Calcium and magnesium induced organic intercalation-microbial reduction synergistic thallium solidifying method

Abstract

The invention discloses a calcium and magnesium induced organic intercalation-microbial reduction synergistic thallium solidification method, and relates to the technical field of heavy metal contaminated soil remediation, the method comprises the following steps: applying clay minerals and an organic molecule solution to thallium contaminated soil, ploughing and uniformly mixing, adjusting the water content of the soil, after balancing, shewanella putrefaciens is inoculated in an anaerobic environment and cultured, and thallium immobilization is completed. According to the method provided by the invention, the natural induction effect of soil background calcium and magnesium ions in the karst area is utilized to drive organic molecules to be embedded into clay mineral layers in situ, then reduction of the structure Fe (III) is mediated through microorganisms, stable immobilization of thallium is realized, and the problems that the aging thallium immobilization efficiency of natural clay minerals in soil is low and the thallium immobilization efficiency is low are effectively solved. The problems of high cost and unstable effect caused by dependence on high-valence complex minerals and exogenous addition of calcium and magnesium salts in the prior art are solved.

Description

Technical Field

[0001] This invention relates to the field of heavy metal contaminated soil remediation technology, specifically to a method for calcium-magnesium induced organic intercalation-microbial reduction synergistic thallium fixation. Background Technology

[0002] Thallium (Tl), a highly toxic and carcinogenic heavy metal, is easily absorbed by crops and leached by groundwater in karst soils, posing a serious threat to the ecological environment and human health. Although clay minerals naturally exist in karst soils, these minerals are generally in an aged state: the interlayer is occupied by impurities such as calcium carbonate and humic debris, resulting in a small specific surface area and extremely low Fe(III) activity, making it difficult for them to form stable bonds with heavy metals.

[0003] Existing soil thallium pollution remediation technologies have significant limitations: some technologies use modified clay minerals, requiring the separate preparation of composite minerals, which is costly and complex; others add exogenous calcium and magnesium salts, which conflict with the high calcium and magnesium background characteristics of karst soils, resulting in unstable intercalation effects. There are no reports on synergistic thallium fixation technologies that utilize exogenous clay minerals combined with soil background calcium and magnesium-induced organic intercalation and microbial reduction. Therefore, developing targeted, low-cost, and efficient thallium fixation methods is of significant practical importance. Summary of the Invention

[0004] To address the aforementioned shortcomings in existing technologies, this invention provides a method for synergistic thallium fixation through calcium-magnesium induced organic intercalation and microbial reduction. This method effectively solves the problems of low thallium fixation efficiency due to the aging of natural clay minerals in soil, and the high cost and unstable effectiveness of existing technologies due to reliance on high-priced composite minerals and the addition of exogenous calcium and magnesium salts.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A method for synergistic thallium fixation via calcium-magnesium induced organic intercalation and microbial reduction, comprising the following steps: S1. Apply a solution of clay minerals and organic molecules to the thallium-contaminated soil and till it to mix it evenly. S2. Adjust the soil moisture content, and after balancing, inoculate with Shewanella putrefactive bacteria for culture to complete the immobilization of thallium.

[0006] Furthermore, in step S1, the contaminated soil is thallium-contaminated soil from a karst area.

[0007] Furthermore, in step S1, the thallium content in the thallium-contaminated soil in the karst area is 1-50 mg / kg.

[0008] Furthermore, the thallium-contaminated soil in the karst area is thallium-contaminated soil exceeding the thallium risk screening value limit stipulated in the "Sichuan Province Construction Land Soil Pollution Risk Control Standard (DB51 / 2978-2023)".

[0009] Furthermore, in step S1, the clay mineral is montmorillonite or chlorometholite.

[0010] The advantages of adopting the above-mentioned further solutions are: low cost and good soil compatibility. Utilizing soil background Ca... 2+ / Mg 2+ Inducing organic molecule intercalation and synergistic microbial reduction to achieve thallium retention.

[0011] Furthermore, in step S1, montmorillonite and chlorometholite are passed through a 200-mesh sieve.

[0012] Furthermore, in step S1, montmorillonite and chlorometholite are washed with deionized water and then vacuum dried and activated.

[0013] The beneficial effects of taking the above-mentioned further measures are: removal of surface impurities and lattice defects.

[0014] Furthermore, in step S1, the organic molecule solution is oxalic acid or humic acid.

[0015] Furthermore, in step S1, the application rate of montmorillonite and chlorometholite is 0.5-5% of the dry weight of the soil.

[0016] Furthermore, in step S1, the concentration of the organic molecule solution is 5-30 mg / L.

[0017] Furthermore, in step S1, the concentration of the organic molecule solution is 20 mg / L.

[0018] Furthermore, in step S1, the mixture is thoroughly mixed by tilling, with a tilling depth of 0-20 cm.

[0019] The beneficial effects of adopting the above-mentioned further measures are: to reduce the soil background Ca... 2+ / Mg 2+ Cation exchange between mineral layers drives the intercalation of organic molecules, forming an intercalation complex system. Furthermore, in step S2, the moisture content is adjusted to 60-80% of the saturated water holding capacity.

[0020] Furthermore, in step S2, equilibration is carried out for 24-48 hours.

[0021] Furthermore, in step S2, the concentration of Shewanella putrefactive in the soil is 1×10⁻⁶. 8 Cells / mL, cultured in an anaerobic environment.

[0022] The beneficial effects of adopting the above-mentioned further scheme are: no external electron donor is required, carbon source metabolism can be utilized from soil and intercalated organic molecules, and it has strong adaptability in high calcium and magnesium environments.

[0023] Furthermore, in step S2, in the laboratory, the anaerobic environment is achieved by sealing culture bottles; on-site, the anaerobic environment is achieved by covering the edges of a double-layer PE film and compacting them.

[0024] Furthermore, in step S2, the culture time is 7-30 days and the culture temperature is 20-35 ℃.

[0025] Furthermore, in step S2, the culture time is 7-14 days and the culture temperature is 25-30 ℃.

[0026] In summary, the present invention has the following beneficial effects: 1. This invention utilizes the natural induction effect of background calcium and magnesium ions in karst soil to drive organic molecules to embed in situ between clay mineral layers, and then achieves stable retention of thallium through microbial-mediated reduction of its Fe(III) structure.

[0027] 2. This invention does not require the separate preparation of composite minerals, nor does it require the addition of calcium and magnesium reagents or external electron donors. It is low in cost, highly targeted, and has a significant thallium fixation efficiency. It is suitable for the ecological restoration of polluted farmland and diffusely polluted soil in karst mining areas. Attached Figure Description

[0028] Figure 1 The image shows the leaching results of thallium during the reduction of Fe(III) with oxalic acid-montmorillonite calcium magnesium ion exchange structure. Figure 2 The diagram shows the changes in functional groups during the reduction of Fe(III) in the calcium-magnesium ion-exchange structure of oxalic acid-montmorillonite. Figure 3 The graph shows the change in specific surface area during the reduction of Fe(III) with oxalate-montmorillonite calcium-magnesium ion exchange structure. Figure 4 The diagram shows the pore volume change during the reduction of Fe(III) in the oxalate-montmorillonite calcium-magnesium ion-exchange structure. Figure 5 The graph shows the redox potential changes during the reduction of Fe(III) in the oxalate-montmorillonite calcium-magnesium ion-exchange structure. Figure 6 The graph shows the change in conductivity during the reduction of Fe(III) with oxalate-montmorillonite calcium-magnesium ion-exchange structure. Figure 7 Three-dimensional fluorescence spectrum of the solution after reduction of Fe(III) in oxalate-montmorillon calcium-magnesium ion exchange structure; Figure 8 The image shows the leaching results of thallium during the reduction of Fe(III) by humic acid-montmorillonite calcium-magnesium ion exchange structure. Figure 9The graph shows the changes in redox potential during the reduction of Fe(III) in the humic acid-montmorillonite calcium-magnesium ion exchange structure. Figure 10 The graph shows the change in conductivity during the reduction of Fe(III) in the humic acid-montmorillonite calcium-magnesium ion-exchange structure. Figure 11 The diagram shows the changes in functional groups during the reduction of Fe(III) in the humic acid-montmorillonite calcium-magnesium ion exchange structure. Figure 12 The graph shows the change in specific surface area during the reduction of Fe(III) in the humic acid-montmorillonite calcium-magnesium ion exchange structure. Figure 13 The diagram shows the pore volume change during the reduction of Fe(III) in the humic acid-montmorillonite calcium-magnesium ion exchange structure. Figure 14 Three-dimensional fluorescence spectrum of solution after Fe(III) reduction of humic acid-montmorillonite calcium-magnesium ion exchange structure; Figure 15 The image shows the leaching results of thallium during the reduction of Fe(III) with calcium magnesium ion exchange structure in oxalate-green trastochastic. Figure 16 The diagram shows the changes in functional groups during the reduction of Fe(III) in the calcium-magnesium ion-exchange structure of oxalic acid-green oxidase. Figure 17 The graph shows the change in specific surface area during the reduction of Fe(III) with calcium-magnesium ion exchange structure in oxalate-green trastite. Figure 18 The diagram shows the pore volume change during the reduction of Fe(III) in the calcium-magnesium ion-exchange structure of oxalate-green trast. Figure 19 The graph shows the changes in redox potential during the reduction of Fe(III) in the calcium-magnesium ion-exchange structure of oxalate-green trast. Figure 20 The graph shows the change in conductivity during the reduction of Fe(III) with calcium-magnesium ion-exchange structure in oxalate-green trast. Figure 21 Three-dimensional fluorescence spectrum of the solution after reduction of Fe(III) in the calcium-magnesium ion exchange structure of oxalate-green trast. Figure 22 The image shows the leaching results of thallium during the reduction of Fe(III) by the calcium-magnesium ion exchange structure of humic acid-green diatomite. Figure 23 The diagram shows the changes in functional groups during the reduction of Fe(III) in the calcium-magnesium ion-exchange structure of humic acid-green diatomite. Figure 24 The graph shows the change in specific surface area during the reduction of Fe(III) in the calcium-magnesium ion exchange structure of humic acid-green diatomite. Figure 25 The diagram shows the pore volume change during the reduction of Fe(III) in the calcium-magnesium ion exchange structure of humic acid-green diatomite. Figure 26 The graph shows the changes in redox potential during the reduction of Fe(III) in the calcium-magnesium ion exchange structure of humic acid-green trastite. Figure 27 The graph shows the change in conductivity during the reduction of Fe(III) in the calcium-magnesium ion-exchange structure of humic acid-green diatomite. Figure 28 The three-dimensional fluorescence spectrum of the solution after Fe(III) reduction of the calcium-magnesium ion exchange structure of humic acid-green oxidase is shown. Detailed Implementation

[0029] The principles and features of this invention are described below. The examples given are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer should be followed. Reagents or instruments used, unless otherwise specified, are all commercially available products.

[0030] Example 1 A method for calcium-magnesium induced organic intercalation-microbial reduction synergistic thallium fixation includes the following steps: S1. Apply montmorillonite and oxalic acid solution to thallium-contaminated soil in karst areas. The thallium content in the thallium-contaminated soil in karst areas is 50 mg / kg. Montmorillonite and chlorotoluene are passed through a 200-mesh sieve, washed with deionized water, and vacuum dried and activated. The application rate of montmorillonite is 2% of the dry weight of the soil, and the concentration of oxalic acid solution is 20 mg / L. Mix evenly by tilling to a depth of 20 cm. S2. Adjust the soil moisture content to 70% of saturated water holding capacity, equilibrate for 36 h, and then inoculate with Shewanella putrefactive bacteria for cultivation. The concentration of Shewanella putrefactive bacteria in the soil is 1×10⁻⁶. 8 The concentration of thallium was measured at 10 cells / mL, and the culture time was 10 days at a temperature of 25 °C to complete the immobilization of thallium.

[0031] Example 2 A method for calcium-magnesium induced organic intercalation-microbial reduction synergistic thallium fixation includes the following steps: S1. Apply montmorillonite and humic acid solution to thallium-contaminated soil in karst areas. The thallium content in the thallium-contaminated soil in karst areas is not higher than 50 mg / kg. The montmorillonite is passed through a 200-mesh sieve, washed with deionized water, and vacuum dried and activated. The application rate of montmorillonite is 2% of the dry weight of the soil, and the concentration of the humic acid solution is 20 mg / L. Mix evenly by tilling to a depth of 20 cm. S2. Adjust the soil moisture content to 75% of saturated water holding capacity, equilibrate for 48 h, and then inoculate with Shewanella putrefactive bacteria for cultivation. The concentration of Shewanella putrefactive bacteria in the soil is 1×10⁻⁶. 8 The concentration of thallium was increased to 10000 cells / mL, and the culture time was 30 days at a temperature of 25 °C to complete the immobilization of thallium.

[0032] Example 3 A method for calcium-magnesium induced organic intercalation-microbial reduction synergistic thallium fixation includes the following steps: S1. Apply chlorite and oxalic acid solution to thallium-contaminated soil in karst areas. The thallium content in the thallium-contaminated soil in karst areas is 50 mg / kg. The chlorite is passed through a 200-mesh sieve, washed with deionized water, and vacuum dried and activated. The application rate of chlorite is 2% of the dry weight of the soil, and the concentration of the oxalic acid solution is 20 mg / L. Mix the chlorite evenly by tilling to a depth of 20 cm. S2. Adjust the soil moisture content to 70% of saturated water holding capacity, equilibrate for 36 h, and then inoculate with Shewanella putrefactive bacteria for cultivation. The concentration of Shewanella putrefactive bacteria in the soil is 1×10⁻⁶. 8 The concentration of thallium was increased to 10 ...

[0033] Example 4 A method for calcium-magnesium induced organic intercalation-microbial reduction synergistic thallium fixation includes the following steps: S1. Apply chlorite and humic acid solution to thallium-contaminated soil in karst areas. The thallium content in the thallium-contaminated soil in karst areas is 50 mg / kg. The chlorite is passed through a 200-mesh sieve, washed with deionized water, and vacuum dried and activated. The application rate of chlorite is 2% of the dry weight of the soil, and the concentration of the humic acid solution is 20 mg / L. Mix the chlorite evenly by tilling to a depth of 20 cm. S2. Adjust the soil moisture content to 75% of saturated water holding capacity, equilibrate for 48 h, and then inoculate with Shewanella putrefactive bacteria for cultivation. The concentration of Shewanella putrefactive bacteria in the soil is 1×10⁻⁶. 8 The concentration of thallium was increased to 10 ...

[0034] Solidification effect of thallium in Experimental Example 1 and Example 1 (1) Montmorillonite clay minerals were ground through a 200-mesh screen, pretreated, and modified by ion exchange and organic intercalation to obtain organic molecularly intercalated clay minerals. Thallium adsorption experiments were then conducted until adsorption saturation. The clay minerals after thallium adsorption were used in subsequent anaerobic reduction experiments. Different culture durations and multiple control groups were set up, with parallel samples in each group. Samples were taken after the corresponding culture duration to analyze the dynamic changes of thallium dissolution over time in different treatment groups. The control group consisted of: natural montmorillonite, without CN32 strain, and only sodium lactate (CK group); oxalic acid-montmorillonite synergistic thallium fixation: calcium and magnesium ions drove oxalic acid intercalation in the clay minerals, with CN32 strain added, but without sodium lactate in the anaerobic reduction experiment; each independent culture system of all treatment groups had 3 parallel samples, and the experimental data were averaged. The dynamic changes of thallium (Tl) dissolution over time in different treatment groups are as follows: Figure 1 As shown, 1, 2, 4, and 7 represent the 1st, 2nd, 4th, and 7th days of the experiment, respectively.

[0035] Depend on Figure 1 It can be seen that the Tl dissolution in the control group showed a slow decreasing trend from day 1 to day 7 of the experimental period, indicating that the natural retention effect of the solid medium on Tl was weak and the process was gradual when no oxalic acid intervention was applied. In contrast, the Tl dissolution in the oxalic acid-treated group remained at a relatively stable level for the first 4 days of the experiment, with fluctuations ranging from 0.5 to 0.6 mg·L⁻¹. -1 However, a significant decrease occurred on day 7, with a dissolution rate of only 0.3 mg·L⁻¹. -1 The value was around [value missing], representing the lowest value throughout the entire experimental period, and its decrease was significantly greater than that of the control group. This result indicates that the immobilization effect of oxalic acid on Tl is time-dependent. With prolonged reaction time, the immobilization effect of oxalic acid on Tl is significantly enhanced in the later stages of the experiment, effectively inhibiting the dissolution of Tl from the solid phase to the liquid phase, leading to a substantial reduction in its dissolution amount. Simultaneously, [details missing]. Figure 1 Ferrous ions (Fe) in the oxalic acid treatment group 2+ According to the leaching data, Fe 2+ The dissolution rate showed a significant upward trend on day 7, exceeding the level of the control group at the same time point. This suggests a possible negative correlation between the reduction and dissolution process of structural iron in the solid medium and the retention behavior of Tl. When the reduction reaction in the oxalic acid-treated group progressed to day 7, the Fe... 2+ With the continuous accumulation of dissolution, the migration ability of Tl is inhibited to a certain extent.

[0036] (2) Infrared spectroscopy analysis: Weigh an appropriate amount of clay minerals that have been removed from the anaerobic chamber and dried, and collect samples at 400-4000 cm⁻¹ using the KBr pellet method (1:150) with a Fourier transform infrared spectrometer (Tianjin Gangdong, FTIR-850). -1Infrared Fourier transform spectra within the wavenumber range, scanned 20 times, functional group infrared spectra results are as follows: Figure 2 As shown.

[0037] Depend on Figure 2 It can be seen that on the 7th day of the reduction reaction, the intensity of the characteristic functional group absorption peak of the oxalic acid treatment group continued to increase. This indicates that the siloxane polymerization reaction, the hydroxyl generation process and the chelation of oxalate and metal ions in the system formed a synergistic strengthening effect. Moreover, this synergistic effect gradually accumulated with the reaction time, and finally formed a stable solid Tl composite structure on the 7th day, providing structural support for the long-term fixation of Tl.

[0038] (3) Specific surface area and pore volume determination: Clay mineral samples were taken 7 days after reduction and measured using a specific surface area and pore volume analyzer (Beijing Bestech, 3H-2000PS4 model). The results are as follows: Figure 3 As shown, the pore volume change results are as follows: Figure 4 As shown.

[0039] Depend on Figure 3 and Figure 4 It is evident that oxalic acid treatment significantly increases the specific surface area of ​​the solid medium, and optimizes and expands its surface pore structure. The increase in specific surface area and pore size directly increases the number of adsorption active sites on the medium surface, enhancing the medium's physical and chemical adsorption capacity for Tl ions. This allows Tl ions to be more firmly adsorbed onto the solid surface, further inhibiting their migration and release into the surrounding environment.

[0040] (4) Physicochemical properties of the solution and determination of total Fe(II) concentration during reduction: During the reduction process, the pH, conductivity (EC), and redox potential (Eh) of the solution were all determined by potentiometry. The determination of total Fe(II) concentration was performed as follows: First, the mineral suspension was transferred to hydrochloric acid solution and allowed to stand for about 6 hours. Then, the supernatant was obtained by centrifugation, and the concentration of ferrous iron in the supernatant was determined by o-phenanthroline spectrophotometry. All experiments were conducted in triplicate, and the final results were averaged. The redox potential changes during the reduction of Fe(III) in the oxalate-montmorillonite calcium-magnesium ion exchange structure were as follows. Figure 5 As shown, the conductivity changes as follows Figure 6 As shown.

[0041] Depend on Figure 5 and Figure 6It is evident that in the synergistic system of microorganisms and oxalic acid, microorganisms reduce the concentration of competing ions in the solution through metabolic activities and maintain a reducing environment. This optimized microenvironment provides favorable conditions for Tl fixation. Under this environment, Tl more readily combines with anions in the system to form insoluble salt compounds, which are stably immobilized in the solid medium. Ultimately, this achieves effective regulation of Tl mobility and bioavailability, providing a theoretical basis and technical support for the remediation of soil Tl pollution.

[0042] (5) Three-dimensional fluorescence spectroscopy (EEM) analysis was performed using a fluorescence spectrophotometer (HITACHI F-7000, Japan). First, 15 mL of the filtrate filtered through 0.45 μm was placed in a 20 mL centrifuge tube. Then, the filtrate was added to a rinsed 1 cm quartz cuvette. The excitation and emission wavelength ranges were both set to 200–800 nm, with a scanning interval of 5 nm. The three-dimensional fluorescence spectrum of the blank ultrapure water sample was subtracted during the three-dimensional fluorescence spectroscopy analysis. Raman normalization was used to eliminate the influence of Raman scattering, and parallel factor analysis (PARAFAC) was used to determine the composition of the DOC fluorescent components. The three-dimensional fluorescence spectrum of the Fe(III) reduction solution after the oxalic acid-montmorillonite calcium-magnesium ion exchange structure is shown in the figure. Figure 7 As shown. Figure 7 In the image, the left image shows the three-dimensional fluorescence spectrum of the control group, and the right image shows the three-dimensional fluorescence spectrum of the oxalic acid-treated group.

[0043] Depend on Figure 7 It was observed that a weak humic acid-like fluorescence signal was present only in the long emission wavelength region (>500 nm), while no obvious characteristic peaks were observed in the short wavelength region (<500 nm). In contrast, the oxalic acid-treated group exhibited significant protein / fulvic acid-like fluorescence peaks in the excitation wavelength region of 250-300 nm and the emission wavelength region of 300-400 nm, with significantly higher fluorescence intensity than the control group. The addition of oxalic acid induced the depolymerization and reconstruction of DOM, releasing active components such as proteins and small-molecule organic acids (corresponding to the newly added fluorescence peaks). The carboxyl and amino functional groups of these components can form stable complexes with Tl, while oxalate ions also combine with Tl to form insoluble thallium oxalate precipitate, directly reducing the solubility of Tl.

[0044] In summary, the fixation effect of acid on thallium (Tl) in solid media is time-dependent, with the fixation effect significantly enhanced in the later stages, effectively inhibiting Tl dissolution; Fe 2+ There may be a negative correlation between dissolution amount and Tl retention behavior. Oxalic acid treatment can optimize the pore structure of the medium, enhance adsorption capacity, promote DOM depolymerization and release of active components, and, combined with the synergistic effect of microorganisms, achieve stable Tl retention through complexation, precipitation and other processes, providing theoretical and technical support for soil Tl pollution remediation.

[0045] Solidification effect of thallium in Experimental Example 2 and Example 2 Montmorillonite clay minerals were ground through a 200-mesh sieve, pretreated, and modified by ion exchange and organic intercalation to obtain organically intercalated clay minerals. Thallium adsorption experiments were then conducted until adsorption saturation. The thallium-adsorbed clay minerals were used in subsequent anaerobic reduction experiments. Different culture durations and multiple control groups were set up, with parallel samples in each group. Samples were taken after the corresponding culture durations to analyze the dynamic changes in thallium leaching over time in different treatment groups. The control groups included: natural montmorillonite, without CN32 strain, and only sodium lactate (CK group); and humic acid-montmorillonite synergistic thallium fixation: calcium and magnesium ions drove humic acid intercalation in the clay minerals, with CN32 strain and sodium lactate added simultaneously in the anaerobic reduction experiment. Each independent culture system in all treatment groups had three parallel samples. Experimental data are presented as averages. The thallium leaching results during the reduction of Fe(III) by the humic acid-montmorillonite calcium-magnesium ion exchange structure in Example 2 are shown below. Figure 8 As shown.

[0046] Depend on Figure 8 It can be seen that the dissolution amount of thallium (Tl) exhibits a significant dynamic change trend over time. The Tl dissolution amount in the humic acid treatment group was significantly higher than that in the control group on day 1 of the experiment, with a peak value reaching approximately 0.9 mg·L⁻¹. -1 Subsequently, the Tl dissolution rate in this group showed a continuous decreasing trend, dropping to approximately 0.3 mg·L⁻¹ by day 7 of the experiment. -1 Furthermore, the Tl dissolution level was significantly lower than that of the control group during the same period, indicating that humic acid has a late-stage inhibitory effect on the dissolution of Tl.

[0047] (2) Changes in redox potential during the reduction of Fe(III) in the humic acid-montmorillonite calcium-magnesium ion exchange structure are as follows: Figure 9 As shown, the conductivity change during the reduction of Fe(III) in the humic acid-montmorillonite calcium-magnesium ion-exchange structure is as follows: Figure 10 As shown, the experimental method is the same as in Example 1.

[0048] Depend on Figure 9 and Figure 10 It can be seen that under the condition of sodium lactate as both an electron donor and a carbon source, the metabolic activity of microorganisms in the system is significantly activated, thereby constructing a microenvironment characterized by high-intensity reduction, accompanied by a significant increase in the system's conductivity. Ferrous ions (Fe...) 2+ The dissolution pattern of ) further corroborates the formation of this microenvironment: on the 7th day of the experiment, the Fe in the humic acid-treated group 2+ The dissolution rate reached approximately 0.4 mg·L⁻¹. -1 The control group Fe 2+ The dissolution rate was almost 0 mg·L -1The above results indicate that there may be a negative correlation between the reductive dissolution process of structural iron and the retention behavior of Tl in the system. That is, the reductive dissolution of structural iron may promote the migration and transformation of Tl from the liquid phase to the solid phase, thereby reducing its dissolution amount.

[0049] (3) The functional group changes during the reduction of Fe(III) in the humic acid-montmorillonite calcium-magnesium ion exchange structure are as follows: Figure 11 As shown, the experimental method is the same as in Example 1.

[0050] Depend on Figure 11 It is known that the humic acid molecule is rich in active functional groups such as hydroxyl groups (-OH). Fourier transform infrared spectroscopy analysis shows that by day 7 of the experiment (the stable stage of the reduction reaction), the characteristic peak intensity of the hydroxyl functional group in the humic acid-treated group significantly increased. The hydroxyl functional group can serve as a coordination site and interact with Tl. + / Tl 3+ The formation of stable complexes promotes the transformation of water-soluble Tl from the liquid phase to the solid-bound state, thereby fundamentally inhibiting the dissolution and release of Tl.

[0051] (4) The change in specific surface area during the reduction of Fe(III) in the humic acid-montmorillonite calcium-magnesium ion exchange structure is as follows: Figure 12 As shown, the change in pore volume is as follows Figure 13 As shown, the experimental method is the same as in Example 1.

[0052] Depend on Figure 12 and Figure 13 It can be seen that after humic acid treatment, the specific surface area of ​​the medium did not change significantly, but the pore volume showed a significant increasing trend. The expansion of the pore size unblocked the previously clogged mesoporous channels, exposing not only more hydroxyl functional groups on the medium surface but also releasing a large number of active surface sites. These exposed functional groups and surface sites can specifically adsorb and fix Tl through surface complexation and ion exchange, further enhancing the Tl retention effect of humic acid and synergistically reducing its environmental migration risk. Under reducing conditions, the surface negative charge of clay minerals and humic acid increases, which is beneficial for Tl... + The adsorption capacity is improved.

[0053] (5) The three-dimensional fluorescence spectrum of the solution after Fe(III) reduction of the humic acid-montmorillonite calcium-magnesium ion exchange structure is shown in the figure. Figure 14 As shown, the left figure is the result of the control group, and the right figure is the result of the humic acid treatment group. The experimental method is the same as in Example 1.

[0054] Depend on Figure 14It can be seen that in the three-dimensional fluorescence spectrum, the control group showed a weak fluorescence signal only in the excitation / emission wavelength (Ex / Em) region of approximately 250-350 nm / 300-500 nm. The humic acid-treated group showed a significantly enhanced fluorescence signal, with obvious fluorescence peaks in the Ex / Em = 250-350 nm / 300-500 nm region, and new fluorescence signals also appeared in the longer wavelength region (Ex / Em > 350 nm / 400 nm), indicating that humic acid introduced more hydroxyl functional groups.

[0055] The results showed that humic acid had a late-stage inhibitory effect on Tl dissolution; the Tl dissolution amount in the treated group was initially high and then decreased, significantly lower than that in the control group on day 7. The hydroxyl functional groups of humic acid can form stable complexes with Tl. Although the treatment did not significantly change the specific surface area of ​​the medium, it increased the pore volume, exposed more active sites, and synergistically enhanced Tl adsorption and fixation by changes in the reducing environment and ionic strength, thus reducing its migration risk.

[0056] Solidification effect of thallium in Experimental Example 3 and Example 3 (1) Green silica clay minerals were ground through a 200-mesh screen, pretreated, and modified by ion exchange and organic intercalation to obtain organic molecular intercalated clay minerals. Thallium adsorption experiments were then conducted until adsorption saturation. The clay minerals after thallium adsorption were used in subsequent anaerobic reduction experiments. Different culture durations and multiple control groups were set up, with parallel samples in each group. Samples were taken after culture for the corresponding duration to analyze the dynamic changes in thallium leaching over time in different treatment groups. The control group consisted of: natural green silica, without CN32 strain, and only sodium lactate added (CK group); humic acid-green silica synergistic thallium fixation: calcium and magnesium ions drove oxalic acid intercalation in the clay minerals, with CN32 strain added and sodium lactate added simultaneously in the anaerobic reduction experiment; each independent culture system of all treatment groups had 3 parallel samples, and the experimental data were averaged. The thallium leaching results during the reduction of Fe(III) by the oxalic acid-green silica calcium-magnesium ion exchange structure in Example 3 are as follows: Figure 15 As shown.

[0057] Depend on Figure 15 It can be seen that the dissolution amount of thallium (Tl) exhibits a significant dynamic change trend over time. In the control group, the overall dissolution rate shows a slow decreasing trend. The dissolution amount is relatively stable from day 1 to day 4, and decreases significantly to approximately 0.6 mg·L⁻¹ on day 7. -1 Oxalic acid treatment group: The dissolution amount was similar to that of the control group on days 1-4, with a slight increase, but decreased significantly to about 0.6 mg·L on day 7. -1The thallium dissolution rate in both groups on day 7 was significantly lower than in the earlier stages, and the oxalic acid-treated group showed a more pronounced thallium fixation effect in the later stages of the experiment. Green silica, as a clay mineral, possesses a layered structure and exchangeable sites, enabling it to fix thallium ions through ion exchange and surface adsorption. Oxalic acid treatment may have enhanced the surface activity of green silica, further improving the thallium fixation efficiency.

[0058] (2) Changes in functional groups during the reduction of Fe(III) in the calcium-magnesium ion exchange structure of oxalic acid-green silicate are as follows: Figure 16 As shown, the experimental method is the same as in Example 1.

[0059] Depend on Figure 16 It can be seen that after oxalic acid treatment, the intensity of the Fe-O vibration peak increases with time and shifts to higher wavenumbers, indicating that oxalic acid promotes the dissolution of iron-containing minerals in chlorite, releasing Fe... 2+ Further oxidized to Fe 3+ Iron (hydrogen) oxides, such as iron hydroxyl oxide, are generated. Simultaneously, the Si-O vibrational peak broadens and shifts, reflecting the activation of the interlayer structure and enhanced ion exchange capacity through the interaction between oxalate ions and the chlorodrastite silicon-oxygen tetrahedra. The significant increase in the intensity of the -OH stretching vibrational peak indicates that the -OH groups in the system can react with Tl... + / Tl 3+ Stable surface hydroxyl complexes are formed. Ultimately, thallium ions are efficiently immobilized within the chlorodemistite through adsorption co-precipitation of iron oxides, activation adsorption between chlorodemistite layers, and complexation assistance of oxalate.

[0060] (3) Changes in specific surface area during the reduction of Fe(III) in the oxalic acid-green silicate calcium-magnesium ion exchange structure are as follows: Figure 17 As shown, the change in pore volume is as follows Figure 18 As shown, the experimental method is the same as in Example 1.

[0061] Depend on Figure 17 and Figure 18 It can be seen that after oxalic acid treatment, the specific surface area of ​​chlorodiasite is significantly increased, providing more adsorption sites for thallium ions. At the same time, the pore volume decreases. This is because oxalic acid promotes the release of Fe. 2+ The iron oxide precipitates, such as ferric hydroxide generated by oxidation, fill part of the pores. These precipitates not only directly fix thallium ions through surface complexation, but also work synergistically with chlorite to enhance the physical adsorption and chemical complexation of thallium, thereby achieving efficient fixation of thallium inside chlorite.

[0062] (4) The redox potential changes during the reduction of Fe(III) in the oxalic acid-green silicate calcium-magnesium ion exchange structure are as follows: Figure 19 As shown, the conductivity change during the reduction of Fe(III) in the oxalate-green silicate calcium-magnesium ion-exchange structure is as follows: Figure 20As shown, the experimental method is the same as in Example 1.

[0063] Depend on Figure 19 and Figure 20 It can be seen that the redox potential of the oxalic acid-treated group was significantly lower than that of the control group and showed a decreasing trend, indicating that oxalic acid introduced a stronger reducing environment, which promoted the Fe in chlorodiasite. 3+ To Fe 2+ The transformation and release of Fe; the continuous increase in conductivity over time reflects the increase in the concentration of dissolved ions in the system, further confirming the dissolving effect of oxalic acid on iron-containing minerals. 2+ During subsequent oxidation, iron (hydride) oxide precipitates such as ferric hydroxide are generated. These precipitates can efficiently immobilize thallium ions through surface adsorption and complexation. At the same time, the reducing environment is also conducive to Tl. 3+ Tl is more easily adsorbed by iron oxides + Morphological transformation, combined with the activation effect of the interlayer structure of chlorodiasite, ultimately achieved efficient fixation of thallium within chlorodiasite.

[0064] (5) The three-dimensional fluorescence spectrum of the oxalic acid-green silicate calcium-magnesium ion exchange structure after Fe(III) reduction is shown in the figure. Figure 21 As shown, the left figure is the three-dimensional fluorescence spectrum of the control group, and the right figure is the three-dimensional fluorescence spectrum of the oxalic acid treatment group. The experimental method is the same as in Example 1.

[0065] Depend on Figure 21 It was observed that the control group showed only a weak fluorescence signal in the three-dimensional fluorescence spectrum, while the oxalic acid-treated group exhibited obvious fluorescence peaks resembling fulvic acid and protein-like substances. This indicates that oxalic acid promoted the release and transformation of organic matter on the surface of chlorodiasite. These soluble organic substances can form stable complexes with thallium ions, enhancing the adsorption and fixation capacity of iron oxides for thallium. Furthermore, the enhanced fluorescence signal also reflects the release of Fe during the oxalic acid-induced mineral dissolution process. 2+ The complex formed by the combination with organic matter generates more ferric hydroxide precipitate after oxidation, which further fixes thallium ions inside the chloroprecipitate through adsorption and co-precipitation, thereby reducing the risk of thallium leaching.

[0066] The results showed that oxalic acid promoted the absorption of Fe in chlorodiasite. 2+ The process involves the release of thallium ions through adsorption and co-precipitation; simultaneously, it activates the interlayer structure of chlorodiasite, increasing the specific surface area to expand adsorption sites. A reducing environment favors the release of thallium ions. 3+ To Tl + The transformation, combined with the complexation of the released soluble organic matter, significantly reduced the amount of thallium leached, and the fixation effect became more pronounced in the later stages of the experiment.

[0067] Solidification effect of thallium in Experiment 4 and Example 4 (1) Green silica clay minerals were ground through a 200-mesh screen, pretreated, and modified by ion exchange and organic intercalation to obtain organic molecular intercalated clay minerals. Thallium adsorption experiments were then conducted until adsorption saturation. The clay minerals after thallium adsorption were used in subsequent anaerobic reduction experiments. Different culture durations and multiple control groups were set up, with parallel samples in each group. Samples were taken after culture for the corresponding duration to analyze the dynamic changes in thallium leaching over time in different treatment groups. The control group consisted of: natural green silica, without CN32 strain, and only sodium lactate added (CK group); humic acid-green silica synergistic thallium fixation: calcium and magnesium ions drove humic acid intercalation in the clay minerals, with CN32 strain added and sodium lactate added simultaneously in the anaerobic reduction experiment; each independent culture system of all treatment groups had 3 parallel samples, and the experimental data were averaged. The thallium leaching results during the reduction of Fe(III) by the humic acid-green silica calcium and magnesium ion exchange structure in Example 4 are as follows: Figure 22 As shown.

[0068] Depend on Figure 22 It was found that the thallium dissolution rate in the humic acid-treated group decreased over time and remained consistently lower than that in the control group, while the ferrous ion dissolution rate significantly increased. This result reveals the mechanism by which humic acid immobilizes thallium within chlorodiasite: on the one hand, humic acid, as a ligand, can undergo complexation reactions with iron and thallium ions on the surface and between layers of chlorodiasite, reducing thallium dissolution and release by forming stable humic acid complexes; on the other hand, humic acid can promote the reduction of iron in the chlorodiasite structure, generating new adsorption sites and more firmly adsorbing and immobilizing thallium ions between or on the mineral layers. Furthermore, the changes in mineral surface charge and the reconstruction of the interlayer structure induced by humic acid further enhance the thallium retention capacity of chlorodiasite, thus jointly achieving stable immobilization of thallium within the chlorodiasite.

[0069] (2) Changes in functional groups during the reduction of Fe(III) in the calcium-magnesium ion exchange structure of humic acid-green silicate: Figure 23 As shown, the experimental method is the same as in Example 1.

[0070] Depend on Figure 23 It can be seen that the chlorite is at 882 cm. -1 and 1027 cm -1 The characteristic peak intensities of Si-O and Fe-O at 3560 cm⁻¹ gradually weakened and shifted over time, indicating that the oxygen-containing functional groups of humic acid underwent a complexation reaction with the silicon and iron sites on the mineral surface, forming a stable organic-mineral complex that provided new binding sites for thallium ions; simultaneously, the intensity of the characteristic peaks of Si-O and Fe-O at 3560 cm⁻¹... -1The -OH stretching vibration peak at the treatment site gradually increased with the extension of treatment time, indicating that humic acid promoted the interlayer hydroxylation of chlorodiasite, enhanced the polarity and adsorption activity of the mineral surface, and further improved the electrostatic adsorption capacity for thallium. In addition, the macromolecular structure of humic acid can also encapsulate chlorodiasite particles through steric hindrance, reducing the dissolution channels of thallium. Thus, through the synergistic effect of complex adsorption, enhanced hydroxylation, and steric hindrance, thallium is stably immobilized inside chlorodiasite.

[0071] (3) Changes in specific surface area during the reduction of Fe(III) in the humic acid-green silicate calcium-magnesium ion exchange structure are as follows: Figure 24 As shown, the pore volume change during the reduction of Fe(III) in the humic acid-green silicate calcium-magnesium ion exchange structure is as follows: Figure 25 As shown, the experimental method is the same as in Example 1.

[0072] Depend on Figure 24 and Figure 25 It was found that the specific surface area and pore volume of the humic acid-treated group were significantly higher than those of the control group. The introduction of humic acid significantly increased the specific surface area of ​​chlorodiasite, providing more adsorption sites for thallium ions. At the same time, the increase in pore volume expanded the pore space of the mineral, which not only enhanced the physical retention capacity of thallium, but also created conditions for thallium ions to enter the internal pores of the mineral and undergo surface complexation, ion exchange and other reactions. In addition, the oxygen-containing functional groups of humic acid can also combine with the active sites on the surface and in the pores of chlorodiasite to form a stable organic-mineral composite structure, further improving the adsorption capacity and fixation stability of the mineral for thallium. Thus, through the synergistic optimization of specific surface area and pore structure, efficient fixation of thallium inside chlorodiasite is achieved.

[0073] (4) The redox potential changes during the reduction of Fe(III) in the humic acid-green silicate calcium-magnesium ion exchange structure are as follows: Figure 26 As shown, the conductivity change during the reduction of Fe(III) in the humic acid-green silicate calcium-magnesium ion exchange structure is as follows: Figure 27 As shown, the experimental method is the same as in Example 1.

[0074] Depend on Figure 26 and Figure 27 It can be seen that the redox potential of the humic acid-treated group was significantly lower than that of the control group and remained in the negative range, indicating that humic acid provided a strong reducing environment for the system. This environment can promote the reduction of high-valence iron in the chlorodemistite structure to low-valence iron, and can also fix thallium in the mineral lattice through co-precipitation. At the same time, the conductivity of the humic acid-treated group was consistently higher than that of the control group, reflecting a higher concentration of soluble ions in the system. This indicates that the complexation effect of humic acid released some mineral-bound ions, and also that the soluble complex formed by humic acid and thallium can be further adsorbed and retained by the interlayer pores and surface sites of chlorodemistite, reducing the dissolution of thallium.

[0075] (5) The three-dimensional fluorescence spectrum of the solution after Fe(III) reduction of the humic acid-green silica calcium-magnesium ion exchange structure is shown in the figure. Figure 28 As shown, the experimental method is the same as in Example 1.

[0076] Depend on Figure 28 It was observed that the humic acid-treated group exhibited significant fulvic acid-like fluorescence peaks at excitation wavelengths of 250-300 nm and emission wavelengths of 300-400 nm, while the control group showed no such characteristic signal. The oxygen-containing functional groups of humic acid (such as carboxyl and hydroxyl groups) can form stable complexes with thallium ions, which is directly confirmed by the characteristic peaks of the fluorescence signal. Simultaneously, these humic acid-thallium complexes can be adsorbed and retained by the interlayer structure and surface sites of chlorite, and the intensity changes of the fluorescence peaks also reflect the enrichment process of the complexes on the mineral surface. Furthermore, the macromolecular structure of humic acid can also encapsulate chlorite particles through steric hindrance, further hindering the dissolution of thallium ions, ultimately achieving stable fixation of thallium within chlorite through the synergistic effect of complexation and adsorption.

[0077] The results showed that the thallium dissolution in the humic acid-treated group was lower than that in the control group and showed a decreasing trend. Iron reduction was enhanced, immobilizing thallium ions through complexation reactions, promoting iron reduction to generate new adsorption sites, and inducing changes in mineral charge and structure. This resulted in a shift in mineral characteristic peaks, enhanced hydroxylation, increased specific surface area and pore volume, and provided more adsorption sites. Creating a reducing environment promoted thallium co-precipitation, forming humic acid-thallium complexes which were then adsorbed. Combined with steric hindrance, this synergistic effect achieved stable thallium immobilization.

[0078] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for synergistic thallium fixation via calcium-magnesium induced organic intercalation and microbial reduction, characterized in that, Includes the following steps: S1. Apply a solution of clay minerals and organic molecules to the thallium-contaminated soil and mix thoroughly. S2. Adjust the soil moisture content, and after balancing, inoculate with Shewanella putrefactive bacteria for culture to complete the immobilization of thallium.

2. The method for calcium-magnesium induced organic intercalation-microbial reduction synergistic thallium fixation as described in claim 1, characterized in that, In step S1, the contaminated soil is thallium-contaminated soil from a karst area, and the thallium content in the karst area thallium-contaminated soil is 1-50 mg / kg.

3. The method for calcium-magnesium induced organic intercalation-microbial reduction synergistic thallium fixation as described in claim 1, characterized in that, In step S1, the clay mineral is montmorillonite or chlorometholite, and the montmorillonite and chlorometholite pass through a 200-mesh sieve.

4. The method for calcium-magnesium induced organic intercalation-microbial reduction synergistic thallium fixation as described in claim 1, characterized in that, In step S1, the organic molecule solution is oxalic acid or humic acid.

5. The method for calcium-magnesium induced organic intercalation-microbial reduction synergistic thallium fixation as described in claim 1, characterized in that, In step S1, the application rate of montmorillonite and chlorometholite is 0.5-5% of the dry weight of the soil, and the concentration of the organic molecule solution is 5-30 mg / L.

6. The method for calcium-magnesium induced organic intercalation-microbial reduction synergistic thallium fixation as described in claim 1, characterized in that, In step S1, the mixture is thoroughly mixed by tilling, with a tilling depth of 0-20cm.

7. The method for calcium-magnesium induced organic intercalation-microbial reduction synergistic thallium fixation as described in claim 1, characterized in that, In step S2, the moisture content is adjusted to 60-80% of the saturated water holding capacity.

8. The method for calcium-magnesium induced organic intercalation-microbial reduction synergistic thallium fixation as described in claim 1, characterized in that, In step S2, equilibrate for 24-48 hours.

9. The method for calcium-magnesium induced organic intercalation-microbial reduction synergistic thallium fixation as described in claim 1, characterized in that, In step S2, the concentration of Shewanella putrefactive bacteria in the soil is 1×10⁻⁶. 8 Cells / mL, cultured in an anaerobic environment.

10. The method for calcium-magnesium induced organic intercalation-microbial reduction synergistic thallium fixation as described in claim 1, characterized in that, In step S2, the culture time is 7-30 days and the culture temperature is 25-30 ℃.

Images