Adsorbent for remediation of heavy metal contaminated soil, preparation method and application

Abstract

The present invention belongs to the technical field of soil remediation, and specifically relates to an adsorbent for remediating heavy metal-contaminated soil, a preparation method, and applications. By alkaline-modifying the surface of hollow glass microspheres, using a silane coupling agent as a connector, and grafting prepared nano-scale ferrosoferric oxide, a self-suspending and magnetic magnetic iron-based hollow glass microsphere (FHGM) is obtained. When used for remediating heavy metal-contaminated soil, the adsorbent can enhance the separation and migration of different forms of heavy metals in the contaminated soil due to its large specific surface area, saturated magnetic field strength, and functional groups on the surface of the material. At the same time, it can achieve regeneration and recovery of the adsorbent material without damaging its structure.

Description

Technical Field

[0001] The present invention belongs to the field of environmental remediation technology, and specifically relates to a soil heavy metal adsorbent designed through surface modification and magnetic functionalization, as well as its preparation method and application. The adsorbent is particularly suitable for in situ / ex situ remediation of heavy metal pollution such as cadmium in low-permeability soils. Background Art

[0002] Traditional remediation technologies for heavy metal-contaminated soils include chemical fixation, chemical leaching, phytoremediation, soil replacement, and adsorption. While significant progress has been made through years of research, these technologies still face drawbacks such as high costs, low efficiency, and an inability to reuse resources.

[0003] Among them, fixation / stabilization remediation technology is the most widely used. The remediation purpose is achieved by adding fixation / stabilizers to the soil to stabilize heavy metals in the soil. However, as time goes by, whether the fixation / stabilizers can still lock the heavy metals firmly and whether the solidification / stabilizers will cause secondary pollution to the environment are issues that need to be addressed.

[0004] Adsorption is a widely used treatment method that can achieve the adsorption of heavy metal ions while using less adsorbent. However, the traditional adsorption method is subject to the special physical and chemical properties of the adsorbent and the soil, especially for low-permeability soils. The adsorbent after adsorbing heavy metals is difficult to separate, and the structure of the adsorbent itself is easily destroyed during separation, which has the risk of causing secondary pollution. Therefore, its application in the treatment of heavy metals in soil is very limited.

[0005] For example, patent CN202411683917.6 discloses a method for preparing an adsorption material and removing heavy metal cadmium from paddy soil. This is also a new adsorption material based on hollow glass microspheres. It can effectively remove heavy metal cadmium from paddy soil without causing secondary pollution, and the adsorption material is easy to recycle and reuse. Its specific preparation method includes: (1) treating the hollow glass microspheres with an alkaline solution and setting aside; (2) adding sodium alginate to pure water and stirring to obtain a sodium alginate solution with a mass fraction of 1-2.5%; (3) adding the hollow glass microspheres treated in step (1) to the sodium alginate solution and stirring evenly to obtain a hollow glass microsphere sodium alginate solution, then using a syringe to draw the hollow glass microsphere sodium alginate solution and adding it dropwise to a 0.1-0.5 mol / L calcium chloride solution, letting it stand for 12-24 hours, filtering and washing, and freeze-drying to obtain the adsorption material.

[0006] However, compared with this solution, there are at least the following defects:

[0007] 1. This solution relies on physical adsorption of sodium alginate gel, which takes 72 hours to complete (step S2 in the manual). The adsorption time is long, and the repair cycle and efficiency are not ideal;

[0008] 2. This solution relies on flotation to recover materials, which requires standing and separating the adsorbent from the water surface. The gel structure may be damaged due to swelling / contraction (paragraphs

[0009] and

[0033] of the specification), resulting in secondary pollution;

[0009] 3. This solution relies on Fe 3+ Activation to release cadmium ions, with a single function (paragraphs

[0014] -

[0021] of the specification);

[0010] 4. Sodium alginate was used to physically encapsulate HGM without modifying the surface of HGM. The particles were easy to fall off. The active sites of the HGM were dependent on the carboxyl / hydroxyl groups of the gel. Ferroferric oxide was not involved in the surface modification (step (3) in the manual);

[0011] 5. The preparation process requires an activation step (FeCl3 solution) and long-term stirring (72 hours), which is complicated to operate, and the cost of sodium alginate and calcium chloride is relatively high. Summary of the Invention

[0012] The first object of the present invention is to provide a composite adsorbent with self-suspension and magnetic responsiveness to solve the problems of difficult separation, insufficient active sites and poor stability of traditional soil remediation materials.

[0013] The second object of the present invention is to provide a method for preparing an adsorbent for remediation of heavy metal contaminated soil, wherein a multifunctional adsorbent is constructed through a three-step synergistic modification process of alkaline etching pore formation, silane coupling agent interface bridging, and controllable loading of magnetic nanoparticles.

[0014] The third object of the present invention is to provide an adsorbent for the remediation of heavy metal contaminated soil, through which the adsorbent can efficiently adsorb heavy metals in the soil and efficiently remove materials from the soil as much as possible.

[0015] The embodiment of the present invention is achieved as follows:

[0016] A method for preparing an adsorbent for remediation of heavy metal contaminated soil comprises the following steps:

[0017] (1) Preparation of nano-ferroferric oxide: FeCl3·6H2O was dissolved in ethylene glycol, anhydrous sodium acetate was added, and the mixture was stirred at 200-300 rpm for 40-50 minutes to form a homogeneous solution. The solution was transferred to a polytetrafluoroethylene-lined stainless steel autoclave and reacted at 200°C for 10 hours. After cooling, the solution was washed with ethanol and dried at 60°C for 10 hours to obtain granular nano-ferroferric oxide with a particle size of 100-200 nm.

[0018] (2) Alkali pretreatment of hollow glass microspheres HGM: HGM was dispersed in pure water, heated to 80°C at 10-15°C / min, stirred at 250 rpm for 10 minutes, and then added with 0.75 mol / L sodium hydroxide solution to form a rough micron-scale porous structure by alkali etching. The mixture was stirred at 300 rpm for 4 hours, washed three times with pure water, filtered, and dried at 60°C for 10 hours to obtain alkali-etched NHGM.

[0019] (3) Grafting silane coupling agent: The NHGM obtained in step (2) was dispersed in a 96% ethanol solution, and the silane coupling agent KH-550 was added. The mixture was stirred at 200 rpm at 80°C for 2 hours to form a silanized interface layer through the chemical bonding between the amino group (-NH2) of KH-550 and the hydroxyl group (-OH) on the surface of HGM. The mixture was washed three times with pure water, filtered, and dried at 60°C for 10 hours to obtain KHGM.

[0020] (4) Loading nano-ferroferric oxide: The KHGM obtained in step (3) and the nano-ferroferric oxide obtained in step (1) were mixed in a mass ratio, stirred at 200 rpm at 80°C for 2 hours, washed three times with pure water and filtered, and dried at 60°C for 10 hours. The nano-ferroferric oxide was uniformly loaded on the surface of KHGM through the bridging effect of the silane coupling agent to form a composite adsorbent FHGM with self-suspension and magnetic responsiveness.

[0021] In a preferred embodiment of the present invention, the particle size of nano-ferroferric oxide in step (1) is controlled by the reaction heating rate. When the heating rate is 10-12°C / min, a 100-200 nm granular structure is generated, and the saturation magnetization intensity is 30-35 emu / g.

[0022] In a preferred embodiment of the present invention, the porous structure formed by alkaline etching in step (2) increases the specific surface area of ​​NHGM by 3-5 times, the pore diameter is 20-40 nm, and the surface hydroxyl density is increased to 2-3 times that of untreated HGM.

[0023] In a preferred embodiment of the present invention, the amino group of the silane coupling agent KH-550 in step (3) forms a coordination effect with the Fe-O bond on the surface of the nano-ferroferric oxide, and the thickness of the silanized interface layer is 10-20 nm.

[0024] In a preferred embodiment of the present invention, the self-suspension property of the FHGM in step (4) is characterized by a suspension time in still water of ≥48 h, and a magnetic responsiveness of 9 emu / g ≤ saturation magnetization intensity <25 emu / g, and 99% of the adsorbent in the soil can be recovered within 10-15 minutes by an external magnetic field.

[0025] In a preferred embodiment of the present invention, the raw material addition ratio in step (1) is FeCl3·6H2O 5.0-5.8 g, ethylene glycol 35-45 ml, and anhydrous sodium acetate 3.0-3.5 g;

[0026] In step (2), the ratio of the raw materials for alkali pretreatment is 8-12 g of HGM, 90-110 ml of pure water, and 180-220 ml of sodium hydroxide solution;

[0027] In step (3), the proportion of silane coupling agent added is NHGM 2±0.1 g, ethanol 28-32 ml, and KH-550 2±0.1 ml;

[0028] In step (4), the mass ratio of nano-ferroferric oxide to KHGM is 0.5-0.7:2.

[0029] In a preferred embodiment of the present invention, the main component of the raw material of the hollow glass microspheres HGM is silicon dioxide, which accounts for at least 70%.

[0030] An adsorbent for remediation of heavy metal-contaminated soil, prepared by any of the aforementioned preparation methods, comprising hollow silica-based glass microspheres as a substrate, and a surface-loaded nano-ferroferric oxide with 100-200 nm granular size and a saturation magnetization of 30-35 emu / g, forming an adsorbent having a flocculent surface texture. The adsorbent has the following properties:

[0031] The surface potential ranges from -20 mV to +15 mV in the pH range of 3-10, and heavy metal ions with opposite charges can be selectively adsorbed by adjusting the pH;

[0032] The surface has -Si-OH, -NH2 and Fe-O active groups, which have multifunctional adsorption sites;

[0033] 9 emu / g≤saturation magnetization intensity<25 emu / g, self-suspension time≥48h, magnetic recovery rate≥99%, with magnetic-suspension synergistic recovery characteristics.

[0034] An application of an adsorbent for remediation of heavy metal contaminated soil. The adsorbent is used to remove heavy metals by mixing the adsorbent with contaminated soil at a ratio of 1:50-1:150 (w / w) and then shaking for 2-6 hours.

[0035] In a preferred embodiment of the present invention, the adsorbent after adsorption is separated from the contaminated soil by magnetic separation and reused ≥5 times, and the adsorption efficiency remains above 75% of the initial value.

[0036] The beneficial effects of the embodiments of the present invention are:

[0037] 1. This scheme uses hollow glass microspheres as raw materials. By alkaline modification of the surface of the hollow glass microspheres, using a silane coupling agent as a connector, and grafting prepared nano-scale ferrosoferric oxide, a self-suspending and magnetic magnetic iron-based hollow glass microsphere (FHGM) is obtained. When used for the remediation of heavy metal-contaminated soil, due to its large specific surface area, saturated magnetic field strength, and functional groups on the material surface, it can enhance the separation and migration of different forms of heavy metals in contaminated soil.

[0038] 2. The adsorbent exhibits different potentials under different pH conditions, so heavy metals with different charges can be adsorbed by adjusting the pH;

[0039] 3. Through the loading of magnetic nano-ferroferric oxide and the bridging effect of silane coupling agent, the adsorbent can absorb Cd 2+ The adsorption capacity reaches 102.7 mg / g, and the adsorption time is only 4 hours. The adsorption efficiency is 18 times higher than that of patent CN202411683917.6, which greatly shortens the repair cycle and is suitable for rapid site repair needs.

[0040] 4. Utilizing the magnetic responsiveness of the magnetic adsorbent, with a saturation magnetization intensity of 9 emu / g or less and less than 25 emu / g, 99% of the material can be recovered within 15 minutes through an external magnetic field. The material can be reused ≥5 times with an efficiency of over 90%. Magnetic recovery is not limited by soil permeability and is particularly suitable for clay soils. The material has high stability, avoiding the risk of secondary contamination.

[0041] 5. The porous structure is formed by alkaline etching, which greatly increases the specific surface area. Combined with the chemical bonding of the silane coupling agent, the nano-ferroferric oxide loading rate is ≥95%. The chemical bonding ensures the loading stability and prevents the nanoparticles from falling off. The porous structure increases the active site density and improves the adsorption kinetics.

[0042] 6. It is suitable for in-situ / ex-situ remediation, has no restrictions on low permeability soils, does not require pretreatment and activation, can be directly adsorbed, and has a low cost and can save costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0044] Figure 1 This is a flow chart of a method for preparing an adsorbent for remediation of heavy metal contaminated soil according to Example 1 of the present invention;

[0045] Figure 2 -5 are scanning electron microscope (SEM) images of the composite adsorbent FHGM prepared in Example 1 of the present invention at 10 μm scale, 5 μm scale, 2 μm scale, and 1 μm scale, respectively;

[0046] Figure 6 This is a graph showing the change in Cd content adsorbed over time using the composite adsorbent FHGM in Example 2 of the present invention;

[0047] Figure 7 This is a comparison chart of the adsorption effects of heavy metal elements in different states in heavy metal contaminated soil without and with the composite adsorbent FHGM according to Example 2 of the present invention;

[0048] Figure 8 This is an SEM image of spherical nano-sized ferrosoferric oxide with a particle size of 8-15 nm in Example 3 of the present invention;

[0049] Figure 9 This is an SEM image of nano-ferroferric oxide with a particle size of 100-200 nm in Example 3 of the present invention;

[0050] Figure 10 This is an SEM image of 3-4 μm sea urchin-shaped ferrosoferric oxide in Example 3 of the present invention;

[0051] Figure 11 This is a comparison chart of the effects of using different morphologies of ferroferric oxide to prepare FHGM for removing various types of heavy metal forms in soil according to Example 3 of the present invention;

[0052] Figure 12 This is a comparison chart of the effects of using different amounts of nano-ferroferric oxide to prepare FHGM to remove various types of heavy metal forms in drilling solid waste according to Example 4 of the present invention;

[0053] Figure 13 This is a comparison chart of the adsorption effects of the composite adsorbent FHGM obtained by controlling different temperature gradients in Example 5 of the present invention;

[0054] Figure 14 This is a comparison chart of the heavy metal adsorption effects of different silane coupling agent dosages on FHGM in Example 6 of the present invention;

[0055] Figure 15 This is a diagram showing the heavy metal removal effect after five complete adsorption-desorption cycle experiments in Example 7 of the present invention. DETAILED DESCRIPTION

[0056] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0057] The application of magnetic nanomaterial ex situ reduction remediation technology in the environmental field is primarily due to its superior adsorption and reduction activity compared to traditional large or fine particles. This technology is applicable to a wide range of pollutants, offering rapid, efficient, and low-cost remediation. Furthermore, it can be separated and collected using an external magnetic field, making it a promising technology for remediating heavy metal contaminated soils.

[0058] FeCl₃·6H₂O, ethylene glycol, anhydrous sodium acetate, ethanol, pure water, and sodium hydroxide solution used in this example were purchased from Aladdin; hollow glass microspheres were purchased from 3M. All chemical reagents were of analytical grade and used directly without further treatment.

[0059] The instruments and equipment included: a high-pressure reactor (Parr 4848, temperature resistance 300°C); a magnetic stirrer (IKA RCT basic model); a vacuum drying oven (BINDER VD53); a VSM vibrating sample magnetometer (Lake Shore 7404); and a specific surface area analyzer (Micromeritics ASAP 2460).

[0060] Example 1

[0061] This example provides a method for preparing an adsorbent for remediation of heavy metal contaminated soil. Figure 1 , the operation steps are:

[0062] (1) Preparation of nano-ferroferric oxide

[0063] 5.4 g of FeCl3·6H2O was dissolved in 40 ml of ethylene glycol, 3.2 g of anhydrous sodium acetate was added, and the mixture was stirred at 250 rpm / min for 45 min. In the process of preparing nano-ferroferric oxide, the raw material addition ratio can be 5.0-5.8 g, 35-45 ml of ethylene glycol, and 3.0-3.5 g of anhydrous sodium acetate. In this example, typical intermediate values / near-intermediate values ​​were selected as representative examples to ensure the reproducibility and implementation stability of the scheme.

[0064] The stirred liquid was transferred into a polytetrachloroethylene stainless steel autoclave, and the temperature was raised to 200°C at a rate of 10-12°C / min (a temperature increase rate of 12°C / min was actually adopted in this embodiment to improve preparation efficiency) and reacted for 10 hours. In this embodiment, a stepwise temperature increase method was adopted, which effectively improved the particle size uniformity of the nano-ferroferric oxide compared to the natural temperature increase method.

[0065] The resulting product was cooled, washed with ethanol, and dried at 60°C for 10 hours to obtain black nano-ferroferric oxide with a particle size of 150±20 nm. The saturation magnetization of the obtained nano-ferroferric oxide was 31.2 emu / g. The nano-ferroferric oxide produced by adjusting the raw material ratio and heating method disclosed in this example, with a saturation magnetization range of 30-35 emu / g and a particle size of 100-200 nm, can be used to prepare the composite adsorbent FHGM.

[0066] (2) Alkali pretreatment of hollow glass microspheres HGM

[0067] The hollow glass microspheres (HGM) used in this example are primarily composed of 70% silicon dioxide. 10g of HGM hollow glass microspheres were placed in a 500ml beaker and mixed with 100ml of pure water. The mixture was then heated to 80°C at a rate of 10-15°C / min. This method employed more uniform heat conduction to reduce thermal stress. Rapid heating can easily damage the pore structure, so this example employed a gradient heating method to achieve superior crystallinity and phase purity.

[0068] Stir at 250 rpm / min for 10 min, place in 0.75 mol / L sodium hydroxide solution (200 ml), and stir at 300 rpm for 4 h;

[0069] In terms of experimental value selection, the ratio of the alkali pretreatment raw materials can be selected as 8-12 g HGM, 90-110 ml pure water, and 180-220 ml sodium hydroxide solution. This example selects a typical intermediate value as the specific implementation value. Based on different process scales, those skilled in the art can adjust the ratio parameter range to adapt to corresponding experimental research or production applications. The ratio provided by the method constitutes a quantitative technical feature of the same inventive concept.

[0070] The alkali-etched hollow glass microspheres HGM were washed three times with ultrapure water, filtered, and dried at 60 °C for 10 h to obtain surface-modified NHGM. The porous structure formed by alkali etching increased the specific surface area of ​​NHGM by 3-5 times, with a pore size of 20-40 nm, and the surface hydroxyl density increased to 2-3 times that of untreated HGM. The BET test showed that the specific surface area increased to 8.3 m 2 / g.

[0071] By controlling the NaOH concentration (0.75 mol / L) and reaction time (4 h), a porous structure was formed on the surface of the hollow glass microspheres HGM, and the generated mesopores provided anchoring points for subsequent loading.

[0072] (3) Grafted silane coupling agent

[0073] 2 g of modified NHGM was placed in 96% ethanol solution (30 ml), 2 ml of silane coupling agent KH-550 and 30 ml of pure water were added, and stirred at 200 rpm / min at 80 °C for 2 h;

[0074] After cooling the suspension to room temperature, the suspension was washed three times with pure water, filtered, and dried at 60°C for 10 h to obtain KHGM.

[0075] The action of silane coupling agents typically involves two steps: 1. Hydrolysis (the hydrolyzable group (X) on the silane coupling agent hydrolyzes in the presence of water to form silanol groups (Si-OH)); and 2. Condensation (the hydrolyzed silanol groups (Si-OH) react with hydroxyl groups (-OH) on the surface of the inorganic material to form Si-O-Si bonds). XPS analysis shows that the Si-O-Si bond peak intensity increases 2.7 times compared to the original HGM.

[0076] This step utilizes a chemical bonding mechanism: the siloxane groups (-Si-O-) of KH-550 condense with the hydroxyl groups on the HGM surface to form covalent bonds, while the amino groups (-NH2) coordinate with the Fe-O bonds, constructing an "inorganic-organic" bridging interface. XPS analysis reveals a 2.7-fold increase in the Si-O-Si bond energy (103.4 eV), and the N 1s peak (399.8 eV) confirms the successful grafting of amino groups. The surface also contains active -Si-OH, -NH2, and Fe-O groups, and AFM measurements indicate an interfacial layer thickness of 10-20 nm.

[0077] (4) Loaded with nano-ferroferric oxide

[0078] In this embodiment, 2 g of KHGM and 0.6 g of nano-ferroferric oxide were stirred at 200 rpm / min at 80° C. for 2 h, washed three times with pure water, filtered, and dried at 60° C. for 10 h to obtain the magnetic adsorption material FHGM.

[0079] The original hollow glass microspheres HGM are spherical, smooth and have cavities. Based on the structure of glass, the specific surface area is as low as 4.22 m 2 / g. By Figure 2-5 The SEM analysis in the results showed that the surface roughness of the adsorbent material FHGM increased after alkali treatment and magnetization modification, and a flocculent structure appeared on the surface. 2 / g expanded to 49 m2 / g (see Table 1), which is attributed to the formation of additional grooves and gaps on the HGM surface caused by alkaline etching. At the same time, the grafted nano-Fe 3 O 4 helps further increase the specific surface area. VSM measurements show a saturation magnetization of 9.23 emu / g, and TEM confirms the uniform loading of nano-Fe 3 O 4 (spacing 50-100 nm).

[0080]

[0081] Example 2

[0082] This example is aimed at heavy metal remediation of drilling solid waste in Northwest China. The Cd content in the contaminated soil is 48 mg / kg. FHGM and drilling solid waste are mixed at a ratio of 1:100 (w / w). After adsorption at 25°C and 150 rpm for 4 hours, see Figure 6 Middle: Cd content decreased to 7.38 mg / Kg.

[0083] from Figure 7 It can be seen that when remediating Cd-contaminated drilling solid waste, the new adsorption material has a significant effect on the removal of iron-manganese oxide-bound and organic-bound heavy metals. This is because the magnetic parts of the iron-manganese oxide-bound and organic-bound heavy metals are adsorbed on the FHGM surface with the addition of FHGM under the action of magnetic force, which makes this adsorbent have a good effect on the removal of stable heavy metals.

[0084] Remarkably, after applying FHGM, the cadmium removal efficiency in the soil reached 84.9%. Crucially, this remediation system not only successfully removed the majority of labile heavy metals (those in exchangeable and carbonate-bound states), but also the relatively stable forms of heavy metals present in the soil (those bound to iron and manganese oxides, organics, and residues). Of this, 41.1% of the labile forms of heavy metal cadmium were removed, while 58.9% were relatively stable forms. This is due to FHGM's high specific surface area, strong magnetism, and the presence of active -Si-OH, -NH2, and Fe-O groups on its surface, which provide active sites for heavy metal adsorption.

[0085] Example 3

[0086] The present invention further discloses a comparative study on the heavy metal removal performance of a composite adsorbent FHGM prepared based on multi-morphological nano-ferroferric oxide. The specific implementation method is as follows:

[0087] Preparation and characterization of composite adsorbent FHGM prepared from multi-morphological ferroferric oxide

[0088] (1) Material preparation, see Figure 8-10SEM images of ferroferric oxide with different morphologies:

[0089] Figure 8 : Nanoparticle type A (yellow bar graph): spherical nano-sized Fe3O4 particles with a particle size of 8-15 nm;

[0090] Figure 9 : Nanoparticle type B (green bar graph): Nano-iron tetroxide with a particle size of 100-200 nm used in this scheme;

[0091] Figure 10 : Microstructure type C (blue bar graph): 3-4 μm sea urchin-shaped ferrosoferric oxide.

[0092] The above three ferrosoferric oxide materials were surface functionalized and composited with the treated KHGM respectively. The composite method was to stir at 200 rpm at 80°C for 2 hours, wash three times with pure water, filter, and dry at 60°C for 10 hours to obtain the adsorption material.

[0093] Comparison of adsorption performance: self-mixed cadmium contaminated soil (Cd 2+ Heavy metal adsorption experiments were conducted using a 300 mg / kg initial concentration (MS / MS) buffer (pH 6.5 ± 0.2, phosphate buffer system) at a solid-liquid ratio of 1:10 (w / v); an oscillation time of 120 min (25°C, 200 rpm).

[0094] Experimental data show that, see Figure 11 :

[0095] Type B adsorbent exhibits the best cadmium adsorption performance, among which the adsorption effects on carbonate-bound, iron-manganese oxide-bound and organic-bound states are particularly impressive, and the absorption capacity for exchangeable cadmium is also outstanding; Type A and Type C adsorbents have certain cadmium absorption capacity, but the effect is not as good as Type B adsorbent. At the same time, the cadmium content for exchangeable cadmium is basically the same as that in the original soil, and the removal effect is not obvious.

[0096] Structure-activity relationship analysis: The performance difference mechanism was revealed through BET specific surface area test and TEM interface analysis. We believe that the A-type material has serious agglomeration due to the nano-particle size (<100 nm) (SEM shows that the agglomerate size is >500 nm), and the specific surface area is reduced from the theoretical value of 25 m 2 / g dropped to the measured value of 8.75m 2 / g, and the dense stacking layer hinders the exposure of active sites. XPS shows that the utilization rate of surface -NH2 functional groups decreases by 42%; the C-type material is limited by its three-dimensional thorn-like morphology (aspect ratio>15), and presents a discontinuous island distribution on the HGM surface. EDS mapping shows that the Fe element coverage is only 39%, resulting in a low effective loading rate; the B-type material, with its optimized mesoporous structure (pore size distribution 20-40 nm) and moderate particle size (150-250 nm), forms a single layer of ordered arrangement on the FHGM surface. AFM shows that the surface roughness is reduced to 8.2 nm. Its Fe-O-Si chemical bonding interface (the presence of Fe2SiO4 characteristic peaks confirmed by XRD) significantly improves the material stability.

[0097] Special note: This paper reveals the strong correlation between the morphology and adsorption performance of ferroferric oxide nanomaterials through systematic research, establishes a quantitative control model of "particle size-dispersion-active site density", and provides theoretical guidance for the targeted design of heavy metal adsorption materials.

[0098] Example 4

[0099] The embodiment of the present invention discloses the effect of regulating the loading amount of nano-ferroferric oxide on the performance of the prepared magnetic adsorption material. The specific implementation steps are as follows:

[0100] Study on the regulation of adsorption performance by nano-ferroferric oxide loading

[0101] (1) Preparation of magnetic adsorption materials:

[0102] 1. Mix different masses of nano-ferroferric oxide (0.2g, 0.4g, 0.6g, 0.8g) with 2g of KHGM. Stir the mixture at 200 rpm for 120 minutes at 80±1°C to achieve stable loading of the nano-ferroferric oxide through chemical bonding mediated by the silane coupling agent.

[0103] 2. After washing with deionized water three times (50 mL each time, ultrasonic-assisted dispersion for 10 minutes), the product was finally treated in a vacuum drying oven at 60°C for 10 hours to obtain functionalized magnetic adsorption material (FHGM).

[0104] Soil remediation performance test:

[0105] Cadmium-containing soil (Cd 2+ The remediation experiment was conducted with the following control conditions: solid-liquid ratio 1:10 (w / v); oscillation time 180 min (25°C, 150 rpm); FHGM dosage 5% (w / w).

[0106] Experimental data show that ( Figure 12Effect of different nano-ferroferric oxide loadings on the properties of the prepared magnetic adsorption materials): Figure 12 It can be seen that when the loading amount of nano-ferroferric oxide increases from 0.2g to 0.8g, Cd 2+ The removal rates were 68.72%, 72.86%, 78.80% and 84.90% respectively.

[0107] Structure-activity mechanism analysis: revealing the loading-performance correlation mechanism through a series of characterization techniques:

[0108] BET specific surface area test:

[0109] When the loading amount of nano-ferroferric oxide is 0.2 g, the specific surface area of ​​FHGM reaches 17.14 m 2 / g, which is about 4 times higher than that of KHGM without nano-ferroferric oxide loading;

[0110] When the loading amount of nano-ferroferric oxide is 0.4 g, the specific surface area of ​​FHGM reaches 33.47 m 2 / g, which is about 7.9 times higher than that without KHGM loading;

[0111] When the loading amount of nano-ferroferric oxide is 0.6 g, the specific surface area of ​​FHGM reaches 49 m 2 / g, which is about 12.8 times higher than that without KHGM loading;

[0112] When the loading amount of nano-ferroferric oxide is 0.7 g, the specific surface area of ​​FHGM reaches 47 m 2 / g, which is 11 times higher than that of unloaded KHGM.

[0113] XPS surface analysis: Fe 2P 3 / 2 The binding energy peak area is positively correlated with the loading amount (R 2 =0.987), confirming the effective increase of the Fe-O-Si bonding interface; VSM magnetic performance test: the saturation magnetization intensity increased from 7.6 emu / g (0.5 g load) to 9.14 emu / g (0.6 g load), ensuring the recyclability of the material (magnetic loss rate <5% after 3 cycles).

[0114] The present invention breaks through the contradictory balance between the active site density and structural stability of traditional adsorption materials by precisely controlling the loading amount of nano-ferroferric oxide. Its linear response characteristics between Cd removal rate and loading amount provide a controllable process window for industrial scale-up.

[0115] Example 5

[0116] See Figure 13 The embodiment of the present invention discloses the effect of temperature gradient control in step (2) on the preparation of composite adsorbent FHGM, and the specific implementation method is as follows:

[0117] (1) Gradient temperature field construction: A programmed temperature control reaction system was used to establish four sets of alkali pretreatment temperature parameters (20°C, 40°C, 60°C, and 80°C). Precision temperature control was achieved through the following steps:

[0118] 1. Immerse hollow glass microspheres (HGM, SiO2 content 72.3 wt%, particle size 50±5 μm) in 0.75 mol / L NaOH etching solution (solid-liquid ratio 1:30);

[0119] 2. Dynamic temperature control (PID accuracy ±0.5°C) was performed at a step heating rate of 10-15°C / min to eliminate thermal hysteresis effects; the preset temperature was maintained for 240 minutes, and mechanical stirring at 300 rpm was simultaneously applied to create a turbulent flow field.

[0120] (2) Characterization of temperature effect:

[0121] Uncovering temperature-structure correlations through multi-scale characterization techniques:

[0122] Dynamic contact angle analysis: The contact angle of the 80°C treatment group decreased to 12.5° (83% lower than the 20°C group), confirming that the surface energy was increased to 65.3 mJ / m 2 (Owens-Wendt model calculation);

[0123] AFM surface topology analysis: The surface roughness Ra value of FHGM prepared at 80℃ reached 128±15 nm (Ra=32±8 nm for the 20℃ group), forming multiple micro-nano groove structures;

[0124] XPS elemental quantification: surface hydroxyl density increased from 8.7 OH / nm at 20℃ 2 Increased to 23.4 OH / nm at 80℃ 2 (O 1s peak fitting calculation).

[0125] Process optimization verification: Comparison of the effects of different pretreatment temperatures in the Fe3O4 loading process:

[0126] 1 Loading efficiency: The Fe element loading in the 80℃ pretreatment group reached 19.8 wt% (EDS detection), which was 3.2 times higher than that in the 20℃ group;

[0127] 2 Adsorption performance: for Cd-containing 2+ The removal rate of drilling mud (initial concentration 156 mg / kg) increased from 41.2% in the 20°C group to 84.7% in the 80°C group (ICP-MS detection);

[0128] 3 Cyclic stability: The surface area retention rate of FHGM prepared at 80℃ after 5 regenerations was 92.3% (BET test), which was significantly better than the 67.8% of the 20℃ group.

[0129] Key mechanism revealed:

[0130] 1. High temperature environment (80℃) reduces the surface tension of the liquid (from 72.1 mN / m to 58.4 mN / m, measured by Wilhelmy plate method), promoting the capillary penetration of the etching solution and forming penetrating surface pits (SEM shows a pore size distribution of 20-40 nm);

[0131] 2. The programmed heating strategy eliminates thermal stress concentration (finite element simulation shows a temperature gradient of <2°C / cm) and avoids damage to the microsphere structure caused by local over-etching (micro-CT shows an integrity of >98%).

[0132] 3. The thermally activated surface produces coordination defect sites (EPR detection g=2.003 characteristic signal intensity increases 4.8 times), providing advantageous anchoring positions for Fe3O4 heterogeneous nucleation.

[0133] Innovation Statement: This invention breaks through the kinetic limitations of traditional isothermal processing by establishing a quantitative mapping relationship between temperature field, interface energy, and active sites (Arrhenius fitting activation energy Ea = 28.6 kJ / mol), shortening the etching cycle by 62% (from 160 minutes to 60 minutes), and providing a thermodynamic control benchmark for the large-scale preparation of high-performance adsorption materials.

[0134] Example 6

[0135] This embodiment discloses the effect of different silane coupling agent input amounts on the heavy metal adsorption performance of FHGM in step (3). The specific implementation method is as follows:

[0136] Study on the synergistic effect between silane coupling agent dosage and interface chemistry

[0137] 1) Dosage gradient design and material preparation:

[0138] 1. Hollow glass microspheres (NHGM, surface hydroxyl density 22.3OH / nm) pretreated with alkali 2 , verified by XPS) as the substrate, the dosage of γ-aminopropyltriethoxysilane (KH-550) was precisely controlled to be 0.5, 1, 1.5, 2.0, 2.5, and 3.0 mL in a 96% ethanol solvent system;

[0139] 2. Achieve interfacial bonding by chemical vapor deposition at 80°C with stirring at 200 rpm for 2 hours.

[0140] 3. Wash with pure water three times and vacuum dry at 60℃ for 10 hours to obtain KHGM material. FHGM is prepared based on the KHGM material.

[0141] (2) Verification of adsorption performance gradient response:

[0142] The prepared FHGM was used for adsorption experiments on the same batch of soil to be repaired. The results showed that ( Figure 14 Figure 3: Effects of adsorbents prepared with different concentrations of silane coupling agents on the removal of various forms of heavy metals in drilling solid waste. The 2.0 mL addition group had the shortest adsorption equilibrium time (120 minutes), a Langmuir saturation adsorption capacity of 118.4 mg / g, and a removal rate of 84.9%.

[0143] The adsorption capacity of the 0.5, 1, and 1.5 mL dosing groups was only 74.6 mg / g (equilibrium time was extended to 150 min) due to insufficient surface functionalization, and the removal rate was 70-75%.

[0144] The adsorption capacity of the 2.5 and 3.0 mL addition groups was affected by silane self-aggregation, and the adsorption capacity decayed to 79.3 mg / g (the pseudo-second-order kinetic fitting rate constant decreased by 42%), and the removal rates were 76% and 69%, respectively.

[0145] (3) Analysis of the structure and effect of dosage-interface characteristics:

[0146] The mechanism of dosage threshold effect is revealed through multi-dimensional characterization:

[0147] XPS depth analysis: The surface Si-O-Si bond ratio of the 2.0 mL group reached 41.2 at% (a 2.3-fold increase compared to the 1.5 mL group), and the N 1s peak half-width was the smallest (1.8 eV), indicating uniform amino monolayer coverage. AFM mechanical mapping: Excessive addition (≥2.2 mL) resulted in a decrease in the adhesion of the silane layer (from 45 nN to 22 nN), and a 63% decrease in the interfacial binding energy (calculated based on the Johnson-Kendall-Roberts model). In situ FTIR monitoring: 1290 cm -1 The Si-CH2 characteristic peak intensity reached its peak at 2.0 mL, and excessive addition resulted in the peak at 1050 cm -1 The Si-O-Si condensation peak at -1 , confirming excessive cross-linking.

[0148] Core findings

[0149] 1. Critical dosing threshold (2.0 mL): Achieving monolayer coverage (calculated coverage 99.1%, based on a modified BET adsorption model), forming a dense and open active interface (the main peak of the BET pore size distribution is at 3.5 nm);

[0150] 2. Negative effects of excessive dosing: It triggers the self-aggregation of the siloxane three-dimensional network (29Si NMR shows that the proportion of T3 structure increases from 15% to 71%), leading to micropore blockage (the porosity measured by mercury intrusion method decreases from 68% to 39%).

[0151] 3. Surface potential regulation: Zeta potential analysis showed that the isoelectric point of the 2.0 mL group shifted to pH 8.5 (pH 4.3 for unmodified KHGM), and electrostatic potential energy calculations showed that Cd 2+ The adsorption capacity was reduced by 87% (DLVO theory verification).

[0152] This study establishes a nonlinear response model for silane dosage, surface bonding density, and adsorption kinetics (with a Hill equation fitting synergy coefficient n=1.8), overcoming the process limitations of traditional trial-and-error methods and revealing the quantitative control of the interfacial chemical state by dosage. Optimizing the process window (2.0±0.1 mL) significantly improves the material's regeneration performance, achieving an adsorption capacity retention rate exceeding 75% after five cycles and a stable magnetic recovery rate exceeding 98.5% (saturation magnetization of 42 emu / g as measured by VSM). This provides a highly precise and controllable interfacial engineering solution for industrial wastewater treatment.

[0153] Example 7

[0154] Typically, adsorbent materials can be reused through acid washing and centrifugation; however, this process can damage the adsorbent material's structure. The composite adsorbent FHGM prepared in this example is recovered by self-suspension followed by adsorption in an external magnetic field. This minimizes structural damage to the composite adsorbent FHGM and avoids secondary contamination.

[0155] In order to evaluate the regeneration and recovery performance of the composite adsorbent FHGM, this example further conducted a series of experiments based on the adsorption work completed by the composite adsorbent FHGM in Example 2.

[0156] The embodiment of the present invention discloses a regeneration and recovery method, and the specific implementation steps are as follows:

[0157] (1) Adsorption treatment: 0.5 g of FHGM adsorbent was accurately weighed in a 500 mL standard beaker, and 50 g of self-prepared cadmium-contaminated soil sample (Cd 2+ The adsorbent was prepared by adding deionized water (with a solid-liquid content of 300 mg / kg) to a controlled solid-liquid ratio of 1:5 (w / v). The mixture was stirred continuously at 250 rpm in a thermostatic magnetic stirrer at 25 ± 1°C for 60 minutes to ensure adequate solid-liquid contact. The composite adsorbent FHGM was able to remain suspended in still water for 48 hours or longer.

[0158] (2) Material recovery: The unique self-suspension and magnetic properties of the composite adsorbent FHGM are used for recovery. A magnetic separation device is used to apply a 0.5 T magnetic field strength to the top of the beaker for recovery. Then, based on the material density parameter (ρ = 0.49 g / cm 3 The combined process uses a self-suspended separation method (lower than the density of water) to separate and magnetically recover cadmium-laden FHGM. Testing has shown that this combined recovery process achieves a total recovery efficiency of 99.2%, with a single treatment cycle of no more than 15 minutes.

[0159] (3) Heavy Metal Desorption: The cadmium-loaded FHGM was placed in a centrifuge tube and centrifuged at 8000 rpm for 10 minutes in a high-speed centrifuge. As shown in Table 2, after multiple desorption operations, the percentage of heavy metals such as cadmium in the uncentrifuged sample gradually increased, reaching 91.99% after three desorption cycles, confirming the high efficiency of the desorption process.

[0160]

[0161] (4) Material regeneration performance: see Figure 15 After five complete adsorption-desorption cycles, FHGM 2+ The adsorption capacity retention rate was 78.9%, demonstrating good regeneration performance. Scanning electron microscopy (SEM) and BET surface area analysis revealed that the adsorption capacity decay was primarily due to a 3.2% surface area loss and the occupation of some surface active sites by heavy metal residues such as cadmium ions (XPS analysis showed 0.8 at% residual cadmium on the surface).

[0162] Of particular note, the synergistic effect of FHGM's regular hollow structure and the externally loaded nano-ferroferric oxide composite magnetic layer gives it both superparamagnetism (saturation magnetization greater than 9 emu / g) and stable self-suspension properties. The abundant amino and carboxylic acid groups on the material's surface (demonstrated by the presence of characteristic -NH2 and -COOH peaks via FTIR) provide multiple coordination sites for heavy metal adsorption. The above-described specific embodiments further illustrate the objectives, technical solutions, and beneficial effects of the present invention. It should be understood that the above description is merely a specific embodiment of the present invention and is not intended to limit its scope. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be included within its scope.

Claims

1. A method for preparing an adsorbent for remediation of heavy metal contaminated soil, characterized in that: The following steps are involved: (1) Preparation of nano-ferroferric oxide: FeCl3·6H2O was dissolved in ethylene glycol, anhydrous sodium acetate was added, and the mixture was stirred at 200-300 rpm for 40-50 minutes to form a homogeneous solution. The solution was transferred to a polytetrafluoroethylene-lined stainless steel autoclave and reacted at 200°C for 10 hours. After cooling, the solution was washed with ethanol and dried at 60°C for 10 hours to obtain granular nano-ferroferric oxide with a particle size of 100-200 nm. (2) Alkali pretreatment of hollow glass microspheres HGM: HGM was dispersed in pure water, heated to 80°C at 10-15°C / min, stirred at 250 rpm for 10 minutes, and then added with 0.75 mol / L sodium hydroxide solution to form a micron-scale porous structure with a rough surface by alkali etching. The mixture was stirred at 300 rpm for 4 hours, washed three times with pure water, filtered, and dried at 60°C for 10 hours to obtain alkali-etched NHGM. The porous structure formed by alkali etching increased the specific surface area of ​​NHGM by 3-5 times, with a pore size of 20-40 nm, and the surface hydroxyl density increased to 2-3 times that of untreated HGM. (3) Grafting silane coupling agent: The NHGM obtained in step (2) is dispersed in a 96% ethanol solution, and the silane coupling agent KH-550 is added. The mixture is stirred at 200 rpm at 80°C for 2 hours. A silanized interface layer is formed by chemical bonding between the amino group -NH2 of KH-550 and the hydroxyl group -OH on the surface of NHGM. The mixture is washed three times with pure water, filtered, and dried at 60°C for 10 hours to obtain silanized KHGM. The amino group of the silane coupling agent KH-550 forms a coordination effect with the Fe-O bond on the surface of the nano-ferroferric oxide, and the thickness of the silanized interface layer is 10-20 nm. (4) Loading nano-ferroferric oxide: The KHGM obtained in step (3) was mixed with the nano-ferroferric oxide obtained in step (1) according to the mass ratio, stirred at 200 rpm at 80°C for 2 hours, washed three times with pure water and filtered, and dried at 60°C for 10 hours. The ferroferric oxide was uniformly loaded on the surface of HGM through the bridging effect of the silane coupling agent to form a composite adsorbent FHGM with self-suspension and magnetic responsiveness.

2. The method for preparing an adsorbent for remediation of heavy metal contaminated soil according to claim 1, characterized in that: In step (1), the particle size of nano-ferroferric oxide is controlled by the reaction heating rate. When the heating rate is 10-12°C / min, a 100-200 nm granular structure is generated, and the saturation magnetization intensity is 30-35 emu / g.

3. The method for preparing an adsorbent for remediation of heavy metal contaminated soil according to claim 1, characterized in that: described The raw material addition ratio in step (1) is FeCl3·6H2O 5.0-5.8 g, ethylene glycol 35-45 ml, and anhydrous sodium acetate 3.0-3.5 g; In step (2), the ratio of the raw materials for alkali pretreatment is 8-12 g of HGM, 90-110 ml of pure water, and 180-220 ml of sodium hydroxide solution; In step (3), the proportion of silane coupling agent added is NHGM 2±0.1 g, ethanol 28-32 ml, and KH-550 2±0.1 ml; In step (4), the mass ratio of nano-ferroferric oxide to KHGM is 0.5-0.7:

2.

4. The method for preparing an adsorbent for remediation of heavy metal contaminated soil according to claim 1, wherein: The main component of the raw material of the hollow glass microspheres HGM is silicon dioxide, which accounts for at least 70%.

5. An adsorbent for remediation of heavy metal contaminated soil, prepared by the preparation method according to any one of claims 1 to 4, characterized in that: The adsorbent is based on silica-based hollow glass microspheres, with 100-200 nm granular nano-ferroferric oxide loaded on the surface with a saturation magnetization of 30-35 emu / g, forming an adsorbent with a flocculent rough structure on the surface. The adsorbent has the following properties: The surface potential ranges from -20 mV to +15 mV in the pH range of 3-10, and heavy metal ions with opposite charges can be selectively adsorbed by adjusting the pH; The surface has -Si-OH, -NH2 and Fe-O active groups, which have multifunctional adsorption sites; 9 emu / g≤saturation magnetization intensity<25 emu / g, self-suspension time≥48h, magnetic recovery rate≥99%, with magnetic-suspension synergistic recovery characteristics.

6. An application of an adsorbent for remediation of heavy metal contaminated soil, using the adsorbent according to claim 5, characterized in that: The adsorbent is mixed with contaminated soil in a mass ratio of 1:50 to 1:150 and then shaken for 2-6 hours to adsorb and remove heavy metals.

7. The use of the adsorbent for remediation of heavy metal contaminated soil according to claim 6, characterized in that: The adsorbent after adsorption was separated from the contaminated soil by magnetic separation and reused ≥5 times, and the adsorption efficiency remained above 75% of the initial value.

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