Method and system for recovering paraquat cations from wastewater

Abstract

The invention discloses a method and a system for recovering paraquat cations from wastewater, and belongs to the technical field of wastewater treatment and resource recovery, and the method comprises the following steps: pretreatment, preparation of special exchange resin, resin adsorption, desorption and refining. The invention solves the problems of low recovery efficiency, high cost, easy secondary pollution, environmental unfriendliness and limited resource utilization value of concentrated ammonium salt when the paraquat cation-containing wastewater is treated in the prior art. By modifying the cation exchange resin and optimizing the resin adsorption and desorption process, the recovery rate of paraquat cations in the wastewater can reach 99% or above, efficient recycling of resources is effectively achieved, and compared with traditional methods such as concentration incineration, energy consumption is low, no harmful gas is discharged in the whole treatment process, and the method is suitable for industrial production. And the content of pollutants in the wastewater is reduced, so that the finally discharged wastewater reaches the environmental protection standard, and the method is simple and convenient to operate and has a good application prospect.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment and resource recycling technology, specifically to a method and system for recovering paraquat cations from wastewater. Background Technology

[0002] Paraquat, chemically known as 1,1'-dimethyl-4,4'-bipyridine cationic salt, is a fast-acting, non-selective herbicide widely used in agricultural production. However, the production of paraquat generates large amounts of wastewater containing paraquat cations. If this wastewater is discharged directly without effective treatment, it will not only cause serious environmental pollution but also lead to a waste of resources.

[0003] Currently, the main problems with treatment methods for wastewater containing paraquat cations are as follows: Traditional chemical oxidation methods, while capable of degrading some organic matter, have poor selectivity for paraquat cations, making efficient recovery difficult and introducing new chemical substances, increasing the complexity of subsequent treatment; concentration and incineration methods are energy-intensive and costly, and may produce harmful gases during incineration. Furthermore, the high paraquat cation content in the concentrated ammonium salts limits their resource utilization value, making paraquat cation recovery impossible; physical adsorption methods, such as activated carbon adsorption, have limited adsorption capacity and are difficult to desorb, hindering large-scale industrial application. Therefore, developing an efficient, low-cost method and system for recovering paraquat cations from wastewater that enables resource recovery is of significant practical importance.

[0004] Patent CN105884105A discloses a wastewater treatment method for the synthesis of paraquat via the ammonia-cyanide process. This process mainly uses chlorine gas to oxidize and break down cyanide and recover ammonium chloride. However, the ammonium chloride recovered by this process has limited resource utilization value due to the high paraquat cation content, and it is also impossible to achieve the recovery and utilization of paraquat cations.

[0005] Patent CN107500463A discloses a process for treating and utilizing paraquat wastewater. This method uses formaldehyde and liquid alkali to break down cyanide in paraquat wastewater. However, the introduction of a large amount of formaldehyde organic matter leads to an increase in the COD of the wastewater, increasing the cost of subsequent treatment. Furthermore, the ammonium sulfate recovered by this process has limited resource utilization value due to the high paraquat cation content, and it is also impossible to achieve the recovery and utilization of paraquat cations.

[0006] Patent CN109607888A discloses a wastewater treatment method and system containing paraquat dichloroate. This method uses activated carbon decolorization and functional group resin adsorption to recover paraquat dichloroate from the wastewater, reducing the paraquat content in the treated wastewater to 0.1 ppm. However, the activated carbon used in this method is difficult to regenerate, causing secondary pollution, increasing the cost of hazardous waste treatment, and is not environmentally friendly. Summary of the Invention

[0007] The purpose of this invention is to provide a method and system for recovering paraquat cations from wastewater, which can achieve efficient recovery of paraquat cations from wastewater, reduce wastewater treatment costs, reduce environmental pollution, and solve the problems mentioned in the background art.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A method for recovering paraquat cations from wastewater includes:

[0010] Pretreatment: The wastewater is filtered using a filter screen with a pore size of 0.1-20μm to remove suspended particles and large impurities. The pH of the wastewater is adjusted to 3-6, and 0.1%-1% of polyaluminum chloride flocculant is added. The mixture is stirred for 10-30 minutes to allow some organic matter and impurities in the wastewater to flocculate and precipitate. The sedimentation time is 1-3 hours. Solid-liquid separation is then performed to obtain pre-purified wastewater. The paraquat particles removed during pretreatment are reused.

[0011] Preparation of special cation exchange resin: Soak the strong acid cation exchange resin in deionized water for 24 hours to wash away surface impurities, then soak it in 5-10% hydrochloric acid solution for 4 hours to transform it into hydrogen-form strong acid cation exchange resin. Wash it with deionized water until neutral, filter it, and dry it for later use. Preparation of amination reaction system: Add the pretreated resin to a three-necked flask, add an appropriate amount of N,N-dimethylformamide solvent, and add an excess amination reagent while stirring. Post-treatment: After the amination reaction is completed, cool it to room temperature, wash the resin repeatedly with deionized water until the filtrate is neutral to remove unreacted amination reagent, wash it with ethanol 3-5 times to remove residual solvent, and dry it under vacuum to obtain the special cation exchange resin.

[0012] Resin adsorption: The pre-purified wastewater is passed into an exchange column consisting of three columns connected in series and filled with special exchange resin. The flow rate of the wastewater is controlled at 1-5 BV / h. When the resin is saturated, the flow of wastewater is stopped.

[0013] Desorption: A 5%-10% hydrochloric acid solution is used as the desorbent and introduced from the bottom of the adsorption column at a flow rate of 0.2-1 BV / h to desorb the paraquat cations adsorbed by the resin. The desorbed liquid is collected. During the desorption process, the temperature is appropriately heated and controlled at 30-50℃ to improve the desorption efficiency.

[0014] Refining: The desorbed liquid is subjected to vacuum distillation at a pressure of -0.07 to -0.1 MPa and a temperature of 50 to 80°C to distill off most of the water and hydrochloric acid, resulting in a concentrated paraquat cationic solution.

[0015] Preferably, the mass ratio of the resin to N,N-dimethylformamide is 1:1 to 1:3.

[0016] Preferably, the mass ratio of the resin to the amination reagent is 1:3 to 1:5.

[0017] Preferably, the amination reaction conditions are: heating to 60-80℃ and stirring for 4-6 hours, wherein the strong acid groups in the pretreated resin undergo an acid-base neutralization reaction with the amino groups of the amination reagent to form a stable modified resin structure.

[0018] Preferably, the amination reagent is one of ethylenediamine, hexamethylenediamine, and p-phenylenediamine.

[0019] According to another aspect of the present invention, a system for recovering paraquat cations from wastewater is provided, for implementing the method for recovering paraquat cations from wastewater as described above, comprising a pretreatment unit, an adsorption unit, a desorption unit, and a purification unit, wherein,

[0020] Pretreatment unit: includes a filter, a pH adjustment tank, and a flocculation sedimentation tank connected in sequence;

[0021] The filter adopts a screen structure for easy screen replacement; the pH adjustment tank is equipped with a pH sensor and dosing device to automatically adjust the pH value of the wastewater; the flocculation sedimentation tank is equipped with a stirrer and inclined tube sedimentation device to improve the solid-liquid separation effect.

[0022] Adsorption unit: includes three adsorption columns connected in series and an outlet tank;

[0023] The three-stage adsorption column is filled with a special exchange resin, and the column body is made of corrosion-resistant material; the effluent tank is used to store qualified effluent after resin adsorption.

[0024] Desorption unit: includes desorbent storage tank, desorbent transfer pump and desorption liquid storage tank;

[0025] The desorbent storage tank is used to store hydrochloric acid desorbent, the desorbent transfer pump is used to deliver the desorbent to the desorption column, and the desorption liquid storage tank is used to store the desorption liquid after resin desorption.

[0026] The refining unit includes a vacuum distillation unit, a desorbent intermediate tank, and a paraquat recovery tank.

[0027] The vacuum distillation unit is used to concentrate the desorbed solution, the desorbent intermediate tank is used to store the distilled hydrochloric acid desorbent, and the paraquat recovery tank is used to store the recovered solution containing paraquat cations.

[0028] Preferably, the three-stage adsorption column includes a primary exchange column, a secondary exchange column, and a tertiary exchange column. The upper ends of the primary, secondary, and tertiary exchange columns are provided with water outlets, and the lower ends of the primary, secondary, and tertiary exchange columns are provided with water inlets. The primary, secondary, and tertiary exchange columns are connected in series via flexible hoses.

[0029] Preferably, the inner sides of the primary, secondary, and tertiary exchange columns are all provided with exchange resin packing and a delay plate, wherein the delay plate is located above the exchange resin packing and the delay plate is provided with delay holes.

[0030] Compared with the prior art, the beneficial effects of the present invention are:

[0031] This invention achieves a paraquat cation recovery rate of over 99% in wastewater by modifying cation exchange resin and optimizing resin adsorption and desorption processes. This effectively realizes the efficient recycling of resources. Compared with traditional methods such as concentration and incineration, it has lower energy consumption, and the resin can be recycled, reducing treatment costs. At the same time, the recovered paraquat cations can be reused to create economic value. The entire treatment process has no harmful gas emissions, reducing environmental pollution. Furthermore, through pretreatment and purification steps, the content of pollutants in the wastewater is reduced, ensuring that the final discharged wastewater meets environmental standards. It also greatly improves the resource utilization rate of concentrated ammonium salts. The process is simple, easy to operate, and easy to implement for industrial production, showing good application prospects. Attached Figure Description

[0032] Figure 1 This is a structural diagram of the system for recovering paraquat cations from wastewater according to the present invention;

[0033] Figure 2 This is a schematic diagram of the three-stage adsorption column of the present invention;

[0034] Figure 3 This is a cross-sectional view of the three-stage adsorption column of the present invention;

[0035] Figure 4 This is a schematic diagram of the structure of the delay plate of the present invention with delay holes.

[0036] In the diagram: 51, primary exchange column; 511, outlet; 512, inlet; 52, secondary exchange column; 53, tertiary exchange column; 54, flexible hose; 55, exchange resin packing; 56, delay plate; 561, delay hole. Detailed Implementation

[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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.

[0038] To address the problems of low recovery efficiency, high cost, secondary pollution, environmental unfriendliness, and limited resource utilization value of concentrated ammonium salts in existing technologies for treating wastewater containing paraquat cations, please refer to... Figures 1-2 This embodiment provides the following technical solution:

[0039] A system for recovering paraquat cations from wastewater includes a pretreatment unit, an adsorption unit, a desorption unit, and a purification unit, wherein...

[0040] Pretreatment unit: includes a filter, a pH adjustment tank, and a flocculation sedimentation tank connected in sequence;

[0041] The filter adopts a screen structure for easy screen replacement; the pH adjustment tank is equipped with a pH sensor and dosing device to automatically adjust the pH value of the wastewater; the flocculation sedimentation tank is equipped with a stirrer and inclined tube sedimentation device to improve the solid-liquid separation effect.

[0042] Adsorption unit: includes three adsorption columns connected in series and an outlet tank;

[0043] The three-stage adsorption column is filled with a special exchange resin, and the column body is made of corrosion-resistant material; the effluent tank is used to store qualified effluent after resin adsorption.

[0044] Desorption unit: includes desorbent storage tank, desorbent transfer pump and desorption liquid storage tank;

[0045] The desorbent storage tank is used to store hydrochloric acid desorbent, the desorbent transfer pump is used to deliver the desorbent to the desorption column, and the desorption liquid storage tank is used to store the desorption liquid after resin desorption.

[0046] The refining unit includes a vacuum distillation unit, a desorbent intermediate tank, and a paraquat recovery tank.

[0047] The vacuum distillation unit is used to concentrate the desorbed liquid, the desorbent intermediate tank is used to store the distilled hydrochloric acid desorbent, and the paraquat recovery tank is used to store the recovered solution containing paraquat cations.

[0048] The three-stage adsorption column includes a primary exchange column 51, a secondary exchange column 52, and a tertiary exchange column 53. The upper ends of the primary, secondary, and tertiary exchange columns 51 and 53 are provided with outlets 511, and the lower ends are provided with inlets 512. The primary, secondary, and tertiary exchange columns 51 and 53 are connected in series via flexible hoses 54. Exchange resin packing 55 and a delay plate 56 are provided on the inner sides of each of the primary, secondary, and tertiary exchange columns 51 and 53. The delay plate 56 is located above the exchange resin packing 55 and has delay holes 561.

[0049] It should be noted that resin adsorption is carried out through a three-stage adsorption column consisting of a primary exchange column 51, a secondary exchange column 52, and a tertiary exchange column 53 connected in series. When the wastewater flows through the primary exchange column 51, the secondary exchange column 52, and the tertiary exchange column 53, the flow of wastewater can be slowed down by the delay holes 561 provided on the delay plate 56, so as to better adsorb the wastewater.

[0050] To better illustrate the process of recovering paraquat cations from wastewater, this embodiment also provides a method for recovering paraquat cations from wastewater. Based on the above-described system implementation for recovering paraquat cations from wastewater, the method includes the following embodiments:

[0051] Example 1

[0052] Pretreatment: Take 1000L of wastewater containing paraquat cations with a concentration of 4000mg / L, filter it through a 0.5μm filter screen to remove visible suspended particles; transfer the wastewater to a pH adjustment tank, add sulfuric acid to adjust the pH value to 4, then add 0.5% polyaluminum chloride, stir for 20 minutes, and then transfer it to a flocculation sedimentation tank for sedimentation for 2 hours to perform solid-liquid separation and obtain pre-purified wastewater. The paraquat particles removed by pretreatment are transferred to a paraquat recovery tank.

[0053] Preparation of special cation exchange resin: A strong acid cation exchange resin (containing sulfonic acid groups) was soaked in deionized water for 24 hours to remove surface impurities. It was then soaked in 5% hydrochloric acid solution for 4 hours to transform into a hydrogen-form strong acid cation exchange resin. The resin was washed with deionized water until neutral, filtered, and dried for later use. Preparation of the amination reaction system: The pretreated resin was added to a three-necked flask, along with an appropriate amount of N,N-dimethylformamide solvent. The mass ratio of resin to N,N-dimethylformamide was 1:1. Excess ethylenediamine was added under stirring, with a mass ratio of resin to ethylenediamine of 1:3. The reaction conditions were: heating to 60℃ and stirring for 4 hours. The sulfonic acid groups (-SO3H) in the pretreated resin underwent an acid-base neutralization reaction with the amino groups (-NH2) of ethylenediamine, forming a stable modified resin structure. Post-treatment: After the reaction, the resin was cooled to room temperature and repeatedly washed with deionized water until the filtrate was neutral (to remove unreacted ethylenediamine). It was then washed three times with ethanol to remove residual solvent and dried under vacuum to obtain the special cation exchange resin.

[0054] Resin adsorption: The pre-purified wastewater is passed into three exchange columns connected in series and filled with special exchange resins. The flow rate of the wastewater is controlled at 3 BV / h (BV is the volume of the resin bed). When the resin is saturated, the flow of wastewater is stopped.

[0055] Desorption: A 5% hydrochloric acid solution was used as the desorbent and introduced from the bottom of the adsorption column at a flow rate of 0.5 BV / h. Desorption was carried out at 40°C, and the desorbed solution was collected.

[0056] Refining: The desorbed liquid is subjected to vacuum distillation at a pressure of -0.07 MPa and a temperature of 60°C to remove most of the water and hydrochloric acid, resulting in a paraquat cationic solution, which is used for the preparation of paraquat aqueous solution.

[0057] The test results showed that the paraquat cation concentration in the raw wastewater after adsorption was 85 mg / L, and the paraquat cation recovery rate in the wastewater was 97.8%.

[0058] Example 2

[0059] Pretreatment: Take 1000L of wastewater containing paraquat cations with a concentration of 4000mg / L, filter it through a 1μm filter screen to remove visible suspended particles; transfer the wastewater to a pH adjustment tank, add sulfuric acid to adjust the pH value to 5, then add 0.8% polyaluminum chloride, stir for 30 minutes, and then transfer it to a flocculation sedimentation tank for sedimentation for 1.5 hours to perform solid-liquid separation and obtain pre-purified wastewater. The paraquat particle solids removed by pretreatment are transferred to a paraquat recovery tank.

[0060] Preparation of special cation exchange resins: Strong acid cation exchange resin (containing sulfonic acid groups) was soaked in deionized water for 24 hours to remove surface impurities. It was then soaked in 10% hydrochloric acid solution for 4 hours to transform into the hydrogen-form strong acid cation exchange resin. Finally, it was washed with deionized water until neutral, filtered, and dried for later use. Preparation of the amination reaction system: The pretreated resin was added to a three-necked flask, along with an appropriate amount of N,N-dimethylformamide solvent. The mass ratio of resin to N,N-dimethylformamide was 1:2. Excess ethyl acetate was added while stirring. The mass ratio of ethylenediamine to resin is 1:5. The reaction conditions are: heating to 70℃ and stirring for 5 hours. In the pretreated resin, the sulfonic acid group (-SO3H) and the amino group (-NH2) of ethylenediamine undergo an acid-base neutralization reaction to form a stable modified resin structure. Post-treatment: After the reaction is completed, the resin is cooled to room temperature and washed repeatedly with deionized water until the filtrate is neutral (to remove unreacted ethylenediamine). Then, it is washed three times with ethanol to remove residual solvent. After vacuum drying, the special exchange resin is obtained.

[0061] Resin adsorption: The pre-purified wastewater is passed into three exchange columns connected in series and filled with special exchange resins. The flow rate of the wastewater is controlled at 2 BV / h (BV is the volume of the resin bed). When the resin is saturated, the flow of wastewater is stopped.

[0062] Desorption: An 8% hydrochloric acid solution was used as the desorbent and introduced from the bottom of the adsorption column at a flow rate of 1 BV / h. Desorption was carried out at 45°C, and the desorbed solution was collected.

[0063] Refining: The desorbed liquid is subjected to vacuum distillation at a pressure of -0.08 MPa and a temperature of 55°C to remove most of the water and hydrochloric acid, resulting in a paraquat cationic solution, which is used for the preparation of paraquat aqueous solution.

[0064] The test results showed that the paraquat cation concentration in the raw wastewater after adsorption was 70 mg / L, and the paraquat cation recovery rate in the wastewater was 98.2%.

[0065] Example 3

[0066] Pretreatment: Take 1000L of wastewater containing paraquat cations with a concentration of 4000mg / L, filter it through a 5μm filter screen to remove visible suspended particles; transfer the wastewater to a pH adjustment tank, add sulfuric acid to adjust the pH value to 5, then add 1.0% polyaluminum chloride, stir for 30 minutes, and then transfer it to a flocculation sedimentation tank for sedimentation for 1 hour to perform solid-liquid separation and obtain pre-purified wastewater. The paraquat particle solids removed by pretreatment are transferred to a paraquat recovery tank.

[0067] Preparation of special cation exchange resins: Strong acid cation exchange resin (containing sulfonic acid groups) was soaked in deionized water for 24 hours to remove surface impurities. It was then soaked in 8% hydrochloric acid solution for 4 hours to transform into the hydrogen-form strong acid cation exchange resin. Finally, it was washed with deionized water until neutral, filtered, and dried for later use. Preparation of the amination reaction system: The pretreated resin was added to a three-necked flask, along with an appropriate amount of N,N-dimethylformamide solvent. The mass ratio of resin to N,N-dimethylformamide was 1:3. Excess hexamethylenetetramine was added while stirring. The mass ratio of hexamethylenediamine to resin is 1:4. The reaction conditions are: heating to 80℃ and stirring for 6 hours. In the pretreated resin, the sulfonic acid group (-SO3H) and the amino group (-NH2) of hexamethylenediamine undergo an acid-base neutralization reaction to form a stable modified resin structure. Post-treatment: After the reaction is completed, cool to room temperature and wash the resin repeatedly with deionized water until the filtrate is neutral (to remove unreacted hexamethylenediamine). Then wash with ethanol 3 times to remove residual solvent. After vacuum drying, the special exchange resin is obtained.

[0068] Resin adsorption: The pre-purified wastewater is passed into three exchange columns connected in series and filled with special exchange resins. The flow rate of the wastewater is controlled at 3 BV / h (BV is the volume of the resin bed). When the resin is saturated, the flow of wastewater is stopped.

[0069] Desorption: A 10% hydrochloric acid solution was used as the desorbent and introduced from the bottom of the adsorption column at a flow rate of 0.7 BV / h. Desorption was carried out at 35°C, and the desorbed solution was collected.

[0070] Refining: The desorbed liquid is subjected to vacuum distillation at a pressure of -0.09 MPa and a temperature of 65°C to remove most of the water and hydrochloric acid, resulting in a paraquat cationic solution, which is used for the preparation of paraquat aqueous solution.

[0071] Testing revealed that the paraquat cation concentration in the raw wastewater after adsorption was 55 mg / L, and the paraquat cation recovery rate in the wastewater was 98.6%.

[0072] Example 4

[0073] Pretreatment: Take 1000L of wastewater containing paraquat cations with a concentration of 4000mg / L, filter it through a 10μm filter to remove visible suspended particles, transfer the wastewater to a pH adjustment tank, add sulfuric acid to adjust the pH to 5, then add 0.7% polyaluminum chloride, stir for 30 minutes, and then transfer it to a flocculation sedimentation tank for sedimentation for 2.5 hours to separate solids and liquids, obtaining pre-purified wastewater. The paraquat particles removed by pretreatment are transferred to a paraquat recovery tank.

[0074] Preparation of special cation exchange resins: Strong acid cation exchange resin (containing sulfonic acid groups) was soaked in deionized water for 24 hours to remove surface impurities. It was then soaked in 9% hydrochloric acid solution for 4 hours to transform into the hydrogen-form strong acid cation exchange resin. Finally, it was washed with deionized water until neutral, filtered, and dried for later use. Preparation of the amination reaction system: The pretreated resin was added to a three-necked flask, along with an appropriate amount of N,N-dimethylformamide solvent. The mass ratio of resin to N,N-dimethylformamide was 1:2. Excess hexane was added while stirring. The mass ratio of amine, resin and hexamethylenediamine is 1:3. The reaction conditions are: heating to 75℃ and stirring for 5.5 hours. In the pretreated resin, the sulfonic acid group (-SO3H) and the amino group (-NH2) of hexamethylenediamine undergo an acid-base neutralization reaction to form a stable modified resin structure. Post-treatment: After the reaction is completed, cool to room temperature and wash the resin repeatedly with deionized water until the filtrate is neutral (to remove unreacted hexamethylenediamine). Then wash with ethanol 4 times to remove residual solvent. After vacuum drying, the special exchange resin is obtained.

[0075] Resin adsorption: The pre-purified wastewater is passed into three exchange columns connected in series and filled with special exchange resins. The flow rate of the wastewater is controlled at 4 BV / h (BV is the volume of the resin bed). When the resin is saturated, the flow of wastewater is stopped.

[0076] Desorption: A 9% hydrochloric acid solution was used as the desorbent and introduced from the bottom of the adsorption column at a flow rate of 0.8 BV / h. Desorption was carried out at 45°C, and the desorbed solution was collected.

[0077] Refining: The desorbed liquid is subjected to vacuum distillation at a pressure of -0.1 MPa and a temperature of 60°C to remove most of the water and hydrochloric acid, resulting in a paraquat cationic solution, which is used for the preparation of paraquat aqueous solution.

[0078] The test results showed that the paraquat cation concentration in the raw wastewater after adsorption was 42 mg / L, and the paraquat cation recovery rate in the wastewater was 99.0%.

[0079] Example 5

[0080] Pretreatment: Take 1000L of wastewater containing paraquat cations with a concentration of 4000mg / L, filter it through a 15μm filter to remove visible suspended particles, transfer the wastewater to a pH adjustment tank, add sulfuric acid to adjust the pH to 6, then add 0.5% polyaluminum chloride, stir for 25 minutes, and then transfer it to a flocculation sedimentation tank for sedimentation for 3 hours to perform solid-liquid separation and obtain pre-purified wastewater. The paraquat particles removed by pretreatment are transferred to a paraquat recovery tank.

[0081] Preparation of special cation exchange resins: Strong acid cation exchange resin (containing sulfonic acid groups) was soaked in deionized water for 24 hours to remove surface impurities. It was then soaked in 10% hydrochloric acid solution for 4 hours to transform into the hydrogen-form strong acid cation exchange resin. Finally, it was washed with deionized water until neutral, filtered, and dried for later use. Preparation of the amination reaction system: The pretreated resin was added to a three-necked flask, along with an appropriate amount of N,N-dimethylformamide solvent. The mass ratio of resin to N,N-dimethylformamide was 1:1.5. Excess solvent was added while stirring. Hexamethylenediamine was used, with a resin-to-hexamethylenediamine mass ratio of 1:4. The reaction conditions were: heating to 70°C and stirring for 5 hours. In the pretreated resin, the sulfonic acid groups (-SO3H) and the amino groups (-NH2) of hexamethylenediamine underwent an acid-base neutralization reaction to form a stable modified resin structure. Post-treatment: after the reaction was completed, the resin was cooled to room temperature and repeatedly washed with deionized water until the filtrate was neutral (to remove unreacted hexamethylenediamine). Then, it was washed four times with ethanol to remove residual solvent. After vacuum drying, the special exchange resin was obtained.

[0082] Resin adsorption: The pre-purified wastewater is passed into three exchange columns connected in series and filled with special exchange resins. The flow rate of the wastewater is controlled at 3 BV / h (BV is the volume of the resin bed). When the resin is saturated, the flow of wastewater is stopped.

[0083] Desorption: A 10% hydrochloric acid solution was used as the desorbent and introduced from the bottom of the adsorption column at a flow rate of 0.5 BV / h. Desorption was carried out at 50°C, and the desorbed solution was collected.

[0084] Refining: The desorbed liquid is subjected to vacuum distillation at a pressure of -0.1 MPa and a temperature of 60°C to remove most of the water and hydrochloric acid, resulting in a paraquat cationic solution, which is used for the preparation of paraquat aqueous solution.

[0085] Testing revealed that the paraquat cation concentration in the raw wastewater after adsorption was 35 mg / L, and the paraquat cation recovery rate in the wastewater was 99.1%.

[0086] Example 6

[0087] Pretreatment: Take 1000L of wastewater containing paraquat cations with a concentration of 4000mg / L, filter it through a 20μm filter to remove visible suspended particles, transfer the wastewater to a pH adjustment tank, add sulfuric acid to adjust the pH to 4, then add 0.5% polyaluminum chloride, stir for 30 minutes, and then transfer it to a flocculation sedimentation tank for sedimentation for 3 hours to perform solid-liquid separation and obtain pre-purified wastewater. The paraquat particles removed by pretreatment are transferred to a paraquat recovery tank.

[0088] Preparation of special cation exchange resins: Strong acid cation exchange resin (containing sulfonic acid groups) was soaked in deionized water for 24 hours to remove surface impurities. It was then soaked in 10% hydrochloric acid solution for 4 hours to transform into the hydrogen-form strong acid cation exchange resin. Finally, it was washed with deionized water until neutral, filtered, and dried for later use. Preparation of the amination reaction system: The pretreated resin was added to a three-necked flask, along with an appropriate amount of N,N-dimethylformamide solvent. The mass ratio of resin to N,N-dimethylformamide was 1:1.5. Excess p-benzene was added while stirring. The mass ratio of resin to p-phenylenediamine is 1:4. The reaction conditions are: heating to 70℃ and stirring for 5 hours. In the pretreated resin, the sulfonic acid group (-SO3H) and the amino group (-NH2) of p-phenylenediamine undergo an acid-base neutralization reaction to form a stable modified resin structure. Post-treatment: After the reaction is completed, the resin is cooled to room temperature and repeatedly washed with deionized water until the filtrate is neutral (to remove unreacted p-phenylenediamine). Then, it is washed 4 times with ethanol to remove residual solvent. After vacuum drying, the special exchange resin is obtained.

[0089] Resin adsorption: The pre-purified wastewater is passed into three exchange columns connected in series and filled with special exchange resins. The flow rate of the wastewater is controlled at 2 BV / h (BV is the volume of the resin bed). When the resin is saturated, the flow of wastewater is stopped.

[0090] Desorption: A 10% hydrochloric acid solution was used as the desorbent and introduced from the bottom of the adsorption column at a flow rate of 0.5 BV / h. Desorption was carried out at 50°C, and the desorbed solution was collected.

[0091] Refining: The desorbed liquid is subjected to vacuum distillation at a pressure of -0.1 MPa and a temperature of 60°C to remove most of the water and hydrochloric acid, resulting in a paraquat cationic solution, which is used for the preparation of paraquat aqueous solution.

[0092] The test results showed that the paraquat cation concentration in the raw wastewater after adsorption was 40 mg / L, and the paraquat cation recovery rate in the wastewater was 99.0%.

[0093] Example 7

[0094] Pretreatment: Take 1000L of wastewater containing paraquat cations with a concentration of 4000mg / L, filter it through a 1μm filter to remove visible suspended particles, transfer the wastewater to a pH adjustment tank, add sulfuric acid to adjust the pH to 5, then add 0.5% polyaluminum chloride, stir for 30 minutes, and then transfer it to a flocculation sedimentation tank for sedimentation for 3 hours to perform solid-liquid separation and obtain pre-purified wastewater. The paraquat particles removed by pretreatment are transferred to a paraquat recovery tank.

[0095] Preparation of special cation exchange resins: Strong acid cation exchange resin (containing sulfonic acid groups) was soaked in deionized water for 24 hours to remove surface impurities. It was then soaked in 10% hydrochloric acid solution for 4 hours to transform into the hydrogen-form strong acid cation exchange resin. After washing with deionized water until neutral, it was filtered and dried for later use. Preparation of the amination reaction system: The pretreated resin was added to a three-necked flask, along with an appropriate amount of N,N-dimethylformamide solvent. The mass ratio of resin to N,N-dimethylformamide was 1:1.5. Excess terephthalamide was added while stirring. The mass ratio of amine, resin and p-phenylenediamine is 1:4. The reaction conditions are: heating to 70℃ and stirring for 5 hours. The sulfonic acid group (-SO3H) in the pretreated resin undergoes an acid-base neutralization reaction with the amino group (-NH2) of p-phenylenediamine to form a stable modified resin structure. Post-treatment: After the reaction is completed, the resin is cooled to room temperature and repeatedly washed with deionized water until the filtrate is neutral (to remove unreacted p-phenylenediamine). Then, it is washed three times with ethanol to remove residual solvent. After vacuum drying, the special exchange resin is obtained.

[0096] Resin adsorption: The pre-purified wastewater is passed into three exchange columns connected in series and filled with special exchange resins. The flow rate of the wastewater is controlled at 1 BV / h (BV is the volume of the resin bed). When the resin is saturated, the flow of wastewater is stopped.

[0097] Desorption: A 10% hydrochloric acid solution was used as the desorbent and introduced from the bottom of the adsorption column at a flow rate of 0.5 BV / h. Desorption was carried out at 50°C, and the desorbed solution was collected.

[0098] Refining: The desorbed liquid is subjected to vacuum distillation at a pressure of -0.1 MPa and a temperature of 60°C to remove most of the water and hydrochloric acid, resulting in a paraquat cationic solution, which is used for the preparation of paraquat aqueous solution.

[0099] The test results showed that the paraquat cation concentration in the raw wastewater after adsorption was 38 mg / L, and the paraquat cation recovery rate in the wastewater was 99.0%.

[0100] Example 8

[0101] Pretreatment: Take 1000L of wastewater containing paraquat cations with a concentration of 4000mg / L, filter it through a 1μm filter to remove visible suspended particles, transfer the wastewater to a pH adjustment tank, add sulfuric acid to adjust the pH to 5, then add 0.5% polyaluminum chloride, stir for 30 minutes, and then transfer it to a flocculation sedimentation tank for sedimentation for 3 hours to perform solid-liquid separation and obtain pre-purified wastewater. The paraquat particles removed by pretreatment are transferred to a paraquat recovery tank.

[0102] Preparation of special cation exchange resins: Strong acid cation exchange resin (containing sulfonic acid groups) was soaked in deionized water for 24 hours to remove surface impurities. It was then soaked in 10% hydrochloric acid solution for 4 hours to transform into the hydrogen-form strong acid cation exchange resin. After washing with deionized water until neutral, it was filtered and dried for later use. Preparation of the amination reaction system: The pretreated resin was added to a three-necked flask, along with an appropriate amount of N,N-dimethylformamide solvent. The mass ratio of resin to N,N-dimethylformamide was 1:1.5. Excess ethyl acetate was added while stirring. The mass ratio of ethylenediamine to resin is 1:4. The reaction conditions are: heating to 70℃ and stirring for 5 hours. In the pretreated resin, the sulfonic acid group (-SO3H) and the amino group (-NH2) of ethylenediamine undergo an acid-base neutralization reaction to form a stable modified resin structure. Post-treatment: After the reaction is completed, the resin is cooled to room temperature and washed repeatedly with deionized water until the filtrate is neutral (to remove unreacted ethylenediamine). Then, it is washed three times with ethanol to remove residual solvent. After vacuum drying, the special exchange resin is obtained.

[0103] Resin adsorption: The pre-purified wastewater is passed into three exchange columns connected in series and filled with special exchange resins. The flow rate of the wastewater is controlled at 1.5 BV / h (BV is the volume of the resin bed). When the resin is saturated, the flow of wastewater is stopped.

[0104] Desorption: A 10% hydrochloric acid solution was used as the desorbent and introduced from the bottom of the adsorption column at a flow rate of 0.5 BV / h. Desorption was carried out at 50°C, and the desorbed solution was collected.

[0105] Refining: The desorbed liquid is subjected to vacuum distillation at a pressure of -0.1 MPa and a temperature of 60°C to remove most of the water and hydrochloric acid, resulting in a paraquat cationic solution, which is used for the preparation of paraquat aqueous solution.

[0106] Testing revealed that the paraquat cation concentration in the raw wastewater after adsorption was 30 mg / L, and the paraquat cation recovery rate in the wastewater was 99.2%.

[0107] Example 9

[0108] Pretreatment: Take 1000L of wastewater containing paraquat cations with a concentration of 4000mg / L, filter it through a 1μm filter to remove visible suspended particles, transfer the wastewater to a pH adjustment tank, add sulfuric acid to adjust the pH to 5, then add 0.5% polyaluminum chloride, stir for 30 minutes, and then transfer it to a flocculation sedimentation tank for sedimentation for 3 hours to perform solid-liquid separation and obtain pre-purified wastewater. The paraquat particles removed by pretreatment are transferred to a paraquat recovery tank.

[0109] Preparation of special cation exchange resins: Strong acid cation exchange resin (containing sulfonic acid groups) was soaked in deionized water for 24 hours to remove surface impurities. It was then soaked in 10% hydrochloric acid solution for 4 hours to transform into the hydrogen-form strong acid cation exchange resin. After washing with deionized water until neutral, it was filtered and dried for later use. Preparation of the amination reaction system: The pretreated resin was added to a three-necked flask, along with an appropriate amount of N,N-dimethylformamide solvent. The mass ratio of resin to N,N-dimethylformamide was 1:2. Excess ethylene glycol was added while stirring. The mass ratio of amine, resin and ethylenediamine is 1:5. The reaction conditions are: heating to 80℃ and stirring for 4 hours. In the pretreated resin, the sulfonic acid group (-SO3H) and the amino group (-NH2) of ethylenediamine undergo an acid-base neutralization reaction to form a stable modified resin structure. Post-treatment: After the reaction is completed, cool to room temperature and wash the resin repeatedly with deionized water until the filtrate is neutral (to remove unreacted ethylenediamine). Then wash with ethanol 3 times to remove residual solvent. After vacuum drying, the special exchange resin is obtained.

[0110] Resin adsorption: The pre-purified wastewater is passed into three exchange columns connected in series and filled with special exchange resins. The flow rate of the wastewater is controlled at 2 BV / h (BV is the volume of the resin bed). When the resin is saturated, the flow of wastewater is stopped.

[0111] Desorption: A 10% hydrochloric acid solution was used as the desorbent and introduced from the bottom of the adsorption column at a flow rate of 0.5 BV / h. Desorption was carried out at 30°C, and the desorbed solution was collected.

[0112] Refining: The desorbed liquid is subjected to vacuum distillation at a pressure of -0.1 MPa and a temperature of 60°C to remove most of the water and hydrochloric acid, resulting in a paraquat cationic solution, which is used for the preparation of paraquat aqueous solution.

[0113] The test results showed that the paraquat cation concentration in the raw wastewater after adsorption was 38 mg / L, and the paraquat cation recovery rate in the wastewater was 99.0%.

[0114] Example 10

[0115] Pretreatment: Take 1000L of wastewater containing paraquat cations with a concentration of 4000mg / L, filter it through a 0.5μm filter screen to remove visible suspended particles, transfer the wastewater to a pH adjustment tank, add sulfuric acid to adjust the pH value to 5, then add 0.5% polyaluminum chloride, stir for 30 minutes, and then transfer it to a flocculation sedimentation tank for sedimentation for 3 hours to perform solid-liquid separation and obtain pre-purified wastewater. The paraquat particle solids removed by pretreatment are transferred to a paraquat recovery tank.

[0116] Preparation of special cation exchange resins: Strong acid cation exchange resin (containing sulfonic acid groups) was soaked in deionized water for 24 hours to remove surface impurities. It was then soaked in 10% hydrochloric acid solution for 4 hours to transform into the hydrogen-form strong acid cation exchange resin. After washing with deionized water until neutral, it was filtered and dried for later use. Preparation of the amination reaction system: The pretreated resin was added to a three-necked flask, along with an appropriate amount of N,N-dimethylformamide solvent. The mass ratio of resin to N,N-dimethylformamide was 1:1.5. Excess ethyl acetate was added while stirring. The mass ratio of ethylenediamine to resin is 1:3. The reaction conditions are: heating to 70℃ and stirring for 6 hours. In the pretreated resin, the sulfonic acid group (-SO3H) and the amino group (-NH2) of ethylenediamine undergo an acid-base neutralization reaction to form a stable modified resin structure. Post-treatment: After the reaction is completed, the resin is cooled to room temperature and washed repeatedly with deionized water until the filtrate is neutral (to remove unreacted ethylenediamine). Then, it is washed three times with ethanol to remove residual solvent. After vacuum drying, the special exchange resin is obtained.

[0117] Resin adsorption: The pre-purified wastewater is passed into three exchange columns connected in series and filled with special exchange resins. The flow rate of the wastewater is controlled at 1 BV / h (BV is the volume of the resin bed). When the resin is saturated, the flow of wastewater is stopped.

[0118] Desorption: A 10% hydrochloric acid solution was used as the desorbent and introduced from the bottom of the adsorption column at a flow rate of 0.5 BV / h. Desorption was carried out at 35°C, and the desorbed solution was collected.

[0119] Refining: The desorbed liquid is subjected to vacuum distillation at a pressure of -0.1 MPa and a temperature of 60°C to remove most of the water and hydrochloric acid, resulting in a paraquat cationic solution, which is used for the preparation of paraquat aqueous solution.

[0120] Testing revealed that the paraquat cation concentration in the raw wastewater after adsorption was 30 mg / L, and the paraquat cation recovery rate in the wastewater was 99.2%.

[0121] Comparative Example

[0122] When the same wastewater was treated using traditional chemical oxidation methods and Fenton's reagent, the removal rate of paraquat cations in the wastewater was only 55%, and the treated wastewater contained a large amount of impurities such as iron ions, making it difficult to meet the discharge standards. At the same time, the recovery and utilization of paraquat cations were not achieved.

[0123] Paraquat cations were recovered from wastewater according to the methods provided in Examples 1-10 and Comparative Examples. The recovery status of paraquat cations in the wastewater is shown in Table 1.

[0124] Table 1: Recovery of paraquat cations from wastewater

[0125] After adsorption, the concentration of paraquat cations in the raw wastewater is... Paraquat cation recovery rate in wastewater Example 1 85mg / L 97.8% Example 2 70mg / L 98.2% Example 3 55mg / L 98.6% Example 4 42mg / L 99.0% Example 5 35mg / L 99.1% Example 6 40mg / L 99.0% Example 7 38mg / L 99.0% Example 8 30mg / L 99.2% Example 9 38mg / L 99.0% Example 10 30mg / L 99.2% Comparative Example 1800mg / L 55.2%

[0126] The comparison of Examples 1-10 and the comparative examples fully demonstrates the superiority of the present invention in recovering paraquat cations from wastewater, effectively solving the problems existing in the prior art, and having significant economic and environmental benefits.

[0127] The core function of strong acid cation exchange resin (containing sulfonic acid groups) is to adsorb cations in solution through ion exchange. Paraquat cation is a typical cation. Although strong acid cation exchange resin (containing sulfonic acid groups) can adsorb paraquat cation, its selectivity is greatly affected by competing ions. Strong acid cation exchange resin (containing sulfonic acid groups) will preferentially adsorb cations with high charge density and matching ionic radius (such as Na⁺, K⁺, Ca²⁺, etc.). However, there are a large number of such competing ions in paraquat wastewater, which will significantly reduce the selective adsorption capacity for paraquat.

[0128] Therefore, by modifying the strongly acidic cation exchange resin (containing sulfonic acid groups), the sulfonic acid groups are replaced with amino groups, which effectively improves the selectivity of the amino cation exchange resin for paraquat cations. The amino groups (-NH2, -NH-, etc.) can specifically bind to paraquat molecules (which contain a bispyridine ring and easily interact with amino groups) through hydrogen bonding, electrostatic attraction (the amino group becomes positively charged after protonation and forms a synergistic effect with paraquat), or hydrophobic interactions, thereby reducing the adsorption of ordinary inorganic cations and improving selectivity.

[0129] In summary, by modifying the cation exchange resin and optimizing the resin adsorption and desorption process, the recovery rate of paraquat cations in wastewater can reach over 99%, effectively achieving efficient recycling of resources.

[0130] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0131] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for recovering paraquat cations from wastewater, characterized in that, include: A filter screen with a pore size of 0.1-20μm is used to remove suspended particles and large impurities from the wastewater. The pH value of the wastewater is adjusted to 3-6, and 0.1%-1% of polyaluminum chloride flocculant is added. The mixture is stirred for 10-30 minutes, and the sedimentation time is 1-3 hours. Solid-liquid separation is carried out to obtain pre-purified wastewater. The paraquat particles removed in the pretreatment are reused. The strong acid cation exchange resin was soaked in deionized water for 24 hours and then in 5-10% hydrochloric acid solution for 4 hours to transform it into a hydrogen-form strong acid cation exchange resin. The resin was washed with deionized water until neutral, filtered, and dried for later use. The pretreated resin was added to a three-necked flask, along with an appropriate amount of N,N-dimethylformamide solvent. An excess amination reagent was added while stirring. After the amination reaction was completed, the resin was cooled to room temperature and repeatedly washed with deionized water until the filtrate was neutral to remove unreacted amination reagent. The resin was then washed with ethanol 3-5 times to remove residual solvent and dried under vacuum to obtain the special exchange resin. The pre-purified wastewater is passed into three exchange columns connected in series and filled with special exchange resin. The flow rate of the wastewater is controlled at 1-5 BV / h. When the resin is saturated, the flow of wastewater is stopped. A 5%-10% hydrochloric acid solution was used as the desorbent and introduced from the bottom of the adsorption column at a flow rate of 0.2-1 BV / h to desorb the paraquat cations adsorbed by the resin. The desorbed liquid was collected and heated during the desorption process, with the temperature controlled at 30-50℃. The desorbed liquid was subjected to vacuum distillation at a pressure of -0.07 to -0.1 MPa and a temperature of 50 to 80°C to remove water and hydrochloric acid, resulting in a concentrated paraquat cationic solution.

2. The method for recovering paraquat cations from wastewater according to claim 1, characterized in that, The mass ratio of the resin to N,N-dimethylformamide is 1:1 to 1:

3.

3. The method for recovering paraquat cations from wastewater according to claim 2, characterized in that, The mass ratio of the resin to the amination reagent is 1:3 to 1:

5.

4. The method for recovering paraquat cations from wastewater according to claim 3, characterized in that, The amination reaction conditions are as follows: heating to 60-80℃ and stirring for 4-6 hours, wherein the strong acid groups in the pretreated resin undergo an acid-base neutralization reaction with the amino groups of the amination reagent to form a stable modified resin structure.

5. A method for recovering paraquat cations from wastewater according to claim 4, characterized in that, The amination reagent is one of ethylenediamine, hexamethylenediamine, and p-phenylenediamine.

6. A system for recovering paraquat cations from wastewater, for implementing the method for recovering paraquat cations from wastewater as described in claim 5, characterized in that, It includes a pretreatment unit, an adsorption unit, a desorption unit, and a purification unit, wherein, Pretreatment unit: includes a filter, a pH adjustment tank, and a flocculation sedimentation tank connected in sequence; The filter adopts a screen structure for easy screen replacement; the pH adjustment tank is equipped with a pH sensor and dosing device to automatically adjust the pH value of the wastewater; the flocculation sedimentation tank is equipped with a stirrer and inclined tube sedimentation device to improve the solid-liquid separation effect. Adsorption unit: includes three adsorption columns connected in series and an outlet tank; The three-stage adsorption column is filled with a special exchange resin, and the column body is made of corrosion-resistant material; the effluent tank is used to store qualified effluent after resin adsorption. Desorption unit: includes desorbent storage tank, desorbent transfer pump and desorption liquid storage tank; The desorbent storage tank is used to store hydrochloric acid desorbent, the desorbent transfer pump is used to deliver the desorbent to the desorption column, and the desorption liquid storage tank is used to store the desorption liquid after resin desorption. The refining unit includes a vacuum distillation unit, a desorbent intermediate tank, and a paraquat recovery tank. The vacuum distillation unit is used to concentrate the desorbed solution, the desorbent intermediate tank is used to store the distilled hydrochloric acid desorbent, and the paraquat recovery tank is used to store the recovered solution containing paraquat cations.

7. A method for recovering paraquat cations from wastewater according to claim 6, characterized in that, The three-stage adsorption column includes a primary exchange column (51), a secondary exchange column (52), and a tertiary exchange column (53). The upper ends of the primary exchange column (51), the secondary exchange column (52), and the tertiary exchange column (53) are provided with water outlets (511), and the lower ends of the primary exchange column (51), the secondary exchange column (52), and the tertiary exchange column (53) are provided with water inlets (512). The primary exchange column (51), the secondary exchange column (52), and the tertiary exchange column (53) are connected in series through a flexible hose (54).

8. A method for recovering paraquat cations from wastewater according to claim 7, characterized in that, The inner sides of the primary exchange column (51), the secondary exchange column (52) and the tertiary exchange column (53) are all provided with exchange resin filler (55) and delay plate (56), wherein the delay plate (56) is located above the exchange resin filler (55) and the delay plate (56) is provided with delay hole (561).

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