Saline-alkali soil improver combining desulfurized gypsum-urea eutectic and soybean urease as well as preparation method and application of saline-alkali soil improver

Abstract

The invention discloses a saline-alkali soil modifier combining desulfurized gypsum-urea eutectic and soybean urease as well as a preparation method and application of the saline-alkali soil modifier, and belongs to the technical field of soil modifiers. According to the saline-alkali soil improver combining the desulfurized gypsum-urea eutectic and the soybean urease, the improvement effect of the saline-alkali soil is improved through the synergistic effect of the desulfurized gypsum-urea eutectic and the soybean urease. The eutecticum can effectively reduce salt and alkaline substances in soil, and the EICP technology provides a better environment for plant growth by improving the soil structure and enhancing the soil stability. The desulfurized gypsum-urea eutectic can convert the salt in the salinized soil and effectively control the accumulation and migration of the internal salt, so that the effect of inhibiting the accumulation of the salt for a long time is achieved. The loss caused by high solubility of the urea is reduced, and the urea becomes a potential candidate material of a plant fertilizer.

Description

Technical Field

[0001] The present invention relates to the technical field of soil conditioners, and in particular to a saline-alkali soil improver utilizing a combination of desulfurized gypsum-urea eutectic and soybean urease, as well as a preparation method and application thereof. Background Art

[0002] The management of saline-alkali soil is a major ecological and agricultural problem facing arid, semi-arid, and coastal regions worldwide. Soil salinization leads to deterioration of soil structure and nutrient imbalance, severely restricting vegetation growth and ecological restoration, and even causing land degradation and food security risks. In traditional saline-alkali soil improvement technologies, gypsum-based materials can replace sodium ions (Na2+) adsorbed by soil colloids with calcium ions. + ), reducing soil alkalinity (exchangeable sodium saturation percentage, ESP), becoming one of the most widely used chemical amendments. However, the traditional single gypsum amendment has limited functions. It can only provide a calcium source, lacks the ability to regulate soil salt migration in the long term, and cannot simultaneously solve the problem of insufficient soil nitrogen. The urease-induced carbonate precipitation technology (EICP) produces carbonate (CO3) by urease-catalyzed urea decomposition. 2- ), combined with calcium ions to form calcium carbonate cement, improving soil aggregate structure and enhancing mechanical properties.

[0003] For example, the Chinese invention patent publication number CN118339970A discloses a method for preventing and reducing salt in saline-alkali land based on a high platform. The method reduces soil permeability by spraying and grouting with EICP, hindering the migration of salt from deep soil layers to the surface layer, and adopts a grouting pipe made of a strong acid cation material to adsorb sodium ions in the soil to solve the soil improvement problem of the high platform saline-alkali land. However, urea has high solubility and has technical problems such as easy loss and shortened aging in practical applications. In addition, the chloride ions in calcium chloride interfere with the absorption of other nutrients by plants in the soil, affecting the normal growth of plants and increasing construction costs and environmental loads.

[0004] Chinese invention patent publication number CN118851694A provides an ecological improvement method for saline soil roadbed fillers based on urea phosphate (EICP) technology. This method uses calcium lignin sulfonate, extracted from papermaking wastewater, as a calcium source, urea phosphate and urea as urea-based sources, and a crude soybean powder extract as urease. The EICP technology is not only environmentally friendly and significantly improves the physical and mechanical properties of saline soil, but also provides essential elements such as nitrogen and phosphorus for plant growth, creating favorable conditions for vegetation restoration. Similarly, the EICP technology in this solution also relies on an external binder, increasing operational complexity. Furthermore, urea is susceptible to nitrogen loss and ammonia volatilization pollution due to its high solubility.

[0005] In summary, developing a saline-alkali soil improver that has both engineering applicability and ecological benefits, breaking through the traditional technology's dependence on cementing fluid, and achieving a multiple combination of salt regulation, nutrient slow release and EICP reaction characteristics has become a technical problem that needs to be solved urgently. Summary of the Invention

[0006] In view of the above-mentioned defects of the prior art, in a first aspect of the present invention, a method for preparing a saline-alkali soil improver is provided, which has a convenient process, utilizes raw materials as resources, and does not require a binder, and comprises the following steps: (1) Prepare urease solution; (2) Desulfurized gypsum and urea are mixed in a certain proportion and subjected to solid phase ball milling to obtain desulfurized gypsum-urea eutectic; (3) Weigh the urease solution and desulfurized gypsum-urea eutectic in proportion and store them separately to obtain a saline-alkali soil conditioner.

[0007] Preferably, in step (1), the urease solution is prepared as follows: roasting soybeans, followed by crushing and screening to obtain soybean powder; adding the soybean powder to a PBS solution to obtain a mixed solution; stirring and centrifuging the mixed solution to remove the dregs, and taking the supernatant of the remaining liquid to obtain a urease solution.

[0008] More preferably, the baking is performed at 35-40° C. for 5-6 h.

[0009] Further preferably, the ratio of soybean powder in the mixed solution is 80-120 g / L.

[0010] Further preferably, the mixed solution is first stirred at 500-1000 rpm for 15-18 min, and then centrifuged at 3000-3500 rpm for 30-35 min to remove the dregs, and the supernatant of the remaining liquid is taken to obtain the urease solution.

[0011] Further preferably, the activity of the urease solution measured based on the conductivity method is ≥12 mm / min.

[0012] Preferably, in step (2), the molar ratio of desulfurized gypsum to urea is 1:4-6.

[0013] Preferably, in step (2), the ball-to-material ratio of the solid-phase ball milling is 4-5:1; a vertical planetary ball milling process is adopted, the ball milling reaction time is 1-1.5 h, and the ball milling speed is 500-800 rpm.

[0014] Preferably, in step (2), after the solid phase ball milling treatment is completed, the desulfurized gypsum-urea eutectic is obtained by screening and drying.

[0015] Preferably, in step (3), the components of the saline-alkali soil conditioner are as follows: 50-60 wt.% of urease solution and 40-50 wt.% of desulfurized gypsum-urea eutectic.

[0016] In a second aspect of the present invention, a saline-alkali soil improver is provided that realizes salt regulation, nutrient slow release and EICP reaction characteristics, and is prepared by the method of the first aspect of the present invention.

[0017] In a third aspect of the present invention, there is provided an application of the saline-alkali soil conditioner according to the second aspect of the present invention, comprising the following steps: S1. Evenly mixing the soil to be improved with the desulfurized gypsum-urea eutectic component to obtain a mixed soil; S2. After an interval of 1 to 2 days, spray the urease solution components onto the mixed soil to cause the EICP reaction to occur, thereby achieving the purpose of solidification and improvement.

[0018] Based on the above technical solutions, the design concept and principle of the present invention are as follows: As a byproduct of flue gas desulfurization (FGD) in coal-fired power plants, over 150 million tons of desulfurized gypsum are produced annually. However, its comprehensive utilization rate has long been below 60%. Large-scale stockpiling poses environmental risks such as land occupation and heavy metal migration, necessitating the development of high-value applications. Compared to the relatively simple composition of natural gypsum, desulfurized gypsum contains not only its primary component, CaSO4·2H2O, but also other components, such as trace elements from fly ash, which are beneficial for plant growth.

[0019] The present invention uses the above or other forms of desulfurized gypsum as raw materials, and reacts the desulfurized gypsum with urea through a solid phase ball milling process to form a eutectic compound. This eutectic has unique physical and chemical properties: on the one hand, its crystal structure can bind urea molecules, reduce the initial solubility of urea in the soil, and achieve a slow release of nitrogen (N). At the same time, it can also release SO4 2- with Na + The ion exchange effect inhibits soil salt (especially Na + ) migration and aggregation, achieving the effect of long-term control of salt accumulation; on the other hand, the Ca released after the eutectic dissolves 2+ Together with urea molecules, they can serve directly as substrates for the EICP reaction, eliminating the need for additional binder fluid. Furthermore, if the eutectic compounds derived from desulfurized gypsum, an industrial solid waste, can be applied on a large scale in saline-alkali soil amelioration, this would not only address solid waste disposal issues but also improve resource efficiency through a "waste-to-treat-harm" model. Using eutectics in large-scale projects such as roadbed treatment and slope stabilization can significantly reduce the consumption of desulfurized gypsum and traditional engineering materials (such as cement), meeting the needs of green infrastructure development.

[0020] The solid-phase ball milling process requires low equipment investment, has low production requirements, is simple to manufacture, handles large amounts of material, and is easily adaptable to industrial production. It boasts high speed, high yield, low energy consumption, high efficiency, and strong practicality. This invention provides a solid waste resource recovery method for desulfurized gypsum, an industrial byproduct, and offers excellent economic benefits.

[0021] Compared with the traditional EICP technology, the present invention does not require the addition of additional chemical cementing fluids such as calcium chloride, and the eutectic itself releases Ca 2+ (Calcium source) and urea (reaction substrate) can be improved by only two steps of "eutectic mixing + urease spraying". The construction process is also simplified compared with the traditional EICP technology. The two-step method is applied separately. Through the synergistic effect of the two, the Ca in the material is reduced. 2+ Can be combined with Na in soil + Ion exchange occurs, and the replaced Na + With SO4 in the material 2- Combined to form Na2SO4, which is soluble in water. Through irrigation or natural precipitation, sodium sulfate is discharged from the soil with water, thereby reducing the salt content in the soil and reducing the sodium adsorption ratio (SAR) of the soil, thereby improving the structure and permeability of the soil. Adding calcium-rich compounds such as desulfurized gypsum to the soil can help fix carbon dioxide by forming CaCO3 precipitation, especially under alkaline conditions. In addition, the improvement of saline-alkali soil by desulfurized gypsum is caused by a variety of biological and non-biological processes, which affect the formation and decomposition of soil organic carbon. Excessive Ca in gypsum 2+ It can enhance the absorption of organic matter into soil particles, promote soil particle aggregation, and improve the physical protection of soil organic carbon. Furthermore, the addition of materials can change the soil's pH and adjust the soil's pH value, creating a more suitable environment for the urease reaction. This allows the materials and soil to undergo a replacement reaction, allowing them to fully release calcium ions. This also ensures the activity of the urease solution, allowing it to remain active and fully bind to the released calcium ions, improving crystallization and enhancing the protective effect.

[0022] Compared with the prior art, the present invention has the following advantages and beneficial effects: The present invention provides a preparation method of a saline-alkali soil conditioner, which adopts a solid-phase ball milling process. The method utilizes raw materials as resources, does not require a binder, and has the advantages of being convenient in process and facilitating large-scale production.

[0023] The present invention provides a saline-alkali soil conditioner, which improves the improvement effect of saline-alkali soil, can effectively reduce the salt and alkaline substances in the soil, improve the soil structure and enhance the soil stability, and takes into account the functions of salt regulation, nutrient slow release and EICP reaction characteristics.

[0024] The present invention provides an application of a saline-alkali soil improver. The construction process is simplified compared with the traditional EICP technology. The improvement can be completed in two steps, and the agent has good construction performance and applicability. DETAILED DESCRIPTION

[0025] The present invention is further illustrated by way of examples below, but the present invention is not limited to the scope of the examples. Experimental methods in the following examples where specific conditions are not specified were performed according to conventional methods and conditions, or selected according to the product specifications.

[0026] Example 1 The preparation method of the saline-alkali soil improver comprises the following steps: (1) Prepare urease solution. Take soybeans and bake them at 40 °C for 6 h, then grind them with a grinder and sieve them through a 0.15 mm mesh to obtain soybean powder. Add 1 g of soybean powder to 10 mL of PBS solution to obtain a 100 g / L mixed solution. Stir the mixed solution with an electromagnetic stirrer at 800 rpm for 15 min. Then put the stirred mixed solution into a centrifugal stirrer and centrifuge it at 3000 rpm for 30 min at 4 °C. After removing the dregs, take the supernatant of the remaining liquid as the urease solution. Determine the urease activity by the conductivity method to ensure that its activity is ≥12 mm / min. Store the extracted urease solution at 4 °C for future use. (2) Take desulfurized gypsum and urea, add them into the ball mill according to the molar ratio of 1:4, add glass balls into the ball mill, and the ball-to-material ratio is 5:1 (at this ratio, SO4 2- The conversion rate was 90.80%), and then the mixture was placed in a ball mill. The ball milling reaction time was 1 hour, the ball mill speed was 500 rpm, and after ball milling, it was placed in an environment with a temperature of 50 ° C and dried for 24 hours to obtain desulfurized gypsum-urea eutectic; (3) According to the ratio of urease solution 60 wt.%, desulfurized gypsum-urea eutectic 40 wt.%, the corresponding components were weighed and stored separately to obtain a saline-alkali soil conditioner.

[0027] Example 2 The preparation method of the saline-alkali soil improver comprises the following steps: (1) Prepare urease solution. Take soybeans and bake them at 40 °C for 6 h, then grind them with a grinder and sieve them through a 0.15 mm mesh to obtain soybean powder. Add 1 g of soybean powder to 10 mL of PBS solution to obtain a 100 g / L mixed solution. Stir the mixed solution with an electromagnetic stirrer at 800 rpm for 15 min. Then put the stirred mixed solution into a centrifugal stirrer and centrifuge it at 3000 rpm for 30 min at 4 °C. After removing the dregs, take the supernatant of the remaining liquid as the urease solution. Determine the urease activity by the conductivity method to ensure that its activity is ≥12 mm / min. Store the extracted urease solution at 4 °C for future use. (2) Take desulfurized gypsum and urea, add them into the ball mill according to the molar ratio of 1:4, add glass balls into the ball mill, and the ball-to-material ratio is 4:1 (at this ratio, SO4 2- The conversion rate was 90.68%), and then the mixture was placed in a ball mill. The ball milling reaction time was 1 hour, the ball mill speed was 500 rpm, and after ball milling, it was placed in an environment with a temperature of 50 ° C and dried for 24 hours to obtain desulfurized gypsum-urea eutectic; (3) According to the ratio of urease solution 60 wt.%, desulfurized gypsum-urea eutectic 40 wt.%, the corresponding components were weighed and stored separately to obtain a saline-alkali soil conditioner.

[0028] Example 3 This embodiment is an application example of a saline-alkali soil improver. The saline-alkali soil improver prepared in Example 1 is used for soil improvement. The steps are as follows: S1. The modifier and soil are applied in a mass ratio of 1:5, and the soil to be improved and the desulfurized gypsum-urea eutectic component are evenly mixed to obtain a mixed soil; S2. After an interval of 1 to 2 days, put the urease solution into the spray bottle, spray the enzyme solution, and wait for the EICP reaction to occur to achieve the purpose of solidification improvement.

[0029] Comparative Example 1 For comparison with the application in Example 3, this comparative example uses the same dosage of desulfurized gypsum as an improver and mixes it into the soil for improvement.

[0030] Comparative Example 2 For comparison with the application in Example 3, this comparative example does not apply any modifier and keeps the saline soil as it is.

[0031] The experimental samples for Example 3 and Comparative Examples 1 and 2 were all the same saline soil sample. The experiments were conducted in a greenhouse, and the soil was evenly distributed in containers. After improvement, the soil's physical and chemical indicators and crop growth indicators were continuously monitored.

[0032] Soil pH, electrical conductivity, and sodium adsorption rate were determined according to the methods in NY / T 1377-2007 (Determination of Soil pH), HJ 802-2016 (Determination of Soil Electrical Conductivity by Electrode Method), and ASTM D4542-22 (Standard Test Method for Exchangeable Cations in Soil), respectively. Seedling emergence rate (%) = number of seeds sown / number of seedlings emerged × 100%, and the observation period was four weeks. The test results for these indicators are shown in Table 1.

[0033] Table 1: Soil improvement index test results

[0034] The above test results show that the pH value of Example 3 dropped from 8.50 of the original soil to 7.20, and the conductivity also dropped from 6.2 dS / m to 5 dS / m, indicating that the improver of the present invention has significant advantages in neutralizing soil alkalinity and reducing salt concentration, and the effect is more obvious than the application of gypsum alone. The SAR of Example 3 dropped to 14, a decrease of 50% compared with the control group, while the comparative example 1 dropped to 20, indicating that the calcium carbonate generated by the reaction of desulfurized gypsum and urease helps to fix the sodium ions in the soil, making it difficult for plants to absorb. In the improved soil, the emergence rate of crops was significantly improved, and Example 3 increased by about 25% compared with the control group, which fully proves that the improvement effect has a promoting effect on crop growth. The improvement method based on desulfurized gypsum and urea combined with urease solution can significantly improve the physical and chemical properties of saline soil, reduce pH, conductivity and sodium adsorption rate, and significantly improve crop growth performance. The experimental data results fully prove that this method has excellent practical application prospects and promotion value in saline soil improvement.

[0035] In summary, the saline-alkali soil conditioner proposed in the present invention utilizes a combination of desulfurized gypsum-urea eutectic and soybean urease, designed to enhance saline-alkali soil improvement through the synergistic effect of the two. The eutectic effectively reduces salinity and alkalinity in the soil, while EICP technology improves soil structure and enhances soil stability, providing a better environment for plant growth. The desulfurized gypsum-urea eutectic can convert salt within saline soil, effectively controlling internal salt accumulation and migration, thereby achieving the effect of long-term inhibition of salt accumulation. It also reduces urea loss due to its high solubility, making it a potential candidate material for plant fertilizer. Furthermore, the combination of desulfurized gypsum-urea eutectic and soybean urease not only solves the problem of desulfurized gypsum disposal but also serves as a reactant for EICP, providing essential calcium ions and urea. Therefore, the desulfurized gypsum-urea eutectic exhibits dual advantages in terms of fertility, opening up a new path for the large-scale resource utilization of desulfurized gypsum.

[0036] The above describes in detail the preferred embodiments of the present invention. It should be understood that those skilled in the art can make numerous modifications and variations based on the concepts of the present invention without inventive effort. Therefore, any technical solutions that can be derived by those skilled in the art through logical analysis, reasoning, or limited experimentation based on the concepts of the present invention and the prior art should be within the scope of protection defined by the claims.

Claims

1. A method for preparing a saline-alkali soil conditioner, characterized in that: The steps include: (1) Prepare urease solution; (2) Desulfurized gypsum and urea are mixed in a certain proportion and subjected to solid phase ball milling to obtain desulfurized gypsum-urea eutectic; (3) Weigh the urease solution and desulfurized gypsum-urea eutectic in proportion and store them separately to obtain a saline-alkali soil conditioner.

2. The method for preparing the saline-alkali soil conditioner according to claim 1, wherein In the step (1), the urease solution is prepared as follows: roasting soybeans, and then crushing and screening to obtain soybean powder; adding the soybean powder to a PBS solution to obtain a mixed solution; stirring and centrifuging the mixed solution to remove the dregs, and taking the supernatant of the remaining liquid to obtain a urease solution.

3. The method for preparing the saline-alkali soil conditioner according to claim 2, wherein: The baking is carried out at 35-40° C. for 5-6 hours; and the proportion of soybean flour in the mixed solution is 80-120 g / L.

4. The method for preparing the saline-alkali soil conditioner according to claim 2, wherein: The mixed solution is first stirred at 500-1000 rpm for 15-18 min, and then centrifuged at 3000-3500 rpm for 30-35 min to remove the dregs, and the supernatant of the remaining liquid is taken to obtain a urease solution; The activity of the urease solution was determined to be ≥12 mm / min based on the conductivity method.

5. The method for preparing the saline-alkali soil conditioner according to claim 1, wherein: In the step (2), the molar ratio of desulfurized gypsum to urea is 1:4-6.

6. The method for preparing the saline-alkali soil conditioner according to claim 1, wherein: In the step (2), the ball-to-material ratio of the solid-phase ball milling is 4-5:1; a vertical planetary ball milling process is adopted, the ball milling reaction time is 1-1.5 h, and the ball milling speed is 500-800 rpm.

7. The method for preparing the saline-alkali soil conditioner according to claim 1, wherein: In the step (2), after the solid phase ball milling treatment is completed, the desulfurized gypsum-urea eutectic is obtained by screening and drying.

8. The method for preparing the saline-alkali soil conditioner according to claim 1, wherein In step (3), the components of the saline-alkali soil conditioner are as follows: 50-60 wt.% of urease solution and 40-50 wt.% of desulfurized gypsum-urea eutectic.

9. A saline-alkali soil conditioner, characterized in that: The method is as described in any one of claims 1 to 8.

10. A use of the saline-alkali soil conditioner according to claim 9, characterized in that: The steps include: S1. Evenly mixing the soil to be improved with the desulfurized gypsum-urea eutectic component to obtain a mixed soil; S2. After an interval of 1 to 2 days, spray the urease solution components onto the mixed soil to cause the EICP reaction to occur, thereby achieving the purpose of solidification and improvement.

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