Method for preparing soil material through synergistic aerobic co-fermentation of Ca-Si-C material, phosphogypsum and sludge

Abstract

The invention discloses a method for preparing a soil material through aerobic co-fermentation of a Ca-Si-C material cooperating with ardealite and sludge, according to the method, the Ca-Si-C material, the ardealite and municipal sludge are used as fermentation substrates, aerobic composting fermentation is performed to prepare the soil material, the C / N ratio of the fermentation substrates is (20-30): 1, and the pH is 6-7; the Ca-Si-C material is obtained by mixing 50%-70% of dry basis municipal sludge and 30%-50% of fly ash, adding water, uniformly mixing and firing at 500-700 DEG C; according to the method, the municipal sludge, the fly ash and the ardealite are combined, a co-calcination and fermentation process is adopted, harmful components in industrial waste are effectively treated, the environmental stability and the resource utilization potential of the final material are improved by utilizing the unique property of the fly ash, and the soil material has the advantages that the environmental pollution is reduced, and meanwhile, the environmental pollution is reduced. A new technical path is provided for solid waste resource utilization; the environmental friendliness and the safety of the whole material are improved.

Description

Technical Field

[0001] The invention relates to a method for preparing soil materials by comprehensive utilization of municipal sludge, fly ash, phosphogypsum and other solid wastes, belonging to the field of recycling of bulk solid wastes and industrial solid wastes, namely, the field of solid waste resource utilization. Background Art

[0002] With the advancement of industrialization, the accumulation of industrial by-products such as phosphogypsum and sludge has become an environmental problem that needs to be solved urgently. As a by-product of phosphoric acid production, phosphogypsum is mainly composed of calcium sulfate dihydrate, accompanied by a certain amount of soluble fluoride and heavy metals. If these harmful substances are not effectively treated, they may pose a long-term pollution risk to soil and water bodies. On the other hand, sludge, as a solid waste in the wastewater treatment process, is rich in organic matter and nutrients, but its heavy metal content also poses a threat to the environment. Fly ash, as a by-product of coal-fired power plants, contains rich compounds such as silicates and aluminates, has good activity and adsorption capacity, and has been widely used in environmental governance and material modification in recent years. How to use the unique characteristics of fly ash to effectively reduce the mobility of harmful substances in sludge and phosphogypsum has become a hot research issue. Summary of the invention

[0003] In view of the problems existing in the prior art, the present invention provides a method for preparing soil materials by aerobic co-fermentation of Ca-Si-C materials with phosphogypsum and sludge, wherein the method uses Ca-Si-C materials, phosphogypsum and municipal sludge as fermentation matrices, performs aerobic composting fermentation to prepare soil materials, and adds wheat straw powder to the fermentation matrix to adjust the C / N ratio; the Ca-Si-C material is obtained by mixing 50%-70% of dry municipal sludge with 30%-50% of fly ash, and then firing at 500-700°C; the present invention forms a Ca-Si-C material with excellent chemical stability by co-calcining sludge and fly ash at an appropriate temperature. On this basis, the material is aerobically co-fermented with phosphogypsum and municipal sludge to finally obtain an environmentally friendly soil material with a stable structure.

[0004] The present invention utilizes the rich silicate and aluminate components in fly ash to form Ca-Si-C materials through high-temperature calcination. The Ca-Si-C materials can play a positive role in the nutrient conversion in soil materials, especially through the following aspects: Calcium and magnesium nutrient supply: The calcium and magnesium elements in the Ca-Si-C materials can not only fix pollutants, but also provide important nutrients for soil materials. These elements are essential for plant growth, especially calcium, which can promote root development and enhance plant resistance. At the same time, magnesium, as a core element of chlorophyll, also plays a key role in plant photosynthesis. Alkaline environment regulation: The alkalinity of the Ca-Si-C material can increase the pH value of the soil, especially under acidic soil conditions. This regulation can improve the soil structure, promote microbial activity, and then enhance the mineralization and conversion efficiency of nutrients, and improve soil fertility. The role of silicon: The silicon element can enhance the disease resistance of plants and improve the growth and development of plants. Especially under adverse conditions, it can improve the resistance of plants to drought, salinity and pests. Additionally, silicon helps stabilize other nutrients in the soil, increasing their availability.

[0005] In addition, Ca-Si-C materials can react with heavy metals in sludge to form hydroxides or carbonates, which are fixed in Ca-Si-C materials due to their low solubility, thus achieving the effect of solidifying and stabilizing heavy metals. In addition, phosphogypsum also contains harmful substances such as soluble fluorine. Through the synergistic reaction with Ca-Si-C materials, the calcium and magnesium in the material can react with the soluble fluorine in phosphogypsum to form insoluble calcium fluoride (CaF 2 ) and other similar fluorides. These substances usually have low solubility and can be fixed in the pore structure of the material, effectively reducing the release of fluorine, thereby greatly reducing the secondary pollution to the environment caused by the leaching of harmful substances such as soluble fluorine.

[0006] The preparation method of the soil material of the present invention is as follows: 1. Pretreatment: Dry the municipal sludge to reduce moisture, screen and remove large particles to obtain dry municipal sludge. Grind and screen the dry municipal sludge and fly ash to 125-200µm, and grind and screen the phosphogypsum; 2. Composition analysis: Chemical analysis of phosphogypsum and municipal sludge to understand its pH value, nitrogen (N), phosphorus (P), potassium (K) content, as well as the content of pollutants such as heavy metals; 3. Preparation of Ca-Si-C material: Mix 50%-70% of dry municipal sludge and 30%-50% of fly ash, add water and mix well, put it in a muffle furnace and heat it to 500-700℃ at a heating rate of 10℃ / min for 30-60min to obtain Ca-Si-C material; 4. Adjust pH and C / N ratio: If the pH value is too low or too high, it needs to be adjusted by adding substances such as lime or sulfuric acid; adding wheat straw powder increases the C / N ratio to 20-30:1; 5. Mix 10%-50% of phosphogypsum and 50%-90% of municipal sludge (water content of 60-80%), and then add Ca-Si-C material of 10%-20% of the total mass of phosphogypsum and municipal sludge, and mix them evenly in a mixer; 6. Fermentation: The mixed fermentation substrate is piled up to ensure good ventilation for the microorganisms to breathe. The composting time is 20-30 days. The moisture content of the fermentation substrate is controlled at 30%-60%. During this period, good fermentation conditions are maintained by conventional means such as water replenishment, turning, and aeration. The fermentation conditions and operation methods of aerobic composting are consistent with conventional composting fermentation methods. In the present invention, the temperature of the pile should be maintained above 70°C to promote microbial activity and eliminate pathogens. After entering the mature stage, as the microbial activity slows down, the temperature of the pile gradually decreases, and the organic matter further decomposes to form stable humus.

[0007] 7. Monitoring: Regularly monitor the temperature, humidity and pH value of the pile and make adjustments when necessary; 8. Stability test: The stability of soil materials is tested through heavy metal content determination, organic matter content determination, nitrogen, phosphorus and potassium content determination and fertilizer efficiency test.

[0008] The beneficial effects of the present invention are: 1. The municipal sludge in the method of the present invention is rich in organic matter and various nutrients required for plant growth, such as nitrogen, phosphorus, potassium, etc. The organic matter in the sludge can be converted into a form beneficial to plants through the aerobic composting process, while reducing potential harmful substances, making it a safe and effective ecological matrix fertilizer and plant nutrient source; the main component of phosphogypsum is calcium sulfate dihydrate (CaSO 4 ·2H 2 O), which can provide crops with important nutrients such as calcium (Ca), sulfur (S), nitrogen (N) and phosphorus (P); 2. The present invention combines municipal sludge, fly ash and phosphogypsum, and adopts a co-calcination and fermentation process, which not only effectively treats harmful components in industrial waste, but also utilizes the unique properties of fly ash to improve the environmental stability and resource utilization potential of the final material. This soil material not only reduces environmental pollution, but also provides a new technical path for the resource utilization of solid waste; it also improves the environmental friendliness and safety of the overall material; The rich silicate and aluminate components in fly ash are used to form Ca-Si-C materials through high-temperature calcination. This process not only gives the material good chemical stability, but also fixes the soluble fluorides and heavy metals in the sludge and phosphogypsum into insoluble compounds through physical and chemical effects during the subsequent fermentation process, significantly reducing the mobility and environmental risks of these harmful substances. This dual treatment mechanism ensures the safety of the final product, allowing it to remain stable for a long time when used in soil improvement and ecological restoration, avoiding secondary pollution to the environment. The Ca-Si-C material has a fixation rate of 85%-90% for soluble fluorine and 90%-95% for heavy metals, and the heavy metal leaching rate is less than the standard value. Therefore, the soil material of the present invention is environmentally friendly and safe. While reducing environmental pollution, the present invention also provides a new technical path for the resource utilization of solid waste. Compared with traditional phosphogypsum and sludge treatment methods, the present invention not only deals with the environmental risks of industrial waste, but also realizes its high-value application in agriculture and ecological restoration. DETAILED DESCRIPTION

[0009] The present invention is further described in detail below in conjunction with specific embodiments, but the protection scope of the present invention is not limited to the contents described above. The methods in the embodiments are conventional methods unless otherwise specified, and the reagents used are conventional commercially available reagents or reagents prepared according to conventional methods unless otherwise specified; Example 1: Method for preparing soil material by aerobic co-fermentation of Ca-Si-C material with phosphogypsum and sludge (1) Municipal sludge (water content 65%) from sewage treatment plants was dried at 40±2℃, crushed and sieved to obtain 150µm dry sludge with a water content of 7.97%; fly ash was crushed and sieved to a particle size of 150µm; phosphogypsum was crushed and sieved to obtain phosphogypsum powder with a particle size of less than 60 mesh, with a water content of 0.2%; (2) Dry sludge and fly ash were mixed in a ratio of 50% to 50% and water was added to mix them evenly. After forming, the mixture was placed in a muffle furnace and heated to 600°C at a rate of 10°C / min for 40 minutes to obtain a Ca-Si-C material. (3) According to the ratio of 30% phosphogypsum and 70% municipal sludge, 30g phosphogypsum and 70g municipal sludge were weighed on an analytical balance, and 20g of Ca-Si-C material was added; the phosphogypsum, municipal sludge and Ca-Si-C material were placed in a blender and stirred thoroughly. During the stirring process, 37.75g of wheat straw powder was added to make the C / N ratio of the mixture 25:1, and the moisture content of the mixture was adjusted to 50%-60%. The pH of the mixture was measured and adjusted to 6.5; the initial organic matter content of the mixture was measured to be 69.06%, the inorganic nitrogen content was 0.86%, and the inorganic phosphorus content was 1529.2mg / kg; (4) Composting fermentation: the mixed materials are piled up, the temperature is controlled at 70°C, and good ventilation is maintained. During the fermentation process, water is added regularly, and the compost is turned over to maintain good fermentation conditions. After 30 days of fermentation, soil materials are obtained. The stability test data of soil materials are shown in the following table: Table 1 Numerical values ​​of various indicators of soil materials after 30 days of fermentation

[0010] It can be seen from the table that the heavy metal fixation rate of the soil material prepared in this embodiment is higher than 91%, the fixation rate of soluble fluorine is 85%, and both soluble fluoride and heavy metals are effectively fixed; in addition, the growth rates of inorganic nitrogen and inorganic phosphorus after 30 days of fermentation are 117.4% and 101.0%, respectively.

[0011] Example 2: Method for preparing soil material by aerobic co-fermentation of Ca-Si-C material with phosphogypsum and sludge (1) Municipal sludge (water content 65%) from sewage treatment plants was dried at 40±2℃, crushed and sieved to obtain 200µm dry sludge with a water content of 7.97%; fly ash was crushed and sieved to a particle size of 200µm; phosphogypsum was crushed and sieved to obtain phosphogypsum powder with a particle size of less than 60 mesh, with a water content of 0.2%; (2) Dry sludge and fly ash were mixed in a ratio of 60% to 40% and water was added to mix them evenly. After forming, the mixture was placed in a muffle furnace and heated to 500°C at a rate of 10°C / min for 60 minutes to obtain a Ca-Si-C material. (3) According to the ratio of 20% phosphogypsum and 80% municipal sludge, 20g phosphogypsum and 80g municipal sludge were weighed on an analytical balance, and 15g of Ca-Si-C material was added; the phosphogypsum, dry sludge and Ca-Si-C material were placed in a blender and stirred thoroughly. During the stirring process, 36.65g of wheat straw powder was added to make the C / N ratio of the mixture 25:1, the moisture content of the mixture was adjusted to 50%-60%, the pH of the mixture was measured, and the pH of the mixture was adjusted to 6.5; the initial organic matter content of the mixture was measured to be 71.75%, the inorganic nitrogen content was 0.90%, and the inorganic phosphorus content was 1124.9mg / kg; (4) Composting fermentation: the mixed materials are piled up, the temperature is controlled at 70°C, and good ventilation is maintained. During the fermentation process, water is added regularly, the compost is turned over, and aeration is performed to maintain good fermentation conditions. After 20 days of fermentation, soil materials are obtained. The stability test data of soil materials are shown in the following table: Table 2 Numerical values ​​of various indicators of soil materials after 20 days of fermentation

[0012] It can be seen from the table that the heavy metal fixation rate of the soil material prepared in this embodiment is higher than 91%, the fixation rate of soluble fluorine is 90%, and both soluble fluoride and heavy metals are effectively fixed; in addition, the growth rates of inorganic nitrogen and inorganic phosphorus after 30 days of fermentation are 48.9% and 90.2%, respectively.

[0013] Example 3: Method for preparing soil material by aerobic co-fermentation of Ca-Si-C material with phosphogypsum and sludge (1) Municipal sludge (water content 60%) from sewage treatment plants was dried at 40±2℃, crushed and sieved to obtain dry sludge of 125µm with a water content of 7.97%; fly ash was crushed and sieved to a particle size of 125µm; phosphogypsum was crushed and sieved to obtain phosphogypsum powder with a particle size of less than 60 mesh and a water content of 0.2%; (2) Dry sludge and fly ash were mixed in a ratio of 70% to 30% and water was added to mix them evenly. After forming, the mixture was placed in a muffle furnace and heated to 700°C at a rate of 10°C / min for 30 minutes to obtain a Ca-Si-C material. (3) According to the ratio of 10% phosphogypsum and 90% municipal sludge, 10g phosphogypsum and 90g municipal sludge were weighed respectively using an analytical balance, and then 10g of Ca-Si-C material was added; the phosphogypsum, dry sludge and Ca-Si-C material were placed in a blender and fully stirred. During the stirring process, 31g of wheat straw powder was added to make the C / N ratio of the mixture 25:1, the moisture content of the mixture was adjusted to 50%-60%, the pH of the mixture was measured, and the pH of the mixture was adjusted to 6.5; the initial organic matter content of the mixture was measured to be 73.41%, the inorganic nitrogen content was 0.94%, and the inorganic phosphorus content was 753.6mg / kg; (4) Composting fermentation: the mixed materials are piled up, the temperature is controlled at 70°C, and good ventilation is maintained. During the fermentation process, water is added regularly, the compost is turned over, and aeration is performed to maintain good fermentation conditions. After 25 days of fermentation, soil materials are obtained. The stability test data of soil materials are shown in the following table: Table 3 Numerical values ​​of various indicators of soil materials after 25 days of fermentation

[0014] It can be seen from the table that the heavy metal fixation rate of the soil material prepared in this embodiment is higher than 90%, the fixation rate of soluble fluorine is 87%, and both soluble fluoride and heavy metals are effectively fixed; in addition, the growth rates of inorganic nitrogen and inorganic phosphorus after 30 days of fermentation are 83.0% and 153.5%, respectively.

Claims

1. A method for preparing soil materials by aerobic co-fermentation of Ca-Si-C materials with phosphogypsum and sludge, characterized in that: Ca-Si-C material, phosphogypsum and municipal sludge are used as fermentation matrices to carry out aerobic composting fermentation to prepare soil material, wherein the fermentation matrix C / N ratio is 20-30:1 and the pH is 6-7; the Ca-Si-C material is obtained by mixing 50%-70% of dry municipal sludge with 30%-50% of fly ash, adding water to mix well and then sintering at 500-700°C.

2. The method for preparing soil material by aerobic co-fermentation of Ca-Si-C material in cooperation with phosphogypsum and sludge according to claim 1, characterized in that: The addition amount of Ca-Si-C material is 10-20% of the total mass of phosphogypsum and municipal sludge, wherein the mass percentage of phosphogypsum is 10%~50% and the mass percentage of municipal sludge is 50%~90%.

3. The method for preparing soil material by aerobic co-fermentation of Ca-Si-C material with phosphogypsum and sludge according to claim 1, characterized in that: Phosphogypsum, dry municipal sludge and fly ash are all crushed and screened.

4. The method for preparing soil material by aerobic co-fermentation of Ca-Si-C material with phosphogypsum and sludge according to claim 1, characterized in that: Ca-Si-C materials can effectively fix heavy metals in municipal sludge during the preparation of soil-based materials. At the same time, they can convert soluble fluorine in phosphogypsum into insoluble CaF2-like substances, and effectively adsorb and fix them in the pore structure, eliminating the secondary pollution caused by soil-based materials to the environment.

5. The method for preparing soil material by aerobic co-fermentation of Ca-Si-C material with phosphogypsum and sludge according to claim 1, characterized in that: The moisture content of the fermentation substrate during aerobic composting is controlled at 30%-60%. Operations during composting include watering, turning, and aeration. The composting time is 20-30 days.

6. The method for preparing soil material by aerobic co-fermentation of Ca-Si-C material with phosphogypsum and sludge according to claim 1, characterized in that: Wheat straw powder was used to adjust the C / N ratio, and lime or sulfuric acid was used to adjust the pH.

7. Application of the soil material prepared by the method for preparing soil material by aerobic co-fermentation of the Ca-Si-C material according to claim 1 with phosphogypsum and sludge in agricultural planting and ecological restoration.

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