Environment-friendly microbial soil remediation agent and preparation method thereof

Abstract

This invention discloses an environmentally friendly microbial soil remediation agent and its preparation method, belonging to the field of soil remediation technology. It is made from the following raw materials in parts by weight: 400-500 parts calcium-magnesium-silica-based waste residue, 300-340 parts humic acid, 40-60 parts modified attapulgite, 4-6 parts mineral-derived potassium fulvate, 30-50 parts ammonium sulfate, 100-120 parts compound microbial agent, 1-3 parts alginic oligosaccharides, and 3-5 parts auxiliary materials. The calcium-magnesium-silica-based waste residue is obtained by pressure filtration, washing with water until the conductivity of the filtrate is <1000 μS / cm, and drying the solid waste from the calcium chloride production process using hydrochloric acid as a byproduct of potassium sulfate. This invention has excellent effects on improving acidic soil and reducing the heavy metal content of soil, and it also enables the reuse of solid waste from the calcium chloride production process, making it green, environmentally friendly, and economically significant.

Description

Technical Field

[0001] This invention belongs to the field of soil remediation technology, specifically relating to an environmentally friendly microbial soil remediation agent and its preparation method. Background Technology

[0002] In recent years, my country has achieved consecutive bumper harvests of grains thanks to the application of nitrogen, phosphorus, and potassium fertilizers. However, because crops deplete large amounts of micronutrients each year without replenishment, the imbalance of nutrients in the soil and crops has worsened, limiting further improvements in crop yield and quality. This has also led to soil acidification and compaction, poor aeration, and reduced fertilizer utilization. Reports indicate that soil acidification and compaction are currently occurring in some parts of my country, necessitating urgent soil remediation and improvement.

[0003] In the process of producing calcium chloride using hydrochloric acid, a byproduct of potassium sulfate, the precipitate in the calcium tank is filtered to produce a solid slurry that does not react with hydrochloric acid. Because this slurry contains a large amount of calcium chloride, it is highly hygroscopic, easily deliquescing and sticking when exposed to air, making it difficult to dry; ordinary machinery cannot adequately physically break it down. In chemical reactions, under suitable conditions, the production of chlorides generally involves varying degrees of moisture absorption, making chemical treatment unsuitable. Therefore, how to achieve resource recycling of the aforementioned solid waste from a more economical perspective is a pressing technical problem that needs to be solved. Summary of the Invention

[0004] The purpose of this invention is to provide an environmentally friendly microbial soil remediation agent, which has a good effect on improving acidic soil and reducing the content of heavy metals in the soil. It can also realize the reuse of solid waste from the calcium chloride production process, making it green, environmentally friendly, and economically effective.

[0005] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows:

[0006] An environmentally friendly microbial soil remediation agent is made from the following raw materials in parts by weight: 400-500 parts calcium-magnesium-silicon-based waste residue, 300-340 parts humic acid, 40-60 parts modified attapulgite, 4-6 parts mineral-derived potassium fulvate, 30-50 parts ammonium sulfate, 100-120 parts compound microbial inoculant, 1-3 parts brown algae oligosaccharides, and 3-5 parts auxiliary materials.

[0007] The calcium-magnesium-silicon-based waste residue is obtained by pressure filtration and water washing of solid waste from the calcium pool in the process of producing calcium chloride from hydrochloric acid, a by-product of potassium sulfate. The filtrate conductivity is then <1000 μS / cm and dried. The composition content meets the following requirements: CaO≥15%, MgO≥5%, SiO22-4%, Cl⁻3-5%, other trace impurities, pH=8.0-10.0.

[0008] Preferably, the modified attapulgite is prepared by the following method:

[0009] Step 1: Add attapulgite to 0.5M HCl solution according to the solid-liquid ratio, stir magnetically at room temperature for 1 hour, filter, wash the solid with deionized water until neutral, and dry to obtain pretreated attapulgite.

[0010] Step 2: Add the pretreated attapulgite to a 0.02 mol / L phytic acid solution according to the solid-liquid ratio. Stir magnetically at room temperature for 30-40 min. Then, slowly add 0.1 mol / L soluble magnesium salt and 0.1 mol / L soluble calcium salt solutions sequentially. Maintain the pH at 5.0-6.5 throughout the dropwise addition process. After the dropwise addition is complete, stir magnetically at 30-35℃ for 1 h. Then, age at room temperature for 2-4 h. Filter, wash with deionized water 3-5 times, dry at 80℃, and grind into powder to obtain modified attapulgite.

[0011] Preferably, in step 1, the solid-liquid ratio of attapulgite clay to HCl solution is 1g:10ml.

[0012] Preferably, in step 2, the solid-liquid ratio of the pretreated attapulgite soil to the phytic acid solution is 1g:20ml.

[0013] Preferably, the soluble magnesium salt is MgCl2 or MgSO4; and the soluble calcium salt is CaCl2.

[0014] Preferably, in step 2, the volume ratio of phytic acid solution, soluble magnesium salt solution, and soluble calcium salt solution is 20:2:(0.5-1).

[0015] Preferably, the compound microbial agent is prepared by activating *Arthrobacter bengali*, *Bacillus megaterium*, and *Bacillus cereus* separately, inoculating them into LB liquid medium, and then incubating them at 30°C with shaking until the bacterial count reaches OD500. 600 ≈2.0, then mix them in a volume ratio of 1:1:1 and freeze-dry under vacuum to obtain the final product.

[0016] Preferably, the *Arthrobacter bengal* strain is CGMCC No. 1.10873, with a deposit date of April 1, 2011; the *Bacillus megaterium* strain is CGMCC No. 1.10466, with a deposit date of March 18, 2010; and the *Bacillus cereus* strain is CGMCC No. 1.9067, with a deposit date of January 19, 2009. The *Arthrobacter bengal*, *Bacillus megaterium*, and *Bacillus cereus* used in this invention were all purchased from the China General Microbiological Culture Collection Center (CGMCC) and can be purchased openly through the CGMCC's strain catalog without the need for additional preservation.

[0017] Preferably, the excipient is sodium carboxymethyl cellulose or mineral oil.

[0018] This invention also provides a method for preparing an environmentally friendly microbial soil remediation agent, which includes the following steps:

[0019] 1) Crush the calcium-magnesium-silicon-based waste residue and humic acid into powder and mix them evenly through an 80-100 mesh sieve;

[0020] 2) Preparation of modified attapulgite soil;

[0021] 3) Preparation of compound microbial inoculants;

[0022] 4) After mixing the mixture obtained in step 1) with modified attapulgite soil, compound microbial agent and other remaining raw materials evenly, granulate, dry at low temperature, cool and sieve to obtain an environmentally friendly microbial soil remediation agent with a particle size of 8-12mm.

[0023] Unless otherwise specified, all raw materials used in this invention are commercially available.

[0024] The calcium-magnesium-silicon-based waste residue used in this invention releases Ca through hydrolysis in the soil. 2+ Mg 2+ OH⁻ and SiO₃ 2- Ions directly neutralize soil acidity and raise pH levels; the released Ca 2+ / Mg 2+ Al adsorbed by soil colloids was replaced by ion exchange. 3+ Iso-acidic ions, blocking the acidification cycle; SiO3 2- It forms silicate co-precipitates with heavy metals, while Ca 2+ This process generates mineral phases such as calcium carbonate / calcium sulfate, permanently fixing heavy metals. Simultaneously, the modified attapulgite prepared in this invention undergoes phytic acid modification, which imparts abundant phosphate groups to the surface, enabling specific chelation of Cd. 2+ Pb 2+ Heavy metals; Ca pre-placed on their surface 2+ / Mg 2+ SiO3 released from waste residue 2- The reaction generates calcium magnesium silicate gel and alkaline substances in situ at the particle interface, achieving efficient and simultaneous remediation of soil acidity and heavy metal pollution.

[0025] In the composite microbial agent used in this invention, three dominant strains work synergistically to regulate soil pH and reduce heavy metal content. Specifically, the organic acids produced by the metabolic products of *Arthrobacter benigra* can dissolve silicates, promoting the release of Ca / Mg from the waste residue. The extracellular polysaccharides (such as dextran and pectin) secreted by *Bacillus megaterium* and *Bacillus cereus* during their metabolism have adhesive properties, promoting soil particle aggregation and forming a stable aggregate structure, while also inhibiting heavy metal leaching. Simultaneously, the humic acid-modified attapulgite soil-waste residue form a multi-level porous structure, providing a shelter for microorganisms and enhancing soil permeability.

[0026] The beneficial effects of this invention are:

[0027] 1) The environmentally friendly microbial soil remediation agent of the present invention can achieve efficient remediation of acidified soil and simultaneously achieve heavy metal pollution control, with excellent results.

[0028] 2) This invention uses solid waste from the calcium pool in the process of producing calcium chloride from hydrochloric acid, a byproduct of potassium sulfate, as one of the main raw materials, thus realizing the resource utilization of industrial waste and reducing environmental pollution. By replacing some conventional remediation materials, it significantly reduces remediation costs and improves economic efficiency. Furthermore, the preparation process of this remediation agent is simple and easy to implement, making it suitable for large-scale production and application.

[0029] 3) This remediation agent improves the soil environment and enhances the availability of soil nutrients, providing a favorable rhizosphere environment for crop growth. Simultaneously, the metabolic activities of the microbial agent, while improving the soil, also produce plant growth regulators, enhancing crop resistance and adaptability, and increasing crop survival and yield under adverse conditions. Attached Figure Description

[0030] Figure 1 The content of available heavy metal Pb in the soil of different treatment groups after rice planting in the field experiment of this invention;

[0031] Figure 2 The content of available heavy metal Cd in the soil of different treatment groups after rice planting in the field experiment of this invention;

[0032] Figure 3 The content of available heavy metal As in the soil of different treatment groups after rice planting in the field experiment of this invention;

[0033] Figure 4 The content of available heavy metal Cr in the soil of different treatment groups after rice planting in the field experiment of this invention;

[0034] Figure 5 This is a picture of the actual product of the environmentally friendly microbial soil remediation agent of this invention. Detailed Implementation

[0035] The technical solution of the present invention will be further described below with reference to specific embodiments, but it is not limited thereto.

[0036] Example 1

[0037] An environmentally friendly microbial soil remediation agent is made from the following raw materials in parts by weight: 400 parts calcium-magnesium-silicon-based waste residue, 300 parts humic acid, 40 parts modified attapulgite, 4 parts mineral-derived potassium fulvate, 30 parts ammonium sulfate, 100 parts compound microbial agent, 1 part brown algae oligosaccharide, and 3 parts sodium carboxymethyl cellulose.

[0038] The calcium-magnesium-silicon-based waste residue is obtained by pressure filtration and water washing of solid waste from the calcium pool in the process of producing calcium chloride from hydrochloric acid, a by-product of potassium sulfate. The filtrate conductivity is then <1000 μS / cm and dried. The composition content meets the following requirements: CaO≥15%, MgO≥5%, SiO22-4%, Cl⁻3-5%, other trace impurities, pH=8.0-10.0.

[0039] The modified attapulgite clay is prepared using the following method:

[0040] Step 1: Add attapulgite to 0.5M HCl solution at a solid-liquid ratio of 1g:10ml, stir magnetically at room temperature for 1 hour, filter, wash the solid with deionized water until neutral, and dry to obtain pretreated attapulgite.

[0041] Step 2: Add the pretreated attapulgite to a 0.02 mol / L phytic acid solution at a solid-liquid ratio of 1 g: 20 ml. Stir magnetically at room temperature for 30-40 min. Then, slowly add 0.1 mol / L soluble magnesium salt and 0.1 mol / L soluble calcium salt solutions sequentially, maintaining the pH at 5.0-6.5 throughout the addition process. After addition, stir magnetically at 30-35℃ for 1 h, then age at room temperature for 2-4 h. Filter, wash 3-5 times with deionized water, dry at 80℃, and grind into powder to obtain the modified attapulgite. The volume ratio of the phytic acid solution, soluble magnesium salt solution, and soluble calcium salt solution is 20:2:0.5.

[0042] The soluble magnesium salt is MgCl2; the soluble calcium salt is CaCl2.

[0043] The compound microbial agent is prepared by activating and inoculating *Arthrobacter benigra*, *Bacillus megaterium*, and *Bacillus cereus* separately into LB liquid medium, and then incubating with shaking at 30°C until the bacterial count reaches OD50. 600 ≈2.0, then mix them in a volume ratio of 1:1:1 and freeze-dry under vacuum to obtain the final product.

[0044] The *Arthrobacter bengal* strain is CGMCC No. 1.10873, deposited on April 1, 2011; the *Bacillus megaterium* strain is CGMCC No. 1.10466, deposited on March 18, 2010; and the *Bacillus cereus* strain is CGMCC No. 1.9067, deposited on January 19, 2009. All *Arthrobacter bengal*, *Bacillus megaterium*, and *Bacillus cereus* used in this invention were purchased from the China General Microbiological Culture Collection Center (CGMCC) and can be purchased through the center's strain catalog without additional deposit.

[0045] A method for preparing an environmentally friendly microbial soil remediation agent includes the following steps:

[0046] 1) Crush the calcium-magnesium-silicon-based waste residue and humic acid into powder and mix them evenly through an 80-100 mesh sieve;

[0047] 2) Preparation of modified attapulgite soil;

[0048] 3) Preparation of compound microbial inoculants;

[0049] 4) After mixing the mixture obtained in step 1) with modified attapulgite soil, compound microbial agent and other remaining raw materials evenly, granulate, dry at low temperature, cool and sieve to obtain an environmentally friendly microbial soil remediation agent with a particle size of 8-12mm.

[0050] Example 2

[0051] An environmentally friendly microbial soil remediation agent is made from the following raw materials in parts by weight: 450 parts calcium-magnesium-silicon-based waste residue, 320 parts humic acid, 50 parts modified attapulgite, 5 parts mineral potassium fulvate, 40 parts ammonium sulfate, 110 parts compound microbial agent, 2 parts brown algae oligosaccharide, and 4 parts mineral oil.

[0052] The calcium-magnesium-silicon-based waste residue is obtained by pressure filtration and water washing of solid waste from the calcium pool in the process of producing calcium chloride from hydrochloric acid, a by-product of potassium sulfate. The filtrate conductivity is then <1000 μS / cm and dried. The composition content meets the following requirements: CaO≥15%, MgO≥5%, SiO22-4%, Cl⁻3-5%, other trace impurities, pH=8.0-10.0.

[0053] The modified attapulgite clay is prepared using the following method:

[0054] Step 1: Add attapulgite to 0.5M HCl solution at a solid-liquid ratio of 1g:10ml, stir magnetically at room temperature for 1 hour, filter, wash the solid with deionized water until neutral, and dry to obtain pretreated attapulgite.

[0055] Step 2: Add the pretreated attapulgite to a 0.02 mol / L phytic acid solution at a solid-liquid ratio of 1 g: 20 ml. Stir magnetically at room temperature for 30-40 min. Then, slowly add 0.1 mol / L soluble magnesium salt and 0.1 mol / L soluble calcium salt solutions sequentially, maintaining the pH at 5.0-6.5 throughout the addition process. After addition, stir magnetically at 30-35℃ for 1 h, then age at room temperature for 2-4 h. Filter, wash 3-5 times with deionized water, dry at 80℃, and grind into powder to obtain the modified attapulgite. The volume ratio of the phytic acid solution, soluble magnesium salt solution, and soluble calcium salt solution is 20:2:1.

[0056] The soluble magnesium salt is MgSO4; the soluble calcium salt is CaCl2.

[0057] The compound microbial agent is prepared by activating and inoculating *Arthrobacter benigra*, *Bacillus megaterium*, and *Bacillus cereus* separately into LB liquid medium, and then incubating with shaking at 30°C until the bacterial count reaches OD50. 600 ≈2.0, then mix them in a volume ratio of 1:1:1 and freeze-dry under vacuum to obtain the final product.

[0058] The *Arthrobacter bengal* strain is CGMCC No. 1.10873, deposited on April 1, 2011; the *Bacillus megaterium* strain is CGMCC No. 1.10466, deposited on March 18, 2010; and the *Bacillus cereus* strain is CGMCC No. 1.9067, deposited on January 19, 2009. All *Arthrobacter bengal*, *Bacillus megaterium*, and *Bacillus cereus* used in this invention were purchased from the China General Microbiological Culture Collection Center (CGMCC) and can be purchased through the center's strain catalog without additional deposit.

[0059] A method for preparing an environmentally friendly microbial soil remediation agent includes the following steps:

[0060] 1) Crush the calcium-magnesium-silicon-based waste residue and humic acid into powder and mix them evenly through an 80-100 mesh sieve;

[0061] 2) Preparation of modified attapulgite soil;

[0062] 3) Preparation of compound microbial inoculants;

[0063] 4) After mixing the mixture obtained in step 1) with modified attapulgite soil, compound microbial agent and other remaining raw materials evenly, granulate, dry at low temperature, cool and sieve to obtain an environmentally friendly microbial soil remediation agent with a particle size of 8-12mm.

[0064] Example 3

[0065] An environmentally friendly microbial soil remediation agent is made from the following raw materials in parts by weight: 500 parts calcium-magnesium-silicon-based waste residue, 340 parts humic acid, 60 parts modified attapulgite, 6 parts mineral-derived potassium fulvate, 50 parts ammonium sulfate, 120 parts compound microbial agent, 3 parts brown algae oligosaccharide, and 5 parts sodium carboxymethyl cellulose.

[0066] The calcium-magnesium-silicon-based waste residue is obtained by pressure filtration and water washing of solid waste from the calcium pool in the process of producing calcium chloride from hydrochloric acid, a by-product of potassium sulfate. The filtrate conductivity is then <1000 μS / cm and dried. The composition content meets the following requirements: CaO≥15%, MgO≥5%, SiO22-4%, Cl⁻3-5%, other trace impurities, pH=8.0-10.0.

[0067] The modified attapulgite clay is prepared using the following method:

[0068] Step 1: Add attapulgite to 0.5M HCl solution at a solid-liquid ratio of 1g:10ml, stir magnetically at room temperature for 1 hour, filter, wash the solid with deionized water until neutral, and dry to obtain pretreated attapulgite.

[0069] Step 2: Add the pretreated attapulgite to a 0.02 mol / L phytic acid solution at a solid-liquid ratio of 1 g: 20 ml. Stir magnetically at room temperature for 30-40 min. Then, slowly add 0.1 mol / L soluble magnesium salt and 0.1 mol / L soluble calcium salt solutions sequentially, maintaining the pH at 5.0-6.5 throughout the addition process. After addition, stir magnetically at 30-35℃ for 1 h, then age at room temperature for 2-4 h. Filter, wash 3-5 times with deionized water, dry at 80℃, and grind into powder to obtain the modified attapulgite. The volume ratio of the phytic acid solution, soluble magnesium salt solution, and soluble calcium salt solution is 20:2:0.8.

[0070] The soluble magnesium salt is MgCl2; the soluble calcium salt is CaCl2.

[0071] The compound microbial agent is prepared by activating and inoculating *Arthrobacter benigra*, *Bacillus megaterium*, and *Bacillus cereus* separately into LB liquid medium, and then incubating with shaking at 30°C until the bacterial count reaches OD50. 600 ≈2.0, then mix them in a volume ratio of 1:1:1 and freeze-dry under vacuum to obtain the final product.

[0072] The *Arthrobacter bengal* strain is CGMCC No. 1.10873, deposited on April 1, 2011; the *Bacillus megaterium* strain is CGMCC No. 1.10466, deposited on March 18, 2010; and the *Bacillus cereus* strain is CGMCC No. 1.9067, deposited on January 19, 2009. All *Arthrobacter bengal*, *Bacillus megaterium*, and *Bacillus cereus* used in this invention were purchased from the China General Microbiological Culture Collection Center (CGMCC) and can be purchased through the center's strain catalog without additional deposit.

[0073] A method for preparing an environmentally friendly microbial soil remediation agent includes the following steps:

[0074] 1) Crush the calcium-magnesium-silicon-based waste residue and humic acid into powder and mix them evenly through an 80-100 mesh sieve;

[0075] 2) Preparation of modified attapulgite soil;

[0076] 3) Preparation of compound microbial inoculants;

[0077] 4) After mixing the mixture obtained in step 1) with modified attapulgite soil, compound microbial agent and other remaining raw materials evenly, granulate, dry at low temperature, cool and sieve to obtain an environmentally friendly microbial soil remediation agent with a particle size of 8-12mm.

[0078] Comparative Example 1

[0079] An environmentally friendly microbial soil remediation agent, whose raw material composition and preparation method are basically the same as those in Example 1, the only difference being that the modified attapulgite soil is replaced with ordinary unmodified attapulgite soil.

[0080] Comparative Example 2

[0081] An environmentally friendly microbial soil remediation agent, whose raw material composition and preparation method are basically the same as those in Example 1, except that the calcium-magnesium-silicon-based waste residue is replaced with an equal amount of quartz sand.

[0082] Comparative Example 3

[0083] An environmentally friendly microbial soil remediation agent has the same raw material composition and preparation method as in Example 1, except that the modified attapulgite is replaced with an equal amount of kaolin.

[0084] Comparative Example 4

[0085] An environmentally friendly microbial soil remediation agent, whose raw material composition and preparation method are basically the same as those in Example 1, the only difference being that the compound microbial agent does not contain Arthrobacter benigra.

[0086] Comparative Example 5

[0087] An environmentally friendly microbial soil remediation agent, whose raw material composition and preparation method are basically the same as those in Example 1, the only difference being that the composite microbial agent does not contain Bacillus megaterium.

[0088] Comparative Example 6

[0089] An environmentally friendly microbial soil remediation agent, whose raw material composition and preparation method are basically the same as those in Example 1, the only difference being that the compound microbial agent does not contain Bacillus cereus.

[0090] Performance testing

[0091] 1. Test on the effect of acidified soil improvement

[0092] Soil from a paddy field was selected as the test soil. After air drying, it was sieved through a 10-mesh sieve, and then the soil pH was adjusted to 4.6 with hydrochloric acid solution. After air drying, the test soil was obtained. A container with a diameter of 15 cm and a height of 25 cm was taken, and 2 kg of the treated test soil was added to the container. The soil remediation agents obtained in Examples 1-3 and Comparative Examples 1-6 were added to the soil at 2% of the dry weight of the test soil. The container was incubated at 37℃ for 60 days. The test soil without any added soil remediation agent was used as a blank. During the incubation period, deionized water was added in a timely manner according to the soil moisture and quality changes to maintain the soil moisture content at 70% of field capacity. Soil samples were collected from all containers after 60 days of incubation, air-dried, ground, and sieved through a 2 mm sieve for the determination of indicators, including soil pH (electrode method), acid-base buffer capacity (pHBC) (pH meter method), exchangeable hydrogen, and exchangeable aluminum (potassium chloride exchange-neutralization titration method). The specific results are shown in Table 1.

[0093] Table 1. Improvement effects of different soil remediation agents on acidified soils

[0094]

[0095] As can be seen from the results in Table 1, the soil remediation agents prepared in Examples 1-3 of the present invention can effectively increase soil pH and pHBC, and can also effectively reduce the content of exchangeable hydrogen and exchangeable aluminum in the soil. The effect is significantly better than that of comparative examples 1-6. This shows that the soil remediation agent of the present invention has a direct treatment effect on acidified soil, can reduce the phenomenon of re-acidification, and can also reduce the potential acidity of the soil, thus having a fundamental treatment effect on acidified soil.

[0096] 2. Verification of the effect of soil heavy metal remediation

[0097] Slightly heavy metal contaminated paddy field soil from a location in Linshu County was selected as the test soil. The soil type was brown soil, and the heavy metal content in the soil was: available Pb 29.8 mg / kg, available Cd 0.51 mg / kg, available Cr 0.051 mg / kg, and available As 0.33 mg / kg. A container with a diameter of 15 cm and a height of 25 cm was used. 2 kg of the test soil (dry weight) was added to the container, along with the soil remediation agents obtained in Examples 1-3 and Comparative Examples 1-6 at 2% of the dry weight of the test soil. The containers were incubated at 37℃ for 100 days. Soil without any added soil remediation agent was used as a blank. During the incubation period, deionized water was added as needed based on soil moisture and quality changes to maintain the soil moisture content at 70% of field capacity. After 100 days of incubation, soil samples from all containers were air-dried, ground, and passed through a 2 mm sieve before being used for index determination. The content of available Pb in soil heavy metals was determined by DTPA extraction-atomic absorption spectrophotometry; the content of available Cd in soil heavy metals was determined by HCl-HNO3-HF-HClO4 micro-thermal digestion-graphite furnace atomic absorption spectrophotometry; the content of available Cr in soil heavy metals was determined by HCl-HNO3-HF-HClO4 micro-thermal digestion-flame atomic absorption spectrophotometry; and the content of available As in soil heavy metals was determined by HNO3-HCl heating digestion-KBH4 reduction-atomic fluorescence spectrometry. Specific results are shown in Table 2.

[0098] Table 2. Effects of different soil remediation agents on heavy metals in soil

[0099]

[0100] As can be seen from Table 2 above, the content of effective soil heavy metals decreased significantly after using the soil remediation agents of Examples 1-3 of the present invention, which indicates that the soil remediation agents of the present invention have a good remediation effect on heavy metals in the soil.

[0101] 3. Field planting experiment

[0102] Experimental site: A moderately polluted plot of land in an administrative village in Luozhuang District, Linyi City was selected as the experimental site. The basic physicochemical properties and heavy metal content of the experimental soil are shown in Table 3.

[0103] Table 3 Basic physicochemical properties of the tested soils

[0104]

[0105] Experimental Methods: The tested rice variety was Xiangjing 9407. The experiment consisted of 10 treatment groups, named 1-10. Groups 1-3 were the treatment groups for Examples 1-3, groups 4-9 were the treatment groups for Comparative Examples 1-6, and group 10 was the blank control group. The specific treatment method for each group was as follows: before planting, the soil remediation agent prepared for each group was applied to the soil along with conventional fertilizer by tilling. The dosage of the soil remediation agent was 40 kg / mu. The blank control group only used conventional fertilizer as base fertilizer and tilled into the soil without using any soil remediation agent. Apart from applying different soil remediation agents before planting, all other field management practices remained consistent across treatment groups. At harvest, 30 consecutive panicles of uniform growth were collected from each treatment group, and the aboveground biomass, rice yield, and yield components were measured. The results are shown in Table 4.

[0106] Table 4 Results of the rice planting experiment

[0107]

[0108] The data above show that, compared with the blank control group, the rice yield was significantly increased after using the soil remediation agent of this invention, and the plant height, number of grains per panicle, and thousand-grain weight were all superior to those of comparative examples 1-6 and the blank control. This is because the environmentally friendly microbial soil remediation agent prepared by this invention can effectively improve the physical and chemical properties of the soil through the synergistic effect of multiple components, thereby significantly improving the soil fertility and health level. This helps to promote plant growth and development, and improve the yield and quality of crops.

[0109] Topsoil samples (0-20cm) were collected after rice harvest. Soil samples were collected from each treatment group using the S-shaped sampling method. During sampling, the soil auger was drilled to a depth of 20cm in a single pass. Three replicates were collected from each treatment group, and the three replicates from the same treatment group were combined into one sample. Visible debris such as gravel and plant roots were removed. Basic physicochemical properties of the soil (see Table 5) and the content of available heavy metals in the soil were determined. Figure 1-4 ).

[0110] Test methods: Soil bulk density was measured using the ring sampler method; pH value was measured using the potentiometric method (water:soil = 2.5:1); organic matter content was measured using the K2Cr2O7 oxidation-external heating method.

[0111] Table 5 Basic physical and chemical properties of soil after rice harvest

[0112]

[0113] As can be seen from the data in Table 5 above, compared with the blank control group, the soil pH increased, bulk density decreased, and organic matter content significantly increased after using the soil conditioner of the present invention, all of which were superior to comparative examples 1-6 and the blank control. This demonstrates that the environmentally friendly microbial soil remediation agent of the present invention can effectively improve the physical and chemical properties of the soil, increase the pH value of acidic soil, increase the soil organic matter content, improve the soil structure, and achieve significant comprehensive soil improvement effects.

[0114] Figure 1-4 The data clearly demonstrates the significant reduction in the bioavailable content of heavy metals in the soil after using the environmentally friendly microbial soil remediation agent of this invention, further proving the effectiveness of this remediation agent in treating heavy metal pollution in soil. Comparative Examples 1-6, however, failed to employ the necessary technical solutions, resulting in significantly inferior performance compared to Examples 1-3 in the relevant performance tests.

[0115] This invention addresses soil acidification and heavy metal pollution simultaneously through a triple synergistic mechanism of waste residue, modified attapulgite soil, and composite microorganisms, while also being economical and ensuring crop safety, significantly outperforming single-function remediation materials.

[0116] It should be noted that the above embodiments are merely some preferred embodiments of the present invention, and not all embodiments. Obviously, based on the above embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

Claims

1. An environmentally friendly microbial soil remediation agent, characterized in that, It is made from the following raw materials in parts by weight: 400-500 parts calcium-magnesium-silicon-based waste residue, 300-340 parts humic acid, 40-60 parts modified attapulgite, 4-6 parts mineral-derived potassium fulvate, 30-50 parts ammonium sulfate, 100-120 parts compound microbial agent, 1-3 parts brown algae oligosaccharide, and 3-5 parts auxiliary materials. The calcium-magnesium-silicon-based waste residue is obtained from the solid waste in the calcium pool during the process of producing calcium chloride from hydrochloric acid, a byproduct of potassium sulfate production. The waste is filtered, washed with water until the conductivity of the filtrate is <1000 μS / cm, and then dried. The composition of the calcium-magnesium-silicon-based waste residue meets the following requirements: CaO ≥ 15%, MgO ≥ 5%, SiO2 2-4%, Cl... - 3-5%, other trace impurities, pH=8.0-10.0; The modified attapulgite clay is prepared using the following method: Step 1: Add attapulgite to 0.5M HCl solution according to the solid-liquid ratio, stir magnetically at room temperature for 1 hour, filter, wash the solid with deionized water until neutral, and dry to obtain pretreated attapulgite. Step 2: Add the pretreated attapulgite to a 0.02 mol / L phytic acid solution according to the solid-liquid ratio. Stir magnetically at room temperature for 30-40 min. Then, slowly add 0.1 mol / L soluble magnesium salt and 0.1 mol / L soluble calcium salt solutions sequentially. Maintain the pH at 5.0-6.5 throughout the dropwise addition process. After the dropwise addition is complete, stir magnetically at 30-35℃ for 1 h. Then, age at room temperature for 2-4 h. Filter, wash with deionized water 3-5 times, dry at 80℃, and grind into powder to obtain modified attapulgite. The compound microbial agent is prepared by activating and inoculating *Arthrobacter benigra*, *Bacillus megaterium*, and *Bacillus cereus* separately into LB liquid medium, and then incubating with shaking at 30°C until the bacterial count reaches OD50. 600 The sample was approximately 2.0, then mixed at a volume ratio of 1:1:1 and freeze-dried under vacuum to obtain the final product. The *Arthrobacter benzi* strain was numbered CGMCC No. 1.10873 and deposited on April 1, 2011. The *Bacillus megaterium* strain was numbered CGMCC No. 1.10466 and deposited on March 18, 2010. The *Bacillus cereus* strain was numbered CGMCC No. 1.9067 and deposited on January 19, 2009.

2. The environmentally friendly microbial soil remediation agent according to claim 1, characterized in that, In step 1, the solid-liquid ratio of attapulgite clay to HCl solution is 1g:10ml.

3. The environmentally friendly microbial soil remediation agent according to claim 1, characterized in that, In step 2, the solid-liquid ratio of the pretreated attapulgite soil to the phytic acid solution is 1g:20ml.

4. The environmentally friendly microbial soil remediation agent according to claim 1, characterized in that, The soluble magnesium salt is MgCl2 or MgSO4; the soluble calcium salt is CaCl2.

5. The environmentally friendly microbial soil remediation agent according to claim 1, characterized in that, In step 2, the volume ratio of phytic acid solution, soluble magnesium salt solution, and soluble calcium salt solution is 20:2:(0.5-1).

6. The environmentally friendly microbial soil remediation agent according to claim 1, characterized in that, The excipients are sodium carboxymethyl cellulose or mineral oil.

7. A method for preparing an environmentally friendly microbial soil remediation agent according to any one of claims 1-6, comprising the following steps: 1) Crush the calcium-magnesium-silicon-based waste residue and humic acid into powder and mix them evenly through an 80-100 mesh sieve; 2) Preparation of modified attapulgite soil; 3) Preparation of compound microbial inoculants; 4) After mixing the mixture obtained in step 1) with modified attapulgite soil, compound microbial agent and other remaining raw materials evenly, granulate, dry at low temperature, cool and sieve to obtain an environmentally friendly microbial soil remediation agent with a particle size of 8-12mm.

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