Phosphogypsum soil conditioner and preparation method thereof

Abstract

The invention discloses an ardealite soil conditioner and a preparation method thereof, and relates to the technical field of microbial growth promoters and soil remediation agents. The ardealite soil conditioner comprises ardealite, organic matters, an alkaline conditioner, a water-retaining agent, a microbial agent and a long-acting microbial growth regulator. The ardealite, the organic matter, the alkaline conditioner, the water-retaining agent and the microbial agent are precisely proportioned, so that a multi-component synergistic effect is realized. The trend shows that the salinity of the soil is continuously reduced, the water retention capacity and the pH adjusting capacity are enhanced, and a more stable remediation mechanism is formed. Compared with the limitation of single-point improvement in the prior art, the method disclosed by the invention shows a more comprehensive and lasting improvement effect in saline-alkali soil or degraded soil.

Description

Technical Field

[0001] This invention relates to the technical field of microbial growth promoters and soil remediation agents, specifically to a phosphogypsum soil conditioner and its preparation method. Background Technology

[0002] Soil improvement plays a crucial role in agricultural production and environmental protection, especially in addressing soil degradation, salinization, and pollution. With population growth and industrialization, declining arable land quality has become a global challenge. Effective soil conditioners can enhance soil fertility, improve structure, and promote crop growth, but current technologies often fail to balance cost-effectiveness and sustainability. For example, traditional conditioners such as organic fertilizers or chemical additives, while providing short-term soil improvement, suffer from rapid nutrient loss and unstable long-term effects, leading to frequent application by farmers, increasing costs and environmental burden.

[0003] As a major byproduct of the phosphate fertilizer industry, phosphogypsum presents particularly significant challenges in its disposal. Millions of tons of phosphogypsum are produced globally each year, containing metallic and acidic substances. Improper dumping of this material can pollute water sources and soil. Although phosphogypsum is rich in beneficial elements such as calcium and sulfur, and has potential applications in soil remediation, current technologies have failed to effectively transform its harmful components. Most treatment methods focus only on physical solidification or simple neutralization, neglecting the comprehensive utilization of phosphogypsum, resulting in resource waste and secondary pollution.

[0004] Existing microbial soil conditioners also face significant limitations. While microbial inoculants are used to promote nutrient decomposition and soil health, their activity and persistence are severely limited. Conventional microbial regulators are susceptible to environmental factors, such as temperature fluctuations or changes in soil moisture, leading to a rapid decline in viable bacterial counts. More critically, the lack of long-term regulatory mechanisms makes it difficult for microorganisms to establish long-term colonization in the soil. This deficiency directly reduces the overall effectiveness of the conditioner, hindering the achievement of sustainable soil remediation goals and limiting its application in saline-alkali or infertile soils.

[0005] Therefore, there is an urgent need to develop a phosphogypsum soil conditioner that can regulate the growth and metabolism of microorganisms and enhance their synergistic effect on phosphogypsum and organic matter, thereby improving the overall performance of the soil conditioner. Summary of the Invention

[0006] To address the three core problems of insufficient resource utilization of phosphogypsum in existing technologies—difficulty in maintaining microbial activity and poor synergy of soil amendment components—this paper proposes a highly efficient and stable phosphogypsum soil amendment. This amendment transforms phosphogypsum into a core amendment matrix, resolving the conflict between waste disposal and resource waste. It enhances the colonization and activity persistence of microbial agents (such as Bacillus) through a novel compound structure (as shown in Formula 1). Furthermore, it achieves a systematic improvement in soil pH regulation, water retention and fertilization, and microbial activity through a multi-component scientific formulation combining organic matter, alkaline conditioners, and water-retaining agents.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is: a phosphogypsum soil conditioner, wherein the soil conditioner comprises phosphogypsum, organic matter, alkaline conditioner, water-retaining agent, microbial agent and long-acting microbial growth regulator; The long-acting microbial growth regulator is the compound shown in Formula 1: Formula 1: ; In Formula 1, R1 is selected from: F, cyano, nitro, trifluoromethyl, alkyl with 1-5 carbon atoms, and alkoxy with 1-5 carbon atoms.

[0008] Furthermore, the alkyl group having 1-5 carbon atoms is selected from: methyl, ethyl, propyl, tert-butyl.

[0009] Furthermore, the alkoxy group having 1-5 carbon atoms is selected from: methoxy group.

[0010] Furthermore, the long-acting microbial growth regulator is any one of the compounds described below: ; ; ; .

[0011] Furthermore, the mass ratio of each component in the soil conditioner is as follows: The phosphogypsum has a mass fraction of 50-80 parts; The organic matter has a mass fraction of 15-40 parts; The alkaline conditioner has a mass fraction of 5-15 parts; The water-retaining agent has a mass fraction of 1-5 parts; The microbial inoculant has a mass fraction of 3-5 parts; The long-acting microbial growth regulator is used in doses of 0.5-1.5 parts.

[0012] Furthermore, the organic matter is a mixture of humic acid and straw fiber, with a mass ratio of 2:1.

[0013] Furthermore, the alkaline conditioner is one of quicklime, slaked lime, oyster shell powder, calcium carbonate, or silicon-calcium-potassium-magnesium fertilizer.

[0014] Furthermore, the water-retaining agent is sodium polyacrylate.

[0015] Furthermore, the microbial agent is one of Bacillus megaterium, Bacillus subtilis, and Bacillus amyloliquefaciens, with an effective viable count ≥ 10 billion / g.

[0016] A method for preparing a phosphogypsum soil conditioner includes the following steps: S1. The phosphogypsum is naturally sun-dried or oven-dried until the moisture content is less than 15%, and then pulverized through a 100-mesh sieve to obtain dried phosphogypsum powder; the organic raw material is pulverized to a particle size of less than 2 mm to obtain pretreated organic matter; S2. Add the dried phosphogypsum powder, pretreated organic matter, and alkaline conditioner into a twin-shaft paddle mixer in proportion and mix for 15-30 minutes to obtain the basic mixture; S3. The basic mixture is fed into a disc granulator or a rotary drum granulator, and atomized water is sprayed at the same time to granulate. After granulation, wet granules with a particle size of 2-4 mm are obtained. S4. Cool the wet granules to room temperature, and then feed them together with the water-retaining agent, microbial agent and long-acting microbial growth regulator into a drum mixer. Mix for 5-10 minutes. After mixing evenly, dry at 50-75℃ until the moisture content is less than 10% to obtain the phosphogypsum soil conditioner.

[0017] Furthermore, the amount of atomized water added in S3 is 8-15% of the total mass of the basic mixture.

[0018] Furthermore, the mixing speed in S4 is 10-20 r / min, and the mixing ambient temperature is not higher than 35℃.

[0019] The structure of the long-acting microbial growth regulator of the present invention is divided into two main parts, as shown in Formula 2; ①——Esterified methionine; ②——Esterified cysteine.

[0020] Formula 2: .

[0021] The long-acting microbial growth regulator described in this invention is lipophilic and can penetrate cell membranes, while its structural stability resists environmental degradation. Upon entering the cell, the regulator undergoes hydrolysis under the action of intracellular lipolytic enzymes, releasing two key amino acids: methionine and cysteine. Methionine participates in protein synthesis and methyl transfer reactions, enhancing microbial enzyme activity and cell division, which is particularly important in soil improvement because microorganisms can accelerate the decomposition of organic matter and improve soil structure. Cysteine, a precursor to glutathione, has antioxidant functions, protecting microorganisms from oxidative stress. Furthermore, it promotes microbial biofilm formation, enhancing their colonization ability in the soil. The long-acting microbial growth regulator maintains high stability in the environment, which is the core of its "long-acting" characteristic. Its stable molecular structure allows it to persist in the soil for a long time, providing continuous support for microbial growth. In phosphogypsum soil conditioners, this mechanism synergistically promotes microbial community prosperity, accelerates phosphogypsum mineralization and soil pH regulation, improves soil water retention and nutrient utilization efficiency, and ultimately achieves soil remediation goals.

[0022] The soil conditioner of this invention is composed of phosphogypsum, organic matter (humic acid and straw fiber mixed in a 2:1 mass ratio), an alkaline conditioner, 1-5 parts of a water-retaining agent, 3-5 parts of microbial inoculants, and 0.5-1.5 parts of a long-acting microbial growth regulator, formulated according to their mass proportions. It achieves efficient improvement of saline-alkali soil through the complementary and synergistic mechanisms of its components. Specifically, phosphogypsum serves as the core improving matrix, providing calcium and sulfur elements and improving soil structure. Organic matter enhances cation exchange capacity through humic acid, and straw fiber provides a carbon source for microorganisms to improve fertility. The alkaline conditioner neutralizes the acidity of phosphogypsum and stabilizes the pH to 6.5-7.5. The water-retaining agent increases soil water holding capacity by 20-30% to maintain a moist environment for microorganisms. The microbial inoculants exert phosphorus-solubilizing, antibacterial, and growth-promoting effects, while the long-acting microbial growth regulator extends the microbial metabolic cycle and establishment time by slowly releasing amino acids and sulfur sources. The components work synergistically to form a "resource transformation-environmental stabilization-microbial activation" system: phosphogypsum is transformed into a safe resource under the action of alkaline conditioners and organic matter (humic acid chelates harmful metals), avoiding waste pollution; the microbial agent's activity is sustained by the long-term nutritional support of the conditioner, the moisture stability of the water-retaining agent, and the pH buffering effect of the alkaline conditioner, overcoming the problem of easy inactivation of traditional microorganisms. Ultimately, this synergistic approach solves the technical problems of insufficient resource utilization of phosphogypsum, difficulty in maintaining microbial activity, and poor component synergy.

[0023] Compared with the prior art, the beneficial effects of the present invention are: 1. More efficient resource utilization of phosphogypsum and reduced environmental pollution risks: Transforming phosphogypsum into a core modified matrix, through scientific pretreatment and component integration, significantly improves the resource conversion efficiency of waste. This trend not only solves the pollution problems of traditional disposal methods but also realizes the recycling of waste, reducing the long-term burden on the environment.

[0024] 2. Significantly enhanced persistence of microbial activity promotes long-term soil remediation: The invention introduces a novel long-acting microbial growth regulator. Its unique structure continuously regulates microbial metabolism, resulting in more stable or even enhanced activity of the inoculant. This trend is particularly evident in comparative tests, where the microbial inoculant exhibits stronger adaptability and reproductive capacity in saline-alkali soils, overcoming the shortcomings of existing technologies in terms of short-lasting activity.

[0025] 3. Enhanced overall soil remediation performance and synergistic optimization of salinity and water retention: Through precise formulation of phosphogypsum, organic matter, alkaline conditioner, water-retaining agent, and microbial inoculant, a multi-component synergistic effect is achieved. Soil salinity is continuously reduced, while water retention and pH regulation capabilities are enhanced, forming a more stable remediation mechanism. Compared to the limitations of single-point remediation in existing technologies, this invention exhibits a more comprehensive and lasting remediation effect in saline-alkali land or degraded soils. Attached Figure Description

[0026] Figure 1 This is the NMR spectrum of the long-acting microbial growth regulator 1 described in this invention. Detailed Implementation

[0027] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are merely 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.

[0028] Preparation Example 1 Synthesis of long-acting microbial growth regulator 1: ; 10 g of raw material 1, 12.54 g of raw material 2, and 150 ml of tetrahydrofuran were added sequentially to a reactor vessel. After stirring until dissolved, the mixture was heated to 80 °C, and 3.29 g of concentrated sulfuric acid was slowly added dropwise. After the addition was complete, the reaction was allowed to proceed for 6 hours. After the reaction was complete, 100 ml of water was added, and the pH of the system was adjusted to neutral with 0.1 mol / L NaOH while continuously stirring. The mixture was allowed to stand and separated, retaining the organic phase. The organic phase was evaporated to dryness and purified by silica gel column chromatography (using a mixed solution of n-heptane / ethyl acetate as the eluent) to obtain 17.14 g of intermediate 1.

[0029] ; 17.14 g of intermediate 1, 7.39 g of raw material 3, and 200 ml of toluene were added sequentially to a reactor vessel. After thorough stirring, 1.48 g of tris(dibenzylacetone)dipalladium, 3.77 g of 1,1'-bis(diphenylphosphine)ferrocene, 2.13 g of 1-ethyl-3-methylimidazolium tetrafluoroborate, and 1.21 g of triethylenediamine were added sequentially under a continuous nitrogen flow. The mixture was heated to 80 °C and stirred for 20 hours. After the reaction was complete, the reaction system was cooled to room temperature, and the pH was adjusted to 6.5-7 with 0.1 mol / L hydrochloric acid aqueous solution. The organic phase was dried over anhydrous sodium sulfate, and the organic phase was evaporated to dryness. The organic phase was then purified by silica gel column chromatography (using a mixed solution of n-heptane / ethyl acetate as the eluent) to obtain 19.18 g of long-acting microbial growth regulator 1.

[0030] Product structure identification: 1. Structural identification of intermediate 1: M / Z: 319 [MS+1]; 2. Structural identification of long-acting microbial growth regulator 1: M / Z: 359 [MS+1]; 3. Structural identification of long-acting microbial growth regulator 1: 1 H NMR (Chloroform-d): δ 7.07-6.89(m, 3H), 5.05 (d, 2H), 4.39 (d, 2H), 3.94 (tt,1H), 3.70 (tt, 1H), 3.08 (m,1H), 2.86 (m 1H), 2.69-2.49 (m, 2H), 2.43-2.27 (m, 1H), 2.20 (d, 3H), 2.05 (m, 1H), 1.88 (s, 3H), 1.65 (t, 1H).

[0031] Preparation Examples 2-6 In Preparation Examples 2-6, long-acting microbial growth regulators were prepared sequentially, replacing raw material 2. The rest remained the same as in Preparation Example 1. The specific structures of raw material 2, the long-acting microbial growth regulators, and the structural identification data are shown in Table 1.

[0032] Table 1.

[0033] Example 1

[0034] Preparation of a phosphogypsum soil conditioner: 1. Raw material components: Phosphogypsum: 70 parts, dried phosphogypsum powder that has been naturally sun-dried or oven-dried until the moisture content is less than 15%, and pulverized through a 100-mesh sieve, purchased from: Guizhou Yukun Technology Group Co., Ltd. Organic matter: 30 parts, of which humic acid and straw fiber are mixed in a mass ratio of 2:1 (i.e., 20 parts humic acid and 10 parts straw fiber), and crushed to a particle size of less than 2 mm. The humic acid was purchased from Sichuan Heipu Biotechnology Co., Ltd., and the straw fiber was purchased from Guangdong Limei New Material Technology Co., Ltd. Alkaline conditioner: 10 parts, selected from quicklime, purchased from Zibo Hanxiang Chemical Co., Ltd.; Water-retaining agent: 3 parts, sodium polyacrylate, purchased from: Hangzhou Juhe Biotechnology Co., Ltd.; Microbial inoculant: 4 portions, selected from Bacillus subtilis, with an effective viable count of 10 billion / g, purchased from Guangzhou Zhenwei Microbial Technology Co., Ltd. Long-acting microbial growth regulator: 1 part, selected from: Long-acting microbial growth regulator 1, prepared in preparation example 1.

[0035] 2. Preparation method: S1. Place the phosphogypsum in a ventilated environment to air dry naturally until its moisture content drops to 12%, then crush it and pass it through a 100-mesh sieve to obtain dry phosphogypsum powder; at the same time, crush the organic raw material to a particle size of less than 2 mm to obtain pretreated organic matter; S2. Add the dried phosphogypsum powder, pretreated organic matter, and alkaline conditioner into a twin-shaft paddle mixer and mix at 15 r / min for 20 minutes to ensure uniform dispersion and obtain the basic mixture; S3. Feed the basic mixture into the rotary drum granulator and spray atomized water (addition amount is 10% of the total mass of the basic mixture). Maintain the rotation speed of 12r / min during the granulation process. After granulation, wet granules with a particle size of 3mm are obtained. S4. Cool the wet granules to room temperature, and then feed them together with the water-retaining agent, microbial agent and long-acting microbial growth regulator into a drum mixer. Set the mixing speed to 15 r / min, control the ambient temperature at 30℃, and mix for 8 minutes. After mixing evenly, transfer the material to a drying oven and dry it at 60℃ for 4 hours until the moisture content drops to 8%, thus obtaining the phosphogypsum soil conditioner.

[0036] Examples 2-6 In Examples 2-6, a phosphogypsum soil conditioner was prepared sequentially. Referring to the raw material composition and preparation method of Example 1, the long-acting microbial growth regulator 1 was replaced with the long-acting microbial growth regulator prepared in Examples 2-6, and the rest remained the same as in Example 1.

[0037] Comparative Example 1 A phosphogypsum soil conditioner, prepared according to the method of Example 1, except that the long-acting microbial growth regulator is replaced with methionine, and the rest remains the same as in Example 1.

[0038] Comparative Example 2 A phosphogypsum soil conditioner, prepared according to the method of Example 1, except that the long-acting microbial growth regulator is replaced with cysteine, and the rest remains the same as in Example 1.

[0039] Comparative Example 3 A phosphogypsum soil conditioner, prepared according to the method of Example 1, except that the long-acting microbial growth regulator is replaced with a combination of methionine and cysteine ​​(i.e., 0.5 parts of methionine and 0.5 parts of cysteine), and the rest remains the same as in Example 1.

[0040] Comparative Example 4 A phosphogypsum soil conditioner, prepared according to the method of Example 1, but without the addition of the long-acting microbial growth regulator, is otherwise identical to Example 1.

[0041] Comparative Example 5 A phosphogypsum soil conditioner, prepared according to the method of Example 1, but without the addition of a water-retaining agent, is otherwise identical to that in Example 1.

[0042] Performance testing: The pH of the saline-alkali soil sample was 8.5 ± 0.2, and the EC was 4.93 mS / cm.

[0043] 1. Microbial activity persistence test: 100g of each of the soil conditioners prepared in Examples 1-6 and Comparative Examples 1-5 were mixed evenly with 1kg of saline-alkali soil. The mixtures were placed in a constant temperature and humidity chamber (25℃, 60% humidity), and sterile deionized water was added every 7 days to maintain the soil moisture content at 20%. 10g of soil was collected at days 0, 30, and 90, and the effective viable count (CFU / g) of Bacillus subtilis was determined using the plate count method (LB medium). The data are shown in Table 2.

[0044] 2. Electrical conductivity (EC) change test: 100g each of the soil conditioners prepared in Examples 1-6 and Comparative Examples 1-5 were mixed evenly with 1kg of saline-alkali soil. The mixtures were placed in a constant temperature and humidity chamber (25℃, 60% humidity), and sterile deionized water was added every 7 days to maintain the soil moisture content at 20%. At 30 and 60 days, 20g of soil was taken, dried to constant weight at 40℃, mixed with 100mL of deionized water, and shaken at 180 rpm for 30 minutes at 25℃, followed by centrifugation at 4000 rpm for 10 minutes. The supernatant was collected and filtered through a 0.45μm filter membrane to obtain a clear soil extract. The EC was measured using an electrical conductivity meter, and the data are shown in Table 2.

[0045] Table 2.

[0046]

[0047] Regarding microbial activity, all examples (using long-acting microbial growth regulators) showed stable or even enhanced microbial activity over a long period, indicating that the microbial inoculants could effectively colonize and reproduce in the soil. Conversely, the comparative examples (using alternative regulators or without regulators) showed significant activity decline, especially in the absence of water-retaining agents, where microbial activity dropped sharply, highlighting the crucial role of long-acting regulators in maintaining microbial community vitality. Because it takes time for Bacillus subtilis to grow from germination to maturity, and high salinity inhibits growth, the effective viable count showed a trend of first decreasing and then increasing.

[0048] Regarding soil electrical conductivity (EC), all examples showed a continuous and significant trend of salinity reduction, reflecting the systematic improvement of salinization by the soil amendment; while the comparative examples showed a weaker salinity reduction effect, with the comparative example without water-retaining agent even showing stable or slightly increased salinity, indicating that the synergy between water-retaining agent and microbial regulator is crucial for controlling salt migration.

[0049] Overall, these trends confirm the key contribution of long-acting microbial growth regulators to improving the overall performance of soil conditioners. They not only enhance the long-term activity of microorganisms but also optimize the salt regulation mechanism, thereby achieving more stable and efficient soil remediation results.

[0050] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A phosphogypsum soil conditioner, characterized in that, The soil conditioner includes phosphogypsum, organic matter, alkaline conditioner, water-retaining agent, microbial agent, and long-acting microbial growth regulator; The long-acting microbial growth regulator is the compound shown in Formula 1: Formula 1: ; In Formula 1, R1 is selected from: F, cyano, nitro, trifluoromethyl, alkyl with 1-5 carbon atoms, and alkoxy with 1-5 carbon atoms.

2. The phosphogypsum soil conditioner according to claim 1, characterized in that, The alkyl group having 1-5 carbon atoms is selected from: methyl, ethyl, propyl, tert-butyl; The alkoxy group having 1-5 carbon atoms is selected from: methoxy group.

3. The phosphogypsum soil conditioner according to claim 1, characterized in that, The long-acting microbial growth regulator is any one of the compounds with the following structures: ； ； ； 。 4. The phosphogypsum soil conditioner according to claim 1, characterized in that, The mass ratio of each component in the soil conditioner is as follows: The phosphogypsum has a mass fraction of 50-80 parts; The organic matter has a mass fraction of 15-40 parts; The alkaline conditioner has a mass fraction of 5-15 parts; The water-retaining agent has a mass fraction of 1-5 parts; The microbial inoculant has a mass fraction of 3-5 parts; The long-acting microbial growth regulator is used in doses of 0.5-1.5 parts.

5. The phosphogypsum soil conditioner according to claim 1, characterized in that, The organic matter is a mixture of humic acid and straw fiber, with a mass ratio of 2:

1.

6. The phosphogypsum soil conditioner according to claim 1, characterized in that, The alkaline conditioner is one of quicklime, slaked lime, oyster shell powder, calcium carbonate, and silicon-calcium-potassium-magnesium fertilizer. The water-retaining agent is sodium polyacrylate.

7. The phosphogypsum soil conditioner according to claim 1, characterized in that, The microbial agent is one of Bacillus megaterium, Bacillus subtilis, or Bacillus amyloliquefaciens, with an effective viable count ≥ 10 billion / g.

8. A method for preparing a phosphogypsum soil conditioner according to any one of claims 1-7, characterized in that, Includes the following steps: S1. The phosphogypsum is naturally sun-dried or oven-dried until the moisture content is less than 15%, and then pulverized through a 100-mesh sieve to obtain dried phosphogypsum powder; the organic raw material is pulverized to a particle size of less than 2 mm to obtain pretreated organic matter; S2. Add the dried phosphogypsum powder, pretreated organic matter, and alkaline conditioner into a twin-shaft paddle mixer in proportion and mix for 15-30 minutes to obtain the basic mixture; S3. The basic mixture is fed into a disc granulator or a rotary drum granulator, and atomized water is sprayed at the same time to granulate. After granulation, wet granules with a particle size of 2-4 mm are obtained. S4. Cool the wet granules to room temperature, and then feed them together with the water-retaining agent, microbial agent and long-acting microbial growth regulator into a drum mixer. Mix for 5-10 minutes. After mixing evenly, dry at 50-75℃ until the moisture content is less than 10% to obtain the phosphogypsum soil conditioner.

9. The method for preparing a phosphogypsum soil conditioner according to claim 8, characterized in that, The amount of atomized water added in S3 is 8-15% of the total mass of the base mixture.

10. The method for preparing a phosphogypsum soil conditioner according to claim 8, characterized in that, The mixing speed in S4 is 10-20 r / min, and the mixing ambient temperature is not higher than 35℃.

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