Preparation process of high-alkalinity wastewater pH self-adaptive polyaluminum chloride modification

Abstract

The application provides a high-alkalinity wastewater pH self-adaptive type polyaluminum chloride modification preparation process and belongs to the technical field of water treatment agents. Through a step-by-step in-situ polymerization process, a basic polyaluminum chloride solution is prepared from hydrochloric acid, aluminum hydroxide and calcium aluminate, then an organic modifier containing a carboxyl-phosphonic acid group, a composite pH buffer component and modified nano magnesium-aluminum hydrotalcite are introduced in sequence, and a pH self-adaptive type modified polyaluminum chloride is obtained through polymerization control. The modified polyaluminum chloride prepared by the application has a salt basicity of 75-90%, and the pH application range is widened to 4-12. The modified polyaluminum chloride can still stably play a coagulation role in high-alkalinity wastewater with pH=10-12 without additional adjustment of the wastewater pH. The removal rate of heavy metal ions such as lead, cadmium and hexavalent chromium is increased by more than 40%, and the alum flower sedimentation speed is increased by more than 35%. The treatment cost and secondary pollution of high-alkalinity wastewater are significantly reduced, and the application is suitable for the treatment of high-alkalinity industrial wastewater such as printing and dyeing, electroplating and chemical industry.

Description

Technical Field

[0001] This invention relates to the field of water treatment agent preparation technology, specifically to a pH-adaptive polyaluminum chloride modification preparation process for high-alkalinity wastewater. Background Technology

[0002] Polyaluminum chloride (PAC) is a widely used inorganic polymeric coagulant with advantages such as rapid flocculation, dense flocs, and good settling performance. It is commonly used in the treatment of drinking water, industrial wastewater, and domestic sewage. However, the pH range suitable for traditional PAC is typically 5.0–9.0. When the wastewater pH is higher than 9.0, PAC undergoes strong hydrolysis, generating a large amount of aluminum hydroxide precipitate, leading to a sharp decline in coagulation effectiveness or even complete failure.

[0003] In the production processes of industries such as printing and dyeing, electroplating, chemicals, and papermaking, large quantities of highly alkaline wastewater are often generated, with pH values ​​typically between 10 and 12. This wastewater also contains high concentrations of suspended solids, organic matter, and heavy metal ions such as lead, cadmium, and hexavalent chromium. Currently, the common practice for treating this type of highly alkaline wastewater is to first add large amounts of acidic substances such as sulfuric acid or hydrochloric acid to adjust the pH to 6-9, followed by the addition of polyaluminum chloride for coagulation. This method of adjusting the pH first and then coagulating not only increases the consumption of acid and alkali reagents and treatment costs but also generates a large amount of saline sludge, causing secondary pollution.

[0004] To address the aforementioned issues, existing technologies attempt to improve the alkalinity adaptability or heavy metal removal capacity of polyaluminum chloride (PAC) through modification. However, most modified products are still prone to precipitation in high-alkalinity environments (pH > 10), and it is difficult to simultaneously achieve wide pH adaptability, high-alkalinity stability, and efficient heavy metal removal. For example, while some modified products can broaden the applicable pH range to some extent, they still require auxiliary pH adjustment in high-alkalinity wastewater or cannot prevent precipitation formation. Other products, although enhancing heavy metal adsorption capacity, suffer from poor stability under high-alkalinity conditions, resulting in a significant decrease in coagulation effectiveness. Therefore, developing a modified PAC that can stably perform coagulation in high-alkalinity environments, requires no additional pH adjustment, and efficiently removes heavy metals is of great significance for simplifying high-alkalinity wastewater treatment processes, reducing treatment costs, and minimizing secondary pollution.

[0005] To address this, a pH-adaptive polyaluminum chloride modification preparation process for high-alkalinity wastewater is proposed. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies, such as easy precipitation and ineffectiveness of traditional polyaluminum chloride in high-alkalinity wastewater, high pH adjustment costs, and low heavy metal removal rates. This invention provides a pH-adaptive polyaluminum chloride modification preparation process for high-alkalinity wastewater. Through a stepwise in-situ polymerization process, this invention grafts highly alkali-resistant carboxyl-phosphonic acid functional groups onto the polyaluminum chloride molecular chain. Simultaneously, it combines a pH-buffering sodium citrate-sodium carbonate system and modified nano-magnesium aluminum hydrotalcite to construct a pH-adaptive coagulation system. This allows the modified polyaluminum chloride to function stably within a wide pH range of 4-12, achieving highly efficient coagulation and heavy metal removal, especially in high-alkalinity wastewater with pH of 10-12, without the need for additional pH adjustment.

[0007] The specific technical solution is as follows: A process for preparing pH-adaptive polyaluminum chloride modified for high-alkalinity wastewater includes the following steps: S1. A basic polyaluminum chloride solution is prepared by mixing hydrochloric acid and aluminum hydroxide for acid hydrolysis, followed by adding calcium aluminate for neutralization and polymerization. S2. Add an organic modifier containing carboxyl-phosphonic acid groups to the basic polyaluminum chloride solution, and carry out an in-situ grafting reaction under stirring conditions. The reaction temperature is 60-90℃, the reaction time is 1-4h, and the grafting rate of the organic modifier is controlled at 10-30%. S3. Add the composite pH buffer component to the reaction solution obtained in step S2, stir and mix evenly for 20-60 minutes. The amount of composite pH buffer component added is 3-10% of the total mass of modified polyaluminum chloride. S4. Add modified nano-magnesium aluminum hydrotalcite to the mixture obtained in step S3, and disperse and compound it under ultrasonic assistance. The ultrasonic power is 200-500W, the ultrasonic time is 30-90min, and the amount of modified nano-magnesium aluminum hydrotalcite added is 2-8% of the total mass of modified polyaluminum chloride. S5. Heat the mixture obtained in step S4 to 75-90℃, maintain the temperature for polymerization for 1-3 hours, then cool it naturally to room temperature and mature for 12-24 hours to obtain pH-adaptive modified polyaluminum chloride for high-alkalinity wastewater.

[0008] The above-mentioned scheme, through step-by-step implementation of organic functional group grafting, pH adaptive system construction, nano-adsorption composite, and polymerization regulation and maturation, makes polyaluminum chloride less prone to hydrolysis and precipitation in high alkalinity environments, while enhancing its binding capacity for pollutants in water, broadening the product's pH applicable range, improving flocculation and sedimentation performance, and simplifying the treatment process for high alkalinity wastewater.

[0009] The above-mentioned pH-adaptive polyaluminum chloride modification process for high-alkalinity wastewater includes the following steps: In step S1, the hydrochloric acid concentration is 20-30%, the mass ratio of aluminum hydroxide to hydrochloric acid is 1:2.5-4.0, the amount of calcium aluminate added is 10-20% of the total mass of the acidolysis reaction solution, the acidolysis reaction temperature is 80-110℃, the reaction time is 2-5 hours, the neutralization polymerization reaction temperature is 70-95℃, the reaction time is 1-3 hours, and the basic polyaluminum chloride solution with a basicity of 60-70% is obtained after pressure filtration. This scheme clearly defines the raw material ratio and reaction conditions in the preparation process of basic polyaluminum chloride, ensuring the stability of the basicity and effective component content of the basic polyaluminum chloride, providing a uniform matrix material for subsequent modification steps, and avoiding the impact of fluctuations in basic raw materials on the quality of the final product.

[0010] The aforementioned pH-adaptive polyaluminum chloride modification process for high-alkalinity wastewater, in step S2, involves an organic modifier containing carboxyl-phosphonic acid groups, which is one or a mixture of aminotrimethylenephosphonic acid, hydroxyethylidene diphosphonic acid, and 2-phosphonobutane-1,2,4-tricarboxylic acid. This method selects specific types of organic modifiers, which can introduce functional groups with high-alkali resistance to the polyaluminum chloride molecular chain, while enhancing the binding capacity for heavy metal pollutants. Different types of modifiers can be flexibly combined to adapt to the treatment needs of different water qualities.

[0011] In the aforementioned pH-adaptive modified polyaluminum chloride preparation process for high-alkalinity wastewater, step S3 involves a composite pH buffer component consisting of a mixture of sodium citrate and sodium carbonate, with a mass ratio of sodium citrate to sodium carbonate of 1:0.5-2.0. By employing a composite buffer component with a specific composition and ratio, the microenvironmental pH around the polyaluminum chloride can be adjusted in high-alkalinity wastewater environments, maintaining the coagulation activity of the product and reducing the use of acid-base regulators during wastewater treatment.

[0012] In the aforementioned pH-adaptive polyaluminum chloride modification preparation process for high-alkalinity wastewater, in step S4, the modified nano-magnesium-aluminum hydrotalcite is a silane coupling agent-modified magnesium-aluminum hydrotalcite with a magnesium to aluminum molar ratio of 2-4:1 and a particle size of 20-100 nm. Controlling the magnesium-aluminum molar ratio and particle size range of the nano-magnesium-aluminum hydrotalcite ensures that the nanomaterials possess good adsorption performance and pH regulation capabilities, while also facilitating uniform dispersion in the polyaluminum chloride system to fully leverage their synergistic effects.

[0013] In the aforementioned pH-adaptive polyaluminum chloride modification process for high-alkalinity wastewater, the silane coupling agent is one or a mixture of two of γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane, and the amount of silane coupling agent added is 1-5% of the mass of nano-magnesium aluminum layered double hydroxide. Modifying nano-magnesium aluminum layered double hydroxide using a specific type and amount of silane coupling agent can improve the compatibility between nanomaterials and polyaluminum chloride, prevent the agglomeration of nanoparticles, and ensure that the adsorption sites on its surface can fully contact pollutants.

[0014] In the above-mentioned pH-adaptive polyaluminum chloride modification preparation process for high-alkalinity wastewater, the modified polyaluminum chloride obtained in step S5 has an alumina mass fraction of 8-12% and a density of 1.15-1.25 g / cm³. 3 The mass fractions of insoluble matter, iron, arsenic, lead, cadmium, mercury, and chromium must be ≤0.005% by mass. This ensures the effective ingredient content, physical properties, and impurity content of the final product, complies with relevant requirements for water treatment chemicals, and avoids the introduction of new pollutants during use.

[0015] This invention also provides a pH-adaptive modified polyaluminum chloride for high-alkalinity wastewater, prepared by the above-described process. The modified polyaluminum chloride has a basicity of 75-90%, a pH of 3.0-4.5 in a 10 g / L aqueous solution, and a pH range of 4-12. The modified polyaluminum chloride prepared by the aforementioned process has suitable basicity and aqueous solution pH, and can stably exert its coagulation effect over a wide pH range. It is particularly suitable for the treatment of high-alkalinity wastewater, eliminating the need for pre-adjustment of the wastewater's pH.

[0016] The aforementioned pH-adaptive modified polyaluminum chloride for high-alkalinity wastewater exhibits the following characteristics: In high-alkalinity wastewater with a pH of 10-12, no aluminum hydroxide precipitate forms after standing for 30 minutes, and the removal rate of lead, cadmium, and hexavalent chromium heavy metal ions is ≥95%. This modified polyaluminum chloride remains stable in high-alkalinity wastewater, does not generate precipitates that affect the treatment effect, and effectively removes heavy metal pollutants from the water, ensuring the quality of the treated effluent.

[0017] This invention also provides an application of pH-adaptive modified polyaluminum chloride (PAC) for treating high-alkalinity industrial wastewater with a pH value of 10-12, and a dosage of 50-300 mg / L of the modified PAC. Applying this modified PAC to the treatment of high-alkalinity industrial wastewater results in a reasonable dosage, simple operation, and effective removal of suspended solids and heavy metal pollutants from the wastewater, thereby reducing the overall cost of wastewater treatment.

[0018] The aforementioned applications include the use of highly alkaline industrial wastewater, encompassing one or more of the following: dyeing and printing wastewater, electroplating wastewater, chemical wastewater, and papermaking black liquor. Clearly defining the specific wastewater types to which this modified polyaluminum chloride is applicable facilitates the appropriate selection of this product for treatment by industries such as dyeing and printing, electroplating, chemicals, and papermaking, based on the characteristics of their generated wastewater.

[0019] The present invention has the following beneficial effects: 1. This invention grafts organic functional groups containing carboxyl-phosphonic acid groups onto the polyaluminum chloride molecular chain. The coordination bond formed between the phosphonic acid group and aluminum ions has a higher bond energy than that between the hydroxyl group and aluminum ions, making it less susceptible to substitution in a high hydroxide ion concentration environment. This avoids the hydrolysis of polyaluminum chloride to form aluminum hydroxide precipitate under high alkalinity. At the same time, the carboxyl and phosphonic acid groups can form stable chelates with heavy metal ions, significantly improving the removal capacity of heavy metal ions such as lead, cadmium, and hexavalent chromium.

[0020] 2. This invention introduces a sodium citrate-sodium carbonate composite pH buffer component, which can regulate the microenvironment pH value in high-alkalinity wastewater through the equilibrium reaction of conjugate acid-base pairs, neutralize the excessively high local hydroxide ion concentration, maintain the microenvironment pH value around polyaluminum chloride within a suitable range, further enhance the stability of modified polyaluminum chloride in high-alkalinity environments, and broaden the product's pH applicable range to 4-12.

[0021] 3. This invention incorporates silane coupling agent-modified nano-magnesium-aluminum hydrotalcite. The nano-magnesium-aluminum hydrotalcite possesses a layered structure and high specific surface area, enabling it to remove heavy metal ions not only through ion exchange and surface adsorption but also exhibiting excellent pH buffering performance. Synergistically, it works with the composite pH buffering component to further enhance the product's pH adaptability. Simultaneously, the silane coupling agent modification improves the compatibility of the nano-magnesium-aluminum hydrotalcite with polyaluminum chloride, preventing nanoparticle aggregation and ensuring sufficient exposure of adsorption sites.

[0022] 4. By optimizing the basicity to 75-90%, this invention improves the extensibility and bridging ability of polyaluminum chloride molecular chains. Combined with the control of polymerization temperature and time, it increases the molecular weight, making the flocs denser, increasing the settling speed by more than 35%, and shortening the residence time of the wastewater treatment unit.

[0023] 5. The modified polyaluminum chloride prepared by this invention does not require additional acid or alkali to adjust the pH when treating high-alkalinity industrial wastewater with pH=10-12, which significantly reduces treatment costs and secondary pollution, and increases the removal rate of heavy metal ions by more than 40%, thus having good economic and environmental benefits. Attached Figure Description

[0024] Figure 1 The flowchart illustrates the pH-adaptive polyaluminum chloride modification preparation process for high-alkalinity wastewater provided in this embodiment of the invention. Detailed Implementation

[0025] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0026] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual images. They should not be construed as limiting the scope of this application. To better illustrate the embodiments of the present invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual dimensions of the product. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0027] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "inner," and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present application. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0028] In the description of this invention, unless otherwise explicitly specified and limited, the term "connection" or similar designation indicating a connection between components should be interpreted broadly. For example, it can refer to a fixed connection, a detachable connection, or an integral part; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can refer to the internal communication between two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances. Example 1

[0029] Reference Figure 1 This embodiment provides a pH-adaptive polyaluminum chloride modification preparation process for high-alkalinity wastewater, including the following steps: Preparation of S1 basic polyaluminum chloride solution: 25% hydrochloric acid and aluminum hydroxide were mixed at a mass ratio of 1:3.0 and acid hydrolysis was carried out at 95°C for 3 hours. After acid hydrolysis, 15% of the total mass of calcium aluminate of the acid hydrolysis reaction solution was added and neutralization polymerization was carried out at 85°C for 2 hours. The basic polyaluminum chloride solution with a basicity of 65% was obtained by pressure filtration. S2 Organic Functional Group Grafting: Aminotrimethylenephosphonic acid was added to the basic polyaluminum chloride solution, and the in-situ grafting reaction was carried out by stirring at 75°C for 2.5 h, with the grafting rate of aminotrimethylenephosphonic acid controlled at 20%. Construction of S3 pH adaptive system: Add a composite pH buffer component consisting of sodium citrate and sodium carbonate mixed in a mass ratio of 1:1 to the reaction solution obtained in step S2, stir and mix for 40 min, the amount of the composite pH buffer component added is 6% of the total mass of modified polyaluminum chloride; S4 Nano-adsorption composite: γ-aminopropyltriethoxysilane-modified nano-magnesium aluminum hydrotalcite was added to the mixture obtained in step S3. The molar ratio of magnesium to aluminum in the nano-magnesium aluminum hydrotalcite was 3:1, the particle size was 50 nm, and the amount of silane coupling agent added was 3% of the mass of the nano-magnesium aluminum hydrotalcite. The mixture was dispersed and composited under ultrasonic power of 350 W for 60 min. The amount of modified nano-magnesium aluminum hydrotalcite added was 5% of the total mass of modified polyaluminum chloride. S5 Polymerization Control and Maturation: The mixture obtained in step S4 is heated to 80℃ and polymerized at this temperature for 2 hours. Then it is naturally cooled to room temperature and matured for 18 hours to obtain pH-adaptive modified polyaluminum chloride for high-alkalinity wastewater.

[0030] In the modified polyaluminum chloride prepared in this embodiment, the mass fraction of alumina is 10%, the density is 1.20 g / cm³, the mass fraction of insoluble matter is 0.2%, the mass fraction of iron is 0.8%, the mass fraction of arsenic is 0.0002%, the mass fraction of lead is 0.001%, the mass fraction of cadmium is 0.0002%, the mass fraction of mercury is 0.00002%, the mass fraction of chromium is 0.002%, the basicity is 82%, and the pH value of a 10 g / L aqueous solution is 3.8. Example 2

[0031] Reference Figure 1 This embodiment provides a pH-adaptive polyaluminum chloride modification preparation process for high-alkalinity wastewater, including the following steps: Preparation of S1 basic polyaluminum chloride solution: 20% hydrochloric acid and aluminum hydroxide were mixed at a mass ratio of 1:2.5 and acid hydrolysis was carried out at 80℃ for 5 hours. After acid hydrolysis, 10% of the total mass of calcium aluminate of the acid hydrolysis reaction solution was added and neutralization polymerization was carried out at 70℃ for 3 hours. The basic polyaluminum chloride solution with a basicity of 60% was obtained by pressure filtration. S2 Organic Functional Group Grafting: Hydroxyethylidene diphosphonic acid was added to the basic polyaluminum chloride solution, and the in-situ grafting reaction was carried out at 60°C with stirring for 4 hours, controlling the grafting rate of hydroxyethylidene diphosphonic acid to be 10%. Construction of S3 pH adaptive system: Add a composite pH buffer component consisting of sodium citrate and sodium carbonate mixed at a mass ratio of 1:0.5 to the reaction solution obtained in step S2, stir and mix for 20 min, the amount of the composite pH buffer component added is 3% of the total mass of modified polyaluminum chloride; S4 Nano-adsorption composite: γ-glycidyl etheroxypropyltrimethoxysilane-modified nano-magnesium aluminum hydrotalcite was added to the mixture obtained in step S3. The molar ratio of magnesium to aluminum in the nano-magnesium aluminum hydrotalcite was 2:1, the particle size was 20 nm, and the amount of silane coupling agent added was 1% of the mass of the nano-magnesium aluminum hydrotalcite. The mixture was dispersed and composited at 200 W ultrasonic power for 90 min. The amount of modified nano-magnesium aluminum hydrotalcite added was 2% of the total mass of modified polyaluminum chloride. S5 Polymerization Control and Maturation: The mixture obtained in step S4 is heated to 75°C and polymerized at this temperature for 3 hours. Then it is naturally cooled to room temperature and matured for 12 hours to obtain pH-adaptive modified polyaluminum chloride for high-alkalinity wastewater.

[0032] In the modified polyaluminum chloride prepared in this embodiment, the mass fraction of alumina is 8%, the density is 1.15 g / cm³, the mass fraction of insoluble matter is 0.25%, the mass fraction of iron is 1.2%, the mass fraction of arsenic is 0.0003%, the mass fraction of lead is 0.0015%, the mass fraction of cadmium is 0.0003%, the mass fraction of mercury is 0.00003%, the mass fraction of chromium is 0.003%, the basicity is 75%, and the pH value of a 10 g / L aqueous solution is 3.0. Example 3

[0033] Reference Figure 1 This embodiment provides a pH-adaptive polyaluminum chloride modification preparation process for high-alkalinity wastewater, including the following steps: Preparation of S1 basic polyaluminum chloride solution: 30% hydrochloric acid and aluminum hydroxide were mixed at a mass ratio of 1:4.0 and acid hydrolysis was carried out at 110℃ for 2 hours. After acid hydrolysis, 20% of the total mass of calcium aluminate of the acid hydrolysis reaction solution was added and neutralization polymerization was carried out at 95℃ for 1 hour. The basic polyaluminum chloride solution with a basicity of 70% was obtained by pressure filtration. S2 Organic Functional Group Grafting: 2-phosphonobutane-1,2,4-tricarboxylic acid was added to the basic polyaluminum chloride solution, and the in-situ grafting reaction was carried out by stirring at 90℃ for 1 h, with the grafting rate of 2-phosphonobutane-1,2,4-tricarboxylic acid controlled at 30%; Construction of S3 pH adaptive system: Add a composite pH buffer component, which is a mixture of sodium citrate and sodium carbonate at a mass ratio of 1:2.0, to the reaction solution obtained in step S2, and stir for 60 min. The amount of composite pH buffer component added is 10% of the total mass of modified polyaluminum chloride. S4 Nano-adsorption Composite: γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane were mixed at a mass ratio of 1:1 to modify nano-magnesium aluminum hydrotalcite. The molar ratio of magnesium to aluminum in the magnesium aluminum hydrotalcite was 4:1, the particle size was 100 nm, and the total amount of silane coupling agent added was 5% of the mass of the nano-magnesium aluminum hydrotalcite. The composite was dispersed and compounded under an ultrasonic power of 500 W for 30 min. The amount of modified nano-magnesium aluminum hydrotalcite added was 8% of the total mass of modified polyaluminum chloride. S5 Polymerization Control and Maturation: The mixture obtained in step S4 is heated to 90°C and polymerized at that temperature for 1 hour. Then it is naturally cooled to room temperature and matured for 24 hours to obtain pH-adaptive modified polyaluminum chloride for high-alkalinity wastewater.

[0034] In the modified polyaluminum chloride prepared in this embodiment, the mass fraction of alumina is 12%, the density is 1.25 g / cm³, the mass fraction of insoluble matter is 0.18%, the mass fraction of iron is 0.5%, the mass fraction of arsenic is 0.0001%, the mass fraction of lead is 0.0008%, the mass fraction of cadmium is 0.0001%, the mass fraction of mercury is 0.00001%, the mass fraction of chromium is 0.001%, the basicity is 90%, and the pH value of a 10 g / L aqueous solution is 4.5.

[0035] Comparative Example 1 This comparative example uses commercially available polyaluminum chloride with an alumina mass fraction of 10%, a basicity of 70%, a pH range of 5.0-9.0, an iron mass fraction of 1.0%, an arsenic mass fraction of 0.0003%, a lead mass fraction of 0.0012%, a cadmium mass fraction of 0.0002%, a mercury mass fraction of 0.00002%, and a chromium mass fraction of 0.002%.

[0036] Comparative Example 2 The difference between this comparative example and Example 1 is that no organic modifier containing carboxyl-phosphonic acid groups was added in step S2; the remaining steps are the same as in Example 1.

[0037] Comparative Example 3 The difference between this comparative example and Example 1 is that no composite pH buffer component was added in step S3, while the remaining steps are the same as in Example 1.

[0038] Comparative Example 4 The difference between this comparative example and Example 1 is that unmodified nano-magnesium aluminum hydrotalcite is added in step S4, while the remaining steps are the same as in Example 1.

[0039] Performance testing Simulated high-alkalinity electroplating wastewater was treated using the products from Examples 1-3 and Comparative Examples 1-4, respectively. The initial pH of the wastewater was 11.0, the suspended solids concentration was 200 mg / L, the lead ion concentration was 10 mg / L, the cadmium ion concentration was 5 mg / L, and the hexavalent chromium ion concentration was 2 mg / L. The dosage of each product was 150 mg / L. The stirring speed was 200 rpm for 2 min, 50 rpm for 10 min, and then allowed to settle for 30 min. The various parameters of the supernatant were measured, and the results are as follows: Example 1: The pH of the supernatant was 8.2, the removal rate of suspended solids was 98.5%, the removal rate of lead ions was 97.2%, the removal rate of cadmium ions was 96.8%, the removal rate of hexavalent chromium was 95.5%, the settling velocity of floc was 1.8 m / h, and no precipitate was formed.

[0040] Example 2: The pH of the supernatant was 8.5, the removal rate of suspended solids was 97.8%, the removal rate of lead ions was 95.6%, the removal rate of cadmium ions was 95.1%, the removal rate of hexavalent chromium was 94.2%, the settling velocity of floc was 1.6 m / h, and no precipitate was formed.

[0041] Example 3: The pH of the supernatant was 8.0, the removal rate of suspended solids was 98.9%, the removal rate of lead ions was 98.1%, the removal rate of cadmium ions was 97.5%, the removal rate of hexavalent chromium was 96.3%, the settling velocity of floc was 1.9 m / h, and no precipitate was formed.

[0042] Comparative Example 1: The pH of the supernatant was 10.8, the removal rate of suspended solids was 42.3%, the removal rate of lead ions was 35.7%, the removal rate of cadmium ions was 32.4%, the removal rate of hexavalent chromium was 28.6%, the settling velocity of floc was 0.7 m / h, and a large amount of white precipitate was generated.

[0043] Comparative Example 2: The pH of the supernatant was 9.1, the removal rate of suspended solids was 85.6%, the removal rate of lead ions was 68.3%, the removal rate of cadmium ions was 65.7%, the removal rate of hexavalent chromium was 62.1%, the settling velocity of floc was 1.2 m / h, and a small amount of white precipitate was generated.

[0044] Comparative Example 3: The pH of the supernatant was 10.2, the removal rate of suspended solids was 78.2%, the removal rate of lead ions was 72.5%, the removal rate of cadmium ions was 69.8%, the removal rate of hexavalent chromium was 66.4%, the settling velocity of floc was 1.1 m / h, and a small amount of white precipitate was generated.

[0045] Comparative Example 4: The pH of the supernatant was 8.4, the removal rate of suspended solids was 92.7%, the removal rate of lead ions was 89.4%, the removal rate of cadmium ions was 87.6%, the removal rate of hexavalent chromium was 85.3%, the settling velocity of floc was 1.4 m / h, and no precipitate was formed.

[0046] The test results show that the modified polyaluminum chloride prepared in Examples 1-3 of this invention did not produce aluminum hydroxide precipitate in high-alkalinity wastewater with pH=11.0. The removal rates of suspended solids and heavy metal ions were significantly higher than those in Comparative Examples 1-4, and the floc settling speed was also significantly faster. In Comparative Example 1, ordinary polyaluminum chloride produced a large amount of precipitate under high alkalinity, resulting in extremely poor treatment performance. Comparative Example 2, without grafted organic functional groups, showed a significant decrease in heavy metal removal rate and the formation of a small amount of precipitate. Comparative Example 3, without the addition of a composite pH buffer component, experienced decreased stability and reduced treatment performance. Comparative Example 4, using unmodified nano-magnesium aluminum hydrotalcite, also showed a decrease in treatment performance due to insufficient exposure of adsorption sites caused by nanoparticle aggregation. This fully demonstrates that this invention, through the synergistic effect of grafted organic functional groups, composite pH buffer components, and modified nano-magnesium aluminum hydrotalcite, achieves pH self-adaptation and efficient heavy metal removal of polyaluminum chloride in high-alkalinity wastewater, representing a significant technological advancement. It is worth noting that the optimal dosage of modified polyaluminum chloride in this application was determined by the following formula: ; In the formula: D represents the optimal dosage of modified polyaluminum chloride, expressed in mg / L. α is the heavy metal chelation coefficient, which is dimensionless and ranges from 0.8 to 1.2. This represents the total concentration of heavy metal ions in the wastewater, expressed in mg / L. G represents the grafting rate of the organic modifier in the modified polyaluminum chloride, expressed as a mass fraction, with a value ranging from 10% to 30%. β is the pH buffer coefficient, with units of mg / L and a value range of 0.2-0.3 mg / L; The initial pH value of the wastewater, ranging from 10 to 12; B represents the content (mass fraction) of the composite pH buffer component in the modified polyaluminum chloride, with a value ranging from 3% to 10%. γ is the flocculation coefficient of suspended solids, which is dimensionless and ranges from 0.3 to 0.7. This represents the concentration of suspended solids in the wastewater, expressed in mg / L. k is the synergistic effect coefficient, which is dimensionless and ranges from 1.2 to 1.8. When substituting the grafting rate G of the organic modifier and the content B of the composite pH buffer component into the formula, decimal form must be used.

[0047] Example: Taking the modified polyaluminum chloride prepared in Example 1 as an example for treating simulated high-alkalinity electroplating wastewater: Product parameters: Organic modifier grafting rate G=20%=0.2, composite pH buffer component content B=6%=0.06; Wastewater parameters: initial pH 0 = 11.0, total heavy metal concentration =17 mg / L (lead 10 mg / L + cadmium 5 mg / L + hexavalent chromium 2 mg / L), suspended solids concentration =200mg / L; Coefficient values: Based on the product formulation and wastewater type, α=1.0, β=0.25mg / L, γ=0.5, k=1.5 are selected; Substitute into the formula to calculate:

[0048]

[0049]

[0050] Field application: Considering the fluctuations in the quality of industrial wastewater, a 15% margin was added to the theoretical calculation value as a safety margin, and the final dosage was determined to be 150 mg / L, which is consistent with the actual dosage in Example 1. After treatment, all indicators of the effluent met the discharge standards.

[0051] Technical Effects: This equation quantitatively correlates the content of the three modified components unique to this invention with wastewater quality parameters, enabling precise calculation of the optimal dosage for treating high-alkalinity wastewater. It avoids the blindness of traditional experience-based dosage methods, preventing both insufficient dosage leading to substandard treatment results and excessive dosage causing reagent waste and secondary pollution. Furthermore, it allows for dynamic adjustment of the dosage based on component differences between different batches of the product, ensuring the stability and consistency of treatment effects and reducing the operating costs and operational difficulty of high-alkalinity wastewater treatment.

[0052] Working principle and process: 1. Wastewater quality testing: Continuously collect water samples at the inlet of the wastewater treatment system and measure the initial pH value, suspended solids concentration and total heavy metal concentration of the wastewater in real time.

[0053] 2. Product parameter acquisition: Extract two key parameters, namely the grafting rate of organic modifier and the content of composite pH buffer component, from the factory quality inspection report of the modified polyaluminum chloride used.

[0054] 3. Coefficient Determination: Based on the specific formulation of the product used and the industry type of the wastewater, select the corresponding heavy metal chelation coefficient, pH buffer coefficient, suspended solids flocculation coefficient, and synergistic effect coefficient.

[0055] 4. Calculation of theoretical dosage: Substitute the water quality parameters and product parameters obtained from the above tests into the formula for calculating the optimal dosage, and the theoretical optimal dosage will be automatically calculated.

[0056] 5. Small-scale test: Conduct a small-scale beaker test with a dosage 5-10% above or below the theoretical dosage to verify the treatment effect and fine-tune the dosage.

[0057] 6. Automatic dosing control: The determined optimal dosage is input into the automatic dosing system, and the dosage of modified polyaluminum chloride is precisely controlled by the metering pump to achieve continuous and stable coagulation treatment.

[0058] The above are merely preferred embodiments of the present invention and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should recognize that any equivalent substitutions and obvious changes made based on the description and illustrations of the present invention should be included within the protection scope of the present invention.

Claims

1. A pH-adaptive polyaluminum chloride modification preparation process for high-alkalinity wastewater, characterized in that, Includes the following steps: S1. A basic polyaluminum chloride solution is prepared by mixing hydrochloric acid and aluminum hydroxide for acid hydrolysis, followed by adding calcium aluminate for neutralization and polymerization. S2. Add an organic modifier containing carboxyl-phosphonic acid groups to the basic polyaluminum chloride solution, and carry out an in-situ grafting reaction under stirring conditions. The reaction temperature is 60-90℃, the reaction time is 1-4h, and the grafting rate of the organic modifier is controlled at 10-30%. S3. Add the composite pH buffer component to the reaction solution obtained in step S2, stir and mix evenly for 20-60 minutes. The amount of composite pH buffer component added is 3-10% of the total mass of modified polyaluminum chloride. S4. Add modified nano-magnesium aluminum hydrotalcite to the mixture obtained in step S3, and disperse and compound it under ultrasonic assistance. The ultrasonic power is 200-500W, the ultrasonic time is 30-90min, and the amount of modified nano-magnesium aluminum hydrotalcite added is 2-8% of the total mass of modified polyaluminum chloride. S5. Heat the mixture obtained in step S4 to 75-90℃, maintain the temperature for polymerization for 1-3 hours, then cool it naturally to room temperature and mature for 12-24 hours to obtain pH-adaptive modified polyaluminum chloride for high-alkalinity wastewater.

2. The preparation process for pH-adaptive polyaluminum chloride modification of high-alkalinity wastewater according to claim 1, characterized in that, In step S1, the mass concentration of hydrochloric acid is 20-30%, the mass ratio of aluminum hydroxide to hydrochloric acid is 1:2.5-4.0, the amount of calcium aluminate added is 10-20% of the total mass of the acid hydrolysis reaction solution, the acid hydrolysis reaction temperature is 80-110℃, the reaction time is 2-5h, the neutralization polymerization reaction temperature is 70-95℃, the reaction time is 1-3h, and the basic polyaluminum chloride solution with a basicity of 60-70% is obtained by pressure filtration.

3. The preparation process for pH-adaptive polyaluminum chloride modification of high-alkalinity wastewater according to claim 1, characterized in that, In step S2, the organic modifier containing carboxyl-phosphonic acid groups is one or a mixture of aminotrimethylene phosphonic acid, hydroxyethylidene diphosphonic acid, and 2-phosphonobutane-1,2,4-tricarboxylic acid.

4. The preparation process for pH-adaptive polyaluminum chloride modification of high-alkalinity wastewater according to claim 1, characterized in that, In step S3, the composite pH buffer component is a mixture of sodium citrate and sodium carbonate, with a mass ratio of sodium citrate to sodium carbonate of 1:0.5-2.

0.

5. The preparation process for pH-adaptive polyaluminum chloride modification of high-alkalinity wastewater according to claim 1, characterized in that, In step S4, the modified nano-magnesium-aluminum hydrotalcite is a silane coupling agent modified magnesium-aluminum hydrotalcite with a magnesium to aluminum molar ratio of 2-4:1 and a particle size of 20-100 nm.

6. The preparation process for pH-adaptive polyaluminum chloride modification of high-alkalinity wastewater according to claim 5, characterized in that, The silane coupling agent is one or a mixture of two of γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane, and the amount of silane coupling agent added is 1-5% of the mass of nano-magnesium aluminum hydrotalcite.

7. The preparation process for pH-adaptive polyaluminum chloride modification of high-alkalinity wastewater according to claim 1, characterized in that, The modified polyaluminum chloride obtained in step S5 has an alumina mass fraction of 8-12%, a density of 1.15-1.25 g / cm³, an insoluble matter mass fraction of ≤0.3%, an iron mass fraction of ≤1.5%, an arsenic mass fraction of ≤0.0005%, a lead mass fraction of ≤0.002%, a cadmium mass fraction of ≤0.0005%, a mercury mass fraction of ≤0.00005%, and a chromium mass fraction of ≤0.005%.

8. A pH-adaptive modified polyaluminum chloride for high-alkalinity wastewater, characterized in that, The modified polyaluminum chloride is prepared by the preparation process described in any one of claims 1-7, wherein the basicity is 75-90%, the pH value of the 10 g / L aqueous solution is 3.0-4.5, and the applicable pH range is 4-12.

9. The pH-adaptive modified polyaluminum chloride for high-alkalinity wastewater according to claim 8, characterized in that, The modified polyaluminum chloride, after standing for 30 minutes in highly alkaline wastewater with pH=10-12, showed no aluminum hydroxide precipitate formation and a removal rate of ≥95% for lead, cadmium, and hexavalent chromium heavy metal ions.

10. The application of the pH-adaptive modified polyaluminum chloride for high-alkalinity wastewater as described in claim 8 in the treatment of high-alkalinity industrial wastewater, characterized in that... The pH value of the high-alkalinity industrial wastewater is 10-12, and the dosage of modified polyaluminum chloride is 50-300 mg / L.

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