Application of magnesium hydroxide in remediation of cadmium contaminated soil

Abstract

The application provides application of magnesium hydroxide in remediation of cadmium contaminated soil, and comprises the following steps: after being exposed to the sun and air-dried, green algae and pig manure are crushed, then magnesium hydroxide mixed slurry is added, stirring is carried out under heating, then bacterial preparation is added and stirring is continuously carried out, so that a remediation agent is obtained; contaminated soil is moistened, then the remediation agent is sprayed on the surface, and the contaminated soil and the sprayed remediation agent are mixed through ploughing; the remediation agent is sprayed and the soil is ploughed every week, and after 2-3 weeks, soil remediation is completed. In the remediation step, the modified potassium hydroxide mixed slurry is mixed with green algae, pig manure and bacterial preparation to prepare the remediation agent, the soil is remediated through reasonable remediation steps, the content of cadmium in the soil is reduced, the content of organic matter is increased, and the soil fertility is improved.

Description

TECHNICAL FIELD

[0001] The application relates to the field of heavy metal contaminated soil remediation, in particular to a method for remediation of cadmium contaminated soil by using magnesium hydroxide. BACKGROUND

[0002] In recent years, the problem of heavy metal pollution in some areas of China has become increasingly serious, which has posed a serious threat to the quality of the soil environment and the safety of agricultural products. Cadmium is a toxic heavy metal pollutant, which has strong mobility. Industrial waste discharge, atmospheric deposition, sewage irrigation and long-term application of phosphorus fertilizer have led to the accumulation of cadmium in nature. This environmental pollution has caused serious problems such as ecological imbalance and has attracted widespread attention worldwide.

[0003] In recent years, researchers have conducted a large number of studies on the remediation technology of cadmium contaminated soil. Traditional remediation methods include plowing and leaching, which reduce the contact between cadmium and plant roots by adding clean soil to the in-situ soil. However, this engineering adsorption technology has many unreasonable aspects and does not effectively reduce the total content of heavy metals in the soil, and even may damage the soil structure.

[0004] The phytoremediation method is a method for removing cadmium ions in soil by super accumulating plants absorbing cadmium ions in soil and transporting them to the plant body. It has the characteristics of small pollution and low cost, but it has limitations in efficiency and recycling.

[0005] The biochar method is a method for promoting the fixation of cadmium ions and reducing their mobility by carbonizing biomass into adsorbent materials with adsorption properties and adding them to cadmium contaminated soil. The adsorbent material has high adsorption rate due to its porous structure and surface active functional groups, and is widely used in practice. However, the large amount of energy consumption generated during the preparation of the adsorbent material has caused cost problems.

[0006] As an adsorbent, magnesium hydroxide has the advantages of good buffering performance, high activity, strong adsorption capacity, non-corrosive, safe and non-toxic, and has been widely used in the fields of acid wastewater treatment, printing and dyeing wastewater decolorization, heavy metal ion removal, wastewater dephosphorization and demercuration, sea(halogen) water deboronization and flue gas desulfurization, and has achieved good results. However, when magnesium hydroxide is used alone as an adsorbent in the remediation of heavy metal contaminated soil, it is not ideal, and even may cause secondary pollution problems. SUMMARY

[0007] In view of this, the application provides a step for remediation of cadmium contaminated soil by using magnesium hydroxide to solve the above problems.

[0008] The technical scheme of the application is implemented as follows: the application of magnesium hydroxide in the remediation of cadmium contaminated soil includes the following steps:

[0009] (1) Grind the Gracilaria and pig manure after sun-drying, then add the magnesium hydroxide mixed slurry, heat to 130-150℃, stir, then add the bacterial preparation and continue stirring to obtain the repair agent;

[0010] (2) Wet the contaminated soil, then spray the repair agent on the surface, mix the 10-15cm thick soil on the surface layer of the contaminated soil with the sprayed repair agent by ploughing;

[0011] (3) Spray the repair agent and plough the soil every week, and complete the soil repair after 2-3 weeks.

[0012] Further, the magnesium hydroxide mixed slurry is prepared by adding the magnesium hydroxide and titanium dioxide mixed powder into the silane coupling agent solution, mixing with a high-speed mixer, heating to 80-90℃, and stirring for 1h to obtain the silane coupling agent modified magnesium hydroxide mixed slurry.

[0013] Further, the mass ratio of the magnesium hydroxide, titanium dioxide, and silane coupling agent solution is 5-10:1-2:4-8, and the mass ratio of the silane coupling agent and water in the silane coupling agent solution is 1:60-80.

[0014] Further, the silane coupling agent is one or more of 3-aminopropyl triethoxysilane, vinyl triethoxysilane, vinyl trimethoxysilane, or vinyl trisilane.

[0015] Further, the bacterial preparation is composed of the following raw materials by weight: 1-5 parts of Acidithiobacillus thiooxidans, 0.2-2 parts of Acidithiobacillus ferrooxidans (T.f), 5-8 parts of Micrococcus Cohn, 1872, 1-3 parts of Lactobacillus plantarum, and 2-5 parts of Pseudomonas aeruginosa.

[0016] Further, the Acidithiobacillus thiooxidans is purchased from Beijing Laiyao Biological Technology Co., Ltd., the Acidithiobacillus ferrooxidans is purchased from Wuhan Hualler Biological Technology Co., Ltd., the Micrococcus Cohn, 1872 is purchased from Shanghai Yuanye Biological Technology Co., Ltd., the Lactobacillus plantarum is purchased from Beijing Putian Tongchuang Biological Technology Co., Ltd., and the Pseudomonas aeruginosa is purchased from Beijing Beinaieliang Biological Technology Research Institute.

[0017] Further, the mass ratio of the Gracilaria, pig manure, magnesium hydroxide mixed slurry, and bacterial preparation is 5-10:4-6:20-35:2-5.

[0018] Further illustrate, the wetting is spraying hydrogen peroxide to soil to wet 0.5-1h, wherein the ratio of contaminated soil to hydrogen peroxide is 1g:2-4ml.

[0019] Further illustrate, in step (3), the spraying amount of the repair agent is 3-5.5% based on the mass of the wet soil.

[0020] Further illustrate, in step (4), the soil is not wet before spraying the repair agent every week, wherein the ratio of contaminated soil to repair agent is 1g:1-3ml.

[0021] Further illustrate, the contaminated soil is cadmium contaminated soil.

[0022] Compared with the prior art, the beneficial effects of the present application are:

[0023] (1) The present application uses titanium dioxide and silane coupling agent to modify magnesium hydroxide, enhances the adsorption capacity of magnesium hydroxide to ions, and mixes magnesium hydroxide mixed slurry, ulva pertusa, pig manure, and bacterial preparation to improve the pH of the soil.

[0024] (2) The present application uses hydrogen peroxide to wet the soil before repair, activates cadmium in the soil, and makes it easy to migrate, then sprays the repair agent and plows, the magnesium hydroxide mixed slurry in the repair agent adsorbs the easily migratable cadmium, and the effective components in ulva pertusa, pig manure, and bacterial preparation coordinate with each other to absorb, solidify, and metabolically transform the cadmium in the soil, reduce the biological effectiveness of cadmium in the soil, further reduce the content of available cadmium in the soil, and also increase the content of organic matter in the soil.

[0025] (3) The repair method of the present application has low cost, good effect, short repair period, and is suitable for cadmium contaminated agricultural soil, which not only removes cadmium but also improves soil fertility. DETAILED DESCRIPTION

[0026] In order to better understand the technical content of the present application, the following specific examples are provided to further illustrate the present application.

[0027] The experimental methods used in the embodiments of the present application are conventional methods unless otherwise specified.

[0028] The materials, reagents, etc. used in the embodiments of the present application can be obtained from commercial channels unless otherwise specified.

[0029] Example 1

[0030] The application of magnesium hydroxide in the repair of cadmium contaminated soil includes the following steps:

[0031] Preparation of silane coupling agent solution: take 3-aminopropyl triethoxysilane and water in the proportion of 1:60, mix and stir at 40-45℃ for 30min to obtain silane coupling agent.

[0032] Preparation of magnesium hydroxide mixed slurry: according to the mass ratio of 5:1:8, add magnesium hydroxide, titanium dioxide mixed powder into the silane coupling agent solution, mix and stir for 30min to obtain the silane coupling agent modified magnesium hydroxide mixed slurry.

[0033] (1) After drying in the sun, grind the Gracilaria and pig manure, then add the magnesium hydroxide mixed slurry, heat to 130℃, stir for 10min, then add the bacterial preparation and continue to stir for 30min to obtain the repair agent;

[0034] Among them, the Gracilaria, pig manure, magnesium hydroxide mixed slurry and bacterial preparation are in the mass ratio of 5:6:35:2;

[0035] The bacterial preparation is composed of the following raw materials by weight fraction: 1 part of Acidithiobacillus thiooxidans, 2 parts of Acidithiobacillus ferroxidans, 5 parts of Micrococcus, 1 part of Lactobacillus plantarum and 2 parts of Pseudomonas aeruginosa.

[0036] (2) Use hydrogen peroxide to wet the cadmium contaminated soil according to the solid-liquid ratio of 1g:2ml, then spray 3% repair agent on the surface, mix the 10-12cm thick soil on the surface layer of the contaminated soil with the sprayed repair agent by ploughing;

[0037] (3) Then, regularly spray the repair agent and turn over the soil according to the solid-liquid ratio of 1g:1ml every week, and complete the soil repair after 2-3 weeks.

[0038] Example 2

[0039] Application of magnesium hydroxide in cadmium contaminated soil remediation, including the following steps:

[0040] Preparation of silane coupling agent solution: take vinyltrisilane and water in the proportion of 1:70, mix and stir at 40-45℃ for 30min to obtain silane coupling agent.

[0041] Preparation of magnesium hydroxide mixed slurry: according to the mass ratio of 8:1:5, add magnesium hydroxide, titanium dioxide mixed powder into the silane coupling agent solution, mix and stir for 30min to obtain the silane coupling agent modified magnesium hydroxide mixed slurry.

[0042] (1) After drying in the sun, grind the Gracilaria and pig manure, then add the magnesium hydroxide mixed slurry, heat to 150℃, stir for 10min, then add the bacterial preparation and continue to stir for 30min to obtain the repair agent;

[0043] Gracilaria, pig manure, magnesium hydroxide mixed slurry, bacterial preparation according to the mass ratio of 7:5:20:5;

[0044] The bacterial preparation is composed of the following raw materials in parts by weight: 5 parts of Acidithiobacillus thiooxidans, 1 part of Acidithiobacillus ferroxidans, 8 parts of Micrococcus, 3 parts of Lactobacillus plantarum, and 4 parts of Pseudomonas aeruginosa.

[0045] (2) The contaminated soil is moistened with hydrogen peroxide according to the solid-liquid ratio of 1 g:3 ml, and then 4% of the repair agent is sprayed on the surface. The 12-15 cm thick surface layer of the contaminated soil is mixed with the sprayed repair agent by plowing;

[0046] (3) Then, the repair agent is sprayed regularly every week according to the solid-liquid ratio of 1 g:2 ml and plowing. After 2-3 weeks, the soil repair is completed.

[0047] Example 3

[0048] The application of magnesium hydroxide in the repair of cadmium-contaminated soil includes the following steps:

[0049] Preparation of silane coupling agent solution: 3-aminopropyl triethoxysilane and vinyl triethoxysilane are weighed according to the ratio of 1:80, mixed with water, and stirred at 40-45℃ for 30 min to obtain the silane coupling agent.

[0050] Preparation of magnesium hydroxide mixed slurry: magnesium hydroxide and titanium dioxide mixed powder are added to the silane coupling agent solution according to the mass ratio of 10:2:4, and stirred for 30 min to obtain the silane coupling agent modified magnesium hydroxide mixed slurry.

[0051] (1) Gracilaria and pig manure are dried by sunning and then crushed. Then, the magnesium hydroxide mixed slurry is added, heated to 140℃, stirred for 10 min, and then the bacterial preparation is added and stirred for another 30 min to obtain the repair agent;

[0052] Gracilaria, pig manure, magnesium hydroxide mixed slurry, bacterial preparation according to the mass ratio of 10:4:25:4;

[0053] The bacterial preparation is composed of the following raw materials in parts by weight: 3 parts of Acidithiobacillus thiooxidans, 0.2 parts of Acidithiobacillus ferroxidans, 6 parts of Micrococcus, 2 parts of Lactobacillus plantarum, and 5 parts of Pseudomonas aeruginosa.

[0054] (2) The contaminated soil is moistened with hydrogen peroxide according to the solid-liquid ratio of 1 g:4 ml, and then 5.5% of the repair agent is sprayed on the surface. The 10-12 cm thick surface layer of the contaminated soil is mixed with the sprayed repair agent by plowing;

[0055] (3) After that, every week, the remediation agent is sprayed and the soil is turned over according to a solid-liquid ratio of 1 g: 3 ml. After 2-3 weeks, the soil remediation is completed.

[0056] Comparative Example 1

[0057] The application of magnesium hydroxide in the remediation of cadmium-contaminated soil includes the following steps:

[0058] Preparation of silane coupling agent solution: 3-aminopropyl triethoxysilane and water are weighed according to a ratio of 1:90, mixed, and stirred at 40-45°C for 30 min to obtain the silane coupling agent.

[0059] Preparation of magnesium hydroxide mixed slurry: magnesium hydroxide and titanium dioxide mixed powder are added to the silane coupling agent solution according to a mass ratio of 5:1:8, mixed and stirred for 30 min to obtain the silane coupling agent modified magnesium hydroxide mixed slurry.

[0060] (1) The green algae and pig manure are dried by sunning, crushed, then the magnesium hydroxide mixed slurry is added, heated to 160°C, stirred for 10 min, then the bacterial preparation is added and stirred for another 30 min to obtain the remediation agent;

[0061] Among them, the green algae, pig manure, magnesium hydroxide mixed slurry, and bacterial preparation are in a mass ratio of 5:6:35:2.

[0062] The bacterial preparation is composed of the following raw materials by weight: 1 part of Acidithiobacillus thiooxidans, 2 parts of Acidithiobacillus ferroxidans, 5 parts of Micrococcus, 1 part of Lactobacillus plantarum, and 2 parts of Pseudomonas aeruginosa.

[0063] (2) The cadmium-contaminated soil is moistened with hydrogen peroxide according to a solid-liquid ratio of 1 g: 2 ml, then 7% of the remediation agent is sprayed on the surface, and the 10-12 cm thick soil layer on the surface of the contaminated soil is mixed with the sprayed remediation agent by plowing.

[0064] (3) After that, every week, the remediation agent is sprayed and the soil is turned over according to a solid-liquid ratio of 1 g: 1 ml. After 2-3 weeks, the soil remediation is completed.

[0065] Comparative Example 2

[0066] The difference between this comparative example and Example 1 is that the green algae is replaced by Gelidium amansii. Specifically, the application of magnesium hydroxide in the remediation of cadmium-contaminated soil includes the following steps:

[0067] Preparation of silane coupling agent solution: 3-aminopropyl triethoxysilane and water are weighed according to a ratio of 1:60, mixed, and stirred at 40-45°C for 30 min to obtain the silane coupling agent.

[0068] Preparation of magnesium hydroxide mixed slurry: according to the mass ratio of 5:1:8, magnesium hydroxide, titanium dioxide mixed powder is added into the silane coupling agent solution, mixed and stirred for 30 min, to obtain the silane coupling agent modified magnesium hydroxide mixed slurry.

[0069] (1) The green seaweed and pig manure are dried in the sun, crushed, then the magnesium hydroxide mixed slurry is added, heated to 130℃, stirred for 10 min, then the bacterial preparation is added and stirred for 30 min to obtain the repair agent;

[0070] Among them, the Gracilaria, pig manure, magnesium hydroxide mixed slurry and bacterial preparation are in a mass ratio of 5:6:35:2.

[0071] The bacterial preparation is composed of the following raw materials by weight fraction: 1 part of Acidithiobacillus thiooxidans, 2 parts of Acidithiobacillus ferroxidans, 5 parts of Micrococcus, 1 part of Lactobacillus plantarum and 2 parts of Pseudomonas aeruginosa.

[0072] (2) Using hydrogen peroxide, the ratio of material to liquid is 1g:2ml of cadmium contaminated soil is moistened, then 1% of the repair agent is sprayed on the surface, and the 10-12cm thick soil on the surface layer of the contaminated soil is mixed with the sprayed repair agent by plowing;

[0073] (3) Then, every week, the repair agent is sprayed regularly according to the ratio of 1g:1ml and the soil is turned over, and after 2-3 weeks, the soil repair is completed.

[0074] Comparative Example 3

[0075] The difference between this comparative example and Example 1 is that the magnesium hydroxide mixed slurry is replaced by a magnesium hydroxide solution, specifically: the application of magnesium hydroxide in cadmium contaminated soil remediation, including the following steps:

[0076] Preparation of magnesium hydroxide solution: according to the mass ratio of 1:6, water and magnesium hydroxide powder are mixed and stirred for 10 min to obtain a magnesium hydroxide solution.

[0077] (1) The Gracilaria and pig manure are dried in the sun, crushed, then the magnesium hydroxide solution is added, heated to 140℃, stirred for 10 min, then the bacterial preparation is added and stirred for 30 min to obtain the repair agent;

[0078] Among them, the Gracilaria, pig manure, magnesium hydroxide mixed slurry and bacterial preparation are in a mass ratio of 10:4:25:4.

[0079] The bacterial preparation is composed of the following raw materials by weight fraction: 3 parts of Acidithiobacillus thiooxidans, 0.2 parts of Acidithiobacillus ferroxidans, 6 parts of Micrococcus, 2 parts of Lactobacillus plantarum and 5 parts of Pseudomonas aeruginosa.

[0080] (2) using hydrogen peroxide to wet the cadmium contaminated soil according to the ratio of 1 g: 4 ml, then spraying 1% of the repair agent on the surface, mixing the 15-20 cm thick soil on the surface of the contaminated soil with the sprayed repair agent by ploughing;

[0081] (3) then spraying the repair agent regularly every week according to the ratio of 1 g: 3 ml and ploughing, after 2-3 weeks, completing the soil repair.

[0082] Comparative Example 4

[0083] The difference between this comparative example and Example 1 is that no micrococcus is added in the bacterial preparation, and the application of magnesium hydroxide in the repair of cadmium contaminated soil, including the following steps:

[0084] Preparation of silane coupling agent solution: weigh vinyltrisilane and water according to the ratio of 1:70, mix and stir at 40-45℃ for 30 min to obtain the silane coupling agent.

[0085] Preparation of magnesium hydroxide mixed slurry: add the mixed powder of magnesium hydroxide and titanium dioxide with a mass ratio of 8:1:5 into the silane coupling agent solution, mix and stir for 30 min to obtain the silane coupling agent modified magnesium hydroxide mixed slurry.

[0086] (1) dry and crush the green algae and pig manure, then add the magnesium hydroxide mixed slurry, heat to 150℃, stir for 10 min, then add the bacterial preparation and continue to stir for 30 min to obtain the repair agent;

[0087] Among them, the green algae, pig manure, magnesium hydroxide mixed slurry and bacterial preparation are in a mass ratio of 7:5:20:5;

[0088] The bacterial preparation is composed of the following raw materials by weight: 5 parts of acidophilic sulfur-oxidizing thiobacillus, 1 part of acidophilic ferrous oxide sulfur bacteria, 3 parts of lactobacillus plantarum and 4 parts of pseudomonas aeruginosa.

[0089] (2) using hydrogen peroxide to wet the cadmium contaminated soil according to the ratio of 1 g: 3 ml, then spraying 2% of the repair agent on the surface, mixing the 12-15 cm thick soil on the surface of the contaminated soil with the sprayed repair agent by ploughing;

[0090] (3) then spraying the repair agent regularly every week according to the ratio of 1 g: 2 ml and ploughing, after 2-3 weeks, completing the soil repair.

[0091] Comparative Example 5

[0092] The difference between this comparative example and Example 3 is that the contaminated soil is not wetted, and the application of magnesium hydroxide in the repair of cadmium contaminated soil, including the following steps:

[0093] Preparation of silane coupling agent solution: 3-aminopropyl triethoxysilane and vinyl triethoxysilane were weighed according to the proportion of 1:80, mixed with water, and stirred at 40-45 DEG C for 30 min to obtain the silane coupling agent.

[0094] Preparation of magnesium hydroxide mixed slurry: magnesium hydroxide, titanium dioxide mixed powder were added into the silane coupling agent solution according to the mass ratio of 10:2:4, mixed and stirred for 30 min to obtain the silane coupling agent modified magnesium hydroxide mixed slurry.

[0095] (1) The green algae and pig manure were dried by sunning, then crushed, and then added into the magnesium hydroxide mixed slurry, heated to 140 DEG C, stirred for 10 min, and then added into the bacterial preparation to continue stirring for 30 min to obtain the repair agent;

[0096] Wherein the green algae, pig manure, magnesium hydroxide mixed slurry and bacterial preparation are in a mass ratio of 10:4:25:4;

[0097] Wherein the bacterial preparation is composed of the following raw materials by weight: 3 parts of acidophilic sulfur-oxidizing thiobacillus, 0.2 parts of acidophilic ferrous oxide sulfur bacteria, 6 parts of micrococcus, 2 parts of lactobacillus plantarum and 5 parts of pseudomonas aeruginosa;

[0098] (2) Spraying 1% repair agent on the surface of the contaminated soil, and mixing the 10-12cm thick soil on the surface of the contaminated soil with the sprayed repair agent by ploughing;

[0099] (3) Then, spraying the repair agent and ploughing every week according to the solid-liquid ratio of 1g:3ml, and completing the soil repair after 2-3 weeks.

[0100] Test example

[0101] The soil repair test of the present application was carried out in Dandong City, Liaoning Province. The cadmium contaminated soil was repaired according to the repair methods of the above examples 1-4 and comparative examples 1-5, and after 20 days, the samples were tested, and the total amount of cadmium in the soil before and after repair, and the total amount of organic matter after repair (the total amount of organic matter in the soil before repair was 1.45%) were calculated.

[0102] Cadmium content test method: 5g of soil before and after repair by different methods was added into 25mL of 0.1mol / L hydrochloric acid solution, mixed, oscillated at 100r / min for 1h, centrifuged at 3200r / min for 20min, and then the supernatant was filtered through a 0.45μm filter membrane, and the content of cadmium in the filtrate was determined by atomic absorption spectrophotometry.

[0103] The testing method of organic matter content is as follows: 1g of the soil sample to be tested is taken and placed in a 50ml centrifugal tube, then 5ml of potassium dichromate and 5ml of concentrated sulfuric acid solution are added, and the mixture is shaken well, and a blank control without soil sample is prepared. Then the treated soil sample is placed in a thermostat together with the centrifugal tube, and treated at 100 DEG C for 90min, and then cooled in a cold water bath. Water is added to the centrifugal tube by using a syringe in two times to reach 50ml, and the mixture is shaken well and centrifuged to make the soil clear, and the supernatant is taken and measured at a wavelength of 590nm, and the blank sample is used to adjust the colorimeter to zero point.

[0104] The test results are as follows:

[0105]

[0106]

[0107] From the above results, it can be seen that the repairing method of the cadmium contaminated soil of the present application not only effectively reduces the content of cadmium in the soil, but also improves the soil organic matter and improves the soil fertility.

[0108] From Examples 1-3, it can be seen that the repairing method of the cadmium contaminated soil of the present application has a high cadmium removal rate, and has an excellent repairing effect on the soil, and is suitable for application in the cadmium contaminated agricultural field. Comparative Examples 1-5 are all different from the repairing method of the present application in different degrees, and the effect is poorer than that of the examples, and the cadmium removal rate of Comparative Examples 2, 3 and 4 is not 60%, which can show that the mixed slurry of the green algae and magnesium hydroxide and the micrococcus have a great influence on the repairing effect.

[0109] In the present application, the soil is moistened by using hydrogen peroxide before repairing, so that the cadmium in the soil is activated and easy to migrate, then the repairing agent is sprayed and ploughed, the mixed slurry of magnesium hydroxide in the repairing agent is adsorbed to the easily migratable cadmium, and the effective components in the green algae, pig manure and bacterial preparation are coordinated with each other to absorb, solidify and metabolically transform the cadmium in the soil, so as to reduce the biological availability of cadmium in the soil and further reduce the content of the available cadmium in the soil, and also improve the content of the organic matter in the soil.

[0110] The above only describes the preferred embodiments of the present application, and is not used to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. The application of magnesium hydroxide in the remediation of cadmium-contaminated soil, characterized in that, Includes the following steps: (1) After sun-drying and air-drying Ulva perforatum and pig manure, crush them and then add magnesium hydroxide mixed slurry. Heat the mixture to 130-150℃, stir, and then add bacterial preparation and continue stirring to obtain the repair agent. (2) Moisten the contaminated soil, then spray the remediation agent on the surface, and mix the 10-15cm thick layer of soil on the surface of the contaminated soil with the sprayed remediation agent by tilling; the moistening is to spray hydrogen peroxide on the soil and let it moisten for 0.5-1h, wherein the material-liquid ratio of contaminated soil to hydrogen peroxide is 1g:2-4ml. (3) Spray the remediation agent and turn the soil over every week. After 2-3 weeks, the soil remediation will be completed. The magnesium hydroxide mixed slurry is prepared by adding magnesium hydroxide and titanium dioxide mixed powders to a silane coupling agent solution, mixing with a high-speed mixer, heating and stirring to obtain a silane coupling agent modified magnesium hydroxide mixed slurry; the bacterial preparation is composed of the following raw materials in parts by weight: 1-5 parts of *Thiobacillus acidophilus*, 0.2-2 parts of *Thiobacillus ferrooxidans*, 5-8 parts of *Micrococcus*, 1-3 parts of *Lactobacillus plantarum* and 2-5 parts of *Pseudomonas aeruginosa*; The mass ratio of magnesium hydroxide, titanium dioxide, and silane coupling agent solution is 5-10:1-2:4-8; the mass ratio of silane coupling agent to water in the silane coupling agent solution is 1:60-80.

2. The application of magnesium hydroxide in the remediation of cadmium-contaminated soil as described in claim 1, characterized in that, The silane coupling agent is one or more of 3-aminopropyltriethoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane, or vinyltrisilane.

3. The application of magnesium hydroxide in the remediation of cadmium-contaminated soil as described in claim 1, characterized in that, The mass ratio of the mixed slurry of Ulva perforatum, pig manure, magnesium hydroxide, and bacterial preparation is 5-10:4-6:20-35:2-5.

4. The application of magnesium hydroxide as described in claim 1 in the remediation of cadmium-contaminated soil, characterized in that, In step (2), the amount of the remediation agent sprayed is 3-5.5% based on the mass of the moistened soil.

5. The application of magnesium hydroxide as described in claim 1 in the remediation of cadmium-contaminated soil, characterized in that, In step (3), the soil should not be moistened before spraying the remediation agent each week. The ratio of contaminated soil to remediation agent is 1g:1-3ml.

6. The application of magnesium hydroxide as described in claim 1 in the remediation of cadmium-contaminated soil, characterized in that, In step (2), the contaminated soil is cadmium-contaminated soil.

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