Modification method and application of modified amorphous alumina defluorination adsorbent

Abstract

The invention discloses a modification method and application of a modified amorphous alumina defluorination adsorbent, and belongs to the technical field of adsorption materials. A modification method of a modified amorphous alumina defluorination adsorbent comprises the following steps: (1) preparation of a precursor: dissolving an aluminum salt with a solvent, adding a regulator, uniformly stirring, and carrying out solvothermal reaction in a reaction kettle with a polytetrafluoroethylene lining to obtain the precursor; (2) preparation of amorphous alumina: calcining the precursor in a muffle furnace to obtain amorphous alumina AlOx; and (3) modifying the amorphous alumina: adding the amorphous alumina into the modifier solution, stirring, standing, filtering and drying to obtain the amorphous alumina. The method is easy and convenient to operate, low in cost, suitable for large-scale production, environmentally friendly and free of pollution, and the modified aluminum oxide is higher in adsorption activity and has excellent regeneration performance.

Description

Technical Field

[0001] The invention belongs to the technical field of adsorption materials and relates to a modification method of a modified amorphous aluminum oxide defluorination adsorbent and application thereof. Background Art

[0002] Fluoride ions are ubiquitous in natural water bodies. A moderate amount of fluoride is beneficial to human health. However, once its concentration exceeds the safe range, it may cause health risks such as dental fluorosis and skeletal fluorosis. Therefore, it is particularly urgent to develop efficient and economical fluoride removal technology.

[0003] Compared with high-concentration fluoride wastewater, low-concentration fluoride wastewater is more difficult to treat, and due to its large emission and wide distribution, the long-term cumulative impact on the environment is more significant. Among them, mine water is an important source of this type of low-concentration fluoride wastewater. The commonly used industrial fluoride wastewater treatment methods mainly include chemical precipitation, flocculation precipitation and adsorption. For high-concentration fluoride wastewater, precipitation is usually used first to reduce the fluoride ion concentration to a certain level, and then adsorption is used for deep treatment to ensure that the water quality meets the standard. When treating low-concentration fluoride wastewater, the adsorption method shows unique advantages. Traditional chemical precipitation methods require sufficient fluoride ion concentration to form visible precipitates, and often cannot achieve ideal removal effects under low concentration conditions. The adsorption method can effectively remove fluoride ions through physical or chemical adsorption of fluoride ions on the active sites on the surface of the adsorbent. In addition, the adsorption method is simple to operate and easy to control. It only requires adding the adsorbent to the wastewater, stirring or allowing the adsorbent to fully contact the wastewater, and then separating the adsorbent that has adsorbed fluoride ions by filtration or precipitation. The entire treatment process does not require complex equipment and cumbersome operating steps, is easy to implement on various scales and under various conditions, and has good regeneration performance and reusability.

[0004] The most commonly used defluoridation agent on the market is alumina, but it has disadvantages such as low adsorption efficiency, long treatment time, and poor regeneration performance, and the defluoridation effect is not ideal. Therefore, in the context of the need to treat a large amount of low-concentration fluoride wastewater, further research and development and optimization of alumina adsorption materials are needed to improve defluoridation efficiency and performance, reduce operating costs and increase efficiency.

[0005] In order to solve the above-mentioned defects of the prior art, a modification method for amorphous alumina defluorination adsorbent was developed, and its application was further developed. Summary of the invention

[0006] The purpose of the present invention is to provide a method for modifying amorphous alumina defluorination adsorbent.

[0007] Another object of the present invention is to provide the application of the modified amorphous alumina defluorination adsorbent.

[0008] In order to achieve the above-mentioned invention object, the present invention adopts the following technical solutions: A modification method for a modified amorphous alumina defluorination adsorbent, comprising the following steps: (1) Preparation of precursor: dissolve aluminum salt in a solvent, add a regulator, stir evenly, place in a polytetrafluoroethylene-lined reactor for solvothermal reaction, and obtain a precursor; (2) Preparation of amorphous aluminum oxide: calcining the precursor in a muffle furnace to obtain amorphous aluminum oxide AlOx; (3) Modification of amorphous alumina: Add shaped alumina into the modifier solution, stir, let stand, filter and dry to obtain the modified alumina.

[0009] Furthermore, the aluminum salt is aluminum chloride, aluminum nitrate or aluminum sulfate, or a mixture thereof in any proportion.

[0010] The solvent is one of ethylene glycol, isopropanol or ethanol, and the concentration of the aluminum salt after dissolution is 0.075-0.3 mol / L.

[0011] The regulator is one of sodium acetate, sodium hydroxide, ammonia water, ammonium carbonate or ammonium bicarbonate or a mixture thereof in any proportion, and the molar ratio of the regulator to the aluminum salt is 2-4:1.

[0012] The stirring in step 1) is performed using a magnetic stirrer for 45-60 min; the temperature of the solvent thermal reaction is 160-200°C, and the reaction time is 12-15 h.

[0013] After the solvent thermal reaction, the precursor is obtained by washing with deionized water and ethanol alternately for 5-6 times and drying at 60-80° C. for 4-12 hours.

[0014] The calcination temperature is 250-400°C, the calcination time is 3-4 h, and the heating rate is 2-5°C / min.

[0015] The modifier is hydrogen peroxide or tert-butyl peroxide, the concentration of the modifier solution is 0.25%-5%, and the mass-to-volume ratio of the amorphous aluminum oxide to the modifier solution is 1g:1-2L.

[0016] The stirring time of step 3) is 12-15 h, the drying temperature is 60-80 °C, and the drying time is 4-12 h.

[0017] Furthermore, the modified amorphous alumina defluorination adsorbent is used in the treatment of fluoride-containing wastewater, the concentration of fluoride ions in the fluoride-containing wastewater does not exceed 20 mg / L, the pH is 5.8-6.2, and the amount of the adsorbent used is 1 g / L.

[0018] In the application, the adsorbent that has reached adsorption saturation after use is regenerated by oscillating and adsorbing in a 1%-3% aluminum sulfate solution in a constant temperature oscillator at 25°C for 12 hours, and then regenerated by filtering, washing, and drying, and the adsorption experiment can be repeated.

[0019] In view of the problems of low efficiency, high cost and poor regeneration performance of existing defluorination technologies when treating low-concentration fluoride wastewater, the present invention proposes a method for modifying amorphous aluminum oxide. By the method of the present invention, the surface of amorphous aluminum oxide is modified, and the aluminum oxide gradually changes from an amorphous structure to a crystalline structure. The adsorption activity of the modified crystalline structure of the aluminum oxide is significantly enhanced, especially its adsorption performance for fluoride can be significantly improved. The modified aluminum oxide adsorbent has excellent regeneration performance and can be reused, thereby reducing the treatment cost.

[0020] Compared with the prior art, the method of the present invention is simple to operate, low in cost, suitable for large-scale production, environmentally friendly, pollution-free, and the modified alumina has stronger adsorption activity and excellent regeneration performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 XRD diagram of amorphous alumina before and after modification; Figure 2 SEM images of amorphous alumina and alumina modified with 0.5% H2O2; Figure 3 The adsorption effect of alumina modified with hydrogen peroxide at different concentrations on fluoride ions; Figure 4 The adsorption effect of 0.5% H2O2 / AlOx; Figure 5 The results of five repeated regeneration adsorption experiments of 0.5% H2O2 / AlOx; Figure 6 This is the adsorption effect of 0.5% H2O2 / AlOx on low-concentration fluoride-containing mine water. DETAILED DESCRIPTION

[0022] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings and embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. Example

[0023] Preparation of hydrogen peroxide-modified amorphous alumina: 15 mmol of aluminum chloride hexahydrate was weighed and slowly added to 80 mL of ethylene glycol. Ultrasonic dispersion was performed for 15 min. After stirring until dissolved, 45 mmol of anhydrous sodium acetate was added and stirred for 60 min. The mixed solution was transferred to a reactor and reacted at 180 °C for 12 h. After the reaction, the precursor was cooled, centrifuged, washed with water and ethanol alternately for 5 times, and dried at 80 °C for 12 h to obtain a precursor. The precursor was placed in a muffle furnace and heated to 400 °C at a heating rate of 5 °C / min in an air atmosphere. The calcination was continued for 3 h, and then naturally cooled to room temperature to obtain amorphous alumina (AlOx). 0.1 g of amorphous alumina was added to hydrogen peroxide solutions of different concentrations (0.25%, 0.5%, 1%, 2%, 3% and 5%), placed at room temperature, stirred for 15 h, allowed to stand, filtered, and dried at 80 °C to obtain hydrogen peroxide-modified alumina (Y% H2O2 / AlOx).

[0024] Performance test of hydrogen peroxide-modified alumina in adsorbing fluoride: Accurately weigh 0.05 g of alumina modified with hydrogen peroxide of different concentrations, add it to 50 mL of wastewater containing 10 mg / L fluoride, mix well, place it in a constant temperature oscillator at 25 °C, adjust the pH to 6, and after adsorption for 2 h, use spectrophotometry to determine the concentration of fluoride ions in the water.

[0025] Figure 1 The XRD patterns of amorphous alumina before and after modification. Figure 1 As can be seen in Figure 1, with the increase of hydrogen peroxide concentration, amorphous aluminum oxide gradually transforms into crystalline boehmite (AlO(OH)) (JCPDS-74-1895).

[0026] Figure 2 The SEM images of amorphous alumina and 0.5% H2O2 modified alumina are shown in Figure 2. Figure 2 It can be seen that many tiny protrusions, depressions and cracks appear on the surface of alumina modified by hydrogen peroxide, and the pore structure between particles is more obvious.

[0027] Figure 3 The adsorption effect of alumina modified with hydrogen peroxide at different concentrations on fluoride ions is shown in Figure 2. Figure 3 It can be seen that compared with the unmodified amorphous alumina, the fluorine removal rate of alumina modified with 0.5% H2O2 increased rapidly from 76.4% to 94% within 5 minutes when the initial fluorine concentration was 10 mg / L.

[0028] Figure 4 The adsorption effect of 0.5% H2O2 / AlOx is Figure 4It can be seen that the adsorption capacity of alumina adsorbent modified with 0.5% H2O2 can reach 9.7 mg / g when the dosage is 3.0 g / L, and the fluoride ion concentration can be reduced from 10 mg / L to 0.88 mg / L when the dosage of the adsorbent is 1.0 g / L. Example

[0029] The 0.5% H2O2 modified alumina in Example 1 that was adsorbed saturated was regenerated using an aluminum sulfate solution. 0.5% H2O2 / AlOx was added to a 3% aluminum sulfate solution, oscillated in a constant temperature oscillator for 12 hours, filtered, washed, and dried at 80°C to perform an adsorption experiment. The above steps were repeated 5 times until the fluorine removal rate decreased.

[0030] Figure 5 The results of five repeated regeneration adsorption experiments of 0.5% H2O2 / AlOx are shown in Figure 2. Figure 5 It can be seen that after five regeneration cycles, the removal rate of fluoride ions by 0.5% H2O2-modified alumina can still reach 79.9%, indicating that it has good reusability. Example

[0031] This example uses the same method as Example 1 to prepare a 0.5% H2O2-modified alumina material, aiming to verify its effectiveness in defluoridation of actual mine water. The experimental water sample comes from Zhaozhuang Coal Industry Co., Ltd., Changzhi City, Shanxi Province. After testing, the initial concentration of fluoride ions in the water sample is 4.2 mg / L. For defluoridation treatment, we selected 0.5% H2O2 / AlOx with a dosage of 1.0 g / L as the treatment agent.

[0032] Figure 6 The adsorption effect of 0.5% H2O2 / AlOx on low-concentration fluoride-containing mine water is shown in Figure 2. Figure 6 It can be seen that the treatment process showed a significant defluorination effect. After only 5 minutes of adsorption, the fluoride ion concentration quickly dropped to 0.68 mg / L, which is lower than the surface water discharge limit in my country (<1.0 mg / L), fully demonstrating the rapid defluorination ability of the material. As the adsorption time was extended to 2 hours, the defluorination rate reached 96.19%, almost achieving complete removal of fluoride ions in the water sample. Example

[0033] 15 mmol of aluminum nitrate nonahydrate was weighed and slowly added to 100 mL of isopropanol. Ultrasonic dispersion was performed for 20 min. After stirring until dissolved, 45 mmol of ammonium bicarbonate was added and stirred for 60 min. The mixed solution was transferred to a reactor and reacted at 160 ℃ for 12 h. After the reaction, it was cooled, centrifuged, washed with water and ethanol alternately for 5 times, and dried at 80 ℃ for 8 h to obtain a precursor. The precursor was placed in a muffle furnace and heated to 300 ℃ at a heating rate of 5 ℃ / min in an air atmosphere. The calcination was continued for 3 h, and then naturally cooled to room temperature to obtain amorphous alumina. 0.1 g of amorphous alumina was added to hydrogen peroxide solutions of different concentrations (0.25%, 0.5%, 1%, 2%, 3% and 5%), placed at room temperature, stirred for 15 h, and then allowed to stand, filtered, and dried at 80 ℃ to obtain hydrogen peroxide-modified alumina.

Claims

1. A method for modifying amorphous alumina defluorination adsorbent, characterized in that: The steps are: (1) Preparation of precursor: dissolve aluminum salt in a solvent, add a regulator, stir evenly, place in a polytetrafluoroethylene-lined reactor for solvothermal reaction, and obtain a precursor; (2) Preparation of amorphous aluminum oxide: calcining the precursor in a muffle furnace to obtain amorphous aluminum oxide AlOx; (3) Modification of amorphous alumina: Add shaped alumina into the modifier solution, stir, let stand, filter and dry to obtain the modified alumina.

2. The method for modifying amorphous alumina defluorination adsorbent according to claim 1, characterized in that: The aluminum salt is aluminum chloride, aluminum nitrate or aluminum sulfate or a mixture thereof in any proportion.

3. The method for modifying amorphous alumina defluorination adsorbent according to claim 1, characterized in that: The solvent is one of ethylene glycol, isopropanol or ethanol, and the concentration of the aluminum salt after dissolution is 0.075-0.3 mol / L.

4. The method for modifying amorphous alumina defluorination adsorbent according to claim 1, characterized in that: The regulator is one of sodium acetate, sodium hydroxide, ammonia water, ammonium carbonate or ammonium bicarbonate or a mixture thereof in any proportion, and the molar ratio of the regulator to the aluminum salt is 2-4:

1.

5. The method for modifying amorphous alumina defluorination adsorbent according to claim 1, characterized in that: The stirring in step 1) is performed using a magnetic stirrer for 45-60 min; the temperature of the solvent thermal reaction is 160-200°C, and the reaction time is 12-15 h.

6. The method for modifying a modified amorphous alumina defluorination adsorbent according to claim 1, characterized in that: After the solvent thermal reaction, the precursor is obtained by washing with deionized water and ethanol alternately for 5-6 times and drying at 60-80° C. for 4-12 hours.

7. The method for modifying a modified amorphous alumina defluorination adsorbent according to claim 1, characterized in that: The calcination temperature is 250-400°C, the calcination time is 3-4 h, and the heating rate is 2-5°C / min.

8. The method for modifying amorphous alumina defluorination adsorbent according to claim 1, characterized in that: The modifier is hydrogen peroxide or tert-butyl peroxide, the concentration of the modifier solution is 0.25%-5%, and the mass-to-volume ratio of the amorphous aluminum oxide to the modifier solution is 1g:1-2L.

9. The method for modifying amorphous alumina defluorination adsorbent according to claim 1, characterized in that: The stirring time of step 3) is 12-15 h, the drying temperature is 60-80 °C, and the drying time is 4-12 h.

10. Use of the modified amorphous alumina defluorination adsorbent prepared by the method according to any one of claims 1 to 9 in the treatment of fluorine-containing wastewater, wherein the concentration of fluoride ions in the fluorine-containing wastewater does not exceed 20 mg / L, the pH is 5.8-6.2, and the amount of the adsorbent used is 1 g / L; the adsorbent that is saturated with adsorption after use is regenerated by oscillating and adsorbing in a 1%-3% aluminum sulfate solution in a constant temperature oscillator at 25°C for 12 hours, and then regenerated by filtering, washing, and drying.

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