A remediation agent for chromium-contaminated laterite soil and a remediation method thereof

Abstract

The application provides a chromium-contaminated laterite soil repairing agent and a repairing method thereof, and the method realizes effective repair of the laterite soil through the steps of pretreating the soil, applying the repairing agent I and applying an electric field, adding the repairing agent II for maintenance, and finally connecting biological strains.The method comprises the following steps: removing sundries, plowing the soil, applying the repairing agent I containing a reducing agent, citric acid and other components, and treating under specific electric field conditions.Subsequently, the repairing agent II, such as organic fertilizer, iron oxide, nano zeolite and chitosan derivative, is added.Finally, specific proportions of aspergillus, citrobacter freundii and psychrobacter are connected for biological repair.The method comprehensively considers physical, chemical and biological repair means, aims to efficiently remove chromium pollution in the soil, improve the soil organic carbon content of the laterite soil, and restore the ecological function of the soil.

Description

Technical Field

[0001] This invention relates to the field of lateritic soil remediation, and particularly to a remediation agent and method for chromium-contaminated lateritic soil. Background Technology

[0002] Lateritic soil is mainly distributed in tropical and subtropical regions. It is a soil type formed under the climatic conditions of high temperature, high humidity and distinct wet and dry seasons through intense weathering and leaching. A large amount of minerals in its parent material are decomposed and leached away, while oxides such as iron and aluminum are relatively enriched, resulting in a deep red or brick-red soil layer. The texture is relatively heavy and clayey, with relatively low porosity and poor aeration and permeability.

[0003] With increasingly frequent human activities, the discharge of industrial waste, unreasonable mining, and the long-term use of fertilizers and pesticides containing heavy metals in agricultural production have further exacerbated the accumulation of heavy metals in lateritic soils. While frequent rainfall and active surface runoff in tropical and subtropical regions contribute to the migration and transformation of soil materials to some extent, they also facilitate the diffusion of some heavy metals already present in the soil, further affecting the distribution pattern of heavy metals in lateritic soils. This leads to heavy metal pollution of the soil, harming soil health, plant growth, and food chain security. Chromium-contaminated lateritic soils not only damage the ecological environment but also pose a potential threat to human health through the food chain. Therefore, remediation technologies for chromium-contaminated lateritic soils have become an important research topic in the field of environmental protection.

[0004] However, existing lateritic soil remediation technologies have many shortcomings. Regarding heavy metal remediation, traditional physical remediation methods such as excavation and landfill, while simple to operate, are costly, prone to secondary pollution, and ineffective against deep soil contamination. Chemical remediation methods, such as chemical leaching and redox reactions, can remove chromium from the soil to some extent, but may damage soil structure, affect soil fertility, and lack guarantees for the long-term stability of the remediated soil. Bioremediation methods, while environmentally friendly, have long remediation cycles, are highly dependent on environmental conditions, and have limited effectiveness in remediating lateritic soil with high concentrations of chromium.

[0005] Meanwhile, traditional remediation technologies mostly focus only on the passivation process of heavy metals, rarely considering the synergistic carbon sequestration role of the soil. In fact, lateritic soils not only have high background heavy metal levels, but also, due to the region's high temperature and humidity, heavy rainfall, and high multiple cropping index, exhibit characteristics such as low organic carbon content, rapid decomposition, difficulty in accumulation, and a low carbon balance point, placing their organic carbon content in the lower-middle range of my country's organic carbon classification. This makes lateritic soil one of my country's most significant low-yield soils; in the past 30 years, the organic carbon content of soil in Hainan Island, a typical lateritic soil region, has decreased by 25%. Existing technologies often lack comprehensive remediation solutions, failing to simultaneously consider the physical, chemical, and biological characteristics of the soil, resulting in unsatisfactory remediation outcomes.

[0006] Therefore, seeking sustainable technologies for heavy metal remediation and carbon sequestration is an important task in solving the current dilemma of heavy metal pollution and carbon poverty in tropical agriculture. Summary of the Invention

[0007] In view of this, the present invention proposes a remediation agent for chromium-contaminated lateritic soil to solve the above problems.

[0008] The technical solution of this invention is implemented as follows: A method for remediating chromium-contaminated lateritic soil includes the following steps:

[0009] S1. Select soil samples for pretreatment to remove impurities and large particles from the soil;

[0010] S2. Apply remediation agent I to the pretreated soil sample, till and improve the soil, till to a depth of 10-15cm, till 2-3 times, apply remediation agent I at a rate of 8-10% of the soil mass, keep the soil moisture content at 20-30%, apply electric field for 3-5h / d, and continue for 7-10 days.

[0011] S3. Continue to add Remediation Agent II to the soil that has been treated with Remediation Agent I. In an environment of 30-40℃, the amount added is 1-3% of the soil mass. Keep the soil moisture at 40-60% and cure for 3-5 days. Stir intermittently during the curing period.

[0012] S4. After the maintenance is completed, inoculate the soil sample with biological inoculum at a rate of 0.5-2% of the soil mass. Continue to till the soil to a depth of 16-20cm, repeating the tilling 5-10 times. Let the soil stand for 7-14 days to obtain the restored soil.

[0013] Furthermore, S1 grinds and pulverizes the soil to a particle size of <10mm.

[0014] Furthermore, a remediation agent for chromium-contaminated lateritic soil includes remediation agent I and remediation agent II. Remediation agent I comprises the following raw materials in parts by weight: 40-60 parts of reducing agent, 15-22 parts of deionized water, 5-10 parts of 40-80% sodium chloride solution, 3-8 parts of 80-85% citric acid solution, and 1-3 parts of rhamnolipid.

[0015] Furthermore, the reducing agent is selected from ferrous chloride, ferrous sulfate, or sodium sulfite.

[0016] Furthermore, the repair agent II comprises the following raw materials in parts by weight: 20-40 parts organic fertilizer, 5-15 parts iron oxide, 50-80 parts nano zeolite, 10-15 parts chitosan derivative, 25-55 parts phosphate solution, 5-10 parts sodium sulfide, 3-8 parts calcium carbonate, and 2-5 parts sodium alginate. The organic fertilizer is selected from one or more combinations of humic acid, straw, and livestock manure. The iron oxide is selected from one or more combinations of ferric oxide, ferrous oxide, and ferric oxide. The chitosan derivative is carboxymethyl chitosan or hydroxyethyl chitosan in a mass ratio of 1:1-3.

[0017] Furthermore, the molar concentration of phosphorus in the phosphate solution is 0.05-0.2 mol / L, and the phosphate is selected from at least one of potassium phosphate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, sodium phosphate, disodium hydrogen phosphate, and sodium dihydrogen phosphate.

[0018] Furthermore, in S2, the voltage of the control electric field is 10-20V / cm, and the current is 0.1-5.0mA / cm. 2 Temperature 20-40℃.

[0019] Furthermore, the stirring rate of S3 is 200-400 rpm, the stirring time is 20-60 min, and the interval is 2-4 h.

[0020] Furthermore, the microbial species in S4 are Aspergillus, Citrobacter freundii, and Cyperus ferruginea in a mass ratio of (1.2-2.5):(3.8-5.5):(2.0-3.5), with an average effective viable count ≥(6.53-8.25)×10⁻⁶. 8 cfu / g.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] In this invention's method for remediating lateritic red soil, soil pretreatment optimizes soil texture and purity, increasing the contact area between the remediation agent and pollutants. A "chemical reduction + stabilization + bioadsorption" approach effectively removes chromium from the soil. Application of remediation agent I ensures sufficient contact with chromium ions, reducing hexavalent chromium to trivalent chromium. Simultaneously, under the assistance of an electric field, the movement speed and reactivity of chromium ions are enhanced, further increasing the reaction efficiency between the remediation agent and chromium ions, thereby effectively reducing the chromium content in the soil. Continued application of remediation agent II can fix trivalent chromium in the soil through adsorption, co-precipitation, and complexation, further reducing... Its bioavailability, solubility, and mobility; the addition of organic fertilizer and iron oxides can mutually promote the formation of stable complexes, synergistically increase carbon sequestration, provide sufficient energy substances for soil microorganisms, and promote the proliferation of beneficial microorganisms; the introduction of biological strains can fix trivalent chromium in the cell or on the cell surface of microbial cells through adsorption or intracellular accumulation, thereby effectively removing chromium from the soil; the method of this invention adopts a comprehensive remediation approach combining physical, chemical, and biological methods to synergistically exert its removal effect, avoiding the limitations of single remediation methods, while reducing the amount of chemical agents used and lowering the risk of secondary pollution to the environment. In addition, by improving soil structure and enhancing fertility, it promotes the restoration and sustainable development of the ecosystem. Detailed Implementation

[0023] To better understand the technical content of this invention, specific embodiments are provided below to further illustrate the invention.

[0024] Unless otherwise specified, the experimental methods used in the embodiments of this invention are all conventional methods.

[0025] Unless otherwise specified, all materials and reagents used in the embodiments of this invention are commercially available.

[0026] The *Acinetobacterium* strain used in this invention was purchased from Ruichu Biotechnology (Jiangsu) Co., Ltd.

[0027] Example 1

[0028] A method for remediating chromium-contaminated lateritic soil includes the following steps:

[0029] S1. Select soil samples for pretreatment. Crush and grind the soil to a particle size of <10mm to remove impurities and large particles from the soil.

[0030] S2. Apply remediation agent I to the pretreated soil sample, then till and improve the soil to a depth of 10 cm, repeating the tillage twice. The application rate of remediation agent I is 8% of the soil mass. Maintain the soil moisture content at 20% after mixing. Apply an electric field for 3 hours per day for 7 days, controlling the voltage at 10 V / cm and the current at 0.1 mA / cm.2 Temperature 20℃;

[0031] Repair Agent I comprises the following raw materials in parts by weight: 40 parts ferrous chloride, 15 parts deionized water, 5 parts 40% sodium chloride solution, 3 parts 80% citric acid solution, and 1 part rhamnolipid.

[0032] S3. Continue to add remediation agent II to the soil that has been treated with remediation agent I at 30°C. The amount added is 1% of the soil mass. Maintain the soil moisture at 40% and cure for 3 days. During the curing period, stir intermittently at a stirring speed of 200 rpm for 20 minutes and with an interval of 2 hours.

[0033] Repair Agent II comprises the following raw materials in parts by weight: 20 parts humic acid, 5 parts iron oxide, 50 parts nano zeolite, 10 parts chitosan derivative, 25 parts potassium phosphate solution, 5 parts sodium sulfide, 3 parts calcium carbonate, and 2 parts sodium alginate. The chitosan derivative is carboxymethyl chitosan and hydroxyethyl chitosan in a mass ratio of 1:1. The molar concentration of phosphorus in the phosphate solution is 0.05 mol / L.

[0034] S4. After the curing period, inoculate soil samples with microbial strains at a rate of 0.5% of soil mass. The microbial strains consist of Aspergillus, Citrobacter fischeri, and Cyperus rotundus in a mass ratio of 1.2:3.8:2.0, with an average viable count ≥6.53 × 10⁻⁶. 8 CFU / g, continue tilling to a depth of 16cm, tilling 5 times, and let stand for 7 days to obtain the repaired soil.

[0035] Example 2

[0036] A method for remediating chromium-contaminated lateritic soil includes the following steps:

[0037] S1. Select soil samples for pretreatment. Crush and grind the soil to a particle size of <10mm to remove impurities and large particles from the soil.

[0038] S2. Apply remediation agent I to the pretreated soil sample, then till and improve the soil to a depth of 15 cm, repeating the tillage three times. The application rate of remediation agent I is 10% of the soil mass. Maintain the soil moisture content at 30% after mixing. Apply an electric field for 5 hours per day for 10 days, controlling the voltage at 20 V / cm and the current at 5.0 mA / cm. 2 Temperature 40℃;

[0039] Repair Agent I comprises the following raw materials in parts by weight: 60 parts ferrous sulfate, 22 parts deionized water, 10 parts 80% sodium chloride solution, 8 parts 85% citric acid solution, and 3 parts rhamnolipid.

[0040] S3. Continue to add Remediation Agent II to the soil that has been treated with Remediation Agent I at 40℃. The amount added is 3% of the soil mass. Maintain the soil moisture at 60% and cure for 5 days. During the curing period, stir intermittently at a stirring speed of 400 rpm for 60 minutes and with an interval of 4 hours.

[0041] Repair Agent II comprises the following raw materials in parts by weight: 40 parts straw, 15 parts ferrous oxide, 80 parts nano zeolite, 15 parts chitosan derivative, 55 parts dipotassium hydrogen phosphate solution, 10 parts sodium sulfide, 8 parts calcium carbonate, and 5 parts sodium alginate. The chitosan derivative is carboxymethyl chitosan and hydroxyethyl chitosan in a mass ratio of 1:3. The molar concentration of phosphorus in the phosphate solution is 0.2 mol / L.

[0042] S4. After the curing period, inoculate soil samples with microbial strains at a rate of 2% of the soil mass. The microbial strains consist of Aspergillus, Citrobacter fischeri, and Cyperus rotundus in a mass ratio of 2.5:5.5:3.5, with an average viable count ≥8.25 × 10⁻⁶. 8 CFU / g, continue tilling to a depth of 20cm, tilling 10 times, and let stand for 14 days to obtain the repaired soil.

[0043] Example 3

[0044] A method for remediating chromium-contaminated lateritic soil includes the following steps:

[0045] S1. Select soil samples for pretreatment. Crush and grind the soil to a particle size of <10mm to remove impurities and large particles from the soil.

[0046] S2. Apply remediation agent I to the pretreated soil sample, then till and improve the soil to a depth of 12 cm, repeating the tillage 3 times. The application rate of remediation agent I is 9% of the soil mass. The soil moisture content after mixing is maintained at 25%. Apply an electric field for 4 hours / day for 8 days, controlling the voltage at 15 V / cm and the current at 3.0 mA / cm. 2 Temperature 30℃;

[0047] Repair Agent I comprises the following raw materials in parts by weight: 50 parts sodium sulfite, 18 parts deionized water, 8 parts 60% sodium chloride solution, 5 parts 83% citric acid solution, and 2 parts rhamnolipid.

[0048] S3. Continue to add Remediation Agent II to the soil that has been treated with Remediation Agent I at 35℃. The amount added is 2% of the soil mass. Maintain the soil moisture at 50% and cure for 4 days. During the curing period, stir intermittently at a stirring speed of 300 rpm for 40 minutes and with an interval of 3 minutes.

[0049] Repair Agent II comprises the following raw materials in parts by weight: 30 parts of livestock and poultry manure, 10 parts of iron oxide, 70 parts of nano zeolite, 12 parts of chitosan derivative, 40 parts of potassium dihydrogen phosphate solution, 8 parts of sodium sulfide, 5 parts of calcium carbonate, and 3 parts of sodium alginate. The chitosan derivative is carboxymethyl chitosan and hydroxyethyl chitosan in a mass ratio of 1:2. The molar concentration of phosphorus in the phosphate solution is 0.15 mol / L.

[0050] S4. After the curing period, inoculate soil samples with microbial strains at a rate of 1% of the soil mass. The microbial strains consist of Aspergillus, Citrobacter fischeri, and Cyperus rotundus in a mass ratio of 2.2:4.8:3.0, with an average viable count ≥7.25 × 10⁻⁶. 8 CFU / g, continue tilling to a depth of 18cm, tilling 8 times, and let stand for 12 days to obtain the repaired soil.

[0051] Example 4

[0052] A method for remediating chromium-contaminated lateritic soil includes the following steps:

[0053] S1. Select soil samples for pretreatment. Crush and grind the soil to a particle size of <10mm to remove impurities and large particles from the soil.

[0054] S2. Apply remediation agent I to the pretreated soil sample, then till and improve the soil to a depth of 12 cm, repeating the tillage 3 times. The application rate of remediation agent I is 9% of the soil mass. The soil moisture content after mixing is maintained at 25%. Apply an electric field for 4 hours / day for 8 days, controlling the voltage at 15 V / cm and the current at 3.0 mA / cm. 2 Temperature 30℃;

[0055] Repair Agent I comprises the following raw materials in parts by weight: 40 parts ferrous chloride, 15 parts deionized water, 5 parts 40% sodium chloride solution, 3 parts 80% citric acid solution, and 1 part rhamnolipid.

[0056] S3. Continue to add Remediation Agent II to the soil that has been treated with Remediation Agent I at 35℃. The amount added is 2% of the soil mass. Maintain the soil moisture at 50% and cure for 4 days. During the curing period, stir intermittently at a stirring speed of 300 rpm for 40 minutes and with an interval of 3 hours.

[0057] Repair Agent II comprises the following raw materials in parts by weight: 30 parts of livestock and poultry manure, 10 parts of iron oxide, 50 parts of nano zeolite, 10 parts of chitosan derivative, 25 parts of potassium phosphate solution, 5 parts of sodium sulfide, 3 parts of calcium carbonate, and 2 parts of sodium alginate. The chitosan derivative is a mixture of carboxymethyl chitosan and hydroxyethyl chitosan in a mass ratio of 1:1. The molar concentration of phosphorus in the phosphate solution is 0.05 mol / L.

[0058] S4. After the curing period, inoculate soil samples with microbial strains at a rate of 1% of the soil mass. The microbial strains consist of Aspergillus, Citrobacter fischeri, and Cyperus rotundus in a mass ratio of 2.2:4.8:3.0, with an average viable count ≥7.25 × 10⁻⁶. 8 CFU / g, continue tilling to a depth of 18cm, tilling 8 times, and let stand for 12 days to obtain the repaired soil.

[0059] Example 5

[0060] A method for remediating chromium-contaminated lateritic soil includes the following steps:

[0061] S1. Select soil samples for pretreatment. Crush and grind the soil to a particle size of <10mm to remove impurities and large particles from the soil.

[0062] S2. Apply remediation agent I to the pretreated soil sample, then till and improve the soil to a depth of 12 cm, repeating the tillage 3 times. The application rate of remediation agent I is 9% of the soil mass. The soil moisture content after mixing is maintained at 25%. Apply an electric field for 4 hours / day for 8 days, controlling the voltage at 15 V / cm and the current at 3.0 mA / cm. 2 Temperature 30℃;

[0063] Repair Agent I comprises the following raw materials in parts by weight: 60 parts ferrous sulfate, 22 parts deionized water, 10 parts 80% sodium chloride solution, 8 parts 85% citric acid solution, and 3 parts rhamnolipid.

[0064] S3. Continue to add Remediation Agent II to the soil that has been treated with Remediation Agent I at 35℃. The amount added is 2% of the soil mass. Maintain the soil moisture at 50% and cure for 4 days. During the curing period, stir intermittently at a stirring speed of 300 rpm for 40 minutes and with an interval of 3 hours.

[0065] Repair Agent II comprises the following raw materials in parts by weight: 30 parts of livestock and poultry manure, 10 parts of iron oxide, 80 parts of nano zeolite, 15 parts of chitosan derivative, 55 parts of dipotassium hydrogen phosphate solution, 10 parts of sodium sulfide, 8 parts of calcium carbonate, and 5 parts of sodium alginate. The chitosan derivative is a mixture of carboxymethyl chitosan and hydroxyethyl chitosan in a mass ratio of 1:3. The molar concentration of phosphorus in the phosphate solution is 0.2 mol / L.

[0066] S4. After the curing period, inoculate soil samples with microbial strains at a rate of 1% of the soil mass. The microbial strains consist of Aspergillus, Citrobacter fischeri, and Cyperus rotundus in a mass ratio of 2.2:4.8:3.0, with an average viable count ≥7.25 × 10⁻⁶. 8CFU / g, continue tilling to a depth of 18cm, tilling 8 times, and let stand for 12 days to obtain the repaired soil.

[0067] Comparative Example 1

[0068] The difference between this comparative example and Example 3 is that no remediation agent I was applied in the remediation method for lateritic soil.

[0069] Comparative Example 2

[0070] The difference between this comparative example and Example 3 is that no electric field treatment was applied in the lateritic soil remediation method described herein.

[0071] Comparative Example 3

[0072] The difference between this comparative example and Example 3 is that the remediation method for lateritic soil in this example did not use remediation agent II.

[0073] Comparative Example 4

[0074] The difference between this comparative example and Example 3 is that no biological strains were introduced in the lateritic soil remediation method described herein.

[0075] Experimental Example 1

[0076] In the restored lateritic soil area, grids were divided, and sampling points were selected according to the predetermined grid size and shape. The organic carbon content in the soil was determined by the potassium dichromate-external heat source method.

[0077] Soil organic carbon content (g / kg) Example 1 18.5 Example 2 20.1 Example 3 22.3 Example 4 21.2 Example 5 19.8 Comparative Example 1 12.4 Comparative Example 2 14.1 Comparative Example 3 13.6 Comparative Example 4 15.2

[0078] This invention demonstrates positive results in increasing the organic carbon content of remediated lateritic soil, showing significant advantages compared to the comparative study. In subsequent lateritic soil management and ecological restoration, these restoration measures can be further optimized or combined with other methods can be explored based on actual conditions to continuously increase the soil organic carbon content, enhance its carbon sequestration function, and contribute to addressing climate change and improving the soil ecological environment.

[0079] Experimental Example 2

[0080] (I) Soil Sample Collection and Pretreatment

[0081] 1. The chromium-contaminated lateritic soil was divided into 9 experimental fields. The 9 experimental fields were tested according to the methods of Examples 1-5 and Comparative Examples 1-4. Soil samples were collected in the remediated lateritic soil area using either a grid sampling method or a serpentine sampling method. The top 0-20cm soil was collected at each sampling point. Multiple soil samples collected in the same area were mixed evenly to form a mixed sample.

[0082] 2. Place the collected soil samples in a cool, ventilated place to air dry naturally, remove impurities such as stones and plant debris from the soil, grind them in a mortar and pestle and pass them through a 100-mesh sieve for later use.

[0083] (II) Determination of hexavalent chromium content in soil (alkali digestion-colorimetric method)

[0084] 1. Weigh 5.0 g (accurate to 0.01 g) of the pretreated soil sample into a 150 mL Erlenmeyer flask and add 50.0 mL of alkaline extraction solution (0.28 mol / L K2HPO4-0.5 mol / L NaOH).

[0085] 2. Place the conical flask in a constant temperature water bath shaker and shake at 30℃ for 2 hours. Then centrifuge at 4000 r / min for 10 minutes and filter the supernatant.

[0086] 3. Take 5.0 mL of filtrate into a 50 mL colorimetric tube, add 0.5 mL of sulfuric acid solution (1+1) and 0.5 mL of phosphoric acid solution (1+1), and shake well.

[0087] 4. Add 2 mL of diphenylcarbazide colorimetric reagent, dilute to the mark with deionized water, shake well, and let stand for 10-15 minutes.

[0088] 5. Using a spectrophotometer at a wavelength of 540 nm, with a blank test as a reference, measure the absorbance of the solution and calculate the content of hexavalent chromium in the soil according to the standard curve.

[0089] (III) Determination of trivalent chromium content in soil (spectrophotometric method)

[0090] 1. Weigh 2.00 g (accurate to 0.0001 g) of pretreated soil sample into a 100 mL beaker, add 20 mL of ammonium chloride solution, and heat in a boiling water bath for 1 h, stirring occasionally. After cooling, transfer to a 100 mL volumetric flask, dilute to volume with deionized water, shake well, and filter. Reserve the filtrate.

[0091] 2. Pipette 10.00 mL of the filtrate into a 50 mL colorimetric tube, add 1 mL of hydrochloric acid solution, and shake well. Add 5% sodium nitrite solution dropwise until the red color just fades, and let stand for 1 minute. Add 1 mL of urea solution, shake well, and let stand for 3 minutes.

[0092] 3. Add 5 mL of sodium pyrophosphate solution and shake well. Then add 2 mL of colorimetric reagent, dilute to the mark with deionized water, and shake well. Let stand for 10 min, and using a blank solution as a reference, measure the absorbance at a wavelength of 540 nm using a spectrophotometer.

[0093] 4. Calculate the content of trivalent chromium in the soil based on the standard curve.

[0094] (iv) Soil leaching toxicity test (turnover method)

[0095] 1. Weigh 100g (accurate to 0.1g) of the pretreated soil sample into a 2L extraction bottle and add 1L of deionized water.

[0096] 2. Install the extraction bottle on the inverted shaker, adjust the speed to 30±2 r / min, and shake at 23±2℃ for 18h.

[0097] 3. After shaking, let stand for 30 minutes, then filter and collect the leachate using a filter membrane.

[0098] 4. The chromium content in the leachate was determined by flame atomic absorption spectrometry, and the soil leaching toxicity was assessed based on the results to determine whether it met the relevant standards.

[0099] (v) Plant effectiveness assessment (plant cultivation trial)

[0100] 1. Select Indian mustard as an indicator plant, fill the repaired soil into flower pots, and sow 25 seeds in each pot.

[0101] 2. Cultivate plants in greenhouse conditions, water and fertilize them regularly, and maintain suitable growing conditions.

[0102] 3. After 30-60 days of cultivation, harvest the plants and divide them into parts such as roots, stems, and leaves.

[0103] 4. Wash the plant samples with deionized water, blanch them at 105℃ for 30 minutes, and then dry them at 70℃ to constant weight.

[0104] 5. Weigh approximately 1.0g of dry samples from roots, stems, and leaves, digest them with nitric acid-perchloric acid, and determine the chromium content in each part of the plant using flame atomic absorption spectrometry to assess the effectiveness of chromium in the remediated soil for the plant and the potential ecological risks.

[0105] The test results are shown in the table below:

[0106]

[0107]

[0108] Among all the remediation methods in this experiment, the remediation method of the example group was better than that of the comparative group for the lateritic soil. After the remediation treatment, the chromium content in the soil of the example group decreased, indicating that the remediation treatment had a certain fixing effect on total chromium, mainly affecting the valence distribution of chromium. The example group significantly reduced the content of hexavalent chromium in the soil, especially Example 3, which reduced it to the lowest level (4 mg / kg), indicating that the remediation treatment had a significant reduction effect on hexavalent chromium.

[0109] Example 3 showed the best remediation effect, effectively reducing the content of hexavalent and trivalent chromium in the soil, reducing the risk of chromium leaching and the absorption and accumulation of chromium by plants.

[0110] Compared with Comparative Example 1, Example 3 comprehensively remediated lateritic soil through the synergistic effects of multiple mechanisms, including the reducing effect of the reducing agent, the solvent effect of deionized water, the ion exchange effect of sodium chloride, the complexing and acidifying effect of citric acid, the dispersing effect of CTAB, and the solubilizing effect of rhamnolipids. These mechanisms work together to significantly reduce the content of hexavalent chromium in the soil, decreasing its migration and bioavailability.

[0111] Compared with Comparative Example 2, Example 3 shows that under the action of an electric field, charged chromium ions in the soil will undergo directional migration. By controlling the electric field conditions appropriately, chromium ions can be removed from the soil.

[0112] Compared with Comparative Example 3, the remediation agent II of the present invention can fix trivalent chromium in the soil through adsorption, co-precipitation, complexation and other effects, so as to reduce its bioavailability, solubility and mobility.

[0113] Nano-zeolite possesses a well-developed porous structure and a large specific surface area, enabling it to adsorb chromium ions from the soil through physical adsorption and ion exchange. This fixes the chromium ions onto the pores and surface of the zeolite, reducing their migration. Chitosan derivatives are rich in amino and hydroxyl functional groups, which can chelate with heavy metal ions to form stable complexes. Phosphate solution can react with chromium ions in the soil to generate insoluble chromium phosphate precipitates, thereby reducing the chromium content in the soil. The precipitation effect of phosphate solution and sodium sulfide, the pH adjustment effect of calcium carbonate, and the adhesion and film-forming effect of sodium alginate work together to achieve the remediation of lateritic soil.

[0114] Compared with Comparative Example 4, Example 3 shows that the introduction of microbial strains can effectively remove chromium from the soil by immobilizing trivalent chromium within or on the cell surface of microbial cells through adsorption or intracellular accumulation. Some Aspergillus species can reduce hexavalent chromium to trivalent chromium through metabolic activities. During their growth, Aspergillus and Citrobacter freundii secrete organic acids that can complex with chromium ions, forming stable complexes that reduce the mobility and bioavailability of chromium ions in the soil, further promoting chromium removal or stabilization. Citrobacter freundii alters the form of heavy metals through redox reactions during metabolism, and the resulting polysaccharides, proteins, and other sticky substances can increase soil particle aggregation, reduce soil erosion, and may, to some extent, immobilize heavy metals in the soil. The structures or secretions on the cell surface of Aspergillus freundii may adsorb chromium ions and transform the chemical form of chromium through their own metabolic pathways.

[0115] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for remediating chromium-contaminated lateritic soil, characterized in that: Includes the following steps: S1. Select lateritic soil samples for pretreatment to remove impurities and large particles from the lateritic soil; S2. Apply remediation agent I to the pretreated lateritic soil sample, and till the lateritic soil to improve it. The tillage depth is 10-15cm, and the tillage is carried out 2-3 times. The amount of remediation agent I applied is 8-10% of the mass of the lateritic soil. The moisture content of the mixed lateritic soil is maintained at 20-30%. The electric field is applied for 3-5h / d for 7-10 days. S3. Continue to add remediation agent II to the soil that has been treated with remediation agent I. The amount added is 1-3% of the weight of the lateritic soil. Keep the soil moisture at 40-60% and cure it at 30-40℃ for 3-5 days. Stir it intermittently during the curing period. S4. After the curing is completed, inoculate the lateritic soil sample with biological inoculum at a rate of 0.5-2% of the lateritic soil mass. Continue to till the soil to a depth of 16-20cm, tilling it 5-10 times. Let it stand for 7-14 days to obtain the repaired soil. The repair agent I comprises the following raw materials in parts by weight: 40-60 parts of reducing agent, 15-22 parts of deionized water, 5-10 parts of 40-80% sodium chloride solution, 3-8 parts of 80-85% citric acid solution, and 1-3 parts of rhamnolipid. The repair agent II comprises the following raw materials in parts by weight: 20-40 parts organic fertilizer, 5-15 parts iron oxide, 50-80 parts nano zeolite, 10-15 parts chitosan derivative, 25-55 parts phosphate solution, 5-10 parts sodium sulfide, 3-8 parts calcium carbonate, and 2-5 parts sodium alginate. The organic fertilizer is selected from one or more combinations of humic acid, straw, and livestock manure. The iron oxide is selected from one or more combinations of iron oxide, ferrous oxide, and iron(III) oxide. The chitosan derivative is carboxymethyl chitosan or hydroxyethyl chitosan in a mass ratio of 1:1-3. The microbial species in step S4 consist of Aspergillus, Citrobacter freundii, and Cyperus ferruginea in a mass ratio of 1.2-2.5:3.8-5.5:2.0-3.5, with an average viable count ≥6.53 × 10⁻⁶. 8 cfu / g.

2. The method for remediating chromium-contaminated lateritic soil as described in claim 1, characterized in that: In step S1, the lateritic soil is also crushed and ground to a particle size of <10mm.

3. The method for remediating chromium-contaminated lateritic soil as described in claim 1, characterized in that: The reducing agent is selected from ferrous chloride, ferrous sulfate, and sodium sulfite.

4. The method for remediating chromium-contaminated lateritic soil as described in claim 1, characterized in that: The phosphate solution has a phosphorus molar concentration of 0.05-0.2 mol / L, and the phosphate is selected from at least one of potassium phosphate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, sodium phosphate, disodium hydrogen phosphate, and sodium dihydrogen phosphate.

5. The method for remediating chromium-contaminated lateritic soil as described in claim 1, characterized in that: In step S2, the electric field strength of the control electric field is 10-20 V / cm, the current density is 0.1-5.0 mA / cm², and the temperature is 20-40℃.

6. The method for remediating chromium-contaminated lateritic soil as described in claim 1, characterized in that: The stirring rate in step S3 is 200-400 rpm, the stirring time is 20-60 min, and the interval is 2-4 h.

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