Preparation method and application of polymetallic mineralizing agent with adsorption, precipitation and reduction functions

Abstract

The invention relates to the technical field of heavy metal pollution treatment, in particular to a preparation method and application of a polymetallic mineralizing agent with adsorption, precipitation and reduction functions. The preparation method comprises the following steps: firstly, preparing an MgFe-LDH precursor with a specific molar ratio through a nucleation-crystallization isolation method, and then inducing the material to generate topological transformation through an accurately controlled hydrogen roasting reduction process to generate a composite structure material integrating a strong adsorption / precipitation function of a mixed oxide substrate and a strong reduction function of a zero-valent iron (Fe (0)) site. The MgFe-X mineralizer disclosed by the invention can realize synergistic, efficient and stable mineralization of Cd (II) (Cd < 2 + >), As (III) (AsO2-) and Cr (III) (CrO4 < 2->) in soil, and exerts the fertilizer-expelling targeting advantage: in the mineralization process, the MgFe-X mineralizer can slowly release nutrient elements Mg < + > and Fe < + > necessary for plants to promote plant growth.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of heavy metal pollution treatment, and particularly relates to a preparation method and application of a multi-metal mineralizer with adsorption, precipitation and reduction functions. BACKGROUND

[0002] With the continuous development of mineral resources, heavy metal pollution has become a serious environmental problem. Although traditional remediation technologies such as chemical precipitation, membrane separation, electrochemistry and photocatalysis are widely used, they are generally faced with high risk of secondary pollution, high energy consumption or efficiency bottleneck, etc. In comparison, in-situ mineralization remediation technology has shown great potential in the field of soil heavy metal treatment due to its advantages of simple operation, outstanding cost-effectiveness and easy availability of materials.

[0003] Currently commonly used in-situ mineralizers mainly include biochar, metal oxides and metal organic frameworks, but they all have obvious defects: carbon-based materials: activated carbon and biochar are low in price, but their adsorption capacity is limited, which restricts their treatment effect metal oxides: poor acid and alkali stability, which limits their application in complex environments. For example, under weakly acidic conditions, the dissolution of Mn 2+ and Fe 3+ will significantly reduce the removal efficiency of Cr(VI)

[0004] Therefore, in recent years, researchers have developed mixed metal oxide (MMO) materials, which are composite oxides formed by calcining precursor layered double hydroxides (LDHs). MMOs have the unique advantages of high dispersion, stable dispersion and uniform dispersion of metal elements and mineralization active sites, and also retain a large number of structural defects, including a large number of: oxygen vacancies, which can expose unsaturated coordination sites to achieve efficient fixation of heavy metal ions through strong chemical bonds; metal vacancies, which further expand the interlayer spacing and specific surface area, promoting ion diffusion and contact. The synergistic effect of the two has important application potential in the field of environmental remediation.

[0005] Zero-valent iron, as a highly active mineralizer with strong reducing ability, has been widely used in the removal of various heavy metal ions. However, nano zero-valent iron (nZVI) often faces the "see-saw" effect of difficult balance between adsorption activity and stability in practical application, which limits its long-term remediation effect. Therefore, developing a mineralization material that can simultaneously treat heavy metal anion and cation combined pollution with high adsorption capacity and high removal efficiency has become an important direction in the field of soil remediation. SUMMARY

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and propose a method for preparing and applying a polymetallic mineralizer that combines adsorption, precipitation and reduction functions. The resulting polymetallic mineralizer can combine the structural and performance advantages of MMO and nZVI, and significantly improve the capture ability of various heavy metals.

[0007] To achieve the above objectives, the technical solution specifically adopted by the present invention is as follows: A method for preparing a multi-metal mineralizer with adsorption, precipitation, and reduction functions is based on the following core design idea: preparing a MgFe-LDH precursor with a specific molar ratio through a nucleation-crystallization isolation method, and then inducing a topological transformation of the material through a precisely controlled hydrogen calcination reduction process to generate a composite material that integrates the strong adsorption / precipitation function of the mixed oxide substrate with the strong reduction function of zero-valent iron (Fe(0)) sites. The method includes the following steps: S1. Synthesizing MgFe-LDH precursor using a nucleation-crystallization isolation method; a. Preparation containing Mg 2+ and Fe 3+ Metal salt solution A, in which Mg 2+ with Fe 3+ The molar ratio is (2.5-3.5):1; preferably 3:1; b. Prepare an alkaline solution B containing sodium hydroxide and sodium carbonate; c. Pour solution A and solution B into a high-speed shearing device with a rotation speed of 3000-5000 rpm at the same time, react for 1-5 minutes to obtain a slurry; d. The slurry is subjected to solid-liquid separation, washed until neutral, and dried at 50-80℃ for 6-24 hours to obtain the MgFe-LDH precursor.

[0008] S2, Preparation of MgFe-X by hydrogen roasting and reduction treatment Under a hydrogen-containing protective atmosphere, the MgFe-LDH precursor was calcined and reduced at a set temperature X to obtain the multimetallic mineralizer MgFe-X. The set temperature X was selected from one or more temperature points within the range of 550℃ to 850℃, and after reaching the set temperature X, it was held at that temperature for 0.5h to 5h. After the calcination and reduction treatment, the obtained product was cooled to room temperature under the protective atmosphere and collected. The collected product was then sealed and stored under an inert gas atmosphere. At 550℃, the MgFe-LDH calcined and reduced by hydrogen undergoes a topological transformation, generating new mixed oxide-based synergistic Fe(0) mineralization sites (MgFe-X), which can further significantly improve the multimetallic synergistic mineralization capacity of the original LDHs-based ultrastable mineralizing materials.

[0009] Further, in step a, solution A is prepared by dissolving 9.23g Mg(NO3)2·6H2O and 4.85g Fe(NO3)3·9H2O in deionized water; In step b, solution B is prepared by dissolving 1.92g NaOH and 5.08g Na2CO3 in deionized water.

[0010] In order to control the degree of Fe(III) reduction, in step S2, the protective atmosphere is a mixture of argon and hydrogen, wherein the volume percentage of hydrogen is 5%-15%, preferably 10%.

[0011] In order to ensure that the material is heated evenly and to avoid structural defects or local sintering caused by thermal stress, in step S2, the temperature is programmed to rise to the set temperature X at a heating rate of 1-10℃ / min, preferably 5℃ / min.

[0012] The polymetallic mineralizer (MgFe-X) prepared by the method described in this invention has significant application effects in environmental remediation, specifically reflected in: Application in water remediation: The mineralizing agent can efficiently remove AsO2 from water. ﹣ Cd 2+ and CrO4 2﹣ Plasma exhibits superior single and synergistic adsorption performance.

[0013] Application in soil remediation: The mineralizing agent is uniformly mixed with soil contaminated with arsenic, cadmium, and chromium at a mass ratio of (0.5-5):100. This mineralizing agent can simultaneously and efficiently immobilize various activated heavy metals in the soil through multiple mechanisms such as adsorption, co-precipitation, surface complexation, and redox, driving them to transform into thermodynamically stable mineral phases. This significantly reduces the bioavailability and toxicity of heavy metals and promotes healthy plant growth. Specifically, the MgFe-X mineralizing agent, after calcination and reduction treatment, slowly and gradually releases magnesium ions (Mg²⁺) during the heavy metal removal process. 2+ ) and iron ions (Fe 3 + Both are essential elements for plant growth and play important physiological and biochemical roles in the soil-plant system. Mg 2+ It is a core component of the chlorophyll molecule, directly participating in photosynthesis and activating various enzymes to promote the synthesis and transport of carbohydrates; Fe 3+As key cofactors of various oxidoreductases and electron transporters, they participate in plant respiration, energy metabolism, and nitrogen assimilation. Their dissolution not only helps improve soil ion balance and nutrient availability, but also alleviates, to some extent, the physiological stress on crops caused by the presence of heavy metals. This comprehensively enhances crop nutrient absorption efficiency, photosynthetic capacity, and stress resistance, exhibiting a multifaceted positive promoting effect on crop growth and development.

[0014] This invention successfully developed a MgFe-LDH-based mineralizer (MgFe-X) modified by hydrogen roasting and reduction. This MgFe-X mineralizer has the following characteristics and beneficial effects: 1) A MgFe-X in-situ mineralizer with both mineralization activity and stability was constructed. Compared to traditional mineralizers such as biochar materials, metal oxides, and metal-organic frameworks, the MgFe-X mineralizer of this invention can simultaneously and efficiently immobilize and stabilize multiple activated heavy metals in water and soil through multiple mechanisms, including surface adsorption, redox reactions, and complexation precipitation, promoting their transformation into thermodynamically stable mineral phases. This solves the "seesaw" effect often faced by nZVI in practical applications, where adsorption activity and stability are difficult to balance. It also possesses high adsorption capacity, high removal efficiency, and the ability to simultaneously and stably remediate complex pollution from multiple heavy metal anions and cations.

[0015] 2) The mineralizer has good acid resistance. MgFe-X mineralizer maintains excellent mineralization performance even in acidic environments (pH=4.0-6.0), giving it a significant advantage in practical applications for treating acidic soils. 3) Mineralizing agents can release Mg 2+ and Fe 3+ Promote plant growth The MgFe-X mineralizer, after roasting and reduction, will be accompanied by Mg during the mineralization of various heavy metals. 2+ and Fe 3+ The leaching and release of these substances can promote the growth and development of corresponding crops in the soil. Attached Figure Description

[0016] Figure 1 The figures show the XRD characterization results of MgFe-CO3 and MgFe-X.

[0017] Figure 2 AsO2 monoadsorbed (mineralized) in aqueous solution ﹣ Cd 2+ and CrO4 2﹣ The ICP-OES test results.

[0018] Figure 3Magnesium ions (Mg) in aqueous solution during the MgFe-850 mineralization process 2+ ) and iron ions (Fe 3+ Dissolution status.

[0019] Figure 4 AsO2 in aqueous solution ﹣ Cd 2+ and CrO4 2﹣ Results of co-adsorption experiments.

[0020] Figure 5 The results of the wheat seedling cultivation experiment. Detailed Implementation

[0021] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. Example 1

[0022] Synthesis of MgFe-LDH MgFe-LDH powder was synthesized using a "nucleation-crystallization isolation" strategy. The specific method is as follows: Preparation of solution A: Accurately weigh 9.23g Mg(NO3)2·6H2O and 4.85g Fe(NO3)3·9H2O into a 250mL beaker, add 100mL deionized water, and stir magnetically at room temperature for 30 minutes until completely dissolved to form a transparent solution; Preparation of solution B: Accurately weigh 1.92g NaOH and 5.08g Na2CO3 into another 250mL beaker, add 100mL deionized water, and stir until completely dissolved; Nucleation-crystallization isolation: Solution A and solution B were quickly poured into a high-speed colloid mill maintained at 25±2℃ and 4000 rpm. After the reaction was maintained for 2 min, the slurry was collected and centrifuged at 8000 rpm. The sample was continuously washed with deionized water until the pH of the supernatant was close to neutral. The supernatant was then discarded, and the centrifuged product was collected. The product was then dried at 60℃ for 12 h and ground to obtain the final product, labeled as MgFe-LDH.

[0023] Synthesis of MgFe-X by hydrogen roasting reduction method (X = calcination temperature, unit is...) o C) Collect the dried MgFe-LDH powder, weigh out 300 mg of MgFe-LDH powder, spread it evenly in a magnetic boat, and calcine and reduce the MgFe-LDH powder under an Ar / H2 (90% / 10%) atmosphere at a heating rate of 5 °C / min: the initial temperature is 150 °C, and the temperature is increased to 850 °C. o C, every 100 o C represents a time interval. The samples were heat-treated at eight key temperatures: 150℃, 250℃, 350℃, 450℃, 550℃, 650℃, 750℃, and 850℃, with each temperature held constant for 120 minutes. The samples obtained after heat treatment at each temperature were uniformly labeled MgFe-X, where "X" represents the specific heat treatment temperature (e.g., a sample calcined at 350℃ is designated MgFe-350). After each isothermal heat treatment, the samples were allowed to cool naturally to room temperature (approximately 25℃) under a continuous Ar / H2 atmosphere. The calcined powder was then collected, protected under a N2 atmosphere, sealed, and stored in a refrigerator for subsequent characterization and testing.

[0024] To systematically study the effect of calcination temperature on the material structure, we performed X-ray diffraction (XRD) characterization on the synthesized MgFe-LDH and the MgFe-X series samples obtained by calcination at different temperatures. The characterization results are as follows: Figure 1 As shown: MgFe-LDH was successfully synthesized. The precursor MgFe-LDH exhibits a typical and well-crystallized layered double hydroxide crystal structure. With increasing calcination temperature, MgFe-LDH gradually loses interlayer anions, first undergoing a structural topological transformation from LDHs to MMOs. Subsequently, Fe(III) is gradually reduced under H2 atmosphere, and the elemental phase Fe(O) appears in MgFe-550. With further increases in calcination temperature, the oxide Mg... 1-x Fe x The crystal forms of O and Fe(0) tend to be complete. Example 2

[0025] Monoadsorption (mineralization) of AsO2 in aqueous solution ﹣ Cd 2+ and CrO4 2﹣ experiment To systematically evaluate the removal performance of the prepared MgFe-LDH and its calcined product MgFe-X series materials on typical heavy metal oxygen anions and cations in water, we conducted a study targeting arsenite (AsO2). ﹣ ), cadmium ions (Cd) 2+ ) and chromate (CrO4) 2﹣ Adsorption experiments of ).

[0026] First, place 25 mg of MgFe-LDH or MgFe-X into a beaker, then add it to a beaker containing 50 mL of a solution of heavy metal pollutants at a specific concentration (C0 = 100 mg / L). ﹣1 (V=50mL, t=0-720min) The solution was magnetically stirred to ensure uniform dispersion. At specific mineralization times, 1mL of solution was collected, and the concentrations of heavy metal ions and Mg in the supernatant were monitored by ICP-OES. 2+ and Fe 3+ The dissolution of Cd. 2+ and CrO4 2﹣ The mineralization experiment was conducted in accordance with the steps described above, except that sodium arsenite was replaced with cadmium nitrate dihydrate (CO = 500 mg / L). ﹣1 Potassium dichromate (CO = 100 mg / L) ﹣1 Except for the initial concentration, all other conditions were the same.

[0027] ICP-OES results show that, as shown in Figure a, for AsO2 ﹣ As the roasting temperature increased, the mineralization capacity showed an increasing trend, until reaching 850. o After C (MgFe-850), the mineralization capacity stabilized at 74.1 mgg. ﹣1 Similar to AsO2 ﹣ As shown in Figure c, MgFe-850 affects CrO4 2﹣ The mineralization capacity remained stable at 220.2 mgg. ﹣1 As for the cation Cd 2+ As shown in Figure b, the trend of mineralization capacity with calcination temperature differs from that of anions: Firstly, MgFe-X has a different effect on Cd. 2+ The mineralization capacity exhibits a volcanic-shaped trend, meaning it first increases and then decreases, reaching its peak at approximately 620.6 mg / g when MgFe-550 is used as the mineralizing agent. ﹣1 Subsequently, as the calcination temperature further increased, the adsorption capacity decreased slightly.

[0028] The above mineralization experiments verified the effects on Cd. 2+ Although MgFe-550 exhibited superior adsorption performance, MgFe-850 demonstrated superior synergistic mineralization capacity when considering overall anion mineralization capacity. After comprehensive consideration, we subsequently used MgFe-850 for our follow-up research.

[0029] At the same time, magnesium ions (Mg) in the aqueous solution were also sampled and monitored regularly during the MgFe-850 mineralization process. 2+ ) and iron ions (Fe 3+ Dissolution status. For example... Figure 3As shown, the ICP-OES results indicate that AsO2 was successfully produced in MgFe-850. ﹣ Cd 2+ and CrO4 2﹣1 After single adsorption, Mg can be detected in the solution. 2+ and Fe 3+ The leaching and release of these substances can promote crop growth and development to a certain extent. Example 3

[0030] AsO2 in aqueous solution ﹣ Cd 2+ and CrO4 2﹣ Co-adsorption experiment Based on the results of the aforementioned single-component adsorption experiments, this study selected the adsorption of AsO2... ﹣ Cd 2+ and CrO4 2﹣ The sample exhibiting the optimal adsorption capacity (denoted as preferred MgFe-X) was used as the adsorbent in the co-adsorption experiment. This experiment aims to simulate the complex hydrochemical environment of multiple ion coexistence and to explore in depth the interaction, competition mechanism, and possible synergistic effect of different heavy metal ions (oxygen anions and cations) at the adsorption sites.

[0031] Preparation of co-adsorption solution and reaction conditions; pollutant preparation: preparation of solution containing AsO2 ﹣ Cd 2+ and CrO4 2﹣ The initial concentration of each of the three ions in the mixed solution was set to 20 mg / L. ﹣1 Using 1 mol / L ﹣1 A dilute HNO3 solution was used to precisely adjust the initial pH of the above mixed solution to 5.0 to eliminate interference from different initial pH values ​​on adsorption competition.

[0032] Adsorption experiment: 50 mL of the prepared co-adsorption solution was measured into the reactor, and 50 mg of the preferred MgFe-X adsorbent was added. Magnetic stirring was started (the speed was the same as in the single adsorption experiment). Samples were taken at specific time intervals (e.g., t = 0, 5, 15, 30, 60, 120, 240, 360, 480, 720 min). 1.0 mL of slurry was accurately drawn using a microsyringe, and the residual concentrations of the three target heavy metal ions in the filtrate were simultaneously determined using ICP-OES. The synergistic removal rate of the material for the three heavy metal ions was calculated based on this.

[0033] like Figure 4 As shown, MgFe-850 exhibits a high affinity for AsO2. ﹣ Cd 2+ and CrO4 2﹣It exhibits excellent synergistic removal effect; when the mineralization time reaches 240 min, the synergistic removal rate of the three heavy metal ions can reach over 92%. Example 4

[0034] Wheat seedling growth and cultivation experiment To visually verify the in-situ fixation and remediation effects of the prepared MgFe-LDH materials (especially MgFe-550 and MgFe-850) on actual composite contaminated soil from a biological perspective, this study designed a greenhouse pot experiment. By observing the growth response of wheat (Triticum aestivum L.) seedlings under different soil conditions, the study evaluated the material's ability to reduce the bioavailability and ecotoxicity of heavy metals in the soil, and explored its potential as a micronutrient fertilizer to promote plant growth.

[0035] Materials and Grouping: The experiment consisted of 6 parallel treatments, with two replicates in each group, as detailed below: Blank control group (groups 1 and 2): 80g of clean soil was used.

[0036] Pollution control group (groups 3 and 4): 80g of soil contaminated with arsenic, cadmium and chromium (the same soil as the soil in the in-situ mineralization experiment).

[0037] MgFe-550 remediation group (group 5): 80g of soil contaminated with arsenic, cadmium and chromium was uniformly mixed with 2wt% MgFe-550 material.

[0038] MgFe-850 remediation group (Group 6): 80g of soil contaminated with arsenic, cadmium and chromium was uniformly mixed with 2wt% MgFe-850 material.

[0039] Seedling Cultivation and Management: Sowing: Sow 50 wheat seeds evenly in the soil of each petri dish. Place the petri dishes in an artificial climate chamber to simulate natural light (light / dark cycle 14h / 10h) and maintain a constant temperature (25±2°C). Add 20mL of deionized water to each group of soil daily to maintain suitable humidity.

[0040] Growth monitoring: On days 5, 6, 7, 8, 9, 11, 12, 13, and 14 after sowing, the seedling height, stem diameter, number of leaves, and biomass (fresh weight and dry weight) of each group were systematically measured and recorded.

[0041] Results: After a 14-day incubation period, wheat seedlings in different treatment groups showed significant differences in growth. Figure 5The seedlings in the blank control group grew normally and showed good health. The seedlings in the polluted control group exhibited obvious symptoms of heavy metal stress: stunted growth, yellowing (chlorosis) of leaves, and poor root development. The seedlings in the in-situ mineralization remediation group showed significant improvement in growth. Among them, the seedlings in the MgFe-850 remediation group showed the best performance in terms of plant height, stem diameter, and leaf vigor, with growth indicators significantly better than the polluted control group and approaching the level of the blank control group. This indicates that the material MgFe-850 can efficiently and synchronously fix various heavy metal ions such as arsenic, cadmium, and chromium in the soil through adsorption and co-precipitation mechanisms, thereby drastically reducing the content of bioavailable heavy metals in the soil and effectively alleviating the toxic effects of heavy metals on wheat seedlings. Simultaneously, the magnesium and iron elements contained in MgFe-850, as essential micronutrients for plant growth, can be slowly released into the soil, playing a positive role in promoting the healthy growth of seedlings. In summary, this plant experiment strongly demonstrates from an ecological perspective that MgFe-850 material can not only effectively passivate heavy metals in soil, but also improve the soil microenvironment and promote plant growth, showing promising application prospects.

[0042] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a multi-metal mineralizer with adsorption, precipitation, and reduction functions, characterized in that: Includes the following steps: S1. Synthesizing MgFe-LDH precursor using a nucleation-crystallization isolation method; S2. Under a hydrogen-containing protective atmosphere, the MgFe-LDH precursor is calcined and reduced at a set temperature X to obtain the polymetallic mineralizer MgFe-X; wherein the set temperature X is selected from one or more temperature points in the range of 150℃ to 850℃, a tube furnace is used for calcination and reduction, the heating rate is 5℃ / min, after the furnace temperature drops to room temperature, the calcined powder is collected and protected under a N2 atmosphere, sealed and stored in a refrigerator.

2. The method for preparing a multi-metal mineralizer with adsorption, precipitation, and reduction functions as described in claim 1, characterized in that: In the MgFe-LDH precursor, Mg 2+ with Fe 3+ The molar ratio is 3:

1.

3. The method for preparing a multi-metal mineralizer with adsorption, precipitation, and reduction functions as described in claim 1, characterized in that: Step S1 includes the following steps: a. Preparation containing Mg 2+ and Fe 3+ Metal salt solution A, in which Mg 2+ with Fe 3+ The molar ratio is 3:1; b. Prepare an alkaline solution B containing sodium hydroxide and sodium carbonate; c. Pour solution A and solution B into a high-speed shearing device with a rotation speed of 3000-5000 rpm at the same time, react for 1-5 minutes to obtain a slurry; d. The slurry is subjected to solid-liquid separation, washed until neutral, and dried at 50-80℃ for 6-24 hours to obtain the MgFe-LDH precursor.

4. The preparation method of a multi-metal mineralizer with adsorption, precipitation and reduction functions as described in claim 3, characterized in that: In step a, solution A is prepared by dissolving 9.23g Mg(NO3)2·6H2O and 4.85g Fe(NO3)3·9H2O in deionized water; In step b, solution B is prepared by dissolving 1.92g NaOH and 5.08g Na2CO3 in deionized water.

5. The method for preparing a multi-metal mineralizer with adsorption, precipitation, and reduction functions as described in claim 1, characterized in that: In step S2, the protective atmosphere is a mixture of argon and hydrogen, wherein the volume percentage of hydrogen is 5%-15%.

6. The method for preparing a multi-metal mineralizer with adsorption, precipitation, and reduction functions as described in claim 1, characterized in that: In step S2, the temperature is increased to the set temperature X at a heating rate of 1-10℃ / min.

7. The application of a polymetallic mineralizer prepared by the method according to any one of claims 1-6 in environmental remediation, characterized in that, The application includes using the mineralizer to fix one or more heavy metal ions.

8. The application as described in claim 7, characterized in that, The environmental remediation refers to water body remediation; the heavy metal ions include AsO2. ﹣ Cd 2+ and CrO4 2﹣ One or more of them.

9. The application as described in claim 7, characterized in that, The environmental remediation is soil remediation; the mass ratio of the mineralizing agent to the contaminated soil is (0.5-5):

100.

10. The application as described in claim 7, characterized in that, The mineralizing agent is used to simultaneously fix AsO2 in water or soil. ﹣ Cd 2+ and CrO4 2﹣ .

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