Composite polymeric ferric aluminum chloride water purifying agent and its preparation method and application

Abstract

The application discloses a composite polymeric aluminum ferric chloride water purifying agent and a preparation method and application thereof, and belongs to the technical field of sewage treatment. The polymeric aluminum ferric chloride powder is prepared through hydrothermal reaction and alkalization polymerization after citric acid modified nano magnesium phosphate is prepared through hydrothermal reaction, then the acidized attapulgite is used as a carrier to load the polymeric aluminum ferric chloride, a composite material is obtained, and finally the composite material is compounded with the citric acid modified nano magnesium phosphate, aged and dried to obtain the water purifying agent. The stable composite structure is constructed through multi-stage assembly, the synergistic effect of electric neutralization, carrier skeleton and deep chelation is utilized, suspended solids, phosphorus, COD and heavy metal ions can be synchronously and efficiently removed, the formed floc is compact and stable and has strong impact resistance, the problems of single function and easy attenuation of synergistic effect of traditional water purifying agents are fundamentally overcome, and the water treatment scene with high requirements on stability, reliability and long-term performance consistency of the agent can be met.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically a composite polyaluminum ferric chloride water purification agent, its preparation method, and its application. Background Technology

[0002] Conventional wastewater treatment processes typically include steps such as screen removal, aeration and grit removal, biochemical degradation of activated sludge, and final disinfection. In this process, coagulation and sedimentation are key physicochemical treatment methods, and their effectiveness directly affects the load of subsequent processes and the quality of effluent. However, traditional single aluminum or iron salt coagulants have obvious limitations in practical applications: aluminum salts are prone to slow hydrolysis at low temperatures, resulting in loose flocs and poor settling; iron salts may cause an increase in effluent color and have a certain degree of corrosiveness.

[0003] Composite polyaluminum ferric chloride (PAFC) is an inorganic polymer water purification agent synthesized by copolymerizing aluminum and iron salts under specific conditions. It combines the advantages of aluminum salts, such as large flocs and good decolorization performance, with iron salts, such as dense flocs, fast settling, and strong temperature adaptability. This product has been widely used in drinking water, industrial water, and various wastewater treatment fields. Especially in dealing with high turbidity water and low-temperature, low-turbidity water, it has shown superior comprehensive performance compared to traditional alum and polyferric sulfate. Its typical advantages include low dosage, good effluent quality, dense flocs that are easy to settle, and good sludge dewatering performance. Therefore, it has gradually become one of the important agents in water treatment.

[0004] Chinese patent application CN114853134A discloses a method for preparing polyaluminum ferric chloride water purifier. The method uses red mud as raw material to extract aluminum and iron components by acid leaching to prepare polyaluminum ferric chloride. The polyaluminum ferric chloride is then physically blended with cationic polyacrylamide and chitosan. The removal of water pollutants is achieved by relying on the synergistic effect of charge neutralization, adsorption bridging and chelation of the three.

[0005] However, this method uses a simple physical compound without chemical bonding. The long chains of polyacrylamide are prone to entanglement and aggregation due to intermolecular interactions, while chitosan is prone to precipitation and deactivation under neutral and alkaline conditions. As a result, the synergistic effect of charge neutralization-adsorption bridging-chelation is easily decayed in storage or dynamic water bodies, which cannot guarantee batch-to-batch performance and long-term treatment effect. It is difficult to meet the water treatment scenarios with stringent requirements for agent stability, reliability and long-term efficacy consistency. Summary of the Invention

[0006] The purpose of this invention is to provide a composite polyaluminum ferric chloride water purifier, its preparation method, and its application. Through multi-level assembly, a stable composite structure is constructed. Utilizing the synergistic effects of charge neutralization, carrier framework, and deep chelation, it can simultaneously and efficiently remove suspended solids, phosphorus, COD, and heavy metal ions. The resulting flocs are dense, stable, and highly resistant to impact. This fundamentally overcomes the problems of traditional water purifiers having single functions and easily diminishing synergistic effects, and can meet the stringent requirements of water treatment scenarios for agent stability, reliability, and long-term consistent efficacy.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] A method for preparing a composite polyaluminum ferric chloride water purification agent includes the following steps:

[0009] Step 1: Citric acid modified nano-magnesium phosphate is prepared by hydrothermal reaction using magnesium hydroxide, phosphoric acid and citric acid as raw materials.

[0010] Step 2: Using aluminum sulfate octadechydrate and ferric chloride hexahydrate as raw materials, polyaluminum chloride ferric sulfate powder is obtained through alkalization polymerization.

[0011] Step 3: After acidification with hydrochloric acid, attapulgite is used as a carrier to load the polyaluminum chloride ferric sulfate powder to obtain the polyaluminum chloride ferric sulfate-attapulgite composite material.

[0012] Step 4: The composite polyaluminum chloride-attapulgite material is compounded with citric acid-modified nano magnesium phosphate, aged and dried to obtain a composite polyaluminum chloride-ferric water purifier.

[0013] Furthermore, the specific preparation steps of the composite polyaluminum ferric chloride water purification agent are as follows:

[0014] Polyaluminum ferric chloride-attapulgite composite material, citric acid modified nano magnesium phosphate and deionized water were added to a reaction vessel and stirred at room temperature and 200-300 r / min for 30-40 min. Then stirring was stopped and the mixture was allowed to stand for aging for 120-150 min. After aging, solid-liquid separation was performed. The solid was dried at 80-90℃, ground and passed through a 200-mesh sieve to obtain the polymeric polyaluminum ferric chloride water purification agent.

[0015] Furthermore, the ratio of aluminum chloride-attapulgite composite material, citric acid-modified nano magnesium phosphate, and deionized water is 20-30g: 1-3g: 100-160mL.

[0016] Furthermore, the specific preparation steps of the polyaluminum chloride ferric sulfate-attapulgite composite material are as follows:

[0017] Acidified attapulgite, polyaluminum ferric chloride sulfate powder, and deionized water were added to a reactor and reacted at 75-85℃ and 200-300 r / min for 5-7 h. The mixture was then ultrasonically treated for 0.5-1.5 h, and allowed to stand for solid-liquid separation. The solid was dried at 105℃, ground, and sieved through a 200-mesh sieve to obtain the polyaluminum ferric chloride sulfate-attapulgite composite material.

[0018] Furthermore, the ratio of acidified attapulgite, polyaluminum ferric sulfate powder, and deionized water is 30-40g: 7.5-10g: 1600-2000mL.

[0019] Furthermore, acidified attapulgite is obtained by treating attapulgite with a 4 mol / L hydrochloric acid solution at a ratio of 30-50 g: 150-250 mL.

[0020] Furthermore, the specific preparation steps for polyaluminum chloride ferric sulfate powder are as follows:

[0021] Aluminum sulfate octahydrate, ferric chloride hexahydrate, and water were added to a reaction vessel and stirred at room temperature and 550-650 r / min for 15-20 min. Then, a 2 mol / L sodium hydroxide solution was slowly added dropwise to the vessel at a rate of 1 mL / min. After the addition was complete, the reaction was carried out at 50-60℃ and 150-250 r / min for 45-75 min. After the reaction was completed, the mixture was naturally cooled to room temperature and allowed to stand for aging for 20-28 h. The product was dried at 60℃ for 40-50 h, ground, and passed through a 200-mesh sieve to obtain polyaluminum chloride ferric sulfate powder.

[0022] Furthermore, the ratio of aluminum sulfate octadechydrate, ferric chloride hexahydrate, water, and sodium hydroxide solution is 20-24g: 3.24-3.9g: 50-70mL: 35-65mL.

[0023] Furthermore, the specific preparation steps for citric acid-modified nano-magnesium phosphate are as follows:

[0024] Weigh magnesium hydroxide powder and distilled water, and stir to obtain magnesium hydroxide emulsion. Add 15% phosphoric acid solution and solid citric acid to the reaction vessel, and stir until dissolved at room temperature and 250-350 r / min. Then, slowly add all the magnesium hydroxide emulsion dropwise at a rate of 1 mL / min. After the addition is complete, adjust the pH of the system to 10, continue stirring for 1 h, seal the reaction vessel, and react at a constant temperature of 140-150℃ for 10-14 h. After naturally cooling to room temperature, centrifuge and wash the product with distilled water, dry it at 85-95℃, grind it and pass it through a 200-mesh sieve to obtain citric acid modified nano magnesium phosphate.

[0025] Furthermore, the ratio of magnesium hydroxide powder, distilled water, phosphoric acid solution, and solid citric acid is 18-22g: 50-80mL: 120-160mL: 10-22g.

[0026] The beneficial effects of this invention are:

[0027] 1. This invention constructs a multi-level chemical assembly composite structure by combining a "polyaluminum chloride ferric sulfate-acidified attapulgite" charge neutralization / adsorption framework with a "citric acid-modified nano magnesium phosphate" deep chelation unit. Through the synergy of coordination bonds, electrostatic interactions, and hydrogen bonds, a stable composite water purification system is formed. This fundamentally solves the problems of easy component separation, rapid attenuation of synergistic effects, and poor long-term stability caused by physical compounding of traditional water purification agents. While significantly improving the simultaneous removal efficiency of suspended solids, phosphorus, COD, and heavy metal ions, it ensures the compactness and impact resistance of the floc structure, and can meet the stringent requirements for agent stability, reliability, and long-term efficacy consistency in water treatment scenarios such as municipal sewage and industrial circulating water.

[0028] 2. The citric acid-modified nano-magnesium phosphate used in this invention has carboxyl functional groups introduced on its surface. These groups endow the material with highly selective adsorption capacity for heavy metal ions, achieving deep removal, while also possessing multiple auxiliary functions: as a pH buffer, it can stabilize the pH environment during the PAFC hydrolysis process; as a floc modifier, it can promote the formation of dense, high-strength flocs through coordination crosslinking, improving sedimentation and dewatering performance; in addition, the environmental friendliness of magnesium-based materials and their similarity to the chemical behavior of aluminum and iron ions further enhance the compatibility and stability of the composite system; finally, this component forms a stable chemical bond with the composite framework through surface carboxyl groups, is firmly anchored, and constructs an integrated synergistic removal pathway of "adsorption-fixation-flocculation enhancement".

[0029] 3. The polyaluminum chloride ferric sulfate powder prepared by this invention has its own unique aluminum-iron polynuclear hydroxyl complex structure and dual anions (SO4). 2- / Cl - The synergistic effect endows the product with high flocculation activity and wide pH adaptability. More importantly, polyaluminum ferric sulfate not only serves as the core of water purification, but also acts as a key "bridge" connecting the various components: its positively charged polymer skeleton can be loaded onto acidified attapulgite through electrostatic interaction, while its abundant Al / Fe-OH active sites can chemically bond with the silanol groups of acidified attapulgite and the carboxyl groups of citric acid-modified nano-magnesium phosphate. This multi-point chemical bond bridging effectively stabilizes the structure of polyaluminum ferric sulfate itself and prevents its hydrolytic deactivation, while fundamentally strengthening the stability and synergistic purification efficiency of the entire organic-inorganic composite system.

[0030] 4. This invention transforms natural attapulgite into a highly active adsorption matrix through acid activation. The resulting composite material serves two purposes: firstly, it provides a high-strength, rigid framework for dispersing polyaluminum chloride ferric sulfate and citric acid-modified nano-magnesium phosphate, enhancing floc performance; secondly, its well-developed pores and surface active sites interlock with the hydrolysis products of polyaluminum chloride ferric sulfate and citric acid-modified nano-magnesium phosphate, jointly constructing a multi-stage purification network of "electroneutralization-adsorption-chelation," thereby significantly improving pollutant capture capacity and removal efficiency, and ensuring the long-term stability of the system in dynamic water flow. Detailed Implementation

[0031] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0032] Example 1: A method for preparing a composite polyaluminum ferric chloride water purification agent, comprising the following steps:

[0033] S1: Weigh 20g of magnesium hydroxide powder and 65mL of distilled water, and stir to form a uniform magnesium hydroxide emulsion; add 140mL of 15% phosphoric acid solution and 16g of solid citric acid to the reaction vessel, and stir until completely dissolved at room temperature and a speed of 300r / min. Then, slowly add all the magnesium hydroxide emulsion dropwise at a rate of 1mL / min. After the addition is complete, add sodium hydroxide solution to adjust the pH of the system to 10, and continue stirring at room temperature for 1h. Seal the reaction vessel and react at a constant temperature of 145℃ for 12h. After the reaction vessel cools naturally to room temperature, centrifuge and wash the product with distilled water, dry it at 90℃, grind it and pass it through a 200-mesh sieve to obtain citric acid modified nano magnesium phosphate.

[0034] Based on the synergistic effect of coordination chemistry and precipitation-hydrothermal crystallization, citric acid and phosphoric acid were first mixed into a ligand solution under stirring at room temperature. Then, magnesium hydroxide emulsion was slowly added dropwise, causing magnesium ions to react with phosphate ions to generate magnesium phosphate precursors. At the same time, the carboxyl groups of citric acid were surface-coordinated with magnesium ions. Subsequently, sodium hydroxide was used to adjust the pH of the system to 10 to stabilize the coordination structure and create an alkaline hydrothermal environment. Finally, hydrothermal crystallization was carried out in a sealed reactor at 145℃, which transformed the amorphous precursors into nano-magnesium phosphate crystals. Meanwhile, citric acid molecules were firmly grafted onto the particle surface through chemical coordination, ultimately obtaining citric acid-modified nano-magnesium phosphate.

[0035] S2: Add 22g of aluminum sulfate octadechydrate, 3.57g of ferric chloride hexahydrate, and 60mL of water to a reaction vessel. Stir for 18min at room temperature and 600r / min until the solid is completely dissolved. Then, while maintaining the stirring speed, slowly add 50mL of 2mol / L sodium hydroxide solution dropwise to the vessel at a rate of 1mL / min. After the addition is complete, stir the reaction at 55℃ and 200r / min for 60min. After the reaction is complete, allow the product to cool naturally to room temperature and let it stand at room temperature for 24h. Finally, take out the aged product, dry it at 60℃ for 45h, and grind it through a 200-mesh sieve to obtain polyaluminum chloride ferric sulfate powder.

[0036] A stepwise alkalization polymerization method was adopted, using aluminum sulfate octadechydrate and ferric chloride hexahydrate as raw materials, in an aqueous solution system at room temperature. The Al released after dissolution of these two materials... 3+ and Fe 3+ Hydrated ions are formed in aqueous solution, and OH- is provided by the slow addition of sodium hydroxide. - Under the influence of the action, hydrated metal ions undergo gradual hydrolysis, OH- - The process involves the substitution of coordinated water molecules to generate hydroxyl ligands, which then form dimers and polynuclear complexes via hydroxyl bridging. During this process, SO4 in the feedstock... 2- and Cl - By combining with the positively charged aluminum-iron hydroxyl polymer backbone through electrostatic interaction, a polyaluminum-iron sulfate powder with the characteristics of "aluminum-iron synergy" and "bi-anion synergy" is constructed.

[0037] S3: Add 40g of attapulgite and 200mL of 4mol / L hydrochloric acid solution to the reaction vessel, stir and react for 24h at room temperature and 250r / min. After the reaction, perform solid-liquid separation, add deionized water to the bottom solid and wash repeatedly until the last wash liquid is neutral. After drying and grinding at 60℃, acidified attapulgite is obtained.

[0038] 35g of acidified attapulgite, 8.75g of polyaluminum ferric chloride sulfate powder and 1800mL of deionized water were added to a reaction vessel and stirred for 6 hours at 80℃ and 250r / min. After the reaction, the mixture was ultrasonically treated for 1 hour and allowed to stand for solid-liquid separation. The bottom solid was dried at 105℃, ground and passed through a 200-mesh sieve to obtain the polyaluminum ferric chloride sulfate-attapulgite composite material.

[0039] S4: Add 25g of polyaluminum ferric chloride-attapulgite composite material, 2g of citric acid modified nano magnesium phosphate and 130mL of deionized water to the reactor. Stir for 35min at room temperature and 250r / min until the mixture is uniform. Then stop stirring and let it stand for 135min. After aging, perform solid-liquid separation on the mixture. Dry the bottom solid at 85℃, grind it and pass it through a 200-mesh sieve to obtain the composite polyaluminum ferric chloride water purification agent.

[0040] Example 2: A method for preparing a composite polyaluminum ferric chloride water purification agent, comprising the following steps:

[0041] S1: Weigh 18g of magnesium hydroxide powder and 50mL of distilled water, and stir to form a uniform magnesium hydroxide emulsion; add 120mL of 15% phosphoric acid solution and 10g of solid citric acid to the reaction vessel, and stir until completely dissolved at room temperature and a speed of 250r / min. Then, slowly add all the magnesium hydroxide emulsion dropwise at a rate of 1mL / min. After the addition is complete, add sodium hydroxide solution to adjust the pH of the system to 10. Continue stirring at room temperature for 1h, seal the reaction vessel, and react at a constant temperature of 140℃ for 10h. After the reaction vessel cools naturally to room temperature, centrifuge and wash the product with distilled water, dry it at 85-95℃, grind it and pass it through a 200-mesh sieve to obtain citric acid modified nano magnesium phosphate.

[0042] S2: Add 20g of aluminum sulfate octadechydrate, 3.24g of ferric chloride hexahydrate, and 50mL of water to a reaction vessel. Stir for 15min at room temperature and 550r / min until the solid is completely dissolved. Then, while maintaining the stirring speed, slowly add 35mL of 2mol / L sodium hydroxide solution dropwise to the vessel at a rate of 1mL / min. After the addition is complete, stir the reaction at 50℃ and 150r / min for 45min. After the reaction is complete, allow the product to cool naturally to room temperature and let it stand at room temperature for 20h. Finally, take out the aged product, dry it at 60℃ for 40h, and grind it through a 200-mesh sieve to obtain polyaluminum chloride ferric sulfate powder.

[0043] S3: Add 30g of attapulgite and 150mL of 4mol / L hydrochloric acid solution to the reaction vessel, stir and react for 20h at room temperature and 200r / min. After the reaction, perform solid-liquid separation, add deionized water to the bottom solid and wash repeatedly until the last washing liquid is neutral. After drying and grinding at 60℃, acidified attapulgite is obtained.

[0044] 30g of acidified attapulgite, 7.5g of polyaluminum ferric chloride powder and 1600mL of deionized water were added to a reaction vessel and stirred for 5h at 75℃ and 200r / min. After the reaction, the mixture was ultrasonically treated for 0.5h, and then allowed to stand for solid-liquid separation. The bottom solid was dried at 105℃, ground and passed through a 200-mesh sieve to obtain the polyaluminum ferric chloride-attapulgite composite material.

[0045] S4: Add 20g of polyaluminum ferric chloride-attapulgite composite material, 1g of citric acid modified nano magnesium phosphate and 100mL of deionized water to the reactor. Stir for 30min at room temperature and 200r / min until the mixture is uniform. Then stop stirring and let it stand for 120min. After aging, perform solid-liquid separation on the mixture. Dry the bottom solid at 80℃, grind it and pass it through a 200-mesh sieve to obtain the composite polyaluminum ferric chloride water purification agent.

[0046] Example 3: A method for preparing a composite polyaluminum ferric chloride water purification agent, comprising the following steps:

[0047] S1: Weigh 22g of magnesium hydroxide powder and 80mL of distilled water, and stir to form a uniform magnesium hydroxide emulsion; add 160mL of 15% phosphoric acid solution and 22g of solid citric acid to the reaction vessel, and stir until completely dissolved at room temperature and a speed of 350r / min. Then, slowly add all the magnesium hydroxide emulsion dropwise at a rate of 1mL / min. After the addition is complete, add sodium hydroxide solution to adjust the pH of the system to 10. Continue stirring at room temperature for 1h, seal the reaction vessel, and react at a constant temperature of 150℃ for 14h. After the reaction vessel cools naturally to room temperature, centrifuge and wash the product with distilled water, dry it at 95℃, grind it, and pass it through a 200-mesh sieve to obtain citric acid modified nano magnesium phosphate.

[0048] S2: Add 24g of aluminum sulfate octahydrate, 3.9g of ferric chloride hexahydrate, and 70mL of water to a reaction vessel. Stir for 20min at room temperature and 650r / min until the solid is completely dissolved. Then, while maintaining the stirring speed, slowly add 65mL of 2mol / L sodium hydroxide solution dropwise to the vessel at a rate of 1mL / min. After the addition is complete, stir the reaction at 60℃ and 250r / min for 75min. After the reaction is complete, allow the product to cool naturally to room temperature and let it stand and age at room temperature for 28h. Finally, take out the aged product, dry it at 60℃ for 50h, and grind it through a 200-mesh sieve to obtain polyaluminum chloride ferric sulfate powder.

[0049] S3: Add 50g of attapulgite and 250mL of 4mol / L hydrochloric acid solution to the reaction vessel, stir and react for 28h at room temperature and 250r / min. After the reaction, perform solid-liquid separation, add deionized water to the bottom solid and wash repeatedly until the last wash liquid is neutral. After drying and grinding at 60℃, acidified attapulgite is obtained.

[0050] 40g of acidified attapulgite, 10g of polyaluminum ferric chloride powder and 2000mL of deionized water were added to a reaction vessel and stirred for 7h at 85℃ and 300r / min. After the reaction, the mixture was ultrasonically treated for 1.5h, and then allowed to stand for solid-liquid separation. The bottom solid was dried at 105℃, ground and passed through a 200-mesh sieve to obtain the polyaluminum ferric chloride-attapulgite composite material.

[0051] S4: Add 30g of polyaluminum ferric chloride-attapulgite composite material, 3g of citric acid modified nano magnesium phosphate and 160mL of deionized water to the reactor. Stir for 40min at room temperature and 300r / min until the mixture is uniform. Then stop stirring and let it stand for 150min. After aging, perform solid-liquid separation on the mixture. Dry the bottom solid at 90℃, grind it and pass it through a 200-mesh sieve to obtain the composite polyaluminum ferric chloride water purification agent.

[0052] The raw materials used in Examples 1-4 of this application are all commercially available. Among them, magnesium hydroxide (AR, purity ≥95%), aluminum sulfate octadechydrate (purity ≥99%) and ferric chloride hexahydrate (purity ≥99%) were purchased from Shanghai Aladdin Biochemical Co., Ltd.; phosphoric acid solution (concentration 15wt%) and attapulgite (purity 98%) were purchased from Shanghai Maclean Biochemical Technology Co., Ltd.; and citric acid (AR) was purchased from Tianjin Yongda Chemical Reagent Co., Ltd.

[0053] Application Example: In wastewater treatment, 150-250 mg / L of the composite polyaluminum ferric chloride water purifier of this invention is added to the mixing tank or aeration tank outlet at the inlet. After the agent and wastewater are thoroughly mixed for 1-2 minutes by rapid stirring (300 r / min), the mixture enters a dedicated catalytic-flocculation reaction tank. In the reaction tank, the system reacts for 15-25 minutes under slow stirring conditions (50-80 r / min), forming dense, coarse flocs with excellent settling properties. These high-quality flocs can achieve rapid and thorough mud-water separation in the subsequent sedimentation tank, with a settling time significantly shorter than that of flocs formed by traditional agents. The system effluent can simultaneously achieve efficient and synergistic removal of suspended solids, total phosphorus, COD, and heavy metal ions.

[0054] Comparative Example 1: Based on Example 1, step S1, preparation of citric acid modified nano-magnesium phosphate, was omitted. Only the polyaluminum chloride-attapulgite composite material was prepared, while all other steps and parameters remained unchanged, resulting in a composite polyaluminum chloride-ferric water purifier.

[0055] Comparative Example 2: Based on Example 1, step S3, the preparation of the polyaluminum chloride-attapulgite composite material, was omitted. In step S4, the polyaluminum chloride powder was directly mixed with citric acid-modified nano magnesium phosphate. All other steps and parameters remained unchanged to obtain the composite polyaluminum chloride water purifier.

[0056] Comparative Example 3: Based on Example 1, the attapulgite in step S3 was replaced with the original attapulgite that had not been acidified with hydrochloric acid, while all other steps and parameters remained unchanged, resulting in a composite polyaluminum ferric chloride water purifier.

[0057] The following performance tests were conducted on the composite polyaluminum ferric chloride water purification agents prepared in Examples 1-3 and Comparative Examples 1-3:

[0058] Take a 500mL wastewater sample (water quality: suspended solids 40mg / L, color 120 times, turbidity 50 degrees, initial total phosphorus concentration 1.54mg / L, initial COD concentration 85mg / L, Cd...). 2+ Initial concentration 1 mg / L, Pb 2+ With an initial concentration of 1.5 mg / L, add 100 mg of compound polyaluminum ferric chloride water treatment agent. First, stir rapidly at 300 r / min for 1 min to fully mix the agent with the wastewater and initially destabilize it. Then, reduce the speed to 70 r / min and stir slowly for 15 min to promote the growth and enlargement of micro-flocculations. After that, stop stirring and let it stand to settle. Record the time required from the start of settling until the flocs have completely settled to the bottom of the container as the flocculation and settling time. The shorter the time, the faster the floc formation rate, the higher the density, and the better the settling performance.

[0059] After standing for 30 minutes, the supernatant was aspirated from 2 cm below the liquid surface and filtered through a 0.22 μm filter membrane to remove residual fine particles. Then, its suspended solids, color, turbidity, total phosphorus, COD, and Cd were measured. 2+ and Pb 2+ The residual concentration of each pollutant is calculated by taking the percentage of the difference between the initial and residual concentrations of each pollutant relative to the initial concentration, and the corresponding removal rate is obtained to comprehensively evaluate the simultaneous purification efficiency of the water purification agent for various pollutants.

[0060] To assess the long-term stability of the flocs, another sample of the treated supernatant (sampling location as above) was taken and its turbidity was measured at 0h (i.e., immediately after settling for 30 minutes), 6h, 24h, and 48h. The turbidity recovery rate was calculated using the following formula: Turbidity recovery rate = (turbidity after settling - turbidity at 0h) / turbidity at 0h × 100%. The higher the turbidity recovery rate, the more unstable the floc structure, and the more likely it is to break or resuspend, leading to secondary deterioration of the effluent quality. Conversely, the lower the turbidity recovery rate, the denser and more stable the floc network structure.

[0061] The results are shown in Table 1:

[0062] Table 1 Performance Test Results of Composite Polyaluminum Ferric Chloride Water Purifier

[0063]

[0064] As shown in Table 1, the composite polyaluminum ferric chloride water purifiers prepared in Examples 1-3 of this invention, by constructing a stable composite structure with aluminum ferric chloride sulfate (PAFC) as the charge neutralization core, acidified attapulgite as the carrier skeleton, and citric acid-modified nano-magnesium phosphate as the deep chelation unit, demonstrate outstanding performance in flocculation sedimentation rate, synergistic removal of multiple pollutants, and floc stability. This fundamentally solves the core defects of weak component binding force and easy attenuation of synergistic effect caused by physical mixing, and significantly improves the batch-to-batch consistency, long-term stability, and adaptability to complex water bodies.

[0065] Comparative Example 1 lacked the citric acid-modified nano-magnesium phosphate component, and its overall performance was significantly inferior to that of the Examples, especially in terms of Cd. 2+ Pb 2+ The removal rate was significantly lower than that of the example, which confirms the key role of citric acid modified nano magnesium phosphate as a "deep heavy metal chelating unit". This component achieves specific capture of heavy metal ions through coordination. Without it, the water purification agent's ability to target and remove heavy metals will be severely insufficient. At the same time, its turbidity recovery rate at 48 hours is higher than that of the example, which also shows that this chelating unit may have an auxiliary effect on enhancing the stability of floc structure.

[0066] Comparative Example 2 lacked the attapulgite carrier, and its performance was the worst among all test groups. The flocculation and settling time was as long as 6.5 minutes, and the removal rates of pollutants such as turbidity and COD were at the lowest level. Moreover, the turbidity recovery rate was as high as 22.3% after 48 hours. This indicates that the attapulgite carrier is the basic framework for constructing the "flocculation-adsorption synergistic system". Without this carrier, polyaluminum chloride ferric sulfate is prone to agglomeration and deactivation, which not only reduces the pollutant capture efficiency, but also leads to loose floc structure and weak anti-breakage ability, making it impossible to maintain the long-term stability of the effluent water quality.

[0067] Comparative Example 3 used unacidified attapulgite, whose performance was between that of the Examples and Comparative Examples 1-2. However, its total phosphorus removal rate, heavy metal removal rate, and turbidity recovery rate after 48 hours did not reach the level of the Examples. This proves that the acidification pretreatment of attapulgite is a necessary step to "activate the hydroxyl groups on the surface of the carrier and expand the porosity". The unacidified carrier cannot fully load the functional components and exert the adsorption efficiency, and thus cannot achieve the best synergistic effect of each component.

[0068] It should be noted that, in this document, terms such as “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0069] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A method for preparing a composite polyaluminum ferric chloride water purification agent, characterized in that, Includes the following steps: Step 1: Citric acid modified nano-magnesium phosphate is prepared by hydrothermal reaction using magnesium hydroxide, phosphoric acid and citric acid as raw materials. Step 2: Using aluminum sulfate octadechydrate and ferric chloride hexahydrate as raw materials, polyaluminum chloride ferric sulfate powder is obtained through alkalization polymerization; Step 3: After acidification with hydrochloric acid, attapulgite is used as a carrier to load the polyaluminum chloride ferric sulfate powder to obtain a polyaluminum chloride ferric sulfate-attapulgite composite material. Step 4: The composite polyaluminum chloride-attapulgite material is compounded with citric acid-modified nano magnesium phosphate, aged and dried to obtain a composite polyaluminum chloride-ferric water purifier.

2. The preparation method of the composite polyaluminum ferric chloride water purification agent according to claim 1, characterized in that, The specific preparation steps of the composite polyaluminum ferric chloride water purification agent are as follows: Polyaluminum ferric chloride-attapulgite composite material, citric acid modified nano magnesium phosphate and deionized water were added to a reaction vessel and stirred at room temperature and 200-300 r / min for 30-40 min. Then stirring was stopped and the mixture was allowed to stand for aging for 120-150 min. After aging, solid-liquid separation was performed. The solid was dried at 80-90℃, ground and passed through a 200-mesh sieve to obtain the polymeric polyaluminum ferric chloride water purification agent.

3. The preparation method of the composite polyaluminum ferric chloride water purification agent according to claim 2, characterized in that, The ratio of the polyaluminum chloride ferric sulfate-attapulgite composite material, citric acid modified nano magnesium phosphate, and deionized water is 20-30g: 1-3g: 100-160mL.

4. The preparation method of the composite polyaluminum ferric chloride water purification agent according to claim 2, characterized in that, The specific preparation steps of the polyaluminum chloride ferric sulfate-attapulgite composite material are as follows: Acidified attapulgite, polyaluminum ferric chloride sulfate powder and deionized water were added to a reaction vessel and reacted at 75-85℃ and 200-300 r / min for 5-7 h. After ultrasonic treatment for 0.5-1.5 h, the solid and liquid were separated by standing. The solid was dried at 105℃, ground and sieved through a 200-mesh sieve to obtain the polyaluminum ferric chloride sulfate-attapulgite composite material. The ratio of acidified attapulgite, polyaluminum ferric sulfate powder, and deionized water is 30-40g: 7.5-10g: 1600-2000mL.

5. The preparation method of the composite polyaluminum ferric chloride water purification agent according to claim 4, characterized in that, The acidified attapulgite is obtained by treating attapulgite with a 4 mol / L hydrochloric acid solution at a ratio of 30-50 g: 150-250 mL.

6. The preparation method of the composite polyaluminum ferric chloride water purification agent according to claim 4, characterized in that, The specific preparation steps for the polyaluminum chloride ferric sulfate powder are as follows: Aluminum sulfate octahydrate, ferric chloride hexahydrate, and water were added to a reaction vessel and stirred at room temperature and 550-650 r / min for 15-20 min. Then, a 2 mol / L sodium hydroxide solution was slowly added dropwise to the vessel at a rate of 1 mL / min. After the addition was completed, the reaction was carried out at 50-60℃ and 150-250 r / min for 45-75 min. After the reaction was completed, the mixture was naturally cooled to room temperature and allowed to stand for 20-28 h. The product was dried at 60℃ for 40-50 h, ground, and passed through a 200-mesh sieve to obtain polyaluminum chloride ferric sulfate powder. The ratio of aluminum sulfate octadechydrate, ferric chloride hexahydrate, water, and sodium hydroxide solution is 20-24g: 3.24-3.9g: 50-70mL: 35-65mL.

7. The preparation method of the composite polyaluminum ferric chloride water purification agent according to claim 2, characterized in that, The specific preparation steps for the citric acid-modified nano-magnesium phosphate are as follows: Weigh magnesium hydroxide powder and distilled water, and stir to obtain magnesium hydroxide emulsion. Add 15% phosphoric acid solution and solid citric acid to the reaction vessel, and stir until dissolved at room temperature and 250-350 r / min. Then, slowly add all the magnesium hydroxide emulsion dropwise at a rate of 1 mL / min. After the addition is complete, adjust the pH of the system to 10, continue stirring for 1 h, seal the reaction vessel, and react at a constant temperature of 140-150℃ for 10-14 h. After naturally cooling to room temperature, centrifuge and wash the product with distilled water, dry it at 85-95℃, grind it and pass it through a 200-mesh sieve to obtain citric acid modified nano magnesium phosphate.

8. The preparation method of the composite polyaluminum ferric chloride water purification agent according to claim 7, characterized in that, The ratio of magnesium hydroxide powder, distilled water, phosphoric acid solution and solid citric acid is 18-22g: 50-80mL: 120-160mL: 10-22g.

9. A composite polyaluminum ferric chloride water purification agent, prepared according to any one of claims 1-8.

10. The application of the composite polyaluminum ferric chloride water purification agent as described in claim 9 in wastewater treatment.

Images