CN112226235B - Heavy metal cadmium contaminated soil remediation agent and preparation method and application thereof - Google Patents
Heavy metal cadmium contaminated soil remediation agent and preparation method and application thereof Download PDFInfo
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Abstract
The invention discloses a heavy metal cadmium contaminated soil remediation agent and a preparation method and application thereof.A pore structure of gasification slag is dredged by modification treatment and irradiation and roasting treatment, so that the specific surface area is obviously increased, and meanwhile, a silicon-aluminum active group is activated, so that the adsorption performance is obviously improved, and heavy metal Cd can be effectively fixed; the structure is modified, and meanwhile, the nutrient and functional components such as root exudates with proper molecular weight and starch are loaded on the gasified slag structure, so that the fertilizer efficiency of the gasified slag repairing agent is increased, the water retention performance of the gasified slag repairing agent is enhanced, the soil repairing performance of the gasified slag repairing agent is enhanced in multiple directions, and the repairing effect of the heavy metal polluted soil in a mining area is obvious.
Description
Technical Field
The invention belongs to the technical field of treatment of cadmium pollution of mining area soil, and particularly relates to a heavy metal cadmium polluted soil remediation agent and a preparation method and application thereof.
Background
With the development of industry and agriculture, the land area of China polluted by heavy metals is increased year by year, wherein the mining area is particularly serious. The northern Shaanxi area is used as an energy chemical base, natural gas and petroleum resources of the northern Shaanxi area are over developed in recent years, and a large amount of soil texture structures are seriously damaged; meanwhile, due to rapid development of chemical enterprises, the barren and fragile soil environment suffers from serious heavy metal pollution, and the healthy survival of human beings is seriously threatened. According to investigation, the cadmium pollution of soil in the district of the energy chemical engineering project of the two-region six-garden of elm is severe and exceeds 149 times of the background value of soil in Shaanxi province, and the soil is in a rising trend year by year (Zhongyefang, Yuanzhiyuan, Zhang 32704g, Sunyejjie. research on heavy metal pollution and ecological safety of soil in energy enrichment regions, taking Shaanbei as an example [ J ] ecological environment report, 2018,27(9): 1758-.
The conventional heavy metal contaminated soil remediation technologies mainly comprise chemical technologies (chemical oxidation-reduction remediation technology, chemical leaching remediation technology, in-situ permeable reactive barrier and the like), physical methods (steam leaching remediation technology, extraction separation remediation technology, electrodynamic remediation technology and the like), and biological methods (microbial remediation technology, plant remediation technology, animal remediation technology and the like). Wangyeiting et al, environmental chemistry, volume 39, phase 9, P1-9 "passivator influences the remediation effect of cadmium contaminated soil and the physiological effect of green vegetables" through the cooperation of powdered bone charcoal, sepiolite and the two to passivate farmland soil cadmium, research finds that: the single application and the matched application of the two passivators can obviously improve the pH value of the soil and promote the conversion of the Cd in the soil from an acid soluble state to a residue state; xu et al (XU ML, LIU YZ, DENG Y, et al. biological diagnosis of cadmium-contaminated soil using an autotrophic and a heterotrophic microorganism RSC Advances,2020,10(44):26090 + 26101.) found that: the removal rate of Cd reaches 32.09%, and the synergistic metabolic activity of the autotrophic strain and the heterotrophic strain is found to have a remarkable effect on the removal of Cd; in the ' orthogonal experimental research on electric remediation of cadmium pollution in red soil ' of No. 9P 79-84 of volume 46 of Industrial safety and environmental protection ', by Xiaohui Nu et al, the maximum removal rate of heavy metal Cd can reach 63.14% by adjusting factors such as voltage gradient, water content, citric acid concentration and the like, and the minimum energy consumption is only 0.383 (kW.h)/g).
The technology has good effect on the aspect of restoring the heavy metal polluted soil, wherein the chemical restoring technology for the heavy metal polluted soil is the most advocated method in the heavy metal polluted soil treatment work due to quick effect, easy operation and high efficiency. In recent years, the application of wastes (such as gasified slag, fly ash, sludge and the like) to replace chemical repairing agents to treat the heavy metal pollution of soil attracts extensive attention of researchers in related fields, and the method not only can repair damaged land, but also realizes the purpose of changing waste into valuables. However, the technical engineering is applied less, and reports on heavy metal pollution remediation of sandy soil in northern Shaanxi mine areas are few.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides a heavy metal cadmium contaminated soil remediation agent and a preparation method and application thereof.
In order to achieve the purpose, the invention provides the following technical scheme: a preparation method of a heavy metal cadmium contaminated soil remediation agent comprises the following specific steps:
s1, roasting and cooling the gasified slag, then soaking the gasified slag in a weak acid aqueous solution, carrying out first gamma ray irradiation, and standing the gasified slag after the irradiation is finished to obtain a first precursor; supplementing a weak acid aqueous solution into the first precursor, then carrying out secondary gamma ray irradiation, separating the first precursor after the irradiation is finished, and washing, drying and grinding the obtained gasified slag granules to obtain a second precursor;
s2, mixing the root system plant secretion and the second precursor obtained in the step S1, carrying out third gamma ray irradiation, and standing after irradiation to obtain a third precursor; and adding starch into the third precursor, carrying out fourth gamma ray irradiation, separating the third precursor after the irradiation is finished, and washing, drying and grinding the obtained solid substance to obtain the modified gasified residue soil remediation agent.
Further, in the step S1, the gasified slag is placed in a muffle furnace and roasted for 3h to 5h at the temperature of 450 ℃ to 600 ℃, the mass ratio of the gasified slag to the weak acid aqueous solution is 1 (5-10), and the weak acid aqueous solution is acetic acid aqueous solution; replenishing a weak acid aqueous solution in the first precursor until the initial solid-liquid mass ratio is reached, wherein the solid-liquid mass ratio is 1 (5-10); and the water washing adopts deionized water, and the gasification slag granules are washed until the floating acid is completely removed.
Further, in the step S1, the condition of the first gamma ray irradiation is that the gamma ray of 300kGy to 450kGy is adopted for irradiation for 6min to 16min at 33 ℃ to 51 ℃, and the irradiation is followed by standing for 13h to 16 h; the second gamma ray irradiation is carried out for 5min to 15min by adopting the gamma ray of 0.3kGy to 1kGy at the temperature of 60 ℃ to 76 ℃.
Further, in the step S2, the mass ratio of the second precursor to the plant root exudate is 1: (1-5), standing at room temperature for 1-3 h; the mass of the starch accounts for 1-5% of the total mass of the roasted gasification slag; the water washing adopts deionized water, and the solid matter is washed until the surface attachments are completely removed.
Further, in the step S2, the third gamma ray irradiation condition is that gamma ray irradiation with 5kGy to 35kGy is performed at room temperature for 11min to 15 min; the condition of the fourth gamma ray irradiation is that the gamma ray irradiation of 0.5kGy-0.8kGy is adopted for 1min-4min at the temperature of 75 ℃ to 79 ℃.
The invention also provides a modified gasification slag soil remediation agent prepared by the preparation method of the heavy metal cadmium contaminated soil remediation agent.
The invention further provides application of the modified gasified slag soil repairing agent, and the modified gasified slag soil repairing agent is applied to an area polluted by heavy metal Cd in a mining area, and can be periodically supplemented to the area seriously polluted.
Further, the modified gasified slag soil remediation agent is applied to a soil layer 5-10cm away from the ground in a region polluted by heavy metal Cd in a mining area, and the application amount of the modified gasified slag soil remediation agent is 10g/m2-100g/m2。
Furthermore, the period of supplementing the modified gasified slag soil remediation agent in the severely polluted area is 6-9 months, and the supplementing amount of the modified gasified slag soil remediation agent is 10% -50% of the first application amount.
Furthermore, greening plants can be planted in the area polluted by the heavy metal Cd in the mining area after the modified gasified residue soil remediation agent is applied to the area.
Compared with the prior art, the invention has at least the following beneficial effects:
the invention provides a preparation method of a heavy metal cadmium contaminated soil remediation agent, and researches show that gasified slag has excellent physical and chemical properties, particularly, the gasified slag has a large specific surface area and a pore structure and can be used as an excellent adsorbent, and meanwhile, the gasified slag also contains a small amount of potassium, boron, iron and other micronutrients (such as molybdenum and zinc) and can be used for improving the structural characteristics of soil. According to the invention, through irradiation and roasting treatment, the pore structure is dredged, the specific surface area is obviously increased, and meanwhile, the silicon-aluminum active group is activated, so that the adsorption performance is obviously improved, and heavy metal Cd can be effectively fixed; the structure is modified, and meanwhile, the nutrient and functional components such as root exudates with proper molecular weight and starch are loaded on the gasified slag structure, so that the fertilizer efficiency of the gasified slag repairing agent is increased, the water retention performance of the gasified slag repairing agent is enhanced, the soil repairing performance of the gasified slag repairing agent is enhanced in multiple directions, and the repairing effect on the heavy metal polluted soil in a mining area is remarkable.
The modified gasified slag soil remediation agent provided by the invention is used for modifying gasified slag and then is used for remediation of soil polluted by heavy metal Cd, so that waste of solidified waste gas and gasified slag is changed into valuable, the deterioration of heavy metal pollution of mining area soil is reduced, and the purpose of improving soil texture is achieved.
The raw materials of the repairing agent are waste, the repairing agent is cheap and easy to obtain, the preparation and application procedures are simple and convenient, the obtained repairing agent can passivate soil Cd and remove the toxicity of heavy metals in the soil, can provide nutrients necessary for metabolism of plants, can effectively lock soil moisture and reduce soil moisture loss, meanwhile, the growth of the plants can be reversed to stabilize and improve the soil in a mining area, and finally, the purposes of repairing the soil polluted by the heavy metals Cd in the mining area and greening the environment are achieved.
Detailed Description
The present invention will be further described with reference to the following embodiments.
In the specific embodiment of the invention, the data in the table are calculated according to the soil agricultural chemical analysis method [ M ]. Beijing, China agricultural science and technology publishing company, 2000.
Example 1
1) Primary pretreatment of gasification slag: roasting a certain amount of gasified slag in a muffle furnace at 450 ℃ for 3 h; cooling, soaking in weak acid aqueous solution with pH of about 6.5 and solid-liquid mass ratio of gasified residue to weak acid aqueous solution of 1:5, irradiating with gamma ray at 33 deg.C for 6min with irradiation dose of 300kGy, cooling the solid-liquid mixture to room temperature, and standing for 13 hr; and (3) supplementing a weak acid aqueous solution to the gasification slag after standing until the initial solid-liquid mass ratio is 1:5, and then irradiating the gasification slag for 5min by using gamma rays again at the temperature of 60 ℃, wherein the irradiation dose is 0.3 kGy. Separating the solid-liquid mixture after irradiation, repeatedly washing the gasified slag with deionized water until the floating acid is completely removed, and then drying and grinding the gasified slag granules to powder;
2) secondary pretreatment of gasified slag: fully mixing the primary pretreatment gasification slag obtained in the step 1) with plant root secretion according to the mass ratio of 1:1, irradiating for 11min by using gamma rays at room temperature, wherein the irradiation dose is 5kGy, cooling the solid-liquid mixture to room temperature after the irradiation is finished, and then standing for 1h at room temperature; and adding a small amount of starch into the solid-liquid mixture after the standing is finished, wherein the mass of the starch accounts for 1 percent of the total mass of the roasted gasification slag, and irradiating the mixture for 1min by using gamma rays again at the temperature of 75 ℃ with the irradiation dose of 0.5 kGy. Separating the solid-liquid mixture, repeatedly washing the gasified slag with deionized water until the surface attachments are completely removed, drying and grinding the gasified slag granules to obtain the modified gasified slag soil repairing agent, and bagging for later use;
3) applying 10g/m of modified gasification slag soil remediation agent to soil layer 5cm away from ground in heavy metal Cd-polluted area2(ii) a Then planting greening plants suitable for growing in the area, and supplementing a gasified slag repairing agent in a period of 6 months for severely polluted areas, wherein the supplementing amount is 10% of the first application amount.
And (5) periodically sampling to analyze the content of heavy metal Cd in the soil, the growth condition of plants and the water content of the soil.
The repairing effect is as follows: see tables 1-1 and 1-2. Tables 1-1 and 1-2 show that: with the application of the repairing agent, the heavy metal Cd in the soil is effectively passivated, and the residue state of the heavy metal Cd in the soil is obviously increased. The plants in the soil applied with the repairing agent grow better, the water content of the soil is higher than that of a blank control group, and the blank control group refers to a sample before repairing.
TABLE 1-1 morphological Change of Cd occurrence in soil under remediation agent action
As can be seen from Table 1-1, after the repairing agent is applied, the residue state of Cd in the soil is obviously increased, and particularly, the residue state proportion of the soil under the combined action of the combined plants reaches 82%, which shows that the repairing agent can effectively passivate the heavy metal Cd in the soil and reduce the bioavailability and the ecological toxicity of the heavy metal Cd in the soil.
TABLE 1-2 changes in nutrient composition of the soil in the mining area before and after remediation
As can be seen from the data in the table 1-2, the nutrient content of the restored mining area soil is obviously improved, and the MC% represents the water content of the soil without plants, so that the water content of the restored mining area soil is 19.6% and is obviously higher than that of the mining area soil before restoration; the same plants are respectively planted in the soil before and after the mining area is restored, after 3 months, the two plants are taken out from the whole plant, the dry basis weight of the plants in the soil before the restoration is measured, the dry basis weight of the plants in the soil before the restoration is 62.3g, the dry basis weight of the plants in the soil after the restoration is 77.9g, the biomass content of the plants in the soil after the restoration can be improved by 25 percent through the following formula, and therefore the technology can effectively restore the soil polluted by the heavy metal Cd in the mining area. Wherein the biomass content is calculated according to the dry basis weight, and the formula is as follows:
in the formula, y is the biomass content increase rate,%; m is1And m2The dry basis weight of biomass before and after restoration in the same growth period is kg.
Example 2
1) Primary pretreatment of gasification slag: roasting a certain amount of gasified slag in a muffle furnace at 430 ℃ for 3.5 h; cooling, soaking in weak acid aqueous solution with pH of about 6.5 and solid-liquid ratio of gasified residue to weak acid aqueous solution of 1:6, irradiating with gamma ray at 40 deg.C for 8min with irradiation dose of 330kGy, cooling the solid-liquid mixture to room temperature, and standing for 14 hr; and (3) supplementing a weak acid aqueous solution to the gasification slag after standing until the initial solid-to-liquid ratio is 1:6, and then irradiating the gasification slag for 7min at 65 ℃ by using gamma rays again, wherein the irradiation dose is 0.5 kGy. Separating the solid-liquid mixture after irradiation, repeatedly washing the gasified slag with deionized water until the floating acid is completely removed, and then drying and grinding the gasified slag granules to powder;
2) secondary pretreatment of gasified slag: fully mixing the primary pretreatment gasification slag obtained in the step 1) with plant root secretion according to the mass ratio of 1:2, irradiating for 12min by using gamma rays at room temperature, wherein the irradiation dose is 10kGy, cooling the solid-liquid mixture to room temperature after the irradiation is finished, and then standing for 1.5h at room temperature; and after the standing is finished, adding a small amount of starch into the solid-liquid mixture, wherein the mass of the starch accounts for 2 percent of the total mass of the roasted gasification slag, and irradiating the mixture for 1.5min by using gamma rays at 76 ℃ again, and the irradiation dose is 0.55 kGy. Separating the solid-liquid mixture, repeatedly washing the gasified slag with deionized water until the surface attachments are completely removed, drying and grinding the gasified slag granules to obtain the modified gasified slag soil repairing agent, and bagging for later use;
3) applying 20g/m of modified gasification slag soil remediation agent to soil layer 6cm away from ground in heavy metal Cd-polluted area2(ii) a Then planting greening plants suitable for growing in the area, and supplementing the gasified slag repairing agent in the seriously polluted area in a period of 7 months, wherein the supplementing amount is 20% of the first applying amount.
The repairing effect is as follows: see tables 2-1 and 2-2.
TABLE 2-1 morphological changes in Cd occurrence in soil under remediation agent action
As can be seen from Table 2-1, after the repairing agent is applied, the residue state of Cd in the soil is obviously increased, and particularly, the residue state proportion of the soil under the combined action of the combined plants reaches 87%, which shows that the repairing agent can effectively passivate the heavy metal Cd in the soil and reduce the bioavailability and the ecological toxicity of the heavy metal Cd in the soil.
TABLE 2-2 changes in nutrient composition of the soil in the mining area before and after remediation
As can be seen from the data in the table 2-2, the nutrient content of the restored mining area soil is obviously improved, and the MC% represents the water content of the soil without plants, so that the water content of the restored mining area soil is 19.8%, which is obviously higher than that of the mining area soil before restoration; the same plants are respectively planted in the soil before and after the restoration of the mining area, after 3 months, the two plants are taken out of the whole plant, the dry basis weight is measured, the dry basis weight of the plants in the soil before the restoration is 62.3g, the dry basis weight of the plants in the soil after the restoration is 77.3g, the biomass content of the plants in the soil after the restoration can be improved by 24 percent through the following formula, and therefore, the technology can effectively restore the damaged soil of the mining area. Wherein the biomass content is calculated according to the dry basis mass, and the formula is as follows:
in the formula, y is the biomass content increase rate,%; m is1And m2The dry basis weight of biomass before and after restoration in the same growth period is kg.
Example 3
1) Primary pretreatment of gasification slag: roasting a certain amount of gasified slag in a muffle furnace at 450 ℃ for 4 hours; cooling, soaking in weak acid aqueous solution with pH of about 6.5 and solid-liquid ratio of gasified residue to weak acid aqueous solution of 1:7, irradiating with gamma ray at 44 deg.C for 10min with irradiation dose of 350kGy, cooling the solid-liquid mixture to room temperature, and standing for 15 hr; and (3) supplementing a weak acid aqueous solution to the gasification slag after standing until the initial solid-to-liquid ratio is 1:7, and then irradiating the gasification slag for 10min at 68 ℃ by using gamma rays again, wherein the irradiation dose is 0.6 kGy. Separating the solid-liquid mixture after irradiation, repeatedly washing the gasified slag with deionized water until the floating acid is completely removed, and then drying and grinding the gasified slag granules to powder;
2) secondary pretreatment of gasified slag: fully mixing the primary pretreatment gasification slag obtained in the step 1) with plant root secretion according to the mass ratio of 1:3, irradiating for 13min by using gamma rays at room temperature, wherein the irradiation dose is 25kGy, cooling the solid-liquid mixture to room temperature after the irradiation is finished, and then standing for 2h at room temperature; and after the standing is finished, adding a small amount of starch into the solid-liquid mixture, wherein the mass of the starch accounts for 3 percent of the total mass of the roasted gasification slag, and irradiating the mixture for 2.3min by using gamma rays at 76 ℃ again, and the irradiation dose is 0.7 kGy. Separating the solid-liquid mixture, repeatedly washing the gasified slag with deionized water until the surface attachments are completely removed, drying and grinding the gasified slag granules to obtain the modified gasified slag soil repairing agent, and bagging for later use;
3) applying 50g/m of modified gasification slag soil remediation agent to a soil layer 7cm away from the ground in a heavy metal Cd-polluted area2(ii) a Then planting greening plants suitable for growing in the area, and supplementing a gasified slag repairing agent in the seriously polluted area in a period of 8.5 months, wherein the supplementing amount is 30% of the first applying amount.
The repairing effect is as follows: see tables 3-1 and 3-2.
TABLE 3-1 morphological changes in Cd occurrence in soil under remediation agent action
As can be seen from Table 3-1, after the repairing agent is applied, the residue state of Cd in the soil is obviously increased, and particularly, the residue state proportion of the soil under the combined action of the combined plants reaches 90%, which indicates that the repairing agent can effectively passivate the heavy metal Cd in the soil and reduce the bioavailability and the ecological toxicity of the heavy metal Cd in the soil.
TABLE 3-2 changes in nutrient composition of the soil in the mining area before and after remediation
As can be seen from the data in the table 3-2, the nutrient content of the restored mining area soil is obviously improved, and the MC% represents the water content of the soil without plants, so that the water content of the restored mining area soil is 20.1%, which is obviously higher than that of the mining area soil before restoration; the same plants are respectively planted in the soil before and after the mining area is restored, after 3 months, the two plants are taken out from the whole plant, the dry basis weight of the plants in the soil before the restoration is measured, the dry basis weight of the plants in the soil before the restoration is 62.3g, the dry basis weight of the plants in the soil after the restoration is 75.4g, the biomass content of the plants in the soil after the restoration can be improved by 21 percent through the following formula, and therefore the technology can effectively restore the soil polluted by the heavy metal Cd in the mining area. Wherein the biomass content is calculated according to the dry basis weight, and the formula is as follows:
in the formula, y is the biomass content increase rate,%; m is1And m2The dry basis weight of biomass before and after restoration in the same growth period is kg.
Example 4
1) Primary pretreatment of gasification slag: roasting a certain amount of gasified slag in a muffle furnace at 550 ℃ for 4.8 h; cooling, soaking in weak acid aqueous solution with pH of about 6.5 and solid-to-liquid ratio of 1:9, irradiating with gamma ray at 50 deg.C for 15min with irradiation dose of 430kGy, cooling the solid-liquid mixture to room temperature, and standing for 15 hr; and (3) supplementing a weak acid aqueous solution to the gasification slag after standing until the initial solid-to-liquid ratio is 1:9, and then irradiating the gasification slag for 14min by using gamma rays again at 73 ℃ with the irradiation dose of 0.9 kGy. Separating the solid-liquid mixture after irradiation, repeatedly washing the gasified slag with deionized water until the floating acid is completely removed, and then drying and grinding the gasified slag granules to powder;
2) secondary pretreatment of gasified slag: fully mixing the primary pretreatment gasification slag obtained in the step 1) with plant root secretion according to the mass ratio of 1:4, irradiating for 14min by using gamma rays at room temperature, wherein the irradiation dose is 30kGy, cooling the solid-liquid mixture to room temperature after the irradiation is finished, and then standing for 2.7h at room temperature; and adding a small amount of starch into the solid-liquid mixture after the standing is finished, wherein the mass of the starch accounts for 4% of the total mass of the roasted gasification slag, and irradiating the mixture for 3.5min by using gamma rays at 78 ℃ again, and the irradiation dose is 0.6 kGy. Separating the solid-liquid mixture, repeatedly washing the gasified slag with deionized water until the surface attachments are completely removed, drying and grinding the gasified slag granules to obtain the modified gasified slag soil repairing agent, and bagging for later use;
3) applying 90g/m of modified gasification slag soil remediation agent to soil layer 9cm away from ground in heavy metal Cd-polluted area2(ii) a Then planting greening plants suitable for growing in the area, and supplementing the gasified slag repairing agent in the seriously polluted area within 7.5 months, wherein the supplementing amount is 40% of the first applying amount.
The repairing effect is as follows: see tables 4-1 and 4-2.
TABLE 4-1 morphological changes in Cd occurrence in soil under remediation agent action
As can be seen from Table 4-1, after the repairing agent is applied, the residue state of Cd in the soil is obviously increased, and particularly, the residue state proportion of the soil under the combined action of the combined plants reaches 91%, which shows that the repairing agent can effectively passivate the heavy metal Cd in the soil and reduce the bioavailability and the ecological toxicity of the heavy metal Cd in the soil.
TABLE 4-2 changes in nutrient composition of the soil in the mining area before and after remediation
As can be seen from the data in Table 4-2, the nutrient content of the restored mining area soil is obviously improved, and the MC% represents the water content of the soil without plants, so that the water content of the restored mining area soil is 21.72%, which is obviously higher than that of the mining area soil before restoration; the same plants are respectively planted in the soil before and after the mining area is restored, after 3 months, the two plants are taken out from the whole plant, the dry basis weight of the plants in the soil before the restoration is measured, the dry basis weight of the plants in the soil before the restoration is 62.3g, the dry basis weight of the plants in the soil after the restoration is 74.8g, the biomass content of the plants in the soil after the restoration can be improved by 20 percent through the following formula, and therefore the technology can effectively restore the soil polluted by the heavy metal Cd in the mining area. Wherein the biomass content is calculated according to the dry basis weight, and the formula is as follows:
in the formula, y is the biomass content increase rate,%; m is1And m2The dry basis weight of biomass before and after restoration in the same growth period is kg.
Example 5
1) Primary pretreatment of gasification slag: roasting a certain amount of gasified slag in a muffle furnace at 600 ℃ for 5 hours; cooling, soaking in weak acid aqueous solution with pH of about 6.5 and solid-liquid ratio of gasified residue to weak acid aqueous solution of 1:10, irradiating with gamma ray at 51 deg.C for 16min with irradiation dose of 450kGy, cooling the solid-liquid mixture to room temperature, and standing for 16 hr; and (3) supplementing a weak acid aqueous solution to the gasification slag after standing until the initial solid-to-liquid ratio is 1:10, and then irradiating the gasification slag for 15min by using gamma rays again at 76 ℃ with the irradiation dose of 1 kGy. Separating the solid-liquid mixture after irradiation, repeatedly washing the gasified slag with deionized water until the floating acid is completely removed, and then drying and grinding the gasified slag granules to powder;
2) secondary pretreatment of gasified slag: fully mixing the primary pretreatment gasification slag obtained in the step 1) with plant root secretion according to the mass ratio of 1:5, irradiating for 15min by using gamma rays at room temperature, wherein the irradiation dose is 35kGy, cooling the solid-liquid mixture to room temperature after the irradiation is finished, and then standing for 3h at room temperature; and after the standing is finished, adding a small amount of starch into the solid-liquid mixture, wherein the mass of the starch accounts for 5 percent of the total mass of the roasted gasification slag, and irradiating for 4min again by using gamma rays at 79 ℃ with the irradiation dose of 0.8 kGy. Separating the solid-liquid mixture, repeatedly washing the gasified slag with deionized water until the surface attachments are completely removed, drying and grinding the gasified slag granules to obtain the modified gasified slag soil repairing agent, and bagging for later use;
3) applying 100g/m of modified gasification slag soil remediation agent to soil layer 10cm away from ground in heavy metal Cd-polluted area2(ii) a Then planting greening plants suitable for growing in the area, and supplementing a gasified slag repairing agent in the severely polluted area in a 9-month period, wherein the supplementing amount is 50% of the first application amount.
The repairing effect is as follows: see tables 5-1 and 5-2.
TABLE 5-1 morphological changes in Cd occurrence in soil under remediation agent action
As can be seen from Table 5-1, after the repairing agent is applied, the residue state of Cd in the soil is obviously increased, and particularly, the residue state proportion of the soil under the combined action of the combined plants reaches 93%, which shows that the repairing agent can effectively passivate the heavy metal Cd in the soil and reduce the bioavailability and the ecological toxicity of the heavy metal Cd in the soil.
TABLE 5-2 changes in nutrient composition of the soil in the mining area before and after remediation
As can be seen from the data in Table 5-2, the nutrient content of the restored mining area soil is obviously improved, and the MC% represents the water content of the soil without plants, so that the water content of the restored mining area soil is 20.5% and is obviously higher than that of the mining area soil before restoration; the same plants are respectively planted in the soil before and after the mining area is restored, after 3 months, the two plants are taken out from the whole plant, the dry basis weight of the plants in the soil before the restoration is measured, the dry basis weight of the plants in the soil before the restoration is 62.3g, the dry basis weight of the plants in the soil after the restoration is 75.4g, the biomass content of the plants in the soil after the restoration can be improved by 21 percent through the following formula, and therefore the technology can effectively restore the soil polluted by the heavy metal Cd in the mining area. Wherein the biomass content is calculated according to the dry basis weight, and the formula is as follows:
in the formula, y is the biomass content increase rate,%; m is1And m2The dry basis weight of biomass before and after restoration in the same growth period is kg.
The method can repair the heavy metal Cd polluted soil with lower cost, can improve the soil quality, improve the soil nutrient and the water locking capacity thereof, realize the resource utilization of the gasification slag solid waste, and has important significance for the treatment of the heavy metal Cd polluted soil in arid areas; according to the method, the heavy metal Cd pollution in the soil is removed by mainly utilizing the adsorption of the modified gasified slag on the heavy metal Cd, meanwhile, the modified gasified slag loaded root exudates and starch with proper molecular weight can provide nutrients required by plant growth, and meanwhile, the repairing agent has a certain water retention property, and has the characteristics of environmental friendliness, low cost, easiness in operation and the like.
The above description is only a basic description of the present invention, and any equivalent changes made according to the technical solution of the present invention should fall within the protection scope of the present invention.
Claims (6)
1. A preparation method of a heavy metal cadmium contaminated soil remediation agent is characterized by comprising the following specific steps:
s1, roasting and cooling the gasified slag, then soaking the gasified slag in a weak acid aqueous solution, carrying out first gamma ray irradiation, and standing the gasified slag after the irradiation is finished to obtain a first precursor; supplementing a weak acid aqueous solution into the first precursor, then carrying out secondary gamma ray irradiation, separating the first precursor after the irradiation is finished, and washing, drying and grinding the obtained gasified slag granules to obtain a second precursor;
s2, mixing the root system plant secretion and the second precursor obtained in the step S1, carrying out third gamma ray irradiation, and standing after irradiation to obtain a third precursor; adding starch into the third precursor, carrying out gamma ray irradiation for the fourth time, separating the third precursor after the irradiation is finished, and washing, drying and grinding the obtained solid substance to obtain a modified gasified residue soil remediation agent;
in the step S1, the gasified slag is placed in a muffle furnace and roasted for 3h to 5h at the temperature of 450 ℃ to 600 ℃, the mass ratio of the gasified slag to the weak acid aqueous solution is 1 (5-10), and the weak acid aqueous solution is acetic acid aqueous solution; replenishing a weak acid aqueous solution in the first precursor until the initial solid-liquid mass ratio is reached, wherein the solid-liquid mass ratio is 1 (5-10); the water washing adopts deionized water, and the gasification slag granules are washed until floating acid is completely removed;
in the step S1, the condition of the first gamma ray irradiation is that the gamma ray of 300kGy-450kGy is adopted for irradiation for 6min-16min at the temperature of 33 ℃ to 51 ℃, and the irradiation is followed by standing for 13h-16 h; the condition of the second gamma ray irradiation is that the gamma ray irradiation of 0.3kGy-1kGy is adopted for 5min-15min at the temperature of 60-76 ℃;
in the step S2, the mass ratio of the second precursor to the plant root exudate is 1: (1-5), standing at room temperature for 1-3 h; the mass of the starch accounts for 1-5% of the total mass of the roasted gasification slag; the water washing adopts deionized water, and the solid matter is washed until the surface attachments are completely removed;
in the step S2, the condition of the third gamma ray irradiation is that 5kGy to 35kGy of gamma ray is adopted for 11min to 15min at room temperature; the condition of the fourth gamma ray irradiation is that the gamma ray irradiation of 0.5kGy-0.8kGy is adopted for 1min-4min at the temperature of 75 ℃ to 79 ℃.
2. The modified gasified residue soil remediation agent prepared by the preparation method of the heavy metal cadmium contaminated soil remediation agent according to claim 1.
3. The use of the modified gasified slag soil remediation agent as claimed in claim 2, wherein the modified gasified slag soil remediation agent is applied to an area polluted by heavy metal Cd in a mining area, and the modified gasified slag soil remediation agent can be periodically supplemented to areas seriously polluted.
4. The use of the modified gasified slag soil remediation agent as claimed in claim 3, wherein the modified gasified slag soil remediation agent is applied to a soil layer 5-10cm away from the ground in a region polluted by heavy metal Cd in a mining area, and the application amount of the modified gasified slag soil remediation agent is 10g/m2-100g/m2。
5. The use of the modified gasified slag soil remediation agent as claimed in claim 3, wherein the period of supplementing the modified gasified slag soil remediation agent in the severely polluted area is 6-9 months, and the supplementing amount of the modified gasified slag soil remediation agent is 10% -50% of the first-time application amount.
6. The use of the modified gasified slag soil remediation agent of claim 3, wherein the area contaminated by heavy metal cadmium in the mining area is planted with green plants after the modified gasified slag soil remediation agent is applied.
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