A method for repairing soil of a west sichuan slope accumulation body and application thereof

Abstract

The application discloses a method suitable for soil remediation of a west Sichuan slope accumulation body and application. The method comprises the following steps: preparing high water-absorbing resin based on highland barley straw, applying the high water-absorbing resin into a soil layer to be remediated of the west Sichuan slope accumulation body, mixing the high water-absorbing resin with the soil of the accumulation body or a plant growth substrate to form a water and fertilizer retaining improved layer, and sowing or planting plants suitable for growth in the west Sichuan region. The high water-absorbing resin based on highland barley straw is formed by using pretreated highland barley straw as a biomass skeleton, using acrylic acid and acrylamide as grafting monomers, using N,N'-methylene bisacrylamide as a crosslinking agent, and performing microwave radiation polymerization under the action of a potassium persulfate / sodium thiosulfate pentahydrate redox initiation system to form a three-dimensional crosslinked network, and in-situ introduction of urea and natural zeolite. The method can improve the water holding capacity of the soil of the west Sichuan slope accumulation body, reduce the migration loss of urea under leaching conditions, improve the water retention stability of the material in a strong ultraviolet radiation environment, and promote early growth of plants, and can be used for soil improvement and ecological remediation of the slope accumulation body after an earthquake.

Description

Technical Field

[0001] This invention relates to the field of soil amendment materials and functional polymer materials, specifically to a barley straw-based composite superabsorbent resin suitable for water and fertilizer retention in silt soils, its preparation method, and its application. Background Technology

[0002] Post-earthquake slope deposits in Ganzi and Luding generally suffer from high gravel content, loose structure, insufficient fine particles, and poor soil continuity, resulting in weak water and fertilizer retention capacity. The unstable water and fertilizer environment in the root zone during the early stages of plant recovery hinders the effectiveness of slope ecological restoration. Meanwhile, the western Sichuan region has a strong ultraviolet radiation environment, meaning that soil amendments used in this type of soil must not only possess water absorption and retention capabilities and slow-release fertilizer retention, but also have a certain degree of resistance to ultraviolet aging.

[0003] Existing water- and fertilizer-retaining materials include organic amendments, mineral materials, carbon-based materials, and polymeric water-retaining materials. Among them, superabsorbent polymers (SAPs) have attracted widespread attention in soil improvement due to their three-dimensional cross-linked network structure, which allows them to rapidly absorb free water and gradually release it as soil water potential decreases. However, existing SAPs are mostly designed for general farmland soils or sandy soils, and are not well-suited for post-earthquake sediments with high gravel content, poor structural continuity, and easy water loss and leaching. Furthermore, urea loading via soaking is prone to premature release, making it difficult to meet the needs of synergistic water and fertilizer regulation.

[0004] Barley straw originates from barley, an important crop in western Sichuan, ensuring a stable source and strong regional adaptability. Using barley straw as a biomass framework, combined with acrylic acid / acrylamide graft polymerization to construct a superabsorbent polymer (SAP), and further integrating urea and natural zeolite in situ to create a composite system, it is expected to synergistically enhance the material's water absorption and retention, slow-release fertilizer retention, and adaptability to complex environments. Therefore, developing a barley straw-based composite SAP suitable for silt soils has significant application value. Summary of the Invention

[0005] The technical problem to be solved by this invention is that existing superabsorbent polymers have poor urea slow-release effect and insufficient resistance to ultraviolet aging in post-earthquake high-gravel soil. At the same time, it aims to realize the high-value resource utilization of local highland barley straw and develop a water-retaining and fertilizer-retaining integrated soil improvement material adapted to the special environment of western Sichuan.

[0006] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for preparing a highland barley straw-based composite superabsorbent resin, comprising the following steps: (1) Pre-treat the barley straw powder in an alkaline solution, wash and dry it for later use; (2) Partially neutralize acrylic acid in an ice-water bath, add acrylamide and adjust the water content of the system, then add initiator and crosslinking agent to obtain a monomer mixture for later use; (3) Mix the pretreated barley straw with water, gelatinize it with microwave, and then cool it. (4) Add the prepared monomer mixture obtained in step (2) to the gelatinized straw system obtained in step (3), stir, add urea and natural zeolite, and then polymerize by ultrasonic dispersion and microwave radiation to obtain the polymer product; (5) The polymer product is washed and dried to obtain the barley straw-based composite superabsorbent resin.

[0007] This invention provides a highland barley straw-based composite superabsorbent resin. The composite superabsorbent resin uses alkali-pretreated highland barley straw as the biomass skeleton, acrylic acid and acrylamide as graft monomers, N,N′-methylenebisacrylamide as a crosslinking agent, and potassium persulfate / sodium thiosulfate pentahydrate as a redox initiation system. It forms a three-dimensional crosslinked network through microwave radiation polymerization. In the polymerization system, urea is further introduced in situ at a fixed amount of 20% and combined with natural zeolite, thereby obtaining a highland barley straw-based composite superabsorbent resin with both water absorption and retention properties and slow-release fertilizer retention properties.

[0008] Furthermore, the degree of neutralization of the acrylic acid is 60%-75%, preferably 70%.

[0009] Furthermore, the mass ratio of acrylic acid to acrylamide is 1:1 to 4:1, preferably 2:1.

[0010] Furthermore, the initiator is a redox initiation system composed of potassium persulfate and sodium thiosulfate pentahydrate, with a molar ratio of 3:1; the amount of the initiator is 0.5%-2.0% of the total mass of the monomers, preferably 1.0%.

[0011] Furthermore, the amount of barley straw added is 8%-14% of the total mass of the monomers, preferably 12%.

[0012] Furthermore, the urea is added at a fixed amount, which is 20% of the total mass of the monomers.

[0013] Furthermore, the natural zeolite is one or two of clinoptilolite and mordenite, and the amount of natural zeolite added is 1%-10% of the total mass of the monomers, preferably 5%.

[0014] The present invention has the following beneficial effects: 1. Using barley straw as the biomass framework combines the availability of regional raw materials with the value of agricultural waste resource utilization; 2. The combination of redox initiation and microwave radiation is beneficial to promoting the rapid grafting of monomers onto the straw skeleton, forming a relatively stable three-dimensional cross-linked network; 3. In-situ introduction of urea can improve the problem of significant early-stage burst release under immersion loading conditions; 4. The introduction of natural zeolite, especially clinoptilolite, can further improve the material's water absorption, UV aging resistance, and slow-release properties; 5. When the obtained composite superabsorbent resin is used in post-earthquake soil, it can improve the maximum water holding capacity and water retention rate of the soil, slow down the short-term leaching of urea, and promote the early germination and seedling growth of plants. Attached Figure Description

[0015] Figure 1 This illustrates the effect of different natural zeolite dosages on the water absorption performance of the composite superabsorbent resin in Example 2.

[0016] Figure 2 This illustrates the effect of the type of natural zeolite on the water retention performance of the composite superabsorbent resin under UV aging in Example 3.

[0017] Figure 3 This is the effect of resin dosage in the clinoptilolite composite system on the water-holding capacity of the soil in Example 4.

[0018] Figure 4 The effect of resin dosage in the clinoptilolite composite system on the water retention capacity of the soil in Example 4.

[0019] Figure 5 The image shows the urea leaching results of the clinoptilolite composite resin system in the soil of Example 4.

[0020] Figure 6 The effect of resin dosage in the clinoptilolite composite system on the 7-day germination rate of wheat in Example 4.

[0021] Figure 7 This is a diagram showing the actual growth of wheat over 7 days in Example 4.

[0022] Figure 8 The effect of resin dosage in the clinoptilolite composite system on the 7-day germination rate of wheat in Example 4.

[0023] Figure 9 This is a diagram showing the actual growth of wheat over 7 days in Example 4. Detailed Implementation

[0024] The present invention will be further described below with reference to the embodiments, but the scope of protection of the present invention is not limited to the following embodiments.

[0025] Example 1: Preparation of highland barley straw-based composite superabsorbent resin The sieved barley straw powder was placed in a 2 wt% sodium hydroxide solution and soaked for 4 hours under stirring to remove some impurities and improve the reactivity of the straw fiber surface. After treatment, it was repeatedly washed with anhydrous ethanol and ultrapure water until the washing solution was nearly neutral, and then dried for later use.

[0026] Acrylic acid was placed in an ice-water bath and partially neutralized with a 20% sodium hydroxide solution to achieve a neutralization degree of 70%, resulting in an acrylic acid-sodium acrylate mixed solution. Acrylamide was then added at a mass ratio of acrylic acid to acrylamide of 2:1, and deionized water was added to maintain the water content of the system at 65%-70%. An initiator and a crosslinking agent were then added. The initiator was a redox initiation system composed of potassium persulfate and sodium thiosulfate pentahydrate, with a molar ratio of 3:1. The amount of initiator was 1.0% of the total monomer mass, and the amount of crosslinking agent N,N′-methylenebisacrylamide was 0.10% of the total monomer mass. The mixture was stirred until fully dissolved and then kept in an ice-water bath for later use.

[0027] Pretreated barley straw was weighed at 12% of the total monomer mass and mixed with distilled water at a mass ratio of 1:10. The mixture was then microwaved for 2 minutes under medium-low heat, followed by rapid cooling in an ice-water bath. The prepared monomer mixture was added to the gelatinized straw system and mechanically stirred for 10 minutes. Urea and natural zeolite were added at this stage, with urea added at a fixed rate of 20% of the total monomer mass and natural zeolite added at 5% of the total monomer mass. Stirring was continued until all components were evenly dispersed. The mixture was then sealed and ultrasonically dispersed at 300 W and 40 kHz for 1 hour. After cooling in an ice-water bath, it was microwaved for low-heat radiation polymerization for 9-10 minutes to obtain a honeycomb product. The product was washed with anhydrous ethanol and soaked for 12 hours to remove unreacted substances, then dried at 75°C to constant weight to obtain the barley straw-based composite superabsorbent resin. The above monomer solution was added to the gelatinization system, mechanically stirred for 10 min, then 3 g of urea was added, ultrasonically dispersed at 300 W and 40 kHz for 1 h, cooled in an ice bath, and then microwaved at low heat for 9 min to obtain a honeycomb elastic product.

[0028] Example 2: Screening of Natural Zeolite Types and Doses Composite superabsorbent resins with different types and amounts of natural zeolite were prepared according to the method in Example 1. The natural zeolite was selected from clinoptilolite and mordenite, and the addition amounts were set to 1%, 3%, 5%, 7% and 10%, respectively. A control group was set up in which only urea was introduced in situ without the addition of natural zeolite.

[0029] Test results show that as the amount of natural zeolite added increases, the equilibrium swelling ratio of the material generally shows a trend of first increasing and then decreasing; when the amount of natural zeolite added is 5%, the material has the best water absorption performance. Among them, the equilibrium swelling ratios of the resin system without natural zeolite, the clinoptilolite composite system resin, and the mordenite composite system resin are 662 g / g, 693 g / g, and 684 g / g, respectively, indicating that the introduction of natural zeolite is beneficial to further improve the water absorption performance of the resin based on the in-situ introduction of urea.

[0030] Example 3: Effect of Natural Zeolite Type on Water Retention Performance of Composite Superabsorbent Resin under UV Aging The 5% addition of natural zeolite obtained in Example 2 was used to investigate its water retention performance under ultraviolet aging. After aging for 5 hours, the water retention rates of the clinoptilolite composite resin, the mordenite composite resin, and the resin without natural zeolite were 38.6%, 35.4%, and 27.3%, respectively. This indicates that the introduction of zeolite has a certain effect on improving the water retention performance of the resin under ultraviolet aging, and the clinoptilolite composite system has the best water retention performance under ultraviolet aging.

[0031] Example 4: Application effect of composite superabsorbent resin in soil accumulation The clinoptilolite composite resin obtained in Example 3 was used for soil improvement of post-earthquake slope deposits, and its application effects in soil water retention, urea leaching regulation and early plant growth promotion were verified.

[0032] In the soil water retention test, the resin dosage was set to 0%, 0.2%, 0.4%, 0.6%, and 0.8%; in the soil column leaching test, the resin dosage was 0.5%; and in the pot test, the resin dosage was set to 0%, 0.2%, 0.4%, 0.6%, and 0.8%.

[0033] Application tests have verified that, under the condition of resin dosage of 0.2%-0.8%, the composite superabsorbent resin applied to the soil of the embankment can improve the water retention capacity of the soil. Specifically, as the dosage of the composite superabsorbent resin increases from 0 to 0.8%, the maximum water holding capacity of the soil increases from 19.2% to 100.2%, and the water retention rate increases from 39.8% to 55.9%, indicating that the composite superabsorbent resin can effectively enhance the water storage capacity of the embankment soil and delay water loss.

[0034] In the soil column leaching test, when the content of the composite superabsorbent resin was 0.5%, the cumulative release rate of pure urea treatment was close to 80% on the first day, and the release was basically completed by the fourth day. In contrast, the cumulative release rate of the clinoptilolite composite resin treatment on the fourth day was 34.2%, and the release process was significantly more gradual. This indicates that the composite superabsorbent resin can regulate the migration and release process of urea in the soil, thereby reducing the risk of concentrated leaching in the early stage.

[0035] Furthermore, in pot experiments, when the content of the composite superabsorbent resin was 0%, 0.2%, 0.4%, 0.6%, and 0.8%, it all showed a promoting effect on the germination of wheat and early seedling growth of *Triticum aestivum*. Among them, as the resin content of the clinoptilolite composite system increased from 0 to 0.8%, the germination rate of wheat increased from 31.2% to 92.3%, and the germination rate of *Triticum aestivum* increased from 27.3% to 82.8%, indicating that the composite superabsorbent resin has a good application effect in improving the soil water and fertilizer environment of the compost and promoting early plant establishment.

[0036] Example 4: Alternative Implementation Without altering the core concept of this invention, natural zeolite can also be mordenite, or a combination of clinoptilolite and mordenite can be used; the amount of natural zeolite added, the amount of highland barley straw added, the degree of neutralization, the amount of initiator and the amount of crosslinking agent can also be adjusted within the scope of this invention, and all of these are within the protection scope of this invention.

Claims

1. A method for soil remediation of slope deposits in western Sichuan, characterized in that, First, a highland barley straw-based composite superabsorbent resin is prepared. Then, the highland barley straw-based composite superabsorbent resin is applied to the soil layer to be repaired on the slope deposit in western Sichuan and mixed with the deposit soil or vegetation substrate to form a water-retaining and fertilizer-retaining improved layer. Subsequently, plants suitable for growth in western Sichuan are sown or planted in the water-retaining and fertilizer-retaining improved layer. The highland barley straw-based composite superabsorbent resin improves the soil's moisture retention capacity, reduces urea leaching, and promotes early plant growth.

2. The method according to claim 1, characterized in that, The preparation method of the barley straw-based composite superabsorbent resin is as follows: barley straw powder is pretreated, the pretreated barley straw is microwave gelatinized, a neutralized acrylic acid system, acrylamide, initiator, crosslinking agent, urea and natural zeolite are added to the gelatinization system, mechanical stirring and ultrasonic dispersion are performed, microwave radiation polymerization is carried out, and the polymerization product is dried and pulverized to obtain the barley straw-based composite superabsorbent resin.

3. The method according to claim 2, characterized in that, The pretreatment of barley straw powder is as follows: First, barley straw is washed, dried at 105℃, pulverized, and passed through a 200-mesh sieve. Then, 20 g of sodium hydroxide and 1 g of sodium carbonate are added to 1 L of ultrapure water to prepare a mixed solution of sodium hydroxide and sodium carbonate. Next, 100 g of barley straw powder is added to 1000 mL of the mixed solution and soaked for 4 h under stirring. Then, the mixture is filtered and retained. The wet precipitate obtained by filtration is immersed and washed once with 500 mL of anhydrous ethanol per 100 g of wet precipitate. After filtration again, it is immersed and washed twice with 500 mL of deionized water per 100 g of wet precipitate. After washing, it is dried at 60 ℃ for 12 h or dried to constant weight to obtain pretreated barley straw.

4. The method according to claim 2, characterized in that, The microwave gelatinization of the pretreated barley straw is performed by mixing the pretreated barley straw with water at a mass ratio of 1:10 and treating it for 2 minutes at a microwave output power of 400 W. The degree of neutralization of the neutralized acrylic acid system is 60% to 75%, preferably 70%. The mass ratio of acrylic acid to acrylamide is 1:1 to 4:1, preferably 2:

1. The total mass of the monomers is the sum of the masses of acrylic acid and acrylamide. The amount of pretreated barley straw added is 8% to 14% of the total mass of the monomers, preferably 12%.

5. The amount of urea added is 10% to 30% of the total mass of the monomer, preferably 20%. The natural zeolite is one or two of clinoptilolite and mordenite, preferably clinoptilolite. The amount of natural zeolite added is 1% to 10% of the total mass of the monomer, preferably 5%.

6. The method according to claim 2, characterized in that, The initiator is a redox initiation system composed of potassium persulfate and sodium thiosulfate pentahydrate, with a molar ratio of 3:

1. The amount of the initiator is 0.5% to 2.0% of the total mass of the monomers, preferably 1.0%. The crosslinking agent is N,N′-methylenebisacrylamide, and the amount of the crosslinking agent is 0.05% to 0.20% of the total mass of the monomers, preferably 0.10%.

7. The method according to claim 2, characterized in that, The mechanical stirring time is 10 min, the ultrasonic dispersion power is 300 W, the frequency is 40 kHz, and the time is 1 h, and the microwave output power of the microwave radiation polymerization is 450 W, and the radiation time is 10 min.

8. The method according to claim 1, characterized in that, The soil deposits on the slopes of western Sichuan include soil deposits at the toe of earthquakes, soil deposits in gullies, soil deposits from landslides, or soil deposits on slopes disturbed by engineering. The method is applicable to the remediation of soil deposits on slopes in western Sichuan under conditions of strong ultraviolet radiation, large diurnal temperature range, distinct dry and wet seasons, and concentrated rainfall during the rainy season. The amount of barley straw-based composite superabsorbent resin applied is 0.2% to 1.0% of the dry soil mass of the soil layer to be remediated, and the thickness of the water-retaining and fertilizer-retaining improvement layer is 5 cm to 30 cm.

9. The method according to claim 1, characterized in that, The plant includes one or more of old wheat, wheat, crested wheat or ryegrass, preferably wheat.

10. The application of the barley straw-based composite superabsorbent resin prepared by the method according to any one of claims 2 to 7 in improving the water retention capacity of the soil in the western Sichuan slope deposits, reducing urea leaching loss, improving the water retention stability of the material under ultraviolet aging conditions, and promoting early plant growth.

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