An improving agent for cadmium contaminated soil and a preparation method thereof

Abstract

The application belongs to the technical field of soil pollution remediation, and particularly relates to a modifier for cadmium contaminated soil and a preparation method thereof. The preparation method is as follows: S1, modified bentonite is prepared: after heat treatment, bentonite is added into deionized water, and then iron sulfate and manganese sulfate are added to obtain solution A; sodium carbonate and sodium phosphate are added into deionized water to obtain solution B; solution A is heated and then added into solution B, and heating reaction is continued to obtain pretreated bentonite; the pretreated bentonite is taken and added into an ethanol aqueous solution, and then a silane coupling agent is added for heating reaction to obtain bentonite modified by the silane coupling agent; the bentonite is mixed with aminotri (methylene) phosphonic acid and urea for heating reaction to obtain modified bentonite; S2, straw source soluble organic matter is prepared; S3, mixing and granulation; S4, coating: the modified bentonite is used as a coating material to perform coating treatment on the composite particles, and after drying, the modifier is obtained. The modifier has excellent slow-release and soil remediation effects.

Description

Technical Field

[0001] This invention belongs to the field of soil pollution remediation technology, specifically relating to a soil conditioner for cadmium-contaminated soil and its preparation method. Background Technology

[0002] Soil is a precious resource upon which humanity depends for survival. However, with the rapid development of industry and agriculture, heavy metal pollution has become a prominent environmental problem threatening global soil health and agricultural product safety. Among them, cadmium (Cd), with its high toxicity, strong mobility, and tendency to accumulate in organisms through the food chain, is considered one of the most harmful heavy metals. Cadmium pollution not only inhibits the normal growth of crops, but more seriously, it can be absorbed by crops and accumulate in edible parts, ultimately entering the human body through dietary means. Long-term intake can seriously damage organs such as the kidneys and bones, posing a continuous threat to public health.

[0003] Currently, my country faces widespread cadmium pollution challenges in arable land. Various technologies exist for remediating cadmium-contaminated soil, but compared to costly and damaging physical engineering measures such as topsoil replacement and leaching, and time-consuming and inefficient phytoremediation techniques, in-situ chemical passivation remediation is considered a highly promising strategy for farmland cadmium pollution control due to its low cost, ease of operation, rapid effectiveness, and suitability for large-scale application. The core of this technology lies in adding amendments to the contaminated soil, altering the form of cadmium in the soil to reduce its bioavailability and mobility.

[0004] Existing soil conditioners, such as quicklime and calcium-magnesium silicate fertilizers, can rapidly reduce available cadmium content by increasing soil pH and promoting the formation of cadmium hydroxides or carbonates. However, their effects are often short-lived. Under conditions of soil acidification caused by rainfall, irrigation, or excessive fertilizer application, fixed cadmium is easily reactivated, leading to a "relapse" and rendering the remediation efforts ineffective. Therefore, developing a novel functional material that can efficiently passivate available cadmium while possessing long-term remediation capabilities has become a current research hotspot and challenge in this field. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the first objective of the present invention is to provide a method for preparing an amendment for cadmium-contaminated soil, which has a simple process.

[0006] The second objective of this invention is to provide a soil conditioner for cadmium-contaminated soil, which has excellent slow-release and soil remediation effects.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing a soil conditioner for cadmium-contaminated soil includes the following steps:

[0009] S1. Preparation of modified bentonite

[0010] (1) Add heat-treated bentonite to deionized water, then add ferric sulfate and manganese sulfate, stir until uniform to obtain solution A; add sodium carbonate and sodium phosphate to deionized water, stir until uniform to obtain solution B; heat solution A to 75-85℃ and then add solution B, continue heating reaction, and after the reaction is completed, pretreated bentonite is obtained.

[0011] (2) Take the pretreated bentonite and add it to an ethanol aqueous solution, then add a silane coupling agent and heat it to react. After the reaction is completed, silane coupling agent modified bentonite is obtained.

[0012] (3) The bentonite modified with the silane coupling agent, aminotrimethylenephosphonic acid, and urea are mixed and heated under inert gas protection to obtain modified bentonite after the reaction is completed.

[0013] S2. Preparation of straw-derived soluble organic matter

[0014] After removing impurities, corn stalks are dried and pulverized to obtain corn stalk powder. The corn stalk powder is added to deionized water and cultured in a sealed container at room temperature and in the dark. After the culture is completed, the mixture is centrifuged, filtered, and freeze-dried to obtain soluble organic matter from straw.

[0015] S3, Mixed Granulation

[0016] The straw-derived soluble organic matter and calcium peroxide are mixed evenly and then granulated to obtain composite particles.

[0017] S4, Encapsulation

[0018] The modified bentonite is used as a coating material to coat the composite particles, and after drying, the conditioner for cadmium-contaminated soil is obtained.

[0019] Preferably, in step (1), the mass ratio of the heat-treated bentonite, ferric sulfate, and manganese sulfate is 1:(0.5-1.5):(1-2); the mass ratio of the sodium carbonate and sodium phosphate is (0.1-0.2):(0.05-0.1); and the mass ratio of the heat-treated bentonite and sodium carbonate is 1:(1.5-2).

[0020] Preferably, the heat treatment in step (1) is performed at a temperature of 170-180°C for 2-3 hours; the heating reaction is performed at a temperature of 75-85°C for 5-6 hours.

[0021] Preferably, in step (2), the ratio of the amount of pretreated bentonite, silane coupling agent, and ethanol aqueous solution is 1g:(0.2-0.5)g:(15-20)mL; the heating reaction temperature is 70-85℃ and the time is 22-26h.

[0022] Preferably, the silane coupling agent is γ-aminopropyltriethoxysilane; the concentration of the ethanol aqueous solution is 50-60 wt%.

[0023] Preferably, in step (3), the ratio of bentonite modified with silane coupling agent, aminotrimethylenephosphonic acid, and urea is 1g:(1-6)mL:(1-5)g; the heating reaction temperature is 130-150℃ and the time is 3-5h.

[0024] Preferably, in step S2, the ratio of corn stalk powder to deionized water is 1g:(20-30)mL; and the sealed culture time is 25-35 days.

[0025] Preferably, in step S3, the mass ratio of straw-derived soluble organic matter to calcium peroxide is 1:(2-4).

[0026] Preferably, in step S4, the mass ratio of composite particles to modified bentonite is 1:(0.1-0.3); the drying temperature is 90-100℃.

[0027] An amendment for cadmium-contaminated soil is prepared using the above-described method.

[0028] The beneficial technical effects of this invention are as follows:

[0029] 1. This invention provides a method for preparing a soil conditioner for cadmium-contaminated soil, which is simple in process.

[0030] 2. This invention also provides a soil conditioner for cadmium-contaminated soil, exhibiting excellent slow-release and soil remediation effects. Specifically, this invention first heat-treats bentonite to increase its porosity and specific surface area. Then, an iron-manganese complex is loaded onto the bentonite through a reaction, exhibiting good adsorption and co-precipitation effects on the heavy metal cadmium. Phosphate ions can form cadmium phosphate precipitates with low solubility with cadmium. Next, an amino group is introduced by modification with a silane coupling agent, and a grafting reaction is carried out with aminotrimethylene phosphonic acid. Aminotrimethylene phosphonic acid contains multiple phosphonic acid groups, which can form insoluble phosphonates with cadmium, exhibiting a strong chelating ability for the heavy metal ion cadmium. Furthermore, straw-derived dissolved organic matter (DOM) contains abundant carboxyl and hydroxyl functional groups, which can assist in the fixation of cadmium through complexation, forming soluble or insoluble complexes with cadmium ions, while improving the soil's physicochemical properties. Calcium peroxide dissolves in water and releases oxygen, which can reduce the availability of cadmium by altering the soil pH. In addition, modified bentonite, as a coating material, has a good slow-release effect and is also a highly efficient passivating agent. It has a good adsorption and chelation effect on cadmium in the soil. When modified bentonite gradually expands and decomposes in the soil, it first plays an adsorption and fixation role, and then begins to slowly release DOM and oxygen, so as to achieve the purpose of long-term improvement and remediation of the soil. Attached Figure Description

[0031] Figure 1 This is a SEM image of the modified bentonite prepared in Example 1. Detailed Implementation

[0032] The following is a further detailed description of the present invention in conjunction with specific preferred embodiments, and it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention. Specific conditions not specified in the embodiments are performed according to conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, all reagents or instruments used are conventional products obtained through commercial channels. Example 1

[0033] A method for preparing a soil conditioner for cadmium-contaminated soil includes the following steps:

[0034] S1. Preparation of modified bentonite

[0035] (1) Bentonite was heat-treated at 175℃ for 2.5h to obtain heat-treated bentonite; the heat-treated bentonite, ferric sulfate, manganese sulfate and deionized water were added to deionized water in a mass ratio of 1:1:1.5:40, and then ferric sulfate and manganese sulfate were added. After stirring evenly, solution A was obtained; sodium carbonate and sodium phosphate were added to deionized water in a mass ratio of 1:0.15:0.08, and after stirring evenly, solution B was obtained; solution A was heated to 80℃, and solution B was added to solution A in a mass ratio of 1:1.7 of heat-treated bentonite and sodium carbonate. The reaction was continued at 80℃ for 5.5h. After the reaction was completed, the bentonite was filtered, washed and dried to obtain pretreated bentonite.

[0036] (2) The pretreated bentonite, silane coupling agent, and ethanol aqueous solution were added in a ratio of 1g:0.3g:18mL. The pretreated bentonite was added to an ethanol aqueous solution with a concentration of 55wt%, and then γ-aminopropyltriethoxysilane was added. The mixture was reacted at 80℃ for 24h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain bentonite modified with silane coupling agent.

[0037] (3) The bentonite modified with silane coupling agent, aminotrimethylenephosphonic acid, and urea were mixed in a ratio of 1g:4mL:3g. The mixture was heated at 140℃ for 4 hours under nitrogen protection. After the reaction was completed, the mixture was filtered, washed, and dried to obtain modified bentonite. The SEM image of the modified bentonite is shown in [reference needed]. Figure 1 As shown;

[0038] S2. Preparation of straw-derived soluble organic matter

[0039] After removing impurities, corn stalks are dried and pulverized to obtain corn stalk powder. The corn stalk powder is added to deionized water at a ratio of 1g:25mL and then sealed and cultured in the dark at room temperature for 30 days. During the culture, deionized water is added to maintain a constant volume. After the culture is completed, the mixture is centrifuged, filtered through a 0.45μm filter membrane, and freeze-dried to obtain straw-derived soluble organic matter.

[0040] S3, Mixed Granulation

[0041] Adjust the tilt angle of the disc granulator to 60° and the heating device to 50°C. Mix the straw-derived soluble organic matter and calcium peroxide in a mass ratio of 1:3 to obtain a mixed powder. Place the mixed powder into the disc of the disc granulator and adjust the speed of the disc granulator to 30 r / min. Depending on the granulation situation, continuously spray water mist at the rising part of the powder with a water mist spray gun and continuously screen out smooth particles with a diameter of 3-5 mm. At the same time, continuously add mixed powder until granulation is completed to obtain composite particles.

[0042] S4, Encapsulation

[0043] Adjust the tilt angle of the drum granulator disc to 60° and the heating device to 50°C. Place the composite particles and modified bentonite in the drum granulator at a mass ratio of 1:0.2. Place the modified bentonite as a coating material in the vibrating feeder and feed it in at a uniform speed. Continuously spray water mist at the rising point of the particles with a water mist spray gun until the coating is completed. Dry at 95°C to constant weight to obtain the conditioner for cadmium-contaminated soil.

[0044] Example 1 also provides a soil conditioner for cadmium-contaminated soil, prepared using the above-described preparation method. Example 2

[0045] A method for preparing a soil conditioner for cadmium-contaminated soil includes the following steps:

[0046] S1. Preparation of modified bentonite

[0047] (1) Heat-treat bentonite at 180℃ for 2 hours to obtain heat-treated bentonite; add heat-treated bentonite, ferric sulfate, manganese sulfate and deionized water in a mass ratio of 1:1.5:2:45, then add ferric sulfate and manganese sulfate, stir evenly to obtain solution A.

[0048] Sodium carbonate and sodium phosphate were added to deionized water in a mass ratio of 1:0.2:0.1 and stirred until homogeneous to obtain solution B. Solution A was heated to 85°C, and solution B was added to solution A in a mass ratio of 1:2 of heat-treated bentonite and sodium carbonate. The reaction was continued at 85°C for 5 hours. After the reaction was completed, the solution was filtered, washed, and dried to obtain pretreated bentonite.

[0049] (2) The pretreated bentonite, silane coupling agent, and ethanol aqueous solution were added in a ratio of 1g:0.5g:20mL. The pretreated bentonite was added to an ethanol aqueous solution with a concentration of 60wt%, and then γ-aminopropyltriethoxysilane was added. The mixture was reacted at 85℃ for 22h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain bentonite modified with silane coupling agent.

[0050] (3) The bentonite modified with silane coupling agent, aminotrimethylene phosphonic acid and urea are mixed in a ratio of 1g:6mL:5g. The mixture is heated at 150°C for 3h under nitrogen protection. After the reaction is completed, it is filtered, washed and dried to obtain modified bentonite.

[0051] S2. Preparation of straw-derived soluble organic matter

[0052] After removing impurities, corn stalks are dried and pulverized to obtain corn stalk powder. The corn stalk powder is added to deionized water at a ratio of 1g:30mL and then sealed and cultured in the dark at room temperature for 35 days. During the culture, deionized water is added to maintain a constant volume. After the culture is completed, the mixture is centrifuged, filtered through a 0.45μm filter membrane, and freeze-dried to obtain straw-derived soluble organic matter.

[0053] S3, Mixed Granulation

[0054] Adjust the tilt angle of the disc granulator to 60° and the heating device to 50°C. Mix the straw-derived soluble organic matter and calcium peroxide in a mass ratio of 1:4 to obtain a mixed powder. Place the mixed powder into the disc of the disc granulator and adjust the speed of the disc granulator to 30 r / min. Depending on the granulation situation, continuously spray water mist at the rising part of the powder with a water mist spray gun and continuously screen out smooth particles with a diameter of 3-5 mm. At the same time, continuously add mixed powder until granulation is completed to obtain composite particles.

[0055] S4, Encapsulation

[0056] Adjust the tilt angle of the drum granulator disc to 60° and the heating device to 50°C. Place the composite particles and modified bentonite in the drum granulator at a mass ratio of 1:0.3. Place the modified bentonite as a coating material in the vibrating feeder and feed it in at a uniform speed. Continuously spray water mist at the rising point of the particles with a water mist spray gun until the coating is completed. Dry the particles at 90-100°C to constant weight to obtain the conditioner for cadmium-contaminated soil.

[0057] Example 2 also provides a soil conditioner for cadmium-contaminated soil, prepared using the above-described method. Example 3

[0058] A method for preparing a soil conditioner for cadmium-contaminated soil includes the following steps:

[0059] S1. Preparation of modified bentonite

[0060] (1) Heat-treat bentonite at 170℃ for 3 hours to obtain heat-treated bentonite; add heat-treated bentonite, ferric sulfate, manganese sulfate and deionized water in a mass ratio of 1:0.5:1:35, then add ferric sulfate and manganese sulfate, stir evenly to obtain solution A.

[0061] Sodium carbonate and sodium phosphate were added to deionized water at a mass ratio of 1:0.1:0.05 and stirred until homogeneous to obtain solution B. Solution A was heated to 75°C, and solution B was added to solution A at a mass ratio of 1:1.5 of heat-treated bentonite and sodium carbonate. The reaction was continued at 75°C for 6 hours. After the reaction was completed, the solution was filtered, washed, and dried to obtain pretreated bentonite.

[0062] (2) The pretreated bentonite, silane coupling agent, and ethanol aqueous solution were added in a ratio of 1g:0.2g:15mL. The pretreated bentonite was added to an ethanol aqueous solution with a concentration of 50wt%, and then γ-aminopropyltriethoxysilane was added. The mixture was reacted at 70℃ for 26h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain bentonite modified with silane coupling agent.

[0063] (3) The bentonite modified with silane coupling agent, aminotrimethylene phosphonic acid and urea are mixed in a ratio of 1g:1mL:1g. The mixture is heated at 130°C for 5h under nitrogen protection. After the reaction is completed, it is filtered, washed and dried to obtain modified bentonite.

[0064] S2. Preparation of straw-derived soluble organic matter

[0065] After removing impurities, corn stalks are dried and pulverized to obtain corn stalk powder. The corn stalk powder is added to deionized water at a ratio of 1g:20mL and then sealed and cultured in the dark at room temperature for 25 days. During the culture, deionized water is added to maintain a constant volume. After the culture is completed, the mixture is centrifuged, filtered through a 0.45μm filter membrane, and freeze-dried to obtain straw-derived soluble organic matter.

[0066] S3, Mixed Granulation

[0067] Adjust the tilt angle of the disc granulator to 60° and the heating device to 50°C. Mix the straw-derived soluble organic matter and calcium peroxide in a mass ratio of 1:2 to obtain a mixed powder. Place the mixed powder into the disc of the disc granulator and adjust the speed of the disc granulator to 30 r / min. Depending on the granulation situation, continuously spray water mist at the rising part of the powder with a water mist spray gun and continuously screen out smooth particles with a diameter of 3-5 mm. At the same time, continuously add mixed powder until granulation is completed to obtain composite particles.

[0068] S4, Encapsulation

[0069] Adjust the tilt angle of the drum granulator disc to 60° and the heating device to 50°C. Place the composite particles and modified bentonite in the drum granulator at a mass ratio of 1:0.1. Place the modified bentonite as a coating material in the vibrating feeder and feed it in at a uniform speed. Continuously spray water mist at the rising point of the particles with a water mist spray gun until the coating is completed. Dry at 90°C to constant weight to obtain the conditioner for cadmium-contaminated soil.

[0070] Example 3 also provides a soil conditioner for cadmium-contaminated soil, prepared using the above-described method.

[0071] Comparative Example 1

[0072] The difference between Comparative Example 1 and Example 1 is as follows:

[0073] Heat-treated bentonite was used instead of the pretreated bentonite in step (2), and the rest of the process was the same as in Example 1.

[0074] Comparative Example 2

[0075] The difference between Comparative Example 2 and Example 1 is as follows:

[0076] Pretreated bentonite was used instead of the modified bentonite in step S4, and the rest of the process was the same as in Example 1.

[0077] Comparative Example 3

[0078] The difference between Comparative Example 3 and Example 1 is as follows:

[0079] Bentonite was used instead of the modified bentonite in step S4, and the rest of the process was the same as in Example 1.

[0080] Experimental Example 1

[0081] The sustained-release properties of the modifiers prepared in Examples 1-3 and Comparative Examples 1-3 were tested, and the specific procedures are as follows:

[0082] Take 1g of the improver prepared in Examples 1-3 and Comparative Examples 1-3 respectively and place it in a 300-mesh filter bag. Place the filter bag in a 250mL Erlenmeyer flask and add 250mL of deionized water. Then place the Erlenmeyer flask in a constant temperature incubator at 25℃ and incubate at 1, 2, 3, 5, 7, 10, 13, 16, 23 days and every 7 days thereafter, up to 100 days.

[0083] All extracts were extracted. After extraction, 250 mL of deionized water was added to the conical flask, and the culture and extraction were continued. After thorough mixing and standing, the content of dissolved active oxygen in the filtrate was measured. The results are shown in Table 1.

[0084] Table 1

[0085] ,

[0086]

[0087] As can be seen from Table 1, compared with Comparative Examples 1-3, the soil conditioner obtained in Example 1 exhibits a longer release time and lower amplitude of active oxygen, and its changes are relatively stable during extraction. Therefore, it can play a role throughout the entire growth period of corn. The above results demonstrate that the soil conditioner obtained in this invention can achieve long-term soil improvement and remediation. This invention uses modified bentonite as a coating material, which has a good slow-release effect. Furthermore, modified bentonite itself is also a highly efficient passivating agent, exhibiting good adsorption and chelation effects on cadmium in the soil. When the modified bentonite gradually expands and decomposes in the soil, it first plays an adsorption and fixation role, and then begins to slowly release straw-derived dissolved organic matter (DOM) and oxygen, ultimately achieving the goal of long-term soil improvement and remediation.

[0088] Experiment Example 2

[0089] The improvement effects of the modifiers prepared in Examples 1-3 and Comparative Examples 1-3 were tested, and the specific process is as follows:

[0090] 1.1 Experimental Procedure

[0091] The maize variety used was Jinnongyu 39. Pot experiments were conducted, and the physicochemical properties of the potting soil are shown in Table 2. The following treatments were set up: a blank control group without amendment; Example 1 group with the amendment obtained in Example 1; Example 2 group with the amendment obtained in Example 2; Example 3 group with the amendment obtained in Example 3; Comparative Example 1 group with the amendment obtained in Comparative Example 1; Comparative Example 2 group with the amendment obtained in Comparative Example 2; and Comparative Example 3 group with the amendment obtained in Comparative Example 3. Based on previous experimental results, the amendment was mixed evenly with the potting soil at 0.3% of the soil mass. Each treatment had three replicates. In each treatment, N 0.25 g / kg, P 0.08 g / kg, and K 0.1 g / kg were added, mixed evenly, and then potted with 3 kg of dry soil per pot. Water was added to maintain the soil moisture content at 70%. Sowing began 7 days later, and routine material management was implemented to ensure normal maize growth. Samples were collected and measured after the grains matured.

[0092] 1.2 Sample Collection and Testing

[0093] After the corn matured, the corn kernels and soil were collected. The available Cd content in the soil was extracted using the DTPA extraction method, and the Cd content in the plants was determined after digestion with HNO3 / HClO4. The results are shown in Table 3.

[0094] Table 2

[0095]

[0096] Table 3

[0097]

[0098] As shown in Table 2, compared with Comparative Examples 1-3, the modifier obtained in Example 1 has a better remediation effect. The above results indicate that modified bentonite can improve the remediation effect. This is because the present invention first heat-treats the bentonite to increase its porosity and specific surface area, and then loads an iron-manganese complex onto the bentonite through a reaction, which has a good adsorption and co-precipitation effect on the heavy metal cadmium. Phosphate can form a cadmium phosphate precipitate with cadmium, which has low solubility. Next, an amino group is introduced by modification with a silane coupling agent, and a grafting reaction is carried out with aminotrimethylene phosphonic acid. Aminotrimethylene phosphonic acid contains multiple phosphonic acid groups, which can form insoluble phosphonates with cadmium, exhibiting a strong chelating ability for the heavy metal ion cadmium. Furthermore, DOM contains abundant carboxyl and hydroxyl functional groups, which can assist in the fixation of cadmium through complexation, forming soluble or insoluble complexes with cadmium ions, while improving the soil's physicochemical properties. Calcium peroxide dissolves in water and releases oxygen, which can reduce the availability of cadmium by changing the soil pH.

[0099] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. The basic principles and main features of the present invention have been described above with specific implementation schemes. Based on the present invention, some modifications or substitutions can be made, but these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of protection claimed by the present invention.

Claims

1. A method for preparing a soil conditioner for cadmium-contaminated soil, characterized in that, Includes the following steps: S1. Preparation of modified bentonite (1) Add heat-treated bentonite to deionized water, then add ferric sulfate and manganese sulfate, stir until uniform to obtain solution A; add sodium carbonate and sodium phosphate to deionized water, stir until uniform to obtain solution B; heat solution A to 75-85℃ and then add solution B, continue heating reaction, and after the reaction is completed, pretreated bentonite is obtained. (2) Take the pretreated bentonite and add it to an ethanol aqueous solution, then add a silane coupling agent and heat it to react. After the reaction is completed, silane coupling agent modified bentonite is obtained. (3) The bentonite modified with the silane coupling agent, aminotrimethylenephosphonic acid, and urea are mixed and heated under inert gas protection to obtain modified bentonite after the reaction is completed. S2. Preparation of straw-derived soluble organic matter After removing impurities, corn stalks are dried and pulverized to obtain corn stalk powder. The corn stalk powder is added to deionized water and cultured in a sealed container at room temperature and in the dark. After the culture is completed, the mixture is centrifuged, filtered, and freeze-dried to obtain soluble organic matter from straw. S3, Mixed Granulation The straw-derived soluble organic matter and calcium peroxide are mixed evenly and then granulated to obtain composite particles. S4, Encapsulation The modified bentonite is used as a coating material to coat the composite particles, and after drying, the amendment for cadmium-contaminated soil is obtained. In step (1), the mass ratio of bentonite, ferric sulfate, and manganese sulfate after heat treatment is 1:(0.5-1.5):(1-2); the mass ratio of sodium carbonate and sodium phosphate is (0.1-0.2):(0.05-0.1); the mass ratio of bentonite and sodium carbonate after heat treatment is 1:(1.5-2); the heat treatment temperature is 170-180℃ and the time is 2-3h; the heating reaction temperature is 75-85℃ and the time is 5-6h. In step (2), the ratio of pretreated bentonite, silane coupling agent, and ethanol aqueous solution is 1 g : (0.2-0.5) g : (15-20) mL; the heating reaction temperature is 70-85℃, and the time is 22-26 h; the silane coupling agent is γ-aminopropyltriethoxysilane; and the concentration of the ethanol aqueous solution is 50-60 wt%. In step (3), the ratio of bentonite modified with silane coupling agent, aminotrimethylenephosphonic acid, and urea is 1g:(1-6)mL:(1-5)g; the heating reaction temperature is 130-150℃ and the time is 3-5h.

2. The method for preparing the soil conditioner for cadmium-contaminated soil according to claim 1, characterized in that, In step S2, the ratio of corn stalk powder to deionized water is 1g:(20-30)mL; the sealed culture time is 25-35 days.

3. The method for preparing the soil conditioner for cadmium-contaminated soil according to claim 1, characterized in that, In step S3, the mass ratio of straw-derived soluble organic matter to calcium peroxide is 1:(2-4).

4. The method for preparing the soil conditioner for cadmium-contaminated soil according to claim 1, characterized in that, In step S4, the mass ratio of composite particles to modified bentonite is 1:(0.1-0.3); the drying temperature is 90-100℃.

5. A soil conditioner for cadmium-contaminated soil, characterized in that, It is prepared by the preparation method according to any one of claims 1-4.

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