CN112898987A

CN112898987A - Magnetic composite material for removing heavy metals in soil and preparation and application thereof

Info

Publication number: CN112898987A
Application number: CN202011509168.7A
Authority: CN
Inventors: 骆永明; 贠豪; 李�远; 杨帅
Original assignee: Yantai Institute of Coastal Zone Research of CAS; Institute of Soil Science of CAS
Current assignee: Yantai Institute of Coastal Zone Research of CAS; Institute of Soil Science of CAS
Priority date: 2020-12-18
Filing date: 2020-12-18
Publication date: 2021-06-04

Abstract

The invention relates to the technical field of soil heavy metal pollution remediation, in particular to a millimeter-scale magnetic composite material and a preparation method and application thereof. The composite material comprises a magnetic matrix, clay minerals and a crosslinking agent according to the mass ratio of (0.5-2): 3: (2-3) mixing and crosslinking to obtain a composite material; wherein the clay mineral is zeolite and attapulgite modified by sulfydryl according to the mass ratio of 1: 1-3. The magnetic composite material is a millimeter-sized uniform sphere; the magnetic composite materialThe surface of the material has a large number of pores. The magnetic composite material is used for treating farmland soil polluted by heavy metal, particularly paddy field soil polluted by heavy metal cadmium (Cd), and has the advantages of large adsorption capacity, high restoration efficiency, convenience in operation, short restoration period, no damage to soil environment and the like; at the same time due to Fe₃O₄The matrix has the advantage of superparamagnetism, and the material is easy to magnetically separate.

Description

Magnetic composite material for removing heavy metals in soil and preparation and application thereof

Technical Field

The invention relates to the technical field of soil heavy metal pollution remediation, in particular to a millimeter-scale magnetic composite material and a preparation method and application thereof.

Background

Heavy metal pollution of soil has become one of the most common and serious environmental problems worldwide, and poses a significant threat to human health and ecological safety. The farmland soil Cd pollution has the characteristics of low concentration, long-term property, accumulation property and the like, excessive accumulation in soil leads to the increase of the absorption of crops on heavy metals, the yield and the quality of crops are influenced, and the heavy metals entering a food chain bring huge risks to the health of human bodies. Therefore, the remediation research on the farmland soil polluted by Cd is urgently needed to improve the quality safety of agricultural products.

At present, in the aspect of heavy metal removal, an adsorption method is widely applied due to the advantages of low cost, simple and easily obtained adsorption material, high treatment efficiency, convenient operation and the like. The adsorption method for removing heavy metals is to use active carbon, molecular sieve, fly ash and the like as adsorbents at first, and the materials have the advantages of fine particles, large specific surface area and low adsorption removal cost, and are suitable for industrial application requirements. However, the traditional materials have fine and loose particles and are difficult to separate, and magnetic adsorption materials are paid more and more attention to separation and recycling of the materials.

Patent CN111871374A discloses a preparation method and application of magnetic biochar, wherein the biochar material is magnetized by a chemical precipitation method, and then pyrolyzed for the second time to obtain magnetic biochar, which has good adsorption capacity to Cd, arsenic (As) and lead (Pb) in soil and good magnetic performance, but the material has high energy consumption, harsh preparation conditions and is difficult to popularize on a large scale; patent CN111111605A discloses a magnetic nano-adsorbent for removing heavy metal chromium (Cr), which is a nano-material of sulfur-doped iron lanthanum bimetallic oxide, has high Cr removal efficiency, no secondary pollution, and strong repeatability and stability, but the material is a nano-material, has a small size, is difficult to operate in the treatment process of farmland soil, and is inconvenient to use in a large area; the patent CN110129058A discloses a core-shell magnetic heavy metal contaminated soil remediation material and a preparation method thereof, the method is to soak magnetite by dilute sulphuric acid and then place the magnetite at high temperature for roasting to obtain a porous core-shell magnetic material, although the preparation process is simple, the material has higher energy consumption and smaller particle size, and is not applied to actual heavy metal contaminated farmland soil; patent CN109908862A discloses a Cd pollution repairing agent, which is an environment-friendly magnetic material using nano-iron, but the material only can passivate Cd in soil, and can not truly remove Cd, and heavy metal reactivation can be caused under natural conditions, so that grain safety is affected.

Based on the limitations of the existing magnetic adsorption material, a safe, efficient, economic and convenient novel millimeter-grade magnetic composite material is urgently needed to be developed to really remove Cd in farmland soil.

Disclosure of Invention

The invention mainly aims to provide a millimeter-scale magnetic composite material for removing heavy metal Cd in soil, and preparation and application thereof.

In order to achieve the purpose, the invention adopts the technical scheme that:

a magnetic composite material for removing heavy metals in soil is prepared from a magnetic matrix, clay minerals and a cross-linking agent according to a mass ratio of (0.5-2): 3: (2-3) mixing and crosslinking to obtain a composite material; wherein the clay mineral is zeolite and attapulgite modified by sulfydryl according to the mass ratio of 1: 1-3.

The sulfhydryl modified attapulgite is prepared by adding attapulgite into water to form uniform turbid liquid; adding a mixed solution of anhydrous ethanol and 3-mercaptopropyltriethoxysilane into the suspension, and mechanically stirring; and then washing, drying, grinding and sieving with a 100-mesh sieve to obtain the sulfhydryl modified attapulgite.

The stirring reaction time is 2-4 hours, the rotating speed is 60-180rpm, the mixture is evenly stirred and put into an oscillating box for oscillation, then the mixture is kept stand for 30-40min, the supernatant is poured off, and the mixture is washed for three times by water.

The mass ratio of the attapulgite to the water in the suspension is 1: (15-25); the mass ratio of the attapulgite to the mixed liquid is 1: (2-2.2); the volume ratio of the 3-mercaptopropyltriethoxysilane to the absolute ethyl alcohol in the mixed solution is 1: (8-10).

The magnetic matrix is Fe₃O₄(ii) a The crosslinking reagent is sodium alginate and calcium chloride.

A composite material is prepared from modified attapulgite, zeolite and Fe₃O₄Mixing the powder and sodium alginate in water to form material dispersion; dropwise adding the material dispersion into a calcium chloride solution to form a magnetic sphere in the solution; and (3) performing solid-liquid separation, cleaning and drying the wet magnetic spheres, and collecting the wet magnetic spheres by using a magnetic rod to obtain the magnetic composite material.

The modified attapulgite, zeolite and Fe₃O₄The mass ratio of the powder to the sodium alginate is 1-3: 1: (0.5-2): (2-3), the ratio of pure water to zeolite is 200: 1 (mL: g); the mass ratio of the dispersion liquid to the calcium chloride solution is 1: 0.5-1.5.

The modified attapulgite, zeolite and Fe₃O₄Mixing the powder and sodium alginate in water, mechanically stirring for 10-20min to form dispersion, and ultrasonically treating for 30-40min to remove bubbles in the dispersion.

Dripping the dispersion into a calcium chloride solution by using a peristaltic pump, setting the rotating speed of the peristaltic pump to be 30-90rpm, and setting the inner diameter of a hose to be 1-2.4 mm; or directly dripping by using an injector; wherein the initial mass fraction of the calcium chloride solution is 2-3.5%.

The drying temperature of the wet magnetic sphere is 80-105 ℃ and the drying time is 4-8 hours.

In the process of modifying the attapulgite by the sulfydryl,the drying and grinding step can be omitted, and the zeolite and the Fe are directly added in proportion₃O₄The powder and the sodium alginate form a dispersion liquid, and other steps are unchanged.

An application of a magnetic composite material in treating heavy metal in farmland soil.

By means of the technical scheme, the invention has the following advantages:

(1) the magnetic composite material mainly comprises three parts, namely a magnetic matrix, clay minerals and a crosslinking reagent. The magnetic matrix has Fe₃O₄The clay mineral part is formed by mixing modified attapulgite and zeolite powder in proportion, and the crosslinking reagent part is sodium alginate and calcium chloride; the magnetic matrix comprises the following components in a specific ratio: clay mineral: crosslinking agent ═ (0.25-1): 1.5: (0.25-1.5), the material fully utilizes the original adsorption capacity of the clay mineral to heavy metals, and simultaneously modifies the sulfydryl of the clay mineral on the basis to make the surface of the clay mineral have negative charges, thereby enhancing the attraction of the heavy metal ions with positive charges and effectively improving the treatment effect.

(2) The repair material prepared by the invention can remove heavy metals from soil, and the material makes full use of Fe₃O₄Is convenient for separation by magnetic separation. The material can really reduce the content of heavy metals, and has certain hardness, so that the material can be repeatedly used and has more practicability.

(3) The composite material obtained by the invention is millimeter-sized, has rich pores on the surface, large adsorption capacity, high adsorption speed and high efficiency, has superparamagnetism, is convenient to separate by magnetic separation, has a simple and convenient preparation method, uses raw materials which are economical and easy to obtain, and is convenient to realize industrial industrialization in production. The physical property of the material makes the material have the possibility of various practical application modes, is convenient to realize mechanization in repair work, and has good application prospect.

Drawings

Fig. 1(a-c) are scanning electron microscope microscopic morphology analysis diagrams of the magnetic composite material provided in embodiment 1 of the present invention under different magnifications, wherein fig. 1a is 45 times, fig. 1b is 1000 times, and fig. 1c is 8000 times;

FIG. 2 is a diagram showing the spectral analysis of a magnetic composite material provided in example 1 of the present invention;

FIG. 3 is a graph showing the removal effect of the magnetic composite material provided in example 1 of the present invention in simulated contaminated soil with three different properties and three Cd content gradients in each case;

FIG. 4 shows the Cd removal effect of the magnetic composite material provided in embodiment 1 of the present invention in various real contaminated soils;

fig. 5 shows the Cd removal effect of the magnetic composite material provided by embodiment 4 of the present invention in two real contaminated soils after the magnetic composite material is prepared by a one-pot method and the material proportion and the source are optimized.

Fig. 6a is a graph of the recycling cumulative effect of the magnetic composite material in soil according to embodiment 4 of the present invention.

Fig. 6b is a graph showing the change of the adsorption capacity of the magnetic composite material according to embodiment 4 of the present invention after recycling.

Detailed Description

To further illustrate the technical means and effects of the present invention adopted to achieve the predetermined objectives, the following will provide a method for preparing a magnetic composite material, a magnetic composite material and applications thereof, and a clear and complete description of embodiments, structures, features and effects thereof, which are provided by the present invention, with reference to the accompanying drawings and specific examples, but it will be understood by those skilled in the art that the following described examples are only a part of examples of the present invention, rather than all examples, and are not intended to limit the scope of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

The magnetic composite material obtained by the invention is a uniform sphere in millimeter level; the above-mentionedThe magnetic composite material has a large number of pores on the surface. The magnetic composite material is used for treating farmland soil polluted by heavy metal, especially paddy field soil polluted by heavy metal Cd, and has the advantages of large adsorption capacity, high repair efficiency, convenient operation, short repair period, no damage to soil environment and the like, and simultaneously, because of Fe₃O₄The method has the advantages of superparamagnetism, strong magnetic response, easy magnetic separation, recycling and reutilization, and reduces the cost of soil remediation, thereby being more practical. The invention creates conditions for environment-friendly rapid remediation and application of heavy metals in farmland soil.

Example 1

The main materials used in the experiment: fe₃O₄Powder (Shanghai Merlin Biochemical technology Co., Ltd.), 3-mercaptopropyltriethoxysilane (Shanghai Merlin Biochemical technology Co., Ltd.), artificial zeolite (national drug group chemical reagent Co., Ltd.), sodium alginate (national drug group chemical reagent Co., Ltd.), anhydrous calcium chloride (national drug group chemical reagent Co., Ltd.), and attapulgite (Jiangsu Changzhou Rong ao new chemical material Co., Ltd.).

Preparing a magnetic composite material: the first step is as follows: putting 10.0g of attapulgite powder into 200mL of deionized water, and uniformly stirring to obtain an attapulgite suspension; adding a mixture of 19.2mL of anhydrous ethanol and 2.4mL of 3-mercaptopropyltriethoxysilane into the suspension, mechanically stirring at room temperature for 2h, standing for 30min, pouring out the supernatant, adding 200mL of deionized water, stirring uniformly, and standing again; repeating the washing for 3 times, drying at 80 ℃, grinding, sieving with a 100-mesh sieve, and storing to obtain sulfhydryl modified attapulgite (SA) powder; the second step is that: mixing 3.0g of sodium alginate and 2.0g of Fe₃O₄2.0g of mercapto-modified attapulgite (SA) powder and 1.0g of zeolite powder are added into 200mL of deionized water, and ultrasonic treatment is carried out for 30min after the mixture is fully stirred for 20min to obtain uniform dispersion liquid; the third step: slowly dripping the dispersion liquid into 3% calcium chloride liquid by using a peristaltic pump to form a large amount of wet magnetic beads; the fourth step: washing with clear water for three times, drying at 80 deg.C for 8 hr, collecting magnetic rod to obtain new magnetic mercapto modified attapulgite @ zeolite (MSAZ) with diameter of1-2mm (see FIG. 1 a).

As can be seen from the three diagrams in fig. 1, the MSAZ material prepared by the research has relatively uniform particles and abundant pores on the surface, and is beneficial to the heavy metal ions entering the solid-liquid boundary layer of the material and further entering the surface and the micro/mesoporous pores of the material to be combined with active sites (such as amino, carboxyl, mercapto and the like) contained in the material, thereby being beneficial to the removal of the heavy metals. Meanwhile, the obtained composite material is subjected to energy spectrum analysis (figure 2), and the mass ratio of O, Si and Al element of the material is respectively 53.5%, 22.0% and 6.28%, which also accords with the characteristic of clay mineral in the composition of the material, and the mass ratio of S element is 2.06%, which indicates that the sulfydryl modification is successfully realized in the preparation process of the material.

Example 2

The magnetic composite material obtained by the embodiment is used for removing effect tests in simulated polluted soil with three different properties and three Cd content gradients in each seed.

Test soil: shandong tobacco terrace brown soil (pH 5.23), Jiangxi Yingtan red soil (pH 4.40), Heilongjiang black soil (pH 5.78)

Preparing simulated contaminated soil: the original soil used in the experiment is brown soil of Shandong tobacco terrace, red soil of Jiangxi Yingtan and black soil of Heilongjiang Helen city. Taking three parts of brown soil, each part of which is 1.0kg, and uniformly spraying 100mL of deionized water and two kinds of CdCl with different concentrations by using a spray bottle respectively₂The solution is stirred while being sprayed. Controlling the water content of the soil to be about 65% of the field water capacity, aging for 30 days at room temperature, then air-drying and grinding, and sieving by a 10-mesh sieve to obtain three types of brown soil with different Cd concentration gradients: ZR1, ZR2, ZR 3. Three kinds of red soil with different Cd concentration gradients can be obtained by the same method: HR1, HR2, HR3, three black soils with different Cd concentration gradients: HT1, HT2 and HT3, wherein the concentration of each gradient is detailed in table 1.

The experimental conditions are as follows: each treatment group weighed 10.00g of target soil into 50mL plastic centrifuge tubes with plugs, respectively, and each centrifuge tube was charged with 20.00mL deionized water, followed by 2.00g of adsorbent material (MSAZ or blank) for each group (i.e., the following setup, e.g., Z)R1 is blank brown soil under the concentration, ZR1+ MSAZ is brown soil added with adsorbing material under the concentration), and the proportion of the adsorbing material to the soil in each test example is 1: 5 (g: g), screwing the centrifugal tube, oscillating at the constant temperature of 25rpm for 24h, centrifuging at 2000rpm for 10min, taking out the supernatant, filtering with 0.45 μm filter membrane, and measuring Cd by ICP-MS²⁺Mass concentration of (2). And sucking out the magnetic material in the residual solid in the centrifugal tube by using a magnetic rod, washing the magnetic small balls on the magnetic rod into a beaker by using deionized water, drying at 80 ℃ after washing, and weighing to determine the recovery rate. Simultaneously drying each group of soil with the magnetic materials removed at 80 ℃, grinding and sieving with a 10-mesh sieve, taking 2.00g of the soil into a 50mL centrifuge tube, adding 20.00mL of 0.43mol/L nitric acid, oscillating at a constant temperature of 25rpm for 4h, taking out, centrifuging at 2000rpm for 10min, taking out supernatant, sieving with a 0.45-micron filter membrane, and measuring Cd by using ICP-MS²⁺Mass concentration of (2). The recovered magnetic pellets were also desorbed using 0.43mol/L nitric acid, the desorption method being the same as the conditions and the soil extraction step described above (see FIG. 3 and Table 1 for experimental results).

Set 9 blank groups (no material), 9 treatment groups, two replicates per group, and data shown as mean values:

ZR1、ZR1+MSAZ、ZR2、ZR2+MSAZ、ZR3、ZR3+MSAZ

HT1、HT1+MSAZ、HT2、HT2+MSAZ、HT3、HT3+MSAZ

HR1、HR1+MSAZ、HR2、HR2+MSAZ、HR3、HR3+MSAZ

TABLE 1 Effect table of different soil treated by adsorption material under different Cd concentrations

As can be seen from the figure 3 and the table 1, the material can well adsorb and remove Cd in the soil, but the treatment effect is different for different soils. The Cd treatment rates of HR2 and HR3 by MSAZ reach 94.8% and 96.1% respectively, and the Cd contents in the strongly-extracted effective state are respectively reduced to 0.22mg/kg and 0.86mg/kg from 4.22mg/kg and 22.0 mg/kg. But the treatment efficiency in simulated contaminated brown and black soils was reduced, 74.8%, 76.0% and 75.7%, 79.9%, respectively. Meanwhile, the removal effect of MSAZ on the simulated polluted soil with higher Cd concentration is higher than that of the simulated polluted soil with lower Cd concentration, and three kinds of soils with different properties all meet the rule.

Example 3

The magnetic composite material obtained by the embodiment has the effect of removing Cd in various actual polluted soils under the same dosage.

Test soil: the six real polluted soils are respectively G1, G2, G3, G4, JS and HN.

Wherein G1-G4 are respectively 4 kinds of Guizhou high background value soil, G1 and G4 are two kinds of farmland soil, G2 and G3 are hillside weed soil, and the pH values of G1-G4 soil are respectively 5.46, 6.53, 6.71 and 5.53; the contents of Cd in effective states of strong extraction in the soil G1-G4 are respectively 0.73mg/kg, 1.44mg/kg, 1.77mg/kg and 1.73 mg/kg.

JS is Jiangsu Taicang farmland soil, the pH value is 6.70, and the content of the strong extraction effective Cd is 0.59 mg/kg.

HN is Hunan Changsha farmland soil, the pH is 6.74, and the content of the strongly extracted effective Cd is 0.32 mg/kg.

Set 6 blank groups (no material), 6 treatment groups, each set 2 replicates (data shown as mean):

G1、G1+MSAZ、G2、G2+MSAZ、G3、G3+MSAZ、G4、G4+MSAZ、JS、JS+MSAZ、HN、HN+MSAZ

the proportion of the adopted materials to the soil is 1: 5 (g: g), the experimental procedure and conditions were the same as those of example 2 (see FIG. 4 and Table 2 for the results).

TABLE 2 Effect table of different soils treated by adsorption material

Example 4

The one-pot preparation procedure used for the magnetic composite material obtained in example 1 was used to prepare the magnetic composite material according to the specific sources of materials in table 3 for Cd removal in two real contaminated soils. Four different magnetic composites were prepared using a one-pot process according to different material ratios and sources, as shown in table 3:

TABLE 3

Preparing a magnetic composite material: the first step is as follows: putting 2.0g of attapulgite powder into 40mL of deionized water in a 250mL conical flask, and uniformly stirring to obtain an attapulgite suspension; adding 3.84mL of absolute ethyl alcohol and 0.48mL of 3-mercaptopropyltriethoxysilane into the suspension, mixing, stirring for 2h, and adding sodium alginate and Fe according to the dosage shown in the table₃O₄Adding zeolite powder and 160mL of deionized water into a conical flask, stirring at room temperature for 10-20min at the stirring speed of 2000rpm, and performing ultrasonic treatment for 30min to obtain a uniform dispersion liquid; the third step: dripping the dispersion into a calcium chloride solution by using a peristaltic pump, setting the rotating speed of the peristaltic pump to be 60rpm, and setting the inner diameter of a used hose to be 2.4mm to form a large amount of wet magnetic small balls; the fourth step: washing with clear water for three times, drying at 105 deg.C for 4h, and collecting with magnetic rod to obtain magnetic composite material with diameter of 1-2 mm.

The operation and conditions of the experiment for removing the effect were the same as those of example 2.

Test soil:

This example set 2 blank groups (no material added), 8 treatment groups, two in parallel, and then treat contaminated soil according to the experimental conditions of example 2, each group using 10g of soil and 2.0g of material. The experimental results are shown in FIG. 5(a-b) and Table 4, and the specific treatment groups are: JS, JS +1, JS +2, JS +3, JS +4, HN +1, HN +2, HN +3, HN +4

(JS +1 means treating Jiangsu Taicang rural soil with Material 1, and so on.)

TABLE 4

As can be seen from fig. 5(a-b) and table 4, the effect of the material 1 is most significant in two actual contaminated soils, but the raw material used for the material 1 is expensive and does not meet the requirement of economic applicability, so the comprehensive selection of the material 4 can be most applied to the actual repair work.

Example 5

The magnetic composite material prepared from the material 4 in the example 4 is adopted to explore the recycling performance of the material, the soil to be tested is Jiangsu Taicang farmland soil, the pH value is 6.70, and the content of the strongly-extracted effective Cd is 0.59 mg/kg. The repeated utilization times are 5 times, and the experiment is divided into two modes. (1) Cycle accumulation removal experiments for soil: in other words, for the same test soil, 0.43mol/L nitric acid desorption material is used after each treatment, the desorbed material is re-added according to the soil mass after each treatment, and the cumulative removal rate of the material after 5 times of oscillation or standing circulation treatment is tested, and the result is shown in FIG. 6a and Table 5; (2) cycle removal performance experiments for materials: that is, for the same batch of materials, after 0.43mol/L nitric acid is used for desorption every time, the materials are added into untreated original Cd-polluted soil again to carry out experiments, and the retention degree of the removal capacity of the materials after 5 times of recycling (oscillation treatment) is tested, and the results are shown in FIG. 6b and Table 6. The treatment time was 24h, and the rest of the experimental operation and measurement procedure were the same as in example 2.

TABLE 5

TABLE 6

The cycling performance of MSAZ is shown in fig. 6. As can be seen from FIG. 6a, when the mass ratio of the material to the soil to be treated is 1: and 5, after 5 times of recycling, the removal rate of the accumulated Cd of the experimental group subjected to standing treatment reaches 88.7%, and the removal rate of the Cd of the experimental group subjected to oscillating treatment reaches 98.1%. Along with reuse's number of times increases, and the cumulative treatment efficiency rises gradually, but the increase rate of treatment efficiency is slowing down gradually, this is because the ratio that draws the shared total Cd of active state in the soil by force descends gradually, is unfavorable for by this material adsorption entrapment. Meanwhile, the accumulated treatment efficiency of the material after the three-time utilization exceeds 80 percent, and the treatment efficiency after the fourth-time utilization is increased by less than 10 percent, so that the three-time utilization times are the best in practical application, an ideal removal effect can be achieved, the repair process can be shortened, and the cost can be effectively controlled. Fig. 6b shows the adsorption performance of the material after recovery, desorption and reuse, and it can be seen that the adsorption performance of the material prepared by the research is slightly reduced but is not significantly reduced with the increase of the number of times of reuse, and 85.5% of adsorption capacity is still maintained after five times of recovery, which proves that the material has strong reusability and good practical application potential.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. The magnetic composite material for removing the heavy metal in the soil is characterized in that: the composite material comprises a magnetic matrix, clay minerals and a crosslinking agent according to the mass ratio of (0.5-2): 3: (2-3) mixing and crosslinking to obtain a composite material; wherein the clay mineral is zeolite and attapulgite modified by sulfydryl according to the mass ratio of 1: 1-3.

2. The magnetic composite material for removing heavy metals from soil according to claim 1, wherein: the sulfhydryl modified attapulgite is prepared by adding attapulgite into water to form uniform turbid liquid; adding a mixed solution of anhydrous ethanol and 3-mercaptopropyltriethoxysilane into the suspension, and mechanically stirring for 2-4 h; and then washing and drying to obtain the mercapto-modified attapulgite.

3. The magnetic composite material for removing heavy metals from soil according to claim 2, wherein: the mass ratio of the attapulgite to the water in the suspension is 1: (15-25); the mass ratio of the attapulgite to the mixed liquid is 1: (2-2.2); the volume ratio of the 3-mercaptopropyltriethoxysilane to the absolute ethyl alcohol in the mixed solution is 1: (8-10).

4. The magnetic composite material for removing heavy metals from soil according to claim 1, wherein: the magnetic matrix is Fe₃O₄(ii) a The crosslinking reagent is sodium alginate and calcium chloride.

5. A method of making a composite material according to claim 1, wherein: mixing modified attapulgite with zeolite and Fe₃O₄Mixing the powder and sodium alginate in water to form material dispersion; dropwise adding the material dispersion into a calcium chloride solution to form a magnetic sphere in the solution; and (3) performing solid-liquid separation, cleaning and drying the wet magnetic spheres, and collecting the wet magnetic spheres by using a magnetic rod to obtain the magnetic composite material.

6. A method of making a composite material according to claim 5, wherein: the modified attapulgite, zeolite and Fe₃O₄The mass ratio of the powder to the sodium alginate is 1-3: 1: (0.5-2): (2-3), the ratio of pure water to zeolite is 200: 1 (mL: g); the mass ratio of the dispersion liquid to the calcium chloride solution is 1: 0.5-1.5.

7. A method of making a composite material according to claim 5, wherein: the modified attapulgite, zeolite and Fe₃O₄Mixing the powder and sodium alginate in water, mechanically stirring for 10-20min to form uniform dispersion, and ultrasonically treating for 30-40min to remove bubbles.

8. A method of making a composite material according to claim 5, wherein: the drying temperature of the wet magnetic spheres is 80-105 ℃.

9. Use of a magnetic composite material according to claim 1 for the treatment of heavy metals in farmland soil.