CN111100644A

CN111100644A - Microcapsule composite material for Cd and Pb polluted soil, preparation method and restoration method

Info

Publication number: CN111100644A
Application number: CN201911396002.6A
Authority: CN
Inventors: 陈林; 蔡晶晶
Original assignee: Zhejiang Sino Geo Clean Soil Co ltd
Current assignee: Zhejiang Sino Geo Clean Soil Co ltd
Priority date: 2019-12-30
Filing date: 2019-12-30
Publication date: 2020-05-05

Abstract

The invention discloses a microcapsule composite material of Cd and Pb polluted soil, a preparation method and a repair method, which comprises the following steps: 20-50% of modified clay mineral, 30-50% of calcium-magnesium based composite material, 5-20% of sulfate and 1-10% of pH regulator. The invention is friendly to soil environment. No secondary pollution. The original granular structure of the soil cannot be damaged, the acid-base buffering capacity of the soil can be improved to a certain extent, and the water-retaining property of the soil is improved; the method has obvious treatment effect on Cd and Pb pollution in soil, long duration, strong adaptability to external environmental factor change and simple construction.

Description

Microcapsule composite material for Cd and Pb polluted soil, preparation method and restoration method

Technical Field

The invention relates to the technical field of soil remediation, in particular to a microcapsule composite material for Cd and Pb contaminated soil, a preparation method and a remediation method.

Background

Cadmium is a dangerous environmental pollution element, has only two valence states of 0 and +2, and the content of cadmium in the rock crib is between 0.1 and 0.2mg/kg on average. Cadmium is commonly associated with zinc and lead in nature, and cadmium in soil only relates to divalent cadmium and compounds thereof. Cadmium is easily absorbed by plants, and as long as the cadmium content in soil is slightly increased, the cadmium content in the plants is correspondingly increased. Cadmium has high toxicity and is close to zinc in chemical properties. Thus, cadmium can act as a chemical analog of zinc in certain biochemical processes, replacing zinc, destroying various nucleases, dehydrogenases and phosphatases associated with the respiratory and digestive processes of the human body. Similarly, cadmium can replace zinc in plants resulting in zinc deficiency, resulting in inhibited growth to death

Lead is a metal widely used in daily life and industrial production, and has two valence states of +2 and +4, mainly Pb²⁺Mainly comprises the following steps. Lead is often present as a sulfide, and is often introduced in the presence of elements such as zinc and copper, with only a small amount of metal. According to statistics, the worldwide lead yield is 560 ten thousand tons every year, and the annual consumption and usage amount is 300 ten thousand tons. Nearly half of the lead is used in the manufacture of batteries and the rest is used as gasoline explosion preventives, cables, explosives, etc., but only 1/4 lead is recycled and most of the lead is discharged into the environment in various forms. Most of the lead that enters the soil remains on the surface of the soil and hardly migrates downward. Excessive lead can hinder the growth and development of crops, mainly manifested by reduced chlorophyll content, affecting plant respiration and photosynthesis, thereby reducing crop yield and quality. Lead has a strong accumulation property, and can be enriched in human body through food chain, thereby interfering with various physiological activities of organism, damaging nervous, immune, digestive and reproductive systems of human body, and posing threat to human health.

The heavy metal pollution of the soil has the characteristics of concealment, long-term property and irreversibility. Harmful heavy metals in soil are accumulated to a certain degree, so that not only can soil degradation be caused, and the crop yield and quality are reduced, but also surface water and underground water can be polluted through runoff and leaching loss, the hydrological environment is deteriorated, and the harmful heavy metals can be directly poisoned by plants or harm human health through a food chain way. At present, the technology for remedying the heavy metal pollution of the soil is widely researched in various countries in the world, and the following remediation measures are specifically provided:

1. engineering repair

The conventional engineering restoration technology for treating the heavy metal polluted soil mainly comprises the measures of soil dressing, soil replacement, deep ploughing and soil turning and the like. Through soil dressing, soil replacement, deep ploughing, soil turning and soil pollution mixing, the content of heavy metals in soil can be reduced, the toxicity of the heavy metals on a soil-plant system is reduced, and the amount of heavy metal elements entering a food chain is reduced, so that agricultural products reach the food sanitation standard. Deep ploughing is generally used for lightly contaminated soils, while soil replacement and dressing are common methods for heavily contaminated areas, and successful experience has been achieved in this regard in japan and many countries.

The engineering restoration is a more classical treatment measure for heavy metal pollution of soil, has the advantages of thoroughness and stability, but has large engineering quantity and high investment cost, and can damage the soil body structure when the measure is improper, thereby causing the soil fertility to be reduced. The soil after being replaced needs to be properly stacked and disposed to prevent secondary pollution, and accordingly, the investment and the operation cost of the project are increased.

2. Physical chemical repair

(1) Electric repair

The principle of electric restoration is that under the action of current and an electric field, heavy metal ions (such as Pb, Cd, Zn and the like) and inorganic ions in soil are transported to an electrode in an electroosmosis and electromigration modes, and then concentrated collection treatment is carried out. Researches find that the pH value, the buffering performance, the soil components and the types of the polluted metals of the soil can influence the repairing effect.

The method is particularly suitable for clay and silt with low permeability, and can control the flowing direction of pollutants. The experimental result on sandy soil shows that Pb in the soil²⁺、Cd³⁺The removal rate of the heavy metal ions can reach 90 percentThe above. The electric restoration is an in-situ restoration technology, does not stir the soil layer, can shorten the restoration time, and is an economical and feasible restoration technology for small-area special areas. But when the method is used for treating large-area pollution, the construction cost and the energy consumption are both large.

(2) Electrothermal repair

The principle of electric heating restoration is that high-frequency voltage is utilized to generate electromagnetic waves to generate heat energy to heat soil, so that pollutants are desorbed from soil particles, separation of volatile heavy metals from the soil is accelerated, and the restoration purpose is achieved. The technology can repair the soil polluted by Hg, Se and other heavy metals. In addition, the soil in the heavy metal pollution area can be placed at high temperature and high pressure to form a glass state substance, so that the aim of fundamentally eliminating the heavy metal pollution of the soil is fulfilled. The electric heating repairing technology is not suitable for treating volatile heavy metal element pollution, has certain limitation in application and has higher operation cost.

(3) Soil leaching

The mechanisms by which soil holds metals can be divided into two broad categories: firstly, the ionic adsorption is carried out on the surface of the soil component; secondly, the formation of a precipitate of metal compounds. The soil leaching is a soil remediation method which transfers heavy metals in a solid phase of soil into a liquid phase of the soil by using a leaching solution and then further recycles and treats wastewater rich in the heavy metals. At present, various types of leaching remediation preparations, such as H, have been developed at home and abroad aiming at the heavy metal contaminated soil₃PO₄、KH₂PO₄Inorganic eluting agent, and surfactant such as EDTA chelating agent SDBS. The restoration technology has the advantages of high speed, high efficiency and the like, and is widely applied to restoration of heavy metals such as soil, waste residues and the like in contaminated sites of industrial and mining enterprises. However, the technology has the problems of damaging the soil structure, causing nutrient loss, introducing secondary pollution and the like, and still has great limitation on the aspect of heavy metal farmland pollution remediation.

3. Chemical remediation

The chemical remediation method is to add the conditioner into the soil, change the occurrence form of the heavy metal pollutants and reduce the migration and biological effectiveness of the heavy metal pollutants through the adsorption, oxidation reduction, antagonism or precipitation of the heavy metals. The key point of the technology is to select an economic and effective modifier. The commonly used modifying agents are lime, zeolite, calcium carbonate, phosphate, silicate and organic substances which promote the reduction action, and the action mechanisms of different modifying agents on heavy metals are different. Chemical remediation processes typically employ passivation techniques to remediate heavy metal contaminated soil.

The passivation technology is to reduce the water solubility, diffusivity and biological effectiveness of soil pollutants by applying a chemical passivator and the like, thereby reducing the capacity of the soil pollutants to enter plants, microorganisms and water bodies and reducing the harm to an ecological system. Generally, in cadmium and copper polluted soil, lime substances are applied to increase the pH value of the soil, so that heavy metals generate oxyhydrogen chemical precipitation, the activity of the heavy metals in the soil is reduced, and the absorption of heavy metals by crops is reduced. Therefore, the application of alkaline substances such as lime, blast furnace slag, slag and fly ash or the application of alkaline fertilizers such as calcium magnesium phosphate fertilizer and silicon fertilizer to the acid soil polluted by heavy metals can reduce the solubility of the heavy metals, thereby effectively reducing the adverse effect of the heavy metals on the soil and reducing the heavy metal concentration of plants. Meanwhile, humic acid fertilizers, organic fertilizers, oxidizing agents/reducing agents and the like can be applied to the soil, so that the toxicity of pollutants can be reduced. With the wide demand for low-cost techniques for soil remediation, low-cost stabilization solidification techniques have rapidly developed.

4. Bioremediation

Bioremediation is a method of treating contaminated soil using biotechnology. The biological reduction and purification of heavy metals in soil or the reduction of heavy metal toxicity are utilized. The method has good effect, low cost and easy operation, and can further repair the vegetation and the ecosystem of the polluted area, so the method is increasingly paid attention by people and becomes a hotspot of the research on the repair of the polluted soil. According to the action process and mechanism, the bioremediation technology of heavy metal contaminated soil can be divided into three types of phytoremediation, microbial remediation and plant-microbial combined remediation.

(1) Phytoremediation

The pollutants in the soil are purified through the functions of absorption, volatilization, root filtration, degradation, stabilization and the like of plants. At present, the most common method is plant extraction, namely, super-accumulative plants are utilized to absorb pollutants from soil, then overground parts are harvested and subjected to centralized treatment, and the plants are continuously planted, so that the aim of reducing or removing heavy metal pollution of the soil is fulfilled. At present, more than 700 kinds of plants with super-accumulated heavy metals are found, the amount of accumulated Cd, Co, Ni, Cu and Pb is generally more than 0.1%, and the amount of Mn and Zn can reach more than 1%. The Thalassia is an identified Zn and Cd hyperaccumulation plant, and Baker and NcGrath research shows that when the soil contains Zn444mg/kg, the Zn content of the overground part of the Thalassia can reach 16 times of that of the soil. Some species of salix can be enriched in Cd in large quantities; the enrichment of Indian mustard for Cd, Ni, Zn and Cu can reach 58 times, 52 times, 31 times, 17 times and 7 times respectively; sinapis and grass and the like have strong accumulation capacity on Se, Pb, Cd, Ni, Zn and Cu; internationally reports that the Ni super-accumulation plant with high biomass can absorb and extract Ni of 168kg per ha; gaoshana species can absorb high concentrations of Cu, Co, Mn, Pb, Se, Cd, and Zn. Chinese scholars also make a great deal of research on plant extraction. For example, a batch of As super-accumulation plants are found in south China; some experts use 10 super-accumulator plants to carry out remediation research on Cd-polluted soil; further research shows that the Indian mustard has good repairing effect on the soil polluted by Cu, Zn and Pb.

(2) Microbial remediation

The method utilizes some microorganisms in the soil to absorb, precipitate, oxidize and reduce heavy metals, and the like, thereby reducing the toxicity of the heavy metals in the soil. For example, some microorganisms can metabolize to produce substances such as citric acid and oxalic acid, and the metabolites can be chelated with heavy metals or form oxalate precipitates, so that the harm of the heavy metals is reduced; zoogloea, cyanobacteria, sulfate reducing bacteria and certain algae, which can produce extracellular polymers (such as polysaccharide, glycoprotein and the like) with a large number of anionic groups, form complexes with heavy metal ions, and thus effectively remove the extracellular polymers from soil; under the stress of heavy metals, the Acinetobacter thiomonale and the Pseudomonas can reduce the activity of heavy metal elements such As As, cu, Mo, Fe, Mn and the like through oxidation, reduction, methylation and demethylation.

(3) Plant-microorganism combined repair

The action principle of the repair technology is shown in the following steps: on one hand, the plants provide good environmental conditions for the growth of microorganisms, and improve the organic matter degradation capacity or the heavy metal activation or fixation capacity of the microorganisms; on the other hand, the microorganisms can change the existing form of the pollutants, reduce the toxicity of the pollutants to plants, or promote the absorption, accumulation and transformation of the pollutants by the plants. For example, Mesorhizobium huakuii bacteria can promote the absorption of the soil Cd by the milk vetch to increase by 1.7-2.0 times; pseudomonas fluorescens bacteria can significantly reduce Cr⁶⁺In reducing Cr⁶⁺The toxicity and the absorption capacity of plants to heavy metals are increased; some rhizosphere growth promoting bacteria can produce cytokinin, ethylene, vitamins and other substances, can promote the synthesis of plant RNA and protein, and increase the cell volume and mass to achieve the growth promoting effect. Plant-microorganism combined restoration as a low-cost enhanced plant restoration technology is gradually becoming the focus of attention at home and abroad in recent years.

5. Combined artificial wet land technology

The combined artificial wetland is a composite system which simulates and imitates the structure and characteristics of different types of natural wetland ecosystems and strengthens the purification and landscape functions of the wetland ecosystems by combined design and engineering means. A common combined constructed wetland system comprises vertical flow, subsurface flow and surface flow wetland units.

The constructed wetland has high application value in liquid-solid waste treatment, the constructed wetland system formed by combination has wide application range, can achieve the treatment target, has the advantages of high benefit, low energy consumption, capability of reusing sewage as an irrigation water source, capability of providing habitats for wild animals and plants and the like, and the treatment method is particularly suitable for areas far away from waste treatment centers. The combined artificial wetland technology can be used for constructing an ecological pollution prevention zone to prevent pollution diffusion, and can also be used for treating percolate and surface runoff of soil in a polluted area to prevent the influence of water and soil loss of the polluted soil on the surrounding environment. However, the artificial wetland technology cannot be directly used for repairing heavy metal contaminated soil, and can only be used as an auxiliary system for treating percolate and surface runoff of the soil.

6. Permeable reactive barrier technology

The technology is a method for removing pollution components in underground water and soil in situ, which is emerging in a plurality of countries such as Europe and America at present. In the 80 s of the 20 th century, american scholars used permeable reactive barrier technology to treat polluted components in polluted water bodies, and the technology was widely popularized and applied in the 90 s. At present, a great deal of engineering and technical research is completed in countries such as Europe and America and enters a commercial application stage. The PRB technical handbook for pollutant remediation, published by the U.S. environmental protection agency (USEPA)1998, defines PRBs as: an active material wall is arranged underground so as to intercept the pollution pinnate body, so that after the pollution pinnate body passes through a reaction medium, the pollutants are converted into another form accepted by the environment, and the aim of enabling the pollutant concentration to reach the environmental standard is fulfilled.

The permeable reactive barrier consists essentially of a permeable reactive media, which is typically placed downstream of the groundwater contamination plume, perpendicular to the groundwater flow. The pollutant removing mechanism comprises biological and non-biological mechanisms, and polluted underground water generates precipitation, adsorption, oxidation reduction and biodegradation reactions when passing through the permeable reactive barrier under the action of the hydraulic gradient of the polluted underground water, so that pollutants in the water can be removed.

In China, the PRB technology is still in the experimental stage. Compared with other technologies, the PRB technology has the advantages of capability of continuously treating various pollutants (such as heavy metals, organic matters and the like) in situ, good treatment effect, convenience in installation and construction, high cost performance and the like. The PRB technology is mainly used for removing underground water pollutants, and still has certain limitation in the treatment of heavy metal polluted soil.

The above repair measures have the following defects:

1. engineering repair: if the soil dressing method is adopted, a large amount of soil dressing needs to be taken, and the equivalent polluted soil needs to be treated;

2. physical and chemical treatment: the method has the disadvantages of serious damage to the soil structure and the soil fertility, complex process control, higher unit cost for treatment, poor technical stability and larger disturbance to the soil.

3. Chemical repair: the passivator has an influence on the activity of heavy metals and the soil structure, and the long-term effect of passivation is not known at present, so that the activity of the heavy metals in the soil can be enhanced and the heavy metals can be absorbed by crops even if the environmental conditions are changed for a long time.

4. Biological repair: the treatment period is long, the later plant collection and treatment process is complex, and the maintenance and management period is long.

5. Artificial wetland: the treatment period is long, the activity of plants is reduced in winter, and the adsorption capacity of heavy metals is reduced; the engineering occupied area is large.

6. Permeable reactive barrier: the construction cost is high, and the treatment effect is influenced by seasonal change of underground water. The soil remediation effect is not direct without leaching.

7. And (3) agricultural ecological restoration: applying organic fertilizer in soil can improve the activity of heavy metals in soil, thereby improving the environmental risk of heavy metals. After the organic materials are added into the soil, the organic materials have different effects on the chelation and fixation of heavy metals due to different decomposition and mineral effects.

Disclosure of Invention

Aiming at the defects in the problems, the invention provides a microcapsule composite material for Cd and Pb polluted soil, a preparation method and a repair method.

The invention aims to provide a microcapsule composite material of Cd and Pb polluted soil, which comprises the following components in percentage by weight:

20-50% of modified clay mineral, 30-50% of calcium-magnesium based composite material, 5-20% of sulfate and 1-10% of pH regulator.

As a further improvement of the invention, the modified clay mineral is a modified zeolite.

As a further improvement of the invention, the calcium-magnesium based composite material comprises one or more of calcium magnesium phosphate fertilizer and calcium superphosphate.

As a further improvement of the invention, the sulfate is sodium sulfate.

As a further improvement of the invention, the pH adjusting agent comprises one or more of heavy magnesium oxide and hydrated lime.

A second object of the present invention is to provide a method for preparing a microcapsule composite material, comprising:

modifying clay mineral by heat to obtain modified clay mineral;

and mixing the modified clay mineral, the calcium-magnesium based composite material, the sulfate and the pH regulator according to a preset proportion to prepare the microcapsule composite material.

As a further improvement of the present invention, a process for producing the modified clay mineral, comprising:

naturally drying, crushing and sieving the clay mineral to obtain a clay mineral pretreatment product;

carrying out heat treatment on the clay mineral pretreatment product to obtain a clay mineral heat treatment product; wherein the temperature of the heat treatment is 200-600 ℃, and the time of the heat treatment is 5-7 hours;

and cooling the clay mineral heat treatment product to obtain the modified clay mineral.

The third purpose of the invention is to provide a repairing method of the microcapsule composite material, which comprises the following steps:

detecting the total amount and effective state of Cd and Pb in the polluted soil;

according to the analysis and detection result of the polluted soil and the standard required to be achieved, uniformly spraying the microcapsule composite material on the surface of the polluted soil to be treated according to the adding proportion of 0.1-0.5% of the mass of the Cd and Pb polluted soil;

according to the characteristics of the polluted soil, turning over and mixing, and adding pollution-free clean water after uniformly mixing;

keeping the water content of 20-30% for 1-3 months, fully reacting the microcapsule composite material with heavy metals Cd and Pb, carrying out dynamic detection, and starting normal planting after sampling detection is qualified.

Compared with the prior art, the invention has the beneficial effects that:

according to the invention, the clay mineral (zeolite) is used as a main component of the repairing material, and the clay mineral with a high surface area is modified, so that the adsorption effect of the clay mineral on heavy metals Cd and Pb is improved, and the repairing effect is obvious; meanwhile, the clay mineral with high surface area has a porous channel, so that the composite material can be conveniently subjected to ion exchange with heavy metals Cd and Pb; the clay mineral is a natural soil mineral substance, is taken from soil, is free from other materials containing heavy metal components, is green and environment-friendly, and does not cause secondary pollution in the repairing process;

the calcium-magnesium-based composite material can provide phosphate ions, the phosphate ions are alkaline, the soil can be adjusted and repaired, and the calcium-magnesium-based composite material and heavy metals Cd and Pb are precipitated and removed;

the sulfate is used for precipitating and removing heavy metal Pb, the pH regulator selects heavy magnesium oxide and/or hydrated lime, the pH regulator is mixed into soil to regulate the acidity and alkalinity of the soil, the pH value in the soil is increased by about 0.1-0.3, the soil is enabled to stably maintain a weak alkaline environment, and the acid-base environment of the soil is not damaged; in alkalescent environment, free Cd²⁺The composite which is difficult to dissolve is easy to form, can be adsorbed and fixed by a repair material, and can not be absorbed by plants and dissolved in water, so that the biological effectiveness and the mobility of the heavy metal cadmium are reduced, and the harm of the heavy metal to the ecological environment is greatly reduced.

Drawings

FIG. 1 is a schematic diagram of effective concentration of Cd in soil repaired by a microcapsule composite material according to an embodiment of the present invention;

fig. 2 is a schematic diagram of the effective concentration of Pb in soil repaired by the microcapsule composite material according to an embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.

The invention is described in further detail below with reference to the attached drawing figures:

the invention provides a microcapsule composite material of Cd and Pb polluted soil, which comprises the following components in percentage by weight:

Wherein:

the modified clay mineral is formed by thermally modifying clay mineral, and the modified clay mineral can adopt other modified clay minerals with larger specific surface area besides modified zeolite. The natural zeolite of the invention comprises one or a mixture of more than one of analcime, heulandite, scolecite, natrolite, chabazite, mordenite and clinoptilolite.

The function of adding the modified zeolite is as follows: the zeolite powder has a plurality of crystal holes and pore channels which are arranged orderly on the surface, has a large specific surface area, can contain a large amount of trace elements in the zeolite powder, has a good adsorption effect on heavy metals, and has the adsorption effect far exceeding that of active carbon and a specific natural molecular sieve. The zeolite molecular sieve is modified by a thermal modification mode, the impurity content on the surface of the modified zeolite material is reduced, the blocked pore channel is dredged, the specific surface area of the repairing material is further increased, the adsorption capacity is improved, and the adsorption capacity of the repairing material on heavy metals is improved; through the control of the modification temperature and time, the pore structure on the surface of the zeolite material is improved, the adsorption efficiency of the zeolite material on heavy metals is improved, the adsorption pertinence of heavy metals Cd and Pb is stronger, and the purification effect of the repair material on the heavy metals is improved; meanwhile, the clay mineral with high surface area has a porous channel, so that the composite material can be conveniently subjected to ion exchange with heavy metals Cd and Pb.

The calcium-magnesium-based composite material comprises one or more of a calcium-magnesium phosphate fertilizer and calcium superphosphate, can provide phosphate ions, is alkaline, can regulate and repair soil, and generates precipitates with heavy metals Cd and Pb to be removed.

The sulfate of the invention is preferably sodium sulfate which is used for precipitating and removing heavy metal Pb;

the pH regulator comprises one or more of heavy magnesium oxide and hydrated lime, and can regulate the pH value of soil when mixed in the soil, so that the pH value in the soil is increased by about 0.1-0.3, the soil is stably maintained in a weak alkaline environment, and the acid-base environment of the soil cannot be damaged; in alkalescent environment, free Cd²⁺The composite which is difficult to dissolve is easy to form, can be adsorbed and fixed by a repair material, and can not be absorbed by plants and dissolved in water, so that the biological effectiveness and the mobility of the heavy metal cadmium are reduced, and the harm of the heavy metal to the ecological environment is greatly reduced.

The invention provides a preparation method of a microcapsule composite material, which comprises the following steps:

s1, performing thermal modification on the clay mineral to obtain a modified clay mineral;

the specific preparation method of the modified clay mineral comprises the following steps:

1) and (3) pretreatment: naturally drying and crushing the clay mineral, and sieving the clay mineral by a 200-mesh sieve to obtain a clay mineral pretreatment product;

2) and (3) heat treatment: carrying out heat treatment on the clay mineral pretreatment product to obtain a clay mineral heat treatment product; wherein the heat treatment temperature is 200-600 ℃, and the heat treatment time is 5-7 hours;

3) and cooling treatment: and (3) putting the clay mineral heat treatment product into a dryer for cooling to obtain the modified clay mineral.

S2, preparing a calcium magnesium base composite material;

s3, mixing the modified clay mineral, the calcium-magnesium based composite material, the sulfate and the pH regulator according to a preset proportion to obtain the microcapsule composite material.

The invention provides a repairing method of a microcapsule composite material, which comprises the following steps:

s1, detecting the total amount and effective state of Cd and Pb in the polluted soil;

s2, uniformly spraying the microcapsule composite material on the surface of the polluted soil to be treated according to the analysis and detection result of the polluted soil and the standard required to be met and the adding proportion of 0.1-0.5% of the mass of the Cd and Pb polluted soil;

s3, ploughing and mixing according to the characteristics of the polluted soil, and adding pollution-free clean water after uniformly mixing;

s4, keeping the water content of 20-30% for 1-3 months, enabling the microcapsule composite material to fully react with heavy metals Cd and Pb, carrying out dynamic detection, and starting normal planting after sampling detection is qualified.

The method specifically comprises the following steps:

aiming at dry farmland:

s11, detecting the total amount and effective state of Cd and Pb in the polluted soil;

s12, ploughing the contaminated soil of the plough layer of 0-20cm, removing branches and gravels, and crushing soil blocks, wherein the diameter of the crushed soil is less than 1 cm;

s13, uniformly spraying the microcapsule composite material on the surface of the polluted soil to be treated according to the analysis and detection result of the polluted soil and the standard required to be met and the adding proportion of 0.1-0.5% of the mass of the Cd and Pb polluted soil;

s14, uniformly mixing the polluted soil and the repairing material, and adding 20-30% of pollution-free clean water after uniform mixing;

s15, keeping the water content of 20-30% for 1-3 months, enabling the microcapsule composite material to fully react with heavy metals Cd and Pb, carrying out dynamic detection, and starting normal planting after sampling detection is qualified.

When aiming at paddy field:

s21, detecting the total amount and effective state of Cd and Pb in the polluted soil;

s22, performing ploughing operation;

s23, uniformly spraying the microcapsule composite material on the surface of the polluted soil to be treated according to the analysis and detection result of the polluted soil and the standard required to be met and the adding proportion of 0.1-0.5% of the mass of the Cd and Pb polluted soil;

s24, covering the renovation material on the ploughed soil surface, ploughing again and stirring to uniformly mix the renovation material and the polluted soil;

and S25, standing the soil for 1-3 months, fully reacting the microcapsule composite material with heavy metals Cd and Pb, carrying out dynamic detection, and starting normal planting after sampling detection is qualified.

Example 1:

the sample for experiment is from a Cd and Pb polluted farmland in certain Tianjin area, and the total amount of Cd and Pb in the soil sample is detected by a method specified in soil environment quality agricultural land soil pollution risk control standard (GB 15618-2018); the method specified in the determination of effective lead and cadmium in soil quality atomic absorption method (GB/T23739-2009) is adopted to detect the effective concentration of Cd and Pb in the soil sample. The detection result shows that the total content of Cd in the farmland polluted soil is 0.8-1.3mg/kg, the total content of Pb in the farmland polluted soil is 934-680mg/kg, the pH value is 7.3-7.8, and the soil remediation target is that the effective state concentration of cadmium and lead in the soil is reduced by 30% after the passivation stabilization technology of the microcapsule composite material is adopted.

30% of modified zeolite, 40% of calcium magnesium phosphate fertilizer, 20% of sodium sulfate and 10% of heavy magnesium oxide.

The invention provides a method for restoring Cd and Pb polluted soil, which comprises the following steps:

s1, taking 100kg of farmland polluted soil, putting 0.5kg of prepared microcapsule composite material (passivator), and uniformly spraying the microcapsule composite material on the soil surface;

s2, stirring to fully and uniformly mix the microcapsule composite material with the contaminated soil, adding water, and stirring for 1-2 times to keep the water content in the soil at 30%;

and S3, covering a black plastic film on the soil, and keeping the water content at about 30%. And carrying out sampling detection when the product is maintained for 5, 10, 20, 30, 60, 90 and 120 days respectively.

The detection results of S4, Cd and Pb are shown in tables 1 and 2;

TABLE 1 initial concentration of Cd in soil in effective state

Time of day	Concentration of active state mg/kg	Rate of passivation
			Day
0	0.9804	0.00％
			5 days	0.8815	10.09％
10 days	0.7543	23.06％
			20 days	0.6046	38.33％
30 days	0.5621	42.67％
			60 days	0.5367	45.26％
90 days	0.5488	44.02％
			120 days	0.5476	44.15％

TABLE 2 initial concentration of Pb in soil in effective state

Time of day	Concentration of active state mg/kg	Rate of passivation
			Day
0	634.45	0.00％
			5 days	478.51	24.58％
10 days	390.47	38.46％
			20 days	377.52	40.50％
30 days	375.31	40.84％
			60 days	364.27	42.58％
90 days	363.28	42.74％
			120 days	373.24	41.17％

The initial effective concentration of Cd in the soil is 0.9804mg/kg, and when the soil is maintained for 120 days, the effective concentration of Cd in the soil is 0.5476mg/kg, the effective concentration of Cd is reduced by 44.15%, and the effective concentration of Cd is lower than the restoration target value of which the effective concentration is reduced by 30%. The initial effective concentration of Pb in the soil is 634.45mg/kg, and when the soil is maintained for 120 days, the effective concentration of Pb in the soil is 373.24mg/kg, the effective concentration of Pb is reduced by 41.17%, and the effective concentration of Pb is already lower than the restoration target value of the effective state reduced by 30%.

Example 2:

the sample for experiments is from a Cd and Pb polluted farmland in certain Shaoxing area, and the total amount of Cd and Pb in the soil sample is detected by a method specified in soil environment quality agricultural land soil pollution risk control standard (GB 15618-2018); the method specified in the determination of effective lead and cadmium in soil quality atomic absorption method (GB/T23739-2009) is adopted to detect the effective concentration of Cd and Pb in the soil sample. The detection result shows that the total amount of Cd in the farmland polluted soil is 1.2-3.5mg/kg, the total amount of Pb in the farmland polluted soil is 800-1400 mg/kg, the pH value is 4.9-7.5, and the soil remediation goal is that the effective state concentration of cadmium and lead in the soil is reduced by 30% after the passivation stabilization technology of the microcapsule composite material is adopted.

20% of modified zeolite, 30% of calcium magnesium phosphate fertilizer, 20% of calcium superphosphate, 20% of sodium sulfate and 10% of heavy magnesium oxide.

The detection results of S4, Cd and Pb are shown in tables 3 and 4;

TABLE 3 initial concentration of Cd in soil in effective state

Time of day	Concentration of active state mg/kg	Rate of passivation
			Day
0	1.32	0.00％
			5 days	0.95	28.03％
10 days	0.81	38.64％
			20 days	0.74	43.94％
30 days	0.71	46.21％
			60 days	0.68	48.48％
90 days	0.69	47.73％
			120 days	0.68	48.48％

TABLE 4 initial concentration of Pb in soil in effective state

Time of day	Concentration of active state mg/kg	Rate of passivation
			Day
0	483.12	0.00％
			5 days	388.59	19.57％
10 days	359.14	25.66％
			20 days	343.18	28.97％
30 days	325.64	32.60％
			60 days	319.77	33.81％
90 days	318.24	34.13％
			120 days	310.15	35.80％

The initial effective concentration of Cd in the soil is 1.32mg/kg, and when the soil is maintained for 120 days, the effective concentration of Cd in the soil is 0.68mg/kg, the effective concentration of Cd is reduced by 48.48%, and the effective concentration of Cd is lower than the restoration target value of which the effective concentration is reduced by 30%. The initial effective concentration of Pb in the soil is 483.12mg/kg, and when the soil is maintained for 120 days, the effective concentration of Pb in the soil is 310.15mg/kg, the effective concentration of Pb is reduced by 35.80%, and the effective concentration of Pb is already lower than the restoration target value of the effective state reduced by 30%.

Example 3:

the sample for experiments is from a Cd and Pb polluted farmland in certain Shaoxing area, and the total amount of Cd and Pb in the soil sample is detected by a method specified in soil environment quality agricultural land soil pollution risk control standard (GB 15618-2018); the method specified in the determination of effective lead and cadmium in soil quality atomic absorption method (GB/T23739-2009) is adopted to detect the effective concentration of Cd and Pb in the soil sample. The detection result shows that the total content of Cd in the farmland polluted soil is 0.6-1.1mg/kg, the total content of Pb in the farmland polluted soil is 400-600mg/kg, the pH value is 6.9-7.6, and the soil remediation target is that the effective state concentration of cadmium and lead in the soil is reduced by 30% after the passivation stabilization technology of the microcapsule composite material.

50% of modified zeolite, 20% of calcium magnesium phosphate fertilizer, 10% of calcium superphosphate, 15% of sodium sulfate and 5% of heavy magnesium oxide.

s1, taking 100kg of farmland polluted soil, putting 0.3kg of prepared microcapsule composite material (passivator), and uniformly spraying the microcapsule composite material on the soil surface;

The detection results of S4, Cd, Pb are shown in tables 5 and 6;

TABLE 5 initial concentration of Cd in soil in effective state

Time of day	Concentration of active state mg/kg	Rate of passivation
			Day
0	0.152	0.00％
			5 days	0.113	25.66％
10 days	0.092	39.47％
			20 days	0.094	38.16％
30 days	0.089	41.45％
			60 days	0.085	44.08％
90 days	0.087	42.76％
			120 days	0.084	44.74％

TABLE 6 initial concentration of Pb in soil in effective state

The initial effective concentration of Cd in the soil is 0.152mg/kg, and when the soil is maintained for 120 days, the effective concentration of Cd in the soil is 0.084mg/kg, the effective concentration of Cd is reduced by 44.74%, and the effective concentration of Cd is lower than the restoration target value of which the effective concentration is reduced by 30%. The initial effective concentration of Pb in the soil is 85.78mg/kg, and when the soil is maintained for 120 days, the effective concentration of Pb in the soil is 47.68mg/kg, the effective concentration of Pb is reduced by 44.42%, and is already lower than the restoration target value of the effective state reduced by 30%.

Example 4:

the experimental sample is from a Cd and Pb polluted farmland in Handan certain area in Hubei, and the total amount of Cd and Pb in the soil sample is detected by a method specified in soil environmental quality agricultural land soil pollution risk control standard (GB 15618-2018); the method specified in the determination of effective lead and cadmium in soil quality atomic absorption method (GB/T23739-2009) is adopted to detect the effective concentration of Cd and Pb in the soil sample. The detection result shows that the total content of Cd in the farmland polluted soil is 0.4-0.7 mg/kg, the total content of Pb in the farmland polluted soil is 600mg/kg, the pH value is 7.2-7.8, and the soil remediation target is that the effective state concentration of cadmium and lead in the soil is reduced by 30% after the passivation stabilization technology of the microcapsule composite material is adopted.

49% of modified zeolite, 25% of calcium magnesium phosphate fertilizer, 20% of calcium superphosphate, 5% of sodium sulfate and 1% of heavy magnesium oxide.

The detection results of S4, Cd, Pb are shown in tables 7 and 8;

TABLE 7 initial concentration of Cd in soil in effective state

TABLE 8 initial concentration of Pb in soil in effective state

Time of day	Concentration of active state mg/kg	Rate of passivation
			Day
0	16.78	0.00％
			5 days	14.45	13.89％
10 days	12.66	24.55％
			20 days	10.98	34.56％
30 days	9.77	41.78％
			60 days	9.24	44.93％
90 days	8.89	47.02％
			120 days	8.85	47.26％

The initial effective concentration of Cd in the soil is 0.115mg/kg, and when the soil is maintained for 120 days, the effective concentration of Cd in the soil is 0.072mg/kg, the effective concentration of Cd is reduced by 37.39%, and the effective concentration of Cd is lower than the restoration target value of which the effective state is reduced by 30%. The initial effective concentration of Pb in the soil is 16.78mg/kg, and when the soil is maintained for 120 days, the effective concentration of Pb in the soil is 8.85mg/kg, the effective concentration of Pb is reduced by 47.26 percent and is already lower than the restoration target value of the effective state reduced by 30 percent.

The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes will occur to those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. The microcapsule composite material for Cd and Pb polluted soil is characterized by comprising the following components in percentage by weight:

2. The microcapsule composite of claim 1, wherein the modified clay mineral is a modified zeolite.

3. The microcapsule composite of claim 1, wherein the calcium magnesium based composite comprises one or more of a calcium magnesium phosphate fertilizer and a calcium superphosphate.

4. The microcapsule composite of claim 1, wherein the sulfate salt is sodium sulfate.

5. The microcapsule composite of claim 1, wherein the pH-adjusting agent comprises one or more of heavy magnesium oxide and hydrated lime.

6. A process for preparing a microcapsule composite according to any one of claims 1 to 5, comprising:

modifying clay mineral by heat to obtain modified clay mineral;

7. The method according to claim 6, wherein the modified clay mineral is prepared by a method comprising:

8. A method of repairing a microcapsule composite according to any one of claims 1 to 5, comprising: