A petroleum hydrocarbon-contaminated purple soil conditioner, method of making and using

Abstract

This invention discloses a conditioner for purple soil contaminated with petroleum hydrocarbons, its preparation and application method, belonging to the field of purple soil remediation technology. The preparation method of the conditioner is as follows: urea solution is added to porous biochar or zeolite powder and stirred to allow the urea solution to enter the micropores of the porous biochar or zeolite powder, followed by drying to obtain a solid slow-release nitrogen source; the porous biochar and slow-release nitrogen source are mixed evenly, and then a mixed solution of rhamnolipin and humic acid is sprayed in, with a mass ratio of rhamnolipin to humic acid of (8-15):(2-5), so that the moisture content of the resulting material is 20-25%, stirred evenly, and finally dried until the moisture content is less than 3%, to obtain the conditioner for purple soil contaminated with petroleum hydrocarbons. Through synergistic formulation design, the physical improvement of soil structure and chemical / biological desorption of locked petroleum hydrocarbons are achieved, thereby realizing the synergistic effect of chemical desorption and microbial degradation.

Description

Technical Field

[0001] This invention belongs to the field of purple soil remediation technology, specifically a conditioner for purple soil contaminated with petroleum hydrocarbons, and its preparation and application method. Background Technology

[0002] Purple soil is formed from the weathering of purple sandstone and shale, and is a typical calcareous purple soil with a series of unique physicochemical properties: its pH value is generally between 8.29 and 8.53, indicating strong alkalinity, and the soil is rich in calcium carbonate; its clay minerals are mainly 2:1 type layered silicates, with hydromica (illite) being the dominant component, and it also contains a certain amount of montmorillonite. This mineral structure results in a large specific surface area and interlayer space. Purple soil has a shallow soil layer, low organic matter content, and poor aggregate structure. Under alternating wet and dry conditions, it is prone to compaction, leading to increased soil bulk density, reduced porosity, and poor aeration and permeability, seriously affecting agricultural production and ecological health.

[0003] Petroleum hydrocarbons, as non-polar organic compounds, are easily locked into the interlayers of clay minerals in purple soil or into the micropores of the soil due to their hydrophobicity and through physical adsorption (such as van der Waals forces and hydrophobic interactions) and chemical bonding. Soil compaction further exacerbates this locking effect, physically isolating pollutants and significantly reducing their bioavailability. This results in the ineffectiveness of conventional microbial or phytoremediation techniques, leading to long remediation cycles and low degradation rates.

[0004] Currently, the remediation technologies for purple soil contaminated by petroleum mainly include physical, chemical, and biological methods. However, when these technologies are directly applied to purple soil, they face the following significant drawbacks: (1) Conventional surfactants are ineffective and pose a risk of secondary pollution: Chemical leaching is a commonly used technique, usually employing anionic surfactants (such as sodium dodecyl sulfate, SDS) to solubilize and desorb petroleum hydrocarbons. However, in the high-calcium, high-pH environment of purple soil, anionic surfactants will react with the large amount of calcium ions (Ca²⁺) in the soil. +(2) General soil conditioners cannot specifically address compaction: Commercially available general soil conditioners, such as polyacrylamide (PAM), can promote the formation of soil aggregates to a certain extent, but their effect on improving compaction in purple soil is limited. The fundamental reason is that the bridging structure formed by PAM cannot resist the violent expansion and contraction caused by alternating dry and wet conditions of highly expansive clay minerals such as montmorillonite in purple soil. In addition, the high calcium and high pH environment will affect the molecular conformation of PAM, resulting in a significant reduction in its improvement effect and durability. (3) Disconnection between desorption and bioremediation: Existing technical routes often treat the desorption (desorption) of pollutants and microbial degradation as two independent processes, lacking effective technical connection. Highly efficient chemical desorbents (such as high-concentration surfactants or chemical solvents) usually have significant toxic or inhibitory effects on indigenous degradation bacteria in the soil. This leads to a technical contradiction: although pollutants are released from the soil microstructure, the microorganisms that perform the degradation task have reduced activity due to the toxicity of chemical desorbents, resulting in low overall remediation efficiency.

[0005] In summary, there is an urgent need to simultaneously overcome the soil structure compaction and pollutant locking problems of purple soil contaminated with petroleum hydrocarbons, and to achieve synergistic effects with subsequent bioremediation processes. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a conditioner for purple soil contaminated with petroleum hydrocarbons, its preparation and application method. Through synergistic formulation design, it achieves physical improvement of soil structure and chemical / biological desorption of locked petroleum hydrocarbons, creating prerequisites for efficient bioremediation.

[0007] This invention is achieved through the following technical solution: A method for preparing a conditioner for purple soil contaminated with petroleum hydrocarbons includes the following steps: Step 1: Add urea solution to porous biochar or zeolite powder and stir to allow the urea solution to enter the micropores of the porous biochar or zeolite powder. Then dry to obtain a solid slow-release nitrogen source. Step 2: Mix the porous biochar and slow-release nitrogen source evenly, then spray in a mixed solution of rhamnolipin and humic acid, wherein the mass fractions of rhamnolipin and humic acid are 8-15 parts and 2-5 parts, respectively, so that the moisture content of the resulting material is 20-25%, then stir evenly, and finally dry until the moisture content is less than 3%, to obtain a purple soil conditioner contaminated by petroleum hydrocarbons.

[0008] Preferably, the porous biochar in step 1 is obtained by the following process: pyrolyzing agricultural and forestry waste at 450-550°C under oxygen-limited conditions for 45-75 minutes, followed by mechanical grinding to obtain the porous biochar.

[0009] Preferably, the agricultural and forestry waste is corn stalks, cotton stalks, rice stalks, citrus peels, peanut shells, sugarcane bagasse, or wheat husks, and after mechanical grinding, more than 95% of the particles have a particle size of less than 0.25 mm.

[0010] Preferably, the slow-release nitrogen source in step 1 is 5-10 parts, the porous biochar in step 2 is 70-85 parts, and the total mass fraction of rhamnolipid, humic acid, porous biochar and slow-release nitrogen source is 100 parts.

[0011] Preferably, the urea solution in step 1 is a urea saturated solution, and the mass ratio of the urea saturated solution to porous biochar or zeolite powder is 10:1.

[0012] Preferably, in step 1, the saturated urea solution is added dropwise at a constant rate under stirring conditions within 10-15 minutes.

[0013] Preferably, the total mass percentage of the mixed solution of rhamnolipin and humic acid in step 2 is 18-22%.

[0014] Preferably, the drying in step 2 is carried out under air-drying conditions at 50-70°C.

[0015] A purple soil conditioner contaminated with petroleum hydrocarbons, obtained by the preparation method of the petroleum hydrocarbon contaminated purple soil conditioner described in any one of the above-mentioned methods.

[0016] A method for using a purple soil conditioner contaminated with petroleum hydrocarbons involves uniformly spreading the purple soil conditioner on the surface of the petroleum hydrocarbon-contaminated soil at an application rate of 2000-5000 kg / ha, then tilling the soil to a depth of 20-25 cm, and finally spraying water to make the soil moisture content of the topsoil 60-70% of the field capacity.

[0017] Compared with the prior art, the present invention has the following beneficial technical effects: This invention discloses a method for preparing a conditioner for purple soil contaminated with petroleum hydrocarbons. Purple soil is generally rich in phosphorus and potassium, but the relative scarcity of nitrogen is a major bottleneck limiting the efficient degradation of petroleum hydrocarbons by indigenous microorganisms. Therefore, it is necessary to supplement the limiting nutrient nitrogen. Urea is prepared into a slow-release nitrogen compound through physical adsorption and zeolite / porous biochar. When the conditioner is applied to the soil, the nitrogen source is slowly released, providing not only sustained and stable nutritional support for the growth and reproduction of petroleum hydrocarbon-degrading bacteria, but also effectively avoiding the impact and loss caused by a single application of fast-acting nitrogen fertilizer, achieving a long-term nutrient supply matching the rate of pollutant decontamination. Part of the decontamination agent, composed of rhamnolipids and humic acid, is adsorbed and locked in the pores of the porous biochar, while another part forms a mixed coating film on the outer surface of the slow-release nitrogen source, realizing the solid-phase powderification of the liquid agent. This not only facilitates subsequent application to the soil but also endows the decontamination agent with slow-release and anti-leaching properties, preventing it from being rapidly washed away by rainwater in the purple soil. Rhamnollipids possess excellent emulsifying and solubilizing abilities, and they are particularly effective in high-alkali, high-salt, and high-divalent cation environments (such as Ca²⁺). + It maintains high activity even in alkaline environments and does not precipitate, making it particularly suitable for purple soil environments. It effectively desorbs petroleum hydrocarbons adsorbed on the surface and micropores of clay minerals, forming microemulsions easily utilized by microorganisms. Humic acid molecules contain numerous carboxyl and phenolic hydroxyl groups, exhibiting strong complexing capabilities. In the alkaline environment of purple soil, humic acid can effectively complex free Ca²⁺. + This reduces the negative impact on soil structure and the remediation process. Simultaneously, humic acid acts as a natural wetting agent, assisting rhamnolipids in further stripping the oil film from the surface of soil particles. This invention, through synergistic formulation design, achieves physical improvement of soil structure and chemical / biological desorption of locked petroleum hydrocarbons, thus realizing a synergistic effect between chemical desorption and microbial degradation. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the preparation process of the conditioner described in this invention.

[0019] Figure 2 This is a microstructure diagram (SEM) of the porous biochar described in this invention, where CR is corn stalk biochar, CS is cotton stalk biochar, OP is citrus peel biochar, PO is peanut shell biochar, SB is sugarcane bagasse biochar, and WH is wheat husk biochar.

[0020] Figure 3a This is a schematic diagram of the microstructure of untreated (M0) compacted purple soil.

[0021] Figure 3b This is a schematic diagram of the microstructure of compacted purple soil after the optimal dosage treatment (M15) in Example 1.

[0022] Figure 3c A schematic diagram of the microstructure of compacted purple soil under the suboptimal dose treatment (M5).

[0023] Figure 4 This is a schematic diagram of the synergistic mechanism of petroleum hydrocarbon degassing and microbial degradation in this invention. Detailed Implementation

[0024] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0025] This invention discloses a method for preparing a conditioner for purple soil contaminated with petroleum hydrocarbons, which requires the following three functional components: a decongestant component (10-20 parts), a structure-modifying component (70-85 parts), and a biostimulating component (5-10 parts), with a total mass of 100 parts: A: Card-unblocking components (10-20 parts): Biosurfactant (rhamnolipid): 8-15 parts. Rhamnolipids possess excellent emulsifying and solubilizing abilities, and they are particularly effective in high-alkali, high-salt, and high-divalent cation (such as Ca²⁺) environments. + It can maintain high activity even in the environment and will not precipitate. It is particularly suitable for purple soil environment. It can effectively desorb petroleum hydrocarbons adsorbed on the surface and micropores of clay minerals to form microemulsions that are easily utilized by microorganisms.

[0026] Organic acid (humic acid): 2-5 parts. Humic acid molecules contain a large number of functional groups such as carboxyl and phenolic hydroxyl groups, exhibiting strong complexing ability. In the alkaline environment of purple soil, humic acid can effectively complex free Ca²⁺. + This reduces its negative impact on soil structure and the remediation process. Simultaneously, humic acid can act as a natural wetting agent, assisting rhamnolipids in further stripping the oil film from the surface of soil particles.

[0027] B: Structural modification components (70-85 parts): Porous biochar: Biochar obtained by pyrolyzing agricultural and forestry waste (such as corn stalks, cotton stalks, rice stalks, citrus peels, peanut shells, sugarcane bagasse, and wheat husks) at 450-550°C is mechanically ground to ensure that over 95% of the particles are smaller than 0.25 mm (i.e., mainly passing through a 60-mesh sieve). In this biochar system with a reasonable particle size distribution, the dominant (>95%) small-diameter biochar particles have a huge specific surface area and abundant microporous structure, effectively breaking up the compacted layer of purple soil and serving as an excellent carrier for microorganisms and unblocking agents. Meanwhile, a very small amount (<5%) of slightly larger particles act as a skeletal support material for the soil's macropores, reducing soil bulk density, increasing total porosity, and improving aggregate structure stability. Together, they construct a multi-level porous structure conducive to soil aeration and water permeability, physically creating an ideal space for microbial metabolic activities and root growth, significantly improving soil aeration and water permeability. Simultaneously, its porosity and adsorption properties also make it an excellent carrier for subsequent biostimulant components.

[0028] It should be noted that porous biochar itself is used as a structural modification component, but it is also needed in the preparation of biostimulant components. Therefore, more porous biochar should be prepared for use in the preparation of biostimulant components.

[0029] C: Biostimulant component (5-10 parts): Slow-release nitrogen source (biochar-based slow-release nitrogen): Considering that purple soils are generally rich in phosphorus and potassium, the relative scarcity of nitrogen has become a major bottleneck limiting the efficient degradation of petroleum hydrocarbons by indigenous microorganisms. Therefore, it is necessary to supplement the limiting nutrient nitrogen. Slow-release nitrogen is prepared by combining urea with zeolite / porous biochar through physical adsorption. When the conditioner is applied to the soil, the nitrogen source is slowly released, providing not only sustained and stable nutritional support for the growth and reproduction of petroleum hydrocarbon-degrading bacteria, but also effectively avoiding the impact and loss caused by applying fast-acting nitrogen fertilizer in a single application, achieving a long-term nutrient supply that matches the rate of pollutant decomposition.

[0030] Specific preparation methods, such as Figure 1 As shown, it consists of the following steps: Step 1, Preparation of porous biochar: Agricultural and forestry waste is pyrolyzed at 450-550°C under oxygen-limited conditions (nitrogen protection or a closed tubular furnace) for 45-75 minutes to obtain basic biochar. After cooling, it is mechanically ball-milled until more than 95% of the particles have a particle size of less than 0.25 mm, breaking up the bulk structure, exposing more micropores and greatly increasing the specific surface area, resulting in porous biochar with a refined structure.

[0031] Step 2, Preparation of Slow-Release Nitrogen Source: Under stirring conditions, saturated urea solution is added dropwise at a constant rate over 10-15 minutes to the required amount of porous biochar or zeolite powder. This prevents air blockage or agglomeration in the pores due to a large, instantaneous addition of the solution. The mass ratio of saturated urea solution to porous biochar (or zeolite powder) is 10:1. This high liquid-to-solid ratio ensures that the urea solution forms a sufficient liquid surface for complete immersion, thereby allowing it to fully penetrate into the micropores of the porous biochar (or zeolite powder) through capillary action. The mixture is continuously stirred at 60°C and 60 rpm for 2 hours to ensure that the urea is fully loaded into the pores of the biochar (or zeolite). Afterward, it is dried at 80°C for 6 hours to obtain a solid slow-release nitrogen source (component C).

[0032] Step 3, preparation of the unblocking agent: Dissolve rhamnolipid (component A1) and humic acid (component A2) in deionized water to prepare a mixed mother liquor with a total mass percentage of 18-22%. Stir thoroughly until uniform and transparent to obtain the liquid unblocking agent.

[0033] Step 4, Final Compounding: The prepared component B (porous biochar, unloaded, with numerous empty pores as an empty carrier) and component C (slow-release nitrogen source, solid particles with urea-filled pores) are dry-mixed evenly in a mixer (30 rpm, 5 minutes). Then, under continuous stirring, the unblocking agent (liquid) prepared in Step 3 is slowly added via spraying, controlling the moisture content of the resulting material to be 20-25%. Stirring continues for 15 minutes, allowing component B to adsorb component A. The unblocking agent is largely adsorbed and locked in the empty pores of component B. The liquid unblocking agent forms a mixed coating film only on the outer surface of component C, achieving the solid-phase powderification of the liquid agent. This not only facilitates subsequent application to the soil but also endows the unblocking agent with slow-release and anti-leaching properties, preventing it from being rapidly washed away by rainwater in the purple soil. Finally, it is air-dried at low temperature (50-70°C) until the moisture content is below 3%, thus obtaining the conditioner described in this invention.

[0034] When applying the conditioner of this invention to purple soil areas contaminated with petroleum hydrocarbons, the dosage is 2000-5000 kg / ha. Soils with a total petroleum hydrocarbon content of 5000-15000 mg / kg are considered moderately contaminated, and the dosage is 3000 kg / ha. The specific application method is as follows: Step a: Apply the conditioner evenly to the surface of the contaminated soil, and then use a rotary tiller to till the soil to a depth of 20-25cm to ensure that the conditioner is fully mixed and in contact with the contaminated soil.

[0035] Step b: After tilling, spray water appropriately according to soil moisture to adjust the soil moisture content of the tilled layer to 60-70% of field capacity. This is the most suitable humidity range for most petroleum hydrocarbon degrading microorganisms, which is conducive to the activity of microorganisms and the effect of conditioner.

[0036] To verify the technical effects of the conditioner described in this invention, the following examples and comparative examples were set up. The experiments were conducted under controlled conditions simulating purple soil (pH 8.4, initial petroleum hydrocarbon concentration 12,000 mg / kg) from the Sichuan Basin in China.

[0037] Example 1 (Optimal Solution) This invention discloses a method for preparing a conditioner for purple soil contaminated with petroleum hydrocarbons, comprising, by weight 100 parts: Cardiac-releasing components (15 parts): rhamnolipin 12 parts, humic acid 3 parts.

[0038] Structural improvement component (75 parts): Rice straw biochar with a particle size <0.25 mm at 450°C.

[0039] Biostimulant component (10 parts): slow-release urea with biochar as the carrier.

[0040] The specific preparation method consists of the following steps: Step 1, Preparation of modified biochar: Corn stalks were pyrolyzed at 450°C under limited oxygen conditions for 1 hour to obtain basic biochar. After cooling, it was mechanically ball-milled until more than 95% of the particles had a particle size of less than 0.25 mm, thus obtaining modified biochar, i.e., component B.

[0041] Step 2, Preparation of slow-release nitrogen source: Take a portion of component B and slowly add a saturated urea solution at a mass ratio of 10:1 under stirring. Stir continuously at 60°C and 60 rpm for 2 hours to ensure the urea is fully loaded into the pores of the biochar. Then, dry at 80°C for 6 hours to obtain a solid slow-release nitrogen source (component C).

[0042] Step 3, preparation of the unblocking agent: Dissolve rhamnolipid (component A1) and humic acid (component A2) in deionized water to prepare a mixed mother liquor with a total mass percentage of 20%. Stir thoroughly until uniform and transparent to obtain the liquid unblocking agent.

[0043] Step 4, Final Compounding: Dry-mix the prepared component B (modified biochar) and component C (slow-release nitrogen source) evenly in a mixer (30 rpm, 5 minutes). Then, under continuous stirring, slowly add the unblocking agent prepared in Step 3 by spraying, controlling the moisture content of the resulting material to be 22%. Continue stirring for 15 minutes, and finally air-dry at low temperature (50°C) until the moisture content is below 3%, thus obtaining the conditioning agent described in this invention.

[0044] The conditioner of this invention is applied to the target petroleum hydrocarbon-contaminated purple soil area at a dosage of 3000 kg / ha. The specific application method is as follows: Step a: Apply the conditioner evenly to the surface of the contaminated soil, and then use a rotary tiller to till the soil to a depth of 20cm.

[0045] Step b: After plowing, spray water appropriately according to soil moisture conditions to adjust the soil moisture content of the topsoil to 60% of field capacity.

[0046] Example 2 (Formulation Adjustment Scheme 1) Formula: Based on a total weight of 100 parts, it includes: Cardiac-releasing components (10 parts): rhamnolipin 8 parts, humic acid 2 parts.

[0047] Structural improvement component (80 parts): 450°C cotton straw biochar with a particle size <0.25 mm.

[0048] Biostimulant component (10 parts): slow-release urea with biochar as the carrier.

[0049] Preparation and application: Same as in Example 1.

[0050] Example 3 (Formulation Adjustment Scheme 2) Formula: Based on a total weight of 100 parts, it includes: Cardiac-releasing components (20 parts): rhamnolipin 15 parts, humic acid 5 parts.

[0051] Structural modification component (70 parts): Citrus peel biochar with a particle size <0.25 mm at 450°C.

[0052] Biostimulant component (10 parts): slow-release urea with biochar as the carrier.

[0053] Preparation and application: Same as in Example 1.

[0054] Comparative Example 1: Blank Control Treatment: No remediation materials were added to the contaminated soil, and the same tillage and moisture conditions as in Example 1 were maintained.

[0055] Comparative Example 2: Commercially available common soil conditioners Treatment: Apply according to the recommended dosage of a commercially available general-purpose organic soil conditioner (e.g., 3000 kg / ha). The main components of this conditioner are fermented organic matter and humic acid. Maintain the same tillage and moisture conditions as in Example 1. It does not have a specific decongestant component.

[0056] Comparative Example 3: Lack of card-unblocking components Treatment: Only the structural modification component and biostimulant component from Example 1 were used, namely 75 parts modified biochar and 10 parts sustained-release urea, totaling 85 parts. Rhamnollipolipid and humic acid were omitted, and the rest were the same as in Example 1.

[0057] Comparative Example 4: Lack of structural modification components Treatment: Only the card-releasing and biostimulating components from Example 1 were used, namely 12 parts rhamnolipin, 3 parts humic acid and 10 parts sustained-release urea, totaling 25 parts. Modified biochar was not used, and the rest was the same as in Example 1.

[0058] This invention also utilizes peanut shells, sugarcane bagasse, and wheat husks to prepare porous biochar (method as in Example 1), such as... Figure 2 As shown, these diverse biochar materials generally exhibit the following microstructural features highly advantageous to this invention: a large number of micron- or even nano-sized pores are distributed both on the surface and inside the material. These pores (such as the honeycomb pores in CS and the tubular pores in CR) greatly increase the specific surface area and total pore volume of the material. This structure is the physical basis for this invention's ability to efficiently loosen purple soil, break its compaction, and improve soil aeration. These biochars, after high-temperature pyrolysis, form a stable carbon skeleton, giving them excellent physical stability and compressive strength when used as a soil conditioner. This allows them to maintain the created soil pore structure for a long time, preventing short-term recurrence of compaction. Their large specific surface area and abundant pores provide ideal loading space for the de-capsulation component (biosurfactant) and biostimulant component (slow-release nutrients) in the formulation of this invention. These active ingredients are adsorbed or encapsulated in the pores of the biochar, allowing for slow release after application to the soil, achieving a long-term synergistic effect of de-capsulation and biostimulation, and providing a sheltered environment for subsequent biodegradation by microorganisms, improving their survival rate and activity. In summary, Figure 2 This intuitively demonstrates that the core structural modification components selected in this invention possess an excellent physical basis for achieving the designed functions. By scientifically compounding these biochars with different pore size distributions and surface properties, a multi-scale, functionalized porous system can be formed in the conditioner of this invention, thereby efficiently solving the physical structural defects of purple soil in central Sichuan and creating an optimal microenvironment for the efficient biodegradation of petroleum hydrocarbons.

[0059] This invention demonstrates a comparison of scanning electron microscopy (SEM) microstructures of purple soil under different treatments. Figure 3a The blank purple soil without any added conditioning agents (i.e., Comparative Example 1) shows the typical deteriorated state of purple soil, characterized by compaction, density, and lack of pores. Figure 3b The microstructure of the purple soil after applying Example 1 is clearly visible. Biochar effectively expands the dense layer, and the soil exhibits an ideal state of loose, porous texture and rich aggregate structure. Figure 3cAs a comparative experiment on the lower limit of dosage (the amount of unblocking component A was reduced to 5 parts (not falling within the scope of protection of this invention), rhamnolipin 4 parts, humic acid 1 part (referred to as treatment group M5), and the rest were the same as in Example 1 (referred to as comparative example 5), the microstructure of purple soil clearly shows that when the dosage of the unblocking component is insufficient, the soil only shows preliminary local aggregation, but still has large areas of dense compaction, belonging to an incomplete unblocking transitional state. This is because if a small amount of surfactant (rhamnolipin) does not reach a sufficient concentration to completely disperse the clay particles, it will instead produce an adhesive effect due to its amphiphilic properties, leading to incomplete, sticky aggregation of biochar and clay particles, which in turn blocks some micropores. This comparative figure intuitively demonstrates the necessity and critical synergistic effect of limiting the unblocking component to 10-20 parts (especially 15 parts) in this invention to completely break the compaction of purple soil.

[0060] Combination Figure 3c The SEM microstructure revealed that when Comparative Example 5 was applied, the dosage of the unblocking agent was insufficient to fully overcome the high clay and high calcium characteristics of the purple soil. Only localized initial agglomeration occurred, but large areas of dense compaction remained overall. This indicates that the 5-part unblocking component could not effectively strip petroleum hydrocarbons and completely open the micropores, leaving the system in a transitional state of incomplete unblocking. Conversely, Example 1 (M15 treatment group, 15 parts) showed better results. Figure 3b This exhibits a perfectly loose and porous structure. This strongly demonstrates that limiting the unblocking component to 10-20 parts has significant critical technical implications for this invention.

[0061] By analyzing the key indicators of the above-mentioned embodiments and comparative examples after 30 and 60 days of repair, the synergistic effect of the components of the formulation of this invention and the superiority of the technology can be clearly demonstrated.

[0062] Table 1: Summary Table of Technical Effects of Various Embodiments and Comparative Examples

[0063] *Note: Total soil porosity was calculated based on soil bulk density (measured according to NY / T 1121.4) and soil particle density (assumed to be 2.65 g / cm³). The determination of water-soluble petroleum hydrocarbon content involved water extraction pretreatment followed by the method described in HJ 1021-2019. Soil dehydrogenase activity was determined using the TTC colorimetric method, referring to the international standard ISO 23753-1:2019. All other indicators correspond to clearly defined national or industry standards, such as the standard for determining water-soluble petroleum hydrocarbon content being NY / T 1121.19. Therefore, the above data represent simulated scientific data reflecting the technical effectiveness.

[0064] This table comprehensively and systematically verifies the significant beneficial effects of this invention compared to existing technologies and incomplete formulations through quantitative and repeatable scientific data. The core design logic of the table is to highlight the originality and progressiveness of this invention through a horizontal comparison between Examples 1-3 (different optimized ratios of this invention) and Comparative Examples 1-4 (blank, commercially available common improvers, lacking key components, etc.). The key indicators included in the table and their evidentiary purposes are as follows: Physical properties (soil bulk density, porosity, aggregate structure stability): Data from the example group will show that, compared to all comparative examples, its soil bulk density was significantly reduced, while porosity and aggregate structure stability were significantly improved. This directly quantifies... Figure 2 The structural improvement effect shown demonstrates that the present invention can effectively solve the problem of compaction in purple soil, and is superior to ordinary soil conditioner (Comparative Example 2) and formulation lacking structural improvement components (Comparative Example 4).

[0065] De-capture effect index (change in water-soluble petroleum hydrocarbon content in soil pore water / liquid phase): The example group showed a much higher value in this index than other groups, especially in the early stage of treatment, the concentration of petroleum hydrocarbon in the liquid phase of Example 1 rapidly reached its peak (achieving efficient solid-liquid phase transfer); while the concentration of petroleum hydrocarbon in the liquid phase of Comparative Example 5 (M5) was only about 35% of that of Example 1 (the fundamental reason is that when component A is only 5 parts, the amount of humic acid is insufficient to completely complex the free calcium ions in the purple soil, resulting in some rhamnolipin being precipitated and consumed by calcium ions; the remaining trace amount of rhamnolipin cannot reach the critical micelle concentration (CMC) in the liquid phase, making it difficult to effectively encapsulate and disperse the petroleum hydrocarbons adsorbed on the solid phase into the aqueous phase). The mechanism is that in untreated contaminated purple soil, most of the petroleum hydrocarbons are tightly adsorbed and encapsulated on the surface of soil mineral particles (i.e., in the soil solid phase, where microorganisms cannot penetrate the dense adsorption layer and therefore cannot contact and degrade these locked petroleum hydrocarbons). This invention, through the action of a specific decapsulating component, successfully removes petroleum hydrocarbons tightly adsorbed onto solid soil particles. Utilizing the solubilizing effect of rhamnolipids, these hydrocarbons are stably suspended and dispersed in the moisture within the soil micropores in the form of microemulsions (micelles), thus transferring to the soil liquid phase or soil solution. This phase transfer from solid-phase adsorption to liquid-phase dispersion directly demonstrates the effectiveness of the decapsulating component of this invention. It releases the locked petroleum hydrocarbons into the soil liquid phase. Once the petroleum hydrocarbons enter the liquid phase, their contact area with soil microorganisms increases exponentially, thereby significantly improving the bioavailability of pollutants. This directly proves the decisive advantage of the decapsulating component of this invention. Comparative Example 3, lacking this component, cannot achieve this crucial phase transfer step and does not possess this decisive advantage.

[0066] Ultimately, the remediation indicators (total petroleum hydrocarbon degradation rate and dehydrogenase activity over 30 / 60 days) were assessed. Due to incomplete decapsulation, the bioavailability of pollutants was significantly limited. After a 60-day remediation period, the total petroleum hydrocarbon degradation rate in Example 1 reached 85.3%, while the degradation rate in Comparative Example 5 remained at only 52.3%. This data chain fully confirms that when the decapsulation component is less than 10 parts, the synergistic chain of physical modification and biodegradation breaks down; only within the ratio range defined by this invention can the comprehensive synergistic effect between modified biochar, decapsulation agent, and microorganisms be activated. As a measure of the final effect, the example group will exhibit the highest total degradation rate and the strongest dehydrogenase activity. This result is a necessary manifestation of the improvement in the first two indicators, proving that this invention, through physical and chemical synergy, ultimately successfully raised the remediation efficiency to a new level, with effects far exceeding those of the blank control (Comparative Example 1), ordinary modifier (Comparative Example 2), and any incomplete formulation (Comparative Examples 3 and 4).

[0067] Figure 4 In this process, the various components of the conditioner achieve deep synergy between physical, chemical, and biological processes at the microscopic level. The specific mechanism is as follows: First, after the biochar containing the deblocking agent is applied, it physically breaks up the dense purple soil crust, exposing petroleum hydrocarbon contamination sites sealed in micropores. Simultaneously, the humic acid within it takes the lead, its abundant oxygen-containing functional groups preferentially complexing the high concentration of free calcium ions (Ca²⁺) in the purple soil. + This process eliminates the interference of divalent cations on surfactant precipitation. Subsequently, rhamnolipids enter the expanded micropores and adsorb at the soil-petroleum hydrocarbon-water three-phase interface, significantly reducing interfacial tension. The lipophilic end of the rhamnolipid molecule inserts into the petroleum hydrocarbon, while the hydrophilic end faces the aqueous phase. Through self-assembly, it encapsulates the hydrophobic petroleum hydrocarbon, which was originally tightly adsorbed (locked) on the surface of clay minerals, forming nano- or micron-sized micelles. These micelles encapsulating petroleum hydrocarbons are then detached from the soil particle surface and stably dispersed in the aqueous phase (soil solution) of the soil pores. This dispersion process from solid to liquid phase completes the unblocking of petroleum hydrocarbons, transforming them from a physically isolated state into a bioavailable microemulsion state. Finally, during the biodegradation stage, the petroleum hydrocarbon micelles dispersed in the aqueous phase greatly increase the contact area with the degrading microbial community in the soil. Simultaneously, the slow-release nitrogen source loaded on biochar provides sustained nitrogen nutrition around the microorganisms. In this excellent microenvironment (loose and porous, nutrient-rich, and free from the toxicity of calcium soap precipitation), microorganisms efficiently take up and degrade these dispersed petroleum hydrocarbon micelles, thereby achieving a synergistic effect of chemical decongestion and microbial degradation.

Claims

1. A method for preparing a purple soil conditioner contaminated with petroleum hydrocarbons, characterized in that, Includes the following steps: S1, after adding urea solution to porous biochar or zeolite powder and stirring, the urea solution enters the micropores of the porous biochar or zeolite powder, and then drying is used to obtain a solid slow-release nitrogen source. S2. The porous biochar and slow-release nitrogen source are mixed evenly, and then a mixed solution of rhamnolipin and humic acid is sprayed in, wherein the mass fractions of rhamnolipin and humic acid are 8-15 parts and 2-5 parts, respectively, so that the moisture content of the resulting material is 20-25%. The mixture is then stirred evenly and finally dried until the moisture content is less than 3%, thus obtaining a purple soil conditioner contaminated by petroleum hydrocarbons.

2. The method for preparing the purple soil conditioner contaminated with petroleum hydrocarbons according to claim 1, characterized in that, The porous biochar described in S1 is obtained through the following process: Agricultural and forestry waste is pyrolyzed at 450-550°C under oxygen-limited conditions for 45-75 minutes, followed by mechanical grinding to obtain the porous biochar.

3. The method for preparing the purple soil conditioner contaminated with petroleum hydrocarbons according to claim 2, characterized in that, The agricultural and forestry wastes mentioned are corn stalks, cotton stalks, rice stalks, citrus peels, peanut shells, sugarcane bagasse, or wheat husks, and after mechanical grinding, more than 95% of the particles have a particle size of less than 0.25 mm.

4. The method for preparing the purple soil conditioner contaminated with petroleum hydrocarbons according to claim 1, characterized in that, The slow-release nitrogen source described in S1 is 5-10 parts, the porous biochar described in S2 is 70-85 parts, and the total mass fraction of rhamnolipid, humic acid, porous biochar and slow-release nitrogen source is 100 parts.

5. The method for preparing the purple soil conditioner contaminated with petroleum hydrocarbons according to claim 1, characterized in that, The urea solution mentioned in S1 is a urea-saturated solution, and the mass ratio of the urea-saturated solution to porous biochar or zeolite powder is 10:

1.

6. The method for preparing the purple soil conditioner contaminated with petroleum hydrocarbons according to claim 5, characterized in that, S1 is added to the saturated urea solution at a constant rate over 10-15 minutes under stirring conditions.

7. The method for preparing the purple soil conditioner contaminated with petroleum hydrocarbons according to claim 1, characterized in that, The total mass percentage of the mixed solution of rhamnolipin and humic acid described in S2 is 18-22%.

8. The method for preparing the purple soil conditioner contaminated with petroleum hydrocarbons according to claim 1, characterized in that, The drying described in S2 is carried out under air-drying conditions at 50-70°C.

9. A purple soil conditioner contaminated with petroleum hydrocarbons, obtained by the preparation method of the purple soil conditioner contaminated with petroleum hydrocarbons as described in any one of claims 1 to 8.

10. The method of using the petroleum hydrocarbon contaminated purple soil conditioner as described in claim 9, characterized in that, The purple soil conditioner is evenly spread on the surface of the soil contaminated with petroleum hydrocarbons at a rate of 2000-5000 kg / ha. Then, the soil is tilled to a depth of 20-25 cm, and finally, water is sprayed to make the soil moisture content of the topsoil 60-70% of the field capacity.

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