PH response type multifunctional slow-release soil conditioner based on raffinate acid and phosphate tailings as well as preparation method and application of pH response type multifunctional slow-release soil conditioner

Abstract

The invention discloses a pH response type multifunctional slow-release soil conditioner based on raffinate acid and phosphate tailings as well as a preparation method and application of the pH response type multifunctional slow-release soil conditioner, and belongs to the technical field of soil remediation. The method comprises the following steps: carrying out gradient leaching on phosphate tailings by utilizing raffinate acid, and adding a heavy metal curing agent to synchronously realize extraction of effective phosphorus, calcium and magnesium and in-situ curing of heavy metals, so as to obtain eutrophic leachate and detoxified tailing slag; the detoxified tailings are subjected to nanocrystallization and mixed with the leachate, sodium alginate, polyglutamic acid and optional functional additives, granulation and drying are performed through an ionic cross-linking reaction, and the conditioner is prepared. The synergistic high-value utilization of the raffinate acid and the phosphate tailings is realized, and the prepared conditioner has the pH intelligent response slow-release characteristic, can act on the acid soil in a targeting manner, regulates the acid for a long time and releases nutrients. The product has multiple functions of improving the soil structure, supplementing nutrients, passivating heavy metals and the like, realizes treatment of wastes with wastes and change of wastes into valuables, and has a wide application prospect in the fields of environmental protection and agriculture.

Description

Technical Field

[0001] This invention belongs to the field of soil remediation technology, specifically to a pH-responsive multifunctional slow-release soil conditioner based on residual acid and phosphate tailings, its preparation method, and its application. Background Technology

[0002] Currently, phosphate chemical enterprises face two major environmental challenges: the storage of phosphate tailings and the treatment of residual raffinate. Co-processing both to achieve "waste-to-waste" treatment is an urgent need for the industry. Residual raffinate is a byproduct of the extraction process in wet-process phosphoric acid production, mainly containing low-concentration phosphoric acid and residual sulfuric acid. Traditional treatment methods are costly and prone to environmental pollution. Phosphate tailings are solid waste discharged after phosphate rock concentrate is extracted through flotation. They are rich in useful minerals such as calcium, magnesium, and residual phosphorus, but contain trace amounts of heavy metals. Large-scale storage of tailings occupies land and poses environmental risks.

[0003] While the patent application with application number CN202510339881.8 solved the problem of phosphorus tailings storage, it reduced their value to building materials or underground filling materials, failing to tap their high added value potential in agricultural applications, and thus had limited economic viability. The patent application with application number CN202411537082.3 had a complex process and focused only on the extraction of a single component (such as phosphorus), failing to achieve the synergistic recovery of valuable components such as calcium and magnesium, resulting in resource waste and high costs.

[0004] Furthermore, existing soil conditioners have limited functionality and cannot meet the multiple objectives of soil improvement, nutrient replenishment, and enhanced biological activity. To effectively utilize the valuable resources in phosphate tailings and residual acid while avoiding environmental pollution from harmful components, the development of a composite conditioner that integrates acidification, nutrient replenishment, organic matter replenishment, and microbial functions holds enormous market potential. Summary of the Invention

[0005] To address the aforementioned issues, this invention aims to provide a pH-responsive multifunctional slow-release soil conditioner based on residual acid and phosphate tailings, its preparation method, and its application. The pH-responsive multifunctional slow-release soil conditioner is safe, efficient, multifunctional, and possesses pH-intelligent response release characteristics, achieving dual benefits for environmental protection and agriculture.

[0006] To achieve the above objectives, the present invention adopts the following solution: A method for preparing a pH-responsive multifunctional slow-release soil conditioner based on residual acid and phosphate tailings includes the following steps: S1. Mix the phosphate tailings with the residual acid from the wet-process phosphoric acid production process and react. S2. After the reaction in step S1 is completed, a heavy metal curing agent is added to the system to carry out the reaction. After the reaction in step S3 and S2 is completed, solid-liquid separation is performed to obtain phosphorus-rich calcium-magnesium leachate and detoxified tailings slag. S4. After drying the detoxified tailings slag obtained in step S3, nano-processing is performed to obtain phosphorus tailings nanoparticles with a particle size ≤100 nm. S5. Add the phosphorus tailings nanoparticles from step S4 to a mixed aqueous solution containing sodium alginate and polyglutamic acid, mix well, then add the phosphorus-rich calcium-magnesium leachate from step S3, and mix thoroughly to form a homogeneous mixed gel solution. S6. The mixed gel liquid obtained in step S5 is added dropwise to CaCl2 solution to carry out ionic cross-linking reaction to form spherical particles. After filtration and drying, the pH-responsive multifunctional slow-release soil conditioner is obtained.

[0007] In the preferred embodiment, the particle size of the phosphorus tailings mentioned in step S1 is no greater than 200 mesh.

[0008] In a preferred embodiment, the concentration of P2O5 in the residual acid in step S1 is 5% to 10%.

[0009] In the preferred embodiment, the mass ratio of phosphorus tailings to residual acid in step S1 is 3~4:14~16.

[0010] In the preferred embodiment, the reaction temperature in step S1 is 50~70 ℃ and the reaction time is 0.5~1.5 h.

[0011] The reactions of phosphorus tailings with acid in step S1 mainly include the reaction of calcite with acid, the reaction of dolomite with acid, and the reaction of fluorapatite with acid. Acid hydrolysis of calcite: CaCO3+2H3PO4→Ca(H2PO4)2+H2O+CO2↑; Acid hydrolysis of dolomite: CaMg(CO3)2+4H3PO4→Ca(H2PO4)2+Mg(H2PO4)2+2H2O+2CO2↑; Acid hydrolysis of fluorapatite: Ca5(PO4)3F+7H3PO4+5H2O→5Ca(H2PO4)2⋅H2O+HF↑; Heavy metal ions (such as Cd) released after acid hydrolysis 2+ Pb 2+ ) and phosphate ions (PO4) in the reaction system 3- The reaction occurs, forming an extremely insoluble phosphate precipitate, which is then solidified.

[0012] In the preferred embodiment, the amount of heavy metal solidifying agent added in step S2 is 3% to 5% of the mass of the phosphate tailings.

[0013] In the preferred embodiment, the heavy metal curing agent mentioned in step S2 is a biochar-supported hydroxyapatite composite material (HAP). HAP strongly adsorbs residual heavy metal ions through its large specific surface area and abundant functional groups.

[0014] In the preferred embodiment, the reaction time in step S2 is 20 to 40 minutes.

[0015] In a preferred embodiment, step S5 further includes the addition of a functional additive, which is selected from potassium salts, trace elements, organic matter, and / or microbial inoculants. The functional additive is organic matter; the phosphorus tailings nanoparticles and organic matter from step S4 are sequentially added to a mixed aqueous solution containing sodium alginate and polyglutamic acid, mixed thoroughly, and then the phosphorus-rich calcium-magnesium leachate from step S3 is added, and the mixture is thoroughly mixed to form a homogeneous mixed gel. Alternatively, the functional additive is potassium salts, trace elements, and / or microbial inoculants. The phosphorus tailings nanoparticles and organic matter from step S4 are sequentially added to a mixed aqueous solution containing sodium alginate and polyglutamic acid, mixed thoroughly, and then the phosphorus-rich calcium-magnesium leachate from step S3 is added, stirred evenly, and then the potassium salts, trace elements, and / or microbial inoculants are added, and the mixture is thoroughly mixed to form a homogeneous mixed gel.

[0016] Step S5 describes the order of addition to construct the gel system, aiming to ensure that each component is uniformly dispersed and ultimately forms a structurally stable and functionally complete gel network. The addition order consists of the following three steps: (1) Sodium alginate + polyglutamic acid (PGA) mixed aqueous solution: to achieve uniform mixing of polymer chains. Sodium alginate and PGA are both water-soluble polymers. Mixing them in an aqueous solution first allows the molecular chains of both to fully extend and entangle in the solution, forming a uniform polymer mixed solution, which lays the foundation for the subsequent construction of interpenetrating networks or synergistic gel systems; (2) Adding phosphorus tailings nanoparticles: after adding calcium ions (Ca) 2+ Adding nanoparticles before the leachate is crucial. At this time, the solution viscosity is moderate (only from polymers), making it easy to uniformly disperse the nanoparticles by stirring and preventing them from agglomerating; (3) Add phosphorus-rich calcium-magnesium leachate, water-soluble additives and microbial agents: potassium salts and trace elements are ions or small molecules, which are very easy to dissolve, while microorganisms are sensitive to shear force (high-speed stirring) and temperature. The leachate is a crosslinking agent (Ca 2+ For carriers containing divalent cations, the leachate must be added only at the last moment after all the aforementioned components (polymers, fillers) have been uniformly dispersed, thereby initiating a cross-linking reaction.

[0017] In a further preferred embodiment, the potassium salt includes potassium sulfate; the trace elements include borax and / or zinc sulfate; the organic matter includes humic acid and / or fulvic acid; and the microbial agents include phosphate-solubilizing bacteria, potassium-solubilizing bacteria, nitrogen-fixing bacteria, and / or Bacillus mucilaginosus.

[0018] In the preferred embodiment, the mass concentration of CaCl2 in the CaCl2 solution in step S6 is 2% to 4%.

[0019] In a preferred embodiment, the drying temperature in step S6 is below 50 °C.

[0020] In a further preferred embodiment, the drying process is either forced-air drying or freeze-drying.

[0021] The pH-responsive multifunctional slow-release soil conditioner is applied at a rate of 1.5 to 2.5 tons per acre in acidic soil remediation, through deep tillage into the soil tillage layer.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The pH-responsive multifunctional slow-release soil conditioner provided by the present invention uses residual acid and phosphorus tailings as raw materials. Its gel network structure is coated with phosphorus, calcium, magnesium nutrients and optional functional additives, and has pH-responsive characteristics.

[0023] (2) This invention co-processes two major problematic materials, namely residual acid and phosphorus tailings, and transforms them into high-value products, realizing a closed loop of circular economy within the phosphorus chemical industrial park and maximizing environmental and economic value.

[0024] (3) Through the modular design of “basic formula + optional additives”, this invention can flexibly produce a series of products such as standard acid-adjusting type, nutritional supplement type, organic fortified type and biological functional type to meet diverse market demands.

[0025] (4) The present invention can also introduce organic matter and microbial agents, which work synergistically with basic mineral nutrients. This not only adjusts acidity and supplements fertilizer, but also significantly improves soil microecology and aggregate structure, achieving a synergistic repair effect of 1+1>2. Detailed Implementation

[0026] The technical solution of the present invention will be further described and illustrated below through examples. All raw materials used in the examples are commercially available or prepared using conventional methods.

[0027] Example 1 A pH-responsive multifunctional slow-release soil conditioner based on raffinate and phosphate tailings comprises the following raw materials in parts by weight: 85 parts phosphate tailings, 375 parts raffinate, 4 parts biochar-supported hydroxyapatite composite material, 8 parts sodium alginate gel matrix, 4 parts polyglutamic acid, 8.4 parts calcium chloride crosslinking agent, 1 part potassium sulfate, and 2 parts humic acid. The phosphorus tailings have a particle size of no more than 200 mesh, and their composition is as follows: P2O5 content is 5.2 wt%, CaO content is 32.2 wt%, and MgO content is 14.5 wt%. The residual acid is generated during the wet process of phosphoric acid production. The original P2O5 mass concentration of the residual acid is 35.2%, which is adjusted to 8% by adding water.

[0028] The preparation method of the pH-responsive multifunctional slow-release soil conditioner based on residual acid and phosphate tailings includes the following steps: S1. Take 425 g of phosphorus tailings and 1875 g of residual raffinate into a reaction vessel and stir at 60 °C for 1 h. After the reaction in step S1 is completed, add 4.7% of the heavy metal solidifying agent biochar-supported hydroxyapatite composite material (based on the mass of phosphate tailings) to the system and continue stirring for 30 min. After the reaction in step S3 and S2 is completed, pressure filtration separation is performed to obtain 2055g of phosphorus-rich calcium-magnesium leachate and 245g of detoxified tailings slag. S4. After drying the detoxified tailings slag obtained in step S3, grind it for 4 hours to obtain a particle size D. 50 Phosphate tailings nanoparticles with a diameter of 85 nm; S5. Prepare 2 L of sodium alginate aqueous solution with a mass concentration of 2%, and add 20 g of polyglutamic acid to form a homogeneous polymer mixed solution. Under stirring, add 245 g of phosphorus tailings nanoparticles and 10 g of humic acid obtained in step S4 in sequence. After stirring evenly, add 2055 g of phosphorus-rich calcium-magnesium leachate obtained in step S3. After stirring evenly, add 5 g of potassium sulfate and stir evenly to obtain a homogeneous mixed gel solution. S6. Using a peristaltic pump, the mixed gel liquid obtained in step S5 is added dropwise to 14 L of CaCl2 solution with a mass concentration of 3% to carry out an ionic cross-linking reaction, forming spherical particles. The particles are collected by filtration and dried by forced air at 55 °C to obtain the pH-responsive multifunctional slow-release soil conditioner.

[0029] Comparative Example 1 A soil conditioner, which is basically the same as in Example 1, except that the biochar-supported hydroxyapatite composite material in its raw materials is 0 parts.

[0030] The preparation method of the soil conditioner is basically the same as that in the example, except that biochar-supported hydroxyapatite composite material is not added in step S2.

[0031] Comparative Example 2 A soil conditioner, which is basically the same as that in Example 1, except that the raw material contains 2 parts of biochar-supported hydroxyapatite composite material.

[0032] The preparation method of the soil conditioner is basically the same as that in the example, except that the amount of biochar-supported hydroxyapatite composite material added in step S2 is 2.35% of the mass of the phosphorus tailings.

[0033] The analytical results of the soil conditioners prepared in Example 1 and Comparative Examples 1-2 are shown in Table 1.

[0034] Table 1. Component analysis results of Example 1 and Comparative Examples 1-2

[0035] Example 2 A pH-responsive multifunctional slow-release soil conditioner based on raffinate and phosphate tailings comprises the following raw materials in parts by weight: 80 parts phosphate tailings, 355 parts raffinate, 3 parts biochar-supported hydroxyapatite composite material, 10 parts sodium alginate gel matrix, 4 parts polyglutamic acid, 9 parts calcium chloride crosslinking agent, 1 part potassium sulfate, and 2 parts humic acid. The phosphate tailings have a particle size of no more than 200 mesh and a composition of: 4.89% P2O5, 34.2% CaO, and 15.5% MgO. The residual acid is generated during the wet process of phosphoric acid production. The original P2O5 mass concentration of the residual acid is 36.5%, which is adjusted to 8% by adding water.

[0036] The preparation method of the pH-responsive multifunctional slow-release soil conditioner based on residual acid and phosphate tailings includes the following steps: S1. Take 400 g of phosphorus tailings and 1775 g of residual raffinate into a reaction vessel and stir at 60 °C for 1 h. S2. After the reaction in step S1 is completed, add 3.75% of the heavy metal solidifying agent biochar-supported hydroxyapatite composite material (based on the mass of phosphate tailings) to the system and continue stirring for 30 min. S3. After the reaction in step S2 is completed, pressure filtration is performed to separate the residue, yielding 1948 g of phosphorus-rich calcium-magnesium leachate and 227 g of detoxified tailings slag; S4. The detoxified tailings slag obtained in step S3 is dried and then ground for 4 h to obtain a particle size D. 50 Phosphate tailings nanoparticles with a diameter of 85 nm; S5. Prepare 2 L of sodium alginate aqueous solution with a mass concentration of 2% and add 20 g of polyglutamic acid to form a homogeneous polymer mixed solution. Under stirring, add 227 g of phosphorus tailings nanoparticles obtained in step S4, 10 g of humic acid, 1948 g of phosphorus-rich calcium-magnesium leachate obtained in step S3, and 5 g of potassium sulfate in sequence, mix evenly, and obtain a mixed gel solution. S6. Using a peristaltic pump, the mixed gel liquid obtained in step S5 is added dropwise to 15 L of CaCl2 solution with a mass concentration of 3% to carry out an ionic cross-linking reaction, forming spherical particles. The particles are collected by filtration and dried by forced air at 55 °C to obtain the pH-responsive multifunctional slow-release soil conditioner.

[0037] Comparative Example 3 A soil conditioner, which is basically the same as in Example 2, except that the biochar-supported hydroxyapatite composite material in its raw materials is 0 parts.

[0038] The preparation method of the soil conditioner is basically the same as that in the example, except that the amount of biochar-supported hydroxyapatite composite material added in step S2 is 0% of the mass of the phosphorus tailings.

[0039] Comparative Example 4 A soil conditioner, which is basically the same as in Example 2, except that the raw material contains 2 parts of biochar-supported hydroxyapatite composite material.

[0040] The preparation method of the soil conditioner is basically the same as that in the example, except that the amount of biochar-supported hydroxyapatite composite material added in step S2 is 2.35% of the mass of the phosphorus tailings.

[0041] The analytical results of the soil conditioners prepared in Example 2 and Comparative Examples 3-4 are shown in Table 2.

[0042] Table 2. Component analysis results of Example 2 and Comparative Examples 3-4

[0043] Based on the analytical results of Examples 1-2 and Comparative Examples 3-4, the biochar-supported hydroxyapatite composite material plays a dual role in this patent as both a "deep heavy metal purifier" and a "soil conditioner and enhancer." Through a synergistic mechanism of physical adsorption and chemical stabilization, it deeply immobilizes heavy metal ions (such as Cd) in phosphate tailings. 2+ Pb 2+ Biochar possesses a large specific surface area and abundant porous structure, enabling it to strongly adsorb heavy metal ions. Simultaneously, the supported hydroxyapatite (HAP) can undergo ion exchange with these ions (Ca). 2+ Being Cd 2+ / Pb 2+ It can replace and generate extremely stable phosphate precipitates (such as Pb5(PO4)3OH), thereby achieving long-term stabilization of heavy metals, effectively reducing the release of heavy metal ions, and completely eliminating the environmental risks of utilizing phosphate tailings.

[0044] Example 3 Soil conditioner pot experiment This pot experiment used uniformly sized plastic pots (top diameter × height × bottom diameter: 30 cm × 25 cm × 20 cm), each filled with 10.0 kg of typical southern acidic red soil (initial pH = 4.82) that had passed through a 5 mm sieve. The experiment included two treatments: a control group (no conditioner applied) and experimental group 1 (applied the conditioner prepared in Example 1, at an application rate equivalent to 2.0 tons / acre), with each treatment replicated 6 times. All pots were randomly arranged in a greenhouse, with 5 corn seeds sown in each pot. After emergence, seedlings were thinned to 2 plants per pot, and managed with standard water and fertilizer. The growth cycle was 90 days.

[0045] Post-harvest measurements showed that the soil pH in the control group was around 4.85, while the soil pH in the experimental group steadily increased to around 6.15, and the corn grain yield increased by an average of 33% compared to the control group. At the same time, the heavy metal content in the soil of the experimental group was lower than the national standard limit (Pb≤50 mg / kg, Cd≤0.5 mg / kg), confirming that the product has the dual effects of improving soil acidity and increasing yield.

[0046] The application of Examples 1-2, Comparative Examples 1-4, and Experimental Example 1 demonstrates that the multifunctional slow-release soil conditioner prepared based on residual acid and phosphate tailings can efficiently and persistently raise the pH value of acidic soil to above 6.0, while simultaneously releasing nutrients such as phosphorus, calcium, and magnesium, thereby increasing crop yield. More importantly, through in-situ solidification technology, it effectively solidifies harmful substances such as heavy metals in phosphate tailings, ensuring that the heavy metal content in crop grains meets national safety standards. It possesses the remarkable effect of combining "improvement, nutrition, and detoxification," providing a brand-new solution for the high-value utilization of industrial and agricultural solid waste and the safe remediation of acidic soil.

[0047] It should be understood that the above embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A method for preparing a pH-responsive multifunctional slow-release soil conditioner based on residual acid and phosphate tailings, characterized in that, Includes the following steps: S1. Mix the phosphate tailings with the residual acid from the wet-process phosphoric acid production process and react. S2. After the reaction in step S1 is completed, a heavy metal curing agent is added to the system to carry out the reaction. After the reaction in step S3 and S2 is completed, solid-liquid separation is performed to obtain phosphorus-rich calcium-magnesium leachate and detoxified tailings slag. S4. After drying the detoxified tailings slag obtained in step S3, nano-processing is performed to obtain phosphorus tailings nanoparticles with a particle size ≤100 nm. S5. Add the phosphorus tailings nanoparticles from step S4 to a mixed aqueous solution containing sodium alginate and polyglutamic acid, mix well, then add the phosphorus-rich calcium-magnesium leachate from step S3, and mix thoroughly to form a homogeneous mixed gel solution. S6. The mixed gel liquid obtained in step S5 is added dropwise to CaCl2 solution to carry out ionic cross-linking reaction to form spherical particles. After filtration and drying, the pH-responsive multifunctional slow-release soil conditioner is obtained.

2. The preparation method of the pH-responsive multifunctional slow-release soil conditioner based on residual acid and phosphate tailings according to claim 1, characterized in that, The particle size of the phosphorus tailings mentioned in step S1 is no greater than 200 mesh; the concentration of P2O5 in the residual acid mentioned in step S1 is 5%~10%; the mass ratio of phosphorus tailings to residual acid mentioned in step S1 is 3~4:14~16.

3. The preparation method of the pH-responsive multifunctional slow-release soil conditioner based on residual acid and phosphate tailings according to claim 1, characterized in that, The reaction in step S1 is carried out at a temperature of 50-70 °C for a duration of 0.5-1.5 h.

4. The preparation method of the pH-responsive multifunctional slow-release soil conditioner based on residual acid and phosphate tailings according to claim 1, characterized in that, The amount of heavy metal curing agent added in step S2 is 3% to 5% of the mass of phosphorus tailings; the heavy metal curing agent in step S2 is a biochar-supported hydroxyapatite composite material.

5. The preparation method of the pH-responsive multifunctional slow-release soil conditioner based on residual acid and phosphate tailings according to claim 1, characterized in that, The reaction time described in step S2 is 20 to 40 minutes.

6. The preparation method of the pH-responsive multifunctional slow-release soil conditioner based on residual acid and phosphate tailings according to claim 1, characterized in that, In step S5, functional additives are also added. The functional additives are selected from potassium salts, trace elements, organic matter, and / or microbial inoculants. The functional additive is organic matter. The phosphorus tailings nanoparticles and organic matter from step S4 are added to a mixed aqueous solution containing sodium alginate and polyglutamic acid and mixed evenly. Then, the phosphorus-rich calcium-magnesium leachate from step S3 is added and thoroughly mixed to form a homogeneous mixed gel liquid. The functional additive is potassium salts, trace elements, and / or microbial inoculants. The phosphorus tailings nanoparticles and organic matter from step S4 are added to a mixed aqueous solution containing sodium alginate and polyglutamic acid and mixed evenly. Then, the phosphorus-rich calcium-magnesium leachate from step S3 is added and stirred evenly. Finally, the potassium salts, trace elements, and / or microbial inoculants are added and thoroughly mixed to form a homogeneous mixed gel liquid.

7. The preparation method of the pH-responsive multifunctional slow-release soil conditioner based on residual acid and phosphate tailings according to claim 6, characterized in that, The potassium salt includes potassium sulfate; the trace elements include borax and / or zinc sulfate; the organic matter includes humic acid and / or fulvic acid; and the microbial agents include phosphate-solubilizing bacteria, potassium-solubilizing bacteria, nitrogen-fixing bacteria, and / or Bacillus mucilaginosus.

8. The preparation method of the pH-responsive multifunctional slow-release soil conditioner based on residual acid and phosphate tailings according to claim 1, characterized in that, The mass concentration of CaCl2 in the CaCl2 solution described in step S6 is 2%~4%; the drying temperature described in step S6 is below 50 ℃.

9. A pH-responsive multifunctional slow-release soil conditioner prepared by the preparation method of the pH-responsive multifunctional slow-release soil conditioner based on residual acid and phosphate tailings as described in any one of claims 1 to 8.

10. The application of a pH-responsive multifunctional slow-release soil conditioner as described in claim 9 in the remediation of acidic soils, characterized in that, The pH-responsive multifunctional slow-release soil conditioner is applied at a rate of 1.5 to 2.5 tons per acre, and is incorporated into the soil tillage layer through deep plowing.

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