasing rotation speed, the increase gradually slows down. When the rotation speed reaches about 600 rpm, the increase in adsorption effect is optimal. After exceeding 600 rpm, the gain of the adsorption effect by the rotation speed tends to level off.

[0136] Example 10

[0137] The effect of adsorbent dosage on adsorption efficiency:

[0138] (1) Heat-treat aluminum-based anode mud at 60℃ for 48h, ball mill it and pass it through an 80-mesh sieve, and take the permeate;

[0139] (2) Add 70% of the treated aluminum-based anode mud to sodium alginate powder and mix thoroughly to obtain a mixture;

[0140] (3) Add deionized water with a solid-liquid mass ratio of 1:3.25 to the mixture of aluminum-based anode mud and sodium alginate and stir thoroughly to form a composite hydrogel;

[0141] (4) After shaping the composite hydrogel in a mold, it is placed in a 0.5 mol / L calcium chloride aqueous solution for cross-linking for 4 hours;

[0142] (5) After filtering the cross-linked composite hydrogel, wash it with deionized water 2-3 times and then age it for 72 hours to complete the preparation of the adsorbent.

[0143] (6) Add dilute sulfuric acid solution and sodium hydroxide solution to the simulated fluorine waste liquid to adjust the pH to about 4;

[0144] (7) Take 0.5g, 0.75g, 1g, 1.5g, and 2g of adsorbent and add them to 50mL of simulated fluoride waste liquid at 20mg / L;

[0145] (8) Add a magnetic stir bar and perform static adsorption at 600 rpm and 60°C for 2 hours.

[0146] like Figure 10 As shown, with the increase of adsorbent dosage, the removal efficiency of fluoride ions continuously increases and tends to stabilize, but the unit adsorption capacity first increases and then decreases. When the adsorbent dosage is 1g to 1.5g, the mass ratio of aluminum-based anode mud@sodium alginate composite microspheres to fluoride in the fluoride-containing wastewater is 1000:1 (wAl:wF=329.5:1), the fluoride removal efficiency increases slightly, but the unit adsorption capacity decreases. Furthermore, when the dosage is 1g, the adsorbent can achieve a removal rate of approximately 95% for 50mL of 20ppm fluoride-containing wastewater, and the concentration of the treated fluoride-containing wastewater is below 1mg / L, meeting the national fluoride-containing wastewater discharge standards.

[0147] Comparative Example 1

[0148] (1) Heat-treat aluminum anodized sludge at 60℃ for 48h, ball mill it and pass it through an 80-mesh sieve, and take the permeate;

[0149] (2) Add 70% sodium alginate powder to the treated aluminum anodized sludge and mix thoroughly to obtain a mixture;

[0150] (3) Add deionized water with a solid-liquid mass ratio of 1:3.25 to the mixture of aluminum anodizing sludge and sodium alginate and stir thoroughly to form a composite hydrogel;

[0151] (4) After shaping the composite hydrogel in different molds (1mm-6mm respectively), it was placed in a 0.5mol / L calcium chloride aqueous solution for cross-linking for 4h;

[0152] (5) After filtering the cross-linked composite hydrogel, wash it with deionized water 2-3 times and then age it for 72 hours to complete the preparation of the adsorbent;

[0153] (6) Add dilute sulfuric acid solution and sodium hydroxide solution to the simulated fluorine waste liquid to adjust the pH to about 4;

[0154] (7) Take 1g of adsorbent with different particle sizes and add it to 50mL of simulated fluoride waste liquid with a concentration of 20mg / L;

[0155] (8) Add a magnetic stir bar and perform static adsorption at 600 rpm and 60°C for 2 hours.

[0156] like Figure 11 As shown, by comparing the adsorption effects of different particle sizes of adsorbent on fluoride-containing solutions under optimal conditions, it was found that when using the same mass of adsorbent spheres for fluoride removal, smaller diameter spheres showed a significantly higher adsorption effect than larger diameter spheres after an adsorption time of 2 hours. Furthermore, the adsorption rate in the first 10 minutes also increased with decreasing diameter. While further reduction in diameter to 2-3 mm resulted in some improvement, the effect became insignificant. Additionally, smaller diameter spheres required a more complex preparation process, longer preparation time, and more precise molds. Therefore, considering all factors, a sphere diameter of 2-3 mm was deemed optimal.

[0157] The above description is merely a preferred embodiment of the present invention and is illustrative rather than restrictive. Those skilled in the art will understand that many changes, modifications, and even equivalents can be made within the spirit and scope defined by the claims of the present invention, all of which will fall within the protection scope of the present invention.

Claims

1. A method for preparing aluminum-based anode mud@sodium alginate composite microspheres, characterized in that, Includes the following steps: S1, heat-treat aluminum-based anode mud, ball-mill it, and sieve it to collect the permeate; S2, the aluminum-based anode mud treated in step S1 is thoroughly mixed with sodium alginate powder, deionized water is added and stirred thoroughly to form a composite hydrogel; S3. The composite hydrogel obtained in step S2 is placed in a mold for shaping and then placed in a calcium chloride aqueous solution for cross-linking. After filtration, washing, and aging, aluminum-based anode mud@sodium alginate composite microspheres are obtained.

2. The preparation method of aluminum-based anode mud@sodium alginate composite microspheres as described in claim 1, characterized in that, In step S1, the heating temperature is 60°C, the heating time is about 48 hours, and the sieve is an 80-mesh sieve.

3. The preparation method of aluminum-based anode mud@sodium alginate composite microspheres as described in claim 1, characterized in that, In step S2, the mass ratio of aluminum-based anode mud is 30%, the mass ratio of sodium alginate is 70%, and the mass of deionized water added is 3.25 times the total mass of aluminum-based anode mud and sodium alginate.

4. The preparation method of aluminum-based anode mud@sodium alginate composite microspheres as described in claim 1, characterized in that, In step S3, the diameter of the sphere made by the mold is 2-3 mm, the concentration of calcium chloride in the calcium chloride aqueous solution is 0.5 mol / L, and the crosslinking time is 4 h.

5. The preparation method of aluminum-based anode mud@sodium alginate composite microspheres as described in claim 1, characterized in that, In step S3, the cleaning process involves washing with deionized water 2-3 times, and the aging time is 72 hours.

6. An aluminum-based anode mud@sodium alginate composite microsphere prepared by the preparation method according to any one of claims 1 to 5.

7. The application of the aluminum-based anode mud@sodium alginate composite microspheres as described in claim 6 in the adsorption of trace amounts of fluorine.

8. The application of the aluminum-based anode mud@sodium alginate composite microspheres as described in claim 7 in the adsorption of trace amounts of fluorine, characterized in that, Adsorbing trace amounts of fluoride from wastewater specifically includes the following steps: A1. Add dilute sulfuric acid solution and sodium hydroxide solution to wastewater containing trace amounts of fluoride to adjust the pH; A2, aluminum-based anode mud@sodium alginate composite microspheres are added to the fluoride-containing wastewater treated in step A1, and static adsorption is carried out after heating and stirring.

9. The application of the aluminum-based anode mud@sodium alginate composite microspheres as described in claim 8 in the adsorption of trace amounts of fluorine, characterized in that, In step A1, the concentration of the dilute sulfuric acid solution is 0.5 mol / L, the concentration of the sodium hydroxide solution is 0.5 mol / L, and the pH of the fluoride-containing wastewater after pH adjustment is 4.

10. The application of the aluminum-based anode mud@sodium alginate composite microspheres as described in claim 8 in the adsorption of trace amounts of fluorine, characterized in that, In step A2, the mass ratio of aluminum-based anode mud@sodium alginate composite microspheres to fluoride in fluoride-containing wastewater is 1000:1; the heating and stirring speed is 600 rpm; the adsorption temperature is 60℃; and the adsorption time is 2 hours.

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