Heavy metal soil remediation material and remediation method

Abstract

The invention relates to the technical field of heavy metal soil remediation, in particular to a heavy metal soil remediation material and a remediation method.The remediation method comprises the following steps that snow shells and mussel shells are dried and smashed, and mixed shell powder is obtained; calcining the mixed shell powder, and adding a mixture of charcoal and wormcast into the calcined mixed shell powder to obtain the soil remediation material, according to the remediation method, the soil remediation material is added into the heavy metal contaminated soil, remediation of the heavy metal contaminated soil is achieved, the metal solidification rate, the soil enzyme activity and the relative abundance of soil microorganisms are improved, the remediation effect is guaranteed, meanwhile, operation is simplified, and practical operability is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of heavy metal soil remediation, and in particular to a heavy metal soil remediation material and a remediation method. Background Art

[0002] With the accelerated development of industrialization, heavy metal pollution incidents have occurred frequently, which has increasingly aroused public concern about the comprehensive management of heavy metals. Among them, soil heavy metal pollution has become a key environmental problem that needs to be solved urgently. As the cornerstone of agricultural production, the heavy metals accumulated in soil are difficult to degrade, highly stable, hidden and persistent. A large amount of heavy metals are discharged into the soil, which not only seriously interferes with the basic functions of the soil such as food production, ecological regulation and cultural bearing, but also may enter the human body through the cumulative effect of the food chain and affect human health.

[0003] Shells are easily available natural materials and are valuable renewable mineral resources. As a biomass material, shell powder is characterized by rich surface pore structure, large porosity and specific surface area, unobstructed pores, and contains alkali metal compounds. The adsorption mechanism includes chemical, physical and ion exchange adsorption, which is suitable for heavy metal adsorption. In addition, my country's shell production ranks first in the world, with an annual waste volume of more than 10 million tons. Large-scale stacking threatens the environment and residents' health. Using shell powder as a heavy metal passivation and repair material can reduce the harm of discarded shells and achieve resource utilization and reduction.

[0004] A Chinese patent with publication number CN115228909A discloses a method for repairing heavy metal contaminated soil. Fly ash is mixed with a calcium source and dissolved in an alkaline solution. A directional reaction is then achieved through a hydrothermal reaction to efficiently activate the fly ash to obtain a soil repair material. The product has high quality and strong ability to adsorb and solidify heavy metals. It is suitable for most soils, but its preparation process is relatively complicated and difficult to operate. Summary of the invention

[0005] In view of the deficiencies of the above-mentioned prior art, the object of the present invention is to provide a heavy metal soil adsorption material and a remediation method. The remediation method of the present invention improves the metal solidification rate, soil enzyme activity and the relative abundance of soil microorganisms, ensures the remediation effect while simplifying the operation, and has practical operability.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions: A heavy metal soil remediation method comprises the following steps: The shells are dried and crushed to obtain shell powder.

[0007] The shell powder is calcined. After calcination, the shell powder cracks at high temperature, adding a large number of gaps, and the specific surface area increases compared to before calcination, becoming more loose and porous. The shell powder can also be converted into calcium oxide, the specific surface area increases, and the adsorption sites increase.

[0008] Biochar and earthworm cast are added to the calcined shell powder, resulting in physical adsorption and chemical passivation to obtain a soil remediation material. Both the shell powder, biochar, and earthworm cast have a porous structure and a large specific surface area, which can fix heavy metal ions in the soil through physical adsorption and reduce their bioavailability. Moreover, components such as humic acid and calcium carbonate contained in the earthworm cast can undergo complexation reactions or precipitation with heavy metals; the shell powder contains more than 90% calcium carbonate, which can increase the pH value after being applied to acidic soil, promoting the formation of carbonate or hydroxide precipitates of heavy metals, and the calcium ions therein undergo displacement reactions with heavy metal ions to reduce the bioavailability of heavy metals; the porous structure and abundant surface functional groups of biochar such as hydroxyl and carboxyl groups can adsorb heavy metal ions and reduce their bioavailability through complexation and precipitation, fixing heavy metals in the soil and reducing their toxicity; the shell powder and biochar provide a protective microenvironment for microorganisms, promoting their metabolic activity and reducing heavy metals to low-toxic forms, and highly active microorganisms such as Pseudomonas and Bacillus subtilis enriched in the earthworm cast can accelerate the transformation of metal forms.

[0009] The soil remediation material is added to the heavy metal-contaminated soil to achieve the remediation of heavy metal-contaminated soil.

[0010] In a preferred embodiment of the present invention, the mass percentage of the soil remediation material in the heavy metal-contaminated soil is 10% - 15%.

[0011] In a preferred embodiment of the present invention, the mass ratio of biochar, earthworm cast to shell powder is 0.8 - 1.2:0.8 - 1.2:0.8 - 1.2.

[0012] In a preferred embodiment of the present invention, the shell is one or both of snow shells and mussel shells. Snow shells and mussel shells are common solid wastes in aquaculture with large yields, and the utilization of these two kinds of shells can play a role in the resource utilization of fishery solid wastes.

[0013] In a preferred embodiment of the present invention, the biochar is rice husk biochar.

[0014] In a preferred embodiment of the present invention, the calcination temperature is 850°C - 900°C, the calcination time is 2 hours - 2.5 hours, and the calcination heating rate is 10°C / min - 15°C / min.

[0015] In a preferred embodiment of the present invention, the heavy metal-contaminated soil includes lead, cadmium, and copper, and the contents of lead, cadmium, and copper in the soil are 2028 mg / kg - 2029 mg / kg, 1.25 mg / kg - 1.35 mg / kg, and 284 mg / kg - 285 mg / kg, respectively.

[0016] In a preferred embodiment of the present invention, the remediation time of the soil remediation material in heavy metal contaminated soil is 5 days to 25 days.

[0017] In a preferred embodiment of the present invention, the snow shell and the mussel shell are crushed and passed through a 40-60 mesh sieve.

[0018] In a preferred embodiment of the present invention, the pH of the heavy metal contaminated soil after remediation by the soil remediation material is 7 to 7.5.

[0019] Another object of the present invention is to provide a heavy metal soil remediation material, which comprises shell powder, biochar and earthworm manure with a mass ratio of 0.8-1.2:0.8-1.2:0.8-1.2.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. In the present invention, by calcining the shell powder, the shell powder cracks at high temperature after calcination, increasing a large number of gaps, and the specific surface area becomes larger compared with that before calcination, becoming more porous. It can also convert the shell powder into calcium oxide, with an increased specific surface area and more adsorption sites. Adding biochar and earthworm manure to the calcined shell powder results in physical adsorption and chemical passivation to obtain a soil remediation material. Both the shell powder, biochar and earthworm manure have a porous structure and a large specific surface area, which can fix heavy metal ions in the soil through physical adsorption, reducing their bioavailability. Moreover, components such as humic acid and calcium carbonate contained in the earthworm manure can undergo complexation reactions or precipitation with heavy metals; the shell powder contains more than 90% calcium carbonate, which can increase the pH value after being applied to acidic soil, prompting heavy metals to form carbonate or hydroxide precipitates, and the calcium ions therein undergo substitution reactions with heavy metal ions, reducing the bioavailability of heavy metals; the porous structure and abundant surface functional groups such as hydroxyl and carboxyl groups of biochar can adsorb heavy metal ions and reduce their bioavailability through complexation and precipitation, fixing heavy metals in the soil and reducing their toxicity; the shell powder and biochar provide a protective microenvironment for microorganisms, promoting their metabolic activity and reducing heavy metals to low-toxic forms. The highly active microorganisms such as Pseudomonas and Bacillus subtilis enriched in the earthworm manure can accelerate the transformation of metal forms. Adding the soil remediation material to heavy metal contaminated soil can achieve the remediation of heavy metal contaminated soil. The present invention simplifies the preparation method of the remediation material while ensuring the remediation effect.

[0021] 2. Synergistic effect: When oyster shell powder, earthworm cast and biochar are used in combination, all three have the ability to adsorb heavy metals, but their adsorption mechanisms and sites are different. Oyster shell powder is rich in calcium carbonate, which helps to reduce the solubility of heavy metals and increase the possibility of their precipitation; earthworm cast is rich in organic matter and humic acid, and its large specific surface area increases the contact area with heavy metal ions, enabling effective adsorption of heavy metal ions; functional groups on the surface of biochar such as hydroxyl groups and carboxyl groups can react with heavy metal ions to form stable metal complexes, thereby fixing heavy metals. Oyster shell powder, earthworm cast and biochar act together through different adsorption mechanisms such as chemical precipitation, physical adsorption and chemical adsorption to effectively adsorb and fix heavy metal ions in the soil. When the three coexist, multiple adsorption mechanisms can be formed to improve the removal efficiency of heavy metals.

[0022] 3. The remediation method of the present invention improves the solidification rate of metals, soil enzyme activity and the relative abundance of soil microorganisms, simplifies the operation while ensuring the remediation effect, and has practical operability. Description of the Drawings

[0023] Figure 1 Effect of different oyster shell powder matrix materials on soil pH.

[0024] Figure 2 Effect of different oyster shell powder matrix materials on cation exchange capacity.

[0025] Figure 3 Effect of oyster shell powder matrix materials with different cultivation times on nitrogen, phosphorus and potassium.

[0026] Figure 4 Effect of oyster shell powder matrix materials with different cultivation times on organic matter.

[0027] Figure 5 Effect of oyster shell powder matrix materials with different cultivation times on five forms of lead. A, B, C, D, E, F, G correspond to sc1, sc2, sw1, sw2, scw1, s, ck respectively.

[0028] Figure 6 Effect of oyster shell powder matrix materials with different cultivation times on total lead content.

[0029] Figure 7 Effect of oyster shell powder matrix materials with different cultivation times on five forms of cadmium. A, B, C, D, E, F, G correspond to sc1, sc2, sw1, sw2, scw1, s, ck respectively.

[0030] Figure 8 Effect of oyster shell powder matrix materials with different cultivation times on total cadmium content.

[0031] Figure 9For the effects of shell powder matrix materials with different cultivation times on five forms of copper, A, B, C, D, E, F, and G correspond to sc1, sc2, sw1, sw2, scw1, s, and ck respectively.

[0032] Figure 10 For the effects of shell powder matrix materials with different cultivation times on the total copper content.

[0033] Figure 11 Among them, (a) is the graph of sucrase activity changing with time, and (b) is the graph of the promotion rate of sucrase activity.

[0034] Figure 12 Among them, (a) is the graph of urease activity changing with time, and (b) is the graph of the promotion rate of urease activity.

[0035] Figure 13 Among them, (a) is the graph of FDAH enzyme activity changing with time, and (b) is the promotion rate of FDAH enzyme activity.

[0036] Figure 14 Among them, (a) is the graph of soil alkaline phosphatase activity changing with time, and (b) is the promotion rate of alkaline phosphatase activity.

[0037] Figure 15 Among them, (a) is the OTU Rank curve graph, and (b) is the OTU Venn diagram.

[0038] Figure 16 It is the bar graph of species classification at the phylum classification level of the sample.

[0039] Figure 17 It is the bar graph of species classification at the genus classification level of the sample.

[0040] Figure 18 It is the heat map of correlation abundance at the phylum level.

[0041] Figure 19 It is the heat map of correlation abundance at the genus level.

[0042] Figure 20 It is the chao index dilution curve graph.

[0043] Figure 21 It is the obs index dilution curve graph.

[0044] Figure 22 It is the simpson dilution curve graph.

[0045] Figure 23 It is the ace dilution curve graph. Specific implementation methods

[0046] Combined with the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described with the preferred embodiments and the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0047] It should be noted that all the professional terms used in the present invention are only for the purpose of describing specific embodiments, and are not intended to limit the protection scope of the present invention. Unless otherwise specifically stated, all kinds of raw materials, reagents, instruments and equipment used in the following embodiments of the present invention can be obtained through market purchase or prepared by existing methods.

[0048] Example 1 A method for repairing heavy metal-contaminated soil, comprising the following steps: (1) Wash the surface impurities of the snow shells and mussel shells used for the experiment, place them in a drying oven and dry at 37°C, then put them into a pulverizer and pulverize for 5 minutes to form granular and powdery substances, and pass through a 40-mesh sieve, and store them sealed.

[0049] (2) Put the two kinds of shell powders into a ceramic muffle furnace and heat them at a heating rate of 10°C per minute, and calcine at 900°C for two hours, take them out after cooling, grind and disperse them in an agate mortar, and store them sealed for the next step.

[0050] (3) Accurately weigh 300 g of the air-dried soil sample passed through a 40-mesh sieve and put it into a breathable flower pot. The contents of lead, cadmium, and copper in the air-dried soil sample are 2028.5 mg / kg, 1.3 mg / kg, and 284.5 mg / kg respectively. Prepare target concentration solutions of PdSO4, CdCl2·2H2O, and CuCl2·2H2O, add them to the soil and stir well, mix evenly, and adjust the water content of the contaminated soil to 70% of the field water holding capacity. After the lead, cadmium, and copper are stably cultured for 3 days, the contaminated soil after culturing is used for this experiment.

[0051] (4) Add 5% of the mixed shell powder, 5% of the biochar, and 5% of the earthworm manure based on the weight of the naturally air-dried soil to the contaminated soil obtained in step (3), mix evenly, and let it stand for 25 days to achieve the repair of the heavy metal soil, denoted as scw1.

[0052] Example 2 A method for repairing heavy metal-contaminated soil, comprising the following steps: (1) Wash the surface impurities of the snow shells and mussel shells used for the experiment, place them in a drying oven and dry at 37°C, then put them into a pulverizer and pulverize for 5 minutes to form granular and powdery substances, and pass through a 40-mesh sieve, and store them sealed.

[0053] (2) Put the two kinds of shell powders into a ceramic muffle furnace and heat them at a heating rate of 10 °C / minute, and calcine them at 900 °C for two hours. After cooling, take them out, grind and disperse them in an agate mortar, and store them sealed for the next step.

[0054] (3) Accurately weigh 300 g of the air-dried soil sample that has passed through a 40-mesh sieve and put it into a breathable flower pot. The lead, cadmium, and copper contents account for 2028.5 mg / kg, 1.3 mg / kg, and 284.5 mg / kg of the weight of the air-dried soil sample respectively. Prepare target concentration solutions of PdSO4, CdCl2·2H2O, and CuCl2·2H2O, add them to the soil and stir well, mix evenly, and adjust the water content of the contaminated soil to 70% of the field water holding capacity. After stabilizing and culturing lead, cadmium, and copper for 3 days, use the contaminated soil after culturing as the contaminated soil for this experiment.

[0055] (4) Add 5% of the mixed shell powder and 5% of the biochar based on the weight of the naturally air-dried soil to the contaminated soil obtained in step (3), mix evenly, and leave it for 25 days to achieve the remediation of heavy metal-contaminated soil, denoted as sc1.

[0056] Example 3 A method for remediating heavy metal-contaminated soil, comprising the following steps: (1) Wash the surface impurities of the snow shells and mussel shells used for the experiment, put them into a drying oven and dry them at 37 °C, then put them into a crusher and crush them into granular and powdery forms for 5 minutes, and pass through a 40-mesh sieve, and store them sealed.

[0057] (2) Put the two kinds of shell powders into a ceramic muffle furnace and heat them at a heating rate of 10 °C / minute, and calcine them at 900 °C for two hours. After cooling, take them out, grind and disperse them in an agate mortar, and store them sealed for the next step.

[0058] (3) Accurately weigh 300 g of the air-dried soil sample that has passed through a 40-mesh sieve and put it into a breathable flower pot. The lead, cadmium, and copper contents account for 2028.5 mg / kg, 1.3 mg / kg, and 284.5 mg / kg of the weight of the air-dried soil sample respectively. Prepare target concentration solutions of PdSO4, CdCl2·2H2O, and CuCl2·2H2O, add them to the soil and stir well, mix evenly, and adjust the water content of the contaminated soil to 70% of the field water holding capacity. After stabilizing and culturing lead, cadmium, and copper for 3 days, use the contaminated soil after culturing as the contaminated soil for this experiment.

[0059] (4) Add 10% of the mixed shell powder and 5% of the biochar based on the weight of the naturally air-dried soil to the contaminated soil obtained in step (3), mix evenly, and leave it for 25 days to achieve the remediation of heavy metal-contaminated soil, denoted as sc2.

[0060] Example 4 A method for remediating heavy metal-contaminated soil, comprising the following steps: (1) Wash the surface impurities of the snow shells and mussel shells used for the experiment, place them in a drying oven at 37 °C for drying, then put them into a crusher and crush for 5 minutes to form granular and powdery substances, and pass through a 40-mesh sieve, and store them sealed.

[0061] (2) Put the two kinds of shell powders into a ceramic muffle furnace and heat them at a heating rate of 10 °C / minute, and calcine them at 900 °C for 2 hours. After cooling, take them out, grind and disperse them in an agate mortar, and store them sealed for the next step.

[0062] (3) Accurately weigh 300 g of the air-dried soil sample passed through a 40-mesh sieve and put it into a breathable flower pot. The contents of lead, cadmium, and copper in the air-dried soil sample account for 2028.5 mg / kg, 1.3 mg / kg, and 284.5 mg / kg of the weight of the air-dried soil sample respectively. Prepare target concentration solutions of PdSO4, CdCl2·2H2O, and CuCl2·2H2O, add them to the soil and stir well, mix evenly, and adjust the water content of the contaminated soil to 70% of the field water holding capacity. After 3 days of stable cultivation of lead, cadmium, and copper, use the contaminated soil after the cultivation is completed for this experiment.

[0063] (4) Add 5% of the mixed shell powder and 5% of earthworm manure by weight of the air-dried soil to the contaminated soil obtained in step (3), mix evenly, and leave it for 25 days for treatment to achieve the remediation of the heavy metal-contaminated soil, denoted as sw1.

[0064] Example 5 A method for remediating heavy metal-contaminated soil, comprising the following steps: (1) Wash the surface impurities of the snow shells and mussel shells used for the experiment, place them in a drying oven at 37 °C for drying, then put them into a crusher and crush for 5 minutes to form granular and powdery substances, and pass through a 40-mesh sieve, and store them sealed.

[0065] (2) Put the two kinds of shell powders into a ceramic muffle furnace and heat them at a heating rate of 10 °C / minute, and calcine them at 900 °C for 2 hours. After cooling, take them out, grind and disperse them in an agate mortar, and store them sealed for the next step.

[0066] (3)Accurately weigh 300 g of the air-dried soil sample that has passed through a 40-mesh sieve and put it into a breathable flower pot. The lead, cadmium, and copper contents account for 2028.5 mg / kg, 1.3 mg / kg, and 284.5 mg / kg of the weight of the air-dried soil sample respectively. Prepare target concentration solutions of PdSO4, CdCl2·2H2O, and CuCl2·2H2O, add them to the soil, stir well, mix evenly, and adjust the water content of the contaminated soil to 70% of the field water holding capacity. After the lead, cadmium, and copper are stably cultured for 3 days, it is used as the contaminated soil after culturing for this experiment.

[0067] (4)Add 10% of the mixed shell powder and 5% of the earthworm manure based on the weight of the naturally air-dried soil to the contaminated soil obtained in step (3), mix evenly, and place for 25 days to achieve the remediation of heavy metal-contaminated soil, denoted as sw2.

[0068] Control 1 A method for remediating heavy metal-contaminated soil, comprising the following steps: (1)Wash the surface impurities of the snow shells and mussel shells used for the experiment, put them into a drying oven and dry at 37 °C, then put them into a pulverizer and pulverize for 5 minutes into granular and powdery forms, and pass through a 40-mesh sieve, and store them sealed.

[0069] (2)Put the two kinds of shell powders into a ceramic muffle furnace and heat at a heating rate of 10 °C per minute, and calcine at 900 °C for two hours, take them out after cooling, grind and disperse them in an agate mortar, and store them sealed for the next step.

[0070] (3)Accurately weigh 300 g of the air-dried soil sample that has passed through a 40-mesh sieve and put it into a breathable flower pot. The lead, cadmium, and copper contents account for 2028.5 mg / kg, 1.3 mg / kg, and 284.5 mg / kg of the weight of the air-dried soil sample respectively. Prepare target concentration solutions of PdSO4, CdCl2·2H2O, and CuCl2·2H2O, add them to the soil, stir well, mix evenly, and adjust the water content of the contaminated soil to 70% of the field water holding capacity. After the lead, cadmium, and copper are stably cultured for 3 days, it is used as the contaminated soil after culturing for this experiment.

[0071] (4)Add 5% of the mixed shell powder based on the weight of the naturally air-dried soil to the contaminated soil obtained in step (3), mix evenly, and place for 25 days to achieve the remediation of heavy metal-contaminated soil, denoted as s.

[0072] Result analysis.

[0073] Study the influence of shell powder matrix materials on the physical and chemical properties of soil.

[0074] The pH of the soil with different treatments was measured as Figure 1As shown, compared with the control group, the pH of all experimental groups was 0.5 - 0.7 higher than that of the control group, which was suitable for plant growth, indicating that adding shell powder matrix materials could increase the pH of the soil and maintain it within the neutral range.

[0075] The cation exchange method of soils with different treatments was measured as Figure 2 shown. The cation exchange capacity of the soils in each experimental group was significantly improved compared with the control group, and the scw1 group was the best, showing the best effect of increasing the cation exchange capacity. This is because the fertilizer retention ability of vermicompost itself can effectively retain the Ca in shell powder + and the cations in biochar in the soil.

[0076] The nutrient content of soils with different treatments was measured as Figure 3 shown. Compared with the control group, at the end of the experiment, the total amounts of the three nutrient elements of nitrogen, phosphorus, and potassium in the six experimental groups applying shell powder matrix materials were significantly higher than those of the control group, and the sw1 group was the best. This is because vermicompost contains rich inorganic salts such as nitrogen, phosphorus, and potassium, as well as humic acid substances and various trace elements, and these substances can increase the nutrient content of the soil.

[0077] The organic matter content of soils with different treatments was measured as Figure 4 shown. The organic matter content of the soils in each experimental group was generally higher than that of the control group. Among them, the organic matter content of the scw1 group of soil was always the highest during the same period, indicating that the shell powder matrix materials had a significant positive effect on improving the organic matter content of the soil.

[0078] The effects of shell powder matrix materials on the forms and contents of heavy metals in the soil.

[0079] The effects of different treatments on the forms and contents of lead were measured as Figure 5 and Figure 6 shown. Among the six experimental groups applying shell powder matrix materials, the content of residual lead in the soil was generally higher than that of the control group. Among them, the proportion of residual lead in the sc1 group was the highest, and the total lead content in this group could reach up to 247 mg / kg at most. This data clearly shows that compared with other experiments in the same group, the passivation and remediation effect of the sc1 group on soil lead pollution was more significant. This is because the loose and porous nature of biochar has a strong adsorption of lead ions, and at the same time contains a large number of alkaline substances such as organic anions and carbonates, which can adsorb and fix heavy metals in the soil and reduce their bioavailability.

[0080] The effects of different treatments on the forms and contents of cadmium were measured as Figure 7 and Figure 8As shown, among the six experimental groups applying shell powder matrix materials, compared with the control group, the residual cadmium content in all experimental groups showed an increasing trend in the first 15 days. The total cadmium content in the sc1 group reached the highest value of 0.298 mg / L at 15 d; the water-soluble cadmium content decreased significantly, and the decrease in the sw1 group was the most significant. This is because the humic acid in earthworm manure is also a strong adsorbent, which can adsorb soluble heavy metals and reduce their bioavailability.

[0081] The effects of different treatments on the copper form and content were measured as Figure 9 and Figure 10 shown. Among the six experimental groups applying shell powder matrix materials, compared with the control group, at the initial stage of the experiment, there was no significant difference in the proportion of residual copper. The proportion of residual copper in the experimental groups applying shell powder matrix materials on the 20th day increased significantly, and the sc1 group had the best effect. It shows that adding shell powder matrix materials can effectively promote the transformation of copper ion forms, thereby reducing their bioavailability and alleviating the toxicity of copper in the soil.

[0082] In summary, applying different shell powder matrix materials all have an impact on the soil heavy metal content, but the effects on the transformation of soil heavy metal forms are different.

[0083] The impact of the process of using shell powder to repair heavy metal contaminated soil on soil enzyme activity.

[0084] The changes in soil sucrase activity in different treatments were measured as Figure 11 shown. Among the six experimental groups applying shell powder matrix materials, compared with the control group, the soil sucrase activity in all experimental groups increased. The sucrase activity in the treatment group of 5% shell powder + 5% biochar + 5% earthworm manure was significantly higher than that of CK. This is mainly because the porous structure and alkaline characteristics of shell powder and biochar can neutralize the acidic soil environment, provide a stable habitat space for microorganisms, promote the increase in the content of microbial biomass carbon and nitrogen, and thus stimulate the metabolic activities of enzyme-producing microorganisms; the humic acid and plant growth hormones in earthworm manure can provide substrates for enzymatic reactions, and the increase in sucrase activity is related to the promotion of carbon source decomposition by humic acid.

[0085] The changes in soil urease activity in different treatments were measured as Figure 12As shown, in the six experimental groups applying shell powder matrix materials, compared with the control group, the soil urease activity in all experimental groups increased. Among them, the urease activity in the treatment group of 5% shell powder + 5% biochar + 5% earthworm cast was the highest, increasing by 19.02% compared with the CK treatment. This is mainly because the porous structure and alkaline properties of shell powder biochar can neutralize the acidic soil environment, provide a stable habitat for microorganisms, promote the increase in the content of microbial biomass carbon and nitrogen, thereby stimulating the metabolic activities of enzyme-producing microorganisms, and thus promoting the urease activity related to nitrogen cycling; each gram of earthworm cast contains more than 100 million beneficial bacteria such as Pseudomonas and Bacillus, significantly increasing the abundance of enzyme-producing bacteria. The increase in urease activity is directly related to the enhanced metabolism of nitrogen-fixing bacteria.

[0086] The changes in soil FDAH enzyme activity in different treatments were measured as Figure 13 As shown, in the six experimental groups applying shell powder matrix materials, compared with the control group, the soil FDAH enzyme activity in all experimental groups increased. Among them, the FDAH enzyme activity in the treatment group of 5% shell powder + 5% biochar + 5% earthworm cast was the highest, increasing by 33.64% compared with the CK treatment. This is mainly because shell powder and biochar contain a large amount of organic carbon and trace elements such as iron, manganese, and copper, which serve as a persistent carbon source for microbial metabolism and directly participate in enzyme synthesis. Its surface functional groups such as carboxyl and hydroxyl can adsorb enzyme molecules, reduce enzyme loss, and improve the stability of FDAH enzyme. The rich organic matter such as amino acids and polysaccharides in earthworm cast can also significantly improve the FDAH enzyme activity.

[0087] The changes in soil alkaline phosphatase activity in different treatments were measured as Figure 14 As shown, in the six experimental groups applying shell powder matrix materials, compared with the control group, the soil alkaline phosphatase activity in all experimental groups increased. Among them, the alkaline phosphatase activity in the treatment group of 5% shell powder + 5% biochar + 5% earthworm cast was the highest, increasing by 31.60% compared with the CK treatment. This is mainly because the pore structure of shell powder and biochar provides a protective barrier for earthworm cast microorganisms, extending their survival cycle. The combination of the two can increase the stability of soil aggregates by 40% - 60%, reduce enzyme leaching, and maintain the long-term effectiveness of alkaline phosphatase activity. Each gram of earthworm cast contains more than 100 million beneficial bacteria such as Pseudomonas and Bacillus, significantly increasing the abundance of enzyme-producing bacteria. For example, the increase in alkaline phosphatase activity results from the proliferation of phosphorus mineralizing bacteria in earthworm cast.

[0088] The effects of different ratios of shell powder repair agents on the microbial community structure of heavy metal contaminated soil.

[0089] OTU rank curves are usually used to represent the species richness or diversity in soil samples. The horizontal broken line of the curve represents species abundance; the wider the length of the horizontal broken line, the greater the species abundance. The vertical axis of the curve is the evenness of the bacterial community; the shorter the vertical broken line, the more uniform the species composition of the sample. Calculate the respective relative abundances of OTUs in the sample and plot them in ascending order of relative abundance, with OTU Rank on the horizontal axis and the corresponding bacterial community abundance of out on the vertical axis. The data was processed using R version 3.1.1. From Figure 15 it can be seen that the species abundance under the CK treatment is the lowest, which is consistent with the enzyme activity data. This proves that the amendment has a significant improvement effect on heavy metal contaminated soil, and the microbial richness of heavy metal contaminated soil has been significantly increased after being repaired by the amendment. In addition, the OTU Venn diagram shows that the number of OTUs common to the species samples is 393, the number of unique OTUs of s is 21, sc2 has 29, sw2 has the most with 42, CK has 28, and swc1 only has 15. The number of OTUs in the soil sample is the best under the amendment of 10% oyster shell powder and 5% earthworm manure. In the earthworm manure treatment, due to the addition of earthworm manure, more organic matter and other nutrients are provided for the soil, so the number of OTUs therein has increased. Biochar, a high-surface area material rich in pores, provides a stable space for the growth of bacteria. Therefore, the number of soil OUTs after being repaired with biochar as an amendment is also at a relatively high level. The calcined oyster shell powder, mainly composed of calcium carbonate with a large number of pores, while adsorbing heavy metals, provides a relatively stable adsorption carrier for the bacteria in the soil. In addition, it contains various inorganic elements such as carbon, sulfur, magnesium, potassium, and iron that are easy for bacteria to grow. Therefore, oyster shell powder has the greatest promotion effect on OUT. When 10% oyster shell powder is added, the number of OUTs is the highest.

[0090] Species annotation analysis.

[0091] Differences in soil conditions have different effects on bacteria and fungi at the phylum and genus levels. The Acidobacteria group is acidophilic bacteria, and acidophilic bacteria play an important role in the ecosystem, which can acidify the soil and dissolve the insoluble mineral nutrients in the soil. As Figure 16 shown, at the phylum classification level, the relative abundance of Armatimonadetes is much higher than that of other bacteria, followed by Bacteroidetes. The relative abundance of bacteria in treatment No. 4 is the highest, that is, under the treatment of 10% mixed oyster shell powder + 5% earthworm manure, the microbial abundance has the greatest increase and the repair effect is the most significant. The microbial abundances of the two bacteria at the phylum level under the CK treatment are the lowest, and the two form a contrast, further confirming the significant repair effect of the amendment.

[0092] From Figure 16Analysis of the community structure at the phylum level showed that the relative abundance of Acidobacteria in the CK treatment was the highest, reaching 1.92%, and it decreased to less than 0.82% in the soil after adding the remediation agent. Acidobacteria are typical acidophilic bacteria in the soil. Acidified soil makes heavy metals in the soil exist in a soluble form, which greatly increases the migration ability of heavy metal ions and increases the potential pollution area. In addition, soluble heavy metals show stronger oxidation activity, which has an adverse impact on other conventional microbial flora in the soil. The abundance of Proteobacteria in the soil after the remediation agent treatment increased from 55.6% to 59.6% - 64.2%. As the conventional flora with the highest proportion in the soil samples, a higher abundance of Proteobacteria can well reflect the remediation and degradation level of microorganisms in the soil.

[0093] From Figure 17 Analysis of the community structure at the genus level showed that the content of Methylophilus in the CK treatment was as high as 3.52%. As an intermediately anaerobic bacterium, its high alkylation ability enables it to produce more biogas during compost fermentation, but this is not conducive to soil health in agricultural soil. The accumulation of heavy metals leads to its large reproduction, and the addition of the remediation agent to the soil greatly slows down this trend, with the content all being less than 0.17%. This is more conducive to the agricultural transformation of contaminated soil, which also shows that the addition of the remediation agent plays a positive role in soil remediation.

[0094] Species heatmap analysis.

[0095] Heatmap, that is, species heatmap analysis, is a way of presenting graphs by representing the data matrix with size and color gradients. Clustering of the species abundance or similarity of soil samples is completed through species heatmap analysis. The clustering results can directly reflect the differences and similarities of species communities in soil samples. Vertical clustering shows how similar the expression of all species is between samples. Lower distances and shorter branch lengths indicate that the species composition and abundance between samples are more similar. Horizontal clustering shows the similarity degree of species abundance between samples. Similar to vertical clustering, lower distances and shorter branch lengths indicate that the species composition between samples is more similar. The histograms of all species are described at the phylum level. Species heatmap analysis is based on the relative abundance of each species in each sample. The relative abundance of a species is highly variable and can affect the clustering of samples. Therefore, a base-10 logarithmic transformation was performed on the relative abundance. If the relative abundance of a certain species in a sample is zero, then the logarithm of half of the minimum abundance of this species in all samples is taken instead. In the R v3.1.1 language, it is through gplots.

[0096] From the heatmap analysis Figure 18It can be seen that the relative abundance of Streptomycetales species is the largest under the CK treatment, followed by the sw2 sample, and the smallest in the sc2 sample; while Figure 19 it can be seen that the relative abundance of Blastocatellia species is the highest under the CK treatment and the lowest in the sw2 sample. This is mainly because the addition of the repair agent improves the organic matter and enzyme activity, etc., and the two play a synergistic role to jointly improve the soil microbial community structure and increase the microbial species abundance. On the one hand, the addition of earthworm manure provides sufficient organic matter for the microorganisms in the soil, thereby improving the soil microbial community structure and increasing the microbial species abundance. On the other hand, the addition of biochar in the soil repair agent improves the adsorption performance of the soil for nutrients, provides sufficient nutrients necessary for the life activities of soil microorganisms, and the two in the repair agent play a synergistic role to jointly improve the soil performance, increase the soil microbial species abundance, and improve the soil microbial community structure.

[0097] Analysis of individual sample diversity.

[0098] The analysis of species diversity in a single sample is called Alpha diversity analysis, including Obs index, Chao index, Ace index, and Shannon index. The indexes of each sample are shown in Table 1. Among them, the Obs index, Chao index, and Ace index reflect the richness of the community in the sample, that is, simply referring to the number of species in the community without considering the abundance of each species in the community. The dilution curves corresponding to these three indexes also reflect whether the sequences of the sample are sufficient. If the curve tends to be horizontal, the sequencing is close to all species. If not, the species concentration in the sample is very high, and there are still some species that are not captured during sequencing. The Shannon index reflects the diversity of the community, which is affected by the species richness and species evenness in the sample community. Under the condition of the same species richness, the greater the evenness of each species in the community, the greater the diversity of the community is considered. The dilution curve is calculated from the relative proportion of known OTUs in the measured sequences and n, where n generally refers to a set of equidistant sequences smaller than the total number of sequences. The allowed value in the present invention is 500. When sampling tags, the expected values of the corresponding α indexes are calculated. In the present invention, the α diversity values of the samples are calculated using the software mothur. v1.31.2, and the corresponding dilution curves are drawn using the software R. v3.1.1.

[0099] Table 1 Statistical results of each diversity index of the samples

[0100] Figure 20 、 Figure 21 、 Figure 22 and Figure 23They are the rarefaction curves of the obs index, chao index, ace index, and Shannon index respectively. The image shows that as the sequencing volume increases, the obs index, chao index, ace index, and Shannon index all continuously increase. And when the sequencing volume reaches 50,000, all four reach a plateau. Vertically, the obs index, chao index, ace index, and Shannon index of the sc2 sample are the highest. This indicates that under the sc2 treatment, that is, the restoration with 10% mixed oyster shell powder + 5% biochar, the microbial diversity recovers best and the bacterial community is the richest, while the indices of the soil samples under the CK treatment are the lowest, that is, the species richness is the lowest. The two form a contrast, verifying that the repair agent formula of 10% mixed oyster shell powder + 5% biochar has a significant effect on restoring the microbial community diversity of heavy metal contaminated soil.

[0101] In summary, the application of oyster shell powder matrix materials can improve the activities of four soil enzymes. Among them, the treatment group of 5% oyster shell powder + 5% biochar + 5% earthworm manure has the best improvement effect. This is because the active substance nutrients in the earthworm manure in the repair agent formula provide sufficient substrates for the enzyme reaction, thus providing favorable conditions for the improvement of enzyme activity. On the other hand, the addition of the repair agent increases the soil organic matter content, while reducing the heavy metal content and improving soil conditions such as physical and chemical indices such as pH, cation exchange capacity, available phosphorus, and available nitrogen, providing a good soil environment for the enzyme reaction.

[0102] It should be noted that when the present invention involves numerical ranges, it should be understood that any value between the two endpoints of each numerical range and the two endpoints can be selected. Since the adopted step methods are the same as those in the embodiments, to prevent repetition, the present invention describes the preferred embodiments. Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they know the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present invention.

[0103] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these modifications and variations.

Claims

1. A heavy metal soil remediation method, characterized in that, It includes the following steps: Dry and crush the shells to obtain mixed shell powder; Calcine the shell powder, and add biochar and earthworm manure to the calcined mixed shell powder to obtain a soil remediation material; Add the soil remediation material to the heavy metal contaminated soil to achieve the remediation of heavy metal contaminated soil.

2. The heavy metal soil remediation method according to claim 1, characterized in that, The mass percentage of the soil remediation material in the heavy metal contaminated soil is 10% - 15%.

3. The heavy metal soil remediation method according to claim 1, characterized in that, The mass ratio of biochar, earthworm manure to shell powder is 0.8 - 1.2:0.8 - 1.2:0.8 - 1.

2.

4. The heavy metal soil remediation method according to claim 1, wherein The biochar is rice husk biochar.

5. The heavy metal soil remediation method according to claim 1, characterized in that, The calcination temperature is 850°C - 900°C, the calcination time is 2 hours - 2.5 hours, and the calcination heating rate is 10°C / min - 15°C / min.

6. The heavy metal soil remediation method according to claim 1, wherein The heavy metal contaminated soil includes lead, cadmium and copper, and the contents of lead, cadmium and copper in the soil are 2028mg / kg - 2029mg / kg, 1.25mg / kg - 1.35mg / kg and 284mg / kg - 285mg / kg respectively.

7. The heavy metal soil remediation method according to claim 1, characterized in that The remediation time of the soil remediation material in the heavy metal contaminated soil is 5 days - 25 days.

8. The heavy metal soil remediation method according to claim 1, characterized in that, The shell is one or both of snow shell and blue mussel shell.

9. The heavy metal soil remediation method according to claim 1, wherein The pH of the heavy metal contaminated soil after being remediated by the soil remediation material is 7 - 7.

5.

10. A heavy metal soil remediation material, characterized in that, The heavy metal soil remediation material includes shell powder, biochar and earthworm manure with a mass ratio of 0.8 - 1.2:0.8 - 1.2:0.8 - 1.2.

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