Method for carboxymethyl chitosan mediated biomineralization solidification of different particle size fine particle tailings

Abstract

The application belongs to the technical field of biological solidification, and particularly discloses a method for solidifying fine-particle tailings with different particle sizes through carboxymethyl chitosan-mediated biomineralization, which comprises the following steps: pretreating the fine-particle tailings; uniformly mixing carboxymethyl chitosan into the tailing particles; preparing enzyme-induced carbonate precipitation solution and microorganism-induced carbonate precipitation solution; respectively injecting the enzyme-induced carbonate precipitation solution and the microorganism-induced carbonate precipitation solution by using a saturated two-way continuous grouting mode; and after flushing with distilled water, curing and drying are performed, so that the solidification is completed. The method for solidifying fine-particle tailings with different particle sizes through carboxymethyl chitosan-mediated biomineralization has the advantages that under the mediation of carboxymethyl chitosan, the mineralization reaction rate of biomineralization and the mineral precipitation form are both optimized, and the mechanical stability of the overall solidification system and the solidification stability of heavy metal pollutants are also significantly enhanced.

Description

A method for biomineralization and solidification of fine tailings of different particle sizes mediated by carboxymethyl chitosan Technical Field

[0001] This invention belongs to the field of biosolidification technology, specifically relating to a method for biomineralization solidification of fine tailings of different particle sizes mediated by carboxymethyl chitosan. Background Technology

[0002] Graphite, as a key strategic material in the global energy structure transformation, has become an indispensable material carrier in emerging fields such as quantum chips and new energy storage systems due to its crucial role in the iteration of clean energy technologies. However, the beneficiation process of natural graphite generates a large amount of fine-grained tailings rich in heavy metal pollutants. The long-term accumulation of fine-grained tailings not only occupies a large amount of land resources, but the heavy metals leached from them also continue to accumulate and migrate in soil and water bodies, posing a threat to the ecological environment. More seriously, the potential risk of tailings dam failure and leakage may lead to large-scale pollution of groundwater and soil, thus posing a huge hidden danger to the surrounding environment and human health. Therefore, the low-carbon, efficient, and green sustainable disposal and utilization of fine-grained tailings is of great practical significance.

[0003] Enzyme-induced carbonate precipitation (EICP) and microbial-induced carbonate precipitation (MICP) are emerging solidification technologies for improving soil mechanical properties and controlling heavy metal pollutants. In recent years, with the large-scale mining of ore resources, the grade of graphite ore has become increasingly lower. Improving grinding fineness and beneficiation processes to ensure graphite recovery has become an inevitable trend. However, this process also leads to increasingly finer particle sizes in newly generated tailings, with a more pronounced difference in particle size compared to existing tailings. The difference in particle size among tailings not only affects their pore structure and permeability but also has a profound impact on the overall stability of tailings ponds, heavy metal migration behavior, and subsequent resource utilization. Therefore, particle size is a crucial and unavoidable factor in the solidification processes of fine tailings using EICP and MIP.

[0004] While existing research indicates that differences in soil particle size significantly affect the cementing properties and remediation effectiveness of biomineralization, the specific impact of fine-grained tailings particle size variations on the mineralization mechanisms of EICP and MICP remains unclear. In particular, systematic research is lacking on how to effectively address the resulting differences in solidification performance and potential adverse effects. Therefore, there is a need in this field to develop a carboxymethyl chitosan-mediated method for biomineralization and solidification of fine-grained tailings of different particle sizes, which can effectively solve the aforementioned problems. Summary of the Invention

[0005] The purpose of this invention is to provide a method for solidifying fine-grained tailings of different particle sizes through carboxymethyl chitosan-mediated biomineralization. Under the mediation of carboxymethyl chitosan (CMCS), the biomineralization reaction rate and mineral precipitation morphology are optimized, while the mechanical stability of the overall solidification system and the ability to stabilize heavy metal pollutants are significantly enhanced. This provides a new approach to solving the problem of the limitation of traditional biomineralization reaction in tailings solidification due to the difference in particle size of fine-grained tailings.

[0006] To achieve the above objectives, the present invention provides a method for biomineralization and solidification of fine tailings of different particle sizes mediated by carboxymethyl chitosan, comprising the following steps:

[0007] Step S1: Pre-treat the fine tailings; after drying, the fine tailings are screened to obtain tailings particles with a particle size of less than 100 mesh, 100-150 mesh, 150-200 mesh, and greater than 200 mesh.

[0008] Step S2: Carboxymethyl chitosan (CMCS) is uniformly incorporated into the tailings particles obtained in step S1 at a mass dosage of 0.05% to 0.2%, and cylindrical samples are obtained by layered filling method combined with mechanical vibration.

[0009] Step S3: Prepare enzyme-induced carbonate precipitation (EICP) solution and microbial-induced carbonate precipitation (MICP) solution;

[0010] Step S4: Using a saturated bidirectional continuous grouting method, the enzyme-induced carbonate precipitation solution and the microbial-induced carbonate precipitation solution prepared in step S3 are injected into the cylindrical sample obtained in step S2, and then allowed to stand.

[0011] Step S5: Repeat steps S42 to 4 times, rinse with distilled water, then cure and dry to complete the curing process.

[0012] Preferably, in step S1, the drying temperature is 100-110°C and the drying time is 70-74 hours.

[0013] Preferably, in step S2, the degree of carboxymethyl substitution of carboxymethyl chitosan is ≥85%, and the degree of deacetylation is ≥90%; the frequency of mechanical vibration is 30-40Hz, and the intensity of mechanical vibration is 15%-25% to enhance the uniformity of tailings samples of different particle sizes with CMCS; in order to reduce the interface effect that may exist between fine tailings in each layer, the tailings are shallowly scratched after each layer is filled using the layered filling method.

[0014] Preferably, step S3 specifically involves:

[0015] Step S31: Prepare plant-derived urease solution;

[0016] Soybeans rinsed with distilled water are ground into powder and mixed with deionized water at a solid-liquid ratio of 1:8 to 1:12. The mixture is stirred to obtain a suspension. The suspension is centrifuged at 3000 to 4000 r / min at 4°C for 30 to 40 minutes. The supernatant is taken as the plant-derived urease solution.

[0017] Step S32: Prepare Bacillus pasteurellium culture;

[0018] Bacillus pasteurellii was inoculated into Luria–Bertani medium under aseptic conditions and cultured at 30°C and 100–150 r / min for 70–74 h to obtain Bacillus pasteurellii bacterial culture.

[0019] Step S33: Prepare the cementing solution;

[0020] Urea and calcium acetate are mixed at a volume ratio of 1:1 to obtain the cementing solution;

[0021] Step S34: Mix the plant-derived urease solution and the cementing solution at a volume ratio of 1:1 to obtain the enzyme-induced carbonate precipitation solution; mix the Bacillus pasteurellium bacterial solution and the cementing solution at a volume ratio of 1:1 to obtain the microbial-induced carbonate precipitation solution.

[0022] Preferably, in step S31, the stirring speed is 900-1100 r / min and the stirring time is 25-35 min.

[0023] Preferably, in step S32, the OD in the Bacillus pasteurellium culture is... 600 =1.0~1.5; In step S32, the molar concentrations of urea and calcium acetate are both 0.6~1.0mol / L.

[0024] Preferably, in step S4, the injection volume of both the enzyme-induced carbonate precipitation solution and the microbial-induced carbonate precipitation solution is equal to the pore volume of the tailings particles, the grouting rate in each direction is 1-3 mL / min, and the settling time is 10-14 h.

[0025] Preferably, in step S5, the distilled water rinsing time is 0.3 to 0.7 hours, and the distilled water rinsing rate is the same as the grouting rate in step S4.

[0026] Preferably, in step S5, the curing temperature is 20-30℃ and the curing time is 5-9 days; the drying temperature is 100-110℃ and the drying time is 12-36 hours.

[0027] The present invention employs the above-mentioned method for biomineralization and solidification of fine tailings of different particle sizes mediated by carboxymethyl chitosan, and the beneficial effects are as follows:

[0028] (1) The solidification method in this invention effectively overcomes the limitation of traditional biomineralization technology in which the strength of tailings solidification decreases significantly with decreasing particle size.

[0029] (2) In this invention, after bio-solidification by CMCS-EICP and CMCS-MICP, the pH values ​​of the leachate from fine-grained tailings of different particle sizes stabilized at 7.81–8.36 and 7.81–8.36, respectively, and the heavy metal ion fixation rates were 89.59%–100% and 93.21%–100%, respectively. Simultaneously, the Cu in the fine-grained tailings leachate… 2+ Mn 2+ and Zn 2+ The fixation capacity is more significantly affected by changes in tailings particle size, while Cd 2+ Pb 2+ and Ni 2+ Relatively stable; when the CMCS dosage was 0.15% and 0.10%, the fixation rate of heavy metal ions in tailings leachate of different particle sizes under CMCS-EICP and CMCS-MICP treatments reached 100%.

[0030] (3) The CMCS in this invention relies on its abundant negatively charged active groups such as -COOH and -NHCOCH3 to synergistically fix free heavy metal ions through electrostatic adsorption and chelation, and enrich Ca. 2+ CMCS participates in competitive adsorption on molecular surfaces, effectively inhibiting the attachment and outward migration of heavy metal ions on the surfaces of bacteria and urease. Furthermore, CMCS provides stable and efficient nucleation sites for the formation and transformation of CaCO3. The effect of CMCS on increasing the CaCO3 formation rate becomes more significant with decreasing tailings particle size. When the CMCS dosage is 0.15% and 0.1%, the average CaCO3 formation rate of different parts of tailings samples with a particle size greater than 200 mesh increased by 225.42% and 307.74%, respectively, after CMCS-EICP and CMCS-MICP treatment, while the increases were 80.27% and 96.50%, respectively, for samples with a particle size less than 100 mesh.

[0031] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0032] Figure 1 shows the effect of CMCS on the mechanical properties of fine tailings of different particle sizes in an experimental example of the method of carboxymethyl chitosan-mediated biomineralization solidification of tailings of different particle sizes according to the present invention; where (a) is the UCS of tailings after CMCS-EICP treatment, (b) is the UCS of tailings after CMCS-MICP treatment, (c) to (f) are the CaCO3 generation rate of tailings after CMCS-EICP treatment, and (g) to (j) are the CaCO3 generation rate of tailings after CMCS-MICP treatment.

[0033] Figure 2 shows the environmental effects of CMCS on the biomineralization of fine tailings of different particle sizes in an experimental example of the method of carboxymethyl chitosan-mediated biomineralization solidification of fine tailings of different particle sizes according to the present invention; where (a) is the pH change of tailings leachate after CMCS-EICP treatment, (b) is the pH change of tailings leachate after CMCS-MICP treatment, (c) to (h) are the fixation of heavy metal ions in tailings leachate by CMCS-EICP, and (i) to (n) are the fixation of heavy metal ions in tailings leachate by CMCS-MICP.

[0034] Figure 3 shows the microstructure of fine tailings of different particle sizes after bio-solidification in an experimental example of the method for biomineralization solidification of fine tailings of different particle sizes mediated by carboxymethyl chitosan according to the present invention. Among them, (a) is the SEM image of tailings particles before treatment and sieving, (b) is the SEM image of tailings particles with a particle size of less than 100 mesh after EICP treatment, (c) is the SEM image of tailings particles with a particle size of more than 200 mesh after EICP treatment, and (d) is the SEM image of tailings particles with a particle size of less than 100 mesh after MICP treatment. (e) is a SEM image of tailings particles with a diameter greater than 200 mesh after MICP treatment; (f) is a SEM image of tailings particles with a diameter less than 100 mesh after CMCS-EICP treatment; (g) is a SEM image of tailings particles with a diameter greater than 200 mesh after CMCS-EICP treatment; (h) is a SEM image of tailings particles with a diameter less than 100 mesh after CMCS-MICP treatment; and (i) is a SEM image of tailings particles with a diameter greater than 200 mesh after CMCS-MICP treatment.

[0035] Figure 4 shows the FTIR and XRD results of fine tailings of different particle sizes after bio-solidification in an experimental example of a method for biomineralization solidification of fine tailings of different particle sizes mediated by carboxymethyl chitosan according to the present invention; wherein, (a) to (b) are the FTIR spectra of tailings after CMCS-EICP and CMCS-MICP treatment, and (c) to (f) are the XRD spectra of tailings after CMCS-EICP and CMCS-MICP treatment and their mineral content ratio. Detailed Implementation

[0036] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0037] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0038] The materials used in this invention were sourced as follows: Fine-grained tailings were obtained from a tailings dam in Jixi City, Heilongjiang Province. Carboxymethyl chitosan was purchased from Sinopharm Chemical Reagent Co., Ltd., and appeared as a light yellow powder. Soybeans were purchased from Shandong Shengfeng Soybean Industry Co., Ltd. Bacillus pasteurellis was purchased from Beijing Zhongke Quality Inspection Co., Ltd. (DSM33). Urea and calcium acetate were both purchased from Sinopharm Chemical Reagent Co., Ltd.

[0039] Example 1

[0040] A method for biomineralizing and solidifying fine tailings of different particle sizes mediated by carboxymethyl chitosan includes the following steps:

[0041] Step S1: Pre-treatment of fine tailings. The fine tailings are dried and then screened. The drying temperature is 105℃ and the drying time is 72h. The tailings particles obtained by screening are less than 100 mesh, 100-150 mesh, 150-200 mesh and greater than 200 mesh.

[0042] Step S2: Carboxymethyl chitosan is uniformly incorporated into the tailings particles obtained in step S1 at mass dosages of 0%, 0.05%, 0.1%, 0.15%, and 0.2%. The mixture is divided into five equal layers according to height using a layered filling method, and each layer is filled and mechanically vibrated to obtain a cylindrical sample (diameter 39.1 mm, height 80 mm).

[0043] The frequency of the mechanical vibration is 35Hz and the intensity of the mechanical vibration is 20%. When using the layered filling method, the tailings are shallowly grazed after each layer is completed.

[0044] Step S3: Prepare enzyme-induced carbonate precipitation solution.

[0045] Step S31: Prepare plant-derived urease solution.

[0046] Soybeans rinsed with distilled water were ground into powder and mixed with deionized water at a solid-liquid ratio of 1:10. The mixture was stirred at 1000 rpm for 30 minutes to obtain a suspension. The suspension was centrifuged at 3500 rpm for 35 minutes at 4°C, and the supernatant was collected as the plant-derived urease solution.

[0047] Step S32: Prepare the cementing solution.

[0048] The cementing solution is obtained by mixing urea and calcium acetate in a volume ratio of 1:1.

[0049] Step S33: Mix the plant-derived urease solution and the cementing solution at a volume ratio of 1:1 to obtain the enzyme-induced carbonate precipitation solution.

[0050] Step S4: To ensure smooth grouting, a filter device consisting of porous silicon carbide and 600-mesh geotextile is placed at both ends of the mold. Using a saturated bidirectional continuous grouting method, the enzyme-induced carbonate precipitation solution prepared in step S3 is injected into the cylindrical sample obtained in step S2, and then allowed to stand.

[0051] The injection volume of the enzyme-induced carbonate precipitation solution was equal to the pore volume of the tailings particles (40 mL), the injection rate in each direction was 2 mL / min, and the settling time was 12 h.

[0052] Step S5: Repeat step S4 3 times, rinsing with distilled water for 0.5 hours at the same rate as the grouting in step S4. Then cure and dry at 25°C for 7 days. The drying temperature is 105°C for 24 hours, completing the curing process (CMCS-EICP bio-curing).

[0053] Example 2

[0054] A method for biomineralizing and solidifying fine tailings of different particle sizes mediated by carboxymethyl chitosan includes the following steps:

[0055] Step S1: Pre-treatment of fine tailings. The fine tailings are dried and then screened. The drying temperature is 105℃ and the drying time is 72h. The tailings particles obtained by screening are less than 100 mesh, 100-150 mesh, 150-200 mesh and greater than 200 mesh.

[0056] Step S2: Carboxymethyl chitosan is uniformly incorporated into the tailings particles obtained in step S1 at mass dosages of 0%, 0.05%, 0.1%, 0.15%, and 0.2%. The mixture is divided into five equal layers according to height using a layered filling method, and each layer is filled and mechanically vibrated to obtain a cylindrical sample (diameter 39.1 mm, height 80 mm).

[0057] The frequency of the mechanical vibration is 35Hz and the intensity of the mechanical vibration is 20%. When using the layered filling method, the tailings are shallowly grazed after each layer is completed.

[0058] Step S3: Prepare a microbial-induced carbonate precipitation solution.

[0059] Step S31: Prepare Pasteurella multocida bacterial culture.

[0060] Bacillus pasteurellii was inoculated into Luria–Bertani medium under aseptic conditions and cultured at 30°C and 120 rpm for 72 h to obtain Bacillus pasteurellii bacterial culture.

[0061] Step S32: Prepare the cementing solution.

[0062] The cementing solution is obtained by mixing urea and calcium acetate in a volume ratio of 1:1.

[0063] Step S33: Mix the Bacillus pasteurellium culture solution and the cementing solution at a volume ratio of 1:1 to obtain the microbial-induced carbonate precipitation solution.

[0064] Step S4: To ensure smooth grouting, a filter device consisting of porous silicon carbide and 600-mesh geotextile is placed at both ends of the mold. Using a saturated bidirectional continuous grouting method, the microbial-induced carbonate precipitation solution prepared in step S3 is injected into the cylindrical sample obtained in step S2, and then allowed to stand.

[0065] The injection volume of the microbial-induced carbonate precipitation solution was equal to the pore volume of the tailings particles (40 mL), the injection rate in each direction was 2 mL / min, and the settling time was 12 h.

[0066] Step S5: Repeat step S4 3 times, rinsing with distilled water for 0.5 hours at the same rate as the grouting in step S4. Then cure and dry at 25°C for 7 days. The drying temperature is 105°C for 24 hours, completing the curing process (CMCS-MICP bio-curing).

[0067] Experimental Example

[0068] The fine-grained tailings from Examples 1 and 2 were subjected to performance testing.

[0069] (a) UCS and CaCO3 formation rate test.

[0070] (1) A universal testing machine was used to perform UCS tests on the solidified fine tailings of different particle sizes. The loading rate was set to 0.5 mm / min, and the maximum axial force was recorded as the final UCS result.

[0071] The test results are shown in Figure 1(a) and Figure 1(b). As the particle size of the fine tailings decreases, the mechanical strength of the EICP and MICP-treated samples decreases significantly. When the particle size of the fine tailings is less than 100 mesh, the compressive strength of the EICP and MICP-treated samples is the highest, reaching 536.7 kPa and 761.9 kPa, respectively. However, when the particle size is greater than 200 mesh, the compressive strength is the lowest, only 253.6 kPa and 274.2 kPa, respectively.

[0072] The CMCS-EICP and CMCS-MICP treatments in Examples 1 and 2 significantly improved the strength of fine-grained tailings samples of different particle sizes. With increasing CMCS dosage, the strength of tailings samples of different particle sizes showed a trend of first increasing and then decreasing. When the CMCS content reaches 0.15% (CMCS-EICP) and 0.10% (CMCS-MICP), respectively, CMCS provides stable and efficient nucleation sites for urease through electrostatic adsorption via its abundant negatively charged active groups such as -COOH and -NHCOCH3, at which point UCS reaches its peak value. Specifically, after CMCS-EICP treatment, the compressive strengths of tailings samples with mesh sizes smaller than 100, 100–150, 150–200, and larger than 200 mesh are 1010.2 kPa, 976.3 kPa, 943.5 kPa, and 917.9 kPa, respectively; while the corresponding peak values ​​after CMCS-MICP treatment are 1409.1 kPa, 1371.1 kPa, 1335.8 kPa, and 1296.9 kPa, respectively. Meanwhile, the UCS of tailings samples with a particle size greater than 200 mesh after EICP and MICP treatment decreased by 52.75% and 64.01% respectively compared to tailings with a particle size less than 100 mesh. However, the difference between CMCS-EICP and CMCS-MICP was significantly reduced after optimal dosage treatment, to only 9.14% and 7.96% respectively.

[0073] The CMCS-EICP and CMCS-MICP treatments in Examples 1 and 2 not only significantly enhanced the tailings strength, but the increase also gradually increased with decreasing particle size, especially for finer-sized tailings. This advantage effectively overcomes the limitation of EICP and MICP treatments where the strength of fine-grained tailings decreases significantly with decreasing particle size.

[0074] (2) Quantitative analysis of CaCO3 formation rate using acid digestion method:

[0075] ① From the specimens that were destroyed after the UCS test, approximately 15g of samples were selected from the upper, middle and lower parts respectively;

[0076] ②Dry the sample to be tested at 65℃ for 12 hours;

[0077] ③ Place the sample in 1 mol / L dilute hydrochloric acid for 24 hours. After the bubble reaction stops, wash thoroughly with deionized water.

[0078] ④ Finally, dry the sample at 105℃ for 12 hours and weigh it.

[0079] The CaCO3 formation rate is calculated according to formula (1).

[0080]

[0081] In the formula: C is the CaCO3 formation rate (%); W1 is the weight of the soil sample before acid washing (g); W2 is the weight of the soil sample after acid washing (g).

[0082] The test results are shown in Figures 1(c) to 1(f) and 1(g) to 1(j), corresponding to the CaCO3 formation rate at different locations in the fine-grained tailings after CMCS-EICP and CMCS-MICP treatments, respectively. It can be observed that as the tailings particle size decreases, the CaCO3 formation rate of the samples treated with both CMCS-EICP and CMCS-MICP shows a significant decreasing trend. When the tailings particle size decreases from less than 100 mesh to greater than 200 mesh, the average CaCO3 formation rate of the samples treated with CMCS-EICP and CMCS-MICP decreases from 6.03% and 7.43% to 2.95% and 3.23%, respectively.

[0083] In Examples 1 and 2, the relatively uniform generation and distribution of CaCO3 in the CMCS-EICP and CMCS-MICP treated samples significantly reduced the formation of the brittle fracture layer, thereby significantly improving the overall strength and structural stability of the samples. Furthermore, compared to EICP and MICP treatments, when the CMCS content was 0.15% and 0.1%, respectively, the average CaCO3 formation rate of the four tailings sample sizes increased by 80.27%, 106.16%, 164.46%, and 225.42% (CMCS-EICP) and 96.50%, 131.65%, 186.04%, and 307.74% (CMCS-MICP), respectively.

[0084] (ii) Leaching test.

[0085] (1) Experimental Procedure: Fine-grained tailings samples of different particle sizes treated with CMCS-EICP and CMCS-MICP were added to deionized water at a solid-liquid ratio of 1:5 and leached continuously for 5 days at 25℃ and 150 r / min. The Cd concentration in the leachate of tailings samples of different particle sizes was determined by atomic absorption spectrophotometry (GB 7475-87). 2+ Pb 2+ Cu 2+ and Zn 2+ Horizontal. Mn 2+ and Ni 2+ The content was determined by flame atomic absorption spectrophotometer according to GB 11911-89 and GB 11912-89, respectively. The pH of the leachate was determined by electrode method according to HJ 1147-2020. The fixation rate of heavy metal ions in tailings of different particle sizes was calculated by formula (2).

[0086]

[0087] In the formula: F is the heavy metal ion fixation rate (%); l i The initial heavy metal ion leaching concentration (mg / L) of the original tailings; s The concentration of heavy metal ions leached from the tailings after biosolidification (mg / L).

[0088] (2) Test Results: As shown in Figures 2(a) to 2(b), after bio-solidification by CMCS-EICP and CMCS-MICP, the pH of the leachate from fine-grained tailings samples with mesh sizes smaller than 100 mesh, 100–150 mesh, 150–200 mesh, and larger than 200 mesh all showed a stable fluctuation trend. Specifically, the pH of the leachate from the samples treated with CMCS-EICP stabilized at 8.10–8.37, 7.99–8.33, 7.92–8.27, and 7.90–8.23, respectively; while the pH of the leachate from the samples treated with CMCS-MICP stabilized at 8.23–8.46, 8.15–8.38, 8.07–8.29, and 8.01–8.22, respectively.

[0089] The original fine-grained tailings, without treatment or screening, had a pH of 7.72, indicating a slightly alkaline pH. Overall, the pH values ​​of the leachate from the fine-grained tailings after CMCS-EICP and CMCS-MICP bio-solidification were significantly higher than those from the untreated original tailings, with CMCS-MICP showing a more pronounced effect on pH enhancement. Compared to the untreated original tailings, the pH values ​​of the leachate from tailings of different particle sizes treated with EICP and MICP remained stable at 7.76–7.82 and 7.80–7.93, respectively.

[0090] After bio-solidification using CMCS-EICP and CMCS-MICP, the pH values ​​of the leachate from tailings of different particle sizes stabilized at 7.90–8.37 and 8.01–8.46, respectively, meeting the Class I limits of the People's Republic of China's "Groundwater Quality Standard". The leachate maintained a stable weakly alkaline pH, which not only enhanced the efficiency of pollutant fixation but also effectively avoided the risk of secondary pollution to the surrounding environment caused by excessive alkalization.

[0091] Cd in untreated and unscreened raw fine tailings 2+ Pb 2+ Ni 2+ Cu 2+ Mn 2+ and Zn 2+The initial leaching concentrations were 0.0067 mg / L, 0.052 mg / L, 0.29 mg / L, 0.72 mg / L, 2.15 mg / L, and 0.51 mg / L, respectively. As shown in Figures 2(c) to 2(d) and Figures 2(i) to 2(k), after CMCS-EICP and CMCS-MICP treatments, the Cd concentrations in the leachate of fine-grained tailings of different particle sizes... 2+ and Pb 2+ The leaching concentration of all tailings decreased to 0 mg / L, and the fixation rate reached 100%, indicating that the difference in tailings particle size did not affect the Cd concentration in the leachate. 2+ and Pb 2+ The fixation rate has a significant impact. Furthermore, as shown in Figure 2(e), the Ni in the leachate... 2+ The fixation rate also reached 100% after CMCS-EICP and CMCS-MICP treatments, demonstrating the effectiveness of CMCS-EICP and CMCS-MICP treatments in reducing Cd in fine-grained tailings. 2+ Pb 2+ and Ni 2+ The fixed advantages of CMCS-EICP and CMCS-MICP treatments. However, the effects of CMCS-EICP and CMCS-MICP treatments on Cu in tailings leachate. 2+ Mn 2+ and Zn 2+ The fixation effect of Cu varies significantly across different particle sizes, and as the tailings particle size decreases, Cu... 2+ Mn 2+ and Zn 2+ The fixation rates all showed a decreasing trend. Specifically, the Cu content in the leachate of tailings with different particle sizes after CMCS-EICP treatment... 2+ Mn 2+ and Zn 2+ The fixation rates were stable at 85.16%–90.77%, 82.13%–88.96%, and 92.91%–96.33% respectively (Figure 2(f)–Figure 2(h)), while the rates after CMCS-MICP treatment were stable at 83.57%–92.17%, 80.94%–90.31%, and 89.32%–97.41% respectively (Figure 2(l)–Figure 2(n)).

[0092] (III) Microscopic testing.

[0093] (1) Experimental Procedure: Microscopic morphology analysis of tailings with different particle sizes before and after CMCS-EICP and CMCS-MICP treatments was performed using SEM. To improve the surface conductivity of fine-grained tailings samples, gold sputtering treatment was required. Transmittance was measured using FTIR with wavenumbers ranging from 400 to 4000 cm⁻¹. -1In addition, to reveal the mineral phase composition and evolution of fine-grained tailings of different particle sizes during the solidification process, XRD scanning analysis was performed at a rate of 2° / min, with a range of 10-80°.

[0094] (2) Test Results: As shown in Figure 3(a), the fine tailings particles, before treatment and screening, have smooth and flat surfaces, disordered particle distribution, and loose structure. After EICP and MICP treatment, obvious carbonate precipitation and aggregation occurred between tailings particles with a particle size of less than 100 mesh, resulting in the partial filling of a large number of pores between the loose fine tailings particles (Figure 3(b) and Figure 3(d)). In contrast, the amount of CaCO3 precipitation in tailings samples with a particle size greater than 200 mesh was significantly less. This indicates that when the particle size of fine tailings is too small, although the pore size between the particles is smaller and the distribution is denser, the permeability is limited. The narrow pore structure is not conducive to the penetration and diffusion of EICP and MICP mineralization solutions and calcium-containing cementing solutions between tailings particles, thus hindering the formation of carbonate crystals during biomineralization (Figure 3(c) and Figure 3(e)).

[0095] As can be seen from Figures 3(f) to 3(i), when the CMCS dosage is 0.15% and 0.1%, respectively, the pore structure between the fine tailings particles after CMCS-EICP and CMCS-MICP treatment is significantly filled and cemented.

[0096] Figure 4(a) and Figure 4(b) show the FTIR spectral characteristics of fine-grained tailings of different particle sizes after treatment with CMCS-EICP and CMCS-MICP under optimal CMCS dosage conditions (0.15% and 0.1%). (1437 cm⁻¹) -1 The nearby wavelengths reflect CO3 2- The symmetrical stretching vibration. After the addition of CMCS, the peak intensity of tailings samples of different particle sizes at this location was significantly enhanced compared with those treated by EICP and MICP, and the degree of enhancement was significantly affected by the tailings particle size; among them, the peak intensity of tailings samples with a particle size of less than 100 mesh was the highest in this band, while the peak intensity of tailings samples with a particle size of more than 200 mesh showed the largest increase, indicating the potential of CMCS to improve urease activity and induce the combination of carbonate and heavy metal ions to form heavy metal carbonate precipitates during biomineralization. At the same time, 881 cm -1 The characteristic peaks of fine tailings with different particle sizes correspond to CO3 in CaCO3. 2- Out-of-plane vibration.

[0097] The XRD patterns and mineral content ratios of fine tailings of different particle sizes treated with CMCS-EICP and CMCS-MICP under the optimal CMCS dosage conditions (0.15% and 0.1%) are shown in Figure 4(c). The XRD patterns and mineral content ratios of fine tailings of different particle sizes treated with CMCS-EICP and CMCS-MICP under the optimal CMCS dosage conditions (0.15% and 0.1%) are shown in Figure 4(c) to Figure 4(f).

[0098] The phase composition of fine-grained tailings of different particle sizes remained relatively stable after CMCS-EICP and CMCS-MICP treatments. Observations revealed that the diffraction peaks of calcite crystals in the XRD patterns of fine-grained tailings of different particle sizes treated with CMCS-EICP appeared at 2θ = 29.62°, 35.99°, 47.32°, and 48.33°, respectively, while those treated with CMCS-MICP appeared at 2θ = 29.51°, 36.31°, 47.20°, and 48.57°. Comparison showed no significant difference in the diffraction peak positions of calcite crystals after CMCS-EICP and CMCS-MICP treatments, further demonstrating the broad applicability of CMCS in EICP and MICP treatments. Quantitative analysis of the XRD results of tailings samples of different particle sizes revealed that the calcite content in untreated fine-grained tailings was only 1.9%. In contrast, the calcite content of tailings samples with a particle size of less than 100 mesh after EICP and MICP treatment was 7.2% and 7.7%, respectively, while that of tailings samples with a particle size of more than 200 mesh was only 4.1% and 3.8%, respectively.

[0099] Therefore, the present invention adopts the above-mentioned method of carboxymethyl chitosan-mediated biomineralization solidification of fine tailings of different particle sizes. Under the CMCS-mediated action, the biomineralization reaction rate and mineral precipitation morphology are optimized, while the mechanical stability of the overall solidification system and the solidification ability of heavy metal pollutants are also significantly enhanced. This provides a new approach to solving the problem of the limitation of traditional biomineralization reaction in tailings solidification due to the difference in fine tailings particle size.

[0100] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for biomineralizing and solidifying fine-grained tailings of different particle sizes mediated by carboxymethyl chitosan, characterized in that, Includes the following steps: Step S1: Pre-treat the fine-grained tailings; after drying, the fine-grained tailings are sieved to obtain tailings particles with diameters less than 100 mesh, 100-150 mesh, 150-200 mesh, and greater than 200 mesh. Step S2: Carboxymethyl chitosan is uniformly incorporated into the tailings particles obtained in Step S1 at a mass ratio of 0.05% to 0.2%, and cylindrical samples are obtained by layered filling combined with mechanical vibration. Step S3: Prepare enzyme-induced carbonate precipitation solution and microbial-induced carbonate precipitation solution. Step S4: Using a saturated bidirectional continuous grouting method, the enzyme-induced carbonate precipitation solution and microbial-induced carbonate precipitation solution prepared in Step S3 are injected into the cylindrical samples obtained in Step S2, and then allowed to stand. Step S5: Repeat Step S4 2-4 times, rinse with distilled water, and then cure and dry to complete the solidification.

2. The method for carboxymethyl chitosan-mediated biomineralization and solidification of fine tailings of different particle sizes according to claim 1, characterized in that: In step S1, the drying temperature is 100-110℃ and the drying time is 70-74h.

3. The method for carboxymethyl chitosan-mediated biomineralization and solidification of fine tailings of different particle sizes according to claim 1, characterized in that: In step S2, the degree of carboxymethyl substitution of carboxymethyl chitosan is ≥85%, and the degree of deacetylation is ≥90%; the frequency of mechanical vibration is 30-40Hz, and the intensity of mechanical vibration is 15%-25%; when using the layered filling method, the tailings are shallowly grazed after each layer is filled.

4. The method for carboxymethyl chitosan-mediated biomineralization and solidification of fine tailings of different particle sizes according to claim 1, characterized in that: Step S3 specifically comprises: Step S31, preparing a plant-derived urease solution; grinding soybeans washed with distilled water into powder, mixing with deionized water at a solid-liquid ratio of 1:8 to 1:12, stirring to obtain a suspension; centrifuging the suspension at 3000 to 4000 r / min for 30 to 40 min at 4°C, and collecting the supernatant, which is the plant-derived urease solution; Step S32, preparing Bacillus pasteurellium bacterial culture; inoculating Bacillus pasteurellium into Luria–Bertan under aseptic conditions. In culture medium i, Bacillus pasteurellii culture is obtained by culturing at 30℃ and 100-150 r / min for 70-74 h; Step S33: Prepare the cementing solution; Mix urea and calcium acetate at a volume ratio of 1:1 to obtain the cementing solution; Step S34: Mix plant-derived urease solution with the cementing solution at a volume ratio of 1:1 to obtain the enzyme-induced carbonate precipitation solution; Mix Bacillus pasteurellii culture with the cementing solution at a volume ratio of 1:1 to obtain the microbial-induced carbonate precipitation solution.

5. The method for carboxymethyl chitosan-mediated biomineralization and solidification of fine tailings of different particle sizes according to claim 4, characterized in that: In step S31, the stirring speed is 900-1100 r / min and the stirring time is 25-35 min.

6. The method for carboxymethyl chitosan-mediated biomineralization and solidification of fine tailings of different particle sizes according to claim 4, characterized in that: In step S32, the OD in the Bacillus pasteurellium culture 600 =1.0~1.5; In step S32, the molar concentrations of urea and calcium acetate are both 0.6~1.0mol / L.

7. The method for carboxymethyl chitosan-mediated biomineralization and solidification of fine tailings of different particle sizes according to claim 1, characterized in that: In step S4, the injection volume of both enzyme-induced carbonate precipitation solution and microbial-induced carbonate precipitation solution is equal to the pore volume of the tailings particles, the injection rate in each direction is 1-3 mL / min, and the settling time is 10-14 h.

8. The method for carboxymethyl chitosan-mediated biomineralization and solidification of fine tailings of different particle sizes according to claim 1, characterized in that: In step S5, the distilled water rinsing time is 0.3 to 0.7 hours, and the distilled water rinsing rate is the same as the grouting rate in step S4.

9. The method for carboxymethyl chitosan-mediated biomineralization and solidification of fine tailings of different particle sizes according to claim 1, characterized in that: In step S5, the curing temperature is 20-30℃ and the curing time is 5-9 days; the drying temperature is 100-110℃ and the drying time is 12-36 hours.

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