CN110934047A - Method for restoring heavy metal pollution of paddy field by using waste straws - Google Patents
Method for restoring heavy metal pollution of paddy field by using waste straws Download PDFInfo
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- A—HUMAN NECESSITIES
- A01—AGRICULTURE; FORESTRY; ANIMAL HUSBANDRY; HUNTING; TRAPPING; FISHING
- A01G—HORTICULTURE; CULTIVATION OF VEGETABLES, FLOWERS, RICE, FRUIT, VINES, HOPS OR SEAWEED; FORESTRY; WATERING
- A01G22/00—Cultivation of specific crops or plants not otherwise provided for
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- A—HUMAN NECESSITIES
- A01—AGRICULTURE; FORESTRY; ANIMAL HUSBANDRY; HUNTING; TRAPPING; FISHING
- A01B—SOIL WORKING IN AGRICULTURE OR FORESTRY; PARTS, DETAILS, OR ACCESSORIES OF AGRICULTURAL MACHINES OR IMPLEMENTS, IN GENERAL
- A01B79/00—Methods for working soil
- A01B79/02—Methods for working soil combined with other agricultural processing, e.g. fertilising, planting
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
- B09C—RECLAMATION OF CONTAMINATED SOIL
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- B09C1/08—Reclamation of contaminated soil chemically
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Abstract
The invention discloses a method for restoring heavy metal pollution of a paddy field by using waste straws, which comprises the following steps: airing crop wastes containing straws, crushing, soaking in a phosphoric acid solution, filtering, drying to constant weight, carbonizing under the protection of nitrogen, and naturally cooling to room temperature to obtain pretreated straws a; grinding the pretreated straws and clay, sieving, stirring in a phosphoric acid solution, filtering, washing and drying to obtain pretreated straws b; under the protection of nitrogen, uniformly stirring the pretreated straw b, the organic silicon betaine surfactant and water, adding a ferrous sulfate solution, continuously stirring, dropwise adding a sodium phosphate solution under the stirring state, continuously stirring, filtering, washing, adding a water-soluble adhesive, stirring, granulating, roasting and cooling to obtain a composite treating agent; before the rice is planted, the soil is deeply loosened and prepared, then the composite treating agent is spread on the surface of the soil, then rotary tillage is carried out, and then the rice is planted.
Description
Technical Field
The invention relates to the technical field of heavy metal pollution remediation, in particular to a method for remediating heavy metal pollution in a paddy field by using waste straws.
Background
With the rapid development of the industrialization and urbanization process of China in recent decades, the problem of heavy metal pollution of farmland soil is increasingly prominent. The investigation result of the soil pollution condition in China shows that the soil is polluted by metals in different degrees in 20183.8X 10 of land7hm2The heavy metal pollution not only affects the rice yield, but also is easy to enrich in rice, seriously affects the sanitary quality and the nutritional quality of the rice, and causes serious potential threat to the human health after being eaten by people. The soil environment total ratio of China is poor, the soil pollution is severe in partial areas, and the first pollutant of the China soil is cadmium. In recent years, with the rapid development of society, heavy metal pollution, especially cadmium pollution, is becoming serious in the rice planting process, and becomes an environmental problem to be solved urgently.
The heavy metal pollution of the paddy field soil not only has toxic action on the paddy rice and reduces the yield and the quality of the paddy rice, but also can be absorbed by the human body in a soil-crop-food migration mode to further harm the health of the human body, so the heavy metal pollution of the paddy field soil is hardly treated.
Disclosure of Invention
Based on the technical problems in the background art, the invention provides a method for restoring heavy metal pollution of a paddy field by using waste straws, which is simple and convenient to operate and low in cost, realizes resource utilization of rural wastes, can realize the effect of restoring while producing by planting rice in heavy metal polluted soil, and can improve the soil fertility.
A method for restoring heavy metal pollution of paddy fields by using waste straws comprises the following steps:
s1, airing and crushing crop wastes containing straws, soaking the wastes in 15-22 wt% phosphoric acid solution at 60-80 ℃ for 20-40h, filtering, drying to constant weight, carbonizing under the protection of nitrogen, heating to 400 ℃ at the speed of 2-4 ℃/min, preserving heat for 10-15min, continuing heating to 650 ℃ at the speed of 14-18 ℃/min, preserving heat for 30-40min, continuing heating to 740 ℃ at the speed of 4-6 ℃/min, preserving heat for 10-15min, and naturally cooling to room temperature to obtain pretreated straws a;
s2, grinding the pretreated straws and the clay, sieving, stirring in a phosphoric acid solution with the concentration of 15-22 wt%, stirring at the temperature of 300 ℃ and 400 ℃, filtering, washing and drying to obtain pretreated straws b;
s3, under the protection of nitrogen, uniformly stirring the pretreated straw b, the organic silicon betaine surfactant and water, adding a ferrous sulfate solution with the concentration of 4-4.6g/L, continuously stirring, dropwise adding a sodium phosphate solution with the concentration of 4.5-5g/L under the stirring state, continuously stirring, filtering, washing, adding a water-soluble adhesive, stirring, granulating, roasting at 200-50 ℃ for 1-2h, and cooling to obtain a composite treating agent;
s4, before planting the rice, performing deep loosening and soil preparation on the soil, then spreading the compound treating agent on the surface of the soil, then performing rotary tillage, and then planting the rice.
Preferably, in S1, the powder is pulverized to a particle size of 10-16 mm.
Preferably, in S1, the crop waste containing straw comprises: at least one of bagasse, coconut shell, rice hull and wheat shell, rice straw and wheat straw.
Preferably, in S2, the weight ratio of the pretreated straws to the clay is 10: 1-4.
Preferably, in S2, the clay is at least one of bentonite, attapulgite clay and kaolin.
Preferably, in S2, the grinding time is 6-10min, the grinding speed is 10000-12000r/min, the grinding pressure is 0.12-0.18MPa, and the ground material is sieved by a sieve with 80-120 meshes.
Preferably, in S2, the pore volume of the pretreated straws b is 0.4-0.48cm3/g。
Preferably, in S3, the mass ratio of the pretreated straw b to the organic silicon betaine surfactant to the ferrous sulfate solution to the sodium phosphate solution to the water-soluble adhesive is 50-100: 1-5: 30-40: 30-40: 1-4.
Preferably, in S3, the water-soluble adhesive is at least one of carboxymethyl cellulose, urea-formaldehyde resin, and polyvinyl formal.
Preferably, in S3, the particle size of the obtained composite treating agent is 5-10mm, the water content is less than or equal to 5%, and the powder falling rate is less than or equal to 1%.
Preferably, in S3, the water-soluble adhesive is at least one of carboxymethyl cellulose, urea-formaldehyde resin, and polyvinyl formal.
Preferably, in S4, the compound treating agent is applied in an amount of 90-110 kg/mu.
Preferably, in S4, the rotary tillage depth is 18-22 cm.
The invention has the following technical effects:
(1) the method realizes resource utilization of rural wastes, can improve the physical and chemical properties of the soil, adjust the pH value of the soil, improve the soil fertility, promote the growth and the fructification of rice, and realize the effects of planting the rice in the heavy metal polluted soil and repairing the rice while producing after adsorbing the soil containing heavy metal ions.
(2) The invention adopts crop wastes containing straws as main raw materials, can form a multistage pore structure by compounding with clay, then is combined with ferrous phosphate, and the ferrous phosphate is fully grafted in the multistage pore and on the surface, so that the surface of the obtained composite treating agent contains negative charges and rich oxygen-containing functional groups, can firmly adsorb metal cations, has little ferrous ion precipitation, can avoid secondary pollution, simultaneously has high organic matter content, and the rich multistage pore structure is beneficial to keeping the nutrition and the moisture in a paddy field and increasing the yield of the paddy.
(3) The invention is verified by tests that in the remediation test of the polluted soil, the invention has excellent adsorption effect on various heavy metal ions, especially the adsorption efficiency on cadmium and arsenic is extremely high, the invention controls the addition amount of ferrous sulfate and sodium phosphate, and granulates and roasts under the coordination of water-soluble adhesive, the obtained adsorption material is equivalent to at least 2 times of the adsorption capacity of the unbelled and roasted material on cadmium, and the reduction degree of the effective cadmium content in the soil can reach 80%.
Detailed Description
The technical solution of the present invention will be described in detail below with reference to specific examples.
Example 1
A method for restoring heavy metal pollution of paddy fields by using waste straws comprises the following steps:
s1, drying 50kg of rice straw, 20kg of wheat straw and 30kg of bagasse in the air, feeding the materials into a pulverizer to pulverize the materials to a particle size of 10mm, soaking the materials in a 22 wt% phosphoric acid solution for 20 hours at a soaking temperature of 80 ℃, filtering the materials, feeding the materials into an oven to dry the materials to a constant weight at a temperature of 60 ℃, feeding the materials into a carbonization furnace, heating the materials to 200 ℃ at a speed of 4 ℃/min under the protection of nitrogen, keeping the temperature for 15min, continuously heating the materials to 650 ℃ at a speed of 14 ℃/min, keeping the temperature for 30min, continuously heating the materials to 700 ℃ at a speed of 6 ℃/min, keeping the temperature for 15min, and naturally cooling the materials to room temperature to obtain pretreated straw a;
s2, feeding 100kg of pretreated straw and 4kg of bentonite into a grinding mill, grinding for 6min at a grinding speed of 10000r/min and a grinding pressure of 0.18MPa, sieving with an 80-mesh sieve, stirring in a 22 wt% phosphoric acid solution at a stirring temperature of 400 ℃ and a stirring speed of 200r/min for 20min, filtering, washing and drying to obtain a product with a pore volume of 0.40cm3Per g of pretreated straw b;
s3, under the protection of nitrogen, uniformly stirring 50kg of pretreated straw b, 5kg of organic silicon betaine surfactant and 200kg of water, adding 40kg of ferrous sulfate solution with the concentration of 4g/L, continuously stirring for 20min, dropwise adding 30kg of sodium phosphate solution with the concentration of 5g/L under the stirring state, continuously stirring for 10min, filtering, washing, adding 4kg of polyvinyl formal, stirring for 5min at the stirring temperature of 50 ℃, then sending into a rotary automatic ball forming machine, granulating and forming, roasting for 2h at the temperature of 200 ℃, and cooling to obtain a composite treating agent;
the obtained composite treating agent has a particle size of 5mm, a water content of 3.9% and a powder falling rate of 0.93%;
s4, before planting rice, performing deep loosening and soil preparation on the soil, then spreading the compound treatment agent on the soil surface according to 110 kg/mu, performing rotary tillage with the rotary tillage depth of 18cm, and then planting the rice.
Example 2
A method for restoring heavy metal pollution of paddy fields by using waste straws comprises the following steps:
s1, drying 30kg of rice straws, 40kg of wheat straws, 15kg of rice hulls and 15kg of wheat hulls in the air, crushing the materials in a crusher until the particle size is 16mm, soaking the materials in a 15 wt% phosphoric acid solution for 40h at the soaking temperature of 60 ℃, filtering, drying the materials in an oven at the temperature of 70 ℃ until the weight is constant, sending the materials into a carbonization furnace, heating to 400 ℃ at the speed of 2 ℃/min under the protection of nitrogen, keeping the temperature for 10min, continuing heating to 600 ℃ at the speed of 18 ℃/min, keeping the temperature for 40min, continuing heating to 740 ℃ at the speed of 4 ℃/min, keeping the temperature for 10min, and naturally cooling to room temperature to obtain pretreated straws a;
s2, feeding 100kg of pretreated straw, 5kg of bentonite and 5kg of kaolin into a grinding mill, grinding for 10min at the grinding speed of 12000r/min and the grinding pressure of 0.12MPa, sieving by a 120-mesh sieve, stirring for 30min in a phosphoric acid solution with the concentration of 15 wt%, the stirring temperature being 300 ℃, the stirring speed being 400r/min, filtering, washing and drying to obtain the product with the pore volume of 0.42cm3Per g of pretreated straw b;
s3, under the protection of nitrogen, uniformly stirring 100kg of pretreated straw b, 1kg of organic silicon betaine surfactant and 300kg of water, adding 30kg of ferrous sulfate solution with the concentration of 4.6g/L, continuously stirring for 10min, dropwise adding 40kg of sodium phosphate solution with the concentration of 4.5g/L under the stirring state, continuously stirring for 20min, filtering, washing, adding 1kg of carboxymethyl cellulose, stirring for 12min at the stirring temperature of 40 ℃, then sending into a rotary automatic ball forming machine for granulation molding, roasting for 1h at the temperature of 240 ℃, and cooling to obtain a composite treating agent;
the particle size of the obtained composite treating agent is 10mm, the water content is 4.9 percent, and the powder falling rate is 0.80 percent;
s4, before planting rice, performing deep loosening and soil preparation on the soil, then spreading the compound treatment agent on the soil surface according to 90 kg/mu, performing rotary tillage with the rotary tillage depth of 22cm, and then planting the rice.
Example 3
A method for restoring heavy metal pollution of paddy fields by using waste straws comprises the following steps:
s1, drying 50kg of rice straw, 30kg of wheat straw and 20kg of coconut shell, crushing the materials in a crusher until the particle size is 12mm, soaking the materials in a 22 wt% phosphoric acid solution for 25 hours at a soaking temperature of 75 ℃, filtering, drying the materials in an oven at a temperature of 63 ℃ to constant weight, sending the materials into a carbonization furnace, heating to 250 ℃ at a speed of 3.5 ℃/min under the protection of nitrogen, keeping the temperature for 14min, continuously heating to 640 ℃ at a speed of 15 ℃/min, keeping the temperature for 33min, continuously heating to 710 ℃ at a speed of 5.5 ℃/min, keeping the temperature for 14min, and naturally cooling to room temperature to obtain pretreated straw a;
s2, feeding 100kg of pretreated straw, 15kg of attapulgite clay and 5kg of kaolin into a grinding mill, grinding for 9min at the grinding speed of 10500r/min and the grinding pressure of 0.16MPa, sieving with a 90-mesh sieve, stirring for 22min in a 20 wt% phosphoric acid solution at the stirring temperature of 370 ℃ and the stirring speed of 250r/min, filtering, washing and drying to obtain the product with the pore volume of 0.43cm3Per g of pretreated straw b;
s3, under the protection of nitrogen, uniformly stirring 80kg of pretreated straw b, 2kg of organic silicon betaine surfactant and 280kg of water, adding 33kg of ferrous sulfate solution with the concentration of 4.4g/L, continuously stirring for 12min, dropwise adding 37kg of sodium phosphate solution with the concentration of 4.6g/L under the stirring state, continuously stirring for 16min, filtering, washing, adding 1kg of carboxymethyl cellulose and 1kg of polyvinyl formal, stirring for 10min at the temperature of 42 ℃, then sending into a rotary automatic granulator, granulating, molding, roasting for 1.2h at the temperature of 230 ℃, and cooling to obtain a composite treating agent;
the particle size of the obtained composite treating agent is 8mm, the water content is 4.6%, and the powder falling rate is 0.84%;
s4, before planting rice, performing deep loosening and soil preparation on the soil, then spreading the compound treating agent on the soil surface according to a ratio of 95 kg/mu, performing rotary tillage with a rotary tillage depth of 21cm, and then planting the rice.
Example 4
A method for restoring heavy metal pollution of paddy fields by using waste straws comprises the following steps:
s1, drying 35kg of rice straw, 45kg of wheat straw, 15kg of bagasse and 5kg of wheat husk, conveying the materials into a pulverizer to pulverize the materials to a particle size of 14mm, soaking the materials in a 15 wt% phosphoric acid solution for 35 hours at a soaking temperature of 65 ℃, filtering the materials, conveying the materials into a drying oven to dry the materials at a temperature of 67 ℃ to a constant weight, conveying the materials into a carbonization furnace, heating the materials to 350 ℃ at a speed of 2.5 ℃/min under the protection of nitrogen, keeping the temperature for 12min, continuously heating the materials to 620 ℃ at a speed of 17 ℃/min, keeping the temperature for 37min, continuously heating the materials to 730 ℃ at a speed of 4.5 ℃/min, keeping the temperature for 12min, and naturally cooling the materials to room temperature to obtain pretreated straw a;
s2, feeding 100kg of pretreated straw, 5kg of bentonite, 5kg of attapulgite clay and 5kg of kaolin into a grinding mill, grinding for 7min at the grinding speed of 11500r/min and the grinding pressure of 0.14MPa, sieving by a 110-mesh sieve, stirring for 28min in 18 wt% phosphoric acid solution at the stirring temperature of 330 ℃ and the stirring speed of 350r/min, filtering, washing and drying to obtain the product with the pore volume of 0.45cm3Per g of pretreated straw b;
s3, under the protection of nitrogen, uniformly stirring 60kg of pretreated straw b, 4kg of organic silicon betaine surfactant and 220kg of water, adding 37kg of ferrous sulfate solution with the concentration of 4.2g/L, continuously stirring for 18min, dropwise adding 33kg of sodium phosphate solution with the concentration of 4.8g/L under the stirring state, continuously stirring for 14min, filtering, washing, adding 1kg of carboxymethyl cellulose, 1kg of urea-formaldehyde resin and 1kg of polyvinyl formal, stirring for 6min at the temperature of 48 ℃, then sending into a rotary automatic granulator, granulating and molding, roasting for 1.8h at the temperature of 210 ℃, and cooling to obtain a composite treating agent;
the particle size of the obtained composite treating agent is 6mm, the water content is 4.2 percent, and the powder falling rate is 0.89 percent;
s4, before planting rice, performing deep loosening and soil preparation on the soil, then spreading the compound treating agent on the surface of the soil according to 105 kg/mu, performing rotary tillage with the rotary tillage depth of 19cm, and then planting the rice.
Example 5
A method for restoring heavy metal pollution of paddy fields by using waste straws comprises the following steps:
s1, drying 40kg of rice straws, 40kg of wheat straws, 10kg of rice hulls and 10kg of wheat hulls in the air, crushing the materials in a crusher until the particle size is 13mm, soaking the materials in a phosphoric acid solution with the concentration of 18 wt% for 30h at the soaking temperature of 70 ℃, filtering, drying the materials in an oven at the temperature of 65 ℃ until the weight is constant, sending the materials into a carbonization furnace, heating the materials to 300 ℃ at the speed of 3 ℃/min under the protection of nitrogen, keeping the temperature for 13min, continuously heating the materials to 630 ℃ at the speed of 16 ℃/min, keeping the temperature for 35min, continuously heating the materials to 720 ℃ at the speed of 5 ℃/min, keeping the temperature for 13min, and naturally cooling the materials to the room temperature to obtain pretreated straws a;
s2, feeding 100kg of pretreated straw, 10kg of bentonite, 5kg of attapulgite clay and 10kg of kaolin into a grinding mill, grinding for 8min at a grinding speed of 11000r/min and a grinding pressure of 0.15MPa, sieving with a 100-mesh sieve, stirring for 25min in a phosphoric acid solution with the concentration of 19 wt%, stirring at a temperature of 350 ℃ and a stirring speed of 300r/min, filtering, washing and drying to obtain a product with the pore volume of 0.48cm3Per g of pretreated straw b;
s3, under the protection of nitrogen, uniformly stirring 70kg of pretreated straw b, 3kg of organic silicon betaine surfactant and 250kg of water, adding 35kg of ferrous sulfate solution with the concentration of 4.3g/L, continuously stirring for 15min, dropwise adding 35kg of sodium phosphate solution with the concentration of 4.7g/L under the stirring state, continuously stirring for 15min, filtering, washing, adding 1.5kg of carboxymethyl cellulose and 1kg of polyvinyl formal, stirring for 8min at the stirring temperature of 45 ℃, then sending into a rotary automatic ball forming machine for granulation and molding, roasting for 1.5h at the temperature of 220 ℃, and cooling to obtain a composite treating agent;
the particle size of the obtained composite treating agent is 7mm, the water content is 4.4 percent, and the powder falling rate is 0.86 percent;
s4, before planting rice, performing deep loosening and soil preparation on the soil, then spreading the compound treatment agent on the soil surface according to 100 kg/mu, performing rotary tillage with the rotary tillage depth of 20cm, covering a film, standing for 1 month, and then planting the rice.
Comparative example 1
A method for remedying heavy metal pollution by waste straws comprises the following steps:
s1, drying 40kg of rice straws, 40kg of wheat straws, 10kg of rice hulls and 10kg of wheat hulls in the air, crushing the materials in a crusher until the particle size is 13mm, soaking the materials in a phosphoric acid solution with the concentration of 18 wt% for 30 hours at the soaking temperature of 70 ℃, filtering, drying the materials in an oven at the temperature of 65 ℃ to constant weight, sending the materials into a carbonization furnace, heating the materials to 720 ℃ under the protection of nitrogen, preserving the heat for 13min, and naturally cooling the materials to room temperature to obtain pretreated straws a;
S2、feeding 100kg of pretreated straw, 10kg of bentonite, 5kg of attapulgite clay and 10kg of kaolin into a grinding mill, grinding for 8min at a grinding speed of 11000r/min and a grinding pressure of 0.15MPa, sieving with a 100-mesh sieve, stirring for 25min in a phosphoric acid solution with the concentration of 19 wt%, wherein the stirring temperature is 350 ℃ and the stirring speed is 300r/min, filtering, washing and drying to obtain the product with the pore volume of 0.48cm3Per g of pretreated straw b;
s3, under the protection of nitrogen, uniformly stirring 70kg of pretreated straw b, 3kg of organic silicon betaine surfactant and 250kg of water, adding 35kg of ferrous sulfate solution with the concentration of 4.3g/L, continuously stirring for 15min, dropwise adding 35kg of sodium phosphate solution with the concentration of 4.7g/L under the stirring state, continuously stirring for 15min, filtering, washing, adding 1.5kg of carboxymethyl cellulose and 1kg of polyvinyl formal, stirring for 8min at the stirring temperature of 45 ℃, then sending into a rotary automatic ball forming machine for granulation and molding, roasting for 1.5h at the temperature of 220 ℃, and cooling to obtain a composite treating agent;
s4, before planting rice, performing deep loosening and soil preparation on the soil, then spreading the compound treatment agent on the soil surface according to 100 kg/mu, performing rotary tillage with the rotary tillage depth of 20cm, covering a film, standing for 1 month, and then planting the rice.
Comparative example 2
A method for remedying heavy metal pollution by waste straws comprises the following steps:
s1, drying 40kg of rice straws, 40kg of wheat straws, 10kg of rice hulls and 10kg of wheat hulls in the air, crushing the materials in a crusher until the particle size is 13mm, soaking the materials in a phosphoric acid solution with the concentration of 18 wt% for 30h at the soaking temperature of 70 ℃, filtering, drying the materials in an oven at the temperature of 65 ℃ until the weight is constant, sending the materials into a carbonization furnace, heating the materials to 300 ℃ at the speed of 3 ℃/min under the protection of nitrogen, keeping the temperature for 13min, continuously heating the materials to 630 ℃ at the speed of 16 ℃/min, keeping the temperature for 35min, continuously heating the materials to 720 ℃ at the speed of 5 ℃/min, keeping the temperature for 13min, and naturally cooling the materials to the room temperature to obtain pretreated straws a;
s2, feeding 100kg of pretreated straws into a grinding mill, grinding for 8min at the grinding speed of 11000r/min and the grinding pressure of 0.15MPa, sieving with a 100-mesh sieve, stirring for 25min in a phosphoric acid solution with the concentration of 19 wt%, wherein the stirring temperature is 350 ℃, and the stirring speed is300r/min, filtering, washing and drying to obtain the porous material with the pore volume of 0.48cm3Per g of pretreated straw b;
s3, under the protection of nitrogen, uniformly stirring 70kg of pretreated straw b, 3kg of organic silicon betaine surfactant and 250kg of water, adding 35kg of ferrous sulfate solution with the concentration of 4.3g/L, continuously stirring for 15min, dropwise adding 35kg of sodium phosphate solution with the concentration of 4.7g/L under the stirring state, continuously stirring for 15min, filtering, washing, adding 1.5kg of carboxymethyl cellulose and 1kg of polyvinyl formal, stirring for 8min at the stirring temperature of 45 ℃, then sending into a rotary automatic ball forming machine for granulation and molding, roasting for 1.5h at the temperature of 220 ℃, and cooling to obtain a composite treating agent;
s4, before planting rice, performing deep loosening and soil preparation on the soil, then spreading the compound treatment agent on the soil surface according to 100 kg/mu, performing rotary tillage with the rotary tillage depth of 20cm, covering a film, standing for 1 month, and then planting the rice.
Comparative example 3
A method for remedying heavy metal pollution by waste straws comprises the following steps:
s1, drying 40kg of rice straws, 40kg of wheat straws, 10kg of rice hulls and 10kg of wheat hulls in the air, crushing the materials in a crusher until the particle size is 13mm, soaking the materials in a phosphoric acid solution with the concentration of 18 wt% for 30h at the soaking temperature of 70 ℃, filtering, drying the materials in an oven at the temperature of 65 ℃ until the weight is constant, sending the materials into a carbonization furnace, heating the materials to 300 ℃ at the speed of 3 ℃/min under the protection of nitrogen, keeping the temperature for 13min, continuously heating the materials to 630 ℃ at the speed of 16 ℃/min, keeping the temperature for 35min, continuously heating the materials to 720 ℃ at the speed of 5 ℃/min, keeping the temperature for 13min, and naturally cooling the materials to the room temperature to obtain pretreated straws a;
s2, feeding 100kg of pretreated straw, 10kg of bentonite, 5kg of attapulgite clay and 10kg of kaolin into a grinding mill, grinding for 8min at a grinding speed of 11000r/min and a grinding pressure of 0.15MPa, sieving with a 100-mesh sieve, stirring for 25min in a phosphoric acid solution with the concentration of 19 wt%, stirring at a temperature of 350 ℃ and a stirring speed of 300r/min, filtering, washing and drying to obtain a product with the pore volume of 0.48cm3Per g of pretreated straw b;
s3, under the protection of nitrogen, uniformly stirring 70kg of pretreated straw b, 3kg of organic silicon betaine surfactant and 250kg of water, adding 35kg of ferrous sulfate solution with the concentration of 4.3g/L, continuously stirring for 15min, dropwise adding 35kg of sodium phosphate solution with the concentration of 4.7g/L under the stirring state, continuously stirring for 15min, filtering, and washing to obtain a composite treating agent;
s4, before planting rice, performing deep loosening and soil preparation on the soil, then spreading the compound treatment agent on the soil surface according to 100 kg/mu, performing rotary tillage with the rotary tillage depth of 20cm, covering a film, standing for 1 month, and then planting the rice.
Selecting a cadmium-resistant hybrid japonica rice variety-Chunyou84 as a test crop; the pot culture is adopted for testing, a porcelain culture pot of 20cm multiplied by 50cm is selected, and 10kg of air-dried rice soil passing through a 5-mesh screen is filled in the porcelain culture pot; cadmium stress treatment is carried out on the experimental group soil before soil loading (1kg of soil is added with a cadmium chloride solution equivalent to 1mg of cadmium and is uniformly mixed), and cadmium is not added into the blank control group;
the composite treating agent obtained in example 5 and comparative examples 1 to 3 is applied to soil along with the NPK compound fertilizer, wherein the application amount of the composite treating agent is 0.416g/kg, the application amount of nitrogen element is 0.15g/kg, the application amount of phosphorus pentoxide is 0.1g/kg, the application amount of potassium oxide is 0.15g/kg, and after being uniformly mixed, a film is covered and kept still;
each group is provided with 10 repetitions, 50 basins in total and arranged in random blocks; inserting 3 stumps into each pot, and managing 3 plants in each stump according to a conventional method; after the rice is ripe, harvesting, drying in the sun, threshing, and simultaneously testing the yield according to the harvest of the pot.
And (3) treating the cadmium stress treatment soil (namely applying each group of compound treatment agent and base fertilizer) in 5-month and 13-day, sowing in 5-month and 20-day days, transplanting in 6-month and 14-day days, and harvesting in 10-month and 9-day days.
The results for each group were as follows:
the harvested rice and soil were detected and analyzed, and the results were as follows:
| group of | Content of cadmium in rice in mg/kg | Cadmium content in soil, mg/kg | pH value of soil |
| Example 5 | 0.12 | 0.208 | 6.8 |
| Comparative example 1 | 0.20 | 0.316 | 6.7 |
| Comparative example 2 | 0.24 | 0.702 | 6.8 |
| Comparative example 3 | 0.22 | 0.746 | 7.0 |
| Blank control group | 0.08 | 0.010 | 6.3 |
From the above results, it can be seen that: by adopting the method to repair the paddy field polluted by heavy metals, the heavy metals (especially cadmium) are firmly adsorbed, the reduction degree of the effective cadmium content in the soil can reach 80 percent, the repairing effect is obvious, and the soil heavy metal index meets the requirement of GB 15618 plus 2018 soil environment quality agricultural land soil pollution risk control standard; and the pH value of the soil can be adjusted, the soil fertility is improved, the growth and fructification of the rice are promoted as much as possible, and the content of heavy metals in the obtained paddy meets the requirement of the pollutant limit in GB 2762-2017 national standard food for food safety.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and the inventive concepts thereof according to the present invention should be equivalent or changed within the scope of the present invention.
Claims (10)
1. A method for restoring heavy metal pollution of paddy fields by using waste straws is characterized by comprising the following steps:
s1, airing and crushing crop wastes containing straws, soaking the wastes in 15-22 wt% phosphoric acid solution at 60-80 ℃ for 20-40h, filtering, drying to constant weight, carbonizing under the protection of nitrogen, heating to 400 ℃ at the speed of 2-4 ℃/min, preserving heat for 10-15min, continuing heating to 650 ℃ at the speed of 14-18 ℃/min, preserving heat for 30-40min, continuing heating to 740 ℃ at the speed of 4-6 ℃/min, preserving heat for 10-15min, and naturally cooling to room temperature to obtain pretreated straws a;
s2, grinding the pretreated straws and the clay, sieving, stirring in a phosphoric acid solution with the concentration of 15-22 wt%, stirring at the temperature of 300 ℃ and 400 ℃, filtering, washing and drying to obtain pretreated straws b;
s3, under the protection of nitrogen, uniformly stirring the pretreated straw b, the organic silicon betaine surfactant and water, adding a ferrous sulfate solution with the concentration of 4-4.6g/L, continuously stirring, dropwise adding a sodium phosphate solution with the concentration of 4.5-5g/L under the stirring state, continuously stirring, filtering, washing, adding a water-soluble adhesive, stirring, granulating, roasting at 200-50 ℃ for 1-2h, and cooling to obtain a composite treating agent;
s4, before planting the rice, performing deep loosening and soil preparation on the soil, then spreading the compound treating agent on the surface of the soil, then performing rotary tillage, and then planting the rice.
2. The method for remediating heavy metal pollution in paddy fields using waste straws as claimed in claim 1, wherein the crop wastes containing straws in S1 include: at least one of bagasse, coconut shells, rice hulls and wheat shells, rice straws and wheat straws; pulverizing to particle size of 10-16 mm.
3. The method for remediating heavy metal pollution in paddy fields by using waste straws as claimed in claim 1, wherein the weight ratio of the pretreated straws to the clay in S2 is 10: 1-4.
4. The method as claimed in claim 1, wherein the grinding time is 6-10min, the grinding speed is 10000-12000r/min, the grinding pressure is 0.12-0.18MPa, and the waste straw is sieved with 80-120 mesh sieve after grinding in S2.
5. The method for remediating heavy metal pollution in paddy fields using waste straws as claimed in claim 1, wherein the pore volume of the pretreated straw b is 0.4-0.48cm in S23/g。
6. The method for remediating heavy metal pollution in a paddy field by using waste straws as claimed in claim 1, wherein in S3, the mass ratio of the pretreated straws b, the organic silicon betaine surfactant, the ferrous sulfate solution, the sodium phosphate solution and the water-soluble adhesive is 50-100: 1-5: 30-40: 30-40: 1-4.
7. The method for remedying the heavy metal pollution in the paddy field by using the waste straw as claimed in claim 1, wherein the particle size of the obtained composite treating agent in S3 is 5-10mm, the water content is less than or equal to 5%, and the powder falling rate is less than or equal to 1%.
8. The method for remediating heavy metal pollution in a paddy field by using waste straws as claimed in claim 1, wherein in S3, the water-soluble adhesive is at least one of carboxymethyl cellulose, urea formaldehyde resin and polyvinyl formal.
9. The method for remedying the heavy metal pollution in the paddy field by using the waste straws as claimed in claim 1, wherein the application amount of the composite treating agent in S4 is 90-110 kg/mu.
10. The method for remediating heavy metal pollution in paddy fields using waste straws as claimed in claim 1, wherein in S4, the rotary tillage depth is 18 to 22 cm.
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