Water-permeable moisture-retaining soil and preparation method and application thereof

Abstract

The present application relates to the technical field of soil, and discloses a water-permeable and moisture-retaining soil, a preparation method and application thereof, the water-permeable and moisture-retaining soil is prepared by mixing yellow soil, sand, rotten straw, modified biochar and modified polylactic acid according to specific weight parts, and can be used for ecological restoration of mines, wherein the modified biochar is obtained by carboxylation modification of pomelo peel biochar, has a multi-level pore structure and a hydrophilic carboxyl functional group; the modified polylactic acid is prepared by modification of a silane coupling agent by grafting a functionalized meglumine to polylactic acid, and hydroxyl groups and siloxane structures are introduced; the soil of the present application builds a continuous and stable water transport pore network through the synergistic effect of the components, has excellent water permeability and water absorption and moisture retention capacity, can effectively improve soil structure, prevent hardening, and improve water and fertilizer utilization rate; the soil of the present application is environmentally friendly and biodegradable, and is suitable for various scenes such as agricultural planting, landscaping and ecological restoration of mines.

Description

Technical Field

[0001] This invention relates to the field of soil technology, specifically to a permeable and moisture-retaining soil, its preparation method, and its application. Background Technology

[0002] In fields such as mine ecological restoration and slope management, the water absorption, retention, and permeability of soil are core indicators determining plant growth, soil and water conservation effectiveness, and ecological stability. Existing soils used for mine ecological restoration and slope management (mostly sourced from native soils in or near mining areas) and greening soils generally suffer from defects such as simple structure and unreasonable pore distribution. Most yellow soils have high clay content and severe compaction, exhibiting poor permeability and aeration, susceptibility to waterlogging during rainfall, insufficient water retention during droughts, and rapid water loss. This not only leads to root rot due to lack of oxygen and hinders fertilizer absorption, affecting plant survival rates, but also easily triggers ecological problems such as surface runoff, soil erosion, and increased soil salinization. While some sandy soils possess some permeability, their excessively large pores and extremely poor water and fertilizer retention capacity result in rapid water infiltration, failing to continuously supply water to plants and making them unsuitable for the needs of refined planting and ecological greening.

[0003] Currently, the technical solutions for improving soil hydrophysical properties in the industry are relatively limited. Traditional improvement methods often involve simply adding river sand to improve soil aeration and permeability, or applying straw or ordinary biochar to enhance soil organic matter and water retention. However, simply mixing sand can only optimize soil permeability in the short term, failing to retain moisture and resulting in a significant loss of water retention capacity, making the soil prone to water shortage and cracking in drought conditions. While simply adding decomposed straw can improve soil looseness and organic matter content, straw degrades quickly, resulting in poor long-term improvement effects and limited water absorption and retention capacity.

[0004] In recent years, biochar has been widely used to improve soil water retention capacity due to its high specific surface area, rich oxygen-containing functional groups and good stability. However, ordinary biochar has a simple pore structure, low surface activity, poor binding with soil, water and fertilizer, and limited improvement effect. In addition, ordinary biochar has a strong hydrophobic surface and is prone to clogging some pores, which will reduce water permeability.

[0005] Conventional superabsorbent and moisture-retaining polymer materials often suffer from poor degradability, easy residue, and problems such as soil compaction and secondary pollution. They also cannot meet the needs of green ecological improvement. For example, although polyacrylate superabsorbent and moisture-retaining resins have extremely strong water absorption and moisture retention ratios, their non-degradability leads to soil microplastic pollution, and excessive swelling can easily close pores and impair permeability. In contrast, polylactic acid, as a biodegradable material, can gradually decompose into lactic acid, water, and carbon dioxide in the soil, leaving no long-term environmental residue. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention discloses a permeable and moisture-retaining soil, its preparation method, and its application. Using yellow soil as the base matrix, it is combined with sand, decomposed straw, modified biochar, and modified polylactic acid in a specific ratio for composite improvement. Through the synergistic combination of these raw materials, it exhibits excellent water absorption, moisture retention, permeability, and water retention properties, making it suitable for various applications such as agricultural planting, landscaping, and mine ecological restoration.

[0007] A permeable and moisture-retaining soil, comprising the following components by weight: 100 parts by weight of yellow soil (the yellow soil is dried and the moisture content is controlled between 15% and 17%), 20-40 parts by weight of sand, 10-20 parts by weight of decomposed straw (using decomposed rice straw or wheat straw), 10-20 parts by weight of modified biochar, and 5-10 parts by weight of modified polylactic acid. Preferably, the method for preparing the permeable and moisture-retaining soil includes the following steps: Add sand to yellow soil that has passed through a 60-mesh sieve, stir and mix evenly, then add decomposed straw, modified biochar, and modified polylactic acid, stir and mix evenly to obtain permeable and moisture-retaining soil.

[0008] The sand used in this application is a rigid granular inert matrix, which can effectively break up the dense structure of heavy and compacted soil, fill and reconstruct the multi-level pore system of soil, accurately improve the soil pore ratio, effectively overcome the disadvantages of soil waterlogging and poor aeration, and can quickly drain excess water during rainfall or irrigation, prevent surface water accumulation and root rot, and steadily improve the overall water permeability and aeration performance of soil. At the same time, the rigid sand particles can support the soil structure and prevent the soil from becoming compacted and collapsing again after long-term waterlogging and compaction.

[0009] Decomposed straw serves as a natural organic amendment substrate. It can be evenly mixed into soil gaps, promoting the formation of a healthy soil aggregate structure and significantly improving soil looseness. Moreover, decomposed straw itself has a rich fibrous pore structure that can absorb and retain moisture and nutrients, significantly enhancing the soil's basic water absorption, moisture retention, and fertilizer retention capabilities. It can also continuously replenish soil organic matter, activate the soil microbial environment, alleviate soil infertility and degradation problems, and provide organic support for long-term soil improvement.

[0010] Preferably, the sand is river sand that has passed through a 3mm soil sieve.

[0011] Preferably, the method for preparing the modified biochar includes the following steps: Step A1: Wash the grapefruit peel, cut it into 5mm pieces, place it in an oven to dry, set the oven temperature to 60℃, and dry for 12 hours. Under nitrogen protection, place it in a tube furnace for high-temperature carbonization. After cooling, grapefruit peel biochar is obtained. Step A2: Place grapefruit peel biochar in a flask, add concentrated sulfuric acid, stir in an ice-water bath for 30 minutes, then add potassium permanganate, heat to 40°C, and stir for 6-8 hours. After the reaction is complete, add hydrogen peroxide solution and stir for 30-50 minutes. Wash with deionized water and ethanol in sequence, and dry to obtain carboxylated biochar.

[0012] Biochar is stable, does not decompose, and does not collapse. When mixed into soil, it can permanently support the voids, acting as a granular skeleton. The grapefruit peel biochar prepared in this application has a large pore structure. After being mixed into the soil, it can communicate with the gaps between existing soil particles, forming a continuous and interconnected water-conducting pore network within the soil. However, the biochar surface is inert and highly hydrophobic, resulting in poor initial water wetting effect and slow water absorption and retention. This application modifies the grapefruit peel biochar by incorporating hydrophilic carboxyl functional groups on its surface. On the one hand, the hydrophilicity of the biochar surface is greatly improved, and a water film can easily spread on the surface of the char particles, resulting in rapid wetting and a significantly improved initial water absorption and retention rate. This allows it to quickly adsorb free water from the surrounding soil, enhancing the overall water absorption and retention capacity of the soil from the root. On the other hand, the carboxyl structure can form hydrogen bonds with the soil and organic matter, promoting the formation of a stable soil aggregate structure.

[0013] Preferably, in step A1, the high-temperature carbonization temperature is 600-650℃, and the carbonization time is 1-2 hours.

[0014] Preferably, the mass ratio of grapefruit peel biochar to potassium permanganate is 1:3-3.5.

[0015] Preferably, the method for preparing the modified polylactic acid includes the following steps: Step B1: Glucamine and γ-(2,3-epoxypropoxy)propyltrimethoxysilane were added to N,N-dimethylformamide solvent. Under nitrogen protection, the temperature was controlled at 80℃, and the mixture was stirred for 4 hours. After the reaction was completed, the mixture was filtered, washed with methanol, and dried to obtain a glucamine-modified silane coupling agent. The ratio of glucamine to γ-(2,3-epoxypropoxy)propyltrimethoxysilane was 1 g:(1-1.2) mL. The synthetic route is as follows: ; Step B2: Add meglumine-modified silane coupling agent and 4-bromo-1-butene to isopropanol solvent, stir and disperse, then reflux for 10-12 hours. After the reaction is complete, distill under reduced pressure and dry to obtain functionalized meglumine-modified silane coupling agent. The mass ratio of meglumine-modified silane coupling agent to 4-bromo-1-butene is 1:0.3-0.35. The reaction synthesis route is as follows: ; Step B3: Dissolve maleic anhydride and dicumyl peroxide in acetone. After stirring and dissolving, add polylactic acid and functionalized meglumine modified silane coupling agent. Stir and mix evenly. After the acetone has completely evaporated, place it in a torque rheometer for melt grafting. Control the temperature at 175-180℃, the rotation speed at 50 r / min, and the grafting reaction time at 8-10 min. After the reaction is completed, reflux in chloroform for purification, precipitate with ethanol, filter, wash, and dry to obtain modified polylactic acid. In this step, dicumyl peroxide is used as an initiator. A meglumine-modified silane coupling agent is used to initiate grafting onto polylactic acid (PLA) segments using alkenyl groups contained in maleic anhydride. This process involves grafting with numerous hydroxyl groups and siloxane structures. Hydroxyl groups are strongly polar hydrophilic functional groups; when introduced into the soil system, they form numerous hydrophilic active sites on the surfaces of soil particles, biochar, and the PLA matrix. These sites rapidly associate with water molecules via hydrogen bonding, significantly reducing the contact angle of water on the soil solid surface. This allows for rapid water spread and infiltration of the soil, significantly improving the initial water absorption and retention rate, and solving the problem of traditional soil hydrophobicity. It addresses the issues of slow infiltration and easy surface runoff. Furthermore, hydroxyl groups can form a stable multilayer hydrogen bond association structure with water molecules, converting free water into bound water and capillary water, thus slowing down the infiltration and loss of gravitational water. It can quickly absorb and retain water while locking in moisture, increasing the soil's field water holding capacity, achieving high water retention and slow-release water, and sustainably supplying water to the roots under drought conditions. In addition, the strong polarity of hydroxyl groups can improve the interfacial bonding between organic components (modified polylactic acid, decomposed straw) and inorganic soil particles and sand particles, preventing separation cracks at the two-phase interface, making the soil pore distribution more uniform, and maintaining a stable permeable framework in the long term.

[0016] When siloxanes come into contact with water, they undergo dehydration and condensation to form a large Si-O-Si inorganic cross-linked network structure. This network structure has high bond energy and strong rigidity. When incorporated into the soil, it can form a three-dimensional support skeleton between soil particles, opening up the spacing between soil particles and forming a continuous, stable, and permeable channel. It is not prone to collapse or shrinkage due to water compaction or alternating wet and dry conditions.

[0017] Preferably, in step B3, the mass ratio of maleic anhydride, dicumyl peroxide, polylactic acid, and functionalized meglumine-modified silane coupling agent is 4-5:0.4-0.8:100:1-2.

[0018] An application of permeable and moisture-retaining soil involves filling the aforementioned permeable and moisture-retaining soil into planting bags or planting troughs for ecological restoration of mine slopes.

[0019] Technical Effects: This invention utilizes carboxylated biochar and modified polylactic acid rich in hydroxyl and siloxane structures for compound modification, combined with sand and decomposed straw for synergistic improvement. This effectively solves the problem of soil's inability to simultaneously achieve both permeability and water retention. Specifically, the carboxylated biochar possesses multi-level interconnected pores and numerous hydrophilic carboxyl functional groups, which can construct unobstructed soil water transport channels, significantly improving soil permeability and drainage performance. Simultaneously, it can adsorb and lock in moisture through hydrogen bonding and electrostatic interactions, promoting the formation of stable soil aggregate structures and further enhancing the soil's water absorption, moisture retention, and water retention capacity. The hydroxyl groups on the surface of the modified polylactic acid can... It constructs a hydrophilic interface, enhances the soil's water absorption, moisture retention, and water retention effects, and reduces water seepage and loss; its siloxane rigid cross-linked structure can stabilize the soil pore skeleton, resist soil collapse and compaction caused by wet-dry cycles and external force compaction, and maintain the soil's water permeability and aeration performance for a long time; the two modified materials have complementary properties and synergistic effects, and when combined with sand and decomposed straw to optimize soil structure and supplement organic matter, the improved soil has coordinated water and air, stable structure, and is green and pollution-free, which can effectively improve water and fertilizer utilization and plant survival rate, and is suitable for a variety of planting and ecological restoration scenarios, with significant application value. Detailed Implementation

[0020] The present invention will be further described in conjunction with the following embodiments.

[0021] Preparation method of meglumine-modified silane coupling agent: 20g meglumine and 24mL of γ-(2,3-epoxypropoxy)propyltrimethoxysilane were added to N,N-dimethylformamide solvent. Under nitrogen protection, the temperature was controlled at 80℃ and the reaction was stirred for 4h. After the reaction was completed, the mixture was filtered, washed with methanol, and dried to obtain meglumine-modified silane coupling agent.

[0022] Preparation method of grapefruit peel biochar: Wash grapefruit peel, cut it into 5mm particles, place it in an oven to dry, set the oven temperature to 60℃, and dry for 12 hours. Under nitrogen protection, place it in a tube furnace for high-temperature carbonization at 600℃ for 2 hours. After cooling, grapefruit peel biochar is obtained.

[0023] Example 1 (1) Place 1g of grapefruit peel biochar in a flask, add 40mL of concentrated sulfuric acid, stir in an ice-water bath for 30min, then add 3g of potassium permanganate, heat to 40℃, stir for 8h, after the reaction is complete, add 65mL of 4% hydrogen peroxide aqueous solution, stir for 30min, wash with deionized water and ethanol in sequence, dry to obtain carboxylated biochar; (2) Add 5g of meglumine-modified silane coupling agent and 1.6g of 4-bromo-1-butene to isopropanol solvent, stir and disperse, reflux for 11h, and after the reaction is completed, distill under reduced pressure and dry to obtain functionalized meglumine-modified silane coupling agent. (3) Dissolve 2g of maleic anhydride and 0.2g of dicumyl peroxide in acetone. After stirring and dissolving, add 50g of polylactic acid and 0.5g of functionalized meglumine modified silane coupling agent. Stir and mix evenly. After the acetone has completely evaporated, place it in a torque rheometer for melt grafting. Control the temperature at 175℃, the rotation speed at 50r / min, and the grafting reaction time at 8min. After the reaction is completed, place it in chloroform for reflux purification, precipitate with ethanol, filter, wash, and dry to obtain modified polylactic acid. (4) Add 20 parts by weight of sand to 100 parts by weight of yellow soil (moisture content 16%) that has passed through a 60-mesh sieve, stir and mix evenly, then add 10 parts by weight of decomposed straw (rice straw, particle size not greater than 2mm), 10 parts by weight of modified biochar, and 5 parts by weight of modified polylactic acid, stir and mix evenly to obtain permeable and moisture-retaining soil.

[0024] Example 2 (1) Place 1g of grapefruit peel biochar in a flask, add 40mL of concentrated sulfuric acid, stir in an ice-water bath for 30min, then add 3g of potassium permanganate, heat to 40℃, stir for 6h, after the reaction is complete, add 65mL of 4% hydrogen peroxide aqueous solution, stir for 40min, wash with deionized water and ethanol in sequence, dry to obtain carboxylated biochar; (2) Add 5g of meglumine-modified silane coupling agent and 1.75g ​​of 4-bromo-1-butene to isopropanol solvent, stir and disperse, reflux for 12h, and after the reaction is completed, distill under reduced pressure and dry to obtain functionalized meglumine-modified silane coupling agent. (3) Dissolve 2.2g of maleic anhydride and 0.3g of dicumyl peroxide in acetone. After stirring and dissolving, add 50g of polylactic acid and 0.8g of functionalized meglumine modified silane coupling agent. Stir and mix evenly. After the acetone has completely evaporated, place it in a torque rheometer for melt grafting. Control the temperature at 180℃, the rotation speed at 50r / min, and the grafting reaction time at 9min. After the reaction is completed, place it in chloroform for reflux purification, precipitate with ethanol, filter, wash, and dry to obtain modified polylactic acid. (4) Add 30 parts by weight of sand to 100 parts by weight of 60-mesh sieve (moisture content 16%), stir and mix evenly, then add 15 parts by weight of decomposed straw (rice straw, particle size not greater than 2mm), 15 parts by weight of modified biochar, and 8 parts by weight of modified polylactic acid, stir and mix evenly to obtain permeable and moisturizing soil.

[0025] Example 3 (1) Place 1g of grapefruit peel biochar in a flask, add 40mL of concentrated sulfuric acid, stir in an ice-water bath for 30min, then add 3g of potassium permanganate, heat to 40℃, stir for 7h, after the reaction is complete, add 65mL of 4% hydrogen peroxide aqueous solution, stir for 50min, wash with deionized water and ethanol in sequence, dry to obtain carboxylated biochar; (2) Add 5g of meglumine-modified silane coupling agent and 1.5g of 4-bromo-1-butene to isopropanol solvent, stir and disperse, reflux for 10h, and after the reaction is completed, distill under reduced pressure and dry to obtain functionalized meglumine-modified silane coupling agent. (3) Dissolve 2.5g of maleic anhydride and 0.4g of dicumyl peroxide in acetone. After stirring and dissolving, add 50g of polylactic acid and 1g of functionalized meglumine modified silane coupling agent. Stir and mix evenly. After the acetone has completely evaporated, place it in a torque rheometer for melt grafting. Control the temperature at 175℃, the rotation speed at 50r / min, and the grafting reaction time at 10min. After the reaction, place it in chloroform for reflux purification, precipitate with ethanol, filter, wash, and dry to obtain modified polylactic acid. (4) Add 40 parts by weight of sand to 100 parts by weight of 60-mesh sieve (moisture content 16%), stir and mix evenly, then add 20 parts by weight of decomposed straw (rice straw, particle size not greater than 2mm), 20 parts by weight of modified biochar, and 10 parts by weight of modified polylactic acid, stir and mix evenly to obtain permeable and moisturizing soil.

[0026] Comparative Example 1: The process of preparing permeable and moisture-retaining soil in this comparative example is roughly the same as that in Example 1, except that step (4) does not contain modified biochar.

[0027] Comparative Example 2 is similar to Example 1 in the process of preparing permeable and moisture-retaining soil, except that step (4) does not contain modified polylactic acid.

[0028] Comparative Example 3 is similar to Example 1 in the process of preparing permeable and moisture-retaining soil, except that in step (4), polylactic acid is used instead of modified polylactic acid.

[0029] The saturated hydraulic conductivity of soil was tested using the double-ring cutter method. Weigh the soil and place it in an oven at 105℃ to dry until constant weight. Weigh the dry soil (m1), soak it in pure water until fully saturated, let it stand to drain the surface free water, weigh the wet soil (m2), and then place it at room temperature for 7 days. Weigh the soil (m3). Soil water absorption and retention rate (%) = (m2-m1) / m1×100%, soil water retention rate (%) = (m3-m1) / (m2-m1)×100%.

[0030] Table 1:

[0031] The higher the water conductivity, the better the permeability; the higher the water absorption and retention rate, the better the water absorption and retention. As shown in the table, the soil prepared by the embodiments of the present invention has excellent water absorption, retention and permeability. Comparative Example 1 does not contain modified biochar, and Comparative Example 2 does not contain modified polylactic acid. Both modified biochar and modified polylactic acid can improve the water absorption, retention and permeability of the soil. Therefore, the water absorption, retention and permeability of the comparative examples are not as good as those of the embodiments of the present invention.

[0032] An application of permeable and moisture-retaining soil: The permeable and moisture-retaining soil from Example 1, Example 2 or Example 3 is placed into a planting bag or planting trough. Crop seeds can be pre-mixed into the permeable and moisture-retaining soil for ecological restoration of mine slopes.

[0033] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention. It should be noted that after planting plants using the permeable and moisture-retaining soil of the present invention, water should be applied regularly every day for the first fifteen days, and thereafter watering should be done according to the crop's growth needs.

Claims

1. A permeable and moisture-retaining soil, characterized in that, The permeable and moisture-retaining soil comprises the following components by weight: 100 parts yellow soil, 20-40 parts sand, 10-20 parts decomposed straw, 10-20 parts modified biochar, and 5-10 parts modified polylactic acid.

2. The permeable and moisture-retaining soil according to claim 1, characterized in that, The sand is river sand that has passed through a 3mm soil sieve.

3. The permeable and moisture-retaining soil according to claim 1, characterized in that, The method for preparing the modified biochar includes the following steps: Step A1: Wash the grapefruit peel, cut it into 5mm pieces, place it in an oven to dry, set the oven temperature to 60℃, and dry for 12 hours. Under nitrogen protection, place it in a tube furnace for high-temperature carbonization. After cooling, grapefruit peel biochar is obtained. Step A2: Place grapefruit peel biochar in a flask, add concentrated sulfuric acid, stir in an ice-water bath for 30 minutes, then add potassium permanganate, heat to 40°C, and stir for 6-8 hours. After the reaction is complete, add hydrogen peroxide solution and stir for 30-50 minutes. Wash with deionized water and ethanol in sequence, and dry to obtain carboxylated biochar.

4. The permeable and moisture-retaining soil according to claim 3, characterized in that, In step A1, the high-temperature carbonization temperature is 600-650℃, and the carbonization time is 1-2 hours.

5. The permeable and moisture-retaining soil according to claim 3, characterized in that, The mass ratio of grapefruit peel biochar to potassium permanganate is 1:3-3.

5.

6. The permeable and moisture-retaining soil according to claim 1, characterized in that, The preparation method of the modified polylactic acid includes the following steps: Step B1: Add meglumine and γ-(2,3-epoxypropoxy)propyltrimethoxysilane to N,N-dimethylformamide solvent. Under nitrogen protection, control the temperature at 80℃ and stir the reaction for 4 hours. After the reaction is completed, filter, wash with methanol, and dry to obtain meglumine-modified silane coupling agent. Step B2: Add meglumine-modified silane coupling agent and 4-bromo-1-butene to isopropanol solvent, stir and disperse, reflux for 10-12 h, after the reaction is completed, distill under reduced pressure and dry to obtain functionalized meglumine-modified silane coupling agent. Step B3: Dissolve maleic anhydride and dicumyl peroxide in acetone. After stirring and dissolving, add polylactic acid and functionalized meglumine modified silane coupling agent, stir and mix evenly. After the acetone has completely evaporated, place it in a torque rheometer for melt grafting. Control the temperature at 175-180℃, the rotation speed at 50 r / min, and the grafting reaction time at 8-10 min. After completion, reflux in chloroform for purification, precipitate with ethanol, filter, wash, and dry to obtain modified polylactic acid.

7. The permeable and moisture-retaining soil according to claim 6, characterized in that, In step B1, the ratio of meglumine to γ-(2,3-epoxypropoxy)propyltrimethoxysilane is 1 g: (1-1.2) mL.

8. The permeable and moisture-retaining soil according to claim 6, characterized in that, In step B2, the mass ratio of meglumine-modified silane coupling agent to 4-bromo-1-butene is 1:0.3-0.

35.

9. The permeable and moisture-retaining soil according to claim 6, characterized in that, In step B3, the mass ratio of maleic anhydride, dicumyl peroxide, polylactic acid, and functionalized meglumine-modified silane coupling agent is 4-5:0.4-0.8:100:1-2.

10. A method for preparing permeable and moisture-retaining soil as described in any one of claims 1-9, comprising the following steps: adding sand to yellow soil that has passed through a 60-mesh sieve, stirring and mixing evenly, then adding decomposed straw, modified biochar, and modified polylactic acid to the soil, stirring and mixing evenly to obtain permeable and moisture-retaining soil.

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