Passivator material as well as preparation method and application thereof

Abstract

The invention discloses a passivator material as well as a preparation method and application thereof, and relates to the technical field of passivator preparation. The method comprises the following steps: mixing coal gangue powder and NaOH, calcining, cooling to obtain slag, adding a NaOH solution, stirring, aging, crystallizing, washing, and drying to obtain a zeolite molecular sieve; and adding into a ferrous sulfate solution, stirring, filtering, drying and sieving to obtain the passivator material. The coal gangue and the ferrous sulfate are used as raw materials, the reducing / passivating agent which is low in price, excellent in performance and simple in preparation process is developed, and the reducing / passivating agent has the reducing and passivating functions. The problem that in the prior art, a reduction / passivation agent which is low in price, excellent in performance and simple in preparation process is lacked is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of passivator preparation, and in particular to a passivator material, a preparation method and an application thereof. Background Art

[0002] Currently, Cr(VI) pollution has become a serious threat, but existing technologies are plagued by high costs and a high risk of secondary pollution, necessitating the development of green and efficient remediation methods. As a typical variable-valence metal element, Cr(VI) is more toxic and mobile than Cr(III). Chemical reduction technology has become a mainstream remediation strategy for Cr(VI)-contaminated sites due to its high efficiency. This technology reduces Cr(VI) to Cr(III) by adding reducing agents such as ferrous salts (such as FeSO4). Although chemical reduction offers the advantages of rapid response and economic efficiency, excessive addition of reducing agents carries the risk of damaging soil structure and causing soil acidification, and its long-term remediation effectiveness is poor.

[0003] To overcome the limitations of single technologies, researchers have recently proposed a synergistic remediation strategy called "chemical reduction-passivation stabilization." This strategy involves the introduction of passivating materials (such as biochar, phosphates, or clay minerals) to simultaneously convert Cr(VI) to Cr(III) while immobilizing Cr(III) through mechanisms such as surface complexation, coprecipitation, or physical encapsulation, thereby inhibiting its remigration and reoxidation. This combined approach not only overcomes the shortcomings of traditional reduction methods but also provides a theoretical basis and technical paradigm for the efficient and long-term treatment of Cr(VI) contamination under complex site conditions. Currently, most commonly used passivating agents are artificially synthesized and expensive, while the direct use of natural materials often yields unsatisfactory results. Therefore, there is an urgent need to develop a cost-effective, high-performance, and simple-to-prepare reducing / passivating agent. Summary of the Invention

[0004] In order to solve the above technical problems, the purpose of the present invention is to provide a passivating agent material and its preparation method and application, so as to solve the problem in the prior art of lacking a reducing / passivating agent with low price, excellent performance and simple preparation process.

[0005] The present invention solves the above technical problems with the following technical solutions: a method for preparing a passivating material is provided, comprising the following steps: (1) Pre-treating the coal gangue to obtain coal gangue powder; (2) mixing the gangue powder obtained in step (1) with NaOH, calcining, cooling, obtaining slag, adding NaOH solution and stirring to obtain a reaction solution, aging, crystallizing, washing, and drying to obtain a zeolite molecular sieve; (3) Adding the zeolite molecular sieve prepared in step (2) into the ferrous sulfate solution, stirring, filtering, drying, and sieving to prepare the passivating agent material.

[0006] On the basis of the above technical solution, the present invention can also be improved as follows: Furthermore, in step (1), the coal gangue is ball-milled, sieved, soaked in a hydrochloric acid solution, stirred, and then filtered and dried to complete the pretreatment process.

[0007] The beneficial effects of adopting this further technical solution are as follows: ball milling mechanically activates the gangue, significantly increasing the specific surface area of ​​the gangue particles. Screening can remove impurities (such as quartz and pyrite nodules) that remain after ball milling and are particularly hard or difficult to grind. The main purpose of acid leaching is to further remove impurities in the gangue, such as dissolving impurities unwanted in the reaction, such as pyrite (FeS2) and calcite (CaCO3), and leaching heavy metal ions such as arsenic, lead, chromium, and cadmium, thereby reducing environmental risks. Furthermore, it can further create pores to increase the specific surface area and activate the gangue's properties, which is beneficial for subsequent reactions.

[0008] Further, pass through a 200-mesh sieve.

[0009] Furthermore, the mass volume ratio of the coal gangue and the hydrochloric acid solution is 1 g:450-550 mL.

[0010] Furthermore, the mass volume ratio of the coal gangue and the hydrochloric acid solution is 1 g:500 mL.

[0011] Furthermore, the concentration of the hydrochloric acid solution is 15-25 wt %.

[0012] Furthermore, the concentration of the hydrochloric acid solution is 20 wt %.

[0013] Further, stirring was carried out for 2.5-3.5 hours.

[0014] Further, stirring was carried out for 3 h.

[0015] Furthermore, in step (1), the coal gangue includes the following components in parts by weight: 54.38 parts of SiO2, 20.93 parts of Al2O3, 1.09 parts of MgO, 0.35 parts of Na2O, 0.95 parts of CaO, 2.5 parts of K2O and 0.52 parts of TiO2.

[0016] Furthermore, in step (2), the mass ratio of the gangue powder to NaOH is 1:1-1.5.

[0017] The beneficial effect of adopting the above-mentioned further technical solution is that co-calcination of coal gangue with sodium hydroxide (NaOH) (commonly known as alkali fusion calcination or sodium roasting) is an important chemical activation method. Its core purpose is to destroy the stable silica-alumina mineral structure in coal gangue through high-temperature solid-phase reaction, and convert it into soluble sodium silicate and sodium aluminate, laying the foundation for the subsequent efficient extraction of valuable components (especially aluminum and silicon) or the synthesis of high-value-added materials.

[0018] Furthermore, in step (2), the mass ratio of coal gangue powder to NaOH is 1:1.2.

[0019] Furthermore, in step (2), the calcination is carried out at 700-800°C for 1.5-2.5h.

[0020] The beneficial effect of adopting the above-mentioned further technical solution is that the reaction is insufficient at 700°C, and insoluble nepheline will be generated above 900°C.

[0021] Furthermore, in step (2), the calcination is carried out at 750° C. for 2 h.

[0022] Furthermore, in step (2), in the reaction solution, Na + and Si 4+ The molar ratio of H2O and Na is 4:1 + The molar ratio is 50:2.

[0023] The beneficial effect of adopting this further technical solution is that a higher sodium-to-silicon ratio can promote the formation of low-silicon-to-aluminum ratio zeolites (such as A-type, X-type, and P-type zeolites, with X-type zeolite being produced in this invention). These zeolites have high ion exchange capacity and are suitable for adsorption and detergent applications. The water-to-sodium ratio primarily affects crystallization speed and uniformity, so a suitable ratio is required.

[0024] Furthermore, in step (2), aging is performed at room temperature for 5-7 hours.

[0025] The beneficial effects of adopting the above further technical solution are: the purpose of aging is to promote gel homogenization and optimize the nucleation environment.

[0026] Furthermore, in step (2), aging is performed at room temperature for 6 hours.

[0027] Furthermore, in step (2), crystallization is performed at 80-90° C. for 7-9 hours.

[0028] The beneficial effect of adopting the above further technical solution is that crystallization is the most critical step in preparing zeolite, and the aged gel is moved to a high temperature for hydrothermal reaction to achieve crystal nucleation and growth.

[0029] Furthermore, in step (2), crystallization is performed at 85° C. for 8 h.

[0030] Furthermore, in step (2), drying is performed at 100-110° C. for 10-15 hours.

[0031] Furthermore, in step (2), the mixture is dried at 105° C. for 12 h.

[0032] Furthermore, in step (3), the ferrous sulfate solution is prepared by the following method: FeSO4·7H2O is dissolved in distilled water to obtain the ferrous sulfate solution.

[0033] Furthermore, in step (3), the concentration of the ferrous sulfate solution is 0.01-0.03 mol / L.

[0034] Furthermore, in step (3), the concentration of the ferrous sulfate solution is 0.02 mol / L.

[0035] Furthermore, in step (3), the mass volume ratio of the zeolite molecular sieve and the ferrous sulfate solution is 1 g:180-220 mL.

[0036] Furthermore, in step (3), the mass volume ratio of the zeolite molecular sieve and the ferrous sulfate solution is 1 g:200 mL.

[0037] Furthermore, in step (3), stirring is performed at 400-500 r / min for 1.5-2.5 h.

[0038] Furthermore, in step (3), stirring was performed at 450 r / min for 2 h.

[0039] Furthermore, in step (3), filtration is performed using a filter membrane.

[0040] Furthermore, in step (3), vacuum drying is adopted.

[0041] The beneficial effects of adopting the above further technical solution are: stirring promotes full contact between the prepared zeolite and ferrous sulfate. Too long a reaction time will lead to oxidation of ferrous sulfate, and the stirring time needs to be controlled. The subsequent vacuum drying is also to prevent oxidation of ferrous sulfate.

[0042] Furthermore, in step (3), the product is sieved through a 200-mesh sieve.

[0043] The present invention also provides a passivator material prepared by the method.

[0044] The present invention also provides application of the passivator material in hexavalent chromium soil remediation.

[0045] The present invention has the following beneficial effects: 1. This study uses coal gangue and ferrous sulfate as raw materials to develop a reducing / passivating agent with low price, excellent performance and simple preparation process, which has both reducing and passivating functions.

[0046] 2. This invention successfully converts coal gangue into a high-surface-area zeolite molecular sieve (FZS-Fe). While retaining the zeolite's porous structure, it achieves efficient Fe²⁺ immobilization through surface complexation (characteristic Fe-O bond peaks in FT-IR) and ion exchange (uniform distribution of iron in EDS). Characterization results demonstrate that the optimized FZS exhibits a regular octahedral structure (SEM), a rich micropore-mesoporous structure (BET surface area of ​​397.9 m² / g), and an aluminosilicate framework (XRD and FT-IR), providing ideal active sites for the subsequent adsorption of Cr(VI).

[0047] 3. In Cr(VI)-contaminated soil, FZS-Fe exhibited a significant passivation effect: at a dosage of 4wt%, the Cr(VI) content in soil with an initial concentration below 2500 mg / kg dropped to below 150 mg / kg after 9 days (lower than the risk management standard for agricultural land), and the effective Cr(VI) decreased by 72.4%. The RAC (risk assessment level) of the remediated soil dropped from high risk to low / medium risk without causing soil acidification (pH stabilized at 8.2-8.5). In highly contaminated soil (2000-2500 mg / kg), Cr(VI) activity was significantly inhibited, and mobility was reduced by 58-65%, verifying the engineering applicability of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 This is the XRD test pattern of FZS-Fe; Figure 2 This is the XRD test pattern of FZS; Figure 3 is the SEM image of FZS-Fe; Figure 4 is the SEM image of FZS; Figure 5 This is the energy spectrum test result of FZS-Fe; Figure 6 is the energy spectrum test result of FZS; Figure 7 The following are the Fourier transform infrared spectroscopy test results of MGS, FZS and FZS-Fe; Figure 8 is the N2 adsorption-desorption isotherm of FZS-Fe; Figure 9 is the pore size distribution curve of FZS-Fe; Figure 10 is the N2 adsorption-desorption isotherm of MGS; Figure 11 is the pore size distribution curve of MGS; Figure 12 is the N2 adsorption-desorption isotherm of FZS; Figure 13 is the pore size distribution curve of FZS; Figure 14 The changes of Cr(VI) concentration in soil with different passivation agent dosage over time; Figure 15 Continuously extract the percentage histogram of each morphology for different dosages of BCR; Figure 16 is the change of Cr(VI) in soils with different moisture contents over time; Figure 17 The percentage of each morphology was continuously extracted for BCR with different moisture contents; Figure 18 The changes of soil hexavalent chromium with different initial concentrations over time; Figure 19 The bar graph shows the percentage of BCR continuously extracted from the original soil with different initial concentrations of pollution; Figure 20 The bar graphs of the percentage of each morphology were continuously extracted for BCR after repair at different initial concentrations; Figure 21 is the RAC index of different treatment groups. DETAILED DESCRIPTION

[0049] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples are only used to explain the present invention and are not intended to limit the scope of the invention. In the embodiments, if specific conditions are not specified, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0050] The gangue used in this application was sampled from a coal mine in Xiyang County, Shanxi Province. The key parameters of gangue are silicon-aluminum content and silicon-aluminum ratio. Gangue with a silicon content and aluminum content of about 70wt% and a silicon-aluminum molar ratio of about 2.6 can be prepared using the steps described in this application.

[0051] In the following examples, the coal gangue includes the following components in parts by weight: 54.38 parts of SiO2, 20.93 parts of Al2O3, 1.09 parts of MgO, 0.35 parts of Na2O, 0.95 parts of CaO, 2.5 parts of K2O, and 0.52 parts of TiO2.

[0052] Example 1: A passivator material, the preparation method of which comprises the following steps: (1) Grind the coal gangue, pass it through a 200-mesh sieve, soak it in a hydrochloric acid solution (concentration of 20 wt%), and stir it for 3 h. Then, filter it, dry it, and complete the pretreatment process to obtain coal gangue powder. (2) The gangue powder obtained in step (1) was mixed with NaOH in a mass ratio of 1:1.2, placed in a muffle furnace, and calcined at 750°C for 2 h. After cooling, slag was obtained, and NaOH solution was added and stirred to obtain a reaction solution. In the reaction solution, Na + and Si 4+ The molar ratio of H2O and Na is 4:1 + The molar ratio of 50:2 was 50:2, aged at room temperature for 6 hours, placed in a hydrothermal reactor, crystallized at 85°C for 8 hours, washed, and dried at 105°C for 12 hours to obtain a zeolite molecular sieve. (3) The zeolite molecular sieve prepared in step (2) was added to a ferrous sulfate solution (prepared by dissolving FeSO4·7H2O in distilled water at a mass volume ratio of 1 g:200 mL) and stirred at 450 r / min for 2 h. The mixture was filtered through a filter membrane, vacuum dried, and passed through a 200-mesh sieve to obtain a passivation agent material (named FZS-FE).

[0053] Example 2: A passivator material, the preparation method of which comprises the following steps: (1) Grind the gangue, pass it through a 200-mesh sieve, soak it in a hydrochloric acid solution (concentration of 15 wt%), and stir it for 2.5 h. Then, filter it, dry it, and complete the pretreatment process to obtain gangue powder. (2) The gangue powder obtained in step (1) was mixed with NaOH in a mass ratio of 1:1, placed in a muffle furnace, and calcined at 700°C for 2.5h. After cooling, slag was obtained, and NaOH solution was added and stirred to obtain a reaction solution. In the reaction solution, Na + and Si 4+ The molar ratio of H2O and Na is 4:1 + The molar ratio of the two is 50:2, the mixture is aged at room temperature for 5 hours, placed in a hydrothermal reactor, crystallized at 80°C for 9 hours, washed, and dried at 100°C for 15 hours to obtain a zeolite molecular sieve. (3) The zeolite molecular sieve prepared in step (2) was added to a ferrous sulfate solution (prepared by dissolving FeSO4·7H2O in distilled water at a mass volume ratio of 1 g:180 mL) and stirred at 400 r / min for 1.5 h. The solution was filtered through a filter membrane, vacuum dried, and passed through a 200-mesh sieve to obtain a passivating agent material.

[0054] Example 3: A passivator material, the preparation method of which comprises the following steps: (1) Grind the gangue, pass it through a 200-mesh sieve, soak it in a hydrochloric acid solution (concentration of 25 wt%), and stir it for 3.5 h. Then, filter it, dry it, and complete the pretreatment process to obtain gangue powder. (2) The gangue powder obtained in step (1) was mixed with NaOH in a mass ratio of 1:1.5, placed in a muffle furnace, and calcined at 800°C for 1.5h. After cooling, slag was obtained, and NaOH solution was added and stirred to obtain a reaction solution. In the reaction solution, Na + and Si 4+ The molar ratio of H2O and Na is 4:1 + The molar ratio of 50:2 was 50:2, aged at room temperature for 7 hours, placed in a hydrothermal reactor, crystallized at 90°C for 7 hours, washed, and dried at 110°C for 10 hours to obtain a zeolite molecular sieve. (3) The zeolite molecular sieve prepared in step (2) was added to a ferrous sulfate solution (prepared by dissolving FeSO4·7H2O in distilled water at a mass volume ratio of 1 g:220 mL) and stirred at 500 r / min for 2.5 h. The solution was filtered through a filter membrane, vacuum dried, and passed through a 200-mesh sieve to obtain a passivating agent material.

[0055] Comparative Example 1: The coal gangue powder (MGS) was prepared in the same manner as in step (1) of Example 1.

[0056] Comparative Example 2: A passivator material, the preparation method of which comprises the following steps: Without step (3), the product obtained in step (2) is a zeolite molecular sieve (named FZS), and the rest is the same as in Example 1.

[0057] Test example 1. Characterization 1. X-ray diffractometer test and analysis The passivation material (FZS-Fe) prepared in Example 1 and the zeolite molecular sieve (FZS) prepared in Comparative Example 2 were subjected to X-ray diffraction detection. The specific detection method is: using X-ray diffractometer (XRD) to analyze the crystal structure of the sample, and using Jade 9.0 software to perform full spectrum fitting and phase identification (refer to ICDD-PDF standard card) to determine the type of molecular sieve prepared. The results are shown in Figure 1-2 .

[0058] Depend on Figure 1-2 It can be seen that a broad diffraction peak appears at 22°, and Fe²⁺ may be highly dispersed in the zeolite pores or surface in the form of nanoparticles (<10 nm), while diffraction peaks of Fe2Si appear at 31.66° and 45.5°, indicating that divalent iron has been successfully loaded onto the coal gangue-based zeolite molecular sieve.

[0059] 2. Scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) analysis The passivation material (FZS-Fe) prepared in Example 1 and the zeolite molecular sieve (FZS) prepared in Comparative Example 2 were analyzed and tested using a scanning electron microscope (SEM) and an energy dispersive spectrometer (EDS). The specific detection method is as follows: the surface morphology and element distribution of the samples were characterized using a scanning electron microscope and an energy dispersive spectrometer. The micro-area images obtained by the secondary electron detector can be used to analyze the surface structural characteristics of the material, including particle size distribution, pores, and surface roughness. The results are shown in FIG. Figure 3-6 ( Figure 2-3 In the figure, a is magnified 2000 times, and b is magnified 5000 times).

[0060] Depend on Figure 3-4 It can be seen that the prepared passivator particles are well dispersed. Compared with the SEM results of comparative example 2 zeolite molecular sieve (FZS), it can be seen that the particle size is more complete and fine particles can be seen on the surface of the particles, which are presumably Fe 2+ The particles are already attached to the surface of the zeolite.

[0061] Depend on Figure 5-6 It can be seen that the iron element has been evenly loaded on the zeolite.

[0062] 3. Fourier transform infrared spectroscopy (FT-IR) analysis The gangue powder (MGS) of comparative example 1, the gangue-modified zeolite molecular sieve (FZS) of comparative example 2, and the passivator material (FZS-FE) prepared in example 1 were subjected to Fourier transform infrared spectroscopy (FT-IR) detection. The specific detection method is: the organic groups of the materials before and after modification are quantitatively characterized by Fourier transform infrared spectrometer (FT-IR). By analyzing the infrared spectrum test data, the evolution of the bond type and the change of functional groups on the surface of the gangue before and after modification are systematically explored. The test wave number range is set to 450-4000 cm⁻¹. The results are shown in Figure 7 .

[0063] Depend on Figure 7 It can be seen from the infrared spectrum of MGS that the -1 The stretching vibration peak of OH is located at 1632 cm -1 The OH bending vibration peak is located at 1108 cm -1 The stretching vibration peak of Si-O-Si in the silicon-oxygen chain is located at 978 cm -1 and 912cm -1 The stretching vibration peak and bending vibration peak of Si-O are located at 798 cm-1 The double peaks nearby are the stretching vibration peak and bending vibration peak of Al-O, which indicates the presence of alumina in the coal gangue.

[0064] When the gangue is modified into zeolite molecular sieve (FZS), it can be seen from the spectrum that the peak at 1108 cm -1 The stretching vibration peak of Si-O-Si in the silicon-oxygen chain shifted to 1071 cm -1 This is because compared with the Si-O-Si or Si-O-Al structure in coal gangue, the molecular sieve prepared in alkali solution has a large amount of Si-O-Na in its structure, which has a smaller bond angle and a longer bond length, so the absorption peak wave number is reduced. At the same time, the original coal gangue at 959 cm -1 and 798 cm -1 The double peaks nearby become a single peak. This is because the original mineral structure will change during the modification of coal gangue to form a new crystal structure, and the synthesis of zeolite molecular sieves involves the redistribution of elements such as aluminum and silicon and changes in the coordination environment. These changes may cause the original infrared active vibration mode to change, thereby merging the original two characteristic peaks into one. These phenomena all indicate that the coal gangue was successfully modified into zeolite molecular sieves during the experiment.

[0065] When ferrous sulfate was added into the synthesis of gangue-modified zeolite molecular sieve, it was found that the infrared spectrum of FZS-FE was located at 874 cm -1 A new characteristic peak appeared near the 2- ) in the stretching vibration peak of S=O or SO, which indicates the addition of sulfate. The infrared spectrum after adding ferrous sulfate is compared with FZS, which is originally located at 3631cm -1 The OH peak at 3290 cm-1 is red-shifted to 3290 cm-2. -1 At the same time, the peak width here is wider, which indicates that the added ferrous sulfate and FZS form an intermolecular force, namely hydrogen bonding. Due to the presence of the added ferrous sulfate and hydrogen bonding, the functional groups in the original image will be "shielded" to some extent, so the peak is located at 750-500cm -1 The peak at the position becomes less obvious. These phenomena indicate that ferrous sulfate and FZS are successfully compounded and FZS-FE is synthesized as a new substance.

[0066] 4. Specific surface area, pore size and pore volume analysis The gangue powder (MGS) of Comparative Example 1, the gangue-modified zeolite molecular sieve (FZS) of Comparative Example 2, and the passivator material (FZS-FE) prepared in Example 1 were subjected to BET testing. The specific testing method is: using a specific surface area and pore size analyzer to quantitatively characterize the pore structure of the materials. Through systematic analysis of nitrogen adsorption-desorption test data, the evolution of key pore structure parameters such as the specific surface area (BET method), total pore volume and pore size distribution (BJH method) of the materials before and after modification can be accurately obtained. The results are shown in Figure 8-13 and Table 1.

[0067] Table 1 Specific surface area and pore size of MGS and FZS-Fe

[0068] Depend on Figure 8-9 It can be seen that according to the IUPAC classification, the isotherm belongs to type IV, and a hysteresis loop caused by coagulation is clearly present in the curve. Specifically, the hysteresis loop belongs to the H4 type hysteresis loop. According to BET theoretical analysis, the specific surface area of ​​the sample is 397.9 m² / g, which is significantly higher than that of Comparative Example 1. The sample has a higher specific surface area. Its pore volume is 0.4 cm³ / g, reflecting the sample's strong pore capacity. The pore diameter is 3.829 nm, indicating that the sample is a mesoporous material.

[0069] Figure 10-11 It can be seen that the N2 adsorption-desorption isotherm shows an IUPAC type IV isotherm, and there is an H4 type hysteresis loop caused by the condensation phenomenon, which proves that the sample has a certain pore structure. According to BET analysis, the specific surface area of ​​the coal gangue after pretreatment in Comparative Example 1 is relatively low, at 34.3m² / g, indicating that its surface area is small and suitable for small molecule adsorption or specific applications. The pore volume is 3.8cm³ / g, and the smaller pore volume may limit its gas storage or adsorption capacity. The pore diameter is 3.830nm, indicating that the sample is a mesoporous material, but the surface activity of its overall pore structure is weaker than that of Example 1.

[0070] Depend on Figure 12-13 As can be seen, the N2 adsorption-desorption isotherm of Comparative Example 2 is also classified as an IUPAC type IV isotherm, and similarly exhibits an H4-type hysteresis loop caused by condensation. This phenomenon indicates that Comparative Example 2 has a pore structure similar to that of Example 1 and is capable of storing gas through capillary condensation. BET analysis shows that Sample 2 has a specific surface area of ​​252.9 m² / g, a pore volume of 0.5 cm³ / g, and a pore diameter of 3.822 nm. Compared to Comparative Example 2, Example 1 has a further improvement in specific surface area.

[0071] 2. Experiment on the remediation effect of hexavalent chromium contaminated soil Two types of soil were used. Uncontaminated soil samples were collected from Xiyang County, Shanxi Province, and then air-dried, crushed, and sieved. Simulated contaminated soil for soil remediation experiments was prepared by adding potassium dichromate solution to uncontaminated soil. The soil was adjusted to saturated moisture with deionized water. After standing at room temperature in the shade for 15 days, the soil was air-dried, crushed, ground, and sieved (60 mesh) for later use.

[0072] A certain amount of the passivator material prepared in Example 1 was added to 1 g of soil containing a certain concentration of Cr(VI). After mixing them evenly, they were placed in a 50 mL centrifuge tube and placed in a dark, dry and ventilated place for reaction. The effects of factors such as reaction time, initial concentration of Cr(VI) in the soil, soil moisture content, and passivator dosage on the passivation repair effect were investigated.

[0073] Environmental risk assessment: According to the method in "Sequential Extraction Procedure for 13 Trace Elements in Soil and Sediment" (GB / T25282-2010), BCR continuous extraction experiments were conducted on heavy metals in the soil before and after remediation, and the weak acid extraction state of heavy metals in the soil was used as the evaluation standard to evaluate the remediation effect. The extraction steps are as follows: Weak Acid Extraction: Weigh 0.5 g of sample using a precision balance and place it into a 50 mL Erlenmeyer flask. Add 25.00 mL of 0.11 mol / L acetic acid solution. Shake thoroughly and oscillate on a reciprocating shaker for 16 hours at 25°C. Centrifuge. Collect the upper layer of liquid in the centrifuge cup, Extract L1, for analysis.

[0074] Add 20 mL of water to the remaining solid in the conical flask, shake on a reciprocating automatic shaker at 25°C, and then centrifuge. Pour out the upper liquid in the centrifuge cup (do not pour out any solid residue). The solid residue R1 is in the centrifuge cup.

[0075] Reducible state: Add 25.00 mL of 0.5 mol / L hydroxylamine hydrochloride solution to the container containing the solid residue R1. Shake well and oscillate on a reciprocating automatic shaker for 16 hours at 25°C; then centrifuge. Collect the upper liquid in the centrifuge cup, i.e., the extract L2, for testing. Add 20 mL of water to the remaining raisin, shake on a reciprocating automatic shaker at 25°C and centrifuge for 20 min. Pour off the upper liquid in the centrifuge cup (do not pour out any solid residue), and the solid residue R2 is in the centrifuge cup.

[0076] Oxidizable state: Slowly add 10.00 mL of hydrogen peroxide to the container containing solid residue R2 and digest at room temperature for 1 hour. Then, heat on a shaker until the volume is less than 3 mL. After cooling, add another 10.00 mL of hydrogen peroxide and continue heating until the volume is approximately 1 mL. After cooling, add 25.00 mL of 1.00 mol / L ammonium acetate solution to the centrifuge cup and shake on a shaker for 16 hours. Then, centrifuge. Collect the upper layer of liquid from the centrifuge cup for analysis. Add 20 mL of water to the remaining solid, shake, and centrifuge. After centrifugation, discard the upper liquid in the centrifuge cup (do not discard any solid residue). The centrifuge cup contains solid residue R3.

[0077] Residue state: The solid residue R3 is heated in a water bath at 60°C until completely dry and then ground. Depending on the heavy metal content, 0.1-0.2 g is taken for digestion and then the heavy metal elements are determined.

[0078] 1. The influence of passivation agent dosage on passivation effect When exploring the FZS-Fe method to repair soil Cr(VI) contamination, the dosage of the passivation material was adjusted to 1wt%, 2wt%, 3wt%, 4wt%, and 5wt%, the initial moisture content was 35wt%, and the initial concentration of hexavalent chromium in the soil was 1000mg / kg. The changes in the content of Cr(VI) and the stabilization efficiency under different dosages were studied. Figure 14 .

[0079] Depend on Figure 14It can be seen that the addition of the passivation material has a significant effect on the Cr(VI) content. Overall, as the amount of passivation material added increases, the Cr(VI) content in the soil decreases significantly. It can be seen that on the first day of the reaction, the hexavalent chromium content in the soil decreased significantly at all different additions. The initial hexavalent chromium concentration in the soil was 1000 mg / kg. When the passivation dosage increased from 1wt% to 5wt%, the Cr(VI) concentrations after one day of reaction were 238.35 mg / kg, 217.13 mg / kg, 201.52 mg / kg, 136.25 mg / kg, and 83.02 mg / kg, respectively. This indicates that the passivation material acts quickly, thanks to the ferrous iron ions loaded in the material, which rapidly reduce the hexavalent chromium in the soil. After the fifth day, the hexavalent chromium content in the soil continued to decrease over time, but at a significantly slower rate than in the previous few days and gradually stabilized, indicating that the passivation material's effect lasted primarily within 5 days. Studies have shown that while the application of ferrous sulfate or other iron-based passivating agents alone to treat hexavalent chromium-contaminated soil offers the advantages of low cost and rapid action, it also faces the problem of yellowing in the later stages of remediation. Therefore, the addition of gangue-based zeolite molecular sieves can help maintain stability in the later stages of remediation. According to the "Soil Environmental Quality Agricultural Land Soil Pollution Risk Control Standard" (GB15618-2018), published in 2018, the chromium soil pollution risk screening value is 250 mg / kg when the pH is greater than 7.5. After nine days of reaction, the soil pH was above 8.5, and the Cr(VI) levels were 96.52 mg / kg, 86.54 mg / kg, 74.08 mg / kg, 55.16 mg / kg, and 45.49 mg / kg, respectively, all below this standard.

[0080] BCR continuous extraction experiments were conducted on different dosage treatment groups. The experimental results are as follows: Figure 15 As shown in the figure, compared with the untreated simulated contaminated soil, the addition of the passivator effectively reduced the acid-extractable Cr(VI) content in the soil. Moreover, as the dosage increased, the acid-extractable hexavalent chromium content in the soil decreased, while the proportion of residual chromium increased. The content of L1 in the original simulated contaminated soil was 38%. As the dosage increased, when the dosage was 5wt%, the content of L1 decreased to 7%, while the content of residual chromium increased to 51%. This indicates that the FZS-Fe passivator material can effectively repair hexavalent chromium-contaminated soil.

[0081] 2. Influence of moisture content on passivation effect When repairing hexavalent chromium, soil moisture is a relatively important factor. In the experiment, the moisture content was adjusted to 25wt%, 30wt%, 35wt%, 40wt%, and 45wt%, respectively. The initial hexavalent chromium content was 1000mg / kg, and the passivation agent dosage was 4wt%. The changes in Cr(VI) content under different moisture content conditions were analyzed. The results are shown in Figure 16 .

[0082] Depend on Figure 16 As can be seen, the Cr(VI) content in soil treated with different initial moisture contents decreased over time. On the first day of the reaction, the Cr(VI) concentrations at moisture contents of 25wt%, 30wt%, 35wt%, 40wt%, and 45wt% were 125.35mg / kg, 149.87mg / kg, 134.89mg / kg, 106.27mg / kg, and 115.81mg / kg, respectively, representing significant decreases compared to the initial concentrations. The figure also shows that there was no significant difference in the Cr(VI) content of the soil when the moisture content varied from 25% to 45%. However, as the reaction time increased, starting from the seventh day, a trend emerged in which the Cr(VI) content decreased with increasing moisture content. On day 7 of the reaction, the Cr(VI) concentrations at 25wt%, 30wt%, 35wt%, 40wt%, and 45wt% were 75.49 mg / kg, 66.86 mg / kg, 64.67 mg / kg, 58.34 mg / kg, and 51.84 mg / kg, respectively. This indicates that increasing the moisture content facilitates the remediation of Cr(VI) contaminated soil by the FZS-Fe material, likely because increasing the soil moisture content facilitates ion exchange. On day 9 of the reaction, the Cr(VI) concentrations were 68.69 mg / kg, 64.19 mg / kg, 57.55 mg / kg, 54.26 mg / kg, and 46.14 mg / kg, respectively. The experimental results also indicate that on day 9 of the reaction, the Cr(VI) concentrations in soil treated with different moisture contents were all below 250 mg / kg, meeting the risk value requirements for agricultural land in the "Soil Environmental Quality Agricultural Land Soil Pollution Risk Control Standard." However, it should be noted that when the soil moisture content is too high, some hexavalent chromium may dissolve in water and penetrate deep into the surface, causing groundwater pollution. In actual experimental operations, it can also be observed that when the soil moisture content is higher than 40%, the soil becomes muddy and water will seep out. Therefore, it is necessary to select a lower moisture content for repair while ensuring the repair effect.

[0083] BCR continuous extraction experiments were also conducted on different water content treatment groups. The experimental results are as follows: Figure 17As shown in the figure, it can be seen that the change in moisture content does not have a very significant impact on the passivation effect, but it can be roughly seen that with the increase in moisture content, the effect of the passivator is enhanced, which shows that high moisture content is conducive to the passivation agent to repair contaminated soil.

[0084] 3. Effect of different initial concentrations on passivation effect The effect of the initial Cr(VI) concentration in the soil on the remediation effect was investigated. The experiment set the initial Cr(VI) content to be 500mg / kg, 1000mg / kg, 1500mg / kg, 2000mg / kg, and 2500mg / kg, respectively. The moisture content was 35wt%, the dosage was 4wt%, and the initial hexavalent chromium concentration was changed. The changes in soil Cr(VI) content and soil pH, Eh, and EC under these gradients were studied. The results are shown in the figure. Figure 18 .

[0085] Depend on Figure 18 It can be seen that with the increase of the initial Cr(VI) content, when the initial Cr(VI) content was 500 mg / kg, 1000 mg / kg, 1500 mg / kg, 2000 mg / kg, and 2500 mg / kg, the Cr(VI) content after 1 day of reaction was 92.24 mg / kg, 170.31 mg / kg, 304.96 mg / kg, 358.82 mg / kg, and 480.68 mg / kg, respectively, and the Cr(VI) content in the soil decreased significantly. After 9 days of reaction, the Cr(VI) content changed to 8.24 mg / kg, 61.62 mg / kg, 158.93 mg / kg, 229.89 mg / kg, and 323.99 mg / kg. Although the remaining Cr(VI) content in the soil increased with increasing initial concentration, the Cr(VI) content in soil with an initial concentration below 2500 mg / kg after 9 days of reaction was already below the risk value for agricultural land. This indicates that the FZS-Fe passivation material can achieve Cr(VI) reduction and stabilization at Cr(VI) concentrations between 500 and 2500 mg / kg.

[0086] At the same time, BCR continuous extraction experiments were carried out on soils treated with different initial concentrations. The experimental results of the control group and the laboratory group are as follows: Figure 19-20 As shown in the figure, it can be seen that the remediation effect of the FZS-Fe passivation material is more obvious. When the initial concentration is 500 mg / kg, the percentage of acid-extractable states in the soil after remediation has been reduced to 2%; under high concentration conditions, the passivation efficiency of the passivator on acid-extractable states in the soil has also reached about 50%. To further improve the remediation effect of high-concentration contaminated soil, it is necessary to increase the dosage of the passivator.

[0087] 4. Environmental risk assessment RAC is calculated based on heavy metal speciation analysis, which uses the exchangeable content of heavy metal chemical forms or the percentage of exchangeable content in the total content to evaluate the risk of heavy metal pollution. The risk assessment index changes of Cr in soils of different treatment groups in this experiment are shown in Figure 2. Figure 21 (The first five are untreated control groups; A1 to A5 are the experimental results of different dosages ranging from 1wt% to 5wt% for 9 days; B1 to B5 are the experimental results after treatment with different moisture contents; C1 to C3 are the experimental results of different initial concentrations, dosage of 4wt%, and reaction time of 9 days).

[0088] Depend on Figure 21 As can be seen, the RAC index of the untreated control soils was high. The control soil with a hexavalent chromium concentration of 500 mg / kg was rated as medium risk, while the control soils with higher concentrations were all rated as high risk. After treatment with the passivation material, the RAC index of the soils at different initial concentrations decreased. The RAC index of the soils with initial concentrations of 500 mg / kg and 1000 mg / kg dropped to low risk, and the RAC index of the soils with higher concentrations also dropped from high risk to medium risk. The results of Group A show that when the dosage is greater than 3wt%, the FZS-Fe passivation material is effective in remediating 1000 mg / kg hexavalent chromium-contaminated soil, effectively reducing its environmental toxicity. The results of Group B show that when the moisture content is greater than 30wt%, a dosage of 4% can reduce the contaminated soil with a hexavalent chromium concentration of 1000 mg / kg to low risk. Overall, the FZS-Fe passivation material is effective in remediating hexavalent chromium-contaminated soil, effectively reducing the toxicity and mobility of hexavalent chromium in the soil.

[0089] 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 in the scope of protection of the present invention.

Claims

1. A method for preparing a passivator material, characterized in that: The following steps are involved: (1) Pre-treating the coal gangue to obtain coal gangue powder; (2) mixing the gangue powder obtained in step (1) with NaOH, calcining, cooling, obtaining slag, adding NaOH solution and stirring to obtain a reaction solution, aging, crystallizing, washing, and drying to obtain a zeolite molecular sieve; (3) Adding the zeolite molecular sieve prepared in step (2) into the ferrous sulfate solution, stirring, filtering, drying, and sieving to prepare the passivating agent material.

2. The method for preparing a passivator material according to claim 1, wherein In step (1), the coal gangue is ball-milled, sieved, soaked in a hydrochloric acid solution, stirred, and then filtered and dried to complete the pretreatment process.

3. The method for preparing the passivator material according to claim 2, wherein: The concentration of the hydrochloric acid solution is 15-25wt%.

4. The method for preparing a passivator material according to claim 1, wherein: In step (2), the mass ratio of gangue powder to NaOH is 1:1-1.

5.

5. The method for preparing a passivator material according to claim 1, wherein: In step (2), calcination is performed at 700-800°C for 1.5-2.5h.

6. The method for preparing a passivator material according to claim 1, wherein: In step (2), in the reaction solution, Na + and Si 4+ The molar ratio of H2O and Na is 4:1 + The molar ratio is 50:

2.

7. The method for preparing a passivator material according to claim 1, wherein: In step (3), the ferrous sulfate solution is prepared by the following method: FeSO4·7H2O is dissolved in distilled water to obtain the ferrous sulfate solution.

8. The method for preparing a passivator material according to claim 1, wherein: In step (3), the mass volume ratio of the zeolite molecular sieve and the ferrous sulfate solution is 1 g:180-220 mL.

9. The passivator material obtained by the method for preparing the passivator material according to any one of claims 1 to 8.

10. Use of the passivator material according to claim 9 in hexavalent chromium soil remediation.

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