Red soil-based copolymer coagulant, preparation method thereof and method for treating sewage

Abstract

The application provides a red soil-based copolymer coagulant, a preparation method thereof and a wastewater treatment method. The method uses red soil as a raw material, and the red soil is subjected to alkali fusion activation, acid leaching extraction and induced copolymer aging treatment to prepare a red soil copolymer coagulant containing silicon, aluminum and iron and having a synergistic effect of multiple components. The coagulant has a high charge density and a three-dimensional network structure, and when treating combined overflow sewage, the coagulant realizes efficient removal of pollutants through rapid mixing, slow loading flocculation and rapid sedimentation. Compared with traditional coagulants, the preparation method of the application is simple, the cost is low, the coagulation and sedimentation speed is fast, the treatment efficiency is high, and the application is suitable for the treatment of combined overflow sewage with high flow and short residence time.

Description

Technical Field

[0001] This invention relates to the field of water treatment, specifically to an environmentally friendly coagulant prepared from natural red soil and its application method in the treatment of combined sewer overflows. Background Technology

[0002] Currently, the water treatment field is widely researching the use of industrial solid waste (such as fly ash, coal gangue, and smelting dust) as raw materials to prepare metal coagulants through processes such as acid leaching and polymerization. This type of technology aims to achieve "waste treatment with waste" and has demonstrated certain turbidity removal and organic matter adsorption performance on a laboratory scale.

[0003] Although industrial waste-based coagulants have certain application prospects, their actual promotion has the following significant shortcomings: 1. Environmental safety risks (secondary pollution): Industrial waste has an extremely complex composition, often rich in heavy metals such as lead, mercury, chromium, and cadmium, as well as residual pollutants. During the preparation and subsequent water treatment processes, these harmful substances are highly likely to dissolve and enter the receiving water bodies, posing a serious risk of secondary pollution and making it difficult to meet increasingly stringent environmental quality standards.

[0004] 2. Large and uncontrollable fluctuations in composition: Due to the limited availability of industrial raw materials, the chemical composition of fly ash or coal gangue fluctuates greatly from batch to batch, resulting in unstable polymerization degree and effective components of the prepared coagulant, making it difficult to achieve standardized industrial production.

[0005] 3. High logistics costs: Industrial waste is often generated in geographically limited areas, and long-distance transportation of raw materials greatly increases production costs.

[0006] Based on the aforementioned technical shortcomings, the following three relevant prior art documents (previous art) with similar technical solutions were retrieved, and their technical solutions are summarized below: Existing technology 1 CN201410701818.6 (authorization announcement number CN104445554B): This document discloses a low-cost polyamine iron-modified red soil formula for removing cyanobacteria. Specifically, it uses polyepoxychloropropane-dimethylamine and polyferric sulfate as flocculants to achieve the aggregation of individual cyanobacteria on the molecular chain. Based on this, red soil is combined as a coagulant aid, utilizing the high density of red soil to drive floc sedimentation. Simultaneously, the naturally occurring active aluminum and iron in the red soil are used as auxiliary coagulants to solve the problems of high energy consumption and low efficiency in traditional algae removal processes. However, this solution has drawbacks: the red soil is only used as a physical weight-increasing coagulant aid; the aluminum and iron metals it contains are not chemically activated and mainly exist in inert mineral form, greatly limiting the coagulation efficiency; and the organic flocculant polyepoxychloropropane-dimethylamine used poses a risk of residual carcinogenicity.

[0007] Existing technology 2 CN202510792118.0 (Announcement No. CN120349016A) discloses a method for preparing and applying a high-efficiency lanthanum silicate polymeric coagulant. Its focus is on introducing lanthanum (La), a rare earth element with high reactivity and specific complexing ability, for the efficient removal of phytoplankton in water, thus overcoming the shortcomings of traditional algae-removing coagulants, such as large dosage, small flocs, and slow settling speed. However, this method mainly focuses on the algae-removing mechanism of lanthanum and does not address the preparation of low-cost coagulants using inexpensive mineral resources (such as red soil). It is particularly lacking in the structural design and application process of coagulants for handling combined sewer overflows with large flow rates, high suspended solids content, and short hydraulic retention times.

[0008] Existing technology 3 CN202511529953.1 (Announcement No. CN121317794A) discloses a polyaluminum zirconium coagulant, its preparation method, and its application. It provides a general approach that organically combines the efficient charge neutralization capabilities of zirconium and aluminum metal ions with the long-chain network structure of polysilicic acid through copolymerization. This method is commonly used to maintain good performance of coagulants over a wide pH range and specifically discloses its application in sludge dewatering to reduce capillary absorption time (CST) and filter cake moisture content. This document also suggests using the copolymerization modification of metal ions with polysilicic acid to improve floc strength for sludge conditioning and dewatering. The treatment targets and process conditions are significantly different from those for rapid purification of combined sewer overflows. However, it does not specifically disclose how to combine this method with the large flow rate, high pollutant concentration impact, and requirement for rapid sludge-water separation of combined sewer overflows, nor does it mention a one-step activated copolymerization strategy using red soil as raw material.

[0009] In summary, existing technologies lack a coagulant and its application method that can simultaneously meet the requirements of clean raw materials, low cost, high performance, and are particularly suitable for high-flow-rate, short-retention-time combined overflow wastewater treatment scenarios. Summary of the Invention

[0010] The purpose of this invention is to provide an environmentally friendly coagulant based on natural red soil and its application method, which improves ecological safety, optimizes resource matching and economy, and enhances the treatment efficiency of combined sewer overflows.

[0011] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a red soil-based copolymer coagulant includes the following steps: Step S1, Activation: Step S11: Collect natural red soil, remove impurities, air dry, crush and sieve; Step S12: Thoroughly mix sodium hydroxide solid with red soil powder at a mass ratio of 1:3-2:1; The mixture was heated to 600℃ at a rate of 15℃ / min and calcined at a constant temperature for 1.5h to convert the aluminum-iron silicate minerals in the red soil into acid-soluble active substances. Step S2, Acid Extraction: A 1.5-6 mol / L hydrochloric acid solution was used as the leaching agent. The activated solid was mixed with hydrochloric acid at a liquid-to-solid ratio of 20:1, and the mixture was reacted at 90℃ for 30 min. After the reaction, the mixture was filtered to obtain a product containing Al. 3+ Fe 3+ and acid leaching solution of soluble Si; Step S3, Induced Copolymerization and Aging: The acid leaching solution is diluted, and NaOH solution is slowly added under continuous stirring to adjust the pH value to 0.5-5. The solution is aged at room temperature for 1-3 hours to allow the silica and metal cations to undergo a copolymerization reaction, forming a red soil copolymer coagulant.

[0012] Preferably, the red soil originates from Hunan, Jiangxi, Yunnan, or Guizhou provinces.

[0013] Preferably, the powder from the crushed red soil in step S1 is passed through an 80-100 mesh sieve.

[0014] Preferably, the pH value in step S3 is 2-4.

[0015] In addition, the present invention also provides a red soil copolymer coagulant, which is prepared by the above preparation method.

[0016] Furthermore, the present invention also provides a method for treating combined sewer overflow wastewater using a red soil copolymer coagulant, comprising the following steps: Step S01, Quick Mixing: Add the red soil copolymer coagulant to the wastewater to be treated at a dosage of 0.5-2.0 mg / L based on metal elements, and stir rapidly at 250-300 rpm for 1-1.5 min. Step S02, Slow Mixing and Loading Flocculation: Reduce the stirring speed to 150-200 rpm, add the loading medium and coagulant polyacrylamide, and continue stirring for 2-3 minutes to form flocs on the surface of the loading medium. Step S03, Sedimentation Separation: Stop stirring and allow the mixture to settle, thus separating the pollutants.

[0017] Preferably, the loading medium is silica sand with a particle size of 80-120 mesh, a specific gravity of 2.64, and an addition amount of 0.5-1.0 g / L.

[0018] Preferably, the polyacrylamide is a nonionic polyacrylamide with a molecular weight of 5-8 million and an addition amount of 0.3-0.8 mg / L.

[0019] Preferably, the settling time in step S03 is 1-2 minutes.

[0020] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention utilizes widely distributed natural red soil instead of complex industrial waste as raw material. Through alkali fusion activation, acid leaching extraction, and induced copolymerization to form a red soil copolymer coagulant, it avoids heavy metals and harmful substances from entering the water cycle system at the source, thus solving the technical problem of secondary pollution risks associated with existing industrial waste-based coagulants and ensuring the ecological safety of treated water. The raw material scheme of this invention is fundamentally different from existing technologies 1-3. The core of existing technology 2 lies in introducing exogenous rare earth element lanthanum to enhance the specific removal of algae, while this application utilizes elements naturally contained in red soil, avoiding the potential environmental risks and cost problems brought by exogenous high-priced rare earth elements. Existing technology 3 uses pure chemical reagents to react with pure polysilicic acid, while this application fully utilizes inexpensive natural minerals through chemical modification, achieving "waste-to-waste treatment," which is more environmentally friendly. In the prior art 1, red soil is only used as a physical weight-increasing coagulant. The aluminum and iron metals contained in it are not chemically activated and mainly exist in the form of inert minerals. The coagulation efficiency is limited by its natural properties. However, this application transforms the inert silicon, aluminum, and iron into a highly active soluble state through a chemical process of alkali fusion activation and acid leaching extraction. This fundamentally changes the utilization method of red soil and stimulates its full potential coagulation efficiency.

[0021] 2. This invention utilizes naturally occurring red soil rich in active components such as SiO2, Al2O3, and Fe2O3, and employs a locally sourced coagulant preparation method. This achieves stable and controllable raw material sources, solving the problems of large fluctuations in raw material composition, low resource matching, and high transportation costs in existing technologies. It significantly reduces raw material acquisition costs and logistics expenditures, improving economic efficiency. This invention leverages widely available and relatively stable red soil, overcoming the problem of large and uncontrollable fluctuations in the composition of industrial waste. Compared to existing technology 2, which pursues high affinity complexation of specific pollutants, its technical path implies the need to introduce exogenous high-valence rare earth elements. Those skilled in the art face obstacles in using inexpensive natural minerals to achieve low-cost coagulation. In existing technology 1, red soil is only used as a physical weight-increasing coagulant aid; its contained aluminum and iron metals are not chemically activated and mainly exist in inert mineral form, greatly limiting coagulation efficiency. This application, however, releases all the activity of red soil through activation. The invention performs alkaline fusion activation and acid leaching extraction on red soil. The high-temperature alkaline fusion destroys the crystal structure of clay minerals such as kaolinite in the red soil, and converts inert silicon, aluminum and iron into highly active soluble states. This achieves efficient utilization of inexpensive mineral resources, significantly reduces raw material costs, and provides feasibility for large-scale, low-cost treatment of high-flow combined sewer overflow sewage.

[0022] 3. This invention, through the construction of a red soil copolymer coagulant combined with a loading flocculation process (including rapid mixing, accelerated sedimentation by loading media, and synergistic effects of coagulants), achieves rapid destabilization and efficient sedimentation of suspended particulate matter in combined sewer overflows (CSOs). This solves the problems of existing wastewater treatment processes struggling to handle large instantaneous flow rates, high suspended solids concentrations, and difficulty in removing dissolved organic matter, achieving low-cost, high-efficiency rapid purification. The technical solution of this invention addresses the short hydraulic retention time and rapid sludge-water separation requirements of high-flow-rate combined sewer overflows. Given the significant differences in fluid dynamics between sludge dewatering (high concentration, low flow rate) and overflow wastewater treatment (low concentration, high flow rate), those skilled in the art have no incentive to directly apply the formulation of prior art 3 to the scenario described in this application, and cannot anticipate that such an application would yield a specific three-dimensional network structure matching the rapid sedimentation requirements of overflow wastewater. This invention employs a specific alkali-fuss activation-acid leaching extraction-induced copolymerization process to impart a high charge density and a three-dimensional network structure to the red soil-based coagulant. Combined with rapid mixing, loading flocculation, and sedimentation processes, this results in rapid floc formation, high density, and extremely fast sedimentation, effectively solving the problem of insufficient performance of conventional coagulants when dealing with high hydraulic load combined sewer overflow sewage.

[0023] 4. This invention solves the technical problems that existing technologies 1-3, whether alone or in combination, cannot address, and its technical effects exceed the reasonable expectations of those skilled in the art. Existing technologies 1 aim to remove algae using the physical weight and natural mineral properties of red soil; existing technology 2 aims to remove algae using the chemical complexation of rare earth lanthanum; and existing technology 3 aims to improve sludge dewatering using highly charged zirconium ions. The technical problems, mechanisms of action, and performance indicators of these three technologies differ. Those skilled in the art, when faced with the problem of "rapid settling of combined sewer overflow sewage," have no incentive to combine expensive lanthanide algae removal schemes or zirconium-based sludge dewatering schemes with unactivated red soil, as this would lead to soaring costs and incompatible mechanisms. Even considering combining existing technologies 1, 2, and 3, significant technical obstacles exist. The red soil in existing technology 1 is unactivated; if it is directly introduced into the polymerization system of existing technologies 2 or 3, the inert minerals in the red soil will act as impurities, interfering with the polymerization reaction and preventing the formation of a uniform and stable "red soil-based copolymer coagulant."

[0024] This application creatively uses red soil as raw material, and through alkali fusion activation and acid leaching extraction, the crystal structure of clay minerals such as kaolinite in the red soil is destroyed by high-temperature alkali fusion, and the inert silicon, aluminum, and iron are transformed into highly active soluble states. Then, through acid leaching and induced copolymerization, a red soil-based copolymeric coagulant with high charge density and a three-dimensional network structure is formed. This solves the technical problems of insufficient efficiency of conventional coagulants, slow floc settling speed, and high treatment costs in the treatment of combined sewer overflows (CSOs) due to high hydraulic load and short retention time. It achieves high-value utilization of inexpensive waste mineral resources, significantly reduces coagulant costs, and exhibits excellent performance in the special working conditions of short hydraulic retention time in combined sewer overflows, with rapid floc formation, high density, and extremely fast settling speed. This effect exceeds the range that can be reasonably expected based on existing technologies 1-3. Existing technology 1 neither discloses nor implies using the chemical modification path of alkali fusion-acid leaching-copolymerization described in this application to activate the potential coagulation efficiency of red soil to solve this problem. This application overcomes the technical obstacle of complex composition and numerous impurities in red soil by simultaneously dissolving silicon, aluminum, and iron in minerals and copolymerizing them in situ through a specific alkali fusion pretreatment. Even if those skilled in the art attempted to activate red soil, they could not have anticipated, based on existing technology, that the specific alkali fusion activation-acid leaching extraction-induced copolymerization aging process of this application could endow red soil-based coagulants with high charge density and a three-dimensional network structure, let alone anticipate that this structure would exhibit excellent performance in treating CSOs with high hydraulic loads, such as rapid floc formation, high density, and extremely fast settling velocity. Attached Figure Description

[0025] Figure 1 A comparison diagram of red soil from different regions and its effective components in a method for treating combined sewer overflow wastewater using a red soil copolymer coagulant provided in an embodiment of the present invention; Figure 2XRD patterns of different NaOH to red soil ratios after calcination in a method for treating combined sewer overflow wastewater using a red soil copolymer coagulant provided in an embodiment of the present invention; Figure 3 This is a graph showing the variation of elemental leaching under different hydrochloric acid concentrations in a method for treating combined sewer overflow wastewater using a red soil copolymer coagulant, as provided in an embodiment of the present invention. Figure 4 The diagram shows the coagulation performance of red soil copolymer coagulant under different aging pH conditions in a method for treating combined sewer overflow wastewater provided in an embodiment of the present invention. Figure 5 The following diagrams illustrate the treatment effect and floc size of coagulants prepared from red soil in different regions in a method for treating combined sewer overflow wastewater using a red soil copolymer coagulant, as provided in this embodiment of the invention. Figure 6 This is a flowchart illustrating the preparation of a copolymer coagulant based on natural red soil, provided as an embodiment of the present invention. Detailed Implementation

[0026] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0027] like Figure 6 As shown in this embodiment, a method for preparing a red soil-based copolymer coagulant is provided. The endogenous aluminum, iron, and silicon components in the red soil are extracted by thermochemical activation, a polymer composite structure is constructed by induced copolymerization, and a loading flocculation process is used to achieve efficient separation of pollutants.

[0028] The steps for preparing a copolymeric coagulant for natural red soil are as follows: Step S1, Activation Raw material selection and pretreatment: The raw material is natural red soil collected from typical red soil areas (including Hunan, Jiangxi, Yunnan, and Guizhou). Its main mineral components include kaolinite, halloysite, and iron and aluminum oxides. The total mass fraction of SiO2, Al2O3, and Fe2O3 in the chemical composition is ≥90%. After removing impurities such as vegetation and gravel, the red soil is dried to constant weight at 100-105℃, crushed, and passed through an 80-100 mesh standard sieve to obtain red soil powder.

[0029] Alkali-melted mixture: Sodium hydroxide (NaOH) solid activator and red soil powder are placed in a mixing and grinding mill at a mass ratio of 1:3-2:1 (preferably 1:1) and mixed thoroughly.

[0030] High-temperature thermal activation: The mixture is placed in a corundum or high-temperature resistant ceramic container and transferred to a muffle furnace. The temperature program is started, and the temperature is increased to 550-650℃ (preferably 600℃) at a rate of 10-20℃ / min (preferably 15℃ / min), and calcined at a constant temperature for 1-2 hours (preferably 1.5 hours). After the reaction is completed, it is naturally cooled to room temperature to obtain activated red soil solid.

[0031] High-temperature alkali melting breaks the stable aluminosilicate mineral lattice in red soil, transforming it into an active amorphous substance that is easily soluble in acid.

[0032] Step S2: Acid leaching to extract effective components Acid solution preparation: Prepare a leachate solution with a concentration of 1.5-6 mol / L (preferably 3 mol / L) using analytical grade hydrochloric acid (HCl). Acid leaching reaction: Mix the leachate solution with activated red soil solid at a liquid-to-solid ratio of 20:1, place the mixture in a reactor equipped with a reflux condenser, and react for 30-60 minutes in a water bath at 80-95℃ (preferably 90℃) with constant temperature magnetic stirring or mechanical stirring (200-400 rpm).

[0033] Solid-liquid separation and detection: After the leachate cools, it is vacuum filtered through a 0.45µm polytetrafluoroethylene (PTFE) membrane. The collected filtrate is the acid leaching mother liquor, which contains highly active Al. 3+ Fe 3+ And soluble silicon. The concentrations of each component were determined using inductively coupled plasma optical emission spectrometry (ICP-OES).

[0034] The acid leaching process can effectively convert the solid phases of Al, Fe, and Si in red soil into soluble components, and filtration can further separate insoluble inert components, ensuring the purity of the finished coagulant.

[0035] Step S3, Induced Copolymerization and Aging Dilution and pH adjustment: Dilute the acid leaching mother liquor with deionized water to the preset volume. While continuously stirring (300-400 rpm), slowly and evenly add a 2-5 mol / L NaOH solution to adjust the maturation pH of the system to 0.5-5 (preferably 2-4).

[0036] Aging reaction: The pH-adjusted solution is left to stand at 15-25℃ for 1-3 hours (preferably 3 hours) for aging. During this process, the silica monomers undergo condensation polymerization to form polysilicic acid chains, and simultaneously, they are bridged with aluminum and iron cations through hydroxyl groups to form a red soil-based copolymer coagulant liquid product with a three-dimensional network structure.

[0037] The aging process promotes hydroxyl bridging and cross-linking reactions between silicic acid and metal cations. This "silicic-aluminum copolymer" structure has a higher molecular weight and a stronger sweeping and trapping effect than simple mixtures.

[0038] In addition, considering the characteristics of large concentration fluctuations and high treatment time requirements of combined sewer overflows (CSOs), this embodiment also provides a method for treating combined sewer overflows using a red soil copolymer coagulant based on natural red soil, including the following steps: Step S01, Quick Mixing: Take a sample of the combined overflow wastewater to be treated, turn on the agitator, and adjust the speed to 250-300 rpm for rapid stirring. Simultaneously, inject the red soil copolymer coagulant prepared in this embodiment into the water sample at a dosage of 1 mg (Al+Fe) / L (based on metal element content), where the dosage is 0.5-2.0 mg / L. Continue rapid stirring for 1-1.5 minutes.

[0039] High shear force is used to rapidly disperse the coagulant. The high positive charge of the red soil copolymer coagulant is used to achieve colloidal charge neutralization and destabilization, and the long chain structure achieves netting and sweeping action to form micro flocs.

[0040] Step S02, Slow Mixing and Loading Flocculation: Reduce the stirring speed to 150-200 rpm to enter the slow-speed stage. Then, sequentially add the loading medium (silica sand, particle size 80-120 mesh, specific gravity 2.64, dosage 0.8 g / L, dosage 0.5-1.0 g / L) and the coagulant aid polyacrylamide (NPAM, molecular weight 5-8 million, dosage 0.5 mg / L, dosage 0.3-0.8 mg / L, and it must be non-ionic polyacrylamide) to the system. Continue stirring for 2-3 minutes.

[0041] In this embodiment, the loading medium is used as the core of the floc. Under the adsorption bridging effect of NPAM, the tiny flocs are guided to wrap around the surface of the medium, forming a high-density, large-size loading floc with a fast settling speed.

[0042] Step S03, Sedimentation Separation: Stop stirring and allow the water sample to settle for 1-2 minutes.

[0043] This embodiment utilizes the high settling velocity of the loaded flocs to rapidly settle pollutants, thus meeting the requirements of efficient treatment and large flow rate for combined sewer overflow.

[0044] To further illustrate the value range and technical function of each key process parameter in this embodiment, the relevant parameters are summarized in the following table: Summary table of process technical parameters

[0045] To verify the preparation process and application effect of the red soil copolymer coagulant in this embodiment, a systematic analysis was conducted on the material composition, activation effect, and coagulation performance under different conditions. The results are as follows: Figures 1-5 As shown.

[0046] (1) Raw material composition analysis like Figure 1 As shown, the total content of SiO2, Al2O3 and Fe2O3 in the red soil of the four regions all exceeded 90%, indicating that the red soil contains a very high proportion of effective precursors and is a high-quality natural raw material for preparing polysilicate metal coagulants.

[0047] The red soils in different regions show obvious differences in composition: Hunan red soil is characterized by high silicon (54.6%), which has a stronger adsorption and bridging ability; Guizhou and Yunnan red soils show high aluminum and high iron characteristics (iron content close to 30%), and the red soil copolymer coagulants prepared have a strong charge neutralization ability.

[0048] The above explanation shows that differences in raw materials directly affect the structural composition and coagulation performance of red soil copolymer coagulants.

[0049] (2) Optimization of activation conditions like Figure 2 As shown, XRD analysis of the alkali fusion products revealed that the activation effect was optimal when the mass ratio of NaOH to red soil was 1:1.

[0050] When the ratio of NaOH to Soil is less than 1:1, the diffraction peak intensity is low, indicating insufficient activation. When the ratio is higher than 1:1, excess NaOH reacts with quartz and kaolinite to form wollastonite, which reduces the activation effect.

[0051] Note 1:1 represents the optimal ratio for lattice disruption and release of active components.

[0052] (3) Optimization of acid leaching conditions like Figure 3 As shown, the element leaching efficiency is highest when the hydrochloric acid concentration is 3 mol / L. Below this concentration, due to insufficient H⁺ activity, it is difficult to completely destroy the structure of the alkali fusion products, resulting in limited leaching. After increasing to 6 mol / L, the leaching rate tends to stabilize without significant improvement, but instead increases acid consumption.

[0053] This indicates that 3 mol / L is the optimal acid leaching condition that balances efficiency and economy.

[0054] (4) Optimization of copolymerization conditions like Figure 4As shown, the residual turbidity was lowest (2.4 NTU) at pH=2, indicating that the copolymer structure formed under this condition is most conducive to sweeping trapping and colloidal destabilization. When the pH increases to 5, metal ions prematurely hydrolyze to form precipitates, reducing the effective charge neutralization capacity.

[0055] This indicates that the optimal copolymer structure can be formed within the pH range of 2-4.

[0056] (5) Verification of application effects, such as Figure 5 As shown, the coagulating agents prepared from red soil in different regions exhibit different coagulation performances. Among them, the coagulating agent prepared from Hunan red soil has the best effect, with a residual turbidity of 1.52 NTU, which is better than traditional aluminum salt and iron salt coagulators, and a UV254 removal rate of 61.5%-65.4%.

[0057] The loaded flocs formed in Yunnan red soil had the largest particle size (37.9µm).

[0058] It was also found that when the Si content decreased (e.g., in Guizhou and Yunnan), it was not conducive to loading flocculation performance, indicating that the formation of the three-dimensional network structure depends on sufficient silicon components.

[0059] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0060] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0061] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a red soil-based copolymer coagulant, characterized in that, Includes the following steps: Step S1, Activation: Step S11: Collect natural red soil, remove impurities, air dry, crush and sieve; Step S12: Thoroughly mix sodium hydroxide solid with red soil powder at a mass ratio of 1:3-2:1; The mixture was heated to 600℃ at a rate of 15℃ / min and calcined at a constant temperature for 1.5h to convert the aluminosilicate minerals in the red soil into acid-soluble active substances. Step S2, Acid Extraction: A 1.5-6 mol / L hydrochloric acid solution was used as the leaching agent. The activated solid was mixed with the acid solution at a liquid-to-solid ratio of 20:1, and the mixture was reacted at 90℃ for 30 min. After the reaction, the mixture was filtered to obtain a product containing Al. 3+ Fe 3+ and acid leaching solution of soluble Si; Step S3, Induced Copolymerization and Aging: The acid leaching solution is diluted, and NaOH solution is slowly added under continuous stirring to adjust the pH value to 0.5-5. The solution is aged at room temperature for 1-3 hours to allow the silica and metal cations to undergo a copolymerization reaction, forming a red soil copolymer coagulant.

2. The method for preparing the red soil-based copolymer coagulant according to claim 1, characterized in that, The red soil is sourced from Hunan, Jiangxi, Yunnan, or Guizhou provinces.

3. The method for preparing the red soil-based copolymer coagulant according to claim 1, characterized in that, In step S1, the powder from the crushed red soil is passed through an 80-100 mesh sieve.

4. The method for preparing the red soil-based copolymer coagulant according to claim 1, characterized in that, The pH value mentioned in step S3 is 2-4.

5. A method for treating combined sewer overflow wastewater using a red soil-based copolymer coagulant prepared according to any one of claims 1-4, characterized in that, Includes the following steps: Step S01, Quick Mixing: Add the red soil copolymer coagulant to the wastewater to be treated at a dosage of 0.5-2.0 mg / L based on metal elements, and stir rapidly at 250-300 rpm for 1-1.5 min. Step S02, Slow Mixing and Loading Flocculation: Reduce the stirring speed to 150-200 rpm, add the loading medium and coagulant polyacrylamide, and continue stirring for 2-3 minutes to allow flocs to form on the surface of the loading medium. Step S03, Sedimentation Separation: Stop stirring and allow the mixture to settle, thus separating the pollutants.

6. A method for treating combined sewer overflow wastewater using the red soil-based copolymer coagulant prepared according to the method described in claim 5, characterized in that: The loading medium is silica sand with a particle size of 80-120 mesh, a specific gravity of 2.64, and a dosage of 0.5-1.0 g / L.

7. A method for treating combined sewer overflow wastewater using the red soil-based copolymer coagulant prepared according to the method described in claim 5, characterized in that: The polyacrylamide is a nonionic polyacrylamide with a molecular weight of 5-8 million and an addition amount of 0.3-0.8 mg / L.

8. A method for treating combined sewer overflow wastewater using the red soil-based copolymer coagulant prepared according to the method described in claim 5, characterized in that: The settling time in step S03 is 1-2 minutes.

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