A heavy metal contaminated saline-alkali soil remediation biochar material and a remediation method

Abstract

The application relates to the technical field of soil remediation, and specifically discloses a biochar material for remediation of heavy metal contaminated saline-alkali soil and a remediation method. The biochar material comprises the following components in parts by weight: modified biochar 55-65 parts, humic acid-sulfur coated microspheres 5-10 parts, sepiolite powder 2-8 parts, poly-lactic acid coated nano zero-valent iron material 2-5 parts, diatomite 2-5 parts and ammonium dihydrogen phosphate 1-3 parts. The modified biochar is biochar loaded with iron-manganese oxide. The humic acid-sulfur coated microspheres are microsphere particles with a degradable poly-lactic acid coating layer, and the degradable poly-lactic acid coating layer is wrapped with humic acid and sulfur. The poly-lactic acid coated nano zero-valent iron material is a core-shell structure material formed by taking poly-lactic acid as a shell and nano zero-valent iron as a core. The modified biochar, the humic acid-sulfur coated microspheres and the poly-lactic acid coated nano zero-valent iron material all have a mesh size of 80-120. The application helps to improve the adsorption capacity for heavy metals in the saline-alkali soil.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of soil remediation, and particularly relates to a biochar material for remediation of heavy metal contaminated saline-alkali soil and a remediation method. BACKGROUND

[0002] The saline-alkali soil is characterized by high soil salt content, high pH value, lack of organic matter and hardening structure, which leads to limited plant growth and low microbial activity. When the saline-alkali soil is simultaneously contaminated by heavy metals (such as cadmium, lead, arsenic, chromium, etc.), the heavy metals are prone to form difficult-to-degrade compounds under alkaline conditions, which further aggravates the degradation of soil ecological function and threatens human health through the food chain. The treatment of such compound pollution needs to simultaneously solve the problems of salt regulation, heavy metal passivation and soil structure improvement, which has a high technical difficulty.

[0003] In the related art, CN105344708A discloses a remediation method for heavy metal contaminated saline-alkali soil, which comprises the following steps: 1) flooding the ground, soaking for 4-6 hours, then draining the water, applying biochar-based fertilizer to the heavy metal contaminated saline-alkali soil, mixing uniformly, and aging for 60-70 days; 2) after the biochar-based fertilizer in step 1) is aged, inoculating a microbial compound inoculum into the soil for 10-15 days; 3) after the microbial compound inoculum in step 2) is inoculated into the soil for 10-15 days, continuously planting castor oil plants for 1-2 cycles, taking the maturation and harvesting of castor oil plant fruits as one cycle, and removing the castor oil plants as a whole after the harvesting of castor oil plant fruits in each cycle; 4) after the castor oil plants are removed as a whole in step 3), flooding the ground, soaking for 4-6 hours, then draining the water, and applying biochar-based fertilizer to the heavy metal contaminated saline-alkali soil again, mixing uniformly, and aging for 60-70 days; 5) after the biochar-based fertilizer in step 4) is aged, inoculating the microbial compound inoculum into the soil again for 10-15 days; 6) after the microbial compound inoculum in step 5) is inoculated into the soil for 10-15 days, continuously planting willows for 1-2 cycles, and removing the willows as a whole after each cycle, taking 10-12 months as one cycle; 7) repeating steps 1)-6) until the content of heavy metals in the soil reaches the safety standard, the biochar-based fertilizer comprises 50-60 parts by weight of biochar made of castor oil plant or willow waste, 10-15 parts by weight of humic acid, 4-6 parts by weight of potassium sulfate, 3-4 parts by weight of calcium sulfate, 8-12 parts by weight of ammonium humate, 15-20 parts by weight of urea, 4-6 parts by weight of citric acid, 3-4 parts by weight of oxalic acid and 6-8 parts by weight of high-temperature slag, the microbial compound inoculum comprises Azotobacter chroococcum, Bacillus licheniformis, Rhodopseudomonas palustris, Bacillus subtilis and plant lactic acid bacteria, and the mass ratio of the Azotobacter chroococcum, Bacillus licheniformis, Rhodopseudomonas palustris, Bacillus subtilis and plant lactic acid bacteria is 2-4:2-4:1.5-2.5:0.75-1.5:1-3.

[0004] However, the biochar made from castor / cottonwood waste as raw materials has low ash content and single pore structure, and the adsorption capacity for heavy metals may be weak. Therefore, it is necessary to develop a biochar material for heavy metal contaminated saline-alkali soil remediation with strong adsorption capacity for heavy metals. SUMMARY

[0005] In order to improve the adsorption capacity for heavy metals in saline-alkali soil, the application provides a biochar material for heavy metal contaminated saline-alkali soil remediation and a remediation method.

[0006] In the first aspect, the application provides a biochar material for heavy metal contaminated saline-alkali soil remediation, which adopts the following technical solution:

[0007] A biochar material for heavy metal contaminated saline-alkali soil remediation comprises the following raw materials by weight: modified biochar 55-65 parts, humic acid-sulfur coated microspheres 5-10 parts, sepiolite powder 2-8 parts, poly lactic acid coated nano zero-valent iron material 2-5 parts, diatomite 2-5 parts, and ammonium dihydrogen phosphate 1-3 parts. The modified biochar is biochar loaded with iron-manganese oxides. The humic acid-sulfur coated microspheres are microsphere particles with a degradable poly lactic acid coating layer, and the degradable poly lactic acid coating layer contains humic acid and sulfur. The poly lactic acid coated nano zero-valent iron material is a core-shell structure material formed by poly lactic acid as a shell and nano zero-valent iron as a core. The modified biochar, humic acid-sulfur coated microspheres, and poly lactic acid coated nano zero-valent iron material are all 80-120 mesh.

[0008] By adopting the above technical solution, iron-manganese oxides can be loaded on the surface of the biochar to form high-activity adsorption sites, and the number of biochar micropore structures is increased, so that the modified biochar still maintains a high adsorption rate under high salinity. The degradable poly lactic acid coating layer gradually dissolves under soil moisture penetration, and can continuously release humic acid and sulfur during the degradation process. Sulfur is oxidized to produce H + , which neutralizes the high pH of saline-alkali soil. At the same time, humic acid dissociates carboxyl groups at pH 6-8, which form stable complexes with heavy metals. Therefore, the humic acid-sulfur coated microspheres can prolong the adsorption time of heavy metals. Moreover, humic acid preferentially adsorbs Ca 2+ / Na + , which can reduce the competition of salt for the heavy metal adsorption sites of the modified biochar. In the poly lactic acid coated nano zero-valent iron material, the poly lactic acid shell isolates oxygen and moisture, greatly extending the half-life of nano zero-valent iron in saline-alkali soil. After the degradation of the poly lactic acid shell, the nano zero-valent iron material is gradually exposed, continuously reducing heavy metals. The degradation product of the poly lactic acid shell, lactic acid, can also complex with Cd 2+ / Pb 2+ , forming low-toxicity lactic acid metal complexes. The layered silicates of sepiolite powder can adsorb Ca2+ / Mg 2+ , which can reduce the competition of saline-alkali cations for heavy metal adsorption sites of modified biochar. The porous structure of diatomaceous earth can physically intercept heavy metal colloidal particles, and the PO4 of ammonium dihydrogen phosphate 3+ With Pb 2+ Producing Pb5(PO4)3OH.

[0009] Therefore, the present application can form a long-term adsorption-reduction-precipitation reaction system that adapts to saline-alkali environment by using the above raw materials. In the first stage, sepiolite selectively adsorbs Ca 2+ , protecting the active sites of biochar, the modified biochar quickly adsorbs heavy metals, and nano zero-valent iron preferentially reduces highly toxic heavy metals. In the second stage, the humic acid-sulfur coated microspheres release humic acid and sulfur to induce heavy metal precipitation, and humic acid neutralizes the high pH of saline-alkali land. The oxidation of sulfur to produce acid synergizes with phosphate buffering to maintain the pH of efficient adsorption reaction, and sepiolite and diatomaceous earth continue to adsorb mobile heavy metals. In the third stage, polylactic acid is completely degraded, and lactic acid complexes the residual free metal ions. The use of the biochar material of this application helps to improve the adsorption capacity of heavy metals in saline-alkali land.

[0010] In a specific embodiment, the biochar material for remediation of heavy metal-contaminated saline-alkali land further includes montmorillonite nanosheets.

[0011] By adopting the above technical solution, under high salinity conditions, the selectivity coefficient of montmorillonite for divalent heavy metals is much higher than that of Na + , K + Monovalent cations such as methyl benzoate can reduce ion competition in saline-alkali land. The micropores of modified biochar adsorb free heavy metals, and montmorillonite nanosheets capture ionic pollutants not adsorbed by biochar through ion exchange, forming a double adsorption barrier. Moreover, the fibrous structure of sepiolite can complement the layered structure of montmorillonite nanosheets to form a three-dimensional adsorption network, which improves the adsorption of Pb. 2+ interception efficiency.

[0012] In a specific embodiment, the biochar material for remediation of heavy metal-contaminated saline-alkali land further includes lignin sulfonate.

[0013] By adopting this technical solution, lignin sulfonate converts incompletely fixed ionic heavy metals on the biochar surface into stable complexes through chelation, helping to improve the efficiency of heavy metal fixation. Furthermore, lignin sulfonate forms complex micelles through hydrophobic interactions and hydrogen bonds, which can reduce the release rate of humic acid, helping to prolong the adsorption time of the biochar material, thereby improving the adsorption effect.

[0014] In one specific embodiment, the biochar material for remediation of heavy metal contaminated saline-alkali soil further comprises chitosan and EDTA, and the mass ratio of chitosan to EDTA is 1:(0.3-0.6).

[0015] By adopting the technical scheme, the chitosan forms a three-dimensional hydrogel network in the alkaline saline-alkali soil, and wraps the biochar and montmorillonite particles, thereby improving the erosion resistance of the material. The EDTA desorbs the heavy metals not adsorbed in the pores of the biochar, and the chitosan captures the desorbed Pb-EDTA through the gel network and converts it into insoluble chitosan-Pb precipitate. The adsorption-desorption-re-fixing process helps to improve the utilization rate of the biochar material. Moreover, the S 2+ Cd chelated with chitosan 2+ In combination, the CdS@chitosan composite particles can be generated, which helps to improve the precipitation rate. Since the excess EDTA can cause excessive dissolution of the heavy metal-EDTA complex and increase the migration risk, the experiment shows that, by adopting the chitosan and EDTA in the above ratio, the gel network of the chitosan can intercept the complex, which helps to further improve the adsorption capacity of the biochar material.

[0016] In a second aspect, the application provides a method for remediation of heavy metal contaminated saline-alkali soil, which adopts the following technical scheme:

[0017] The method for remediation of heavy metal contaminated saline-alkali soil comprises the following steps:

[0018] The modified biochar, humic acid-sulfur coated microspheres, sepiolite powder, poly lactic acid coated nano zero-valent iron material, diatomite and ammonium dihydrogen phosphate are mixed in a proportion to obtain a biochar material;

[0019] The biochar material is applied to the surface layer of the heavy metal contaminated saline-alkali soil at a rate of 3-5 kg / m 2 The surface layer of the heavy metal contaminated saline-alkali soil is mixed by rotary tillage to a depth of 15-25 cm, and 3-6 L / m 2 A polyaspartic acid solution with a mass concentration of 0.1-0.2% is sprayed, and the solution is left to stand for 5-10 days;

[0020] The biochar material is applied to the surface layer of the heavy metal contaminated saline-alkali soil at a rate of 3-5 kg / m 2 The microbial agent is applied to the surface of the heavy metal contaminated saline-alkali soil, and the soil is lightly raked and covered;

[0021] The salt-tolerant Suaeda is planted at a planting density of 28-34 plants / m 2 After the salt-tolerant Suaeda is grown for 100-150 days, the salt-tolerant Suaeda is harvested, and then 1-2 plants / 2 m 2The planting density of the salt-tolerant halophyte Suaeda salsa is 0.5-1.0m x 0.5-1.0m, and the planting density of the plant Lycium barbarum is 0.5-1.0m x 0.5-1.0m. After the Lycium barbarum grows for 210-260 days, the aboveground parts of the Lycium barbarum are harvested. The harvested Suaeda salsa and Lycium barbarum are dried, and then pyrolyzed at 480-520°C under oxygen deficiency for 2-3 hours to obtain the biochar that can be backfilled. After the biochar that can be backfilled is washed with 4-6% phosphoric acid, the biochar is backfilled into the heavy metal contaminated saline-alkali soil.

[0022] The above steps are repeatedly performed in cycles until the content of the heavy metal in the heavy metal contaminated saline-alkali soil reaches a safety standard.

[0023] By adopting the technical solution, the biochar material is scattered on the saline-alkali soil and rotary plowed to a depth of 15-25cm, which helps the biochar material to fully contact with the contaminated soil. Spraying the polyaspartic acid solution with the above concentration can chelate the heavy metal and avoid excessive desorption to cause migration risk. The carboxyl group of the polyaspartic acid competes with the biochar to adsorb Pb 2+ , converts the fixed state Pb into a Pb-aspartic acid complex, and promotes plant absorption. The polyaspartic acid is combined with Ca 2+ , reduces the pore blockage caused by soil CaCO3 cementation. Then, the bacterial agent is sprayed. The bacterial agent takes the humic acid-sulfur microspheres as an electron donor, reduces S 0 to S 2- , and can promote CdS precipitation. The extracellular polymer produced by bacterial agent metabolism can wrap the biochar, and can reduce the dissolution of iron and manganese oxides on the modified biochar caused by saline-alkali stress. Then, the Suaeda salsa-Lycium barbarum rotation is performed. The Suaeda salsa extracts the surface heavy metal, the bacterial agent promotes the upward migration of deep pollutants, the Lycium barbarum extracts the middle and lower heavy metal, and the biochar continuously stabilizes the rhizosphere environment. Then, the crops are pyrolyzed into biochar and backfilled, and the material cycle is completed. Therefore, the remediation method realizes the deep synergy of pollution control, plant extraction, material regeneration, and ecological restoration, and helps to improve the adsorption effect of the heavy metal in the saline-alkali soil.

[0024] In a specific implementable embodiment, the bacterial agent includes Halomonas: Bacillus: Streptomyces with a mass ratio of 5:(2-4):(1-2).

[0025] By adopting the technical solution, the Halomonas can quickly establish saline-alkali adaptability, and provide a survival microenvironment for the Bacillus and the Streptomyces. The Bacillus can efficiently passivate the heavy metal and supplement the Pb / Cd fixation ability of the Halomonas. The Streptomyces enhances the stability through EPS and antibiotic systems, and avoids the imbalance of the bacterial flora. Through the functional complementation and synergistic metabolism of the three, the heavy metal bio-adsorption effect in the saline-alkali soil is significantly improved.

[0026] In a specific implementable embodiment, the preparation method of the modified biochar includes the following steps:

[0027] The sawdust and rice straw are mixed according to a mass ratio of 3-5:1, crushed, soaked in a 1-2% mass concentration of citric acid for 22-28 hours, washed with deionized water until neutral, dried, and obtained as standby material;

[0028] The standby material is pyrolyzed at 280-320°C in a nitrogen atmosphere for 1-1.2 hours, heated to 580-620°C, pyrolyzed for 2-2.2 hours, naturally cooled, and obtained as biochar;

[0029] A 0.3-0.6 mol / L Fe(NO3)3 solution and a 0.2-0.4 mol / L KMnO4 solution are mixed according to a volume ratio of 1:(0.7-1.2) to obtain a mixed solution, the biochar is soaked in the mixed solution, shaken for 22-28 hours, filtered out, dried, calcined at 330-380°C in a nitrogen atmosphere for 2-2.5 hours, naturally cooled, and sieved to obtain modified biochar with a mesh size of 80-120.

[0030] By using the above technical solution, the sawdust has a high cellulose content, and the rice straw has a silicon content of 10-15%. After mixing according to a ratio of 3-5:1 and pyrolysis, a multi-level pore structure can be formed. The silicon in the straw generates amorphous SiO2 at high temperatures, which is combined with the carbon skeleton of the sawdust to enhance the ion exchange capacity of Cd 2+ and Pb 2+ . Soaking in 1-2% citric acid removes ash and lipids in the raw material, reducing pore blockage during pyrolysis. Slow pyrolysis of lignin and hemicellulose at low temperatures generates a rigid carbon skeleton, avoiding pore collapse caused by direct pyrolysis at high temperatures. This stage produces a large number of mesopores, providing space for subsequent metal oxide loading. Further high temperature promotes graphitization of the carbon layer, enhancing the structural stability. Calcination at 330-380°C allows Fe / Mn oxides to be combined with biochar through C-O-Fe / Mn covalent bonds, which can reduce metal leaching. The modified biochar prepared by the above steps has excellent synergistic effect with other raw materials, which can improve the removal rate of heavy metals.

[0031] In a specific embodiment, the humic acid-sulfur coated microspheres include a core and a coating layer wrapping the core, and the core includes the following raw materials in parts by weight based on the total weight of the core: 55-65 parts of sulfur powder, 25-35 parts of humic acid, 2-5 parts of sodium dodecyl sulfate, and 2-5 parts of sodium carboxymethyl cellulose; and the coating layer includes ethyl cellulose and polylactic acid in a weight ratio of (7-8):1.

[0032] The preparation method of the humic acid-sulfur coated microspheres includes the following steps: dissolving sodium dodecyl sulfate in water to obtain a 4-6% mass concentration of sodium dodecyl sulfate aqueous solution; mixing sulfur powder and humic acid in a certain proportion, adding the sodium dodecyl sulfate aqueous solution, and shear emulsifying to obtain a suspension;

[0033] Sodium carboxymethyl cellulose is dissolved in water to obtain a carboxymethyl cellulose aqueous solution with a mass concentration of 4-6%, and the suspension is added to the carboxymethyl cellulose aqueous solution, and stirred until the viscosity reaches 500-800 mPa·s to obtain a mixed slurry;

[0034] The mixed slurry is spray granulated, and microsphere cores with a particle size of 100-200 μm are collected;

[0035] Acetone and ethanol are mixed in a volume ratio of 3:(6-8) to obtain a mixed alcohol solution, ethyl cellulose and poly-lactic acid are dissolved in the mixed alcohol solution, and stirred until completely dissolved to obtain a coating liquid;

[0036] The core microspheres are placed in a fluidized bed and preheated to 40-50℃, and the coating liquid is sprayed at a rate of 8-12 mL / min, and after solidification, sieving is performed to obtain humic acid-sulfur coated microspheres with a particle size of 80-120 mesh.

[0037] By using the above technical solution, sodium dodecyl sulfate reduces the interfacial tension of sulfur-humic acid, making the particle size of the emulsified suspension uniform and improving the density of the microsphere core. Sodium carboxymethyl cellulose forms a three-dimensional network structure, and the slurry viscosity reaches 500-800 mPa·s, reducing the microsphere breakage rate during spray granulation. In the fluidized bed spraying process, preheating to 40-50℃ activates the surface of the microsphere core, the coating liquid forms a dense film layer, improves the compressive strength, and avoids damage during field mechanical application. The humic acid-sulfur coated microspheres prepared by the above steps can have excellent synergistic effect with other raw materials, and can improve the heavy metal removal rate.

[0038] In a specific embodiment, the poly-lactic acid coated nano zero-valent iron material includes the following raw materials by weight: nano zero-valent iron 30-40 parts, poly-lactic acid 55-65 parts, polyvinylpyrrolidone 3-5 parts, and trisodium citrate 2-3 parts;

[0039] The preparation method of the poly-lactic acid coated nano zero-valent iron material includes the following steps:

[0040] Poly-lactic acid is dissolved in dichloromethane to obtain a poly-lactic acid solution with a mass concentration of 4-5%, and polyvinylpyrrolidone and trisodium citrate are added to the poly-lactic acid solution, and ultrasonic dispersion is performed to obtain an organic phase solution;

[0041] Nano zero-valent iron is dispersed in a SDS / deoxy water solution with a mass concentration of 0.1-0.3% at a solid-liquid ratio of 1:(45-55), and ultrasonic dispersion is performed to obtain an aqueous phase solution;

[0042] The aqueous phase and the organic phase are mixed at a volume ratio of 1:(2-4), and high-speed shear emulsification is performed to obtain a W / O emulsion;

[0043] The W / O emulsion is rotary evaporated at 40-50℃, 180-220mbar to remove dichloromethane until the microspheres are solidified, the microspheres are collected by centrifugation, and after washing the microspheres, freeze-drying is performed to obtain dry particles;

[0044] The dry particles are heat-treated at 80-85℃ for 1-1.5 hours under a nitrogen atmosphere, sieved, and a polylactic acid-coated nano zero-valent iron material with a mesh size of 80-120 is obtained.

[0045] By using the above technical scheme, the microemulsion with a water core diameter of 100-200nm is formed by using water phase: organic phase = 1:2-4, which can improve the encapsulation efficiency. High-speed shearing emulsification makes the nano zero-valent iron uniformly dispersed in the water phase droplets, avoiding agglomeration. Slow evaporation of dichloromethane at low temperature and reduced pressure avoids the breakage of the coating caused by the rapid volatilization of the nano zero-valent iron. Freeze-drying maintains the porous structure of the microspheres, avoiding the oxidation of the nano zero-valent iron caused by high-temperature drying. Heat treatment at 80-85℃ under nitrogen protection promotes the rearrangement of polylactic acid molecular chains, which helps to improve the tensile strength of the coating. Controlling the particle size to be 150-180μm is more suitable for the soil pores of saline-alkali soil, which helps to improve the migration and diffusion efficiency. The polylactic acid-coated nano zero-valent iron material prepared by the above steps can have excellent synergistic effect with other raw materials, which can improve the removal rate of heavy metals.

[0046] In summary, the present application has the following beneficial effects:

[0047] 1. The biochar material of the present application forms an adsorption-reduction-precipitation reaction system that adapts to the saline-alkali environment and has a long-term effect, which helps to improve the adsorption capacity of heavy metals in saline-alkali soil.

[0048] 2. In the present application, montmorillonite nanosheets and lignosulfonate are preferably used, which can form a three-dimensional adsorption network to improve the interception efficiency of Pb 2+ or prolong the adsorption time of the biochar material.

[0049] 3. The method of the present application realizes the deep synergy of pollution control, plant extraction, material regeneration and ecological restoration, which helps to improve the adsorption effect of heavy metals in saline-alkali soil. DETAILED DESCRIPTION

[0050] Unless otherwise specified, the raw materials used in the present application are commercially available, wherein the halomonas is Halomonas hancockii DSM 21196, the bacillus is Ji Shengda JY-015Y, and the streptomyces is Streptomyces microflavus with a viable bacterial count of 100 billion per gram.

[0051] The present application is further described in detail below in combination with examples and comparative examples.

[0052] EXAMPLE

[0053] Example 1

[0054] The embodiment provides a biochar material for remediation of heavy metal contaminated saline-alkali soil, which comprises the following raw materials: 55 kg of modified biochar, 10 kg of humic acid-sulfur coated microspheres, 8 kg of sepiolite powder, 5 kg of polylactic acid coated nano zero-valent iron material, 5 kg of diatomite and 3 kg of ammonium dihydrogen phosphate. The modified biochar, the humic acid-sulfur coated microspheres and the polylactic acid coated nano zero-valent iron material are all 80-120 mesh.

[0055] The modified biochar is prepared by the following steps:

[0056] Wood chips and rice straw are mixed according to a mass ratio of 3:1, crushed, soaked in 1% citric acid for 28 hours, and filtered to obtain solid materials, which are washed to neutral with deionized water, dried, and obtained as standby materials.

[0057] The standby materials are pyrolyzed at 280°C under a nitrogen atmosphere for 1.2 hours, and then pyrolyzed at 580°C for 2.2 hours, and then naturally cooled to obtain biochar.

[0058] 0.3 mol / L Fe(NO3)3 solution and 0.2 mol / L KMnO4 solution are mixed according to a volume ratio of 1:0.7 until uniform to obtain a mixed solution. Then, the biochar is soaked in the mixed solution, shaken for 22 hours, filtered out, dried, calcined at 330°C under a nitrogen atmosphere for 2.5 hours, naturally cooled, and sieved to obtain modified biochar with a mesh size of 80-120.

[0059] The humic acid-sulfur coated microspheres are prepared by the following steps:

[0060] The humic acid-sulfur coated microspheres comprise a core and a coating layer wrapping the core, and the core comprises the following raw materials: 55 kg of sulfur powder, 35 kg of humic acid, 5 kg of sodium dodecyl sulfate and 5 kg of sodium carboxymethyl cellulose; and the coating layer comprises ethyl cellulose and polylactic acid at a weight ratio of 7:1.

[0061] Sodium dodecyl sulfate is dissolved in water to obtain a 4% sodium dodecyl sulfate aqueous solution. The sulfur powder and the humic acid are mixed according to a proportion, and then added to the sodium dodecyl sulfate aqueous solution to obtain a suspension by shear emulsification.

[0062] Sodium carboxymethyl cellulose is dissolved in water to obtain a 4% sodium carboxymethyl cellulose aqueous solution, and then the suspension is added to the sodium carboxymethyl cellulose aqueous solution and stirred until the viscosity reaches 500 mPa·s to obtain a mixed slurry.

[0063] The mixed slurry is subjected to spray granulation, and microsphere cores with a particle size of 100-200 μm are collected.

[0064] Mix acetone and ethanol according to the volume ratio of 1:2 to obtain a mixed alcohol solution, dissolve ethyl cellulose and polylactic acid in the mixed alcohol solution, and stir until completely dissolved to obtain a coating solution.

[0065] Place the core microspheres in a fluidized bed, preheat to 40℃, spray the coating solution at a rate of 8mL / min, sieve after solidification to obtain humic acid-sulfur coated microspheres with a particle size of 80-120 mesh.

[0066] The polylactic acid coated nano zero-valent iron material is prepared according to the following steps:

[0067] The polylactic acid coated nano zero-valent iron material comprises the following raw materials: nano zero-valent iron 30kg, polylactic acid 65kg, polyvinylpyrrolidone 5kg, and trisodium citrate 3kg;

[0068] Dissolve the polylactic acid in dichloromethane to obtain a polylactic acid solution with a mass concentration of 4%, add polyvinylpyrrolidone and trisodium citrate to the polylactic acid solution, and ultrasonically disperse to obtain an organic phase solution.

[0069] Disperse the nano zero-valent iron in a 0.1% SDS / deoxy water solution with a solid-liquid ratio of 1:45, and ultrasonically disperse to obtain an aqueous phase solution.

[0070] Mix the aqueous phase and the organic phase according to the volume ratio of 1:2, and high-speed shear emulsify to obtain a W / O emulsion.

[0071] Rotary evaporate the W / O emulsion at 40℃ and 220mbar to remove dichloromethane until the microspheres solidify, centrifuge to collect the microspheres, wash the microspheres, and freeze-dry to obtain dry particles.

[0072] Heat treat the dry particles in a nitrogen atmosphere at 80℃ for 1.5 hours, sieve to obtain polylactic acid coated nano zero-valent iron material with a mesh size of 80-120.

[0073] The method for repairing heavy metal contaminated saline-alkali soil comprises the following steps:

[0074] According to the proportion, mix the modified biochar, humic acid-sulfur coated microspheres, sepiolite powder, polylactic acid coated nano zero-valent iron material, diatomite, and ammonium dihydrogen phosphate to obtain a biochar material.

[0075] Spread the above biochar material according to 3kg / m 2 on the surface of the heavy metal contaminated saline-alkali soil, spin till mixed to a depth of 15cm, and spray 3L / m 2 of a 0.2% polyaspartic acid solution on the heavy metal contaminated saline-alkali soil, and stand for 5 days.

[0076] According to 85g / m 2Apply Halomonas to the surface of saline-alkali land contaminated by heavy metals, shallowly harrow and cover with soil.

[0077] According to 28 plants / m 2 Plant the Suaeda salsa at a planting density of 1 plant / 2m 2 Plant wolfberry at a planting density of 1000 nm and harvest the above-ground parts of wolfberry after 210 days of growth. Dried salsa salsa and wolfberry are pyrolyzed at 480°C in anoxic conditions for 3 hours to obtain backfill biochar. The backfill biochar is washed with 4% phosphoric acid and backfilled into heavy metal-contaminated saline-alkali land.

[0078] The above steps are repeated in a cycle until the content of heavy metals in the heavy metal-contaminated saline-alkali land reaches a safety standard.

[0079] Example 2

[0080] The only difference between this embodiment and Example 1 is that the biochar material for remediation of heavy metal-contaminated saline-alkali land includes the following raw materials: 65 kg of modified biochar, 5 kg of humic acid-sulfur coated microspheres, 2 kg of sepiolite powder, 2 kg of polylactic acid-coated nano zero-valent iron material, 2 kg of diatomaceous earth, and 1 kg of ammonium dihydrogen phosphate.

[0081] Example 3

[0082] This example differs from Example 1 only in that the biochar material for remediating heavy metal-contaminated saline-alkali land comprises the following raw materials: 55 kg of modified biochar, 10 kg of humic acid-sulfur-coated microspheres, 8 kg of sepiolite powder, 5 kg of polylactic acid-coated nano-zero-valent iron material, 5 kg of diatomaceous earth, 3 kg of ammonium dihydrogen phosphate, and 5 kg of montmorillonite nanosheets. In the method for remediating heavy metal-contaminated saline-alkali land, the modified biochar, humic acid-sulfur-coated microspheres, sepiolite powder, polylactic acid-coated nano-zero-valent iron material, diatomaceous earth, ammonium dihydrogen phosphate, and montmorillonite nanosheets are uniformly mixed according to the desired ratio to produce the biochar material.

[0083] Example 4

[0084] This example differs from Example 1 only in that the biochar material for remediating heavy metal-contaminated saline-alkali land comprises the following raw materials: 55 kg of modified biochar, 10 kg of humic acid-sulfur-coated microspheres, 8 kg of sepiolite powder, 5 kg of polylactic acid-coated nano-zero-valent iron material, 5 kg of diatomaceous earth, 3 kg of ammonium dihydrogen phosphate, and 3 kg of lignin sulfonate. In the method for remediating heavy metal-contaminated saline-alkali land, the modified biochar, humic acid-sulfur-coated microspheres, sepiolite powder, polylactic acid-coated nano-zero-valent iron material, diatomaceous earth, ammonium dihydrogen phosphate, and lignin sulfonate are uniformly mixed according to the appropriate proportions to produce the biochar material.

[0085] Example 5

[0086] The difference between this embodiment and embodiment 1 is only that the biochar material for repairing heavy metal contaminated saline-alkali soil comprises the following raw materials: modified biochar 55 kg, humic acid-sulfur coated microspheres 10 kg, sepiolite powder 8 kg, poly lactic acid coated nano zero-valent iron material 5 kg, diatomite 5 kg, ammonium dihydrogen phosphate 3 kg, montmorillonite nanosheet 5 kg, and lignin sulfonate 3 kg. In the repairing method of the heavy metal contaminated saline-alkali soil, the modified biochar, the humic acid-sulfur coated microspheres, the sepiolite powder, the poly lactic acid coated nano zero-valent iron material, the diatomite, the ammonium dihydrogen phosphate, the montmorillonite nanosheet, and the lignin sulfonate are uniformly mixed according to the proportion to obtain the biochar material.

[0087] Embodiment 6

[0088] The difference between this embodiment and embodiment 1 is only that the biochar material for repairing heavy metal contaminated saline-alkali soil comprises the following raw materials: modified biochar 55 kg, humic acid-sulfur coated microspheres 10 kg, sepiolite powder 8 kg, poly lactic acid coated nano zero-valent iron material 5 kg, diatomite 5 kg, chitosan 2 kg, and EDTA 0.3 kg. In the repairing method of the heavy metal contaminated saline-alkali soil, the modified biochar, the humic acid-sulfur coated microspheres, the sepiolite powder, the poly lactic acid coated nano zero-valent iron material, the diatomite, the chitosan, and the EDTA are uniformly mixed according to the proportion to obtain the biochar material.

[0089] Embodiment 7

[0090] The difference between this embodiment and embodiment 1 is only that the biochar material for repairing heavy metal contaminated saline-alkali soil comprises the following raw materials: modified biochar 55 kg, humic acid-sulfur coated microspheres 10 kg, sepiolite powder 8 kg, poly lactic acid coated nano zero-valent iron material 5 kg, diatomite 5 kg, chitosan 2 kg, and EDTA 0.6 kg. In the repairing method of the heavy metal contaminated saline-alkali soil, the modified biochar, the humic acid-sulfur coated microspheres, the sepiolite powder, the poly lactic acid coated nano zero-valent iron material, the diatomite, the chitosan, and the EDTA are uniformly mixed according to the proportion to obtain the biochar material.

[0091] Embodiment 8

[0092] The difference between this embodiment and embodiment 1 is only that the biochar material for repairing heavy metal contaminated saline-alkali soil comprises the following raw materials: modified biochar 55 kg, humic acid-sulfur coated microspheres 10 kg, sepiolite powder 8 kg, poly lactic acid coated nano zero-valent iron material 5 kg, diatomite 5 kg, chitosan 2 kg, and EDTA 1.2 kg. In the repairing method of the heavy metal contaminated saline-alkali soil, the modified biochar, the humic acid-sulfur coated microspheres, the sepiolite powder, the poly lactic acid coated nano zero-valent iron material, the diatomite, the chitosan, and the EDTA are uniformly mixed according to the proportion to obtain the biochar material.

[0093] Example 9

[0094] This example differs from Example 1 only in that the biochar material for remediating heavy metal-contaminated saline-alkali land comprises the following raw materials: 55 kg of modified biochar, 10 kg of humic acid-sulfur-coated microspheres, 8 kg of sepiolite powder, 5 kg of polylactic acid-coated nano-zero-valent iron material, 5 kg of diatomaceous earth, 2 kg of chitosan, and 1.5 kg of EDTA. In the method for remediating heavy metal-contaminated saline-alkali land, the modified biochar, humic acid-sulfur-coated microspheres, sepiolite powder, polylactic acid-coated nano-zero-valent iron material, diatomaceous earth, ammonium dihydrogen phosphate, chitosan, and EDTA are uniformly mixed according to the appropriate proportions to produce the biochar material.

[0095] Example 10

[0096] This example differs from Example 1 only in that the biochar material for remediating heavy metal-contaminated saline-alkali land includes the following raw materials: 55 kg of modified biochar, 10 kg of humic acid-sulfur-coated microspheres, 8 kg of sepiolite powder, 5 kg of polylactic acid-coated nano-zero-valent iron material, 5 kg of diatomaceous earth, 3 kg of ammonium dihydrogen phosphate, 5 kg of montmorillonite nanosheets, 3 kg of lignin sulfonate, 2 kg of chitosan, and 0.6 kg of EDTA. In the method for remediating heavy metal-contaminated saline-alkali land, the modified biochar, humic acid-sulfur-coated microspheres, sepiolite powder, polylactic acid-coated nano-zero-valent iron material, diatomaceous earth, 3 kg of ammonium dihydrogen phosphate, 5 kg of montmorillonite nanosheets, 3 kg of lignin sulfonate, chitosan, and EDTA are uniformly mixed according to the appropriate proportions to produce the biochar material.

[0097] Example 11

[0098] The only difference between this embodiment and embodiment 1 is that the method for repairing heavy metal-contaminated saline-alkali land includes the following steps:

[0099] The modified biochar, humic acid-sulfur coated microspheres, sepiolite powder, polylactic acid coated nano zero-valent iron material, diatomaceous earth and ammonium dihydrogen phosphate are mixed uniformly according to a ratio to obtain a biochar material;

[0100] The above biochar material was pressurized at 5 kg / m 2 Spread on the surface of heavy metal polluted saline-alkali land, rotary tillage and mix to a depth of 25 cm, at a rate of 6L / m 2 , spray a polyaspartic acid solution with a mass concentration of 0.1% on the heavy metal contaminated saline-alkali land and let it stand for 10 days.

[0101] Press 110g / m 2 Apply Halomonas to the surface of saline-alkali land contaminated by heavy metals, shallowly harrow and cover with soil.

[0102] According to 34 plants / m 2The Suaeda salsa is planted at a planting density of 2 plants per 2 m2, and the Suaeda salsa is harvested after growing for 150 days; then the Suaeda salsa is planted at a planting density of 2 plants per 2 m2 2 The Lycium barbarum is planted at a planting density of 2 plants per 2 m2, and the aboveground part of the Lycium barbarum is harvested after growing for 260 days; then the harvested Suaeda salsa and Lycium barbarum are dried, and the dried Suaeda salsa and Lycium barbarum are pyrolyzed at 520 DEG C under oxygen deficiency for 2 hours to obtain the biochar that can be backfilled, and the biochar that can be backfilled is washed with 6% phosphoric acid and then backfilled into the Halomonas.

[0103] The above steps are repeatedly performed in cycles until the content of the heavy metal in the heavy metal contaminated saline-alkali soil reaches a safety standard.

[0104] Example 12

[0105] The difference between this example and example 1 is that, in the method for repairing the heavy metal contaminated saline-alkali soil, the Halomonas is replaced by an equal amount of a microbial agent, and the microbial agent comprises Halomonas, Bacillus and Streptomyces in a mass ratio of 5:1:1.

[0106] Example 13

[0107] The difference between this example and example 1 is that, in the method for repairing the heavy metal contaminated saline-alkali soil, the Halomonas is replaced by an equal amount of a microbial agent, and the microbial agent comprises Halomonas, Bacillus and Streptomyces in a mass ratio of 5:2:1.

[0108] Example 14

[0109] The difference between this example and example 1 is that, in the method for repairing the heavy metal contaminated saline-alkali soil, the Halomonas is replaced by an equal amount of a microbial agent, and the microbial agent comprises Halomonas, Bacillus and Streptomyces in a mass ratio of 5:3:2.

[0110] Example 15

[0111] The difference between this example and example 1 is that, in the method for repairing the heavy metal contaminated saline-alkali soil, the Halomonas is replaced by an equal amount of a microbial agent, and the microbial agent comprises Halomonas, Bacillus and Streptomyces in a mass ratio of 5:4:2.

[0112] Example 16

[0113] The difference between this example and example 1 is that, in the method for repairing the heavy metal contaminated saline-alkali soil, the Halomonas is replaced by an equal amount of a microbial agent, and the microbial agent comprises Halomonas, Bacillus and Streptomyces in a mass ratio of 5:5:3.

[0114] Example 17

[0115] The difference between this example and example 1 is that, the modified biochar is prepared according to the following steps:

[0116] The sawdust and rice straw are mixed in a mass ratio of 5:1, crushed, soaked in a 2% citric acid solution for 22 hours, filtered to obtain a solid material, washed with deionized water until neutral, dried, and obtained as a standby material.

[0117] The standby material is pyrolyzed at 320°C under a nitrogen atmosphere for 1 hour, and then heated to 620°C for 2 hours. After natural cooling, a biochar is obtained.

[0118] A 0.6 mol / L Fe(NO3)3 solution and a 0.4 mol / L KMnO4 solution are mixed in a volume ratio of 1:1.2 until uniform, to obtain a mixed solution. Then, the biochar is soaked in the mixed solution, shaken for 28 hours, filtered, dried, calcined at 380°C under a nitrogen atmosphere for 2 hours, naturally cooled, and sieved to obtain a modified biochar with a mesh size of 80-120.

[0119] Example 18

[0120] The difference between this example and Example 1 is that the humic acid-sulfur coated microspheres are prepared as follows:

[0121] The humic acid-sulfur coated microspheres include a core and a coating layer wrapping the core, the core including the following raw materials: 65 kg of sulfur powder, 25 kg of humic acid, 2 kg of sodium dodecyl sulfate, and 2 kg of sodium carboxymethyl cellulose; and the coating layer including ethyl cellulose and polylactic acid in a weight ratio of 8:1.

[0122] The sodium dodecyl sulfate is dissolved in water to obtain a 6% sodium dodecyl sulfate aqueous solution. The sulfur powder and the humic acid are mixed in proportion, and added to the sodium dodecyl sulfate aqueous solution, and sheared and emulsified to obtain a suspension.

[0123] The sodium carboxymethyl cellulose is dissolved in water to obtain a 6% carboxymethyl cellulose aqueous solution, and the suspension is added to the carboxymethyl cellulose aqueous solution, and stirred until the viscosity reaches 800 mPa·s, to obtain a mixed slurry.

[0124] The mixed slurry is spray granulated, and microsphere cores with a particle size of 100-200 μm are collected.

[0125] The acetone and ethanol are mixed in a volume ratio of 3:8 to obtain a mixed alcohol solution, and the ethyl cellulose and polylactic acid are dissolved in the mixed alcohol solution, and stirred until completely dissolved, to obtain a coating liquid.

[0126] The core microspheres are placed in a fluidized bed, preheated to 50°C, and the coating liquid is sprayed at a rate of 12 mL / min. After solidification, sieving is performed to obtain humic acid-sulfur coated microspheres with a particle size of 80-120 mesh.

[0127] Example 19

[0128] The embodiment differs from Example 1 only in that the polylactic acid-coated nano zero-valent iron material is prepared according to the following steps:

[0129] The polylactic acid-coated nano zero-valent iron material comprises the following raw materials: nano zero-valent iron 40 kg, polylactic acid 55 kg, polyvinylpyrrolidone 3 kg, and trisodium citrate 2 kg;

[0130] The polylactic acid is dissolved in dichloromethane to obtain a polylactic acid solution with a mass concentration of 5%, and the polyvinylpyrrolidone and trisodium citrate are added to the polylactic acid solution and ultrasonically dispersed to obtain an organic phase solution.

[0131] The nano zero-valent iron is dispersed in a 0.3% SDS / deoxy water solution with a solid-liquid ratio of 1:55 and ultrasonically dispersed to obtain an aqueous phase solution.

[0132] The aqueous phase and the organic phase are mixed at a volume ratio of 1:4 and high-speed sheared to emulsify to obtain a W / O emulsion.

[0133] The W / O emulsion is rotary evaporated at 50°C and 180 mbar to remove the dichloromethane until the microspheres are solidified, the microspheres are collected by centrifugation, and after washing the microspheres, freeze-drying is performed to obtain dry particles.

[0134] The dry particles are heat-treated at 85°C for 1 hour in a nitrogen atmosphere, sieved, and polylactic acid-coated nano zero-valent iron material with a mesh size of 80-120 is obtained.

[0135] Comparative Example

[0136] Comparative Example 1

[0137] This comparative example differs from Example 1 only in that in the raw materials of the biochar material for remediation of heavy metal contaminated saline-alkali soil, an equal amount of rice husk biochar is used to replace the modified biochar.

[0138] Comparative Example 2

[0139] This comparative example differs from Example 1 only in that in the raw materials of the biochar material for remediation of heavy metal contaminated saline-alkali soil, an equal amount of humic acid is used to replace the humic acid-sulfur coated microspheres.

[0140] Comparative Example 3

[0141] This comparative example differs from Example 1 only in that in the raw materials of the biochar material for remediation of heavy metal contaminated saline-alkali soil, an equal amount of sulfur is used to replace the humic acid-sulfur coated microspheres.

[0142] Comparative Example 4

[0143] The difference between this comparative example and Example 1 is only that in the raw material of the biochar material for remediation of heavy metal contaminated saline-alkali soil, the humic acid-sulfur coated microspheres are replaced with an equal amount of a mixture of humic acid and sulfur with a weight ratio of 1:1.

[0144] Comparative Example 5

[0145] The difference between this comparative example and Example 1 is only that in the raw material of the biochar material for remediation of heavy metal contaminated saline-alkali soil, the polylactic acid coated nano zero-valent iron material is replaced with an equal amount of nano zero-valent iron.

[0146] Comparative Example 6

[0147] The difference between this comparative example and Example 1 is only that in the raw material of the biochar material for remediation of heavy metal contaminated saline-alkali soil, no sepiolite powder is contained.

[0148] Comparative Example 7

[0149] The difference between this comparative example and Example 1 is only that in the raw material of the biochar material for remediation of heavy metal contaminated saline-alkali soil, no diatomite is contained.

[0150] Performance detection test

[0151] The performance of the biochar materials obtained from Examples 1-19 and Comparative Examples 1-7 and the remediation method of heavy metal contaminated saline-alkali soil were detected.

[0152] Cd 2+ and Pb 2+ containing simulated contaminated saline-alkali soil with a concentration of 500 mg / kg was prepared, and the pH was adjusted to 8.5. Then the following experiments were carried out:

[0153] 1. Adsorption experiment on heavy metal adsorption capacity of biochar material:

[0154] 30 g of biochar material was mixed uniformly with 1 kg of simulated contaminated saline-alkali soil, and filled into a glass column (diameter 5 cm, height 30 cm).

[0155] Simulated groundwater (containing 0.1 mol / L NaCl, pH = 8.5) was introduced into the glass column at a flow rate of 0.5 mL / min. After 60 days, the concentration of heavy metals in the simulated contaminated saline-alkali soil was detected according to GB15618-2018 "Soil Environmental Quality Risk Control Standards for Agricultural Soil (Trial)".

[0156] 2. Detection of actual adsorption effect of the remediation method of heavy metal contaminated saline-alkali soil:

[0157] The above-mentioned simulated contaminated saline-alkali soil was used as heavy metal-contaminated saline-alkali land. After one round of operation according to the remediation method of each embodiment and comparative example, the concentration and pH of heavy metals in the simulated contaminated saline-alkali soil were detected in accordance with GB15618-2018 "Soil Environmental Quality Agricultural Land Soil Risk Control Standard (Trial)".

[0158] The test results are shown in Table 1.

[0159] Table 1

[0160]

[0161]

[0162]

[0163] Combining Example 1 with Comparative Examples 1-7 and Table 1, it can be seen that after 60 days of adsorption, the biochar materials of Comparative Examples 1-7 had higher concentrations of heavy metals in the simulated contaminated saline-alkali soil compared to Example 1. After one cycle of the remediation method, the concentrations of heavy metals in the simulated contaminated saline-alkali soil were higher. Furthermore, the pH values ​​of the simulated contaminated saline-alkali soils of Comparative Examples 1, 5-7 were also higher. This demonstrates that the biochar materials and remediation method of Example 1 can improve the adsorption of heavy metals in saline-alkali soil and reduce the pH value of saline-alkali soil.

[0164] Combining Examples 1-19 and Table 1, it can be seen that compared with Comparative Examples 1-7, the biochar materials of Examples 1-19 adsorbed Cd in the simulated contaminated saline-alkali soil for 60 days. 2+ The concentrations were all less than 3 mg / kg, Pb 2+ The concentrations were all less than 100 mg / kg. After one round of remediation, the Cd 2+ The concentrations were all less than 1 mg / kg, Pb 2+ The concentrations were all less than 70 mg / kg, and the pH values ​​were all less than 8. This indicates that the biochar materials and remediation methods of Examples 1-19 can improve the adsorption effect of heavy metals in saline-alkali land and reduce the pH value of saline-alkali land.

[0165] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A biochar material for remediation of heavy metal contaminated saline-alkali soil, characterized in that, The raw materials include the following components by weight: modified biochar 55-65 parts, humic acid-sulfur coated microspheres 5-10 parts, sepiolite powder 2-8 parts, polylactic acid coated nano zero-valent iron material 2-5 parts, diatomite 2-5 parts, and ammonium dihydrogen phosphate 1-3 parts; The modified biochar is biochar loaded with iron-manganese oxides; the humic acid-sulfur coated microspheres are microsphere particles with a degradable polylactic acid coating layer, and the degradable polylactic acid coating layer contains humic acid and sulfur; the polylactic acid coated nano zero-valent iron material is a core-shell structure material with polylactic acid as the shell and nano zero-valent iron as the core; and the modified biochar, humic acid-sulfur coated microspheres and polylactic acid coated nano zero-valent iron material are all 80-120 mesh.

2. The biochar material for remediating heavy metal contaminated saline-alkali soil according to claim 1, characterized in that, The biochar material for remediation of heavy metal contaminated saline-alkali soil further comprises montmorillonite nanosheets.

3. The biochar material for remediating heavy metal contaminated saline-alkali soil according to claim 1, characterized in that, The biochar material for remediation of heavy metal contaminated saline-alkali soil further comprises lignin sulfonate.

4. The biochar material for remediating heavy metal contaminated saline-alkali soil according to claim 1, characterized in that, The biochar material for remediation of heavy metal contaminated saline-alkali soil further comprises chitosan and EDTA, and the mass ratio of chitosan to EDTA is 1:(0.3-0.6).

5. A method for remediation of heavy metal contaminated saline-alkali soil, characterized in that, The method comprises the following steps: According to the proportion, the modified biochar, humic acid-sulfur coated microspheres, sepiolite powder, polylactic acid coated nano zero-valent iron material, diatomite and ammonium dihydrogen phosphate are uniformly mixed to obtain the biochar material for remediation of heavy metal contaminated saline-alkali soil according to claim 1. The biochar material for the restoration of heavy metal polluted saline-alkali land is 3-5kg / m 2 Spread on the surface of heavy metal polluted saline-alkali land, rotary tillage and mix to a depth of 15-25cm, at a rate of 3-6L / m 2 Spray a polyaspartic acid solution with a mass concentration of 0.1-0.2% and let it stand for 5-10 days; 85-110 g / m2 2 The microbial agent is applied to the surface of the heavy metal contaminated saline-alkali soil, shallow harrowing and soil covering. Planting density of 28-34 plants / m 2 Suaeda salsa is planted at a planting density of 28-34 plants / m, and after growing for 100-150 days, Suaeda salsa is harvested; then, Lycium barbarum is planted at a planting density of 1-2 plants / 2m 2 After growing for 210-260 days, the aboveground part of Lycium barbarum is harvested, and the harvested Suaeda salsa and Lycium barbarum are dried, then pyrolyzed at 480-520 DEG C under oxygen deficiency for 2-3 hours to obtain a backfillable biochar, and after the backfillable biochar is washed with 4-6% phosphoric acid, the backfillable biochar is backfilled into the heavy metal contaminated saline-alkali soil. The above steps are repeatedly performed in cycles until the content of heavy metals in the heavy metal contaminated saline-alkali soil reaches the safety standard.

6. The method of claim 5, wherein the heavy metal contaminated saline-alkali soil is a soil contaminated with at least one of heavy metals selected from the group consisting of lead, cadmium, chromium, arsenic, mercury, and zinc. The bacterial agent comprises halomonas: bacillus: streptomyces in a mass ratio of 5:(2-4):(1-2).

7. The method of claim 5, wherein the heavy metal contaminated saline-alkali soil is selected from the group consisting of soil contaminated with heavy metals, soil contaminated with heavy metals and organic pollutants, and soil contaminated with heavy metals and radioactive materials. The preparation method of the modified biochar comprises the following steps: The sawdust and rice straw are mixed in a mass ratio of (3-5):1, crushed, soaked in a 1-2% citric acid solution for 22-28 hours, washed with deionized water until neutral, and dried to obtain standby material; The standby material is pyrolyzed at 280-320℃ under a nitrogen atmosphere for 1-1.2 hours, heated to 580-620℃, pyrolyzed for 2-2.2 hours, and naturally cooled to obtain biochar; A 0.3-0.6 mol / L Fe(NO3)3 solution and a 0.2-0.4 mol / L KMnO4 solution are mixed in a volume ratio of 1:(0.7-1.2) to obtain a mixed solution, the biochar is soaked in the mixed solution, shaken for 22-28 hours, filtered out, dried, calcined at 330-380℃ under a nitrogen atmosphere for 2-2.5 hours, naturally cooled, and sieved to obtain modified biochar with a mesh size of 80-120.

8. The method of claim 5, wherein the heavy metal contaminated saline-alkali soil is a soil contaminated with heavy metals and salts. The humic acid-sulfur coated microspheres comprise a core and a coating layer wrapping the core, and the core comprises the following components by weight based on the total weight of the core: sulfur powder 55-65 parts, humic acid 25-35 parts, sodium dodecyl sulfate 2-5 parts, and sodium carboxymethyl cellulose 2-5 parts; and the coating layer comprises ethyl cellulose and polylactic acid in a weight ratio of (7-8):

1. The preparation method of the humic acid-sulfur coated microspheres comprises the following steps: dissolving sodium dodecyl sulfate in water to obtain a sodium dodecyl sulfate aqueous solution with a mass concentration of 4-6%; mixing sulfur powder and humic acid in a certain proportion, and adding the mixture into the sodium dodecyl sulfate aqueous solution to obtain a suspension by shear emulsification; Dissolving sodium carboxymethyl cellulose in water to obtain a sodium carboxymethyl cellulose aqueous solution with a mass concentration of 4-6%, and adding the suspension into the sodium carboxymethyl cellulose aqueous solution to stir until the viscosity reaches 500-800 mPa·s, thereby obtaining a mixed slurry; Spray granulating the mixed slurry to collect microsphere cores with a particle size of 100-200 μm; Mixing acetone and ethanol in a volume ratio of 3:(6-8) to obtain a mixed alcohol solution, dissolving ethyl cellulose and polylactide in the mixed alcohol solution, and stirring until completely dissolved to obtain a coating liquid; Placing the core microspheres in a fluidized bed, preheating to 40-50℃, and spraying the coating liquid at a rate of 8-12 mL / min, and after solidification, sieving to obtain humic acid-sulfur coated microspheres with a particle size of 80-120 mesh.

9. The method of claim 5, wherein the heavy metal contaminated saline-alkali soil is selected from the group consisting of soil contaminated with heavy metals, soil contaminated with heavy metals and organic pollutants, and soil contaminated with heavy metals and radioactive materials. The poly-lactic acid coated nano zero-valent iron material comprises the following raw materials by weight: 30-40 parts of nano zero-valent iron, 55-65 parts of poly-lactic acid, 3-5 parts of polyvinylpyrrolidone, and 2-3 parts of trisodium citrate; The preparation method of the poly-lactic acid coated nano zero-valent iron material comprises the following steps: Dissolving poly-lactic acid in dichloromethane to obtain a poly-lactic acid solution with a mass concentration of 4-5%, adding polyvinylpyrrolidone and trisodium citrate into the poly-lactic acid solution, and ultrasonic dispersing to obtain an organic phase solution; Dispersing nano zero-valent iron in a SDS / deoxy water solution with a mass concentration of 0.1-0.3% at a solid-liquid ratio of 1:(45-55), and ultrasonic dispersing to obtain an aqueous phase solution; Mixing the aqueous phase and the organic phase at a volume ratio of 1:(2-4), and high-speed shear emulsifying to obtain a W / O type emulsion; Rotary evaporating the W / O type emulsion at 40-50℃ and 180-220 mbar to remove dichloromethane until the microspheres are solidified, centrifuging to collect the microspheres, washing the microspheres, and freeze-drying to obtain dry particles; Heat treating the dry particles at 80-85℃ for 1-1.5 hours in a nitrogen atmosphere, and sieving to obtain poly-lactic acid coated nano zero-valent iron material with a mesh size of 80-120.

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