A polyaluminum chloride medicament suitable for coagulation treatment of fine particle suspended matters in high-turbidity mine water, a preparation method and application thereof

Abstract

The application discloses a kind of polyaluminium chloride reagent suitable for high turbidity mine water fine particle suspended matter coagulation treatment and its preparation method and application, belong to mine wastewater treatment technical field.Aluminum-containing waste and hydrochloric acid are mixed, steam is passed, acid dissolution reaction is carried out, calcium aluminate powder is added to the obtained liquid, hydrolysis polymerization reaction is carried out, to obtain reagent stock solution, the reagent stock solution is carried out solid-liquid separation, to obtain supernatant and precipitate, the supernatant is dehydrated and dried, to obtain the polyaluminium chloride reagent, the precipitate and the aluminum slag generated in the dehydration process are mixed to obtain aluminum-containing by-products, to prepare aluminum-containing waste using the aluminum-containing by-products and bauxite as raw materials for recycling.The polyaluminium chloride reagent prepared by the application can significantly reduce the dosage (15-30%) while obtaining faster flocculation speed, denser flocs and lower effluent turbidity when treating high turbidity mine water.

Description

Technical Field

[0001] This invention belongs to the field of mine wastewater treatment technology, and in particular relates to a polyaluminum chloride agent suitable for coagulation treatment of fine particulate suspended solids in high-turbidity mine water, its preparation method and application. Background Technology

[0002] Mine water treatment and resource utilization are key technologies for the green development of the coal industry. High turbidity, high salinity, and fine suspended particulate matter in mine water pose major challenges in the treatment process. Studies show that suspended matter in mine water mainly consists of coal dust and clay minerals, with small particle sizes and negatively charged surfaces. Furthermore, its density is generally lower than that of suspended matter in surface water, making natural sedimentation difficult. As the degree of coalification increases, the wettability of coal dust decreases, weakening its affinity for coagulants and increasing the difficulty of coagulation treatment.

[0003] Polyaluminum chloride (PAC), as a highly efficient inorganic polymeric coagulant, has been widely used in water treatment, including mine water purification, due to its high coagulation efficiency and wide applicable pH range. Currently, the mainstream method for large-scale industrial production of PAC is the acid dissolution method, which involves reacting hydrochloric acid with aluminum-containing raw materials such as bauxite, aluminum hydroxide, or calcium aluminate powder. This technology is mature, and product quality control mainly focuses on basic chemical indicators such as alumina (Al2O3) content and basicity. It is a general-purpose product that can meet the general water treatment needs of municipal wastewater and ordinary industrial circulating water.

[0004] However, general-purpose PACs were originally designed for common surface water qualities, and their composition was not optimized for the characteristics of mine water, such as high turbidity, high hardness, the presence of specific fine suspended minerals (such as coal dust and rock dust), and complex ionic environments. The surface charge and particle size distribution of suspended particles in mine water differ from those in common water bodies, requiring coagulants to provide a more suitable charge neutralization and adsorption bridging capacity. The "one-size-fits-all" composition of general-purpose PACs cannot achieve this specific and efficient matching, resulting in the following in practical applications: excessive dosage is required to achieve the target effluent quality, but the resulting flocs are often loosely structured with poor settling performance, making it difficult to consistently optimize the effluent quality, leading to high treatment costs and low efficiency.

[0005] Furthermore, the core objective of existing acid dissolution processes is to rapidly achieve macroscopic chemical indicators (such as high aluminum content and high basicity). The reaction process is vigorous, lacking precise control over the intermediate pathways of the complex aluminum salt hydrolysis-polymerization process. This directly leads to two consequences: firstly, even slight fluctuations in raw materials or reaction conditions between different batches can easily affect the distribution of aluminum speciation in the final product (such as monomeric Al). a Polymer Al b Gel Al cThe significant difference in the proportion of aluminum and high-polymerization materials leads to poor product quality stability; secondly, the process objectively tends to generate a large amount of gel-state aluminum and highly polymerized materials. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides a polyaluminum chloride (PAC) agent suitable for coagulation treatment of fine particulate suspended solids in high-turbidity mine water, along with its preparation method and application. The preparation method of the PAC agent provided by this invention can directionally and stably increase the content of specific components with advantageous effects on mine water treatment, producing a coagulant highly matched to the characteristics of mine water. Under the same conditions, this results in a faster flocculation rate, larger floc particle size, and lower effluent turbidity compared to general-purpose PAC, achieving efficient, economical, and stable mine water coagulation treatment.

[0007] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing a polyaluminum chloride agent suitable for coagulation treatment of fine particulate suspended solids in high-turbidity mine water, comprising the following steps: mixing aluminum-containing waste with hydrochloric acid, introducing steam to carry out an acid dissolution reaction, adding calcium aluminate powder to the resulting liquid to carry out a hydrolysis and polymerization reaction to obtain a reagent stock solution, performing solid-liquid separation on the reagent stock solution to obtain a supernatant and a precipitate, dehydrating and drying the supernatant to obtain the polyaluminum chloride agent, mixing the precipitate and aluminum slag generated during the dehydration process to obtain an aluminum-containing by-product, and using the aluminum-containing by-product and bauxite as raw materials to prepare aluminum-containing waste for recycling.

[0008] Furthermore, the mass ratio of the aluminum-containing waste, hydrochloric acid, and calcium aluminate powder is 0.4:1:0.4.

[0009] Furthermore, the content of Al2O3 in the aluminum-containing waste is 40-60 wt.%; the mass concentration of the hydrochloric acid is 30-36 wt.%; and the content of Al2O3 in the calcium aluminate powder is 30-50 wt.%.

[0010] Furthermore, the acid dissolution reaction is carried out at a temperature of 70-90℃, for a reaction time of 3 hours, and at a pH of 3-5.

[0011] Furthermore, the hydrolysis polymerization reaction is carried out at a temperature of 70-90℃, for a reaction time of 3 hours, and at a pH of 3-5.

[0012] Furthermore, the temperature for the dehydration and drying is 200-300℃.

[0013] This invention provides a customized production process based on acid dissolution, utilizing inexpensive raw materials and industrial byproducts to achieve low-cost production of high-performance polyaluminum chloride agents through precise process control. Regarding raw material formulation optimization and cost control, solid polyaluminum chloride is produced using industrial hydrochloric acid (30-36 wt.%), calcium aluminate powder, bauxite, and aluminum-containing waste from sedimentation tanks. This fully utilizes inexpensive bauxite and aluminum-containing waste generated during the production process, achieving "waste treatment with waste" and fundamentally establishing a cost advantage for polyaluminum chloride agents.

[0014] Secondly, the present invention provides a polyaluminum chloride agent prepared by the above preparation method, suitable for coagulation treatment of fine particulate suspended solids in high-turbidity mine water.

[0015] Thirdly, the present invention provides an application of the above-mentioned polyaluminum chloride agent suitable for coagulation treatment of fine particulate suspended matter in high turbidity mine water in mine water coagulation treatment. The polyaluminum chloride agent is added to the mine water, and after rapid stirring, it is stirred slowly. Then, a polymeric flocculant is added, and the stirring is continued slowly to further improve the flocculation effect.

[0016] Furthermore, the rapid stirring time is 1 minute and the rotation speed is 300 r / min; the slow stirring time is 2-3 minutes and the rotation speed is 60 r / min; the continued slow stirring time is 5 minutes and the rotation speed is 60 r / min.

[0017] This invention utilizes a novel reverse design approach of "analysis and identification-directional control," overcoming the limitations of conventional PAC acid dissolution processes that only control macroscopic chemical indicators. Specifically, it first identifies the key active components (such as specific aluminum forms and specific forms of other elements) that truly play a crucial role in mine water coagulation from high-performance samples using instrumental analysis. Then, based on these identification results, it reverse-engineers and precisely controls the raw materials, reaction, and maturation conditions in the production process to achieve the directional enrichment and stabilization of these key components. Simultaneously, by precisely controlling the product's basicity within the optimized range of 70-90%, this invention constructs an ideal basic performance framework for the efficient action of these key components.

[0018] Compared with the prior art, the present invention has the following advantages and technical effects: (1) The product design achieves precision and efficiency: by locking and enriching the advantageous components, the product is transformed from a "general mixture" into a "special tool" for the characteristics of mine water quality (such as the surface electrical properties of specific suspended particles), thereby improving the coagulation efficiency from the source of the working principle.

[0019] (2) Ensures the stability and superiority of product performance: precise basicity and Al cContent control ensures that the product has the best charge neutralization capacity and polymerization stability, overcoming the defects of traditional products that are loose flocs and slow sedimentation due to excessive base content or excessive gel components.

[0020] (3) The economic and reliability issues in the application are comprehensively solved: the special PAC product polyaluminum chloride agent obtained in the end can significantly reduce the dosage (15-30%) when treating mine water, while obtaining faster flocculation speed, denser flocs and lower effluent turbidity, thus realizing efficient, stable and low-cost mine water coagulation treatment, fundamentally solving the problems existing in the prior art. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 A production flow diagram of PAC for coagulation treatment of fine particulate suspended solids in high-turbidity mine water provided by the present invention; Figure 2 Changes in zeta potential of mine water under different PAC dosages prepared in Example 1; Figure 3 A graph showing the turbidity and rate of change of effluent; Figure 4 This is a graph showing the dynamic changes in particle size. Figure 5 The graphs show the changes in particle size over time for each dosage range. (a), (b), (c), (d), and (e) represent the trends of PAC dosage of 0, 10, 20, 30, and 50 mg / L at a rapid stirring speed of 300 r / min, respectively, and the changes in floc particle size over time in the ranges of ≤2 μm, 2-10 μm, 10-50 μm, and ≥50 μm. Figure 6 The volume percentage change rate at each stage is shown in (a), (b), (c), and (d), which represent the comparison of the volume percentage decrease rate and the volume percentage of ≥50 μm in the ≤2 μm, 2-10 μm, and 10-50 μm ranges under different dosages at the same time in the rapid floc growth zone, the peak floc size zone, the stable process, and the stable zone. Figure 7 This is a diagram showing the overall variation of median particle size. Figure 8 This is a comparison chart of real-time changes in median particle size. Figure 9The particle size distribution frequency diagram (a), cumulative distribution curve (b), and volume percentage diagram (c) of the ≤10μm, 10-100μm, 10-100μm, and ≥100μm ranges are shown. Figure 10 (a) is the curve of the relationship between the proportion of residual turbidity and time (Pi~t curve), (b) is the curve of the distribution of mine water settling velocity (Pi~ui curve), (c) is the curve of the relationship between turbidity removal rate and settling time (ET~t curve), (d) is the curve of the relationship between turbidity removal rate and settling velocity (ET~ui curve), and (e) is the comparison chart of residual turbidity; Figure 11 The graphs show the changes in floc particle size during the coagulation process of the polyaluminum chloride agent prepared in Example 1 and the conventional commercial PAC at different dosages. (a) represents a dosage of 10 mg / L, (b) represents a dosage of 30 mg / L, and (c) represents a dosage of 50 mg / L. The special PAC is the polyaluminum chloride agent prepared in Example 1, and the conventional PAC is the traditional commercial PAC. Figure 12 Particle size distribution of residual particles in the effluent from mine water coagulation treatment, as shown in the polyaluminum chloride agent (a) prepared in Example 1 and conventional commercial PAC (b). Detailed Implementation

[0023] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0024] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0025] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0026] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0027] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0028] This invention provides a method for preparing a polyaluminum chloride agent suitable for coagulation treatment of fine particulate suspended solids in high-turbidity mine water, comprising the following steps: mixing aluminum-containing waste with hydrochloric acid, introducing steam to carry out an acid dissolution reaction, adding calcium aluminate powder to the resulting liquid to carry out a hydrolysis and polymerization reaction to obtain a reagent stock solution, separating the reagent stock solution into solid and liquid phases to obtain a supernatant and a precipitate, dehydrating and drying the supernatant to obtain the polyaluminum chloride agent, mixing the precipitate and the aluminum slag obtained from dehydration and drying to obtain an aluminum-containing byproduct, and using the aluminum-containing byproduct and bauxite as raw materials to prepare aluminum-containing waste for recycling.

[0029] In a preferred embodiment of the present invention, the mass ratio of the aluminum-containing waste, hydrochloric acid and calcium aluminate powder is 0.4:1:0.4.

[0030] In a preferred embodiment of the present invention, the content of Al2O3 in the aluminum-containing waste is 40-60 wt.%; the mass concentration of the hydrochloric acid is 30-36 wt.%; and the content of Al2O3 in the calcium aluminate powder is 30-50 wt.%.

[0031] Aluminum-containing waste is prepared by mixing the waste generated during the production process of this invention with bauxite. The prepared aluminum raw material must contain no less than 40% aluminum, and the use of waste from other aluminum processing products is not permitted. Only industrial by-product hydrochloric acid with slight impurities can be used in this invention; hazardous waste acid is prohibited.

[0032] The PAC preparation method for coagulation treatment of fine particulate suspensions in high-turbidity mine water provided by this invention is divided into three key stages: acid dissolution reaction, polymerization control, and solid-liquid separation and drying. Figure 1 The production flow diagram of PAC suitable for coagulation treatment of fine particulate suspended solids in high-turbidity mine water provided by this invention is shown below: (1) Acid dissolution reaction stage: Bauxite and precipitated waste are mixed with hydrochloric acid in a reactor, steam is introduced, and the reaction temperature is precisely controlled at 70-90℃. The reaction is continued for 3 hours. During this stage, the pH of the system is maintained at an acidic environment of 3-5, which aims to maximize the dissolution of aluminum.

[0033] (2) Basicity adjustment stage: Calcium aluminate powder is slowly added to the acid-dissolved liquid and its alkalinity is used to carry out hydrolysis polymerization reaction. By precisely controlling the addition rate and total amount of calcium aluminate powder, the basicity of the final product is precisely stabilized in the optimal performance range of 70%-90%, and the reaction continues for 3 hours at the same temperature (70-90℃). This step is the core link of the directional induction of high-polymer aluminum.

[0034] (3) Solid-liquid separation and drying molding stage: After polymerization, the reagent stock solution enters the sedimentation tank for preliminary solid-liquid separation. The supernatant is dried rapidly at a temperature of 200-300℃ using drum drying technology to finally obtain a solid product with a water content of ≤30%, namely polyaluminum chloride reagent.

[0035] This invention also provides a polyaluminum chloride agent prepared by the above method, suitable for coagulation treatment of fine particulate suspended solids in high-turbidity mine water.

[0036] The polyaluminum chloride agent prepared by this invention has an Al2O3 content of 24-28 wt.% and a basicity of 70-80%. c The content of the active ingredient should be greater than 80%, the insoluble matter content less than 5 wt.%, the moisture content less than 30 wt.%, the pH value between 3.5 and 5, and the heavy metal content should meet the requirements of the national standard (GB / T 22627) to prevent excessive heavy metal content. Controlling the Al2O3 content is crucial to ensuring the effectiveness of the active ingredient. Controlling the basicity can prevent excessive polymerization that could lead to insufficient charge neutralization. c Controlling the content of different forms ensures that polyaluminum chloride (PAC) agents have sufficient adsorption and bridging effects to compensate for their limited charge neutralization capacity. Controlling the insoluble content prevents the introduction of excessive inert components. Controlling the moisture content ensures the stability of the solid product, and maintaining a suitable pH level ensures the stability of the PAC form. Strict control of PAC performance indicators ensures the stability and high efficiency of its efficacy.

[0037] This invention also provides an application of the above-mentioned polyaluminum chloride agent suitable for coagulation treatment of fine particulate suspended solids in high-turbidity mine water in mine water coagulation treatment. The polyaluminum chloride agent is added to the mine water, and after rapid stirring, it is stirred slowly. Then, a polymeric flocculant is added, and stirring is continued slowly.

[0038] In a preferred embodiment of the present invention, the rapid stirring time is 1 minute and the rotation speed is 300 r / min; the slow stirring time is 2-3 minutes and the rotation speed is 60 r / min.

[0039] To facilitate understanding, the following explanations will first address several technical terms: Basicity is one of the core indicators for evaluating the performance of inorganic polymeric flocculants such as polyaluminum chloride. It reflects the presence of hydroxyl (OH) groups in the compound. - The degree of binding between hydroxyl groups and aluminum ions indirectly reflects the product's degree of polymerization, charge density, and charge neutralization ability. Basicity is one-third of the equivalent percentage of hydroxyl groups and aluminum ions in the product. Gel aluminum (Al) c Aluminum sol is a key form of aluminum sol system in the field of water treatment, specifically referring to highly polymerized sol or gel-like aluminum species, which is the core effective component constituting aluminum sol. Essentially, it is a macromolecular polymer formed through the hydrolysis-polymerization reaction of aluminum ions, possessing a unique colloidal structure and physicochemical properties, playing a decisive role in flocculation, adsorption, and other performance aspects of water treatment.

[0040] In this embodiment of the invention, the initial aluminum-containing waste material used to prepare the polyaluminum chloride agent is clinker bauxite with an equivalent alumina content of 40-60%. The hydrochloric acid used in the embodiments of this invention is industrial hydrochloric acid with an industrial concentration of 30-36 wt.%. In this embodiment of the invention, the calcium aluminate powder used is conventional calcium aluminate powder with a particle size of 80-120 mesh.

[0041] The mine water source used in this invention is a typical mine water treatment station in the Xishan area of ​​Shanxi Province, which is high-turbidity and high-mineralization mine water.

[0042] Example 1: A method for preparing a polyaluminum chloride agent suitable for coagulation treatment of fine particulate suspensions in high-turbidity mine water. Weigh the following raw materials: 0.4t aluminum-containing waste, 0.4t calcium aluminate powder, and 1t hydrochloric acid. The specific preparation method is as follows: (1) Acid dissolution reaction: Bauxite, aluminum-containing waste and hydrochloric acid are mixed in a reactor, steam is introduced, the reaction temperature is controlled at 70-90℃, and the reaction is continued for 3 hours. During this stage, the pH of the system is maintained at 3-5. (2) Hydrolysis polymerization reaction: Calcium aluminate powder is slowly added to the acid-dissolved liquid obtained in step (1). The addition rate and total amount of calcium aluminate powder are precisely controlled (addition is completed within 30 min). The reaction is continued at 70-90℃ for 3 h to obtain the original reagent solution. (3) Solid-liquid separation and drying molding stage: The original liquid of the agent prepared in step (2) is added to the sedimentation tank for solid-liquid separation to obtain the supernatant and precipitate. The supernatant is dried rapidly at a temperature of 200-300℃ using drum drying technology to obtain polyaluminum chloride agent with a water content of ≤30%.

[0043] The formation, growth, and characteristics of flocs in the PAC prepared in Example 1 during the coagulation process were investigated: 1. Destabilizing effect of PAC on suspended particulate matter in mine water The fine particulate suspended matter in high-turbidity mine water mainly consists of coal dust and rock dust, whose surface-covering carboxyl and hydroxyl functional groups can release H2O. + Therefore, the surface of suspended particles in the water body is negatively charged, which makes the mine water dispersion system tend to be stable. The suspended particles cannot effectively aggregate and settle. After the addition of PAC, PAC hydrolyzes to generate a large number of positively charged hydroxyl complex products, which causes compression of the double electric layer and adsorption charge neutralization, resulting in the destabilization of suspended particles in the mine water. The change of Zeta potential can effectively characterize the destabilization ability of PAC. Figure 2 The zeta potential changes in mine water under different PAC dosages prepared in Example 1. Figure 2 As shown, with the increase of PAC dosage, the absolute value of the effluent Zeta potential shows a significant decreasing trend (i.e., the potential approaches zero), indicating that the surface charge of the particles is gradually neutralized, the stability of suspended particles decreases, and the destabilization efficiency of particles gradually increases. Specifically, with the addition of PAC, the effluent Zeta potential of the mine water decreased from -14.42 mV (the original mine water Zeta potential value) to -6.13 mV. In the coagulation process, in order to achieve the purpose of destabilizing suspended particles, the Zeta potential does not need to be completely reduced to zero; approaching -10 mV is sufficient to achieve the destabilization and sedimentation effect. When the absolute value of the Zeta potential is below 10 mV, the double electric layer of the particles can be further fully compressed, the repulsive force between particles is greatly weakened, and the particles are rapidly aggregated to form large-sized flocs, thereby significantly improving the sedimentation efficiency.

[0044] 2. Investigation into the variation pattern of effluent turbidity A programmable coagulation (PAC) experimental simulation was conducted on mine water using a programmable coagulation (PAC) mixer. The PAC dosage was set at eight gradients: 0, 5, 10, 15, 20, 25, 30, and 50 mg / L. The coagulation program was set as follows: rapid stirring at 300 r / min for 1 min, slow stirring at 60 r / min for 10 min, followed by settling for 30 min. The experimental results are as follows: Figure 3 The effluent turbidity and its rate of change are shown. Specifically, when the PAC dosage was 0 mg / L, after the mine water underwent a coagulation process, the effluent turbidity decreased from 204 NTU to 149 NTU. Figure 3 It can be seen that as the PAC dosage increases from 0 mg / L to 50 mg / L, the effluent turbidity shows a trend of first decreasing and then increasing. When the PAC dosage is 0 mg / L, the effluent turbidity is 149 NTU ( Figure 3(Not shown in the figure, obtained through measurement), indicating that when suspended particles are not destabilized, co-directional flocculation alone cannot effectively remove them. When the dosage was increased to 5 mg / L, the turbidity decreased significantly to 33.7 NTU, then decreased to 15.5 NTU and 10.6 NTU at 10 mg / L and 15 mg / L, respectively, and finally reached a minimum value of 9.64 NTU at 20 mg / L, with a turbidity removal rate of 95.27%. However, when the dosage was further increased to 25 mg / L, 30 mg / L and 50 mg / L, the effluent turbidity actually increased to 11.7 NTU, 15.9 NTU and 19.4 NTU, respectively, showing obvious back-turbidity.

[0045] Without the addition of PAC, the turbidity removal rate reached 26.96%, indicating that particulate matter mainly aggregates slowly through collisions, with van der Waals forces playing a dominant role. PAC, as an inorganic polymeric coagulant, primarily promotes the destabilization and flocculation of suspended particles through adsorption charge neutralization and adsorption bridging. At lower dosages, the high-charge hydrolysis products (such as Al) generated by PAC hydrolysis... 13 Al 30 PAC (Polyac precipitates), including PAC (Polyac Hydrolysate), neutralizes negatively charged suspended particles, reducing electrostatic repulsion between particles, thereby increasing aggregation efficiency and forming micro-flocs, leading to a gradual decrease in turbidity. At a PAC dosage of 5 mg / L, the neutralization effect is insufficient due to the limited amount of high-charge hydrolysis products generated by PAC hydrolysis, resulting in relatively high effluent turbidity. As the dosage increases to 20 mg / L, the neutralization effect is fully realized, weakening the electrostatic repulsion between particles and promoting the aggregation and sedimentation of destabilized particles. However, when the PAC dosage continues to increase, PAC may inhibit bridging through competitive adsorption or cause excessive dispersion and breakage of flocs, thus reducing sedimentation performance and resulting in a rebound in turbidity.

[0046] 3. Dynamic evolution characteristics of PAC flocs in the mixed section This invention investigated the particle size distribution (D) during floc growth under a fixed rapid stirring speed of 300 r / min. The effects of different PAC dosages (0, 10, 20, 30, and 50 mg / L) on the particle size distribution (D) were investigated. 50 The dynamic evolution law of ). Figure 4 This is a dynamic change graph of particle size, from Figure 4 It can be seen that after the addition of PAC, the floc particle size rapidly increased to a peak within 1 minute, then gradually decreased and tended to stabilize. At a dosage of 20 mg / L, D... 50Within 20 s, the particle size rapidly increased from 13.19 μm to 22.14 μm, reaching a peak of approximately 36 μm at 50 s, demonstrating a rapid and efficient floc formation process. This phenomenon is highly consistent with the result that the turbidity removal rate reached a peak of 95.23% at 20 mg / L. Mechanistically, the charge neutralization effect of PAC hydrolysis products on the particle surface is crucial in this stage—as the dosage increases, the absolute value of the Zeta potential continuously decreases to below 10 mV, reducing the energy barrier between particles and creating favorable conditions for floc growth. With increasing stirring time, D... 50 The particle size gradually decreased to around 28 μm, revealing a dynamic equilibrium between floc structure and fluid dynamics under sustained shear. Significant differences in structure and density existed in the initial floc formation stages under varying initial dosages. At lower dosages (10 mg / L), charge neutralization was relatively weak, and particles were primarily connected through weak van der Waals forces or limited bridging, resulting in a relatively loose but potentially more flexible initial floc structure. At higher dosages (20, 30 mg / L), while a larger floc skeleton formed initially due to strong charge neutralization and trapping effects, these flocs often exhibited higher internal porosity and were structurally fragile. Under a constant shear force of 300 r / min, all types of flocs simultaneously underwent a dynamic process of breakage and regeneration. Excessively large, poorly structured flocs were peeled off or broken by the shear force; while excessively fine particles or sufficiently strong micro-flocs had the opportunity to reattach through collision. Ultimately, the floc systems under different initial conditions all tended towards a particle size limit that could stably exist at that specific shear strength, approximately 28 μm. When the PAC dosage increased to 50 mg / L, although the growth rate of flocs in the early stage of formation was more rapid, reaching 36.36 μm in 0.34 min, and the peak particle size appeared earlier, a significant particle size decay phenomenon was subsequently observed. 50 The continuous decrease in particle size from 36.36 μm to 24.64 μm indicates that excessive PAC leads to the formation of loosely structured, low-strength flocs that are easily broken under continuous shearing. This phenomenon corresponds to the decrease in turbidity removal rate under high dosage. The underlying mechanism may involve two aspects: First, although the Zeta potential is always negative, excessive hydrolyzed aluminum species may form initial flocs through adsorption bridging and net sweeping, and these flocs have weak internal binding force; second, although the charge state near the isoelectric point is conducive to initial aggregation, the resulting floc structure may not be dense enough and has poor shear resistance. This is because the electrostatic repulsion barrier between particles does not decrease to 0 when the Zeta potential is 0 mV. Excessive PAC causes the repulsion barrier between some particles to rise again, thus exhibiting a loose floc structure that is prone to breakage.

[0047] 3.1 Volume percentage of flocs with different particle sizes at different times under the same PAC dosage Under different PAC dosages, the particle size distribution of the particle community during the coagulation process of mine water exhibits a significant dynamic evolution pattern, and its evolution trajectory profoundly reveals the complex influence mechanism of coagulant dosage on floc formation, growth, and stability. By monitoring the volume percentage of four characteristic particle size ranges (≤2 μm, 2-10 μm, 10-50 μm, and ≥50 μm), the particle size variation law during the coagulation process was obtained.

[0048] Figure 5 The graphs show the changes in particle size over time for each dosage range. (a), (b), (c), (d), and (e) represent the trends of PAC dosage changes over time for 0, 10, 20, 30, and 50 mg / L, respectively, under the condition of a rapid stirring speed of 300 r / min, in the floc particle size ranges of ≤2 μm, 2-10 μm, 10-50 μm, and ≥50 μm.

[0049] Figure 5 Figure (a) shows that, without the addition of PAC, under simple hydraulic shearing, the suspended particulate matter system in mine water underwent physical migration and reorganization. With prolonged stirring time (0–4 min), the proportion of suspended particles ≤2 μm decreased from 5.69% to 3.96%, the proportion of fine particles (2–10 μm) decreased from 31.66% to 21.55%, while the proportion of medium-sized particles (10–50 μm) significantly increased from 60.94% to 73.22%. This particle size distribution evolution reveals that shear-induced co-directional flocculation is dominant. The fluid kinetic energy provided by rapid stirring promotes effective collisions between small particles (especially the 2–10 μm component), achieving adsorption and aggregation between particles through physical interactions such as van der Waals forces, thereby continuously migrating and transforming towards larger particle sizes (10–50 μm). However, the proportion of coarse particles ≥50 μm remained at a low level (<2%) and showed no significant increasing trend, indicating that the interparticle repulsion barrier was not effectively eliminated without external coagulants. The physical aggregation force achieved solely by van der Waals forces was insufficient to support their stable growth to above 50 μm. The upper limit of particle growth was limited by their own physicochemical properties and the balance of forces, causing the system to quickly reach a dynamic equilibrium of aggregation and fragmentation. This phenomenon confirms that relying solely on hydraulic conditions is insufficient to effectively remove stable suspended particles and fine particulate matter (≤10 μm still accounts for >25% of the total) in mine water, highlighting the necessity of adding PAC for charge neutralization and bridging to achieve destabilization.

[0050] Figure 5Figures (b)-(e) show that the particulate matter conversion process exhibits similar trends under PAC dosages of 10, 20, 30, and 50 mg / L, but differs in conversion efficiency and final effect. In the initial stage of coagulation (0-1 min), the particulate system under all dosage conditions showed a clear migration pattern of "fine particle consumption - coarse particle generation." The proportion of fine particles (≤2 μm and 2-10 μm) continuously decreased, while the proportion of coarse particles (≥50 μm) increased rapidly. This directly confirms that PAC effectively reduces the repulsive energy barrier between particles through charge neutralization and adsorption bridging, promoting the conversion of fine particles into large-sized flocs. However, further analysis of the evolution path under different dosages reveals significant differences in their underlying mechanisms. When the dosage was 10 mg / L, the growth of the ≥50 μm population was relatively slow and the peak value was the lowest (only 23.21% at 1.02 min). Meanwhile, the proportion of the 10-50 μm population remained at a high level, indicating that the insufficient dosage of the agent resulted in high stability of the suspended particles (Zeta potential = -10.4 mV), high interparticle repulsion, and the inability of the suspended particles to aggregate effectively.

[0051] In contrast, increasing the dosage to 20-30 mg / L significantly enhanced coagulation efficiency. The ≥50 μm floc reached peak proportions of 33.87% and 36.27% at 1.02 min, respectively, demonstrating the strengthening effect of sufficient coagulant on floc growth rate and ultimate size. However, a key phenomenon was the significant decrease in the proportion of the ≥50 μm floc after reaching its peak (approximately 7-15 percentage points each), while the proportion of the 10-50 μm floc correspondingly increased. This indicates that under continuous shear, the already formed large-sized flocs underwent large-scale breakage, with the broken flocs mainly falling back to the medium-sized range of 10-50 μm. This suggests that even at the seemingly optimal dosage, the formed flocs still face significant mechanical instability.

[0052] Furthermore, anomalies were observed at a dosage of 50 mg / L. The ≥50 μm particle population exhibited more severe and earlier decay in the later stages, while the proportion of fine particles (2-10 μm) rebounded in the later experimental stages (from 13.54% at 2.04 min to 14.63% at 4.08 min). These data characteristics collectively point to the conclusion that excessive PAC dosage leads to a fundamental deterioration of the floc structure. Oversaturated coagulant may interfere with the formation of dense flocs through the "suspended particle protection" effect or by generating a large number of amorphous hydroxide suspended particles, thus producing a large number of loosely structured flocs with weak internal cohesion. These flocs are easily broken under fluid shear, and their breakage products are even finer, even leading to system restatement, thereby fundamentally weakening the coagulation efficiency.

[0053] 3.2 Decrease rate of the proportion of different particle size ranges of flocs at different stages Based on data on the removal efficiency of particles in different particle size ranges and the proportion of coarse particles at different coagulation stages, the dynamic influence and intrinsic mechanism of polyaluminum chloride (PAC) dosage on particle community migration behavior during mine water coagulation can be systematically revealed.

[0054] Figure 6 The volume percentage change rate is shown in (a), (b), (c), and (d), which represent the comparison of the volume percentage decrease rate in the ≤2 μm, 2-10 μm, and 10-50 μm ranges and the volume percentage rate in the ≥50 μm range at the same dosage during the growth zone, peak zone, stabilization process, and stabilization zone at the same time.

[0055] from Figure 6 As can be seen, in the rapid floc growth zone (0.51 min), the proportion of particles ≥50 μm increased continuously with the increase of PAC dosage from 10 mg / L to 50 mg / L (from 16.44% to 34.37%). This indicates that in the initial stage of coagulation, increasing the coagulant dosage directly enhances the charge neutralization and bridging effect, effectively promotes the aggregation of suspended particles, and rapidly generates micro-flocs.

[0056] In the peak particle size region of the flocs, the removal rate of particles in each size range and the proportion of particles ≥50 μm both showed a trend of first increasing and then decreasing with the increase of PAC dosage. When the dosage was increased from 10 mg / L to 20-30 mg / L, the reduction rate of the two fine particle ranges ≤2 μm and 2-10 μm significantly increased, indicating that an appropriate amount of PAC significantly promoted the destabilization and aggregation of fine particles through effective charge neutralization and adsorption bridging, thereby transforming them into larger flocs. This is reflected in the simultaneous increase in the volume proportion of ≥50 μm particles. However, when the dosage was increased to 50 mg / L, although the proportion of ≥50 μm particles reached a high level during the rapid growth period, this proportion significantly decreased in the subsequent peak region and stabilization process, and the removal efficiency of fine particles also declined. This phenomenon reveals that although excessive coagulant can quickly form a large number of flocs, these flocs are more prone to breakage under continuous fluid shear due to their loose structure and weak binding force. This causes the already aggregated coarse particles to break up again and fall back into the small and medium particle size range. It may even cause the system to become stable again due to the protective effect of suspended particles.

[0057] Further analysis of data from the stabilization process to the stabilization range revealed a complex reconstruction of particle distribution across different size ranges under the dominance of floc fragmentation. Compared to the peak period, the proportion of coarse particles ≥50 μm decreased under all addition conditions, confirming the physical breakdown of large flocs under continuous shear. The fragments generated by the fragmentation re-entered the water body and were mainly distributed in the medium-sized particle range of 10–50 μm; simultaneously, some finer fragments directly led to a rebound in the volume proportion of particles ≤2 μm and 2–10 μm.

[0058] Meanwhile, the optimal mixing and rapid stirring time was determined by analyzing the evolution of the removal rate of different floc size ranges over time. At a stirring intensity of 300 r / min, the critical equilibrium point between floc growth and fluid shear occurred at approximately 1 min (1.02 min). Before this time point, the hydrolysis, diffusion, and collision-adsorption processes of the coagulant were essentially completed, and the floc size reached or approached its peak value. Beyond this time, continuous high-intensity stirring would lead to ineffective dissipation of input energy and irreversible shear damage to the already formed floc structure, resulting in a decrease in the proportion of ≥50 μm particles and a resurgence in the proportion of fragments in the medium-sized particle size range (10-50 μm).

[0059] For this mine water system, the PAC dosage was controlled at 20-30 mg / L, and the rapid stirring time was set to 1 min, forming an optimized process combination for achieving efficient coagulation. This combination ensures that the flocs can quickly reach their maximum size during the growth stage and maintain sufficient structural integrity in the subsequent shear environment, thus laying a key foundation for obtaining excellent solid-liquid separation and effluent quality.

[0060] 4. Dynamic evolution characteristics of floc particle size during slow stirring of PAC This invention focuses on mine water systems and conducts experimental research on the evolution of floc particle size during slow agitation of PAC (polyacrylamide). Based on the above research results, the experiment set two gradients of PAC dosage: 20 mg / L and 30 mg / L. After a fixed rapid agitation time of 1 min, slow agitation was continued for 10 min, and the dynamic changes in floc particle size were monitored in real time using a laser particle size analyzer. Figure 7 The graph shows the overall variation of median particle size throughout the process. By analyzing the trend of median particle size change in flocs over time, the aim is to identify the time point when the particle size tends to stabilize during the slow stirring stage, providing a basis for selecting the timing of subsequent PAM addition, thereby optimizing the staged and precise addition strategy of reagents during the coagulation process.

[0061] from Figure 7 It can be seen from the above that: in the initial stage of stirring (0-1 min), D under the two dosages 50Both showed a rapid upward trend. At a dosage of 20 mg / L, the floc particle size increased from 18.83 μm to 56.42 μm, and at a dosage of 30 mg / L, the floc particle size increased from 17.53 μm to 52.15 μm. This indicates that PAC rapidly hydrolyzes and undergoes charge neutralization and adsorption bridging with the particles, promoting rapid aggregation of micro-flocs. As stirring continued (1-3 min), D... 50 Growth gradually slowed, entering a slow growth phase. The 20 mg / L and 30 mg / L groups reached peak values ​​of 66.62 μm and 63.53 μm, respectively, at approximately 3 minutes. Notably, after this phase, the D... 50 None of them continued to increase significantly; instead, they remained within a relatively stable fluctuation range during long-term slow stirring for 3-8 minutes: 20 mg / L group D 50 The particle size fluctuated slightly within the range of 63-66 μm, while the 30 mg / L group remained basically stable at 60-64 μm. This phenomenon indicates that after about 3 minutes, the growth and breakup of the flocs have basically reached a dynamic equilibrium, and the system enters a "particle size stable state." At this point, further extending the slow stirring time will not continue to increase the floc size; on the contrary, the continuous shearing may cause slight reorganization and refinement of the floc structure.

[0062] Comparing the dosages, the final stable particle size of the 30 mg / L group was slightly lower than that of the 20 mg / L group. This may be related to the fact that excessive PAC produces more fine floc nuclei, resulting in a relatively loose floc structure and slightly weaker shear resistance. In addition, both groups of data showed slight fluctuations within 5-10 minutes, reflecting that the flocs continuously experienced a dynamic equilibrium of "aggregation-breakup-reaggregation" during slow stirring, but the overall mean remained stable, indicating that the system has good structural stability.

[0063] In summary, this experiment demonstrates that under current water quality conditions, the particle size of microflocs tends to stabilize after approximately 2-3 minutes of slow agitation with PAC, and further extending the agitation time has no significant effect on increasing floc size. This result provides a clear basis for selecting the timing of subsequent PAM addition: PAM should be added after approximately 2-3 minutes of slow agitation with PAC and after the microflocs have stabilized, in order to achieve the optimal synergy between the "charge neutralization-bridging" two-stage flocculation, thereby obtaining flocs with dense structure and excellent settling performance.

[0064] Analysis of Floc Characteristics of PAC Combined with PAM (Polymer Flocculant) Prepared in Example 1 1. Effect of PAM addition on median particle size of flocs A comparative experiment was designed to investigate the effect of PAM (0.1 mg / L) addition timing on floc growth under the conditions of PAC dosage (20 mg / L) and rapid stirring time (300 r / min, 1 min). Two addition schemes were set up: (1) PAM was added immediately after rapid stirring; (2) after rapid stirring, slow stirring (60 r / min) was performed for 2 min, and PAM was added after the micro-flocs formed by PAC tended to stabilize, and slow stirring was continued for 5 min. The dynamic changes of floc particle size were monitored online by a laser particle size analyzer, and the floc size under the two conditions was analyzed in detail. 50 The study aimed to reveal the influence mechanism of PAM addition time on floc structure formation, thereby providing a basis for optimizing the dosing strategy of reagents in coagulation processes. Results are as follows... Figure 8 Comparison of real-time changes in median particle size.

[0065] Depend on Figure 8 It was observed that under the condition of adding PAM at the "end point of rapid stirring," the floc particle size increased rapidly in the initial stage, reaching a peak of 118.3 μm at around 3 minutes, and then entered a dynamic equilibrium stage, eventually stabilizing at around 120 μm. This phenomenon indicates that adding PAM immediately after rapid stirring can quickly capture the micro-flocs and dispersed particles already formed in the water through adsorption bridging, promoting rapid aggregation of flocs in a short period of time. However, because the hydrolysis of PAC and the destabilization of particles are not yet fully completed, the premature addition of PAM may limit its binding to the effective action sites on the particle surface, resulting in a relatively loose floc structure, an early reaching of the upper limit of particle size growth, and partial breakage and reorganization due to shearing during subsequent slow stirring, ultimately presenting a stable but limited particle size. In contrast, under the condition of the "slow stirring stabilization point" (slow stirring for 2 minutes before adding PAM), the growth of floc particle size showed a more delayed but continuously increasing trend. In the initial stage of slow stirring (0-2 min), PAC is fully hydrolyzed and gradually forms stable micro-flocs, effectively neutralizing the particle surface potential and creating favorable conditions for the subsequent bridging effect of PAM. After PAM addition, the floc particle size gradually increases from about 35 μm, reaching a peak of 209.5 μm within 5 min, and although there are slight fluctuations thereafter, it remains at a relatively high level of 190-220 μm. This indicates that delayed PAM addition provides sufficient "pre-flocculation" time for PAC, resulting in a denser micro-floc structure and surface properties that are more conducive to the attachment and extension of polymer chains, thus forming larger and more stable flocs. In addition, the sustained high stability of floc particle size under these conditions also reflects its strong shear resistance, which is more conducive to achieving efficient solid-liquid separation in subsequent precipitation processes.

[0066] From a mechanistic perspective, the timing of PAM addition substantially affects the process of the "charge neutralization-bridging" synergistic effect. When added immediately, PAC and PAM act on the particulate system almost simultaneously, potentially leading to competitive adsorption and overlapping effects, limiting the final size and density of the flocs. Delayed addition, however, allows for staged control—PAC first completes charge neutralization and micro-floc construction, followed by PAM bridging and coarse floc enhancement. This separation in timing significantly optimizes the floc structure. The results of this invention demonstrate that in mine water coagulation processes, appropriately delaying PAM addition (e.g., adding after slow stirring and stabilization) can significantly improve floc particle size and stability.

[0067] 1.1 Particle size distribution characteristics of flocs under different PAM addition times To deeply analyze the essential differences in floc population structure caused by different pathways, this invention selects four characteristic time points: the end point of rapid stirring, the stabilization point of slow stirring, the stabilization point after immediate PAM addition, and the stabilization point after delayed PAM addition, for point-to-point comparison of particle size distribution. The particle size distribution frequencies at these four points are plotted and analyzed. Figure 9 The cumulative distribution curves in Figure 9 (a) and Figure 9 (b) are examined, with a focus on the volume percentage of the ≤10μm, 10-100μm, 10-100μm and ≥100μm ranges in Figure 9 (c). Furthermore, the regulation mechanism of PAM addition timing on the final floc community formation is quantitatively revealed from multiple dimensions such as distribution width, uniformity and range migration.

[0068] Depend on Figure 9 As shown in (a), there are significant differences in particle size distribution among the four characteristic nodes. After rapid mixing with PAC, the particles are mainly distributed in the particle size range of 1 μm to 40 μm, with a distribution peak at approximately 34 μm. This distribution characteristic indicates that during the rapid mixing stage, the hydrolysis products of PAC destabilize the suspended particles through charge neutralization, forming a large number of primary micro-aggregates, which are small in size and relatively dispersed. After 2 minutes of slow mixing, the particle size distribution changes significantly, with the main range of particle size distribution shifting significantly to the right, and the peak appearing at approximately 69 μm. The volume percentage corresponding to this peak is higher than that at the end of rapid mixing. At the same time, the proportion of particles smaller than 10 μm decreases significantly. This transformation confirms that under suitable fluid shear force, primary micro-aggregates effectively grow through collision, adsorption, and coagulation, forming larger micro-flocs.

[0069] The addition of PAM resulted in drastically different final floc structures from two different addition methods. When PAM was added immediately after rapid stirring, the resulting flocs exhibited an extremely wide particle size distribution, with a main peak at approximately 124 μm, but also a wide distribution in the finer and coarser particle size ranges on either side. This indicates that PAM molecules simultaneously act on primary aggregates of varying sizes and stability; while their bridging and trapping effects promoted particle aggregation, they failed to achieve homogeneous particle size growth, resulting in a mixture of flocs of various sizes. In stark contrast, delayed PAM addition produced a highly concentrated single-peak particle size distribution with a sharp peak at approximately 222 μm. Figure 9 As shown in (c), the volume fraction of particles smaller than 50 μm is close to zero. This indicates that when PAM acts on microflocs that have undergone slow-stirring growth and whose size and structure are optimized, its bridging effect is more selective and efficient. The pre-formed microflocs provide a large number of effective adsorption sites and a stable structural framework, enabling PAM to primarily bridge between these microflocs, thereby driving them to efficiently assemble into large flocs with uniform size and compact structure, achieving directional enrichment of particulate matter within the target particle size range.

[0070] Figure 9 The cumulative distribution data in (b) further quantifies the aforementioned evolution path. At the end of rapid stirring, the cumulative curve rises slowly in the finer particle size range. After slow stirring stabilizes, the curve shifts to the right overall, with a larger upward slope in the 10-50 μm range. The final cumulative curves under the two PAM addition methods differ significantly. The curve after immediate addition rises relatively gently across the entire particle size range, indicating that particles of all sizes are present in a considerable proportion. The cumulative curve after delayed addition shows a nearly vertical upward segment in the 50-100 μm range, and then tends to flatten in the high particle size region. This indicates that the vast majority of particulate matter completes the rapid transformation into large flocs within a narrow particle size window, with extremely high particle size crossing efficiency.

[0071] Figure 9 The volume percentage of specific intervals in (c) provides precise numerical evidence for structural differences. From the initial state to slow stirring stabilization, particulate matter clearly migrated from the ≤10 μm and 10-50 μm intervals to the 50-100 μm interval. The intervention of PAM further enriched particulate matter in the ≥100 μm interval, but the two methods had different efficiencies. After immediate addition of PAM, some particles were still not fully converted, and the final proportion of ≥100 μm flocs was 62.6%. However, the performance of delayed addition was quite different. ≤10 μm and 10-50 μm particles were almost completely removed (0.07% and 2.8%, respectively), and the proportion of material in the 10-100 μm interval was also extremely low (5.93%), with as much as 91.2% of the material being converted into large flocs of ≥100 μm.

[0072] By synthesizing the three sets of data and corroborating them with the median particle size evolution process, it can be concluded that the core influencing mechanism of PAM addition timing lies in the state difference of the particle matrix on which PAM acts. When added immediately, PAM acts on unstable, polydisperse primary aggregates, with its bridging effect occurring simultaneously at multiple scales. While promoting growth, it easily forms a broadly distributed flocculent mixture system, resulting in a slow increase in median particle size. When added with a delay, PAM acts on micro-flocs (mainly located at 50-100 μm) that have undergone slow stirring and pre-growth, exhibiting relatively stable structure and concentrated distribution. At this time, the bridging effect mainly occurs between these "prefabricated units," with a more efficient and specific pathway, thereby driving a collective, leapfrog size increase in particulate matter, forming highly homogenized large flocs, which directly corresponds to the leap in median particle size. Therefore, during the coagulation process, adding polymeric flocculants after the micro-flocs formed by inorganic coagulants have fully grown and stabilized can maximize the bridging efficiency of the latter and achieve optimized control of the floc structure from "polydispersity" to "monodispersity". This is of decisive significance for improving the efficiency of subsequent solid-liquid separation.

[0073] 1.2 Analysis of enhanced floc settling performance (settling velocity, settling volume) This invention systematically evaluates the impact of different PAM addition timings on the solid-liquid separation efficiency after coagulation. Based on a fixed PAC dosage (20 mg / L), the settling performance of flocs formed under three conditions was compared: PAC addition alone, PAM addition at the end of rapid stirring, and PAM addition at the stabilization point of slow stirring. Through settling column experiments, turbidity changes at a fixed sampling depth (1 cm below the liquid surface) were periodically measured to obtain dynamic data on suspended solids removal during settling. The residual turbidity percentage-time relationship curve (Pi~t curve) and the mine water settling velocity distribution curve (Pi~ui curve) were plotted, see [link to relevant documentation]. Figure 10 (a) and (b). The total turbidity removal rate ET in mine water was used to plot the mine water settling characteristic curves, namely the turbidity removal rate-settling time curve (ET~t curve) and the turbidity removal rate-settling velocity curve (ET~ui curve), see [reference]. Figure 10 (c) and (d). From the dual dimensions of sedimentation kinetics and final separation efficiency, the influence of PAM addition timing on the sedimentation behavior of coagulated effluent is quantitatively revealed.

[0074] Based on the systematic processing and analysis of the above sedimentation experimental data, the profound influence and underlying mechanism of different PAM addition timing on the sedimentation behavior of the coagulated system can be revealed. From the time-residual turbidity ratio curve ( Figure 10As shown in (a)), the residual turbidity percentage decreased with time under all three conditions, but the rate of decrease differed significantly from the final stable value. Under the condition of adding PAM at the slow-stirring stable point, the residual turbidity percentage rapidly decreased to 0.1189 within the first 3 minutes, significantly lower than that of PAC alone (0.5013) and addition at the end of the fast-stirring point (0.2567), indicating that the floc structure formed under this condition was more conducive to early and rapid settling. As settling progressed to 30 minutes, the residual turbidity percentage of the slow-stirring stable point system finally stabilized at 0.0386, lower than the other two (0.0523 and 0.0427), indicating that it had the lowest content of difficult-to-settle fine particles and better floc integrity.

[0075] From the settling velocity-residual turbidity distribution curve ( Figure 10 As can be further seen in (b), under the same settling velocity, the residual turbidity percentage at the slow-stirring stable point is always the lowest. For example, when the settling velocity is 0.0833 cm / min, the residual turbidity percentage is only 0.0566, while under the same conditions, the PAC system alone is as high as 0.2525. This indicates that under equivalent hydraulic loading, the slow-stirring stable point system can retain finer particles, and its floc particle size distribution is more concentrated in a larger size range. This characteristic is consistent with the median particle size data obtained in the aforementioned laser particle size experiment (highest at the slow-stirring stable point).

[0076] The trend of turbidity removal rate over time ( Figure 10 (c) further quantified the differences in settling efficiency. The slow-stirring stable point system achieved a removal rate of 88.11% after 3 minutes of settling, which was 13.78 and 38.24 percentage points higher than the fast-stirring end point system and the PAC system alone, respectively. It is noteworthy that in the later stages of settling (12-30 minutes), the growth rate of removal rates for all systems slowed down, but the final removal rate of the slow-stirring stable point system (96.14%) still maintained a relative advantage, indicating that it not only had a fast settling speed but also removed fine particles more thoroughly. Settling speed-turbidity removal rate curve ( Figure 10 The middle (d) provides important basis from the design perspective: when the requirement is to achieve a turbidity removal rate of about 90%, the slow stirring stable point system only requires a surface load of 0.1998 m³ / (m²·h), while the fast stirring end point system requires as low as 0.100 m³ / (m²·h). This shows that optimizing the timing of PAM addition can significantly improve the treatment capacity of the sedimentation tank.

[0077] The combined data from the four sets indicate that the flocs formed when PAM is added at the slow-stirring stable point exhibit optimal settling performance. This is primarily attributed to the synergistic effect of two-stage flocculation: PAC fully completes charge neutralization and micro-floc construction during the slow-stirring stage, providing a stable particle matrix with suitable surface properties for subsequent PAM bridging, thus forming dense flocs with a concentrated particle size distribution. These flocs not only settle rapidly but also exhibit strong shear resistance during settling, effectively reducing the secondary release of fine particles caused by breakage.

[0078] Comparative Example 1 This comparative example compares the polyaluminum chloride agent prepared in Example 1 with traditional commercial PAC (national standard 28% commercial PAC) in terms of indicator control, as detailed in Table 1.

[0079] Table 1 Comparison of indicators between polyaluminum chloride (PAC) reagents and traditional commercial PAC products Analysis revealed that the polyaluminum chloride agent prepared in Example 1 exhibits different characteristics from traditional commercial PAC. In terms of composition and morphological properties, due to the presence of waste and high impurity content in the raw materials, the polyaluminum chloride agent prepared in Example 1 has a relatively high insoluble content. However, its polymerization process ensures that the product's Al content is higher than 80%, enabling the polyaluminum chloride agent prepared by this invention to possess both a certain charge neutralization capacity and superior adsorption bridging and net-trapping / sweeping capabilities. In terms of economics, because this invention uses inexpensive raw materials and byproducts, its production cost is significantly lower than that of similar qualified products on the market, giving it a significant price advantage.

[0080] To evaluate the actual performance of the polyaluminum chloride agent prepared in Example 1, this invention conducted a coagulation comparison test with commercial PAC that meets national standards under the same conditions.

[0081] 1. Comparison of destabilization performance of difficult-to-settle particulate matter in mine water Table 2 shows the zeta potential changes of the polyaluminum chloride agent prepared in Example 1 and conventional commercial PAC at different dosages. As can be seen from Table 2, the polyaluminum chloride agent prepared in Example 1 exhibits a clear and stable charge-neutralizing ability, significantly increasing the system's zeta potential from -23.3 mV (the zeta potential value of the original mine water). At the same dosage, its charge-neutralizing ability (measured by the increase in zeta potential) is slightly inferior to conventional PAC, but when the dosage is increased to 30 mg / L, the absolute value of the zeta potential is stably reduced to below 15 mV. Further increasing the dosage does not significantly reduce the absolute value of the zeta potential. According to the colloid stability theory (DLVO theory), when the absolute value of the zeta potential drops to the critical region of 15 mV, the electrostatic repulsion barrier between particles has decreased, sufficient to allow van der Waals attraction to take effect, indicating that the particles have slightly destabilized.

[0082] Table 2 Zeta potential (mV) 2. Dynamic comparison of median particle size of flocs during coagulation process Without the addition of PAC, mine water cannot form effective large flocs by mechanical agitation alone, resulting in a final floc size D. 50 For particles smaller than 25 μm, after adding the polyaluminum chloride agent prepared in Example 1 and conventional commercial PAC, the mixture was rapidly stirred at 300 r / min for 1 min, then slowly stirred at 60 r / min for 10 min, and allowed to stand for 30 min. All systems showed a significant increase in floc size during the rapid stirring stage due to charge neutralization, but exhibited different characteristics in subsequent stages. Figure 11 The changes in floc particle size during coagulation of the polyaluminum chloride agent prepared in Example 1 and conventional commercial PAC at different dosages are shown. (a) is a dosage of 10 mg / L, (b) is a dosage of 30 mg / L, and (c) is a dosage of 50 mg / L. The special PAC is the polyaluminum chloride agent prepared in Example 1, and the conventional PAC is the conventional commercial PAC.

[0083] from Figure 11 As can be seen in (a), at lower dosages (10 mg / L), the charge neutralization effect of both PACs is weak, and the floc growth is limited during the rapid stirring stage (ΔD). 50 <10 μm), the main growth of flocs occurs during the slow stirring stage, relying on adsorption bridging and net trapping and sweeping action.

[0084] from Figure 11 As can be seen in (b), under a moderate dosage (30 mg / L), the performance differences between the two PACs begin to emerge. During the rapid stirring stage, both exhibit significant charge neutralization and destabilization capabilities, with a rapid increase in floc particle size (ΔD). 50 >20 μm). After entering the slow stirring stage, the flocs formed by the special PAC continued to grow, with the median particle size increasing from about 28 μm to 43 μm, while the flocs of conventional PAC grew more slowly and eventually stabilized at about 33 μm. This indicates that the insoluble matter and high polymer content of the special PAC enable it to continue to capture fine particles and promote floc growth during the slow stirring stage through more efficient adsorption bridging and trapping effects.

[0085] from Figure 11As shown in (c), at a higher dosage (50 mg / L), conventional PAC exhibited a typical "overdosing" phenomenon, with its flocs breaking down after reaching their peak size (approximately 40 μm), resulting in a particle size decrease of about 12%. In contrast, the dedicated PAC, due to the buffering effect of its components, showed better floc stability and did not exhibit significant breakage. The experiment showed that there was no direct positive correlation between floc particle size and the alumina content of the PAC. Conventional PAC mainly relies on the synergistic mechanism of charge neutralization and adsorption bridging, performing optimally at the optimal dosage, but with a narrow dosage window. Although the dedicated PAC has a slightly weaker charge neutralization capacity, its strong adsorption bridging and net-like sweeping effects enable it to form larger and more stable flocs, with stronger resistance to overdosing interference and better operational flexibility.

[0086] 3. Comparison of coagulation and turbidity removal effects and effluent particle size distribution Table 3 shows the residual turbidity results of the polyaluminum chloride reagent prepared in Example 1 and the conventional commercial PAC.

[0087] Table 3. Comparison of Residual Turbidity (Unit: NTU) Table 3 shows that, under different dosages, both types of PAC achieved excellent turbidity removal (<10 NTU) in the low dosage range (10-30 mg / L), demonstrating comparable effectiveness. This proves that the polyaluminum chloride agent prepared in Example 1 can fully exert its coagulation efficiency at this dosage. At higher dosages (50-70 mg / L), the polyaluminum chloride agent prepared in Example 1 exhibited superior deep turbidity removal potential, with its residual turbidity consistently lower than that of traditional commercial PACs. This indicates that with increasing dosage, its rich Al content... c The adsorption bridging and trapping effects of the morphology are further enhanced, resulting in more thorough capture of fine particles. Experimental results show that the polyaluminum chloride agent prepared in Example 1 operates under the mode of "enhanced adsorption bridging under effective charge neutralization." Although its direct charge neutralization capacity per unit mass is not the strongest, at a relatively low dosage of 30 mg / L, it can simultaneously achieve effective destabilization of the system (absolute value of Zeta potential <15 mV) and deep removal of turbidity (<10 NTU), and its overall treatment efficiency is comparable to or even better than that of traditional commercial PAC.

[0088] Figure 12 The particle size distribution of residual particles in the effluent from mine water coagulation treatment is shown in the diagrams of the polyaluminum chloride agent (a) prepared in Example 1 and the conventional commercial PAC (b). Figure 12As shown, the polyaluminum chloride (PAC) agent prepared in Example 1 has a high proportion of small particles in the effluent, demonstrating excellent removal of large particles from the raw water. In contrast, traditional commercial PAC residues are mainly large particles, indicating its excellent destabilization ability. It effectively destabilizes small particles, causing them to form micro-flocs. However, a considerable portion of the micro-flocs still remain in the water, reflecting a slightly different dominant coagulation mechanism. In the effluent of the PAC agent prepared in Example 1, small-diameter particles (0 ~ 5 μm) accounted for as high as 65.04% (0 ~ 1 μm: 24.98%, 1 ~ 2 μm: 11.57%, 2 ~ 5 μm: 29.49%), while large-diameter flocs (≥ 20 μm) accounted for only 17.45%, and no flocs larger than 50 μm were formed. This phenomenon is closely related to its high insoluble content (5%): undissolved aluminum hydroxide colloids and large insoluble particles act as crystal nuclei, enhancing the trapping and sweeping effects and promoting the rapid sedimentation of large particles. However, due to its high impurity content and low concentration of high-charge hydrolyzed aluminum, its charge neutralization capacity is insufficient (Zeta potential only drops to -12.09 mV), and its ability to compress the electric double layer is limited, causing fine particles to fail to aggregate effectively due to surface charge repulsion. This phenomenon indicates that although relying solely on physical trapping mechanisms can quickly remove large particles, it is limited by low destabilization capacity, and fine particles are prone to remain.

[0089] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a polyaluminum chloride agent suitable for coagulation treatment of fine particulate suspended solids in high-turbidity mine water, characterized in that, Includes the following steps: Aluminum-containing waste is mixed with hydrochloric acid, and steam is introduced to carry out an acid dissolution reaction; Add calcium aluminate powder to the obtained liquid and carry out hydrolysis and polymerization reaction to obtain the reagent stock solution; The original pharmaceutical solution is subjected to solid-liquid separation to obtain a supernatant and a precipitate. The supernatant is then dehydrated and dried to obtain the polyaluminum chloride agent. The precipitate and aluminum slag produced during the dehydration process are mixed to obtain an aluminum-containing byproduct. The aluminum-containing byproduct and bauxite are used as raw materials to prepare aluminum-containing waste for recycling.

2. The preparation method according to claim 1, characterized in that, The mass ratio of the aluminum-containing waste, hydrochloric acid, and calcium aluminate powder is 0.4:1:0.

4.

3. The preparation method according to claim 2, characterized in that, The aluminum-containing waste contains 40-60 wt.% Al2O3; the hydrochloric acid has a mass concentration of 30-36 wt.%; and the calcium aluminate powder contains 30-50 wt.% Al2O3.

4. The preparation method according to claim 1, characterized in that, The acid dissolution reaction is carried out at a temperature of 70-90℃ for 3 hours, with a pH of 3-5.

5. The preparation method according to claim 1, characterized in that, The hydrolysis-polymerization reaction is carried out at a temperature of 70-90℃, for a reaction time of 3 hours, and at a pH of 3-5.

6. The preparation method according to claim 1, characterized in that, The dehydration and drying temperature is 200-300℃.

7. A polyaluminum chloride agent prepared by the preparation method according to any one of claims 1-6, suitable for coagulation treatment of fine particulate suspended solids in high-turbidity mine water.

8. The application of the polyaluminum chloride agent of claim 7, suitable for coagulation treatment of fine particulate suspended solids in high-turbidity mine water, in mine water coagulation treatment, characterized in that... The polyaluminum chloride agent is added to the mine water, and after rapid stirring, it is stirred slowly. Then, the polymeric flocculant is added, and the stirring continues slowly.

9. The application according to claim 8, characterized in that, The rapid stirring time is 1 minute, and the rotation speed is 300 r / min; the slow stirring time is 2-3 minutes, and the rotation speed is 60 r / min; the continued slow stirring time is 5 minutes, and the rotation speed is 60 r / min.

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