Modified chitosan flocculant for slime water treatment and preparation method thereof

Abstract

The invention provides a modified chitosan flocculant for slime water treatment. The modified chitosan flocculant is prepared from the following raw materials: chitosan, dimethyl diallyl ammonium chloride, acrylamide, acetic acid and potassium persulfate. The invention also provides a preparation method of the modified chitosan flocculant for slime water treatment. The preparation method comprises the following steps: dissolving chitosan in a dilute acetic acid solution with the mass concentration of 60%, and stirring; adding acrylamide and dimethyl propyl chloride cyclic amine into the mixed solution, uniformly stirring, adding a potassium persulfate solution with the mass concentration of 4%, and introducing nitrogen for 20 minutes; then carrying out microwave reaction, and cooling to room temperature after the reaction is completed; adding absolute ethyl alcohol, centrifuging for 10 minutes, taking out, and continuously soaking in absolute ethyl alcohol for 12 hours, so as to obtain a final insoluble substance which is a graft polymer CS-g-ADM; and drying the polymer in a drying box at 105 DEG C until no weight loss occurs, and then grinding and storing. The flocculating agent disclosed by the invention has relatively good flocculability.

Description

Technical Field

[0001] The invention belongs to the field of flocculants, and in particular relates to a modified chitosan flocculant for treating coal slime water and a preparation method thereof. Background Art

[0002] Coal slurry water treatment has long plagued coal production companies. This is due, in part, to varying water quality in different regions and, in part, to significant variations in the composition and degree of sludge formation within the slurry. Ultimately, the difficulty in settling slurry water stems from the formation of a stable colloidal system within the slurry water by fine, negatively charged slurry particles. The most direct approach to addressing this issue has been to identify a novel, non-polluting polymer flocculant and to investigate the interaction between flocculant molecules and suspended particles in the slurry water.

[0003] At present, the widely recognized flocculation mechanisms can be simply divided into: (1) Electrical neutralization: Through electrical neutralization, negatively charged colloidal particles in sewage are adsorbed and a coating is formed on the surface of the colloidal particles. The flocculant competes with the water molecules in the hydration membrane for adsorption positions, changing the chemical properties and charge distribution on the surface of the colloidal particles. Eventually, the colloidal particles lose their hydration membrane. The original repulsive effect between the destabilized colloidal particles is weakened and even becomes an attractive effect, which makes it easier for the colloidal particles to form flocculants.

[0004] (2) Charge repair: Through charge repair, the ions or molecules in the flocculant will quickly adsorb to the surface of the colloidal particles, forming a non-uniform coating. This coating changes the charge state of the colloidal particle surface, and the surface presents an uneven charge distribution. This distribution will cause a local difference in positive and negative charges on the surface of the colloidal particles. According to Coulomb's law, positive charges will generate an attractive force between negative charges, causing electrostatic attraction between these charge-unbalanced particles, causing them to approach each other and aggregate, accelerating the flocculation process.

[0005] (3) Bridging flocculation: The adsorption bridging effect mainly refers to the mutual adsorption between high molecular substances and colloid particles, but the colloid particles themselves are not in direct contact, and the colloid particles are condensed into large flocs.

[0006] (4) Netting and sweeping: Metal salts or metal oxides and hydroxides are used as flocculants. When the dosage is large enough to quickly form metal oxide or metal carbonate precipitates, the colloid particles in the water can be netted by these precipitates when they are formed.

[0007] In the actual treatment of coal sludge water in coal preparation plants, two types of flocculants are commonly used: inorganic and organic flocculants. However, inorganic flocculants are sensitive to the pH value of the coal sludge water system, and their treatment effectiveness is significantly affected by fluctuations in water quality. Furthermore, the treated water may contain metal residues. In recent years, coal preparation plants have frequently used organic flocculants to treat coal sludge water. However, the residues of polyacrylamide, a widely used industrial material, in the water may pose a potential threat to the ecological environment and human health.

[0008] Therefore, how to develop a new flocculant is a problem that those skilled in the art need to solve. Summary of the Invention

[0009] An object of the present invention is to provide a modified chitosan flocculant for use in coal slime water treatment and a method for preparing the same, and to provide at least the advantages to be described later.

[0010] The invention provides a modified chitosan flocculant for treating coal slime water and a preparation method thereof. Chitosan, acrylamide, dimethyl diallyl ammonium chloride and the like are used as raw materials, and graft copolymerization is carried out through microwave technology to prepare the modified chitosan flocculant, which has good flocculation property.

[0011] The technical solutions of the present invention are as follows: The invention discloses a modified chitosan flocculant for treating coal slime water. The raw materials for preparing the modified chitosan flocculant include chitosan, dimethyl diallyl ammonium chloride, acrylamide, acetic acid and potassium persulfate.

[0012] Preferably, in the modified chitosan flocculant for coal slime water treatment, the ratio of chitosan, dimethyl diallyl ammonium chloride and acrylamide in parts by weight is 1:0.5-1.5:0.5-2.5.

[0013] Preferably, in the modified chitosan flocculant for coal slime water treatment, Acrylamide was prepared in 60% acetic acid solution; Potassium persulfate uses a potassium persulfate solution with a mass concentration of 4%; The ratio of the potassium persulfate solution with a mass concentration of 4% and the acetic acid solution with a mass concentration of 60% is 1:2 by volume.

[0014] The preparation method of a modified chitosan flocculant for coal slime water treatment comprises the following steps: Dissolve 1g of chitosan in 20ml of 60% dilute acetic acid solution, place the beaker containing the mixed solution on a magnetic stirrer and stir at a speed of 150rpm for 30min. Add 0.5-2.5g of acrylamide and 0.5-1.5g of dimethylpropyl chlorocyclamine to the mixed solution, stir evenly, add 10ml of 4% potassium persulfate solution, and introduce nitrogen for 20min; Then, microwave reaction was carried out in a microwave reactor at a temperature of 50°C for 30 min. After the reaction was completed, the mixture was cooled to room temperature. Transfer to a centrifuge bottle, add anhydrous ethanol and centrifuge for 10 minutes, take out and continue to soak in anhydrous ethanol for 12 hours. The final insoluble matter is the grafted polymer CS-g-ADM; The polymer is dried in a drying oven at 105° C. until no more weight loss occurs, and then ground and stored to obtain a modified chitosan flocculant for coal slime water treatment.

[0015] The present invention has the following beneficial effects: (1) Chitosan is a natural polysaccharide with good biodegradability. It will not cause long-term pollution to the environment after use. Chitosan is derived from natural substances. Compared with some traditional chemical flocculants (such as aluminum salts, iron salts, etc.), chitosan is safer and has good flocculation effect. It can effectively remove suspended matter, fine particles and harmful substances in water. Its molecular structure contains amino (-NH2) and hydroxyl (-OH) functional groups. These functional groups can react with charged particles in water to form larger flocs, which are eventually removed by sedimentation or filtration. Chitosan can be used under different pH conditions and has strong adaptability. It can undergo flocculation reactions in acidic, neutral and weakly alkaline environments and is particularly suitable for treating various types of wastewater, such as agricultural wastewater, industrial wastewater, sewage treatment, etc. The performance of chitosan can be further improved or customized by chemical modification or combination with other substances. For example, its flocculation effect can be enhanced or its stability under specific conditions can be improved by cross-linking, sulfonation, etc. Chitosan not only removes solid particles from water but also effectively removes soluble harmful substances, such as heavy metal ions (lead, copper, cadmium, etc.) and organic pollutants. Its surface amino and hydroxyl groups have an affinity for these pollutants, thereby purifying water. Chitosan's advantages as a flocculant include its natural, non-toxic, biodegradable nature, wide applicability, high efficiency in removing water pollutants, and environmental friendliness. With technological advancements, its potential for application in water treatment, wastewater recycling, and ecological restoration will continue to expand.

[0016] (2) Acrylamide monomers can form high molecular weight polyacrylamide (PAM) through polymerization reaction. This long chain structure can effectively adsorb suspended particles and promote flocculation. The amide group (-CONH2) in the polyacrylamide molecule can interact with suspended particles in water through hydrogen bonds, electrostatic effects, etc., enhancing adsorption capacity. Charged groups (such as cations or anions) can be introduced through modification. These charged groups can neutralize the surface charge of suspended particles, reduce the repulsive force between particles, and promote aggregation. The long chain structure of polyacrylamide can form a "bridge" between multiple suspended particles, aggregating small particles into large flocs, which are easy to settle or filter. Polyacrylamide can adapt to different water qualities and treatment requirements by adjusting molecular weight and functional groups, and is widely used in drinking water, industrial wastewater, sludge dewatering and other fields. As a flocculant, polyacrylamide has a small dosage and good effect, which can significantly improve water treatment efficiency and reduce treatment costs.

[0017] (3) Dimethyldiallyl ammonium chloride (DMDAAC) is a cationic monomer that is often used to introduce positive charges in polymerization reactions. In the polymerization reaction of chitosan and acrylamide, DMDAAC introduces quaternary ammonium groups into the polymer chain through polymerization reaction, giving the polymer a positive charge. These positive charges can adsorb negatively charged suspended particles through electrostatic action, enhancing the flocculation effect. The introduction of DMDAAC improves the hydrophilicity of the polymer, making it more soluble in water and easier to use in water treatment. The cationic properties of DMDAAC help neutralize the negative charge of suspended particles, reduce the repulsive force between particles, promote particle aggregation, and form larger flocs, which are easier to settle or filter. The introduction of DMDAAC improves the chemical stability of the polymer, allowing it to maintain good performance in a wide pH range and different water quality conditions. DADMAC can copolymerize with chitosan and acrylamide to form a polymer with multiple functional groups, which combines the biocompatibility of chitosan and the high molecular weight characteristics of acrylamide. The cationic groups of DADMAC enhance the adsorption capacity of the polymer for negatively charged substances (such as organic matter and colloidal particles), thereby improving the water treatment effect.

[0018] (4) The present invention uses chitosan as the main chain, acrylamide and dimethyldiallylammonium chloride as the grafted side chains, and potassium sulfate as the initiator using microwave technology to synthesize a new cationic flocculant. The preparation method is simple, rapid and efficient.

[0019] (5) The modified chitosan flocculant prepared by the present invention contains a large number of amino, hydroxyl and amide groups, which work together to give the flocculant excellent flocculation performance, water solubility and stability, making it perform outstandingly in applications such as coal slime water treatment.

[0020] Other advantages, objectives and features of the present invention will be reflected in part from the following description and will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The chemical reaction equation of the modified chitosan flocculant for coal slime water treatment provided by the present invention; Figure 2 The infrared spectrum analysis diagram of the modified chitosan flocculant and chitosan for coal slime water treatment provided by the present invention; Figure 3 Thermogravimetric analysis diagram of the modified chitosan flocculant and chitosan for coal slime water treatment provided by the present invention; Figure 4 The modified chitosan flocculant for coal slime water treatment provided by the present invention and the microscopic morphology image of chitosan; Figure 5 The modified chitosan flocculant for coal slime water treatment provided by the present invention and the nuclear magnetic resonance spectrum of chitosan; Figure 6 This is a graph showing the Zeta potential results of the modified chitosan flocculant for coal slime water treatment provided by the present invention, raw coal, and chitosan at different pH values. DETAILED DESCRIPTION

[0022] The present invention is further described in detail below with reference to the embodiments so that those skilled in the art can implement the invention with reference to the description.

[0023] It should be understood that terms such as “having,” “including,” and “comprising” used herein do not prescribe the existence or addition of one or more other elements or combinations thereof.

[0024] The invention provides a modified chitosan flocculant for treating coal slime water. The raw materials for preparing the modified chitosan flocculant include chitosan, dimethyl diallyl ammonium chloride, acrylamide, acetic acid and potassium persulfate.

[0025] The proportion of chitosan, dimethyl diallyl ammonium chloride and acrylamide is 1:0.5-1.5:0.5-2.5 in parts by weight.

[0026] Acrylamide was prepared in 60% acetic acid solution; Potassium persulfate uses a potassium persulfate solution with a mass concentration of 4%; The ratio of the potassium persulfate solution with a mass concentration of 4% and the acetic acid solution with a mass concentration of 60% is 1:2 by volume.

[0027] The present invention also provides a method for preparing a modified chitosan flocculant for coal slime water treatment, which comprises the following steps: Dissolve 1g of chitosan in 20ml of 60% dilute acetic acid solution, place the beaker containing the mixed solution on a magnetic stirrer and stir at a speed of 150rpm for 30min. Add 0.5-2.5g of acrylamide and 0.5-1.5g of dimethylpropyl chlorocyclamine to the mixed solution, stir evenly, add 10ml of 4% potassium persulfate solution, and introduce nitrogen for 20min; Then, microwave reaction was carried out in a microwave reactor at a temperature of 50°C for 30 min. After the reaction was completed, the mixture was cooled to room temperature. Transfer to a centrifuge bottle, add anhydrous ethanol and centrifuge for 10 minutes, take out and continue to soak in anhydrous ethanol for 12 hours. The final insoluble matter is the grafted polymer CS-g-ADM; The polymer is dried in a drying oven at 105° C. until no more weight loss occurs, and then ground and stored to obtain a modified chitosan flocculant for coal slime water treatment.

[0028] The experimental methods in the following examples are conventional methods unless otherwise specified; the experimental materials and experimental equipment used in the following examples are purchased from commercial channels unless otherwise specified. Example 1:

[0029] S1. Accurately weigh 1 g of chitosan and place it in a beaker. Add 20 mL of 60% acetic acid solution to the beaker, place it on a magnetic stirrer, and stir at 150 rpm until the chitosan is completely dissolved in the acetic acid solution. S2. Accurately weigh 0.5 g of acrylamide and 0.5 g of dimethyldiallylammonium chloride and add them to the reaction system. Continue stirring until the reaction system is uniform. Add 10 ml of potassium persulfate with a catalyst concentration of 4% on top, and introduce nitrogen for 20 minutes to remove oxygen. Then transfer the mixture to a microwave reactor and set the reaction temperature to 50° C. for 30 minutes. S3. After the reaction is completed, cool to room temperature, transfer to a centrifuge bottle, add anhydrous ethanol and centrifuge for 10 minutes, take out and continue to soak in anhydrous ethanol for 12 hours. The final insoluble matter is the grafted polymer CS-g-ADM. Dry the polymer in a drying oven at 105°C until no more weight loss occurs, then grind and store for future use.

[0030] The chemical reaction equation is as follows Figure 1 shown. Example 2:

[0031] S1. Accurately weigh 1.0 g of chitosan and place it in a beaker. Add 20 mL of 60% acetic acid solution to the beaker, place it on a magnetic stirrer, and stir at 150 rpm until the chitosan is completely dissolved in the acetic acid solution. S2. Accurately weigh 1.0 g of acrylamide and 1.0 g of dimethyldiallylammonium chloride and add them to the reaction system. Continue stirring until the reaction system is uniform. Add 10 ml of potassium persulfate with a catalyst concentration of 4% on top, and introduce nitrogen for 20 minutes to remove oxygen. Then transfer the mixture to a microwave reactor and set the reaction temperature to 50° C. for 30 minutes. S3. After the reaction is completed, cool to room temperature, transfer to a centrifuge bottle, add anhydrous ethanol and centrifuge for 10 minutes, take out and continue to soak in anhydrous ethanol for 12 hours. The final insoluble matter is the grafted polymer CS-g-ADM. Dry the polymer in a drying oven at 105°C until no more weight loss occurs, then grind and store for future use. Example 3:

[0032] S1. Accurately weigh 1.0 g of chitosan and place it in a beaker. Add 20 mL of 60% acetic acid solution to the beaker, place it on a magnetic stirrer, and stir at 150 rpm until the chitosan is completely dissolved in the acetic acid solution. S2. Accurately weigh 2.5 g of acrylamide and 1.5 g of dimethyldiallylammonium chloride and add them to the reaction system. Continue stirring until the reaction system is uniform. Add 10 ml of potassium persulfate with a catalyst concentration of 4% on top, and pass nitrogen for 20 minutes to remove oxygen. Then transfer the mixture to a microwave reactor and set the reaction temperature to 50° C. and the reaction time to 30 minutes. S3. After the reaction is completed, cool to room temperature, transfer to a centrifuge bottle, add anhydrous ethanol and centrifuge for 10 minutes, take out and continue to soak in anhydrous ethanol for 12 hours. The final insoluble matter is the grafted polymer CS-g-ADM. Dry the polymer in a drying oven at 105°C until no more weight loss occurs, then grind and store for future use.

[0033] The parameters of the flocculants prepared in the three examples are compared in the following table.

[0034] Table 1 Parameter comparison of three embodiments flocculants <![CDATA[ Intrinsic viscosity (dL·g -1 )]]> Grafting efficiency CS-g-ADM#1 4.8 79.36 CS-g-ADM#2 6.2 73.52 CS-g-ADM#3 6.41 89.5 As can be seen from the above table, the intrinsic viscosity and grafting efficiency of Example 3 are higher than those of the other two examples, and the flocculant obtained by using the component ratio in Example 3 has the best performance.

[0035] Performance testing: The high-efficiency flocculant prepared in Example 1 was used, and a traditional flocculant (commercially available cationic polyacrylamide and anionic polyacrylamide, produced by Shanghai Aladdin Reagent Co., Ltd.) was used as a control to treat mine water.

[0036] The mine water is taken as an example from the feed of the coal preparation plant concentrator in Loufan, Shanxi Province. The sampling time is March 26, 2025. The pH value of the raw water is 8.74 and the conductivity is 2.59 μS·cm. -1 .

[0037] The results are shown in Table 2.

[0038] Table 2 Comparison of the effects of using high-efficiency flocculants and traditional flocculants on mine water treatment Types of flocculants Compression layer thickness (cm) Transmittance of supernatant (%) Filter cake moisture (%) CS-g-ADM 2.2 93 21.95 CPAM 2.41 89.6 45.59 APAM 2.83 78 48.13 Table 2 lists the results of CS-g-ADM and commercial flocculants at a dosage of 6 mg·L -1 The effect of flocculation and dehydration on coal slurry water was studied. The sedimentation effect of flocculants was studied by comparing three sedimentation indices. Transmittance, as one of the most important indices, plays a decisive role in the selection of flocculants; it is usually expected that the sedimentation rate is a fast value, and the thickness of the compression layer should be as small as possible. Compared with the results of CPAM, the clarity of the coal slurry suspension treated with CS-g-ADM is higher, which is equivalent to the clarity of the supernatant after CPAM treatment and significantly better than APAM; and the thickness of the compression layer after CS-g-ADM treatment is the lowest, indicating that the flocs after CS-g-ADM treatment are more compact. The filter cake treated with CS-g-ADM has the lowest moisture content, indicating that the coal slurry particles are closely arranged, forming flocs with small pores and dense structure, and the filter cake has a low moisture content. Comprehensive analysis shows that 6 mg·L -1 CS-g-ADM performs well in all aspects, with a sedimentation rate of 63 cm·min -1 , the transmittance is 93.00%, and the thickness of the compression layer is only 2.2 cm.

[0039] Currently, coal preparation plants typically use an integrated flocculation, sedimentation, and dehydration process to treat coal sludge water. CS-g-ADM's excellent dehydration performance improves solid-liquid separation of wastewater. Furthermore, PAM is biodegradable and toxic, posing a risk of secondary pollution. Therefore, CS-g-ADM can replace PAM as an environmentally friendly and efficient flocculant for solid-liquid separation of kaolin suspensions.

[0040] Infrared spectroscopy analysis: The composite flocculant prepared in Example 1 was characterized by infrared spectroscopy. Equal amounts of chitosan and the composite flocculant prepared in Example 1 were ground uniformly with KBr. The functional group structure of the sample was characterized by FTIR (Nicolet iS20, Thermo, Waltham, MA, USA) to understand the functional group structure of the product. The resolution was 4 cm -1 The number of scans was 32, and the wavenumber range of the test was 600–4000 cm -1 .

[0041] like Figure 2 The following is the infrared spectrum analysis of the composite flocculant, dimethyldiallylammonium chloride, acrylamide and chitosan prepared in Example 1. Compared with the FTIR spectrum of CS, the FTIR spectrum of CS-g-ADM is -1 The amino group (NH) stretching vibration peak is shown at 2932.4 cm, which does not exist before grafting. This amino group is attributed to the amide group (–NH2) in AM. -1 The asymmetric stretching vibration peak corresponding to the methylene (–CH2) on DMDAAC and CS is located at 1649 cm -1 The stretching vibration peak at 1427 cm is attributed to the introduction of carbonyl groups (C=O) in CS and AM. -1 and 966.6 cm -1 The bending vibration corresponding to –CH is adjacent to the quaternary ammonium, and (–N + (CH3)3) in DMDAAC. In addition, compared with the FTIR spectra of CS and DMDAAC, the FTIR spectrum of CS-g-ADM at 1600 cm -1 The stretching vibration of the six rings of CS was retained. These data confirmed that DMDAAC and AM were successfully transplanted into CS, indicating that the composite flocculant prepared in Example 1 was successfully prepared.

[0042] Thermogravimetric analysis: The thermal stability of dried CS-G-ADM was analyzed using a thermogravimetric analyzer in a nitrogen atmosphere. During the experiment, the nitrogen flow rate was maintained at 50 mL / min. Approximately 10 mg of the sample was placed in a crucible and then heated from 30°C to 800°C at a rate of 10°C / min. The sample's weight loss over temperature was analyzed.

[0043] Figure 3 a and Figure 3b shows the thermogravimetric curves of CS and CS-g-ADM in Example 1. The results show that the thermal decomposition process of CS can be divided into three stages: the first stage (28.41-234.32°C, 8.5% weight loss) is primarily characterized by the release of bound water from CS; the second stage (234.32-232.13°C, 36.5% weight loss) is primarily characterized by the oxidative degradation of hydroxyl groups and the cleavage of fatty chains, producing H2O, CO2, and ammonia; and the third stage (above 232.32°C, 22.7% weight loss) is characterized by the destruction of the glucose structure, resulting in a charred residue. Compared to CS, the thermal decomposition of CS-g-ADM can be divided into four stages: the first stage (28.41-234.32°C, 8.7% weight loss) is characterized by the evaporation of surface water; the second stage (157-241°C, 30.2% weight loss) is characterized by oxidative degradation of hydroxyl groups and scission of fatty chains; the third stage (244.18-322.42°C, 36.5% weight loss) is characterized by the decomposition of amide and quaternary ammonium groups in AM and DMDAAC; and the fourth stage (above 322.42°C, 42.5% weight loss) is characterized by the destruction of the hexacyclic ring structure. The differential thermal analysis of CS-g-ADM shows a weak exothermic peak at 522.74°C, indicating that the grafting of AM and DMDAAC has altered the thermal decomposition characteristics of CS.

[0044] Scanning electron microscopy: The morphology of the dried gel structure was investigated using scanning electron microscopy (SEM). The freeze-dried product was coated with a thin layer of palladium-gold alloy and imaged using a scanning electron microscope (HITACHI).

[0045] Figure 4 The scanning electron microscope images of CS-g-ADM and chitosan in Example 1 are shown in FIG. Figure 4The microstructures of CS and grafted CS-g-ADM at magnifications of 1000x, 2000x, and 5000x are shown. As shown in Figures (a)-(c), chitosan exhibits an irregular, blocky structure with relatively large particles. The surface is relatively smooth, with no apparent pores. As the magnification increases, the edges of the blocks become more distinct and lack a complex internal structure, indicating a relatively simple microstructure. As shown in Figures (d)-(f), the grafted CS-g-ADM still exhibits a blocky structure, but the block morphology becomes more irregular compared to chitosan, and the particle size distribution appears more dispersed. Significantly different from chitosan, the surface exhibits abundant pores of varying sizes and a relatively random distribution. As the magnification increases, the pore details become more distinct, revealing a porous, sponge-like structure. This structural change is likely due to the fact that the grafting of acrylamide onto chitosan alters the molecular interactions and arrangement, forming a new microstructure. Comparing the two, the grafting reaction significantly alters the chitosan's microstructure, transforming it from a smooth, blocky structure to a porous structure. This porous structure increases the material's specific surface area, improving its adsorption properties and chemical reactivity. This characteristic enhances the CS-g-ADM's ability to reticulate and sweep suspended particles, allowing the resulting flocs to settle quickly.

[0046] NMR spectrum analysis: pass 1 H-NMR, 13 C-NMR (PLUS 600 MHz model, Bruker, Germany) was used to characterize the structure of the samples, and deuterated reagent heavy water (D2O) was used to dissolve the samples.

[0047] Figure 5 For AM, DMAAC, CS and CS-g-ADM 1 H-NMR spectra, comparing DMAAC and CS-g-ADM 1 The H-NMR spectrum shows that the chemical shift of CS-g-ADM at δ = 3.75 corresponds to the signal peak of the methylene group connected to the nitrogen on the main chain of the DMAAC molecule, and the chemical shift at δ = 2.9 corresponds to the signal peak of the methyl group connected to the nitrogen on the main chain of the DMAAC molecule.

[71] Comparison of DMAAC and CS 1 The H-NMR spectrum shows that the chemical shift at δ=1.9 corresponds to the signal peak of the methine in CS. 1 From the H-NMR spectrum, it can be seen that the chemical shifts at δ = 2.0-2.2 and 3.0-3.1 correspond to the methylene signal peaks of the AM group.

[0048] Zeta potential is an important indicator of the charge characteristics of solid surfaces or liquid interfaces. It is often used to study the charge properties of flocculants and mineral particles and their interactions. The zeta potential can be used to infer the flocculation mechanism: when the flocculant and coal slime particles have opposite charges, electrostatic attraction is the primary mechanism that destabilizes the particles, causing them to aggregate and settle. When the charges are equal or the flocculant is electrically neutral, a bridging effect promotes particle aggregation and sedimentation.

[0049] In order to study the charged properties of CS-g-ADM and its mechanism of action in coal slime water, the Zeta potential changes of CS, coal slime and CS-g-ADM at different pH were analyzed. Figure 6 The results showed that the zeta potential of CS, CS-g-ADM, and coal slurry decreased with increasing pH. This is due to the decreased hydrogen ion concentration and reduced surface charge under alkaline conditions. Coal slurry is always negatively charged, making it suitable for cationic flocculants to neutralize electrostatic charge. CS has a negative zeta potential due to its negative functional groups, such as hydroxyl groups, and its hydrophilic surface. CS-g-ADM is positively charged under acidic conditions, with an isoelectric point of pH 8.1. The introduction of DMDAAC quaternary ammonium groups significantly increases the number of positive charges, resulting in a positive charge over a wide pH range. Under acidic conditions, CS-g-ADM exhibits better charge neutralization; under alkaline conditions, it exerts adsorption, bridging, and net-sweeping effects through its high molecular weight, multi-branched structure, and surface roughness.

[0050] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the description and implementation methods. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to specific details.

Claims

1. A modified chitosan flocculant for coal slime water treatment, characterized in that: The preparation raw materials include chitosan, dimethyldiallylammonium chloride, acrylamide, acetic acid and potassium persulfate.

2. The modified chitosan flocculant for coal slime water treatment according to claim 1, characterized in that The proportion of chitosan, dimethyl diallyl ammonium chloride and acrylamide is 1:0.5-1.5:0.5-2.5 in parts by weight.

3. The modified chitosan flocculant for coal slime water treatment according to claim 2, characterized in that Acrylamide was prepared in 60% acetic acid solution; Potassium persulfate uses a potassium persulfate solution with a mass concentration of 4%; The ratio of the potassium persulfate solution with a mass concentration of 4% and the acetic acid solution with a mass concentration of 60% is 1:2 by volume.

4. The method for preparing a modified chitosan flocculant for coal slime water treatment according to claim 1, wherein: The following steps are involved: Dissolve 1g of chitosan in 20ml of 60% dilute acetic acid solution, place the beaker containing the mixed solution on a magnetic stirrer and stir at a speed of 150rpm for 30min. Add 0.5-2.5g of acrylamide and 0.5-1.5g of dimethylpropyl chlorocyclamine to the mixed solution, stir evenly, add 10ml of 4% potassium persulfate solution, and introduce nitrogen for 20min; Then, microwave reaction was carried out in a microwave reactor at a temperature of 50°C for 30 min. After completion of the reaction, the mixture was cooled to room temperature. Transfer to a centrifuge bottle, add anhydrous ethanol and centrifuge for 10 minutes, take out and continue to soak in anhydrous ethanol for 12 hours. The final insoluble matter is the grafted polymer CS-g-ADM; The polymer is dried in a drying oven at 105° C. until no more weight loss occurs, and then ground and stored to obtain a modified chitosan flocculant for coal slime water treatment.

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