Insoluble lignin-chitosan flocculant, its preparation method and application

Abstract

The present application relates to a kind of insoluble lignin-chitosan flocculants and its preparation method and application, belong to water treatment technical field.The biomass flocculant is prepared by modifying basic lignin and chitosan with quaternary ammonium reagent CHPTAC under specific pH, temperature, with high flocculation activity, environmental friendly and biodegradable characteristics.When used with polyaluminum chloride (PAC), it can achieve efficient turbidity removal (turbidity reduced to below 0.465 NTU) and significantly reduce residual aluminum content.The present application provides an optimized preparation process, compounding method and wide application, suitable for industrial wastewater, municipal sewage and surface water treatment.Experiments show that the yield of the flocculant under optimal conditions is 75%, the turbidity removal rate of the compound treatment is more than 98%, the residual aluminum is reduced by more than 48%, and it has economy and practicability.

Description

Technical Field

[0001] This invention belongs to the field of flocculant technology in water treatment, specifically an insoluble lignin-chitosan flocculant, its preparation method, and its application. Background Technology

[0002] With the acceleration of industrialization and urbanization, water pollution problems are becoming increasingly severe. Flocculants, as core reagents in water treatment, directly affect treatment effectiveness and environmental impact. Currently, inorganic flocculants such as polyaluminum chloride (PAC) are widely used due to their low cost and good flocculation effect. However, long-term use leads to increased residual aluminum content in the effluent and fails to simultaneously remove heavy metal pollutants. The accumulation of aluminum in the environment may pose potential hazards to aquatic ecosystems and human health, such as neurotoxicity. Meanwhile, heavy metals such as Pb and Cd are highly carcinogenic and bioaccumulative, posing significant risks to drinking water safety. Therefore, the development of flocculants with low residue, biodegradability, and the ability to simultaneously remove heavy metals has become a research hotspot.

[0003] Natural polymers such as chitosan and lignin are considered ideal alternatives due to their wide availability (chitosan comes from crustacean shells, and lignin from papermaking waste), renewability, and environmental friendliness. Chitosan is cationic and biocompatible, but its low charge density and small molecular weight when used alone result in poor flocculation. While lignin has adsorption properties, its water solubility and active groups are limited. Existing technologies have explored chemical modification (such as quaternization) to improve the performance of these materials, but these studies mostly focus on single-component modification. For example, CN120622641A discloses a modified chitosan flocculant, but its synthesis process is complex and its turbidity removal effect is limited; or CN110229289A reports a lignin-based flocculant, but it suffers from high cost and complex processing. Summary of the Invention

[0004] The purpose of this invention is to address the environmental risks associated with traditional flocculants such as PAC in the prior art and to provide a green and efficient alternative. It also addresses the shortcomings of chitosan or lignin-modified flocculants, such as insufficient flocculation performance, unstable efficiency, and inability to simultaneously reduce turbidity, residual aluminum, and heavy metals.

[0005] This invention provides a biomass flocculant prepared by chemical modification of natural polymer materials alkaline lignin and chitosan through a quaternization copolymerization reaction. Furthermore, this invention includes a method for preparing the flocculant, its compound application with the inorganic flocculant polyaluminum chloride (PAC), and a process for removing turbidity, reducing aluminum residue, and simultaneously purifying heavy metals in water treatment.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: According to a first aspect of the present invention, an alkaline lignin-chitosan biomass flocculant is provided, said flocculant being obtained by quaternization reaction of the hydroxyl groups of alkaline lignin and chitosan with a quaternary ammonium salt.

[0007] Preferably, the pH conditions for the quaternization reaction are pH 4.0-9.0.

[0008] Preferably, the quaternary ammonium salt is 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHPTAC).

[0009] Preferably, the alkaline lignin has a purity of ≥80% and a hydroxyl content of ≥5.0 mmol / g.

[0010] Preferably, the chitosan has a degree of deacetylation ≥85% (more preferably ≥90%) and a viscosity-average molecular weight limited to 50,000-200,000 Da (defined as medium molecular weight).

[0011] This invention provides an alkaline lignin-chitosan biomass flocculant with excellent flocculation performance and environmental friendliness, which has high charge density and stability.

[0012] According to a second aspect of the present invention, the present invention provides a method for preparing an alkaline lignin-chitosan biomass flocculant, comprising the following steps: (1) Dissolve chitosan in an acid solution to obtain a chitosan solution; (2) Disperse alkaline lignin in water and mix it with the chitosan solution obtained in step (1). Adjust the pH of the mixture and then add the quaternization reagent CHPTAC. React at 50-70°C for 3-6 hours. (3) After the reaction is complete, ethanol is added to precipitate the product. After separation, drying and grinding, a solid flocculant product is obtained. Preferably, the acid solution in step (1) is an aqueous solution of acetic acid with a volume concentration of 1%-3%; and / or, the mass-volume ratio of chitosan to acid solution is 1g: (80-120)mL.

[0013] Preferably, the chitosan in step (1) is chitosan with a degree of deacetylation ≥90% and a viscosity-average molecular weight of 50,000-200,000 Da; And / or, the alkaline lignin described in step (2) has a purity of ≥80% and a hydroxyl content of ≥5.0 mmol / g; The mass ratio of chitosan to alkaline lignin in step (2) is (2:1) to (1:2); And / or, the pH is adjusted to 4.0-9.0; And / or, the amount of CHPTAC added is: 3-8 mL of 65% weight concentration (w / w) CHPTAC aqueous solution per gram of total mass of chitosan and alkaline lignin.

[0014] In this invention, the concentration of CHPTAC is labeled as 65% by weight (w / w), which means that every 100g of CHPTAC aqueous solution contains 65g of pure CHPTAC. This is the conventional labeling method for industrial-grade CHPTAC, which can be directly obtained through market purchase.

[0015] Preferably, the mass ratio of chitosan to alkaline lignin is 1:1; And / or, the pH is adjusted to 4.5; And / or, the amount of CHPTAC added is: 3 mL of 65% (w / w) CHPTAC aqueous solution per gram of total mass of chitosan and alkaline lignin.

[0016] In some embodiments of the present invention, the method specifically comprises: (1) Pre-dissolve chitosan: Dissolve 1 part by mass of chitosan with a viscosity-average molecular weight of 50,000-200,000 Da and a degree of deacetylation of >90% in 100 parts by volume of 2% (v / v) acetic acid aqueous solution and stir at 25°C until clear.

[0017] (2) Mixing and Quaternization Reaction: 1 part by mass of industrial-grade alkaline lignin extracted from papermaking black liquor with a purity ≥80% and a hydroxyl content ≥5.0 mmol / g was dispersed in 100 parts by volume of ultrapure water. After stirring and mixing, it was mixed with the chitosan acetate solution obtained in step (1) and stirred to form a homogeneous mixture. The pH of the mixture was adjusted to 4.5 with a dilute alkaline solution, and then 6 parts by volume of 65% (w / w) CHPTAC aqueous solution was added. The mixture was reacted at 60°C for 4 hours.

[0018] (3) Precipitation and post-treatment: After the reaction is completed, anhydrous ethanol of 1 volume is added to the reaction solution for precipitation. After standing for 1 hour, centrifugation is performed. The precipitate is dried and ground to obtain the biomass flocculant powder.

[0019] This preparation method is based on the principle of quaternization modification: CHPTAC undergoes a quaternization reaction with the amino groups of chitosan and the hydroxyl groups of basic lignin within the pH range of 4.0-9.0 (preferably acidic conditions pH=4.5) as specified in this invention, introducing quaternary ammonium groups and enhancing the cationic charge density and dispersibility in water. pH control is crucial; acidic conditions (pH 4.5) are beneficial for charge neutralization and improve flocculation efficiency.

[0020] This invention clearly defines the quality parameters of chitosan and alkaline lignin, which are necessary conditions for achieving optimal flocculation effect: a degree of deacetylation ≥90% ensures sufficient amino content, providing enough active sites for the quaternization reaction. If the deacetylation is too low, insufficient amino content will lead to insufficient cation charge density, affecting the charge neutralization effect; the viscosity-average molecular weight is limited to 50,000-200,000 Da (defined as medium molecular weight). This range can balance solubility and flocculation bridging ability—when the molecular weight is below 50,000 Da, the molecular chains are too short, making it difficult to form effective flocs; when it is above 200,000 Da, the dispersibility of chitosan in acetic acid aqueous solution deteriorates, resulting in uneven mixing with alkaline lignin and insufficient quaternization reaction; the purity of alkaline lignin ≥80% can avoid impurities affecting the quaternization reaction, and the hydroxyl content ≥5.0 mmol / g is the key to ensuring effective cross-linking with CHPTAC. If the hydroxyl content is too low, it will lead to insufficient adsorption activity of the modified flocculant. Experiments have shown that chitosan can only achieve efficient quaternization modification in synergy with alkaline lignin when it simultaneously meets the above requirements for degree of deacetylation and medium molecular weight. Ultimately, when combined with PAC, it achieves a triple effect of "deep turbidity removal + low aluminum residue + heavy metal purification".

[0021] According to a second aspect of the present invention, the present invention provides a method for preparing the flocculant, which achieves high yield and high activity by controlling reaction conditions (such as pH, temperature, reagent ratio and key quality parameters of materials).

[0022] According to a third aspect of the present invention, an alkaline lignin-chitosan biomass flocculant prepared by the method described in the second aspect is provided. The flocculant of the present invention is an insoluble solid powder, but it can form a stable dispersion system in water, ensuring that its flocculation activity is fully utilized.

[0023] According to a fourth aspect of the present invention, the present invention provides the use of the alkaline lignin-chitosan biomass flocculant described in the first aspect or the alkaline lignin-chitosan biomass flocculant prepared by the method described in the second aspect, for forming a composite flocculant with PAC.

[0024] The specific method involves adding PAC and the alkaline lignin-chitosan biomass flocculant to the water to be treated. In some embodiments, PAC and the alkaline lignin-chitosan biomass flocculant may be added simultaneously or sequentially.

[0025] According to a fifth aspect of the present invention, the present invention provides a composite flocculant comprising PAC and the alkaline lignin-chitosan biomass flocculant described in the first aspect or the alkaline lignin-chitosan biomass flocculant prepared by the method described in the second aspect.

[0026] According to a sixth aspect of the present invention, the present invention provides a flocculation treatment method, wherein PAC and the alkaline lignin-chitosan biomass flocculant described in the first aspect or the biomass flocculant prepared by the method described in the second aspect are added to water to be treated and stirred.

[0027] Preferably, PAC and the alkaline lignin-chitosan biomass flocculant can be added simultaneously or sequentially. The above-mentioned biomass flocculant is used in combination with polyaluminum chloride (PAC), which utilizes the charge neutralization effect of PAC and the adsorption bridging effect of the biomass flocculant for synergistic effect. This invention provides a method for using this flocculant in combination with PAC to achieve the triple objectives of highly efficient turbidity removal (turbidity ≤ 0.465 NTU), low residual aluminum (more than 48% reduction compared to single PAC treatment), and simultaneous heavy metal purification (compliant with GB 5749-2022), thereby improving the economy and safety of water treatment.

[0028] Preferably, the PAC is industrial-grade polyaluminum chloride powder (Al2O3 mass fraction ≥28%), and the dosage is 10-30 mg / L; And / or, the dosage of the biomass flocculant is 3-10 mg / L.

[0029] In this invention, PAC is added directly in the form of industrial-grade polyaluminum chloride powder. The dosage of 10-30 mg / L (optimal 15 mg / L) refers to the mass concentration of the PAC powder. The Al2O3 mass fraction of PAC is limited to ≥28% because this indicator is the standard for industrial-grade PAC and can ensure a stable content of active ingredients. If the Al2O3 mass fraction is too low, the actual active ingredients will be insufficient, and the expected charge neutralization effect cannot be achieved. If it is higher than 28% (e.g., 30%), the PAC activity is stronger, and the dosage range of this invention is still applicable without additional adjustment.

[0030] Experimental verification: When industrial-grade PAC powder with an Al2O3 mass fraction of 28%-30% is added at a dosage of 10-30 mg / L and combined with the biomass flocculant of this invention, the turbidity can be reduced to below 0.465 NTU and the residual aluminum can be reduced by more than 48%, ensuring the reproducibility of the technical solution.

[0031] Preferably, after adding PAC and the biomass flocculant, the mixture is rapidly stirred at a speed of 150-250 rpm for 1-3 minutes, followed by slow stirring at 40-80 rpm for 10-20 minutes.

[0032] Preferably, the PAC is industrial-grade polyaluminum chloride powder (Al2O3 mass fraction ≥28%), and the dosage is 15 mg / L, while the dosage of the biomass flocculant is 5 mg / L.

[0033] In some implementations, treating a simulated water sample with an initial turbidity of 32 NTU includes the following steps: a. Add PAC and the biomass flocculant to the water to be treated. PAC is industrial-grade polyaluminum chloride powder (Al2O3 mass fraction ≥28%), with a dosage of 10-30 mg / L. The biomass flocculant is added at a dosage of 3-10 mg / L. Stir rapidly (150-250 rpm) for 1-3 minutes. b. Then switch to slow stirring (40-80 rpm) for 10-20 minutes; c. After standing for 10-20 minutes to settle, take the supernatant. The turbidity of the water can be reduced to below 1 NTU.

[0034] Preferably, the PAC is industrial-grade polyaluminum chloride powder (Al2O3 mass fraction ≥28%), and the dosage is 15 mg / L. The dosage of the biomass flocculant is 5 mg / L. The mixture is stirred quickly for 2 minutes (200 rpm) and then slowly for 20 minutes (60 rpm).

[0035] This invention combines chitosan and alkaline lignin to achieve complementary advantages: chitosan provides cationic charge, while alkaline lignin enhances adsorption bridging. Furthermore, through system optimization, such as precise control of mass ratio, pH, and reagent dosage, it addresses the issue of unstable flocculation efficiency in existing technologies. In addition, this first-time combination with PAC achieves multiple objectives: efficient purification of aluminum and heavy metals with low residual levels.

[0036] Existing technologies do not disclose a method for compounding quaternized ammonium-modified alkaline lignin-chitosan flocculant with PAC in a 15:5 ratio. Surprisingly, this compounding method simultaneously achieves a turbidity reduction to below 0.465 NTU, a residual aluminum reduction of over 48%, and heavy metal content meeting drinking water standards. Experiments demonstrate that this method, while deeply removing turbidity, can control residual aluminum within safe thresholds and simultaneously purify heavy metals, filling a gap in existing technologies.

[0037] The present invention has the following beneficial effects: (1) High efficiency in turbidity removal: deep treatment down to below 0.465 NTU One of the core beneficial effects of this invention is its high efficiency in turbidity removal. Experimental data shows that, after combining PAC and biomass flocculant, water samples with an initial turbidity of 32 NTU can be treated to below 0.465 NTU, with a removal rate exceeding 97%. This effect is far superior to traditional methods, and its specific advantages are reflected in the following aspects: Mechanism analysis: The biomass flocculant introduces cationic groups through quaternization modification, enhancing its charge neutralization capacity; simultaneously, its porous structure provides adsorption bridging. When combined with PAC, PAC first neutralizes the colloidal charge, and the biomass flocculant then captures tiny flocs through its polymer chains, achieving deep turbidity removal. Experimental data show that after the combined treatment (PAC 15 mg / L + biomass flocculant 5 mg / L), the turbidity decreased to 0.465 NTU, while the residual turbidity after single PAC treatment (Comparative Example 1) was 1.86 NTU, demonstrating synergistic effect.

[0038] Data support: Under optimal conditions (Example 1), the flocculant itself has high activity; the combined fast-stirring-slow-stirring process optimizes mass transfer, and the settling is thorough. The turbidity removal rate is calculated to be (32-0.465) / 32 × 100% = 98.55%, which meets the drinking water standard (<1 NTU).

[0039] (2) Advantages of low residual aluminum: significantly reduced environmental and health risks

[0040] The main drawback of traditional PAC flocculants is the high residual aluminum content in the effluent, which may lead to environmental accumulation and health problems (such as neurotoxicity). This invention, through the compounding of biomass flocculants, significantly reduces the residual aluminum content by more than 48%, with specific benefits including: Comparative data: The residual aluminum in Comparative Example 1 (single PAC treatment) was 0.0815 mg / L, while the residual aluminum in the combined treatment of Example 1 was reduced to 0.0468 mg / L, a reduction of 42.6%. This level is lower than the World Health Organization's recommended limit for residual aluminum in drinking water (0.2 mg / L), significantly improving water quality safety.

[0041] Mechanism explanation: The introduction of biomass flocculants reduced the PAC dosage (from 40 mg / L to 15 mg / L), immobilizing aluminum ions through adsorption and encapsulation to prevent their release. Simultaneously, the quaternary ammonium groups formed stable complexes with aluminum ions, promoting sedimentation.

[0042] Environmental significance: Low residual aluminum means reduced damage to aquatic ecosystems and lower long-term human exposure risks, aligning with green water treatment trends. This is particularly important in municipal wastewater and surface water treatment, contributing to the achievement of sustainable development goals.

[0043] (3) Advantages of heavy metal purification: simultaneous removal of toxic pollutants

[0044] This invention's compound formulation utilizes the porous structure and functional group adsorption of biomass flocculants to simultaneously remove toxic heavy metals such as Pb and Cd from water. ICP-OES testing confirms that after treatment, Pb residue is ≤0.0088 mg / L, Cd residue is ≤0.0025 mg / L, Fe residue is ≤0.1835 mg / L, and Sr residue is ≤0.0374 mg / L, all strictly complying with the "Standards for Drinking Water Quality" (GB 5749-2022). This solves the problem of traditional PAC treatment potentially introducing heavy metal impurities, making it particularly suitable for surface water treatment with slight heavy metal contamination.

[0045] (4) Environmentally friendly characteristics: biodegradable and resource recycling

[0046] This invention is based on natural polymer materials (chitosan and lignin), which are inherently environmentally friendly, and its beneficial effects are reflected in: Biodegradability: Both chitosan and lignin are biomass-based, and the flocculant can naturally degrade in the environment after use, avoiding secondary pollution such as microplastics. This material replaces traditional aluminum / iron salts, reducing the consumption of non-renewable resources.

[0047] Waste utilization: Alkaline lignin often comes from papermaking waste; this invention transforms it into a valuable resource, promoting a circular economy. Chitosan originates from crustacean waste, has a wide range of sources, and reduces production costs.

[0048] Ecological compatibility: FTIR analysis confirmed that no toxic groups were introduced during the modification process and the product had no toxic side effects.

[0049] In addition, the flocculant uses ethanol precipitation during its preparation process, and the solvent can be recovered, further reducing its environmental footprint.

[0050] (5) Economic analysis: Outstanding cost-effectiveness

[0051] This invention offers significant economic advantages while ensuring performance: Dosage optimization: In the compound formulation, the dosage of biomass flocculant is only 3-10 mg / L (optimal 5 mg / L), and the dosage of PAC is reduced to 10-30 mg / L (optimal 15 mg / L). Compared with single PAC treatment (40 mg / L), the aluminum salt consumption is reduced by 62.5%, directly saving more than 20% of the reagent cost.

[0052] Low preparation cost: Example 1 shows that the flocculant yield reaches 75%, and the raw material is an industrial-grade reagent (such as a 65% w / w CHPTAC aqueous solution), eliminating the need for expensive purification. Based on an annual production of thousands of tons, the cost is 30% lower than that of synthetic flocculants.

[0053] Operational benefits: The fast-stirring-slow-stirring process (150-250 rpm for 1-3 minutes fast stirring, 40-80 rpm for 10-20 minutes slow stirring) has low energy consumption, short processing time, and improves processing efficiency. In application example 1, the total processing time is approximately 25 minutes, faster than traditional methods.

[0054] The economic viability of this invention makes it suitable for large-scale application, especially in resource-limited regions.

[0055] (6) Comprehensive synergistic effect

[0056] The compounding scheme of this invention is not a simple addition, but achieves a "1+1>2" effect through synergistic action: Synergistic mechanism: PAC provides rapid charge neutralization, and biomass flocculants enhance the trapping effect; its porous structure (as shown in the SEM image) expands the adsorption area, simultaneously achieving turbidity removal, aluminum fixation, and heavy metal adsorption.

[0057] Long-term benefits: Reduced sludge production (due to the biodegradability of biomass), lower disposal costs; increased public acceptance, and compliance with regulations. Attached Figure Description

[0058] Figure 1 Scanning electron microscope (SEM) image of the biomass flocculant prepared in Example 1 of this invention.

[0059] Figure 2 : The Fourier Transform Infrared (FTIR) spectrum of the biomass flocculant prepared in Example 1 of this invention. Detailed Embodiments

[0060] The present invention will be further described in detail below with reference to embodiments and comparative examples, but the scope of protection of the present invention is not limited thereto. Experimental methods in the embodiments that do not specify specific conditions are generally carried out under conventional conditions or conditions recommended by the manufacturer. Reagents used, unless otherwise specified, are all commercially available industrial-grade reagents.

[0061] Example 1: Preparation of biomass flocculant (optimal conditions)

[0062] The mass ratio of chitosan to alkaline lignin was 1:1, the reaction pH was 4.5, the reaction temperature was 60°C, the reaction time was 4 hours, and the amount of CHPTAC used was 6 mL of 65% commercial-grade CHPTAC aqueous solution. The product was a brownish-brown powder, and the yield was determined to be 75% (actual dry weight of flocculant obtained / total dry weight of chitosan and alkaline lignin) × 100%.

[0063] S1 Pre-dissolved Chitosan: Dissolve 1 part by mass of chitosan with a viscosity-average molecular weight of 50,000-200,000 Da and a degree of deacetylation >90% in 100 parts by volume of 2% (v / v) aqueous acetic acid solution and stir at 25°C until clear.

[0064] S2 Mixing and Quaternization Reaction: 1 part by mass of industrial-grade alkaline lignin extracted from papermaking black liquor, with a purity ≥80% and a hydroxyl content ≥5.0 mmol / g, was dispersed in 100 parts by volume of ultrapure water. After stirring and mixing, it was mixed with the chitosan acetate solution obtained in step (1) and stirred to form a homogeneous mixture. The pH of the mixture was adjusted to 4.5 with a dilute alkaline solution, and then 6 parts by volume of 65% (w / w) CHPTAC aqueous solution was added. The mixture was reacted at 60°C for 4 hours.

[0065] S3 Precipitation and Post-treatment: After the reaction is completed, anhydrous ethanol of 1 volume is added to the reaction solution for precipitation. After standing for 1 hour, the precipitate is separated by centrifugation. The precipitate is dried and ground to obtain the biomass flocculant powder.

[0066] Example 2: Preparation of biomass flocculant (investigating the effect of pH)

[0067] Except for adjusting the pH to 7.0, the process was the same as in Example 1. The flocculation activity of the product decreased compared to Example 1, indicating that acidic conditions were more favorable.

[0068] Example 3: Preparation of biomass flocculant (investigating the effect of pH)

[0069] Except for adjusting the pH to 9.0, the process was the same as in Example 1. The flocculation effect of the product was poor and decreased compared to Example 1, confirming that alkalinity is unfavorable.

[0070] Example 4: Preparation of biomass flocculant (investigating the effect of mass ratio)

[0071] Except for changing the mass ratio to 2:1 (chitosan 1.33g, alkaline lignin 0.67g), the rest was the same as in Example 1. The flocculation effect was slightly lower than that of the 1:1 ratio, but still better than that of a single component.

[0072] Example 5: Preparation of biomass flocculant (investigating the effect of mass ratio)

[0073] Except for changing the mass ratio to 1:2 (0.67g chitosan, 1.33g alkaline lignin), the results were the same as in Example 1. The flocculation effect was lower than that of a 1:1 ratio, but still better than that of a single component.

[0074] Comparative Example 1: Simulated water sample treated with a single PAC

[0075] Take 1L of kaolin-based simulated water sample with an initial turbidity of 32 NTU, add only PAC, and treat according to the conventional flocculation and sedimentation procedure (fast stirring-slow stirring-setting). Measure the residual turbidity and residual aluminum and heavy metal content of the supernatant.

[0076] Comparative Example 2: Simulated water samples treated with a single biomass flocculant

[0077] Take 1L of kaolin-sodium humate simulated water sample with an initial turbidity of 32 NTU, add only 20 mg / L of the biomass flocculant prepared in Example 1, process it according to the conventional flocculation and sedimentation procedure, and determine the residual turbidity and residual aluminum and heavy metal content of the supernatant.

[0078] Application Example 1: Compound Treatment of Simulated Water Samples

[0079] Take 1L of kaolin-based simulated water sample with an initial turbidity of 32 NTU, and operate according to the "flocculation treatment method" described in this invention: add 15 mg / L PAC and 5 mg / L of the biomass flocculant prepared in Example 1, stir rapidly (200 rpm) for 2 minutes, then stir slowly (60 rpm) for 20 minutes, and let it stand for 15 minutes to settle. Measure the remaining turbidity, residual aluminum, and heavy metal content of the supernatant.

[0080] Application Example 2: Scale-up Experiment: Treatment of Simulated Water Samples with Compound

[0081] Take 1L of kaolin-sodium humate simulated water sample with an initial turbidity of 32 NTU, add 15 mg / L PAC and 5 mg / L of biomass flocculant prepared in the scale-up experiment (preparation process is the same as in Example 1, 10 times production), treat it according to the operating conditions of Application Example 1, and determine the residual turbidity, residual aluminum and heavy metal content of the supernatant.

[0082] Note: In this application example, 'scale-up experiment' refers to the preparation of biomass flocculants where the amount of raw materials (chitosan, alkaline lignin) and modifier (CHPTAC) is increased 10 times according to Example 1, while the preparation process remains the same; the flocculation experiment is still conducted on a 1L simulated water sample to verify the performance stability of the flocculant after scale-up preparation.

[0083] Regarding the above-mentioned water purification flocculation, the turbidity of the supernatant was measured. The test results obtained from the above examples, comparative examples, and application examples are as follows: Table 1: Turbidity removal efficiency (NTU) of different treatment schemes

[0084] As shown in Table 1, the biomass flocculants prepared in Examples 1-5 of this invention all exhibited certain turbidity removal capabilities at different dosages, but the compound application examples demonstrated significant advantages. Application Example 1, using a compound scheme of PAC and biomass flocculant (PAC 15 mg / L + flocculant 5 mg / L, total dosage equivalent to 20 mg / L), achieved a residual turbidity as low as 0.465 NTU, far lower than the single-component treatment. For example, at a dosage of 20 mg / L, the residual turbidity of Example 1 (flocculator prepared under optimal conditions) and Comparative Example 2 (single biomass) was 2.79 NTU, while Comparative Example 1 (single PAC treatment) was 3.72 NTU, indicating that the synergistic effect of the compound formulation improved the turbidity removal efficiency by approximately 85%. As the dosage increased, the residual turbidity in the application example remained stable below 1.39 NTU, while the turbidity in the examples and comparative examples fluctuated (e.g., the turbidity in Example 1 rose to 15.81 NTU at 80 mg / L), demonstrating that the compound formulation can achieve deep turbidity removal over a wide dosage range.

[0085] Comparing the performance differences among different embodiments further verifies the necessity of optimizing the preparation conditions. Example 1 (pH 4.5, mass ratio 1:1) performed best at low doses (turbidity 2.79 NTU at 20 mg / L), while Examples 2 (pH 7.0) and 3 (pH 9.0) showed residual turbidities of 12.55 NTU and 26.50 NTU, respectively, at the same dose, indicating that acidic conditions (pH 4.5) are more conducive to the quaternization reaction and enhance flocculation activity. Examples 4 (mass ratio 2:1) and 5 (mass ratio 1:2) showed turbidities of 5.12 NTU and 3.26 NTU, respectively, at medium doses (60 mg / L), which were better than the examples under alkaline conditions but still inferior to Example 1, confirming that a 1:1 ratio of chitosan to alkaline lignin is the optimal ratio. These data highlight that the present invention maximizes flocculant performance by precisely controlling pH and mass ratio.

[0086] Comparative Example 1 (single PAC treatment) showed the lowest residual turbidity (1.86 NTU) at 40 mg / L, but this increased to 6.51 NTU when the dosage was increased to 120 mg / L, with a higher residual aluminum content. This reflects the susceptibility of single inorganic flocculants to dosage fluctuations and the associated environmental risks. In contrast, Application Example 1 reduced turbidity to 0.465 NTU at a total dosage of 20 mg / L, and its residual aluminum and heavy metal content were superior to Comparative Example 1, demonstrating that the compounded approach can achieve better results with lower dosages while avoiding aluminum residue and heavy metal pollution problems. In summary, the data in Table 1 fully support the superiority of the compounded strategy of this invention: it not only improves the turbidity removal efficiency to 98.55%, but also reduces dependence on chemical agents through synergistic effects, aligning with the trend of green water treatment.

[0087] Table 2: Comparison of residual aluminum content under different treatment methods

[0088] The comparison data of residual aluminum content in Table 2 show that the compound formulation of this invention exhibits a significant advantage in reducing residual aluminum in water. After treatment with Comparative Example 1 (single PAC treatment, PAC dosage of 40 mg / L), the residual aluminum content in the water was 0.0815 mg / L, which meets the World Health Organization's recommended limit for residual aluminum in drinking water (0.2 mg / L). In Application Example 1, after treatment with a compound of PAC (15 mg / L) and biomass flocculant (5 mg / L), the residual aluminum content decreased to 0.0468 mg / L, a reduction rate of 42.6%. In Application Example 2 (scale-up experiment compound formulation), the residual aluminum was further reduced to 0.0422 mg / L, a reduction rate of 48.1%, all far below the WHO limit and the requirements of the "Standards for Drinking Water Quality" (GB 5749-2022). This data fully verifies that the invention achieves its effect through synergistic compounding (the functional groups of biomass flocculant and Al...). 3+ The technology of complexation and fixation, which reduces free residues, further confirms the core value of the solution in reducing environmental and health risks. It complements the high-efficiency turbidity removal performance shown in Table 1, and together supports the dual technical advantages of "high efficiency + low risk" of this invention.

[0089] Table 3: Test results of heavy metal element residues under various treatment schemes (ICP-OES measurement)

[0090] Table 3 shows the ICP-OES test results of five key elements, Sr, Fe, Pb, Cd, and Al, under each treatment scheme, further verifying the environmental safety of the compounding scheme of the present invention. The initial water sample contained ultrafine kaolin and sodium humate, resulting in excessive Pb (0.0200 mg / L). Comparative Example 1 (single PAC treatment) not only failed to remove Pb, but impurities in the PAC raw materials caused Pb residue to rise to 0.1073 mg / L (10 times the standard limit), and Fe residue was also close to the national standard limit (0.2595 mg / L), posing a risk of secondary pollution. However, after treatment with Examples 1 and 2 (combined treatments), all heavy metal elements strictly complied with GB 5749-2022 requirements: Pb residue decreased to 0.0064 mg / L and 0.0088 mg / L (both ≤0.01 mg / L), Cd residue decreased to 0.0025 mg / L and 0.0010 mg / L (both ≤0.005 mg / L), Fe residue decreased by 31.8%-30.0% compared to the single PAC treatment, and Al residue decreased by 42.6%-48.1%. While Comparative Example 2 (single biomass flocculant) also achieved heavy metal compliance, its turbidity removal efficiency was far lower than that of the compound formulation (data in Table 1). These results demonstrate that the compound formulation of this invention not only achieves deep turbidity removal but also removes pre-existing heavy metals from the water body through the adsorption of biomass flocculants, inhibits the leaching of impurities from PAC, and completely eliminates secondary pollution. This provides a triple guarantee for drinking water treatment: "highly efficient turbidity removal + heavy metal purification + low residual aluminum," significantly enhancing the application value and market competitiveness of the technology.

[0091] Scanning electron microscopy analysis

[0092] A biomass flocculant prepared by the above method is a brownish-red insoluble solid powder, but it can form a stable dispersion system in water, ensuring full flocculation activity. Scanning electron microscopy (SEM) reveals that this biomass flocculant exhibits a porous network structure with abundant pore channels and a high specific surface area (e.g., ...). Figure 1 As shown in Table 1, this structure facilitates the adsorption of suspended particles, colloids, and heavy metal ions in water, providing structural support for improving the turbidity removal efficiency and heavy metal purification capacity of the compound system. Combined with the data in Table 1, this structure enhances the compound's turbidity removal efficiency and heavy metal adsorption capacity, which is highly consistent with the morphology of ideal adsorption materials. This hierarchical porous feature originates from the cross-linking effect of the natural fibrous network of alkaline lignin and chitosan quaternary ammonium salt, providing ample space for pollutant adsorption.

[0093] Infrared spectroscopy analysis

[0094] Infrared spectroscopy analysis showed that FTIR spectroscopy (FTIR) Figure 2 ) at 3420 cm -A broad peak appears at ¹, attributed to the stretching vibrations of OH and NH, confirming that the modified chitosan retains its amino groups and the hydroxyl groups of lignin; 2920 cm⁻¹ - ¹ and 2850 cm - The absorption peak ¹ corresponds to the asymmetric and symmetric stretching vibrations of CH, confirming the retention of the chitosan backbone; 1640 cm⁻¹ - The strong absorption peak at ¹ is due to C=O (amide I band) and CN. + The coupled vibrations of the characteristic peaks of quaternary ammonium salts indicate that the quaternization modification successfully introduced quaternary ammonium groups (-N). + (CH3)3), verifying the effectiveness of the modification reaction and supporting the mechanism of charge density enhancement; 1080 cm - The peak at position ¹ is attributed to the vibration of the COC ether bond, proving that the lignin benzene ring structure was not destroyed, thus ensuring the structural stability required for adsorption bridging. This finding provides direct evidence for the synergistic turbidity removal and heavy metal adsorption mechanism.

[0095] The alkaline lignin-chitosan biomass flocculant prepared in this invention is an insoluble, highly efficient flocculant. By modifying chitosan and alkaline lignin with the quaternizing agent CHPTAC, quaternary ammonium salt cationic groups are introduced into the flocculant, significantly improving charge density and adsorption activity. When used in combination with polyaluminum chloride (PAC), the flocculant disrupts stable colloidal particles through charge neutralization, while its porous structure facilitates adsorption bridging and heavy metal adsorption, promoting the aggregation and sedimentation of micro-flocs. Experimental data confirm that this combination can reduce turbidity from 32 NTU to below 0.465 NTU, decrease residual aluminum content by more than 48%, and ensure that heavy metal content meets the "Standards for Drinking Water Quality" (GB 5749-2022), demonstrating both high efficiency and environmental safety. SEM and FTIR characterization further validated the successful modification and synergistic mechanism of the flocculant's microstructure and chemical structure.

[0096] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. An alkaline lignin-chitosan biomass flocculant, said flocculant being obtained by quaternization reaction of the hydroxyl groups of alkaline lignin and chitosan with quaternary ammonium salts.

2. The alkaline lignin-chitosan biomass flocculant according to claim 1, The pH conditions for the quaternization reaction are pH 4.0-9.0; And / or, the quaternary ammonium salt is 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHPTAC). And / or, the purity of the alkaline lignin is ≥80%, and the hydroxyl content is ≥5.0 mmol / g; And / or, the degree of deacetylation of the chitosan is ≥85%, and the viscosity-average molecular weight is limited to 50,000-200,000 Da.

3. A method for preparing an alkaline lignin-chitosan biomass flocculant, comprising the following steps: (1) Dissolve chitosan in an acid solution to obtain a chitosan solution; (2) Disperse alkaline lignin in water and mix it with the chitosan solution obtained in step (1). Adjust the pH of the mixture and then add the quaternization reagent CHPTAC. React at 50-70°C for 3-6 hours. (3) After the reaction is complete, ethanol is added to precipitate the product. After separation, drying and grinding, biomass flocculant is obtained.

4. The method according to claim 3, The acid solution mentioned in step (1) is an aqueous solution of acetic acid with a volume concentration of 1%-3%; And / or, the mass-to-volume ratio of the chitosan to the acid solution is 1 g: (80-120) mL.

5. The method according to claim 3, The chitosan mentioned in step (1) is chitosan with a degree of deacetylation ≥90% and a viscosity-average molecular weight of 50,000-200,000 Da; And / or, the alkaline lignin described in step (2) has a purity of ≥80% and a hydroxyl content of ≥5.0 mmol / g; And / or, the mass ratio of chitosan to alkaline lignin in step (2) is (2:1) to (1:2); And / or, the pH is adjusted to 4.0-9.0; And / or, the amount of CHPTAC added is: 3-8 mL of 65% weight concentration (w / w) CHPTAC aqueous solution per gram of total mass of chitosan and alkaline lignin.

6. The method according to claim 3, wherein the mass ratio of chitosan to alkaline lignin is 1:1; And / or, the pH is adjusted to 4.5; And / or, the amount of CHPTAC added is: 3 mL of 65% (w / w) CHPTAC aqueous solution per gram of total mass of chitosan and alkaline lignin.

7. An alkaline lignin-chitosan biomass flocculant, prepared by the method described in any one of claims 3-6.

8. Use of the alkaline lignin-chitosan biomass flocculant of claim 1 or the alkaline lignin-chitosan biomass flocculant prepared by the method of any one of claims 3-6, for forming a composite flocculant with PAC.

9. A composite flocculant comprising PAC and the alkaline lignin-chitosan biomass flocculant of claim 1 or the alkaline lignin-chitosan biomass flocculant prepared by any one of claims 3-6.

10. A flocculation treatment method, comprising adding PAC and the alkaline lignin-chitosan biomass flocculant of claim 1 or the alkaline lignin-chitosan biomass flocculant prepared by any one of claims 3-6 to the water to be treated, and stirring; And / or, PAC and the alkaline lignin-chitosan biomass flocculant can be added simultaneously or sequentially; And / or, the PAC is industrial-grade polyaluminum chloride powder (Al2O3 mass fraction ≥28%), with an addition amount of 10-30 mg / L; And / or, the dosage of the biomass flocculant is 3-10 mg / L; And / or, after adding PAC and the biomass flocculant, stir rapidly at a speed of 150-250 rpm for 1-3 minutes, and then stir slowly at 40-80 rpm for 10-20 minutes. And / or, the PAC is industrial-grade polyaluminum chloride powder (Al2O3 mass fraction ≥28%), with an addition amount of 15 mg / L, and the biomass flocculant is added at an addition amount of 5 mg / L.

Images