Method for preparing high-performance polyaluminum chloride water purifying agent through waste acid-polymerization coupling

Abstract

The invention belongs to the field of preparation of water treatment chemicals, particularly relates to a method for preparing a high-performance polyaluminum chloride water purifying agent through waste acid-polymerization coupling, and aims at solving the problems that a product is unstable, the impurity content is high, and the waste residue amount is large. The method comprises the following steps: performing oxidation impurity removal pretreatment on industrial waste hydrochloric acid; synthesizing a polyaluminum chloride solution in a medium polymerization state aluminum form as a seed crystal by adopting an aluminum source raw material under the condition of controlling proper basicity; mixing the pretreated waste acid with medium-polymerization-state aluminum seed crystals, pumping the mixture into an inorganic ceramic membrane coupling reactor for polymerization reaction, and promoting the hydrolytic polymerization reaction balance of aluminum to move towards the direction of generating high-polymerization-degree aluminum seeds through the separation effect of a ceramic membrane; after the reaction is completed, the solution is purified and separated through a nanofiltration membrane system, the intercepted liquid is the high-performance polyaluminum chloride water purifying agent, and the permeated liquid is a salt solution containing sodium chloride and the like which can be recycled. The method fully utilizes industrial waste acid to prepare polyaluminum chloride, and has obvious environmental protection benefits and application values.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of water treatment chemicals, and particularly relates to a method for preparing high-performance polyaluminum chloride water purifying agent through waste acid-polymerization coupling. BACKGROUND

[0002] Polyaluminum chloride is a water-soluble inorganic polymer flocculant between AlCl3 and Al(OH)3, which is widely used as a high-efficiency coagulant in water treatment, and has the advantages of fast alum flower formation, fast sedimentation speed, wide applicable pH range, small corrosion, etc. The coagulation performance of polyaluminum chloride is closely related to the internal aluminum form distribution, and the aluminum form is usually divided into monomer or oligomeric aluminum, medium polymerization state aluminum and high polymerization state aluminum. Among them, the medium polymerization state aluminum form is considered to be the most active component in polyaluminum chloride due to its high positive charge and stability. Studies have shown that polyaluminum chloride containing higher medium polymerization state aluminum content and higher salt base degree often has better water purification performance. However, different production processes will cause great differences in the content of alumina, salt base degree and impurity level of polyaluminum chloride products, which will affect the stability of product quality and use effect. For example, the composition of waste acid for corrosion foil is complex, and may contain a small amount of impurities and trace amounts of organic additives, which will interfere with the hydrolysis-polymerization path of aluminum and ultimately affect the product purity, color and coagulation effect. The traditional production methods of polyaluminum chloride mainly include neutralization method, electrochemical method, etc., such as directly reacting aluminum ash, calcium aluminate or aluminum hydroxide with acid to prepare polyaluminum chloride, such as patent CN106745602A discloses a method for preparing polyaluminum chloride using waste acid and aluminum salt waste liquid, extracting organic matter with dichloromethane, adding calcium aluminate powder to react, and adjusting the aluminum content, salt base degree and pH value by adding water. However, for direct acid dissolution-neutralization method, especially when industrial by-product waste acid is used as raw material, the following problems often exist: 1. Slow reaction rate, long maturation period; 2. Sensitive to fluctuations in raw material composition, low medium polymerization state aluminum content in the product and poor batch stability; 3. Incomplete aluminum dissolution, producing a large amount of waste slag containing iron, silicon and other impurities; 4. Cl - All of the Cl in the waste acid is finally left in the product, resulting in high salt content of the product, which limits its application in sensitive water areas.

[0003] Therefore, how to effectively utilize industrial waste acid resources while improving the purity and performance of polyaluminum chloride products and reducing by-product solid waste is a technical problem to be solved in the field. SUMMARY

[0004] The present application aims to overcome the deficiencies of the prior art, and provide a method for preparing high-performance polyaluminum chloride water purifying agent by waste acid-polymerization coupling. The method is aimed at the problems of unstable product quality, high impurity content and large amount of waste residue in the traditional process. The method proposes steps such as impurity removal by pretreatment, seed-guided polymerization, and membrane coupling reaction and separation, fully utilizes industrial waste acid to prepare polyaluminum chloride water purifying agent with high purity and high and medium polymerization state aluminum content, and realizes resource utilization and efficient clean production of industrial waste acid.

[0005] A method for preparing high-performance polyaluminum chloride water purifying agent by waste acid-polymerization coupling, the specific technical solutions are as follows: S1: 95-105 parts of industrial by-product waste hydrochloric acid are taken, impurities are removed by microfiltration, then 0.5-1 parts of 30% hydrogen peroxide solution is added dropwise under stirring, the temperature is controlled to be not more than 40℃, the reaction is carried out for 30 minutes, and the solution is statically placed for 1 hour. The filtered precipitate is obtained by using a sand filter, and a clear waste acid solution after pretreatment is obtained; Further, the microfiltration for removing impurities in step S1 is specifically using a ceramic microfiltration membrane with a pore size of 0.1 μm to remove suspended impurities.

[0006] S2: 45-55 parts of 25% hydrochloric acid solution are added to a reaction kettle, the temperature is raised to 70℃, and 10-20 parts of aluminum hydroxide is added in batches. After all the aluminum hydroxide is added, the stirring reaction is continued for 1 hour, and then the alkalinity is controlled to prepare a polyaluminum chloride seed solution; Further, the batch addition in step S2 is specifically adding Al(OH)3 in 5 times, stirring and dissolving for 10 minutes after each addition, and then adding the next time.

[0007] Further, the alkalinity control in step S2 is specifically adding sodium bicarbonate solution to control the alkalinity of the system to 2.0.

[0008] S3: 90-100 parts of the pretreated waste acid solution prepared in step S1 and 18-22 parts of the polyaluminum chloride seed solution prepared in step S2 are added to the reaction tank of the membrane reactor, the temperature is raised to 80-95℃, and the ceramic membrane circulating pump is started. Then 48-52 parts of aluminum source is added, and then the pressure is applied and the temperature is raised, and the stirring reaction is continued for 1 hour, and then the product is filtered and cooled to room temperature to prepare a polyaluminum chloride crude product solution; Further, the ceramic membrane circulating pump in step S3 is made of α-Al2O3 with a pore size of 50 nm.

[0009] Further, the aluminum source in step S3 is aluminum hydroxide powder.

[0010] Further, the pressure application and temperature raising in step S3 are specifically applying a transmembrane pressure of 0.1-0.3 MPa on the membrane side, and the reaction temperature is 80-95℃.

[0011] S4: The polyaluminum chloride crude product solution prepared in step S3 is purified by using an organic nanofiltration membrane assembly, and the polyaluminum chloride crude product solution is subjected to cross-flow filtration by using a nanofiltration membrane to obtain a retentate and a permeate; the retentate is a high-performance polyaluminum chloride water purifying agent of the application; the permeate contains NaCl and CaCl2, and industrial salt is obtained by evaporation and concentration, so that the by-product salt is recovered.

[0012] Further, the nanofiltration membrane in step S4 has a molecular weight cut-off of 200-400 Da.

[0013] Further, the cross-flow filtration in step S4 is set at a pressure of 0.4-0.6 MPa.

[0014] Compared with the prior art, the application has the following beneficial effects: (1) The application uses waste acid as raw material to reduce pollution, converts hazardous waste into a water treatment product, and avoids the harm of direct disposal of waste acid to the environment.

[0015] (2) The application significantly improves the proportion of medium polymerization state aluminum in the polyaluminum chloride by using seed guiding and membrane coupling to strengthen polymerization, thereby significantly improving the product purity; after pre-oxidation and nanofiltration purification, the product has low impurity ion content and few insoluble substances, and has good stability.

[0016] (3) The method filters out a small amount of impurities in the pretreatment stage, and no large amount of hydroxide precipitate is generated in the reaction process, so that the aluminum conversion rate is high; the nanofiltration separation produces a recyclable salt solution, and there is no need to treat solid waste, thereby significantly reducing the solid waste treatment cost.

[0017] (4) The application realizes semi-continuous or continuous production by using a ceramic membrane to couple the reaction and the continuous separation process, and the energy utilization is more efficient compared with the traditional long-time heating and curing process; the membrane assembly has long corrosion-resistant service life, and the overall process is safe and controllable. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 The figure is a preparation process flow chart of the application of a waste acid-polymerization coupled preparation of a high-performance polyaluminum chloride water purifying agent.

[0019] Figure 2 The figure is an absorbance curve graph of Examples 1-3 and Comparative Examples 1-2.

[0020] Figure 3 The figure is a comparison graph of salt base test results of Examples 1-3 and Comparative Examples 1-2.

[0021] Figure 4A comparison chart of the test results of the proportion of medium polymerization state aluminum in the total aluminum and the test results of the alumina content in Examples 1-3 and Comparative Examples 1-2 is shown in FIG. 1. DETAILED DESCRIPTION

[0022] The following examples further explain and illustrate the technical solutions of the present application. It is particularly pointed out that each specific embodiment is a specific embodiment and explanation of the technical solutions, and should not be regarded as a limitation on the protection scope of the present application. Those skilled in the art still have the right to modify the technical solutions of these examples, to make equivalent replacements to some or all of the technical features, and these modifications or replacements do not change the essence of the corresponding technical solutions, and do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions described in the present application. As shown in the accompanying drawings, Figure 1 The preparation process flow of the preparation of high-performance polyaluminum chloride water purifying agent by waste acid-polymerization coupling is shown in FIG. 1, and the detailed preparation steps are as follows: 1. Waste acid pretreatment First, the industrial waste acid is subjected to oxidation-filtration pretreatment. The waste acid is a by-product waste hydrochloric acid solution generated in the industrial process. The suspended solid particles in the waste hydrochloric acid are removed, and then hydrogen peroxide solution is added to oxidize the waste acid. The divalent iron ions are oxidized to trivalent iron ions. The temperature is controlled during the oxidation process, and the divalent iron ions are fully converted to trivalent iron ions by stirring for a certain period of time. Through this oxidation pretreatment, the divalent iron ions in the waste acid are converted to trivalent iron ions, avoiding the interference of divalent iron on the polymerization state of aluminum in the subsequent reaction; at the same time, the oxidation of hydrogen peroxide can also decompose a small amount of organic impurities that may be contained in the waste acid, improving the purity of the raw material acid. A small amount of precipitate is generated after pretreatment, which is filtered to remove and obtain a clear pretreated acid solution.

[0023] 2. Preparation of medium polymerization state aluminum seed A polyaluminum chloride solution seed rich in medium polymerization state aluminum form is prepared by using aluminum source raw material and acid agent under the condition of controlling the degree of alkalization. The aluminum source raw material can be aluminum hydroxide powder; the acid agent is selected from high-purity hydrochloric acid solution, which can be diluted and purified after pretreatment of part of the waste acid or industrial synthesis hydrochloric acid to reduce the introduction of impurities. A certain amount of aluminum source raw material is added to the acid agent to generate a pre-polymerization aluminum chloride solution with a medium polymerization state aluminum form. Specifically, high-purity hydrochloric acid is prepared into a solution of a certain concentration, heated and placed in a reaction container; then aluminum hydroxide powder is added to the acid solution, and the reaction is carried out under stirring to partially dissolve and hydrolysis polymerization. After the aluminum source is added, continue to heat and stir for a certain period of time to fully react, and then add sodium bicarbonate solution to control the alkalization degree of the system. The obtained solution is a polyaluminum chloride seed solution rich in medium polymerization degree aluminum seed.

[0024] The seed solution has high content of medium polymerization state aluminum and less impurity ions, and can induce the aluminum polymerization in the waste acid system to the direction of medium polymerization state aluminum as the "seed" of the subsequent main reaction. Meanwhile, the seed solution itself is also a high-efficiency flocculant component, which helps to improve the performance of the final product.

[0025] 3. Membrane-coupled polymerization reaction The pretreated waste acid and the medium polymerization state aluminum seed solution are put into the inorganic ceramic membrane-coupled reactor for the main polymerization reaction. The membrane material of the inorganic ceramic membrane-coupled reactor is acid and alkali resistant α-Al2O3 ceramic, and the average pore size of the membrane is 50 nm. Before the reaction starts, the pretreated waste acid solution can be added to the reactor and heated to the reaction temperature, and then the aluminum source raw material and a certain amount of seed solution are added. During the reaction, the aluminum source continuously dissolves in the acid and reacts with Cl - to generate aluminum hydrolysis products, and under the guidance of the seed, multi-core aluminum polymers are formed. Since the reaction of aluminum source with acid generates water, the accumulation of water will dilute the system, reduce the aluminum concentration and possibly limit the polymerization reaction to high polymerization degree. The present application ingeniously synchronizes the reaction and separation through membrane coupling technology: while the polymerization reaction is taking place, a certain transmembrane pressure is applied to the ceramic membrane, so that the water and part of the low molecular solutes generated during the reaction, such as unreacted free acid and small impurity ions, continuously pass through the membrane and are discharged from the reactor, while the larger size of polymerized aluminum species and undissolved aluminum source particles are retained in the reactor. By continuously removing water, it is equivalent to continuously increasing the concentration of aluminum and the basicity of the reaction solution, promoting the hydrolysis polymerization to continue to generate more medium polymerization state aluminum. At the same time, the retention effect of the membrane makes it almost impossible to lose the aluminum polymerization products during the reaction, ensuring the conversion rate of aluminum. The feeding rate and membrane filtration rate can be appropriately controlled during the reaction to maintain the stability of the liquid level and reactant concentration in the reactor. When the reaction proceeds to the predetermined time or the basicity of the system reaches the target and no longer changes significantly, the aluminum source feeding is stopped and the filtration is continued for a period of time to remove as much excess water as possible. Then stop the pressurized filtration and end the polymerization reaction stage. Through the above membrane-coupled reaction, a polymerized aluminum chloride solution mainly composed of medium polymerization state aluminum can be efficiently obtained without generating insoluble residues.

[0026] 4. Nanofiltration purification The crude polyaluminum chloride product solution from the membrane reactor is purified and separated by a nanofiltration membrane system. The nanofiltration membrane has the characteristics of certain rejection rate to multivalent ions and macromolecules and high permeability to monovalent small ions. A nanofiltration membrane with a molecular weight cut-off of 200-400 Da is used to filter the product at room temperature or under appropriate pressure. The nanofiltration process can use cross-flow filtration to separate the product solution into two parts: the retentate and the permeate. Since the polyaluminum species is positively charged and has a relatively large molecular weight, it is mostly rejected and enriched on the nanofiltration membrane. Small monovalent ions such as Na + 、Cl - are easily permeated into the permeate. Therefore, the main polyaluminum product can be separated from the inorganic impurity salt by nanofiltration. The concentrated solution obtained on the nanofiltration rejection side is a liquid polyaluminum chloride water purifying agent with high purity and high medium polymeric aluminum content. The main component of the dilute salt solution obtained on the permeate side is NaCl, which can be concentrated and crystallized to recover industrial salt, or directly recycled to other production processes, realizing the resource utilization of by-products and not producing secondary pollution.

[0027] Example 1 A method for preparing a high-performance polyaluminum chloride water purifying agent by coupling waste acid and polymerization is prepared as follows: S1: Take 100 parts of industrial by-product waste hydrochloric acid, first remove suspended impurities through a ceramic microfiltration membrane with a pore size of 0.1 μm, then add 0.7 parts of 30% hydrogen peroxide solution under stirring, control the temperature not to exceed 40°C, react for 30 minutes, stand for 1 hour, filter the precipitate with a sand filter to obtain a clear waste acid solution after pretreatment; S2: Add 50 parts of 25% hydrochloric acid solution to the reaction kettle, heat to 70°C, and then add aluminum hydroxide powder in batches, a total of 15 parts of aluminum hydroxide, add in 5 times, after each addition, stir and dissolve for 10 minutes before the next addition, after all the additions are completed, continue to stir for 1 hour, then add sodium bicarbonate solution, control the alkalinity of the system to 2.0, prepare a polyaluminum chloride seed solution; S3: Add 95 parts of the pretreated waste acid solution prepared in step S1 and 20 parts of the polyaluminum chloride seed solution prepared in step S2 to the reaction tank of the membrane reactor, heat to 85°C, start the ceramic membrane circulating pump to make the reaction liquid circulate in the membrane tube. The ceramic membrane material is α-Al2O3 with a pore size of 50 nm; then add 50 parts of aluminum hydroxide powder as the main aluminum source in batches, apply a transmembrane pressure of 0.2 MPa on the membrane side, react at 85°C with continuous stirring for 1 hour to fully polymerize, then stop heating and pressurization filtration, cool to room temperature, and prepare a crude polyaluminum chloride product solution; S4: The polyaluminum chloride crude product solution prepared in step S3 is purified using an organic nanofiltration membrane assembly, the nanofiltration membrane used has a molecular weight cut-off of 3400 Da, the polyaluminum chloride crude product solution is subjected to cross-flow filtration at a pressure of 0.5 MPa to obtain a retentate and a permeate; the retentate is a high-performance polyaluminum chloride water purifying agent of the present application; the permeate mainly contains NaCl and a small amount of CaCl2, and industrial salt can be obtained by evaporation and concentration, thereby realizing the recovery of by-product salt.

[0028] Example 2 The preparation method of Reference Example 1 is referred to, but differs in that: In step S1: 95 parts of industrial by-product waste hydrochloric acid, 0.5 parts of hydrogen peroxide solution; In step S2: 45 parts of hydrochloric acid solution, 10 parts of aluminum hydroxide; In step S3: 900 parts of the pretreated waste acid solution obtained in step S1, 18 parts of seed solution, heating to 80℃, 48 parts of aluminum hydroxide powder; the transmembrane pressure is 0.1 MPa, and the reaction temperature is 80℃; In step S4: the nanofiltration membrane used has a molecular weight cut-off of 200 Da; the pressure for cross-flow filtration is 0.6 MPa.

[0029] Example 3 The preparation method of Reference Example 1 is referred to, but differs in that: In step S1: 105 parts of industrial by-product waste hydrochloric acid, 1 part of hydrogen peroxide solution; In step S2: 55 parts of hydrochloric acid solution, 20 parts of aluminum hydroxide; In step S3: 100 parts of the pretreated waste acid solution obtained in step S1, 22 parts of seed solution, heating to 95℃, 52 parts of aluminum hydroxide powder; the transmembrane pressure is 0.3 MPa, and the reaction temperature is 95℃; In step S4: the nanofiltration membrane used has a molecular weight cut-off of 400 Da; the pressure for cross-flow filtration is 0.4 MPa.

[0030] Comparative Example 1 The preparation method of Reference Example 1 is referred to, but in step S3, no medium polymeric aluminum seed is added, i.e. the operation of step S2 is not performed. The remaining steps are the same.

[0031] Comparative Example 2 The preparation method of Reference Example 1 is referred to, but no membrane coupling is used, and polyaluminum chloride is prepared only by traditional batch reaction, i.e. the operation of step S3 is changed to placing 95 parts of pretreated waste acid in a traditional reaction kettle, heating to 90℃, adding 50 parts of aluminum hydroxide powder, stirring for 2 hours, and then adding 20 parts of medium polymeric aluminum seed solution for reaction to obtain a crude polyaluminum chloride solution. The remaining steps are the same.

[0032] The high-performance polyaluminum chloride water purifying agent was prepared by waste acid-polymer coupling according to examples 1-3 and comparative examples 1-2, and the comprehensive performance was determined. Salt base test: tested according to standard GB / T 22627-2022 "Water treatment agent polyaluminum chloride", the salt base is defined as OH - Molar ratio percentage with aluminum; take 1.0g sample, dissolve with deionized water, use methyl orange as indicator, titrate to endpoint with 0.5mol / L hydrochloric acid standard solution, calculate OH - content; another sample was determined by EDTA titration method to determine the aluminum content, and the salt base was calculated; Medium polymerization state aluminum proportion test: using Ferron time-dependent complexing colorimetry, taking 0.1g sample diluted to 100mL, mixed with 0.2% w / v Ferron reagent, monitoring the change of absorbance with time at 370nm wavelength, calculating the proportion of medium polymerization aluminum; Alumina content test: tested according to standard GB / T 22627-2022 "Water treatment agent polyaluminum chloride", take 1.0g sample, dissolve with nitric acid, add excess EDTA standard solution, titrate back with zinc acetate standard solution, calculate the aluminum content and convert to alumina content.

[0033] Stability test: using industry accelerated storage method, 100mL sample was sealed in a transparent container and stored in a 40°C incubator for 30 days. Observe the precipitation production.

[0034] The specific test comparison results are shown in Table 1, Figure 2 , Figure 3 , Figure 4 Table 1 Comparison of comprehensive performance of examples 1-3 and comparative examples 1-2 From the above comparison results, in comparative example 1, it is shown that without seed guiding, although membrane coupling can still achieve high salt base, the proportion of medium polymerization state aluminum is reduced, which may be because the lack of crystal nucleus induction, the formation path of aluminum polynuclear body is limited, which is significantly lower than the level when using crystal seed, which proves that the medium polymerization state aluminum seed plays a key role in promoting the generation of efficient aluminum form; In comparative example 2, without membrane coupling to remove water, it is difficult to achieve high salt base and medium polymerization state aluminum content while ensuring solution stability, and traditional batch process is prone to produce unreacted residue and precipitation, and the product quality and yield are not good.

[0035] ​From the above examples and comparative tests, it can be seen that the method of the present application significantly improves the quality and performance of the polyaluminum chloride product through the cooperation of each innovative step. Among them, the membrane coupling reaction ensures the stability of the solution under high salt base and the output of high and medium polymeric aluminum content, the introduction of medium polymeric aluminum seed promotes the formation of high-efficiency polymerization form, the impurity removal of pretreatment ensures the product purity, and the nanofiltration purification realizes the effective removal and resource recovery of impurities.

Claims

1. A method for preparing high-performance polyaluminum chloride water purification agent via waste acid-polymerization coupling, comprising pretreatment, polymerization reaction, and purification to obtain the water purification agent, characterized in that, The polymerization reaction is a directional polymerization reaction carried out in a pressurized filter membrane coupled environment with the assistance of the addition of inducing seed crystals; the inducing seed crystals are aluminum seed solutions with a basicity range of 60% to 80%; the pressurized filter membrane coupling is wherein the filter membrane can retain polymerized aluminum species and undissolved aluminum source particles, while water can pass through the filter membrane without being retained.

2. The method for preparing high-performance polyaluminum chloride water purification agent by waste acid-polymerization coupling according to claim 1, characterized in that, Includes the following steps: S1: Take 95-105 parts of industrial by-product hydrochloric acid, remove impurities by microfiltration, then add 0.5-1 part of 30% hydrogen peroxide solution dropwise under stirring, control the temperature not to exceed 40℃, react for 30 minutes, let stand and filter to obtain a pretreated waste acid solution; S2: Add 45-55 parts of 25% hydrochloric acid solution to the reactor, heat to 70°C, add 10-20 parts of aluminum hydroxide in batches, and continue stirring for 1 hour after all the aluminum hydroxide has been added. Then, control the alkalinity to prepare a polyaluminum chloride seed solution. S3: Add 90-100 parts of the pretreated waste acid solution prepared in step S1 and 18-22 parts of the polyaluminum chloride seed solution prepared in step S2 into the reaction vessel of the membrane reactor, heat to 80-95℃, and start the ceramic membrane circulation pump; then add 48-52 parts of aluminum source, apply pressure and heat, and continuously stir the reaction for 1 hour, filter, and cool to room temperature to prepare the crude polyaluminum chloride product solution; S4: The crude polyaluminum chloride product solution prepared in step S3 is purified using an organic nanofiltration membrane module. The crude polyaluminum chloride product solution is subjected to cross-flow filtration to obtain retentate and permeate. The retentate is the high-performance polyaluminum chloride water purifier of this invention. The permeate contains NaCl and CaCl2. It is evaporated and concentrated to obtain industrial salt, thereby realizing the recovery of by-product salt.

3. The method for preparing high-performance polyaluminum chloride water purification agent by waste acid-polymerization coupling according to claim 2, characterized in that, The microfiltration impurity removal mentioned in step S1 specifically involves using a ceramic microfiltration membrane with a pore size of 0.1 μm to remove suspended impurities.

4. The method for preparing high-performance polyaluminum chloride water purification agent by waste acid-polymerization coupling according to claim 2, characterized in that, The batch addition mentioned in step S2 specifically involves adding aluminum hydroxide in 5 separate additions, stirring and reacting for 10 minutes after each addition before adding the next addition.

5. The method for preparing high-performance polyaluminum chloride water purification agent by waste acid-polymerization coupling according to claim 2, characterized in that, The alkalinity control mentioned in step S2 specifically involves adding sodium bicarbonate solution dropwise to control the alkalinity of the system at 2.

0.

6. The method for preparing high-performance polyaluminum chloride water purification agent by waste acid-polymerization coupling according to claim 2, characterized in that, The ceramic membrane circulating pump described in step S3 uses an α-Al2O3 ceramic membrane with a pore size of 50 nm.

7. The method for preparing high-performance polyaluminum chloride water purification agent by waste acid-polymerization coupling according to claim 2, characterized in that, The aluminum source mentioned in step S3 is aluminum hydroxide powder.

8. The method for preparing high-performance polyaluminum chloride water purification agent by waste acid-polymerization coupling according to claim 2, characterized in that, The pressure and temperature increase mentioned in step S3 specifically involves applying a transmembrane pressure of 0.1 to 0.3 MPa to the membrane side, and the reaction temperature is 80 to 95°C.

9. The method for preparing high-performance polyaluminum chloride water purification agent by waste acid-polymerization coupling according to claim 2, characterized in that, The nanofiltration membrane described in step S4 has a molecular weight cutoff of 200–400 Da.

10. The method for preparing high-performance polyaluminum chloride water purification agent by waste acid-polymerization coupling according to claim 2, characterized in that, The cross-flow filtration described in step S4 has its parameters set to a pressure of 0.4–0.6 MPa.

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