Method for activating coal slime ash to produce efficient silicon fertilizer

Abstract

This invention discloses an activation method for producing high-efficiency silicon fertilizer from coal slime ash, relating to the technical field of industrial solid waste resource utilization and high-efficiency fertilizer preparation. This invention involves mixing sodium carbonate, calcium carbonate, and pretreated coal slime ash to form a mixture. + and Ca + By disrupting the silicon-aluminum lattice structure of coal slime ash through ion exchange, the silicon is initially activated, laying the foundation for subsequent deep dissociation. By placing the pre-activated mixture in a supercritical carbon dioxide-liquid ammonia system, the high mass transfer efficiency and strong alkalinity of the system are utilized to further and thoroughly dissociate silicon-oxygen bonds along the microcracks in the lattice, completely converting the sparingly soluble silicon into water-soluble / citrate-soluble silicates that are easily absorbed by plants. At the same time, liquid ammonia, as an alkaline medium of the supercritical system, can also introduce a nitrogen source into the product, forming a quaternary nutrient system of silicon, sodium, calcium, and nitrogen with the Na and Ca supplemented by sodium and calcium adjuvants and the Si in the coal slime ash. This enables the prepared high-efficiency silicon fertilizer to achieve multiple benefits from a single material, increasing the added value of the product.

Description

Technical Field

[0001] This invention relates to the field of industrial solid waste resource utilization and high-efficiency fertilizer preparation technology, and more specifically to an activation method for producing high-efficiency silicon fertilizer from coal slime ash. Background Technology

[0002] Coal slime ash is a solid waste generated during coal washing and combustion. Its main component is silicon dioxide, which can reach 40-60%, making it a high-quality and inexpensive raw material for preparing silicon fertilizer. However, the silicon dioxide in coal slime ash exists mostly in crystalline form, with a stable crystal structure and low chemical activity, making it difficult for crops to directly absorb and utilize. It must be activated to convert it into effective silicon that can be absorbed by plants in order to realize its value as a raw material for silicon fertilizer.

[0003] Currently, the activation methods for preparing silicon fertilizer from coal slime ash mainly include high-temperature calcination activation and acid-base chemical activation. Among them, the single high-temperature calcination method has high energy consumption, incomplete activation, and low effective silicon activation rate, which is difficult to meet the requirements of high-efficiency silicon fertilizer. Although the acid-base activation method can destroy the crystal structure of silicon dioxide to a certain extent, it easily generates a large amount of acidic or alkaline waste liquid, which is environmentally unfriendly and has high subsequent waste liquid treatment costs, which does not conform to the concept of green production.

[0004] In summary, existing processes for producing silicon fertilizer from coal slime ash are inadequate and struggle to achieve efficient activation of the coal slime ash. Therefore, this invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide an activation method for producing high-efficiency silicon fertilizer from coal slime ash in order to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention specifically adopts the following technical solution: An activation method for producing high-efficiency silicon fertilizer from coal slime ash includes the following steps: S1. Pre-treatment of coal slime ash; S2. Sodium carbonate, calcium carbonate and pretreated coal slime ash are mixed in a mass ratio of 100:(10~20):(10~20) to form a mixture. S3. Mix the mixture and liquid ammonia at a mass ratio of 1:(0.6~1.0) and put them into a supercritical reactor and introduce carbon dioxide. Stir and react at 120~180℃ for 2~4 hours. S4. After the reaction is complete, the carbon dioxide is recovered and recycled, and the product is quenched and cooled with water to obtain high-efficiency silicon fertilizer.

[0007] Preferably, the specific method for pretreating coal slime ash includes: After the coal slime ash is screened to remove impurities and washed with water to remove salt, it is dried at 105℃ until the moisture content is ≤2%, and then crushed to 120 mesh. Among them, the silica content in the ash of the pretreated coal slime is ≥40%.

[0008] Preferably, the mass ratio of sodium carbonate, calcium carbonate, and pretreated coal slime ash is 100:15:15.

[0009] Preferably, the purity of the liquid ammonia is ≥99.5%, and the purity of the carbon dioxide is ≥99%.

[0010] Preferably, the mass ratio of the mixture to liquid ammonia is 1:0.8.

[0011] Preferably, in step S3, the heating rate is 5°C / min, the reaction pressure is 8~12MPa, the pressure increase rate is 0.5MPa / min, and the stirring rate is 250r / min.

[0012] Preferably, the reaction pressure is 10 MPa, the reaction temperature is 150°C, and the reaction time is 3 h.

[0013] Preferably, the water quenching temperature is 20~30℃ and the time is 9~11min.

[0014] Preferably, the water quenching temperature is 25°C and the time is 10 minutes.

[0015] Preferably, the silica content in the coal slime ash before pretreatment is ≥45%.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. A mixture is formed by mixing sodium carbonate, calcium carbonate, and pretreated coal slime ash. Na + and Ca + By disrupting the silicon-aluminum lattice structure of coal slime ash through ion exchange, the initial activation of silicon is achieved, laying the foundation for subsequent deep dissociation. 2. By placing the pre-activated mixture in a supercritical carbon dioxide-liquid ammonia system, the high mass transfer efficiency and strong alkalinity of the system are utilized to further and completely dissociate silicon-oxygen bonds along the microcracks in the crystal lattice, completely converting the sparingly soluble silicon into water-soluble / citrate-soluble silicates that are easily absorbed by plants. At the same time, liquid ammonia, as an alkaline medium of the supercritical system, can also introduce a nitrogen source into the product, forming a quaternary nutrient system of silicon, sodium, calcium, and nitrogen with the Na and Ca supplemented by sodium and calcium adjuvants and the Si from coal ash. This enables the prepared high-efficiency silicon fertilizer to achieve multiple effects from a single material, thereby increasing the added value of the product. Detailed Implementation

[0017] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. The materials and instruments used in the following embodiments are all commercially available.

[0018] An activation method for producing high-efficiency silicon fertilizer from coal slime ash includes steps S1 to S4.

[0019] S1. Pre-treatment of coal slime ash; Specifically, the coal slime ash is screened to remove impurities and washed with water to remove salt, then dried at 105℃ until the moisture content is ≤2%, and then pulverized to 120 mesh; wherein, the silica content in the coal slime ash before pretreatment is ≥45%.

[0020] This activation method targets the solid waste characteristics of coal slime ash, sequentially screening, washing and desalting, drying and pulverizing the coal slime ash. The pretreated ash has a silica content ≥40%, converting low-value coal slime ash into a silicon source specifically for silicon fertilizer. This achieves solid waste resource utilization and solves the problems of high raw material costs and resource dependence in traditional silicon fertilizer production. The heavy metal content in the pretreated coal slime ash meets the standards of "Limits of Toxic and Hazardous Substances in Fertilizers" (GB38400-2019), with Pb, Cd, and Hg contents all ≤0.005mg / kg, satisfying the environmental protection and application safety requirements for silicon fertilizer products.

[0021] S2. Sodium carbonate, calcium carbonate and pretreated coal slime ash are mixed in a mass ratio of 100:(10~20):(10~20) to form a mixture. The preferred mass ratio of sodium carbonate, calcium carbonate, and pretreated coal slime ash is 100:15:15.

[0022] S3. Mix the mixture and liquid ammonia at a mass ratio of 1:(0.6~1.0) and put them into a supercritical reactor and introduce carbon dioxide. Stir and react at 120~180℃ for 2~4 hours. The purity of the liquid ammonia is ≥99.5%, and the purity of the carbon dioxide is ≥99%. The preferred mass ratio of the mixture to liquid ammonia is 1:0.8. In step S3, the heating rate is 5℃ / min, the reaction pressure is 8~12MPa, the pressure increase rate is 0.5MPa / min, and the stirring rate is 250r / min. The reaction pressure is 10MPa. In step S3, the heating rate is 5℃ / min, the reaction pressure is 10MPa, the reaction temperature is 150℃, and the reaction time is 3h.

[0023] The core of this activation method lies in the construction of a two-step progressive activation system consisting of sodium-calcium adjuvant pre-activation and supercritical carbon dioxide-liquid ammonia coupling, and the realization of synergistic integration of activation medium and nutrient supply. Specifically, sodium carbonate, calcium carbonate, and pretreated coal slime ash are mixed in a mass ratio of 100:(10~20):(10~20) to form a mixture. + and Ca + The silicon-aluminum lattice structure of coal slime ash is disrupted through ion exchange, achieving initial activation of silicon and laying the foundation for subsequent deep dissociation. Secondly, the pre-activated mixture is placed in a supercritical carbon dioxide-liquid ammonia system. Utilizing the system's high mass transfer efficiency and strong alkalinity, the silicon-oxygen bonds are further and thoroughly dissociated along the microcracks in the lattice, completely converting insoluble silicon into water-soluble / citrate-soluble silicates easily absorbed by plants. Simultaneously, liquid ammonia, as the alkaline medium of the supercritical system, can also introduce a nitrogen source into the product, forming a quaternary nutrient system of silicon, sodium, calcium, and nitrogen with the Na and Ca supplemented by sodium-calcium adjuvants and the Si from the coal slime ash. This enables the prepared high-efficiency silicon fertilizer to achieve multiple benefits from a single application, increasing the product's added value.

[0024] S4. After the reaction is complete, the carbon dioxide is recovered and recycled, and the product is quenched and cooled with water to obtain high-efficiency silicon fertilizer.

[0025] Specifically, the water quenching temperature is 20~30℃ and the time is 9~11 minutes. The water quenching temperature is 25℃ and the time is 10 minutes.

[0026] After the reaction is completed, the pressure is first released and the temperature is lowered to room temperature, and then the carbon dioxide is recovered for recycling. After the product is quenched and cooled by water, it is crushed to 80 mesh to obtain high-efficiency silicon fertilizer.

[0027] The specific performance indicators of high-efficiency silicon fertilizer are as follows: water-soluble silicon (calculated as silicon dioxide) ≥18%, citrate-soluble silicon (calculated as silicon dioxide) ≥90%, available silicon (calculated as silicon dioxide) ≥25%, nitrogen content ≥3%, calcium content ≥5%, and moisture ≤3%.

[0028] The present invention will be further analyzed below with reference to specific embodiments and comparative examples.

[0029] Example 1 This embodiment provides an activation method for producing high-efficiency silicon fertilizer from coal slime ash, comprising the following steps: Raw material pretreatment: Coal slime ash with a silica content of 45% was sieved to remove impurities with a particle size >0.1mm, then washed and desalted with water, dried at 105℃ to a moisture content of 1.5%, and pulverized to 120 mesh; the heavy metal content was found to be Pb 0.003mg / kg, Cd 0.002mg / kg, and Hg 0.001mg / kg, which meets the requirements of the standard "Limits of Toxic and Hazardous Substances in Fertilizers" (GB38400-2019); Additive mixing: Take 100 kg of the pretreated coal slime ash, 15 kg of anhydrous sodium carbonate, and 15 kg of calcium carbonate, and put them into a mixer. Stir for 20 minutes until the mixture is uniform to obtain the mixture. Coupled activation: The above mixture and 104 kg of liquid ammonia were put into a supercritical reactor, carbon dioxide was introduced into the reactor, the temperature was increased to 150°C at a heating rate of 5°C / min, the pressure was increased to 10 MPa at a pressure rate of 0.5 MPa / min, the supercritical state was maintained, and the reaction was carried out at a constant temperature and pressure for 3 h with a stirring speed of 250 r / min. Post-processing: After the reaction is completed, the supercritical reactor is slowly depressurized and cooled to room temperature to recover carbon dioxide with a recovery rate of 95%; the reaction product is cooled by water quenching at 25°C for 10 minutes, then taken out and crushed to 80 mesh to obtain the high-efficiency silicon fertilizer product. Example 2 The difference between this embodiment and Embodiment 1 is that: Additive mixture: 100 kg of coal slime ash, 10 kg of anhydrous sodium carbonate, and 10 kg of calcium carbonate; Coupled activation: 72 kg of liquid ammonia, temperature of 120 °C in supercritical reactor, reaction time of 2 h and reaction pressure of 8 MPa; Post-treatment: Water quenching at a temperature of 20℃ for 9 minutes; The remaining steps are the same as in Example 1; Example 3 The difference between this embodiment and Embodiment 1 is that: Additive mixture: 100 kg of coal slime ash, 20 kg of anhydrous sodium carbonate, and 20 kg of calcium carbonate; Coupled activation: 140 kg of liquid ammonia, temperature of 180 °C in supercritical reactor, reaction time of 4 h and reaction pressure of 12 MPa; Post-treatment: Water quenching at 30℃ for 11 minutes; The remaining steps are the same as in Example 1.

[0030] The following is a comparative analysis of the performance test data of Examples 1-3: The high-efficiency silicon fertilizer products of Examples 1-3 were tested for indicators including silicon activation rate, available silicon (calculated as silicon dioxide), water-soluble silicon (calculated as silicon dioxide), citric acid solubility (calculated as silicon dioxide), nitrogen content, calcium content, and moisture content. Specific test data are shown in Table 1.

[0031] Table 1 Detection data from Examples 1-3 As can be seen from Examples 1-3 and Table 1, the silicon activation rate and citric acid solubility rate of Example 1 are the highest, indicating that the activation method provided by the present invention has a better activation effect on silicon in coal slime ash and the silicon nutrients that crops can absorb and utilize are released most fully. Due to the higher dosage of additives and reactants and the more intense reaction conditions, the effective silicon, water-soluble silicon, nitrogen and calcium content of Example 3 were slightly higher than those of Example 1. However, the silicon activation rate and citric acid solubility were lower than those of Example 1, indicating that excessively increasing the input of raw materials and intensifying the reaction conditions could not further improve the activation effect of silicon. Example 2 had lower performance in all aspects than Example 1 due to the smaller amount of raw materials and weaker reaction conditions; In summary, Example 1 is the most preferred embodiment.

[0032] Comparative Example 1 The difference between this comparative example and Example 1 is that this comparative example does not use supercritical carbon dioxide-liquid ammonia coupling, but only uses traditional high-temperature calcination activation.

[0033] Comparative Example 2 The difference between this comparative example and Example 1 is that this comparative example only uses supercritical carbon dioxide for single activation.

[0034] Comparative Example 3 The difference between this comparative example and Example 1 is that this comparative example replaces the silicon source and uses conventional quartz sand as raw material.

[0035] The following is a comparative analysis of the performance test data of Example 1 and Comparative Examples 1-3: The finished silicon fertilizer products of proportions 1-3 were tested for indicators including silicon activation rate, available silicon (calculated as silicon dioxide), water-soluble silicon (calculated as silicon dioxide), citric acid solubility (calculated as silicon dioxide), nitrogen content, calcium content and moisture content. The specific test data are shown in Table 2.

[0036] Table 2 Detection data of Comparative Examples 1-3 As can be seen from Tables 1 and 2, Example 1 and Comparative Example 1, Comparative Example 1 uses traditional high-temperature calcination activation without supercritical carbon dioxide-liquid ammonia coupling system. Although the effective silicon content is relatively high, the water-soluble silicon is extremely low, and the silicon activation rate and citric acid solubility are much lower than those of Example 1. This indicates that the traditional calcination process has limited activation of silicon in coal slime ash and it is difficult to convert a large amount of inert silicon into a form that crops can directly absorb and utilize. As can be seen from Tables 1 and 2, Example 1 and Comparative Example 2, Comparative Example 2 only used supercritical carbon dioxide for single activation and did not form a coupled activation system with liquid ammonia. The silicon activation rate, effective silicon, water-soluble silicon and citric acid solubility all decreased significantly, indicating that there is a significant synergistic activation effect between supercritical carbon dioxide and liquid ammonia. Without the coupling of liquid ammonia, it is impossible to achieve efficient activation of coal slime ash. As shown in Tables 1 and 2, Example 1 and Comparative Example 3, when using conventional quartz sand to replace coal slime ash as the silicon source, Comparative Example 3 had the lowest values ​​for all indicators, indicating that silicon could not be effectively activated. This demonstrates that the activation method provided by this invention is highly compatible with coal slime ash raw materials and can achieve efficient activation only for amorphous siliceous raw materials such as coal slime ash. It is difficult to achieve the same activation effect for crystalline quartz sand.

[0037] In summary, this invention involves mixing sodium carbonate, calcium carbonate, and pretreated coal slime ash at a mass ratio of 100:(10~20):(10~20) to form a mixture; then mixing the mixture with liquid ammonia at a mass ratio of 1:(0.6~1.0) and adding it to a supercritical reactor while introducing carbon dioxide. The reactor is stirred and reacted at 120~180℃ for 2~4 hours. After the reaction, the carbon dioxide is recovered and recycled, and the product is water-quenched to obtain a high-efficiency silicon fertilizer. The high-efficiency silicon fertilizer product exhibits good comprehensive performance in terms of silicon activation rate, available silicon (calculated as silica), water-soluble silicon (calculated as silica), citrate solubility (calculated as silica), nitrogen content, calcium content, and moisture content.

Claims

1. An activation method for producing high-efficiency silicon fertilizer from coal slime ash, characterized in that, Includes the following steps: S1. Pre-treatment of coal slime ash; S2. Sodium carbonate, calcium carbonate and pretreated coal slime ash are mixed in a mass ratio of 100:(10~20):(10~20) to form a mixture. S3. Mix the mixture and liquid ammonia at a mass ratio of 1:(0.6~1.0) and put them into a supercritical reactor and introduce carbon dioxide. Stir and react at 120~180℃ for 2~4 hours. S4. After the reaction is complete, the carbon dioxide is recovered and recycled, and the product is quenched and cooled with water to obtain high-efficiency silicon fertilizer.

2. The activation method for producing high-efficiency silicon fertilizer from coal slime ash according to claim 1, characterized in that, Specific methods for pretreatment of coal slime ash include: After the coal slime ash is screened to remove impurities and washed with water to remove salt, it is dried at 105℃ until the moisture content is ≤2%, and then crushed to 120 mesh. Among them, the silica content in the pretreated coal slime ash is ≥40%.

3. The activation method for producing high-efficiency silicon fertilizer from coal slime ash according to claim 1, characterized in that, The preferred mass ratio of sodium carbonate, calcium carbonate, and pretreated coal slime ash is 100:15:

15.

4. The activation method for producing high-efficiency silicon fertilizer from coal slime ash according to claim 1, characterized in that, The purity of the liquid ammonia is ≥99.5%, and the purity of the carbon dioxide is ≥99%.

5. The activation method for producing high-efficiency silicon fertilizer from coal slime ash according to claim 1, characterized in that, The preferred mass ratio of the mixture to liquid ammonia is 1:0.

8.

6. The activation method for producing high-efficiency silicon fertilizer from coal slime ash according to claim 1, characterized in that, In step S3, the heating rate is 5℃ / min, the reaction pressure is 8~12MPa, the pressure increase rate is 0.5MPa / min, and the stirring rate is 250r / min.

7. The activation method for producing high-efficiency silicon fertilizer from coal slime ash according to claim 6, characterized in that, The reaction pressure is 10 MPa, the reaction temperature is 150 °C, and the reaction time is 3 h.

8. The activation method for producing high-efficiency silicon fertilizer from coal slime ash according to claim 1, characterized in that, The water quenching temperature is 20~30℃ and the time is 9~11min.

9. The activation method for producing high-efficiency silicon fertilizer from coal slime ash according to claim 8, characterized in that, The water quenching temperature is 25℃ and the time is 10 minutes.

10. The activation method for producing high-efficiency silicon fertilizer from coal slime ash according to claim 1, characterized in that, The silica content in the coal slime ash before pretreatment is ≥45%.

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