Preparation method of bio-based interpenetrating network hydrogel and application of bio-based interpenetrating network hydrogel in curing of fine-grained tailings

Abstract

The invention relates to a bio-based interpenetrating network hydrogel preparation method and application in curing fine grain tailings, and the bio-based interpenetrating network hydrogel preparation method comprises the following steps: S1, adding carboxymethyl cellulose (CMC) and hydroxyethyl cellulose (HEC) into a three-neck flask filled with deionized water according to a mass ratio of (3: 1)-(5: 4), dissolving the CMC and the HEC in the deionized water, and dissolving under magnetic stirring at the temperature of 40-50 DEG C and the speed of 300rpm to form a transparent homogeneous solution; s2, nitrogen is introduced into the solution obtained in the step S1 for 30 min, then ammonium persulfate APS and methylene bisacrylamide MBA are sequentially added, APS is an initiator, and MBA is a cross-linking agent. The CMC-HEC interpenetrating network hydrogel acts on tailings through a'physical wrapping-functional group complexing-interpenetrating network synergy 'triple mechanism, carboxyl of CMC, tailings particles and heavy metal ions form a rigid framework through ionic bonding, and a hydroxyethyl chain of HEC fills pores through hydrogen-bond interaction to form a flexible network, so that the flexibility of the tailings is improved. Furthermore, the two components construct an interpenetrating network through MBA cross-linking, so that the strengthening effect of combining rigidity and softness is realized.

Description

Technical Field

[0001] This invention relates to the field of hydrogel preparation and fine-grained tailings application technology, specifically a method for preparing bio-based interpenetrating network hydrogels and the application of solidified fine-grained tailings. Background Technology

[0002] Against the backdrop of continuously increasing global mineral resource development intensity and the refinement of mineral processing technology, the output of fine-grained tailings (mostly less than 0.075 mm in diameter, with large specific surface area and high mud content) from various ferrous, non-ferrous, and non-metallic mines is constantly increasing. Fine-grained tailings are usually transported to tailings ponds or storage sites in a slurry form with high water content. Long-term and large-scale stockpiling not only occupies land resources and affects the layout of land use in and around mining areas, but also significantly increases environmental risks due to the characteristics of ultra-fine particles, high surface activity, and carrying mineral processing reagents. Current engineering projects often use hydraulic conveying to tailings dam enclosure sedimentation ponds for natural settling. However, this method has two hidden dangers: on the one hand, the construction and maintenance costs of tailings dams are high and the land area is large; on the other hand, the flotation reagents (such as collectors, frothers, inhibitors, etc.) and heavy metals contained in the tailings are prone to migrate into the soil-groundwater system under long-term infiltration and leaching, resulting in a decrease in the organic matter content of the contaminated soil, destruction of the aggregate structure and accumulation of biotoxicity, which seriously threatens regional ecological security and sustainable agricultural use.

[0003] Currently, the conventional disposal of fine-grained tailings still mainly relies on tailings dam storage, while research on resource utilization focuses primarily on two directions: utilization in building materials and solidification / stabilization treatment. Regarding utilization in building materials, attempts have been made to incorporate fine-grained tailings into cement products, sintered or unfired bricks, ceramic materials, and asphalt mixtures. However, the uneven particle size distribution, high proportion of clay particles, and large porosity of fine-grained tailings often lead to insufficient early strength and high sensitivity to drying shrinkage cracking in the solidified body or product. To meet strength requirements, it is often necessary to increase the amount of cementing material, which can easily induce problems such as increased brittleness and reduced durability. In terms of curing / stabilization, cement and its-based composite curing agents are mainly used to improve mechanical properties and fix heavy metals by filling and encapsulating hydration products. However, there are several shortcomings: First, the preparation process of cement clinker is energy-intensive and has a large carbon emission, which contradicts the current "dual carbon" target. Second, in environments such as acid rain and acidic leachate, cement hydration products are easily decomposed and dissolved, and the solidified heavy metals may be released again, posing a risk of secondary pollution. Third, the surface of fine-grained tailings often carries a negative charge or adsorbs organic reagent films, and the interface between cement hydration products and these materials has poor compatibility, easily forming a weak bonding layer at the interface, which limits the strength and long-term stability of the solidified body.

[0004] Therefore, existing technologies for the treatment and resource utilization of fine-grained tailings still fall short of meeting engineering requirements in terms of balancing mechanical strengthening, long-term stable fixation of heavy metals, and environmental friendliness. There is an urgent need to develop a novel solidification material and its application method that is widely available, low-carbon, environmentally friendly, and has good interfacial compatibility with fine-grained tailings. Based on this, this invention proposes a method for preparing a bio-based interpenetrating network hydrogel and its application in the solidification of fine-grained tailings. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing bio-based interpenetrating network hydrogels and their application in solidifying fine-grained tailings. This addresses the problems mentioned in the background art, such as the difficulty of improving the strength and durability of the solidified body simultaneously at low dosages due to the fine particle size, large specific surface area, and high porosity of fine-grained tailings, as well as the problems of high dosage, high carbon emissions, and easy dissolution of traditional cement-based solidifying agents in acidic environments, leading to the re-release of fixed heavy metals and the risk of secondary pollution. Furthermore, it addresses the problems of poor interfacial compatibility and insufficient interfacial bonding between the fine-grained tailings and cement hydration products due to residual mineral processing agent film and charged characteristics on the surface of the tailings, thus limiting the long-term stability of the solidified body.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a bio-based interpenetrating network hydrogel, comprising the following steps:

[0007] S1: Carboxymethyl cellulose (CMC) and hydroxyethyl cellulose (HEC) are added to deionized water and dissolved under stirring to obtain a transparent homogeneous solution;

[0008] S2: Introduce nitrogen gas and add initiator and crosslinking agent;

[0009] S3: The solution in S2 is then heated and continuously stirred to carry out the graft copolymerization reaction until a significant increase in solution viscosity is observed and an elastic gel is formed, thus forming a coarse gel.

[0010] S4: After the reaction solution has cooled to room temperature, the crude gel is transferred to a beaker. Anhydrous ethanol is added to the beaker and the mixture is continuously soaked to remove unreacted monomers. The crude gel is then placed in a vacuum drying oven and dried to constant weight to obtain a white hydrogel powder, which is the bio-based interpenetrating network hydrogel powder.

[0011] Preferably, the mass ratio of CMC to HEC in step S1 is (3:1) to (5:4), the stirring temperature in step S1 is 40 to 50°C, and the stirring speed is 300 rpm;

[0012] In step S2, the nitrogen gas is introduced for 30 minutes, the initiator is ammonium persulfate (APS), and the crosslinking agent is methylenebisacrylamide (MBA).

[0013] Preferably, the solution temperature in step S3 is 70-80°C, and the stirring time in step S3 is 40-60 min.

[0014] In step S4, the amount of anhydrous ethanol added is 200 mL, and the soaking time is 12 h. The temperature of the vacuum drying oven in step S4 is 60 °C.

[0015] Preferably, in step S1, the optimal mass ratio of CMC to HEC is 5:4, the amount of CMC added is 5g, the amount of HEC added is 4g, the amount of APS added is 0.01g, and the amount of MBA added is 0.4g.

[0016] A bio-based interpenetrating network hydrogel is obtained by the preparation method described above.

[0017] The application of a bio-based interpenetrating network hydrogel in the solidification of fine-grained tailings has achieved efficient and green solidification of fine-grained tailings, while simultaneously improving mechanical strength, heavy metal fixation capacity, and environmental sustainability.

[0018] A method for preparing fine-grained tailings using a bio-based interpenetrating network hydrogel includes the following steps:

[0019] Step A: Mix the hydrogel powder with fine tailings using a dry mixing method, ensuring that the hydrogel is evenly dispersed on the surface of the tailings particles during mixing;

[0020] Step B: Fill the mold with the mixture in 5 layers, with each layer containing 1 / 5 of the total mass;

[0021] Step C: Use a standard compaction hammer to compact each layer of the mold 25 or 30 times evenly. After each layer is compacted, use a scraper to lightly roughen the surface to enhance the interlayer bonding force and prevent the delamination interface from becoming a weak area.

[0022] Step D: After all 5 layers of the mold in Step B have been compacted, let it stand for 10 minutes to release the internal stress, and then slowly demold.

[0023] Step E: Place the demolded specimen in a drying oven and dry at 105℃ for 48 hours. Then, remove the specimen and smooth the surface to obtain solidified fine-grained tailings.

[0024] Preferably, the amount of hydrogel added is 0.5 to 3.0% of the dry weight of the tailings.

[0025] Preferably, the amount of hydrogel added is 1.0 to 2.0% of the dry weight of the tailings.

[0026] Compared with the prior art, the beneficial effects of the preparation method of the present invention are:

[0027] 1. The CMC-HEC interpenetrating network hydrogel of the present invention applies to fine-grained tailings through a multi-mechanism of "physical encapsulation – functional group complexation – network interpenetration synergy". Under the synergistic effect of CMC carboxyl groups and HEC hydroxyethyl groups and the covalent cross-linking effect of MBA, a three-dimensional interpenetrating network is formed. It can significantly improve the unconfined compressive strength and splitting tensile strength of the solidified body at a low dosage, and improve the problems of high brittleness and weakened interface of traditional cement-based solidified bodies.

[0028] 2. This invention utilizes the abundant carboxyl and hydroxyl groups in the hydrogel to complex, coordinate, and hydrogen bond with metal ions in tailings, and uses a three-dimensional network structure to physically encapsulate heavy metals, thereby achieving efficient fixation of various heavy metal ions, reducing their leaching and migration risks, and improving the environmental safety of the solidified body.

[0029] 3. The CMC-HEC interpenetrating network hydrogel of the present invention forms a dense and continuous organic phase coating layer and bridging structure on the surface of tailings particles, which significantly refines the pores and improves the density of the structure, so that the solidified layer maintains a high quality integrity under repeated water erosion and has excellent water erosion resistance.

[0030] 4. This invention uses renewable cellulose derivatives as the main raw material. The preparation process has a low reaction temperature and low energy consumption. Compared with the traditional cement clinker calcination process, the carbon emissions per unit material are significantly reduced. Moreover, the hydrogel material can re-enter the natural carbon cycle through microbial degradation after long-term service, which meets the requirements of low carbon and environmental protection. Attached Figure Description

[0031] Figure 1 This is a particle size distribution diagram of the graphite tailings of the present invention;

[0032] Figure 2 This is a diagram showing the oxide content in the graphite tailings of this invention.

[0033] Figure 3 This is a trend chart showing the influence of quality factor A (CMC) of the present invention on the measurement indicators.

[0034] Figure 4 This is a trend chart showing the influence of the quality factor B of the HEC of this invention on the measurement indicators;

[0035] Figure 5 This is a trend graph showing the influence of the quality factor C of the MBA invention on the measurement indicators.

[0036] Figure 6 This is a trend chart showing the influence of the quality factor D of the APS of this invention on the measurement indicators;

[0037] Figure 7 The FTIR spectra of CMC, HEC, and CMC-HEC of this invention are shown below;

[0038] Figure 8The XRD patterns of CMC, HEC, and CMC-HEC of this invention are shown below.

[0039] Figure 9 This is a scanning electron microscope (SEM) image of the CMC of this invention;

[0040] Figure 10 This is a scanning electron microscope (SEM) image of the HEC of this invention;

[0041] Figure 11 This is a scanning electron microscope (SEM) image of the CMC-HEC of this invention;

[0042] Figure 12 This is a diagram showing the mechanical properties of graphite tailings solidified by CMC according to the present invention.

[0043] Figure 13 The mechanical properties diagram of the HEC-cured graphite tailings of this invention is shown.

[0044] Figure 14 The mechanical properties diagram of the CMC-HEC cured graphite tailings of this invention;

[0045] Figure 15 This is a diagram illustrating the immobilization effect of heavy metal ions in CMC-HEC solidified graphite tailings according to the present invention.

[0046] Figure 16 This is a diagram showing the test results of the water erosion resistance of the graphite tailings solidified layer of this invention;

[0047] Figure 17 The images show the FTIR spectra of graphite tailings from this invention, as well as graphite tailings cured by CMC, HEC, and CMC-HEC.

[0048] Figure 18 The images show the XRD patterns of graphite tailings and graphite tailings cured by CMC, HEC and CMC-HEC according to the present invention.

[0049] Figure 19 This is a SEM image of the graphite tailings from the present invention.

[0050] Figure 20 This is a SEM image of the CMC-cured graphite tailings of this invention.

[0051] Figure 21 This is a SEM image of the HEC-cured graphite tailings of this invention.

[0052] Figure 22 This is a SEM image of the graphite tailings cured by CMC-HEC according to the present invention;

[0053] Figure 23 This is a SEM-EDS scanning electron microscope-energy dispersive spectroscopy (EDS) image of the graphite tailings from this invention.

[0054] Figure 24 This is a SEM-EDS scanning electron microscope-energy dispersive spectroscopy (EDS) image of the CMC-cured graphite tailings of this invention.

[0055] Figure 25 This is a SEM-EDS scanning electron microscope-energy dispersive spectroscopy (EDS) image of the HEC-cured graphite tailings of this invention.

[0056] Figure 26 This is a SEM-EDS scanning electron microscope-energy dispersive spectroscopy (EDS) image of the graphite tailings cured by CMC-HEC according to the present invention.

[0057] Figure 27 This is a molecular dynamics simulation diagram of the mass density change of the CMC-HEC of this invention;

[0058] Figure 28 This is the adsorption energy diagram of CMC-HEC of the present invention;

[0059] Figure 29 This is a graph showing the root mean square displacement variation of the CMC-HEC of the present invention. Detailed Implementation

[0060] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0061] Please see Figure 1 The first embodiment of the present invention provides a method for preparing a bio-based interpenetrating network hydrogel, comprising the following steps:

[0062] S1: Carboxymethyl cellulose (CMC) and hydroxyethyl cellulose (HEC) are mixed and dissolved in deionized water, and then magnetically stirred to form a transparent homogeneous solution.

[0063] S2: Introduce nitrogen gas and add initiator and crosslinking agent;

[0064] S3: The solution in S2 is then heated and continuously stirred to carry out the graft copolymerization reaction until a significant increase in solution viscosity is observed and an elastic gel is formed, thus forming a coarse gel.

[0065] S4: After the reaction solution has cooled to room temperature, the crude gel is transferred to a beaker. Anhydrous ethanol is added to the beaker and the gel is continuously soaked to remove unreacted monomers. The crude gel is then placed in a vacuum drying oven and dried to constant weight to obtain a white hydrogel powder, namely bio-based interpenetrating network hydrogel powder.

[0066] In step S1, the mass ratio of CMC to HEC is (3:1) to (5:4), the stirring temperature in step S1 is 40 to 50°C, and the stirring speed is 300 rpm.

[0067] In step S2, nitrogen gas is introduced for 30 minutes, the initiator is ammonium persulfate (APS), and the crosslinking agent is methylenebisacrylamide (MBA).

[0068] The solution temperature in step S3 is 70-80℃, and the stirring time in step S3 is 40-60 min.

[0069] The soaking time in step S4 is 12 hours, and the temperature of the vacuum drying oven in step S4 is 60°C.

[0070] In step S1, the optimal mass ratio of CMC to HEC is 5:4, the amount of CMC added is 5g, the amount of HEC added is 4g, the amount of APS added is 0.01g, and the amount of MBA added is 0.4g.

[0071] The second embodiment of the present invention provides a bio-based interpenetrating network hydrogel, which is obtained by the above preparation method.

[0072] The third embodiment of the present invention provides: the application of a bio-based interpenetrating network hydrogel in the solidification of fine-grained tailings, which realizes efficient and green solidification of fine-grained tailings, and simultaneously improves mechanical strength, heavy metal fixation capacity and environmental sustainability.

[0073] The fine-grained tailings are graphite tailings.

[0074] The fourth embodiment of the present invention: a method for solidifying fine-grained tailings with hydrogel prepared using a bio-based interpenetrating network hydrogel, comprising the following steps:

[0075] Step A: Mix the hydrogel powder with the fine tailings using a dry mixing method. During mixing, ensure that the hydrogel is evenly dispersed on the surface of the tailings particles.

[0076] Step B: Fill the mold with the mixture in 5 layers, with each layer containing 1 / 5 of the total mass;

[0077] Step C: Use a standard compaction hammer to compact each layer of the mold 25 or 30 times evenly. After each layer is compacted, use a scraper to lightly roughen the surface to enhance the interlayer bonding force and prevent the delamination interface from becoming a weak area.

[0078] Step D: After all 5 layers of the mold in Step B have been compacted, let it stand for 10 minutes to release the internal stress, and then slowly demold.

[0079] Step E: After demolding, the specimen is placed in an oven at 105°C and dried to constant weight for unconfined compressive strength and splitting tensile strength tests. The surface of the specimen is then smoothed to obtain solidified fine-grained tailings.

[0080] The amount of hydrogel added is 0.5 to 3.0% of the dry weight of the tailings.

[0081] The amount of hydrogel added is 1.0 to 2.0% of the dry weight of the tailings.

[0082] The experimental examples provided by this invention: Regarding the experimental materials, the main experimental materials used in this invention are as follows: carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), ammonium persulfate (APS), methylenebisacrylamide (MBA), deionized water, and graphite tailings. The particle size and compound composition of the graphite tailings are shown in the attached figure. Figure 1 and Figure 2 As shown.

[0083] First, prepare the hydrogel binder and the sample:

[0084] Weigh CMC and HEC accurately at a mass ratio of 3:1. Add the CMC and HEC powders to a three-necked flask containing deionized water and dissolve them in a 45°C water bath with magnetic stirring at 300 rpm until the solution is transparent and homogeneous.

[0085] After purging with nitrogen for another 30 minutes, APS and MBA were added to the solution in sequence.

[0086] The reaction system was then heated to 75°C and the graft copolymerization reaction was carried out with continuous stirring for 45 minutes. The reaction was terminated when the solution viscosity was observed to increase significantly and an elastic gel was formed.

[0087] After the reaction solution cooled to room temperature, the coarse gel was transferred to a 500 mL beaker and soaked in 200 mL of anhydrous ethanol for 12 h to remove unreacted monomers.

[0088] The gel was then dried in a vacuum drying oven at 60°C until constant weight, finally yielding a white hydrogel powder, namely a bio-based interpenetrating network hydrogel.

[0089] The hydrogel was then mixed with the graphite tailings using a dry mixing method, ensuring that the hydrogel was evenly dispersed on the surface of the tailings particles during mixing.

[0090] The mixture is placed into a cylindrical mold with a diameter of 39.1 mm and a height of 80 mm in 5 layers, with each layer containing approximately 1 / 5 of the total mass. The mixture is then compacted evenly with a standard compaction hammer 25 or 30 times. After each layer is compacted, the surface is lightly roughened with a scraper to enhance interlayer bonding and prevent the delamination interfaces from becoming weak points.

[0091] The preferred number of times the mixture is uniformly compacted by a standard compaction hammer is 30.

[0092] After all 5 layers are compacted, let it stand for 10 minutes to release internal stress, and then slowly demold.

[0093] After demolding, the specimens were placed in a drying oven and dried at 105°C for 48 hours before being removed.

[0094] The surface of the specimen was then smoothed to ensure uniform stress during the test loading, thereby obtaining hydrogel-cured fine-grained tailings.

[0095] Regarding the testing methods for this material, the present invention employs six methods for testing;

[0096] First experimental method: Orthogonal experimental design:

[0097] This experiment used L 16 (4 4 A normalized orthogonal array design combined with range analysis was used to optimize the formulation of CMC-HEC hydrogel dust suppressant. Experimental factors included the mass of CMC (denoted as A, levels of 5.0g, 6.0g, 7.0g, and 8.0g), the mass of HEC (denoted as B, levels of 2.0g, 3.0g, 4.0g, and 5.0g), the mass of MBA (denoted as C, levels of 0.10g, 0.20g, 0.30g, and 0.40g), and the mass of APS (denoted as A). D, with levels of 0.01g, 0.02g, 0.03g, and 0.04g respectively, uses the average unconfined compressive strength (UCS) and splitting tensile strength (STS) measured three times as evaluation indicators. UCS reflects the ability of the cured body to resist compressive loads, while STS characterizes the ability of the cured body to resist bending deformation. The synergistic improvement of the two is the core requirement to ensure the long-term stability of the cured body. The CMC-HEC orthogonal test factor level table and the CMC-HEC mix proportion orthogonal test table and results are shown in Table 1.

[0098] Table 1: Factor level table and proportional orthogonal experiment table for CMC-HEC orthogonal experiment;

[0099]

[0100] The second test method: Mechanical property test design:

[0101] According to GB / T 50123-2019 "Standard for Geotechnical Testing Methods", graphite tailings samples cured by CMC-HEC hydrogel, CMC and HEC were cured and dried, and unconfined compressive strength (UCS) and splitting tensile strength (STS) tests were carried out to evaluate their mechanical properties. Axial compressive loads were applied at loading rates of 0.5 mm / min and 1 mm / min respectively until the sample failed, and the maximum axial load was recorded as the test result.

[0102] The third experimental method: Heavy metal leaching test design:

[0103] Different contents (0%, 1%, 2%, 3%) of graphite tailings solidified with CMC-HEC hydrogel were mixed with deionized water at a solid-liquid ratio of 1:5 and placed in a constant temperature shaking chamber. The mixture was continuously shaken at 25°C and 150 r / min. The leachate was filtered through a 0.45 μm microporous membrane. The concentrations of metal ions such as Cu²⁺ and Zn²⁺ were determined by graphite furnace atomic absorption spectrometry. The concentrations of Mn²⁺ and Ni²⁺ were detected by flame atomic absorption spectrophotometry. The detection limits were 0.05 μg / L and 0.1 μg / L, respectively. The pollutant fixation rate was calculated based on equation (1). (%), to investigate the adsorption effect of CMC-HEC hydrogel content on solidified heavy metals:

[0104] Equation (1): 00%

[0105] Where: F represents the solidification rate of heavy metals in graphite tailings by CMC-HEC hydrogel. The concentration of heavy metals in the leachate is expressed in mg / L. The total heavy metal content in the tailings (mg / kg).

[0106] Fourth test method: Water erosion resistance test design for cured layer:

[0107] Graphite tailings were evenly spread in a petri dish, and CMC-HEC hydrogel was sprayed onto the surface of the graphite tailings until completely wetted. The mixture was then dried at room temperature to constant weight, and the initial total mass was recorded. The sample was then immersed in deionized water and left to stand for 10 minutes. After removal, the surface integrity of the cured layer was observed, and the sample was dried in an oven at 40°C until constant weight. The residual total mass was recorded. Repeat the soaking-drying operation 5 times, and the calculation formula (2) is as follows:

[0108] Equation (2): 00%

[0109] Where Q is the mass loss rate (%), For the first The total mass (g) after each cycle For the first Total mass after the next cycle The initial total mass (g), The mass (g) of the petri dish.

[0110] Fifth experimental method: Microstructure characterization experimental design:

[0111] Graphite tailings samples, after being cured by CMC, HEC, CMC-HEC and CMC, HEC and CMC-HEC hydrogels respectively, were dried in a vacuum drying chamber at 60℃ until the quality was stable. They were then ground to obtain 200-mesh particles and mixed with KBr to press into thin sheets. The prepared samples were then placed in an infrared spectrometer for infrared experiments to determine the changes in the reactive functional groups. The test wavelength was 400-4000 cm-1.

[0112] X-ray diffraction was used to characterize the crystal structure of graphite tailings samples after solidification of CMC, HEC, CMC-HEC, and CMC, HEC, and CMC-HEC hydrogels, respectively. The testing system was equipped with a CuKα radiation source (λ=1.5406nm), operating voltage 40kV, current 40mA, scanning range covering 5–60° with a 2θ reflection angle, scanning rate set to 10° / min, and sampling step width 0.02°. The evolution of the crystalline phase of the material was analyzed to determine whether the graft copolymerization process induced amorphous region expansion, lattice distortion, and other aggregated structure reconstruction phenomena. The phase composition and crystallinity of the precipitates in the graphite tailings before and after the test were also analyzed.

[0113] To observe the morphology and surface structure characteristics of graphite tailings samples after solidification of CMC, HEC, CMC-HEC and CMC, HEC and CMC-HEC hydrogels, the sample solutions were first drop-cast onto a pretreated copper substrate, and then vacuum dried and solidified to form a uniform thin film. A gold film of about 5 nm thickness was deposited on the surface of the film using an ion sputtering instrument, and the elemental composition of the tailings surface was analyzed using SEM-eds.

[0114] The sixth experimental method: Molecular dynamics simulation design.

[0115] Construction of CMC-HEC hydrogel and based on Figure 2 A composite model of graphite tailings mineral surfaces was developed based on the compound composition of graphite tailings. Simulations were performed using Materials Studio 2024 software and the COMPASS II force field under the NVT ensemble. The hydrogen bond strength between carboxyl and hydroxyl groups in the hydrogel and Si-O and Ca-O bonds on the mineral surface was quantified. The coverage and penetration depth of the hydrogel on the mineral surface were analyzed, elucidating the multi-scale inhibition mechanism of the hydrogel on tailings particle migration.

[0116] Regarding the experimental results and analysis, the six experimental results of this invention are as follows:

[0117] First experimental result: First, analyze the optimal ratio of CMC-HEC:

[0118] The unconfined compressive strength (UCS) and splitting tensile strength (STS) of hydrogel-cured graphite tailings are core indicators characterizing the curing performance of CMC-HEC hydrogels. Based on orthogonal experimental results, the influence of various factors on curing performance was analyzed (the influence trends of each component on UCS and STS are shown in [link to relevant documentation]). Figures 3 to 6 Finally, the optimal ratio of each component of the CMC-HEC hydrogel can be determined, and the results are as follows: Figures 3 to 6 As shown, the primary and secondary order and the optimal combination are shown in Table 2.

[0119] Table 2: Primary sorting, secondary sorting, and optimal combination;

[0120]

[0121] Depend on Figure 3 It can be seen that when the CMC content increases from 4g to 7g, the unconfined compressive strength (UCS) and splitting tensile strength (STS) increase by 8.0% and 40%, respectively. This increase is mainly attributed to the fact that the carboxymethyl and hydroxyl groups in the CMC molecular chain bridge the tailings particles through hydrogen bonding, effectively bonding the hydrophobic graphite flakes, quartz sand and silicate minerals in the tailings, thereby strengthening the interparticle adhesion.

[0122] At the same time, by Figure 3 It can be seen that CMC has a weak effect on UCS (range R = 0.07 MPa), and K2 (6.0 g) reaches 4.80 MPa and then decreases slightly with increasing dosage; its effect on STS is more significant than that on UCS (R = 0.26 MPa), with K1 (5.0 g) reaching a peak of 1.06 MPa and then continuously decreasing. As an anionic cellulose ether, CMC mainly improves the dispersibility of the system by adsorbing onto the particle surface to form electrostatic repulsion. At low dosage, CMC molecular chains can bridge adjacent particles and promote interfacial adhesion, thereby increasing STS; however, when the dosage is excessive, entanglement is easily formed between molecular chains, resulting in excessively high local viscosity, which in turn hinders the uniform diffusion of reactive monomers, causing UCS growth to stagnate and STS to decrease due to increased defects in the interfacial transition region.

[0123] Depend on Figure 4It can be seen that HEC is the strongest influencing factor on both UCS (R=0.40MPa) and STS (R=0.38MPa), and the trends are highly consistent: it first increases and then decreases with the increase of dosage, and K3 (4g) reaches a double peak (UCS=4.93MPa, STS=1.06MPa). As a non-ionic thickener, HEC forms a three-dimensional network structure by forming hydrogen bonds with inorganic particles through molecular chain hydroxyl groups. When the dosage is 4g, the network density is moderate, which can provide sufficient structural support (maximum UCS) and dissipate shear energy through chain segment slip. When the dosage is insufficient (2-3g), the network is sparse and the load-bearing capacity is weak. When the dosage is too high (5g), the molecular chains are excessively stacked, resulting in internal stress concentration, easy propagation of microcracks, and a decrease in strength.

[0124] Depend on Figure 5 It can be seen that MBA has a stronger effect on UCS (R=0.20MPa) than STS (R=0.14MPa). UCS reaches 4.86MPa at K3 (0.3g), while STS continues to increase with the amount used (K4=0.97MPa). As a crosslinking agent, MBA initiates crosslinking between polymer chains through diene functional groups. When the amount is 0.3g, the crosslinking density is moderate, and the polymer network has both rigidity (highest UCS) and a certain degree of toughness. When the amount is increased to 0.4g, the crosslinking point density is too high, the network rigidity is enhanced but the brittleness is increased, resulting in a slight decrease in UCS (4.77MPa), while STS still increases slightly because the crosslinking structure hinders shear slip.

[0125] Depend on Figure 6 It can be seen that APS has similar but opposite effects on UCS (R=0.17MPa) and STS (R=0.16MPa). UCS increases continuously with increasing dosage (K4=4.88MPa), while STS decreases continuously (K1=0.99MPa→K4=0.83MPa). As a free radical initiator, the dosage of APS determines the polymerization rate and molecular weight distribution. At low dosages (0.01g), the initiation efficiency is low, the polymer molecular weight is large and widely distributed, and the chain segment flexibility is good, resulting in a higher STS. At high dosages, the number of initiation sites increases, the molecular weight decreases but the distribution is more uniform, and the network structure is denser, thus significantly improving UCS. However, the slippage ability between small molecule chain segments decreases, leading to a decrease in STS. The optimal ratio of CMC-HEC hydrogel was finally determined to be: 5g CMC, 4g HEC, 0.01g APS, and 0.4g MBA. With this ratio, the UCS of the cured body is close to 96.6% of the theoretical optimum, and the STS reaches the optimum value.

[0126] Subsequently, FTIR spectral analysis was performed to characterize CMC-HEC:

[0127] from Figure 7As can be seen from the original CMC and HEC spectra, both exhibit typical polysaccharide characteristics. The OH stretching vibration peak indicates a rich hydroxyl hydrogen bond network; the CH asymmetric stretching vibration peak around 2990 cm⁻¹ and the C=O vibration peak of the carboxylic acid group around 1600 cm⁻¹ correspond to the characteristics of carbon-hydrogen bonds and carboxylic acid groups, respectively. After hydrogel formation, significant spectroscopic evolution occurred—the OH peak shifted to higher wavenumbers and broadened significantly, confirming that CMC and HEC construct a dense physical cross-linked network through strong hydrogen bonds; the shift in the C=O peak position reveals that the carboxylic acid group and hydroxyethyl undergo dipole-dipole interactions, further verifying the chemical coupling mechanism of the bifibrillary interpenetrating network; the newly appearing weak absorption peak at 1758 cm⁻¹ clearly belongs to the C=O stretching vibration of the amide I band of the cross-linking agent MBA, providing direct evidence for covalent cross-linking; and the COC vibration peak located at 1359 cm⁻¹ confirms the integrity of the ether bond structure of the cellulose backbone. The spectral characteristics ultimately confirmed that the CMC-HEC hydrogel constructs a structurally stable three-dimensional polymer network through the synergistic effect of enhanced molecular chain entanglement via hydrogen-bonded interpenetrating networks and the establishment of rigid nodes via MBA covalent crosslinking.

[0128] Simultaneously perform XRD analysis:

[0129] Depend on Figure 8 As a cellulose derivative, CMC exhibits multiple sharp peaks in its XRD pattern, indicating that it retains some of the crystalline structure of cellulose. However, due to carboxymethyl substitution, its crystallinity is generally lower than that of natural cellulose. HEC shows a broadened peak only at 20.38°, indicating that its crystallinity is extremely low, even approaching amorphous. This is because the introduction of hydroxyethyl groups disrupts the hydrogen bond network between cellulose molecules, hindering the orderly arrangement of molecular chains and significantly weakening the original cellulose crystalline structure, retaining only a small amount of short-range ordered amorphous scattering characteristics. Compared with the single material, the XRD pattern of CMC-HEC hydrogel shows characteristics such as "broadened main peak, partial peak shift, and disappearance of the 34° peak." This is because the amorphous structure of HEC and the crystalline region of CMC interpenetrate. The hydroxyethyl groups in HEC and CMC molecular chains are entangled through hydrogen bonds or electrostatic interactions, restricting the orderly arrangement of CMC-HEC hydrogel molecular chains. The interface between the crystalline region of CMC and the amorphous region of HEC forms an amorphous layer due to molecular chain mixing, further weakening the intensity of the 20.38° peak. The disappearance of the 34° peak is the most significant change, indicating that the ordered arrangement of the 004 crystal plane corresponding to this peak in CMC has been completely disrupted. HEC molecular chains preferentially insert into the interstitial space of this crystal plane in CMC, breaking the periodic stacking of molecular chains on this crystal plane through steric hindrance or strong interactions, thus causing the diffraction conditions of this crystal plane to no longer hold.

[0130] Finally, SEM analysis was performed:

[0131] Scanning electron microscopy (SEM) was used to examine the microstructure of CMC, HEC, and CMC-HEC powders. Figures 9 to 11 As shown in the image, at 1000x SEM, CMC exhibits typical irregular blocky aggregates. Upon magnification to 5000x, a finer fibrous skeletal network is exposed on its surface, with densely distributed irregular pores on the fiber surface. This hierarchical porous system provides multi-scale anchoring points for active groups such as carboxymethyl groups. The pores serve as macroscopic reaction chambers for the grafting reaction, while the pores create a high-specific-surface-area microenvironment for the penetration and fixation of polymer chains. At 5000x, HEC resembles a "soft brush" structure, with reduced surface roughness compared to CMC. While this low roughness reduces physical anchoring points, the directional hydrogen bond donor of hydroxyethyl groups can specifically couple with the carboxymethyl groups of the CMC matrix, triggering a recognition effect for in-situ grafting reactions. Observing the 2000x and 5000x images of CMC-HEC reveals that the fibrous skeleton of CMC interweaves with the short fibers or spherical particles of HEC, forming a well-defined interpenetrating network. Macroscopic gaps between CMC fibers form interconnected channels, while HEC particles intersect with CMC fibers to form pores. The pores on the CMC fiber surface and the depressions in the HEC particles together constitute a multi-scale rough surface. The crosslinking agent MBA forms particulate agglomerates at the interface between CMC and HEC, bridging the two phases through chemical bonds, and locally presenting a dense crosslinked network with "point-line" connections.

[0132] Second type of test results: Mechanical property test:

[0133] according to Figure 12As shown, the CMC content regulates the mechanical properties of the material through a dual mechanism of chemical bonding and physical network. In the 1%–3% content range, the carboxyl groups of the CMC molecular chain form a cross-linked network with the metal cations (such as Ca²⁺ and Fe³⁺) on the surface of graphite tailings particles through ionic bonding. Simultaneously, hydroxyl groups (-OH) generate hydrogen bonds, significantly enhancing interparticle forces and promoting structural densification by filling pores. Similarly, the biopolymer guar gum forms hydrogen bonds with soil particles through hydroxyl groups in its molecular chain, constructing a hydrogel network to fill pores, resulting in a significant increase in the unconfined compressive strength (UCS) of the soil sample with increasing content. The unconfined compressive strength (UCS) increased from 1.82 MPa to 3.134 MPa. However, when the admixture content exceeds 3%, the supersaturation effect leads to the accumulation of unhydrated CMC molecular clusters, forming weak interlayers. Simultaneously, excessive polymer competes for moisture, thickening the water film between particles and weakening the frictional interlocking force. This is consistent with the pattern observed in guar gum-modified soil: when the admixture content exceeds 1%, the high-viscosity gel solution hinders soil particle compaction, leading to a decrease in dry density. Furthermore, excessive polymer may form non-uniform clusters due to insufficient hydration, similar to the 'weak interlayer' effect, causing the UCS to drop to 2.564 MPa. Within the admixture content range of 1% to 4%, the long CMC chains construct a flexible bridging network between particles, dispersing stress through elastic deformation and inhibiting crack propagation, causing the tensile strength STS to continuously increase from 0.23 MPa to 0.84 MPa. However, when the admixture content exceeds 4%, excessive molecular chain entanglement forms localized brittle gel regions. Combined with the drying shrinkage stress induced by the high polymer content, this leads to the initiation of internal microcracks, causing the STS to decline.

[0134] Depend on Figure 13It is known that within the dosage range of 1% to 5%, HEC long-chain molecules form a three-dimensional network by encapsulating tailings particles through hydrogen bonds. Their hydroxyethyl side chains adsorb water molecules to form a lubricating hydration film, promoting dense particle arrangement. Simultaneously, the polymer network continuously fills pores and reduces stress concentration. Similar phenomena were observed in studies of xanthan gum-modified silty soil: polymer molecules fill the pores between soil particles and form a fibrous network structure. By enhancing interparticle adhesion and the stability of the adsorbed water film, the dynamic shear modulus increases with increasing dosage. Furthermore, it reduces the sensitivity of deformation characteristics to changes in matrix suction during wetting, demonstrating the improving effect of the hydrogen-bonded network on the material's water stability. This increases the UCS from 1.87 MPa to 3.62 MPa. Simultaneously, the flexible HEC chains build elastic bridges between particles, efficiently dispersing stress through reversible chain extension, increasing the STS from 0.37 MPa to 0.92 MPa. The synchronous growth of UCS and STS in this stage stems from the optimal balance between network densification and chain extensibility at a 5% dosage. When the content exceeds 5%, the steric hindrance effect causes excessive HEC chains to repel each other, forming loose gel clusters and destroying structural uniformity. At the same time, the high concentration of polymer locks in too much free water, delaying the particle compaction process and weakening rigidity. STS decay is caused by excessive molecular chain entanglement forming topological nodes that restrict chain segment movement, making the material brittle. Furthermore, the interface between the HEC enrichment zone and the tailings is weakened, becoming the preferred path for bending fracture.

[0135] Depend on Figure 14It is evident that the CMC-HEC composite system achieves a breakthrough in mechanical properties compared to single CMC or HEC through the synergy of a rigid framework and flexible network, coupled with interfacial hydrogen bonding. At a dosage of 5%, the UCS reaches 5.32 MPa and the STS reaches 1.37 MPa, both significantly higher than the optimal values ​​of single CMC / HEC. The -COO⁻ of CMC crosslinks with tailings metal cations to form a rigid framework, while the hydrogen-bonded hydration network of HEC fills the pores, constructing a "reinforced concrete" dual-network structure. The composite treatment of guar gum and PET fiber also exhibits a similar synergistic effect: the hydrogel network of GG fills the pores and forms a chemical bond, i.e., a rigid framework, while PET fiber disperses stress and inhibits crack propagation through a bridging effect, achieving flexible enhancement. This results in a 24% increase in CBR value and a 77% reduction in the compression index compared to single GG treatment. The CMC carboxyl groups and HEC hydroxyethyl groups are bridged by intermolecular hydrogen bonds, eliminating the interfacial weaknesses of single components. The water-retention capacity of HEC buffers the drying shrinkage stress of CMC, and the CMC crosslinking inhibits the water retention and softening of HEC, resulting in a UCS / STS decrease of only 10.5% / 9.4% at a 6% dosage. The rigid CMC chains prevent the topological entanglement and embrittlement of HEC molecular chains; the HEC hydration layer disperses the supersaturated crystallization stress of CMC ions. This verifies the triple synergistic mechanism of "rigid chemical crosslinking + flexible physical hydration + interfacial coupling". Similarly, Weng et al. found that xanthan gum XG generates a cementing effect through interaction with metal ions such as Mg²⁺ and Fe²⁺ in red clay, and forms a dense composite matrix by filling pores and expanding the particle contact area, which has the same synergistic mechanism as the present invention.

[0136] Third type of test result: Heavy metal leaching test:

[0137] Depend on Figure 15 The CMC-HEC hydrogel showed a significant effect on the fixation of heavy metal ions in graphite tailings. A 2% concentration of CMC-HEC hydrogel exhibited a significant solidification effect on five heavy metals, Cu, Mn, Ni, and Zn, in graphite tailings. After treatment, the contents of each metal decreased significantly: Cu decreased from 0.72 to 0.1093 (a decrease of 84.8%), Mn decreased from 2.15 to 0.598 (a decrease of 72.2%), Ni decreased from 0.29 to 0.0772 (a decrease of 73.4%), and Zn decreased from 0.51 to 0.1953 (a decrease of 61.7%).

[0138] Its curing mechanism stems from a dual effect: first, chemical adsorption, where the carboxyl groups in the hydrogel dissociate into -COO⁻ and then form stable complexes with heavy metal cations (such as Cu²⁺ and Ni²⁺) through electrostatic attraction; hydroxyl groups (-OH) assist in adsorption through hydrogen bonding or coordination, jointly reducing the free state of heavy metals; second, physical encapsulation, where the three-dimensional network structure formed during hydrogel curing effectively encapsulates ions, limiting migration and diffusion. The difference in curing efficiency among different metals is related to ionic characteristics: ions with high charge density or small radius are more likely to bind to functional groups, while Zn²⁺, due to its full-shell structure, has high chemical stability and therefore weaker complexing ability. The efficient curing of hydrogels can significantly reduce the risk of heavy metal migration from tailings to soil and groundwater, reducing ecotoxicity and health hazards; Cu, Ni, and Mn all have curing rates exceeding 70%, highlighting the material's advantages, while Zn's moderate curing rate (61.7%) may be further improved by increasing carboxyl density or adjusting the degree of crosslinking.

[0139] Fourth test result: Water erosion resistance test of graphite tailings solidified layer:

[0140] Depend on Figure 16 The water erosion resistance mass loss rate shows that after the third cycle, the solidified layers of single CMC and HEC were almost completely peeled off, and the remaining mass remained essentially unchanged, with the corresponding mass loss rate remaining at a high level close to 100%, indicating solidified layer failure. In contrast, CMC-HEC maintained a high retention rate of 97% after 5 cycles, demonstrating excellent long-term water erosion resistance stability. The failure of HEC and CMC is closely related to their molecular structure characteristics: HEC, as a non-ionic cellulose ether, although possessing certain film-forming properties, contains only hydroxyethyl groups in its molecular chains, making it prone to swelling under water erosion. Although some unswollen chain segments can re-enter to form temporary structures, repeated swelling-shrinkage cycles lead to molecular chain breakage. CMC, as an anionic cellulose ether, has carboxyl groups that easily undergo complexation reactions with cations such as Ca²⁺ and Mg²⁺ in water, forming insoluble precipitates and consuming effective functional groups, resulting in loss of adhesion in subsequent cycles. The anti-erosion advantage of CMC-HEC hydrogel stems from the synergistic effect of its components: on the one hand, the carboxyl groups of CMC and the silanol and aluminol groups on the surface of graphite tailings provide strong interfacial adhesion through hydrogen bonding and coordination complexation; on the other hand, the long-chain hydroxyethyl groups of HEC fill the gaps in the CMC network through steric hindrance, hindering the diffusion of water molecules into the gel interior, while its non-ionic properties prevent cation complexation loss and maintain the integrity of the molecular chains. Through intermolecular entanglement and network interpenetration, the two components form a denser three-dimensional cross-linked structure, such as... Figure 10The 2000x SEM image revealed interpenetrating network characteristics, which effectively suppressed the swelling-dissolution process, thus maintaining a high retention rate of 97% after 5 cycles. Microscopic molecular dynamics simulations further confirmed this phenomenon: the hydrogel formed a dense layer of 15-45 Å at the tailings interface, hindering the penetration of water molecules.

[0141] Fifth type of test result: Microscopic characterization of the solidified body:

[0142] Depend on Figure 17 The graphite tailings treated by CMC, HEC, and CMC-HEC, along with their FTIR spectra, show that the graphite tailings exhibit strong double peaks at 3625 cm⁻¹ and 3426 cm⁻¹, indicating the presence of two independent active hydroxyl sites on their surface, both of which are fully exposed. After CMC curing, the hydroxyl peak shifts to 3403 cm⁻¹, retaining only a single associated peak, with a significantly reduced peak width. This phenomenon stems from the formation of coordination bonds between the carboxymethyl groups of CMC and the metal ions on the tailings surface, shortening the OH bond length and covering the free hydroxyl sites. In contrast, HEC curing relies solely on weak hydrogen bonding, resulting in a minimal shift in the hydroxyl peak, demonstrating limited surface isolation. The CMC-HEC composite gel exhibits a gentle broadening of the hydroxyl peak, with no free peak and minimal fluctuation. Its three-dimensional network of carboxyl and hydroxyethyl groups forms a uniform interface layer through cross-linking, completely covering the free hydroxyl groups and retaining only the uniformly distributed associated hydroxyl groups within the gel network, achieving the most thorough site isolation. In the water molecule adsorption region (1642 cm⁻¹), the strong HOH bending vibration peak of the tailings indicates that the surface is rich in polar water molecules. CMC solidification causes a slight shift in this peak because the ionic bonds formed by the carboxylate and metal ions partially cover the adsorbed water. Although HEC solidification shifts to 1629 cm⁻¹, the peak intensity is largely retained, reflecting insufficient shielding of water by its physical entanglement. CMC-HEC solidification weakens the HOH peak to 1641 cm⁻¹, attributed to the dense network significantly reducing the exposure of adsorbed water, and the carboxylate-hydroxyethyl co-coordination with metal ions forming a stable chelate, further suppressing water vibration. The strong Si-O-Si peak in the silicate framework region (1025 cm⁻¹) confirms that the inorganic framework of the tailings is completely exposed. All three curing agents reduced the peak intensity and peak shape fluctuation, but their mechanisms differed. CMC relied on carboxyl-metal ion coordination to form a local capping layer, partially shielding the Si-O-Si vibration; HEC achieved physical capping through hydrogen bonding and molecular chain entanglement, but the structure was loose; CMC-HEC, on the other hand, formed a dense ether bond network through the superposition of methylene ether bonds constructed by the MBA crosslinking agent and the COC ether bonds of the polymer backbone, homogenizing the silicon-oxygen bond vibration environment, significantly reducing peak intensity and stabilizing peak shape. XRD analysis by Weng et al. also showed that xanthan gum-cured red clay improved structural order through cementation and filling effects. The multi-peak pattern in the low-frequency region (400–900 cm⁻¹) reflects the presence of active sites such as silicates and metal oxides in the tailings.

[0143] Figure 18 XRD patterns of graphite tailings under different treatment conditions were observed. The XRD pattern of the original graphite tailings showed multiple diffraction peaks at 21.14°, 26.94°, and 29.76°, corresponding to characteristic crystal planes of natural minerals such as silicates and carbonates. However, all peak intensities were the lowest because the graphite tailings surface contained a large amount of amorphous material and defects such as crystal distortion and interface roughness, resulting in strong X-ray scattering and significant weakening of the ordered diffraction signal. The carboxymethyl group of CMC dissociates into a carboxylate in an alkaline environment, forming a coordination structure with metal ions on the tailings surface through ionic bonds. This chemical coordination partially covers the amorphous material on the surface, reducing X-ray scattering and resulting in higher peak intensities than the original tailings. Simultaneously, the coordinated carboxylate, as an ordered crystal, exhibits new peaks at 30.18° and 30.98° in the XRD. The hydroxyethyl group of HEC binds to the hydroxyl groups of the tailings through weak hydrogen bonds, with the molecular chains entangling and wrapping the particles to form a physical coating layer. This physical encapsulation reduces the exposure of amorphous materials on the surface, decreases scattering, and further enhances peak intensity. However, the low degree of cross-linking and weak hydrogen bonding of CMC and HEC, coupled with a thin and discontinuous coating layer, limits their shielding against defects, resulting in peak intensities still lower than those of the composite gel. The three-dimensional network of the CMC-HEC hydrogel covers most of the amorphous materials and defect sites on the tailings surface, significantly reducing X-ray scattering and substantially improving crystal order. The uniformity of the cross-linked network reduces crystal structure distortion, making diffraction peaks sharper and further enhancing peak intensity. This achieves excellent interface coverage and crystal protection.

[0144] Depend on Figures 19 to 22 As can be seen, scanning electron microscopy clearly revealed the differences in microstructure among the original graphite tailings, CMC, HEC, and CMC-HEC composite hydrogel solidified tailings samples.

[0145] like Figure 23 The original graphite tailings exhibit a typical loose accumulation state, mainly composed of irregular angular and platy mineral particles with a wide particle size distribution. The particles are primarily in point contact, forming numerous irregular pores, resulting in an overall loose and porous structure. In contrast, the pure polymer samples exhibit drastically different characteristics:

[0146] After drying, CMC exhibits a lamellar or highly porous interwoven fiber network structure, as shown in... Figure 24 It has significant wrinkles and cracks, and its porosity originates from the aggregation of polymer chains and drying shrinkage.

[0147] HECs, on the other hand, tend to form relatively more continuous and dense thin-film structures. Figure 25 Both also exhibit wrinkles on their surfaces, and both demonstrate the typical amorphous polymer morphology of hydrophilic cellulose ethers.

[0148] Figure 26 As shown in the CMC-HEC hydrogel-cured tailings sample: the original loosely packed morphology of the tailings was completely reconstructed. High-magnification SEM images clearly show that the tailings particles are tightly wrapped by a continuous CMC-HEC polymer matrix, and the particle surface is often covered with a uniform polymer film, indicating good wetting and adsorption.

[0149] Between adjacent tailings particles, "bridging" or "neck-connection" structures formed by the polymer can be observed, providing direct microscopic evidence of effective bonding force. Simultaneously, the CMC-HEC blend network itself forms a unique honeycomb or sponge-like porous structure after curing and drying. These polymer networks deeply penetrate and effectively fill the large pore spaces between the original tailings particles, segmenting and refining them into a smaller, more uniformly distributed, and more complex pore system. The discrete particles and large pore structure in the original tailings undergo significant changes after polymer curing. The particle surface is tightly wrapped by the polymer matrix, bridging structures are formed between particles, and the original large pores are filled and refined by the porous polymer network. This microstructural transformation significantly improves the compactness and mechanical strength of the cured body and effectively reduces its permeability.

[0150] The original graphite tailings were mainly composed of silica minerals (Si 37.90 wt%, O 38.35 wt%), containing residual carbon (20.91 wt%). Their highly hydrophilic surface made them sensitive to water erosion. Due to discontinuous encapsulation, the carbon content of the HEC solidified layer dropped sharply by 44% (to 9.07 wt%), while iron was locally enriched at 20.54 wt%, exposing the defects of uneven mineral coverage, which was directly related to the 12.3% mass loss rate in the water erosion resistance test. The CMC solidified layer was limited by the strong hydrophilic carboxyl groups (O content increased by 30% to 49.74 wt%) and sodium ion migration (Na 2.37 wt%), and the carbon signal was suppressed (5.87 wt%), causing the cemented network to swell and disintegrate (corresponding to 18.6% mass loss). The carbon content of the CMC-HEC hydrogel solidified layer significantly increased to 26.58 wt%, demonstrating that the continuous polymer phase completely encapsulates the tailings particles, simultaneously diluting and uniformly dispersing mineral signals such as silicon and iron, far lower than the local enrichment of HEC. Optimization of the C / O ratio indicates that the carboxyl groups of CMC and the hydroxyl groups of HEC are cross-linked through hydrogen bonds, reducing free hydrophilic groups. Sodium ion locking (Na 0.31 wt%, 87% lower than CMC) confirms that the interpenetrating network (IPN) blocks ion channels and inhibits water permeation pathways. This synergistic mechanism enables the composite solidified layer to comprehensively surpass single-systems in elemental distribution uniformity, organic phase continuity, and chemical stability, directly supporting its superior water erosion resistance. Combined with macroscopic water erosion resistance test results, it is evident that the uniformity of elemental distribution and the continuity of the organic phase at the microscopic level are the foundation for its excellent macroscopic water erosion resistance.

[0151] Sixth type of experimental result: Molecular dynamics simulation:

[0152] Depend on Figures 27 to 29 It can be seen that the solidification effect of CMC-HEC hydrogel on graphite tailings is due to the coupling of intermolecular reaction mechanism and multi-scale structural synergy.

[0153] Firstly, the three-dimensional network structure and particle encapsulation: The CMC-HEC hydrogel forms a three-dimensional interpenetrating network through graft copolymerization, which not only provides mechanical support for the solidified body but also serves as an important carrier for heavy metal encapsulation. SEM results show that tailings particles are tightly encapsulated by a continuous polymer film, forming "bridging" or "neck-like connections" between particles. This is a physical bond formed by the polymer chains penetrating into the interparticle gaps and solidifying. The hydrogel itself has a honeycomb porous structure, which can effectively fill the large pores in the tailings, constructing a denser and more uniform microporous system. EDS elemental distribution analysis shows that the carbon content of the composite hydrogel (26.58 wt%) is significantly higher than that of single CMC (5.87 wt%) and HEC (9.07 wt%), and the mineral signals such as silicon and iron are uniformly dispersed, proving that the polymer network achieves complete coverage of the tailings particles and reduces local enrichment defects.

[0154] Secondly, the synergistic effect of interpenetrating networks: Compared with single CMC or HEC, the interpenetrating network (IPN) structure significantly enhances structural stability and long-term curing performance through functional complementarity. Although CMC has a strong complexing ability, its carboxyl groups in an aqueous environment easily compete for coordination with Ca²⁺, Mg²⁺, etc., leading to network swelling and disintegration, releasing heavy metals. Although HEC can form a continuous coating film, its non-ionic nature makes its structure susceptible to damage under water erosion conditions, affecting heavy metal fixation. In the CMC-HEC composite system, the long hydroxyethyl chain of HEC is embedded in the gaps of the CMC network, providing a steric hindrance effect and effectively preventing water molecule diffusion; at the same time, the carboxyl groups and hydroxyethyl groups form a dense cross-link through hydrogen bonds, constructing a highly stable network structure. Molecular dynamics simulations show that this structure can form a dense layer with a thickness of 15–45 Å and a density of 1.32 g / cm³ at the tailings interface, significantly inhibiting the swelling and erosion processes. After five water erosion cycles, the solidified body still maintained a quality retention rate of up to 97%, ensuring long-term stable storage of heavy metals and effectively preventing the risk of secondary release.

[0155] The optimal ratio (CMC:HEC = 5:4) was determined through orthogonal experiments. The unconfined compressive strength (UCS) and splitting tensile strength (STS) of the solidified body were 40% and 50% higher, respectively, than those of the single-component system. SEM observation of the solidified body showed that the carboxyl groups of CMC coordinated with metal ions in the tailings to form a rigid framework, while the hydroxyethyl groups of HEC filled the pores through hydrogen bonding. The interpenetrating network structure of the two achieved a "rigid-flexible synergy". Molecular dynamics simulations confirmed that the hydrogel formed a dense layer of 15–45 Å (density 1.32 g / cm³) at the tailings interface, with a stable adsorption energy (-15300 kJ / mol), inhibiting particle migration.

[0156] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for preparing a bio-based interpenetrating network hydrogel, characterized in that, Includes the following steps: S1: Carboxymethyl cellulose (CMC) and hydroxyethyl cellulose (HEC) are added to deionized water and dissolved under stirring to obtain a transparent homogeneous solution; S2: Introduce nitrogen gas and add initiator and crosslinking agent; S3: The solution in S2 is then heated and continuously stirred to carry out the graft copolymerization reaction until a significant increase in solution viscosity is observed and an elastic gel is formed, thus forming a coarse gel. S4: After the reaction solution has cooled to room temperature, transfer the crude gel to a beaker and add anhydrous ethanol to the beaker to soak it continuously to remove unreacted monomers. Then place the crude gel in a vacuum drying oven to dry to constant weight, and finally obtain a white hydrogel powder.

2. The method for preparing a bio-based interpenetrating network hydrogel according to claim 1, characterized in that: In step S1, the mass ratio of CMC to HEC is (3:1) to (5:4), the stirring temperature in step S1 is 40 to 50°C, and the stirring speed is 300 rpm. In step S2, the nitrogen gas is introduced for 30 minutes, the initiator is ammonium persulfate (APS), and the crosslinking agent is methylenebisacrylamide (MBA).

3. The method for preparing a bio-based interpenetrating network hydrogel according to claim 1, characterized in that: The solution temperature in step S3 is 70-80℃, and the stirring time in step S3 is 40-60 min. In step S4, the amount of anhydrous ethanol added is 200 mL, and the soaking time is 12 h. The temperature of the vacuum drying oven in step S4 is 60 °C.

4. The method for preparing a bio-based interpenetrating network hydrogel according to claim 1, characterized in that: In step S1, the optimal mass ratio of CMC to HEC is 5:4, the amount of CMC added is 5g, the amount of HEC added is 4g, the amount of APS added is 0.01g, and the amount of MBA added is 0.4g.

5. A bio-based interpenetrating network hydrogel, characterized in that, It is obtained by the preparation method described in any one of claims 1-4.

6. The application of the bio-based interpenetrating network hydrogel of claim 5 in the solidification of fine-grained tailings, characterized in that, It achieves efficient and green solidification of fine-grained tailings, while simultaneously improving mechanical strength, heavy metal fixation capacity, and environmental sustainability.

7. The application of the bio-based interpenetrating network hydrogel according to claim 6 in the solidification of fine-grained tailings, characterized in that, The fine-grained tailings are graphite tailings.

8. A method for solidifying fine-grained tailings using the bio-based interpenetrating network hydrogel of claim 5, characterized in that, Includes the following steps: Step A: Mix the hydrogel powder with fine tailings using a dry mixing method, ensuring that the hydrogel is evenly dispersed on the surface of the tailings particles during mixing; Step B: Fill the mold with the mixture in 5 layers, with each layer containing 1 / 5 of the total mass; Step C: Use a standard compaction hammer to compact each layer of the mold 25 or 30 times evenly. After each layer is compacted, use a scraper to lightly roughen the surface to enhance the interlayer bonding force and prevent the delamination interface from becoming a weak area. Step D: After all 5 layers of the mold in Step B have been compacted, let it stand for 10 minutes to release the internal stress, and then slowly demold. Step E: Place the demolded specimen into a drying oven and dry it at 105°C for 48 hours. Then, remove the specimen and smooth the surface to obtain solidified fine-grained tailings.

9. The method for hydrogel solidification of fine-grained tailings according to claim 8, characterized in that: The amount of hydrogel added is 0.5 to 3% of the dry weight of the tailings.

10. The method for hydrogel solidification of fine-grained tailings according to claim 8, characterized in that: The amount of hydrogel added is 1.0 to 2.0% of the dry weight of the tailings.

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