Polyaluminum ferric chloride flocculant as well as preparation method and application thereof

Abstract

The invention discloses a polyaluminum ferric chloride flocculant as well as a preparation method and application thereof, and belongs to the technical field of sewage treatment.The preparation method comprises the steps that cobalt ferrite is loaded on the surface of nano mesoporous silica through a coprecipitation-calcination method, supported silica is obtained, then amination modification and tartaric acid modification are performed by using a silane coupling agent KH550, and the polyaluminum ferric chloride flocculant is obtained. And finally, blending the composite silicon dioxide with an aluminum salt, an iron salt and hydrogen peroxide under an acidic condition, and forming and loading a polyaluminum ferric chloride flocculation layer on the surface through in-situ hydrolytic polymerization and catalytic oxidation synergy to obtain the polyaluminum ferric chloride flocculant. Quadruple synergy of magnetic separation, catalytic oxidation, deep adsorption and enhanced flocculation is realized, and suspended matters, soluble organic matters, phosphorus and chromaticity are efficiently removed.

Description

Technical Field

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

[0002] Polyaluminum ferric chloride (PAFC) is a new type of highly efficient inorganic polymeric flocculant prepared by hydrolysis and polymerization reactions using aluminum salts and iron salts as core raw materials. Its core effective component is an inorganic polymeric compound containing polynuclear complex ions, which combines the strong bridging adsorption capacity of aluminum salt flocculants with the high charge density advantage of iron salt flocculants.

[0003] This product is available in both liquid and solid forms. It is readily soluble in water and forms a stable colloidal system after dissolution. It possesses core characteristics such as large molecular weight, wide applicable pH range, and strong anti-interference ability. It can efficiently separate water pollutants through the synergistic effect of "flocculation-sedimentation". It can widely remove suspended solids, color, chemical oxygen demand (COD), biochemical oxygen demand (BOD), and some toxic and harmful substances from water. It is widely used in drinking water purification, industrial wastewater treatment, and municipal sewage treatment. To further improve the overall performance of PAFC and expand its applicability in complex pollution scenarios, multifunctional composite modifiers such as magnetic particles, targeted adsorption sites, and hydrophilic modifiers can be introduced to achieve the synergistic effect of "flocculation-adsorption-sedimentation" or fillers such as silica can be added to enhance the flocculation effect.

[0004] Chinese invention patent application CN112158933A discloses a polyaluminum ferric chloride flocculant and its preparation method. By precisely controlling the molar ratio of aluminum salt to iron salt and the amount of alkali added, a simple process of room temperature polymerization and long-term curing is adopted to prepare solid polyaluminum ferric chloride flocculant. It effectively combines the advantages of aluminum salt and iron salt flocculants and obtains high efficiency in phosphorus removal and turbidity removal.

[0005] Existing polyaluminum ferric chloride flocculants can only remove pollutants in colloidal or suspended states when treating complex wastewater containing oils, dyes, and antibiotics. They cannot effectively degrade organic molecules in dissolved states with stable C-Cl bond structures. In subsequent biological treatment stages, the residual organic molecules and biotoxicity will inhibit microbial activity, reduce their metabolic functions, and affect the overall removal efficiency of wastewater pollutants. Summary of the Invention

[0006] The purpose of this invention is to provide a polyaluminum ferric chloride flocculant, its preparation method, and its application. Using nanoporous silica as a rigid framework, cobalt ferrite, amino and tartaric acid functional groups are sequentially loaded on its surface, and finally anchored to aluminum-iron hydrolysate polymer, a solid composite particle with magnetic, catalytic activity, specific adsorption, and flocculation functions is constructed; achieving synergistic removal and efficient separation of heavy metals, recalcitrant organic matter, and conventional pollutants.

[0007] The objective of this invention can be achieved through the following technical solutions: A method for preparing a polyaluminum ferric chloride flocculant includes the following steps: Step 1: Cobalt ferrite is loaded onto nanoporous silica using a co-precipitation-calcination method to obtain supported silica.

[0008] Step 2: The supported silica is modified by amylation using silane coupling agent KH550, and then tartaric acid is grafted through amidation reaction to obtain composite silica.

[0009] Step 3: Mix composite silica with aluminum salt and iron salt in an acidic medium, add hydrogen peroxide, and a polyaluminum ferric chloride flocculant layer is generated and firmly loaded on the surface of composite silica to obtain polyaluminum ferric chloride flocculant.

[0010] Furthermore, the specific preparation steps for supported silica are as follows: Cobalt chloride hexahydrate and ferric chloride hexahydrate were dissolved in deionized water, and nanoporous silica was added. The mixture was sonicated for 20-30 min, the pH was adjusted to 10 with ammonia, and the mixture was stirred for 30-40 min. The mixture was then kept in a water bath at 70-80℃ for 1-2 h, aged at room temperature for 3-4 h, centrifuged at 8000-9000 rpm for 10-15 min, and the precipitate was collected. The precipitate was washed 3-5 times with ultrapure water, dried under vacuum to constant weight, transferred to a muffle furnace, and calcined at 550-600℃ at 10℃ / min under oxygen-limited conditions for 1-2 h. After cooling, the calcined silica was ground and passed through a 100-mesh sieve to obtain supported silica.

[0011] Furthermore, the ratio of cobalt chloride hexahydrate, ferric chloride hexahydrate, deionized water, and nanoporous silica is 2.86-3.62g: 6.48-8.26g: 800-1000mL: 8-10g.

[0012] Furthermore, the specific preparation steps for composite silica are as follows: Tartaric acid, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide, N-hydroxysuccinimide, and 100-120 mL of deionized water were added to a three-necked flask and ultrasonically dispersed for 20-30 min. The mixture was then magnetically stirred for 4-5 h to activate the carboxyl groups of tartaric acid. Modified supported silica was then added, and the mixture was magnetically stirred for 18-22 h. The mixture was centrifuged at 12000-13000 rpm for 10-20 min, and the precipitate was collected. The precipitate was washed 3-5 times alternately with deionized water and anhydrous ethanol, and then vacuum dried to constant weight to obtain composite silica.

[0013] Further, the mass ratio of tartaric acid, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide, N-hydroxysuccinimide, deionized water, and modified supported silica is 20-30:8-12:5-7:100-120. Further, the specific preparation steps of the modified supported silica are as follows: Add the supported silica to toluene and stir for 30-40 min. Add deionized water and stir for 1-2 h. Add silane coupling agent KH-550 dropwise and transfer to an oil bath equipped with a cooling reflux device. Stir at 85-90℃ for 20-22 h. Remove the flask and centrifuge the sample at 8000-9000 rpm for 5-10 min. Wash the precipitate with ethanol 3-5 times and vacuum dry to constant weight to obtain modified supported silica.

[0014] Furthermore, the ratio of supported silica, toluene, deionized water and silane coupling agent KH-550 is 10-12g: 250-300mL: 3-5mL: 10-15mL.

[0015] Furthermore, the specific preparation steps of polyaluminum ferric chloride flocculant are as follows: Composite silica was added to a 50wt% aqueous solution of glycerol, along with aluminum chloride and ferric chloride. The pH was adjusted to 2 with hydrochloric acid, and the temperature was raised to 40-50℃. A 30wt% hydrogen peroxide solution was slowly added dropwise, and the reaction was allowed to proceed for 3-4 hours. The pH was then adjusted to neutral with sodium hydroxide, and the reaction was continued for another 2-3 hours. The solid product was collected, washed, and dried to obtain polyaluminum ferric chloride flocculant.

[0016] Furthermore, the ratio of composite silica, 50wt% glycerol aqueous solution, aluminum chloride, ferric chloride and 30wt% hydrogen peroxide solution is 10-12g: 200-300mL: 2-3g: 1-1.5g: 1-2mL.

[0017] This invention also provides an application of polyaluminum ferric chloride flocculant in wastewater treatment.

[0018] The beneficial effects of this invention are: 1. This invention employs a "magnetic core-coordination interface-flocculation shell" design, using covalently anchored cobalt ferrite as a dual-functional core for both magnetic and catalytic processes. This achieves magnetic separation of flocs and catalytic generation of hydroxyl radicals for pre-oxidation of pollutants. Tartaric acid grafted with amide bonds forms a multidentate coordination interface, which both stably regulates the hydrolysis of aluminum and iron ions to generate highly active flocs and directly complexes and adsorbs pollutants such as phosphates. Finally, a highly efficient polyaluminum ferric chloride flocculent shell is formed in situ on the outer layer. This achieves a quadruple synergy of magnetic separation, catalytic oxidation, deep adsorption, and enhanced flocculation, efficiently removing suspended solids, dissolved organic matter, phosphorus, and color. In particular, the binding of tartaric acid acts as a spatial barrier, preventing the aggregation of complex silica in the flocs, helping to maintain a highly active surface and continuously exert photocatalytic degradation of antibiotics, thus avoiding affecting the activity of microorganisms during subsequent advanced wastewater treatment and improving wastewater treatment efficiency.

[0019] 2. The supported silica in this invention uses nanoporous silica as a rigid framework, which not only has a high specific surface area, providing loading sites and structural support for subsequent functional layers, but also firmly loads cobalt ferrite on its surface through a co-precipitation-calcination method, giving the material significant magnetic response capabilities. This enables rapid separation and recycling of flocs under an applied magnetic field. The cobalt ferrite provides abundant metal active sites, enhancing the specific adsorption capacity for new pollutants such as antibiotics, and can actively degrade organic pollutants and chromophores under oxidants such as hydrogen peroxide or persulfate.

[0020] 3. The modified supported silica in this invention is modified by covalently grafting amino functional groups onto the surface of a magnetic support using the silane coupling agent KH-550, thereby achieving the amination modification of the support. The introduced amino groups not only provide reaction sites for the subsequent strong bonding of tartaric acid, but also improve the charge distribution and interfacial compatibility of the support surface, enhance its compatibility with the organic reaction system, and alleviate the internal stress between different material layers to a certain extent.

[0021] 4. The composite silica in this invention grafts tartaric acid molecules onto its surface via amide bonds, forming a polydentate coordination network rich in carboxyl and hydroxyl groups. This network effectively anchors and stabilizes aluminum and iron ions, regulates their hydrolysis-polymerization behavior, and induces the formation of polymer morphologies with high flocculation activity. This organic layer further expands the specific surface area and adsorption sites of the material, enabling efficient complexation and removal of pollutants such as phosphates. Detailed Implementation

[0022] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments in 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.

[0023] Example 1: A method for preparing a polyaluminum ferric chloride flocculant, comprising the following steps: S1: Dissolve 2.86g of cobalt chloride hexahydrate and 6.48g of ferric chloride hexahydrate in 800mL of deionized water, add 8g of nano-mesoporous silica, sonicate for 20min, adjust the pH to 10 with ammonia, stir for 30min, keep warm in a water bath at 70℃ for 1h, age at room temperature for 3h, centrifuge at 8000rpm for 10min, collect the precipitate, wash the precipitate three times with ultrapure water, vacuum dry to constant weight, transfer to a muffle furnace, calcine at 550℃ at 10℃ / min under oxygen-limited conditions for 1h, cool and grind, pass through a 100-mesh sieve to obtain supported silica.

[0024] The coprecipitation-calcination method is adopted. Cobalt salt and iron salt are dissolved in water and added to a nanoporous silica carrier. By adjusting the pH to alkaline, the metal ions are coprecipitated into hydroxide precursors and attached to the carrier. High-temperature calcination is then carried out to form cobalt ferrite from the hydroxide precursors.

[0025] S2: Add 10g of supported silica to 250mL of toluene and stir for 30min. Add 3mL of deionized water and stir for 1h. Add 10mL of silane coupling agent KH-550 dropwise and transfer to an oil bath equipped with a cooling reflux device. Stir at 85℃ for 20h. Remove the flask and centrifuge the sample at 8000rpm for 5min. Wash the precipitate three times with ethanol and dry it under vacuum at 60℃ to constant weight to obtain modified supported silica.

[0026] The silane coupling agent KH-550 is hydrolyzed to generate a silanol intermediate, which then undergoes a dehydration condensation reaction with the silanol groups on the surface of supported silica to form stable Si-O-Si covalent bonds, thus achieving amination modification.

[0027] S3: Add 2g tartaric acid, 0.8g 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide, 0.5g N-hydroxysuccinimide and 100mL deionized water to a three-necked flask, sonicate for 20min, and magnetically stir for 4h to activate the carboxyl groups of tartaric acid. Then add 10g modified supported silica, magnetically stir for 18h, centrifuge at 12000rpm for 10min, collect the precipitate, wash the precipitate three times alternately with deionized water and anhydrous ethanol, and vacuum dry at 60℃ to constant weight to obtain composite silica.

[0028] After the carboxyl group on the tartaric acid molecule is activated, it undergoes an amidation covalent reaction with the amino group on the modified silica surface, removing small molecule byproducts to form a stable covalent amide bond, thus covalently grafting tartaric acid onto the silica surface.

[0029] S4: Add 10g of composite silica to 200mL of 50wt% glycerol aqueous solution, add 2g of aluminum chloride and 1g of ferric chloride, adjust the pH to 2 with hydrochloric acid, heat to 40℃, slowly add 1mL of 30wt% hydrogen peroxide solution, react for 3h, adjust the pH to neutral with sodium hydroxide, continue the reaction for 2h, collect the solid product, wash and dry to obtain polyaluminum ferric chloride flocculant.

[0030] Example 2: A method for preparing a polyaluminum ferric chloride flocculant, comprising the following steps: S1: Dissolve 3.24g of cobalt chloride hexahydrate and 7.37g of ferric chloride hexahydrate in 900mL of deionized water, add 9g of nano-mesoporous silica, sonicate for 25min, adjust the pH to 10 with ammonia, stir for 35min, keep warm in a water bath at 75℃ for 1.5h, age at room temperature for 3.5h, centrifuge at 8500rpm for 12.5min, collect the precipitate, wash the precipitate 4 times with ultrapure water, vacuum dry to constant weight, transfer to a muffle furnace, calcine at 575℃ at 10℃ / min under oxygen-limited conditions for 1.5h, cool and grind, pass through a 100-mesh sieve to obtain supported silica.

[0031] S2: Add 11g of supported silica to 275mL of toluene and stir for 35min. Add 4mL of deionized water and stir for 1.5h. Add 12.5mL of silane coupling agent KH-550 dropwise and transfer to an oil bath equipped with a cooling reflux device. Stir at 87.5℃ for 21h. Remove the flask and centrifuge the sample at 8500rpm for 7.5min. Wash the precipitate four times with ethanol and dry it under vacuum at 65℃ to constant weight to obtain modified supported silica.

[0032] S3: Add 2.5g tartaric acid, 1.0g 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide, 0.6g N-hydroxysuccinimide and 110mL deionized water to a three-necked flask, sonicate for 25min, and magnetically stir for 4.5h to activate the carboxyl groups of tartaric acid. Then add 11g modified supported silica, magnetically stir for 20h, centrifuge at 12500rpm for 15min, collect the precipitate, wash the precipitate four times alternately with deionized water and anhydrous ethanol, and vacuum dry at 65℃ to constant weight to obtain composite silica.

[0033] S4: Add 11g of composite silica to 250mL of 50wt% glycerol aqueous solution, add 2.5g of aluminum chloride and 1.25g of ferric chloride, adjust the pH to 2 with hydrochloric acid, heat to 45℃, slowly add 1.5mL of 30wt% hydrogen peroxide solution, react for 3.5h, adjust the pH to neutral with sodium hydroxide, continue the reaction for 2.5h, collect the solid product, wash and dry to obtain polyaluminum ferric chloride flocculant.

[0034] Example 3: A method for preparing a polyaluminum ferric chloride flocculant, comprising the following steps: S1: Dissolve 3.62g of cobalt chloride hexahydrate and 8.26g of ferric chloride hexahydrate in 1000mL of deionized water, add 10g of nano-mesoporous silica, sonicate for 30min, adjust the pH to 10 with ammonia, stir for 40min, keep warm in a water bath at 80℃ for 2h, age at room temperature for 4h, centrifuge at 9000rpm for 15min, collect the precipitate, wash the precipitate 5 times with ultrapure water, vacuum dry to constant weight, transfer to a muffle furnace, calcine at 600℃ under oxygen-limited conditions at a rate of 10℃ / min for 2h, cool and grind, pass through a 100-mesh sieve to obtain supported silica.

[0035] S2: Add 12g of supported silica to 300mL of toluene and stir for 40min. Add 5mL of deionized water and stir for 2h. Add 15mL of silane coupling agent KH-550 dropwise and transfer to an oil bath equipped with a cooling reflux device. Stir at 90℃ for 22h. Remove the flask and centrifuge the sample at 9000rpm for 10min. Wash the precipitate with ethanol 5 times and vacuum dry at 70℃ to constant weight to obtain modified supported silica.

[0036] S3: Add 3g tartaric acid, 1.2g 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide, 0.7g N-hydroxysuccinimide and 120mL deionized water to a three-necked flask, sonicate for 30min, and magnetically stir for 5h to activate the carboxyl groups of tartaric acid. Then add 12g modified supported silica, magnetically stir for 22h, centrifuge at 13000rpm for 20min, collect the precipitate, wash the precipitate alternately with deionized water and anhydrous ethanol 5 times, and vacuum dry at 70℃ to constant weight to obtain composite silica.

[0037] S4: Add 12g of composite silica to 300mL of 50wt% glycerol aqueous solution, add 3g of aluminum chloride and 1.5g of ferric chloride, adjust the pH to 2 with hydrochloric acid, heat to 50℃, slowly add 2mL of 30wt% hydrogen peroxide solution, react for 4h, adjust the pH to neutral with sodium hydroxide, continue the reaction for 3h, collect the solid product, wash and dry to obtain polyaluminum ferric chloride flocculant.

[0038] In Examples 1-3, cobalt chloride hexahydrate was selected from Hubei Watson Chemical Technology Co., Ltd., CAS No. 7791-13-1; ferric chloride hexahydrate was selected from Shandong Duoju Chemical Co., Ltd., CAS No. 10025-77-1; nanoporous silica was selected from Qinghe County Chaotai Metal Materials Co., Ltd., CAS No. 1332-4-5, with a particle size of 300nm; tartaric acid was selected from Shandong Yaojia Chemical Co., Ltd., CAS No. 133-37-9; glycerol was selected from Shandong Shengyong Biotechnology Co., Ltd., CAS No. 56-81-5; and the remaining raw materials were all commercially available products.

[0039] Application example: In wastewater treatment processes, 200-300 mg / L of polyaluminum ferric chloride flocculant is added to the wastewater tank. After rapid mixing with the wastewater, it enters the catalytic-flocculation reaction tank and reacts for 20-30 minutes under slow stirring conditions, forming dense flocs with excellent settling properties. These flocs settle rapidly in the subsequent sedimentation tank, thus achieving efficient and stable wastewater treatment results.

[0040] Comparative Example 1: The difference from Example 1 is that step S1 is omitted, and the supported silica in step S2 is replaced with commercially available nano silica. The remaining steps remain unchanged, and polyaluminum ferric chloride flocculant is prepared.

[0041] Comparative Example 2: The difference from Example 1 is that step S2 is omitted, and the modified supported silica in step S3 is replaced with the supported silica in step S1, while the other steps remain unchanged, to prepare polyaluminum ferric chloride flocculant.

[0042] Comparative Example 3: The difference from Example 1 is that step S3 is omitted, and the composite silica in step S4 is replaced with the modified supported silica in step S2. The remaining steps remain unchanged, and polyaluminum ferric chloride flocculant is prepared.

[0043] The following performance tests were conducted on the polyaluminum ferric chloride flocculants prepared in Examples 1-3 and Comparative Examples 1-3: Take a 1000 mL wastewater sample (water quality: suspended solids 40 mg / L, color 120 times, turbidity 50 degrees, initial total phosphorus concentration 1.54 mg / L, initial COD concentration 85 mg / L, initial tetracycline concentration 50 mg / L), add 25 mg of flocculant, stir at 3000 rpm for 2 min, then switch to 1500 rpm for 10 min, then stop stirring and allow 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. After standing for 30 minutes, the supernatant was collected at a depth of 2 cm below the liquid surface. After filtration through a 0.22 μm filter membrane, the suspended solids, color, turbidity, and total phosphorus concentration were measured. The removal rate was calculated by the percentage difference between the initial and equilibrium concentrations of each pollutant. After standing for another 24 hours under natural light (to ensure equilibrium was reached), the solution was filtered through a 0.22 μm filter membrane, and the equilibrium concentration of tetracycline was measured. The removal rate of tetracycline was calculated by the percentage difference between the initial and equilibrium concentrations of tetracycline.

[0044] The results are shown in Table 1: Table 1 Performance Test Results of Polyaluminum Ferric Chloride Flocculant As can be seen from Table 1, when the polyaluminum ferric chloride flocculants prepared in Examples 1-3 are applied to urban domestic sewage treatment, they are significantly better than Comparative Examples 1-3 in terms of turbidity removal rate, color removal rate, COD removal rate, flocculation speed and adsorption of antibiotics.

[0045] In Comparative Example 1, the turbidity removal rate, color removal rate, COD removal rate, total phosphorus removal rate, and antibiotic adsorption capacity all decreased significantly, and the flocculation time was significantly prolonged. This may be because the mesoporous nano-silica lacked a cobalt ferrite loading, causing the carrier to lose its strong magnetic support. During the flocculation process, it relied solely on the gravity sedimentation of pure nano-silica. However, its loose mesoporous structure and poor hydrodynamic properties further increased the sedimentation resistance. By uniformly distributing cobalt ferrite nanoparticles on the silica carrier, transition metal active sites were provided. These sites not only enable the efficient adsorption of antibiotic molecules such as tetracycline through Lewis acid interactions and coordination interactions, but also have the potential to activate oxidants such as hydrogen peroxide, generating free radicals to degrade organic pollutants and achieve deep COD removal.

[0046] The removal rate of antibiotics in the comparative examples was lower than that in the examples, indicating that the polyaluminum ferric chloride flocculant prepared in the examples can help adsorb and decompose antibiotics, possibly through electron transfer induced by oxygen vacancies in cobalt ferrites, thereby providing photocatalytic degradation of adsorbed tetracycline. Comparative examples 2 and 3 show that the degradation rate decreases after the binding of tartaric acid is lacking, possibly due to the steric hindrance effect of the lack of tartaric acid, which makes the complex silica in the flocs easy to agglomerate and unable to maintain a high active surface, thus reducing the effect of photocatalytic degradation of antibiotics.

[0047] In Comparative Example 2, the removal rates of turbidity, color, COD, and total phosphorus decreased, and the flocculation time was prolonged. This may be due to the absence of amino groups introduced by the silane coupling agent KH-550, which resulted in poor performance of the subsequent covalently grafted tartaric acid molecular layer. This caused the material surface to lack strong organic adsorption sites, significantly weakening its pre-enrichment capacity for pollutants. The absence of amino groups resulted in the carrier surface being dominated by electrically neutral silanol groups, which could not form protonated amino ions under acidic conditions. This greatly reduced the ability of electrostatic adsorption to capture negatively charged pollutants (suspended solids, phosphate, etc.) in wastewater. Furthermore, without amino anchoring points, tartaric acid was difficult to graft stably and could not form a chelate structure with aluminum and iron ions in the polyaluminum ferric chloride flocculant through polycarboxyl groups. This led to unstable loading, easy ionization, and small flocs with slow settling.

[0048] In Comparative Example 3, the turbidity removal rate, color removal rate, COD removal rate, and total phosphorus removal rate all decreased relatively, and the flocculation time was relatively prolonged. This may be because only amination modification was performed without grafting tartaric acid molecules. Although amino groups are present, the adsorption capacity and specific binding ability with various pollutants are far inferior to the tartaric acid molecular layer with a multi-carboxyl structure. Without tartaric acid, the dispersibility and loading stability of polyaluminum ferric chloride flocculant on the carrier surface cannot be improved through multi-toothed chelation, resulting in uneven distribution, partial agglomeration, and reduced utilization of effective active sites.

[0049] 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 variations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A method for preparing a polyaluminum ferric chloride flocculant, characterized in that, Includes the following steps: Step 1: Cobalt ferrite is loaded onto nanoporous silica using a co-precipitation-calcination method to obtain supported silica; Step 2: Amide modification of supported silica is carried out using silane coupling agent KH550, followed by grafting tartaric acid through amidation reaction to obtain composite silica. Step 3: Mix composite silica with aluminum salt and iron salt in an acidic medium, add hydrogen peroxide, and a polyaluminum ferric chloride flocculant layer is generated and firmly loaded on the surface of composite silica to obtain polyaluminum ferric chloride flocculant.

2. The preparation method of the polyaluminum ferric chloride flocculant according to claim 1, characterized in that, The specific preparation steps for the supported silica are as follows: Cobalt chloride hexahydrate and ferric chloride hexahydrate were dissolved in deionized water, and nanoporous silica was added. The mixture was sonicated for 20-30 min, the pH was adjusted to 10 with ammonia, and the mixture was stirred for 30-40 min. The mixture was then kept in a water bath at 70-80℃ for 1-2 h, aged at room temperature for 3-4 h, centrifuged at 8000-9000 rpm for 10-15 min, and the precipitate was collected. The precipitate was washed 3-5 times with ultrapure water, dried under vacuum to constant weight, transferred to a muffle furnace, and calcined at 550-600℃ at 10℃ / min under oxygen-limited conditions for 1-2 h. After cooling, the calcined silica was ground and passed through a 100-mesh sieve to obtain supported silica.

3. The method for preparing a polyaluminum ferric chloride flocculant according to claim 2, characterized in that, The ratio of cobalt chloride hexahydrate, ferric chloride hexahydrate, deionized water, and nanoporous silica is 2.86-3.62g: 6.48-8.26g: 800-1000mL: 8-10g.

4. The method for preparing a polyaluminum ferric chloride flocculant according to claim 1, characterized in that, The specific preparation steps for the composite silica are as follows: Tartaric acid, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide, N-hydroxysuccinimide, and 100-120 mL of deionized water were added to a three-necked flask and ultrasonically dispersed for 20-30 min. The mixture was then magnetically stirred for 4-5 h to activate the carboxyl groups of tartaric acid. Modified supported silica was then added, and the mixture was magnetically stirred for 18-22 h. The mixture was centrifuged at 12000-13000 rpm for 10-20 min, and the precipitate was collected. The precipitate was washed 3-5 times alternately with deionized water and anhydrous ethanol, and then vacuum dried to constant weight to obtain composite silica.

5. The method for preparing a polyaluminum ferric chloride flocculant according to claim 4, characterized in that, The mass ratio of tartaric acid, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide, N-hydroxysuccinimide, deionized water, and modified supported silica is 20-30:8-12:5-7:100-120.

6. The method for preparing a polyaluminum ferric chloride flocculant according to claim 4, characterized in that, The specific preparation steps for the modified supported silica are as follows: Add the supported silica to toluene and stir for 30-40 min. Add deionized water and stir for 1-2 h. Add silane coupling agent KH-550 dropwise and transfer to an oil bath equipped with a cooling reflux device. Stir at 85-90℃ for 20-22 h. Remove the flask and centrifuge the sample at 8000-9000 rpm for 5-10 min. Wash the precipitate with ethanol 3-5 times and vacuum dry to constant weight to obtain modified supported silica.

7. The method for preparing a polyaluminum ferric chloride flocculant according to claim 6, characterized in that, The ratio of the supported silica, toluene, deionized water and silane coupling agent KH-550 is 10-12g: 250-300mL: 3-5mL: 10-15mL.

8. The method for preparing a polyaluminum ferric chloride flocculant according to claim 1, characterized in that, The specific preparation steps of the polyaluminum ferric chloride flocculant are as follows: Composite silica was added to a 50wt% aqueous solution of glycerol, aluminum chloride and ferric chloride were added, the pH was adjusted to 2 with hydrochloric acid, the temperature was raised to 40-50℃, and 30wt% hydrogen peroxide solution was slowly added dropwise. The reaction was carried out for 3-4 hours, the pH was adjusted to neutral with sodium hydroxide, and the reaction was continued for 2-3 hours. The solid product was collected, washed and dried to obtain polyaluminum ferric chloride flocculant. The ratio of the composite silica, 50wt% glycerol aqueous solution, aluminum chloride, ferric chloride and 30wt% hydrogen peroxide solution is 10-12g: 200-300mL: 2-3g: 1-1.5g: 1-2mL.

9. A polyaluminum ferric chloride flocculant, prepared according to any one of claims 1-8.

10. The application of the polyaluminum ferric chloride flocculant as described in claim 9 in wastewater treatment.

Images