Biochar-based soil structure modifier as well as preparation method and use method thereof

Abstract

The invention discloses a charcoal-based soil structure improver as well as a preparation method and a use method thereof, and relates to the technical field of soil improvement. The method comprises the following steps: firstly, standing biochar without large impurities in a detergent for 4-6 hours, and draining water to obtain modified biochar; uniformly mixing the sieved ardealite with the modified biochar to obtain the biochar-based soil structure modifier. When in use, the charcoal-based soil structure improver is added into soil according to the mass content of 0.3-0.6%, the water content of the soil is maintained to be 80% of the field moisture capacity, and the soil is cultured. Through a matched field use method, the product can significantly promote the generation of soil aggregates, coordinate the soil pore proportion, improve the soil structure, create a good environment for crop growth, realize the resource utilization of ardealite and municipal sludge biochar, reduce environmental pollution and increase economic benefits.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of soil improvement, and particularly relates to a biochar-based soil structure modifier, a preparation method and a use method thereof. BACKGROUND

[0002] Soil is a valuable resource for human survival, and the sustainable use of arable land resources is related to the protection and improvement of arable land productivity. After long-term farming, the fertility of arable land will gradually decrease, resulting in a decrease in the productivity of arable land. Therefore, soil improvement and maintenance is an important means to protect arable land. Adding fertility substances to soil can improve soil function by supplementing nutrients, optimizing soil structure and biological activity, which is an effective soil improvement method. In the prior art, the fertility substance is mostly selected as biochar, which is a stable porous carbon material generated by pyrolysis of biomass under anaerobic conditions. The source of biochar is relatively wide, and the raw materials cover agricultural straw, forestry residues, livestock and poultry manure, and other organic biomass. At present, the research on the influence of biochar prepared from biomass straw and the like on soil improvement and plant growth is relatively more, while the research on sludge charcoal in this field is very few.

[0003] It is an effective carbon reduction approach to make sludge into sludge charcoal, and the use of sludge charcoal in soil improvement and plant growth can achieve the purpose of solid waste resource utilization, which not only solves the disposal problem of municipal sludge and the like, but also provides rich nutrient substances for soil and plants. In addition, sludge charcoal also has the function of adsorbing and solidifying heavy metals, and can realize the stabilization, resource utilization and reduction of soil. As a kind of biochar, sludge charcoal made of sludge also has the function of soil improvement. Yuan Haoran et al. found that the addition of sludge biochar can increase the content of N, P, K and other nutrient elements in soil, and can effectively reduce the loss of NO 3- , NH 4+ , K + and PO4 3- , thereby improving the fertility of soil. In addition, with the increase of pyrolysis temperature, the ability of biochar to maintain soil nutrient elements will become stronger. The addition of raw sludge and sludge biochar to soil can increase the soil cation exchange capacity, total organic carbon content and pH value. Compared with raw sludge, sludge biochar can significantly reduce the leaching risk and mobility of soil heavy metals Zn and Cd, and the absorption amount of Zn and Cd by plants in sludge improved soil is significantly greater than that in sludge biochar improved soil.

[0004] However, directly adding sludge biochar to the soil to be improved is easy to cause seedling burning and is not conducive to crop seed germination. In the use process of traditional improvers, only the improvement of soil nutrients by the improver is emphasized, and the change of soil structure by the improver is ignored, and there is a lack of a long-period method for promoting soil aggregate development, coordinating soil pore structure, and realizing comprehensive improvement of soil structure such as soil water, fertilizer, gas, and heat. SUMMARY

[0005] In order to overcome the shortcomings of the prior art, the purpose of the present application is to provide a biochar-based soil structure improver, a preparation method and a use method, to solve the problem that the direct use of current municipal sludge biochar soil improver is not conducive to crop seed germination, and to provide a long-period method for promoting soil comprehensive performance improvement.

[0006] In order to achieve the above-mentioned purpose, the following technical solutions are adopted in the present application: The first purpose of the present application is to provide a biochar-based soil structure improver, which comprises the following components: 5-15 parts by mass of modified biochar and 1-3 parts by mass of phosphogypsum; the modified biochar is obtained by modifying municipal sludge by heating pyrolysis, and the phosphogypsum is a by-product in the production process of phosphoric acid method phosphate fertilizer; The preparation method of the modified biochar comprises the following steps: taking municipal sludge, heating the municipal sludge to 80-110 DEG C and keeping it for 1.5-2 hours, then continuing to heat it to 450-550 DEG C and keeping it for 3-5 hours to obtain biochar; then immersing the biochar in a mixed solution of a surfactant and an alkaline solution for 4-8 hours for chemical modification, and obtaining the chemically modified modified biochar after draining.

[0007] Preferably, the surfactant is sodium dodecyl sulfate or sodium cetylphenyl sulfonate.

[0008] Preferably, the mass ratio of the biochar to the surfactant is 1000: (0.1-0.5), the concentration of the alkaline solution is 0.01 mol / L, and the ratio of the biochar to the alkaline solution is 1:1 (g / mL).

[0009] Preferably, the alkaline solution is selected from lauryl alcohol amine solution, trisodium phosphate solution, potassium hydroxide solution or sodium hydroxide solution.

[0010] Preferably, the maximum particle size of the phosphogypsum is not more than 2 mm, and the D50 is 0.08-0.1 mm.

[0011] Preferably, the water content of the modified biochar is 60-70%.

[0012] Preferably, the harmful elements in the modified biochar meet the NY 1110-2016 water-soluble fertilizer standard requirements, and the total amount of effective nitrogen, phosphorus and potassium is less than 20% of the dry basis of biochar, which meets the requirements of crop seedling.

[0013] The second object of the present application is to provide a preparation method of the above-mentioned biochar-based soil structure modifier, which is to mix the modified biochar and phosphogypsum into particles with a fineness of less than 2 mm.

[0014] Preferably, the preparation method of the above-mentioned biochar-based soil structure modifier comprises: mixing the biochar-based soil structure modifier with topsoil at a proportion of 0.3-0.6 wt % on a dry basis, irrigating and maintaining the water content at 60%-90% of the field water holding capacity, and cultivating the soil for more than 15 days before sowing.

[0015] The third object of the present application is to provide a use method of the above-mentioned biochar-based soil structure modifier, wherein the topsoil is soil with a depth of not more than 20 cm from the land surface.

[0016] Compared with the prior art, the present application has the following beneficial effects: The present application takes into account the different requirements of soil water and fertilizer characteristics at different growth stages of crops, and the soil structure modifier meeting the requirements of crop germination is obtained by first modifying the municipal sludge by pyrolysis to obtain sludge biochar, then chemically modifying the sludge biochar, and mixing it with the by-product phosphogypsum in the production process of phosphoric acid method phosphorus fertilizer. The present application effectively reduces the soil cultivation time, and the raw material of the biochar is municipal sludge. In the soil cultivation process, the modified biochar prepared from phosphogypsum and municipal sludge has a synergistic effect under the action of soil microorganisms. The phosphogypsum can be used as a phosphorus source for soil microorganisms to make up for the low effective phosphorus content of the municipal sludge biochar. At the same time, the surface potential of the phosphogypsum is lower than that of the test soil and the biochar, which can balance the surface potential of the materials and promote the formation of soil aggregates. The phosphogypsum and the biochar also have obvious synergistic effect in reducing the pH of the soil, which can better balance and maintain the stability of the pH value of the soil. The present application fully utilizes the synergistic effect of the phosphogypsum and the modified biochar, and relatively safely and quickly realizes the improvement of soil acidity and alkalinity, the improvement of soil nutrients, the adjustment of soil pore composition, and the promotion of the formation of soil aggregates, solving the problems of current municipal sludge biochar soil modifier, such as being not conducive to the germination of crop seeds, and ignoring the characteristics of long soil improvement period and insufficient consideration of comprehensive improvement of soil water, fertilizer, gas and heat. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 The soil aggregate composition diagram of the present application and the comparative examples. DETAILED DESCRIPTION

[0018] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the 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.

[0019] Studies have found that sludge pyrolysis, when used for soil amendment, exhibits characteristics such as high plant nutrient content, low heavy metal leaching rate, and well-developed pore structure. Adding sludge pyrolysis and other soil amendments can improve soil pH, increase soil nutrients, adjust soil pore composition, and promote the formation of soil aggregates. Converting sludge into sludge pyrolysis is an effective carbon reduction method, while using sludge pyrolysis for soil amendment and plant growth achieves the goal of solid waste resource utilization. This solves the problem of sludge disposal and provides abundant nutrients for soil and plants. Furthermore, sludge pyrolysis can adsorb and solidify heavy metals, achieving stabilization, resource recovery, and volume reduction.

[0020] Existing research unilaterally emphasizes the enhancing effect of biochar on soil fertility; however, experiments have shown that directly adding sludge biochar to soil to be improved can easily cause seedling burn and is not conducive to crop seed germination. Furthermore, the use of soil structure modifiers has neglected the long-term nature of soil improvement, resulting in insufficient research on the soil structure improvement process, which involves the natural accumulation of soil aggregates, the coordination of soil pore structure, and the comprehensive improvement of soil water, fertilizer, air, and heat.

[0021] Based on the above understanding, the present invention first proposes a biochar-based soil structure improver, comprising the following components: 5-15 parts by weight of modified biochar dry basis and 1-3 parts by weight of phosphogypsum; wherein the modified biochar is obtained by heating and pyrolysis modification of municipal sludge, and the phosphogypsum is a by-product of the phosphoric acid process for producing phosphate fertilizer.

[0022] Modified biochar has increased porosity and enhanced surface activity compared to unmodified biochar, and can directly act as a natural aggregate. The fine pores inside the modified biochar particles can retain soil moisture, and the larger modified biochar particles can disrupt the overall structure of the clay system, thereby coordinating the soil porosity ratio, achieving water and air synergy, and creating favorable conditions for crop growth.

[0023] Modified biochar also provides essential attachment sites and organic nutrients for soil microorganisms. The growth and development of microorganisms can decompose simple components in the modified biochar, increasing its porosity and surface hydrophilicity, further enhancing soil water retention capacity. Simultaneously, the production of mycelia and organic colloids promotes the formation of soil aggregates, improving soil texture and enhancing water retention and root permeability.

[0024] During soil culture, phosphogypsum and modified biochar exhibit synergistic effects under the influence of soil microorganisms. Phosphogypsum can serve as a phosphorus source for soil microorganisms, compensating for the low available phosphorus content of municipal sewage sludge biochar. Simultaneously, the surface potential of phosphogypsum is lower than that of the tested soil and biochar, which can balance the surface potential of the materials and promote the formation of soil aggregates. Furthermore, experiments revealed a significant synergistic effect between phosphogypsum and biochar in reducing soil pH.

[0025] In some embodiments of the present invention, the method for preparing modified biochar includes the following steps: Municipal sludge is taken and added to a rotary drying / carbonization integrated furnace. According to gradient energy utilization technology, part of the flue gas from the carbonization section is recycled to the drying section, with a flue gas recycling rate of 5-15%. The drying process is heated to 80-110℃ at a heating rate of 4-6℃ / min and held for 1.5-2 hours. The carbonization process is heated to 450-550℃ at the same heating rate and held for 3-5 hours to obtain biochar. Then, the biochar is immersed in a mixed solution of surfactant and alkali for 4-8 hours for chemical modification. After draining, the chemically modified biochar is obtained.

[0026] The resource utilization method for municipal sewage sludge proposed in this invention, which involves pyrolysis, modification, and agricultural application, features low economic cost, low environmental risk, and high resource utilization. During the pyrolysis process, this invention controls the cost of wet sludge treatment to 75 yuan per ton by regulating key parameters such as flue gas recirculation, pyrolysis temperature, and heating rate, reducing the cost by approximately 50% compared to conventional pyrolysis processes. Through sludge carbon modification and integrated agricultural application methods, the upstream and downstream links of municipal sewage sludge resource utilization are connected, reducing carbon emissions from sludge treatment and potentially enabling the recycling of nutrients between urban and rural ecosystems. Compared to traditional treatment methods such as landfill, incineration, and composting, this method offers advantages such as low leaching rates of harmful elements, small processing area, high product added value, and environmental friendliness.

[0027] The biochar has a D50 of 0.87 mm, and tests showed that the leaching toxicity of harmful elements such as mercury, cadmium, chromium, lead, and arsenic all met the standard requirements for soil conditioner raw materials.

[0028] In some embodiments of the present invention, the surfactant is sodium dodecyl sulfate or sodium hexadecylbenzenesulfonate. By compounding the surfactant with an alkaline solution, the critical micelle concentration of the mixed system is reduced, and the surfactant solubility is increased, which can significantly improve the detergency of the system. During the impregnation process, the inert ash in the biochar dissolves, the specific surface area and porosity increase, and the salt content decreases. The modified sludge biochar improves the soil's water retention capacity while avoiding the problem of increased soil salinity.

[0029] In some embodiments of the present invention, during the chemical modification process, the mass ratio of biochar to surfactant is 1000:(0.1~0.5), the concentration of the alkali solution is 0.01mol / L, and the volume ratio of biochar to alkali solution is 1:1 (g / mL). The chemical modification process is as follows: for every kilogram of biochar, add 0.1~0.5 g of surfactant, add 1L of 0.01mol / L alkali solution, let stand for a period of time, drain the water to obtain modified biochar, and the washing solution cannot be reused.

[0030] In some embodiments of the present invention, the maximum particle size of phosphogypsum does not exceed 2 mm, and the D50 is 0.08~0.1 mm. The phosphogypsum used in the embodiments of the present invention is a by-product of the phosphoric acid process for producing phosphate fertilizer, with a D50 of 0.086 mm. Testing showed that the leaching toxicity of harmful elements such as mercury, cadmium, chromium, lead, and arsenic all met the standard requirements for soil conditioner raw materials. To ensure uniform mixing of the materials, the phosphogypsum was sieved through a 2 mm sieve.

[0031] In some embodiments of the present invention, the modified biochar has a water content of 60-70%.

[0032] According to the standard method for determining the leaching toxicity of solid waste, the leachate of sludge-modified biochar was obtained. The harmful elements in the modified biochar were found to meet the requirements of the NY 1110-2016 water-soluble fertilizer standard (the standard selection was based on the "Agreement on Matters of the Fertilizer Registration Review Committee of the Ministry of Agriculture and Rural Affairs" issued by the General Office of the Ministry of Agriculture and Rural Affairs), and the total effective nitrogen, phosphorus and potassium content was less than 20% of the dry basis of the modified biochar, which meets the requirements for crop seedling cultivation.

[0033] The present invention also discloses a method for preparing the above-mentioned biochar-based soil structure conditioner, which involves preparing modified biochar and phosphogypsum into particles with a fineness of less than 2 mm and mixing them uniformly.

[0034] In an embodiment of the present invention, the method of using the above-mentioned biochar-based soil structure conditioner includes: mixing the biochar-based soil structure conditioner with the topsoil at a mass fraction of 0.3-0.6%, irrigating and maintaining the moisture content at 60%-90% of field capacity, and cultivating the soil for more than 15 days before sowing.

[0035] This invention also discloses a method for using the aforementioned biochar-based soil structure conditioner. The mass ratio of the soil structure conditioner added is calculated based on the topsoil mass, with a topsoil depth of 15-20 cm. Field water holding capacity is determined by actual measurement after mixing with the materials. During the cultivation process, the soil bulk density can be assumed to remain constant, and the initial moisture content can be maintained. The set requirement of 80% of field water holding capacity meets field management requirements.

[0036] Soil incubation aims to promote the development of soil aggregates through the action of soil microorganisms, resulting in a favorable soil pore structure before sowing. With modified biochar, the incubation time before spring plowing can be shortened to approximately 15 days.

[0037] The sludge used in this embodiment of the invention comes from the plate and frame filter press workshop of the Weinan Second Wastewater Treatment Plant. The phosphogypsum used in this embodiment of the invention comes from the phosphogypsum stockpile of Gansu Wengfu Chemical Co., Ltd. In the following embodiments of the present invention, conventional instruments and equipment in the art are used. Unless otherwise stated, all raw materials and reagents used are commercially available products with specifications that are conventional in the art, or can be prepared or formulated by known methods or reagent instructions. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or according to the manufacturer's recommendations.

[0038] This invention provides a method for preparing and using a biochar-based soil structure conditioner. The conditioner is mainly composed of the following components: 1-3 parts of sieved phosphogypsum and 10-15 parts of modified biochar.

[0039] The preparation process mainly includes the following three stages: 1) Raw material pretreatment: Municipal sewage sludge is heated to 80-110℃ at a heating rate of 4-6℃ / min and held for 1.5-2 hours. Then, the temperature is increased to 450-550℃ at the same rate and held for 3-5 hours to obtain biochar. Impurities are removed by sorting.

[0040] Phosphogypsum produced in industrial production is selected, crushed and screened to remove large impurities, and then sieved to obtain phosphogypsum particles with a particle size of less than 2 mm.

[0041] 2) Biochar modification: Commercially available sodium dodecyl sulfate or sodium hexadecylbenzenesulfonate was used as the surfactant. The following material ratio was applied: 0.1–0.5 g of surfactant was added per kilogram of biochar, along with one liter of saturated sodium hydroxide solution to prepare a washing and modification system. The system was allowed to stand for 4–6 hours, and the water was drained to obtain the modified biochar.

[0042] The washing solution was tested and found to be unusable. The modified biochar after draining had a moisture content of 60-70%. The modified sludge char leachate was obtained according to the standard method for determining the toxicity of solid waste leaching. The measured harmful elements met the standard requirements, and the total available nitrogen, phosphorus, and potassium content was less than 20% of the dry basis of the biochar, which meets the requirements for crop seedling cultivation.

[0043] 3) Preparation and use of modifiers: A soil structure conditioner is obtained by uniformly mixing 5-15 parts of modified biochar with 1-3 parts of sieved phosphogypsum. The mass ratio of the soil structure conditioner added is calculated based on the topsoil mass, with a topsoil depth of 15-20 cm. Field water holding capacity is determined by actual measurement after mixing the materials. During the cultivation process, the soil bulk density can be assumed to remain constant, maintaining the initial moisture content setting. The set moisture content requirement of 80% of field water holding capacity meets field management requirements. The purpose of soil cultivation is to promote the development of soil aggregates under the action of soil microorganisms, resulting in a good soil pore structure before sowing. With modified biochar, the cultivation time before spring plowing can be shortened to about 15 days.

[0044] The following is a detailed description with reference to specific examples.

[0045] Example 1 The main components of the soil structure improver are: 1 part sieved phosphogypsum and 15 parts modified biochar.

[0046] The specific process of raw material pretreatment is as follows: municipal sludge is heated to 110°C at a heating rate of 4°C / min and held for 2 hours. Then, it is heated to 450°C at the same heating rate and held for 5 hours to obtain biochar. Impurities are then removed by selection.

[0047] Phosphogypsum produced in industrial production is selected, crushed and screened to remove large impurities, and then sieved to obtain phosphogypsum particles with a particle size of less than 2 mm.

[0048] The specific process of biochar modification is as follows: Commercially available sodium dodecyl sulfate was used as the surfactant. The following material ratio was used: 0.3 g of surfactant was added per kilogram of biochar, along with 1 L of 0.01 mol / L sodium hydroxide solution, to prepare a washing and modification system. The system was allowed to stand for 5 hours, and the water was drained to obtain the modified biochar.

[0049] Preparation and use of modifiers: A soil structure conditioner was prepared by uniformly mixing 15 parts modified biochar with 1 part sieved phosphogypsum. A sample of topsoil at a depth of 15 cm and a soil bulk density of 1.3 kg / m³ was taken, and the soil structure conditioner was added at a mass ratio of 0.6%. The field water holding capacity was then measured after mixing the materials. The soil moisture content was maintained at 80% of field water holding capacity and incubated for 15 days.

[0050] Example 2 The main components of the soil structure improver are: 3 parts sieved phosphogypsum and 10 parts modified biochar.

[0051] Raw material pretreatment: Municipal sludge was heated to 100°C at a heating rate of 5°C / min and held for 1.5 hours. Then, it was heated to 450°C at the same heating rate and held for 4 hours to obtain biochar. Impurities were removed by sorting.

[0052] Phosphogypsum produced in industrial production is selected, crushed and screened to remove large impurities, and then sieved to obtain phosphogypsum particles with a particle size of less than 2 mm.

[0053] The specific process of biochar modification is as follows: Commercially available sodium dodecyl sulfate was used as the surfactant. The following material ratio was used: 0.3 g of surfactant was added per kilogram of biochar, along with 1 L of 0.01 mol / L sodium hydroxide solution, to prepare a washing and modification system. The system was allowed to stand for 5 hours, and the water was drained to obtain the modified biochar.

[0054] Preparation and use of modifiers: A soil structure conditioner was prepared by uniformly mixing 10 parts modified biochar and 3 parts sieved phosphogypsum. A sample of topsoil at a depth of 15 cm and a soil bulk density of 1.3 kg / m³ was used, with the soil structure conditioner added at a mass ratio of 0.6%. Field capacity was then measured after mixing the materials. The soil moisture content was maintained at 80% of field capacity, and the mixture was incubated for 15 days.

[0055] Example 3 The main components of the soil structure improver are: 1 part sieved phosphogypsum and 15 parts modified biochar.

[0056] Raw material pretreatment: Municipal sludge was heated to 80°C at a heating rate of 6°C / min and held for 1.5 hours. Then, it was heated to 500°C at the same heating rate and held for 4 hours to obtain biochar. Impurities were removed by sorting.

[0057] Phosphogypsum produced in industrial production is selected, crushed and screened to remove large impurities, and then sieved to obtain phosphogypsum particles with a particle size of less than 2 mm.

[0058] The specific process of biochar modification is as follows: Commercially available sodium dodecyl sulfate was used as the surfactant. The following material ratio was used: 0.3 g of surfactant was added per kilogram of biochar, along with 1 L of 0.01 mol / L sodium hydroxide solution, to prepare a washing and modification system. The system was allowed to stand for 5 hours, and the water was drained to obtain the modified biochar.

[0059] Preparation and use of modifiers: A soil structure conditioner was prepared by uniformly mixing 15 parts modified biochar with 1 part sieved phosphogypsum. A sample of topsoil at a depth of 15 cm and a soil bulk density of 1.3 kg / m³ was used, with the soil structure conditioner added at a mass ratio of 0.4%. Field capacity was then measured after mixing the materials. The soil moisture content was maintained at 80% of field capacity and incubated for 15 days.

[0060] Example 4 The main components of the soil structure improver are: 3 parts sieved phosphogypsum and 10 parts modified biochar.

[0061] Raw material pretreatment: Municipal sludge was heated to 110°C at a heating rate of 6°C / min and held for 2 hours. Then, it was heated to 550°C at the same heating rate and held for 5 hours to obtain biochar. Impurities were removed by sorting.

[0062] Phosphogypsum produced in industrial production is selected, crushed and screened to remove large impurities, and then sieved to obtain phosphogypsum particles with a particle size of less than 2 mm.

[0063] The specific process of biochar modification is as follows: Commercially available sodium dodecyl sulfate was used as the surfactant. The following material ratio was used: 0.3 g of surfactant was added per kilogram of biochar, along with 1 L of 0.01 mol / L sodium hydroxide solution, to prepare a washing and modification system. The system was allowed to stand for 5 hours, and the water was drained to obtain the modified biochar.

[0064] Preparation and use of modifiers: A soil structure conditioner was prepared by uniformly mixing 10 parts modified biochar and 3 parts sieved phosphogypsum. A topsoil sample with a depth of 15 cm and a bulk density of 1.3 kg / m³ was taken, and the soil structure conditioner was added at a mass ratio of 0.4%. The field water holding capacity was then measured after mixing the materials. The soil moisture content was maintained at 80% of field water holding capacity, and the mixture was incubated for 15 days.

[0065] Comparative Example 1 Raw material pretreatment: Municipal sludge was heated to 110°C at a heating rate of 6°C / min and held for 2 hours. Then, it was heated to 550°C at the same heating rate and held for 5 hours to obtain biochar. Impurities were then removed by sorting.

[0066] Unmodified biochar, otherwise the same as in Example 1.

[0067] The main components of the improver are: 1 part sieved phosphogypsum and 15 parts biochar.

[0068] Raw material pretreatment: biochar, sorting to remove impurities.

[0069] Phosphogypsum produced in industrial production is selected, crushed and screened to remove large impurities, and then sieved to obtain phosphogypsum particles with a particle size of less than 2 mm.

[0070] Preparation and use of modifiers: A soil structure conditioner was prepared by uniformly mixing 15 parts biochar and 1 part sieved phosphogypsum. A sample of topsoil at a depth of 15 cm with a bulk density of 1.3 kg / m³ was taken, and the soil structure conditioner was added at a mass ratio of 0.6%. The field capacity was then measured after mixing the materials. The soil moisture content was maintained at 80% of field capacity, and the mixture was incubated for 15 days.

[0071] Comparative Example 2 Raw material pretreatment: Municipal sludge was heated to 110°C at a heating rate of 6°C / min and held for 2 hours. Then, it was heated to 550°C at the same heating rate and held for 5 hours to obtain biochar. Impurities were then removed by sorting.

[0072] Unmodified biochar, otherwise the same as in Example 1.

[0073] The main component of the improver is modified biochar.

[0074] Raw material pretreatment: biochar, sorting to remove impurities.

[0075] Biochar modification: Commercially available sodium dodecyl sulfate was used as the surfactant. The following material ratio was used: 0.3 g of surfactant was added per kilogram of biochar, along with 1 L of 0.01 mol / L sodium hydroxide solution, to prepare a washing and modification system. The system was allowed to stand for 5 hours, and the water was drained to obtain the modified biochar.

[0076] Preparation and use of modifiers: Topsoil samples were taken at a depth of 15 cm, with a soil bulk density of 1.3 kg / m³. Modified biochar was added at a mass ratio of 0.6%. Field capacity was measured after mixing the materials. Soil moisture content was maintained at 80% of field capacity for 15 days.

[0077] Comparative Example 3 The amount of soil structure conditioner added was 2%, and the rest was the same as in Example 1.

[0078] The main components of the soil structure improver are: 1 part sieved phosphogypsum and 15 parts modified biochar.

[0079] Raw material pretreatment: biochar, sorting to remove impurities.

[0080] Phosphogypsum produced in industrial production is selected, crushed and screened to remove large impurities, and then sieved to obtain phosphogypsum particles with a particle size of less than 2 mm.

[0081] Biochar modification: Commercially available sodium dodecyl sulfate was used as the surfactant. The following material ratio was used: 0.3 g of surfactant was added per kilogram of biochar, along with 1 L of 0.01 mol / L sodium hydroxide solution, to prepare a washing and modification system. The system was allowed to stand for 5 hours, and the water was drained to obtain the modified biochar.

[0082] Preparation and use of modifiers: A soil structure conditioner was prepared by uniformly mixing 15 parts modified biochar and 1 part sieved phosphogypsum. A topsoil sample with a depth of 15 cm, a soil bulk density of 1.3 kg / m³, and a soil structure conditioner mass ratio of 2% was used. Field capacity was measured after mixing the materials. The soil moisture content was maintained at 80% of field capacity and incubated for 15 days.

[0083] Comparative Example 4 The amount of modifier added was 2%, and the rest was the same as in Example 2.

[0084] The main components of the improver are: 3 parts sieved phosphogypsum and 10 parts modified biochar.

[0085] Raw material pretreatment: biochar, sorting to remove impurities.

[0086] Phosphogypsum produced in industrial production is selected, crushed and screened to remove large impurities, and then sieved to obtain phosphogypsum particles with a particle size of less than 2 mm.

[0087] Biochar modification: Commercially available sodium dodecyl sulfate was used as the surfactant. The following material ratio was used: 0.3 g of surfactant was added per kilogram of biochar, along with 1 L of 0.01 mol / L sodium hydroxide solution, to prepare a washing and modification system. The system was allowed to stand for 5 hours, and the water was drained to obtain the modified biochar.

[0088] Preparation and use of modifiers: A soil structure conditioner was prepared by uniformly mixing 10 parts modified biochar and 3 parts sieved phosphogypsum. A topsoil sample with a depth of 15 cm, a soil bulk density of 1.3 kg / m³, and a soil structure conditioner mass ratio of 2% was used. Field capacity was measured after mixing the materials. The soil moisture content was maintained at 80% of field capacity and incubated for 15 days.

[0089] Test case According to the implementation example, a soil culture experiment was conducted. The test soil was taken from Hexibao, Jinchang City, Gansu Province. After the soil was naturally air-dried, large stones (over 1 cm in diameter for easier subsequent handling) and dead branches and leaves were removed, and the soil was crushed and sieved through a 2 mm sieve. The test soil was pre-mixed according to the designed amendment addition ratio, and filled into flower pots with a diameter of 8.0 cm and a height of 15.0 cm, with 0.8 kg of soil per pot, controlling the soil height to 12 cm, so that the filling bulk density is 1.3. The blank control group did not add any amendment. Each experimental group had 5 replicates and one pretreatment. All treatments were uniformly watered with 0.3 kg of deionized water (a small amount of muddy water could be observed seeping from the bottom of the pot). After 24 hours, the field water holding capacity of the pretreatment group was measured using the ring cutter method. The soil moisture content of each experimental group was controlled to be 80% of the corresponding field water holding capacity of the pretreatment group. After 15 days of cultivation, the soil pH, electrical conductivity, aeration porosity, capillary porosity (determined by calculation from field water holding capacity), and aggregate quantity were measured.

[0090] Experimental results: Results 1 are shown in Table 1: Soil pH All four examples significantly reduced soil alkalinity. Compared to Comparative Example 2, phosphogypsum and sludge peat have a synergistic effect in reducing soil pH. Comparative Example 1 demonstrates that, under the experimental conditions, the modification treatment had no significant effect on the alteration of soil pH by biochar. Comparative Examples 3 and 4 demonstrate that increasing the dosage of the amendment is beneficial for reducing the pH of alkaline soils.

[0091] Table 1 Soil pH Changes

[0092] Result 2: Changes in soil electrical conductivity Comparing with the blank control, it can be seen that within the recommended dosage range of the amendment in this invention, the amendment has no significant effect on the soluble salt content of the soil. Compared with Comparative Examples 2, 3, and 4, the examples show that phosphogypsum is the main cause of the increased electrical conductivity of the system; when the dosage is within the recommended range, biochar has a certain salt-controlling function. Example 1, compared with Comparative Example 1, shows that biochar modification effectively reduced its own salt content and gave it a certain salt-controlling ability.

[0093] Table 2. Changes in Soil Electrical Conductivity

[0094] Result 3: Changes in soil pore structure During the determination of soil ineffective water, it was found that the proportion of ineffective water to the maximum soil moisture content is less than 0.5%. Therefore, ineffective porosity is not considered in the calculation process, i.e., total porosity = aeration porosity + capillary porosity.

[0095] Compared with the blank control, it can be seen that within the range of the amendment dosage recommended in this invention, the amendment can maintain a high aeration porosity while increasing the proportion of soil capillary pores, thus effectively coordinating the soil's water-air relationship and achieving both aeration and water retention. Compared with Comparative Examples 3 and 4, the examples show that as the amendment dosage increases, the ratio of soil aeration porosity to capillary pores approaches one. Compared with Comparative Example 2, Examples 1 and 2 show that increasing the proportion of phosphogypsum in the amendment is not conducive to improving soil water retention capacity. Compared with Comparative Example 1, Example 1 shows that the modification treatment effectively improves the water retention capacity of biochar.

[0096] Table 3. Changes in Soil Pore Structure

[0097] Result 4: Changes in soil aggregates The particle size distribution of agglomerated particles in each experimental group was determined using a combination of wet sieving and pipette methods. Figure 1 .

[0098] Depend on Figure 1 It is known that the addition of materials has no significant effect on the number of soil particles with a diameter greater than 0.25 mm. The results of each embodiment show that the addition of the amendment effectively promotes the transformation of soil particles with a diameter less than 0.05 mm into a larger particle size range of 0.05~0.25 mm, meaning that the amendment promotes the formation of aggregates. Compared with Comparative Examples 3 and 4, the embodiments show that within the recommended ratio range of phosphogypsum to modified biochar, excessively high amounts of amendment are not conducive to soil aggregation. Compared with Comparative Example 2, Embodiments 1 and 2 show that increasing the proportion of phosphogypsum is beneficial to the formation of aggregates. Compared with Comparative Example 1, Embodiment 1 shows that after 15 days of soil cultivation, whether or not the biochar is modified is not a key influencing factor on the number of soil aggregates.

[0099] In summary, within the recommended proportions and application rates of the soil conditioner in this invention, modification of biochar reduces soil alkalinity while preventing excessive increases in soil salinity. Through the combined action of phosphogypsum and modified biochar, at the recommended application rate, a more balanced ratio between aeration pores and capillary pores is achieved, coordinating soil water and air processes and improving soil water retention and aeration capacity. Simultaneously, with the accompanying field application method, the number of soil aggregates significantly increased after fifteen days of cultivation, resulting in improved soil structure.

[0100] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A biochar-based soil structure conditioner, characterized in that, It includes the following components: 5-15 parts by weight of modified biochar (dry basis) and 1-3 parts by weight of phosphogypsum; The modified biochar is obtained by pyrolysis modification of municipal sludge, and the phosphogypsum is a byproduct of the phosphoric acid fertilizer production process. The preparation method of modified biochar includes the following steps: take municipal sludge, heat the municipal sludge to 80~110℃ and keep it at that temperature for 1.5~2 h, then continue to heat it to 450~550℃ and keep it at that temperature for 3~5 h to obtain biochar; then immerse the biochar in a mixed solution of surfactant and alkaline solution for 4~8 h to complete the chemical modification, and drain it to obtain modified biochar.

2. The biochar-based soil structure conditioner according to claim 1, characterized in that, The surfactant is sodium dodecyl sulfate or sodium hexadecylbenzenesulfonate.

3. The biochar-based soil structure conditioner according to claim 1, characterized in that, The mass ratio of biochar to surfactant is 1000:(0.1~0.5), the concentration of alkaline solution is 0.01mol / L, and the volume ratio of biochar to alkaline solution is 1:1 (g / mL).

4. The biochar-based soil structure conditioner according to claim 1, characterized in that, The alkaline solution is selected from dodecyl alcoholamine solution, trisodium phosphate solution, potassium hydroxide solution, or sodium hydroxide solution.

5. The biochar-based soil structure conditioner according to claim 1, characterized in that, The maximum particle size of the phosphogypsum is no more than 2 mm, and the D50 is 0.08~0.1 mm.

6. The biochar-based soil structure conditioner according to claim 1, characterized in that, The modified biochar has a water content of 60-70%.

7. The biochar-based soil structure conditioner according to claim 1, characterized in that, The modified biochar contains harmful elements that meet the requirements of the NY 1110-2016 water-soluble fertilizer standard, and the total effective nitrogen, phosphorus and potassium content is less than 20% of the dry basis of the biochar, which meets the requirements for crop seedling cultivation.

8. A method for preparing a biochar-based soil structure conditioner as described in any one of claims 1 to 7, characterized in that, Modified biochar and phosphogypsum were made into particles with a fineness of less than 2 mm and then uniformly mixed.

9. A method of using a biochar-based soil structure conditioner as described in any one of claims 1 to 7, characterized in that, include: The biochar-based soil conditioner is mixed evenly with the topsoil at a ratio of 0.3-0.6 wt% on a dry basis, and then irrigated to maintain the moisture content at 60%-90% of field capacity. The soil is then cultivated for more than 15 days before sowing.

10. The method of using the biochar-based soil structure conditioner according to claim 9, characterized in that, The topsoil is soil with a depth of no more than 20 cm below the land surface.

Images