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

Abstract

The invention belongs to the technical field of soil remediation, and particularly relates to an adsorbent for heavy metal contaminated soil remediation and a preparation method and application thereof.Alkaline modification is conducted on the surfaces of hollow glass microspheres, a silane coupling agent is used as a connecting agent, prepared nanoscale ferroferric oxide is grafted, and the adsorbent is used for remediation of heavy metal contaminated soil. When the magnetic iron-based hollow glass microsphere FHGM is used for heavy metal contaminated soil remediation, due to the large specific surface area, the saturated magnetic field intensity, functional groups existing on the material surface and the like, separation and migration of different forms of heavy metal in the contaminated soil can be enhanced, and meanwhile on the basis that the structure of an adsorption material is not damaged, the magnetic iron-based hollow glass microsphere FHGM has the self-suspension property and magnetism. And regeneration and recovery of the adsorption material are realized.

Description

Technical Field

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

[0002] Traditional remediation technologies for heavy metal contaminated soil include chemical fixation method, chemical leaching method, phytoremediation, soil replacement method, adsorption method, etc. Although significant progress has been made through years of research by those skilled in the art, there are still defects such as high cost, low efficiency, and inability to realize the reuse of resources.

[0003] Among them, the fixed / stabilization remediation technology is the most widely used. By adding a fixing / stabilizing agent to the soil to stabilize heavy metals in the soil to achieve the remediation purpose. However, over time, whether the fixing / stabilizing agent can still firmly lock heavy metals and whether the fixing / stabilizing agent causes secondary pollution to the environment are all problems that need to be solved.

[0004] As a widely used treatment method, the adsorption method can achieve the adsorption of heavy metal ions with less adsorbent. However, due to the traditional adsorption method being restricted by the special physical and chemical properties of the adsorbent and the soil, especially for low-permeability soil, it is difficult to separate the adsorbent after adsorbing heavy metals, and it is easy to damage the structure of the adsorbent itself during separation, with the risk of causing secondary pollution, and its application in the treatment of heavy metals in soil is very limited.

[0005] For example, a method for preparing an adsorption material and removing heavy metal cadmium from paddy soil disclosed in patent CN202411683917.6, which is also a novel adsorption material based on hollow glass microspheres, can effectively remove heavy metal cadmium in paddy soil without causing secondary pollution, and this adsorption material is conducive to recycling and reuse. Its specific preparation method includes: (1) treating hollow glass microspheres with an alkali solution for later use; (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 sucking the hollow glass microsphere-sodium alginate solution with a syringe and dropping it drop by drop into a 0.1-0.5 mol / L calcium chloride solution, standing for 12-24 h, filtering, washing, and freeze-drying to obtain the adsorption material.

[0006] However, compared with this solution, it has at least the following defects: 1. This solution relies on the physical adsorption of sodium alginate gel and requires 72 hours to complete adsorption (step S2 of the specification), with a long adsorption time and unsatisfactory repair cycle and efficiency; 2. This solution relies on flotation to recover materials, requires standing still and separating the adsorbent on the water surface, and its gel structure may be damaged due to swelling / shrinking (paragraphs

[0009] and

[0033] of the specification), resulting in secondary pollution; 3. This solution relies on Fe 3+ activation to achieve the release of cadmium ions, with a single function (paragraphs

[0014] -

[0021] of the specification); 4. Sodium alginate is used to physically wrap HGM without surface modification of HGM, the particles are prone to falling off, the loaded active sites rely on the carboxyl / hydroxyl groups of the gel, and magnetite does not participate in surface modification (step (3) of the specification); 5. The preparation process requires an activation step (FeCl3 solution) and long-term stirring (72 hours), the operation is complex, and the costs of sodium alginate and calcium chloride are relatively high. Summary of the Invention

[0007] The first object of the present invention is to provide a composite adsorbent with self-suspension and magnetic responsiveness, so as to solve the problems of difficult separation, insufficient active sites and poor stability of traditional soil remediation materials.

[0008] The second object of the present invention is to provide a method for preparing an adsorbent for heavy metal contaminated soil remediation, and to construct a multifunctional adsorbent through a three-step collaborative modification process of alkali etching for pore formation - silane coupling agent interfacial bridging - controllable loading of magnetic nanoparticles; The third object of the present invention is to provide an application of an adsorbent for heavy metal contaminated soil remediation. While the adsorbent can efficiently adsorb heavy metals in the soil, it can efficiently remove the material from the soil as much as possible.

[0009] The embodiments of the present invention are implemented as follows: A method for preparing an adsorbent for heavy metal contaminated soil remediation, comprising the following steps: (1) Preparation of nano-magnetite: Dissolve FeCl3·6H2O in ethylene glycol, add anhydrous sodium acetate, stir at 200 - 300 rpm for 40 - 50 minutes to form a homogeneous solution, transfer it to a stainless steel high-pressure reaction kettle with a polytetrafluoroethylene liner, react at 200°C for 10 hours, wash with ethanol after cooling and dry at 60°C for 10 hours to obtain particulate nano-magnetite with a particle size of 100 - 200 nm; <x (2) Alkali pretreatment of hollow glass microspheres HGM: Disperse HGM in pure water, heat it to 80°C at a rate of 10 - 15°C / min, stir at 250 rpm for 10 minutes, then add 0.75 mol / L sodium hydroxide solution, form a micron-level porous structure with a rough surface through alkali etching, stir at 300 rpm for 4 hours, wash three times with pure water and then filter, dry at 60°C for 10 hours to obtain alkali-etched NHGM; (3) Grafting silane coupling agent: Disperse the NHGM obtained in step (2) in a 96% ethanol solution, add silane coupling agent KH-550, stir at 80 °C at 200 rpm for 2 hours, and 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. After washing three times with pure water and then filtering, dry at 60 °C for 10 hours to obtain KHGM; (4) Loading nano-ferroferric oxide: Mix the KHGM obtained in step (3) and the nano-ferroferric oxide prepared in step (1) according to the mass ratio, stir at 80 °C at 200 rpm for 2 hours, wash three times with pure water and then filter, dry at 60 °C for 10 hours, and uniformly load the nano-ferroferric oxide on the surface of KHGM through the bridging action of the silane coupling agent to form a composite adsorbent FHGM with self-suspension and magnetic responsiveness.

[0010] In a preferred embodiment of the present invention, the particle size of the nano-ferroferric oxide in step (1) is controlled by the reaction heating rate. When the heating rate is 10 - 12 °C / min, 100 - 200 nm granular structures are formed, and the saturation magnetization intensity is 30 - 35 emu / g.

[0011] In a preferred embodiment of the present invention, the porous structure formed by alkali etching in step (2) increases the specific surface area of NHGM by 3 - 5 times, the pore size is 20 - 40 nm, and the surface hydroxyl density increases to 2 - 3 times that of the untreated HGM.

[0012] 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.

[0013] In a preferred embodiment of the present invention, the self-suspension of FHGM in step (4) is manifested as a suspension time ≥ 48 h in still water, and the magnetic responsiveness is manifested as 9 emu / g ≤ saturation magnetization intensity < 25 emu / g, and 99% of the adsorbent in the soil can be recovered within 10 - 15 minutes through an external magnetic field.

[0014] In a preferred embodiment of the present invention, the raw material dosage ratio in step (1) is 5.0 - 5.8 g of FeCl3·6H2O, 35 - 45 ml of ethylene glycol, and 3.0 - 3.5 g of anhydrous sodium acetate; The raw material ratio for alkali pretreatment in step (2) is 8 - 12 g of HGM, 90 - 110 ml of pure water, and 180 - 220 ml of sodium hydroxide solution; The dosage ratio of the silane coupling agent in step (3) is 2 ± 0.1 g of NHGM, 28 - 32 ml of ethanol, and 2 ± 0.1 ml of KH-550; In step (4), the mass ratio of nano-ferroferric oxide to KHGM is 0.5 - 0.7:2.

[0015] In a preferred embodiment of the present invention, the main component of the raw material of the hollow glass microspheres HGM is silica, and silica accounts for at least 70%.

[0016] An adsorbent for heavy metal contaminated soil remediation, prepared by using any one of the foregoing preparation methods, the adsorbent is based on silica-based hollow glass microspheres, and nano-ferroferric oxide with a particle size of 100 - 200 nm and a saturation magnetization intensity of 30 - 35 emu / g is loaded on the surface to form an adsorbent with a flocculent rough structure on the surface, which has the following properties: The surface potential is -20 mV to +15 mV in the pH range of 3 - 10, and heavy metal ions with opposite charges are selectively adsorbed by adjusting the pH; -Si-OH, -NH2 and Fe-O active groups coexist on the surface, having multifunctional adsorption sites; 9 emu / g ≤ saturation magnetization intensity < 25 emu / g, self-suspension time ≥ 48 h, magnetic recovery rate ≥ 99%, having magnetic-suspension synergistic recovery characteristics.

[0017] An application of an adsorbent for heavy metal contaminated soil remediation, using this adsorbent, the adsorbent and the contaminated soil are mixed at a ratio of 1:50 - 1:150 (w / w) and shaken for 2 - 6 hours to remove heavy metals.

[0018] In a preferred embodiment of the present invention, the adsorbed adsorbent is separated from the contaminated soil by magnetic separation and reused ≥ 5 times, and the adsorption efficiency remains above 75% of the initial value.

[0019] The beneficial effects of the embodiments of the present invention are: 1. This solution uses hollow glass microspheres as raw materials, through alkaline modification of the surface of the hollow glass microspheres, and uses a silane coupling agent as a linker to graft the prepared nano-ferroferric oxide to obtain a magnetic iron-based hollow glass microsphere (FHGM) with self-suspension and magnetism. When used for heavy metal contaminated soil remediation, due to its large specific surface area, saturation magnetic field strength, and the presence of functional groups on the material surface and other performance conditions, it can strengthen the separation and migration of different forms of heavy metals in the contaminated soil.

[0020] 2. The adsorbent shows different potentials under different pH conditions, so heavy metals with different electricities can be adsorbed by adjusting the pH; 3. Through the loading of magnetic nano-ferroferric oxide and the bridging effect of the silane coupling agent, the adsorbent has an adsorption effect on Cd 2+The adsorption capacity reaches 102.7 mg / g, the adsorption time only needs 4 hours, and the adsorption efficiency is 18 times higher than that of Patent CN202411683917.6, greatly shortening the repair cycle and meeting the rapid site repair requirements; 4. Utilize the magnetic responsiveness of the magnetic adsorbent, with 9 emu / g ≤ saturation magnetization < 25 emu / g. 99% of the material can be recovered within 15 minutes through an external magnetic field and can be reused ≥ 5 times, with the efficiency remaining above 90%. Magnetic recovery is not restricted by soil permeability and is especially suitable for cohesive soils; The material has high stability, avoiding the risk of secondary pollution; 5. Form a porous structure through alkali etching, significantly increasing the specific surface area. Combined with the chemical bonding of silane coupling agent, the loading rate of nano-ferroferric oxide ≥ 95%. Chemical bonding ensures the loading stability and avoids the shedding of nanoparticles; The porous structure increases the density of active sites and improves the adsorption kinetics; 6. Suitable for in-situ / ex-situ remediation, without restrictions on low-permeability soils, no need for pretreatment activation, directly adsorb, and the cost is low, which can save costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the embodiments. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0022] Figure 1 It is a flow chart of the preparation method of the adsorbent for heavy metal contaminated soil in Embodiment 1 of the present invention; Figure 2 -5 are the scanning electron microscope (SEM) images of the composite adsorbent FHGM prepared in Embodiment 1 of the present invention with a 10 μm scale, a 5 μm scale, a 2 μm scale, and a 1 μm scale respectively; Figure 6 It is a graph showing the change of Cd content adsorbed by the composite adsorbent FHGM over time in Embodiment ② of the present invention; Figure 7 It is a comparison graph of the adsorption effects of heavy metal elements in different states in heavy metal contaminated soil without and with the composite adsorbent FHGM in Embodiment ② of the present invention; Figure 8 It is a SEM image of spherical nano-ferroferric oxide with a particle size of 8 - 15 nm in Embodiment ③ of the present invention; Figure 9 It is a SEM image of nano-ferroferric oxide with a particle size of 100 - 200 nm in Embodiment ③ of the present invention; Figure 10SEM image of 3-4 μm sea urchin-like magnetite in Example 3 of the present invention; Figure 11 Comparison chart of the effects of FHGM prepared from magnetite with different morphologies on removing various heavy metal forms in soil in Example 3 of the present invention; Figure 12 Comparison chart of the effects of FHGM prepared from different amounts of nano-magnetite on removing various heavy metal forms in drilling solid waste in Example 4 of the present invention; Figure 13 Comparison chart of the adsorption effects of the composite adsorbent FHGM prepared by regulating different temperature gradients in Example 5 of the present invention; Figure 14 Comparison chart of the heavy metal adsorption effects of FHGM with different input amounts of silane coupling agent in Example 6 of the present invention; Figure 15 Heavy metal removal effect diagram after five complete adsorption-desorption cycle experiments in Example 7 of the present invention. Detailed implementation manners

[0023] The endpoints and any values within the ranges disclosed herein are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the values between the endpoints of each range, between the endpoints and individual point values of each range, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0024] The application of magnetic nanomaterial ex-situ reduction remediation technology in the environmental field is mainly due to its better adsorption and reduction activities compared with traditional large particles or microparticles. This technology is applicable to a variety of pollutants, has a fast remediation speed, high efficiency, low cost, and can be separated and collected by an external magnetic field, making it a very promising technology for remediating soil heavy metal pollution.

[0025] FeCl3·6H2O, ethylene glycol, anhydrous sodium acetate, ethanol, pure water, sodium hydroxide solution, etc. used in this example were purchased from Aladdin; hollow glass microspheres were purchased from 3M. All chemical reagents were of analytical grade and were used directly without further treatment.

[0026] Instrumentation includes: high-pressure reactor (Parr 4848, temperature-resistant 300°C); magnetic stirrer (IKA RCT basic type); vacuum drying oven (BINDER VD53); VSM vibrating sample magnetometer (Lake Shore 7404); specific surface area analyzer (Micromeritics ASAP 2460).

[0027] Example 1 This embodiment provides a method for preparing an adsorbent for heavy metal contaminated soil remediation. Please refer to Figure 1 , and its operation steps are as follows: (1) Prepare nano-ferroferric oxide Dissolve 5.4 g of FeCl3·6H2O in 40 ml of ethylene glycol, add 3.2 g of anhydrous sodium acetate, and stir at 250 rpm for 45 min; during the preparation of nano-ferroferric oxide, the raw material dosage 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 embodiment, the typical middle value / value approaching the middle value is selected as the representative example to ensure the reproducibility and implementation stability of the scheme.

[0028] Transfer the stirred liquid into a polytetrafluoroethylene stainless steel autoclave, and heat it to 200 °C at a rate of 10 - 12 °C / min (in this embodiment, the actual heating rate of 12 °C / min is adopted) and react for 10 h; in this embodiment, a stepped heating method is adopted. Compared with the natural heating method, the particle size uniformity of nano-ferroferric oxide can be effectively improved; After the obtained product is cooled, it is washed with ethanol and dried at 60 °C for 10 h to obtain nano-ferroferric oxide with a black color and a particle size of 150 ± 20 nm. The saturation magnetization intensity of the prepared nano-ferroferric oxide is 31.2 emu / g. The nano-ferroferric oxide with a saturation magnetization intensity range of 30 - 35 emu / g and a particle size of 100 - 200 nm in the form of particles prepared by adjusting the raw material ratio and heating method disclosed in this embodiment can all be used to prepare the composite adsorbent FHGM.

[0029] (2) Alkaline pretreatment of hollow glass microspheres HGM In this embodiment, the hollow glass microspheres HGM are used as raw materials, and the main component is 70% silica. Place 10 g of hollow glass microspheres HGM in 100 ml of pure water and mix in a 500 ml beaker, and heat it to 80 °C at a heating rate of 10 - 15 °C / min to adopt more uniform heat conduction and reduce thermal stress; rapid heating is likely to damage the pore structure. In this embodiment, a gradient heating method is selected, showing better crystallinity and phase purity; Stir at 250 rpm for 10 min, put it into a 0.75 mol / L sodium hydroxide solution (200 ml), and stir at 300 rpm for 4 h; In the selection of experimental values, the proportions of the alkali-pretreated raw materials can be HGM 8 - 12 g, pure water 90 - 110 ml, and sodium hydroxide solution 180 - 220 ml. In this embodiment, typical intermediate values are selected as the specific implementation values. Based on different process scales, those skilled in the art can adjust the proportion parameter range to adapt to corresponding experimental research or production applications. The proportions provided by the method constitute quantitative technical features of the same inventive concept.

[0030] After the alkali-etched hollow glass microspheres HGM are washed 3 times with ultrapure water and then filtered, they are dried at 60 °C for 10 h to obtain surface-modified NHGM. The porous structure formed by alkali etching increases the specific surface area of NHGM by 3 - 5 times, the pore diameter is 20 - 40 nm, and the surface hydroxyl density increases to 2 - 3 times that of the untreated HGM. BET test shows that the specific surface area is increased to 8.3 m 2 / g.

[0031] By controlling the NaOH concentration (0.75 mol / L) and reaction time (4 h), a porous structure is formed on the surface of the hollow glass microspheres HGM, and the generated mesopores provide anchoring sites for subsequent loading.

[0032] (3) Grafting silane coupling agent Place 2 g of the modified NHGM in a 96% ethanol solution (30 ml), add 2 ml of silane coupling agent KH-550 and 30 ml of pure water, and stir at 80 °C at 200 rpm / min for 2 h; After cooling the suspension to room temperature, wash it three times with pure water and then filter, and dry it at 60 °C for 10 h to obtain KHGM.

[0033] The action process of the silane coupling agent usually consists of two steps: 1. Hydrolysis reaction (the hydrolyzable group (X) on the silane coupling agent hydrolyzes in the presence of water to form silanol groups (Si-OH)); 2. Condensation reaction (the hydrolyzed silanol groups (Si-OH) react with the hydroxyl groups (-OH) on the surface of the inorganic material to form Si-O-Si bonds). XPS analysis shows that the intensity of the Si-O-Si bonding peak increases by 2.7 times compared with the original HGM.

[0034] This step adopts a chemical bonding mechanism: the siloxane group (-Si-O-) of KH-550 condenses with the hydroxyl groups on the HGM surface to form covalent bonds, and the amino group (-NH2) coordinates with the Fe-O bond of, constructing an "inorganic-organic" bridging interface; XPS analysis shows that the intensity of the Si-O-Si bonding energy (103.4 eV) increases by 2.7 times, and the N 1s peak (399.8 eV) confirms the successful grafting of the amino group; active groups such as -Si-OH, -NH2, and Fe-O coexist on the surface, and the AFM measures the interfacial layer thickness to be 10 - 20 nm.

[0035] (4) Loaded nano-ferroferric oxide In this example, 2 g of KHGM and 0.6 g of nano-ferroferric oxide were stirred at 200 rpm / min at 80 °C for 2 h. After being washed three times with pure water and then filtered, they were dried at 60 °C for 10 h to obtain the magnetic adsorbent FHGM.

[0036] The original hollow glass microspheres HGM were spherical, with a smooth surface and formed cavities. Based on the structure of glass, the specific surface area was as low as 4.22 m 2 / g. Through Figures 2 - 5 Scanning electron microscope (SEM) analysis in 2 showed that the surface roughness of the adsorbent FHGM increased after alkali treatment and magnetization modification, and there were flocculent structures on the surface. The specific surface area expanded from 4.22 m 2 / g to 49 m

[0037]

[0038] Example Two In this example, heavy metal remediation was carried out for the solid waste from oilfield drilling in the northwest region. The Cd content in the contaminated soil was 48 mg / Kg. After mixing FHGM and the drilling solid waste at a ratio of 1:100 (w / w), they were oscillated and adsorbed at 25 °C and 150 rpm for 4 h. Please refer to Figure 6 in which: the Cd content was reduced to 7.38 mg / Kg.

[0039] From Figure 7 it can be seen that when repairing Cd-contaminated drilling solid waste, the new adsorbent has a significant effect on removing heavy metals in the forms of iron and manganese oxide-bound and organic-bound heavy metals. This is because the magnetic parts of the iron and manganese oxide-bound and organic-bound heavy metals are adsorbed on the surface of FHGM with the addition of FHGM under the action of magnetic force, making this adsorbent have a good effect on removing stable heavy metals.

[0040] It should be noted that after the application of FHGM, the removal efficiency of cadmium in the soil reached 84.9%. Importantly, this remediation system not only successfully removed most of the unstable heavy metals (heavy metals present in the exchangeable state and carbonate-bound state), but also removed the relatively stable heavy metal forms present in the soil (heavy metals present in the iron-manganese oxide-bound state, organic-bound state, and residual state). Among them, the unstable form of the removed heavy metal cadmium accounted for 41.1%, while the relatively stable heavy metal form accounted for 58.9%. This is because FHGM has a high specific surface area, strong magnetism, and active groups such as -Si-OH, -NH2, and Fe-O on the material surface, which can provide active sites for the adsorption of heavy metals.

[0041] Example 3 This embodiment of the present invention further discloses a comparative study on the heavy metal removal performance of the composite adsorbent FHGM prepared based on multi-morphology nano-ferroferric oxide. The specific implementation method is as follows: Preparation and performance characterization of the composite adsorbent FHGM prepared from multi-morphology ferroferric oxide (1) Material preparation, please refer to Figures 8 - 10 the SEM images of different morphologies of ferroferric oxide in Figure 8 : Nano-particle type A (yellow bar chart): Spherical nano-scale ferroferric oxide particles with a particle size of 8 - 15 nm; Figure 9 : Nano-particle type B (green bar chart): Nano-ferroferric oxide with a particle size of 100 - 200 nm used in this scheme; Figure 10 : Microstructure type C (blue bar chart): Sea urchin-like ferroferric oxide with a size of 3 - 4 μm.

[0042] The above three ferroferric oxide materials were respectively surface-functionalized and compounded with the treated KHGM. The compounding method was to stir at 200 rpm for 2 hours at 80°C, wash three times with pure water and then filter, and dry at 60°C for 10 hours to obtain the adsorption material.

[0043] Adsorption performance comparison: A heavy metal adsorption experiment was carried out on the self-prepared cadmium-contaminated soil (Cd 2+ initial concentration 300 mg / kg). The control conditions were: solid-liquid ratio 1:10 (w / v); pH 6.5 ± 0.2 (phosphate buffer system); oscillation time 120 minutes (25°C, 200 rpm).

[0044] The experimental data shows, please refer to Figure 11 : The type B adsorbent exhibits optimal cadmium adsorption performance, with relatively remarkable adsorption effects on carbonate-bound, iron-manganese oxide-bound, and organic-bound cadmium, and also outstanding cadmium absorption capacity for exchangeable cadmium; the type A and type C adsorbents have certain cadmium absorption capacity, but the effect is not as good as that of the type B adsorbent. At the same time, for exchangeable cadmium, it is basically the same as the cadmium content in the original soil, and the removal effect is not obvious.

[0045] Structure-activity relationship analysis: By revealing the mechanism of performance differences through BET specific surface area testing and TEM interface analysis, we believe that due to the nano-scale particle size (<100 nm) of the type A material, serious agglomeration phenomenon occurs (SEM shows that the aggregate size > 500 nm), and the specific surface area decreases from the theoretical value of 25 m 2 / g to the measured value of 8.75 m 2 / g, and the dense packing layer hinders the exposure of active sites. XPS shows that the utilization rate of surface -NH2 functional groups decreases by 42%; the type C material is limited by its three-dimensional spiky morphology (aspect ratio > 15), showing a discontinuous island-like distribution on the HGM surface. EDS mapping shows that the Fe element coverage is only 39%, resulting in a low effective loading rate; the type B material, with an optimized mesoporous structure (pore size distribution of 20 - 40 nm) and a moderate particle size (150 - 250 nm), forms a monolayer ordered arrangement on the FHGM surface. AFM shows that the surface roughness is reduced to 8.2 nm, and its Fe-O-Si chemical bonding interface (the characteristic peak of Fe2SiO4 is confirmed to exist by XRD) significantly improves the material stability.

[0046] Special note: Through systematic research, the present invention reveals the strong correlation between the morphology and adsorption performance of magnetite nanomaterials, establishes a quantitative regulation model of "particle size - dispersion degree - active site density", and provides theoretical guidance for the directional design of heavy metal adsorption materials.

[0047] Example 4 The embodiment of the present invention discloses the influence of regulating the loading amount of nano-magnetite on the performance of the prepared magnetic adsorption material. The specific implementation steps are as follows: Research on the regulation of the adsorption performance by the loading amount of nano-magnetite (1) Preparation of magnetic adsorption material: 1. Different masses of nano-magnetite (0.2 g, 0.4 g, 0.6 g, 0.8 g) are mixed with 2 g of KHGM, and the mixed system is stirred at a constant speed of 200 rpm for 120 minutes at 80 ± 1 °C, and the stable loading of nano-magnetite is achieved through the chemical bonding action mediated by the silane coupling agent; 2. After washing three times with deionized water (50 mL each time, ultrasonic-assisted dispersion for 10 minutes), it is finally treated in a vacuum drying oven at 60 °C for 10 hours to obtain the functionalized magnetic adsorption material (FHGM).

[0048] Soil remediation performance test: A remediation experiment was conducted on cadmium-containing soil (Cd 2+ 300 mg / kg, pH 9.8), and the control conditions were: solid-liquid ratio 1:10 (w / v); oscillation time 180 minutes (25 °C, 150 rpm); FHGM dosage 5% (w / w).

[0049] The experimental data showed ( Figure 12 the influence of different loadings of nano-ferroferric oxide on the performance of the prepared magnetic adsorbent material): It can be seen from Figure 12 that when the loading of nano-ferroferric oxide increased from 0.2 g to 0.8 g, the Cd 2+ removal rates were 68.72%, 72.86%, 78.80%, and 84.90% in sequence.

[0050] Analysis of structure-activity mechanism: The loading-performance correlation mechanism was revealed through a series of characterization techniques: BET specific surface area test: When the loading of nano-ferroferric oxide was 0.2 g, the specific surface area of FHGM reached 17.14 m 2 / g, which was about 4 times higher than that of KHGM without loading nano-ferroferric oxide; When the loading of nano-ferroferric oxide was 0.4 g, the specific surface area of FHGM reached 33.47 m 2 / g, which was about 7.9 times higher than that of unloaded KHGM; When the loading of nano-ferroferric oxide was 0.6 g, the specific surface area of FHGM reached 49 m 2 / g, which was about 12.8 times higher than that of unloaded KHGM; When the loading of nano-ferroferric oxide was 0.7 g, the specific surface area of FHGM reached 47 m 2 / g, which was 11 times higher than that of unloaded KHGM.

[0051] XPS surface analysis: The peak area of the Fe 2P 3 / 2 binding energy was positively correlated with the loading (R 2 = 0.987), confirming the effective increase in the Fe-O-Si bonding interface; VSM magnetic property test: The saturation magnetization increased from 7.6 emu / g (0.5 g loading) to 9.14 emu / g (0.6 g loading), ensuring the recyclability of the material (magnetic loss rate < 5% after 3 cycles).

[0052] By precisely regulating the loading of nano-ferroferric oxide, the present invention breaks through the contradictory balance between the active site density and structural stability of traditional adsorbent materials, and its linear response characteristic of Cd removal rate and loading provides a controllable process window for industrial scale-up.

[0053] Example 5 Please refer to Figure 13 , the present invention embodiment discloses the influence of temperature gradient regulation in step (2) on the prepared composite adsorbent FHGM, and the specific implementation manner is as follows: (1) Gradient temperature field construction: Four groups of alkali pretreatment temperature parameters (20 °C, 40 °C, 60 °C, 80 °C) are established by using a programmable temperature control reaction system, and precise temperature control is achieved through the following steps: 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); 2. Perform dynamic temperature control at a stepped heating rate of 10-15 °C / min (PID accuracy ±0.5 °C) to eliminate the thermal lag effect; maintain the preset temperature for 240 minutes, and simultaneously apply mechanical stirring at 300 rpm to form a turbulent flow field.

[0054] (2) Temperature effect characterization: Reveal the temperature-structure correlation through multi-scale characterization techniques: Dynamic contact angle analysis: The contact angle of the 80 °C treatment group drops to 12.5° (83% lower than that of the 20 °C group), confirming that the surface energy is increased to 65.3 mJ / m 2 (calculated by Owens-Wendt model); AFM surface topology analysis: The surface roughness Ra value of FHGM prepared at 80 °C reaches 128 ± 15 nm (Ra = 32 ± 8 nm for the 20 °C group), forming a multi-scale micro-nano groove structure; XPS element quantification: The surface hydroxyl density increases from 8.7 OH / nm at 20 °C 2 to 23.4 OH / nm at 80 °C 2 (calculated by O 1s peak fitting).

[0055] Process optimization verification: Compare the influence of different pretreatment temperatures in the Fe3O4 loading process: 1 Loading efficiency: The Fe element loading amount of the 80 °C pretreatment group reaches 19.8 wt% (detected by EDS), which is 3.2 times higher than that of the 20 °C group; 2 Adsorption performance: The removal rate of Cd-containing 2+ drilling mud (initial concentration 156 mg / kg) is increased from 41.2% of the 20 °C group to 84.7% of the 80 °C group (detected by ICP-MS); 3 Cycle stability: The specific surface area retention rate of FHGM prepared at 80 °C after 5 regenerations is 92.3% (tested by BET), which is significantly better than 67.8% of the 20 °C group.

[0056] Revealing of Key Mechanisms: 1. The high-temperature environment (80 °C) promotes the capillary penetration of the etching solution by reducing the liquid surface tension (from 72.1 mN / m to 58.4 mN / m, measured by the Wilhelmy plate method), forming through-surface etching pits (SEM shows that the pore size distribution is 20 - 40 nm); 2. The programmed heating strategy eliminates the phenomenon of thermal stress concentration (finite element simulation shows that the temperature gradient < 2 °C / cm), avoiding the damage of the microsphere structure caused by local over-etching (micro-CT shows that the integrity > 98%); 3. The thermally activated surface generates coordination defect sites (the characteristic signal intensity of EPR detection g = 2.003 increases by 4.8 times), providing advantageous anchoring sites for the heterogeneous nucleation of Fe3O4.

[0057] Innovation Statement: By establishing a quantitative mapping relationship of temperature field - interfacial energy - active sites (Arrhenius fitting activation energy Ea = 28.6 kJ / mol), the present invention breaks through the kinetic limitations of traditional isothermal treatment processes, shortening the etching cycle by 62% (from 160 minutes to 60 minutes), providing a thermodynamic regulation benchmark for the large-scale preparation of high-performance adsorption materials.

[0058] Example Six This example discloses the influence of different dosages of silane coupling agents in step (3) on the heavy metal adsorption performance of FHGM. The specific implementation is as follows: Study on the Synergistic Effect of Silane Coupling Agent Dosage - Interfacial Chemistry 1) Dosage Gradient Design and Material Preparation: 1. Using hollow glass microspheres pretreated with alkali (NHGM, surface hydroxyl density 22.3 OH / nm 2 , verified by XPS) as the substrate, accurately control the dosage of γ-aminopropyltriethoxysilane (KH-550) to be 0.5, 1, 1.5, 2.0, 2.5, 3.0 mL in a 96% ethanol solvent system; 2. Stir at 200 rpm for 2 hours at 80 °C to achieve interfacial bonding through chemical vapor deposition; 3. Wash three times with pure water and dry in vacuum at 60 °C for 10 hours to obtain KHGM materials, and prepare FHGM according to the KHGM materials.

[0059] (2) Verification of the Gradient Response of Adsorption Performance: Use the prepared FHGM for the adsorption experiment of the same batch of soil to be repaired. The results show that ( Figure 14Adsorption effect diagrams of heavy metal species in drilling solid waste removed by adsorbents prepared with different concentrations of silane coupling agent: The 2.0 mL dosing group reached the adsorption equilibrium in the shortest time (120 minutes), with a Langmuir saturated adsorption capacity of 118.4 mg / g and a removal rate of 84.9%; For the 0.5, 1, and 1.5 mL dosing groups, due to insufficient surface functionalization, the adsorption capacity was only 74.6 mg / g (equilibrium time extended to 150 minutes), and the removal rate was 70 - 75%; For the 2.5 and 3.0 mL dosing groups, affected by silane self - polymerization, the adsorption capacity decreased 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.

[0060] (3)Dosing amount - interfacial property structure - activity analysis: Reveal the mechanism of the dosing amount threshold effect through multi - dimensional characterization: XPS depth profiling: The proportion of Si - O - Si bonds on the surface of the 2.0 mL group reached 41.2 at% (2.3 times higher than that of the 1.5 mL group), and the full width at half - maximum of the N 1s peak was the smallest (1.8 eV), indicating uniform monolayer coverage of amino groups; AFM mechanical mapping: Excessive dosing (≥2.2 mL) led to a decrease in the adhesion force of the silane layer (from 45 nN to 22 nN), and the interfacial binding energy decreased by 63% (calculated based on the Johnson - Kendall - Roberts model); In - situ FTIR monitoring: The intensity of the Si - CH2 characteristic peak at 1290 cm -1 reached its peak at 2.0 mL, and excessive dosing caused the Si - O - Si condensation peak at 1050 cm -1 to redshift by 12 cm -1 , confirming excessive cross - linking.

[0061] Core findings 1. Critical dosing threshold (2.0 mL): Achieve monolayer limit coverage (calculated coverage rate 99.1%, based on the modified BET adsorption model), forming a dense and open active interface (the main peak of the BET pore size distribution is located at 3.5 nm); 2. Negative effect of excessive dosing: Trigger the self - polymerization of the silicone three - dimensional network (29Si NMR shows that the proportion of the T3 structure increases from 15% to 71%), resulting in micropore blockage (the porosity measured by mercury intrusion method decreases from 68% to 39%); 3. Surface potential regulation: Zeta potential analysis shows that the isoelectric point of the 2.0 mL group shifts to pH 8.5 (the unmodified KHGM is pH 4.3), and electrostatic potential calculation shows that the Cd 2+ adsorption capacity decreases by 87% (verified by the DLVO theory).

[0062] The present invention establishes a non-linear response model of silane dosage - surface bonding density - adsorption kinetics (Hill equation fitting with a synergistic coefficient n = 1.8), breaking through the process limitations of traditional empirical trial-and-error methods and revealing the quantitative regulation law of dosage on the interfacial chemical state. The optimized process window (2.0 ± 0.1 mL) significantly improves the regeneration performance of the material. After 5 cycles, the adsorption capacity retention rate is > 75%, and the magnetic recovery rate is stably above 98.5% (the saturation magnetization intensity measured by VSM is 42 emu / g), providing a high-precision controllable interfacial engineering technical solution for industrial wastewater treatment.

[0063] Example VII Generally, the adsorbent material can be reused by pickling / centrifugation; however, this process may damage the structure of the adsorbent material. The recovery method of the composite adsorbent FHGM prepared in this example is to recover it by self-suspension and then using an external magnetic field for adsorption, which can reduce the structural damage of the composite adsorbent FHGM and avoid secondary pollution at the same time.

[0064] To evaluate the regeneration and recovery performance of the composite adsorbent FHGM, a series of experiments were also carried out in this example based on the completion of the adsorption work of the composite adsorbent FHGM in Example II.

[0065] The present invention discloses a regeneration and recovery method, and the specific implementation steps are as follows: (1) Adsorption treatment: Weigh 0.5 g of FHGM adsorbent precisely in a 500 mL standard beaker, add 50 g of self-prepared cadmium-contaminated soil sample (Cd 2+ content is 300 mg / kg), and add deionized water with a solid-liquid ratio of 1:5 (w / v). Place the mixed system in a constant-temperature magnetic stirrer and continuously stir at a speed of 250 rpm for 60 minutes under the condition of 25 ± 1 °C to ensure full contact between the solid and liquid, and the composite adsorbent FHGM can suspend in still water for ≥ 48 h.

[0066] (2) Material recovery: Utilize the unique self-suspension and magnetic material characteristics of the composite adsorbent FHGM for recovery. Apply a magnetic field intensity of 0.5 T through a magnetic separation device at the upper part of the beaker for recovery, and then perform self-suspension separation based on the material density parameter (ρ = 0.49 g / cm 3 lower than the density of water), and magnetically recover the cadmium-loaded FHGM during separation. Tests show that the total recovery efficiency of this combined recovery process reaches 99.2%, and the single treatment cycle does not exceed 15 minutes.

[0067] (3) Heavy metal desorption: Place the cadmium-loaded FHGM in a centrifuge tube and centrifuge it in a high-speed centrifuge at an angular velocity of 8000 rpm for 10 minutes. Refer to Table 2. After multiple desorption operations, the percentage of heavy metals such as cadmium in the non-centrifuged sample gradually increases and reaches 91.99% after three times, confirming the high-efficiency desorption effect.

[0068]

[0069] (4) Material regeneration performance: Refer to Figure 15 , after five complete adsorption-desorption cycle experiments, the adsorption capacity retention rate of FHGM for Cd 2+ is 78.9%, showing good regeneration performance. Through characterization by scanning electron microscopy (SEM) and specific surface area analysis (BET), it is found that the attenuation of the adsorption capacity is mainly due to a 3.2% loss of specific surface area and the occupation of some surface active sites by heavy metal residues such as cadmium ions (XPS detection shows that the surface residual cadmium accounts for 0.8 at%).

[0070] It should be particularly noted that the synergistic effect of the regular hollow structure of FHGM and the externally loaded nano-magnetite composite magnetic layer endows it with both superparamagnetism (saturation magnetization greater than 9 emu / g) and stable self-suspension characteristics. The rich amine and carboxylic acid groups on the material surface (confirmed by the presence of -NH2 and -COOH characteristic peaks through FTIR) provide multiple coordination sites for heavy metal adsorption. The above-described specific embodiments further elaborate on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above is only the specific embodiments of the present invention and is not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation method of an adsorbent for heavy metal contaminated soil remediation, characterized in that, It includes the following steps: (1) Preparation of nano-ferroferric oxide: Dissolve FeCl3·6H2O in ethylene glycol, add anhydrous sodium acetate, stir at 200 - 300 rpm for 40 - 50 minutes to form a homogeneous solution, transfer it to a stainless-steel autoclave lined with polytetrafluoroethylene, react at 200 °C for 10 hours, wash with ethanol after cooling and dry at 60 °C for 10 hours to obtain granular nano-ferroferric oxide with a particle size of 100 - 200 nm; (2) Alkaline pretreatment of hollow glass microspheres HGM: Disperse HGM in pure water, heat it to 80 °C at a rate of 10 - 15 °C / min, stir at 250 rpm for 10 minutes, then add 0.75 mol / L sodium hydroxide solution, form a micron-scale porous structure with a rough surface through alkali etching, stir at 300 rpm for 4 hours, wash three times with pure water and then filter, dry at 60 °C for 10 hours to obtain alkali-etched NHGM; The porous structure formed by alkali etching increases the specific surface area of NHGM by 3 - 5 times, the pore size is 20 - 40 nm, and the surface hydroxyl density increases to 2 - 3 times that of untreated HGM; (3) Grafting silane coupling agent: Disperse the NHGM obtained in step (2) in a 96% ethanol solution, add silane coupling agent KH-550, stir at 80 °C and 200 rpm for 2 hours, form a silanized interface layer through the chemical bonding of the amino group -NH2 of KH-550 and the hydroxyl group -OH on the surface of NHGM, wash three times with pure water and then filter, dry at 60 °C for 10 hours to obtain silanized KHGM; The amino group of silane coupling agent KH-550 forms a coordination interaction with the Fe-O bond on the surface of nano-ferroferric oxide, and the thickness of the silanized interface layer is 10 - 20 nm; (4) Loading nano-ferroferric oxide: Mix the KHGM obtained in step (3) and the nano-ferroferric oxide prepared in step (1) according to the mass ratio, stir at 80 °C and 200 rpm for 2 hours, wash three times with pure water and then filter, dry at 60 °C for 10 hours, and uniformly load ferroferric oxide on the surface of HGM through the bridging action of the silane coupling agent to form a composite adsorbent FHGM with self-suspension and magnetic responsiveness.

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

3. The preparation method of the adsorbent for heavy metal contaminated soil according to claim 1, characterized in that, In step (4), the self-suspension of FHGM is manifested as a suspension time of ≥48 h in still water, and the magnetic responsiveness is manifested as 9 emu / g ≤ saturation magnetization intensity < 25 emu / g, and 99% of the adsorbent in the soil can be recovered within 10 - 15 minutes through an external magnetic field.

4. The method for preparing an adsorbent for heavy metal contaminated soil remediation according to claim 1, wherein, The In step (1), the raw material dosage ratio is 5.0 - 5.8 g of FeCl3·6H2O, 35 - 45 ml of ethylene glycol, and 3.0 - 3.5 g of anhydrous sodium acetate; In step (2), the raw material ratio for alkaline 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 dosing ratio of the silane coupling agent 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.

5. The preparation method of the adsorbent for heavy metal contaminated soil according to claim 1, characterized in that, The main raw material component of the hollow glass microspheres HGM is silica, and silica accounts for at least 70%.

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

7. Application of an adsorbent for heavy metal contaminated soil remediation, using the adsorbent according to claim 6, characterized in that, The adsorbent and the contaminated soil are mixed at a ratio of 1:50 - 1:150 (w / w) and oscillated for 2 - 6 hours to adsorb and remove heavy metals.

8. Use of the adsorbent for heavy metal contaminated soil remediation according to claim 7, characterized in that, The adsorbed adsorbent is separated from the contaminated soil by magnetic separation and reused ≥ 5 times, and the adsorption efficiency remains above 75% of the initial value.

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