Magnetic soil remediation microspheres and their preparation, application and recycling method

Abstract

The present invention belongs to the technical field of soil remediation, and discloses a magnetic soil remediation microsphere and its preparation, application and recycling method. First, hydrotalcite, magnetic iron oxide and sodium alginate are made into a mixed solution, and then the mixed solution is added dropwise to a calcium chloride solution for solidification to obtain magnetic soil remediation microspheres. The magnetic soil remediation microspheres are used to repair chromium-contaminated soil. After the remediation is completed, the used magnetic soil remediation microspheres in the soil are recovered by the action of a magnetic field, and then added to a calcium nitrate solution for regeneration to obtain regenerated magnetic soil remediation microspheres. The preparation method of the magnetic soil remediation microspheres of the present invention is simple, and when applied to chromium-contaminated soil, it can achieve a good treatment effect in a short time, and is easy to recycle and regenerate, and has the characteristics of being recyclable and regenerated multiple times. It has broad market application prospects in the field of chromium-contaminated soil remediation.

Description

Technical Field

[0001] The present invention belongs to the technical field of soil remediation, and in particular relates to a magnetic soil remediation microsphere and a preparation, application and recycling method thereof. Background Art

[0002] The heavy metal chromium (Cr) is widely used in chemical industries such as textile dyeing, leather processing, and electroplating and surface treatment due to its corrosion resistance and high hardness. These chemical products are involved in 15% of my country's commodity products. However, uncontrolled mining of chromium ore, the disorderly discharge of chromium industrial wastewater, and the overuse of pesticides and fertilizers have led to a significant increase in chromium content in the soil. The limited self-purification capacity of the soil is no longer able to cope with the increasingly serious chromium pollution. In addition, the inherent characteristics of chromium, such as its hidden nature, accumulation, long residual life, and difficulty in degradation, greatly increase the difficulty of preventing and controlling chromium pollution in soil.

[0003] The main remediation technologies for chromium-contaminated soil include physical remediation, bioremediation, and chemical remediation. A typical physical remediation method is electric remediation, which uses electric current to transport chromium to electrodes and then collects and processes it in a centralized manner. Although it can separate chromium from the soil, the engineering workload is large, the cost is high, and the soil quality is highly demanding, so its application is limited. Bioremediation often uses plants, animals, and microorganisms to absorb chromium from the soil. Although it is relatively simple to implement and has low costs, the treatment cycle is long, the effect is not significant, and it cannot treat heavily contaminated soil. Chemical remediation methods mainly include chemical leaching technology and chemical reduction technology. Chemical leaching technology refers to the use of leaching liquid to transfer chromium in the soil to the liquid phase, and then the chromium-rich wastewater is recycled and treated. Although the treatment effect is obvious, the remediation cost is high and it is easy to damage the soil structure. Chemical reduction technology refers to the use of chemical reducing agents to reduce highly toxic and highly mobile Cr(VI) to less toxic and more stable Cr(III), thereby reducing the mobility and biotoxicity of chromium to achieve the purpose of repair. Although the repair time is short and the effect is good, the drug consumption is large and the cost is high, and the use of large amounts of chemical agents can easily cause secondary pollution.

[0004] Compared to the aforementioned technologies, solidification and stabilization remediation is a more economical, efficient, and more applicable remediation technology. This involves adding exogenous remediation agents to react with heavy metals through a series of reactions, including adsorption, precipitation, ion exchange, and redox reactions. This fixes the chromium in the soil or converts it into a chemically inactive form, preventing its migration and diffusion in the environment and thus reducing the toxicity of heavy metals. The key to this technology lies in the remediation agent. Therefore, developing a low-cost, highly efficient remediation agent is of great significance for the promotion and implementation of this technology and the remediation of chromium-contaminated soils. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to address the shortcomings of existing chromium-contaminated soil remediation technologies and provide a magnetic soil remediation microsphere and its preparation, application and recycling and regeneration method. The preparation method of the magnetic soil remediation microsphere is simple, and when applied to chromium-contaminated soil, it can achieve good remediation effects in a short time, and it is easy to recycle and regenerate, and has the characteristics of being recyclable and regenerated multiple times.

[0006] In order to solve the technical problem raised by the present invention, the present invention provides a method for preparing magnetic soil remediation microspheres, comprising the following steps:

[0007] 1) Dispersing hydrotalcite uniformly in water, adding magnetic iron oxide and mixing uniformly, then adding sodium alginate, heating and stirring to form a uniform mixed solution;

[0008] 2) The mixed solution is added dropwise to a calcium chloride solution to cause a solidification reaction, and the obtained solid is washed with water and dried to obtain magnetic soil remediation microspheres.

[0009] In the above solution, the hydrotalcite is one of nitrate type and chloride type.

[0010] In the above solution, the hydrotalcite, magnetic iron oxide and sodium alginate are all solid powders.

[0011] In the above scheme, the heating temperature is 60-80°C.

[0012] In the above scheme, the stirring rate is 30 to 50 rpm, and the stirring time is 10 to 40 minutes.

[0013] In the above solution, the mass concentration of hydrotalcite in the mixed solution is 1-10%.

[0014] In the above solution, the mass concentration of magnetic iron oxide in the mixed solution is 1-5%.

[0015] In the above solution, the mass concentration of sodium alginate in the mixed solution is 0.8-2%.

[0016] In the above scheme, the mass concentration of the calcium chloride solution is 1-3%.

[0017] In the above scheme, the volume ratio of the calcium chloride solution to the water in the mixed solution is (80-100):50.

[0018] In the above scheme, the mixed solution is added dropwise using a rubber-tipped dropper, the diameter of the tube mouth of the rubber-tipped dropper is 0.2-0.5 mm, and the dropping rate is 1-3 mL / min.

[0019] In the above solution, the curing reaction time is 20 to 60 minutes.

[0020] In the above scheme, the drying temperature is 40-60° C., and the drying time is 1-4 hours.

[0021] The present invention also provides a magnetic soil remediation microsphere, which is prepared according to the above scheme.

[0022] In the above scheme, the particle size of the magnetic soil remediation microspheres is 0.7-2 mm, and the magnetic strength is ≥20emu / g.

[0023] The present invention also provides an application of magnetic soil remediation microspheres in remediating chromium-contaminated soil. The application method is: dispersing the chromium-contaminated soil in water, then adding the magnetic soil remediation microspheres, and reacting under mixing conditions to obtain remediated soil.

[0024] In the above scheme, the content of Cr(VI) in the chromium-contaminated soil is 200-1000 mg / kg.

[0025] In the above solution, the pH of the chromium-contaminated soil is 5-10.

[0026] In the above solution, the particle size of the chromium-contaminated soil is ≤200 mesh.

[0027] In the above scheme, the mass ratio of the chromium-contaminated soil to the volume of water is (0.1-1) g:1 mL.

[0028] In the above solution, the mass of the magnetic soil remediation microspheres is 3-10% of the mass of the chromium-contaminated soil.

[0029] In the above scheme, the mixing rate is 30 to 50 rpm, and the mixing time is 12 to 24 hours.

[0030] The present invention also provides a method for recycling and regenerating magnetic soil remediation microspheres after remediating chromium-contaminated soil, comprising the following steps:

[0031] 1) Recovery: The repaired soil is placed in a magnetic field environment and the magnetic soil remediation microspheres are recovered from the soil through the magnetic field.

[0032] 2) Regeneration: adding the used magnetic soil remediation microspheres to a calcium nitrate solution, reacting under mixing conditions, rinsing the obtained microspheres with water, and drying to obtain regenerated magnetic soil remediation microspheres.

[0033] In the above solution, the magnetic field intensity of the magnetic field environment is ≥1000GS.

[0034] In the above scheme, the concentration of the calcium nitrate solution is 0.1 to 0.5 mol / L.

[0035] In the above scheme, the volume ratio of the mass of the used magnetic soil remediation microspheres to the calcium nitrate solution is (0.001-0.01 g):1 mL.

[0036] In the above scheme, the mixing rate is 30 to 50 rpm, and the mixing time is 12 to 24 hours.

[0037] In the above scheme, the drying temperature is 40-60° C., and the drying time is 1-4 hours.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] 1) The present invention utilizes the property of sodium alginate that it can shrink violently in a short period of time under the action of calcium ion crosslinking agent, and embeds hydrotalcite and magnetic iron oxide into balls at room temperature. The size of the microspheres is controlled by controlling the diameter of the rubber-tipped dropper, thereby obtaining magnetic soil remediation microspheres with a suitable particle size; the microspheres are placed in chromium-contaminated soil. Due to the unique layered structure of hydrotalcite, the main layers composed of metal cations contain easily exchangeable NO3 - or Cl - The weak cross-linking between the metal ion layers allows the interlayer spacing to expand or shrink, thus being able to adsorb Cr2O7 in the soil. 2- And they are exchanged between the layers for fixation to achieve the purpose of soil remediation; this remediation process has no special requirements for soil quality and is applicable to both acidic and alkaline soils, and can achieve good results in a short time, without the precipitation of toxic substances and without generating secondary pollution, and is particularly suitable for the treatment of heavily polluted soils.

[0040] 2) The structure of the magnetic soil remediation microspheres of the present invention is a calcium alginate shell wrapped with hydrotalcite and magnetic iron oxide, which improves the coexistence characteristics of traditional remediation agents and soil. On the one hand, the microspheres react with the soil independently of each other. Combined with the magnetization characteristics, the microspheres are easily separated from the soil after use, facilitating the subsequent regeneration process. On the other hand, due to the unique stability of the calcium alginate shell, the microspheres can still maintain their own structure after multiple regenerations, maintaining a high remediation efficiency, greatly improving the material availability, and saving costs for the implementation of soil remediation projects.

[0041] 3) The preparation, application and recycling process of the magnetic soil remediation microspheres of the present invention are simple, the reaction conditions are mild, and they are easy to industrialize and suitable for popularization and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 Schematic diagram of magnetic soil remediation microspheres in Example 1.

[0043] Figure 2 This is the hysteresis loop diagram of the magnetic soil remediation microspheres in Example 1.

[0044] Figure 3 These are the Fourier transform infrared spectra of the magnetic soil remediation microspheres before and after use in Application Example 1.

[0045] Figure 4 These are the XRD patterns of the magnetic soil remediation microspheres before and after use in Application Example 1.

[0046] Figure 5 These are the SEM images of the magnetic soil remediation microspheres (a) before and (b) after use in Application Example 1.

[0047] Figure 6 This is the efficiency diagram of the magnetic soil remediation microspheres after regeneration 1-5 times in recycling example 1. DETAILED DESCRIPTION

[0048] In order to better understand the present invention, the content of the present invention is further illustrated below in conjunction with the examples, but the content of the present invention is not limited to the following examples.

[0049] In the following examples, the hydrotalcite, magnetic iron oxide, and sodium alginate used are all solid powders, wherein the hydrotalcite is nitrate type or chloride type. The specific steps for preparing nitrate type hydrotalcite by hydrothermal coprecipitation are as follows: Mg(NO3)2·6H2O and Al(NO3)3·9H2O are added to 50 mL of The mixture was uniformly mixed with 0.5 mol / L NaNO3 solution, the molar ratio of NaNO3 to Mg(NO3)2·6H2O was 1.5:1, and the molar ratio of Mg to Al was 2:1; the pH of the solution was adjusted to 10±0.02 with 2 mol / L NaOH solution, and the solution was then transferred into a polytetrachloroethylene reactor, sealed and placed in a 100°C oven for aging for 36 hours. The solution was then cooled to room temperature and centrifuged at 8000 rpm for 3 minutes using a high-speed centrifuge. The supernatant was removed, the obtained white precipitate was washed and placed in a 50°C oven to dry, and then taken out and ground to obtain hydrotalcite powder; similarly, chloride ion hydrotalcite was prepared by hydrothermal co-precipitation method.

[0050] In the following application example, to evaluate the remediation effect of magnetic soil remediation microspheres on chromium-contaminated soil, deionized water was used to extract and determine the available Cr(VI) in the soil. The specific steps were as follows: 1g of soil and 5mL of deionized water were added to a centrifuge tube. The centrifuge tube was placed on a rotary mixer and mixed at 30rpm for 24h. The clear liquid in the centrifuge tube was extracted using a syringe and a 0.45μm filter, and the Cr(VI) concentration in the clear liquid was determined using diphenylcarbazide spectrophotometry.

[0051] Example 1

[0052] A magnetic soil remediation microsphere is prepared according to the following steps:

[0053] 1) Disperse 3.5 g of hydrotalcite evenly in 50 mL of water, add 0.5 g of magnetic iron oxide and mix thoroughly, then add 0.5 g of sodium alginate. Heat to 70°C and stir at 30 rpm for 30 min to form a uniform mixed solution.

[0054] 2) Using a rubber-tipped dropper with a nozzle diameter of 0.21 mm, the mixed solution was added dropwise to 80 mL of a 2% mass concentration calcium chloride solution at a rate of 1 mL / min. The curing reaction was allowed to proceed for 30 min. The obtained solid was rinsed three times with water and dried in an oven at 40°C for 4 h to obtain magnetic soil remediation microspheres.

[0055] Figure 1 Schematic diagram of the magnetic soil remediation microspheres in this embodiment. As can be seen from the figure, the microspheres are uniform in size, with a particle size of about 0.7 to 2 mm.

[0056] Figure 2 This is the hysteresis loop diagram of the magnetic soil remediation microspheres in this embodiment. The magnetic strength of the magnetic soil remediation microspheres was tested using a vibrating sample magnetometer (VSM). The spectrum magnetization curve did not show hysteresis, indicating that it has good superparamagnetism and the magnetization saturation intensity is 23.96emu / g.

[0057] Example 2

[0058] A magnetic soil remediation microsphere is prepared according to the following steps:

[0059] 1) Disperse 3 g of hydrotalcite evenly in 50 mL of water, add 1 g of magnetic iron oxide and mix thoroughly, then add 0.5 g of sodium alginate. Heat to 80°C and stir at 40 rpm for 30 min to form a uniform mixed solution.

[0060] 2) Using a rubber-tipped dropper with a nozzle diameter of 0.31 mm, the mixed solution was added dropwise to 90 mL of a 2% mass concentration calcium chloride solution at a rate of 1.5 mL / min. The curing reaction was allowed to proceed for 30 min. The obtained solid was rinsed three times with water and dried in an oven at 50°C for 3 h to obtain magnetic soil remediation microspheres.

[0061] Example 3

[0062] A magnetic soil remediation microsphere is prepared according to the following steps:

[0063] 1) Disperse 2.5 g of hydrotalcite evenly in 50 mL of water, add 1.5 g of magnetic iron oxide and mix thoroughly, then add 0.5 g of sodium alginate. Heat to 80°C and stir at 50 rpm for 30 min to form a uniform mixed solution.

[0064] 2) Using a rubber-tipped dropper with a nozzle diameter of 0.5 mm, the mixed solution was added dropwise to 100 mL of a 2% mass concentration calcium chloride solution at a rate of 2 mL / min. The curing reaction was allowed to proceed for 30 min. The obtained solid was rinsed three times with water and dried in an oven at 60°C for 4 h to obtain magnetic soil remediation microspheres.

[0065] Example 4

[0066] A magnetic soil remediation microsphere, the preparation method of which is the same as that of Example 1 in terms of other steps and conditions, except that the hydrotalcite used is of chloride ion type.

[0067] Application Example 1

[0068] The magnetic soil remediation microspheres in Example 1 were used to remediate chromium-contaminated soil. The Cr(VI) content in the chromium-contaminated soil was 400 mg / kg, the soil pH was 6.21, and the soil particle size was 200 mesh. The application steps were as follows: 1 g of chromium-contaminated soil was dispersed in 5 mL of water, 0.05 g of magnetic soil remediation microspheres was added, and the mixture was mixed and reacted at a rate of 40 rpm for 24 hours to obtain the remediated soil.

[0069] Figure 3 The Fourier transform infrared (FTIR) spectra of the magnetic soil remediation microspheres before and after use in this application example are marked as LDH-Fe3O4 (before) and LDH-Fe3O4 (after). The FTIR spectrum is between 600-4000 cm -1 The characteristic peaks of the microspheres before and after the reaction are similar: in the range of 3000-3500 cm -1 The broad peak in the hydrotalcite layer can be attributed to the OH stretching vibration of water between the hydrotalcite layers, about 1600 cm -1 The weaker infrared response at 1362 cm is the bending vibration of OH; -1 The peaks on the left and right are CO3 2- characteristic peaks; this indicates that the microspheres still maintain the structure of hydrotalcite during use. In particular, in the spectrum before the reaction, NO3 - The characteristic peak appears at 1406.3 cm -1 The position of the NO3 between the hydrotalcite layers disappears in the curve after the reaction, which indicates that the NO3 - It has completely reacted with Cr(VI) in the soil, and the carbonates in the soil can react with NO3 in a free form. - Exchange between layers.

[0070] Figure 4The XRD patterns of the magnetic soil remediation microspheres in this application example before and after use are labeled LDH-Fe3O4 beads (before) and LDH-Fe3O4 beads (after), respectively. The XRD curve before use shows that the characteristic peaks of LDH appear at 2θ = 11.36°, 22.86°, 34.97°, and 61.46°, respectively, while the characteristic peaks of Fe3O4 appear at 2θ = 30.19°, 35.52°, 43.22°, 57.05°, and 62.68°. Comparing the XRD patterns after use, there is no significant shift in the positions of the characteristic peaks of LDH and Fe3O4. This further demonstrates that the structure of the microspheres remains unchanged before and after use.

[0071] Figure 5 The SEM images of the magnetic soil remediation microspheres in this application example (a) before and (b) after use show that hydrotalcite powder and magnetic iron oxide are encapsulated into spheres by calcium alginate. The distinct black particles attached to the microsphere surface are Fe3O4 nanoparticles, which are the source of the microspheres' magnetism. The raised portions of the microsphere surface exhibit irregular, flaky structures, representing the hydrotalcite within the microspheres. The crosslinking of calcium alginate also provides a large number of pores for the exchange of anions within the microspheres. Their presence enhances the material's adsorption properties and provides pathways for interlayer ion exchange. Comparing the SEM images before and after use reveals an increase in white particles on the surface of the magnetic microspheres after use. This is due to the swelling of the alginate during the reaction, exposing the hydrotalcite particles to the surface, thereby partially masking the magnetic iron oxide.

[0072] Application Example 2

[0073] The magnetic soil remediation microspheres in Example 1 were used to remediate chromium-contaminated soil. The Cr(VI) content in the chromium-contaminated soil was 600 mg / kg, the soil pH was 5, and the soil particle size was 200 mesh. The application steps were as follows: 1 g of chromium-contaminated soil was dispersed in 5 mL of water, 0.03 g of magnetic soil remediation microspheres was added, and the mixture was mixed and reacted at a rate of 30 rpm for 12 h to obtain the remediated soil.

[0074] Application Example 3

[0075] The magnetic soil remediation microspheres in Example 1 were used to remediate chromium-contaminated soil. The Cr(VI) content in the chromium-contaminated soil was 800 mg / kg, the soil pH was 7, and the soil particle size was 200 mesh. The application steps were as follows: 1 g of chromium-contaminated soil was dispersed in 5 mL of water, 0.01 g of magnetic soil remediation microspheres was added, and the mixture was mixed and reacted at a rate of 40 rpm for 24 hours to obtain the remediated soil.

[0076] Application Example 4

[0077] The magnetic soil remediation microspheres in Example 1 were used to remediate chromium-contaminated soil. The Cr(VI) content in the chromium-contaminated soil was 1000 mg / kg, the soil pH was 10, and the soil particle size was 200 mesh. The application steps were as follows: 1 g of chromium-contaminated soil was dispersed in 5 mL of water, 0.07 g of magnetic soil remediation microspheres was added, and the mixture was mixed and reacted at a rate of 50 rpm for 12 h to obtain the remediated soil.

[0078] Application Example 5

[0079] The magnetic soil remediation microspheres in Example 4 were used to remediate chromium-contaminated soil, and the application steps and conditions were the same as those in Application Example 1.

[0080] Comparative Example 1

[0081] A magnetic soil remediation microsphere, prepared by the same method as in Example 1 with the same steps and conditions except that the hydrotalcite used was carbonate-type. The magnetic soil remediation microsphere was applied to remediate chromium-contaminated soil according to the steps and conditions of Application Example 1.

[0082] The effects of repairing chromium-contaminated soil in Examples 1-5 and Comparative Example 1 were tested, and the results are shown in Table 1.

[0083] Table 1

[0084]

[0085] As can be seen from the table above, most Cr(VI) in soil exists in a water-soluble, available form, with only a small amount complexed with soil organic matter. This indicates that chromium easily migrates from the soil environment into water, contributing to its high toxicity. Therefore, using the removal rate of available Cr(VI) in soil to assess remediation effectiveness is a common method used by those skilled in the art.

[0086] Comparing the data of application examples 1-5, it was found that the magnetic soil remediation microspheres produced excellent treatment effects on soils with different pH and different Cr(VI) contents, with removal rates ranging from 86.07% to 94.54%. As the Cr(VI) content in the soil increased, the treatment efficiency decreased slightly, but for heavily contaminated soil with a concentration of 1000 mg / kg, the removal rate was still above 85%, demonstrating the high efficiency of magnetic soil remediation microspheres in treating chromium-contaminated soil.

[0087] Compared with the application example, the removal rate of comparative example 1 is significantly reduced, which is only 19.55%. This is because the magnetic soil remediation microspheres in comparative example 1 are prepared from carbonate-type hydrotalcite, CO3 2- The intercalated hydrotalcite has weak anion adsorption performance, so the chromium removal rate cannot meet our expectations.

[0088] Recycling Example 1

[0089] The repaired soil in Application Example 1 was placed in a magnetic field environment with a magnetic field strength of 3000 GS, and the used magnetic soil repair microspheres in the soil were recovered by the action of the magnetic field; 0.05 g of the used magnetic soil repair microspheres was added to 5 mL of 0.5 mol / L calcium nitrate solution, and the mixture was mixed and reacted at a rate of 40 rpm for 24 hours. The obtained microspheres were rinsed with water and dried in an oven at 50°C for 3 hours to obtain regenerated magnetic soil repair microspheres; this was a single regeneration.

[0090] The regenerated magnetic soil remediation microspheres were reapplied to remediate chromium-contaminated soil according to the procedures and conditions of Application Example 1, and then recovered and regenerated according to the above steps; this constitutes secondary regeneration. This cycle of use and regeneration was repeated five times, and the removal rate of available Cr(VI) in the chromium-contaminated soil was measured after each regeneration.

[0091] Figure 6 This is the efficiency diagram of the magnetic soil remediation microspheres after regeneration 1-5 times in recycling and regeneration example 1. It can be seen from the figure that with the increase of recycling and regeneration times, the removal rate of the microspheres for the effective Cr(VI) in chromium-contaminated soil gradually decreases, but still maintains a high removal rate. After four regenerations, the removal rate is still above 80%, and after five regenerations, the removal rate is still above 65%, indicating that the magnetic soil remediation microspheres have good repeated regeneration performance.

[0092] Recycling Example 2

[0093] A method for recycling magnetic soil remediation microspheres after remediation of chromium-contaminated soil comprises the following steps:

[0094] 1) Recovery: The soil repaired in Application Example 1 is placed in a magnetic field environment with a magnetic field strength of 4000 GS, and the magnetic soil remediation microspheres used in the soil are recovered by the magnetic field;

[0095] 2) Regeneration: 0.05 g of used magnetic soil remediation microspheres were added to 5 mL of 0.3 mol / L calcium nitrate solution, and the mixture was mixed and reacted at a rate of 50 rpm for 24 h. The resulting microspheres were rinsed with water and dried in an oven at 40°C for 4 h to obtain regenerated magnetic soil remediation microspheres.

[0096] The above embodiments are merely examples for clarification and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications may be made based on the above descriptions. It is not necessary and impossible to enumerate all implementation methods here, and any obvious variations or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. Application of magnetic soil remediation microspheres in remediating chromium-contaminated soil, characterized in that: The application method is: dispersing chromium-contaminated soil in water, then adding magnetic soil remediation microspheres, and reacting under mixing conditions to obtain remediated soil; the preparation method of the magnetic soil remediation microspheres includes the following steps: 1) Dispersing hydrotalcite uniformly in water, adding magnetic iron oxide and mixing uniformly, then adding sodium alginate, heating and stirring to form a uniform mixed solution; wherein the mass concentration of hydrotalcite in the mixed solution is 1-10%, the mass concentration of magnetic iron oxide is 1-5%, and the mass concentration of sodium alginate is 0.8-2%; and the hydrotalcite is in nitrate or chloride form; 2) The mixed solution is added dropwise to a calcium chloride solution to cause a solidification reaction. The resulting solid is rinsed with water and dried to obtain magnetic soil remediation microspheres with a particle size of 0.7-2 mm and a magnetic strength of ≥20 emu / g; The particle size of the chromium-contaminated soil is ≤200 mesh, the pH is 5-10, and the Cr(VI) content is 200-1000 mg / kg; the mass of the magnetic soil remediation microspheres is 3-10% of the mass of the chromium-contaminated soil; and the magnetic soil remediation microspheres are regenerated by a 0.1-0.5 mol / L calcium nitrate solution after use.

2. The use of the magnetic soil remediation microspheres according to claim 1 in remediating chromium-contaminated soil, characterized in that: The mixed solution is added dropwise using a rubber-tipped dropper with a tube orifice diameter of 0.2-0.5 mm and a dropping rate of 1-3 mL / min.

3. The use of the magnetic soil remediation microspheres according to claim 1 in remediating chromium-contaminated soil, characterized in that: The curing reaction time is 20-60 minutes; the drying temperature is 40-60° C., and the drying time is 1-4 hours.

4. The use of the magnetic soil remediation microspheres according to claim 1 in remediating chromium-contaminated soil, characterized in that: The regeneration specifically comprises the following steps: 1) Recycling: The remediated soil is placed in a magnetic field environment and the magnetic field is used to recover the used magnetic soil remediation microspheres in the soil; 2) Regeneration: adding the used magnetic soil remediation microspheres to a calcium nitrate solution, reacting under mixing conditions, rinsing the obtained microspheres with water, and drying to obtain regenerated magnetic soil remediation microspheres.

5. The use of the magnetic soil remediation microspheres according to claim 4 in remediating chromium-contaminated soil, characterized in that: The magnetic field intensity of the magnetic field environment is ≥1000 GS.

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