Recyclable sodium sulfate wastewater treatment agent and preparation method thereof

Abstract

The invention discloses a recyclable sodium sulfate wastewater treatment agent and a preparation method thereof, and belongs to the technical field of industrial wastewater treatment agents. The preparation method comprises the following steps: mixing amination modified activated carbon, modified cyclodextrin coated crown ether and anhydrous acetone, heating to 40-50 DEG C, reacting for 4-5 hours, cooling to 25 DEG C, adding a reducing agent, and reacting for 50-70 minutes to obtain the wastewater treatment agent. After amination modified activated carbon and modified cyclodextrin coated crown ether are mixed and reacted, reduction treatment is performed, and finally vacuum drying is performed to obtain the wastewater treatment agent, so that the recovery efficiency of sodium sulfate is improved.

Description

Technical Field

[0001] This invention belongs to the technical field of industrial wastewater treatment agents, specifically relating to a recyclable sodium sulfate wastewater treatment agent and its preparation method. Background Technology

[0002] Wastewater treatment agents are functional materials used to purify and remediate aquatic environments. They possess a microscopic structure characterized by micro- and nano-porous structures, high specific surface area, and abundant surface active sites, exhibiting excellent adsorption, flocculation, catalytic oxidation, and ion exchange properties. They are widely used in industrial wastewater treatment in electroplating, dyeing, pharmaceuticals, and food processing. However, their micron- or nano-sized particle morphology and non-magnetic structure inherently lead to difficulties in solid-liquid separation and low recovery rates in practical applications. This deficiency is amplified when used to treat high-salt wastewater rich in sodium sulfate: the salt effect and strong ionic strength caused by high salinity compress the electric double layer and compete for active sites, not only reducing the removal efficiency of the agent for target pollutants but also making it difficult to effectively separate and recover the agent after use due to increased dispersibility and aggregate dissociation. This results in significant agent loss, high operating costs, and potential secondary pollution. Currently, the main approach to addressing this problem is through structural design and process innovation of the treatment agents themselves.

[0003] Patent CN109289765A discloses an activated carbon wastewater treatment agent and its preparation method. This invention uses activated carbon, zeolite powder, bentonite, high-temperature coal tar, emulsifier, adhesive, and tributyl phosphate as raw materials. The invention fully utilizes the regular pore structure and cation exchange capacity of natural zeolite to effectively adsorb and exchange ammonia nitrogen and heavy metal ions in water. Simultaneously, high-temperature coal tar is coated on the surface of materials such as activated carbon. During the subsequent carbonization and activation stage, the organic matter in the coal tar decomposes and volatilizes, leaving new and richer pore structures inside the material, thereby significantly increasing the specific surface area and adsorption capacity. This results in a composite wastewater treatment agent with lower cost, stronger adsorption performance, and synergistic treatment effect. However, in this invention, although zeolite captures heavy metal ions through ion exchange and has a large exchange capacity, it also adsorbs a large number of other cations in the wastewater, such as calcium, magnesium, and sodium ions, which compete with the target heavy metal ions for sites and contaminate subsequent recovery products, leading to a decrease in product recovery rate.

[0004] Therefore, improving the recovery efficiency of sodium sulfate is of great significance. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention utilizes amination-modified activated carbon and modified cyclodextrin-encapsulated crown ethers, followed by a reduction treatment and finally vacuum drying to obtain a wastewater treatment agent. This improves the recovery efficiency of sodium sulfate, thereby solving the technical problems mentioned in the background art. Specifically, the technical solution of this invention includes the following: One objective of this invention is to provide a method for preparing a recyclable sodium sulfate wastewater treatment agent, the method comprising the following steps: Aminated modified activated carbon, modified cyclodextrin-encapsulated crown ether, and anhydrous acetone are mixed and heated to 40-50℃ for 4-5 hours. Then, the mixture is cooled to 25℃ and a reducing agent is added for 50-70 minutes to obtain a wastewater treatment agent.

[0006] Furthermore, the preparation method of the aminated modified activated carbon includes the following steps: Modified activated carbon is obtained by mixing pretreated activated carbon and concentrated sulfuric acid at a mass ratio of 1:10~12. Aminated modified activated carbon was obtained by mixing and reacting modified activated carbon, anhydrous ethanol, 3-aminopropyltriethoxysilane and deionized water in a mass ratio of 10:80~120:3~5:8~12.

[0007] Furthermore, the method for preparing the pretreated activated carbon includes the following steps: Activated carbon and deionized water are mixed and stirred for 2 hours at a mass ratio of 1:8~12 to obtain water-washed activated carbon; Water-washed activated carbon and hydrochloric acid are mixed and stirred at a mass ratio of 1:5~8, and then heated to 80℃ and stirred for 2 hours to obtain pretreated activated carbon.

[0008] Furthermore, the activated carbon has a mesh size of 20.

[0009] Furthermore, the hydrochloric acid has a mass fraction of 10%.

[0010] Furthermore, the concentrated sulfuric acid has a mass fraction of 75%.

[0011] Furthermore, the conditions for the reaction of the pretreated activated carbon and concentrated sulfuric acid include a rotation speed of 200 r / min, a temperature of 170~180℃, and a reaction time of 2~3 h.

[0012] Furthermore, the conditions for the mixed reaction of the modified activated carbon, anhydrous ethanol, 3-aminopropyltriethoxysilane and deionized water include an ultrasonic power of 300-400W, an ultrasonic time of 25-30min, a temperature of 50-60℃, a reaction time of 4h, and a pH of 5.

[0013] Furthermore, the preparation method of the modified cyclodextrin-encapsulated crown ether includes the following steps: Modified cyclodextrin was obtained by mixing β-cyclodextrin, deionized water, and sodium periodate in a mass ratio of 10:100~150:4~6. Benzo-15-crown-5 and anhydrous ethanol were mixed and stirred at a mass ratio of 1:10~15 to obtain a benzo-15-crown-5 premixed solution; Modified cyclodextrin and benzo-15-crown-5 premix were mixed and stirred at a mass ratio of 10:10~15 to obtain modified cyclodextrin-encapsulated crown ether.

[0014] Furthermore, the reaction conditions for the mixture of β-cyclodextrin, deionized water, and sodium periodate include a rotation speed of 200 r / min, a temperature of 30-40 °C, a reaction time of 2-3 h, and a pH of 5-6.

[0015] Furthermore, the reducing agent includes sodium borohydride.

[0016] Furthermore, the mass ratio of the aminated modified activated carbon, the modified cyclodextrin-encapsulated crown ether, the anhydrous acetone, and the reducing agent is 10:2~4:50~80:0.1~0.2.

[0017] A second objective of this invention is to provide a recyclable sodium sulfate wastewater treatment agent.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention first utilizes activated carbon to bind cyclodextrin through the physical action of hydrogen bonds. However, in wastewater treatment, the scouring effect of water flow will generate mechanical force on the surface of activated carbon, reducing the balance of physical forces and causing cyclodextrin to fall off the surface of activated carbon. Therefore, it is necessary to modify the activated carbon to increase the adsorption between it and cyclodextrin. First, activated carbon is modified to form a hierarchical pore structure, increasing the number of surface active groups. Then, through the condensation reaction of silanol groups generated by the hydrolysis of 3-aminopropyltriethoxysilane with oxygen-containing hydroxyl groups on the surface of the modified activated carbon, stable grafting of amino groups is achieved, resulting in aminated modified activated carbon. After the amino group is introduced through modification, it can chemically bond with the aldehyde group of the crown ether of the modified cyclodextrin to form a Schiff base structure. Then, a reduction treatment is performed to form a stable secondary amine structure, preventing the Schiff base structure from easily hydrolyzing and breaking in the wastewater treatment environment, thus improving its stability in wastewater and making the adsorption effect more durable. This solves the problem of the lack of specific active sites in the adsorption process of activated carbon and cyclodextrin. At the same time, when cyclodextrin is used as a wastewater adsorbent, it is easy to detach from the adsorption system, resulting in poor adsorption stability and sustained effect. Therefore, cyclodextrin needs to be modified and then linked with aminated modified activated carbon through specific interactions to construct a composite adsorption system, thereby improving the adhesion stability of cyclodextrin in wastewater and ensuring long-term adsorption performance. β-Cyclodextrin is first oxidized to a certain extent by sodium periodate, causing the carbon-carbon bonds to break and generate aldehyde groups. The introduced aldehyde groups provide active sites for subsequent bonding. Then, through the hydrophobic cavity structure of cyclodextrin, benzo-15-crown-5, which has a selective recognition effect on sodium ions, is encapsulated inside the cyclodextrin, resulting in modified cyclodextrin-encapsulated crown ether. The wastewater treatment agent formed by the covalent condensation of the modified cyclodextrin-encapsulated crown ether and aminated modified activated carbon gives the wastewater treatment agent the ability to specifically target sodium ions, while overcoming the defect of easy loss of cyclodextrin-encapsulated crown ether in the adsorption system. Finally, the aminated modified activated carbon and the modified cyclodextrin-encapsulated crown ether are reduced through the condensation reaction of aldehyde and amino groups to achieve chemical bonding and stability, thus jointly constructing a wastewater treatment agent that can improve the recovery efficiency of sodium sulfate. Detailed Implementation

[0019] The technical solution of the present invention will be clearly and completely described below through embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Unless otherwise stated, all raw materials and reagents used in this invention are commercially available or can be prepared by known methods.

[0021] Preparation Example 1 The preparation of pretreated activated carbon is as follows: Weigh 1 part by mass of 20-mesh activated carbon and 8 parts by mass of deionized water and mix them in a container. Stir at 1000 r / min for 40 min to obtain water-washed activated carbon. Weigh 1 part by mass of water-washed activated carbon and 5 parts by mass of 10% hydrochloric acid and mix them in a container. Then heat to 80℃ and stir at 200 r / min for 2 h. Filter and collect the precipitate. Wash the precipitate with deionized water until the pH of the filtrate is 7. Finally, dry at 105℃ for 6 h to obtain pretreated activated carbon.

[0022] Preparation Example 2 The preparation of pretreated activated carbon is as follows: Weigh 1 part by mass of 20-mesh activated carbon and 10 parts by mass of deionized water and mix them in a container. Stir at 1000 r / min for 40 min to obtain water-washed activated carbon. Weigh 1 part by mass of water-washed activated carbon and 7 parts by mass of 10% hydrochloric acid and mix them in a container. Then heat to 80℃ and stir at 200 r / min for 2 h. Filter and collect the precipitate. Wash the precipitate with deionized water until the pH of the filtrate is 7. Finally, dry at 105℃ for 6 h to obtain pretreated activated carbon.

[0023] Preparation Example 3 The preparation of pretreated activated carbon is as follows: Weigh 1 part by mass of 20-mesh activated carbon and 12 parts by mass of deionized water and mix them in a container. Stir at 1000 r / min for 40 min to obtain water-washed activated carbon. Weigh 1 part by mass of water-washed activated carbon and 8 parts by mass of 10% hydrochloric acid and mix them in a container. Then heat to 80℃ and stir at 200 r / min for 2 h. Filter and collect the precipitate. Wash the precipitate with deionized water until the pH of the filtrate is 7. Finally, dry at 105℃ for 6 h to obtain pretreated activated carbon.

[0024] Preparation Example 4 The preparation of pretreated activated carbon is as follows: Weigh 1 part by mass of 100-mesh activated carbon and 12 parts by mass of deionized water and mix them in a container. Stir at 1000 r / min for 40 min to obtain water-washed activated carbon. Weigh 1 part by mass of water-washed activated carbon and 8 parts by mass of 10% hydrochloric acid and mix them in a container. Then heat to 80℃ and stir at 200 r / min for 2 h. Filter and collect the precipitate. Wash the precipitate with deionized water until the pH of the filtrate is 7. Finally, dry at 105℃ for 6 h to obtain pretreated activated carbon.

[0025] Preparation Example 5 The preparation of amination-modified activated carbon is as follows: One part by mass of the pretreated activated carbon obtained in Example 1 and ten parts by mass of 75% concentrated sulfuric acid were weighed and placed in a flask. The flask was then placed in an oil bath and heated to 170°C. The mixture was stirred at 200 rpm for 2 hours at this temperature. After the reaction was completed, the mixture was allowed to cool naturally to 25°C. The precipitate was collected by filtration and washed with deionized water until the pH of the washing solution reached 7. Finally, the precipitate was dried in a high-temperature oven at 105°C for 12 hours to obtain modified activated carbon. Ten parts by mass of the modified activated carbon, 80 parts by mass of anhydrous ethanol, and 8 parts by mass of deionized water were weighed and placed in a container. The mixture was ultrasonically dispersed at 300 W for 25 minutes and then transferred to an oil bath. Three parts by mass of 3-aminopropyltriethoxysilane were added while stirring at 200 rpm. The pH was then adjusted to 5 and the mixture was heated to 50°C. The reaction was timed and carried out for 4 hours. After the reaction was completed, the filter cake was collected by vacuum filtration, washed with anhydrous ethanol, rinsed with deionized water, and finally dried in a high-temperature oven at 105℃ for 10 hours to obtain aminated modified activated carbon.

[0026] Preparation Example 6 The preparation of amination-modified activated carbon is as follows: One part by mass of the pretreated activated carbon obtained in Preparation Example 2 and 11 parts by mass of 75% concentrated sulfuric acid were weighed and placed in a flask. The flask was then placed in an oil bath and heated to 175°C. The mixture was stirred at 200 rpm for 2.5 h at this temperature. After the reaction was completed, the mixture was allowed to cool naturally to 25°C. The precipitate was collected by filtration and washed with deionized water until the pH of the washing solution reached 7. Finally, the precipitate was dried in a high-temperature oven at 105°C for 12 h to obtain modified activated carbon. Ten parts by mass of the modified activated carbon, 100 parts by mass of anhydrous ethanol, and 10 parts by mass of deionized water were weighed and placed in a container. The mixture was ultrasonically dispersed at 350 W for 25 min and then transferred to an oil bath. Four parts by mass of 3-aminopropyltriethoxysilane were added while stirring at 200 rpm. The pH was then adjusted to 5 and the mixture was heated to 55°C. The reaction was timed and carried out for 4 h. After the reaction was completed, the filter cake was collected by vacuum filtration, washed with anhydrous ethanol, rinsed with deionized water, and finally dried in a high-temperature oven at 105℃ for 10 hours to obtain aminated modified activated carbon.

[0027] Preparation Example 7 The preparation of amination-modified activated carbon is as follows: One part by mass of the pretreated activated carbon obtained in Preparation Example 3 and 12 parts by mass of 75% concentrated sulfuric acid were weighed and placed in a flask. The flask was then placed in an oil bath and heated to 180°C. The mixture was stirred at 200 rpm for 3 hours at this temperature. After the reaction was completed, the mixture was allowed to cool naturally to 25°C. The precipitate was collected by filtration and washed with deionized water until the pH of the washing solution reached 7. Finally, the precipitate was dried in a high-temperature oven at 105°C for 12 hours to obtain modified activated carbon. Ten parts by mass of the modified activated carbon, 120 parts by mass of anhydrous ethanol, and 12 parts by mass of deionized water were weighed and placed in a container. The mixture was ultrasonically dispersed at 400 W for 30 minutes and then transferred to an oil bath. Five parts by mass of 3-aminopropyltriethoxysilane were added while stirring at 200 rpm. The pH was then adjusted to 5 and the mixture was heated to 60°C. The reaction was timed and carried out for 4 hours. After the reaction was completed, the filter cake was collected by vacuum filtration, washed with anhydrous ethanol, rinsed with deionized water, and finally dried in a high-temperature oven at 105℃ for 10 hours to obtain aminated modified activated carbon.

[0028] Preparation Example 8 The preparation of amination-modified activated carbon is as follows: The pretreated activated carbon in Preparation Example 7 was replaced with the pretreated activated carbon obtained in Preparation Example 4, and the rest of the preparation process was the same as in Preparation Example 7.

[0029] Preparation Example 9 The preparation of amination-modified activated carbon is as follows: Weigh 1 part by mass of the pretreated activated carbon obtained in Preparation Example 3 and 12 parts by mass of concentrated sulfuric acid with a mass fraction of 95% and place them together in a flask. Then place it in an oil bath and heat it to 180°C. At this temperature, stir the reaction at a speed of 200 r / min for 4 h. The rest of the preparation process is the same as in Preparation Example 7.

[0030] Preparation Example 10 The preparation of amination-modified activated carbon is as follows: The amount of 3-aminopropyltriethoxysilane in Preparation Example 7 was increased to 10 parts by mass, while the rest of the preparation process remained the same as in Preparation Example 7.

[0031] Preparation Example 11 The preparation of amination-modified activated carbon is as follows: Weigh 1 part by mass of the pretreated activated carbon obtained in Preparation Example 3 and 12 parts by mass of concentrated sulfuric acid with a mass fraction of 95% and place them together in a flask. Then place it in an oil bath and heat it to 180°C. At this temperature, stir the reaction at a speed of 200 r / min for 4 h. The rest of the preparation process is the same as in Preparation Example 7.

[0032] Preparation Example 12 The preparation of modified cyclodextrin-encapsulated crown ethers is as follows: Weigh 10 parts by weight of β-cyclodextrin and 100 parts by weight of deionized water into a reaction flask, heat to 30°C and stir at 200 r / min until the β-cyclodextrin is completely dispersed and homogeneous. Then adjust the pH to 5, add 4 parts by weight of sodium periodate, then protect from light and stir at 30°C for 2 hours to obtain modified cyclodextrin. Weigh 1 part by weight of benzo-15-crown-5 and 10 parts by weight of anhydrous ethanol into a reaction vessel, mix and stir at 200 r / min to obtain benzo-15-crown-5 premix. Weigh 10 parts by weight of modified cyclodextrin. Cyclodextrin and 10 parts by mass of benzo-15-crown-5 premix were placed in a reaction vessel and mixed. The mixture was heated to 50°C and stirred at 200 r / min for 6 h. The mixture was then placed in a rotary evaporator with the temperature set at 50°C and the vacuum degree at 0.08 MPa. After rotary evaporation for 30 min, the mixture was poured into 50 parts by mass of anhydrous ethanol and allowed to stand for 1 h. The mixture was then centrifuged at 8000 r / min for 10 min, and the precipitate was collected. The precipitate was washed with anhydrous ethanol and then rinsed with deionized water. Finally, the mixture was dried in a vacuum drying oven at 40°C for 12 h to obtain the modified cyclodextrin-encapsulated crown.

[0033] Preparation Example 13 The preparation of modified cyclodextrin-encapsulated crown ethers is as follows: Weigh 10 parts by weight of β-cyclodextrin and 130 parts by weight of deionized water and place them in a reaction flask. Heat to 35°C and stir at 200 r / min until the β-cyclodextrin is completely dispersed and homogeneous. Then adjust the pH to 5, add 5 parts by weight of sodium periodate, and then protect from light and stir at 35°C for 2.5 h to obtain modified cyclodextrin. Weigh 1 part by weight of benzo-15-crown-5 and 10 parts by weight of anhydrous ethanol and place them in a reaction vessel. Mix and stir at 200 r / min to obtain benzo-15-crown-5 premix. Weigh 10 parts by weight of modified cyclodextrin. Cyclodextrin and 13 parts by mass of benzo-15-crown-5 premix were placed in a reaction vessel and mixed. The mixture was heated to 50°C and stirred at 200 r / min for 6 h. The mixture was then placed in a rotary evaporator with the temperature set at 50°C and the vacuum degree at 0.08 MPa. After rotary evaporation for 30 min, the mixture was poured into 50 parts by mass of anhydrous ethanol and allowed to stand for 1 h. The mixture was then centrifuged at 8000 r / min for 10 min, and the precipitate was collected. The precipitate was washed with anhydrous ethanol and then rinsed with deionized water. Finally, the mixture was dried in a vacuum drying oven at 40°C for 12 h to obtain modified cyclodextrin-encapsulated crowns.

[0034] Preparation Example 14 The preparation of modified cyclodextrin-encapsulated crown ethers is as follows: Weigh 10 parts by weight of β-cyclodextrin and 150 parts by weight of deionized water and place them in a reaction flask. Heat to 40°C and stir at 200 r / min until the β-cyclodextrin is completely dispersed and homogeneous. Then adjust the pH to 6, add 6 parts by weight of sodium periodate, and then protect from light and stir at 40°C for 3 hours to obtain modified cyclodextrin. Weigh 1 part by weight of benzo-15-crown-5 and 10 parts by weight of anhydrous ethanol and place them in a reaction vessel. Mix and stir at 200 r / min to obtain benzo-15-crown-5 premix. Weigh 10 parts by weight of modified cyclodextrin. Cyclodextrin and 15 parts by mass of benzo-15-crown-5 premix were placed in a reaction vessel and mixed. The mixture was heated to 50°C and stirred at 200 r / min for 6 h. The mixture was then placed in a rotary evaporator with the temperature set at 50°C and the vacuum degree at 0.08 MPa. After rotary evaporation for 30 min, the mixture was poured into 50 parts by mass of anhydrous ethanol and allowed to stand for 1 h. The mixture was then centrifuged at 8000 r / min for 10 min, and the precipitate was collected. The precipitate was washed with anhydrous ethanol and then rinsed with deionized water. Finally, the mixture was dried in a vacuum drying oven at 40°C for 12 h to obtain the modified cyclodextrin-encapsulated crown.

[0035] Preparation Example 15 The preparation of modified cyclodextrin-encapsulated crown ethers is as follows: The amount of sodium periodate in Preparation Example 14 was increased to 10 parts by mass, while the rest of the preparation process remained the same as in Preparation Example 14.

[0036] Preparation Example 16 The preparation of modified cyclodextrin-encapsulated crown ethers is as follows: The amount of sodium periodate in Preparation Example 14 was increased to 10 parts by mass, while the rest of the preparation process remained the same as in Preparation Example 14.

[0037] Example 1 A method for preparing a recyclable sodium sulfate wastewater treatment agent specifically includes the following steps: Ten parts by mass of the aminated modified activated carbon obtained in Preparation Example 5 and 50 parts by mass of anhydrous acetone were weighed and placed together in a reaction vessel. The mixture was ultrasonically dispersed at 300 W for 30 min. Then, two parts by mass of the modified cyclodextrin-encapsulated crown ether obtained in Preparation Example 12 were added. The mixing temperature was adjusted to 40°C, and the mixture was stirred at 100 r / min for 4 h. After the reaction was complete, the temperature was lowered to 25°C, and 0.1 parts by mass of sodium borohydride were added and stirred for 50 min. After the reaction was complete, the solid was obtained by filtration. The solid particles were first washed with anhydrous ethanol, then washed with deionized water until the pH of the washed waste liquid reached neutral. The waste liquid was then dried in a dryer at 55°C for 12 h to obtain granular wastewater treatment agent.

[0038] Example 2 A method for preparing a recyclable sodium sulfate wastewater treatment agent specifically includes the following steps: Ten parts by mass of the aminated modified activated carbon obtained in Preparation Example 6 and 70 parts by mass of anhydrous acetone were weighed and placed together in a reaction vessel. The mixture was ultrasonically dispersed at 300 W for 30 min. Then, three parts by mass of the modified cyclodextrin-encapsulated crown ether obtained in Preparation Example 13 were added. The mixing temperature was adjusted to 45°C, and the mixture was stirred at 100 r / min for 4.5 h. After the reaction was completed, the temperature was lowered to 25°C, and 0.15 parts by mass of sodium borohydride were added and stirred for 60 min. After the reaction was completed, the solid was obtained by filtration. The solid particles were first washed with anhydrous ethanol, then washed with deionized water until the pH of the washed waste liquid reached neutral. The waste liquid was then dried in a dryer at 55°C for 12 h to obtain granular wastewater treatment agent.

[0039] Example 3 A method for preparing a recyclable sodium sulfate wastewater treatment agent specifically includes the following steps: Ten parts by mass of the aminated modified activated carbon obtained in Preparation Example 7 and 80 parts by mass of anhydrous acetone were weighed and placed together in a reaction vessel. The mixture was ultrasonically dispersed at 300 W for 30 min. Then, four parts by mass of the modified cyclodextrin-encapsulated crown ether obtained in Preparation Example 14 were added. The mixing temperature was adjusted to 50°C, and the mixture was stirred at 100 r / min for 5 h. After the reaction was completed, the temperature was lowered to 25°C, and 0.2 parts by mass of sodium borohydride were added and stirred for 70 min. After the reaction was completed, the solid was obtained by filtration. The solid particles were first washed with anhydrous ethanol, then washed with deionized water until the pH of the washed waste liquid reached neutral. The waste liquid was then dried in a dryer at 55°C for 12 h to obtain granular wastewater treatment agent.

[0040] Comparative Example 1 A method for preparing a recyclable sodium sulfate wastewater treatment agent specifically includes the following steps: Ten parts by mass of the aminated modified activated carbon obtained in Preparation Example 8 and 80 parts by mass of anhydrous acetone were weighed and placed together in a reaction vessel. The mixture was ultrasonically dispersed at 300 W for 30 min. Then, four parts by mass of the modified cyclodextrin-encapsulated crown ether obtained in Preparation Example 14 were added. The mixing temperature was adjusted to 50°C, and the mixture was stirred at 100 r / min for 5 h. After the reaction was completed, the temperature was lowered to 25°C, and 0.2 parts by mass of sodium borohydride were added and stirred for 70 min. After the reaction was completed, the solid was obtained by filtration. The solid particles were first washed with anhydrous ethanol, then washed with deionized water until the pH of the washed waste liquid reached neutral. The waste liquid was then dried in a dryer at 55°C for 12 h to obtain granular wastewater treatment agent.

[0041] Comparative Example 2 A method for preparing a recyclable sodium sulfate wastewater treatment agent specifically includes the following steps: Ten parts by mass of the aminated modified activated carbon obtained in Preparation Example 9 and 80 parts by mass of anhydrous acetone were weighed and placed together in a reaction vessel. The mixture was ultrasonically dispersed at 300 W for 30 min. Then, four parts by mass of the modified cyclodextrin-encapsulated crown ether obtained in Preparation Example 14 were added. The mixing temperature was adjusted to 50°C, and the mixture was stirred at 100 r / min for 5 h. After the reaction was completed, the temperature was lowered to 25°C, and 0.2 parts by mass of sodium borohydride were added and stirred for 70 min. After the reaction was completed, the solid was obtained by filtration. The solid particles were first washed with anhydrous ethanol, then washed with deionized water until the pH of the washed waste liquid reached neutral. The waste liquid was then dried in a dryer at 55°C for 12 h to obtain granular wastewater treatment agent.

[0042] Comparative Example 3 A method for preparing a recyclable sodium sulfate wastewater treatment agent specifically includes the following steps: Ten parts by mass of the aminated modified activated carbon obtained in Preparation Example 10 and 80 parts by mass of anhydrous acetone were weighed and placed together in a reaction vessel. The mixture was ultrasonically dispersed at 300 W for 30 min. Then, four parts by mass of the modified cyclodextrin-encapsulated crown ether obtained in Preparation Example 14 were added. The mixing temperature was adjusted to 50°C, and the mixture was stirred at 100 r / min for 5 h. After the reaction was complete, the temperature was lowered to 25°C, and 0.2 parts by mass of sodium borohydride were added and stirred for 70 min. After the reaction was complete, the solid was obtained by filtration. The solid particles were first washed with anhydrous ethanol, then washed with deionized water until the pH of the washed waste liquid reached neutral. The waste liquid was then dried in a dryer at 55°C for 12 h to obtain granular wastewater treatment agent.

[0043] Comparative Example 4 A method for preparing a recyclable sodium sulfate wastewater treatment agent specifically includes the following steps: Ten parts by mass of the aminated modified activated carbon obtained in Preparation Example 11 and 80 parts by mass of anhydrous acetone were weighed and placed together in a reaction vessel. After ultrasonic dispersion at 300 W for 30 min, four parts by mass of the modified cyclodextrin-encapsulated crown ether obtained in Preparation Example 14 were added. The mixing temperature was adjusted to 50 °C, and the mixture was stirred at 100 r / min for 5 h. After the reaction was completed, the temperature was lowered to 25 °C, and 0.2 parts by mass of sodium borohydride were added and stirred for 70 min. After the reaction was completed, the solid was obtained by filtration. The solid particles were first washed with anhydrous ethanol, and then washed with deionized water until the pH of the washed waste liquid reached neutral. The waste liquid was then dried in a dryer at 55 °C for 12 h to obtain granular wastewater treatment agent.

[0044] Comparative Example 5 A method for preparing a recyclable sodium sulfate wastewater treatment agent specifically includes the following steps: Ten parts by mass of the aminated modified activated carbon obtained in Preparation Example 7 and 80 parts by mass of anhydrous acetone were weighed and placed together in a reaction vessel. The mixture was ultrasonically dispersed at 300 W for 30 min. Then, four parts by mass of the modified cyclodextrin-encapsulated crown ether obtained in Preparation Example 15 were added. The mixing temperature was adjusted to 50°C, and the mixture was stirred at 100 r / min for 5 h. After the reaction was complete, the temperature was lowered to 25°C, and 0.2 parts by mass of sodium borohydride were added and stirred for 70 min. After the reaction was complete, the solid was obtained by filtration. The solid particles were first washed with anhydrous ethanol, then washed with deionized water until the pH of the washed waste liquid reached neutral. The waste liquid was then dried in a dryer at 55°C for 12 h to obtain granular wastewater treatment agent.

[0045] Comparative Example 6 A method for preparing a recyclable sodium sulfate wastewater treatment agent specifically includes the following steps: Ten parts by mass of the aminated modified activated carbon obtained in Preparation Example 7 and 80 parts by mass of anhydrous acetone were weighed and placed together in a reaction vessel. The mixture was ultrasonically dispersed at 300 W for 30 min. Then, four parts by mass of the modified cyclodextrin-encapsulated crown ether obtained in Preparation Example 16 were added. The mixing temperature was adjusted to 50°C, and the mixture was stirred at 100 r / min for 5 h. After the reaction was complete, the temperature was lowered to 25°C, and 0.2 parts by mass of sodium borohydride were added and stirred for 70 min. After the reaction was complete, the solid was obtained by filtration. The solid particles were first washed with anhydrous ethanol, then washed with deionized water until the pH of the washed waste liquid reached neutral. The waste liquid was then dried in a dryer at 55°C for 12 h to obtain granular wastewater treatment agent.

[0046] Comparative Example 7 A method for preparing a recyclable sodium sulfate wastewater treatment agent specifically includes the following steps: Ten parts by mass of the aminated modified activated carbon obtained in Preparation Example 7 and 80 parts by mass of anhydrous acetone were weighed and placed together in a reaction vessel. After ultrasonic dispersion at 300 W for 30 min, four parts by mass of the modified cyclodextrin-encapsulated crown ether obtained in Preparation Example 14 were added. The mixing temperature was adjusted to 50 °C, and the mixture was stirred at 100 r / min for 5 h. After the reaction was completed, the solid was obtained by filtration. The solid particles were first washed with anhydrous ethanol, and then washed with deionized water until the pH of the washed waste liquid reached neutral. The waste liquid was then dried in a dryer at 55 °C for 12 h to obtain granular wastewater treatment agent.

[0047] Take 500 mL of sodium sulfate wastewater (concentration of 500 mg / L) to be treated, filter it through a 0.45 μm microporous membrane to remove suspended impurities in the water, and adjust the pH to 7 to obtain pretreated sodium sulfate wastewater; Accurately weigh 0.5g of the wastewater treatment agent prepared in Examples 1-3 and Comparative Examples 1-7 using an electronic analytical balance, place it in a 250mL Erlenmeyer flask, add 100mL of the pretreated sodium sulfate wastewater, place the Erlenmeyer flask in a constant temperature shaker, set the temperature to 25℃ and the shaking rate to 150r / min, and shake and adsorb for 4h. After adsorption, immediately filter the mixture using a vacuum filtration device, collect filtrate A, retain the filter cake, wash the filter cake twice with a small amount of deionized water, and combine the washing liquid with filtrate A; add 10% dilute hydrochloric acid to filtrate A, stir and heat to 60℃, adjust the pH to 2, and then add the following solution dropwise: Add 8% dilute ammonia solution while stirring to adjust the pH to 5. Let stand for 30 minutes, filter to remove the precipitate, and collect filtrate B. Transfer the filter cake to a new 250 mL Erlenmeyer flask, add 50 mL of 1 mol / L hydrochloric acid, and place in a constant temperature shaker. Shake at 25°C and 150 r / min for 2 hours to desorb the ammonia. After desorption, centrifuge at 8000 r / min for 10 minutes and collect the eluent B. Slowly pour the eluent B into the filtrate B while stirring. At this time, the sodium ions in the eluent and the sulfate ions in the filtrate B will recombine to form sodium sulfate. After mixing, adjust the pH to 3 with 1:1 nitric acid to obtain the solution to be tested. Transfer the entire solution to be tested to a 250mL round-bottom flask, add 2-3 boiling chips to prevent bumping, and set the rotary evaporator to 70℃, 0.08MPa, and 80r / min. Begin evaporation, observing the liquid state during the process. When the liquid volume is concentrated to 1 / 4 of its original volume, stop heating and transfer the concentrated solution to a 50mL beaker. After naturally cooling at 25℃ for 30 minutes, transfer it to a constant-temperature water bath at 5℃ and let it stand overnight. Slowly pour the overnight mixture into a Buchner funnel, turn on the vacuum pump (0.08MPa), and continuously filter for 10 minutes to obtain crystals. Slowly rinse the surface of the crystals with 10mL of deionized water at 5℃. The crystals were filtered until dry, and washed three times. The crystals were rinsed with 5 mL of anhydrous ethanol and filtered until dry. 2 mL of the final washing solution was taken, and one drop of 0.1 mol / L silver nitrate solution was added. If no white precipitate formed, the crystals were clean; if precipitate formed, the crystals needed to be washed 1-2 more times. The cleaned sodium sulfate crystals were transferred to a pre-weighed weighing bottle, and the mass m of the pre-weighed weighing bottle was recorded. The weighing bottle was placed in a vacuum drying oven, and the temperature was set to 110℃ and the vacuum degree to 0.08 MPa for 3 hours. After drying, the vacuum drying oven was closed, and the weighing bottle was allowed to cool to 25℃. The total mass M of the "weighing bottle + crystals" was weighed using an electronic analytical balance. The mass of the purified sodium sulfate was calculated: Sodium sulfate mass = Mm. The results are shown in Table 1.

[0048] Table 1 Sodium sulfate recovery test

[0049] The following conclusions can be drawn from Table 1 above: (1) As can be seen from Examples 1 to 3, when the wastewater treatment agent obtained by the present invention is modified, it improves the quality of sodium sulfate recovery when applied to wastewater containing sodium sulfate, indicating that the wastewater treatment agent prepared by the present invention has good recovery efficiency for sodium sulfate.

[0050] (2) Comparative Example 1 shows that the sodium sulfate recovery effect of the prepared wastewater treatment agent is poor. This may be because the activated carbon with a high mesh size has a well-developed specific surface area and pore structure. When it is oxidized with concentrated sulfuric acid, the pore structure may collapse due to the high oxidation intensity of the system, which in turn affects the adsorption effect.

[0051] (3) Comparative Example 2 shows that the sodium sulfate recovery effect of the prepared wastewater treatment agent is poor. This may be because although concentrated sulfuric acid oxidation can increase the oxygen-containing groups on the surface of activated carbon, which is beneficial to the grafting modification of 3-aminopropyltriethoxysilane, the concentration of concentrated sulfuric acid in this system is too high and the oxidation time is too long, resulting in excessive oxidation, which may damage the structure of activated carbon and affect the adsorption effect.

[0052] (4) Through comparative examples 3-4, it can be found that the wastewater treatment agent obtained by modification in this invention has a low recovery test result. This may be because the silanol groups generated by the hydrolysis of 3-aminopropyltriethoxysilane undergo a condensation reaction with the oxygen-containing groups on the surface of the modified activated carbon, and the amino groups are stably grafted onto the surface of the modified activated carbon. An appropriate amount of 3-aminopropyltriethoxysilane can form a uniformly distributed amino layer on the surface of the activated carbon. This layer will not cause pore blockage due to excessive coverage, and it can provide sufficient amino active sites to chemically bond with the aldehyde groups on the surface of the modified cyclodextrin-encapsulated crown ether, thereby achieving loading of the modified cyclodextrin-encapsulated crown ether, enhancing the adsorption effect, and thus improving the adsorption of sodium ions in the wastewater. In Comparative Example 3, the excessive amount of 3-aminopropyltriethoxysilane may lead to excessive accumulation of amino groups on the surface of the modified activated carbon, forming a steric hindrance effect that hinders the contact between the modified cyclodextrin-encapsulated crown ether and the adsorption sites, thus reducing the adsorption of sodium ions in the wastewater. In Comparative Example 4, the insufficient amount of 3-aminopropyltriethoxysilane may lead to insufficient amino grafting rate, reducing the number of amino active sites on the surface of the aminated modified activated carbon, reducing the chemical bonding with the modified cyclodextrin-encapsulated crown ether aldehyde group, reducing the adsorption of sodium ions in the wastewater, and consequently reducing the adsorption of sodium sulfate.

[0053] (5) Comparative Examples 5 and 6 show that the wastewater treatment agent obtained by modification in this invention has a lower recovery test result. This may be because an appropriate amount of sodium periodate can oxidize and break the carbon-carbon bonds of β-cyclodextrin to generate β-cyclodextrin with aldehyde groups. The aldehyde groups can react with the amino groups on the surface of the aminated modified activated carbon, so that the modified cyclodextrin is wrapped with crown ether and loaded on the surface of the aminated modified activated carbon, avoiding detachment during adsorption and improving the adsorption of sodium ions in wastewater. However, in Comparative Example 5, the excessive amount of sodium periodate may lead to excessive oxidation and breakage of the β-cyclodextrin molecular chain, destroying its cavity structure, reducing the adsorption capacity for benzo-15-crown-5, and reducing the adsorption of sodium ions in wastewater. In Comparative Example 6, the amount of sodium periodate is too low, and the oxidation of β-cyclodextrin may be insufficient, reducing the number of surface active aldehyde groups and decreasing the chemical bonding ability with the aminated modified activated carbon, thus reducing the adsorption of sodium ions in wastewater and consequently reducing the adsorption of sodium sulfate.

[0054] (6) Comparative Example 7 shows that the sodium sulfate recovery effect of the prepared wastewater treatment agent is poor. This may be because although the aminated modified activated carbon can be cross-linked by amino groups and modified cyclodextrin to form Schiff base structures and then linked together, the Schiff base structure is unstable and easily hydrolyzed and broken in the wastewater environment, resulting in poor adsorption effect of the wastewater treatment agent.

[0055] The embodiments described above provide a detailed explanation of the technical solutions and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Various changes and modifications can be made to the present invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed.

Claims

1. A method for preparing a recyclable sodium sulfate wastewater treatment agent, characterized in that, The preparation method includes the following steps: Aminated modified activated carbon, modified cyclodextrin-encapsulated crown ether, and anhydrous acetone are mixed and heated to 40-50℃ for 4-5 hours. Then, the mixture is cooled to 25℃ and a reducing agent is added for 50-70 minutes to obtain a wastewater treatment agent.

2. The method for preparing a recyclable sodium sulfate wastewater treatment agent according to claim 1, characterized in that, The preparation method of the aminated modified activated carbon includes the following steps: Modified activated carbon is obtained by mixing pretreated activated carbon and concentrated sulfuric acid at a mass ratio of 1:10~12. Aminated modified activated carbon was obtained by mixing and reacting modified activated carbon, anhydrous ethanol, 3-aminopropyltriethoxysilane and deionized water in a mass ratio of 10:80~120:3~5:8~12.

3. The method for preparing a recyclable sodium sulfate wastewater treatment agent according to claim 2, characterized in that, The conditions for the reaction of the pretreated activated carbon and concentrated sulfuric acid include a rotation speed of 200 r / min, a temperature of 170~180℃, and a reaction time of 2~3 h.

4. The method for preparing a recyclable sodium sulfate wastewater treatment agent according to claim 2, characterized in that, The conditions for the reaction of the modified activated carbon, anhydrous ethanol, 3-aminopropyltriethoxysilane and deionized water include an ultrasonic power of 300-400W, an ultrasonic time of 25-30min, a temperature of 50-60℃, a reaction time of 4h and a pH of 5.

5. The method for preparing a recyclable sodium sulfate wastewater treatment agent according to claim 1, characterized in that, The preparation method of the modified cyclodextrin-encapsulated crown ether includes the following steps: Modified cyclodextrin was obtained by mixing β-cyclodextrin, deionized water, and sodium periodate in a mass ratio of 10:100~150:4~6. Benzo-15-crown-5 and anhydrous ethanol were mixed and stirred at a mass ratio of 1:10~15 to obtain a benzo-15-crown-5 premixed solution; Modified cyclodextrin and benzo-15-crown-5 premix were mixed and stirred at a mass ratio of 10:10~15 to obtain modified cyclodextrin-encapsulated crown ether.

6. The method for preparing a recyclable sodium sulfate wastewater treatment agent according to claim 5, characterized in that, The reaction conditions for the mixture of β-cyclodextrin, deionized water and sodium periodate include a rotation speed of 200 r / min, a temperature of 30~40℃, a reaction time of 2~3 h and a pH of 5~6.

7. The method for preparing a recyclable sodium sulfate wastewater treatment agent according to claim 1, characterized in that, The reducing agent includes sodium borohydride.

8. The method for preparing a recyclable sodium sulfate wastewater treatment agent according to claim 1, characterized in that, The mass ratio of the aminated modified activated carbon, the modified cyclodextrin-encapsulated crown ether, the anhydrous acetone, and the reducing agent is 10:2~4:50~80:0.1~0.

2.

9. A recyclable sodium sulfate wastewater treatment agent, characterized in that, The wastewater treatment agent is prepared by the method for preparing a recyclable sodium sulfate wastewater treatment agent as described in any one of claims 1 to 8.

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