Polyaluminum chloride and preparation method and application thereof

Abstract

The present application relates to the technical field of water treatment coagulant, in particular to a kind of polyaluminum chloride and its preparation method and application.The present application is input phosphorus radical donor in the high base polyaluminum chloride base fluid of base degree 90%~95%, and the mass ratio of two is 1: (0.007~0.022), is fully mixed to prepare a kind of polyaluminum chloride.Polyphosphate can match Al 13 、Al 30 Characteristic multi-nuclear hydroxyl aluminum cluster coordination site, with multi-nuclear aluminum cluster as structural unit, with Al-O-P covalent bridge as connecting node, constructs three-dimensional cross-linked stable coordination complex, and then significantly improves the cohesion and shear resistance of flocculation, fundamentally improves the problem of flocculation loose and slow settlement caused by insufficient hydrolysis power at low temperature.Therefore, the polyaluminum chloride prepared by the method can efficiently remove water suspended solids and turbidity, has low reagent dosage and small secondary pollution risk, and is especially suitable for river water purification treatment in winter.

Description

Technical Field

[0001] This application relates to the field of water treatment coagulant technology, and in particular to a polyaluminum chloride, its preparation method and application. Background Technology

[0002] Polyaluminum chloride (PAC), as a highly efficient inorganic polymeric flocculant, is widely used in drinking water purification, industrial wastewater treatment, and urban sewage treatment due to its advantages such as strong charge neutralization ability, rapid floc formation, and wide pH range adaptability. However, when treating river water with low temperature and low turbidity in winter, the performance of traditional PAC faces severe challenges, mainly in the following aspects: (1) Poor low temperature adaptability: The decrease in water temperature leads to a slowdown in the hydrolysis rate of PAC, insufficient generation of hydroxyl complexes, slow and loose floc formation, and decreased sedimentation performance. (2) Low turbidity removal rate: Under low temperature conditions, the zeta potential of colloidal particles tends to be close to a stable state, and the charge neutralization ability of traditional PAC is insufficient, making it difficult to effectively break the colloidal stability. (3) Excessive dosage (>30mg / L): Existing technologies require increasing the dosage to compensate for the weakening of the flocculation effect due to the low temperature effect, which not only significantly increases the operating cost of water treatment, but also easily causes the residual aluminum content in the water to exceed the standard, posing a significant ecological safety hazard.

[0003] To address the aforementioned issues, existing technologies primarily employ two approaches for improvement: first, compounding coagulants to improve floc structure and settling performance, compensating for the loose flocs and slow settling of PAC at low temperatures; and second, increasing the basicity of PAC products (the percentage of OH to Al equivalents in the sample) to increase its hydroxyl complex content and charge neutralization capacity, thereby solving the problems of destabilization difficulties and insufficient charge neutralization at low temperatures, and thus reducing the dosage of the reagent. However, both of these approaches have limitations: while compounding coagulants alone can improve floc structure, at low suspended solids levels, the fine colloidal particles and dissolved organic matter remaining in the water are difficult to capture and remove sufficiently, resulting in unsatisfactory purification effects; while increasing basicity alone can enhance charge neutralization capacity, it is still difficult to efficiently capture fine colloidal particles at low temperatures, limiting the improvement in turbidity removal. For example, Chinese patent application CN116354375A discloses a method for preparing high-basicity (85%-95%) polyaluminum chloride water purifier by polymerization reaction using hydrochloric acid and aluminum hydroxide as raw materials under the action of calcium aluminate powder and calcium carbonate powder. Although this method enhances the charge neutralization capacity by increasing basicity, in actual low-temperature and low-turbidity water applications, the destabilization of colloidal particles and turbidity removal rate still need further improvement. In addition, even if a few technical solutions simply combine two methods, they do not achieve precise matching and synergistic control of basicity and coagulant components, which easily leads to problems such as poor agent compatibility and limited synergistic effect, and still cannot meet the purification requirements of low-temperature and low-turbidity water.

[0004] Therefore, there is an urgent need to develop a new type of polyaluminum chloride that combines high basicity with a suitable compound system to overcome the shortcomings of traditional single or simple combined modification methods, thereby significantly improving its flocculation performance in low-temperature and low-turbidity river water. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the defects and shortcomings of the existing PAC water purification technology under low temperature conditions, which cannot simultaneously achieve low dosage, high efficiency flocculation and high turbidity removal rate, and to provide a method for preparing polyaluminum chloride.

[0006] Another object of the present invention is to provide polyaluminum chloride prepared by the above preparation method.

[0007] Another object of the present invention is to provide the application of the above-mentioned polyaluminum chloride in water purification.

[0008] Another object of the present invention is to provide a water purification agent.

[0009] The above-mentioned objective of this invention is achieved through the following technical solution: This invention protects a method for preparing polyaluminum chloride, comprising the following steps: Add phosphate donor to a high basicity polyaluminum chloride-based solution, mix well, and you will get polyaluminum chloride; The basicity of the high-basicity polyaluminum chloride-based liquid is 90%~95%; The mass ratio of the high basicity polyaluminum chloride-based liquid to the phosphate donor is 1:(0.007~0.022).

[0010] This invention provides a method for preparing polyaluminum chloride, using phosphate donors as coagulation aids and modifiers. Unlike conventional anions that only weakly bind to aluminum species through electrostatic interactions, phosphate can precisely match the Al content in high-basicity polyaluminum chloride. 13 Al 30 The coordination sites of characteristic polynuclear aluminum hydroxyl clusters are used to construct stable three-dimensional cross-linked coordination complexes with polynuclear aluminum clusters as structural units and Al-OP covalent bridges as connecting nodes. This unique cross-linked structure can significantly improve the cohesiveness and shear resistance of flocs, fundamentally improving the problems of loose flocs and slow sedimentation caused by insufficient hydrolysis kinetics at low temperatures. Its synergistic effect is far superior to that of traditional modified anions such as silicates and carbonates. This method effectively overcomes the shortcomings of existing improved technologies. The resulting polyaluminum chloride has excellent removal efficiency of suspended solids in water, requires low dosage, and has a low risk of secondary pollution, making it particularly suitable for the purification of river water at low temperatures in winter.

[0011] Furthermore, the Al2O3 content in the high basicity polyaluminum chloride-based liquid is 10.2%~11.2%.

[0012] In this invention, the determination of Al2O3 content includes the following steps: Weigh out a sample of mass m, transfer it to a 250 mL volumetric flask, dilute to volume, and shake well to prepare the sample solution. Accurately transfer 10 mL of the sample solution to a 250 mL Erlenmeyer flask, accurately add 15 mL of EDTA solution, add 3-4 drops of thymol blue solution, neutralize with ammonia solution until the solution changes from red to yellow (pH around 2.8), and boil for 2 minutes. After cooling, add 10 mL of acetate-sodium acetate buffer solution and 2-4 drops of xylenol orange indicator solution, and titrate with zinc chloride standard solution until the solution changes from pale yellow to slightly red, which is the endpoint. Perform a blank test simultaneously. Calculate the Al2O3 content using the following formula: Al2O3%=[C×(V0-V)×0.05098×25 / m]×100; In the formula, V0 is the volume of zinc chloride standard titration solution consumed in the blank test, in mL; V is the volume of zinc chloride standard titration solution consumed in the determination test, in mL; C is the actual concentration of zinc chloride standard titration solution, in mol / L; and m is the mass of the sample to be tested, in g.

[0013] In this invention, the determination of basicity includes the following steps: Weigh out a sample of mass m, transfer it to a 250 mL volumetric flask, dilute to volume, and shake well to prepare the sample solution. Accurately transfer 10 mL of the sample solution to a beaker, add 50 mL of pure water, add 3-4 drops of phenolphthalein indicator, and immediately titrate with 0.2 mol / L sodium hydroxide standard solution until the solution changes from colorless to slightly pink (the color does not fade within 30 seconds), which is the endpoint. The formula for calculating basicity B% is as follows: B%=[1-(0.017×C1×V1×25 / m×Al2O3%)]×100; In the formula, V1 is the volume of sodium hydroxide standard titration solution consumed in the test, in mL; C1 is the actual concentration of sodium hydroxide standard titration solution, in mol / L; m is the mass of the sample to be tested, in g; and Al2O3% is the Al2O3 content in the sample to be tested, in g.

[0014] Furthermore, the phosphate donor includes one or more of ammonium phosphate, magnesium phosphate, and calcium phosphate.

[0015] Furthermore, the mass ratio of the high basicity polyaluminum chloride-based liquid to the phosphate donor is 1:(0.01~0.02).

[0016] Furthermore, the mixing time is 5 to 30 minutes.

[0017] Furthermore, the mixing process also includes a dilution step.

[0018] Furthermore, the solvent used for dilution is water.

[0019] Preferably, the dilution involves adjusting the Al2O3 content in the polyaluminum chloride to 10.0%, which is a commonly used concentration in the field and facilitates product storage, transportation, and metering.

[0020] Preferably, the mass ratio of water to the mixed reaction solution is 1:(0.5~1.5).

[0021] Furthermore, the Al2O3 content in the polyaluminum chloride is 10%~10.8%.

[0022] The core functions of polyaluminum chloride (PAC), such as flocculation, turbidity removal, and colloid destabilization, are achieved by the active aluminum component in the system. The industry generally uses Al2O3 content as the core indicator of the total effective components of PAC, thus requiring strict control. If the Al2O3 content is too low, the product will lack sufficient effective active components, significantly weakening the flocculation and purification effect. In practical applications, this necessitates increasing the dosage and raising usage costs. Conversely, if the Al2O3 content is too high, it not only wastes raw materials and reduces production economics but also damages the stability of the product system, easily leading to hydrolysis, stratification, and precipitation problems, shortening the product's storage period. Furthermore, excessive aluminum components can cause aluminum residue in the treated water to exceed standards, failing to meet environmental protection requirements. Precise control of the Al2O3 content ensures stable and excellent performance of PAC, maintains consistent batch quality, and adapts to the process requirements of various application conditions.

[0023] Furthermore, the basicity of the polyaluminum chloride is 90%~95%.

[0024] Furthermore, the source of the high basicity polyaluminum chloride-based liquid is not limited; it can be obtained commercially or by self-production.

[0025] Furthermore, as a preferred embodiment, the preparation method of the high basicity polyaluminum chloride-based liquid includes the following steps: S1. A hydrochloric acid solution with a mass ratio of (4.5~5.5):1 and aluminum hydroxide are mixed and reacted to obtain an aluminum chloride solution; S2. Add calcium aluminate to the aluminum chloride solution obtained in step S1, filter after reaction, collect the filtrate, and obtain polyaluminum chloride-based solution; S3. Add calcium carbonate to the polyaluminum chloride base solution obtained in step S2, and control the pH to 2.8~3.2 to carry out the reaction, so as to obtain a high basicity polyaluminum chloride base solution with a basicity of 90%~95%.

[0026] This application controls a suitable high basicity by precisely adjusting the pH to 2.8-3.2. Below pH 2.8, the hydrolysis polymerization reaction is inhibited, making it difficult to generate sufficient amounts of highly active polyaluminum chloride, thus reducing coagulation efficiency. Above pH 3.2, amorphous Al(OH)3 colloids are easily formed, encapsulating and deactivating the active components, leading to product failure. This defined range enhances charge neutralization capacity while avoiding the drawbacks of decreased product stability and increased aluminum residue caused by simply increasing basicity.

[0027] Furthermore, the hydrochloric acid solution contains 29% to 31% hydrogen chloride by mass.

[0028] Furthermore, the Al2O3 content in the aluminum hydroxide is not less than 64%.

[0029] Furthermore, in step S1, the reaction temperature is 90~110 ℃.

[0030] Furthermore, in step S1, the reaction time is 2-4 hours.

[0031] Furthermore, in step S1, the reaction step also includes dilution.

[0032] Furthermore, the dilution is achieved by diluting the reaction solution with water.

[0033] Preferably, the volume ratio of water to reaction solution is 1:(2~6).

[0034] Furthermore, the Al2O3 content in the aluminum chloride solution is 5.0%~7.0%.

[0035] Furthermore, the basicity of the aluminum chloride solution is -20% to -5%. This negative basicity is due to the excess hydrochloric acid in the system: basicity is used to characterize the ratio of aluminum ions to hydroxyl groups; when there is excess hydrochloric acid in the aluminum chloride solution, the hydrolysis of aluminum ions is completely inhibited, there are no effective hydroxyl groups in the system and a large number of free hydrogen ions are enriched. According to the calculation rules of aluminum salt basicity, excess free acid is equivalent to negative hydroxyl groups, and the final calculated basicity is negative.

[0036] Furthermore, the formula for calculating the amount of calcium aluminate powder added, y (tons), is as follows: y = v1 × r1 × a1 × x / a2; Where, x = (n1 - n2) / (n2 + 2m); n1 = 6 × (1 - B1); n2 = 6 × (1 - B2); In the above formula, v1 is the volume of the aluminum chloride solution in mL; r1 is the specific gravity (density) of the aluminum chloride solution in g / mL; a1 is the Al2O3 content in the aluminum chloride solution in %; B1 is the true basicity of the aluminum chloride solution in %; B2 is the required basicity after the reaction with added calcium aluminate powder in %; a2 is the Al2O3 content simulated by calcium aluminate powder in %; and m is the dissolution rate of calcium aluminate powder in %.

[0037] Furthermore, in step S2, the reaction temperature is 90~110 ℃.

[0038] Furthermore, in step S2, the reaction time is 0.5 to 2 hours.

[0039] Furthermore, as a preferred method, the filtration is performed using a vacuum filter press or a plate and frame filter press.

[0040] Furthermore, the Al2O3 content in the polyaluminum chloride-based liquid is 10%~12%.

[0041] Furthermore, the basicity of the polyaluminum chloride-based liquid is 50% to 70%.

[0042] Furthermore, the formula for calculating the amount M of calcium carbonate added is as follows: M=0.49×N×A×[6×(B2-B1) / ω]; In the formula: M is the mass of calcium carbonate, in g; N is the mass of polyaluminum chloride base solution, in g; A is the Al2O3 content in polyaluminum chloride, in %; B1 is the basicity of polyaluminum chloride base solution, in %; B2 is the basicity of high-basicity polyaluminum chloride, in %; ω is the calcium carbonate content, in %.

[0043] In this invention, pH can specifically be 2.8, 2.9, 3.0, 3.1, 3.2, etc., or any specific point value between the above values, or any range of these values.

[0044] Furthermore, in step S3, the reaction temperature is 90~110 ℃.

[0045] Furthermore, in step S3, the reaction time is 0.5 to 2 hours.

[0046] This invention protects the polyaluminum chloride prepared by the aforementioned preparation method.

[0047] This invention protects the aforementioned application of polyaluminum chloride in water purification.

[0048] This invention protects a water purification agent, which includes the aforementioned polyaluminum chloride.

[0049] Furthermore, the mass concentration of the polyaluminum chloride is 18~30 mg / L.

[0050] Furthermore, the mass concentration of the polyaluminum chloride is 20~25 mg / L.

[0051] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a method for preparing polyaluminum chloride (PAC). A phosphate donor is added to a high-basicity PAC-based liquid with a basicity of 90%–95% at a mass ratio of 1:(0.007–0.022), and the mixture is homogenized to obtain PAC. The phosphate donor precisely matches the Al content in the high-basicity PAC. 13 Al 30 The coordination sites of characteristic polynuclear aluminum hydroxyl clusters are used to construct stable three-dimensional cross-linked coordination complexes with polynuclear aluminum clusters as structural units and Al-OP covalent bridges as connecting nodes. This unique cross-linking structure can significantly improve the cohesiveness and shear resistance of flocs, fundamentally improving the problem of loose flocs and slow sedimentation caused by insufficient hydrolysis kinetics at low temperatures. As a result, the obtained polyaluminum chloride can efficiently remove suspended solids and turbidity from water bodies, with low dosage and low risk of secondary pollution, making it particularly suitable for river water purification in winter. Attached Figure Description

[0052] Figure 1 This is a schematic diagram of the preparation of polyaluminum chloride in Example 1. Detailed Implementation

[0053] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in this technical field.

[0054] Unless otherwise specified, all reagents and materials used in the following examples are commercially available.

[0055] Commercially available polyaluminum chloride (Al2O3 content ≥10%, basicity ≥60%) was purchased from Huaqing Water Purification Technology Co., Ltd., Dongguan City, Guangdong Province.

[0056] (1) The determination of Al2O3 content includes the following steps: Weigh out a sample of mass m, transfer it to a 250 mL volumetric flask, dilute to volume, and shake well to prepare the sample solution. Accurately transfer 10 mL of the sample solution to a 250 mL Erlenmeyer flask, accurately add 15 mL of EDTA solution, add 3-4 drops of thymol blue solution, neutralize with ammonia solution until the solution changes from red to yellow (pH around 2.8), and boil for 2 minutes. After cooling, add 10 mL of acetate-sodium acetate buffer solution and 2-4 drops of xylenol orange indicator solution, and titrate with zinc chloride standard solution until the solution changes from pale yellow to slightly red, which is the endpoint. Perform a blank test simultaneously. Calculate the Al2O3 content using the following formula: Al2O3%=[C×(V0-V)×0.05098×25 / m]×100; In the formula, V0 is the volume of zinc chloride standard titration solution consumed in the blank test, in mL; V is the volume of zinc chloride standard titration solution consumed in the determination test, in mL; C is the actual concentration of zinc chloride standard titration solution, in mol / L; and m is the mass of the sample to be tested, in g.

[0057] (2) The determination of basicity includes the following steps: Weigh out a sample of mass m, transfer it to a 250 mL volumetric flask, dilute to volume, and shake well to prepare the sample solution. Accurately transfer 10 mL of the sample solution to a beaker, add 50 mL of pure water, add 3-4 drops of phenolphthalein indicator, and immediately titrate with 0.2 mol / L sodium hydroxide standard solution until the solution changes from colorless to slightly pink (the color does not fade within 30 seconds), which is the endpoint. The formula for calculating basicity is as follows: B%=[1-(0.017×C1×V1×25 / m×Al2O3%)]×100; In the formula, V1 is the volume of sodium hydroxide standard titration solution consumed in the test, in mL; C1 is the actual concentration of sodium hydroxide standard titration solution, in mol / L; m is the mass of the sample to be tested, in g; and Al2O3% is the Al2O3 content in the sample to be tested, in g.

[0058] (3) The formula for calculating the amount of calcium aluminate powder added, y (tons), is as follows: y = v1 × r1 × a1 × x / a2; Where, x = (n1 - n2) / (n2 + 2m); n1 = 6 × (1 - B1); n2 = 6 × (1 - B2); In the above formula, v1 is the volume of the aluminum chloride solution in mL; r1 is the specific gravity (density) of the aluminum chloride solution in g / mL; a1 is the Al2O3 content in the aluminum chloride solution in %; B1 is the basicity of the aluminum chloride solution in %; B2 is the required basicity after the reaction with added calcium aluminate powder in %; a2 is the Al2O3 content simulated by calcium aluminate powder in % and is taken as 49%; m is the dissolution rate of calcium aluminate powder in % and is taken as 97%.

[0059] (4) The formula for calculating the amount of calcium carbonate powder added is as follows: M=0.49×N×A×[6×(B2-B1) / ω]; In the formula: M is the mass of calcium carbonate, in g; N is the mass of polyaluminum chloride base solution, in g; A is the Al2O3 content in polyaluminum chloride, in %; B1 is the basicity of polyaluminum chloride base solution, in %; B2 is the basicity of high-basicity polyaluminum chloride, in %; ω is the calcium carbonate content, in %.

[0060] Example 1: Preparation of polyaluminum chloride A schematic diagram of the process for preparing polyaluminum chloride is shown below. Figure 1 As shown.

[0061] S1. In a 250 mL conical flask, add 126 g of hydrochloric acid with a hydrogen chloride mass fraction of 31% and 28 g of aluminum hydroxide with an Al2O3 content of 64.5% (i.e., the mass ratio of hydrochloric acid to aluminum hydroxide is 4.5:1). Stir the reaction at 100 °C for 2.5 h until the reaction system is clear and transparent and the aluminum hydroxide is completely dissolved. Add 40 mL of water to dilute and obtain an AlCl3 solution with an Al2O3 content of 6.0% and a basicity of -10.85%. S2. Add 22.62 g of calcium aluminate powder with an Al2O3 content of 49% to the AlCl3 solution obtained in step S1, stir and react at 100℃ for 1 h, and filter the reaction solution under reduced pressure using a vacuum filter to obtain 180 g of clear, light yellow polyaluminum chloride-based liquid. The Al2O3 content in the liquid is 11.2%, and the basicity is 64.55%. S3. Add 15.39 g of calcium carbonate powder (CaCO3 content of 98%) to 100 g of polyaluminum chloride base liquid obtained in step S2, control the pH at 3.0, and react at 100 ℃ for 1 h to obtain a high basicity polyaluminum chloride base liquid with a basicity of 90.2% and an Al2O3 content of 10.5%. S4. Take 20 g of the high basicity polyaluminum chloride base liquid obtained in step S3, add ammonium phosphate, the mass ratio of the two is 1:0.01, stir for 10 min to mix evenly, add 22 mL of water, and you will get polyaluminum chloride with a basicity of 90.1% and an Al2O3 content of 10.1%.

[0062] Example 2 Preparation of polyaluminum chloride The difference from Example 1 is that in step S4, the mass ratio of high basicity polyaluminum chloride base liquid and ammonium phosphate is replaced from 1:0.01 to 1:0.015; the resulting polyaluminum chloride has a basicity of 90.2% and an Al2O3 content of 10.0%.

[0063] The other steps and conditions are the same as in Example 1.

[0064] Example 3 Preparation of polyaluminum chloride The difference from Example 1 is that in step S1, the mass ratio of high basicity polyaluminum chloride base liquid and ammonium phosphate is replaced from 1:0.01 to 1:0.02; the resulting polyaluminum chloride has a basicity of 90.0% and an Al2O3 content of 10.5%.

[0065] The other steps and conditions are the same as in Example 1.

[0066] Comparative Example 1: Preparation of polyaluminum chloride The difference from Example 1 is that in step S4, ammonium phosphate is replaced with sodium dihydrogen phosphate, that is, the acid radical ion is replaced by dihydrogen phosphate instead of phosphate; the basicity of the resulting polyaluminum chloride is 90.0% and the Al2O3 content is 10.0%.

[0067] The other steps and conditions are the same as in Example 1.

[0068] Comparative Example 2: Preparation of polyaluminum chloride The difference from Example 1 is that in step S4, ammonium phosphate is replaced with sodium monohydrogen phosphate, that is, the acid radical ion is replaced by monohydrogen phosphate instead of phosphate; the basicity of the resulting polyaluminum chloride is 89.8%, and the Al2O3 content is 10.1%.

[0069] The other steps and conditions are the same as in Example 1.

[0070] Comparative Example 3: Preparation of polyaluminum chloride The difference from Example 1 is that in step S4, ammonium phosphate is replaced with magnesium phosphite, that is, the acid radical ion is replaced by phosphite instead of phosphate; the basicity of the resulting polyaluminum chloride is 90.2% and the Al2O3 content is 10.3%.

[0071] The other steps and conditions are the same as in Example 1.

[0072] Comparative Example 4: Preparation of polyaluminum chloride The difference from Example 1 is that in step S4, ammonium phosphate is replaced with sodium hypophosphite, that is, the acid radical ion is replaced by hypophosphite instead of phosphate; the basicity of the resulting polyaluminum chloride is 90.0%, and the Al2O3 content is 10.0%.

[0073] The other steps and conditions are the same as in Example 1.

[0074] Comparative Example 5: Preparation of polyaluminum chloride The difference from Example 1 is that step S4 was not performed, i.e., ammonium phosphate was not added, and the Al2O3 content of the obtained polyaluminum chloride was controlled to be 10.0% by adding water; the basicity of the obtained polyaluminum chloride was 90.2%, and the Al2O3 content was 10.0%.

[0075] The other steps and conditions are the same as in Example 1.

[0076] Comparative Example 6: Preparation of Polyaluminum Chloride The difference from Example 1 is that in step S4, the mass ratio of high basicity polyaluminum chloride base liquid to ammonium phosphate is replaced from 1:0.01 to 1:0.005; the resulting polyaluminum chloride has a basicity of 89% and an Al2O3 content of 10.0%.

[0077] The other steps and conditions are the same as in Example 1.

[0078] Comparative Example 7: Preparation of Polyaluminum Chloride The difference from Example 1 is that in step S4, ammonium phosphate is replaced with sodium silicate; the resulting polyaluminum chloride has a basicity of 90.2% and an Al2O3 content of 10.0%, and is denoted as HPAC-Si.

[0079] The other steps and conditions are the same as in Example 1.

[0080] Comparative Example 8: Preparation of Polyaluminum Chloride The difference from Example 1 is that in step S4, sodium carbonate and ammonium phosphate are combined, and the specific steps are as follows: S4. Add ammonium phosphate and sodium carbonate sequentially to 20 g of the high basicity polyaluminum chloride base solution obtained in step S3, with a mass ratio of 1:0.005:0.005. Stir for 10 min to mix evenly, then add 4.5 mL of water to obtain polyaluminum chloride with a basicity of 90.2% and an Al2O3 content of 10.0%, denoted as HPAC-PC.

[0081] The other steps and conditions are the same as in Example 1.

[0082] Comparative Example 9: Preparation of polyaluminum chloride The difference from Example 1 is that in step S4, sodium carbonate, sodium silicate, and ammonium phosphate are used in combination, and the specific steps are as follows: S4. Add ammonium phosphate, sodium carbonate and sodium silicate sequentially to 20 g of the high basicity polyaluminum chloride base solution obtained in step S3, with a mass ratio of 1:0.0033:0.0033:0.0033. Stir for 10 min to mix evenly, then add 4.5 mL of water to obtain polyaluminum chloride with a basicity of 90.2% and an Al2O3 content of 10.0%, denoted as HPAC-PCS.

[0083] The other steps and conditions are the same as in Example 1.

[0084] Comparative Example 10: Preparation of Polyaluminum Chloride The difference from Example 1 is that in step S4, tannic acid and ammonium phosphate are combined, and the specific steps are as follows: S4. Add ammonium phosphate and tannic acid sequentially to 20 g of the high basicity polyaluminum chloride base solution obtained in step S3, with a mass ratio of 1:0.005:0.005. Stir for 10 min to mix evenly, then add 4.5 mL of water to obtain polyaluminum chloride with a basicity of 90.2% and an Al2O3 content of 10.0%, denoted as HPAC-PT.

[0085] The other steps and conditions are the same as in Example 1.

[0086] Comparative Example 11: A type of polyaluminum chloride The polyaluminum chloride prepared in Example 1 was replaced with commercially available ordinary polyaluminum chloride, and the basicity was found to be 70.0% and the Al2O3 content was 10.0%.

[0087] Experimental Example 1: Water purification performance test of polyaluminum chloride under different dosage conditions 1. Experimental Methods Accurately weigh 1.000 g of the polyaluminum chloride sample obtained in Example 1, and dilute to 100 mL with deionized water to prepare a stock solution with a concentration of 10.0 g / L. Take six 1 L beakers, add 1.00 L of raw water to each, and place them in a coagulation test stirrer. Set the stirring program as follows: rapid mixing stage (500 r / min, 30 s), slow flocculation stage (100 r / min, 5 min), and settling for 10 min. Within 10 s after the start of rapid mixing, add different volumes of stock solution to the six beakers, so that the dosage of the reagent is 5, 10, 15, 20, 25, and 30 mg / L (corresponding to dosage volumes of 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 mL, respectively). After settling, take the supernatant 2 cm below the liquid surface, measure the residual turbidity (NTU) using a turbidimeter, and calculate the turbidity removal rate.

[0088] Test standards: The flocculation effect is evaluated in accordance with GB5749-2022 "Standards for Drinking Water Quality" and GB / T 14591-2025 "General Technical Conditions for Water Treatment Agents and Flocculants". For drinking water treatment, the residual turbidity is required to be ≤1 NTU, and for industrial wastewater flocculation treatment, the turbidity removal rate is required to be ≥90%.

[0089] 2. Experimental Results Table 1. Water purification data of polyaluminum chloride at different dosages

[0090] The results are shown in Table 1. When the dosage of polyaluminum chloride is <20 mg / L, the turbidity of the supernatant is ≥0.85 NTU, and the turbidity removal rate is ≤82.3%, indicating poor water purification effect. When the dosage of polyaluminum chloride is ≥20 mg / L, the turbidity of the supernatant is ≤0.39 NTU, and the turbidity removal rate is ≥91.9%, showing a significant improvement in water purification effect. To balance effluent quality and reagent cost, 20 mg / L was determined to be the optimal dosage of the high-efficiency polyaluminum chloride of this invention for treating low-temperature river water in winter.

[0091] Experiment Example 2: Water purification performance test of polyaluminum chloride at the optimal dosage 1. Experimental Methods Raw water from the Nanshui River in Shaoguan during winter was collected, with the following water quality parameters: water temperature 4.2 ℃, initial turbidity 6.24 NTU, and pH 7.2. 1.000 g of each example and comparative sample was accurately weighed and diluted to 100 mL in a volumetric flask with deionized water to prepare a 10.00 g / L stock solution. Using a six-stage coagulation test stirrer, 2.00 mL of the stock solution (corresponding to a polyaluminum chloride dosage of 20 mg / L) was added to 1.00 L of raw water. The stirring program was set as follows: rapid mixing (500 r / min, 30 s), slow flocculation (100 r / min, 5 min), followed by settling for 10 min. After settling, the supernatant was carefully aspirated from 2 cm below the surface, and its residual turbidity was measured using a turbidimeter. Each sample was tested in triplicate, and the average value was taken.

[0092] Test standards: The flocculation effect is evaluated in accordance with GB5749-2022 "Standards for Drinking Water Quality" and GB / T 14591-2025 "General Technical Conditions for Water Treatment Agents and Flocculants". For drinking water treatment, the residual turbidity is required to be ≤1 NTU, and for industrial wastewater flocculation treatment, the turbidity removal rate is required to be ≥90%.

[0093] 2. Experimental Results Table 2. Water purification performance data of each embodiment and comparative example.

[0094] The results are shown in Table 2. The turbidity of Examples 1-3 was ≤0.39 NTU, and the removal rate was ≥91.9%. This indicates that the polyaluminum chloride of this application can achieve efficient flocculation and high turbidity removal rate for water purification under low temperature conditions with a dosage of only 20 mg / L.

[0095] In Comparative Examples 1-4, sodium dihydrogen phosphate, sodium monohydrogen phosphate, magnesium phosphite, and sodium hypophosphite were used to replace ammonium phosphate, respectively. The monohydrogen phosphate and dihydrogen phosphate had reduced complexation regulation due to protonation, resulting in a weakened synergistic flocculation effect. The coordination structures of phosphite and hypophosphite were significantly different from those of orthophosphate, making it impossible to form an effective phosphorus-aluminum modified complex system. The gain effect was limited, ultimately leading to a deterioration in both turbidity and removal rate.

[0096] Comparative Examples 5 and 6 showed that the turbidity and removal rate both deteriorated due to the absence of ammonium phosphate or the insufficient amount of ammonium phosphate added.

[0097] Comparative Example 7 showed a significant decrease in both turbidity and removal rate due to the use of sodium silicate instead of ammonium phosphate.

[0098] In Comparative Examples 8-10, sodium carbonate and ammonium phosphate were used in combination, sodium silicate, sodium silicate and ammonium phosphate were used in combination, and tannic acid and ammonium phosphate were used in combination to replace the single phosphate system, respectively. The results showed that when multiple acid radicals coexisted, due to competitive complexation and system mismatch, no synergistic effect was produced. Instead, the specific complexation effect of phosphate radicals with highly polymerized aluminum was weakened, resulting in a significant decrease in both turbidity and removal rate.

[0099] Comparative Example 11, due to the use of commercially available polyaluminum chloride, exhibited complexation and turbidity, resulting in a significant deterioration in both turbidity and removal rate.

[0100] 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. A method for preparing polyaluminum chloride, characterized in that, Includes the following steps: Add phosphate donor to a high basicity polyaluminum chloride-based solution, mix well, and you will get polyaluminum chloride; The basicity of the high-basicity polyaluminum chloride-based liquid is 90%~95%; The mass ratio of the high basicity polyaluminum chloride-based liquid to the phosphate donor is 1:(0.007~0.022).

2. The preparation method according to claim 1, characterized in that, The polyaluminum chloride contains 10% to 10.8% Al2O3.

3. The preparation method according to claim 1, characterized in that, The basicity of the polyaluminum chloride is 90%~95%.

4. The preparation method according to claim 1, characterized in that, The phosphate donor includes one or more of ammonium phosphate, magnesium phosphate, and calcium phosphate.

5. The preparation method according to claim 1, characterized in that, The mass ratio of the high basicity polyaluminum chloride-based solution to the phosphate donor is 1:(0.01~0.02).

6. The preparation method according to claim 1, characterized in that, The high basicity polyaluminum chloride-based liquid contains 10.2% to 11.2% Al2O3.

7. The polyaluminum chloride prepared by the preparation method according to any one of claims 1 to 6.

8. The application of the polyaluminum chloride according to claim 7 in water purification.

9. A water purification agent, characterized in that, The water purification agent includes the polyaluminum chloride as described in claim 7.

10. The water purification agent according to claim 9, characterized in that, The mass concentration of the polyaluminum chloride is 18~30 mg / L.

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