CN112808759B - Heavy metal polluted farmland restoration method - Google Patents
Heavy metal polluted farmland restoration method Download PDFInfo
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- CN112808759B CN112808759B CN202011639458.3A CN202011639458A CN112808759B CN 112808759 B CN112808759 B CN 112808759B CN 202011639458 A CN202011639458 A CN 202011639458A CN 112808759 B CN112808759 B CN 112808759B
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
- B09C—RECLAMATION OF CONTAMINATED SOIL
- B09C1/00—Reclamation of contaminated soil
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
- B09C—RECLAMATION OF CONTAMINATED SOIL
- B09C1/00—Reclamation of contaminated soil
- B09C1/08—Reclamation of contaminated soil chemically
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Abstract
The application relates to the technical field of soil remediation, and particularly discloses a heavy metal contaminated farmland remediation method. The heavy metal polluted farmland restoration method comprises the following steps: 1) stripping surface soil of the polluted farmland, and then uniformly mixing the stripped surface soil with the composite fixing agent to obtain solidified soil; 2) digging downwards the cultivated land with the surface soil stripped in the step 1) to obtain middle-layer soil, and then uniformly mixing the dug middle-layer soil with a compound fertilizer to obtain planting soil; 3) backfilling the solidified soil obtained in the step 1) to the surface of the cultivated land excavated in the step 2) to form a solidified layer, and then backfilling the planting soil obtained in the step 2) to the solidified layer to form a planting layer; 4) planting crops on the planting layer formed in the step 3). Compared with the traditional agricultural production process, the heavy metal polluted farmland restoration method does not affect the period of agricultural production, and production and restoration are really realized.
Description
Technical Field
The application relates to the technical field of soil remediation, in particular to a heavy metal contaminated farmland remediation method.
Background
When the cultivated land is contaminated by heavy metal, the cultivated land may be no longer suitable for cultivation, which is also an important factor for reducing the area of the cultivated land suitable for cultivation. Therefore, the treatment of the heavy metal polluted farmland to make the farmland suitable for cultivation is an important measure for protecting the farmland.
When the heavy metal polluted farmland is repaired, if the polluted soil is collected and then is subjected to centralized landfill treatment, the heavy metal pollution can be reduced, and the secondary pollution is avoided, but the heavy metal polluted farmland has large engineering quantity and high cost, and is not suitable for large-scale farmland repair and treatment. In-situ remediation is a simple and easy-to-operate soil heavy metal pollution treatment technology, can make up for the defects, is suitable for remedying large-area cultivated land with excessive heavy metal, and can also achieve production and remediation.
In the in-situ remediation process, a heavy metal adsorbent is generally added into the farmland soil, and the coprecipitation of heavy metal ions and remediation materials and the like is promoted by changing the pH value of the soil and the chemical form and occurrence state of heavy metal elements in the soil, so that the effective state of the heavy metal elements in the soil is converted into a form which is unavailable for organisms, and the migration and bioavailability of the heavy metal elements in the soil are inhibited.
However, a large amount of heavy metal elements still exist in the cultivated land repaired in such a way, and once the environment of the heavy metal elements changes, the heavy metal elements still can be converted into a bioavailable state along with the progress of agricultural production, and absolute safety cannot be realized.
The Chinese patent application with the application publication number of CN110814005A discloses a method for restoring soil polluted by heavy metal cadmium in northern arable land, which comprises the following steps: 1) applying a heavy metal activator to the farmland soil before the planting season; 2) ploughing the farmland soil applied with the heavy metal activator; 3) irrigating water into the ploughed soil for maintenance; 4) after the maintenance period is finished, planting heavy metal-enriched plants on the cultivated land, and performing field management; 5) when the plants are harvested in the seasons, harvesting the overground parts of the heavy metal-enriched plants; 6) uniformly airing the harvested straws on the overground part of the heavy metal-enriched plant; 7) and conveying the dried straws to a biomass power plant for disposal. The method can reduce the absolute content of heavy metal elements in the cultivated land by collecting the heavy metal elements through enrichment plants.
In view of the above-mentioned related art, the inventors consider that the repair cycle of the above-mentioned repair method is long and the influence on agricultural production is large.
Disclosure of Invention
In order to reduce the restoration period, the application provides a heavy metal polluted farmland restoration method.
The application provides a heavy metal pollution arable land restoration method adopts the following technical scheme:
a heavy metal polluted farmland restoration method comprises the following steps:
1) stripping surface soil of the polluted farmland, and then uniformly mixing the stripped surface soil with a composite fixing agent to obtain solidified soil; the composite fixing agent is prepared from the following raw materials in parts by weight: 15-25 parts of humic acid, 260 parts of powdered rock phosphate, 50-60 parts of biochar, 80-100 parts of clay and 30-50 parts of zeolite;
2) digging the farmland with the surface soil stripped in the step 1) upwards and downwards to obtain middle-layer soil, and then uniformly mixing the dug middle-layer soil with a compound fertilizer to obtain planting soil;
3) backfilling the solidified soil obtained in the step 1) to the surface of the excavated farmland in the step 2) to form a solidified layer, and backfilling the planting soil obtained in the step 2) to the solidified layer to form a planting layer;
4) planting crops on the planting layer formed in the step 3).
By adopting the technical scheme, most heavy metal elements in the heavy metal polluted cultivated land are concentrated in the surface soil, the heavy metal polluted cultivated land restoration method is characterized in that the surface soil is stripped and then is used as solidified soil after being added with the compound fixing agent, then deep middle soil is excavated and then is used as planting soil after being mixed with the compound fertilizer, the solidified soil is backfilled to the lower layer, the planting soil is backfilled to the upper layer, the positions of the two layers of soil are exchanged, the content of the heavy metal elements in the initial surface soil is relatively higher, the initial surface soil and the compound fixing agent are mixed and then are placed in the lower layer, when crops are planted, the root systems of the crops are not easy to absorb the heavy metal elements in the lower layer, the compound fixing agent can also solidify the heavy metal elements in the solidified layer in the lower layer, and further the heavy metal elements are prevented from being diffused to the upper layer. Humic acid, biochar and the like in the composite fixing agent can promote heavy metal elements to be converted from an unstable state to a stable state, and the biochar can adsorb and fix the heavy metal elements. The formation of the solidified layer can also reduce the pollution of underground water caused by downward permeation of high-concentration heavy metal elements in the original surface soil, and is beneficial to protecting water sources.
According to the heavy metal polluted farmland restoration method, the soil layer excavation and mixing procedures are adopted to replace the land turning only in the normal agricultural production process, the workload is increased less, the planting period of agricultural production is not affected, and the restoration while production is really realized.
Preferably, the stripping depth of the topsoil in the step 1) is 25-40 cm; the excavation depth of the middle layer soil in the step 2) is 25-40 cm.
Through adopting above-mentioned technical scheme, the excavation depth of topsoil is difficult for the undersize to guarantee that the soil polluted by heavy metal can fully be excavated out. The excavation depth of the middle-layer soil is not too small easily, so that the amount of planting soil is ensured, the thickness of a finally formed planting layer is improved, and the probability of the root system of the crop growing into the curing layer is reduced.
Preferably, the mass ratio of the topsoil to the composite fixing agent in the step 1) is 15-20: 1.
Through adopting above-mentioned technical scheme, because this application will contain the more topsoil of heavy metal element and arrange the lower floor in through the exchange, the heavy metal element has been reduced by the absorptive probability of crop, consequently adopts less compound fixative can reach good heavy metal element fixed effect.
Preferably, the mass ratio of the middle layer soil to the compound fertilizer in the step 2) is 5-8: 1.
By adopting the technical scheme, the proportion of the middle-layer soil and the compound fertilizer is set to be larger, part of elements in the compound fertilizer in the middle-layer soil can be compounded with a small amount of heavy metal elements in the middle-layer soil, and the bioavailability of the heavy metal elements can be further reduced while the normal growth of crops is ensured.
Preferably, the solidified soil is backfilled in the step 3) and then rolled to form a solidified layer, and the compaction coefficient of the rolling is 0.93-0.98.
Through adopting above-mentioned technical scheme, the compaction coefficient that this application set up to roll is great, guarantees that the density of the layer of solidifying is higher, has further reduced the probability of heavy metal element in the layer of solidifying upwards layer diffusion, has also reduced the probability that heavy metal element carries out the migration through groundwater, has reduced secondary pollution's risk.
Preferably, the crop planted in the step 4) is wheat, and the variety of the wheat is any one of Zhengmai 379, Xinke mai 168, Huachuan 919, xu mai 168 and Bainong 207.
By adopting the technical scheme, the wheat is selected as the crop planted on the planting layer, the amount of water to be irrigated is less in the planting period, and the probability of diffusion of heavy metal elements to the root system part of the crop is further reduced. And through screening of wheat varieties with low accumulation of heavy metal elements, the absorption capacity of the heavy metal elements of the wheat varieties is lower.
Preferably, the foliage blocking agent is sprayed to the foliage of the crops 200-250 days after the crops are planted in the step 4), and the foliage blocking agent is sprayed once every 2-5 days, wherein the spraying amount is 120 kg/mu each time.
By adopting the technical scheme, the accumulation of heavy metal elements in crops can be further reduced by spraying the foliage barrier agent to the foliage of the crops in the growth period. The foliage blocking agent is sprayed when the wheat is planted for 200-250 days, the growth of wheat plants is faster, various elements are absorbed more quickly, the blocking effect of the foliage blocking agent is more obvious, the distribution of heavy metal elements in crops can be obviously changed, the heavy metal is inhibited from being transported to edible parts of the crops, and the heavy metal content in agricultural products is reduced. The heavy metal elements can be separated on the cell walls of the leaves by spraying the leaf surface blocking agent, so that the resistance of plants to the heavy metals is improved, and the threat of the heavy metal elements to food is further reduced.
Preferably, the foliage blocking agent is prepared from the following raw materials in parts by weight: 10-15 parts of calcium chloride, 5-8 parts of magnesium nitrate, 0.5-0.8 part of boric acid, 20-30 parts of ferrous sulfate, 20-25 parts of ethylene diamine tetraacetic acid, 25-30 parts of citric acid, 80-100 parts of monopotassium phosphate, 30-40 parts of potassium humate, 25-30 parts of amino acid, 20-40 parts of sodium stearate and 2000 parts of water.
By adopting the technical scheme, the leaf surface blocking agent is added with medium elements such as calcium, magnesium and the like, also added with trace elements such as boron, iron and the like, and also added with major elements such as potassium and the like, and the elements are rich in variety, so that the heavy metal elements and other elements are more fully compounded. Chelating agents such as ethylene diamine tetraacetic acid and citric acid are added into the leaf surface blocking agent, and heavy metal elements can be further prevented from being gathered to the top of crops. The boron element can also generate antagonism with the heavy metal element, and the destruction of the heavy metal element is relieved.
Preferably, the foliar blocking agent is prepared by a method comprising the steps of: adding calcium chloride, magnesium nitrate, boric acid and ferrous sulfate into water, mixing, adding ethylenediamine tetraacetic acid and citric acid, reacting at 70-75 deg.C for 0.5-1h, adding potassium dihydrogen phosphate, potassium humate, amino acid and sodium stearate, and mixing.
By adopting the technical scheme, when the foliage blocking agent is prepared, the medium trace elements are added into water, and then the ethylenediamine tetraacetic acid and the citric acid are added and react at a higher temperature, so that the medium trace elements and the chelating agent can be promoted to be fully chelated, and a small amount of medium trace elements can be uniformly dispersed in the blocking agent and can be more easily fixed in a plant body.
Preferably, the raw materials for preparing the leaf surface blocking agent also comprise zinc oxide and copper sulfate, and the mass ratio of the zinc oxide to the copper sulfate to the calcium chloride is 3-5:10-12: 10-15.
By adopting the technical scheme, zinc oxide and copper sulfate are also added into the leaf surface blocking agent, and a zinc element and a copper element are introduced into the blocking agent under the action of water and acid, so that the blocking and curing effects on heavy metal elements are better.
In summary, the present application has the following beneficial effects:
1. according to the heavy metal polluted farmland restoration method, the surface soil and the middle soil of polluted farmland soil are subjected to position exchange, the surface soil is mixed with the composite fixing agent before being replaced to the lower layer, heavy metal elements in the surface soil are fixed and form a fixed layer, and the heavy metal elements are prevented from being diffused to the upper layer to the greatest extent. Compared with the traditional agricultural production process, the heavy metal polluted farmland restoration method has the advantages that the working procedures are not changed greatly, the period of agricultural production is not influenced, and the restoration while production is really realized.
2. The heavy metal pollution arable land restoration method of this application further rolls after backfilling solidification soil and forms the solidification layer, rolls and has adopted higher compaction coefficient, has guaranteed that the solidification layer has higher degree of compactness, has further improved the separation ability of the heavy metal element of solidification layer.
Detailed Description
The present application will be described in further detail with reference to examples.
The heavy metal element in the heavy metal polluted farmland repaired by the heavy metal polluted farmland repairing method is mainly Cd. Further preferably, the heavy metal polluted farmland is a cadmium polluted farmland in Longan district of Anyang city, Henan province.
The phosphorus content (calculated by phosphorus pentoxide) in the powdered rock phosphate is 25-32 percent by mass. Preferably, the phosphorus content of the ground phosphate rock is 30 percent or 32 percent. The particle size of the ground phosphate rock is 100 meshes.
The biochar can be selected from commercially available coconut shell carbon or shell carbon. Preferably, the specific surface area of the biochar is 750-1000m2The grain diameter is 200-400 meshes. The iodine value is 600-900 mg/g. More preferably, the biochar is biochar compounded with microorganisms, and further, the mass of the microorganisms compounded on the biochar accounts for 2% of the total mass of the biochar. The microorganism compounded on the charcoal is bacillus amyloliquefaciens.
The granularity of the clay is 100-200 meshes.
The zeolite has a particle size of 12-80 mesh (0.18-1.5 mm).
The humic acid is commercially available humic acid, or the humic acid is prepared by a method comprising the following steps: adding the lignite particles into ammonia water with the mass fraction of 15%, and carrying out closed reaction for 7 days to obtain the lignite particles. The mass fraction of humic acid in the lignite is 50%.
Preferably, the composite fixing agent also comprises 8-10 parts by weight of perlite, and the particle size of the perlite is 90-100 meshes.
And uniformly mixing the stripped surface soil with the composite fixing agent, namely spreading the surface soil, then spreading the composite fixing agent on the spread surface soil, uniformly stirring, flattening, airing for 2-5h, uniformly stirring, collecting and stacking to obtain the solidified soil. The thickness of the topsoil after the first flattening is 25-30 cm. Spreading the composite fixing agent, uniformly stirring, and flattening to a thickness of 25-30 cm.
The compound fertilizer can adopt ammonium dihydrogen phosphate or urea, and is preferably prepared by mixing ammonium dihydrogen phosphate and urea according to the mass ratio of 1: 1-2.
The step of uniformly mixing the middle layer soil and the compound fertilizer is to spread the middle layer soil, then spread the compound fertilizer on the spread middle layer soil, and collect and stack the compound fertilizer after uniformly stirring. The thickness of the flattening is 20-30 cm.
Preferably, the amino acid is obtained by mixing glycine and arginine in a mass ratio of 1: 1.
The variety of the wheat is any one of Zheng wheat 379, Xinke wheat 168, Huai Chuan 919, xu wheat 168 and Bainong 207, and after the heavy metal polluted farmland restoration method and the low accumulation test screening, the accumulation amount of cadmium of the Zheng wheat 379 and the Xinke wheat 168 is minimum, so the variety of the wheat is preferably Zheng wheat 379 or the Xinke wheat 168. The seeding rate of wheat is 10-15 kg/mu, preferably 15 kg/mu.
Spraying the foliage blocking agent to the foliage of the crops 200-250 days after the crops are planted, namely continuously spraying the foliage blocking agent from 200 th to 250 th days every 2-5 days during the period of 200-250 days after the crops are planted. The time of each spraying is 9 am before, and preferably, the spraying time is between 8 am and 9 am. When the spraying agent is sprayed, the front side and the back side of the leaves of the crops are sprayed, so that more liquid drops are formed on the front side and the back side of the leaves.
When the leaf surface blocking agent is prepared, ethylenediamine tetraacetic acid and citric acid are added to react for 0.5-1h at 70-75 ℃, preferably for 0.5h at 70 ℃.
Examples
Example 1
The heavy metal polluted farmland restoration method comprises the following steps:
1) stripping surface soil of the polluted farmland to a stripping depth of 30cm, then flattening the stripped surface soil to a thickness of about 30cm, spreading a composite fixing agent on the surface of the flattened surface soil, uniformly stirring, flattening again to a thickness of about 30cm, standing for 2h, uniformly stirring again, and collecting and accumulating to serve as solidified soil for later use;
the mass ratio of the surface soil to the composite fixing agent is 20: 1;
the composite fixing agent is obtained by mixing and stirring humic acid, ground phosphate rock, biochar, clay and zeolite according to the mass ratio of 15:260:50:80: 30; wherein the phosphorus-containing (calculated by phosphorus pentoxide) mass fraction in the phosphorite powder is 28%, and the particle size is 100 meshes. The particle size of the biochar is 200 meshes, and the specific surface area is 850m2(ii) in terms of/g. The particle size of the clay is 100 meshes. The particle size of the zeolite was 12 mesh.
2) Digging downwards a cultivated land base (namely the surface formed after the surface soil is stripped) from which the surface soil is stripped in the step 1) to obtain middle soil, wherein the digging depth of the middle soil is about 25cm, then flattening the dug middle soil to the thickness of about 30cm, scattering compound fertilizer on the surface of the flattened surface soil, uniformly stirring, and then collecting and stacking the compound fertilizer to be used as planting soil for later use;
the mass ratio of the middle layer soil to the compound fertilizer is 5: 1;
the compound fertilizer is prepared by mixing ammonium dihydrogen phosphate and urea according to the mass ratio of 1: 1.
3) Backfilling the solidified soil in the step 1) to the surface of the cultivated land excavated in the step 2), and compacting by adopting mechanical rolling, wherein the compaction coefficient is 0.93 to form a solidified layer;
then, paving the planting soil obtained in the step 2) on the surface of the solidified layer, wherein the paving thickness is 30cm, and forming a planting layer;
4) sowing wheat on the planting layer in the step 3), wherein the variety of the wheat is Zheng wheat 379, and the sowing amount of the wheat is 15 kg/mu.
Example 2
The heavy metal polluted farmland restoration method comprises the following steps:
1) stripping surface soil of the polluted farmland to a stripping depth of 40cm, then flattening the stripped surface soil to a thickness of about 25cm, spreading a composite fixing agent on the surface of the flattened surface soil, uniformly stirring, standing for 5h, uniformly stirring again, and then collecting and stacking the soil to serve as solidified soil for later use;
the mass ratio of the surface soil to the composite fixing agent is 15: 1;
the composite fixing agent is obtained by mixing and stirring humic acid, ground phosphate rock, biochar, clay and zeolite in a mass ratio of 25:225:60:95: 50; wherein the phosphorus-containing (calculated by phosphorus pentoxide) mass fraction in the phosphorite powder is 28%, and the particle size is 100 meshes. The particle size of the biochar is 200 meshes, and the specific surface area is 850m2(ii) in terms of/g. The particle size of the clay is 100 meshes. The particle size of the zeolite was 12 mesh.
2) Digging downwards a cultivated land base (namely the surface formed after the surface soil is stripped) from which the surface soil is stripped in the step 1) to obtain middle soil, wherein the digging depth of the middle soil is about 40cm, then flattening the dug middle soil to the thickness of about 20cm, scattering compound fertilizer on the surface of the flattened surface soil, uniformly stirring, and then collecting and stacking the compound fertilizer to be used as planting soil for later use;
the mass ratio of the middle layer soil to the compound fertilizer is 8: 1;
the compound fertilizer is prepared by mixing ammonium dihydrogen phosphate and urea according to the mass ratio of 1: 1.
3) Backfilling the solidified soil obtained in the step 1) to the surface of the excavated farmland obtained in the step 2), and performing mechanical rolling compaction to obtain a solidified layer with the compaction degree of 0.98;
then, paving the planting soil obtained in the step 2) on the surface of the solidified layer, wherein the paving thickness is 40cm, and forming a planting layer;
4) sowing wheat on the planting layer in the step 3), wherein the wheat variety is Xinke wheat 168, and the sowing amount of the wheat is 15 kg/mu.
Example 3
The method for remediating the heavy metal polluted farmland of the embodiment is different from the method of the embodiment 2 in that in the step 1), the phosphorus-containing (calculated by phosphorus pentoxide) powder contains 30% of phosphorus by mass and has a particle size of 100 meshes; the particle size of the biochar is 400 meshes, and the specific surface area is 1000m2(ii) in terms of/g. The particle size of the clay is 200 meshes. The particle size of the zeolite was 80 mesh.
The others are the same as in example 2.
Example 4
The method for restoring the heavy metal polluted farmland is different from the method in the embodiment 3 in that the compound fertilizer is prepared by mixing ammonium dihydrogen phosphate and urea according to the mass ratio of 1: 2.
The others are the same as in example 3.
Example 5
The method for repairing the heavy metal polluted farmland of the embodiment is different from the embodiment 4 in that after wheat is planted in the step 4), the leaf surface blocking agent is sprayed to the leaf surfaces of the wheat in the growth period of the wheat, the agent is sprayed once every 3 days, the spraying time is 8-9 am each time, the spraying amount is 100kg per mu, and the agent is sprayed to the front and back surfaces of the leaf surfaces during specific operation, so that the front and back surfaces of the leaf surfaces are preferably fully stained with liquid drops.
The foliage blocking agent is prepared from calcium chloride, magnesium nitrate, boric acid, ferrous sulfate, ethylene diamine tetraacetic acid, citric acid, monopotassium phosphate, potassium humate, amino acid, sodium stearate and water in a mass ratio of 15:8:0.5:20:20:25:80:30:25:20: 2000; the amino acid is glutamic acid.
The preparation method of the leaf surface blocking agent comprises the following steps: adding calcium chloride, magnesium nitrate, boric acid and ferrous sulfate into water, uniformly mixing, then adding ethylene diamine tetraacetic acid and citric acid, carrying out chelation reaction for 0.5h at 70 ℃, then adding monopotassium phosphate, potassium humate, amino acid and sodium stearate, and uniformly mixing to obtain the leaf surface blocking agent.
The others are the same as in example 4.
Example 6
The method for repairing the heavy metal polluted farmland of the embodiment is different from the embodiment 5 in that the leaf surface blocking agent is prepared from calcium chloride, magnesium nitrate, boric acid, ferrous sulfate, ethylenediamine tetraacetic acid, citric acid, potassium dihydrogen phosphate, potassium humate, amino acid, sodium stearate and water in a mass ratio of 10:5:0.8:30:25:30:100:40:30:40: 2000; the amino acid is obtained by mixing glycine and arginine in a mass ratio of 1: 1.
The others are the same as in example 5.
Example 7
The method for repairing the heavy metal polluted farmland of the embodiment is different from the embodiment 5 in that the leaf surface blocking agent is prepared from calcium chloride, magnesium nitrate, boric acid, ferrous sulfate, zinc oxide, copper sulfate, ethylenediamine tetraacetic acid, citric acid, potassium dihydrogen phosphate, potassium humate, amino acid, sodium stearate and water in a mass ratio of 10:5:0.8:30:4:12:25:30:100:40:30:40: 2000; the amino acid is obtained by mixing glycine and arginine in a mass ratio of 1: 1.
The preparation method of the leaf surface blocking agent comprises the following steps: adding calcium chloride, magnesium nitrate, boric acid, ferrous sulfate, zinc oxide and copper sulfate into water, mixing uniformly, adding ethylenediamine tetraacetic acid and citric acid, mixing uniformly, adding potassium dihydrogen phosphate, potassium humate, amino acid and sodium stearate, and mixing uniformly to obtain the product.
The others are the same as in example 5.
Example 8
The method for repairing the heavy metal polluted farmland of the embodiment is different from the embodiment 7 in that the raw materials for preparing the leaf surface blocking agent further comprise potassium silicate and sodium selenite, and the mass ratio of the potassium silicate to the sodium selenite to the calcium chloride is 3:0.8: 10. The leaf surface blocking agent is prepared by adding potassium silicate, sodium selenite and calcium chloride simultaneously.
The others are the same as in example 7.
Comparative example
Comparative example 1
The method for repairing the heavy metal polluted farmland of the comparative example is different from the method of the example 1 in that the composite fixing agent in the step 1) is obtained by mixing humic acid and ground phosphate rock in a mass ratio of 15: 260.
The others are the same as in example 1.
Comparative example 2
The method for repairing the heavy metal polluted farmland of the comparative example is different from the method of the embodiment 1 in that the compaction is not carried out after the solidified soil is backfilled in the step 3).
The others are the same as in example 1.
Performance test
The heavy metal content detection is carried out on the planting soil after the heavy metal contaminated farmland is repaired by the heavy metal contaminated farmland repairing method (small-range local repair) in the examples 1 to 8 and the comparative examples 1 to 2 and the wheat harvested in the first year, and the detection results are shown in the table 1.
TABLE 1 comparison of heavy metal contaminated cultivated land remediation methods in examples 1 to 8 and comparative examples 1 to 2
As can be seen from example 1, comparative example 1 and table 1, the composite fixative of the present application can reduce the content of heavy metal elements in soil as compared to comparative example 1, but has a limited effect on the content of heavy metals in agricultural products of crops.
According to the example 1, the comparative example 2 and the table 1, compared with the comparative example 2, the application has the advantages that the grinding of the solidified soil has less influence on the content of heavy metal elements in the planting soil, but the heavy metal content in agricultural products can be greatly reduced.
In conclusion, the method for repairing the polluted cultivated land by adopting the mode of soil turning and replacement can greatly reduce the content of heavy metals in the planting soil, further reduce the content of heavy metals in crops, greatly reduce the repair period and have no influence on the normal planting of the crops.
Claims (6)
1. The heavy metal polluted farmland restoration method is characterized by comprising the following steps:
1) stripping surface soil of the polluted farmland, and then uniformly mixing the stripped surface soil with a composite fixing agent to obtain solidified soil;
the composite fixing agent is prepared from the following raw materials in parts by weight: 15-25 parts of humic acid, 260 parts of powdered rock phosphate, 50-60 parts of biochar, 80-100 parts of clay and 30-50 parts of zeolite;
2) digging downwards the cultivated land with the surface soil stripped in the step 1) to obtain middle-layer soil, and then uniformly mixing the dug middle-layer soil with a compound fertilizer to obtain planting soil;
3) backfilling the solidified soil obtained in the step 1) to the surface of the excavated farmland in the step 2) to form a solidified layer, and backfilling the planting soil obtained in the step 2) to the solidified layer to form a planting layer;
4) planting crops on the planting layer formed in the step 3);
in the step 1), the mass ratio of the surface soil to the composite fixing agent is 15-20: 1;
backfilling the solidified soil in the step 3), and then rolling to form a solidified layer, wherein the compaction coefficient of rolling is 0.93-0.98;
spraying a leaf surface blocking agent to the leaf surfaces of the crops 200-250 days after the crops are planted in the step 4), wherein the leaf surface blocking agent is sprayed once every 2-5 days, and the spraying amount is 120 kg/mu each time;
the leaf surface blocking agent is prepared from the following raw materials in parts by weight: 10-15 parts of calcium chloride, 5-8 parts of magnesium nitrate, 0.5-0.8 part of boric acid, 20-30 parts of ferrous sulfate, 20-25 parts of ethylene diamine tetraacetic acid, 25-30 parts of citric acid, 80-100 parts of monopotassium phosphate, 30-40 parts of potassium humate, 25-30 parts of amino acid, 20-40 parts of sodium stearate and 2000 parts of water.
2. The heavy metal contaminated cultivated land restoration method according to claim 1, wherein the depth of the peeling of topsoil in step 1) is 25-40 cm; the excavation depth of the middle layer soil in the step 2) is 25-40 cm.
3. The heavy metal contaminated cultivated land restoration method according to claim 1, wherein the mass ratio of the subsoil to the compound fertilizer in step 2) is 5-8: 1.
4. The heavy metal contaminated cultivated land restoration method according to any one of claims 1 to 3, wherein the crop planted in step 4) is wheat, and the variety of wheat is any one of Zheng wheat 379, Xinke wheat 168, Huai Chuan 919, xu Ke 168, Bai nong 207.
5. The heavy metal contaminated arable land restoration method according to claim 4, wherein the foliar blocking agent is prepared by a method comprising the steps of: adding calcium chloride, magnesium nitrate, boric acid and ferrous sulfate into water, mixing, adding ethylenediamine tetraacetic acid and citric acid, reacting at 70-75 deg.C for 0.5-1h, adding potassium dihydrogen phosphate, potassium humate, amino acid and sodium stearate, and mixing.
6. The method for remediating heavy metal contaminated arable land as claimed in claim 4, wherein the raw materials for preparing the leaf surface blocking agent further comprise zinc oxide and copper sulfate, and the mass ratio of the zinc oxide to the copper sulfate to the calcium chloride is 3-5:10-12: 10-15.
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