Activated carbon loaded cerium dioxide composite adsorbent as well as preparation method and application thereof

Abstract

The invention discloses an activated carbon loaded cerium dioxide composite adsorbent as well as a preparation method and application thereof. According to the composite adsorbent, activated carbon is taken as a carrier, and cerium dioxide is taken as an active component and is uniformly loaded on the surface and in pores of the activated carbon; the mass ratio of the cerium dioxide to the activated carbon is 0.1: 1-0.5: 1. The composite adsorbent is large in adsorption capacity, high in adsorption rate, wide in pH application range, easy to regenerate and low in cost; the preparation method is simple, mild in condition and easy for large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of functional materials technology for water treatment, specifically relating to an activated carbon-supported cerium dioxide composite adsorbent, its preparation method, and its application. Background Technology

[0002] Fluorine is an essential trace element for the human body, but long-term excessive intake of fluoride can lead to serious health problems such as dental fluorosis and skeletal fluorosis. Industrial activities, such as semiconductor manufacturing, electroplating, glass and ceramics production, and phosphate fertilizer production, generate large amounts of wastewater with high concentrations of fluoride. If not properly treated, this will pose a significant threat to the aquatic environment and human health.

[0003] Currently, common defluorination methods include chemical precipitation, coagulation precipitation, membrane separation, and adsorption. Among these, adsorption is particularly noteworthy due to its simplicity, relatively low cost, and high effectiveness. However, traditional adsorbents such as activated alumina and bone char suffer from drawbacks including low adsorption capacity, slow adsorption rate, narrow pH range (e.g., activated alumina performs best at pH 5-6), and difficulty in regeneration.

[0004] Cerium dioxide is widely recognized as a highly promising defluorination material due to its abundant hydroxyl (-OH) groups on its surface, which can strongly coordinate with fluoride ions to form stable Ce-F bonds. However, pure cerium dioxide particles are small and easily aggregate in water, leading to a decrease in specific surface area. Furthermore, solid-liquid separation is difficult in practical applications, limiting its large-scale use.

[0005] Activated carbon is an inexpensive adsorbent with a well-developed pore structure and a large specific surface area, but its specific adsorption capacity for fluoride ions is relatively weak. If cerium dioxide can be highly dispersedly loaded onto activated carbon, the advantages of both can be combined: activated carbon acts as a supporting framework, preventing cerium dioxide agglomeration and providing a large loading area and mass transfer channels; cerium dioxide acts as active sites, achieving highly efficient and specific chemisorption of fluoride ions. Currently, there are few patent reports on the use of activated carbon and cerium dioxide composites for deep fluoride removal, and there is still room for optimization in existing technologies regarding cerium dioxide loading methods, loading amounts, and synergistic effects with the support. Summary of the Invention

[0006] Technical problem solved: To address the above-mentioned technical problems, this invention provides an activated carbon-supported cerium dioxide composite adsorbent, its preparation method, and its application. This composite adsorbent has a large adsorption capacity, fast adsorption rate, wide pH adaptability range, is easy to regenerate, and has low cost. The preparation method is simple, the conditions are mild, and it is easy to scale up production.

[0007] Technical solution: In a first aspect, the present invention provides an activated carbon-supported cerium dioxide composite adsorbent, wherein the composite adsorbent uses activated carbon as a carrier and cerium dioxide as an active component uniformly loaded on the surface and inside the pores of the activated carbon; the mass ratio of cerium dioxide to activated carbon is 0.1:1 to 0.5:1, which can ensure a sufficient number of active sites and avoid cerium dioxide clogging the pores of the activated carbon or excessive agglomeration.

[0008] Preferably, the activated carbon is powdered activated carbon or granular activated carbon; the cerium dioxide has a grain size of 5-30 nm.

[0009] In a second aspect, the present invention provides a method for preparing the activated carbon-supported cerium dioxide composite adsorbent as described in the first aspect, comprising the following steps: a. Activated carbon pretreatment: The activated carbon is acid-washed, specifically by soaking it in 0.1-1 mol / L dilute nitric acid or dilute hydrochloric acid at room temperature for 2-6 hours, wherein the mass (g) ratio of activated carbon to the volume (mL) of dilute nitric acid or dilute hydrochloric acid is 1:5, in order to remove surface impurities and ash and increase oxygen-containing functional groups; then it is washed with deionized water until neutral, and finally dried at 105℃ to obtain pretreated activated carbon; b. Preparation of cerium source solution: Dissolve soluble cerium salt in deionized water to prepare a cerium source solution with a concentration of 0.1-0.5 mol / L; c. Impregnation and Precipitation: Add the pretreated activated carbon to the cerium source solution prepared in step b, and impregnate with magnetic stirring at room temperature for 0.5-2 hours to allow cerium ions to fully diffuse into the pores of the activated carbon; then, continuously stir at a speed of 150-400 rpm. Slowly add a 0.5-2.0 mol / L precipitant solution, controlling the amount of precipitant solution added to ensure that the OH- ions in the precipitant are within acceptable limits. - The molar ratio of cerium ions to cerium ions is 4:1 to 6:1. At the same time, the dropping rate is controlled so that the pH of the reaction system is 8-11. Under these alkaline conditions, cerium ions are uniformly precipitated on activated carbon in the form of cerium hydroxide or basic cerium carbonate. The reaction is stirred for another 2-6 hours to obtain a mixture. d. Aging and washing: Let the mixture obtained in step c stand for 6-12 hours to make the precipitation process more complete; filter and wash thoroughly with deionized water until no chloride or nitrate ions are detected in the filtrate or the conductivity remains basically unchanged when tested with a conductivity meter to obtain a solid product; e. Drying and calcination: The solid product obtained in step d is dried at 80-120℃ for 6-12 hours, and then calcined in a muffle furnace at 300-500℃ for 2-4 hours to completely convert cerium hydroxide or basic cerium carbonate into cerium dioxide with high adsorption activity, thus obtaining activated carbon-supported cerium dioxide composite adsorbent.

[0010] Preferably, the soluble cerium salt in step b is one of cerium nitrate hexahydrate, cerium chloride heptahydrate, or cerium sulfate.

[0011] Preferably, the precipitant in step c is a sodium hydroxide solution.

[0012] Thirdly, the present invention provides the application of the activated carbon-supported cerium dioxide composite adsorbent described in the first aspect or the activated carbon-supported cerium dioxide composite adsorbent prepared by the preparation method described in the second aspect in the removal of fluoride ions from wastewater.

[0013] Preferably, the specific process of the application is as follows: take a certain amount of fluoride-containing wastewater, adjust its initial pH value to the range of 3-10 with dilute hydrochloric acid or sodium hydroxide solution; add activated carbon-supported cerium dioxide composite adsorbent at a dosage of 0.5-5 g / L, and place it in a constant temperature shaker at 15-45℃ and a rotation speed of 150-200 rpm for 1-12 hours; after the reaction is completed, take a sample for filtration, use the fluoride ion selective electrode method to determine the residual fluoride ion concentration in the filtrate, and calculate the adsorption capacity and removal rate.

[0014] Preferably, for saturated activated carbon-supported cerium dioxide composite adsorbents, regeneration can be performed: the saturated activated carbon-supported cerium dioxide composite adsorbent is filtered and collected, then immersed in a 0.1-1.0 mol / L sodium hydroxide solution and shaken for 2-4 hours; the OH⁻ ions in the sodium hydroxide solution can exchange with the adsorbed F⁻ ions, causing fluoride ions to desorb into the solution, thereby regenerating the adsorbent; the regenerated activated carbon-supported cerium dioxide composite adsorbent can be washed with deionized water until neutral and reused in the defluorination process, maintaining a high adsorption efficiency even after multiple cycles.

[0015] Beneficial effects: 1) Synergistic effect: This invention cleverly combines the physical adsorption characteristics of activated carbon with the chemical adsorption characteristics of cerium dioxide, achieving a synergistic effect of "1+1>2"; activated carbon provides a huge specific surface area and abundant pores, promoting the mass transfer of fluoride ions to active sites; cerium dioxide provides a high density of specific adsorption sites, greatly improving the overall adsorption capacity and rate. 2) Wide pH range: Compared with traditional adsorbents (such as activated alumina), this composite adsorbent can maintain excellent defluorination performance under acidic, neutral and weakly alkaline conditions (pH 3-10), and has stronger adaptability. 3) Easy to separate and regenerate: Cerium dioxide is firmly fixed on millimeter / micrometer-sized activated carbon particles, solving the problem of solid-liquid separation of powder materials; at the same time, the adsorbent can be efficiently regenerated through simple alkaline washing, reducing operating costs; 4) Low cost and environmentally friendly: The activated carbon used as raw material is widely available and inexpensive, the preparation process is simple, energy consumption is low, and it is easy to scale up production; the adsorbent itself is non-toxic and harmless and will not cause secondary pollution. Detailed Implementation

[0016] The present invention will be described in detail below with reference to specific embodiments: Example 1

[0017] 1) Preparation: Take 10 g of powdered activated carbon, soak it in 0.5 mol / L nitric acid for 4 hours, wash and dry it to obtain pretreated activated carbon. Dissolve 4.34 g of cerium nitrate hexahydrate in 50 mL of deionized water, add the pretreated activated carbon, and soak for 1 hour. Under stirring, slowly add 50 mL of 1 mol / L sodium hydroxide solution, control the pH to 10, and react for 4 hours. After standing and aging for 10 hours, filter and wash. Dry the solid at 105℃ for 10 hours, and then calcine it in a muffle furnace at 400℃ for 3 hours to obtain composite adsorbent A (CeO2 loading of about 20%).

[0018] 2) Application: 100 mL of fluoride-containing wastewater with an initial fluoride ion concentration of 50 mg / L and pH=7 was used as a simulated sample. 0.1 g of adsorbent A (dosage 1 g / L) was added, and the mixture was shaken and reacted at 25℃ for 4 hours. The results showed that the fluoride ion removal rate reached 96.5%, and the adsorption capacity was 48.25 mg / g.

[0019] 3) Regeneration: After filtering the saturated adsorbent, it was placed in a 0.5 mol / L NaOH solution and shaken for 3 hours for regeneration. After washing, it was reused. After 5 adsorption-regeneration cycles, its removal rate of fluoride ions remained above 85%. Example 2

[0020] 1) Preparation: The activated carbon pretreatment method is the same as in Example 1. Weigh 2.17 g of cerium nitrate hexahydrate and dissolve it in 50 mL of deionized water (concentration approximately 0.1 mol / L). Add 10 g of pretreated activated carbon to the cerium source solution and impregnate for 1 hour. While stirring, slowly add approximately 30 mL of 0.5 mol / L sodium hydroxide solution, controlling the final pH of the system to 8, and continue the reaction for 4 hours. After standing and aging for 6 hours, filter and wash with deionized water until the filtrate is neutral. Dry at 100°C for 10 hours, and then calcine at 300°C for 3 hours to obtain composite adsorbent B (CeO2 loading approximately 10%).

[0021] 2) Application: Under the same application conditions as in Example 1, the composite adsorbent B achieved a fluoride ion removal rate of 78.5% and an adsorption capacity of 39.25 mg / g.

[0022] 3) Feasibility Analysis: Although the removal rate and adsorption capacity are lower than those of Example 1, the performance is improved by more than 6 times compared to pure activated carbon (12% removal rate) in Comparative Example 1. This indicates that the technical solution is still effective even with a lower loading (10%), a lower precipitant concentration (0.5 mol / L), and a lower precipitation pH (8). This example provides a feasible solution for low-cost application scenarios. Example 3

[0023] 1) Preparation: Weigh 6.51 g of cerium nitrate hexahydrate and dissolve it in 50 mL of deionized water (concentration approximately 0.3 mol / L). Add 10 g of the pretreated activated carbon prepared in Example 1 to the cerium source solution and impregnate for 1.5 hours. While stirring, slowly add 2.0 mol / L sodium hydroxide (NaOH) solution, controlling the final pH of the system to 11, and continue the reaction for 2 hours. After standing and aging for 12 hours, filter and wash with deionized water until the filtrate is neutral. Dry at 120°C for 8 hours, and then calcine at 500°C for 2 hours to obtain composite adsorbent C (CeO2 loading approximately 30%).

[0024] 2) Application: Under the same application conditions as in Example 1, the composite adsorbent C achieved a fluoride ion removal rate of 99.2% and an adsorption capacity of 49.6 mg / g.

[0025] 3) Feasibility Analysis: This embodiment achieved the best adsorption performance within the scope of this invention, with a removal rate of up to 99.2%, demonstrating the feasibility of high loading (30%), high pH (11), and sodium hydroxide as a precipitant. It should be noted that when using a strong alkali (NaOH), the dropping rate needs to be controlled to avoid localized over-alkaliness, but uniform loading can be achieved through proper operation. This embodiment demonstrates the upper limit of the high performance achievable by this invention. Example 4

[0026] 1) Preparation: Weigh 3.73 g of cerium chloride heptahydrate and dissolve it in 50 mL of deionized water. Add 10 g of the pretreated activated carbon prepared in Example 1 to the cerium source solution and impregnate for 1 hour. While stirring, slowly add 1.5 mol / L ammonia water, controlling the final pH of the system to 9.5, and continue the reaction for 5 hours. After standing and aging for 8 hours, filter and wash with deionized water until chloride ions (Cl⁻) are undetectable with silver nitrate solution. Then dry at 110℃ for 10 hours and calcine at 400℃ for 3 hours to obtain composite adsorbent D (CeO₂ loading approximately 25%).

[0027] 2) Application: Under the same application conditions as in Example 1, the composite adsorbent D achieved a fluoride ion removal rate of 97.8% and an adsorption capacity of 48.9 mg / g.

[0028] 3) Feasibility Analysis: This embodiment used cerium chloride and ammonia as reactants. Under moderate process parameters (loading 25%, pH 9.5), excellent defluorination effect (97.8% removal rate) was also obtained. This strongly demonstrates that the preparation method of the present invention has good applicability and reproducibility for different soluble cerium salts (nitrates, chlorides) and different concentrations of precipitants.

[0029] Comparative Example 1 Compared to Example 1, this comparative example only used unloaded pretreated activated carbon to treat a simulated sample of fluoride-containing wastewater under the same conditions. Its fluoride ion removal rate was only 12%, and its adsorption capacity was 6 mg / g.

[0030] The results of Examples 1-4 and Comparative Example 1 are shown in Table 1 below: Table 1 Results of Examples 1-4 and Comparative Example 1 , As can be seen from the above examples and comparative examples, the activated carbon-supported cerium dioxide composite adsorbent provided by the present invention has significant advantages in adsorption performance, ease of operation, and regenerability. The present invention ingeniously combines the physical adsorption characteristics of activated carbon with the chemical adsorption characteristics of cerium dioxide, achieving a synergistic effect of "1+1>2". Activated carbon provides a huge specific surface area and abundant pores, promoting the mass transfer of fluoride ions to active sites; cerium dioxide provides a high density of specific adsorption sites, greatly improving the overall adsorption capacity and rate; compared with traditional adsorbents (such as activated alumina), the composite adsorbent of the present invention maintains excellent fluoride removal performance under acidic, neutral, and weakly alkaline conditions (pH 3-10), demonstrating good reproducibility and wide applicability; cerium dioxide is firmly fixed on millimeter / micrometer-sized activated carbon particles, solving the problem of solid-liquid separation of powder materials. Meanwhile, the composite adsorbent can be efficiently regenerated through simple alkaline washing, reducing operating costs; the activated carbon used as raw material is widely available and inexpensive, the preparation process is simple, energy consumption is low, and it is easy to scale up production; the adsorbent itself is non-toxic and harmless, and will not cause secondary pollution.

[0031] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An activated carbon-supported cerium dioxide composite adsorbent, characterized in that: The composite adsorbent uses activated carbon as a carrier, with cerium dioxide as the active component uniformly loaded on the surface and inside the pores of the activated carbon; the mass ratio of cerium dioxide to activated carbon is 0.1:1 to 0.5:

1.

2. The activated carbon-supported cerium dioxide composite adsorbent according to claim 1, characterized in that, The activated carbon is in powder form or granular form; the cerium dioxide has a grain size of 5-30 nm.

3. The method for preparing the activated carbon-supported cerium dioxide composite adsorbent according to claim 1 or 2, characterized in that, Includes the following steps: a. Pretreatment of activated carbon: The activated carbon is acid washed by soaking it in 0.1-1 mol / L dilute nitric acid or dilute hydrochloric acid for 2-6 hours, then washing it with deionized water until neutral, and finally drying it to obtain the pretreated activated carbon. b. Preparation of cerium source solution: Dissolve soluble cerium salt in deionized water to prepare a cerium source solution with a concentration of 0.1-0.5 mol / L; c. Impregnation and precipitation: Add the pretreated activated carbon to the cerium source solution prepared in step b, and impregnate thoroughly for 0.5-2 hours; then, while continuously stirring at 150-400 rpm, slowly add a 0.5-2.0 mol / L precipitant solution, controlling the amount of precipitant solution added to ensure that the OH- ions in the precipitant are within acceptable limits. - The molar ratio of cerium ions to cerium ions is 4:1 to 6:

1. The pH of the reaction system is controlled at 8-11. The reaction is stirred for 2-6 hours to obtain a mixture. d. Aging and washing: Let the mixture obtained in step c stand for aging for 6-12 hours, filter, and wash thoroughly with deionized water until no chloride or nitrate ions are detected in the filtrate to obtain a solid product; e. Drying and calcination: The solid product obtained in step d is dried at 80-120℃ for 6-12 hours, and then calcined in a muffle furnace at 300-500℃ for 2-4 hours to obtain activated carbon-supported cerium dioxide composite adsorbent.

4. The preparation method according to claim 3, characterized in that, The soluble cerium salt mentioned in step b is cerium nitrate hexahydrate, cerium chloride heptahydrate, or cerium sulfate.

5. The preparation method according to claim 3, characterized in that, The precipitant mentioned in step c is a sodium hydroxide solution.

6. The application of the activated carbon-supported cerium dioxide composite adsorbent according to claim 1 or 2 in the removal of fluoride ions from wastewater.

7. The application according to claim 6, characterized in that, The specific process of the application is as follows: the activated carbon-supported cerium dioxide composite adsorbent is added to fluoride-containing wastewater at a dosage of 0.5-5 g / L, and the reaction is carried out by shaking or stirring for 1-12 hours under the conditions of pH value of 3-10 and temperature of 15-45℃.

8. The application according to claim 6, characterized in that, The saturated activated carbon-supported cerium dioxide composite adsorbent after use is regenerated with a sodium hydroxide solution of 0.1-1.0 mol / L, and then reused to remove fluoride from wastewater.