A composite material for desert soil improvement, its preparation method and application

Abstract

This invention belongs to the fields of desertification control, soil improvement, and agricultural water conservation technology, and specifically relates to a composite soil improvement material for desertification, its preparation method, and its application. The material is made from the following components in parts by weight: 70-92 parts of undisturbed desert sand, 5-25 parts of gradient composite clay minerals, 0.01-0.15 parts of composite water-retaining agent, 0.01-0.05 parts of NPK compound fertilizer, and 0.1-0.5 parts of phosphorus-rich organic fertilizer. The gradient composite clay minerals are prepared by mixing coarse-grained framework clay (0.05-0.25 mm), medium-grained filling clay (0.005-0.05 mm), and fine-grained cementing clay (<0.005 mm). The composite water-retaining agent is prepared by mixing SAP superabsorbent polymer, xanthan gum, and polyacrylamide. This invention utilizes the gradient gradation mechanism of the gradient composite clay minerals and the synergistic water-retaining mechanism of the composite water-retaining agent to construct a stable aggregate structure and a sustainable water-retaining system in situ within desert sand.

Description

Technical Field

[0001] This invention belongs to the fields of desertification control, soil improvement and agricultural water conservation technology, and specifically relates to a composite material for desert soil improvement, its preparation method and application. Background Technology

[0002] Desert soils are predominantly aeolian sandy soils with a simple particle size distribution. Studies show that the median particle size of surface soils in the Taklamakan Desert is mainly distributed between 90 μm and 225 μm, consisting mainly of fine and very fine sand, with extremely low or even complete absence of clay (particle size <0.002 mm) and silt (0.002~0.05 mm) content. This extreme particle size distribution results in a lack of fine-grained components necessary for the formation of soil aggregates in desert sand. The desert sand has a loose structure, high porosity, and poor water and fertilizer retention capacity, making it difficult for crops to achieve stable and high yields.

[0003] The desert amendments commonly used in existing technologies mainly include (1) desert amendments that physically mix high-molecular water-retaining agents (such as polyacrylamide PAM, sodium carboxymethyl cellulose CMC, etc.) with desert sand. Although this type of amendment can delay water loss through the water absorption-release effect of the water-retaining agent, it cannot change the surface properties of the sand particles themselves or the structural defects between particles. Once the water is released, the sand particles return to a loose state. Even if multiple water-retaining agents are mixed, different components may produce antagonistic effects due to competition for water absorption, entanglement of polymer chains, or mismatch in degradation rates, which will destroy their respective effective network structures and make it difficult to achieve a stable connection of water retention effects. Therefore, this type of method does not have the function of stabilizing the soil aggregate structure and the ability to continuously retain water.

[0004] (2) Desert amendments using a mixture of coal gangue powder and clay minerals such as bentonite with desert sand. For example, patent announcement number CN114830991B discloses a sea buckthorn planting structure, which includes a desert amendment made of desert sand, coal gangue powder, PAM / CMC bentonite, or expanded vermiculite. Although this type of amendment can utilize the binding properties of clay minerals such as bentonite to make some sand particles form a physical aggregate state, the resulting aggregate structure is not a water-stable aggregate structure with cohesive force. When encountering alternating wet and dry conditions, the physical aggregate state of these water-stable aggregate structures without cohesive force is easily redispersed and disintegrated, causing the originally adsorbed water-retaining agent to seep away along with the fine particles. The fundamental reason is that the expansion of the water-retaining agent and the shrinkage and cementation of the clay minerals lack a synergistic response mechanism. When water is absorbed, the expansion stress may damage the fragile connection, and when water is lost, the shrinkage cannot provide continuous skeletal support. As a result, the stable aggregate structure and continuous water retention cannot be achieved at the same time, and the integrated effect of structural stability and continuous water retention cannot be realized. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a composite material for desert soil improvement, its preparation method, and its application. This composite material, through the synergistic combination of gradient composite clay minerals and composite water-retaining agents, achieves a gradient gradation mechanism of coarse-grained skeleton support, medium-grained pore filling, and fine-grained surface cementation, along with a synergistic water-retention mechanism of rapid water absorption, gel water locking, and long-term water retention. This constructs a stable aggregate structure and a continuous water-retaining system in desert sand. It achieves an integrated improvement effect of water retention, fertilization, and growth promotion. Field trials show that after applying this material, peanut yield increased by 787% compared to pure desert soil, field water holding capacity increased to more than 6 times that of pure sand, and water holding time was extended to more than 10 times that of pure sand. This invention eliminates the need for grinding desert sand, all materials are widely available and inexpensive, and the process involves only physical mixing, making it suitable for large-scale industrial application in desert soil improvement in extremely arid regions.

[0006] To address the aforementioned technical problems, this invention provides a desert soil improvement composite material, which is composed of the following components in parts by weight: 70-92 parts of undisturbed desert sand; 5-25 parts of gradient composite clay minerals; 0.01-0.15 parts of composite water-retaining agent; 0.01-0.05 parts of NPK compound fertilizer; and 0.1-0.5 parts of phosphorus-rich organic fertilizer. Among them, the unprocessed desert sand is natural desert sand that has not undergone any physical grinding treatment, with a particle size distribution in the range of 0.05mm to 0.5mm, accounting for ≥95%; The gradient composite clay mineral is prepared by grading coarse-grained skeleton clay with a particle size of 0.05 mm to 0.25 mm, medium-grained filler clay with a particle size of 0.005 mm to 0.05 mm, and fine-grained cementing clay with a particle size of <0.005 mm. The fine-grained cementing clay with a single layer thickness of 1 to 100 nm is preferred. The specific surface area of ​​this fine-grained cementing clay can reach 800 m² / g, and it has extremely strong adsorption and cementing capacity. The composite water-retaining agent is prepared by mixing SAP superabsorbent polymer, xanthan gum and polyacrylamide, wherein the mass ratio of SAP superabsorbent polymer, xanthan gum and polyacrylamide PAM is 4~7:2~4:1~3.

[0007] The gradient composite clay minerals and composite water-retaining agents in this desert soil improvement material form a composite functional structure with three levels of complementary particle sizes and synergistic effects of the three water-retaining agents. At the complementary particle size level, the coarse-grained clay minerals (0.05mm~0.25mm) are similar in size to desert sand particles. After being uniformly dispersed, they form a skeleton network with the sand particles to support the aggregates and increase their mechanical stability. The medium-grained clay minerals (0.005mm~0.05mm) fill the large pores of the skeleton network, transforming the original non-capillary pores of the desert sand into capillary pores, significantly reducing the porosity of the desert sand, reducing deep water infiltration, and greatly improving water retention capacity. The fine-grained clay minerals (<0.005mm) have a large specific surface area and abundant surface charge. Through surface charge and hydrogen bonding, they can tightly bind sand, coarse clay, and medium clay into a whole, forming a stable clay bridging that firmly connects loose particles to form water-stable aggregates. In terms of water retention and synergistic effects, SAP possesses a three-dimensional cross-linked network structure, enabling it to rapidly absorb hundreds or even thousands of times its own weight in water through hydration, forming a gel. Its water absorption and retention capacity far surpasses that of CMC and PAM. SAP's framework is a moderately cross-linked network structure, where nutrient molecules within the resin molecules can be temporarily immobilized, delaying nutrient release. It combines the functions of water retention and slow-release fertilizer, and thanks to its ultra-high water absorption rate, it rapidly absorbs large amounts of water during irrigation or rainfall to form a hydrogel, achieving rapid and substantial water absorption. Xanthan gum is a natural polysaccharide polymer produced by Xanthomonas auricula-judae fermentation, exhibiting extremely high pseudoplasticity and viscosity stability. Upon contact with water, xanthan gum forms a viscous gel network, not only locking in moisture but, more importantly, its strong adhesive force firmly binds sand and clay mineral particles together, significantly enhancing the water stability and wind erosion resistance of the aggregates. Furthermore, xanthan gum forms a protective film on the particle surface under drought conditions, reducing water evaporation. Therefore, through its high adhesion and gel network, it locks the hydrogel within the aggregates, preventing rapid water infiltration under gravity and achieving gel water retention. Polyacrylamide (PAM) is a linear, water-soluble polymer with numerous amide groups on its molecular chain. It can adsorb onto the surface of sand and clay minerals through hydrogen bonding and electrostatic interactions, forming a durable water-retaining layer. PAM is characterized by its long-lasting water-retaining effect. After the short-term high-efficiency water-retaining effects of SAP and xanthan gum decay, PAM can maintain the basic soil moisture content over a longer timescale, achieving long-term water retention. These three water-retaining agents form a relay-style water-retention chain over time, from rapid water absorption to gel water retention and then to long-term water retention.

[0008] Furthermore, the negative surface charge of fine-grained clay minerals interacts with the hydroxyl and amide groups on the molecular chains of xanthan gum and polyacrylamide (PAM) through hydrogen bonding and electrostatic interactions to form a clay-polymer composite gel. This composite gel exhibits significantly better water retention and structural stability than single clay or single water-retaining agent. Simultaneously, the composite gel network encapsulates NPK compound fertilizer and phosphorus-rich organic fertilizer, enabling the slow release of nutrients.

[0009] Preferably, the mass ratio of coarse-grained skeleton clay, medium-grained filling clay, and fine-grained cementing clay is 2~4:3~5:2~4. This ensures that the modified aggregates have mechanical strength to resist external damage (skeleton support), water stability to resist water dispersion (cementing effect), and can also transform ineffective seepage pores into effective water-holding pores (filling effect).

[0010] Preferably, when the mass ratio of coarse-grained skeleton clay, medium-grained filling clay and fine-grained cementing clay is 3:4:3, the modified aggregates exhibit the best mechanical strength (skeleton support) against external force damage, ensure water stability against water dispersion (cementation), and effectively transform ineffective seepage pores into effective water-holding pores (filling).

[0011] Preferably, the coarse-grained skeleton clay is one or more of coal gangue, fly ash, or shale tailings; the medium-grained filling clay is one or more of bentonite, attapulgite, or kaolin tailings; and the fine-grained cementing clay is one or more of bentonite ultrafine powder, illite powder, or kaolin nanoparticles. This combination not only provides relatively common, readily available, and inexpensive materials, but also results in improved aggregates that exhibit better performance in terms of mechanical strength against external forces (skeleton support), water stability against water dispersion (cementation), and the transformation of ineffective seepage pores into effective water-holding pores (filling effect).

[0012] Bentonite and attapulgite have good water absorption and swelling properties as well as cation exchange capacity, which can further lock in moisture and nutrients.

[0013] Preferably, the mass ratio of SAP superabsorbent polymer, xanthan gum, and polyacrylamide is 5:3:2, which can form a relay-style water retention chain from rapid water absorption to gel water locking and then to long-term water retention over time.

[0014] Preferably, the SAP superabsorbent resin is sodium polyacrylate or acrylic-acrylamide copolymer, with a particle size of 0.1 mm to 0.5 mm and a water absorption ratio of 300 g / g to 500 g / g; the viscosity of a 1% aqueous solution of xanthan gum is ≥1200 mPa·s; and the polyacrylamide is anionic with a molecular weight of 8 million to 12 million.

[0015] This invention also provides a method for preparing a composite material for desert soil improvement, comprising the following steps: Industrial waste clay mineral raw materials are crushed, ground and screened to obtain coarse-grained skeleton clay with a particle size of 0.05mm~0.25mm, medium-grained filling clay with a particle size of 0.005~0.05mm and fine-grained cemented clay with a particle size of <0.005mm, thus preparing gradient composite clay minerals. SAP superabsorbent polymer, xanthan gum and polyacrylamide are mixed to obtain a composite water-retaining agent; Natural wind-blown sand is sieved to remove impurities, thus obtaining the original desert sand. Gradient composite clay minerals, composite water-retaining agent, undisturbed desert sand, NPK compound fertilizer, and phosphorus-rich organic fertilizer are mixed evenly according to their weight proportions to obtain desert soil improvement materials.

[0016] The present invention also provides the application of a desert soil-modifying composite material in crop cultivation in arid regions.

[0017] Preferably, the desert soil improvement composite material is applied to a depth of 0-30cm below the surface of the desert sand, and then irrigated until the soil moisture content of the desert sand field is 70%-100% of the field water holding capacity. The field water holding capacity of the desert sand field is increased to more than 5 times that of pure sand, and the water holding time is extended to more than 8 times that of pure sand.

[0018] Preferably, the crop is peanut or wheat, and the crop yield after applying desert soil improvement compound material is more than 500% higher than that of unimproved pure desert.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: 0. The gradient composite clay minerals and composite water-retaining agents in the desert soil improvement composite material provided by this invention form a three-level complementary particle size distribution (coarse-grained skeleton support, medium-grained pore filling, and fine-grained surface cementation) and a synergistic composite functional structure of three water-retaining agents in the original desert sand. Among them, in the particle size complementarity level, the coarse-grained clay minerals (0.05~0.25mm) are comparable in size to the desert sand particles. After being uniformly dispersed, they together with the sand particles form an aggregate skeleton network, which plays a skeleton support role and enhances agglomeration. The medium-sized clay minerals (0.005~0.05mm) fill the large pores in the skeleton network, transforming non-capillary pores into capillary pores, reducing porosity, reducing deep water leakage, and improving water retention capacity; the fine-sized clay minerals (<0.005mm) have a large specific surface area and abundant surface charge, which can bind sand, coarse and medium-sized clay into a tight bond through surface charge and hydrogen bonding, forming a stable clay bridging, and firmly connecting loose particles into water-stable aggregates. In terms of water retention synergy, SAP, with its ultra-high water absorption ratio, rapidly absorbs large amounts of water to form a hydrogel during irrigation or rainfall, achieving rapid and large-volume water absorption; Xanthan gum, with its high adhesion and gel network, locks in water while firmly binding sand and clay mineral particles, enhancing the water stability and wind erosion resistance of the aggregates, and locking the hydrogel inside the aggregates to prevent rapid water infiltration, thus achieving gel water locking; PAM, with its persistent adsorption capacity of molecular chains, continues to maintain the basic soil moisture even after SAP and xanthan gum gradually lose water, achieving long-term water retention. The three water-retaining agents form a relay-style water-retaining chain over time, from rapid water absorption and gelation to long-term water retention. This constructs a five-stage segmented synergistic and continuous water-retaining system that includes rapid water absorption, gelation, long-term water retention, slow release, and long-term maintenance, significantly improving the continuous water-retaining capacity. At the same time, the negative charge on the surface of fine-grained clay minerals and the hydroxyl and amide groups on xanthan gum and PAM molecular chains form a clay-polymer composite gel through hydrogen bonding and electrostatic interactions. Its water-retaining capacity and structural stability are significantly better than those of single clay or single water-retaining agent, achieving an integrated effect of structural stability and continuous water retention.

[0020] 2. The raw materials for preparing the gradient composite clay minerals in the desert soil improvement composite material provided in this invention are: coal gangue, fly ash, bentonite tailings, kaolin tailings, shale tailings, etc. These are all low-value waste or tailings or waste generated during industrial mining or mineral processing, with no excessive heavy metal content. Their sources are extremely wide, and their costs are extremely low, even zero. Through simple crushing and grading, resource utilization for waste-to-land conversion is achieved, reducing the overall cost by more than 60% compared to using commercial clay, demonstrating outstanding practicality. Furthermore, the gradient composite clay minerals are weighed and physically mixed with unprocessed desert sand, NPK compound fertilizer, phosphorus-rich organic fertilizer, and a composite water-retaining agent composed of SAP superabsorbent resin, xanthan gum, and polyacrylamide, according to requirements, to prepare the desert soil improvement composite material. The preparation process of this desert soil improvement composite material is simple, without any chemical reactions, high-temperature calcination, or microbial cultivation steps. The entire preparation process only requires simple mechanical stirring equipment, resulting in extremely low overall production costs, making it particularly suitable for large-scale mechanized promotion in the desert regions of Northwest China.

[0021] 3. After application, the desert soil improvement composite material provided by this invention increases the water holding capacity of desert sandy fields to more than 6 times that of pure sand, extends the water holding time to more than 10 times that of pure sand, increases the wheat emergence rate by more than 35 percentage points compared with pure desert, increases peanut yield by more than 500% compared with pure desert, increases soil organic matter content to more than 9.0 g / kg, and maintains a stable supply of available nitrogen, phosphorus and potassium throughout the entire crop growth period. Detailed Implementation

[0022] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. Unless otherwise specified, the experimental methods described in the embodiments of the present invention are conventional methods.

[0023] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as in Examples 1 to 3, preferred embodiments are described to avoid redundancy. However, this invention is not limited to these, but can be implemented in other ways within the scope of the technical solutions defined in the appended claims. All raw materials, reagents, instruments, and equipment used in the following embodiments of this invention can be purchased commercially or prepared using existing methods.

[0024] The following detailed description, in conjunction with embodiments of the present invention, provides a clear and complete illustration of the technical solutions presented in these embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0025] The coarse-grained skeleton clay provided in this invention is one or more of coal gangue, fly ash, or shale tailings; the medium-grained filling clay is one or more of bentonite, attapulgite, or kaolin tailings; and the fine-grained cementing clay is one or more of bentonite ultrafine powder, illite powder, or kaolin nanopowder.

[0026] Sodium polyacrylate or acrylic-acrylamide copolymer SAP superabsorbent polymers with a particle size of 0.1 mm to 0.5 mm and a water absorption ratio of 300 g / g to 500 g / g can be used to prepare composite water-retaining agents. In the following examples, sodium polyacrylate superabsorbent polymers with a particle size of 0.15 to 0.3 mm and a water absorption ratio of 450 g / g are preferred. The sodium polyacrylate superabsorbent polymers SAP are purchased from commercially available industrial-grade products.

[0027] Xanthan gum: food grade, viscosity ≥1200 mPa·s (1% aqueous solution), purchased from commercially available industrial grade products; PAM: Anionic polyacrylamide, molecular weight 8-12 million, purchased from commercially available industrial-grade products. Example 1 The desert soil improvement composite material is made from the following components by weight: 90 parts original desert sand; 8 parts gradient composite clay minerals; 0.06 parts composite water-retaining agent; 0.03 parts NPK compound fertilizer; 0.2 parts phosphorus-rich organic fertilizer; based on 1 cubic meter of desert sand (approximately 1500 kg), this consists of 1350 kg of original desert sand; 120 kg of gradient composite clay minerals; 0.9 kg of composite water-retaining agent; 0.45 kg of NPK compound fertilizer; and 3.0 kg of phosphorus-rich organic fertilizer.

[0028] The preparation method of desert soil improvement composite material includes the following steps: Coal gangue (waste gangue from coal mining) and fly ash (waste from coal-fired power plants) are mixed at a mass ratio of 2:1, crushed in a crusher, ground in a ball mill, and then passed through 60-mesh and 300-mesh sieves. The middle portion between the two sieves is collected to obtain coarse-grained skeleton clay with a particle size of 0.05~0.25mm. Bentonite tailings (bentonite ore beneficiation tailings) and kaolinite tailings (kaolinite ore beneficiation tailings) are mixed at a mass ratio of 3:1, ball-milled, and then passed through a 300-mesh sieve. The undersize portion is collected to obtain medium-grained filling clay with a particle size of 0.005~0.05mm. Bentonite tailings (bentonite ore beneficiation tailings) are then ultrafine ball-milled to D...90 <5μm, fine-grained cemented clay with a particle size <0.005mm was obtained. Coarse-grained skeleton clay, medium-grained filling clay and fine-grained cemented clay were mixed in a mass ratio of 3:4:3 to obtain gradient composite clay minerals. Add SAP superabsorbent polymer, xanthan gum and anionic polyacrylamide in a mass ratio of 5:3:2 to a mixer and mix at low speed for 10 minutes to obtain a composite water-retaining agent. Natural wind-blown sand is passed through a 2mm sieve to remove impurities, thus obtaining the original desert sand. Add 90 parts of unprocessed desert sand, 8 parts of gradient composite clay minerals, 0.06 parts of composite water-retaining agent, 0.03 parts of NPK compound fertilizer, and 2 parts of phosphorus-rich organic fertilizer to a mixer and mix at 60 rpm for 15 minutes to obtain desert soil improvement material.

[0029] Example 2 The difference between Example 2 and Example 1 is that coarse-grained skeleton clay, medium-grained filler clay and fine-grained cemented clay are mixed in a mass ratio of 2:3:2, and SAP superabsorbent resin, xanthan gum and polyacrylamide (PAM) are mixed in a mass ratio of 4:2:1.

[0030] Example 3 The difference between Example 3 and Example 1 is that coarse-grained skeleton clay, medium-grained filler clay and fine-grained cemented clay are mixed in a mass ratio of 4:5:4, and SAP superabsorbent resin, xanthan gum and polyacrylamide (PAM) are mixed in a mass ratio of 7:4:3.

[0031] Example 4 The difference between Example 4 and Example 1 is that the clay used is coarse-grained skeleton clay, medium-grained filling clay, and fine-grained cemented clay.

[0032] Coal gangue and shale tailings are mixed at a mass ratio of 2:1, crushed by a crusher, ground by a ball mill, and then passed through 60-mesh and 300-mesh sieves. The middle part between the two sieves is taken to obtain coarse-grained skeleton clay with a particle size of 0.05~0.25mm. Bentonite tailings and attapulgite were mixed at a mass ratio of 3:1, ball-milled, and passed through a 300-mesh sieve. The undersize portion was taken to obtain medium-sized filler clay with a particle size of 0.005~0.05mm. illite is obtained by ultra-fine ball milling to D 90 <5μm, resulting in fine-grained cemented clay with a particle size of <0.005mm.

[0033] Example 5 The difference between Example 5 and Example 1 is that it uses coarse-grained skeleton clay, medium-grained filling clay, and fine-grained cemented clay.

[0034] Coal gangue, fly ash and shale tailings are mixed, crushed by a crusher and ground by a ball mill, and then passed through 60-mesh and 300-mesh sieves. The middle part between the two sieves is taken to obtain coarse-grained skeleton clay with a particle size of 0.05~0.25mm. Bentonite tailings, kaolin tailings and attapulgite are mixed, ball-milled and passed through a 300-mesh sieve. The undersize portion is taken to obtain medium-sized filler clay with a particle size of 0.005~0.05mm. Bentonite, illite, and kaolin were ball-milled to D... 90 <5μm, resulting in fine-grained cemented clay with a particle size of <0.005mm.

[0035] Example 6 The difference between Example 6 and Example 1 is that the clay used is coarse-grained skeleton clay, medium-grained filling clay, and fine-grained cemented clay.

[0036] After being crushed by a crusher and ground by a ball mill, the coal gangue is passed through 60-mesh and 300-mesh sieves. The middle part between the two sieves is taken to obtain coarse-grained skeleton clay with a particle size of 0.05~0.25mm. Bentonite tailings are ball-milled and passed through a 300-mesh sieve. The undersize portion is taken to obtain medium-sized filler clay with a particle size of 0.005~0.05mm. Bentonite and kaolin were ball-milled to D. 90 <5μm, resulting in fine-grained cemented clay with a particle size of <0.005mm.

[0037] Example 7 The difference between Example 7 and Example 1 is that the desert soil improvement composite material is made from the following components in parts by weight: 70 parts of undisturbed desert sand; 5 parts of gradient composite clay minerals; 0.01 parts of composite water-retaining agent; 0.01 parts of NPK compound fertilizer; 0.1 parts of phosphorus-rich organic fertilizer; based on approximately 1500 kg of desert sand per cubic meter, this equates to 1398 kg of undisturbed desert sand; 99.84 kg of gradient composite clay minerals; 0.20 kg of composite water-retaining agent; 0.20 kg of NPK compound fertilizer; and 2 kg of phosphorus-rich organic fertilizer.

[0038] Example 8 The difference between Example 8 and Example 1 is that the desert soil improvement composite material is made from the following components in parts by weight: 92 parts of undisturbed desert sand; 25 parts of gradient composite clay minerals; 0.15 parts of composite water-retaining agent; 0.05 parts of NPK compound fertilizer; 0.5 parts of phosphorus-rich organic fertilizer; based on approximately 1500 kg of desert sand per cubic meter, this equates to 1172 kg of undisturbed desert sand; 318 kg of gradient composite clay minerals; 1.9 kg of composite water-retaining agent; 0.64 kg of NPK compound fertilizer; and 6.4 kg of phosphorus-rich organic fertilizer.

[0039] Example 9 The difference between Example 9 and Example 1 is that 8 parts of gradient composite clay minerals are replaced with 5 parts.

[0040] Example 10 The difference between Example 10 and Example 1 is that 8 parts of gradient composite clay minerals were replaced with 12 parts.

[0041] Example 11 The difference between Example 11 and Example 1 is that 8 parts of gradient composite clay minerals are replaced with 20 parts.

[0042] Example 12 The difference between Example 12 and Example 1 is that 8 parts of gradient composite clay minerals were replaced with 25 parts.

[0043] Comparative Example 1 pure desert sand Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that the gradient composite clay minerals were replaced with coal gangue powder with a particle size of 0.05~0.25mm, and the composite water-retaining agent was replaced with SAP.

[0044] The desert soil improvement composite material is made from the following components by weight: 90 parts unprocessed desert sand; 8 parts coal gangue powder with a particle size of 0.05~0.25mm; 0.06 parts SAP; 0.03 parts NPK compound fertilizer; 2 parts phosphorus-rich organic fertilizer; based on 1 cubic meter of desert sand (approximately 1500kg), the composition is: 1350kg unprocessed desert sand; 120kg coal gangue powder; 0.9kg SAP; 0.45kg NPK compound fertilizer; 3.0kg phosphorus-rich organic fertilizer.

[0045] The preparation method of desert soil improvement composite material includes the following steps: After crushing the coal gangue (waste gangue from coal mining) with a crusher and grinding it with a ball mill, it is passed through 60-mesh and 300-mesh sieves. The middle part between the two sieves is taken to obtain coal gangue powder with a particle size of 0.05~0.25mm. Natural wind-blown sand is passed through a 2mm sieve to remove impurities, thus obtaining the original desert sand. Add 90 parts of unprocessed desert sand, 8 parts of coal gangue powder, 0.06 parts of SAP, 0.03 parts of NPK compound fertilizer, and 2 parts of phosphorus-rich organic fertilizer to a mixer and mix at 60 rpm for 15 minutes to obtain desert soil improvement material.

[0046] Comparative Example 3 The only difference between Comparative Example 3 and Example 1 is that 8 parts of composite clay minerals were replaced with a mixture of 4 parts of coarse-grained skeleton clay and 4 parts of medium-grained filler clay.

[0047] The desert soil improvement composite material is made from the following components by weight: 90 parts original desert sand; 8 parts composite clay minerals; 0.06 parts composite water-retaining agent; 0.03 parts NPK compound fertilizer; 2 parts phosphorus-rich organic fertilizer; based on 1 cubic meter of desert sand (approximately 1500 kg), this is equivalent to 1350 kg of original desert sand; 120 kg of composite clay minerals; 0.9 kg of composite water-retaining agent; 0.45 kg of NPK compound fertilizer; and 3.0 kg of phosphorus-rich organic fertilizer.

[0048] The preparation method of desert soil improvement composite material includes the following steps: Coal gangue (waste gangue from coal mining) and fly ash (waste from coal-fired power plants) are mixed at a mass ratio of 2:1, crushed by a crusher, ground by a ball mill, and then passed through 60-mesh and 300-mesh sieves. The middle portion between the two sieves is taken to obtain coarse-grained skeleton clay with a particle size of 0.05~0.25mm. Bentonite tailings (bentonite ore beneficiation tailings) and kaolin tailings (kaolin ore beneficiation tailings) are mixed at a mass ratio of 3:1, ball-milled, and then passed through a 300-mesh sieve. The undersize portion is taken to obtain medium-grained filler clay with a particle size of 0.005~0.05mm. A composite clay mineral is prepared by mixing 4 parts coarse-grained skeleton clay and 4 parts medium-grained filler clay. The composite water-retaining agent is obtained by mixing SAP superabsorbent resin, xanthan gum and anionic polyacrylamide in a mass ratio of 5:3:2 in a mixer at low speed for 10 minutes.

[0049] Natural wind-blown sand is passed through a 2mm sieve to remove impurities, thus obtaining the original desert sand. Add 90 parts of unprocessed desert sand, 8 parts of coal gangue powder, 0.06 parts of SAP, 0.03 parts of NPK compound fertilizer, and 2 parts of phosphorus-rich organic fertilizer to a mixer and mix at 60 rpm for 15 minutes to obtain desert soil improvement material.

[0050] The desert soil-modifying composite materials prepared in Examples 1 to 12 above can all be used in the experimental field on the southern edge of the Taklamakan Desert. Now, the desert soil-modifying composite materials prepared in Example 1 are preferred and compared with the desert soil-modifying composite materials given in Comparative Examples 1 to 3 in a comparative experiment.

[0051] In an experimental field on the southern edge of the Taklamakan Desert, the desert soil improvement composite material prepared in Example 1 and the desert soil improvement composite materials given in Comparative Examples 1 to 3 were each used to treat an area of ​​20 square meters, with three replicates. Peanut variety Yihua No. 1 was planted. The experimental results are as follows: Table 1 shows the experimental results obtained by improving the desert soil composite amendment material prepared in Example 1 and the desert soil composite amendment materials given in Comparative Examples 1 to 3 under the same conditions in an experimental field on the southern edge of the Taklamakan Desert. As shown in Table 1, the peanut yield of Comparative Example 3 increased by approximately 50% compared to Comparative Example 2, demonstrating that the introduction of medium-grained filling clay significantly enhanced the integrity of the aggregate structure. Example 1 further increased the peanut yield by approximately 36% compared to Comparative Example 3, and the content of water-stable aggregates jumped from 15.2% to 24.8%, proving that the introduction of fine-grained cementing clay qualitatively improved the stability and water-holding capacity of the aggregates.

[0052] Comparative Example 4 The only difference between Comparative Example 4 and Example 1 is that 0.06 parts of composite water-retaining agent were replaced with 0.06 parts of SAP.

[0053] Comparative Example 5 The only difference between Comparative Example 5 and Example 1 is that 0.06 parts of the composite water-retaining agent were replaced with 0.06 parts of PAM.

[0054] Comparative Example 6 The only difference between Comparative Example 6 and Example 1 is that 0.06 parts of the composite water-retaining agent were replaced with 0.06 parts of a mixture of SAP and PAM in a mass ratio of 1:1.

[0055] The desert soil-modifying composite materials prepared in Examples 1 to 12 above can all be used in the experimental field on the southern edge of the Taklamakan Desert. Now, the desert soil-modifying composite materials prepared in Example 1 are preferred and compared with the desert soil-modifying composite materials given in Comparative Examples 4 to 6 in a comparative experiment.

[0056] In an experimental field on the southern edge of the Taklamakan Desert, the desert soil improvement composite material prepared in Example 1 and the desert soil improvement composite materials given in Comparative Examples 4 to 6 were each used to treat an area of ​​20 square meters, with three replicates. Peanut variety Yihua No. 1 was planted. The experimental results are as follows: Table 2 shows the experimental results obtained by improving the desert soil composite improvement material prepared in Example 1 and the desert soil composite improvement materials given in Comparative Examples 4 to 6 under the same conditions in the experimental field on the southern edge of the Taklamakan Desert.

[0057] As shown in Table 2, the desert soil-modifying composite material prepared in Example 1 exhibited significantly better water retention and final yield than the desert soil-modifying composite materials prepared in Comparative Examples 4 to 6 at all time points. Particularly noteworthy is that at 7 days, the water content of the desert soil-modifying composite material prepared in Comparative Example 1 had decreased to near-pure sand levels, while the water content of the desert soil-modifying composite material prepared in Example 1 remained at 19.6%, more than three times that of Comparative Example 1. This demonstrates that the rapid water absorption, gelation, and long-term water retention relay chain formed by the three water-retaining agents over time produces a significant synergistic effect, which cannot be achieved by any single water-retaining agent or simple combination.

[0058] Comparative Example 7 The desert soil improvement compound material is made from the following components by weight: 90 parts pure desert sand and 0.03 parts NPK compound fertilizer; 0.2 parts phosphorus-rich organic fertilizer.

[0059] Comparative Example 8 The only difference between Comparative Example 8 and Example 1 is that the desert soil improvement composite material is made from the following components in parts by weight: 90 parts of unprocessed desert sand; 2.5 parts of gradient composite clay minerals; 0.06 parts of composite water-retaining agent; 0.03 parts of NPK compound fertilizer; 0.2 parts of phosphorus-rich organic fertilizer; based on approximately 1500 kg of desert sand per cubic meter, this equates to 1455 kg of unprocessed desert sand; 40.42 kg of gradient composite clay minerals; 0.97 kg of composite water-retaining agent; 0.49 kg of NPK compound fertilizer; and 3.2 kg of phosphorus-rich organic fertilizer.

[0060] The desert soil-modifying composite materials prepared in Examples 1 to 12 above can all be used in experimental fields on the southern edge of the Taklamakan Desert. Now, the desert soil-modifying composite materials prepared in Examples 1, 9 to 12 are preferred, and the desert soil-modifying composite materials given in Comparative Examples 7 to 8 are used in a field application control experiment in the desert oasis transition zone on the southern edge of the Taklamakan Desert (7 treatments were set up, 1 mu for each treatment).

[0061] In June 2025, the land was prepared, and the improvement material was applied to the surface layer at a depth of 0-30cm. Peanut Yihua No. 1 was then sown, and various indicators were measured during the seedling stage, flowering and pegging stage, pod-setting stage, and maturity stage.

[0062] Table 3 shows the results of various indicators measured during the land preparation in June 2025, when the improvement material was applied to the surface layer at a depth of 0-30cm, peanut "Yihua No. 1" was planted, and peanuts were sown.

[0063] As shown in Table 3, Example 11 achieved an optimal yield of 315.8 kg / mu, representing a yield increase of 787%. Example 12 showed a slight decrease in yield because the excessive clay addition led to slight soil compaction. This indicates that the gradient composite clay minerals of the present invention have an optimal addition range (5 parts to 25 parts). Beyond this range, the effect no longer improves and may even decrease, which also indirectly proves the inventiveness of the precise proportioning range of the present invention.

[0064] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A composite material for improving desert soil, characterized in that, This desert soil improvement composite material is made from the following components in parts by weight: 70-92 parts of original desert sand; 5-25 parts of gradient composite clay minerals; 0.01-0.15 parts of composite water-retaining agent; 0.01-0.05 parts of NPK compound fertilizer; and 0.1-0.5 parts of phosphorus-rich organic fertilizer. Among them, the unprocessed desert sand is natural desert sand that has not undergone any physical grinding treatment, with a particle size distribution in the range of 0.05mm to 0.5mm, accounting for ≥95%; The gradient composite clay mineral is prepared by grading coarse-grained skeleton clay with a particle size of 0.05 mm to 0.25 mm, medium-grained filler clay with a particle size of 0.005 mm to 0.05 mm, and fine-grained cemented clay with a particle size of <0.005 mm. The composite water-retaining agent is prepared by mixing SAP superabsorbent polymer, xanthan gum and polyacrylamide, wherein the mass ratio of SAP superabsorbent polymer, xanthan gum and polyacrylamide is 4~7:2~4:1~3.

2. The desert soil improvement composite material according to claim 1, characterized in that, The mass ratio of coarse-grained skeleton clay, medium-grained filling clay and fine-grained cemented clay is 2~4:3~5:2~4.

3. The desert soil improvement composite material according to claim 2, characterized in that, The mass ratio of coarse-grained skeleton clay, medium-grained filling clay and fine-grained cemented clay is 3:4:

3.

4. The desert soil improvement composite material according to claim 1, characterized in that, The coarse-grained skeleton clay is one or more of coal gangue, fly ash, or shale tailings; the medium-grained filler clay is one or more of bentonite, attapulgite, or kaolin tailings; and the fine-grained cementing clay is one or more of bentonite ultrafine powder, illite powder, or kaolin nanopowder.

5. The desert soil improvement composite material according to claim 1, characterized in that, The mass ratio of SAP superabsorbent polymer, xanthan gum, and polyacrylamide is 5:3:

2.

6. The desert soil improvement composite material according to claim 1, characterized in that, The SAP superabsorbent polymer is sodium polyacrylate or acrylic-acrylamide copolymer, with a particle size of 0.1 mm to 0.5 mm and a water absorption ratio of 300 g / g to 500 g / g; the viscosity of a 1% aqueous solution of xanthan gum is ≥1200 mPa·s; the polyacrylamide is anionic, with a molecular weight of 8 million to 12 million.

7. The method for preparing the desert soil improvement composite material according to any one of claims 1 to 6, characterized in that, Includes the following steps: Industrial waste clay mineral raw materials are crushed, ground and screened to obtain coarse-grained skeleton clay with a particle size of 0.05mm~0.25mm, medium-grained filling clay with a particle size of 0.005~0.05mm and fine-grained cemented clay with a particle size of <0.005mm, thus preparing gradient composite clay minerals. SAP superabsorbent polymer, xanthan gum and polyacrylamide are mixed to obtain a composite water-retaining agent; Natural wind-blown sand is sieved to remove impurities, thus obtaining the original desert sand. Gradient composite clay minerals, composite water-retaining agent, undisturbed desert sand, NPK compound fertilizer, and phosphorus-rich organic fertilizer are mixed evenly according to their weight proportions to obtain desert soil improvement materials.

8. The application of the desert soil improvement composite material according to claim 1 in crop cultivation in arid areas.

9. The application according to claim 8, characterized in that, The desert soil improvement composite material is applied to a depth of 0-30cm below the surface of the desert sand, and then irrigated until the soil moisture content of the desert sand field is 70%-100% of the field water holding capacity. The field water holding capacity of the desert sand field is increased to more than 5 times that of pure sand, and the water holding time is extended to more than 8 times that of pure sand.

10. The application according to claim 9, characterized in that, The crops were peanuts or wheat. After applying desert soil improvement materials, the crop yield increased by more than 500% compared with the unimproved pure desert.

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