Alkaline rare earth waste residue-carboxymethyl chitosan composite coagulant and application thereof

Abstract

The application discloses a kind of base formula rare earth waste residue-carboxymethyl chitosan composite coagulant and application thereof, the coagulant is obtained by following preparation method: by sulfuric acid low-temperature calcination-salt precipitation-carbonate process tailings is obtained rare earth waste residue, it is alkalinized with methacrylic acid again, methacrylic acid provides polymerization double bond for rare earth waste residue;Carboxymethyl chitosan solution is mixed with methacrylic acid again, under the action of ammonium persulfate, carboxymethyl chitosan and methacrylic acid graft copolymer, i.e.CMCS-g-MAA;Finally, methacrylic acid-rare earth waste residue and CMCS-g-MAA are mixed, and dimethyl sulfoxide and ammonium persulfate are added to prepare base formula rare earth waste residue-carboxymethyl chitosan composite coagulant.The application forms synergistic effect and compound synergistic effect by base formula rare earth waste residue and carboxymethyl chitosan, improves the removal efficiency of turbidity, chroma and chemical oxygen demand in dye wastewater, and maximizes coagulation effect.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of water treatment, and particularly relates to a basic rare earth waste residue-carboxymethyl chitosan composite coagulant and application thereof. BACKGROUND

[0002] With the rapid development of the dye and printing and dyeing industry, a series of environmental problems have also been generated, one of which is the generation of a large amount of dye and printing and dyeing wastewater. The dye wastewater in China has the characteristics of complex composition, high concentration and deep color. The organic components in the wastewater are mostly aromatic hydrocarbons and heterocyclic compounds, and have color-developing groups and polar groups. The dye wastewater also contains a large amount of raw materials and by-products, such as halides, nitro compounds, anilines, phenols and inorganic salts. Due to the large variety of dyes and the development of dyes in the direction of resistance to photolysis, oxidation and biodegradation, the difficulty of treating dye wastewater is increased. The printing and dyeing wastewater contains dyes, sizing agents, auxiliaries, oil agents, acids and bases, fiber impurities and inorganic salts, and also has the problems of high content, high alkalinity, difficult treatment and unstable treatment effect. The first problem to be solved in the treatment of this kind of wastewater is to reduce the chemical oxygen demand (COD) and decolorization. The commonly used wastewater treatment methods include biological method, chemical method and physical method, among which the chemical coagulation method is widely used in the treatment of dye and printing and dyeing wastewater due to its strong adaptability, simple operation, small equipment occupation, high COD and color removal rate and low capital investment.

[0003] In recent years, rare earths have been widely used in the field of wastewater treatment. In view of the unique physicochemical properties of rare earths, they have become increasingly active in the development and application of flocculants. However, the compositions of the current rare earth coagulants are different, and the prices are different, so new processes should be actively developed to use rare earth waste residues to prepare coagulants, so that waste can be effectively utilized.

[0004] Carboxymethyl chitosan overcomes the poor solubility of chitosan itself and has typical properties such as flocculation, antibacterial and bacteriostatic properties, color fixing properties and the like. Due to its low cost, non-toxicity, good biocompatibility and easy degradation, carboxymethyl chitosan has potential application value in the field of textile processing. SUMMARY

[0005] The present application aims at the deficiencies of the prior art, and provides a basic rare earth waste residue-carboxymethyl chitosan composite coagulant and application thereof. The present application has low manufacturing cost and good coagulation effect, effectively improves the recycling value of rare earth waste residues and reduces the discharge amount of rare earth waste residues.

[0006] The purpose of the present application is achieved by the following technical solutions: the present application provides a basic rare earth waste residue-carboxymethyl chitosan composite coagulant in the first aspect of the embodiments, which is obtained by the following preparation method:

[0007] (1) Rare earth tailings are sequentially subjected to sulfuric acid low-temperature roasting reaction, double salt precipitation, and carbonate conversion to obtain usable rare earth waste residue;

[0008] (2) The rare earth waste residue and sodium hydroxide (NaOH) solution are mixed and then sequentially subjected to distillation, filtration, and water bath curing to obtain alkali rare earth waste residue;

[0009] (3) The alkali rare earth waste residue and methacrylic acid are mixed, and then sequentially subjected to distillation, suction filtration to obtain clear filtrate, and vacuum distillation. After vacuum distillation, anhydrous ethanol is added and stirred until solids precipitate. After suction filtration and drying, methacrylic acid-alkali rare earth waste residue is obtained;

[0010] (4) Carboxymethyl chitosan is dissolved in water, ammonium persulfate and methacrylic acid are added, and mechanical stirring and water bath heating are performed. After washing and drying, a graft copolymer of carboxymethyl chitosan and methacrylic acid is obtained and named CMCS-g-MAA;

[0011] (5) The methacrylic acid-alkali rare earth waste residue and CMCS-g-MAA are mixed, and ammonium persulfate and dimethyl sulfoxide are added. Mechanical stirring, water bath heating, centrifugation, and ethanol washing are performed to obtain alkali rare earth waste residue-carboxymethyl chitosan composite coagulant after drying.

[0012] Further, in step (1), in the sulfuric acid low-temperature roasting reaction, the rare earth tailings are mixed with concentrated sulfuric acid at a feed ratio of 3-4 g: 1 mL, and the sulfuric acid low-temperature roasting reaction is performed at a temperature of 180-300°C for 2-4 hours. After roasting, the sample is slightly cooled and then hot water is added for leaching. After stirring for 1.5 hours, suction filtration is performed to obtain rare earth waste residue filtrate;

[0013] In the double salt precipitation process, the rare earth waste residue filtrate is mixed with excess sodium sulfate at a mass ratio, wherein the sodium sulfate is 50-100% excess compared to the rare earth waste residue filtrate, and stirring is performed at a temperature of 70-80°C for 1 hour to obtain rare earth waste residue sulfuric acid double salt;

[0014] In the carbonate conversion process, the rare earth waste residue sulfuric acid double salt is mixed with a sodium carbonate solution at a mass ratio, wherein the sodium carbonate solution is 20-50% excess compared to the rare earth waste residue sulfuric acid double salt, and stirring is performed at a temperature of 60-80°C for 2 hours. After washing with water, suction filtration and drying are performed to obtain rare earth waste residue after complete washing.

[0015] Further, in step (2), the feed ratio of the rare earth waste residue to the NaOH solution is 1 g: 10-20 ml, and the concentration of the sodium hydroxide solution is 2-4 mol / L;

[0016] The mixed solution is heated to boiling in the distillation process, and the boiling reaction time is 1-3 hours.

[0017] The temperature of the water bath curing is 60-80 DEG C, and the time of the water bath curing is 1-3 hours.

[0018] Further, in the step (3), the feeding ratio of the alkali rare earth waste residue and the methacrylic acid is 1g:10-20ml;

[0019] In the distillation process, the water bath temperature is 85-90 DEG C, and the solution is heated until clear, and then the clear filtrate is obtained by standing and suction filtration; the filtrate is subjected to 90 DEG C reduced pressure distillation treatment to remove part of the excess methacrylic acid solvent; the remaining solution is mixed with 100-200ml of anhydrous ethanol, and stirring is performed until solid is precipitated; then, suction filtration is performed, and the alkali rare earth waste residue-methacrylic acid is obtained by vacuum drying.

[0020] Further, in the step (4), the carboxymethyl chitosan is dissolved in water, mechanical stirring is performed under water bath heating at a temperature of 50-70 DEG C, nitrogen is slowly and uniformly introduced for 20-30 minutes, then ammonium persulfate is added, the feeding ratio of the carboxymethyl chitosan and the ammonium persulfate is 1g:0.1-0.5g, nitrogen is continuously introduced for 10 minutes, then methacrylic acid is added, the feeding ratio of the carboxymethyl chitosan and the methacrylic acid is 1g:6-10ml, the reaction is performed for 3-4 hours, then the pH is adjusted to 7 by using a 10% sodium hydroxide solution, and then the product is obtained by washing with distilled water and drying.

[0021] Further, in the step (5), the alkali rare earth waste residue-methacrylic acid and the CMCS-g-MAA are mixed according to a feeding ratio of 1-4g:1g, then ammonium persulfate and dimethyl sulfoxide are added, the dimethyl sulfoxide (solvent) is 50-100ml, the ammonium persulfate (initiator) is 0.1-0.5g, mechanical stirring is performed under water bath heating at a temperature of 60-70 DEG C for 2-5 hours, the reaction solution is cooled, high-speed centrifugation is performed at a speed of 11000-20000rpm for 15-20 minutes, the solid substance is taken out, washed with anhydrous ethanol, and dried to obtain the alkali rare earth waste residue-carboxymethyl chitosan composite coagulant.

[0022] The second aspect of the embodiment of the present application provides application of the above-mentioned alkali rare earth waste residue-carboxymethyl chitosan composite coagulant in dyeing and printing wastewater.

[0023] The alkali rare earth waste residue prepared in the application has a high removal effect on colority, and after mixing with methacrylic acid, the unsaturated acid ligand-methacrylic acid can provide double bonds for polymerization of the rare earth waste residue, so that the rare earth waste residue has a certain polymerization capacity, thereby laying a foundation for subsequent preparation of coagulants. The carboxymethyl chitosan is a kind of derivative of chitosan after carboxymethylation modification, has good degradability, water solubility and adsorbability, and also contains rich hydroxyl, amino and carboxyl groups, so that the adsorption of ions can be increased.

[0024] Compared with the prior art, the application has the following beneficial effects:

[0025] (1) The coagulant is prepared from the low-cost raw material rare earth waste residue, has the superior performances of fast flocculation and sedimentation speed, dense and large particle size of flocculation, high removal rates of turbidity and COD, etc.; the rare earth contained in the rare earth waste residue has unique physicochemical properties, can form rare earth compounds with multiple valence states and multiple coordination numbers, has adsorption effect on harmful substances in wastewater, and can effectively remove pollutants in wastewater; the rare earth waste residue is a waste after reaction, and the use of the rare earth waste residue as the coagulant can make the waste be reused.

[0026] (2) The carboxymethyl modified chitosan has the special adsorption performance of chitosan, overcomes the defect of insolubility of chitosan in water, and plays an important role as a flocculant in wastewater treatment; in addition, the carboxymethyl chitosan can treat industrial dyes and printing and dyeing wastewater, has many advantages such as low equipment requirement, simple operation, short process flow, etc., and will not cause secondary pollution to the environment, and the flocculation product can be recycled.

[0027] (3) The alkali rare earth waste residue-carboxymethyl chitosan composite coagulant is prepared by a free radical graft copolymerization method, and the rare earth waste residue and the carboxymethyl chitosan are polymerized in a chemical bond manner instead of a simple physical mixing manner, so that the prepared composite coagulant can exist more stably in the application process, and the effect of treating dyes and printing and dyeing wastewater is better. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 A removal rate diagram of colority, turbidity and COD in wastewater under different coagulant dosing conditions of the application;

[0029] Figure 2 A removal rate diagram of colority, turbidity and COD in wastewater under different reaction time conditions of the application;

[0030] Figure 3 A comparison diagram of removal rates of colority, turbidity and COD in wastewater of the examples and the comparative examples provided by the application;

[0031] Figure 4SEM image of the graft copolymer of the basic rare earth waste residue and carboxymethyl chitosan. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present application will be clearly and completely described below in combination with the embodiments of the present application. The described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0033] The materials and reagents used in the following examples can be obtained from commercial channels if no special instructions are given.

[0039] Example 1: Preparation of basic rare earth waste residue-carboxymethyl chitosan composite coagulant

[0035] (1) 50 g of rare earth tailings raw material was mixed with 13 ml of concentrated sulfuric acid, and was calcined at a temperature of 240 DEG C for 3 hours. After the calcination was completed, the sample was slightly cooled, and then was added with water for leaching while hot. After stirring for 1.5 hours, the rare earth waste residue filtrate was obtained by suction filtration. Then, the rare earth waste residue filtrate was mixed with excess 90% sodium sulfate at a temperature of 80 DEG C for stirring for 1 hour to obtain the rare earth waste residue sulfuric acid double salt. Finally, the rare earth waste residue sulfuric acid double salt was added into excess 30% sodium carbonate solution, and was stirred at a temperature of 70 DEG C for 2 hours. After the reaction was completed, the product was washed with water, suction filtered and dried to obtain the rare earth waste residue.

[0036] (2) 6 g of the rare earth waste residue was weighed into a round-bottom flask, 100 ml of NaOH solution with a concentration of 3 mol / L was added, and several zeolites were put into the round-bottom flask. The round-bottom flask was stoppered, and a condenser was used for condensation. The electric furnace rotary switch was turned on, and the solution was boiled. After boiling, the solution was heated with medium fire to keep it boiling. After 3 hours of heating, the flask was removed, and the mixture was cooled. The cooled mixture was filtered into a conical flask through a funnel, and was then placed in a water bath at 80 DEG C for 3 hours of water bath aging to obtain the basic rare earth waste residue.

[0037] (3) 6 g of the basic rare earth waste residue was weighed into a 150 ml three-necked flask with a spherical condenser, 100 ml of methyl methacrylic acid was added, and the flask was placed in a water bath. The circulating condenser water was turned on, and mechanical stirring was performed. The water bath was heated at 90 DEG C until the solution was clear. After standing for a period of time, the clear filtrate was obtained by suction filtration. Then, the filtrate was transferred into a 150 ml round-bottom flask, and was subjected to 90 DEG C water bath vacuum distillation. Finally, the remaining solution in the round-bottom flask was transferred into a beaker, and anhydrous ethanol was added. The mixture was continuously stirred until a large amount of solid was precipitated. The product was suction filtered and vacuum dried at 40 DEG C to obtain the methyl methacrylic acid-rare earth waste residue.

[0038] (4) Weigh carboxymethyl chitosan in a 250ml three-necked flask, dissolve in distilled water, heat in a 65℃ water bath, slowly and uniformly pass nitrogen for 20 minutes, add 0.5g ammonium persulfate under stirring, continue to pass nitrogen for 10 minutes, then add methacrylic acid under stirring, the feeding ratio of carboxymethyl chitosan and methacrylic acid is 1g:8ml, after 4 hours of reaction, transfer into a beaker, adjust pH to 7 with 10% NaOH solution, wash the precipitate with distilled water to remove excess alkali, dry to obtain the graft copolymer of carboxymethyl chitosan and methacrylic acid, namely CMCS-g-MAA.

[0039] (5) Weigh methacrylic acid-rare earth waste residue and CMCS-g-MAA in a 250ml three-necked flask, dissolve in distilled water, the feeding ratio between the two is 2g:1g, then add 50ml dimethyl sulfoxide and 0.5g ammonium persulfate, mechanically stir and heat in a 65℃ water bath for 2 hours, after the reaction solution is cooled, centrifuge at a speed of 11000rpm for 15 minutes, take out the solid material, wash with anhydrous ethanol for 2 times, then dry to obtain the basic rare earth waste residue-carboxymethyl chitosan composite coagulant.

[0040] Example 2: Preparation of basic rare earth waste residue-carboxymethyl chitosan composite coagulant

[0041] The difference between this example and example 1 is that the amount of basic rare earth waste residue in step (2) is changed from 6g to 7g. The other steps and parameters are the same as in example 1.

[0042] Example 3: Preparation of basic rare earth waste residue-carboxymethyl chitosan composite coagulant

[0043] The difference between this example and example 1 is that the amount of basic rare earth waste residue in step (2) is changed from 6g to 8g. The other steps and parameters are the same as in example 1.

[0044] Example 4: Preparation of basic rare earth waste residue-carboxymethyl chitosan composite coagulant

[0045] The difference between this example and example 2 is that the feeding ratio of carboxymethyl chitosan and methacrylic acid in step (4) is changed from 1g:8ml to 1g:9ml. The other steps and parameters are the same as in example 2.

[0046] Example 5: Preparation of basic rare earth waste residue-carboxymethyl chitosan composite coagulant

[0047] The difference between this example and example 2 is that the feeding ratio of carboxymethyl chitosan and methacrylic acid in step (4) is changed from 1g:8ml to 1g:10ml. The other steps and parameters are the same as in example 2.

[0048] Example 6: Preparation of basic rare earth residue-carboxymethyl chitosan composite coagulant

[0049] The difference between this example and example 4 is that the feeding ratio of methacrylic acid-rare earth residue to CMCS-g-MAA in step (5) is changed from 2g:1g to 3g:1g. Other steps and parameters are the same as those in example 4.

[0050] Example 7: Preparation of basic rare earth residue-carboxymethyl chitosan composite coagulant

[0051] The difference between this example and example 4 is that the feeding ratio of methacrylic acid-rare earth residue to CMCS-g-MAA in step (5) is changed from 2g:1g to 4g:1g. Other steps and parameters are the same as those in example 4.

[0052] Comparative example 1:

[0053] Only rare earth residue is used to treat wastewater without being combined with carboxymethyl chitosan.

[0054] Comparative example 2:

[0055] Only chitosan is used to treat wastewater without being carboxymethylated and combined with rare earth residue.

[0056] Application example:

[0057] The wastewater produced in a certain dye factory is used in this example. The COD content in the dye wastewater in the production process is about 2800mg / L, the colority is about 1400, and the turbidity is about 1050NTU. The coagulant prepared in example 1 is used to treat the wastewater under different dosages (0.5g / L, 1.0g / L, 1.5g / L, 2.0g / L, 2.5g / L, 3.0g / L). Different amounts of the coagulant prepared in example 1 are added to 1000ml of wastewater. The temperature is 25 degrees, the pH is 7, and the reaction time is 30 minutes. The removal efficiency of colority, turbidity and COD in the dye wastewater is shown in table 1 and Figure 1 .

[0058] Table 1: Removal efficiency of colority, turbidity and COD in wastewater under different dosages

[0059] Coagulant dosage (g / L) Turbidity removal rate (%) COD removal rate (%) Decolorization rate (%) 0.5 41.15 34.68 36.77 1.0 50.68 42.27 48.16 1.5 62.32 54.11 59.24 2.0 60.04 50.03 53.33 2.5 58.77 47.91 45.23 3.0 56.39 44.66 40.55

[0060] The composite material prepared in example 1 is used to treat the wastewater under different reaction times (10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, 60 minutes). 1.5g of the composite material prepared in example 1 is added to 1000ml of wastewater. The temperature is 25 degrees, the pH is 7, and the removal efficiency of colority, turbidity and COD in the dye wastewater is shown in table 2 and Figure 2 .

[0061] Table 2: Removal efficiency of color, turbidity and COD in water at different reaction times

[0062] Reaction time (min) Turbidity removal rate (%) COD removal rate (%) Decolorization rate (%) 10 30.17 20.98 45.23 20 45.96 37.64 49.99 30 62.42 54.23 55.24 40 66.43 60.21 70.74 50 60.68 57.63 67.60 60 57.74 50.92 61.18

[0063] The coagulants prepared in Examples 1-7, the rare earth waste residue described in Comparative Example 1 and the chitosan described in Comparative Example were respectively taken 1.5 g into 1000 ml of wastewater, the temperature was 25 degrees, the PH was controlled to 7, the reaction time was 40 minutes, and the removal efficiency of color, turbidity and COD in water is shown in Table 3 and Figure 3 .

[0064] Table 3: Removal efficiency of color, turbidity and COD in water of examples and comparative examples

[0065] Group Turbidity removal rate (%) COD removal rate (%) Decolorization rate (%) Example 1 66.43 60.21 70.74 Example 2 73.76 63.04 76.29 Example 3 70.17 61.63 73.06 Example 4 84.22 72.79 85.55 Example 5 76.94 76.25 82.86 Example 6 97.68 80.13 90.54 Example 7 86.04 73.11 84.17 Comparative Example 1 55.23 34.68 36.77 Comparative Example 2 60.67 56.30 50.44

[0066] As can be seen from Table 1, the dosage of the basic rare earth waste residue and carboxymethyl chitosan composite has a great influence on the removal effect of turbidity, color and COD of wastewater. As can be seen from Figure 1 , the greater the dosage of the basic rare earth waste residue-carboxymethyl chitosan composite coagulant, the better the treatment effect, when the dosage of the basic rare earth waste residue-carboxymethyl chitosan composite coagulant reaches 1.5 g / L, the turbidity removal rate, decolorization rate and COD removal rate all begin to decrease, among which the COD removal rate decreases the fastest. According to Figure 2 , the reaction time also has a significant influence on the coagulation effect. When the reaction time is less than 10 min, the turbidity removal rate, decolorization rate and COD removal rate of wastewater are all smaller because the coagulation effect has not yet played a role. When the reaction time is extended to 40 minutes, the removal effect of color and COD in wastewater reaches the optimum, and after that, the removal efficiency basically no longer changes with the extension of the reaction time, and there is no back mixing phenomenon. Therefore, according to Table 1, Figure 1 and Table 2, Figure 2 , the best dosage of the coagulant prepared in Example 1 is 1.5 g / L and the best reaction time is 40 minutes in wastewater with COD content of about 2800 mg / L, color of about 1400 and turbidity of about 1050 NTU.

[0067] As can be seen from Table 3 and Figure 3 Figure 4 , the coagulants prepared in Examples 1-7 have good turbidity, color and COD removal efficiency. The turbidity, color and COD removal efficiency of the coagulants prepared in Examples 1-7 are all higher than 60%, 70% and 60% respectively.

[0068] Compared with Comparative Examples 1-2, the removal efficiencies of COD and color by the complex coagulant of the alkali rare earth waste residue and the carboxymethyl chitosan are both improved significantly, and the treatment effect of Example 6 is the best, the removal rates of turbidity, color and COD are 97.68%, 80.13% and 90.54% respectively, which shows that the complex coagulant of the alkali rare earth waste residue and the carboxymethyl chitosan has a good treatment effect on the dye wastewater, and the two have a good synergistic effect and a complex synergistic effect.

[0069] Compared between Example 4, Example 6 and Example 7, it can be seen that the mass ratio of the rare earth waste residue and the carboxymethyl chitosan in the complex coagulant of the alkali rare earth waste residue and the carboxymethyl chitosan should be controlled in a proper range, and the ratio between the two is too large or too small, which will affect the treatment effect on the dye wastewater.

[0070] The above description is only the preferred embodiments of the present application, although the present application has been disclosed as above with the preferred embodiments, however, it is not intended to limit the present application. Any skilled person in the art, without departing from the technical solution of the present application, can make many possible changes and modifications to the technical solution of the present application by using the disclosed methods and technical contents, or modify as equivalent embodiments. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present application, which does not depart from the content of the technical solution of the present application, still belongs to the protection scope of the technical solution of the present application.

Claims

1. A basic rare earth waste residue-carboxymethyl chitosan composite coagulant, characterized in that, It is obtained through the following preparation method: (1) The rare earth tailings are subjected to low-temperature roasting reaction of sulfuric acid, double salt precipitation and carbonate conversion in sequence to obtain rare earth waste residue; in step (1), the low-temperature roasting reaction of sulfuric acid is carried out by mixing rare earth tailings and concentrated sulfuric acid at a feeding ratio of 3~4g:1mL, and the low-temperature roasting reaction of sulfuric acid is carried out at a temperature of 180~300℃ for 2~4 hours. After the roasted sample is cooled slightly, water is added and leached while it is still hot. After stirring for 1.5 hours, the sample is filtered to obtain rare earth waste residue filtrate. During the precipitation of the double salt, the rare earth waste residue filtrate is mixed with excess sodium sulfate at a mass ratio, wherein the sodium sulfate is 50-100% excess compared to the rare earth waste residue filtrate, and the mixture is stirred at 70-80℃ for 1 hour to obtain rare earth waste residue sulfate double salt. In the carbonate conversion process, rare earth waste residue sulfate double salt and sodium carbonate solution are mixed in a mass ratio, wherein the sodium carbonate solution is 20-50% in excess of rare earth waste residue sulfate double salt. The mixture is stirred at 60-80℃ for 2 hours and then washed with water. After complete washing, it is filtered and dried to obtain rare earth waste residue. (2) After mixing rare earth waste residue and sodium hydroxide solution, distillation, filtration and water bath aging are carried out in sequence to obtain basic rare earth waste residue; (3) Mix basic rare earth waste residue and methacrylic acid, and then distill and filter the mixture in sequence to obtain a clear filtrate. Then, distill the filtrate under reduced pressure. After the reduced pressure distillation is completed, add anhydrous ethanol and stir until solid precipitates. After filtration and drying, obtain methacrylic acid-basic rare earth waste residue. (4) Dissolve carboxymethyl chitosan in water, add ammonium persulfate and methacrylic acid, then mechanically stir and heat in a water bath, wash and dry to obtain a graft copolymer of carboxymethyl chitosan and methacrylic acid, and name it CMCS-g-MAA; (5) Mix methacrylic acid-basic rare earth waste residue with CMCS-g-MAA, then add ammonium persulfate and dimethyl sulfoxide, mechanically stir, heat in a water bath, centrifuge, wash with ethanol and dry to obtain basic rare earth waste residue-carboxymethyl chitosan composite coagulant.

2. The basic rare earth waste residue-carboxymethyl chitosan composite coagulant according to claim 1, characterized in that, In step (2), the feeding ratio of the rare earth waste residue to the sodium hydroxide solution is 1g:10~20ml, and the concentration of the sodium hydroxide solution is 2~4mol / L; During the distillation process, the mixed solution is heated to boiling, and the boiling reaction time is 1-3 hours. The water bath curing temperature is 60~80℃, and the water bath curing time is 1~3h.

3. The basic rare earth waste residue-carboxymethyl chitosan composite coagulant according to claim 1, characterized in that, In step (3), the feeding ratio of basic rare earth waste residue and methacrylic acid is 1g:10~20ml; The water bath temperature during the distillation process is 85~90℃. The solution is heated until it becomes clear, then allowed to stand and filtered to obtain a clear filtrate. The filtrate is then subjected to vacuum distillation at 90℃ to remove some of the excess methacrylic acid solvent. The remaining solution is mixed with 100~200ml of anhydrous ethanol and stirred until solids precipitate out. The mixture is then filtered and vacuum dried to obtain methacrylic acid-basic rare earth waste residue.

4. The basic rare earth waste residue-carboxymethyl chitosan composite coagulant according to claim 1, characterized in that, In step (4), carboxymethyl chitosan is dissolved in water and heated in a water bath at a temperature of 50-70°C while being mechanically stirred. Nitrogen gas is slowly and uniformly introduced for 20-30 minutes, and then ammonium persulfate is added. The ratio of carboxymethyl chitosan to ammonium persulfate is 1g:0.1-0.5g. Nitrogen gas is introduced for another 10 minutes, and then methacrylic acid is added. The ratio of carboxymethyl chitosan to methacrylic acid is 1g:6-10ml. After reacting for 3-4 hours, the pH is adjusted to 7 with a 10% sodium hydroxide solution. The mixture is then washed with distilled water and dried to obtain a graft copolymer of carboxymethyl chitosan and methacrylic acid.

5. The basic rare earth waste residue-carboxymethyl chitosan composite coagulant according to claim 1, characterized in that, In step (5), methacrylic acid-basic rare earth waste residue and CMCS-g-MAA are mixed at a feeding ratio of 1~4g:1g, and then ammonium persulfate and dimethyl sulfoxide are added, wherein the dimethyl sulfoxide is 50~100ml and the ammonium persulfate is 0.1~0.5g. The mixture is mechanically stirred for 2~5 hours at a water bath heating temperature of 60~70℃. After the reaction solution is cooled, it is centrifuged at a high speed of 11000~20000rpm for 15~20 minutes. The solid material is taken out, washed with anhydrous ethanol, and dried to obtain basic rare earth waste residue-carboxymethyl chitosan composite coagulant.

6. The application of any one of the basic rare earth waste residue-carboxymethyl chitosan composite coagulants according to claims 1-5 in dye and printing and dyeing wastewater.

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