Slow-release fertilizer based on microwave modification treatment of molten ash and preparation method of slow-release fertilizer

Abstract

The invention discloses a slow-release fertilizer based on microwave modification treatment of molten ash and a preparation method of the slow-release fertilizer. The method comprises the following steps: crushing the molten ash until the particle size is 100-500 microns; adding a phosphoric acid solution for dipping, and pressurizing and stirring at constant temperature; filtering and dehydrating; mixing with an initiator solution, and pretreating for 3-5 minutes by adopting multi-mode cavity microwave equipment with the power of 5-8 kW; the method comprises the following steps of: 1, vaporizing surface moisture under the conditions of 8-10 kW, 2-3 minutes and 180-200 DEG C; stage 2, internal vapor pressure is established at the temperature of 150-170 DEG C under the conditions of 6-7 kW and 4-5 min; stage 3, maintaining pore channel expansion at the temperature of 120-140 DEG C under the conditions of 3-4kW and 7-8min; and stage 4, stabilizing the structure at the temperature of 80-100 DEG C under the conditions of 1-2kW and 3-4min. The fertilizer can realize long-acting, stable and slow release of nutrients, meets the requirements of crops for nutrients in different growth stages, and improves the utilization rate of the fertilizer.

Description

Technical Field

[0001] The present invention belongs to the technical field of slow-release fertilizer preparation, and particularly relates to a slow-release fertilizer based on microwave modification treatment of molten slag and a preparation method thereof. Background Art

[0002] With the rapid development of global agriculture and the increasing requirements for environmental protection, the preparation technology of high-efficiency and environmentally friendly fertilizers has become the research focus. There are many limitations in the traditional methods for preparing slow-release fertilizers. For example, in some conventional physical mixing methods for preparing slow-release fertilizers, only the fertilizer components are simply mixed with the carrier, making it difficult to achieve precise control of nutrient release. Often, the initial release of nutrients is too fast, and the later supply is insufficient, unable to meet the needs of the entire growth cycle of crops. The fertilizer utilization rate is usually only between 30% and 50%.

[0003] The traditional roasting method is often used to improve the pore structure of the fertilizer carrier to achieve the slow-release effect, but this method has extremely high energy consumption, not only increasing the production cost but also not conforming to the current social development trend of energy conservation and emission reduction. Moreover, it is difficult to precisely control the temperature and time during the roasting process, easily resulting in uneven pore structure of the carrier, affecting the stability of the slow-release performance, and causing large fluctuations in the nutrient release curve, which is not conducive to the stable absorption of nutrients by crops.

[0004] In current society, as a large amount of waste in the industrial production process, if molten slag cannot be effectively utilized, it will not only occupy a large amount of land resources but also may cause potential pollution to the ecological environment such as soil and water bodies. Most of the existing slag treatment methods are limited to simple landfill or low-end building material preparation, failing to fully explore its potential value as a fertilizer carrier and resulting in waste of resources. Summary of the Invention

[0005] Technical problems to be solved: In view of the above technical problems, the present invention provides a slow-release fertilizer based on microwave modification treatment of molten slag and a preparation method thereof, which can achieve long-term and stable slow release of nutrients, meet the nutrient requirements of crops at different growth stages, and improve the fertilizer utilization rate.

[0006] Technical solution: A preparation method of a slow-release fertilizer based on microwave modification treatment of molten slag includes the following steps: Step 1: Crush the molten slag to a particle size of 100 - 500 μm; Step 2: Add phosphoric acid solution to the crushed molten slag for impregnation, stir at a constant temperature and pressure, and control the moisture content after impregnation to be 25 - 30% and the conductivity > 2000 μS / cm; Step 3: Filter and dehydrate the impregnated molten slag, and retain the moisture in the internal pores; Step 4: Mix the dehydrated molten slag with the initiator solution, and perform pretreatment on it using a multi-mode cavity microwave device. The pretreatment power is 5 - 8 kW, and the time is 3 - 5 min; Step 5: Activate the pretreated molten slag using a multi-mode cavity microwave device to obtain the slow-release fertilizer. The activation procedure is as follows: Stage 1, power 8 - 10 kW, time 2 - 3 min, target temperature 180 - 200 °C, vaporize the surface moisture; Stage 2, power 6 - 7 kW, time 4 - 5 min, target temperature 150 - 170 °C, establish the internal vapor pressure; Stage 3, power 3 - 4 kW, time 7 - 8 min, target temperature 120 - 140 °C, maintain the pore expansion; Stage 4, power 1 - 2 kW, time 3 - 4 min, target temperature 80 - 100 °C, stabilize the structure.

[0007] Preferably, in Step 1, first use a jaw crusher to coarsely crush to an output particle size ≤ 5 mm, and then use a ball mill to finely grind to a particle size of 100 - 500 μm.

[0008] Preferably, in Step 1, the molten slag is the molten slag generated in the iron and steel metallurgy industry.

[0009] Preferably, in Step 1, the particle size distribution is monitored in real time by a laser particle size analyzer to ensure that the specific surface area of the crushed molten slag is 50 - 80 m 2 / g, and the pore size retains micro-pores of 1 - 100 μm and nano-pores of 50 - 500 nm.

[0010] Preferably, in Step 2, the concentration of the phosphoric acid solution is 0.5 - 1.5 mol / L, and the mass ratio of the phosphoric acid solution to the crushed molten slag is 1:2.

[0011] Preferably, in Step 2, the control program for constant temperature and pressure stirring is as follows: maintain at 40 - 60 °C, 2 bar, and continuously stir for 30 min; 5 bar, continuously stir for 1 h; 8 bar, continuously stir for 2 h.

[0012] Preferably, in Step 4, the initiator is hydrogen peroxide, and the concentration is 0.1 - 0.5 mol / L.

[0013] Preferably, in Step 4 and Step 5, the frequency of the multi-mode cavity microwave device is 2.45 GHz.

[0014] The slow-release fertilizer prepared by the above method.

[0015] Preferably, the open hole rate of the blind holes of the slow-release fertilizer > 85%, and the specific surface area is 120 - 150 m2 / g.

[0016] Beneficial effects: The preparation of slow-release fertilizers with high specific surface area by using microwave modification treatment of molten slag in the present invention has significant advantages: Through the unique action mechanism of microwaves, the modification of slag can be accurately and quickly achieved. The selective heating characteristic of microwaves reduces the energy consumption by more than 40% compared with the traditional roasting method, effectively reducing the production cost and meeting the requirements of energy conservation and emission reduction. During the preparation process, multi-step collaborative operations such as crushing, pressure impregnation, microwave-induced chemical activation, and microwave activation of the slag can precisely control the internal pore structure of the slag to form a multi-level pore channel. Not only does the specific surface area increase significantly, enabling it to load more nutrients, but also the nutrient slow-release period can be extended to 90 - 120 days, precisely matching the growth law of crops, and the fertilizer utilization rate can be significantly improved, reaching more than 95%. At the same time, the efficient utilization of molten slag by this method realizes the resource utilization of waste, solves the problem of slag treatment, avoids environmental pollution, and perfectly meets the multiple requirements of social development for agricultural efficiency increase, resource recycling, and ecological protection. Description of the Drawings

[0017] Figure 1 is the preparation flow chart of the present invention. Detailed Embodiments

[0018] The present invention will be further described below with reference to the drawings and specific embodiments.

[0019] As Figure 1 shown, a preparation method of a slow-release fertilizer based on microwave modification treatment of molten slag includes the following steps: Step 1: Select molten slag with relatively stable sources and small composition fluctuations. Preferably, select molten slag generated in the iron and steel metallurgy industry. Crush the molten slag. First, coarsely crush it with a jaw crusher until the discharge particle size ≤ 5 mm, and then finely grind it with a ball mill, precisely controlling the particle size within 100 - 500 μm. At the same time, use a laser particle size analyzer to monitor the particle size distribution in real time to ensure that the specific surface area of the crushed slag reaches 50 - 80 m 2 / g, and retain micron pores with pore sizes of 1 - 100 μm and nano pores with pore sizes of 50 - 500 nm; Step 2: Put the crushed molten slag into a high-pressure reaction kettle with a stirring function, add a phosphoric acid solution with a concentration of 0.5 - 1.5 mol / L, strictly control the mass ratio of the added phosphoric acid solution to the crushed slag to be 1:2, apply a specific pressure gradient, that is, 2 bar for 30 min, 5 bar for 1 h, 8 bar for 2 h, and keep the temperature at 40 - 60 °C all the time. Use jacket heating to achieve precise temperature control. After impregnation, control the moisture content to be 25 - 30%, and control the conductivity > 2000 μS / cm; Step 3: Naturally filter and dehydrate the impregnated ash residue to retain the moisture in the internal pores; Step 4: Mix the dehydrated molten ash residue with an appropriate amount of hydrogen peroxide initiator solution with a concentration of 0.1 - 0.5 mol / L, and use a multi-mode cavity microwave device with a frequency of 2.45 GHz to pre-treat it. The pre-treatment power is set to 5 - 8 kW, and the time is 3 - 5 min, so as to promote the decomposition of the initiator to generate free radicals, initiate chemical reactions on the surface and in the pores of the ash residue, promote the chemical bonding between the minerals in the ash residue and the active components such as phosphate groups introduced by impregnation, generate stable phosphate mineral phases, and ensure the structural stability during the pore expansion in subsequent microwave modification.

[0020] Step 5: Use a multi-mode cavity microwave device with a frequency of 2.45 GHz, equipped with an infrared temperature measurement system and a rotating stage, and activate the pre-treated molten ash residue according to a specific power program to obtain the slow-release fertilizer. The activation program is as follows: Stage 1, power 10 kW, time 3 min, target temperature 180 - 200 °C, quickly vaporize the surface moisture; Stage 2, power 7 kW, time 5 min, target temperature 150 - 170 °C, establish the internal vapor pressure; Stage 3, power 4 kW, time 8 min, target temperature 120 - 140 °C, maintain the pore expansion; Stage 4, power 2 kW, time 4 min, target temperature 80 - 100 °C, stabilize the structure.

[0021] As can be seen from the CT scan, the blind pore opening rate of the slow-release fertilizer > 85%, and the specific surface area is 120 - 150 m 2 / g.

[0022] Example 1

[0023] Select the molten ash residue from a certain iron and steel metallurgical plant. After being detected by a high-precision spectral analyzer in the laboratory, the iron element content is stably between 20 - 22%, the calcium element content fluctuates between 10 - 12%, the magnesium element content is maintained at 8 - 10%, and the content of other trace elements such as manganese and silicon is also within a very small fluctuation range. The standard deviation of the overall main mineral element content does not exceed 1%; crush this molten ash residue: Coarsely crush it with a jaw crusher, and control the discharge particle size to 4 mm. Then put it into a ball mill and finely grind it for 3 hours. It is found by real-time monitoring with a laser particle size analyzer that the ash residue particle size is accurately controlled at 300 μm. At this time, the specific surface area of the crushed ash residue reaches 65 m² / g, and the pore size retains micron pores of 50 μm and nano pores of 300 nm; Put 500 g of the crushed ash residue into a high-pressure reactor with a stirring function, and add 250 g of 1 mol / L phosphoric acid solution; When applying pressure, 2 bar for 30 min, 5 bar for 1 h, and 8 bar for 2 h, the temperature was stably controlled at 50 °C using jacket heating. After the impregnation was completed, the moisture content of the ash residue was measured to be 28%, and the conductivity reached 2300 μS / cm; After the impregnation was completed, the ash residue was naturally filtered and dehydrated to retain the moisture in the internal pores; Before microwave activation, the dehydrated ash residue was uniformly mixed with 300 ml of a hydrogen peroxide initiator solution with a concentration of 0.3 mol / L. Then, it was irradiated using a multimode cavity microwave device with a frequency of 2.45 GHz, the power was set at 6 kW, and the time was 4 min; The multimode cavity microwave device with a frequency of 2.45 GHz was enabled again, equipped with an infrared temperature measurement system and a rotating stage, and activated according to the established power program: Stage 1, power 10 kW, time 3 min. The infrared temperature measurement showed that the target temperature reached 190 °C, and the surface moisture was rapidly vaporized; Stage 2, power 7 kW, time 5 min. The temperature was stabilized at 160 °C, and the internal vapor pressure was successfully established; Stage 3, power 4 kW, time 8 min. The temperature was maintained at 130 °C to effectively maintain the pore expansion; Stage 4, power 2 kW, time 4 min. The temperature was kept at 90 °C to achieve structural stability; Verified by CT scan, the open rate of blind holes reached 88%, and the specific surface area was increased to 135 m 2 / g. Thus, the preparation of the slow-release fertilizer with a high specific surface area was completed.

[0024] Application process: Select a farmland with an area of 1 mu to plant corn. Before sowing, the prepared slow-release fertilizer was evenly spread on the soil surface at a rate of 30 kg per mu, and then plowed to fully mix the fertilizer with the soil.

[0025] During the entire growth cycle of corn, no other fertilizers were applied.

[0026] On the 30th, 60th, 90th, and 120th days of corn growth, soil samples were collected respectively to measure the contents of main nutrients such as nitrogen, phosphorus, and potassium in the soil.

[0027] The results showed that on the 30th day, the nitrogen content in the soil was 120 mg / kg, the phosphorus content was 35 mg / kg, and the potassium content was 180 mg / kg; on the 60th day, the nitrogen content was 90 mg / kg, the phosphorus content was 25 mg / kg, and the potassium content was 150 mg / kg; on the 90th day, the nitrogen content was 60 mg / kg, the phosphorus content was 15 mg / kg, and the potassium content was 120 mg / kg; on the 120th day, the nitrogen content was 30 mg / kg, the phosphorus content was 8 mg / kg, and the potassium content was 90 mg / kg.

[0028] Example 2

[0029] Molten slag from a certain iron and steel metallurgical plant was selected. After being detected by a high-precision spectral analyzer in the laboratory, the iron element content was stable between 20% and 22%, the calcium element content fluctuated between 10% and 12%, the magnesium element content remained between 8% and 10%, and the content of other trace elements such as manganese and silicon was also within a very small fluctuation range. The standard deviation of the content of the main mineral elements as a whole did not exceed 1%; the molten slag was subjected to crushing treatment: It was coarsely crushed using a jaw crusher, and the discharge particle size was controlled at 4 mm. Then it was put into a ball mill for fine grinding for 3 hours. Through real-time monitoring with a laser particle size analyzer, it was found that the particle size of the slag was accurately controlled at 300 μm. At this time, the specific surface area of the crushed slag reached 70 m² / g, and the pore size retained micron pores of 50 μm and nano pores of 300 nm; 500 g of the crushed slag was put into a high-pressure reactor with a stirring function, and 250 g of 1 mol / L phosphoric acid solution was added; When applying pressure, 2 bar was maintained for 30 min, 5 bar for 1 h, and 8 bar for 2 h. The temperature was stably controlled at 50 °C using jacket heating. After the impregnation was completed, the moisture content of the slag was measured to be 29%, and the conductivity reached 2500 μS / cm; After the impregnation was completed, the slag was naturally filtered and dehydrated to retain the moisture in the internal pores; Before microwave activation, the dehydrated slag was uniformly mixed with 300 ml of a 0.3 mol / L hydrogen peroxide initiator solution, and then irradiated with a multi-mode cavity microwave device with a frequency of 2.45 GHz. The power was set at 6 kW and the time was 4 min; The multi-mode cavity microwave device with a frequency of 2.45 GHz was used again, and an infrared temperature measurement system and a rotating stage were equipped, and activation was carried out according to the established power program: Stage 1, power 10 kW, time 3 min. Infrared temperature measurement showed that the target temperature reached 190 °C, and the surface moisture was quickly vaporized; Stage 2, power 7 kW, time 5 min. The temperature was stabilized at 160 °C, and the internal vapor pressure was successfully established; Stage 3, power 4 kW, time 8 min, temperature maintained at 130 °C, effectively maintaining the pore expansion; Stage 4, power 2 kW, time 4 min, temperature kept at 90 °C, achieving structural stability; Verified by CT scan, the opening rate of blind holes reached 90%, and the specific surface area increased to 137 m 2 / g, thus completing the preparation of the slow-release fertilizer with high specific surface area.

[0030] Application process: Select a greenhouse for growing tomatoes with an area of 100 square meters. Before transplanting tomato seedlings, apply the slow-release fertilizer into the soil at a rate of 0.5 kg per square meter and plow it deeply and evenly. During the growth period of tomatoes, only carry out normal management operations such as watering and pest control, without additional fertilization.

[0031] Collect soil samples at the seedling stage, flowering stage, fruiting stage, and full fruiting stage of tomato growth to detect nutrient content. The nitrogen content in the soil at the seedling stage is 100 mg / kg, the phosphorus content is 30 mg / kg, and the potassium content is 160 mg / kg; at the flowering stage, the nitrogen content is 80 mg / kg, the phosphorus content is 22 mg / kg, and the potassium content is 130 mg / kg; at the fruiting stage, the nitrogen content is 55 mg / kg, the phosphorus content is 16 mg / kg, and the potassium content is 100 mg / kg; at the full fruiting stage, the nitrogen content is 35 mg / kg, the phosphorus content is 10 mg / kg, and the potassium content is 70 mg / kg.

[0032] To verify the effect of the mass ratio of phosphoric acid solution to crushed slag being 1:2, set the following comparative examples: Comparative example 1: Select the molten slag from the same source as in Example 1, only change the mass ratio of phosphoric acid solution to crushed slag to 1:1. Process according to the steps in Example 1. After crushing, put 500 g of slag into a high-pressure reactor, add 500 g of phosphoric acid solution with a concentration of 1 mol / L, and the subsequent steps such as pressure application, temperature control, filtration and dehydration, mixing with hydrogen peroxide initiator, and microwave treatment are all the same as in Example 1.

[0033] Finally, prepare a slow-release fertilizer sample.

[0034] After testing, the opening rate of blind holes of this slow-release fertilizer is 70%, and the specific surface area is 100 m² / g. This shows that too high a proportion of phosphoric acid solution will cause excessive reaction of the internal structure of the slag, resulting in the destruction of the pore structure and being unfavorable for the long-term and stable slow release of nutrients.

[0035] Comparative example 2: Select the molten slag from the same source as in Example 1, only change the mass ratio of phosphoric acid solution to crushed slag to 1:3.

[0036] Processed according to the steps in Example 1. After crushing, 500 g of ash residue was placed in a high-pressure reactor, and about 167 g of phosphoric acid solution with a concentration of 1 mol / L was added. The subsequent steps, such as pressure application, temperature control, filtration and dehydration, mixing with a hydrogen peroxide initiator, and microwave treatment, were all consistent with Example 1.

[0037] Finally, a slow-release fertilizer sample was prepared.

[0038] After testing, the blind hole opening rate of the slow-release fertilizer was 75%, and the specific surface area was 110 m² / g. It shows that the proportion of the phosphoric acid solution is too low to react fully with the ash residue, unable to effectively activate the internal structure of the ash residue, resulting in a reduction in the sites that can carry nutrients and also affecting the nutrient release effect.

[0039] From the comparison between the above comparative examples and examples, it can be seen that when the mass ratio of the phosphoric acid solution to the crushed ash residue is 1:2, an ideal pore structure can be formed in the ash residue during the subsequent treatment process, realizing the long-term and stable slow release of nutrients, meeting the nutrient requirements of crops at different growth stages, and improving the fertilizer utilization rate.

Claims

1. A preparation method of a slow-release fertilizer based on microwave modification treatment of molten slag, characterized in that, It includes the following steps: Step 1: Crush the molten slag to a particle size of 100 - 500 μm; Step 2: Add phosphoric acid solution to the crushed molten slag for impregnation, stir at a constant temperature and under pressure, control the water content after impregnation to be 25 - 30%, and the conductivity > 2000 μS / cm; Step 3: Filter and dehydrate the impregnated molten slag, retaining the moisture in the internal pores; Step 4: Mix the dehydrated molten slag with an initiator solution, and perform pretreatment on it using a multi-mode cavity microwave device, with a pretreatment power of 5 - 8 kW and a time of 3 - 5 min; Step 5: Activate the pretreated molten slag using a multi-mode cavity microwave device to obtain the slow-release fertilizer. The activation procedure is as follows: Stage 1, power 8 - 10 kW, time 2 - 3 min, target temperature 180 - 200 °C, vaporize the surface moisture; Stage 2, power 6 - 7 kW, time 4 - 5 min, target temperature 150 - 170 °C, establish the internal vapor pressure; Stage 3, power 3 - 4 kW, time 7 - 8 min, target temperature 120 - 140 °C, maintain the pore expansion; Stage 4, power 1 - 2 kW, time 3 - 4 min, target temperature 80 - 100 °C, stabilize the structure.

2. The preparation method of a slow-release fertilizer based on microwave modification treatment of molten slag according to claim 1, characterized in that, In the said Step 1, first use a jaw crusher for coarse crushing until the discharge particle size ≤ 5 mm, and then use a ball mill for fine grinding to a particle size of 100 - 500 μm.

3. The preparation method of a slow-release fertilizer based on microwave modification treatment of molten slag according to claim 1, characterized in that, In the said Step 1, the molten slag is the molten slag generated in the iron and steel metallurgy industry.

4. The preparation method of a slow-release fertilizer based on microwave modification treatment of molten slag according to claim 1, characterized in that In the first step, the particle size distribution is monitored in real time by a laser particle size analyzer to ensure that the specific surface area of the molten slag after crushing is 50 - 80 m 2 / g, and the pore size retains micropores of 1 - 100 μm and nanopores of 50 - 500 nm.

5. The preparation method of a slow-release fertilizer based on microwave modification treatment of molten slag according to claim 1, characterized in that, In the said Step 2, the concentration of the phosphoric acid solution is 0.5 - 1.5 mol / L, and the mass ratio of the phosphoric acid solution to the crushed molten slag is 1:

2.

6. The preparation method of a slow-release fertilizer based on microwave modification treatment of molten slag according to claim 1, characterized in that, In the said Step 2, the control program for stirring at a constant temperature and under pressure is as follows: maintain at 40 - 60 °C, 2 bar, stir continuously for 30 min; 5 bar, stir continuously for 1 h; 8 bar, stir continuously for 2 h.

7. The preparation method of a slow-release fertilizer based on microwave modification treatment of molten slag according to claim 1, characterized in that, In the said Step 4, the initiator is hydrogen peroxide, with a concentration of 0.1 - 0.5 mol / L.

8. The preparation method of a slow-release fertilizer based on microwave modification treatment of molten slag according to claim 1, characterized in that, In the said Step 4 and Step 5, the frequency of the multi-mode cavity microwave device is 2.45 GHz.

9. A slow-release fertilizer prepared by the method according to claim 1.

10. The slow-release fertilizer according to claim 9, wherein The blind hole opening rate of the slow-release fertilizer is > 85%, and the specific surface area is 120 - 150 m 2 / g.

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