A composite microsphere material of silica gel-gellan gum-potassium humate hydrogel based on coal gasification coarse slag and its application.

Abstract

This invention discloses a composite microsphere material of coal gasification coarse slag based on silica gel-gellan gum-potassium humate hydrogel and its application, belonging to the field of solid waste utilization and agricultural materials. Using coal gasification coarse slag as raw material, the inert crystalline silicon is converted into highly active soluble silicon through an alkali calcination-acid leaching process, and a silica gel is prepared. The silica gel dispersion is then mixed with a gellan gum solution, and spherical microparticles are formed in an oil-phase medium using a droplet molding method. Finally, these microparticles are impregnated in a potassium humate solution and composited through ionic crosslinking and physical embedding to obtain a dark brown spherical composite microsphere material. This material exhibits a three-dimensional network porous structure, excellent mechanical properties, and good water retention, realizing the high-value utilization of coal gasification coarse slag. It combines silicon replenishment, water retention, and growth promotion, and has good prospects for agricultural application.

Description

Technical Field

[0001] This invention relates to the field of solid waste utilization and agricultural materials, specifically to a composite microsphere material of coal gasification coarse slag based on silica gel-gellan gum-potassium humate hydrogel and its application. Background Technology

[0002] The modern coal chemical industry is developing steadily, and the clean conversion of coal gasification generates a large amount of coal gasification coarse slag industrial solid waste. This solid waste is rich in mineral components such as SiO2 and has good potential for preparing functional materials. However, the development of related high-value utilization technologies is slow, and its application is mostly limited to low-end fields such as building material production and site backfilling. There is a serious lack of high-value-added utilization channels in agriculture. Currently, a large amount of coal gasification coarse slag is disposed of by open-air stockpiling, which not only occupies land and generates dust pollution, but also allows the soluble salts and heavy metals it contains to leach into the soil and groundwater with rainwater, causing many ecological and environmental problems. Therefore, it is urgent to improve the level of large-scale, harmless, and resource-based utilization of this solid waste.

[0003] Against this backdrop, the development of coal-based solid waste-based soil amendment materials has become a research hotspot, but existing technologies still have significant shortcomings. Existing technology, such as Chinese patent (CN119410372A), discloses a soil amendment prepared from coal-based solid waste and its preparation method. However, this process suffers from cumbersome procedures and low production efficiency, requiring multiple independent steps including magnetic separation and crushing, inorganic salt heating modification, biochar acid washing and calcination, and multi-component mixing and ball milling, resulting in a long preparation cycle. Furthermore, this process is relatively crude in its resource utilization of coal-based solid waste, failing to fully exploit the high-value conversion potential of active components in the solid waste. The resulting amendment relies solely on ion exchange for soil desalination, exhibiting a limited function and lacking additional properties such as water retention and slow nutrient release. Simultaneously, the reagents used in the preparation process, such as calcium chloride, ferric chloride, and nitric acid solution, generate salt- and acid-containing wastewater, placing a heavy burden on environmental treatment. Moreover, the final powder product is prone to dust generation and leaching during application, resulting in insufficient long-term amendment effects and hindering the large-scale application of this technology.

[0004] Coal gasification slag is rich in SiO2. To fully exploit the utilization value of this component and develop it into a functional raw material for improving soil and enhancing soil fertility, this invention involves alkaline calcination and acid leaching to extract silicon from the coal gasification slag, transforming inert crystalline silicon into highly active soluble silicon, and then preparing a silicon-based gel material. This not only enables the high-value utilization of large quantities of coal-based solid waste but also provides the soil with effective silicon and water that can be absorbed and utilized by plants. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a composite microsphere material of coal gasification coarse slag based on silica gel-gellan gum-potassium humate hydrogel and its application. Targeting the silica component in coal gasification coarse slag, the inert crystalline silicon in the raw material is converted into highly active soluble silicon through alkaline calcination and acid leaching, thereby preparing a silica-based gel material. This process not only achieves high-value resource utilization of bulk coal-based solid waste but also continuously replenishes the soil with plant-absorbable silicon, effectively increasing soil silicon content, improving soil quality, enhancing soil fertility, and simultaneously improving soil water retention. Details are as follows: In a first aspect, the present invention discloses a composite microsphere material based on coal gasification coarse slag silica gel-gellan gum-potassium humate hydrogel. The composite microsphere material comprises three active components: silica gel, gellan gum, and potassium humate. The silica gel is obtained from coal gasification coarse slag through an alkaline fusion activation-acid leaching extraction process. The three active components, silica gel, gellan gum, and potassium humate, are compositely formed into spherical particles through ionic crosslinking and physical encapsulation.

[0006] Secondly, this invention provides a composite microsphere material of coal gasification coarse slag-gellan gum-potassium humate hydrogel for replenishing soil silicon nutrients, the preparation method of which includes: Step 1: The coarse coal gasification slag is first coarsely crushed in a ball mill, and then finely ground in a mortar and pestle to screen the coarse coal gasification slag particles with a mesh size of 100. Step 2: Mix anhydrous potassium carbonate with the coal gasification coarse slag screened above, perform alkaline melting and calcination in a muffle furnace, and then finely grind it through a 100-mesh sieve in a mortar to obtain clinker; Step 3: Immerse the above-mentioned material in sulfuric acid solution, centrifuge to obtain the supernatant, and allow the gel to stand; wash the gel with deionized water, purify and adjust the pH of the system to 5-7, centrifuge to remove the supernatant to obtain silica gel; add deionized water to the silica gel and stir evenly to obtain silica gel dispersion. Step 4: Prepare the gellan gum solution using a microwave oven. Add the silica gel dispersion to the gellan gum solution and stir until homogeneous to obtain a silica-based mixture. Use a syringe to draw up the silica-based mixture and use a constant flow pump to drop it into a petri dish containing silicone oil. Then remove it and wash it with deionized water until there is no oil residue on the surface to obtain silica gel-gellan gum microspheres. Step 5: Prepare a potassium humate solution. Immerse the above-mentioned silica gel-gellan gum microspheres in the potassium humate solution, then remove them and wash them twice with deionized water to remove the unadsorbed free potassium humate on the surface, thus obtaining a coking coal gasification slag-based silica gel-gellan gum-potassium humate hydrogel composite microsphere material, abbreviated as silica gel-gellan gum-potassium humate microspheres.

[0007] Furthermore, in step 1, the power of the mechanical grinding equipment for pre-treated coal gasification coarse slag is 0.75kW, the rotation speed is 70-670r / min, and the grinding time is 1-2h.

[0008] Furthermore, in step 2, calcination is carried out in an air atmosphere using a muffle furnace for 2 hours at a temperature of 900°C, and the mass ratio of alkali residue from alkali fusion calcination is 1:1.

[0009] Furthermore, in step 3, the centrifuge used has a rotation speed of 12000 r / min and a time of 10 min; the sulfuric acid solution has a concentration of 6 mol / L; and the silica gel dispersion concentration is 100 g / L.

[0010] Furthermore, in step 3, the sulfuric acid solution is prepared as follows: Take 33.12 mL of sulfuric acid stock solution (95-98 wt%, take the intermediate value of 96.5 wt% to prepare the solution) and dissolve it in 66.88 mL of deionized water to obtain a 6 mol / L sulfuric acid solution; the silica gel dispersion is prepared as follows: Take 5 g of silica gel in a beaker, add 50 mL of deionized water, and stir evenly to obtain a 100 g / L silica gel dispersion.

[0011] Furthermore, in step 4, the microwave oven used has a rated frequency of 50Hz, a rated input power of 1150W, and a microwave output power of 700W; the constant flow pump has a flow rate of 4mL / min; the syringe has a flow rate of 15mL; the gellan gum solution has a flow rate of 25g / L; the height of the silicone oil in the petri dish is 1cm, and the height of the droplet is 2cm.

[0012] Furthermore, in step 4, the preparation method of the gellan gum solution is as follows: Take 2.5g of gellan gum into a beaker, add 100mL of deionized water, heat it in a microwave oven on high for 10s, remove the beaker and shake it for 5s, then put the beaker back into the microwave oven. Repeat the above steps a total of three times to obtain a gellan gum solution of 25g / L.

[0013] Furthermore, in step 5, the potassium humate solution used is 20 g / L, and the soaking time is 15 min.

[0014] Furthermore, in step 5, the potassium humate solution is prepared as follows: Dissolve 2g of potassium humate in 100mL of deionized water in a beaker and stir until homogeneous to obtain a 20g / L potassium humate solution.

[0015] Furthermore, the prepared material is dark brown in color and has a macroscopic spherical shape with a diameter of approximately 4 mm. The contact angle between the material surface and water droplets in air is approximately 0°, exhibiting superhydrophilic properties. It demonstrates excellent water retention; after standing in air with a relative humidity of 10-15% and a temperature of 23.1-27.3℃ for 2 hours, the water retention rate still reaches 37.66%, and the water loss rate slows down thereafter, indicating good water retention. The material also exhibits excellent mechanical properties, with a peak stress of 16.5 kPa at 25% strain. It shows no significant breakage during compression, strong structural stability, and can remain stable in soil.

[0016] Thirdly, the heavy metal leaching concentration of the raw material coal gasification slag used in this patent was determined by a third-party testing institution according to the standards "Determination of 32 Elements in Water by Inductively Coupled Plasma Atomic Emission Spectrometry" (HJ 776-2015) and "Determination of Mercury, Arsenic, Selenium, Bismuth and Antimony in Solid Waste by Microwave Digestion / Atomic Fluorescence Method" (HJ 702-2014). The results were compared with the allowable leaching concentration limits specified in the "Identification Standard for Hazardous Waste: Leaching Toxicity Identification" (GB 5085.3-2007). The test results show that the leaching concentrations of major heavy metal elements such as Pb, Cr, Cd, Hg, and As in the coal gasification slag are all lower than the national standard limits, indicating good environmental safety, meeting the requirements for use as soil amendment materials, and posing no risk of secondary pollution to soil and water bodies.

[0017] Fourthly, this invention utilizes bulk industrial solid waste—coal gasification coarse slag—as raw material. Based on its resource utilization potential and combined with the hydrophilic and water-retaining properties and slow-release nutrient properties of hydrogel materials, a coal gasification coarse slag-gellan gum-potassium humate hydrogel composite microsphere material for replenishing soil silicon nutrients is prepared. This material can optimize the soil moisture environment, alleviate drought stress, enhance fertility, and promote crop growth while supplementing silicon nutrients, demonstrating good application prospects and economic benefits.

[0018] Fifthly, the present invention provides the application of the composite microsphere material in soil improvement, wherein the composite microsphere material is applied to the target soil to increase the effective silicon content of the soil, improve the soil water retention capacity, and / or promote plant seed germination and seedling growth.

[0019] In the hydroponic experiment, the silica gel-gellan gum-potassium humate microsphere group of this invention exhibited the fastest seed germination rate and the best growth. After 11 days of hydroponics, the bud and root lengths of 5 pak choi seedlings were measured, with an average bud length of approximately 2.78 cm and an average root length of approximately 4.89 cm. In the pot experiment in saline-alkali soil, the silica gel-gellan gum-potassium humate microsphere group of this invention effectively enhanced the plant's resistance to adverse conditions and prevented lodging. After 15 days of pot cultivation, the bud and root lengths of 5 pak choi seedlings were measured, with an average bud length of approximately 3.17 cm and an average root length of approximately 2.96 cm. After 15 days of pot cultivation, the available silicon content in the soil increased from the initial 295.06 mg / kg to 310.43 mg / kg.

[0020] Furthermore, it can be used to improve the plant's resistance to saline-alkali stress and / or prevent plant lodging.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention, for the first time, uses coal gasification coarse slag as raw material. Through alkaline calcination and acid leaching for silicon extraction, the inert crystalline silicon is converted into highly active soluble silicon, which is then prepared into a silicon gel. This gel is then combined with gellan gum and potassium humate to form a composite microsphere material with silicon replenishment, water retention, and growth promotion functions. Compared with existing coal-based solid waste soil conditioners that rely solely on ion exchange for desalination and have limited functionality, this invention achieves high-value conversion and targeted utilization of silicon components in coal gasification coarse slag. While replenishing the soil with effective silicon nutrients, it synergistically exerts water retention and growth promotion effects, significantly improving the functional integration.

[0022] 2. This invention uses a droplet molding method to prepare spherical microparticles. Relying on the low-temperature self-gelling properties of gellan gum, and combined with impregnation and loading modification methods, the three active components of silica gel, gellan gum, and potassium humate are combined into one. The resulting microsphere material has a three-dimensional network porous structure and excellent mechanical properties (peak stress reaches 16.5 kPa at 25% compressive strain, and there is no breakage during compression). It can maintain structural integrity in soil, overcoming the technical defects of traditional powder amendments, such as easy dust generation, easy leaching and loss, and poor long-term effectiveness during application.

[0023] 3. The composite microsphere material prepared by this invention has superhydrophilic surface properties (water droplet contact angle approaches 0°, spreading and penetration time ≤0.02s) and good water retention performance (after standing for 2 hours under environmental conditions of 23.1-27.3℃ and 10-15% relative humidity, the water retention rate still reaches 37.66%, and the water loss rate tends to be slow in the later stage), which can realize the slow release supply of soil moisture, effectively alleviate drought stress, and is superior to the shortcomings of existing coal-based solid waste amendments that do not have water retention function.

[0024] 4. The composite microsphere material prepared by this invention can slowly release available silicon. After a 15-day pot experiment in saline-alkali soil, the available silicon content in the soil increased from the initial 295.06 mg / kg to 310.43 mg / kg, which can continuously improve the availability of silicon in the soil. The results of hydroponic and pot experiments both show that this material can significantly promote the germination of Chinese cabbage seeds and the growth of seedlings. Under saline-alkali stress conditions, it can effectively enhance the plant's resistance and prevent lodging. The overall growth-promoting effect is better than that of the commercial water-retaining agent group and the blank control group.

[0025] 5. The crude coal gasification residue used in this invention has been tested and found that the leaching concentrations of major heavy metal elements such as Pb, Cr, Cd, Hg, and As are all lower than the limits specified in GB 5085.3-2007. It has good environmental safety, a lighter burden of waste liquid treatment, and avoids the risk of chloride salt pollution caused by the introduction of reagents such as calcium chloride and ferric chloride. It meets the requirements of green and sustainable solid waste resource utilization.

[0026] 6. This invention transforms bulk coal-based solid waste coal gasification slag into high-value-added agricultural functional materials. The preparation process is relatively simple, the steps are continuous, the raw materials are widely available and the cost is low. It is conducive to promoting the large-scale disposal of coal chemical solid waste and the coordinated development of agricultural soil improvement technology, and has good economic and social benefits. Attached Figure Description

[0027] Figure 1 The image shows the actual silica gel prepared in Example 1 of this invention; where a is the nascent silica gel and b is the silica gel after water washing and purification.

[0028] Figure 2 The images show X-ray diffraction patterns of the coal gasification coarse slag, clinker, and silica gel in Example 1; where a is the coal gasification coarse slag, b is the clinker, and c is the silica gel.

[0029] Figure 3 The image shows a photograph of the silica gel-gellan gum-potassium humate microspheres prepared in Example 1.

[0030] Figure 4 The infrared spectrum of the silica gel-gellan gum-potassium humate microspheres prepared in Example 1 is shown.

[0031] Figure 5 The image shows a scanning electron microscope (SEM) image of the silica gel-gellan gum-potassium humate microspheres prepared in Example 1; where a is a scale bar of 200 μm, b is a scale bar of 100 μm, and c is a scale bar of 50 μm.

[0032] Figure 6 Stress-strain diagram of the silica gel-gellan gum-potassium humate microspheres prepared in Example 1.

[0033] Figure 7 The image shows the contact angle test results between the surface of the silica gel-gellan gum-potassium humate microspheres prepared in Example 1 and a water droplet.

[0034] Figure 8 The graph shows the variation of effective silicon leaching rate and actual concentration in calcined coal gasification coarse slag under different alkali-slag mass ratios; where a is the effective silicon leaching rate and b is the actual effective silicon concentration.

[0035] Figure 9 The graph shows the variation of effective silicon leaching rate and actual concentration in calcined coal gasification slag at different calcination temperatures; where a is the effective silicon leaching rate and b is the actual effective silicon concentration.

[0036] Figure 10 The graph shows the variation of effective silicon leaching rate and actual concentration in calcined coal gasification slag under different calcination times; where a is the effective silicon leaching rate and b is the actual effective silicon concentration.

[0037] Figure 11The graph shows the change in water retention rate of silica gel-gellan gum-potassium humate microspheres over time.

[0038] Figure 12 The images show the dynamic recordings of the effects of three hydroponic experiments on the germination and seedling growth of Chinese cabbage seeds under normal water conditions; where af represents the dynamic recordings on days 1, 3, 5, 7, 9, and 11 of cultivation, respectively.

[0039] Figure 13 This is a comparison chart of the length of seedlings of bok choy in three hydroponic experiments.

[0040] Figure 14 The images show the dynamic recordings of the effects of three pot experiments on the germination and seedling growth of Chinese cabbage seeds under saline-alkali soil conditions; where ah represents the dynamic recordings on days 1, 3, 5, 7, 9, 11, 13, and 15 of cultivation, respectively.

[0041] Figure 15 This is a comparison chart of the sprout lengths of three groups of potted bok choy seedlings. Detailed Implementation

[0042] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] Table 1 below lists the sources and characteristics of the raw materials / reagents used in this invention.

[0044] Table 1. Sources and characteristics of experimental materials / reagents

[0045] Example 1 This embodiment provides a composite hydrogel microsphere material based on coal gasification coarse slag silica gel-gellan gum-potassium humate hydrogel for replenishing soil silicon nutrients and moisture. This material is prepared by the following method: Step 1: The coarse coal gasification slag is first coarsely crushed in a ball mill, and then finely ground in a mortar and pestle to screen out 100-mesh coarse coal gasification slag particles. The ball mill has a power of 0.75kW, a rotation speed of 400rpm, and a grinding time of 1h.

[0046] Step 2: Mix anhydrous potassium carbonate with the coal gasification coarse slag screened above at a mass ratio of 1:1, and activate it by alkaline calcination in a muffle furnace under air atmosphere for 2 hours at a calcination temperature of 900℃; then grind it finely in a mortar and pass it through a 100-mesh sieve to obtain clinker.

[0047] Step 3: Prepare a 6 mol / L sulfuric acid solution: Dissolve 33.12 mL of stock sulfuric acid solution (95-98 wt%, use the intermediate value of 96.5 wt% to prepare the solution) in 66.88 mL of deionized water to obtain a 6 mol / L sulfuric acid solution; weigh 5 g of the clinker from Step 2 into a beaker, add 15 mL of deionized water, then add 16 mL of the above 6 mol / L sulfuric acid solution, stir for 30 min, and centrifuge at 12000 r / min for 10 min. After n, take the supernatant and let it stand at room temperature for 4 hours to obtain silica gel; transfer the silica gel to a beaker, add 200 mL of deionized water and stir for 30 min, centrifuge again and discard the supernatant, repeat the above water washing and centrifugation steps until the supernatant shows a pH of 5-7 when tested with pH paper, and you can get the water-washed purified silica gel; prepare a 100 g / L silica gel dispersion: take 5 g of water-washed silica gel in a beaker, add 50 mL of deionized water, stir evenly to obtain a 100 g / L silica gel dispersion.

[0048] Figure 1 The images shown are actual photos of the silica gel (a) prepared in Example 1 of this invention and the silica gel (b) after washing and purification.

[0049] Figure 2 The image shows the X-ray diffraction patterns of the coarse coal gasification slag (a), clinker (b), and silica gel (c) in Example 1 of this invention. From... Figure 2 As can be seen from this, compared with the crisscross quartz-type SiO2 standard card (card number: 51-1381), the silicon component in the coarse slag of coal gasification mainly exists in a stable crystalline form with strong chemical inertness and low reactivity, making it difficult to utilize directly; from Figure 2 b shows that after activation by alkali fusion calcination at 900℃ for 2 hours with potassium carbonate, the original SiO2 crystalline phase in the X-ray diffraction pattern of the clinker disappeared, and an active aluminosilicate phase mainly composed of Al2(SiO4)O was generated, laying the foundation for subsequent acid leaching and silicon extraction; from Figure 2 As can be seen from c, the silicon gel obtained by further acid leaching treatment exhibits obvious diffuse broad peaks in the 20-30° range in its X-ray diffraction pattern, without sharp crystalline diffraction peaks. This confirms that the active aluminosilicate phase is decomposed during the acid leaching process, and finally an amorphous silicon-based material with amorphous SiO2 as the main phase is formed, realizing the transformation from inert crystalline silicon to highly active amorphous silicon.

[0050] Step 4: Prepare a 25 g / L gellan gum solution: Take 2.5 g of gellan gum in a beaker, add 100 mL of deionized water, and heat in a microwave oven on high for 10 seconds. The microwave oven's rated frequency is 50 Hz, rated input power is 1150 W, and microwave output power is 700 W. Remove the beaker and shake for 5 seconds, then put the beaker back into the microwave oven. Repeat the above steps three times to obtain a 25 g / L gellan gum solution. Take 8 mL of gellan gum in a beaker, add 20 mL of silica gel dispersion, and stir for 15 minutes to obtain a silica-based mixture. Use a 15 mL syringe to draw up the mixture and use a constant flow pump to drop it into a petri dish containing silicone oil at a flow rate of 4 mL / min. The height of the silicone oil in the petri dish is 1 cm, and the height of the droplet is 2 cm. Then, remove the droplet and wash it with deionized water until there is no oil residue on the surface to obtain silica gel-gellan gum microspheres.

[0051] Step 5: The method for preparing a 20 g / L potassium humate solution is as follows: Dissolve 2 g of potassium humate in 100 mL of deionized water in a beaker and stir until homogeneous to obtain a 20 g / L potassium humate solution; Immerse the silica gel-gellan gum microspheres prepared in Step 4 in the 20 g / L potassium humate solution for 15 min, then remove them and wash them twice with deionized water to remove the unadsorbed free potassium humate on the surface, thus obtaining silica gel-gellan gum-potassium humate microspheres.

[0052] Figure 3 The image shown is a physical picture of the silica gel-gellan gum-potassium humate microspheres prepared in Example 1 of this invention. As can be seen from the image, the silica gel-gellan gum-potassium humate microspheres prepared in this example are dark brown and spherical in shape. Measurements show that their diameter is approximately 4.07 mm, and their apparent volume V can be calculated. b =0.0353cm 3 The mass m of the aerogel was weighed using an electronic analytical balance. b =0.039g.

[0053] Figure 4 The image shown is the infrared spectrum of the silica gel-gellan gum-potassium humate microspheres prepared in Example 1 of this invention. Comparing the infrared spectra of the silica gel powder and the microspheres, it can be found that both have an infrared spectrum at 1052 cm⁻¹. -1 A distinct characteristic absorption peak appeared at the point, which corresponds to the stretching vibration of the Si-O-Si bond, proving that the silica gel has been successfully composited into the silica gel-gellan gum-potassium humate microspheres.

[0054] Figure 5 The image shown is a scanning electron microscope (SEM) image of the silica gel-gellan gum-potassium humate microspheres prepared in Example 1 of this invention at different scales; wherein, Figure 5 a (scale bar 200 μm) represents the overall morphology at low magnification. Figure 5 b (scale bar 100μm) represents a medium-multiple pore structure. Figure 5 c (scale bar 50μm) represents high-magnification surface details. For example... Figure 5 As shown in Figure a, at a scale of 200 μm, the gel microspheres exhibit a three-dimensional network morphology composed of stacked layered structures, with abundant internal pores; as shown in Figure a. Figure 5 As shown in b, at a 100 μm scale, the interconnectedness of the pores can be further observed, with thin and continuous pore walls; as... Figure 5 As shown in c, under a 50μm scale, the smooth surface of the sheet and the intact macroporous structure inside can be clearly observed, providing ample space for the transport of water and nutrients.

[0055] Figure 6 The figure shows the stress-strain diagram of the silica gel-gellan gum-potassium humate microspheres prepared in Example 1 of the present invention. The stress of the material increases nonlinearly with strain, reaching a peak stress of about 16.5 kPa at about 25% strain. The material did not show obvious breakage or damage during the entire compression process, and has both good flexibility and mechanical stability, which can ensure its long-term stable use in soil.

[0056] A video optical contact angle meter was used to dynamically test the wetting properties of the material surface, recording the spreading behavior and contact angle changes of water droplets after they contacted the material surface. Figure 7 As shown, water droplets begin to spread rapidly upon contact with the material surface (0s); by 0.01s, the droplets have clearly spread out, and the contact angle decreases rapidly; by 0.02s, the droplets have completely spread out and penetrated into the material, with the contact angle approaching 0°. This dynamic process demonstrates that the composite microsphere material prepared in this invention possesses excellent superhydrophilic properties, allowing water to be captured and absorbed by the material within ≤0.02s. This characteristic is mainly attributed to the abundant hydrophilic functional groups (such as silanol groups Si–OH, carboxyl groups –COOH, etc.) on the material surface and the capillary effect generated by its three-dimensional network porous structure. These two factors synergistically endow the material with extremely fast water response and transport capabilities, providing a crucial structural and performance basis for its applications in soil water retention, slow water release, and promoting crop growth in drought conditions.

[0057] Furthermore, the present invention conducts the following experiments to study the influence of important factors in the process of the present invention.

[0058] Experiment 1 In this experiment, anhydrous K2CO3 was used as the alkali-fusing calcining agent. Single-factor experiments were conducted on three process parameters: alkali-slag mass ratio, calcination temperature, and calcination time. The effective silicon dissolution was measured using an ultraviolet spectrophotometer and used as the evaluation standard to explore the influence of a single variable on the calcination effect of coal gasification coarse slag, providing a basis for the selection of optimal experimental conditions in the future.

[0059] Figure 8The figure shows the curves of effective silicon leaching rate versus actual concentration in calcined coal gasification slag under different alkali-slag mass ratios, where a represents the effective silicon leaching rate and b represents the actual effective silicon concentration. Figure 8 As can be seen from a and b, as the alkali-slag mass ratio decreases from 1.8:1 to 1:1, both the effective silicon leaching rate and the actual concentration show an upward trend, reaching a peak at 1:1; when the ratio continues to decrease to 1:2, both indicators show a significant decrease. Therefore, it can be determined that the suitable alkali-slag ratio in step 2 of Example 1 of this invention is 1:1, at which point the calcination effect of the coal gasification coarse slag is optimal, and the effective silicon leaching reaches its maximum.

[0060] Figure 9 The figure shows the curves of effective silicon leaching rate and actual concentration in calcined coal gasification slag at different calcination temperatures, where a represents the effective silicon leaching rate and b represents the effective silicon actual concentration. As the calcination temperature increases from 800℃ to 900℃, both the effective silicon leaching rate and the actual concentration show an upward trend. The leaching rate tends to stabilize after 850℃, while the actual concentration reaches its peak at 900℃. When the temperature continues to rise to 950℃, the actual concentration shows a significant decrease. Therefore, it can be determined that the suitable calcination temperature for step 2 in Example 1 of this invention is 900℃, at which point the calcination effect of the coal gasification slag is optimal, and the effective silicon leaching amount reaches its maximum.

[0061] Figure 10 The figure shows the curves of effective silicon leaching rate and actual concentration in calcined coal gasification slag under different calcination times. As the calcination time increases from 1.0 h to 2.0 h, both the effective silicon leaching rate and the actual concentration reach their peak at 2.0 h. Further extending the time to 2.5 h, both indicators decline. When the time is extended to 3.0 h, the leaching rate rebounds again, but the actual concentration does not increase significantly. Therefore, it can be determined that the suitable calcination time in step 2 of Example 1 of this invention is 2.0 h, at which point the calcination effect of the coal gasification slag is optimal, and the effective silicon leaching reaches its maximum.

[0062] In summary, repeated verification experiments were conducted on the obtained optimal conditions, confirming that when the alkali-slag mass ratio was 1:1, the calcination temperature was 900℃, and the calcination time was 2h, the crystal structure of the coal gasification coarse slag was fully destroyed and the amount of active silicon dissolved was the highest.

[0063] Experiment 2 In this experiment, the water-holding capacity of the silica gel-gellan gum-potassium humate composite hydrogel microspheres was evaluated by the water retention rate, and the potential of the material in soil moisture regulation was determined.

[0064] Experimental method: The silica gel-gellan gum-potassium humate microspheres were completely immersed in deionized water. The saturated water-absorbing samples were placed in an indoor environment with a temperature of 23.1-27.3℃ and a relative humidity of 10-15%. The mass change was recorded by weighing at regular intervals, and the water retention rate at different times was calculated to evaluate the water holding capacity of the material.

[0065] Water retention formula:

[0066] Because hydrogels have a three-dimensional cross-linked network structure, the polymer backbone undergoes severe shrinkage and collapse after drying, resulting in extremely low residual mass of the dry gel, which is negligible compared to the mass of the hydrogel in its saturated water-absorbing state. Therefore, in this experiment, the mass of the dry gel, m0, is considered to be 0 g to simplify the calculation of water retention rate. After immersing the material in deionized water for 24 hours until saturation, the material is removed from the deionized water and the surface moisture is absorbed with filter paper. The mass is recorded as m1 (unit: g). Subsequently, the material is allowed to stand at room temperature, and the mass is recorded again every 30 minutes, as m2 (unit: g).

[0067] Figure 11 The figure shows the water retention rate of silica gel-gellan gum-potassium humate gel microspheres over time. The curve generally exhibits a rapid decrease in the initial stage followed by a gradual flattening. After standing in air at a relative humidity of 10-15% and a temperature of 23.1-27.3℃ for 2 hours, the material still retained 37.66% of its water content, after which the water loss rate slowed significantly. After standing for 3 hours, the water loss curve flattened, and the water retention rate decreased slowly and gradually stabilized. This trend indicates that the material experiences rapid water loss in the initial stage, but maintains a stable water retention effect in the later stage, demonstrating good slow-release water supply capability.

[0068] In summary, the silica gel-gellan gum-potassium humate microsphere material prepared by this invention has good water retention properties.

[0069] Experiment 3 To verify the biosafety and seedling-promoting effect of the composite hydrogel microspheres prepared in this invention, a commercial water-retaining agent group, a gellan gum-potassium humate microsphere group, and the silica gel-gellan gum-potassium humate microsphere group of this invention were set up for comparison. The preparation method of the gellan gum-potassium humate microspheres (control sample) is as follows: using a 25 g / L gellan gum solution as a precursor, the solution was drawn up with a 15 mL syringe and added dropwise at a constant flow rate of 4 mL / min to dimethyl silicone oil with a liquid level of 1 cm (drop height 2 cm). After forming, the microspheres were removed, washed with deionized water until no oil residue remained on the surface, and then immersed in a 20 g / L potassium humate solution for 15 min. The free potassium humate was then removed by washing with water, thus obtaining the gellan gum-potassium humate microspheres. The remaining operating parameters were the same as steps 4 and 5 of Example 1.

[0070] Experimental conditions: Chinese cabbage was used as the test plant. Twelve seeds were placed in each petri dish. Under uniform environmental management conditions, a hydroponic experiment was conducted for 11 days. The commercial water-retaining agent group used agricultural water-retaining agent produced by Renqiu Runda Chemical Co., Ltd., whose main component is potassium polyacrylate. Two tablets were added to this group, with a total mass of 0.033g before water absorption. The gellan gum-potassium humate microsphere group had four gel microspheres added, with a total mass of 0.205g before water absorption. Similarly, the silica gel-gellan gum-potassium humate microsphere group also had four gel microspheres added, with a total mass of 0.203g before water absorption. Throughout the process, crop growth was observed and photographed regularly. After hydroponics, the germination time, bud length, and root length parameters of each group of bok choy were recorded. The culture dishes used for hydroponics were all placed in the laboratory with a relative humidity of 10-15%, a temperature of 23.1-27.3℃, and light intensity that met the photosynthetic growth requirements of the plants. During the entire culture period, 5mL of deionized water was added to each culture dish daily. No additional fertilizers, pesticides, or other human interventions were added. The soil conditioner itself provided nutrients, ensuring that the experimental conditions of each group were consistent and accurately reflecting the effect of the coal gasification coarse slag-based silica gel-gellan gum-potassium humate composite hydrogel microsphere soil conditioner on plant growth.

[0071] Figure 12 The figure shows the dynamic record of the effects of three hydroponic experiments on the germination and seedling growth of Chinese cabbage seeds under conventional water conditions (a–f represent the growth status on days 1, 3, 5, 7, 9, and 11 of cultivation, respectively; each sub-figure represents the commercial water-retaining agent group, gellan gum-potassium humate microsphere group, and silica gel-gellan gum-potassium humate microsphere group from left to right).

[0072] Figure 13 The image shows the sprout lengths of three groups of bok choy seedlings in a hydroponic experiment. From left to right, the areas within the red boxes represent the commercial water-retaining agent group, the gellan gum-potassium humate microsphere group, and the silica gel-gellan gum-potassium humate microsphere group. Figure 12 , 13It can be seen that the seeds in the commercial water-retaining agent group germinated the latest, with only a few seeds showing white sprouts on the 3rd day of cultivation. The sprout length on the 5th day was not significantly different from that on the 3rd day, and the sprout length was less than 0.1cm on the 11th day. Moreover, most seeds were moldy and rotten, resulting in the worst overall growth. The germination time of the gellan gum-potassium humate microsphere group was slightly later than that of the silica gel-gellan gum-potassium humate microsphere group. Its seeds began to show white sprouts on the 3rd day, and the seedlings were growing well on the 5th day. The sprout length was about 2.5cm and the root length was about 1cm on the 11th day, resulting in the second best overall performance. It should be noted that the moldy phenomenon in the commercial water-retaining agent group may be related to the fact that the water-retaining agent maintained excessively high humidity after absorbing water, leading to local hypoxia around the seeds. The silica gel-gellan gum-potassium humate microsphere group showed the fastest seed germination, with seeds clearly showing white sprouts on the 3rd day, and the best sprout growth on the 5th day. On the 11th day, the sprout length was about 2.8cm and the root length was about 4.9cm. There was no wilting throughout the entire culture period, and the overall performance was the best.

[0073] In summary, the silica gel-gellan gum-potassium humate microsphere material prepared by this invention has good biocompatibility and seedling-promoting effects, and can effectively promote seed germination and growth.

[0074] Experiment 4 In this experiment, the biosafety and seedling-promoting effect of silica gel-gellan gum-potassium humate microspheres were further verified through pot experiments. The method for preparing the gellan gum-potassium humate microspheres was the same as in Experiment 3, specifically as follows: steps 1-3 of Example 1 were not required; step 4 of Example 1 was adjusted to directly use a 15mL syringe to draw the prepared 25g / L gellan gum solution and drop it dropwise into a petri dish containing silicone oil using a constant flow pump. The remaining operating steps and parameters were the same as in Example 1. The prepared hydrogel material was designated as gellan gum-potassium humate microspheres.

[0075] Experimental conditions: The saline-alkali soil used in the pot experiment was sieved through a 10-mesh sieve. Chinese cabbage was used as the test plant, and a 15-day pot experiment was conducted. Ten Chinese cabbage seeds were evenly sown in each pot. The two groups of microspheres were mixed with the saline-alkali soil at a mass ratio of 1:50, potted, and planted under a unified daily management system. The potted plants were placed indoors in the laboratory with a relative humidity of 10-15%, a temperature of 23.1-27.3℃, and light intensity sufficient for photosynthetic growth. Throughout the cultivation period, except for the first day when 10 mL of water was added to maintain soil moisture, 5 mL of deionized water was added daily thereafter to maintain soil moisture within the suitable growth range. No additional fertilizers or pesticides were applied; the soil relied solely on the nutrients provided by the amendment itself and the existing nutrients in the soil, eliminating interference from external fertilizers.

[0076] The experiment was set up in three groups. Figure 14The figure shows the dynamic record of the effects of three pot experiments on the germination and seedling growth of Chinese cabbage seeds under saline-alkali soil conditions (a–h represent the growth status on days 1, 3, 5, 7, 9, 11, 13, and 15 of cultivation, respectively; each sub-figure represents the blank control group, the silica gel-gellan gum-potassium humate microsphere group, and the gellan gum-potassium humate microsphere group from left to right).

[0077] Figure 15 The image shows the sprout lengths of Chinese cabbage seedlings in three potted plant experiments. From left to right, they are: blank control group, silica gel-gellan gum-potassium humate microsphere group, and gellan gum-potassium humate microsphere group. Figure 14 , 15 It can be seen that the blank control group, without any modified materials, had the earliest seed emergence time, with seedlings appearing on the 3rd day. However, the seedlings were weak and shortest, and lodging and wilting were observed first after the 9th day, indicating poor plant stability. On the 15th day, the seedling length was approximately 2.6 cm and the root length was approximately 1.9 cm. The seed emergence time of the gellan gum-potassium humate microsphere group was synchronized with that of the silica gel-gellan gum-potassium humate microsphere group, with seedlings emerging on the 5th day. The seedling growth of both groups was better than that of the blank control group, and the seedling length was moderate. However, in the later stages of cultivation (days 13-15), some seedlings lodged, and their resistance to adverse conditions was weaker than that of the silica gel-gellan gum-potassium humate microsphere group. On day 15, the bud length was approximately 2.7 cm and the root length was approximately 1.6 cm. The emergence time of the silica gel-gellan gum-potassium humate microsphere group was slightly later than that of the blank control group, with seedlings emerging on day 5. The overall growth was good, and the plant stability and resistance to adverse conditions were the best among the three groups. On day 15, the bud length was approximately 3.2 cm and the root length was approximately 3.0 cm.

[0078] In summary, the silica gel-gellan gum-potassium humate microsphere material prepared by this invention showed the best overall performance in the pot experiment of Chinese cabbage in saline-alkali soil. The seedlings exhibited good growth, the highest values ​​for bud and root length, and the plant stability and stress resistance were also stronger than the other two groups.

[0079] Experiment 5 Available silicon is one of the functional indicators for this material to achieve soil fertility improvement, growth promotion and yield increase. In this experiment, the available silicon content in the soil and original soil leachate of the silicon gel-gellan gum-potassium humate microsphere group on the 15th day of the pot experiment was determined by the silicon molybdenum blue spectrophotometer using a UV-Vis spectrophotometer to evaluate its available silicon slow release ability.

[0080] The test results are shown in Table 2: Table 2 Results of soil available silicon content analysis

[0081] Experimental Results Analysis: As shown in Table 2, after a 15-day pot experiment, the available silicon content in the soil increased from the initial 295.06 mg / kg to 310.43 mg / kg. This indicates that the silica gel-gellan gum-potassium humate gel microspheres have a stable ability to release available silicon gradually, thus continuously improving the availability of silicon in the soil.

[0082] In summary, the silica gel-gellan gum-potassium humate microsphere material prepared by this invention can continuously increase the effective silicon content in the soil through a stable and effective silicon slow-release effect, thereby enhancing the soil fertility effect and providing key support for subsequent growth promotion and yield increase. This fully demonstrates that the material has good effective silicon slow-release ability and soil water retention potential.

Claims

1. A composite microsphere material of silica gel-gellan gum-potassium humate hydrogel based on coal gasification coarse slag, characterized in that, The composite microsphere material comprises three active components: silica gel, gellan gum, and potassium humate. The silica gel is obtained from coal gasification coarse slag through an alkaline fusion activation-acid leaching extraction process. The silica gel, gellan gum, and potassium humate are composited into spherical particles through ionic crosslinking and physical encapsulation.

2. The composite microsphere material as described in claim 1, characterized in that, The preparation method of the composite microsphere material is as follows: (1) The coarse slag from coal gasification is crushed and ground to obtain coarse slag powder with a particle size of no more than 150 μm; (2) The coarse slag powder is mixed with anhydrous potassium carbonate and then roasted at high temperature to obtain activated clinker; (3) The activated clinker is treated with sulfuric acid solution for acid leaching. After solid-liquid separation, the acid leaching solution is collected, allowed to stand and age to form silica gel, and then washed and purified with water to pH 5-7. The silica gel dispersion is then dispersed in deionized water. (4) The silica gel dispersion is mixed evenly with the gellan gum solution, and spherical microparticles are formed in the oil phase medium by droplet forming method. After washing and degreasing with water, silica gel-gellan gum composite microspheres are obtained. (5) The silica gel-gellan gel composite microspheres are immersed in an aqueous solution of potassium humate, so that potassium humate is loaded inside and / or on the surface of the microspheres. After washing with water to remove free potassium humate, the composite microsphere material is obtained.

3. The composite microsphere material according to claim 2, characterized in that, In step (2), the mass ratio of the coarse slag powder to anhydrous potassium carbonate is 1:1, the high-temperature roasting temperature is 900℃, and the roasting time is 2h.

4. The composite microsphere material according to claim 2, characterized in that, In step (3), the concentration of the sulfuric acid solution is 6 mol / L; the solid content of the silica gel dispersion is 100 g / L.

5. The composite microsphere material according to claim 2, characterized in that, In step (4), the concentration of the gellan gum solution is 25 g / L, and the volume ratio of the silica gel dispersion to the gellan gum solution is 2.5:1; the droplet forming method uses a constant flow pump to drop the mixture into silicone oil to form a droplet with a droplet height of 2 cm, and the oil phase medium is dimethyl silicone oil with a liquid level of 1 cm.

6. The composite microsphere material according to claim 2, characterized in that, In step (5), the concentration of the potassium humate aqueous solution is 20 g / L, and the immersion time is 15 min.

7. The composite microsphere material according to any one of claims 1 to 6, characterized in that, The composite microsphere material has a spherical shape with a diameter of 3-5 mm. The material surface has superhydrophilic properties, with a water droplet contact angle close to 0°. After standing for 2 hours at an environment with a temperature of 23.1-27.3℃ and a relative humidity of 10-15%, the water retention rate is 37.66%.

8. The composite microsphere material according to claim 7, characterized in that, The composite microsphere material has a three-dimensional network porous structure and a peak stress of 16.5 kPa at 25% compressive strain.

9. The application of the composite microsphere material as described in any one of claims 1-8 in soil improvement, characterized in that, The composite microsphere material is applied to the target soil to increase the effective silicon content of the soil, improve the soil water retention capacity, and / or promote plant seed germination and seedling growth.

10. The application of the composite microsphere material according to any one of claims 1-8 in soil improvement, characterized in that, Used to improve the plant's resistance to salt and alkali stress and / or prevent plant lodging.

Images