Organic fertilizer for heavy metal soil pollution and preparation method thereof

Abstract

The invention belongs to the technical field of organic fertilizer preparation, and relates to an organic fertilizer for heavy metal soil pollution and a preparation method thereof.The preparation method specifically comprises the following steps that nano-hydroxyapatite, Mg-Al-LDH, compound bacterium powder, normal saline and modified biochar are mixed and oscillated, and a compound functional base material is obtained; mixing and granulating the composite functional base material, the fermented organic matter and the binder, and coating the granules to obtain the organic fertilizer, according to the invention, through the material composite design of nano-hydroxyapatite / Mg-Al-LDH / modified charcoal, a microorganism-passivator preloading process, a coating technology and other technologies, the defects of single function, low microorganism survival rate, short-term effect of remediation and the like of the existing organic fertilizer exposed in the heavy metal contaminated soil are overcome.

Description

Technical Field

[0001] The invention belongs to the technical field of organic fertilizer preparation and relates to an organic fertilizer for heavy metal-contaminated soil and a preparation method thereof. Background Art

[0002] Traditional organic fertilizers (such as livestock and poultry manure compost and plant straw fertilizer) mainly provide nutrients but lack the ability to fix heavy metals. Although some improved products add passivators (such as biochar and apatite), they still have the following problems:

[0003] 1) The passivator is unevenly dispersed. Physical mixing results in discontinuous distribution of the passivator in the fertilizer particles, and the efficiency of contact with heavy metals is low. 2) Poor synergy. A single passivator is only effective for specific heavy metals (such as hydroxyapatite fixing lead and LDH fixing arsenic), and cannot cope with complex contaminated soils. 3) Inhibition of microbial activity. When the passivator is directly mixed with functional microorganisms, the heavy metal adsorption process may encapsulate the microorganisms and reduce their activity. 4) High concentrations of heavy metals in contaminated soils will directly poison functional microorganisms (such as Bacillus), resulting in the inability of microorganisms to effectively reproduce in the rhizosphere and reduced ability to degrade / transform heavy metals. 5) Although traditional coating technologies (such as resin coating) can delay the release of nutrients, they cannot coordinate the release of passivators. Premature release of passivators is easily washed away by rainwater, making it difficult to maintain the soil remediation effect for a long time. 6) Low resource utilization. The bacterial liquid residues produced during the fermentation process are often treated as waste liquid and are not recycled, increasing the burden on the environment.

[0004] Therefore, providing a composite organic fertilizer for heavy metal soil pollution has become an urgent problem to be solved. Summary of the Invention

[0005] In order to solve the above problems, the present invention provides an organic fertilizer for heavy metal contaminated soil and a preparation method thereof, which specifically comprises the following steps:

[0006] Step 1: Mix the biochar and the organic acid solution in a mass ratio of 1:4, ultrasonicate at 60-70°C and 40-50kHz for 30-40 minutes, then let it stand at 30-35°C for 24-36 hours, filter, remove the filtrate, wash the residue with deionized water until the pH of the washing liquid is 6.5-7.0, and dry at 100-110°C to constant weight to obtain modified biochar.

[0007] Preferably, the biomass charcoal includes straw biochar, rice husk biochar and sawdust biochar in a mass ratio of 2:1:3.

[0008] Preferably, the organic acid solution is one or more of an 8%-12% by mass citric acid solution, a 12%-15% by mass oxalic acid solution, and a 10-15% by volume acetic acid solution. Most preferably, the organic acid solution is an 8%-12% by mass citric acid solution, a 12%-15% by mass oxalic acid solution, and a 10-15% by volume acetic acid solution, in a mass ratio of 4:3:2.

[0009] Step 2: Mix nanohydroxyapatite, Mg-Al-LDH, composite bacterial powder and physiological saline, shake at 35-40°C and 90-120rpm for 2-2.5h, then add modified biochar, shake at 38-42°C and 90-120rpm for 4-5h, filter, and the filtrate is the bacterial liquid residue. The filter residue is dried at (-30)-(-20)°C and 0.1-0.3Pa to a moisture content of ≤3% to obtain a composite functional substrate.

[0010] Preferably, the mass ratio of the nano-hydroxyapatite, Mg-Al-LDH, modified biochar, composite bacterial powder and physiological saline is (10-20):(10-20):(10-30):(1-2):(150-200).

[0011] Preferably, the preparation method of the nano-hydroxyapatite is to mix CaCl2 solution, Na2HPO4 solution and chitosan solution in a volume ratio of 4:4:1, hydrothermally react at 110-130°C for 6-7h, centrifuge at 8000-9000rpm for 10-15min, remove the filtrate, and dry the residue at 30-40°C to constant weight to obtain nano-hydroxyapatite.

[0012] Most preferably, the concentration of the CaCl2 solution is 0.1 mol / L, the concentration of the Na2HPO4 solution is 0.06 mol / L, and the chitosan solution comprises chitosan solid, acetic acid and water in a ratio of 5 g:2 mL:98 mL.

[0013] Preferably, the preparation method of the Mg-Al-LDH is to mix Mg(NO3)2, Al(NO3)3 and deionized water, and add alkaline solution dropwise to adjust the pH to 9.8-10.2, age at 60-70°C for 11-13h, centrifuge at 8000-9000rpm for 10-15min, remove the filtrate, wash the residue with 50% volume fraction ethanol solution until the washing liquid is neutral, and then dry at 30-40°C to constant weight to obtain Mg-Al-LDH.

[0014] Most preferably, the mass ratio of Mg(NO3)2, Al(NO3)3 and deionized water is 2:1:20, and the alkaline solution is 2 mol / L NaOH solution.

[0015] Step 3: Mix plant straw, livestock manure, soybean meal, cassava residue, sugar residue, peanut meal, humic acid, seaweed powder, bacterial solution residue and composite bacterial powder in a mass ratio of (30-40):(40-50):(15-20):(25-35):(10-20):(10-15):(3-5):(8-12):(1-2):(1-2), and adjust the moisture content to 50-60% and the oxygen flow rate to 0.3-0.5m 3 / h, humidity 60-65%, fermentation at 30-40℃ for 4-5d, and drying the fermented material at 40-50℃ to a moisture content ≤8% to obtain fermented organic matter.

[0016] Preferably, the plant straw is one or more of rice straw, corn straw, soybean straw and wheat straw. Most preferably, the plant straw is corn straw.

[0017] Preferably, the livestock manure is one or more of cow manure, horse manure, sheep manure, pig manure and chicken manure. Most preferably, the livestock manure is cow manure.

[0018] Preferably, the composite bacterial powder is Bacillus subtilis powder, Bacillus licheniformis powder and Bacillus mucilaginosus powder, with a mass ratio of 2:1:1.

[0019] Step 4: The composite functional substrate, fermented organic matter and binder are mixed and granulated in a mass ratio of (20-30):(70-80):(3-5), with a particle size of 3-5 mm. The particles are dried at 35-40° C. to a moisture content of ≤8%, and then the particles are placed in a fluidized bed and coated with a coating agent to obtain a weight gain rate of 10-12% to obtain organic fertilizer.

[0020] Preferably, the binder is a carboxymethyl cellulose solution with a mass fraction of 1-1.5%.

[0021] Preferably, the coating agent is a sodium alginate solution with a mass fraction of 3-5%.

[0022] The present invention has the following advantages:

[0023] (1) The present invention pre-loads the composite bacterial powder onto nanohydroxyapatite, Mg-Al-LDH, and modified biochar through step-by-step oscillation, embedding the microorganisms into the pores of the passivator (such as the microporous structure of biochar) to avoid direct poisoning by heavy metals. The passivator is constructed to form a "three-in-one" synergistic network. Nanohydroxyapatite fixes lead and cadmium (forming phosphate precipitation), and Mg-Al-LDH adsorbs arsenic and chromium (layered structure ion exchange). The modified biochar adsorbs copper, zinc, etc. (surface functional group complexation), solving the problem that traditional physical mixing cannot achieve uniform loading and synergistic efficiency on a microscopic scale.

[0024] (2) The present invention uses a mixed acid of citric acid / oxalic acid / acetic acid to treat biochar, which significantly enhances the biochar's ability to treat heavy metal ions and solves the problem of low adsorption capacity and easy saturation of unmodified biochar.

[0025] (3) The present invention adds the bacterial liquid residue of step 1 (containing bacterial metabolites enriched in trace elements) into the fermentation system to realize resource utilization. It can not only provide the trace elements and signal molecules required for microbial growth, but also reduce the fermentation cost, thus solving the problem of directly discarding the bacterial liquid and wasting resources in the traditional process.

[0026] (4) The present invention combines Bacillus subtilis (for organic matter degradation), Bacillus licheniformis (for antibiotic production), and Bacillus mucilaginosus (for phosphorus and potassium release) to form a functionally complementary bacterial community, maintaining community stability under heavy metal stress and simultaneously achieving organic matter degradation and nutrient release. This solves the problem of single bacterial species being easily inactivated and unable to remediate soil in multiple ways.

[0027] (5) The present invention uses sodium alginate to coat the particles, forming an ion-crosslinked network film on the surface of the particles, controlling the simultaneous release of the passivation agent and nutrients, and avoiding failure due to erosion by heavy rain. In addition, the material is biodegradable and has no secondary pollution, thus solving the problem that chemical coatings cannot take into account both environmental protection and functionality.

[0028] (6) The low-temperature vacuum drying of the present invention retains the activity of microorganisms to the maximum extent, and aerobic fermentation accelerates the humification of organic matter, generating humic acid to enhance the heavy metal complexing ability, thereby solving the problem of high-temperature drying inactivating microorganisms in traditional processes and extensive fermentation conditions leading to nutrient loss. DETAILED DESCRIPTION

[0029] The following is a clear and complete description of the technical solutions in the embodiments of the invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0030] Example 1

[0031] Step 1: Rice straw biochar, rice husk biochar, sawdust biochar, and an organic acid solution are mixed in a mass ratio of 2:1:3:24, ultrasonicated at 65°C and 45kHz for 35 minutes, then allowed to stand at 35°C for 30 hours, filtered, and the filtrate removed. The filter residue is washed with deionized water until the pH of the washing solution is 6.5-7.0, and dried at 105°C to constant weight to obtain modified biochar. The organic acid solution is a 10% by mass citric acid solution, a 14% by volume oxalic acid solution, and a 13% by volume acetic acid solution in a mass ratio of 4:3:2.

[0032] Step 2: Mix 0.1 mol / L CaCl2 solution, 0.06 mol / L Na2HPO4 solution, and chitosan solution in a volume ratio of 4:4:1. Hydrothermally react at 120°C for 6.5 hours, centrifuge at 8000 rpm for 15 minutes, remove the filtrate, and dry the residue at 35°C to constant weight to obtain nanohydroxyapatite. The chitosan solution contains chitosan solid, acetic acid, and water in a ratio of 5 g:2 mL:98 mL.

[0033] Mg(NO3)2, Al(NO3)3 and deionized water were mixed in a mass ratio of 2:1:20, and 2 mol / L NaOH solution was added dropwise to adjust the pH to 9.8-10.2. The mixture was aged at 65°C for 12 h, centrifuged at 8000 rpm for 15 min, the filtrate was removed, and the residue was washed with 50% ethanol solution by volume until the washing liquid was neutral, and then dried at 35°C to constant weight to obtain Mg-Al-LDH.

[0034] Nanohydroxyapatite, Mg-Al-LDH, composite bacterial powder, and saline were mixed and shaken at 37°C and 100 rpm for 2 hours. Modified biochar was then added and shaken at 40°C and 120 rpm for 4 hours. The mixture was filtered, and the filtrate was the bacterial solution residue. The filter residue was dried at -30°C and 0.2 Pa to a moisture content of ≤3% to obtain a composite functional substrate. The mass ratio of nanohydroxyapatite, Mg-Al-LDH, modified biochar, composite bacterial powder, and saline was 15:15:20:1:180.

[0035] Step 3: Mix corn straw, cow dung, soybean meal, cassava residue, sugar residue, peanut meal, humic acid, seaweed powder, bacterial solution residue and composite bacterial powder in a mass ratio of 35:45:17:30:15:15:4:10:2:1, and adjust the moisture content to 55% and the oxygen flow rate to 0.4m 3 / h, humidity 62%, fermentation at 35℃ for 4 days, and drying the fermented material at 45℃ to a moisture content of ≤8% after fermentation to obtain fermented organic matter. The composite bacterial powder comprises Bacillus subtilis powder, Bacillus licheniformis powder and Bacillus mucilaginosus powder in a mass ratio of 2:1:1.

[0036] Step 4: The composite functional substrate, fermented organic matter and 1% carboxymethyl cellulose solution are mixed in a mass ratio of 25:75:4 to form granules with a particle size of 3-5 mm. The granules are dried at 38° C. to a moisture content of ≤8%. The granules are then placed in a fluidized bed and coated with a 4% sodium alginate solution to obtain an organic fertilizer with a weight gain rate of 10-12%.

[0037] Test Example 1

[0038] 1. Experimental Materials

[0039] Test soil: Heavy metal complex contaminated soil (Pb 850 mg / kg, Cd 35 mg / kg, As 110 mg / kg) collected from a lead-zinc mining area.

[0040] Experimental group: organic fertilizer prepared by the method of Example 1

[0041] Control group 1: fermented sheep manure fertilizer produced by Hebei Woermei Biotechnology Co., Ltd.

[0042] Control group 2: T1201 metal passivator produced by Jinan Yunuo Chemical Co., Ltd.

[0043] Control group 3: blank soil

[0044] Crop: Chinese cabbage.

[0045] 2. Experimental Methods

[0046] Potted experiment: Each pot was filled with 2 kg of soil and 30 g / kg of fertilizer, with five replicates.

[0047] Culture conditions: greenhouse temperature 25±2℃, light intensity 12h / d, regular watering to maintain soil water holding capacity at 60%.

[0048] Sampling and Analysis: Soil samples were collected 30, 60, and 90 days after fertilization to test for available heavy metals and nutrients. Plants were harvested to measure aboveground biomass and heavy metal accumulation.

[0049] Monitoring of soil remediation effects: air-dry the soil after fertilization, pass it through a 2mm sieve, take 50g of soil and add 0.01mol / LCaCl2 solution (soil-liquid ratio 1:10), shake it at 25℃ for 2h, and centrifuge to obtain the supernatant.

[0050] The supernatant was filtered through a 0.45 μm filter membrane, and the concentrations of Pb, Cd, and As were determined by ICP-MS. The fixation rate was calculated as: (1-experimental group concentration / CK3 concentration)×100%.

[0051] Nutrient index detection: organic matter - potassium dichromate oxidation method, fast-acting nitrogen - alkaline diffusion method, fast-acting phosphorus - molybdenum antimony colorimetric method, fast-acting potassium - flame photometry.

[0052] Plant analysis: Measure the fresh and dry weights of aboveground parts after harvest. Measure heavy metal content by ICP-MS after plant tissue digestion. Calculate the transfer coefficient: heavy metal content in aboveground parts divided by total heavy metal content in soil.

[0053] Table 1 Effective fixation rate of heavy metals (%)

[0054]

[0055] Table 2 Soil nutrient improvement effect (90 days)

[0056] Experimental group Control group 1 Control group 3 Organic matter (g / kg) 23.7±1.8 21.2±2.1 18.5±1.2 Available nitrogen (mg / kg) 185.6±12.3 152.4±10.5 65.3±8.7 Available phosphorus (mg / kg) 45.3±3.2 38.1±2.9 9.6±1.5 Fast-acting potassium (mg / kg) 320.5±15.7 265.8±14.2 85.4±7.3

[0057] Table 3 Effects on the growth of Chinese cabbage

[0058] Biomass (g / plant) Pb transfer coefficient Cd transfer coefficient Leaf chlorophyll (SPAD) Experimental group 28.7±1.5 0.08±0.01 0.05±0.01 42.3±1.2 Control group 1 22.4±1.2 0.31±0.03 0.28±0.02 35.6±1.8 Control group 3 10.5±0.8 0.92±0.05 0.85±0.04 24.1±2.1

[0059] As can be seen from Tables 1-3, the organic fertilizer prepared by the present invention simultaneously achieves a heavy metal fixation rate of >90% (through hydroxyapatite-Pb / Cd precipitation + LDH-As interlayer adsorption + modified biochar-Cu / Zn complexation), significantly increases soil organic matter (the bacterial liquid residue promotes humification), and reduces the accumulation of heavy metals in pakchoy by 83% (encapsulation barrier + microbial passivation).

[0060] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing organic fertilizer for heavy metal contaminated soil, characterized in that: The following steps are involved: Step 1: nano-hydroxyapatite, Mg-Al-LDH, composite bacterial powder and physiological saline are mixed and shaken, and then modified biochar is added, and the mixture is shaken again. The mixture is filtered, and the filtrate is the bacterial liquid residue. The filter residue is dried to a moisture content of ≤3% to obtain a composite functional substrate; Step 2: mixing plant straw, livestock manure, soybean meal, cassava residue, sugar residue, peanut meal, humic acid, seaweed powder, bacterial solution residue and composite bacterial powder, adjusting the moisture content, aerobically fermenting for 4-5 days, and drying the fermented product to a moisture content of ≤8% after fermentation to obtain fermented organic matter; Step 3: Combine the composite functional substrate, fermented organic matter and binder in a mass ratio. (20-30):(70-80):(3-5) mixing and granulating, drying the granules at 35-40° C. to a moisture content of ≤8%, then placing the granules in a fluidized bed, coating the granules with a coating agent, and achieving a weight gain of 10-12% to obtain an organic fertilizer.

2. The method for preparing an organic fertilizer for heavy metal soil pollution according to claim 1, wherein: The mass ratio of nanohydroxyapatite, Mg-Al-LDH, modified biochar, composite bacterial powder and physiological saline in step 1 is (10-20):(10-20):(10-30):(1-2):(150-200).

3. The method for preparing an organic fertilizer for heavy metal soil pollution according to claim 1, wherein: The preparation method of the modified biochar described in step 1 is to mix the biochar with the organic acid solution, perform ultrasonic treatment, let it stand, filter, remove the filtrate, wash the filter residue with deionized water to a pH of 6.5-7.0, and dry it at 100-110°C to constant weight to obtain the modified biochar.

4. The method for preparing an organic fertilizer for heavy metal soil pollution according to claim 3, wherein: The organic acid solution is one or more of a citric acid solution with a mass fraction of 8%-12%, an oxalic acid solution with a volume fraction of 12%-15%, and an acetic acid solution with a volume fraction of 10-15%.

5. The method for preparing an organic fertilizer for heavy metal contaminated soil according to claim 1, wherein: The preparation method of the nano-hydroxyapatite in step 1 is to mix the CaCl2 solution, the Na2HPO4 solution and the chitosan solution, perform a hydrothermal reaction at 110-130°C for 6-7h, centrifuge at 8000-9000rpm for 10-15min, remove the filtrate, and dry the residue at 30-40°C to constant weight to obtain the nano-hydroxyapatite.

6. The method for preparing an organic fertilizer for heavy metal contaminated soil according to claim 1, characterized in that: The preparation method of Mg-Al-LDH described in step 1 is to mix Mg(NO3)2, Al(NO3)3 and deionized water, and add alkaline solution dropwise to adjust the pH to 9.8-10.2, age at 60-70°C for 11-13 hours, centrifuge at 8000-9000rpm for 10-15 minutes, remove the filtrate, wash the residue with 50% volume fraction ethanol solution until the washing liquid is neutral, and then dry at 30-40°C to constant weight to obtain Mg-Al-LDH.

7. The method for preparing an organic fertilizer for heavy metal contaminated soil according to claim 1, characterized in that: The mass ratio of plant straw, livestock manure, soybean meal, cassava residue, sugar residue, peanut meal, humic acid, seaweed powder, bacterial liquid residue and composite bacterial powder in step 2 is (30-40):(40-50):(15-20):(25-35):(10-20):(10-15):(3-5):(8-12):(1-2):(1-2).

8. The method for preparing an organic fertilizer for heavy metal contaminated soil according to claim 1, characterized in that: The composite bacterial powder in step 1 and step 2 is Bacillus subtilis powder, Bacillus licheniformis powder and Bacillus mucilaginosus powder, with a mass ratio of 2:1:

1.

9. The method for preparing an organic fertilizer for heavy metal contaminated soil according to claim 1, wherein: In step three, the binder is a carboxymethyl cellulose solution with a mass fraction of 1-1.5%, and the coating agent is a sodium alginate solution with a mass fraction of 3-5%.

10. Organic fertilizer for heavy metal contaminated soil prepared by the method according to any one of claims 1 to 9.

Images