Repairing agent and repairing method for chromium-polluted brick red soil

Abstract

The invention provides a chromium-polluted brick red soil repairing agent and a repairing method thereof.The method comprises the steps of soil pretreatment, application of a repairing agent I and application of an electric field, addition of a repairing agent II for maintenance, final inoculation of biological strains and the like, and effective repairing of brick red soil is achieved. The method comprises the following steps: removing impurities, ploughing soil, applying a repairing agent I containing a reducing agent, citric acid and other components, and treating under a specific electric field condition. Then, organic fertilizer, iron oxide, nano zeolite, chitosan derivatives and other repairing agents II are added; and finally, inoculating aspergillus, citrobacter freundii and ice-living bacteria in a specific proportion to carry out bioremediation. According to the method, physical, chemical and biological remediation means are comprehensively considered, chromium pollution in the soil is efficiently removed, the content of organic carbon in the brick red soil is increased, and the ecological function of the soil is restored.

Description

Technical Field

[0001] The invention relates to the field of brick red soil restoration, and in particular to a restoration agent for chromium-polluted brick red soil and a restoration method thereof. Background Art

[0002] Brick red soil is mainly distributed in tropical and subtropical regions. It is a type of soil formed by strong weathering and leaching under high temperature, high humidity and distinct dry and wet seasons. The minerals in its parent material are decomposed and leached in large quantities, and oxides such as iron and aluminum are relatively enriched, showing a deep red or brick red soil layer with a relatively heavy texture, relatively low porosity, and poor air permeability and water permeability.

[0003] With the increasing frequency of human activities, the discharge of industrial "three wastes", unreasonable mineral mining, and the long-term use of large amounts of heavy metal-containing fertilizers and pesticides in agricultural production have further aggravated the accumulation of heavy metals in the brick red soil. Frequent rainfall and active surface runoff in tropical and subtropical regions, although to a certain extent, help the migration and transformation of soil substances, also make some heavy metals originally present in the soil more easily diffuse, further affecting the distribution pattern of heavy metals in the brick red soil, causing the soil to be contaminated by heavy metals, endangering soil health, plant growth and food chain safety. Chromium-contaminated brick red soil not only destroys the ecological environment, but also poses a potential threat to human health through the food chain. Therefore, the remediation technology of chromium-contaminated brick red soil has become an important research topic in the field of environmental protection.

[0004] However, the existing brick red soil remediation technology has many shortcomings. In terms of heavy metal remediation, traditional physical remediation methods such as excavation and landfill, although simple to operate, are costly, prone to secondary pollution, and are powerless against deep soil pollution. Chemical remediation methods such as chemical leaching and oxidation-reduction, although they can remove chromium from the soil to a certain extent, may damage the soil structure, affect soil fertility, and lack guarantee for the long-term stability of the repaired soil. Although the biological remediation method is environmentally friendly, the remediation cycle is long, the effect is greatly affected by environmental conditions, and the remediation effect on brick red soil contaminated with high concentrations of chromium is limited.

[0005] At the same time, most traditional remediation technologies only focus on the passivation process of heavy metals, and rarely consider the synergistic carbon fixation effect of soil. In fact, not only does the brick red soil have a high background value of heavy metals, but also, due to the characteristics of high temperature and humidity, high rainfall intensity, and high multiple cropping index in the area, the organic carbon in the brick red soil has the characteristics of low content, fast decomposition, not easy to accumulate, and low carbon balance point. The organic carbon content is in the middle and lower levels of my country's organic carbon grade classification. This makes brick red soil one of the most important low-yield soils in my country. In the past 30 years, Hainan Island, a typical brick red soil area, has seen a 25% decrease in soil organic carbon content. Existing technologies often lack comprehensive remediation solutions, and it is difficult to simultaneously consider the physical, chemical, and biological properties of the soil, resulting in unsatisfactory remediation effects.

[0006] Therefore, seeking sustainable heavy metal remediation and carbon sequestration technologies is an important task to solve the current dual dilemma of heavy metal pollutants and carbon poverty in tropical agriculture. Summary of the invention

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

[0008] The technical solution of the present invention is achieved as follows: A method for repairing chromium-contaminated brick red soil comprises the following steps:

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

[0010] S2, applying repair agent I to the pretreated soil sample, plowing and improving the soil, the plowing depth is 10-15cm, the plowing frequency is 2-3 times, the application amount of repair agent I is 8-10% of the soil mass, the soil moisture content after mixing is maintained at 20-30%, and the electric field is applied for 3-5h / d for 7-10 days;

[0011] S3, continue to add repair agent II to the soil applied with repair agent I, add 1-3% of the soil mass under 30-40°C environment, keep the soil moisture at 40-60%, and cure for 3-5 days, stirring intermittently during the curing period;

[0012] S4. After the maintenance, biological bacteria are inoculated into the soil sample at a rate of 0.5-2% of the soil mass. The soil is tilled continuously at a depth of 16-20 cm and 5-10 times. The soil is left to stand for 7-14 days to obtain the repaired soil.

[0013] Furthermore, the S1 crushes and grinds the soil to a particle size of less than 10 mm.

[0014] Furthermore, a repair agent for chromium-contaminated brick red soil includes a repair agent I and a repair agent II, wherein the repair agent I includes the following raw materials in parts by weight: 40-60 parts of a reducing agent, 15-22 parts of deionized water, 5-10 parts of a 40-80% sodium chloride solution, 3-8 parts of an 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 includes the following raw materials in parts by weight: 20-40 parts of organic fertilizer, 5-15 parts of iron oxide, 50-80 parts of nano zeolite, 10-15 parts of chitosan derivative, 25-55 parts of phosphate solution, 5-10 parts of sodium sulfide, 3-8 parts of calcium carbonate, and 2-5 parts of sodium alginate. The organic fertilizer is selected from one or more combinations of humic acid, straw, and livestock and poultry manure. The iron oxide is selected from one or more combinations of ferric oxide, ferrous oxide, and ferrosoferric oxide. The chitosan derivative is carboxymethyl chitosan and 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, the voltage of the electric field controlled in S2 is 10-20 V / cm, and the current is 0.1-5.0 mA / 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 rest time is 2-4 h.

[0020] Furthermore, the biological strains of S4 are Aspergillus, Citrobacter freundii and Ice bacteria in a mass ratio of (1.2-2.5):(3.8-5.5):(2.0-3.5), and the average effective viable count is ≥(6.53-8.25)×10 8 cfu / g.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] In the method for repairing red soil of the present invention, soil texture and purity are optimized by soil pretreatment, and the contact area between the repair agent and the pollutants is increased; the chromium content in the soil is effectively removed by the method of "chemical reduction + stabilization + biological adsorption"; the repair agent I is applied to fully contact with the chromium ions to reduce the hexavalent chromium in the soil to trivalent chromium, and at the same time, under the auxiliary effect of the electric field, the movement speed and reaction activity of the chromium ions are improved, and the reaction efficiency of the repair agent and the chromium ions is further enhanced, thereby effectively reducing the chromium content in the soil; the repair agent II is continuously applied to fix the trivalent chromium in the soil through adsorption, coprecipitation, complexation and the like, so as to reduce Its biological effectiveness, solubility and mobility; the addition of organic fertilizer and iron oxide can promote the formation of stable complexes, synergistically increase carbon fixation, provide sufficient energy substances for soil microorganisms, and promote the proliferation of beneficial microorganisms; the access to biological strains can fix trivalent chromium in microbial cells or on the cell surface through adsorption on the cell surface or intracellular accumulation, thereby effectively removing chromium from the soil; the method of the present invention adopts a comprehensive repair method combining physical, chemical and biological methods to synergistically exert its removal effect, avoiding the limitations of a single repair method, while reducing the use of chemical agents and reducing the risk of secondary pollution to the environment. In addition, by improving soil structure and enhancing fertility, the restoration and sustainable development of the ecosystem are promoted. DETAILED DESCRIPTION

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

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

[0025] Unless otherwise specified, the materials, reagents, etc. used in the embodiments of the present invention can be obtained from commercial sources.

[0026] The Jubing bacteria of the present invention were purchased from Ruichu Biotechnology (Jiangsu) Co., Ltd.

[0027] Example 1

[0028] A method for repairing chromium-contaminated brick red soil comprises the following steps:

[0029] S1. Select soil samples for pretreatment, grind the soil to a particle size of less than 10 mm, and remove debris and large particles in the soil;

[0030] S2, apply repair agent I to the pretreated soil sample, plow the soil to improve, the plowing depth is 10cm, the plowing frequency is 2 times, the application amount of repair agent I is 8% of the soil mass, the moisture content of the mixed soil is maintained at 20%, the electric field is applied for 3h / d for 7 days, the voltage of the electric field is controlled at 10V / cm, the current is 0.1mA / cm2 , temperature 20℃;

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

[0032] S3, continue to add repair agent II to the soil applied with repair agent I, add 1% of the soil mass under 30°C environment, maintain the soil moisture at 40%, and maintain for 3 days. Stir intermittently during the curing period, the stirring rate is 200rpm, the stirring time is 20min, and the intermittent time is 2h;

[0033] Repair agent II includes the following raw materials in parts by weight: 20 parts of humic acid, 5 parts of iron oxide, 50 parts of nano zeolite, 10 parts of chitosan derivatives, 25 parts of potassium phosphate solution, 5 parts of sodium sulfide, 3 parts of calcium carbonate, and 2 parts of sodium alginate. The chitosan derivatives are 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, biological strains were inoculated into the soil samples at a rate of 0.5% of the soil mass. The biological strains were Aspergillus, Citrobacter freundii and Icebergia in a mass ratio of 1.2:3.8:2.0. The average number of effective live bacteria was ≥6.53×10 8 cfu / g, and continued tilling to a depth of 16 cm, ploughing 5 times, and left it to stand for 7 days to obtain the repaired soil.

[0035] Example 2

[0036] A method for repairing chromium-contaminated brick red soil comprises the following steps:

[0037] S1. Select soil samples for pretreatment, grind the soil to a particle size of less than 10 mm, and remove debris and large particles in the soil;

[0038] S2, apply repair agent I to the pretreated soil sample, plow the soil to improve, the plowing depth is 15cm, the plowing frequency is 3 times, the application amount of repair agent I is 10% of the soil mass, the moisture content of the mixed soil is maintained at 30%, the electric field is applied for 5h / d for 10 days, the voltage of the electric field is controlled at 20V / cm, the current is 5.0mA / cm 2 , temperature 40℃;

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

[0040] S3, continue to add repair agent II to the soil applied with repair agent I, add 3% of the soil mass under 40°C environment, maintain the soil moisture at 60%, and maintain for 5 days. Stir intermittently during the curing period, the stirring rate is 400rpm, the stirring time is 60min, and the intermittent time is 4h;

[0041] Repair agent II includes the following raw materials in parts by weight: 40 parts of straw, 15 parts of ferrous oxide, 80 parts of nano zeolite, 15 parts of chitosan derivatives, 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 derivatives are 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, biological strains were inoculated into the soil samples at a rate of 2% of the soil mass. The biological strains were Aspergillus, Citrobacter freundii and Ice bacteria in a mass ratio of 2.5:5.5:3.5. The average number of effective live bacteria was ≥8.25×10 8 cfu / g, and continued tilling with a depth of 20 cm and 10 times of tilling. After standing for 14 days, the repaired soil was obtained.

[0043] Example 3

[0044] A method for repairing chromium-contaminated brick red soil comprises the following steps:

[0045] S1. Select soil samples for pretreatment, grind the soil to a particle size of less than 10 mm, and remove debris and large particles in the soil;

[0046] S2. Apply repair agent I to the pretreated soil sample, till the soil to improve, tillage depth of 12 cm, tillage times of 3 times, application of repair agent I is 9% of the soil mass, the soil moisture content after mixing is maintained at 25%, the electric field is applied for 4 h / d for 8 days, the electric field voltage is controlled at 15 V / cm, the current is 3.0 mA / cm 2 , temperature 30℃;

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

[0048] S3, continue to add repair agent II to the soil applied with repair agent I, add 2% of the soil mass under 35°C environment, keep the soil moisture at 50%, and maintain for 4 days. Stir intermittently during the curing period, the stirring rate is 300rpm, the stirring time is 40min, and the intermittent time is 3;

[0049] The repair agent II includes the following raw materials in parts by weight: 30 parts of livestock and poultry manure, 10 parts of ferroferric oxide, 70 parts of nano zeolite, 12 parts of chitosan derivatives, 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 derivatives are 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, biological strains were inoculated into the soil samples at a rate of 1% of the soil mass. The biological strains were Aspergillus, Citrobacter freundii and Icebergia in a mass ratio of 2.2:4.8:3.0, and the average number of effective live bacteria was ≥7.25×10 8 cfu / g, and continued tilling to a depth of 18 cm, 8 times of tilling, and left it to stand for 12 days to obtain the repaired soil.

[0051] Example 4

[0052] A method for repairing chromium-contaminated brick red soil comprises the following steps:

[0053] S1. Select soil samples for pretreatment, grind the soil to a particle size of less than 10 mm, and remove debris and large particles in the soil;

[0054] S2. Apply repair agent I to the pretreated soil sample, till the soil to improve, tillage depth of 12 cm, tillage times of 3 times, application of repair agent I is 9% of the soil mass, the soil moisture content after mixing is maintained at 25%, the electric field is applied for 4 h / d for 8 days, the electric field voltage is controlled at 15 V / cm, the current is 3.0 mA / cm 2 , temperature 30℃;

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

[0056] S3, continue to add repair agent II to the soil applied with repair agent I, add 2% of the soil mass under 35°C environment, keep the soil moisture at 50%, and maintain for 4 days. Stir intermittently during the curing period, the stirring rate is 300rpm, the stirring time is 40min, and the intermittent time is 3h;

[0057] The repair agent II includes the following raw materials in parts by weight: 30 parts of livestock and poultry manure, 10 parts of ferroferric oxide, 50 parts of nano zeolite, 10 parts of chitosan derivatives, 25 parts of potassium phosphate solution, 5 parts of sodium sulfide, 3 parts of calcium carbonate, and 2 parts of sodium alginate. The chitosan derivatives are 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, biological strains were inoculated into the soil samples at a rate of 1% of the soil mass. The biological strains were Aspergillus, Citrobacter freundii and Icebergia in a mass ratio of 2.2:4.8:3.0, and the average number of effective live bacteria was ≥7.25×10 8 cfu / g, and continued tilling to a depth of 18 cm, 8 times of tilling, and left it to stand for 12 days to obtain the repaired soil.

[0059] Example 5

[0060] A method for repairing chromium-contaminated brick red soil comprises the following steps:

[0061] S1. Select soil samples for pretreatment, grind the soil to a particle size of less than 10 mm, and remove debris and large particles in the soil;

[0062] S2. Apply repair agent I to the pretreated soil sample, till the soil to improve, tillage depth of 12 cm, tillage times of 3 times, application of repair agent I is 9% of the soil mass, the soil moisture content after mixing is maintained at 25%, the electric field is applied for 4 h / d for 8 days, the electric field voltage is controlled at 15 V / cm, the current is 3.0 mA / cm 2 , temperature 30℃;

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

[0064] S3, continue to add repair agent II to the soil applied with repair agent I, add 2% of the soil mass under 35°C environment, keep the soil moisture at 50%, and maintain for 4 days. Stir intermittently during the curing period, the stirring rate is 300rpm, the stirring time is 40min, and the intermittent time is 3h;

[0065] The repair agent II includes the following raw materials in parts by weight: 30 parts of livestock and poultry manure, 10 parts of ferroferric oxide, 80 parts of nano zeolite, 15 parts of chitosan derivatives, 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 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, biological strains were inoculated into the soil samples at a rate of 1% of the soil mass. The biological strains were Aspergillus, Citrobacter freundii and Icebergia in a mass ratio of 2.2:4.8:3.0, and the average number of effective live bacteria was ≥7.25×10 8cfu / g, and continued tilling to a depth of 18 cm, 8 times of tilling, and left it to 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 the repair agent I is not applied in the repair method of the brick red soil.

[0069] Comparative Example 2

[0070] The difference between this comparative example and Example 3 is that no electric field treatment is applied in the method for repairing the red soil.

[0071] Comparative Example 3

[0072] The difference between this comparative example and Example 3 is that the repair agent II is not applied in the repair method of the red soil.

[0073] Comparative Example 4

[0074] The difference between this comparative example and Example 3 is that no biological bacteria are introduced into the remediation method of the red soil.

[0075] Test Example 1

[0076] Grids were divided in the restored brick red soil area, and sample points were selected according to the predetermined grid size and shape. The potassium dichromate-external heat source method was used to determine the organic carbon content in the soil.

[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] The present invention has a positive performance in improving the organic carbon content of the restored brick red soil, and has obvious advantages over the comparative case. In the subsequent brick red soil management and ecological restoration work, these restoration measures can be further optimized according to actual conditions or the combined application of multiple restoration methods can be explored to continuously improve the soil organic carbon content of the brick red soil, enhance its carbon fixation function, and help cope with climate change and improve the soil ecological environment.

[0079] Test Example 2

[0080] 1. Soil sample collection and pretreatment

[0081] 1. The chromium pollution test brick red soil land was divided into 9 test fields. The 9 test fields were tested according to the methods of the above embodiments 1-5 and comparative examples 1-4. In the restored brick red soil area, soil samples were collected according to the grid distribution method or the serpentine distribution method. 0-20 cm of surface 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 and ventilated place to dry naturally, remove impurities such as stones and plant residues in the soil, grind them with a mortar and pass them through a 100-mesh sieve for later use.

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

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

[0085] 2. Place the conical flask in a constant temperature water bath oscillator, oscillate at 30°C 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 volume with deionized water, shake well, and let stand for 10-15 minutes.

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

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

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

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

[0092] 3. Add 5 mL of sodium pyrophosphate solution and shake well. Then add 2 mL of color developer, dilute to scale with deionized water, and shake well. Leave for 10 minutes, and use the blank solution as a reference to measure the absorbance at a wavelength of 540 nm using a spectrophotometer.

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

[0094] (IV) Soil leaching toxicity determination (inversion method)

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

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

[0097] 3. After the shaking is completed, let it stand for 30 minutes and collect the extract by filtering with a filter membrane.

[0098] 4. Use flame atomic absorption spectrometry to determine the chromium content in the leaching solution, and determine whether the soil leaching toxicity meets the relevant standards based on the measurement results.

[0099] (V) Plant effectiveness evaluation (plant planting test)

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

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

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

[0103] 4. Wash the plant samples with deionized water, sterilize at 105°C for 30 min, and then dry at 70°C to constant weight.

[0104] 5. Weigh about 1.0 g of dry samples of roots, stems, and leaves, digest them with nitric acid-perchloric acid, and use flame atomic absorption spectrometry to determine the chromium content in various parts of the plant to evaluate the effectiveness and potential ecological risks of chromium in the repaired soil to plants.

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

[0106]

[0107]

[0108] Among all the remediation methods in this experiment, the remediation effect of the embodiment group on the brick red soil was better than that of the control group. After the remediation treatment of the embodiment group, the chromium content in the soil decreased, indicating that the remediation treatment had a certain fixing effect on the total chromium, and the main impact was on the valence distribution of chromium. The embodiment group significantly reduced the hexavalent chromium content in the soil, especially Example 3, which was reduced to the lowest (4 mg / kg), indicating that the remediation treatment had a significant effect on the reduction of hexavalent chromium.

[0109] Among them, the repair effect of Example 3 is the best, which can effectively reduce the content of hexavalent chromium and trivalent chromium in the soil, reduce the risk of chromium leaching and the absorption and accumulation of chromium by plants.

[0110] Compared with Comparative Example 1, Example 3 uses the synergistic effects of multiple mechanisms, such as the reducing effect of the reducing agent, the solvent effect of deionized water, the ion exchange effect of sodium chloride, the complexing and acidification effect of citric acid, the dispersing effect of CTAB, and the solubilization effect of rhamnolipid, to comprehensively repair the red soil. These mechanisms work together to significantly reduce the content of hexavalent chromium in the soil, and reduce its mobility and bioavailability.

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

[0112] Compared with Comparative Example 3, the repair agent II of the present invention can fix trivalent chromium in the soil through adsorption, coprecipitation, complexation, etc., so as to reduce its bioavailability, solubility and mobility;

[0113] Nano zeolite has a developed pore structure and a large specific surface area. It can adsorb chromium ions in the soil through physical adsorption and ion exchange, fix the chromium ions in the pores and surface of the zeolite, and reduce its mobility. Chitosan derivatives have rich 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 can jointly achieve the restoration of brick red soil.

[0114] Compared with Example 4, the accessed biological strains can fix trivalent chromium in microbial cells or on the cell surface through adsorption on the cell surface or intracellular accumulation, thereby effectively removing chromium from the soil. Some Aspergillus can reduce hexavalent chromium to trivalent chromium through metabolic activities. Aspergillus and Citrobacter freundii secrete some organic acids during growth that can react with chromium ions to form stable complexes, reduce the mobility and biological effectiveness of chromium ions in the soil, and further promote the removal or stabilization of chromium. Citrobacter freundii changes the form of heavy metals through redox reactions during metabolism, and the polysaccharides, proteins and other sticky substances produced at the same time can increase the aggregation of soil particles, reduce soil erosion, and may fix heavy metals in the soil to a certain extent. The structure or secretion on the surface of the ice bacteria cell may adsorb chromium ions and transform the chemical form of chromium using its 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 principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for repairing chromium-contaminated brick red soil using a repair agent, characterized in that: The following steps are involved: S1. Select a red soil sample for pretreatment to remove debris and large particles in the red soil; S2, applying the repair agent I to the pretreated brick red soil sample, plowing and improving the brick red soil, the plowing depth is 10-15cm, the plowing frequency is 2-3 times, the application amount of the repair agent I is 8-10% of the mass of the brick red soil, the moisture content of the mixed brick red soil is maintained at 20-30%, and the electric field is applied for 3-5h / d for 7-10 days; S3, continue to add repair agent II to the soil applied with repair agent I, add 1-3% of the mass of the brick red soil under the environment of 30-40°C, keep the soil moisture at 40-60%, and cure for 3-5 days, stirring intermittently during the curing period; S4. After the maintenance, biological bacteria are inoculated into the brick red soil sample, the inoculation amount is 0.5-2% of the mass of the brick red soil, and the soil is continuously tilled to a depth of 16-20 cm, 5-10 times, and left to stand for 7-14 days to obtain the repaired soil.

2. The method for repairing chromium-contaminated laterosoil according to claim 1, characterized in that: The S1 crushes and grinds the red soil to a particle size of less than 10 mm.

3. A repair agent for chromium-contaminated brick red soil, characterized in that: The invention comprises a repairing agent I and a repairing agent II. The repairing agent I comprises the following raw materials in parts by weight: 40-60 parts of a reducing agent, 15-22 parts of deionized water, 5-10 parts of a 40-80% sodium chloride solution, 3-8 parts of an 80-85% citric acid solution, and 1-3 parts of rhamnolipid.

4. The repairing agent for chromium-contaminated brick red soil according to claim 3, characterized in that: The reducing agent is selected from ferrous chloride, ferrous sulfate or sodium sulfite.

5. The repairing agent for chromium-contaminated laterosoil according to claim 3, characterized in that: The repair agent II includes the following raw materials in parts by weight: 20-40 parts of organic fertilizer, 5-15 parts of iron oxide, 50-80 parts of nano zeolite, 10-15 parts of chitosan derivative, 25-55 parts of phosphate solution, 5-10 parts of sodium sulfide, 3-8 parts of calcium carbonate, and 2-5 parts of sodium alginate. The organic fertilizer is selected from one or more combinations of humic acid, straw, and livestock and poultry manure. The iron oxide is selected from one or more combinations of ferric oxide, ferrous oxide, and ferrosoferric oxide. The chitosan derivative is carboxymethyl chitosan and hydroxyethyl chitosan in a mass ratio of 1:1-3.

6. The repairing agent for chromium-contaminated laterosoil according to claim 5, characterized in that: 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.

7. The repairing agent for chromium-contaminated laterosoil according to claim 1, characterized in that: The voltage of the electric field controlled in S2 is 10-20 V / cm, and the current is 0.1-5.0 mA / cm 2 , temperature 20-40℃.

8. The repairing agent for chromium-contaminated laterosoil according to claim 1, characterized in that: The stirring rate of S3 is 200-400 rpm, the stirring time is 20-60 min, and the rest time is 2-4 h.

9. The repairing agent for chromium-contaminated laterosoil according to claim 1, characterized in that: The biological strains of S4 are Aspergillus, Citrobacter freundii and Ice bacteria in a mass ratio of (1.2-2.5):(3.8-5.5):(2.0-3.5), and the average effective viable count is ≥(6.53-8.25)×10 8 cfu / g.

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