Modified polyaluminum chloride suitable for low temperature and preparation method and application thereof

Abstract

The application provides a modified polyaluminum chloride suitable for low temperature and a preparation method and application thereof, and belongs to the technical field of sewage treatment agents. The modified polyaluminum chloride is of a core-shell structure, the core layer comprises a multi-core hydroxyl complex of aluminum, magnesium and titanium, and the shell layer comprises a cationic organic polymer and an activated diluent. The modified polyaluminum chloride can still quickly complete colloid destabilization under the condition of low temperature of 0-5 DEG C, effectively avoids the problem that the residual aluminum in effluent exceeds the standard, simultaneously reduces the operation cost of water treatment, and is suitable for low-temperature water treatment in winter or high-latitude areas.

Description

Technical Field

[0001] This application relates to the field of wastewater treatment agents, and in particular to a modified polyaluminum chloride suitable for low temperatures, its preparation method, and its application. Background Technology

[0002] At low temperatures (0~5℃), the viscosity coefficient of water increases significantly, the Brownian motion of colloidal particles in water weakens, the absolute value of the Zeta potential increases, and the hydration film between particles thickens, causing colloidal particles to become more stable and less prone to destabilization and aggregation.

[0003] Polyaluminum chloride (PAC) is currently the most widely used inorganic polymeric flocculant. However, conventional PAC has the following significant drawbacks at low temperatures (0~5℃): First, the hydrolysis rate of aluminum salts decreases sharply, leading to slow formation of polynuclear hydroxyl complexes that play a role in charge neutralization, and the flocculant cannot effectively neutralize the colloidal charge in a short time; second, the flocs (lumps) formed at low temperatures are small and loose, with extremely slow settling speeds, resulting in a large number of micro-flocs carried in the effluent from the sedimentation tank, seriously affecting the effluent quality; third, to meet effluent quality standards, several times the dosage is often required compared to that at room temperature, which not only increases operating costs but also brings the risk of excessive residual aluminum in the effluent. Therefore, developing a water treatment flocculant that can still function efficiently under low-temperature conditions is an urgent need in the industry.

[0004] To improve the low-temperature flocculation performance of PAC, existing technologies attempt to introduce a second metal component to modify its chemical structure. For example, introducing Mg... 2+ The formed polyaluminum magnesium chloride (PAMC) or the introduction of Ti 4+ Polyaluminum titanium chloride (PATC) is formed. These binary metal composite flocculants enhance the treatment effect of conventional PAC to some extent by strengthening the positive charge of doped ions or forming metal oxide coagulation nuclei. However, the improvement of such binary modification is limited. The fundamental reason is that in low-temperature, weakly acidic to neutral water bodies, the incorporated metal components easily form independent hydroxide precipitates or oxide particles during the preparation process, making it difficult to form extensive chemical bonds with the hydroxyl polymer network of aluminum at the molecular scale. This makes the modified products essentially physical mixtures of various inorganic components, rather than novel compounds with homogeneous structures and truly synergistic effects. In application, the decomposition and onset rates of each component are inconsistent, making it impossible to achieve simultaneous and efficient synergy of charge neutralization, adsorption, and bridging effects in low-temperature environments. Summary of the Invention

[0005] This application is made in view of the above-mentioned problems, and its purpose is to provide a modified polyaluminum chloride suitable for low temperature, a method for its preparation and its application.

[0006] Specifically, the first aspect of this application provides a modified polyaluminum chloride suitable for low temperatures. The modified polyaluminum chloride has a core-shell structure, with the core layer comprising a polynuclear hydroxyl complex of aluminum, magnesium, and titanium, and the shell layer comprising a cationic organic polymer and an activating diluent.

[0007] Furthermore, the cationic organic polymer is polydiallyldimethylammonium chloride and / or cationic polyacrylamide with a cationicity of 20% to 40%.

[0008] Furthermore, the activating diluent is selected from at least one of sorbitol, glycerol, or polyethylene glycol.

[0009] The second aspect of this application provides a method for preparing the modified polyaluminum chloride suitable for low temperatures, comprising the following steps: S1: Under stirring conditions, an acidic solution containing titanium and magnesium and an alkaline aluminum solution are added to a polyaluminum chloride base solution, and a copolymerization reaction is carried out under conditions of pH 3.0 to 3.8 to obtain a sol; the obtained sol is aged to obtain an aluminum-magnesium-titanium polynuclear hydroxy polymer sol. S2: Mix the activating diluent with the cationic organic polymer solution and stir at 40-60°C for 20-40 min to form a mixture; then mix the mixture with the aluminum-magnesium-titanium polynuclear hydroxy polymer sol obtained in step S1 at 25-35°C under shear stirring at 3000-5000 rpm to obtain a mixed solution. S3: Spray dry the mixture to obtain the modified polyaluminum chloride suitable for low temperature.

[0010] Furthermore, the polyaluminum chloride base solution described in step S1 is prepared by reacting calcium aluminate powder with hydrochloric acid.

[0011] Further, the acidic solution containing titanium and magnesium in step S1 is an aqueous solution containing titanium tetrachloride, magnesium chloride and hydrochloric acid; the alkaline aluminum solution is a sodium aluminate solution.

[0012] Furthermore, step S1 specifically includes: First, add the first part of alkaline aluminum solution to the polyaluminum chloride base solution for prepolymerization, so that the pH of the system reaches 3.5-3.8; Subsequently, the acidic solution containing titanium and magnesium, along with the remaining alkaline aluminum solution, were added dropwise to the obtained prepolymer solution under stirring, and the pH of the system was controlled at 3.0–3.5 to carry out the copolymerization reaction.

[0013] Further, the aging treatment in step S1 involves aging the obtained sol at 50-60°C under microwave conditions for 30-60 minutes, and then adjusting the pH to 3.8-4.2.

[0014] Furthermore, in step S3, the inlet air temperature of the spray dryer is 180–200°C, and the outlet air temperature is 80–95°C.

[0015] A third aspect of this application provides an application of the modified polyaluminum chloride suitable for low temperatures in the field of wastewater treatment.

[0016] The present invention has the following beneficial effects: The modified polyaluminum chloride provided by this invention adopts a core-shell structure design, with an aluminum-magnesium-titanium polynuclear hydroxyl complex formed by molecular-scale copolymerization as the core layer. This can fully utilize the synergistic charge neutralization effect of the three metal hydroxyl components, significantly improving the charge neutralization and destabilization ability of stable colloidal particles at low temperatures. The shell layer composed of cationic organic polymers can use its own long molecular chains to play an adsorption bridging role, promoting the rapid aggregation and growth of fine flocs, thus solving the problem of fine flocs and slow sedimentation at low temperatures.

[0017] This invention ensures uniform molecular-level bonding of titanium and magnesium components in the aluminum hydroxyl polymer network through a stepwise preparation process, avoiding phase separation and independent precipitation of the modified components. Compared with modified products based on simple physical blending, each component can function simultaneously in low-temperature water, significantly improving flocculation efficiency. In the treatment of low-temperature, low-turbidity water at 0-5℃, only a lower dosage than conventional PAC is required to achieve qualified effluent quality, reducing treatment costs and the risk of excessive residual aluminum in the effluent. It is very suitable for wastewater treatment applications in low-temperature water bodies during winter and in high-latitude regions. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this application clearer, the following description and illustration are provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. All other embodiments obtained by those skilled in the art based on the embodiments provided in this application without inventive effort are within the scope of protection of this application.

[0019] Obviously, the following description is merely some examples or embodiments of this application. Those skilled in the art can apply this application to other similar scenarios without any inventive effort. Furthermore, it is understood that although the effort involved in such development may be complex and lengthy, for those skilled in the art related to the content disclosed in this application, any changes to design, manufacturing, or production based on the technical content disclosed in this application are merely conventional technical means and should not be construed as insufficient disclosure of the content of this application.

[0020] An embodiment of the first aspect of this application provides a modified polyaluminum chloride suitable for low temperatures, wherein the modified polyaluminum chloride has a core-shell structure, the core layer comprising a polynuclear hydroxyl complex of aluminum, magnesium and titanium, and the shell layer comprising a cationic organic polymer and an activating diluent.

[0021] The modified polyaluminum chloride described above utilizes a multinuclear hydroxyl composite structure formed at the molecular scale by three metals, combined with an outer cationic organic polymer shell. This enables multiple synergistic effects of charge neutralization, adsorption bridging, and coagulation nuclei in low-temperature water, solving the problems of component dispersion and insufficient synergistic effect in conventional modified PAC. Aluminum in the core layer is the basic component of the hydroxyl polymerization framework. Magnesium ions can increase the positive charge density of the entire core polymer layer through doping, rapidly neutralizing the negative charge on the surface of colloidal particles at low temperatures, reducing colloidal stability, and promoting destabilization. Titanium ions can enter the hydroxyl polymerization network to form a more stable composite structure and can also act as coagulation nuclei to induce the aggregation of destabilized particles. Compared with single-component or binary metal modification, this is more conducive to the initial formation of flocs at low temperatures. The outer cationic organic polymer shell further enhances the positive charge characteristics of the particle surface and, through its long molecular chains, acts as an adsorption bridging agent, rapidly connecting and agglomerating tiny initial aggregates to form larger, denser flocs, significantly improving sedimentation performance.

[0022] In this embodiment, the cationic organic polymer is polydiallyldimethylammonium chloride and / or cationic polyacrylamide with a cationicity of 20% to 40%. Preferably, the cationic organic polymer is polydiallyldimethylammonium chloride. The polydiallyldimethylammonium chloride molecular chain has a high density of positive charges and good compatibility with aluminum-magnesium-titanium inorganic hydroxyl sol. During the composite process, it can be more uniformly dispersed in the product, thus better exerting the synergistic effect of adsorption bridging and charge compensation.

[0023] In this embodiment, the activating diluent is selected from at least one of sorbitol, glycerol, or polyethylene glycol. The activating diluent improves the dispersibility of the cationic organic polymer during dissolution, while preventing excessive coiling and aggregation of the shell polymer molecular chains, ensuring uniform shell coating, avoiding performance degradation of the modified product during storage, and extending the product's shelf life.

[0024] A second aspect of the present invention provides a method for preparing modified polyaluminum chloride suitable for low temperatures, comprising the following steps: S1: Under stirring conditions, an acidic solution containing titanium and magnesium and an alkaline aluminum solution are added to the polyaluminum chloride base solution in step S1, and a copolymerization reaction is carried out under the condition of pH 3.0 to 3.8 to obtain a sol; the obtained sol is aged to obtain an aluminum-magnesium-titanium polynuclear hydroxy polymer sol. S2: Mix the activating diluent with the cationic organic polymer solution and stir at 40-60°C for 20-40 min; then mix the cationic organic polymer solution containing the activating diluent with the aluminum-magnesium-titanium polynuclear hydroxy polymer sol obtained in step S1 at 25-35°C under shear stirring at 3000-5000 rpm to obtain a mixture. S3: Spray dry the composite liquid to obtain the modified polyaluminum chloride suitable for low temperature.

[0025] In this embodiment, the preparation of the polyaluminum chloride base solution in step S1 is as follows: 20%–25% hydrochloric acid (by mass) is added to a reaction vessel, heated to 55–70°C, and calcium aluminate powder is added in batches with stirring over a period of 1–1.5 hours. After addition, the reaction is maintained at this temperature for 2–3 hours to obtain a yellow-green transparent liquid. Insoluble matter is removed by filtration to obtain the polyaluminum chloride base solution. This step is used to prepare the aluminum hydroxyl polymer backbone precursor, providing a reaction basis for the subsequent bonding copolymerization of magnesium and titanium ions, and avoiding the direct precipitation of magnesium and titanium.

[0026] In this embodiment, the acidic solution containing titanium and magnesium in step S1 is an aqueous solution containing titanium tetrachloride, magnesium chloride and hydrochloric acid; the alkaline aluminum solution is a sodium aluminate solution.

[0027] Step S1 specifically includes: S1.1: First, cool the base solution from step S1 to 30-40°C, and add sodium aluminate solution (Al2O3 content 15%-20%) dropwise while stirring. Control the pH value at 3.5-3.8 to obtain a prepolymer solution containing more medium and low-polymerized aluminum. S1.2: Under ice-water bath and vigorous stirring, titanium tetrachloride was slowly added to deionized water, followed by the addition of an appropriate amount of concentrated hydrochloric acid to clarify the solution, and then magnesium chloride was added to dissolve it, thus preparing Ti... 4+ Concentration 1.0–1.5 mol / L, Mg 2+ A mixed acid solution with a concentration of 2.0–3.0 mol / L and a hydrogen ion concentration of 0.5–1.0 mol / L. This solution must be kept below 10°C throughout the process and is ready for use. S1.3: Under stirring at 30-40℃ and 400-500 rpm, the titanium-magnesium mixed acid solution (5℃) prepared in step S1.2 is added dropwise at a constant rate of 8-12.0 mL / min. Maintaining a constant 400-500 rpm, sodium aluminate solution (same specifications as in S1.1) is immediately added dropwise at an initial rate of 3-3.5 mL / min. When the pH rises to 2.6-3.0, the rate is reduced to 1.5-2.0 mL / min, controlling the final pH at 3-3.5. The mixture is then stirred for 3-8 minutes to equilibrate. After the addition is complete, stirring is continued at 30-40℃ and 400-500 rpm for another 30 minutes. This step maintains a stable pH by adding the solution dropwise, allowing titanium and magnesium ions to gradually bond into the polymer backbone as the aluminum hydroxyl polymer grows. This avoids hydrolysis due to excessively high local concentrations of titanium and magnesium ions, which would generate independent hydroxide precipitates, thus ensuring uniform bonding and copolymerization of the three metals at the molecular scale. S1.4: Transfer the sol obtained in step S1.3 into a microwave reactor and irradiate it at a frequency of 2450 MHz and a power density of 15–25 W / L to raise the material to 50–60 °C and maintain the temperature for 30–60 min. During this period, a trace amount of sodium aluminate solution can be added to adjust the final pH to 3.8–4.2. An Al, Mg, and Ti polynuclear hydroxyl polymer sol is obtained. Microwave bulk heating ensures uniform heating inside and outside the particles, promoting further diffusion and bonding of titanium and magnesium ions within the aluminum hydroxyl backbone, improving copolymerization uniformity, shortening aging time, promoting the stability of the polynuclear hydroxyl structure, and reducing performance degradation during subsequent storage or use.

[0028] In this embodiment, step S2 involves mixing the activating diluent with a cationic organic polymer solution and stirring at 40–60°C for 20–40 min, allowing the activating diluent and cationic organic polymer to form a complex through hydrogen bonding. Then, at 25–35°C, the cationic organic polymer solution containing the activating diluent is mixed uniformly with the aluminum-magnesium-titanium polynuclear hydroxyl polymer sol obtained in step S1 under shear stirring at 3000–5000 rpm to obtain a mixed solution. This step promotes the uniform adsorption of the cationic organic polymer on the surface of the aluminum-magnesium-titanium polynuclear hydroxyl composite particles through high-speed shear stirring, forming a uniform core-shell structure, avoiding polymer molecule aggregation, ensuring that each inorganic particle is coated by an organic shell, and fully leveraging the synergistic effect of inorganic-organic interaction.

[0029] In this embodiment, step S3 involves directly feeding the aforementioned composite liquid into a spray drying tower for drying. The inlet air temperature is controlled at 180–200°C, and the outlet air temperature at 80–95°C. A white to pale yellow powdery solid is collected, which is the modified polyaluminum chloride product suitable for low temperatures. Spray drying can quickly remove moisture, retain the amorphous polynuclear hydroxyl structure of the product to the greatest extent, avoid structural agglomeration and damage during the drying process, and ensure that the finished product dissolves quickly and has high activity.

[0030] Example The following examples describe the disclosure of this invention in more detail. These examples are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of this disclosure. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on weight. Unless otherwise stated, all reagents used in the examples are available commercially or synthesized using conventional methods and are ready for use without further processing. Unless otherwise stated, all instruments used in the examples are available commercially.

[0031] Example 1 A method for preparing modified polyaluminum chloride suitable for low temperatures includes the following steps: S1: Add 413g of 25% hydrochloric acid to the reactor, heat to 65℃, and add 96g of calcium aluminate powder (53% Al2O3, 30% CaO) in batches with stirring over a period of 1.5 hours. After addition, maintain the temperature for 2.5 hours, filter, and obtain the polyaluminum chloride base solution. S2.1: First, cool the base solution from step S1 to 35°C, then add 300g of sodium aluminate solution (Al2O3 content 18%) dropwise while stirring, and control the pH value at 3.6 to obtain the prepolymer solution; S2.2: Preparation of titanium-magnesium mixture: Under ice-water bath and vigorous stirring, 22.8 g of titanium tetrachloride was slowly added to deionized water, followed by the addition of concentrated hydrochloric acid to clarify the solution. Then, 93.9 g of magnesium chloride was added to dissolve the solution, and the volume was adjusted to 100 mL in a volumetric flask to prepare the Ti... 4+ Concentration 1.2 mol / L, Mg 2+ A titanium-magnesium mixed acid solution with a concentration of 4.6 mol / L and a hydrogen ion concentration of 0.8 mol / L was maintained at 5°C throughout the process. S2.3: Under stirring at 35℃ and 450 rpm, transfer 89 mL (5℃) of the titanium-magnesium mixed acid solution prepared in step S2.2 to a constant pressure dropping funnel at a dropping rate of 10.0 mL / min. After the addition is complete, maintain a constant 450 rpm and add 153 g of sodium aluminate solution (same specifications as in S2.1) at an initial rate of 3.3 mL / min. When the pH rises to 2.8, reduce the rate to 1.8 mL / min. Control the final pH at 3.3. After the addition is complete, continue stirring at 35℃ and 450 rpm for 30 minutes. S2.4: The sol obtained in step S2.3 is microwave irradiated at a frequency of 2450 MHz and a power density of 20 W / L to raise the material to 55℃ and hold it for 45 min. During this period, 30% NaOH solution is added to adjust the final pH to 4.0 to obtain aluminum magnesium titanium polynuclear hydroxy polymer sol. S3: Sorbitol was mixed with a 40% (w / w) aqueous solution of polydiallyldimethylammonium chloride, wherein the dry weight ratio of sorbitol to polydiallyldimethylammonium chloride (CAS No.: 26062-79-3, molecular weight 200,000-350,000) was 1:12. The mixture was stirred at 50°C for 30 min. Then, at 30°C, the cationic organic polymer solution containing the activating diluent was mixed with the aluminum magnesium titanium polynuclear hydroxyl polymer sol obtained in step S2 under shear stirring at 4000 rpm until homogeneous. The amount of polymer added was such that the polymer accounted for 1.2% of the dry weight of the final product, and a mixture was obtained. S4: Spray dry the composite liquid, controlling the inlet air temperature to 195℃ and the outlet air temperature to 90℃, to obtain modified polyaluminum chloride suitable for low temperature.

[0032] Example 2 This embodiment is basically the same as Embodiment 1, except that, in S2.2: preparation of titanium-magnesium mixture: under ice-water bath and vigorous stirring, 34.6 g of titanium tetrachloride is slowly added to deionized water, then concentrated hydrochloric acid is added to clarify the solution, and then 52.9 g of magnesium chloride is added to dissolve it. After dissolution, deionized water is added to bring the total volume to 152 mL to ensure that the hydrogen ion concentration is 0.8 mol / L. The solution is kept at 5°C throughout the process. Step S2.3: Under stirring at 35℃ and 450 rpm, 152 mL (5℃) of the titanium-magnesium mixed acid solution prepared in step S2.2 was transferred to a constant pressure dropping funnel at a dropping rate of 10.0 mL / min. After the addition was completed, the remaining sodium aluminate solution of 153 g was added dropwise while maintaining a constant 450 rpm. The final pH was controlled at 3.3, and the mixture was stirred for 30 min. S3: Mix sorbitol with a 40% (w / w) aqueous solution of polydiallyldimethylammonium chloride (the dry weight ratio of sorbitol to polydiallyldimethylammonium chloride is 0.12:1.5, and the amount of polydiallyldimethylammonium chloride is 1.5% of the dry weight of the final product).

[0033] Example 3 This embodiment is basically the same as Embodiment 1, except that the microwave irradiation time in step S2.4 is 30 minutes (maintaining 55°C).

[0034] The product composition is basically the same as that in Example 1.

[0035] Example 4 This embodiment is basically the same as that of Example 1, except that in step S3, sorbitol (0.1% by dry weight) is mixed with an aqueous solution of cationic polyacrylamide with a cationicity of 30% (molecular weight 150,000, CAS No.: 9003-05-8) and added at 0.8% by dry weight of the final product. The mixture is stirred and mixed at 30°C. Then it is mixed with the sol obtained in S2 under shear at 4000 rpm.

[0036] Example 5 This embodiment is basically the same as Embodiment 1, except that in step S2.2: preparing titanium-magnesium mixture: under ice-water bath and vigorous stirring, 14.8 g of titanium tetrachloride is slowly added to deionized water, then concentrated hydrochloric acid is added to clarify the solution, and then 42.3 g of magnesium chloride is added to dissolve it. After dissolving, deionized water is added to bring the total volume to 65 mL to ensure that the hydrogen ion concentration is 0.8 mol / L. The solution is kept at 5°C throughout the process. Step S2.3: Under stirring at 35℃ and 450 rpm, transfer 65 mL (5℃) of the titanium-magnesium mixed acid solution prepared in step S2.2 to a constant pressure dropping funnel at a dropping rate of 10.0 mL / min; after the addition is complete, maintain 450 rpm and add the remaining sodium aluminate solution of 153 g, control the endpoint pH at 3.3, and stir for 30 min. S3: Mix glycerol with a 40% aqueous solution of polydiallyldimethylammonium chloride (the dry weight ratio of glycerol to polydiallyldimethylammonium chloride is 1:6) and stir at 50°C for 30 min.

[0037] Comparative Example 1 This comparative example is basically the same as Example 1, except that in step S2.2: under an ice-water bath, 63.4 g of magnesium chloride hexahydrate was dissolved in deionized water, then concentrated hydrochloric acid was added to clarify the solution, and the volume was adjusted to 60 mL. + The concentration was 0.8 mol / L, and the solution was maintained at 5℃ throughout the process. Step S2.3: At 35℃ and 450 rpm, 60 mL of the above magnesium chloride solution was added dropwise to the prepolymer solution, and 153 g of sodium aluminate solution was added dropwise simultaneously. The endpoint pH was controlled at 3.3±0.2, and the mixture was stirred for 30 min.

[0038] In step S3, sorbitol and 40% polydiallyldimethylammonium chloride solution are mixed at a dry weight ratio of 1:12 and stirred at 50°C for 30 min. The mixture is then sheared at 30°C and 4000 rpm and mixed with the sol obtained in S2. The polydiallyldimethylammonium chloride solution accounts for 1.2% of the dry weight.

[0039] Comparative Example 2 This comparative example is basically the same as Example 1, except that step S2.4 does not use microwave irradiation, but is replaced by water bath heating and aging at 55°C for 45 minutes.

[0040] The product composition is basically the same as that in Example 1.

[0041] Comparative Example 3 This comparative example is basically the same as Example 1, except that step S1 is the same as in Example 1, to obtain the base liquid and cool it to 35°C. The step of preparing the prepolymer solution in step S2.1 is omitted; Step S2.2: Prepare the titanium-magnesium mixed acid solution as in Example 1; In step S2.3, at 35℃ and 450 rpm, the base solution was used directly as the bottom solution, and simultaneously 89 mL of titanium-magnesium mixed acid solution and 453 g of sodium aluminate solution (total amount equal to the sum of the original S2.1 and S2.3) were added dropwise. By adjusting the drop rates of the two solutions, the pH of the system was gradually increased, with the final pH being 3.3 ± 0.2. After the addition was completed, the mixture was stirred for 30 min. Step S2.4 Microwave at 55℃ for 45 min, then add 30% NaOH to adjust the pH to 4.0.

[0042] Experimental Case The products prepared in Examples 1-5 and Comparative Examples 1-3 were used in the following tests: Kaolin (200 mesh) and humic acid were added to municipal tap water. After stirring for 30 minutes, the mixture was allowed to settle for 24 hours. The supernatant was collected as concentrated water. Before use, it was diluted with refrigerated deionized water to the desired turbidity, and a small amount of sodium bicarbonate / hydrochloric acid was added to adjust the alkalinity to 50 mg / L (calculated as CaCO3). After thorough stirring, the mixture was kept at a constant temperature of 2℃ for at least 4 hours to obtain simulated low-temperature, low-turbidity water for the experiment. Water quality parameters: turbidity 15.0±0.5 NTU, water temperature 2.0±0.5℃, pH 7.3±0.1, UV... 254 0.110±0.005 cm -1 .

[0043] The same amount of the products prepared in Examples 1-5 and Comparative Examples 1-4 were added to the simulated low temperature and low turbidity water used in the experiment. The mixture was stirred at 300 rpm for 1 min and then at 40 rpm for 10 min. After coagulation and stirring, the water sample was immediately transferred to a 1000 mL stoppered glass graduated cylinder and allowed to settle in a constant temperature environment of 2.0±0.5℃ for 30 min before testing.

[0044] Turbidity was measured using a Hach 2100N turbidity meter; UV 254 The particle size was measured using a UV spectrophotometer after filtration through a 0.45 μm filter membrane; the volume average particle size was determined online using a laser particle size analyzer (Malvern Mastersizer 3000), and the test results are shown in Table 1.

[0045]

[0046] As shown in Table 1, the modified polyaluminum chloride prepared by this invention still exhibits excellent flocculation treatment effect on low-turbidity water at a low temperature of 2℃. The turbidity removal rate and UV254 removal rate are significantly higher than those of commercially available polyaluminum chloride, and the resulting floc particles are larger, demonstrating superior flocculation and sedimentation performance. Comparative Example 1, lacking titanium components and only containing magnesium and organic modification, showed a significant decrease in overall flocculation performance, indicating that titanium participation in copolymerization significantly enhances charge neutralization and adsorption capacity at low temperatures, making it a key component for improving flocculation. Comparative Example 2, using traditional water bath heating instead of microwave aging, showed lower flocculation performance than the product prepared by microwave aging according to this invention, demonstrating that microwave bulk heating promotes uniform bonding of titanium and magnesium ions, effectively improving product flocculation performance and achieving a superior copolymer structure. Comparative Example 3 omitted the prepolymer preparation step and directly carried out the copolymerization reaction; the final product performance was also lower than that of this invention, indicating that the segmented copolymerization process design effectively controls the titanium ion hydrolysis rate, ensuring uniform copolymerization and guaranteeing excellent low-temperature flocculation performance. In practical applications, the modified polyaluminum chloride of this invention can achieve the same treatment effect with a lower dosage in low-temperature water treatment in winter compared with traditional products, reducing operating costs and producing less sludge, thus reducing the burden of subsequent sludge treatment.

[0047] After settling for 30 minutes, the volume of the interface between the settled floc (sludge) layer and the upper clear liquid was read directly from the graduated cylinder. This volume represents the sludge level after 30 minutes of settling, expressed in mL / L. The results are shown in Table 2.

[0048]

[0049] As shown in Table 2, the modified polyaluminum chloride prepared by this invention produces smaller flocs after flocculation, and the sludge layer height is lower in the same settling time. This indicates that the floc structure formed by this product is more compact, has better compression performance, and correspondingly better dewatering performance. It can effectively reduce the cost and difficulty of subsequent sludge treatment. This further confirms the advantages of the uniform bonding and reasonable structure of each component of this product. Compared with the comparative examples, it has more suitable application characteristics for low-temperature water quality treatment.

[0050] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A modified polyaluminum chloride suitable for low temperatures, characterized in that, The modified polyaluminum chloride has a core-shell structure, with the core layer containing a polynuclear hydroxyl complex of aluminum, magnesium and titanium, and the shell layer containing a cationic organic polymer and an activating diluent.

2. The modified polyaluminum chloride suitable for low temperatures according to claim 1, characterized in that, The cationic organic polymer is polydiallyldimethylammonium chloride and / or cationic polyacrylamide with a cationicity of 20% to 40%.

3. The modified polyaluminum chloride suitable for low temperatures according to claim 1, characterized in that, The activating diluent is selected from at least one of sorbitol, glycerin, or polyethylene glycol.

4. A method for preparing modified polyaluminum chloride suitable for low temperature as described in any one of claims 1-3, characterized in that, Includes the following steps: S1: Under stirring conditions, an acidic solution containing titanium and magnesium and an alkaline aluminum solution are added to a polyaluminum chloride base solution, and a copolymerization reaction is carried out under conditions of pH 3.0 to 3.8 to obtain a sol; the obtained sol is aged to obtain an aluminum-magnesium-titanium polynuclear hydroxy polymer sol. S2: Mix the activating diluent with the cationic organic polymer solution and stir at 40-60°C for 20-40 min to form a mixture; then mix the mixture with the aluminum-magnesium-titanium polynuclear hydroxy polymer sol obtained in step S1 at 25-35°C under shear stirring at 3000-5000 rpm to obtain a mixed solution. S3: Spray dry the mixture to obtain the modified polyaluminum chloride suitable for low temperature.

5. The method for preparing modified polyaluminum chloride suitable for low temperature according to claim 4, characterized in that, The polyaluminum chloride base solution described in step S1 is prepared by reacting calcium aluminate powder with hydrochloric acid.

6. The method for preparing modified polyaluminum chloride suitable for low temperature according to claim 4, characterized in that, The acidic solution containing titanium and magnesium in step S1 is an aqueous solution containing titanium tetrachloride, magnesium chloride and hydrochloric acid; the alkaline aluminum solution is a sodium aluminate solution.

7. The method for preparing modified polyaluminum chloride suitable for low temperature according to claim 4, characterized in that, Step S1 specifically includes: First, add the first part of alkaline aluminum solution to the polyaluminum chloride base solution for prepolymerization, so that the pH of the system reaches 3.5-3.8; Subsequently, the acidic solution containing titanium and magnesium, along with the remaining alkaline aluminum solution, were added dropwise to the obtained prepolymer solution under stirring, and the pH of the system was controlled at 3.0–3.5 to carry out the copolymerization reaction.

8. The method for preparing modified polyaluminum chloride suitable for low temperature according to claim 4, characterized in that, The aging process described in step S1 involves aging the obtained sol at 50-60°C under microwave conditions for 30-60 minutes, followed by adjusting the pH to 3.8-4.

2.

9. The method for preparing modified polyaluminum chloride suitable for low temperature according to claim 4, characterized in that, The inlet air temperature of the spray drying in step S3 is 180-200℃, and the outlet air temperature is 80-95℃.

10. The application of a modified polyaluminum chloride suitable for low temperature as described in claims 1-3 or a modified polyaluminum chloride prepared by the method of any one of claims 5-9 in the field of wastewater treatment.

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