Use of a heteropoly compound / pva composite for water retention in sandy soil

Abstract

This invention discloses the application of a heteropoly compound / PVA composite in water retention of sandy soil. The invention prepares the heteropoly compound / PVA composite by mixing polymer polyvinyl alcohol with a Standberg-type heteropoly compound or its derivatives, which is then used for water retention in sandy soil. The heteropoly compound / PVA composite of this invention can significantly improve the water and fertilizer retention capacity of sandy soil, and has high adhesion ability. It can withstand strong winds in arid regions, is not easily blown away and loses its effectiveness, and will not disperse into the air causing particulate pollution. After gradually losing water, the sand amendment forms a porous membrane on the surface of the gravel, maintaining the soil's aeration and permeability, and plays a positive role in the restoration of degraded soils in desert areas.

Description

Technical Field

[0001] This invention belongs to the field of ecological restoration technology for degraded soil, specifically relating to the application of a heteropoly compound / PVA complex in water retention of sandy soil. Background Technology

[0002] my country is one of the world's major arid countries, with low annual precipitation in its arid and semi-arid regions, resulting in exceptionally fragile ecosystems and severe land degradation. Land remediation in these regions is a key project in a series of ecological engineering initiatives in my country. However, the progress of land remediation in these areas remains unsatisfactory, particularly in soil remediation in arid regions, which faces significant challenges.

[0003] Soils in arid regions, such as brown desert soils, are typical zonal soils found in desert areas, including the Hexi Corridor in Gansu, the piedmont plains of the Qilian Mountains in western Gansu, the northwestern Ordos Plateau in Inner Mongolia, the southern Junggar Basin in Xinjiang, the sloping plains on both sides of the Tianshan Mountains, and the Gashun and Jiangjun Gobi deserts in my country. These areas are extremely arid, with some years experiencing no rain at all, and an aridity index >4, meaning soil moisture is primarily generated through evaporation. Besides severe water scarcity, another reason for the difficulty in soil remediation is that these areas are located in arid and windy zones. Fine soil material formed by in-situ weathering is often blown away by the wind, leaving mostly coarse gravel and gravel mounds on the surface. Strong winds further lead to rapid soil moisture loss. Due to drought and water scarcity, surface vegetation grows slowly, mainly consisting of succulent, deep-rooted, drought-resistant semi-shrubs and shrubs, often distributed as single plants or small clumps. Vegetation cover in arid regions is extremely low, and plant remains decompose rapidly, resulting in weak accumulation of soil organic matter and an indistinct humus layer.

[0004] Land degradation caused by climate change and human activities is a severe global environmental problem. Restoring degraded land is crucial for sustainable ecosystem management and socio-economic development decisions. A pressing issue in soil remediation in arid regions is improving the water and fertilizer retention capacity of sandy soils. Currently, soil conditioners for improving the water and fertilizer retention capacity of aeolian sandy soils mainly include natural conditioners such as bentonite, synthetic conditioners, and biological conditioners. Natural conditioners include bentonite, crop straw, and livestock manure; synthetic conditioners include polyacrylamide, polyethylene glycol, urea-formaldehyde resin, and polyvinyl alcohol resin; and biological conditioners include microorganisms and earthworms. Clearly, these conditioners face several theoretical and technical challenges in practical application, such as large application rates, long application periods with short durations of effect, and issues with application methods, thus limiting their widespread adoption. Summary of the Invention

[0005] To address the shortcomings and deficiencies of existing technologies, the present invention aims to provide an application of a heteropoly compound / PVA composite in water retention in sandy soil.

[0006] This invention uses a Standberg-type heteropoly compound or its derivative aqueous solution to a high molecular weight polyvinyl alcohol (PVA) aqueous solution to obtain a heteropoly compound / PVA composite that can be used for water retention in sandy soil.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] Application of a heteropoly compound / PVA complex in water retention of sandy soil, wherein the heteropoly compound / PVA complex is a gel-like substance composed of a Standberg type heteropoly compound and / or its derivatives, PVA and water, wherein the Standberg type heteropoly compound and / or its derivatives account for 20-60% of the dry weight of PVA, and the mass ratio of PVA to water is 1:7-21.

[0009] Preferably, the Standberg-type heteropoly compound and / or its derivatives account for 40-60% of the dry weight of PVA, and the mass ratio of PVA to water is 1:10-21.

[0010] Preferably, the Standberg-type heteropoly compound is an inorganic polyoxometalate, and its anionic molecular formula is [X₂M₅O₂]. 21～23 ] n- Where X = P, Se, or S, M = Mo or W, and the cation is NH4. + Na + and K + At least one of them.

[0011] Preferably, the Standberg-type heteropoly compound derivative is an organic-inorganic hybrid compound formed by replacing some heteroatoms and / or oxygen atoms in the Standberg-type heteropoly compound anion with organic ligands, wherein the organic ligand substituent is at least one of -HPO3, -CH3PO3, -C2H5PO3, -O2CCH2PO3 and NH3C2H4PO3.

[0012] More preferably, the Standberg-type heteropoly compound or its derivative is K4[Se2Mo5O] 21 ]、(NH4)4[S2Mo5O 21 ]、K4[(HPO3)2Mo5O 23 ] and (NH4)6[P2Mo5O 23 At least one of the following; more preferably K4[(HPO3)2Mo5O] 23 ] and (NH4)6[P2Mo5O 23 The optimal choice is (NH4)6[P2Mo5O]; 23 ].

[0013] Preferably, the synthesis method of the Standberg-type heteropoly compound is described in reference (Kwak W, Pope MT, Scully TF. Stable organic derivatives of heteropoly anions, pentamolybdobisphosphonates. J Am Chem Soc, 1975, 97: 5735-5738), using (NH4)6[P2Mo5O 23 For example, specifically, 28g of 30wt% phosphorous acid aqueous solution was mixed with 15mL of 24wt% concentrated ammonia solution, and 140mL of water was added. The mixture was stirred until homogeneous, and the solution was heated to boiling. Under boiling conditions, 29g of Na2MoO4 was added to the solution, and the mixture was continuously stirred and heated for 30min. The solution was then filtered. The filtrate was heated again, and 0.5mL of concentrated ammonia solution was slowly added dropwise during the heating process. Finally, the solution was cooled, and the water was evaporated at room temperature to obtain the crystalline product. The product was washed with cold water to obtain the Standberg type heteropoly compound (NH4)6[P2Mo5O] 23 ].

[0014] Preferably, the synthetic method of the Standberg-type heteropoly compound derivative is described in reference (Kwak W, Pope M T, Scully T F. Stable organic derivatives of heteropoly anions, pentamolybdobisphosphonates. J Am Chem Soc, 1975, 97: 5735-5738), using (NH4)4[(HPO3)2Mo5O 23 For example, 28g of 30wt% phosphorous acid aqueous solution was mixed with 50mL of water, then 15mL of 24wt% concentrated ammonia was added and stirred until homogeneous. The solution was then heated to boiling. Under boiling conditions, 29g of MoO3 was slowly added to the solution, and the mixture was continuously stirred and heated for 45min. The solution was then filtered. The filtrate was heated again to obtain a saturated solution. Finally, the solution was cooled, and the water was evaporated at room temperature to obtain a crystalline product. The product was washed with cold water to obtain the Standberg-type heteropoly compound derivative (NH4)4[(HPO3)2Mo5O] 23 ].

[0015] Preferably, the average molecular weight of the PVA is 100,000 to 150,000, and the degree of hydrolysis is ≥98%; more preferably, it is PVA-124, with an average molecular weight of 105,000 and a degree of hydrolysis of ≥98%.

[0016] Preferably, the heteropoly compound / PVA complex is a gel-like substance prepared by mixing an aqueous solution of a Standberg-type heteropoly compound and / or its derivatives with an aqueous solution of PVA at a volume ratio of 1:1 to 1:9.5, wherein the aqueous solution of the Standberg-type heteropoly compound and / or its derivatives contains 0.12 to 0.4 g / mL, and the mass percentage of PVA in the aqueous solution of PVA is 5 to 15%.

[0017] More preferably, the heteropoly compound / PVA complex is a gel-like substance prepared by mixing an aqueous solution of a Standberg-type heteropoly compound and / or its derivatives with an aqueous solution of PVA in a volume ratio of 1:9 to 9.5.

[0018] More preferably, the PVA aqueous solution contains 5-10% PVA by mass, and the aqueous solution of the Standberg type heteropoly compound and / or its derivatives contains 0.3-0.4 g / mL.

[0019] More preferably, the heteropoly compound / PVA complex is obtained by mixing an aqueous solution of a Standberg-type heteropoly compound and / or its derivatives with an aqueous solution of PVA at room temperature and then aging for 2 to 4 weeks.

[0020] Preferably, the application of the heteropoly compound / PVA complex in water retention of sandy soil specifically involves mixing the heteropoly compound / PVA complex and sandy soil at a mass ratio of 1:10 to 1:20.

[0021] The technical principle of this invention: Highly hydrolyzed PVA is a hydroxyl-rich polymer with good water solubility and adhesion, easily adhering to gravel to provide a water- and fertilizer-retaining layer. However, in dry, windy environments, PVA easily dehydrates and detaches from the gravel surface, failing to perform its function. This invention utilizes Standberg-type heteropoly compounds and their derivatives to regulate the intermolecular hydrogen bonds and intermolecular entanglement of PVA, improving its physical properties and transforming the PVA sol from a Newtonian fluid to a non-Newtonian fluid. The Standberg-type heteropoly compounds and their derivatives stabilize the hydrogen bonds between PVA and water molecules, enabling PVA to maintain its water- and fertilizer-retaining effect on sandy soil even in dry, windy environments. After a single application of the water-retaining amendment provided by this invention in a high-temperature, ventilated environment for 48 hours, the moisture content of the sandy soil still reaches 1.5%, providing a lifeline for organisms in dire conditions.

[0022] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0023] (1) The raw material PVA of this invention can be used by microorganisms as a carbon source, and one of its decomposition products is water, which can be used by organisms; Standberg type heteropoly compounds and their derivatives are a type of coordinated metal-oxygen cluster compound, rich in elements such as N, P, K, and Mo, all of which are essential elements for organisms; these materials will not cause secondary pollution when used for soil remediation.

[0024] (2) The heteropoly compound / PVA composite of the present invention has the function of sand fixation; in arid areas, the surface vegetation is generally sparse and it is prone to strong winds, and the surface fine soil is easily blown away to form mobile sand or semi-fixed sand; the heteropoly compound / PVA composite of the present invention has strong adhesion ability and can bind and fix fine sand particles.

[0025] (3) The heteropoly compound / PVA complex of the present invention forms a porous structure during the gradual dehydration process, which will not cause the soil to deteriorate in terms of aeration and water permeability, and will not cause problems such as soil compaction.

[0026] (4) The heteropoly compound / PVA complex of the present invention is easy to use and can be reused; the heteropoly compound / PVA complex of the present invention can strongly adhere to the surface of sand and gravel, and after completing a water retention cycle, it can absorb water again after full irrigation and be used for the next water retention cycle. Attached Figure Description

[0027] Figure 1 This is a polyhedral structure diagram of anions of Standberg-type heteropoly compounds and their derivatives.

[0028] Figure 2 The infrared spectrum of the Standberg-type heteropoly compound prepared in Example 1.

[0029] Figure 3 The infrared spectrum of the Standberg-type heteropoly compound derivative prepared in Example 2.

[0030] Figure 4 The UV-Vis absorption spectrum of the Standberg-type heteropoly compound prepared in Example 3 is shown.

[0031] Figure 5 The image shows the UV-Vis absorption spectrum of the Standberg-type heteropoly compound prepared in Example 4.

[0032] Figure 6 The peel strength curves are for the sandy soil water-retaining improvement materials prepared in Examples 1-4.

[0033] Figure 7 The image shows a scanning electron microscope image of the sand-modified material prepared in Example 1 after it lost water and formed a porous structure.

[0034] Figure 8The image shows a scanning electron microscope image of the sand-modified material prepared in Example 2 after it lost water and formed a porous structure.

[0035] Figure 9 The image shows a scanning electron microscope image of the sand-based soil amendment material prepared in Example 3 after it lost water, which formed a porous structure.

[0036] Figure 10 The image shows a scanning electron microscope image of the sand-modified material prepared in Example 4 after it lost water and formed a porous structure.

[0037] Figure 11 The water retention effect of the sand-soil improvement materials prepared in Examples 1-4 is shown. Detailed Implementation

[0038] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the implementation of the present invention is not limited thereto.

[0039] Unless otherwise specified in the embodiments of this invention, the conditions shall be performed according to conventional conditions or conditions recommended by the manufacturer. All raw materials and reagents used, unless otherwise specified, are commercially available conventional products.

[0040] Example 1

[0041] Preparation of Standberg-type heteropoly compounds (NH4)6[P2Mo5O] using the method described in the reference. 23 [(Kwak W, Pope MT, Scully TF. Stable organic derivatives of heteropoly anions, pentamolybdobisphosphonates. J Am Chem Soc, 1975, 97: 5735-5738), specifically as follows: 28g of 30wt% aqueous phosphorous acid solution was mixed with 15mL of 24wt% concentrated ammonia solution, and 140mL of water was added. The mixture was stirred until homogeneous, and the solution was heated to boiling. Under boiling conditions, 29g of Na2MoO4 was added to the solution, and the mixture was continuously stirred and heated for 30min. The solution was then filtered. The filtrate was reheated to boiling, and 0.5mL of 24wt% concentrated ammonia solution was slowly added dropwise during the heating process. Finally, the solution was cooled, and the water was evaporated at room temperature to obtain the crystalline product. The product was washed with cold water to obtain the Standberg-type heteropoly compound (NH4)6[P2Mo5O] 23 The structure of its anion is as follows: Figure 1 The left figure shows the infrared spectrum of the Standberg-type heteropoly compound; the right figure shows the left figure shows ... left figure shows the right figure shows the left figure shows the left figure shows the right figure shows the left figure shows the left figure shows the left figure shows the right figure shows the left figure shows the left figure shows the left figure shows the left figure shows the left figure shows the left figure shows the left Figure 2As shown. 5g of PVA-124 (Kuraray Co., Ltd., Japan, molecular weight 105000, degree of alcoholysis 98%) was added to 45mL of water and heated at 90°C for 1 hour with magnetic stirring until the PVA was completely dissolved, yielding a 10% PVA aqueous solution. The solution was then cooled to room temperature. 2g of Standberg-type heteropoly compound (NH4)6[P2Mo5O] was added. 23 Dissolve the compound in 5 mL of water, and mix the solution with the cooled PVA aqueous solution by magnetic stirring until homogeneous. After aging for two weeks, a heteropoly compound / PVA composite material for improving the water retention of sandy soil is obtained.

[0042] Example 2

[0043] Preparation of Standberg-type heteropoly compound K4[(HPO3)2Mo5O] using the method described in the reference. 23 [(Kwak W, Pope MT, Scully TF. Stable organic derivatives of heteropoly anions, pentamolybdobisphosphonates. J Am Chem Soc, 1975, 97: 5735-5738), specifically as follows: 28 g of 30 wt% aqueous solution of phosphorous acid was mixed with 300 mL of water, and then 22.5 g of KCl was added and stirred until a colorless and transparent solution was obtained. The pH of the solution was adjusted to 3.0 with 38 wt% concentrated hydrochloric acid, and the solution was heated to boiling and refluxed for 1 hour. The solution was cooled to room temperature and filtered. A colorless crystalline product was obtained by ethanol diffusion, and washed with cold water to obtain the Standberg-type heteropoly compound derivative K4[(HPO3)2Mo5O] 23 The structure of its anion is as follows: Figure 1 The right figure shows the infrared spectrum of the Standberg-type heteropoly compound derivative; the right figure shows the infrared spectrum of the derivative. Figure 3 As shown. 5g of PVA-124 (Kuraray Co., Ltd., Japan, molecular weight 105000, degree of alcoholysis 98%) was added to 95mL of water and heated at 80℃ for 2 hours with magnetic stirring until the PVA was completely dissolved, yielding a 5% PVA aqueous solution. The solution was then cooled to room temperature. 3g of the Standberg-type heteropoly compound derivative K4[(HPO3)2Mo5O] was added. 23 The solution was dissolved in 10 mL of water, and the solution was mixed evenly with the cooled PVA aqueous solution by magnetic stirring. After aging for two weeks, a heteropoly compound / PVA composite material for improving the water retention of sandy soil was obtained.

[0044] Example 3

[0045] Preparation of Standberg-type heteropoly compound K4[Se2Mo5O] using the method described in the reference. 21(Kwak W, Pope MT, Scully TF. Stable organic derivatives of heteropoly anions, pentamolybdobisphosphonates. J Am Chem Soc, 1975, 97: 5735-5738), specifically as follows: 3.0 g KCl, 37 g ammonium molybdate tetrahydrate, and 5.55 g selenium dioxide were added to a round-bottom flask, and 200 mL of water was added. The mixture was magnetically stirred until the solution became clear. The pH was adjusted to 3.5 with 17.5 mol / L glacial acetic acid solution. After standing at room temperature for 2 weeks, colorless crystals were obtained, which were the Standberg-type heteropoly compound K4[Se2Mo5O] 21 The structure of its anion is as follows: Figure 1 The left figure shows the UV-Vis spectrum of the Standberg-type heteropoly compound; the left figure shows the UV-Vis spectrum of the Standberg-type heteropoly compound. Figure 4 As shown. 3g of PVA-124 (Kuraray Co., Ltd., Japan, molecular weight 105000, degree of alcoholysis 98%) was added to 17mL of water and heated at 95°C for 2 hours with magnetic stirring until the PVA was completely dissolved, yielding a 15% PVA aqueous solution. The solution was then cooled to room temperature. 0.6g of the Standberg-type heteropoly compound derivative K4[Se2Mo5O] was added. 21 Dissolve the compound in 5 mL of water, and mix the solution with PVA aqueous solution by magnetic stirring until homogeneous. After aging for four weeks, a heteropoly compound / PVA composite material for improving the water retention of sandy soil is obtained.

[0046] Example 4

[0047] Preparation of Standberg-type heteropoly compounds (NH4)4[S2Mo5O] using the method described in the reference. 21 (Kwak W, Pope MT, Scully T F. Stable organic derivatives of heteropoly anions, pentamolybdobisphosphonates. J Am Chem Soc, 1975, 97: 5735-5738), specifically as follows: 18g of ammonium molybdate was fully dissolved in 60mL of water, and then SO2 gas was bubbled into the solution until the solution gradually turned yellow. At this point, the SO2 gas in the solution was saturated. The solution was then quickly cooled in an ice-water bath to obtain a pale yellow solid compound, which is the Standberg type heteropoly compound (NH4)4[S2Mo5O 21 The structure of its anion is as follows: Figure 1 The left figure shows the UV-Vis spectrum of the Standberg-type heteropoly compound; the left figure shows the UV-Vis spectrum of the Standberg-type heteropoly compound. Figure 5As shown. 5g of PVA-124 (Kuraray Co., Ltd., Japan, molecular weight 105000, degree of alcoholysis 98%) was added to 45mL of water and heated at 95°C for 1 hour with magnetic stirring until the PVA was completely dissolved, yielding a 10% PVA aqueous solution. The solution was then cooled to room temperature. 2g of a Standberg-type heteropoly compound derivative (NH4)4[S2Mo5O] was added. 21 Dissolve in 10 mL of water, and mix the solution with PVA aqueous solution by magnetic stirring until homogeneous. After aging for four weeks, a heteropoly compound / PVA composite material for improving soil water retention is obtained.

[0048] Example 5

[0049] The water-retention and fertilizer-retention effects of the heteropoly compound / PVA composite material prepared in Examples 1-4 are specifically illustrated.

[0050] First, an indoor soil column leaching test was used to test the water retention performance of the heteropoly compound / PVA composite material used to improve soil water retention. The sand used for the test was taken from the Ulan Buh Desert in Wuhai City, Inner Mongolia. After being air-dried, the sand was divided into 6 groups. One group of sand served as a blank control, while the other four groups of sand were mixed with the heteropoly compound / PVA composite material prepared in Examples 1-4 at a mass ratio of 20:1 to form the experimental groups. The last group of sand was a mixed sand mixture with potted clay at a mass ratio of 10:1 to form the control group. The test column was a 60cm long PVC pipe with an inner diameter of 10cm. 80-mesh fine gauze was laid at the bottom of the PVC pipe, and then the sand sample used for the test was evenly filled into the PVC pipe, with each pipe filled with 40cm of sand or mixed sand. Each PVC pipe was filled with a 2 mmol / L diammonium phosphate solution from the top, with a total of 1 L of solution flowing through the soil sample within the pipe. The volume of solution flowing through was measured every 10 minutes, and the infiltration time was recorded when more than 85% of the solution had flowed out (Table 1). In the blank control group, the sandy soil was entirely composed of sand particles, resulting in a rapid solution flow rate, a total infiltration time of 30 minutes, and the largest total infiltration volume of 975.57 mL, indicating a rapid loss of water within just half an hour. In the experimental group, after using the sandy soil water-retaining amendments prepared in Examples 1-4, the total infiltration time of the sandy soil was significantly extended to 150, 120, 180, and 150 minutes, respectively. Potted clay is often used to improve soil quality. Referring to the results of the control group, it can be seen that potted clay can also extend the total infiltration time to 90 minutes, demonstrating a certain water retention capacity. In summary, comparing the total infiltration time results, the sandy soil water-retaining amendments prepared in Examples 1-4 all significantly reduced the infiltration rate and effectively improved soil water retention.

[0051] Table 1 Comparison of infiltration time and total infiltration volume.

[0052]

[0053] After 4 hours, the soil samples were poured out of the PVC pipe, and 1g × 3 samples were taken from each group and placed in sample bottles to test their moisture content. The soil samples were then placed in cardboard boxes, leveled, and the soil layer was approximately 5cm thick. The boxes were then placed in a forced-air drying oven at 40℃, and samples were taken at 24 and 48 hours to measure the moisture content of the bottom layer. As shown in Table 2, the blank control group sandy soil lost almost all its moisture in a warm and well-ventilated environment, with the bottom soil moisture content less than 2% after 24 hours and close to 0 after 48 hours. The soil improved with potted clay had a bottom soil moisture content of 2.61% after 24 hours, but only 0.67% after 48 hours. The experimental groups, after using the sandy soil water-retaining improvement materials prepared in Examples 1-4, maintained a bottom soil moisture content of over 5% after 24 hours and over 1.5% after 48 hours. The sandy soil improved with the sandy soil water-retaining improvement material prepared in Example 3 still maintained a 48-hour moisture content of 5.73%. The results above demonstrate that the soil water retention improvement materials prepared in Examples 1-4 can significantly reduce the rate of soil moisture loss in high-temperature and ventilated environments, and effectively improve soil water retention.

[0054] Table 2 Comparison of Soil Moisture Content Changes in Soil Samples

[0055]

[0056]

[0057] The soil samples thoroughly soaked in diammonium phosphate solution were divided into two portions. One portion was analyzed using the KCl extraction-indophenol blue colorimetric method to determine the ammonium nitrogen content, while the other portion was analyzed using the NaHCO3 method to determine the available phosphorus content. The ammonium nitrogen and available phosphorus contents retained in each group of soil samples were calculated. Table 3 shows that the leaching solution of the blank control group sandy soil had the highest total ammonium nitrogen and available phosphorus content. The sandy soil water-retaining improvement materials prepared in Examples 1-4 and the sandy soil treated with potted clay showed significant reductions in total ammonium nitrogen in their leaching solutions, decreasing by 38.3%, 46.7%, 44.1%, 45.5%, and 63.5%, respectively. The ammonium nitrogen content retained in these soil samples was higher than that in the blank control group sandy soil. The available phosphorus content in the leachate of the sandy soil water-retention amendments prepared in Examples 1-4 and the sandy soil treated with potted clay all showed significant reductions, decreasing by 33.4%, 43.5%, 31.8%, 38.7%, and 44.0%, respectively. The available phosphorus content in these soil samples was higher than that in the blank control group. It should be noted that the proportion of potted clay was twice that of the sandy soil water-retention amendments prepared in Examples 1-4, therefore its total leached ammonium nitrogen content was relatively low. The sandy soil treated with the sandy soil water-retention amendments prepared in Examples 1-4 showed increases in both ammonium nitrogen and available phosphorus content, increasing by more than 35% and 30% respectively compared to the control group, indicating that the sandy soil amendments prepared in Examples 1-4 have good fertilizer retention capacity.

[0058] Table 3 Comparison of Leached Ammonium Nitrogen Content and Leached Available Phosphorus Content in Soil Samples

[0059]

[0060]

[0061] The experimental results show that the sandy soil amendment materials prepared in Examples 1-4 have outstanding water retention capacity, surpassing that of potted clay. In conventional soil improvement implementation plans, clay is typically added to degraded soil to enhance its water and fertilizer retention capacity. In experimental tests, the higher the amount of clay applied, the better the improvement in water and fertilizer retention capacity. However, in actual sandy soil improvement, due to the harsh environment of sandy soil, clay is either easily dispersed by strong winds due to its small particle size, or its high adsorption capacity and small interparticle gaps easily cause soil compaction, resulting in poor aeration and water permeability, and thus the improvement effect is less than satisfactory. After the sandy soil amendment materials prepared in Examples 1-4 were laid as a film on a marble slab, the peel strength of the film was measured. Figure 6As shown, the peel strength of the membranes is higher than that of the transparent tape, indicating that the sand-modified material can withstand strong winds and will not disperse into the air, causing particulate pollution. Before water loss, the sand-modified material composites prepared in Examples 1-4 are similar to glue; after gradual water loss, they form porous membranes with pore sizes of approximately 1-5 micrometers. Figures 7-10 Small molecules such as air, water, and inorganic salts can easily pass through, maintaining a certain level of aeration and water permeability in the soil.

[0062] Most soil conditioners also suffer from loss and ineffectiveness, making them difficult to reuse multiple times and requiring frequent replenishment to achieve the desired soil improvement effect. The sand used for testing was taken from the Ulan Buh Desert in Wuhai City, Inner Mongolia. After air-drying, the sand was divided into five groups. Four groups were mixed with the heteropoly compound / PVA composite soil conditioner prepared in Examples 1-4 at a mass ratio of 20:1 to form the experimental group. The last group was a mixed sand with potted clay at a mass ratio of 10:1 to form the control group, resulting in sand treated with the soil conditioner. The sand treated with the soil conditioner underwent a 40°C, 48-hour water loss test, followed by thorough watering and rinsing, and the water retention effect of the soil conditioner was tested again. This process was repeated a second time, with the sand undergoing a 40°C, 48-hour water loss test and thorough watering and rinsing, and the water retention effect was measured again. This cycle was repeated a third and fourth time, with the sand undergoing a 40°C, 48-hour water loss test and thorough watering and rinsing, and the results are as follows: Figure 11 As shown, watering the sandy soil easily washes away the clay soil from the potted plant, causing the soil's water infiltration rate to gradually increase and its water retention rate to gradually decrease. The sandy soil amendments prepared in Examples 1-4 all showed better resistance to watering than the potted clay soil. In particular, the sandy soil amendment prepared in Example 1 showed relatively low water infiltration rate even after repeated watering, indicating that the sandy soil amendment prepared in Example 1 has a good long-term water retention effect.

[0063] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. The application of a heteropoly compound / PVA composite in water retention in sandy soil, characterized in that, The heteropoly compound / PVA complex is a gel-like substance composed of a Standberg-type heteropoly compound and / or its derivatives, PVA, and water, wherein the Standberg-type heteropoly compound and / or its derivatives account for 20-60% of the dry weight of PVA, and the mass ratio of PVA to water is 1:7-21; The Standberg-type heteropoly compound is an inorganic polyoxometalate, and its anionic molecular formula is [X₂M₅O₂]. 21～23 ] n- Where X = P, Se, or S, M = Mo or W, and the cation is NH4. + Na + and K + At least one of them; The Standberg-type heteropoly compound derivative is an organic-inorganic hybrid compound formed by replacing some heteroatoms and / or oxygen atoms in the Standberg-type heteropoly compound anion with organic ligands. The organic ligand substituent is at least one of -HPO3, -CH3PO3, -C2H5PO3, -O2CCH2PO3 and NH3C2H4PO3.

2. The application of the heteropoly compound / PVA composite according to claim 1 in water retention of sandy soil, characterized in that, The Standberg-type heteropoly compound or its derivative is K4[Se2Mo5O] 21 ]、(NH4)4[S2Mo5O 21 ]、K4[(HPO3)2Mo5O 23 ] and (NH4)6[P2Mo5O 23 At least one of the following.

3. The application of the heteropoly compound / PVA composite according to claim 1 in water retention of sandy soil, characterized in that, The average molecular weight of the PVA is 100,000 to 150,000, and the degree of alcoholysis is ≥98%.

4. The application of the heteropoly compound / PVA composite according to claim 1 in water retention of sandy soil, characterized in that, The Standberg-type heteropoly compound and / or its derivatives comprise 40-60% of the dry weight of PVA, and the mass ratio of PVA to water is 1:10-21.

5. The application of the heteropoly compound / PVA composite according to claim 1 in water retention of sandy soil, characterized in that, The heteropoly compound / PVA complex is a gel-like substance prepared by mixing an aqueous solution of a Standberg-type heteropoly compound and / or its derivatives with an aqueous solution of PVA at a volume ratio of 1:1 to 1:9.5, wherein the concentration of the aqueous solution of the Standberg-type heteropoly compound and / or its derivatives is 0.12 to 0.4 g / mL, and the mass percentage of PVA in the aqueous solution is 5% to 15%.

6. The application of the heteropoly compound / PVA composite according to claim 5 in water retention of sandy soil, characterized in that, The heteropoly compound / PVA complex was obtained by mixing an aqueous solution of a Standberg-type heteropoly compound and / or its derivatives with an aqueous solution of PVA at room temperature and then aging for 2 to 4 weeks.

7. The application of the heteropoly compound / PVA composite according to claim 5 in water retention of sandy soil, characterized in that, The heteropoly compound / PVA complex is a gel-like substance prepared by mixing an aqueous solution of a Standberg-type heteropoly compound and / or its derivatives with an aqueous solution of PVA in a volume ratio of 1:9 to 9.

5.

8. The application of the heteropoly compound / PVA composite according to claim 5 in water retention of sandy soil, characterized in that, The PVA aqueous solution contains 5-10% PVA by mass. The concentration of the aqueous solution of the Standberg-type heteropoly compound and / or its derivatives is 0.3–0.4 g / mL.

9. The application of the heteropoly compound / PVA composite according to claim 1 in water retention of sandy soil, characterized in that, Specifically, the heteropoly compound / PVA complex and sand are mixed evenly at a mass ratio of 1:10 to 1:20.

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