A method for treating red mud soil

Abstract

The present invention discloses a method for treating red mud soil. The present invention performs red mud soil remediation through processes such as red mud soil pretreatment, red mud soil improvement and red mud soil plant remediation. Modified sodium alginate is modified by a modifier, polyethylene glycol is modified by a grafting agent, and the two are mixed to prepare modified sodium alginate; humic acid is coated with the modified sodium alginate as a carrier, and mixed with biochar to prepare a soil conditioner, and the soil conditioner and other raw materials are then applied to red mud soil. Compared with the prior art, the treatment method of the present invention enables the treated red mud soil to have the advantages of good water resistance and slow release of nutrients, which is beneficial to prolonging plant growth time.

Description

Technical Field

[0001] The invention relates to the technical field of red mud soil remediation, and in particular to a red mud soil treatment method. Background Art

[0002] Red mud, also known as red mud, is one of the unique soil types in my country. Because it is rich in metal oxides such as iron, aluminum, and manganese, it is red or reddish brown, hence the name red mud. Red mud soil has high fertility and is suitable for the growth of crops. However, in recent years, due to the acceleration of human activities, industrialization, and urbanization, red mud soil is facing serious ecological and environmental problems. Heavy metal elements in red mud soil have gradually accumulated in the process of industrialization, leading to increasingly serious soil pollution problems. These heavy metal elements can enter the human body through the food chain, posing a potential threat to human health. In addition, problems such as organic pollutants and pesticide residues in red mud soil are also prominent. The over-exploitation and utilization of red mud soil has led to a gradual decline in soil fertility. On the one hand, unreasonable agricultural planting methods have caused an imbalance in soil nutrients and destroyed the structure of microbial communities; on the other hand, soil erosion, soil erosion, and other phenomena have intensified, further weakening the fertility of the soil.

[0003] CN116675582A discloses a red mud soil conditioner and its preparation method, and a red mud soil repair and treatment method. The red mud soil conditioner is obtained by mixing and stirring a nutrient additive, a desalination and alkali conditioner, a water retaining agent, a biological fertilizer, a bentonite, and a straw composting agent; the red mud soil repair and treatment method of the invention comprises the following steps: harrowing and watering the red mud soil to obtain pre-treated red mud soil; mixing the pre-treated red mud soil with the above-mentioned red mud soil conditioner to obtain improved red mud soil; sowing plant seeds on the surface of the improved red mud soil. After the red mud soil is repaired, the soil porosity, field water holding capacity and other properties are better, but the method does not retain the nutrients in the red mud soil, which is not conducive to plant growth.

[0004] CN111837494B discloses a method for soil pore transformation of red mud, which sequentially generates micro capillary pore cavities with plant powder (straw powder, wood powder, rice husk, wheat husk), generates medium or above capillary pore cavities and block ventilation pore cavities with plant block (peanut shell, crushed corn cob), generates linear ventilation pore cavities with wheat straw, and finally forms a three-level pore connection system suitable for plant growth. Although this method can improve the ventilation pores in red mud and is conducive to plant growth, it does not retain the nutrients in the red mud soil, which is not conducive to the long-term growth of plants. Summary of the invention

[0005] In view of the above-mentioned defects of the prior art, the technical problem to be solved by the present invention is to repair red mud soil, improve the water resistance and nutrient release capacity of red mud soil, and prolong the growth period of plants.

[0006] To achieve the above object, the present invention provides a method for treating red mud soil, comprising the following steps, measured in parts by weight:

[0007] S1. Red mud soil pretreatment: 0.5-2 mu of red mud soil is used to irrigate cultivated land to obtain pretreated red mud soil;

[0008] S2, red mud soil improvement: 50-120 parts of soil conditioner and 30-80 parts of basic raw material are mixed evenly, and spread on the surface of the red mud soil pretreated in S1 to obtain improved red mud soil;

[0009] S3. Red mud soil phytoremediation: Planting plants on the surface of the modified red mud soil prepared in S2.

[0010] Preferably, the preparation method of the soil conditioner comprises the following steps, in parts by weight:

[0011] Ultrasonic dispersion of 2-8 parts of biochar in 40-70 parts of humic acid, stirring for 20-30 hours in dark conditions, then adding 5-40 parts of modified sodium alginate, stirring at 500-800 rpm for 20-40 minutes at 20-40°C, then dripping into 80-150 parts of calcium chloride solution, finally filtering out the formed gel balls with a filter, washing with water 1-4 times, and freeze-drying to obtain the soil conditioner.

[0012] Preferably, the preparation method of the modified sodium alginate comprises the following steps:

[0013] Step 1: Weigh sodium alginate, dissolve it in water, add a modifier, and stir to dissolve;

[0014] Step 2: dissolving 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and a grafting agent in a mixed solvent of dimethyl sulfoxide aqueous solution to obtain a mixed solution;

[0015] Step 3, adding the mixed solution obtained in step 2 to the system in step 1 under vigorous stirring, adjusting the pH value to 4.0-5.0 with hydrochloric acid, stirring at room temperature for 24-30 hours, dialyzing for 5-7 days, and storing in a refrigerator at 0-4°C after freeze-drying to obtain substance A;

[0016] Step 4: Under a nitrogen atmosphere, polyethylene glycol, a grafting agent, and 4-dimethylaminopyridine are dissolved in tetrahydrofuran to obtain a grafting mixed solution;

[0017] Step 5, dissolve dicyclohexylcarbodiimide in tetrahydrofuran, add the material in step 5 to the grafting mixture obtained in step 4 at a temperature of -2°C to 2°C with stirring, stir at room temperature for 20-25h, filter, add the filtrate dropwise into ether, filter to obtain a white product, dissolve the white product in tetrahydrofuran, precipitate in ether, repeat the operation 1-3 times, and dry in vacuo at 20-30°C to obtain substance B;

[0018] Step 6. Weigh substance A and substance B and dissolve them in water. After rapid stirring, adjust the pH to 5-6. Seal the mixture and place it at 32-38°C for 20-30h to obtain modified sodium alginate.

[0019] More preferably, the preparation method of the modified sodium alginate comprises the following steps, in parts by weight:

[0020] Step 1: Weigh 1-8 parts of sodium alginate, dissolve it in 100-300 parts of water, add 8-20 parts of modifier, and stir to dissolve;

[0021] Step 2, dissolving 0.5-3 parts of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 0.5-3 parts of a grafting agent in a mixed solvent of 5-15 parts of a dimethyl sulfoxide aqueous solution to obtain a mixed solution;

[0022] Step 3, adding the mixed solution obtained in step 2 to the system in step 1 under vigorous stirring, adjusting the pH value to 4.0-5.0 with hydrochloric acid, stirring at room temperature for 24-30 hours, dialyzing for 5-7 days, and storing in a refrigerator at 0-4°C after freeze-drying to obtain substance A;

[0023] Step 4: Under a nitrogen atmosphere, dissolve 2-10 parts of polyethylene glycol, 0.5-6 parts of a grafting agent, and 0.05-2 parts of 4-dimethylaminopyridine in 60-80 parts of tetrahydrofuran to obtain a grafting mixed solution;

[0024] Step 5, dissolve 1-5 parts of dicyclohexylcarbodiimide in 10-25 parts of tetrahydrofuran, add the material in step 5 to the grafting mixture obtained in step 4 at a temperature of -2°C to 2°C and under stirring, stir at room temperature for 20-25 hours, filter, add the filtrate dropwise into 300-600 parts of ether, filter to obtain a white product, dissolve the white product in tetrahydrofuran, precipitate in ether, repeat the operation 1-3 times, and dry in vacuo at 20-30°C to obtain substance B;

[0025] Step 6. Weigh substance A and substance B and dissolve them in water. After rapid stirring, adjust the pH to 5-6. Seal the mixture and place it at 32-38°C for 20-30h to obtain modified sodium alginate.

[0026] Preferably, the modifier is any one of benzohydrazide, tebufenozide and stearylhydrazide.

[0027] More preferably, the modifier is stearyl hydrazide.

[0028] Preferably, the grafting agent is any one of 3-formyl-2-pyridinecarboxylic acid, 1-naphthoylcarboxylic acid, and 2-[(2-formylphenyl)dithio]-benzoic acid.

[0029] Preferably, the basic raw material is a mixture of nutrient additives, desalination improvers, fertilizers, and bentonite in a mass ratio of (1-3): (1-2): (2-8): (5-15).

[0030] In this recipe, the ingredients and their functions are as follows:

[0031] Sodium alginate: Sodium alginate is non-toxic, easily degradable, and low in cost. 2+ The properties of sodium alginate such as the interaction of divalent metal cations to prepare gel balls are widely used in soil remediation. In soil remediation, sodium alginate can be used as a soil stabilizer and chelating agent to improve the soil. Sodium alginate can easily form a thin film on the soil surface, which can significantly improve the compressive strength of the soil. At the same time, it can accelerate the restoration of arid and semi-arid soils by biocrust technology and promote the growth of plants such as cyanobacteria on sandy land. Microspheres loaded with humic acid were prepared by using sodium alginate as a carrier, and biochar was used to improve the slow-release performance, in order to enhance the utilization efficiency of sodium alginate-based soil conditioners and extend their use time.

[0032] Humic acid: Humic acid is a soil conditioner that promotes the formation of soil aggregate structure, improves soil fertility, promotes nutrient absorption, and stabilizes the soil. However, humic acid loses water and exerts its effect in a short time. High concentrations of humic acid can also affect the growth and development of crops. Modified sodium alginate is used as a carrier to provide a sustained release effect, which plays a key role in maintaining the long-term presence of humic acid in the soil and maximizing its effectiveness.

[0033] Biochar: Biochar is often used as a highly effective soil conditioner due to its large specific surface area, rich pore structure and multiple surface functional groups. It can effectively adsorb soil pollutants, improve soil physical and chemical properties, increase crop yields and soil carbon storage. After applying biochar, the soil bulk density decreased and the porosity increased, which may be due to the aggregation process induced by the addition of biochar.

[0034] Modifier: The modifier contains hydrazide functional groups, which can react with functional groups in sodium alginate to modify the sodium alginate, so that the sodium alginate is grafted with hydrazide groups. The hydrazide groups in the modified sodium alginate react with the carbonyl groups in the modified polyethylene glycol to obtain acylhydrazone bonds to obtain modified sodium alginate. This reaction is often carried out under mild conditions. This acylhydrazone bond cross-linked hydrogel usually has self-healing properties, temperature sensitivity and pH responsiveness.

[0035] 1-(3-Dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride: 1-(3-Dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride is a commonly used carboxylic acid activator, which can react with the carboxyl group in the sodium alginate molecule to form an active ester intermediate. This process is called carboxylic acid activation and is an important step in the subsequent reaction of sodium alginate and modifiers.

[0036] Grafting agent: The grafting agent is a compound containing carbonyl and carboxyl functional groups. The carboxyl functional group in the grafting agent can react with the hydroxyl group in polyethylene glycol, so that the grafted polymer contains a carbonyl functional group, and the carbonyl functional group can react with the amide group to obtain an acylhydrazone bond, thereby preparing modified sodium alginate.

[0037] Dimethyl sulfoxide: Dimethyl sulfoxide is a polar organic solvent that can dissolve a variety of organic substances.

[0038] Polyethylene glycol: Polyethylene glycol has the advantages of hydrophilicity and good biocompatibility. The carboxyl functional groups contained in the grafting agent are reacted with polyethylene glycol to modify polyethylene glycol, so as to exert the biological function of polyethylene glycol hydrogel.

[0039] Grafting agent: The grafting agent contains carboxyl and carbonyl functional groups. The grafting agent can modify the polyethylene glycol molecules and increase the diversity of the polyethylene glycol molecules.

[0040] 4-Dimethylaminopyridine: 4-Dimethylaminopyridine acts as a catalyst and has a catalytic effect.

[0041] Tetrahydrofuran: Tetrahydrofuran is a polar organic solvent that can dissolve a variety of organic substances, including polyethylene glycol, grafting agents, dicyclohexylcarbodiimide, etc. This allows these compounds to mix and react thoroughly in solution.

[0042] Dicyclohexylcarbodiimide: Dicyclohexylcarbodiimide is a commonly used dehydrating agent, which can react with carboxylic acid or hydroxyl groups in the grafting agent to remove water, thereby promoting the grafting reaction. At a temperature of -2°C to 2°C, dicyclohexylcarbodiimide is mixed with the grafting agent to form a new mixture, which is then added to the grafting mixture to accelerate the grafting reaction.

[0043] Diethyl ether: Diethyl ether is a non-polar organic solvent that is compatible with organic matter in tetrahydrofuran and is used to extract water-soluble products from tetrahydrofuran. By adding diethyl ether dropwise and filtering, white products can be obtained, which are water-soluble and insoluble in diethyl ether. After dissolving the white product in tetrahydrofuran, the product can be further purified to remove impurities by settling and repeating the operation.

[0044] Nutritional additives: As one of the basic raw materials, the main function of nutritional additives is to provide the nutrients needed for plant growth, promote plant growth and the recovery of soil ecosystems.

[0045] Desalination and alkali conditioner: The main function of desalination and alkali conditioner is to adjust the pH value of the soil and remove salt from the soil, thereby improving the chemical properties of the soil.

[0046] Fertilizer: As one of the basic raw materials, fertilizer mainly provides necessary nutrients for plant growth, promotes plant growth and the recovery of soil ecosystem. The preferred fertilizer of the present invention is organic fertilizer.

[0047] Bentonite: Bentonite has strong water absorption and expansion properties, which can increase the porosity of the soil, improve the air permeability and water permeability of the soil, and is beneficial to the growth of plant roots.

[0048] Beneficial effects of the present invention:

[0049] 1. Compared with the prior art, sodium alginate modified by a modifier is reacted with a Schiff base of a carbonyl-terminated polyethylene glycol preparation to prepare an acylhydrazone bond cross-linked polymer, and then humic acid is coated with the polymer to prepare modified sodium alginate microspheres, and then the modified sodium alginate microspheres are mixed with biochar to obtain a soil conditioner, and finally the soil conditioner is used for red mud soil remediation.

[0050] 2. The soil conditioner prepared by using modified sodium alginate, humic acid and biochar is beneficial to improving the red mud soil repair capacity and the slow-release performance of humic acid; first, the coating material can effectively reduce the influence of environmental factors such as water and air; second, it realizes the persistence of soil nutrient utilization and reduces the number of times pesticides and conditioners are applied; third, it reduces the pesticide damage caused by excessive pesticide concentration. Therefore, slow / controlled release technology can not only improve the utilization efficiency of soil nutrients, but also reduce labor costs and realize the controlled release of soil nutrients. DETAILED DESCRIPTION

[0051] Parameters for specific chemical substances used, sources.

[0052] 3-Formyl-2-pyridinecarboxylic acid, CAS No.: 19182-29-7.

[0053] 1-Naphthoylcarboxylic acid, CAS number: 26153-26-4.

[0054] 2-[(2-formylphenyl)dithio]-benzoic acid,benzoic acid,2-[(2-formylphenyl)dithio],CAS No.:569656-04-8.

[0055] Humic acid, product number: SJYFZSN-050, Houma Shengjiayou Biotechnology Development Co., Ltd.

[0056] Biochar, item number: YKT-032, Suzhou Yituolian International Trade Co., Ltd.

[0057] Desalination alkali improver, model: zw12317, Shandong Zhenwei New Materials Co., Ltd.

[0058] The nutritional additive is medical stone powder, 325 mesh.

[0059] Bentonite, 325 mesh.

[0060] Polyethylene glycol, model: PEG400, Jinan Xinke Chemical Co., Ltd.

[0061] Fertilizer, product number: SWYJF293, organic matter ≥50%, effective live bacteria count ≥500 million / g, Hebei Thumb Up Biological Organic Fertilizer Co., Ltd.

[0062] Example 1

[0063] A method for treating red mud soil comprises the following steps:

[0064] S1. Red mud soil pretreatment: 1 mu of red mud soil is irrigated and cultivated, the tillage depth is 25 cm, the red mud is broken into pieces with a particle size of 2 cm, and the water content of the red mud soil is maintained at 15%, thereby obtaining pretreated red mud soil;

[0065] S2, red mud soil improvement: 80 kg soil conditioner, 10 kg nutrient additive, 10 kg desalination improver, 20 kg fertilizer, and 10 kg bentonite were stirred at 200 rpm for 10 min, and then spread on the surface of the pretreated red mud soil in S1 at a density of 130 kg / mu to obtain improved red mud soil;

[0066] S3. Red mud soil phytoremediation: Rose seedlings were planted on the surface of the modified red mud soil prepared in S2. The seedlings were 3 months old, the planting depth was 4 cm, the plant spacing was 25 cm, and the row spacing was 30 cm.

[0067] The method for preparing the soil conditioner comprises the following steps:

[0068] 5 g of biochar was ultrasonically dispersed in 50 mL of humic acid at 500 W, stirred at 300 rpm for 24 h in the dark, then 10 g of modified sodium alginate was added, stirred at 700 rpm for 30 min at 30 ° C, then dropped into 100 mL of 10 wt% calcium chloride aqueous solution, and finally the formed gel balls were filtered out with a 50-mesh filter, washed with water 3 times, and freeze-dried at -50 ° C for 24 h to obtain the soil conditioner.

[0069] Wherein, the preparation method of the modified sodium alginate comprises the following steps:

[0070] Step 1: Weigh 5 g of sodium alginate, dissolve it in 200 mL of water, add 10 g of stearyl hydrazide, and stir at 200 rpm for 30 min;

[0071] Step 2: Dissolve 1 g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 2 g of 2-[(2-formylphenyl)dithio]-benzoic acid in 8 mL of a dimethyl sulfoxide aqueous solution mixed solvent having a volume ratio of 1:1 of dimethyl sulfoxide and water to obtain a mixed solution;

[0072] Step 3, adding the mixed solution obtained in step 2 to the system in step 1 under stirring at 1000 rpm, adjusting the pH value to 4.0 with 1.5 wt % hydrochloric acid, stirring at room temperature for 24 h, dialyzing for 5 d, freeze-drying and storing in a refrigerator at 0°C to obtain substance A;

[0073] Step 4: Under a nitrogen atmosphere, 5 g of polyethylene glycol, 6 g of 2-[(2-formylphenyl)dithio]-benzoic acid, and 0.08 g of 4-dimethylaminopyridine were dissolved in 70 mL of tetrahydrofuran to obtain a grafting mixture;

[0074] Step 5, dissolve 3 g of dicyclohexylcarbodiimide in 20 mL of tetrahydrofuran, stir at 300 rpm in an ice bath at -2 ° C, add the material in step 5 to the grafted mixed solution obtained in step 4, stir at room temperature for 24 hours, filter, add the filtrate dropwise into 500 mL of ether, filter to obtain a white product, dissolve the white product in 100 mL of tetrahydrofuran, and precipitate in 200 mL of ether, repeat the operation 3 times, and vacuum dry at 22 ° C and 1.02 Kpa to obtain substance B;

[0075] Step 6: Weigh substance A and substance B, add them into 40 mL of water, stir at 600 rpm for 1 h, adjust the pH to 5 with 1.5 wt % hydrochloric acid, seal the mixture and place it at 32° C. for 24 h to obtain modified sodium alginate.

[0076] Example 2

[0077] The difference between Example 2 of the present application and Example 1 is that the stearyl hydrazide in Example 1 is replaced by benzoyl hydrazide.

[0078] Example 3

[0079] The difference between Example 3 of the present application and Example 1 is that the stearyl hydrazide in Example 1 is replaced by tebufenozide.

[0080] Example 4

[0081] The difference between Example 4 of the present application and Example 1 is that the 2-[(2-formylphenyl)dithio]-benzoic acid in Example 1 is replaced by 3-formyl-2-pyridinecarboxylic acid.

[0082] Example 5

[0083] The difference between Example 5 of the present application and Example 1 is that the 2-[(2-formylphenyl)dithio]-benzoic acid in Example 1 is replaced by 1-naphthoylcarboxylic acid.

[0084] Comparative Example 1

[0085] The difference between this comparative example 1 and example 1 is that the stearic acid hydrazide in example 1 is replaced by adipic acid dihydrazide.

[0086] Comparative Example 2

[0087] The difference between Comparative Example 2 and Example 1 is that the 2-[(2-formylphenyl)dithio]-benzoic acid in Example 1 is replaced by p-formylbenzoic acid.

[0088] Test Example 1

[0089] Red mud soil slow-release performance test: 350 rose seedlings with similar growth status were divided into 7 groups, each with 50 pots, and planted with red mud soil prepared in Examples 1-5 and Comparative Examples 1-2 of the same mass, and the growth period (branch length), flower bud differentiation period (number of flower buds), and flowering period (days) were recorded. The results are shown in Table 1:

[0090] Table 1 Sustained release performance test

[0091] Experimental groups Branch length / cm Number of flower buds / pair Flowering period / d Example 1 45.6 10 13 Example 2 31.3 7 8 Example 3 32.5 7 9 Example 4 33.2 8 9 Example 5 34.6 8 10 Comparative Example 1 25.7 5 6 Comparative Example 2 20.2 4 5

[0092] Test Example 2

[0093] Water resistance refers to the ability of a material to resist water damage. The longer the particles remain in the water, the stronger the water resistance. Weigh 5.0 g of the red mud soil of Examples 1-5 and Comparative Examples 1-2 into a 250 mL beaker, add 150 mL of deionized water, place in a constant temperature biochemical incubator at 25°C, and closely observe the dissolution of the soil particles. The results are recorded in Table 2.

[0094] Table 2 Water resistance test

[0095] Experimental groups Dissolution time / d Example 1 22 Example 2 18 Example 3 17 Example 4 15 Example 5 16 Comparative Example 1 9 Comparative Example 2 11

[0096] Test Example 3

[0097] Red mud soil improvement performance test:

[0098] Humus content detection: The red mud soil repaired and treated in Examples 1-5 and Comparative Examples 1-2 was tested for humus content in accordance with the detection method in NY / T1867-2010 "Determination of soil humus composition".

[0099] Nitrogen element determination: 10 g of the red mud soil produced in Examples 1-5 and Comparative Examples 1-2 were weighed, respectively, and each was soaked in 250 g of clean water and placed in a constant temperature box at 25° C. The nitrogen element dissolution rate was determined according to GB / T23348-2009 standard at 24 h and 14 d. The test results are shown in Table 3:

[0100] Table 3 Soil improvement performance test

[0101]

[0102] Through the test data results in test examples 1-3 and Tables 1 to 3, it can be found that the water resistance, humic acid slow-release performance and red mud soil improvement effect of the red mud soil treated in Example 1 are the best. Biodegradability generally refers to reducing the content of harmful substances (such as heavy metals, alkaline substances, etc.) in the soil through microbial activity, improving soil structure and fertility. By increasing the activity of microorganisms through soil conditioners, while decomposing harmful substances in red mud, they may also participate in the conversion process of nitrogen, thereby improving the dissolution rate and utilization efficiency of nitrogen. Therefore, a high nitrogen dissolution rate can also show good biodegradability.

[0103] Comparing the data of Examples 1-3 and Comparative Example 1, it is found that the differences between the data are quite obvious, which may be due to the use of different modifiers. First, the modifier contains a hydrazide group, which can modify sodium alginate, and a grafting agent containing both carbonyl and carboxyl functional groups can modify polyethylene glycol. Finally, the modified sodium alginate containing a hydrazide group is reacted and cross-linked with the modified polyethylene glycol containing a carbonyl group to prepare modified sodium alginate. The reaction principle is that the functional carbonyl reacts with the hydrazide compound to form a dynamic acylhydrazone bond. This reaction can often be carried out under mild conditions, and the yield is very high. In order to accelerate the reaction, an appropriate amount of acid is usually added to catalyze the reaction. Under weak acid solution or high temperature catalysis, the acylhydrazone bond will reversibly break, showing temperature and pH correspondence, and thus can adjust the pH of red mud soil. The coordination ability of acylhydrazone compounds may help metal ions in the soil to form more stable complexes or precipitates with organic matter, minerals, etc., thereby improving the structure and texture of the soil. This helps reduce soil heaviness and improves soil aeration and water retention capacity.

[0104] In addition to containing hydrazide groups, the modifier in Example 1 also has a long alkyl carbon chain, which is a hydrophobic monomer that can provide hydrophobic groups, and can achieve hydrophobic interactions in the modified alginate hydrogel. The corresponding polymer chains are prone to hydrophobic interactions. At the same time, the longer side groups of stearic hydrazide aggravate the physical entanglement between the macromolecular chains of modified sodium alginate. Therefore, under the multiple physical effects of hydrophobic interactions and chain entanglements, the prepared red mud soil has a good hydrophobic effect. At the same time, the modified sodium alginate is coated with humic acid to prepare microspheres, and then mixed with biochar to obtain a soil conditioner. The humic acid inclusions are regulated and controlled to a certain extent before release and conversion, thereby achieving the purpose of reducing the loss of inclusions, improving their utilization, extending the use time and controlling release. Among the advantages, on the one hand, the modified sodium alginate coating material can effectively reduce the influence of environmental factors such as water and air; second, it realizes the persistence of soil nutrient utilization and reduces the number of applications of pesticides and improvers; third, it reduces the pesticide damage caused by excessive pesticide concentration and realizes the controlled release of soil nutrients. The use of biochar can significantly reduce the pesticide residues in the soil, and with the increase in the amount of biochar, the adsorption effect is significantly enhanced, which has a good repair effect on red mud soil. Therefore, the water resistance, soil nutrient slow release effect and soil repair effect of the red mud soil in Example 1 are the best.

[0105] Comparing the data in the tables of Example 1, Examples 4-5 and Comparative Example 2, it is found that the data are different, and the reason for these differences may be that different grafting agents are used. The main function of the grafting agent is to modify the polyethylene glycol, that is, the carboxyl group in the grafting agent reacts with the hydroxyl group of the polyethylene glycol. The modified polyethylene glycol also contains a carbonyl group, and the carbonyl group can react with the hydrazide group in the modified sodium alginate to obtain an acylhydrazone group. In addition to the carbonyl and carboxyl functional groups participating in the reaction, the 2-[(2-formylphenyl) dithio]-benzoic acid in Example 1 also contains a disulfide bond group. The introduction of a disulfide bond in the natural polymer modified sodium alginate molecular gel can often accelerate the degradation of the hydrogel and show good biodegradability. In the remediation of red mud soil, the introduction of a disulfide bond makes the red mud soil in Example 1 have good biodegradability. This can enhance the recovery of soil ecosystems during red mud soil remediation. By improving the physical and chemical properties of the soil, providing nutrients and a suitable living environment, it can support the growth and reproduction of plants and microorganisms, thereby accelerating the ecological restoration process of the red mud dump.

Claims

1. A method for treating red mud soil, characterized in that: The method comprises the following steps, in parts by weight: S1. Red mud soil pretreatment: 0.5-2 mu of red mud soil is used for irrigation of cultivated land to obtain pretreated red mud soil; S2, red mud soil improvement: 50-120 parts of soil conditioner and 30-80 parts of basic raw material are mixed evenly, and spread on the surface of the red mud soil pretreated in S1 to obtain improved red mud soil; S3, red mud soil phytoremediation: planting plants on the surface of the modified red mud soil prepared in S2; The preparation method of the soil conditioner comprises the following steps, measured in parts by weight: Ultrasonic dispersion of 2-8 parts of biochar in 40-70 parts of humic acid, stirring for 20-30 hours in dark conditions, then adding 5-40 parts of modified sodium alginate, stirring at 500-800 rpm for 20-40 minutes at 20-40°C, then dripping into 80-150 parts of calcium chloride solution, finally filtering out the formed gel balls with a filter, washing with water 1-4 times, and freeze-drying to obtain a soil conditioner; The preparation method of the modified sodium alginate comprises the following steps, calculated in parts by weight: Step 1: Weigh 1-8 parts of sodium alginate, dissolve it in 100-300 parts of water, add 8-20 parts of modifier, and stir to dissolve; Step 2, dissolving 0.5-3 parts of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 0.5-3 parts of a grafting agent in a mixed solvent of 5-15 parts of a dimethyl sulfoxide aqueous solution to obtain a mixed solution; Step 3, adding the mixed solution obtained in step 2 to the system in step 1 under stirring, adjusting the pH value to 4.0-5.0 with hydrochloric acid, stirring at room temperature for 24-30 hours, dialyzing for 5-7 days, and storing in a refrigerator at 0-4°C after freeze-drying to obtain substance A; Step 4: Under a nitrogen atmosphere, dissolve 2-10 parts of polyethylene glycol, 0.5-6 parts of a grafting agent, and 0.05-2 parts of 4-dimethylaminopyridine in 60-80 parts of tetrahydrofuran to obtain a grafting mixed solution; Step 5, dissolve 1-5 parts of dicyclohexylcarbodiimide in 10-25 parts of tetrahydrofuran, add the material in step 5 to the grafting mixture obtained in step 4 at a temperature of -2°C to 2°C and under stirring, stir at room temperature for 20-25 hours, filter, add the filtrate dropwise into 300-600 parts of ether, filter to obtain a white product, dissolve the white product in tetrahydrofuran, precipitate in ether, repeat the operation 1-3 times, and dry in vacuo at 20-30°C to obtain substance B; Step 6, weigh substance A and substance B, dissolve them in water, quickly stir them evenly, adjust the pH to 5-6, seal the mixture and place it at 32-38°C for 20-30h to obtain modified sodium alginate; The modifier is any one of benzohydrazide, tebufenozide and stearylhydrazide; The grafting agent is any one of 3-formyl-2-pyridinecarboxylic acid, 1-naphthoylcarboxylic acid, and 2-[(2-formylphenyl)dithio]-benzoic acid; The basic raw material is a mixture of nutrient additives, desalination and alkali improvers, fertilizers, and bentonite in a mass ratio of (1-3): (1-2): (2-8): (5-15).

2. The red mud soil treatment method according to claim 1, characterized in that: The modifier is stearyl hydrazide.

3. Application of the red mud soil treatment method as claimed in claim 1 in soil remediation.

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