A trichloroisocyanuric acid mother liquor recovery treatment process

Abstract

The present application relates to wastewater recycling treatment technical field, especially to a kind of trichloro isocyanuric acid mother liquor recycling treatment process;With crosslinking degradable temperature-sensitive flocculants as the first step main flocculant, cooperate with temperature-sensitive dissociation washing, realize the green closed loop circulation of flocculant;With cationic cyclodextrin flocculant cooperates inert electrode electroflocculation as second step deep purification, solve the problem that residual microfine particles persist in suspension in supernatant after natural sedimentation, effluent turbidity and pipeline scale, realize the thorough clarification of effluent;The core functional unit of the crosslinking degradable temperature-sensitive flocculant is the microgel network formed by chitosan grafting poly-N-isopropyl acrylamide and oxidized starch crosslinking;The cationic cyclodextrin flocculant is maleic anhydride esterification β-cyclodextrin, acrylamide and 2-methacryloyloxyethyl trimethylammonium chloride radical copolymer.

Description

Technical Field

[0001] This invention relates to the field of wastewater recycling and treatment technology, and in particular to a process for recycling and treating trichloroisocyanuric acid mother liquor. Background Technology

[0002] Currently, the industrial production of trichloroisocyanuric acid using the chlorination process generates a large amount of mother liquor containing unreacted materials and byproducts. This mother liquor contains multiple components such as cyanuric acid, sodium chloride, and hypochlorous acid. Direct discharge not only wastes resources but also causes serious environmental pollution. The industry commonly employs an acidification-alkalization series process to treat the mother liquor, converting cyanuric acid into a sodium cyanurate suspension. The sodium cyanurate solid is then recovered through natural sedimentation and filtration, thus achieving the recycling of the effective components in the mother liquor.

[0003] To achieve a high recovery rate of sodium cyanurate, it is necessary to separate fine particles through sedimentation as thoroughly as possible. However, the newly formed sodium cyanurate particles are extremely small, typically ranging from submicron to several micrometers in size. Natural sedimentation requires a settling time of tens of hours, and even then, complete sedimentation is not achieved, leaving fine particles suspended in the supernatant. These particles are discharged with the supernatant and precipitate again when the transport pipeline and ambient temperature change, causing secondary pollution problems such as pipeline blockage and turbidity of the receiving water. To achieve thorough clarification of the discharged water, more stringent separation methods are required, but existing conventional filtration equipment is insufficient for economically and efficiently handling such large quantities of low-concentration fine suspensions.

[0004] Therefore, existing technologies suffer from limited recovery rates and incomplete purification of wastewater. There is a lack of a systematic solution that balances high recovery rates, recyclable flocculants, and deep purification of wastewater, which severely restricts the development of clean recovery processes for trichloroisocyanuric acid mother liquor. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies and proposes a process for recovering and treating trichloroisocyanuric acid mother liquor. This process utilizes a cross-linked biodegradable temperature-sensitive flocculant for flocculation and deposition, and a cationic cyclodextrin flocculant for electrocoagulation, to achieve high recovery rate, recyclable flocculant, and deep purification of external wastewater. The core functional unit of the cross-linked biodegradable temperature-sensitive flocculant is a microgel network formed by cross-linking chitosan with polynitro-isopropylacrylamide and oxidized starch. It has a three-dimensional cross-linked structure with chitosan as the biodegradable main chain, temperature-sensitive side chains grafted by atom transfer radical polymerization, and condensation of polyaldehyde groups of oxidized starch with residual amino groups of chitosan. It is used to achieve efficient flocculation and sedimentation under weak alkaline conditions at room temperature by exerting the triple synergistic effect of cationic charge neutralization, temperature-sensitive chain extension bridging and cross-linked network sweeping. In the temperature-sensitive dissociation washing stage, the side chain thermal condensation and cross-linked bond acid-induced hydrolysis are used to achieve intelligent detachment and recycling of flocculant. The cationic cyclodextrin flocculant is a free radical copolymer of maleic anhydride esterified β-cyclodextrin, acrylamide, and 2-methacryloyloxyethyltrimethylammonium chloride. Its side chains simultaneously suspend β-cyclodextrin, hydrophobic inclusion cavities, and quaternary ammonium salt cationic groups, which are used to achieve deep capture of residual submicron particles through a triple mechanism of cationic charge neutralization, cyclodextrin host-guest inclusion recognition, and polymer bridging under the synergy of an electric field.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a process for recovering and treating trichloroisocyanuric acid mother liquor, comprising the following steps: Step S1: Acidification and alkalization of trichloroisocyanuric acid mother liquor: The trichloroisocyanuric acid mother liquor is subjected to acidification and alkalization treatment in sequence to obtain a sodium cyanurate suspension; Step S2: First step flocculation and sedimentation recovery: The sodium cyanurate suspension is passed into a settling tank and a cross-linked biodegradable temperature-sensitive flocculant is added for flocculation and sedimentation to separate the first underflow and the first supernatant; the first underflow is subjected to temperature-sensitive dissociation washing to recover the sodium cyanurate solid, and the flocculant in the washing liquid is separated and recycled; Step S3: Second step of electrocoagulation purification: The first supernatant is sent into the electrocoagulation device and cationic cyclodextrin flocculant is added to separate the second underflow and the second supernatant. The second underflow is returned to step S2 for combined processing. Step S4: pH adjustment of external drainage: Adjust the pH of the second supernatant to 5.5±0.1 and drain it externally.

[0007] Furthermore, in step S1: the acidification endpoint pH is 1.0-1.5, and hydrochloric acid is used for acidification; the alkalization endpoint pH is 7.5-8.0, and sodium hydroxide is used for alkalization.

[0008] In step S2: the dosage of cross-linked biodegradable temperature-sensitive flocculant is 1–3 mg / L; the flocculation and sedimentation temperature is 25±5℃, and the sedimentation time is 12h; the operating conditions for temperature-sensitive dissociation washing are: washing water temperature 45℃, and the pH of the washing solution is adjusted to 5.0 with 5wt% dilute hydrochloric acid.

[0009] In step S3: the dosage of cationic cyclodextrin flocculant is 0.5–1.0 mg / L; the electrocoagulation treatment uses coated titanium electrodes and graphite electrodes, with the cathode and anode arranged alternately, the electrode spacing is 30 mm, and the current density is 20 A / m. 2 The stay time is 10 minutes.

[0010] Step S2 Flocculation and Dissociation Cycle Mechanism: Under weakly alkaline conditions at room temperature, the free amino groups of the chitosan backbone in the cross-linked degradable temperature-sensitive flocculant are protonated and neutralized with the negative charge on the surface of sodium cyanurate particles; the poly-N-isopropylacrylamide side chains are in a fully extended state due to the temperature being below their low critical dissolution temperature, playing a long-range polymer bridging role; the microgel network formed by cross-linking of oxidized starch simultaneously encapsulates multiple particles through a sweeping mechanism, forming large-sized, densely structured flocculent aggregates that settle rapidly under gravity. The flocs obtained from sedimentation separation are transferred to a 45°C warm water environment during the temperature-sensitive dissociation washing stage. The side chains of poly(N-isopropylacrylamide) shrink rapidly due to the temperature exceeding the lower critical dissolution temperature and detach from the particle surface. At the same time, under acidic conditions, the imine crosslinking bonds undergo partial hydrolysis, and the three-dimensional network disintegrates into low molecular weight fragments or single chains, further promoting separation from the particles. The detached and dissolved flocculant fragments are concentrated with the washing liquid through membrane separation and returned to the flocculant preparation tank. After cooling to room temperature, the poly(N-isopropylacrylamide) chains re-expand and partially restore flocculation activity, achieving recycling.

[0011] Step S3 Electrocoagulation Deep Purification Mechanism: Submicron-sized residual particles remain in the first supernatant after step S2. Under the action of an electric field, the negatively charged residual particles migrate electrophoretically towards the anode and accumulate in the anode region; the quaternary ammonium salt groups of the cationic cyclodextrin flocculant provide supplementary positive charges, and the specific inclusion of the cyclodextrin cavity enhances the affinity with the residual particles, ensuring that the fine particles are thoroughly captured and aggregated; the recovered material contained in the second underflow is returned to step S2 for combined treatment, ensuring that the overall recovery rate of sodium cyanurate is maximized.

[0012] The cross-linked biodegradable temperature-sensitive flocculant is prepared by the following steps: Step A1: Mix chitosan and acetic acid solution, stir at 300 rpm and 25°C, add sodium dodecyl sulfate, stir for 12 h, filter, centrifuge at 3000 rpm for 5 min, remove supernatant 1 and collect precipitate 1, wash precipitate 1 with deionized water, freeze dry to obtain pretreated chitosan. Step A2: Mix bromoisobutyric acid, N,N'-dicyclohexylcarbodiimide, N-hydroxysuccinimide and 1-methyl-2-pyrrolidone, and react for 24 h at a stirring rate of 300 rpm and 40 °C. Filter to remove precipitate 2 and collect filtrate 2. Mix pretreated chitosan, filtrate 2 and dimethyl sulfoxide, and react for 48 h at a stirring rate of 120 rpm and 40 °C. Dissolve in diethyl ether / acetone, centrifuge at 3000 rpm for 10 min, remove supernatant 3 and collect precipitate 3. Precipitate 3 is the chitosan initiator. Step A3: Chitosan initiator, N-isopropylacrylamide, dimethyl sulfoxide, bipyridine and copper bromide are mixed and reacted at 150 rpm and 60 °C for 24 h under nitrogen protection. Tris-HCl buffer solution is then added to adjust the pH to 8 and stirred for 1 h to dissociate sodium dodecyl sulfate. Subsequently, the mixture is dialyzed with deionized water for 48 h. The contents of the dialysis bag are collected and freeze-dried to obtain a biodegradable temperature-sensitive flocculant. Step A4: Mix the biodegradable temperature-sensitive flocculant, oxidized starch and deionized water, stir for 3 minutes at 1200 rpm and 25°C, then add acetic acid solution to adjust the pH to 5.5, stir and react for 12 hours at 120 rpm and 30°C, and freeze dry to obtain the cross-linked biodegradable temperature-sensitive flocculant. Furthermore, in step A1, the mass ratio of chitosan, sodium dodecyl sulfate, and acetic acid solution is 1:(2-4):80, and the mass concentration of acetic acid solution is 1%.

[0013] Furthermore, in step A2, the molar ratio of bromoisobutyric acid, N,N'-dicyclohexylcarbodiimide, and N-hydroxysuccinimide is 1:(1.0-1.2):(1.0-1.2); the mass ratio of bromoisobutyric acid to pretreated chitosan is 1:(5-15); and the mass ratio of pretreated chitosan to dimethyl sulfoxide is 1:30.

[0014] Furthermore, in step A3: the mass ratio of chitosan initiator, N-isopropylacrylamide, bipyridine, and copper bromide is 1:(5-20):(0.1-0.5):(0.05-0.2), the mass ratio of chitosan initiator to dimethyl sulfoxide is 1:40, and the mass fraction of Tris-HCl buffer solution is 15% with a pH of 9.

[0015] Furthermore, in step A4: the mass ratio of the biodegradable temperature-sensitive flocculant to oxidized starch is 1:(0.05-0.15), the mass ratio of the biodegradable temperature-sensitive flocculant to deionized water is 1:(30-40), and the mass fraction of the acetic acid solution is 1%.

[0016] Step A1: Preparation of chitosan pretreatment: Chitosan is dissolved in acetic acid solution, and the amino groups on its molecular chain are protonated and become positively charged; sodium dodecyl sulfate is an anionic surfactant, and its sulfonic acid groups interact with the protonated amino groups of chitosan to form ionic complexes, so that chitosan is uniformly precipitated in the form of ionic complexes; this ionic complex pretreatment can protect the amino groups from excessive consumption by subsequent side reactions, while giving chitosan certain hydrophobic microdomains, which is beneficial to improving its dispersibility in organic solvents and providing a suitable reaction environment for subsequent atom transfer radical polymerization.

[0017] Step A2: Preparation of chitosan initiator: Bromoisobutyric acid first generates an activated ester intermediate under the action of N,N'-dicyclohexylcarbodiimide and N-hydroxysuccinimide; the activated ester undergoes an acylation coupling reaction with the hydroxyl groups on the chitosan backbone, chemically linking the bromine-containing initiating group to the chitosan backbone; Step A3 Preparation of the biodegradable temperature-sensitive flocculant: Under nitrogen protection, using the chitosan initiator obtained in step A2 as the macromolecular initiator, N-isopropylacrylamide as the monomer, bipyridine as the ligand, and copper bromide as the catalyst, atom transfer radical polymerization was carried out in dimethyl sulfoxide. The poly(N-isopropylacrylamide) side chains grew uniformly from the initiation sites on the chitosan backbone, and the degree of polymerization was controlled by the ratio of monomer to initiator. After the reaction was completed, Tris-HCl buffer solution was added to adjust the pH of the system to 8. Tris(hydroxymethyl)aminomethane, as a competitive cation, dissociated sodium dodecyl sulfate from the amino sites of chitosan, restoring the reactivity of the amino group. After dialysis purification, a temperature-responsive biodegradable temperature-sensitive flocculant was obtained, with a lower critical dissolution temperature of 32°C. Below this temperature, the poly(N-isopropylacrylamide) side chains hydrophilically extended, and above this temperature, they hydrophobically shrank.

[0018] Step A4: Preparation of crosslinked biodegradable temperature-sensitive flocculant: The amino groups retained on the backbone of the biodegradable temperature-sensitive flocculant obtained in step A3 undergo Schiff base condensation reaction with the aldehyde groups on the oxidized starch molecular chain under weakly acidic conditions to generate imine crosslinking bonds; the multi-aldehyde group characteristics of oxidized starch enable the formation of a micro-crosslinked network structure between multiple chitosan graft chains, transforming the linear chitosan graft copolymer into a crosslinked biodegradable temperature-sensitive flocculant with a three-dimensional microgel structure; this microgel exists in aqueous solution as swollen microparticles, with a higher effective adsorption surface area and more abundant particle capture sites per unit mass.

[0019] The cationic cyclodextrin flocculant is prepared by the following steps: Step B1: Mix β-cyclodextrin, maleic anhydride and N,N-dimethylformamide and react at 300 rpm and 60 ℃ for 8 h. After the reaction is complete, slowly pour the reaction solution into anhydrous diethyl ether to precipitate. Centrifuge at 5000 rpm for 10 min, remove the supernatant 4 and collect precipitate 4. Wash with ethanol and dry under vacuum to obtain functionalized cyclodextrin. Step B2: Functionalized cyclodextrin, acrylamide, 2-methacryloyloxyethyltrimethylammonium chloride and deionized water were mixed and stirred at 300 rpm and 60°C under nitrogen protection. Ammonium persulfate and sodium bisulfite were added and the mixture was reacted for 6 h. After cooling to room temperature, ethanol was added to precipitate the mixture. The mixture was centrifuged at 8000 rpm for 20 min, the supernatant 5 was removed and the precipitate 5 was collected. The precipitate was washed with ethanol / water and dried under vacuum to obtain cationic cyclodextrin flocculant.

[0020] Furthermore, in step B1: the molar ratio of β-cyclodextrin to maleic anhydride is 1:(0.5-1.5), and the mass ratio of β-cyclodextrin to N,N-dimethylformamide is 1:6.

[0021] Furthermore, in step B2: the mass ratio of functionalized cyclodextrin, acrylamide and 2-methacryloyloxyethyltrimethylammonium chloride is 1:(2-5):(1-3), the mass ratio of functionalized cyclodextrin to deionized water is 1:5, the molar ratio of ammonium persulfate and sodium bisulfite is 1:1, and the total amount of ammonium persulfate and sodium bisulfite is 0.8% of the total mass of the monomers.

[0022] Step B1 Preparation of functionalized cyclodextrin: Maleic anhydride undergoes an esterification ring-opening reaction with the hydroxyl groups on the β-cyclodextrin molecule, introducing maleic anhydride monoester groups containing polymerizable carbon-carbon double bonds onto the hydroxyl groups of β-cyclodextrin, while releasing carboxyl groups, so that the functionalized cyclodextrin has both polymerizability and water solubility. Step B2: Preparation of the cationic cyclodextrin flocculant: The double bonds of functionalized cyclodextrin are copolymerized with acrylamide and 2-methacryloyloxyethyltrimethylammonium chloride in aqueous solution via free radical polymerization. Ammonium persulfate and sodium bisulfite redox initiation generate primary free radicals, triggering chain growth reactions to produce a water-soluble copolymer with a carbon-carbon backbone and β-cyclodextrin groups and quaternary ammonium salt cationic groups suspended in the side chains. The quaternary ammonium salt cationic groups provide positive charges to neutralize and destabilize the negatively charged sodium cyanurate particles; the acrylamide segments provide polymeric bridging; and the β-cyclodextrin cavities selectively recognize and bind to the triazine ring structure of cyanurate through hydrophobic inclusion. These three components synergistically achieve highly efficient flocculation.

[0023] Compared with the prior art, the beneficial effects of the present invention are: This invention discloses a process for recovering and treating trichloroisocyanuric acid mother liquor. It uses a cross-linked biodegradable temperature-sensitive flocculant as the main flocculant in the first step, combined with temperature-sensitive dissociation washing and membrane concentration circulation, to achieve green closed-loop recycling of the flocculant. The second step of deep purification uses cationic cyclodextrin flocculant in conjunction with inert electrode electrocoagulation, which solves the problems of persistent suspension of residual fine particles in the supernatant after natural sedimentation, turbidity of external drainage, and scaling in pipelines, and achieves thorough clarification of external drainage.

[0024] This invention employs a cross-linked, biodegradable, temperature-sensitive flocculant combined with temperature-sensitive dissociation washing technology to form a reversible polymeric bridging network on the surface of sodium cyanurate particles. At room temperature, the flocculant chains extend and the cross-linked network remains intact, efficiently capturing and settling fine particles. When heated to 45°C and washed under weakly acidic conditions, the side chains of poly(N-isopropylacrylamide) shrink and the imine cross-linking bonds hydrolyze, causing flocculant fragments to intelligently detach from the particle surface. This results in the organic residue in the recovered sodium cyanurate solid being less than 100 ppm. After entering the subsequent chlorination reactor, it can be completely oxidized and degraded by chlorine gas into carbon dioxide, water, and nitrogen, with no risk of any toxic residue. The detached flocculant is then concentrated through a membrane and recycled.

[0025] This invention employs a cationic cyclodextrin flocculant synergistic electric field purification technology. An inert electrode provides the electric field driving force, and the specific inclusion recognition of cyclodextrin cavities and the charge neutralization effect of quaternary ammonium salt cations complement each other, so that residual particles are completely removed under the multiple effects of electrophoretic enrichment, air flotation separation and flocculation sedimentation. Combined with pH adjustment to 5.5, the problem of solid precipitation in the delivery pipeline and salt field is completely eliminated.

[0026] This invention employs a two-step hierarchical coupling architecture. The first step achieves efficient recovery of the main body of sodium cyanurate, and the second step achieves deep purification of residual particles. The material flow and energy flow are interconnected between the two steps, and the underflow is returned and merged for recovery, thus constructing a closed-loop process from mother liquor to recovered product and from clear liquid to standard discharge. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the process proposed in this invention. Detailed Implementation

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with existing known technologies. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0029] Preparation Example 1: Crosslinked biodegradable temperature-sensitive flocculant was prepared by the following steps: Step A1: 100g chitosan, 300g sodium dodecyl sulfate and 8000g acetic acid solution with a mass concentration of 1% were mixed and stirred for 12h at a stirring rate of 300rpm and 25℃; filtered, centrifuged at 3000rpm for 5min, the supernatant 1 was removed and precipitate 1 was collected; precipitate 1 was washed 3 times with deionized water and freeze-dried at -50℃ for 48h to obtain pretreated chitosan.

[0030] Step A2: Mix 10.0g of bromoisobutyric acid, 7.5g of N,N'-dicyclohexylcarbodiimide, 6.9g of N-hydroxysuccinimide, and 200mL of 1-methyl-2-pyrrolidone, and react at 300rpm and 40℃ for 24h. Filter to remove precipitate 2 and collect filtrate 2. Take 100g of the pretreated chitosan obtained in step A1 and add it to 3000g of dimethyl sulfoxide and stir evenly. Then add all of filtrate 2 and react at 120rpm and 40℃ for 48h. After the reaction, add 3000mL of a 1:1 mixture of diethyl ether and acetone to precipitate the product. Centrifuge at 3000rpm for 10min, remove the supernatant 3, and collect precipitate 3. Wash precipitate 3 twice with a mixture of diethyl ether and acetone, and vacuum dry to obtain chitosan initiator.

[0031] Step A3: Add 100g of chitosan initiator, 1200g of N-isopropylacrylamide, 30g of bipyridine, and 10g of copper bromide obtained in step A2 to 4000g of dimethyl sulfoxide and mix thoroughly. Under nitrogen protection, react at 150rpm and 60℃ for 24h. After the reaction, add a 15% Tris-HCl buffer solution with a pH of 9 to adjust the pH of the system to 8 and stir for 1h. Put the reaction solution into a dialysis bag with a molecular weight cutoff of 50,000 Daltons and dialyze with deionized water for 48h, changing the water every 6h. Collect the contents of the dialysis bag and freeze-dry at -50℃ for 48h to obtain a biodegradable temperature-sensitive flocculant.

[0032] Step A4: Mix 100g of biodegradable temperature-sensitive flocculant, 10g of oxidized starch and 3500g of deionized water, and stir for 3 minutes at a stirring rate of 1200 rpm and 25℃; then add 1% acetic acid solution to adjust the pH to 5.5, and stir at 120 rpm and 30℃ for 12 hours; after the reaction is completed, freeze dry at -50℃ for 48 hours to obtain cross-linked biodegradable temperature-sensitive flocculant.

[0033] Preparation Example 2: Compared with Preparation Example 1, the mass ratio of biodegradable temperature-sensitive flocculant to oxidized starch in step A4 was adjusted from 1:0.10 to 1:0.05, that is, the amount of oxidized starch was adjusted from 10g to 5g; the remaining steps and parameters were the same as in Preparation Example 1.

[0034] Preparation Example 3: Compared with Preparation Example 1, the mass ratio of biodegradable temperature-sensitive flocculant to oxidized starch in step A4 was adjusted from 1:0.10 to 1:0.15, that is, the amount of oxidized starch was adjusted from 10g to 15g; the remaining steps and parameters were the same as in Preparation Example 1.

[0035] Comparative Preparation Example 1: Compared with Preparation Example 1, Comparative Preparation Example 1 completely omits the oxidized starch crosslinking treatment in step A4, that is, it directly uses the biodegradable temperature-sensitive flocculant obtained in step A3 as the final product without oxidized starch crosslinking modification; the remaining steps and parameters are the same as those in Preparation Example 1.

[0036] Comparative Preparation Example 2: Compared with Preparation Example 1, the acetic acid solution in step A4 of Comparative Preparation Example 2 was replaced with sodium hydroxide solution and the pH was adjusted to 9.0, that is, the crosslinking reaction was carried out under alkaline conditions; the remaining steps and parameters were the same as those in Preparation Example 1.

[0037] Preparation Example 4: Step B1: Mix 100g of β-cyclodextrin, 8.6g of maleic anhydride and 600g of N,N-dimethylformamide, i.e., the molar ratio of β-cyclodextrin to maleic anhydride is 1:1; react for 8h in the dark under stirring speed of 300rpm and 60℃; after the reaction is completed, slowly pour the reaction solution into 4800mL of anhydrous diethyl ether to precipitate, centrifuge at 5000rpm for 10min, remove the supernatant 4 and collect precipitate 4; wash precipitate 4 twice with anhydrous ethanol and dry under vacuum at 40℃ to obtain functionalized cyclodextrin.

[0038] Step B2: Mix 100g of the functionalized cyclodextrin obtained in Step B1, 300g of acrylamide, 200g of 2-methacryloyloxyethyltrimethylammonium chloride, and 500g of deionized water evenly, purge with nitrogen for 30min, and heat to 60℃; under nitrogen protection and stirring at 300rpm, add 1.4g of ammonium persulfate and 1.1g of sodium bisulfite; after reacting for 6h, cool to room temperature; pour the reaction solution into 3000mL of anhydrous ethanol to precipitate, centrifuge at 8000rpm for 20min, remove the supernatant 5 and collect precipitate 5; wash precipitate 5 twice with a mixed solution of ethanol and water at a volume ratio of 7:3, and dry under vacuum at 40℃ to constant weight to obtain cationic cyclodextrin flocculant.

[0039] Preparation Example 5: Compared with Preparation Example 4, the mass ratio of functionalized cyclodextrin, acrylamide and 2-methacryloyloxyethyltrimethylammonium chloride in step B2 was adjusted from 1:3:2 to 1:2:1, that is, the amount of acrylamide was adjusted to 200g and the amount of 2-methacryloyloxyethyltrimethylammonium chloride was adjusted to 100g; the remaining steps and parameters were the same as in Preparation Example 4.

[0040] Preparation Example 6: Compared with Preparation Example 4, the mass ratio of functionalized cyclodextrin, acrylamide and 2-methacryloyloxyethyltrimethylammonium chloride in step B2 was adjusted from 1:3:2 to 1:5:3, that is, the amount of acrylamide was adjusted to 500g and the amount of 2-methacryloyloxyethyltrimethylammonium chloride was adjusted to 300g; the remaining steps and parameters were the same as in Preparation Example 4.

[0041] Comparative Preparation Example 3: Compared with Preparation Example 4, 2-methacryloyloxyethyltrimethylammonium chloride in step B2 was completely removed in Comparative Preparation Example 3, that is, no cationic monomer was added, and only functionalized cyclodextrin was copolymerized with acrylamide; the remaining steps and parameters were the same as in Preparation Example 4.

[0042] Comparative Preparation Example 4: Compared with Preparation Example 4, the maleic anhydride esterification treatment in step B1 was completely omitted in Comparative Preparation Example 4. That is, unmodified β-cyclodextrin was directly used to replace the functionalized cyclodextrin in the copolymerization reaction in step B2; the remaining steps and parameters were the same as in Preparation Example 4.

[0043] Preparation Example 7: Compared with Preparation Example 1, the mass ratio of chitosan initiator to N-isopropylacrylamide in step A3 was adjusted from 1:12 to 1:5, that is, the amount of N-isopropylacrylamide was adjusted from 1200g to 500g; the remaining steps and parameters were the same as in Preparation Example 1.

[0044] Preparation Example 8: Compared with Preparation Example 1, the mass ratio of chitosan initiator to N-isopropylacrylamide in step A3 was adjusted from 1:12 to 1:20, that is, the amount of N-isopropylacrylamide was adjusted from 1200g to 2000g; the remaining steps and parameters were the same as in Preparation Example 1.

[0045] Comparative Preparation Example 5: Compared with Preparation Example 1, the mass ratio of chitosan initiator to N-isopropylacrylamide in step A3 was adjusted from 1:12 to 1:2, that is, the amount of N-isopropylacrylamide was adjusted from 1200g to 200g; the remaining steps and parameters were the same as in Preparation Example 1.

[0046] Comparative Preparation Example 6: Compared with Preparation Example 1, the mass ratio of chitosan initiator to N-isopropylacrylamide in step A3 was adjusted from 1:12 to 1:30, that is, the amount of N-isopropylacrylamide was adjusted from 1200g to 3000g; the remaining steps and parameters were the same as in Preparation Example 1.

[0047] Example 1: A process for recovering and treating trichloroisocyanuric acid mother liquor includes the following steps: Step S1: Pump 1000L of trichloroisocyanuric acid mother liquor into the acidification reactor. Under stirring at 25℃, slowly add 30% industrial hydrochloric acid by mass until the pH of the system stabilizes at 1.2. The chlorine gas generated in the reaction is introduced into the tail gas absorption tower for absorption by alkaline solution. After acidification, slowly add 30% sodium hydroxide solution by mass, control the system temperature to not exceed 45℃, and adjust the pH to 7.8 to obtain a sodium cyanuric acid suspension with a solid content of 5wt%.

[0048] Step S2: Adjust the temperature of the sodium cyanurate suspension obtained in Step S1 to 25°C, and add the cross-linked biodegradable temperature-sensitive flocculant solution obtained in Preparation Example 1 online through a pipeline mixer at a dosage of 2 mg / L; the mixture enters a settling tank and is allowed to settle at 25°C for 12 hours; after settling, the first underflow concentrate is discharged from the bottom of the settling tank, and the first supernatant is collected from the overflow outlet. The first underflow concentrate is filtered through a plate and frame filter press, and the resulting filter cake is transferred to a washing tank. 45°C warm water is added, with a water-to-cake mass ratio of 3:1. The pH of the washing solution is adjusted to 5.0 with 5% hydrochloric acid by mass, and the mixture is stirred and washed for 20 minutes; the washing slurry is filtered twice, the filter cake is rinsed with a small amount of water, and dried at 80°C to obtain the recovered sodium cyanurate solid. After the washing filtrate is cooled to 25°C, it is concentrated by an ultrafiltration membrane with a molecular weight cutoff of 30 kDa. The concentrated liquid is returned to the flocculant preparation tank for recycling, and the permeate is incorporated into the first supernatant storage tank.

[0049] Step S3: The first supernatant obtained in step S2 is pumped into an electrocoagulation device, using a coated titanium electrode as the anode and a graphite electrode as the cathode, with the cathode and anode arranged alternately, an electrode spacing of 30 mm, a current density of 20 A / m2, and a residence time of 10 min; the cationic cyclodextrin flocculant obtained in Preparation Example 4 is added at the inlet of the electrocoagulation device, with an addition amount of 0.8 mg / L of the first supernatant; the electrocoagulated effluent enters an inclined plate sedimentation tank, where the second underflow and the second supernatant are separated; the second underflow is returned to the settling tank of step S2 and combined with the first underflow for further treatment.

[0050] Step S4: Introduce the second supernatant obtained in step S3 into the adjustment tank, add 5% dilute hydrochloric acid by mass to adjust the pH to 5.5, stir thoroughly and then discharge.

[0051] Example 2: Compared with Example 1, the cross-linked biodegradable temperature-sensitive flocculant used in step S2 is replaced by the one from Example 1; the remaining steps and parameters are the same as in Example 1.

[0052] Example 3: Compared with Example 1, the cross-linked biodegradable temperature-sensitive flocculant used in step S2 is replaced by the one used in Example 3; the remaining steps and parameters are the same as in Example 1.

[0053] Example 4: Compared with Example 1, the cationic cyclodextrin flocculant used in step S3 is replaced by Preparation Example 5; the remaining steps and parameters are the same as in Example 1.

[0054] Example 5: Compared with Example 1, the cationic cyclodextrin flocculant used in step S3 is replaced by Preparation Example 6 instead of Preparation Example 4; the remaining steps and parameters are the same as in Example 1.

[0055] Example 6: Compared with Example 1, the dosage of cross-linked biodegradable temperature-sensitive flocculant in step S2 was adjusted from 2 mg / L to 1 mg / L, and the dosage of cationic cyclodextrin flocculant in step S3 was adjusted from 0.8 mg / L to 0.5 mg / L; the remaining steps and parameters were the same as in Example 1.

[0056] Example 7: Compared with Example 1, the dosage of cross-linked biodegradable temperature-sensitive flocculant in step S2 was adjusted from 2 mg / L to 3 mg / L, and the dosage of cationic cyclodextrin flocculant in step S3 was adjusted from 0.8 mg / L to 1 mg / L; the remaining steps and parameters were the same as in Example 1.

[0057] Example 8: Compared with Example 1, the cross-linked biodegradable temperature-sensitive flocculant used in step S2 in Example 8 is replaced by Preparation Example 7 instead of Preparation Example 1; the remaining steps and parameters are the same as in Example 1.

[0058] Example 9: Compared with Example 1, the cross-linked biodegradable temperature-sensitive flocculant used in step S2 is replaced by Preparation Example 8 instead of Preparation Example 1; the remaining steps and parameters are the same as in Example 1.

[0059] Comparative Example 1: Compared with Example 1, the cross-linked biodegradable temperature-sensitive flocculant used in step S2 was replaced by the control preparation example 1, that is, a biodegradable temperature-sensitive flocculant without oxidized starch cross-linking was used; the remaining steps and parameters were the same as in Example 1.

[0060] Comparative Example 2: Compared with Example 1, the cross-linked biodegradable temperature-sensitive flocculant used in step S2 was replaced by the cross-linked product obtained by oxidizing starch under alkaline conditions in Comparative Example 2 instead of the preparation example 1; the remaining steps and parameters were the same as in Example 1.

[0061] Comparative Example 3: Compared with Example 1, the cationic cyclodextrin flocculant used in step S3 was replaced by the control example 3 instead of the preparation example 4, that is, the uncationized functionalized cyclodextrin and acrylamide copolymer was used; the remaining steps and parameters were the same as in Example 1.

[0062] Comparative Example 4: Compared with Example 1, the cationic cyclodextrin flocculant used in step S3 of Comparative Example 4 was replaced by the control preparation example 4, that is, the unesterified β-cyclodextrin direct copolymer product was used; the remaining steps and parameters were the same as those of Example 1.

[0063] Comparative Example 5: Compared with Example 1, Comparative Example 5 completely omits the electrocoagulation treatment in step S3, and directly enters the first supernatant obtained in step S2 into step S4 for pH adjustment before discharge; the remaining steps and parameters are the same as in Example 1.

[0064] Comparative Example 6: Compared with Example 1, the cross-linked biodegradable temperature-sensitive flocculant in step S2 was replaced with commercially available conventional polyacrylamide flocculant, with the same dosage; the temperature-sensitive dissociation washing step in step S2 was omitted and replaced with washing the filter cake directly with room temperature tap water; the remaining steps and parameters were the same as in Example 1.

[0065] Comparative Example 7: Compared with Example 1, the cross-linked biodegradable temperature-sensitive flocculant used in step S2 was replaced by Comparative Example 5 instead of Preparation Example 1; the remaining steps and parameters were the same as in Example 1.

[0066] Comparative Example 8: Compared with Example 1, the cross-linked biodegradable temperature-sensitive flocculant used in step S2 in Comparative Example 8 was replaced by Comparative Example 6 instead of Preparation Example 1; the remaining steps and parameters were the same as in Example 1.

[0067] Performance testing was conducted using the processes described in the reference examples and comparative examples: 1) Determination of recovery rate of sodium cyanurate: Weigh the mass of the recovered and dried sodium cyanurate solid, and calculate the mass percentage recovery rate according to the total amount of sodium cyanurate that can be theoretically recovered in the mother liquor; 2) Determination of suspended solids concentration in the first supernatant: Referring to GB11901-1989, the mass concentration of suspended solids in the first supernatant obtained in step S2 was determined by filtration through a 0.45µm filter membrane and drying at 103-105℃ and weighing. 3) Determination of suspended solids concentration in external wastewater: Refer to GB11901-1989 and determine the mass concentration of suspended solids in external wastewater in step S4; 4) Observation of solid precipitation in external water drainage: Take 500 mL of each external water drainage from step S4 and place it in a reagent bottle. Keep it at a constant temperature of 5℃, 25℃, and 50℃ for 72 h respectively. Observe whether white solid precipitates on the bottle wall and bottom. 5) Flocculant recycling rate: Record the percentage of fresh flocculant that needs to be replenished after each cycle relative to the initial input, expressed as a percentage.

[0068] The test results are shown in the table below: Table 1 Test Results

[0069] As can be seen from the test results in the table shown, the examples are compared with the comparative examples.

[0070] Example 1 uses a flocculant with all preparation parameters within the preferred range. The crosslinking density is moderate, the temperature-sensitive chain length is uniform, and the ratio of cationic charge to cyclodextrin is balanced. The first step involves a microgel network that efficiently captures particles, while temperature-sensitive washing enables intelligent flocculant detachment and recycling. The second step, in conjunction with an electric field, thoroughly removes residual particles. This demonstrates that when all parameters are within the preferred range, a two-step, staged, coupled process can achieve the overall goals of high recovery, recyclability, and clarified discharge.

[0071] In Example 2, the ratio of oxidized starch was reduced from 1:0.10 to 1:0.05. The crosslinking density decreased, the microgel network became looser, the sweeping and coating ability weakened, the suspended solids in the supernatant increased, and the recovery rate decreased; however, the network disintegrated more rapidly during washing, and desorption was more thorough. This indicates that when the amount of oxidized starch is too low, the flocculation force is insufficient but desorption is easier, and a balance needs to be struck between the two.

[0072] In Example 3, the ratio of oxidized starch was increased from 1:0.10 to 1:0.15. The increased crosslinking density resulted in a denser network, enhanced sweeping ability, reduced suspended solids in the supernatant, and improved recovery rate. However, the denser network caused some flocculant to be deeply embedded, making it difficult for the washing water to fully dissolve, thus reducing washing and desorption efficiency. This indicates that there is an upper limit to the amount of oxidized starch used; excessive amounts will hinder washing and desorption.

[0073] Example 4 adjusted the monomer ratio of the cationic flocculant from 1:3:2 to 1:2:1. The simultaneous reduction of acrylamide and cationic monomers lowered the main chain molecular weight, shortened the bridging span, decreased the charge density, and weakened both charge neutralization, destabilization, and bridging capabilities, resulting in an increase in suspended solids in the effluent. This demonstrates that the monomer dosage in the cationic flocculant directly affects the deep purification efficiency and should be controlled above the lower limit.

[0074] Example 5 adjusted the monomer ratio of the cationic flocculant from 1:3:2 to 1:5:3. This increased the molecular weight of the main chain, improved the charge density, enhanced bridging and destabilizing capabilities, and further reduced suspended solids in the effluent. However, excessively high cationicity caused the formation of microscale aggregates with anions during acid adjustment, resulting in slight fluctuations in the measured values. This indicates that there is an optimal range for cationicity, and excessively high levels can trigger side effects.

[0075] In Example 6, the flocculant dosage was reduced to 1 mg / L in the first step and to 0.5 mg / L in the second step. The reduced flocculant concentration decreased the probability of collision between microgels and particles, reduced the number of cationic copolymer molecules, and increased suspended solids in both the supernatant and effluent. The recovery rate decreased, but all indicators remained within acceptable limits. This demonstrates that the dosage range is economical and effective, and can be flexibly adjusted according to water quality.

[0076] Example 7 increased the flocculant dosage in the first step to 3 mg / L and in the second step to 1.0 mg / L. The increased flocculant concentration improved microgel capture and cation bridging efficiency, reduced suspended solids in both the supernatant and effluent, and increased recovery rate. This demonstrates that increasing the dosage within the preferred range can further improve the effect, but the economical dosage needs to be determined based on the actual treatment objectives.

[0077] Comparative Example 1 omitted the oxidative starch crosslinking step, and the product was only a linear copolymer. Lacking the three-dimensional sweeping capability of the microgel network and relying solely on single-chain bridging, the suspended solids in the supernatant increased significantly, and the recovery rate decreased markedly. This fully demonstrates that the microgel network formed by oxidative starch crosslinking is the key structural basis for achieving efficient flocculation.

[0078] Comparative Example 2 involved oxidative starch crosslinking under alkaline conditions. The Schiff base reaction reversed, aldehyde groups underwent disproportionation and were consumed by side reactions, resulting in fewer effective crosslinking points and poor network development. Carboxylic acid impurities, a byproduct, contaminated the product, and precipitation occurred in the external drainage. This clearly demonstrates that weakly acidic conditions are the decisive factor in ensuring crosslinking efficiency and product purity.

[0079] Comparative Example 3, a cationic flocculant, contained no cationic monomers. Lacking the positive charge of quaternary ammonium salts, it lost the driving force for neutralizing and destabilizing negatively charged particles. Although cyclodextrins could still encapsulate and acrylamides could still bridge, the absence of the destabilization step significantly increased the suspended solids in the effluent. This clearly demonstrates that cationic charges are essential functional groups for particle destabilization.

[0080] Comparative Example 4 omitted the maleic anhydride esterification step. The unmodified β-cyclodextrin lacked polymerizable double bonds and could not be covalently linked to the copolymer backbone. The product effectively lacked cyclodextrin groups, losing its specific inclusion recognition function for the triazine ring, resulting in increased suspended matter in the effluent. This clearly demonstrates that the esterification step is a crucial pretreatment step for covalently linking cyclodextrin into the polymer.

[0081] Comparative Example 5 completely omitted the second step of electrocoagulation. The residual submicron particles in the first supernatant were not physically separated; instead, their solubility was increased solely by acid adjustment. Upon temperature changes, these particles re-precipitated and grew, resulting in severely excessive suspended solids in the effluent, and the appearance of white solids at low temperatures. This clearly demonstrates that deep purification via electrocoagulation is an indispensable step for the complete separation of residual particles.

[0082] Comparative Example 6 replaced the crosslinking temperature-sensitive flocculant with conventional polyacrylamide, omitting temperature-sensitive washing. Conventional polyacrylamide has no temperature-sensitive response and cannot intelligently detach from the product surface. A large amount of polyacrylamide remains in the recycled solids, posing a risk of monomer release and organic chlorination in subsequent chlorination processes, and is completely non-recyclable. This fully demonstrates the fundamental advantages of the temperature-sensitive reversible structure in eliminating toxic residues and achieving recycling.

[0083] Example 8 reduced the amount of N-isopropylacrylamide from 1:12 to 1:5. The shortening of the temperature-sensitive side chain reduced the bridging span, increased the suspended solids in the supernatant, and decreased the recovery rate. However, the reduced short-chain shrinkage decreased the hydrophobic contact area with the particles, resulting in more thorough desorption and a lower recycling rate. This illustrates the inverse relationship between grafted chain length and bridging efficiency and desorption effect.

[0084] In Example 9, the dosage of N-isopropylacrylamide was increased from 1:12 to 1:20. Thermosensitive side chains increased in length, bridging span increased, suspended solids in the supernatant decreased, and recovery rate improved. However, after the long chains contracted, they formed multi-point hydrophobic contacts with the particles, slowing down desorption kinetics and increasing the recycling replenishment rate. This indicates that there is a reasonable upper limit to the grafted chain length; excessive length will impair washing, desorption, and recycling performance.

[0085] Comparative Example 7 reduced the N-isopropylacrylamide ratio from 1:12 to 1:2. The extremely short side chains resulted in the loss of thermosensitive phase transition behavior and effective bridging function, leading to a sharp increase in suspended solids in the supernatant, a significant decrease in recovery rate, and precipitation in the effluent. This clearly demonstrates that the grafted chain length must reach a threshold to effectively perform both thermosensitive response and bridging functions.

[0086] In Comparative Example 8, the amount of N-isopropylacrylamide was increased from 1:12 to 1:30. Excessively long side chains caused inter-chain entanglement, forming physical microgels that shielded free amino groups and interfered with the uniformity of chemical cross-linking. During washing, long chains were difficult to completely desorb, leading to an increased replenishment rate. This clearly demonstrates that there is an upper limit to the length of the grafted chains; excessive length results in entanglement interfering with cross-linking and reducing desorption efficiency.

[0087] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A process for recovering and treating trichloroisocyanuric acid mother liquor, characterized in that: Includes the following steps: Step S1: Acidification and alkalization of trichloroisocyanuric acid mother liquor: The trichloroisocyanuric acid mother liquor is subjected to acidification and alkalization treatment in sequence to obtain a sodium cyanurate suspension; Step S2: First step flocculation and sedimentation recovery: The sodium cyanurate suspension is passed into a settling tank and a cross-linked biodegradable temperature-sensitive flocculant is added for flocculation and sedimentation to separate the first underflow and the first supernatant; the first underflow is subjected to temperature-sensitive dissociation washing to recover the sodium cyanurate solid, and the flocculant in the washing liquid is separated and recycled; Step S3: Second step of electrocoagulation purification: The first supernatant is sent into the electrocoagulation device and cationic cyclodextrin flocculant is added to separate the second underflow and the second supernatant. The second underflow is returned to step S2 for combined processing. Step S4: pH adjustment of external drainage: Adjust the pH of the second supernatant to 5.5±0.1 and drain it externally; The core functional unit of the cross-linked biodegradable temperature-sensitive flocculant is a microgel network formed by cross-linking chitosan grafted with polynitro-isopropylacrylamide and oxidized starch. The cationic cyclodextrin flocculant is a free radical copolymer of maleic anhydride esterified β-cyclodextrin, acrylamide, and 2-methacryloyloxyethyltrimethylammonium chloride.

2. The process for recovering and treating trichloroisocyanuric acid mother liquor according to claim 1, characterized in that: In step S1: the acidification endpoint pH is 1.0-1.5, and hydrochloric acid is used for acidification; the alkalization endpoint pH is 7.5-8.0, and sodium hydroxide is used for alkalization.

3. The process for recovering and treating trichloroisocyanuric acid mother liquor according to claim 1, characterized in that: In step S2: the dosage of cross-linked biodegradable temperature-sensitive flocculant is 1–3 mg / L; the flocculation and sedimentation temperature is 25±5℃, and the sedimentation time is 12h; the operating conditions for temperature-sensitive dissociation washing are: washing water temperature 45℃, and the pH of the washing solution is adjusted to 5.0 with 5wt% dilute hydrochloric acid.

4. The process for recovering and treating trichloroisocyanuric acid mother liquor according to claim 1, characterized in that: In step S3: the dosage of cationic cyclodextrin flocculant is 0.5–1.0 mg / L; the electrocoagulation treatment uses coated titanium electrodes and graphite electrodes, with the cathode and anode arranged alternately, the electrode spacing is 30 mm, and the current density is 20 A / m. 2 The stay time is 10 minutes.

5. The process for recovering and treating trichloroisocyanuric acid mother liquor according to claim 1, characterized in that: The cross-linked biodegradable temperature-sensitive flocculant is prepared by the following steps: Step A1: Mix chitosan and acetic acid solution, stir at 300 rpm and 25°C, add sodium dodecyl sulfate, stir for 12 h, filter, centrifuge at 3000 rpm for 5 min, remove supernatant 1 and collect precipitate 1, wash precipitate 1 with deionized water, freeze dry to obtain pretreated chitosan. Step A2: Mix bromoisobutyric acid, N,N'-dicyclohexylcarbodiimide, N-hydroxysuccinimide and 1-methyl-2-pyrrolidone, and react for 24 h at a stirring rate of 300 rpm and 40 °C. Filter to remove precipitate 2 and collect filtrate 2. Mix pretreated chitosan, filtrate 2 and dimethyl sulfoxide, and react for 48 h at a stirring rate of 120 rpm and 40 °C. Dissolve in diethyl ether / acetone, centrifuge at 3000 rpm for 10 min, remove supernatant 3 and collect precipitate 3. Precipitate 3 is the chitosan initiator. Step A3: Chitosan initiator, N-isopropylacrylamide, dimethyl sulfoxide, bipyridine and copper bromide are mixed and reacted at 150 rpm and 60 °C for 24 h under nitrogen protection. Tris-HCl buffer solution is then added to adjust the pH to 8 and stirred for 1 h to dissociate sodium dodecyl sulfate. Subsequently, the mixture is dialyzed with deionized water for 48 h. The contents of the dialysis bag are collected and freeze-dried to obtain a biodegradable temperature-sensitive flocculant. Step A4: Mix the biodegradable temperature-sensitive flocculant, oxidized starch and deionized water, stir for 3 minutes at 1200 rpm and 25°C, then add acetic acid solution to adjust the pH to 5.5, and stir at 120 rpm and 30°C for 12 hours. Freeze dry to obtain the cross-linked biodegradable temperature-sensitive flocculant.

6. The process for recovering and treating trichloroisocyanuric acid mother liquor according to claim 5, characterized in that: In step A1, the mass ratio of chitosan, sodium dodecyl sulfate, and acetic acid solution is 1:(2-4):80, and the mass concentration of acetic acid solution is 1%. In step A2: the molar ratio of bromoisobutyric acid, N,N'-dicyclohexylcarbodiimide, and N-hydroxysuccinimide is 1:(1.0-1.2):(1.0-1.2); the mass ratio of bromoisobutyric acid to pretreated chitosan is 1:(5-15); and the mass ratio of pretreated chitosan to dimethyl sulfoxide is 1:

30. In step A3: the mass ratio of chitosan initiator, N-isopropylacrylamide, bipyridine, and copper bromide is 1:(5-20):(0.1-0.5):(0.05-0.2), the mass ratio of chitosan initiator to dimethyl sulfoxide is 1:40, and the mass fraction of Tris-HCl buffer solution is 15% with a pH of 9. In step A4: the mass ratio of biodegradable temperature-sensitive flocculant to oxidized starch is 1:(0.05-0.15), the mass ratio of biodegradable temperature-sensitive flocculant to deionized water is 1:(30-40), and the mass fraction of acetic acid solution is 1%.

7. The process for recovering and treating trichloroisocyanuric acid mother liquor according to claim 1, characterized in that: The cationic cyclodextrin flocculant is prepared by the following steps: Step B1: Mix β-cyclodextrin, maleic anhydride and N,N-dimethylformamide and react at 300 rpm and 60 ℃ for 8 h. After the reaction is complete, slowly pour the reaction solution into anhydrous diethyl ether to precipitate. Centrifuge at 5000 rpm for 10 min, remove the supernatant 4 and collect precipitate 4. Wash with ethanol and dry under vacuum to obtain functionalized cyclodextrin. Step B2: Functionalized cyclodextrin, acrylamide, 2-methacryloyloxyethyltrimethylammonium chloride and deionized water were mixed and stirred at 300 rpm and 60°C under nitrogen protection. Ammonium persulfate and sodium bisulfite were added and the mixture was reacted for 6 h. After cooling to room temperature, ethanol was added to precipitate the mixture. The mixture was centrifuged at 8000 rpm for 20 min, the supernatant 5 was removed and the precipitate 5 was collected. The precipitate was washed with ethanol / water and dried under vacuum to obtain cationic cyclodextrin flocculant.

8. The process for recovering and treating trichloroisocyanuric acid mother liquor according to claim 7, characterized in that: In step B1: the molar ratio of β-cyclodextrin to maleic anhydride is 1:(0.5-1.5), and the mass ratio of β-cyclodextrin to N,N-dimethylformamide is 1:6; Furthermore, in step B2: the mass ratio of functionalized cyclodextrin, acrylamide and 2-methacryloyloxyethyltrimethylammonium chloride is 1:(2-5):(1-3), the mass ratio of functionalized cyclodextrin to deionized water is 1:5, the molar ratio of ammonium persulfate and sodium bisulfite is 1:1, and the total amount of ammonium persulfate and sodium bisulfite is 0.8% of the total mass of the monomers.

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