Mine water coagulation treatment method based on floc property optimization

Abstract

The application discloses a mine water coagulation treatment method based on floc property optimization and belongs to the technical field of water treatment. In view of the problems of PAM dosage depending on experience, unreasonable hydraulic parameters and weak water quality fluctuation resistance in the existing polyaluminum chloride-polyacrylamide (PAC-PAM) combined process, the floc structure and the settling performance are synergistically optimized by precisely regulating the dosage of reagent and the flocculation hydraulic condition. The method is as follows: 30 mg / L of PAC is added to mine water, fast stirring is carried out at 500 r / min for 1 min; then 0.8 mg / L of PAM is added, and slow stirring is carried out at 80 r / min for 15 min. After the above parameter control, the coagulation floc is in a dense network shape, the median particle size increases to 1004 mu m, the settling rate is significantly improved, the residual turbidity decreases to 1.31 NTU; the particle size distribution span is 1.216, the fractal dimension is 1.752, the strength factor is 82.13%, and the recovery factor is 70.07%, so that the excellent structure strength and self-repairing capacity are combined. The application determines the PAM dosage critical threshold, establishes the quantitative correlation of "process parameters-floc structure-settling performance", and provides a precise controllable technical scheme for mine water treatment.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and in particular to a method for coagulation treatment of mine water based on optimization of floc properties. Background Technology

[0002] Mine water is the main wastewater generated during coal mining, and its efficient treatment and resource utilization are key to promoting the green development of the coal industry. In the mainstream "coagulation-sedimentation-filtration" treatment process, the coagulation effect directly determines the load of subsequent processes and the final effluent quality. The combined use of PAC and APAM is a classic technology for enhancing coagulation: PAC exerts its effect of compressing the double electric layer and neutralizing charge to initially destabilize colloids, while APAM achieves floc construction, growth, and structural strengthening through "adsorption-bridging".

[0003] However, the existing PAC-APAM combined process has the following technical bottlenecks: (1) Lack of precise control basis for PAM dosage: APAM solution has high viscosity and is difficult to disperse. In engineering, the dosage is mostly estimated based on experience. Insufficient dosage leads to loose floc structure and slow sedimentation, while excessive dosage causes "colloidal protection" effect, which not only increases treatment costs, but may also lead to an increase in the concentration of residual organic matter in the water, resulting in the risk of blockage and secondary pollution in subsequent processes. However, existing studies mostly focus on macroscopic effluent indicators such as turbidity, and lack systematic characterization of floc microstructure (particle size distribution, fractal dimension, intensity factor, recovery factor) across the entire range from insufficient to excessive dosage, resulting in an unclear PAM dosage threshold.

[0004] (2) Lack of targeted design for hydraulic parameters in the flocculation stage: The key hydraulic parameters (slow stirring speed G value and reaction time T value) that determine the floc structure and settling performance mostly follow the traditional water purification design specifications, while the response mechanism of the PAM-dominated flocculation process to shear force is fundamentally different from that of inorganic coagulants. The setting of slow stirring speed (G value) and time (T value) in the existing process lacks theoretical guidance for the adsorption bridging mechanism of PAM, resulting in the coexistence of "excessive shear" and "incomplete flocculation", and the system's ability to resist water quality fluctuations is weak.

[0005] (3) The structure-performance correlation mechanism of flocs is unclear: The suspended particles in mine water with high suspended matter have the characteristics of small particle size, strong surface negative charge, and low density, which puts forward higher requirements for the adsorption bridging efficiency of PAM. However, existing studies have not yet established a systematic correlation framework of "process parameters (dosage, G value, T value) - floc structure (particle size, fractal dimension) - macroscopic performance (sedimentation performance, dynamic stability)", making it difficult to achieve the leap from empirical regulation to precise control.

[0006] Therefore, there is an urgent need in this field for a mine water coagulation treatment method based on floc morphology optimization, which specifies the dosage of PAC and APAM and hydraulic conditions. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention provides a mine water coagulation treatment method based on floc property optimization. By adding a fixed amount and type of coagulant and flocculant, and with optimized stirring conditions, solid particles in the mine water settle rapidly, effectively reducing the turbidity of the mine water, and giving the flocs excellent structural strength and self-repairing ability. By analyzing the changes in the floc properties of the mine water after adding coagulant and flocculant, the optimal coagulation treatment scheme is determined.

[0008] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for coagulation treatment of mine water based on the optimization of floc properties, wherein a coagulant and a flocculant are added to the mine water, with the coagulant dosage being 30 mg / L and the flocculant dosage being 0.8 mg / L.

[0009] Furthermore, the coagulant is polyaluminum chloride, and the flocculant is anionic polyacrylamide.

[0010] Furthermore, the polyaluminum chloride has an alumina content of 26%, and the anionic polyacrylamide has a molecular weight of 12 million.

[0011] Furthermore, the order of adding coagulant and flocculant is to add coagulant first, and then add flocculant.

[0012] Furthermore, after adding the coagulant, the mixture was stirred at a speed of 500 r / min for 1 min.

[0013] Furthermore, after adding the flocculant, the mixture was stirred at a speed of 60 r / min for 15 min.

[0014] Furthermore, before adding the coagulant, dissolve the coagulant in water to a concentration of 30 g / L.

[0015] Furthermore, before adding the flocculant, the flocculant is dissolved in water with stirring during the dissolution process, and the concentration after dissolution is 1 g / L.

[0016] With the above parameters controlled, the coagulated flocs form a dense network with a median particle size of 1004 μm, significantly improved settling rate, and reduced residual turbidity to 1.31 NTU; the particle size distribution span is 1.216, the fractal dimension is 1.752, the strength factor is 82.13%, and the recovery factor is 70.07%, exhibiting both excellent structural strength and self-healing ability.

[0017] Compared with the prior art, the present invention has at least the following advantages and technical effects: A PAM dosing strategy based on the microstructure response of flocs was established, and the critical threshold for the transition from "adsorption bridging" to "colloidal protection" was clarified. Unlike existing technologies that rely on empirical estimation and use effluent turbidity as the final criterion, this invention investigated the evolution of floc particle size, fractal dimension, strength, and recovery ability across the entire range of PAM dosage from insufficient to excessive, determining 0.8 mg / L as the optimal dosage. At this dosage, the coagulated flocs exhibited a dense network structure, with a median particle size increasing to 915.4 μm, a significantly improved settling rate, and a reduction in residual turbidity of the effluent to 1.69 NTU. The strength factor was 79.46%, and the recovery factor was 71.91%, solving the problem of achieving both floc strength and toughness in traditional processes. The recovery factor can serve as a quantitative indicator for evaluating the regeneration capacity of flocs after shearing.

[0018] This paper proposes optimized parameters for the velocity gradient (G value) in the PAM-dominated flocculation process. In existing water purification processes, the slow stirring speed often follows empirical values ​​for aluminum salt coagulants (which are typically low), failing to adequately consider the shear response characteristics of PAM polymer chains, easily leading to "excessive shearing" or "incomplete flocculation." This invention, by adjusting the slow stirring speed, discovers an optimal velocity gradient range for PAM flocculation, determining G = 35 s. -1 The vicinity of this value represents the equilibrium point. At this G value, floc growth and breakup reach a dynamic equilibrium, resulting in optimal particle size distribution concentration, peak fractal dimension, and lowest residual turbidity in the effluent. Furthermore, the flocs exhibit both high shear strength and good resilience. In contrast, lower G values ​​lead to incomplete flocculation and smaller floc size; higher G values ​​are prone to "excessive shearing," causing large flocs to break up and reducing structural toughness.

[0019] A technical solution for synergistic optimization of "chemical-hydraulic" dual parameters has been developed. This invention combines optimized PAM dosage with slow stirring speed, resulting in flocs with multiple advantages, including large particle size, high density, rapid settling, strong shear resistance, and good regeneration capacity. Compared with traditional experience-based control, this solution helps reduce chemical waste and the risk of secondary pollution, enhances the adaptability to hydraulic shocks in water treatment, and ensures stable effluent quality. Attached Figure Description

[0020] 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.

[0021] Figure 1The dynamic characteristics and microstructure of flocs under different APAM dosages in Example 1 and Comparative Examples 1-7 are shown, where (a) is the dynamic change curve of D50; (b) is the microstructure of flocs at a dosage of 0.2 mg / L; and (c) is the microstructure of flocs at a dosage of 0.8 mg / L. Figure 2 The changes in floc particle size distribution for different APAM dosages in Example 1 and Comparative Examples 1-7 are shown, where (a) is the differential change in particle size volume distribution; (b) is the change in the volume ratio of particles in different particle size segments; (c) is the integral change in particle size volume distribution; and (d) is the change in characteristic particle sizes (D10, D50, D90). Figure 3 The images show the microstructure of flocs under different APAM dosages in Example 1 and Comparative Examples 1-7, where (a) is Comparative Example 1; (b) is Comparative Example 2; (c) is Comparative Example 3; (d) is Comparative Example 4; (e) is Example 1; (f) is Comparative Example 5; (g) is Comparative Example 6; and (h) is Comparative Example 7. Figure 4 The values ​​of the two-dimensional fractal dimension (Df) of the flocs under different APAM dosages in Example 1 and Comparative Examples 1-7 are given. Figure 5 The settling curves of flocs under different APAM dosages in Example 1 and Comparative Examples 1-7 are shown. Figure 6 The dynamic changes of D50 in the floc crushing-regeneration process under different APAM dosages in Example 1 and Comparative Examples 1-7; Figure 7 The dynamic change curves of floc D50 under different slow stirring speeds in Example 1 and Comparative Examples 8-11 are shown: (a) 20 and 40 r / min; (b) 60, 80 and 100 r / min. Figure 8 The following are floc particle size distribution diagrams for Example 1 and Comparative Examples 8-11 under different slow stirring speeds, where (a) particle size volume differential distribution; (b) particle volume percentage of different particle size segments; (c) particle size volume accumulation; and (d) characteristic particle size (D10, D50, D90) distribution. Figure 9 The microstructures of flocs under different slow stirring speeds in Example 1 and Comparative Examples 8-11 are shown. Figure 10 The images are grayscale and binarized images of flocs under different slow stirring speeds in Example 1 and Comparative Examples 8-11. Figure 11 Statistical analysis of floc Df under different slow stirring speeds in Example 1 and Comparative Examples 8-11; Figure 12Coagulation effect and floc settling behavior at different slow stirring speeds for Example 1 and Comparative Examples 8-11: (a) residual turbidity; (b) floc settling curves; Figure 13 The dynamic changes of D50 in the floc crushing-regeneration process under different slow stirring speeds in Example 1 and Comparative Examples 10-11 are shown. Detailed Implementation

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] This invention provides a method for coagulation treatment of mine water based on the optimization of floc properties, wherein a coagulant and a flocculant are added to the mine water, with the coagulant dosage being 30 mg / L and the flocculant dosage being 0.8 mg / L.

[0028] In some embodiments of the present invention, the coagulant is polyaluminum chloride and the flocculant is anionic polyacrylamide.

[0029] In some embodiments of the present invention, the polyaluminum chloride has an alumina content of 26%, and the anionic polyacrylamide has a molecular weight of 12 million.

[0030] In some embodiments of the present invention, the order of adding coagulant and flocculant is to add coagulant first, and then add flocculant.

[0031] In some embodiments of the present invention, after adding the coagulant, stirring is performed at a stirring rate of 500 r / min for a stirring time of 1 min.

[0032] In some embodiments of the present invention, after adding the flocculant, the mixture is stirred at a stirring rate of 60 r / min for 15 min.

[0033] In some embodiments of the present invention, the coagulant is dissolved in water before being added, and the concentration after dissolution is 30 g / L.

[0034] In some embodiments of the present invention, the flocculant is dissolved in water before being added, and the dissolution process is stirred, with the concentration after dissolution being 1 g / L.

[0035] The mine water sample used in this embodiment of the invention was taken from the inlet of the pre-sedimentation and equalization tank of a wastewater treatment plant in a mining area of ​​Shanxi Province. The water sample was typically brownish-brown. After three parallel measurements, its basic water quality indicators were as follows: weakly alkaline pH, high turbidity, high suspended solids concentration, high total dissolved solids content, belonging to mine water with high suspended solids and high mineralization, and a strongly negative particle zeta potential, indicating strong stability.

[0036] The coagulant used in this example was polyaluminum chloride (PAC), and the flocculant was anionic polyacrylamide (APAM, molecular weight 12 million). Both PAC and APAM stock solutions were prepared on the day of the experiment. The APAM stock solution was prepared using a magnetic stirrer with continuous stirring to ensure complete dissolution and was stored at low temperature. All stock solutions were used within the specified time. The concentration of the PAC stock solution was 30 g / L, and the concentration of the APAM stock solution was 1 g / L.

[0037] Example 1 A method for coagulation treatment of mine water based on optimized floc characteristics includes the following steps: PAC stock solution is added to the mine water to a concentration of 30 mg / L, followed by rapid stirring at 500 r / min for 1 min. Then, APAM stock solution is added to a concentration of 0.8 mg / L, followed by slow stirring at 60 r / min for 15 min. After stirring, the mixture is allowed to settle.

[0038] Comparative Example 1 A method for coagulation treatment of mine water based on floc characteristics optimization is different from Example 1 only in that APAM is not added, while the other steps are the same as in Example 1.

[0039] Comparative Example 2 A method for coagulation treatment of mine water based on optimization of floc properties is different from Example 1 only in that APAM is added to 0.2 mg / L, and the other steps are the same as in Example 1.

[0040] Comparative Example 3 A method for coagulation treatment of mine water based on optimization of floc properties is different from Example 1 only in that APAM is added to 0.4 mg / L, and the other steps are the same as in Example 1.

[0041] Comparative Example 4 A method for coagulation treatment of mine water based on floc characteristics optimization is different from Example 1 only in that APAM is added to 0.6 mg / L, and the other steps are the same as in Example 1.

[0042] Comparative Example 5 A method for coagulation treatment of mine water based on floc characteristics optimization is different from Example 1 only in that APAM is added to 1.0 mg / L, and the remaining steps are the same as in Example 1.

[0043] Comparative Example 6 A method for coagulation treatment of mine water based on floc characteristics optimization is different from Example 1 only in that APAM is added to 1.2 mg / L, and the remaining steps are the same as in Example 1.

[0044] Comparative Example 7 A method for coagulation treatment of mine water based on floc characteristics optimization is different from Example 1 only in that APAM is added to 1.4 mg / L, and the remaining steps are the same as in Example 1.

[0045] Comparative Example 8 A method for coagulation treatment of mine water based on optimization of floc properties is different from Example 1 only in that after adding APAM stock solution, the mixture is slowly stirred at 20 r / min for 15 min, and the remaining steps are the same as in Example 1.

[0046] Comparative Example 9 A method for coagulating mine water based on the optimization of floc properties is different from Example 1 only in that after adding APAM stock solution, the mixture is slowly stirred at 40 r / min for 15 min, and the remaining steps are the same as in Example 1.

[0047] Comparative Example 10 A method for coagulation treatment of mine water based on floc characteristics optimization is different from Example 1 only in that after adding APAM stock solution, the mixture is slowly stirred at 80 r / min for 15 min, and the remaining steps are the same as in Example 1.

[0048] Comparative Example 11 A method for coagulation treatment of mine water based on optimization of floc properties is different from Example 1 only in that after adding APAM stock solution, the mixture is slowly stirred at 100 r / min for 15 min, and the remaining steps are the same as in Example 1.

[0049] Figure 1 The dynamic characteristics and microstructure of flocs under different APAM dosages show that the floc growth behavior of Example 1 and Comparative Examples 1-7 differs significantly, accompanied by obvious dynamic fluctuations. This indicates that floc growth is not unidirectional aggregation, but is essentially a dynamic equilibrium process: under fluid shearing, the flocs simultaneously undergo interparticle collision aggregation and shear breakage, and the macroscopic particle size change is a direct manifestation of the competition between shear force and floc cohesion. Based on this mechanism, flocs under different APAM dosages exhibit differentiated growth characteristics.

[0050] Without APAM (0 mg / L), the D50 value remained consistently low and changed gradually, indicating that the floc structure formed solely by PAC charge neutralization was small and difficult to aggregate and grow effectively. After APAM addition, the floc growth process showed a clear concentration dependence. At low dosages (0.2, 0.4 mg / L), D50 gradually decreased in the initial stage of slow stirring, indicating that the APAM bridging effect was limited at this time, resulting in a loose and weak floc structure that was dominated by breakage under continuous fluid shear. However, when the dosage was increased to 0.6 mg / L and above, the floc growth behavior changed: D50 increased rapidly and remained stable at a higher level, indicating that the increased APAM molecules provided sufficient bridging, and the formed floc structure had sufficient cohesion to resist shear, achieving a balance between aggregation and breakage. However, when the dosage was further increased to 1.0 mg / L and above, although flocs could form rapidly, their steady-state D50 peak value gradually decreased with increasing dosage, showing a growth inhibition phenomenon.

[0051] The differences in the aforementioned growth processes are visually confirmed by the microstructure of the flocs. Figure 1 As shown in (b), at a dosage of 0.2 mg / L, the flocs exhibit an open, sparse, dendritic structure with limited bridging points, corresponding to their relatively weak shear resistance; while at a dosage of 0.8 mg / L, Figure 1 The flocs shown in (c) are larger in size and more tightly connected, exhibiting a network-like aggregate structure with significantly improved structural strength.

[0052] As slow stirring continued, the D50 values ​​of all experimental groups entered a stable stage with minimal fluctuations in the later stages of slow stirring (12-15 min), indicating that floc growth and breakage had reached a dynamic equilibrium. Based on this, the present invention defines the end of slow stirring (15 min) as the "steady state" of the flocs, providing a unified benchmark for subsequent systematic comparisons of the final structure, settling performance, and dynamic stability of flocs under different dosages.

[0053] Figure 2 The variation in floc particle size distribution with different APAM dosages was determined by... Figure 2 As shown in (a), unlike the bimodal distribution of raw water, the volume differential distribution exhibits a single broad peak with the peak position to the left when only PAC is added. This indicates that although charge neutralization and trapping can promote initial particle aggregation, the resulting flocs are limited in size and dispersed. Under appropriate APAM dosage (≤0.8 mg / L), with increasing dosage, the peak position continuously shifts to the right and the peak value significantly increases, indicating that APAM promotes floc growth and concentrates their distribution through sufficient bridging. Figure 2 As shown in (b), the change in the proportion of particle size further confirms that the proportion of ≤100μm flocs drops to below 5% after the dosage is >0.4mg / L, while the proportion of ≥500μm flocs reaches a peak of 81.28% at 0.8 mg / L. Figure 3 As shown in (c) and (d), the volume accumulation curve shifted to the right overall, the characteristic particle size D50 increased to 915.4 μm, and D10 and D90 also increased simultaneously, which together indicate that an appropriate amount of APAM can significantly enhance the floc aggregation ability.

[0054] However, this trend reversed when the dosage was ≥1.0 mg / L. For example... Figure 2 As shown in (a), the peak position of the volume differential distribution shifts to the left and the peak value decreases, which is consistent with... Figure 1 (a) The steady-state D50 shows a consistent downward trend; Figure 2 As shown in (b), the total proportion of flocs ≥500μm decreased, with the proportion of flocs ≥1000μm decreasing significantly from 42.94% to 20.87%, while the proportion of flocs 500~1000μm increased to 46.61%~48.58%, becoming dominant. This indicates that if the dosage exceeds a certain range, it will not only inhibit the further growth of flocs, but also weaken the internal structural connection strength of the already formed large flocs, making them easy to break and transform into small-sized flocs under shear action. Figure 2 The left gyration of the volume accumulation curve in (c) Figure 2 (d) shows that D50 and D90 decrease continuously, further confirming that excessive addition will hinder effective aggregation between particles, inhibit floc growth, and thus lead to a reduction in particle size.

[0055] Figure 3 To illustrate the microstructure of flocs under different APAM dosages, by Figure 3As shown in (a), when only PAC is added, the flocs are highly dispersed fine particle aggregates, which are typical "dense aggregates" formed under the dominance of charge neutralization. Figure 3 Figure (b) shows that after adding 0.2 mg / L APAM, the flocs transformed into a sparse, open, dendritic structure, but still maintained a high degree of dispersion. Figure 3 As shown in (c) and (d), as the dosage increases to 0.4 and 0.6 mg / L, the floc volume increases, the chain structure cross-links with each other and transitions to a cluster structure. Figure 3 Figure (e) shows that at 0.8 mg / L, large, well-defined, and densely structured network flocs are formed. However, when the dosage exceeds 1.0 mg / L, the binding... Figure 3 As can be seen from (f), (g), and (h), the floc structure gradually becomes loose and irregular.

[0056] Figure 4 The numerical values ​​of the two-dimensional fractal dimension (Df) of the flocs under different APAM dosages are derived from... Figure 4 It can be seen that when only PAC is added, the floc Df value is the highest (1.760±0.022), and the data distribution is concentrated. At this time, the floc growth mainly relies on the charge neutralization mechanism, which easily forms a dense structure. After adding 0.2 mg / L APAM, Df decreases sharply (1.468±0.033), and the data distribution is dispersed. This is because the long chains of APAM can play a bridging role between the dispersed colloidal particles, promoting the interconnection of originally independent micro-flocs and forming water-containing flocs with larger volume, rich internal pores, and relatively loose structure. As the APAM dosage increases to 0.4 and 0.6 mg / L, Df gradually increases (1.559±0.032; 1.600±0.031), indicating that the increased polymer molecules provide more effective bridging sites, promoting the reconstruction of the floc into a denser network structure. When the dosage reached 0.8 mg / L, Df was at a relatively high level (1.703±0.015) and the data distribution was concentrated, indicating that under this condition, ideal flocs with uniform structure and density were formed.

[0057] When the dosage reached 1.0 mg / L, the Df value (1.708±0.032) was basically the same as that at 0.8 mg / L, indicating that the floc density did not continue to increase. However, when the dosage was further increased, the Df value showed a decreasing trend (1.2 mg / L: 1.671±0.034; 1.4 mg / L: 1.652±0.038). This is mainly attributed to the mutual repulsion and crowding of excessive APAM molecular chains on the particle surface and in the pores, leading to an increase in the internal porosity of the floc; at the same time, its adsorption ends form a dense adsorption layer and hydration shell around the colloidal particles, generating a strong steric hindrance effect, hindering the effective aggregation between particles, thereby causing the overall floc structure to be loose and the average density to decrease.

[0058] Table 1. Effects of APAM dosage on floc settling performance and effluent quality Note: y0: Fitted platform turbidity, representing the theoretical final effluent quality of the sedimentation process; A1: Attenuation amplitude, representing the theoretical total amount of turbidity that can be removed by gravity sedimentation (A1=y(t=0)-y0); t1: Time constant, the smaller the value, the faster the floc sedimentation rate. The initial turbidity is the measured value at the start of sedimentation (0 min); the remaining turbidity is the measured value after 15 min of sedimentation.

[0059] The sedimentation curves of flocs under different APAM dosages are as follows: Figure 5 As shown, a first-order exponential decay model (y=y0+A1·exp(-x / t1)) is used to quantitatively analyze the settlement process. The coefficient of determination (R²) of all fitted curves is... 2 The values ​​were all above 0.99, and the fitting parameters and effluent water quality are shown in Table 1. The results indicate that the addition of APAM and PAC produced a significant synergistic effect. The attenuation magnitude A1 continuously decreased to 33.3 NTU with increasing dosage, which is consistent with the systematic decrease in initial turbidity. Together, they indicate that during the flocculation stage, APAM molecules effectively captured more suspended particles and converted them into settleable flocs through "adsorption-bridging" action, thereby significantly reducing the turbidity load of the system before sedimentation began. Within the dosage range of 0–0.8 mg / L, the time constant t1 decreased from 1.066 min to 0.094 min with increasing dosage, and the apparent sedimentation rate characterized by its reciprocal increased by approximately 11 times. This improvement is mainly due to the enhanced bridging effect resulting from the increased dosage: more APAM molecular chains bridge each other to form a gradually improving and denser three-dimensional network structure, which can effectively capture and bridge more particles, increasing the volume and mass of flocs, thereby improving their free sedimentation efficiency; its porous spatial structure also simultaneously enhances the efficiency of netting and sweeping fine particles, and the two together promote the acceleration of solid-liquid separation. At the same time, the platform turbidity y0 (theoretical final effluent turbidity) continued to decrease to 1.98 NTU, indicating that the system achieved simultaneous optimization of sedimentation rate and effluent quality within this dosage range.

[0060] However, when the APAM dosage increases to 1.0 mg / L or higher, the settling performance systematically deteriorates, the time constant t1 rebounds, and both the platform turbidity y0 and the measured residual turbidity increase significantly. Furthermore, the settling curve exhibits a clear "back-mixing" phenomenon. The root cause lies in the deterioration of the floc's internal structure due to excessive APAM molecules. During the settling stage, these flocs with inherent structural defects are prone to secondary breakage under their own weight, generating a large number of fragments. This leads to the resuspension of fine particles, which macroscopically manifests as an abnormal rebound in turbidity and a deterioration in effluent efficiency in the later stages of the settling curve.

[0061] like Figure 6 As shown, after shearing and breakage, the D50 of all flocs decreased sharply, and they exhibited varying degrees of regeneration during the recovery phase, but none could return to the pre-breakage level, indicating a certain degree of inherent irreversibility in the APAM flocculation process. The mechanism is related to the molecular characteristics of APAM: the network structure formed by the polymer is easily disintegrated under shearing, potentially even causing the breakage of C-C bonds in the APAM molecular chain, which is difficult to recover from. Simultaneously, the polymer chain segments remaining after shearing occupy effective adsorption sites on the particle surface, thus limiting the re-aggregation of flocs. These mechanisms work together to hinder the degree of floc regeneration.

[0062] Table 2. Flocculation strength and recovery factor under different APAM dosages The intensity factor (Sf) and recovery factor (Rf) calculated based on dynamic curves are shown in Table 2. Without APAM, the flocs exhibited some shear resistance (Sf = 52.85%), but had the worst recovery ability (Rf = 34.59%). This is consistent with its flocculation mechanism: the floc structure formed by charge neutralization is relatively dense and possesses a certain initial strength, but it is difficult to regenerate after breakage due to the lack of efficient bridging materials. After adding 0.2 mg / L of APAM, the floc formation mechanism shifted to being dominated by polymer adsorption-bridging. Although the initially formed open dendritic structure had weak bridging forces and was easily destroyed, resulting in a lower intensity factor (Sf = 49.53%), the bridging effect of APAM during the floc recovery stage helped restore the floc particle size, significantly improving its recovery factor (Rf = 41.51%). As the dosage increased to 0.8 mg / L, both the floc strength factor and the recovery factor significantly increased, with Sf increasing to 79.46% and Rf increasing to 71.91%. This indicates that an appropriate amount of APAM, through the bridging and trapping effect of its long molecular chains, formed more and stronger connection points between micro-flocs, constructing a stable floc structure with both excellent shear resistance and self-repair capabilities.

[0063] However, when the dosage increased to 1 mg / L or higher, the Sf value remained at a high level (74.56%~73.44%) with minimal change, while the Rf value decreased from 56.88% to 44.18%. This indicates that the dominant irreversible factors differ under different dosages: at low dosages, APAM molecular chains are insufficient, making it difficult to rebridge after shear breakage; at high dosages, the adsorption sites on the particle surface tend to be saturated, and the broken fragments lack active sites for re-aggregation. Therefore, only under appropriate dosage conditions can APAM balance shear resistance requirements and structural regeneration potential to form flocs with both strength and toughness. In actual water treatment, the recovery factor should be used as a key dynamic indicator to balance floc strength and regeneration toughness, thereby mitigating the increased system load and water quality fluctuations caused by fine particles generated by hydraulic shear.

[0064] In summary, the strongest overall floc performance was observed when the PAC dosage was 30 mg / L and the APAM dosage was 0.8 mg / L. This resulted in a significantly improved settling rate in mine water, a reduction in residual turbidity to 1.69 NTU, a significantly increased median particle size (D50), a dense network-like floc structure, and a fractal dimension (Df) increasing to 1.703. At a dosage of 0.8 mg / L, the floc performance reached its optimal level, with strength factor (Sf) and recovery factor (Rf) reaching as high as 79.46% and 71.91%, respectively.

[0065] according to Figure 7 (a) It can be seen that the floc growth process is abnormal at lower rotation speeds (20 and 40 r / min). When the rotation speed is 20 r / min, the D50 fluctuates greatly in the range of 400-500 μm during the initial stage of slow stirring, indicating that the shear force is seriously insufficient, which leads to mutual interference between floc formation and sedimentation, and the system is extremely unstable. After about 8 minutes, the fluctuation slows down, and the D50 eventually stabilizes at a low level of 115.9 μm. After the rotation speed is increased to 40 r / min, the fluctuation of the D50 curve weakens and quickly approaches a stable value of 770.8 μm, indicating that the shear force provided by this rotation speed range has reached the critical shear condition for effective flocculation, but overall the flocculation efficiency is low and the size of the formed flocs is limited.

[0066] In stark contrast, floc growth characteristics were observed at higher rotational speeds (60, 80, and 100 r / min). Figure 7(b) Within this range, all D50 curves rose rapidly after rapid agitation and quickly entered a high-level stable stage, indicating that the hydraulic conditions in this range were sufficient to ensure particle suspension and collision, achieving rapid and stable floc growth. It is noteworthy that an optimal value exists within this range: the steady-state D50 reaches a peak of 1004.0 μm at 80 r / min, while it decreases to 937.6 μm at 100 r / min. This initially suggests that excessive shear force has begun to inhibit floc growth.

[0067] Figure 7 (a) shows that the differential distribution of flocs exhibits a single-peak morphology at all rotational speeds, but the peak position and shape differ significantly. (20 r / min (G=5.50 s)) -1 At rotational speeds of 40 r / min and above, the differential distribution peak shifted significantly to the left, with a peak particle size of 177.7 μm, much lower than at other rotational speeds. This indicates that the shear force at this speed cannot provide sufficient hydrodynamic conditions for effective particle collision and floc growth. When the rotational speed increased to 40 r / min and above, the differential distribution peak position stabilized around 1000 μm, but the peak height and width changed. This suggests that further increasing the shear force will no longer significantly increase the dominant size of the flocs, but instead mainly affect the uniformity of the floc particle size distribution. The particle size distribution span (…) The concentration of particle size distribution was quantitatively characterized. The spans at 20, 40, 60, 80, and 100 r / min were 2.183, 1.667, 1.411, 1.216, and 1.244, respectively, showing a trend of first decreasing and then increasing. The span was largest at 20 r / min, indicating the widest particle size distribution and the worst uniformity; the span decreased to a minimum of 1.216 at 80 r / min, consistent with the sharp peak in the figure, indicating that this G value (G=35.37 s) was... -1 ) can achieve optimal PAM dispersion and uniform floc growth; when the rotation speed reaches 100 r / min, the span increases to 1.244, and the peak shape widens slightly. From a quantitative point of view, it is confirmed that excessive shear force causes floc breakage, resulting in a decrease in particle size uniformity.

[0068] Table 3. Volume percentage (%) of flocs in different particle size ranges under different slow stirring speeds. Particle size range percentage data ( Figure 7(b), Table 3) further quantifies the effect of rotational speed on floc composition. At 20 r / min, the system is dominated by fine particles ≤100 μm (accounting for 43.77%), while flocs ≥500 μm account for less than 0.3%, confirming that flocculation is incomplete at low rotational speeds, and insufficient shear force prevents particles from effectively aggregating, resulting in a dispersed system with poor settling performance. When the rotational speed increases to 40 r / min, the proportion of flocs ≥500 μm jumps to 68.62% (of which ≥1000 μm accounts for 33.1%), while the proportion of fine particles drops sharply to 3.77%, indicating that the shear force is sufficient to drive PAM to fully exert its bridging effect and promote particle migration to larger-diameter flocs. However, under this condition, the proportion of flocs 100~500 μm still reaches 27.61%, with a relatively wide particle size distribution, which is consistent with the low peak shape in the differential distribution. As the rotational speed increases, the floc structure continues to optimize and reaches its best at 80 r / min, where the proportion of flocs ≥1000 μm reaches a peak of 50.43%, indicating that the flocs grow sufficiently and have a dense and uniform structure under this shear strength. When the rotational speed increases to 100 r / min, the proportion of flocs ≥1000 μm decreases to 44.53%, while the proportion of flocs in the 500~1000 μm range increases from 35.36% to 40.63%, indicating that excessive shear causes large flocs to break down and migrate to smaller particle size ranges, resulting in overall structural deterioration.

[0069] The increase and inflection point of the overall particle size of the flocs are also reflected in the cumulative distribution curve ( Figure 7 (c) and characteristic particle size ( Figure 7 (b) As the rotational speed increased from 20 r / min to 80 r / min, the cumulative curve shifted to the right, and the characteristic particle sizes D10, D50, and D90 all increased significantly, indicating that optimizing the stirring intensity can comprehensively promote the growth of flocs at all sizes. When the rotational speed reached 100 r / min, the trend reversed: D50 and D90 decreased compared to 80 r / min, while D10 continued to increase to 407.6 μm. This indicates that excessive hydraulic shear preferentially breaks up the most unstable large flocs (leading to a decrease in D90), and the floc fragments are incorporated into the medium particle size range, thus leading to a decrease in D50, which characterizes the average particle size; while the continuous increase in D10 indicates that even the micro-flocs produced by the breakup are much larger than the original discrete particles. This pattern is consistent with the floc breakup kinetics, that is, large and loose flocs are most sensitive to shear.

[0070] Typical microstructures of flocs at different rotation speeds are as follows: Figure 9 As shown. At 20 r / min ( Figure 9 (a) The flocs were small, isolated micro-flocs, failing to form an effective spatial network, indicating severely insufficient shear force and inadequate particle collision and aggregation. After increasing the rotation speed to 40 r / min and 60 r / min ( Figure 9(b), (c)), the floc size increases significantly and begins to connect with each other to form a preliminary network structure. At 80 r / min ( Figure 9 (d)), the flocs grow into large, dense, and clearly defined aggregates. When the rotation speed is further increased to 100 r / min ( Figure 9 (e) The regularity of the floc structure decreased.

[0071] Figure 10 The images of flocs under different slow stirring speeds in Example 1 and Comparative Examples 8-11 are grayscale and binarized images. The Df of the flocs was calculated using the box counting method. Thirty independent flocs were randomly analyzed under each condition, and the statistical results are shown below. Figure 11 .

[0072] like Figure 11 As shown, the quantitative results of the fractal dimension are consistent with the morphological observations. At 20 r / min, the Df value is the lowest (1.571 ± 0.035), quantitatively confirming that the floc structure is loose and heterogeneous under these conditions. As the rotational speed increases to 40 r / min and 60 r / min, the Df value gradually increases (1.683 ± 0.028 and 1.710 ± 0.023, respectively), indicating that moderate shear force effectively promotes particle aggregation and structural compaction. When the rotational speed reaches 80 r / min, the Df value reaches its peak (1.750 ± 0.020), and the box plot is the most compact, indicating that the floc density is the highest and the structural uniformity is optimal at this point. When the rotational speed increases to 100 r / min, the Df value decreases (1.731 ± 0.026), and the dispersion also increases. This is because excessively high shear rates may cause breakage or erosion of the internal structure of the floc, leading to a decrease in its density and uniformity.

[0073] The residual turbidity of Examples 1 and Comparative Examples 8-11 after 15 min of coagulation and sedimentation is as follows: Figure 12As shown in (a), the residual turbidity exhibits a non-monotonic trend of first significantly decreasing and then slightly increasing with increasing stirring speed. In the low stirring speed range (20 and 40 r / min), the residual turbidity is at a relatively high level (12.3 NTU and 6.26 NTU), indicating that the shear force is severely insufficient in this range, the flocculation reaction is incomplete, and flocs with excellent settling performance cannot be formed. When the stirring speed is increased to 60 r / min, the residual turbidity drops sharply to 2.10 NTU, a decrease of 66.5%, indicating that the shear force at this time can ensure that PAM can fully play its bridging role. When the stirring speed is further increased to 80 r / min, the residual turbidity reaches the lowest value of 1.31 NTU, indicating that the floc growth and breakage reach the optimal dynamic balance at this time, and the solid-liquid separation is the most thorough. When the stirring speed is further increased to 100 r / min, the residual turbidity rises back to 2.07 NTU, indicating that excessive shear force may cause floc breakage, leading to a slight deterioration of the effluent water quality.

[0074] The dynamic changes in turbidity of the supernatant during sedimentation are shown in the following results. Figure 12 As shown in (b), two distinctly different sedimentation behaviors can be observed in the figure. For the operating conditions of 20 r / min and 40 r / min, the sedimentation curves consistently maintain a high turbidity level, and the sedimentation is extremely slow. Crucially, the turbidity at the start of sedimentation (0 min) for both groups is abnormally low, at 21.1 NTU and 14 NTU, respectively.

[0075] A breakup-regeneration experiment was conducted on the steady-state flocs formed within the effective flocculation range (60~100 r / min): First, a strong shearing at 500 r / min was applied for 2 min to simulate hydraulic impact, then the original slow stirring speed was restored for 8 min to monitor the regeneration process. The results are as follows: Figure 13 As shown in Table 4, the floc strength and recovery factor were further calculated based on the dynamic changes of D50 to quantitatively evaluate its structural stability.

[0076] Table 4. Characteristic particle size, strength, and recovery factor of flocs at different stirring speeds. Combination Figure 13 Analysis of the data in Table 4 shows that the structural stability of the flocs is closely related to the shear strength they are subjected to. Under the condition of 80 r / min, the flocs exhibit the best overall structural stability, with their strength factor and recovery factor reaching the highest levels of 82.13% and 70.07%, respectively. This indicates that the optimized shear force (G = 35.37 s⁻¹) is... -1The flocs formed at the lowest speed (60 r / min) have the densest internal structure and a stable PAM bridging network, resulting in strong shear resistance and high regeneration efficiency after crushing. In contrast, at 60 r / min, the floc growth and compaction are limited due to relatively insufficient shear force, and its strength factor and recovery factor are the lowest among the three. At 100 r / min, the excessively high shear force approaches or exceeds its structural bearing capacity critical point, leading to a significant decrease in recovery ability after crushing (reduction in Rf), indicating that its structural toughness has deteriorated.

[0077] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for coagulation treatment of mine water based on optimization of floc properties, characterized in that, Coagulant and flocculant were added to the mine water at a dosage of 30 mg / L for coagulant and 0.8 mg / L for flocculant.

2. The mine water coagulation treatment method based on floc property optimization according to claim 1, characterized in that, The coagulant is polyaluminum chloride, and the flocculant is anionic polyacrylamide.

3. The mine water coagulation treatment method based on floc property optimization according to claim 2, characterized in that, The polyaluminum chloride has an alumina content of 26%, and the anionic polyacrylamide has a molecular weight of 12 million.

4. The mine water coagulation treatment method based on floc property optimization according to claim 1, characterized in that, The order of adding coagulant and flocculant is to add coagulant first, then flocculant.

5. The mine water coagulation treatment method based on floc property optimization according to claim 4, characterized in that, After adding the coagulant, stir at a speed of 500 r / min for 1 min.

6. The mine water coagulation treatment method based on floc property optimization according to claim 4, characterized in that, After adding the flocculant, the mixture was stirred at a speed of 60 r / min for 15 min.

7. The mine water coagulation treatment method based on floc property optimization according to claim 1, characterized in that, Before adding the coagulant, dissolve it in water to a concentration of 30 g / L.

8. The mine water coagulation treatment method based on floc property optimization according to claim 1, characterized in that, Before adding the flocculant, dissolve it in water while stirring during the dissolution process. The concentration after dissolution should be 1 g / L.

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