Method for repairing acidic cadmium-polluted soil by combined application of alkaline calcium source

Abstract

The invention discloses a method for repairing acidic cadmium-polluted soil by using combined application of an alkaline calcium source, and belongs to the technical field of polluted soil repairing. The method comprises the following steps: calculating the amount of an alkaline calcium source required to be applied according to the pH value and the cadmium pollution level in the acidic cadmium polluted soil, spreading the alkaline calcium source and a fertilizer on the surface of the soil, and uniformly mixing to realize the remediation of the acidic cadmium polluted soil. The soil conditioner can improve the pH value of soil, increase the fertility of the soil, passivate soil cadmium, change the retention form of cadmium, reduce the absorption of plants to heavy metal cadmium, relieve heavy metal cadmium pollution from the two aspects of soil and plant absorption, achieve the purposes of reducing acid and cadmium and improving the product quality, especially reduce the cadmium content in rice grains, and improve the yield of rice. And the safety range specified by the national standard can be reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of contaminated soil remediation, and in particular relates to a method for remediating acidic cadmium-contaminated soil by utilizing an alkaline calcium source. Background Art

[0002] Controlling heavy metal pollution in farmland soil is to control soil heavy metal pollution from the root, so that the contaminated soil can be effectively treated and no longer affect crops. Common soil remediation technologies include physical, chemical and biological methods.

[0003] Physical remediation methods mainly include guest soil method, soil replacement method, and electric remediation method. Guest soil method is to add clean soil to cadmium-contaminated soil, thereby reducing the cadmium content in the soil or reducing the contact between plant roots and pollutants. This method is suitable for areas where the pollutant content is not high and soil collection is convenient. By adding clean soil, the concentration of pollutants in the soil is diluted and the toxic effect of cadmium on plants is reduced; the soil replacement method is to replace the contaminated soil with clean soil for off-site storage or treatment. This method is only suitable for soil pollution control with a small pollution area and soil can be collected nearby. This method can completely solve the problem of cadmium-contaminated soil treatment, but the treatment cost of the replaced contaminated soil is high and the transportation volume is large; the electric remediation method is to use the directional migration of heavy metal ions under the electrokinetic effect of an external electric field to enrich the heavy metal ions in the soil in the electrode area, and further process or separate the heavy metals. Due to the small amount of engineering work implemented by this technology, it is particularly suitable for the in-situ removal of heavy metal pollution in dense soil, but this technology has certain requirements on the permeability of the soil, pH stability, etc., and its scope of application is not wide.

[0004] Chemical remediation technology changes the existing form of cadmium in farmland soil and reduces the bioavailability of cadmium by applying corresponding chemical agents to farmland soil, so that the absorption of cadmium by plants is effectively inhibited. Chemical remediation technology is mainly divided into in-situ chemical stabilization method and chemical leaching method. In-situ chemical stabilization method refers to adding passivating agents such as calcareous substances, carbon materials, clay minerals, etc. to contaminated soil to reduce the solubility and diffusivity of pollutants, thereby reducing their biological toxicity; in recent years, some scholars at home and abroad have applied organic matter, lime, phosphate fertilizer and other materials to the in-situ passivation remediation of heavy metal contaminated soil, and achieved good results. The leaching method uses the leaching liquid to transfer the cadmium in the soil solid phase to the soil liquid phase, and recycles the cadmium-containing wastewater to achieve the purpose of soil cadmium pollution control. The difficulty of this method is to find a suitable leaching liquid that meets the requirements of soil cadmium pollution control while not destroying the soil structure and causing secondary pollution.

[0005] Biological methods refer to the treatment methods that absorb and degrade soil pollutants and reduce the biological activity of heavy metals in the soil through the metabolic activities of certain specific microorganisms, animals or plants. It has the advantages of small soil disturbance, in-situ, and no secondary pollution. It is generally divided into three types: microbial remediation, animal remediation, and plant remediation. Soil microorganisms are of many types and large numbers, with large specific surface areas, electric charges, and vigorous metabolic activities. Some microorganisms can fix, migrate or transform heavy metals in the soil, thereby achieving the purpose of detoxification and detoxification. Animal remediation is to use the characteristics of certain lower animals in the soil, such as earthworms and rodents, to absorb heavy metals, to reduce the content of heavy metals in the contaminated soil to a certain extent, and achieve the purpose of animal remediation of heavy metal-contaminated soil. The characteristics of certain plants that can tolerate and accumulate certain heavy metals in excess are used to remove cadmium from the soil. More than 400 hyperaccumulators have been discovered so far, which can absorb and accumulate a large amount of cadmium. The cadmium content accumulated by hyperaccumulators is generally above 0.1%. Indian mustard turns yellow when it absorbs 200 mg / kg of cadmium, and accumulates cadmium 52 times; the British alpine mustard species, etc., can absorb high concentrations of cadmium.

[0006] The cadmium content in the soil directly affects the ecological environment and human health, so sufficient attention must be paid to the cadmium pollution problem. For the already contaminated soil, a more economical and efficient remediation method needs to be found. Since chemical improvement measures are simple to operate, low in cost and effective, they have been widely used in the treatment of cadmium-contaminated soil. At the same time, the prevention and control of cadmium pollution is not only a technical issue, but also requires the attention of the whole society to control or reduce the discharge of cadmium into the soil, cut off the pollution source, and increase the remediation efforts for the already contaminated soil, so as to more effectively control and treat the cadmium pollution in the soil.

[0007] Soil pH is one of the most important physical and chemical properties of soil. Its change will lead to changes in the existence form, adsorption sites and coordination properties of heavy metal cadmium. Among them, the impact on the cadmium form is the most direct reason for the change in bioavailability. Generally speaking, the change in soil pH has a more obvious effect on the exchangeable cadmium content in the soil, and there is a negative correlation between the two. The prior art has found that alkaline substances such as alkaline calcium sources can increase the pH value of the soil, promote metal hydrolysis reactions and / or co-precipitation, thereby leading to the immobilization of heavy metals. Alkaline calcium sources indirectly affect the heavy metal content in the soil by changing the soil properties. Applying alkaline calcium sources to improve the soil will increase the soil pH, especially in acidic soils. The increase in soil pH can reduce the dissolution of heavy metals, enhance the adsorption and complexation of heavy metals by the soil, and reduce the mobility and bioavailability of heavy metals in the soil.

[0008] At present, one of the research hotspots is to use the antagonism between competitive cations and heavy metals to reduce the absorption of heavy metals by the edible parts of crops or transfer heavy metals to the non-edible parts of crops. For soil contaminated by cadmium, applying a certain amount of exogenous substances (such as repair agents containing elements such as Ca, Fe, Zn, Mn, etc.) to the contaminated soil can alleviate the toxic effects of cadmium on crops to a certain extent. Calcium and cadmium have similar ionic radii and chemical properties, so they can share many transport proteins, ion transport channels and binding sites in crop roots in plants, thereby inhibiting the accumulation and transport of cadmium in crops. Summary of the invention

[0009] In order to solve the problems of the above-mentioned prior art, the present invention proposes a method for repairing acidic cadmium-contaminated soil by applying an alkaline calcium source. By measuring the pH value and cadmium content in the soil, the amount of the alkaline calcium source to be applied is calculated, and soil repair is achieved by applying the alkaline calcium source and fertilizer.

[0010] In order to solve the above problems, the technical solution adopted by the present invention is as follows:

[0011] A method for repairing acidic cadmium-contaminated soil by applying an alkaline calcium source. The method comprises the following steps: calculating the amount of alkaline calcium source required to be applied according to the pH value and cadmium pollution level in the acidic cadmium-contaminated soil; spreading the alkaline calcium source and fertilizer on the soil surface; and evenly mixing them to achieve the repair of the acidic cadmium-contaminated soil.

[0012] Furthermore, the pH value in the acidic cadmium contaminated soil is determined by (calcium chloride extraction method: weigh 10.0g of air-dried soil sample passing through a 2mm sieve, add 25ml of 0.01mol / L calcium chloride solution, oscillate on a reciprocating horizontal constant temperature oscillator for 3 minutes, let stand for 1 hour, and measure with a PHS-3G pH meter); the cadmium pollution level in the acidic cadmium contaminated soil is determined by (soil effective cadmium: weigh 10.0g of air-dried soil sample passing through a 1mm sieve, add 50ml of 0.1mol / L calcium chloride solution, oscillate at 20°C for 2 hours, filter, and measure with a 6810 atomic absorption spectrophotometer).

[0013] Furthermore, the alkaline calcium source is selected from calcium carbonate and calcium hydroxide; the particle size of calcium carbonate is (2 to 3 microns), and the particle size range of calcium hydroxide is (4 to 6 microns).

[0014] Furthermore, in the alkaline calcium source, the total mass of calcium carbonate and calcium hydroxide accounts for 100%; the mass of calcium carbonate: the mass of calcium hydroxide is 0-100%: 100%-0.

[0015] Furthermore, the pH value of the acidic cadmium-contaminated soil is (5-6), and the cadmium contamination level is (0.75-1 mg / kg).

[0016] Furthermore, the mass ratio of the applied amount of the alkaline calcium source to the acidic cadmium contaminated soil is 2 to 3 g / kg.

[0017] Furthermore, the fertilizers are divided into phosphate fertilizer, potash fertilizer and nitrogen fertilizer; the phosphate fertilizer is P2O5, the potash fertilizer is K2O, and the nitrogen fertilizer is urea with a N content of ≥46%.

[0018] Furthermore, the phosphorus fertilizer is applied entirely as base fertilizer; the potassium fertilizer and nitrogen fertilizer are applied separately as base fertilizer, tillering fertilizer and ear fertilizer.

[0019] Furthermore, the application ratio of base fertilizer, tillering fertilizer and ear fertilizer is 5:3:2.

[0020] Further, the fertilizer application rate was N 200kg / ha, P2O5 100kg / ha, and K2O 200kg / ha.

[0021] Compared with the prior art, the advantages of the present invention are as follows:

[0022] 1) The calcium sources calcium carbonate (CaCO3) and calcium hydroxide (Ca(OH)2) used in the present invention are both alkaline substances, which can neutralize acidic substances in the soil and increase the pH value of the soil, thereby reducing or eliminating the problem of soil acidification, facilitating the transformation and circulation of nutrients in the soil, and improving the effectiveness of soil nutrients. The application method of calcium carbonate and calcium hydroxide is relatively simple, easy to operate and control, and is suitable for a wide range of soil remediation.

[0023] 2) The present invention can improve soil pH, increase soil fertility, passivate soil cadmium, change the retention form of cadmium, reduce the absorption of heavy metal cadmium by plants, alleviate heavy metal cadmium pollution from two aspects of soil and plant absorption, and simultaneously achieve the purpose of reducing acid and cadmium and improving product quality, especially reducing the cadmium content in rice grains, which can be reduced to the safety range specified by national standards.

[0024] 3) Compared with the single application of Ca(OH)2, the combined application of calcium carbonate and calcium hydroxide in the present invention has lower cost and is widely available and easy to obtain.

[0025] 4) Compared with other soil remediation methods, the present invention has CaCO3 and Ca(OH)2 that dissolve slowly in the soil and can be regarded as a slow-release fertilizer, which can maintain the effect of long-term acid neutralization and passivation of cadmium.

[0026] 5) The calcium hydroxide added in the present invention can react chemically with heavy metal ions such as cadmium (Cd) in the soil to form insoluble precipitates, thereby reducing the bioavailability of cadmium and reducing the absorption of cadmium by plants.

[0027] 6) The calcium carbonate added in the present invention can increase the calcium content of the soil, improve the soil structure, enhance the buffering capacity of the soil, and is beneficial to the activities of microorganisms in the soil and the growth of plants.

[0028] 7) The method of the present invention does not involve a complicated chemical treatment process, has little negative impact on the environment, and complies with the principle of green environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a graph showing the effects of different proportions of alkaline calcium sources on paddy field soil pH at different rice growth stages.

[0030] Figure 2 This graph shows the effect of different proportions of alkaline calcium sources on the available cadmium in paddy field soil at different rice growth stages.

[0031] Figure 3 This is a diagram showing the effects of different proportions of alkaline calcium sources on four forms of cadmium in the soil during the tillering period; among them, F1: exchangeable state; F2: reducible state; F3: oxidizable state; F4: residual state.

[0032] Figure 4 This graph shows the effects of different proportions of alkaline calcium sources on water-soluble calcium in paddy field soil at different rice growth stages.

[0033] Figure 5 This is a graph showing the effects of different proportions of alkaline calcium sources on the cadmium content in various parts of rice at different growth stages. DETAILED DESCRIPTION

[0034] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with specific embodiments.

[0035] The raw materials and reagents used in the following examples are all commercially available products unless otherwise specified.

[0036] Among them, the sources of calcium carbonate are as follows:

[0037] 1) Natural minerals: Calcium carbonate can be obtained from natural minerals such as calcite, limestone, chalk, marble, etc. These minerals are mechanically crushed or chemically treated to obtain calcium carbonate products.

[0038] 2) Industrial by-products: In the industrial production process, calcium carbonate can be recovered and utilized as a by-product.

[0039] 3) Synthetic production: through chemical synthesis methods, such as calcining limestone (CaCO3) to produce calcium oxide (CaO) and carbon dioxide (CO2), then reacting calcium oxide with water to produce calcium hydroxide (Ca(OH)2), and finally through carbonization reaction to produce calcium carbonate.

[0040] The sources of calcium hydroxide are:

[0041] 1) Limestone calcination: Limestone (CaCO3) is calcined at high temperature to produce calcium oxide (CaO) and carbon dioxide (CO2), and then the calcium oxide reacts with water to form calcium hydroxide (Ca(OH)2).

[0042] 2) Seawater or brine treatment: Calcium hydroxide can be produced by chemical treatment of seawater or brine.

[0043] 3) Industrial synthesis: In industry, calcium hydroxide can be prepared by a variety of chemical synthesis methods, such as using calcium chloride (CaCl2) and sodium hydroxide (NaOH) to react to produce calcium hydroxide.

[0044] These two compounds have various sources and can be obtained from natural minerals, industrial byproducts or through chemical synthesis. In practical applications, their production and use need to consider cost, efficiency and environmental impact.

[0045] Overview of the test site:

[0046] The test soil was taken from paddy soil in Yizhou, Hechi, Guangxi, which was contaminated with cadmium and acidified (the soil pH range was 5-6; the soil available cadmium content was 0.75-1 mg / kg). After natural air drying, it was crushed with a wooden mallet and passed through a 2 mm sieve for soil property analysis and potted plant experiments.

[0047] Soil: Determine soil pH, electrical conductivity, available phosphorus, available potassium, available calcium, cation exchange capacity, total exchangeable acid, exchangeable hydrogen, exchangeable aluminum, total cadmium, available cadmium, and four forms of cadmium.

[0048] Plants: Determine the content in the roots, stems, leaves, shells and seeds of the plants

[0049] Weigh 10 kg of test soil and place it in a plastic box with a length of 15 cm, a width of 15 cm, and a height of 15 cm for potting experiments.

[0050] Before rice planting, calcium source and basal fertilizer were added to each kilogram of air-dried soil, mixed thoroughly, and soaked in water 2-3 cm above the soil surface for 24 hours.

[0051] The phosphate fertilizer used is P2O5, which is applied as basal fertilizer; the potassium fertilizer used is K2O, and the nitrogen fertilizer used is urea (N≥46%), which is divided into basal fertilizer, tillering fertilizer (applied 7 days after transplanting), and ear fertilizer, and applied in a ratio of 5:3:2.

[0052] The fertilizer application rate was unified as N 200kg / ha, P2O5 100kg / ha, and K2O 200kg / ha.

[0053] In the following embodiments, calcium carbonate (CaCO3) is used as follows:

[0054] (1) Soil test: First, soil test was conducted to determine the pH value and cadmium pollution level of the soil. (The pH value was determined by calcium chloride extraction method: 10.0 g of air-dried soil sample that passed through a 2 mm sieve was weighed, 25 ml of 0.01 mol / L calcium chloride solution was added, and the mixture was shaken on a reciprocating horizontal constant temperature oscillator for 3 minutes, left to stand for 1 hour, and then measured using a PHS-3G pH meter; the cadmium pollution level in the soil was determined by calcium chloride extraction method: 10.0 g of air-dried soil sample that passed through a 1 mm sieve was weighed, 50 ml of 0.1 mol / L calcium chloride solution was added, and the mixture was shaken at 20°C for 2 hours, filtered, and then measured using a 6810 atomic absorption spectrophotometer.)

[0055] (2) Determination of application amount: Based on the soil test results, calculate the amount of calcium carbonate that needs to be added per mu of soil (soil depth is 15 cm, soil bulk density is 1.25 g / cm 3 , taking 2g of calcium carbonate per kilogram of soil as an example: 1. Calculate the volume of the soil, volume = area (1 mu) * depth = 666.67m 2 *0.15m=100m 3 ; 2. Calculate the mass of soil: soil mass = soil volume * bulk density = 100m 3 *1250kg / m 3 =125000kg; 3. The amount of calcium carbonate required per mu = soil mass * the amount of calcium carbonate required per kilogram of soil = 125000kg * 2g / kg = 250kg).

[0056] (3) Even spreading: Spread calcium carbonate evenly on the soil surface, either mechanically or manually.

[0057] (4) Soil mixing: Mixing calcium carbonate with the soil to ensure even distribution. This can be done by ploughing or other soil cultivation methods.

[0058] (5) Monitoring and adjustment: After adding calcium carbonate, regularly monitor soil pH and cadmium content and adjust the application amount of calcium carbonate as needed.

[0059] (6) Long-term management: Since calcium carbonate dissolves slowly, its effects can last longer, but long-term soil management and monitoring are still required.

[0060] The usage of calcium hydroxide (Ca(OH)2) is as follows:

[0061] (1) Soil testing: As with calcium carbonate, soil testing is first performed to determine the extent of cadmium contamination and soil pH.

[0062] (2) Calculate the application amount: According to the soil test results, calculate the amount of calcium hydroxide required per mu of soil (soil depth is 15cm, soil bulk density is 1.25g / cm 3 , take 2g of calcium hydroxide per kilogram of soil as an example: 1. Calculate the volume of the soil, volume = area (1 mu) * depth = 666.67m 2 *0.15m=100m 3 ; 2. Calculate the mass of soil: soil mass = soil volume * bulk density = 100m 3 *1250kg / m 3 =125,000kg; 3. The amount of calcium hydroxide required per mu = soil mass * the amount of calcium hydroxide required per kilogram of soil = 125,000kg * 2g / kg = 250kg). When the soil pH is raised to the same value, the amount of calcium hydroxide applied is usually less than that of calcium carbonate because it has a higher neutralizing capacity.

[0063] (3) Application: Sprinkle calcium hydroxide evenly on the soil surface, or mix it with water and spray it on the soil.

[0064] (4) Soil mixing: Mix calcium hydroxide and soil evenly by plowing or other soil cultivation methods.

[0065] (5) Monitoring and adjustment: After adding calcium hydroxide, regularly monitor soil pH and cadmium content and adjust the application rate as needed.

[0066] (6) Pay attention to safety: Calcium hydroxide is corrosive, so appropriate safety measures should be taken during operation, such as wearing protective clothing and gloves.

[0067] Example 1

[0068] 0.2% Ca(OH)2 (i.e. 20g Ca(OH)2 is applied to a pot of 10kg soil before rice planting) and fertilizer treatment are applied, and the mixture is fully mixed and soaked in water 2-3cm above the soil surface for 24 hours. P2O5 is used as phosphate fertilizer and all is applied as basal fertilizer; K2O is used as potash fertilizer and urea (N≥46%) is used as nitrogen fertilizer, which is divided into basal fertilizer, tillering fertilizer (applied 7 days after transplanting) and ear fertilizer, and applied in a ratio of 5:3:2. The fertilizer application amount is uniformly N 200kg / ha, P2O5 100kg / ha, K2O 200kg / ha.

[0069] Example 2

[0070] 0.05% CaCO3 and 0.15% Ca(OH)2 (i.e. 5g CaCO3 and 15g Ca(OH)2 were applied to 10kg of air-dried soil (soil pH value was 5.74, soil effective cadmium content was 0.75mg / kg) before rice planting, and fertilization was applied, and the mixture was fully mixed and soaked in water 2-3cm above the soil surface for 24 hours. P2O5 was used as phosphate fertilizer, and all of it was applied as basal fertilizer; K2O was used as potash fertilizer, and urea (N≥46%) was used as nitrogen fertilizer, which was divided into basal fertilizer, tillering fertilizer (applied 7 days after transplanting), and ear fertilizer, and applied in a ratio of 5:3:2. The fertilizer application rate was uniformly 200kg / ha of N, 100kg / ha of P2O5, and 200kg / ha of K2O.

[0071] Example 3

[0072] 0.1% CaCO3 and 0.1% Ca(OH)2 (i.e., 10g CaCO3 and 10g Ca(OH)2 were applied to 10kg of air-dried soil (soil pH value was 5.74, soil effective cadmium content was 0.75mg / kg) before rice planting, and fertilization treatment was applied, and the mixture was fully mixed, and then soaked in water 2-3cm above the soil surface for 24 hours. P2O5 was used as phosphate fertilizer, and all of it was applied as basal fertilizer; K2O was used as potash fertilizer, and urea (N≥46%) was used as nitrogen fertilizer, which was divided into basal fertilizer, tillering fertilizer (applied 7 days after transplanting), and ear fertilizer, and applied in a ratio of 5:3:2. The fertilizer application amount was unified as N 200kg / ha, P2O5 100kg / ha, and K2O 200kg / ha.

[0073] Example 4

[0074] 0.15% CaCO3 and 0.05% Ca(OH)2 (i.e., 15g CaCO3 and 5g Ca(OH)2 were applied to 10kg of air-dried soil (soil pH value was 5.74, soil effective cadmium content was 0.75mg / kg) before rice planting, and fertilization was applied, and the mixture was fully mixed, and then soaked in water 2-3cm above the soil surface for 24 hours. P2O5 was used as phosphate fertilizer, and all of it was applied as basal fertilizer; K2O was used as potash fertilizer, and urea (N≥46%) was used as nitrogen fertilizer, which was divided into basal fertilizer, tillering fertilizer (applied 7 days after transplanting), and ear fertilizer, and applied in a ratio of 5:3:2. The fertilizer application amount was uniformly 200kg / ha of N, 100kg / ha of P2O5, and 200kg / ha of K2O.

[0075] Example 5

[0076] Add 0.2% CaCO3 (i.e., 20g CaCO3 is applied to a pot of 10kg soil) and fertilizer to the 10kg air-dried soil before planting rice (soil pH is 5.74, soil effective cadmium content is 0.75mg / kg), mix thoroughly, and soak in water 2-3cm above the soil surface for 24 hours. P2O5 is used as phosphate fertilizer, all of which is applied as basal fertilizer; K2O is used as potash fertilizer, and urea (N≥46%) is used as nitrogen fertilizer, which is divided into basal fertilizer, tillering fertilizer (applied 7 days after transplanting), and ear fertilizer, and applied in a ratio of 5:3:2. The fertilizer amount is unified as N 200kg / ha, P2O5 100kg / ha, K2O 200kg / ha.

[0077] Comparative Example 1 (blank control)

[0078] The above 10kg air-dried soil (soil pH value is 5.74, soil effective cadmium content is 0.75mg / kg) before planting rice is directly fertilized, fully mixed, and soaked in water 2-3cm above the soil surface for 24 hours. P2O5 is used as phosphate fertilizer, all of which is applied as basal fertilizer; K2O is used as potash fertilizer, and urea (N≥46%) is used as nitrogen fertilizer, which is divided into basal fertilizer, tillering fertilizer (applied 7 days after transplanting), and ear fertilizer, and applied in a ratio of 5:3:2. The fertilizer amount is unified as N 200kg / ha, P2O5 100kg / ha, K2O 200kg / ha.

[0079] The effects of different proportions of alkaline calcium sources on the pH of paddy field soil at different rice growth stages in the above Examples 1 to 5 and Comparative Example 1 were respectively measured. Figure 1 ), the effect of different proportions of alkaline calcium sources on the effective cadmium content in paddy soil at different rice growth stages (e.g. Figure 2 ), the effects of different proportions of alkaline calcium sources on the content of four forms of cadmium in soil during the tillering period (e.g. Figure 3 ), the effects of different proportions of alkaline calcium sources on water-soluble calcium in paddy soil at different rice growth stages (e.g. Figure 4 ) and different proportions of alkaline calcium sources on the cadmium content in various parts of rice (roots, stems, leaves, shells, and grains) at different growth stages (e.g. Figure 5 ).

[0080] Depend on Figure 1 It can be seen that compared with Comparative Example 1 (no calcium source was applied), the pH of the paddy field soil in Examples 1 to 5 of the present invention during the tillering, filling and maturity stages of rice was higher than that of the control group, especially when 0.15% CaCO3 and 0.05% Ca(OH)2 were applied in Example 4, the soil pH during the tillering stage of rice was the highest, reaching 7.21 (CK was 5.56).

[0081] Depend on Figure 2It can be seen that when 0.15% CaCO3 and 0.05% Ca(OH)2 were applied in Example 4, the available cadmium content in the soil during the tillering period of rice was the lowest, at 0.2 mg / kg (CK was 0.35 mg / kg).

[0082] Depend on Figure 3 It can be seen that the proportion of exchangeable cadmium in Examples 4 to 5 of the present invention is lower than that in Example 1, and the proportion of residual cadmium in Examples 4 to 5 is higher than that in Example 1, indicating that the lower the proportion of exchangeable cadmium, the less it is absorbed and utilized by rice.

[0083] Depend on Figure 4 It can be seen that the soluble calcium content of the soil during the tillering period of rice in Examples 1 to 5 of the present invention is higher than that in Comparative Example 1, and when 0.15% CaCO3 and 0.05% Ca(OH)2 are applied in Example 4, the soluble calcium content of the soil during the tillering period of rice is the highest, reaching 314.24 mg / kg (CK is 114.82 mg / kg).

[0084] Depend on Figure 5 It can be seen that compared with Comparative Example 1 (no calcium source was added), the cadmium content in the rice grains of each embodiment of the present invention was significantly reduced, especially in Example 4, when 0.15% CaCO3 and 0.05% Ca(OH)2 were applied, the cadmium content of the rice grains was the lowest, at 0.07 mg / kg, and far below the national standard of 0.2 mg / kg (CK is 0.23 mg / kg), indicating that the greater the solubility of the calcium source, the greater the impact on soil acidity and the bioavailability of cadmium and the cadmium content in the grains.

[0085] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for repairing acidic cadmium-contaminated soil by using an alkaline calcium source, characterized in that: According to the pH value and cadmium pollution level in the acidic cadmium contaminated soil, the amount of alkaline calcium source required to be applied is calculated, and the alkaline calcium source and fertilizer are spread on the soil surface and mixed evenly to achieve the remediation of the acidic cadmium contaminated soil.

2. The method for repairing acidic cadmium contaminated soil by using an alkaline calcium source according to claim 1, characterized in that: The method for determining the pH value in the acidic cadmium-contaminated soil is as follows: weigh 10.0 g of an air-dried soil sample that has passed a 2 mm sieve, add 25 ml of a 0.01 mol / L calcium chloride solution, oscillate on a reciprocating horizontal constant temperature oscillator for 3 minutes, let stand for 1 hour, and measure with a PHS-3G pH meter; the method for determining the cadmium pollution level in the acidic cadmium-contaminated soil is as follows: weigh 10.0 g of an air-dried soil sample that has passed a 1 mm sieve, add 50 ml of a 0.1 mol / L calcium chloride solution, oscillate at 20° C. for 2 hours, filter, and measure with a 6810 atomic absorption spectrophotometer.

3. The method for repairing acidic cadmium contaminated soil by using an alkaline calcium source according to claim 1, characterized in that: The alkaline calcium source is selected from calcium carbonate and calcium hydroxide; the particle size of the calcium carbonate is 2 to 3 μm, and the particle size of the calcium hydroxide is 4 to 6 μm.

4. The method for repairing acidic cadmium contaminated soil by using an alkaline calcium source according to claim 1, characterized in that: In the alkaline calcium source, the total mass of calcium carbonate and calcium hydroxide accounts for 100%; the mass of calcium carbonate: the mass of calcium hydroxide is 0-100%: 100%-0.

5. The method for repairing acidic cadmium-contaminated soil by using an alkaline calcium source according to claim 1, characterized in that: The pH value of the acidic cadmium-contaminated soil is 5-6, and the cadmium contamination level is 0.75-1 mg / kg.

6. The method for repairing acidic cadmium-contaminated soil by using an alkaline calcium source according to claim 1, characterized in that: The mass ratio of the applied amount of the alkaline calcium source to the acidic cadmium-contaminated soil is 2 to 3 g / kg.

7. The method for repairing acidic cadmium-contaminated soil by using an alkaline calcium source according to claim 1, characterized in that: The fertilizers are divided into phosphate fertilizer, potash fertilizer and nitrogen fertilizer; the phosphate fertilizer is P2O5, the potash fertilizer is K2O, and the nitrogen fertilizer is urea with a N content of ≥46%.

8. The method for repairing acidic cadmium-contaminated soil by using an alkaline calcium source according to claim 7, characterized in that: The phosphorus fertilizer is applied entirely as base fertilizer; the potassium fertilizer and nitrogen fertilizer are applied as base fertilizer, tillering fertilizer and ear fertilizer.

9. The method for repairing acidic cadmium-contaminated soil by using an alkaline calcium source according to claim 8, characterized in that: The application ratio of base fertilizer, tillering fertilizer and ear fertilizer is 5:3:

2.

10. The method for repairing acidic cadmium-contaminated soil by using an alkaline calcium source according to claim 1, characterized in that: The fertilizer application rate is N 200kg / ha, P2O5 100kg / ha, K2O 200kg / ha.

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