A saPO-20 / mcm-48 zeolite soil passivator, its preparation method and application
By preparing SAPO-20/MCM-48 zeolite soil passivating agent using coal gangue as raw material, the problems of high cost or poor applicability of existing materials were solved, achieving efficient passivation and stabilization of heavy metals and avoiding changes in soil properties.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SICHUAN UNIV
- Filing Date
- 2024-04-22
- Publication Date
- 2026-05-29
AI Technical Summary
Existing remediation materials for heavy metal contaminated soil are either costly or have poor applicability, and may alter the physical and chemical properties of the soil. There is a lack of green, efficient, and low-cost passivating agents.
Using coal gangue as raw material, SAPO-20/MCM-48 zeolite was prepared. It was then used to form coordination bonds with heavy metals, adsorb and passivate Pb, Cd, and Cu ions in the soil, change their form, and reduce their migration ability.
The prepared SAPO-20/MCM-48 zeolite passivating agent effectively reduces the available content of Pb, Cd, and Cu in the soil, enhances the stability of heavy metals, reduces their migration ability, and does not change the soil properties.
Smart Images
Figure CN118387893B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of solid waste resource utilization and soil heavy metal pollution control technology, specifically involving a SAPO-20 / MCM-48 zeolite soil passivating agent, its preparation method and application. Background Technology
[0002] Currently, soil remediation for heavy metal contamination mainly includes physical remediation, bioremediation, and chemical remediation. Among these, chemical remediation has gained widespread attention and application due to its advantages such as high efficiency, thoroughness, and applicability to heavily contaminated soils. Passivation technology in chemical remediation can effectively reduce the migration properties of soil pollutants and is simple and easy to implement. Materials that can be used as heavy metal passivating agents include activated carbon, phosphate rock powder, and quicklime; however, these materials are either expensive or have poor applicability, and their application can severely alter the physicochemical properties of the soil. Therefore, it is particularly important to seek a new type of green, efficient, and low-cost heavy metal passivating agent that possesses both low material cost and good passivation ability.
[0003] Therefore, based on this, the present invention is proposed. Summary of the Invention
[0004] To address the problems existing in the prior art, the present invention provides a method for preparing SAPO-20 / MCM-48 zeolite soil passivating agent, the preparation method comprising the following steps:
[0005] (1) The coal gangue is crushed, sieved and roasted in sequence to obtain coal gangue powder;
[0006] (2) The coal gangue powder and NaOH powder are mixed evenly and then calcined to obtain a mixture;
[0007] (3) Sodium silicate and water are added to the mixture in sequence, and the mixture is stirred and aged to obtain a mixed solution;
[0008] (4) The mixture is subjected to a hydrothermal crystallization reaction to obtain SAPO-20;
[0009] (5) Add CTAB, NaOH and NAF to heated deionized water and stir until clear and homogeneous to obtain solution No. 1;
[0010] (6) Add TEOS to the first solution and stir to obtain the second solution;
[0011] (7) Add SAPO-20 to the second solution, and perform crystallization once after sonication and stirring to obtain a crystallized solution;
[0012] (8) Add acetic acid to the crystallization solution, adjust the pH and carry out secondary crystallization. Wash, dry and calcine the product after secondary crystallization to obtain SAPO-20 / MCM-48 zeolite soil passivator.
[0013] Preferably, in step (1), the sieve used for screening has a mesh size of 200; the roasting is carried out in a muffle furnace at a temperature of 800°C for 2 hours. It should be noted that the coal gangue comes from a coal mine slag heap in southern Sichuan, and its main components include: silicon dioxide (mass percentage ≥ 40%), aluminum oxide (mass percentage ≥ 25%), and iron oxides (mass percentage ≥ 10%); the iron oxides are a mixture of iron(III) oxide and ferric oxide.
[0014] Preferably, in step (2), the mass ratio of the coal gangue powder to the NaOH powder is 1:(1.0-1.4), more preferably, the mass ratio is 1:1.2; the calcination is carried out in a muffle furnace at a temperature of 650°C for 3 hours.
[0015] Preferably, in step (3), after adding sodium silicate, the molar ratio of SiO2 to Al2O3 in the coal gangue powder is 3.5 to 4.5, more preferably, the molar ratio is 4.0; after adding water, the alkalinity of the system is 2.5 to 3.5 mol / L, more preferably, the alkalinity of the system is 3.0 mol / L; the mixture is stirred and aged for 8 hours at room temperature using a magnetic stirrer to obtain the mixture.
[0016] Preferably, in step (4), the hydrothermal crystallization reaction involves transferring the mixture into a stainless steel reactor lined with polytetrafluoroethylene and crystallizing it in an oven at 110°C for 12 hours.
[0017] Preferably, in step (5), the mass ratio of CTAB, NaOH, NaF and deionized water is 0.83:1.0:0.2:110; the heating temperature is 40°C and the stirring time is 50 min.
[0018] Preferably, in step (6), the mass ratio of the added TEOS to the added NaOH in step (5) is 2:1; and the stirring time is 1 hour.
[0019] Preferably, in step (7), the amount of SAPO-20 added is 3-7 wt.% of the second solution; the ultrasonication time is 5 min; the stirring time is 1 h; the temperature of the first crystallization is 100-110℃, and the time of the first crystallization is 48-96 h. More preferably, the amount of SAPO-20 added is 5 wt.%, the temperature of the first crystallization is 105℃, and the duration of the first crystallization is 72 h.
[0020] Preferably, the pH value is adjusted to around 8 (e.g., 7-9); the secondary crystallization time is 24 hours; the calcination temperature is 550°C, and the calcination time is 6 hours.
[0021] Based on the same technical concept, another aspect of the present invention is to provide a SAPO-20 / MCM-48 zeolite soil passivator prepared by the above method.
[0022] Based on the same technical concept, another aspect of the present invention is to provide an application of SAPO-20 / MCM-48 zeolite soil passivating agent in the remediation of contaminated soil, wherein the application is as follows:
[0023] (S1) The contaminated soil, water and SAPO-20 / MCM-48 zeolite soil passivating agent are mixed evenly to obtain a mixture; wherein: the solid content of the mixture is 20-80%, and the mass fraction of SAPO-20 / MCM-48 zeolite soil passivating agent in the solid is 0.5-2%;
[0024] (S2) The mixture is cured for a period of ≥1 month.
[0025] The beneficial effects of this invention are as follows:
[0026] (1) This invention explores the preparation conditions based on the original components of inferior coal gangue and prepares a new type of zeolite soil passivating agent, SAPO-20 / MCM-48, which solves the problem of large-scale stockpiling of coal gangue in mining areas and provides a new idea for soil heavy metal chemical remediation technology, achieving the ideal goal of environmental governance of "treating waste with waste".
[0027] (2) The zeolite prepared in this invention can adsorb Pb, Cd, and Cu heavy metal ions in soil. The passivating agent contains some hydroxyl groups, which can interact with heavy metals in the soil to form coordination bonds, thus exhibiting a good passivation effect on the target heavy metal ions. More specifically:
[0028] The novel SAPO-20 / MCM-48 zeolite soil passivating agent prepared in this invention is produced using a crystal growth method. SAPO-20 serves as the crystal nucleus, and the Si-OH groups in the silicon framework structure of MCM-48 chemically interact with SAPO-20 to form a spherical composite product. This composite product contains some hydroxyl groups, which can interact with heavy metals in the soil to form coordination bonds, providing corresponding reaction and adsorption sites for heavy metal adsorption, thereby stabilizing heavy metals in the soil.
[0029] (3) The SAPO-20 / MCM-48 novel zeolite soil passivator prepared in this invention was applied and tested. The results showed that the SAPO-20 / MCM-48 novel zeolite soil passivator had a good passivation effect on Pb, Cd and Cu in the soil. This passivator changed the existence form of each heavy metal in the soil and reduced the migration ability of each heavy metal in the soil. Attached Figure Description
[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0031] Figure 1 The images show the wide-angle XRD patterns of SAPO-20 and SAPO-20 / MCM-48 novel zeolite soil passivating agents obtained in Example 1.
[0032] Figure 2 The small-angle XRD patterns of the novel zeolite soil passivating agents MCM-48 and SAPO-20 / MCM-48 obtained in Example 1 are shown.
[0033] Figure 3 The images show the FTIR spectra of SAPO-20, MCM-48, and the novel zeolite soil passivating agents SAPO-20 / MCM-48 obtained in Example 1. Detailed Implementation
[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.
[0035] Example
[0036] This embodiment provides a method for preparing SAPO-20 / MCM-48 zeolite soil passivating agent, the preparation method comprising the following steps:
[0037] (1) The inferior coal gangue from the slag heap was crushed, ground into powder, and passed through a 200-mesh sieve. It was then calcined in a muffle furnace at 800°C for 2 hours to obtain coal gangue powder. The coal gangue came from a coal mine slag heap in southern Sichuan. Its main components included: silicon dioxide (43.3%), aluminum oxide (25.6%), and iron oxide (11.6%, all by mass percentage).
[0038] (2) The coal gangue powder (1 kg) and NaOH powder are uniformly mixed and then calcined to obtain a mixture. The mass ratio of coal gangue powder to NaOH powder is 1:1.2. The mixture is calcined in a muffle furnace at 650°C for 3 hours to obtain the mixture.
[0039] (3) Sodium silicate and water are added to the mixture in sequence, and the mixture is stirred and aged to obtain a mixed solution. The molar ratio of SiO2:Al2O3 in the mixture is adjusted to 4:1, and then deionized water is added to adjust the alkalinity of the mixture to 3.0 mol / L. The mixture is stirred and aged for 8 hours at room temperature using a magnetic stirrer (400 r / min) to obtain a mixed solution.
[0040] (4) The mixture was subjected to a hydrothermal crystallization reaction to obtain SAPO-20. The mixture was transferred to a stainless steel reactor with a polytetrafluoroethylene liner and crystallized in an oven at 110°C for 12 hours. After the hydrothermal reaction was completed, the mixture was filtered, washed with deionized water until neutral, and dried at 100°C for 12 hours to obtain a powdery red sample, which was SAPO-20.
[0041] (5) Add CTAB, NaOH, and NAF to the No. 1 solution after heating and stirring until clear and homogeneous. The ratio of CTAB:NaOH:NaF:H2O added is 0.83:1.0:0.2:110 (mass ratio). The heating temperature is 40℃ and the stirring time is 50min.
[0042] (6) Add TEOS dropwise to solution one and stir to obtain solution two. The ratio of TEOS to NaOH added is 2:1 (mass ratio), and the stirring time is 1 hour.
[0043] (7) Add a certain amount of SAPO-20 to solution No. 2, and perform a single crystallization after sonication and stirring. The amount of SAPO-20 added is 5 wt.% (compared to solution No. 2); the sonication time is 5 min, the stirring time is 1 h, the crystallization temperature is 105℃, and the single crystallization time is 72 h.
[0044] (8) Add acetic acid to the solution after primary crystallization, adjust the pH to 8, and then perform secondary crystallization for 24 hours. Wash the product after secondary crystallization, dry it at 100℃ for 12 hours, and then calcine it at 550℃ to obtain SAPO-20 / MCM-48 zeolite soil passivating agent.
[0045] Characterization example
[0046] X-ray diffraction tests were performed on the product obtained in Example 1. Figure 1The image shows a wide-angle XRD pattern. The main diffraction peaks of SAPO-20 appear at 2θ = 13.98°, 19.82°, 24.3°, 28.12°, 31.45°, and 34.55°, corresponding to the (110), (200), (211), (220), (310), and (222) crystal planes, respectively. The positions of these peaks are consistent with the characteristic peaks of SAPO-20 molecular sieves.
[0047] at the same time Figure 2 The small-angle X-ray diffraction pattern shows that the main diffraction peaks of MCM-48 appear at 2θ = 2.38, 2.74, 4.05, 4.40, and 4.57, corresponding to (211), (220), (420), (332), and (431), respectively. These peak positions are consistent with the characteristic peaks of MCM-48 molecular sieves. After composite preparation, the small-angle X-ray diffraction pattern still retains the (211) and (220) crystal planes, while the wide-angle X-ray diffraction pattern still retains the (110), (211), (220), and (222) crystal planes, proving that the composite preparation of the product was successful.
[0048] The product obtained in Example 1 was subjected to infrared spectroscopy. In the infrared spectrum of MCM-48, its value was at 3455 cm⁻¹. -1 1636cm -1 1092cm -1 969cm -1 798cm -1 and 471cm -1 There is a distinct absorption peak at 3455 cm⁻¹. -1 The broad peak at 1636 cm⁻¹ is caused by the -OH stretching vibration; -1 The absorption peak at 1092 cm⁻¹ corresponds to the bending vibration absorption peak of water-OH groups adsorbed on the material surface; -1 The absorption peak at 969 cm⁻¹ corresponds to the Si-O-Si antisymmetric stretching vibration on the silicon framework in the MCM-48 structure. -1 The absorption peak at 798 cm⁻¹ is due to the stretching vibration of Si-OH. -1 The absorption peak at 471 cm⁻¹ corresponds to the Si-O-Si symmetric stretching vibration on the silicon framework. -1 The absorption peak at 3455 cm⁻¹ corresponds to the Si-O bending vibration. In the infrared spectrum of SAPO-20, the peak at 3455 cm⁻¹ is due to the Si-O bending vibration. -1 The absorption peak at 1636 cm⁻¹ is due to the -OH stretching vibration. -1 The absorption peak at 1482 cm⁻¹ is due to the stretching vibration of the -OH group in adsorbed water. -1 The absorption peak at 455 cm⁻¹ is related to the CH deformation vibration in -CH₃. -1 The absorption peak at 979 cm⁻¹ corresponds to the lattice MO bending vibration. In the infrared spectrum of the composite material, compared to the MCM-48 infrared spectrum, its peak at 979 cm⁻¹ is [missing information]. -1The absorption peak at the point almost disappeared, indicating that after the addition of SAPO-20, it chemically interacted with the Si-OH in the silicon framework structure of MCM-48, indicating that MCM-48 partially adsorbed SAPO-20, proving that the composite preparation of the product was successful.
[0049] Verification Example
[0050] The SAPO-20 / MCM-48 zeolite prepared in Example 1 was used for soil passivation. The specific implementation plan is as follows:
[0051] Contaminated soil (mainly Pb, Cd, and Cu contaminated) from Area 1 of a mining area in southern Sichuan was selected. 500g portions of soil were weighed using an analytical balance and placed in small earthenware pots. SAPO-20 / MCM-48 zeolite passivating agent was added at dry weight ratios of 0.5%, 1%, 1.5%, and 2%, respectively. A control group (CK) was also included. The soil was submerged in ultrapure water, stirred thoroughly, and air-dried at room temperature. Ultrapure water was added periodically to maintain the soil moisture content at approximately 30%. Three parallel experiments were conducted for one month. After the reaction, the available Pb, Cd, and Cu content in the soil was measured. Speciation analysis was performed on the passivated soil. The results are shown in Tables 1-6.
[0052] Table 1. Available content of lead (Pb) in soil after passivation
[0053] passivating agent addition amount / % 0 0.5 1.0 1.5 2.0 Effective content / mg / kg 227.23 180.21 164.15 159.33 147.73
[0054] Table 2. Heavy metal speciation of lead (Pb) after soil passivation
[0055]
[0056]
[0057] Table 3. Bioavailable content of heavy metal cadmium (Cd) after soil passivation
[0058] passivating agent addition amount / % 0 0.5 1.0 1.5 2.0 Effective content / mg / kg 2.06 1.81 1.72 1.69 1.63
[0059] Table 4. Heavy metal speciation of cadmium (Cd) after soil passivation
[0060] passivating agent addition amount / % 0 0.5 1.0 1.5 2.0 % of exchangeable states 80.44 80.21 79.72 79.32 78.91 Reducible state percentage 17.05 17.35 17.41 17.66 17.83 % of oxidizable states 1.70 1.51 1.84 1.91 2.00 Residual state percentage % 0.81 0.93 1.03 1.11 1.26
[0061] Table 5. Available content of heavy metal copper (Cu) after soil passivation
[0062] passivating agent addition amount / % 0 0.5 1.0 1.5 2.0 Effective content / mg / kg 16.10 14.31 13.60 12.78 11.84
[0063] Table 6. Heavy metal speciation of cadmium (Cu) after soil passivation
[0064] passivating agent addition amount / % 0 0.5 1.0 1.5 2.0 % of exchangeable states 24.22 23.73 23.15 22.72 22.45 Reducible state percentage 46.98 47.29 47.43 47.51 47.67 % of oxidizable states 2.86 2.24 2.23 2.89 2.40 Residual state percentage % 25.94 26.74 27.19 26.88 27.48
[0065] The results in Tables 1-6 show that SAPO-20 / MCM-48 passivating agent can significantly reduce the available content of Pb, Cd, and Cu in soil, and has a certain passivation effect on Pb, Cd, and Cu in contaminated soil. Taking Table 1 as an example, when the addition ratio of SAPO-20 / MCM-48 passivating agent increased from 0 to 2%, the available content of lead in the soil decreased from 227.23 mg / kg to 147.73 mg / kg. When the addition amount of SAPO-20 / MCM-48 passivating agent was 2%, the reduction rate of available Pb in the soil was 35.0%, the reduction rate of available Cd in the soil was 20.9%, and the reduction rate of available Cu in the soil was 26.5%.
[0066] In summary, the addition of SAPO-20 / MCM-48 molecular sieves can alter the occurrence forms of heavy metals Pb, Cd, and Cu, reducing the exchangeable form and increasing the content of reducible and residual forms. Specifically, Pb is reduced by 2.78%, Cd by 1.53%, and Cu by 1.77%, thereby effectively enhancing the stability of heavy metals in soil and reducing the migration ability of Pb, Cd, and Cu.
[0067] In addition, polluted soil (mainly Pb contamination) from area 2 of a mining area in southern Sichuan was selected. The soil passivating agent obtained in Example 1 was compared with the existing Fe-NaX zeolite passivating agent. The application methods were the same. The content of available lead in the soil after one month is shown in Table 7.
[0068] Table 7. Available lead (Pb) content in soil after passivation with Fe-NaX zeolite passivating agent
[0069] passivating agent addition amount / % 0 0.5 1.0 1.5 2.0 Effective content / mg / kg 129.3 118.3 102.4 90.1 89.3
[0070] The results showed that using Fe-NaX molecular sieves from inferior coal gangue in slag heaps reduced the available lead content in the soil by only 40 mg / kg. When the addition amount was 2%, the reduction rate of available Pb in the soil was the highest at 30%, which was lower than that of SAPO-20 / MCM-48 passivating agent. The SAPO-20 / MCM-48 soil passivating agent prepared in this study has a better passivation effect on soil Pb pollution.
[0071] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.
Claims
1. A method for preparing a SAPO-20 / MCM-48 zeolite soil passivating agent, characterized in that, The preparation method includes the following steps: (1) The coal gangue is crushed, sieved and roasted in sequence to obtain coal gangue powder; (2) The coal gangue powder and NaOH powder are mixed evenly and then calcined to obtain a mixture; (3) Sodium silicate and water are added to the mixture in sequence, and the mixture is stirred and aged to obtain a mixed solution; (4) The mixture is subjected to a hydrothermal crystallization reaction to obtain SAPO-20; (5) Add CTAB, NaOH and NaF to heated deionized water and stir until clear and homogeneous to obtain solution No. 1; (6) Add TEOS to the first solution and stir to obtain the second solution; (7) Add SAPO-20 to the second solution, and perform crystallization once after sonication and stirring to obtain a crystallized solution; the amount of SAPO-20 added is 3 to 7 wt.% of the second solution; (8) Add acetic acid to the crystallization solution, adjust the pH to 7-9 and then carry out secondary crystallization. Wash, dry and calcine the product after secondary crystallization to obtain SAPO-20 / MCM-48 zeolite soil passivator.
2. The preparation method of the SAPO-20 / MCM-48 zeolite soil passivating agent according to claim 1, characterized in that, In step (1), the sieve used for sieving has a mesh size of 200 mesh.
3. The preparation method of the SAPO-20 / MCM-48 zeolite soil passivating agent according to claim 1, characterized in that, In step (1), the roasting is carried out in a muffle furnace at a temperature of 800°C for 2 hours.
4. The preparation method of the SAPO-20 / MCM-48 zeolite soil passivating agent according to claim 1, characterized in that, In step (2), the mass ratio of the coal gangue powder to the NaOH powder is 1:(1.0 to 1.4).
5. The preparation method of the SAPO-20 / MCM-48 zeolite soil passivating agent according to claim 1, characterized in that, In step (2), the calcination is carried out in a muffle furnace at a temperature of 650°C for 3 hours.
6. The preparation method of the SAPO-20 / MCM-48 zeolite soil passivating agent according to claim 1, characterized in that, In step (3), after adding sodium silicate, the molar ratio of SiO2 to Al2O3 in the coal gangue powder is 3.5 to 4.
5. And / or, after adding water, the alkalinity of the system is 2.5–3.5 mol / L.
7. The preparation method of the SAPO-20 / MCM-48 zeolite soil passivating agent according to claim 1, characterized in that, In step (4), the hydrothermal crystallization reaction is carried out at 110°C for 12 hours.
8. The preparation method of the SAPO-20 / MCM-48 zeolite soil passivating agent according to claim 1, characterized in that, In step (5), the mass ratio of CTAB, NaOH, NaF and deionized water is 0.83:1.0:0.2:110; And / or, the heating temperature is 40°C and the stirring time is 50 min.
9. The preparation method of the SAPO-20 / MCM-48 zeolite soil passivating agent according to claim 1, characterized in that, In step (6), the mass ratio of the added TEOS to the added NaOH in step (5) is 2:1; And / or, the stirring time is 1 hour.
10. The preparation method of the SAPO-20 / MCM-48 zeolite soil passivating agent according to claim 1, characterized in that, In step (7), the ultrasound duration is 5 minutes; And / or, the stirring time is 1 hour; And / or, the temperature of the primary crystallization is 100-110°C, and the time of the primary crystallization is 48-96 hours.
11. The preparation method of the SAPO-20 / MCM-48 zeolite soil passivating agent according to claim 1, characterized in that, In step (8), the secondary crystallization time is 24 hours; And / or, the calcination temperature is 550°C and the calcination time is 6 hours.
12. The SAPO-20 / MCM-48 zeolite soil passivator obtained by the preparation method according to any one of claims 1 to 11.
13. The application of the SAPO-20 / MCM-48 zeolite soil passivating agent according to claim 12 in the remediation of contaminated soil, characterized in that, The application method is as follows: (S1) The contaminated soil, water and SAPO-20 / MCM-48 zeolite soil passivating agent are mixed evenly to obtain a mixture; wherein: the solid content of the mixture is 20-80%, and the mass fraction of SAPO-20 / MCM-48 zeolite soil passivating agent in the solid is 0.5-2%; (S2) The mixture is cured for a period of ≥1 month.