A soil remediation agent for heavy metal pollution and a preparation method thereof

Abstract

The application relates to the technical field of environmental remediation, and particularly discloses a soil remediation agent for heavy metal pollution and a preparation method thereof, the soil remediation agent comprising the following components in parts by weight: modified biomass charcoal 30-40 parts, chitosan-humic acid composite gel 15-20 parts, arbuscular mycorrhizal fungal spore suspension 5-8 parts, heavy metal-resistant microbial strain 3-5 parts, plant-based nano zero-valent iron 2-3 parts, sodium alginate solution 10-15 parts, composite enzyme preparation 1-2 parts and bio-based calcium carbonate 8-12 parts. The application prepares an adsorption material by using waste biomass, combines microbial microencapsulation and multi-component synergistic proportioning, constructs a dynamic response remediation system, realizes efficient heavy metal fixation, soil ecological protection and remediation cost optimization, and solves the problems of high reversibility risk, large ecological disturbance and insufficient soil adaptability of traditional remediation agents.

Description

Technical Field

[0001] This invention relates to the field of environmental remediation technology, and more specifically, to a soil remediation agent for heavy metal pollution and its preparation method. Background Technology

[0002] With the acceleration of industrialization and the aggravation of agricultural non-point source pollution, soil heavy metal pollution (such as Pb, Cd, Cr, etc.) has become increasingly serious, threatening ecological security and food quality safety. Existing remediation technologies need to balance high efficiency and eco-friendliness while meeting the cost requirements for large-scale application. Developing sustainable composite remediation systems has become an urgent need for the industry.

[0003] Traditional soil remediation agents have significant drawbacks: solidification / stabilization technologies are prone to secondary release of heavy metals due to environmental changes, chemical leaching is prone to secondary pollution and is costly, and bioremediation efficiency is significantly limited by the environment. In addition, remediation agents cause significant disturbance to soil microbial communities and enzyme activity, lack adaptive design for different soil types, and the ecological risks and long-term safety of new materials also lack effective assessment.

[0004] Therefore, it is necessary to design a composite remediation agent based on biomass-based materials and microbial-plant synergistic remediation to solve the problems of unstable remediation efficiency, large ecological disturbance, insufficient soil adaptability, high cost and lack of long-term safety in existing technologies, and to achieve the synergistic goal of efficient heavy metal fixation and optimized cost of soil ecological protection and remediation. Summary of the Invention

[0005] In view of this, the present invention proposes a soil remediation agent for heavy metal pollution, aiming to solve the problems of unstable remediation efficiency, large ecological disturbance, insufficient soil adaptability, high cost and lack of long-term safety in the existing technology, and to achieve the synergistic goal of efficient heavy metal fixation, soil ecological protection and cost optimization of remediation.

[0006] On the one hand, this invention proposes a soil remediation agent for heavy metal pollution, comprising the following components in parts by weight:

[0007] 30-40 parts modified biochar, 15-20 parts chitosan-humic acid composite gel, 5-8 parts arbuscular mycorrhizal fungal spore suspension, 3-5 parts heavy metal resistant microbial strains, 2-3 parts plant-based nano-zero valent iron, 10-15 parts sodium alginate solution, 1-2 parts composite enzyme preparation, and 8-12 parts modified bio-based calcium carbonate.

[0008] On the other hand, the present invention also proposes a method for preparing a soil remediation agent for heavy metal pollution, comprising the following steps:

[0009] Waste biomass is carbonized at high temperature and then ground to obtain modified biochar.

[0010] Modified bio-based calcium carbonate is obtained by calcining bio-based calcium carbonate at high temperature.

[0011] The modified biochar and modified bio-based calcium carbonate are mixed and ground to obtain a first mixture;

[0012] After culturing heavy metal-resistant microbial strains, they were mixed with sodium alginate solution and then dripped to obtain a second mixture.

[0013] The first mixture, the second mixture, and chitosan-humic acid composite gel, arbuscular mycorrhizal fungal spore suspension, plant-based nano-zero-valent iron, and composite enzyme preparation were mixed and stirred to obtain a third mixture:

[0014] Water and binder are added to the third mixture, and granules are obtained by extrusion and granulation.

[0015] The soil remediation agent is obtained by drying the granular mixture.

[0016] Furthermore, the high-temperature carbonization temperature is 700-900℃, and the high-temperature carbonization time is 2-4 hours.

[0017] Furthermore, the high-temperature calcination temperature is 900-1000℃, and the high-temperature calcination time is 2-6 hours.

[0018] Furthermore, the culture temperature for culturing the heavy metal resistant microbial strain is 25-37℃, the relative humidity is 70%-85%, and the culture time is 16-48 hours.

[0019] Furthermore, in the process of obtaining the second mixture through dripping, the dropper orifice diameter is 0.5-2.0 mm, the dripping speed is 1-5 mL / min, and the dripping temperature is 20-30℃.

[0020] Furthermore, when the first mixture, the second mixture, the chitosan-humic acid composite gel, the arbuscular mycorrhizal fungal spore suspension, the plant-based nano-zero-valent iron, and the composite enzyme preparation are mixed and stirred, the mass ratios of the first mixture, the second mixture, the arbuscular mycorrhizal fungal spore suspension, the plant-based nano-zero-valent iron, and the composite enzyme preparation to the chitosan-humic acid composite gel are respectively:

[0021] The mass ratio of the first mixture to the chitosan-humic acid composite gel is (2-5):1;

[0022] The mass ratio of the second mixture to the chitosan-humic acid composite gel is (1-3):1;

[0023] The mass ratio of arbuscular mycorrhizal fungal spore suspension to chitosan-humic acid composite gel was (0.3-0.5):1.

[0024] The mass ratio of plant-based nano-zero valent iron to chitosan-humic acid composite gel is (0.1-0.2):1.

[0025] The mass ratio of the compound enzyme preparation to the chitosan-humic acid composite gel is (0.05-0.1):1.

[0026] Furthermore, the mixing process specifically involves: first mixing at a low speed of 50-100 rpm for 15-22 minutes, and then mixing at a medium speed of 100-200 rpm for 20-30 minutes, with a mixing temperature of 20-30℃.

[0027] Furthermore, the extrusion pressure of the granular mixture obtained by extrusion and granulation is 1-5 MPa; the drying time of the drying process is 8-24 hours; and the drying temperature is 40-60℃.

[0028] On the other hand, the present invention also proposes the application of a soil remediation agent in soil contaminated with heavy metals.

[0029] Compared with existing technologies, the beneficial effects of this invention are as follows: It utilizes waste biomass and bio-based calcium carbonate to achieve waste recycling, reducing costs and being environmentally friendly; multiple technologies work synergistically, with modified biochar and bio-based calcium carbonate adsorbing and solidifying heavy metals, microencapsulation of microorganisms combined with fungi to improve remediation efficiency, and nano-zero-valent iron and composite enzyme preparations specifically transforming heavy metals, achieving broad-spectrum remediation of complex pollution; chitosan-humic acid gel is biodegradable, and processes such as low-temperature stirring reduce ecological disturbance; the process is highly adaptable, adapting to different soils through segmented stirring and parameter control, and the production process is mature, low-cost, and short-cycle, possessing both economic and technological advantages.

[0030] It is understood that the application of the soil remediation agent provided by this invention in soil contaminated with heavy metals has the same or similar beneficial effects as a method for preparing a soil remediation agent for heavy metal contamination, and will not be elaborated here. Attached Figure Description

[0031] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0032] Figure 1 A flowchart illustrating the method for preparing a soil remediation agent according to an embodiment of the present invention. Detailed Implementation

[0033] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the disclosure to those skilled in the art. It should be noted that, unless otherwise specified, embodiments and features in the embodiments of the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0034] On the one hand, in some embodiments of this application, a soil remediation agent for heavy metal pollution comprises the following components in parts by weight:

[0035] 30-40 parts modified biochar, 15-20 parts chitosan-humic acid composite gel, 5-8 parts arbuscular mycorrhizal fungal spore suspension, 3-5 parts heavy metal resistant microbial strains, 2-3 parts plant-based nano-zero valent iron, 10-15 parts sodium alginate solution, 1-2 parts composite enzyme preparation, and 8-12 parts modified bio-based calcium carbonate.

[0036] The soil remediation agent of the present invention preferably comprises the following components in parts by weight: 35-40 parts modified biochar, 18-20 parts chitosan-humic acid composite gel, 6-8 parts arbuscular mycorrhizal fungal spore suspension, 4-5 parts heavy metal resistant microbial strains, 2 parts plant-based nano-zero valent iron, 12-15 parts sodium alginate solution, 2 parts composite enzyme preparation, and 10-12 parts modified bio-based calcium carbonate.

[0037] The soil remediation agent of the present invention comprises the following components in parts by weight, preferably: 32 parts modified biochar, 20 parts chitosan-humic acid composite gel, 7 parts arbuscular mycorrhizal fungal spore suspension, 4.5 parts heavy metal resistant microbial strains, 13 parts sodium alginate solution, and 11 parts modified bio-based calcium carbonate.

[0038] On the other hand, some embodiments of the present invention provide a method for preparing a soil remediation agent for heavy metal pollution, see reference. Figure 1 The flowchart of the soil remediation agent provided by the present invention specifically includes the following steps:

[0039] S1. The waste biomass is carbonized at high temperature and then ground to obtain modified biochar.

[0040] S2. Calcine bio-based calcium carbonate at high temperature to obtain modified bio-based calcium carbonate;

[0041] S3. The modified biochar and modified bio-based calcium carbonate are mixed and ground to obtain a first mixture;

[0042] S4. After culturing the heavy metal resistant microbial strain, mix it with sodium alginate solution and then drip it to obtain the second mixture;

[0043] S5. Mix the first mixture, the second mixture, chitosan-humic acid composite gel, arbuscular mycorrhizal fungal spore suspension, plant-based nano-zero valent iron, and composite enzyme preparation to obtain a third mixture.

[0044] S6. Add water and binder to the third mixture, and obtain a granular mixture by extrusion and granulation;

[0045] S7. The granular mixture is dried to obtain the soil remediation agent.

[0046] Specifically, the waste biomass is first crushed and pretreated to a particle size of 2-5 mm before being carbonized at high temperature. After high-temperature carbonization, it is cooled for 3-6 hours and then ground to 100-200 mesh to obtain modified biochar.

[0047] Preferably, the cooling time is 4 hours, and the material is ground to 150 mesh.

[0048] Specifically, the bio-based calcium carbonate is pretreated before high-temperature calcination to improve calcination efficiency. The pretreatment involves first cleaning the bio-based calcium carbonate, and then pulverizing it to 100-200 mesh.

[0049] Preferably, the bio-based calcium carbonate is pulverized to 150 mesh.

[0050] Specifically, bio-based calcium carbonate is calcined at high temperature, then hydrated and carbonized to produce active calcium carbonate, thus obtaining modified bio-based calcium carbonate.

[0051] Specifically, the mass ratio of modified biochar to modified bio-based calcium carbonate is 1:3. The waste biomass is selected from either rice husks or corn stalks; the bio-based calcium carbonate is selected from seashells or eggshells.

[0052] Specifically, the grinding time for obtaining modified biochar is 30-50 minutes; the grinding time for obtaining the first mixture is 20-40 minutes.

[0053] Specifically, the modified biochar and modified bio-based calcium carbonate are mixed by stirring at a speed of 100-200 rpm, preferably 150 rpm, for a time of 30-60 minutes, preferably 40 minutes.

[0054] Specifically, the preferred heavy metal-resistant microbial strain is Bacillus subtilis.

[0055] Specifically, when culturing heavy metal-resistant microbial strains, at a concentration of 20 mg / L Cd... 2+They were cultured in LB medium at a pH of 6.5-7.5, preferably 7.

[0056] Specifically, the mass ratio of the cultured heavy metal-resistant microbial strain to the sodium alginate solution is (3-5):(10-15). The mixed solution is then added to the calcium chloride solution by dripping to carry out a cross-linking reaction, resulting in a second mixture.

[0057] Specifically, the second mixture is in the form of microcapsules, with calcium chloride solution as a cross-linking agent. The concentration of the calcium chloride solution is 0.1-0.5 mol / L, preferably 0.3 mol / L.

[0058] Specifically, the compound enzyme preparation is a urease-phosphatase complex or A3660 type acid phosphatase, preferably a urease-phosphatase complex, with a mass ratio of urease to phosphatase of 1:1.

[0059] Specifically, the preparation method of arbuscular mycorrhizal fungal spore suspension is as follows: Arbuscular mycorrhizal fungi are cultured at 28℃ and 150r / min under alternating light and dark conditions until obvious hyphae grow in the culture medium suspension, and then filtered to obtain arbuscular mycorrhizal fungal spore suspension.

[0060] Specifically, the present invention does not impose any special limitations on the preparation methods of chitosan-humic acid composite gel and plant-based nano-zero valent iron, which can be obtained by using commercially available products or by using technical solutions well known to those skilled in the art.

[0061] As a preferred embodiment, the chitosan-humic acid composite gel can be prepared using existing technologies, such as reverse suspension crosslinking or freeze-drying. For example, the specific preparation method can be found in the technology of the published patent CN114471478A.

[0062] For example, the chitosan-humic acid composite gel provided in the specific embodiment is prepared by the following method:

[0063] (1) Add 1g of soluble sodium humate to 50mL of water and stir magnetically to dissolve it. Add 1g of chitosan powder to the solution and stir magnetically to disperse it evenly. Then add 0.5mL of acetic acid and stir magnetically to completely dissolve the chitosan to obtain an aqueous solution system.

[0064] (2) Take 250 mL of cyclohexane, add 1 mL of Span 80, and stir with a glass rod to obtain an organic system;

[0065] (3) Prepare a homogeneous crosslinking system by mixing 5 mL of 25% glutaraldehyde, 10 mL of cyclohexane and 50 mL of ethanol;

[0066] (4) After stirring the organic system and aqueous solution system at high speed, heat to 45°C, then add the cross-linking system dropwise and react for 1.5 h. Then add 2 g of polyacrylic acid to the solution to increase the mechanical strength of the previously solidified small balls. Filter out the small balls and measure the particle size to be about 2.5-3 mm. Wash with ethanol 3 times and then with ultrapure water 3 times to obtain chitosan-humic acid composite gel.

[0067] Plant-based nano-zero-valent iron can be synthesized using existing technologies with plant extracts as reducing agents, such as the reduction method using locust tree leaf extract. For specific preparation methods, please refer to the technology published in patent CN114984911B.

[0068] For example, the preparation method of the plant-based nano-zero valent iron provided in a specific embodiment of the present invention includes:

[0069] (1) After the tea residue waste was naturally air-dried, it was crushed to a particle size of about 10mm to obtain tea residue powder. Then, 5g of tea residue powder was ground and mixed with 3g of Fe(NO3)3 and placed in a crucible. The crucible was wrapped with two layers of tin foil and placed in a muffle furnace. It was then roasted at 450℃ for 2 hours in a static air atmosphere. After roasting, the muffle furnace was naturally cooled to room temperature to obtain a plant-based γ-Fe2O3 complex.

[0070] (2) The plant-based γ-Fe2O3 complex was mixed with NaOH at a mass ratio of 1:1.5 and then placed in a crucible. The crucible was wrapped with two layers of tin foil and placed in a muffle furnace. It was calcined at 600°C for 2 hours in a static air atmosphere. After natural cooling, it was washed with softened water and dried in a constant temperature drying oven at 80°C for 4 hours to obtain the plant-based nano-zero valent iron complex, in which iron accounted for 45% of the mass percentage of the complex.

[0071] Specifically, the binder is selected from either pregelatinized corn starch binder or sodium carboxymethyl cellulose, and the amount of binder added is 1%-3% of the mass of the third mixture. After extrusion granulation, the particle size of the granular mixture is screened and the particle size is 2-5 mm. The amount of water added is 10%-15% of the mass of the third mixture.

[0072] Specifically, after drying, the moisture content of the soil remediation agent is tested. If the moisture content is ≤10%, the soil remediation agent with qualified moisture content is sealed and packaged for moisture protection.

[0073] Understandably, modified biochar provides adsorption sites, nano-zero-valent iron reduces heavy metals, microorganisms and enzymes promote biodegradation, fungi enhance plant root absorption, and the composite gel encapsulates each component and slowly releases active ingredients.

[0074] It can be seen that step-by-step preparation and mixing ensure the activity and stability of each functional component; the particulate structure and gel encapsulation enable the slow release of active ingredients and prolong the repair cycle.

[0075] It can be seen that utilizing waste biomass and bio-based calcium carbonate to achieve waste recycling reduces costs and is environmentally friendly; multiple technologies work together, with modified biochar and bio-based calcium carbonate adsorbing and solidifying heavy metals, microencapsulation of microorganisms combined with fungi to improve remediation efficiency, and nano-zero-valent iron and compound enzyme preparations specifically transforming heavy metals, achieving broad-spectrum remediation of complex pollution; chitosan-humic acid gel is biodegradable, and processes such as low-temperature stirring reduce ecological disturbance; the process is highly adaptable, adapting to different soils through segmented stirring and parameter control, and the production process is mature, low-cost, and short-cycle, combining economic and technological advantages.

[0076] In some embodiments of this application, the temperature of the high-temperature carbonization is 700-900°C, and the time of the high-temperature carbonization is 2-4 hours.

[0077] Specifically, the preferred high-temperature carbonization temperature is 800°C, and the preferred high-temperature carbonization time is 3 hours.

[0078] Specifically, the heating rate of high-temperature carbonization is 5-10℃ / min, and the carbonization process is carried out in an inert atmosphere to prevent the oxidation and combustion of biomass.

[0079] Specifically, high-temperature carbonization is carried out in a nitrogen atmosphere.

[0080] It is understandable that biochar formed at 700-900℃ has abundant micropores and mesopores, with a specific surface area of ​​300-600m². 2 / g, which enhances the adsorption capacity for heavy metals.

[0081] In some embodiments of this application, the high-temperature calcination temperature is 900-1000℃, and the high-temperature calcination time is 2-6 hours.

[0082] Preferably, the high-temperature calcination temperature is 950℃ and the high-temperature calcination time is 4 hours.

[0083] Specifically, the bio-based calcium carbonate is pretreated before high-temperature calcination to improve calcination efficiency. The pretreatment involves first cleaning the bio-based calcium carbonate, and then pulverizing it to 100-200 mesh.

[0084] Preferably, the bio-based calcium carbonate is pulverized to 150 mesh.

[0085] Understandably, high-temperature calcination disrupts the crystal structure of calcium carbonate, increasing its specific surface area and porosity, thereby enhancing its adsorption and precipitation capacity for heavy metals. The calcination process also decomposes organic matter and volatile impurities, improving the purity of calcium carbonate.

[0086] In some embodiments of this application, the culture temperature for culturing the heavy metal resistant microbial strain is 25-37°C, the relative humidity is 70%-85%, and the culture time is 16-48 hours.

[0087] Specifically, the concentration of the cultured heavy metal-tolerant microbial strain solution was: 10 7 -10 10 CFU / mL.

[0088] Preferably, the culture temperature is 35℃, the relative humidity is 80%, the culture time is 40 hours, and the concentration of the heavy metal-resistant microbial strain solution after culture is 10. 8 CFU / mL.

[0089] It is understandable that heavy metal-tolerant microbial strains are cultivated to ensure the acquisition of strains with high heavy metal tolerance and degradation capabilities. Culture conditions are controlled within the optimal growth range of the microorganisms to maintain high metabolic and enzymatic activity.

[0090] In some embodiments of this application, during the process of obtaining the second mixture by dripping, the dropper orifice diameter is 0.5-2.0 mm, the dripping speed is 1-5 mL / min, and the dripping temperature is 20-30 °C.

[0091] Specifically, the concentration of the second mixture is 0.1-0.5 mol / L.

[0092] Preferably, the dropper orifice diameter is 1.2 mm, the dripping speed is 4 mL / min, the dripping temperature is 25 °C, and the concentration of the second mixture is 0.4 mol / L.

[0093] Specifically, a peristaltic pump or syringe is used to precisely control the drip rate, and the droplets cross-link in the calcium chloride solution for 10-30 minutes to ensure the formation of a stable microcapsule structure.

[0094] Specifically, after cross-linking, the microcapsules need to be washed with sterile water to remove residual calcium chloride and impurities on the surface.

[0095] Specifically, the microcapsule particle size is controlled between 200-500 μm by adjusting the dropper orifice size and flow rate.

[0096] Understandably, the microcapsule structure protects microorganisms from external environmental stresses while allowing small molecules, such as heavy metal ions, to diffuse in. The network structure of calcium alginate gel enables the slow release of microorganisms, prolonging the repair cycle. Optimized cross-linking conditions ensure that the microcapsules have sufficient strength in the soil and are not easily ruptured.

[0097] In some embodiments of this application, when the first mixture, the second mixture, and the chitosan-humic acid composite gel, the arbuscular mycorrhizal fungal spore suspension, the plant-based nano-zero-valent iron, and the composite enzyme preparation are mixed and stirred, the mass ratios of the first mixture, the second mixture, the arbuscular mycorrhizal fungal spore suspension, the plant-based nano-zero-valent iron, and the composite enzyme preparation to the chitosan-humic acid composite gel are respectively:

[0098] The mass ratio of the first mixture to the chitosan-humic acid composite gel is (2-5):1; the mass ratio of the second mixture to the chitosan-humic acid composite gel is (1-3):1; the mass ratio of the arbuscular mycorrhizal fungal spore suspension to the chitosan-humic acid composite gel is (0.3-0.5):1; the mass ratio of plant-based nano-zero valent iron to the chitosan-humic acid composite gel is (0.1-0.2):1; and the mass ratio of the composite enzyme preparation to the chitosan-humic acid composite gel is (0.05-0.1):1.

[0099] Specifically, chitosan-humic acid composite gel is first mixed with plant-based nano-zero valent iron to form a stable dispersion, and then the first mixture, the second mixture, arbuscular mycorrhizal fungal spore suspension, and the composite enzyme preparation are added in sequence.

[0100] Understandably, adjustable formulation systems are provided to improve remediation efficiency for different levels of pollution and soil types. A proper ratio of microorganisms to enzymes ensures the continuous biodegradation process, while the gel slowly releases nutrients to maintain microbial activity.

[0101] In some embodiments of this application, the mixing and stirring specifically involves: first stirring at a low speed of 50-100 rpm for 15-22 minutes, and then stirring at a medium speed of 100-200 rpm for 20-30 minutes, with a stirring temperature of 20-30℃.

[0102] Preferably, the mixture is first stirred at a low speed of 70 rpm for 18 minutes, and then stirred at a medium speed of 150 rpm for 25 minutes, with a stirring temperature of 25°C.

[0103] Specifically, planetary mixers or twin-helix cone mixers are used for mixing to ensure that high-viscosity materials are fully mixed.

[0104] Understandably, segmented stirring ensures that the high-viscosity composite gel is fully mixed with other solid or liquid components, avoiding agglomeration; low-temperature stirring reduces mechanical damage to enzymes and microorganisms, maintaining the bioactivity of the repair agent; and mixing at a specific mass ratio optimizes the interaction between the components.

[0105] Understandably, low-speed dispersion prevents the agglomeration of nanomaterials, while medium-speed shearing ensures that the gel fully encapsulates each component.

[0106] In some embodiments of this application, the extrusion pressure of obtaining the granular mixture by extrusion and granulation is 1-5 MPa; the drying time of the drying process is 8-24 hours; and the drying temperature is 40-60℃.

[0107] Preferably, the extrusion pressure is 3 MPa, the drying time is 16 hours, and the drying temperature is 50°C.

[0108] As can be seen, the above embodiments utilize waste biomass and bio-based calcium carbonate to achieve waste recycling, reducing costs and being environmentally friendly; multiple technologies work together, with modified biochar and bio-based calcium carbonate adsorbing and solidifying heavy metals, microencapsulation of microorganisms combined with fungi to improve remediation efficiency, and nano-zero-valent iron and composite enzyme preparations specifically transforming heavy metals, achieving broad-spectrum remediation of complex pollution; chitosan-humic acid gel is biodegradable, and processes such as low-temperature stirring reduce ecological disturbance; the process is highly adaptable, adapting to different soils through segmented stirring and parameter control, and the production process is mature, low-cost, and short-cycle, combining economic and technological advantages.

[0109] On the other hand, the present invention also proposes the application of a soil remediation agent in soil contaminated with heavy metals.

[0110] Example 1

[0111] This embodiment provides a soil remediation agent for heavy metal pollution, the raw material composition of which includes: rice husk: 32 parts, chitosan-humic acid composite gel: 20 parts, arbuscular mycorrhizal fungal spore suspension: 7 parts, Bacillus subtilis: 4.5 parts, plant-based nano-zero valent iron: 2 parts, sodium alginate solution: 13 parts, urease-phosphatase complex enzyme (urease + phosphatase mass ratio of 1:1): 2 parts, and seashell: 11 parts.

[0112] The method for preparing a soil remediation agent for heavy metal pollution provided in this embodiment specifically includes the following steps:

[0113] S1. Crush the rice husks to 3mm, carbonize them at 800℃ for 3 hours in a nitrogen atmosphere, cool them for 4 hours, and then grind them for 40 minutes until they reach 150 mesh to obtain modified rice husks.

[0114] S2. The shells are first cleaned and then crushed to 150 mesh, and then calcined at 950℃ for 4 hours to obtain modified shells.

[0115] S3. Mix the modified rice husks and modified seashells at a ratio of 1:3, and grind for 30 minutes to obtain the first mixture.

[0116] S4. Bacillus subtilis in a solution containing 20 mg / L d 2+ The bacteria were cultured in LB medium at 35°C and 80% relative humidity for 30 hours, resulting in a bacterial concentration of 10.8 Stop culturing when CFU / mL; mix the cultured bacterial solution with sodium alginate solution at a ratio of 1:3, and add the mixture dropwise through a 1.2 mm dropper at a rate of 4 mL / min into a 0.4 mol / L calcium chloride solution. Crosslink the mixture at 25 °C for 20 minutes to obtain a second mixture in microcapsule form.

[0117] S5. Mix the first mixture, the second mixture, the arbuscular mycorrhizal fungal spore suspension, the plant-based nano-zero valent iron, and the urease phosphatase complex enzyme with the chitosan-humic acid complex gel at a mass ratio of 3:2:0.4:0.15:0.08:1. First, mix the chitosan-humic acid complex gel with the plant-based nano-zero valent iron, and then add the first mixture, the second mixture, the arbuscular mycorrhizal fungal spore suspension, and the complex enzyme preparation in sequence. When mixing, stir at low speed (70 rpm) for 18 minutes at 25°C, and then stir at medium speed (150 rpm) for 25 minutes to obtain the third mixture.

[0118] S6. Add 12% water and 2% pregelatinized corn starch by mass of the third mixture to the third mixture, and granulate by extrusion under a pressure of 3 MPa to obtain a granular mixture.

[0119] S7. Dry the granular mixture at 50°C for 16 hours to reduce its moisture content to 8% to obtain the soil remediation agent.

[0120] Example 2

[0121] This embodiment provides a soil remediation agent for heavy metal pollution, the raw material composition of which includes: rice husk: 30 parts, chitosan-humic acid composite gel: 15 parts, arbuscular mycorrhizal fungal spore suspension: 5 parts, Bacillus subtilis: 3 parts, plant-based nano zero-valent iron: 2.5 parts, sodium alginate solution: 12 parts, urease phosphatase complex enzyme: 1.5 parts, and seashell: 10 parts.

[0122] The preparation method of soil remediation agents for heavy metal pollution includes the following steps:

[0123] S1. Crush the rice husks to 2mm, carbonize them at 700℃ for 4 hours in a nitrogen atmosphere, cool them for 3 hours, and then grind them for 30 minutes until they reach 100 mesh to obtain modified rice husks.

[0124] S2. The shells are first cleaned and then crushed to 100 mesh, and then calcined at 900℃ for 6 hours to obtain modified shells.

[0125] S3. Mix the modified rice husks and modified seashells at a ratio of 1:3, and grind for 20 minutes to obtain the first mixture.

[0126] S4. Bacillus subtilis in a solution containing 20 mg / L d 2+The bacteria were cultured in LB medium at 25°C and 70% relative humidity for 16 hours, resulting in a bacterial concentration of 10⁻⁶. 7 Stop culturing when CFU / mL; mix the cultured bacterial solution with sodium alginate solution at a ratio of 4:11, and add the mixture dropwise through a 0.5 mm dropper at a rate of 1 mL / min to a 0.1 mol / L calcium chloride solution. Crosslink the mixture at 30 °C for 10 minutes to obtain a second mixture in microcapsule form.

[0127] S5. Mix the first mixture, the second mixture, the arbuscular mycorrhizal fungal spore suspension, the plant-based nano-zero valent iron, and the urease phosphatase complex enzyme with the chitosan-humic acid complex gel at a mass ratio of 2:1:0.3:0.1:0.05:1. First, mix the chitosan-humic acid complex gel with the plant-based nano-zero valent iron, and then add the first mixture, the second mixture, the arbuscular mycorrhizal fungal spore suspension, and the complex enzyme preparation in sequence. When mixing, stir at low speed (50 rpm) for 22 minutes at 20°C, and then stir at medium speed (100 rpm) for 30 minutes to obtain the third mixture.

[0128] S6. Add 13% water and 1% pregelatinized corn starch by mass of the third mixture to the third mixture, and granulate by extrusion under a pressure of 1 MPa to obtain a granular mixture.

[0129] S7. Dry the granular mixture at 60°C for 8 hours to reduce its moisture content to 8% to obtain the soil remediation agent.

[0130] Example 3

[0131] This embodiment provides a soil remediation agent for heavy metal pollution, the raw material composition of which includes: corn straw: 40 parts, chitosan-humic acid composite gel: 17 parts, arbuscular mycorrhizal fungal spore suspension: 8 parts, Bacillus subtilis: 5 parts, plant-based nano zero-valent iron: 3 parts, sodium alginate solution: 15 parts, urease phosphatase complex enzyme: 1 part, eggshell: 12 parts.

[0132] The preparation method of soil remediation agents for heavy metal pollution includes the following steps:

[0133] S1. Crush the rice husks to 5mm, carbonize them at 900℃ for 2 hours in a nitrogen atmosphere, cool them for 6 hours, and then grind them for 50 minutes until they reach 200 mesh to obtain modified rice husks.

[0134] S2. The shells are first cleaned and then crushed to 200 mesh, and then calcined at 1000℃ for 2 hours to obtain modified shells.

[0135] S3. Mix the modified rice husks and modified seashells at a ratio of 1:3, and grind for 40 minutes to obtain the first mixture.

[0136] S4. Bacillus subtilis in a solution containing 20 mg / L d 2 The culture was carried out in LB medium at 37°C and 85% relative humidity for 48 hours, until the bacterial concentration reached 10. 10 Stop culturing when CFU / mL; mix the cultured bacterial solution with sodium alginate solution at a ratio of 3:10, and add the mixture dropwise through a 2 mm dropper at a rate of 5 mL / min to a 0.5 mol / L calcium chloride solution. Crosslink the mixture at 20 °C for 30 minutes to obtain a second mixture in microcapsule form.

[0137] S5. Mix the first mixture, the second mixture, the arbuscular mycorrhizal fungal spore suspension, the plant-based nano-zero valent iron, and the urease phosphatase complex enzyme with the chitosan-humic acid complex gel at a mass ratio of 5:3:0.5:0.2:0.1:1. First, mix the chitosan-humic acid complex gel with the plant-based nano-zero valent iron, and then add the first mixture, the second mixture, the arbuscular mycorrhizal fungal spore suspension, and the complex enzyme preparation in sequence. When mixing, stir at low speed (100 rpm) for 15 minutes at 30°C, and then stir at medium speed (200 rpm) for 20 minutes to obtain the third mixture.

[0138] S6. Add 14% water and 3% sodium carboxymethyl cellulose by mass of the third mixture to the third mixture, and granulate by extrusion under a pressure of 5 MPa to obtain a granular mixture.

[0139] S7. Dry the granular mixture at 40°C for 24 hours to reduce its moisture content to 8% to obtain the soil remediation agent.

[0140] Comparative Example 1

[0141] The only difference between this comparative example and Example 1 is that it does not include the urease-phosphatase complex enzyme; all other steps are the same.

[0142] Comparative Example 2

[0143] The only difference between this comparative example and Example 1 is that it does not include plant-based nano-zero valent iron; all other steps are the same.

[0144] Comparative Example 3

[0145] The only difference between this comparative example and Example 1 is that it does not include the second mixture; all other steps are the same.

[0146] Comparative Example 4

[0147] The only difference between this comparative example and Example 1 is that it does not include the chitosan-humic acid composite gel; all other steps are the same.

[0148] Comparative Example 5

[0149] The only difference between this comparative example and Example 1 is that the amount of chitosan-humic acid composite gel added is 10 parts; all other steps are the same.

[0150] Comparative Example 6

[0151] The only difference between this comparative example and Example 1 is that in S5, the low-speed stirring speed is 40 rpm.

[0152] Comparative Example 7

[0153] The only difference between this comparative example and Example 1 is that in S5, the low-speed stirring speed is 150 rpm.

[0154] Comparative Example 8

[0155] The only difference between this comparative example and Example 1 is that in S5, the medium-speed stirring speed is 80 rpm.

[0156] Comparative Example 9

[0157] The only difference between this comparative example and Example 1 is that in S5, the medium-speed stirring speed is 240 rpm.

[0158] Comparative Example 10

[0159] The only difference between this comparative example and Example 1 is that in S5, the components are directly stirred at a stirring speed of 100 rpm for 35 minutes after mixing to obtain the third mixture.

[0160] The soil remediation agents prepared in Examples 1-3 and Comparative Examples 1-7 were used to conduct remediation tests on soil contaminated with heavy metals. The contents of Cd and Pb in the remediated soil were then detected to characterize the remediation effect.

[0161] The heavy metal soil sample of this invention was taken from contaminated soil near an industrial area in Lanzhou. After passing through a 60-mesh sieve to remove impurities, the soil was sterilized. The Cd content, Pb content, and Hg content in the soil were tested to be 75-80 mg / kg, 1720-1790 mg / kg, and 265-280 mg / kg, and the pH value was 6.43-6.65.

[0162] The methods for measuring heavy metal content include: testing cadmium (Cd) content according to GB / T 17141-1997; testing lead (Pb) content according to GB / T 17141-1997; and testing Hg content according to GB / T 22105.1-2008. The results are shown in Table 1.

[0163] Table 1 shows the remediation efficiency of the remediation agents provided in the examples and comparative examples for heavy metal contaminated soil.

[0164]

[0165] As shown in Table 1, Example 1 demonstrated the best remediation efficiency for heavy metal contaminated soil. Using the technical solution of this invention, the components exhibit synergistic effects, and the 10-day removal rate results show that the remediation agent of this application can achieve a long-lasting effect in removing heavy metals. Furthermore, the results of Comparative Examples 6-10 also indicate that the stirring speed during the mixing of the components in this invention has a significant impact on the effectiveness.

[0166] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A soil remediation agent for heavy metal pollution, characterized in that, The components include the following parts by mass: 30-40 parts modified biochar, 15-20 parts chitosan-humic acid composite gel, 5-8 parts arbuscular mycorrhizal fungal spore suspension, 3-5 parts heavy metal resistant microbial strains, 2-3 parts plant-based nano zero-valent iron, 10-15 parts sodium alginate solution, 1-2 parts composite enzyme preparation, and 8-12 parts modified bio-based calcium carbonate. Waste biomass is carbonized at high temperature and then ground to obtain modified biochar. Modified bio-based calcium carbonate is obtained by calcining bio-based calcium carbonate at high temperature. The bio-based calcium carbonate is a seashell or eggshell; The compound enzyme preparation is a urease-phosphatase complex, with a mass ratio of urease to phosphatase of 1:

1. Methods for preparing plant-based nano-zero valent iron include: (1) After the tea residue waste is naturally air-dried, it is crushed to a particle size of about 10 mm by a crusher to obtain tea residue powder. Then, 5g of tea residue powder is ground and mixed with 3g of Fe(NO3)3 and placed in a crucible. The crucible is wrapped with two layers of tin foil and placed in a muffle furnace. It is roasted at 450℃ for 2 hours in a static air atmosphere. After roasting, the muffle furnace is naturally cooled to room temperature to obtain plant-based-γ-Fe2O3 complex. (2) The plant-based γ-Fe2O3 complex was mixed with NaOH at a mass ratio of 1:1.5 and then placed in a crucible. The crucible was wrapped with two layers of tin foil and placed in a muffle furnace. It was calcined at 600°C for 2 hours in a static air atmosphere. After natural cooling, it was washed with softened water and dried in a constant temperature drying oven at 80°C for 4 hours to obtain the plant-based nano-zero valent iron complex, in which iron accounted for 45% of the mass percentage of the complex.

2. A method for preparing a soil remediation agent for heavy metal pollution as described in claim 1, characterized in that, Includes the following steps: The modified biochar and modified bio-based calcium carbonate are mixed and ground to obtain a first mixture; After culturing heavy metal-resistant microbial strains, they were mixed with sodium alginate solution and then dripped to obtain a second mixture. The first mixture, the second mixture, chitosan-humic acid composite gel, arbuscular mycorrhizal fungal spore suspension, plant-based nano-zero valent iron, and composite enzyme preparation were mixed and stirred to obtain a third mixture; Water and binder are added to the third mixture, and granules are obtained by extrusion and granulation. The soil remediation agent is obtained by drying the granular mixture.

3. The method for preparing the soil remediation agent for heavy metal pollution according to claim 2, characterized in that, The high-temperature carbonization temperature is 700-900℃, and the high-temperature carbonization time is 2-4 hours.

4. The method for preparing the soil remediation agent for heavy metal pollution according to claim 2, characterized in that, The high-temperature calcination temperature is 900-1000℃, and the high-temperature calcination time is 2-6 hours.

5. The method for preparing the soil remediation agent for heavy metal pollution according to claim 4, characterized in that, The culture temperature for culturing the heavy metal resistant microbial strains is 25-37℃, the relative humidity is 70%-85%, and the culture time is 16-48 hours.

6. The method for preparing a soil remediation agent for heavy metal pollution according to claim 2, characterized in that, During the process of obtaining the second mixture through dripping, the dropper orifice diameter is 0.5-2.0 mm, the dripping speed is 1-5 mL / min, and the dripping temperature is 20-30℃.

7. The method for preparing a soil remediation agent for heavy metal pollution according to claim 2, characterized in that, When the first mixture, the second mixture, the chitosan-humic acid composite gel, the arbuscular mycorrhizal fungal spore suspension, the plant-based nano-zero-valent iron, and the composite enzyme preparation are mixed and stirred, the mass ratios of the first mixture, the second mixture, the arbuscular mycorrhizal fungal spore suspension, the plant-based nano-zero-valent iron, and the composite enzyme preparation to the chitosan-humic acid composite gel are respectively: The mass ratio of the first mixture to the chitosan-humic acid composite gel is (2-5):1; The mass ratio of the second mixture to the chitosan-humic acid composite gel is (1-3):1; The mass ratio of arbuscular mycorrhizal fungal spore suspension to chitosan-humic acid composite gel was (0.3-0.5):

1. The mass ratio of plant-based nano-zero valent iron to chitosan-humic acid composite gel is (0.1-0.2):

1. The mass ratio of the compound enzyme preparation to the chitosan-humic acid composite gel is (0.05-0.1):

1.

8. The method for preparing the soil remediation agent for heavy metal pollution according to claim 7, characterized in that, The mixing process specifically involves: first mixing at a low speed of 50-100 rpm for 15-22 minutes, then mixing at a medium speed of 100-200 rpm for 20-30 minutes, with a mixing temperature of 20-30℃.

9. The method for preparing a soil remediation agent for heavy metal pollution according to claim 2, characterized in that, The extrusion pressure of the granulated mixture obtained by extrusion and granulation is 1-5 MPa; the drying time of the drying process is 8-24 hours; and the drying temperature is 40-60℃.

10. The application of the soil remediation agent as described in claim 1 in soil contaminated with heavy metals.

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