An adaptive nutrient slow-release aggregate, a preparation method and application thereof

Abstract

The application belongs to the technical field of building materials, and discloses a self-adaptive nutrient slow-release aggregate, a preparation method and application thereof. The self-adaptive nutrient slow-release aggregate has a core-shell structure, and the mass ratio of the core to the shell is (4-6):1. The core comprises raw materials in the following mass percentages: potassium-magnesium phosphate cement 45-60%, sludge 20-30%, biomass waste 10-20%, nutrient substance 2-5%, and solid waste admixture 5-10%. The shell comprises raw materials in the following mass percentages: potassium-magnesium phosphate cement 70-90%, waste thermal shrinkage particulate matter 5-20%, and solid waste admixture 5-10%. The self-adaptive nutrient slow-release aggregate is prepared by using potassium-magnesium phosphate cement and various solid wastes as main components and adding nutrient substances required by plants, and has a core-shell structure, so that the core is rich in pores for storing nutrients, and the shell can self-adaptively control mass transfer. The self-adaptive nutrient slow-release aggregate is particularly suitable for a substrate layer of a green roof.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to an adaptive nutrient slow-release aggregate, its preparation method, and its application. Background Technology

[0002] Green roofs, as an important component of "sponge city" construction, can effectively regulate rainwater runoff and urban water quality, and increase urban green space to mitigate the heat island effect. A green roof refers to the construction of an ecological vegetation layer on the top layer of a building, consisting of a substrate layer and surface vegetation. The design of the substrate material is crucial for the healthy growth of the vegetation on the green roof.

[0003] Currently, widely used substrate materials for green roofs include planting soil, biochar, and vermiculite. For example, CN201821354711.9 discloses an assembled green roof planter, whose nutrient substrate layer is composed of organic fertilizer, leaf mold, garden soil, etc.; CN201710448543.3 discloses a special substrate for roof greening, including compost, garden soil, and expanded clay pebbles. However, such substrates are expensive, and the humus they contain is easily dispersed by rainwater runoff, causing pollution. Furthermore, their operation and maintenance require significant manpower and resources. Aggregates, due to their low cost and rich porosity, are very suitable as a nutrient-bearing substrate for green roofs. However, existing aggregates do not have the characteristic of adaptively releasing the nutrients needed for vegetation growth according to changes in surrounding environmental conditions.

[0004] Therefore, it is necessary to develop a functional aggregate that can adaptively release nutrients required for vegetation growth according to changes in surrounding environmental conditions, so as to be suitable for the substrate layer of green roofs. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to address the shortcomings of the existing technology by providing an adaptive nutrient slow-release aggregate, its preparation method and application. The aggregate uses potassium magnesium phosphate cement and various solid wastes as the main components and adds nutrients required by plants. It is prepared by stacking core and shell structures to form a nutrient slow-release aggregate with a core rich in pores to store nutrients and an outer shell that adaptively controls mass transfer. It is particularly suitable for the substrate layer of green roofs.

[0006] To solve the technical problem proposed in this invention, this invention provides an adaptive nutrient slow-release aggregate, which has a core-shell structure, and the raw material mass ratio of its core to its shell is (4-6):1;

[0007] The core comprises the following raw materials in the following mass percentages: 45-60% potassium magnesium phosphate cement, 20-30% sludge, 10-20% biomass waste, 2-5% nutrients, and 5-10% solid waste admixture;

[0008] The outer shell comprises the following raw materials in the following weight percentages: 70-90% potassium magnesium phosphate cement, 5-20% waste heat shrinkable particulate matter, and 5-10% solid waste admixture.

[0009] In the above scheme, the potassium magnesium phosphate cement is composed of magnesium oxide, potassium dihydrogen phosphate and sodium borate.

[0010] Furthermore, the components of the potassium magnesium phosphate cement, by mass parts, are: 380-450 parts magnesium oxide, 280-320 parts potassium dihydrogen phosphate, and 40-50 parts sodium borate.

[0011] In the above scheme, the particle size of the potassium magnesium phosphate cement is ≤50 mesh.

[0012] In the above scheme, the sludge is at least one of municipal sludge, river and lake silt, and industrial sludge.

[0013] In the above scheme, the sludge has a SiO2 content of 40-60%, an Al2O3 content of 5-20%, an organic matter content of ≥20%, a moisture content of ≤5%, and a particle size of ≤100 mesh.

[0014] In the above scheme, the sludge is pretreated before use. The pretreatment method is as follows: the sludge is placed in a microwave reduction decomposition furnace for heating and heat preservation, and then naturally cooled to room temperature to obtain pretreated sludge.

[0015] Furthermore, the heating temperature is 350–450°C, and the holding time is 2–3 hours.

[0016] In the above scheme, the biomass waste is at least one of agricultural straw, reed stalks, and corn cobs.

[0017] In the above scheme, the inorganic content of the biomass waste is ≤10%, the moisture content is ≤5%, and the waste is crushed and ground to a fiber and particle size (fiber includes diameter and length, and particle includes diameter) ≤5mm.

[0018] In the above scheme, the biomass waste is pretreated before use. The pretreatment method is as follows: water is added to the biomass waste and mixed evenly, and then left to stand at room temperature for water aging to obtain pretreated biomass waste.

[0019] Furthermore, the mass ratio of the biomass waste to water is (1.5 to 1):1.

[0020] Furthermore, the room temperature is 20–25°C, and the settling time is 1–2 days.

[0021] In the above scheme, the nutrients are fertilizers required for plant growth, specifically nitrogen, phosphorus, and potassium ternary compound fertilizers with a moisture content ≤5% and a particle size ≤50 mesh.

[0022] In the above scheme, the solid waste admixture is a commonly used cement admixture, specifically at least one of slag and silica fume, with a specific surface area ≥ 400 m². 2 / kg.

[0023] In the above scheme, the waste heat-shrinkable particulate matter is waste trans-1,4-polyisoprene rubber, which includes the residue, waste, and scrap generated during the production of trans-1,4-polyisoprene rubber products, as well as the waste generated during use, with a particle size ≤50 mesh.

[0024] This invention also provides a method for preparing adaptive nutrient slow-release aggregate, comprising the following steps:

[0025] 1) The sludge and biomass waste are pretreated separately to obtain pretreated sludge and pretreated biomass waste;

[0026] 2) Mix potassium magnesium phosphate cement, pretreated sludge, pretreated biomass waste, nutrients, solid waste admixture and water evenly to obtain core mixture, granulate it and let it stand to solidify to obtain core.

[0027] 3) Mix potassium magnesium phosphate cement, waste thermal shrinkable particles, solid waste admixtures and water evenly to obtain the outer shell mixture, coat it on the core surface, and after curing, obtain adaptive nutrient slow-release aggregate.

[0028] In the above scheme, the particle size of the kernel is 5-10 mm.

[0029] In the above scheme, the moisture content of the core mixture is 15-25%.

[0030] In the above scheme, the moisture content of the outer shell mixture is 15-25%.

[0031] In the above scheme, the curing temperature is 20-25℃, the humidity is 30-60%, and the time is 1-2 hours.

[0032] In the above scheme, the curing temperature is 20-25℃, the humidity is 30-60%, and it can be put into use after curing for 3-7 days.

[0033] The present invention also provides an application of adaptive nutrient slow-release aggregate in green roofs, wherein the application method is as follows: the adaptive nutrient slow-release aggregate is used as the matrix layer of the green roof.

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0035] 1) This invention uses potassium magnesium phosphate cement and various solid wastes as the main components, and adds nutrients required by plants. It prepares a nutrient slow-release aggregate by stacking core and shell structures to form a core with rich pores to store nutrients and an outer shell that adaptively controls mass transfer. Compared with existing aggregates, the aggregate prepared by this invention integrates functions such as nutrition, interception, filtration and adsorption, which changes the status quo that existing aggregates are not suitable for green roofs. It also has the characteristic of being able to adaptively release the nutrients required for vegetation growth, and is particularly suitable for the substrate layer of green roofs.

[0036] 2) This invention's adaptive nutrient-releasing aggregate, on the one hand, utilizes waste thermally shrinkable particles to allow the aggregate to adjust the pore size at the particle-cement paste interface according to changes in the surrounding environment. During sunny, high-temperature weather (≥40℃), the thermally deformed particles soften and shrink, expanding the release channels and increasing the water and nutrient release rate, which is beneficial for the rapid growth of green roof plants. During rainy, low-temperature weather, the thermally deformed particles rebound and harden, narrowing the release channels and reducing the water and nutrient release rate, ensuring long-term use. On the other hand, biomass waste further regulates the porosity and nutrient release of the aggregate. After long-term decomposition, the biomass waste is slowly released along with nutrients, gradually reducing the core porosity. As the water absorption and retention rate of the aggregate gradually increases with usage time, it is beneficial to provide the long-term water and nutrients required for green roof plants, reducing the frequency of manual watering and maintenance. Furthermore, after pretreatment, it generates adsorbent carbon components, which can adsorb and filter pollutants. In addition, by adding potassium magnesium phosphate cement, its main hydration product, K-type struvite, has an excellent solidification effect on harmful ions such as heavy metals in the solid waste raw materials used in this invention, ensuring the safety of the material. Therefore, the aggregate of this invention is not only low in cost and stable in performance, but also green and safe, and has excellent prospects for promotion. Detailed Implementation

[0037] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0038] In the following examples, the nutrients used are NPK ternary compound fertilizers, whose composition meets the requirements of GB / T15063-2020 "Compound Fertilizers", with a total nutrient content of ≥40% by mass, a moisture content of ≤5%, and a particle size of ≤50 mesh. The waste heat-shrinkable particles used are waste trans-1,4-polyisoprene rubber, including residues, waste materials, and offcuts generated during the production of trans-1,4-polyisoprene rubber products, as well as waste materials generated during use, with a particle size of ≤50 mesh.

[0039] Example 1

[0040] An adaptive nutrient-release aggregate has a core-shell structure with a raw material mass ratio of 4:1 for the core and shell. The core comprises the following raw materials by mass percentage: 60% potassium magnesium phosphate cement, 20% sludge, 10% biomass waste, 5% nutrients, and 5% solid waste admixture. The shell comprises the following raw materials by mass percentage: 85% potassium magnesium phosphate cement, 5% waste thermal shrinkable particles, and 10% solid waste admixture.

[0041] The components of the potassium magnesium phosphate cement, by mass parts, are: 405 parts magnesium oxide, 320 parts potassium dihydrogen phosphate, and 40 parts sodium borate, with a particle size ≤50 mesh; the sludge is municipal sludge with a SiO2 content of 52.39%, an Al2O3 content of 8.70%, an organic matter content of 23.64%, a moisture content ≤5%, and a particle size ≤100 mesh; the biomass waste is agricultural straw with an inorganic matter content of 7.26%, a moisture content of 3.5%, and is crushed and ground to a size ≤5mm; the solid waste admixture is slag with a specific surface area of ​​400-500 m². 2 / kg.

[0042] The preparation method of adaptive nutrient slow-release aggregate in this embodiment includes the following steps:

[0043] 1) Place the sludge in a microwave reduction decomposition furnace and heat it to 400℃ for 2 hours, then let it cool naturally to room temperature to obtain pretreated sludge; mix biomass waste and water at a mass ratio of 1:1 and let it stand at room temperature (20-25℃) for 1 day to age it with water content to obtain pretreated biomass waste.

[0044] 2) Mix potassium magnesium phosphate cement, pretreated sludge, pretreated biomass waste, nutrients, solid waste admixture and water evenly to obtain a core mixture with a moisture content of 18%. After granulation, let it stand and solidify for 1 hour at a temperature of 22℃ and a humidity of 50% to obtain a core with a particle size of 5mm.

[0045] 3) Mix potassium magnesium phosphate cement, waste thermal shrinkable particles, solid waste admixture and water evenly to obtain an outer shell mixture with a moisture content of 25%. Coat the inner core surface with the mixture and cure it for 3 days at a temperature of 22℃ and a humidity of 50% to obtain adaptive nutrient slow-release aggregate.

[0046] Example 2

[0047] An adaptive nutrient-release aggregate has a core-shell structure with a raw material mass ratio of 5:1 for the core and shell. The core comprises the following raw materials by mass percentage: 55% potassium magnesium phosphate cement, 20% sludge, 15% biomass waste, 5% nutrients, and 5% solid waste admixture. The shell comprises the following raw materials by mass percentage: 85% potassium magnesium phosphate cement, 5% waste thermal shrinkable particles, and 10% solid waste admixture.

[0048] The components of the potassium magnesium phosphate cement, by mass parts, are: 450 parts magnesium oxide, 300 parts potassium dihydrogen phosphate, and 45 parts sodium borate, with a particle size ≤50 mesh; the sludge is river and lake silt with a SiO2 content of 58.92%, an Al2O3 content of 10.46%, an organic matter content of 24.89%, a moisture content ≤5%, and a particle size ≤100 mesh; the biomass waste is reed stalks with an inorganic matter content of 6.13%, a moisture content of 2.9%, and is crushed and ground to a size ≤5mm; the solid waste admixture is silica fume with a specific surface area of ​​1800–2000 m². 2 / kg.

[0049] The preparation method of adaptive nutrient slow-release aggregate in this embodiment includes the following steps:

[0050] 1) Place the sludge in a microwave reduction decomposition furnace and heat it to 350℃ for 2.5h, then let it cool naturally to room temperature to obtain pretreated sludge; mix biomass waste and water at a mass ratio of 1:1 and let it stand at room temperature (20~25℃) for 1 day for water aging to obtain pretreated biomass waste.

[0051] 2) Mix potassium magnesium phosphate cement, pretreated sludge, pretreated biomass waste, nutrients, solid waste admixture and water evenly to obtain a core mixture with a moisture content of 20%. After granulation, let it stand and solidify for 2 hours at a temperature of 22℃ and a humidity of 50% to obtain a core with a particle size of 5mm.

[0052] 3) Mix potassium magnesium phosphate cement, waste thermal shrinkable particles, solid waste admixture and water evenly to obtain an outer shell mixture with a moisture content of 20%. Coat the inner core surface with the mixture and cure it for 3 days at a temperature of 22℃ and a humidity of 50% to obtain adaptive nutrient slow-release aggregate.

[0053] Example 3

[0054] An adaptive nutrient-release aggregate has a core-shell structure with a raw material mass ratio of 5:1 for the core and shell. The core comprises the following raw materials by mass percentage: 50% potassium magnesium phosphate cement, 28% sludge, 15% biomass waste, 2% nutrients, and 5% solid waste admixture. The shell comprises the following raw materials by mass percentage: 80% potassium magnesium phosphate cement, 15% waste thermal shrinkable particles, and 5% solid waste admixture.

[0055] The components of the potassium magnesium phosphate cement, by mass parts, are: 450 parts magnesium oxide, 300 parts potassium dihydrogen phosphate, and 45 parts sodium borate, with a particle size ≤50 mesh; the sludge is river and lake silt with a SiO2 content of 58.92%, an Al2O3 content of 10.46%, an organic matter content of 24.89%, a moisture content ≤5%, and a particle size ≤100 mesh; the biomass waste is reed stalks with an inorganic matter content of 6.13%, a moisture content of 2.9%, and is crushed and ground to a size ≤5mm; the solid waste admixture is silica fume with a specific surface area of ​​1800–2000 m². 2 / kg.

[0056] The preparation method of adaptive nutrient slow-release aggregate in this embodiment includes the following steps:

[0057] 1) Place the sludge in a microwave reduction decomposition furnace and heat it to 350℃ for 2.5 hours, then let it cool naturally to room temperature to obtain pretreated sludge; mix biomass waste and water at a mass ratio of 1.5:1 and let it stand at room temperature (20-25℃) for 2 days to age it with water content to obtain pretreated biomass waste.

[0058] 2) Mix potassium magnesium phosphate cement, pretreated sludge, pretreated biomass waste, nutrients, solid waste admixture and water evenly to obtain a core mixture with a moisture content of 20%. After granulation, let it stand and solidify for 2 hours at a temperature of 22℃ and a humidity of 50% to obtain a core with a particle size of 10mm.

[0059] 3) Mix potassium magnesium phosphate cement, waste thermal shrinkable particles, solid waste admixture and water evenly to obtain an outer shell mixture with a moisture content of 20%. Coat the inner core surface with the mixture and cure it for 7 days at a temperature of 22℃ and a humidity of 50% to obtain adaptive nutrient slow-release aggregate.

[0060] Example 4

[0061] An adaptive nutrient-release aggregate has a core-shell structure with a raw material mass ratio of 6:1 for the core and shell. The core comprises the following raw materials by mass percentage: 45% potassium magnesium phosphate cement, 30% sludge, 18% biomass waste, 2% nutrients, and 10% solid waste admixture. The shell comprises the following raw materials by mass percentage: 85% potassium magnesium phosphate cement, 5% waste thermal shrinkable particles, and 10% solid waste admixture.

[0062] The components of the potassium magnesium phosphate cement, by mass parts, are: 405 parts magnesium oxide, 320 parts potassium dihydrogen phosphate, and 50 parts sodium borate, with a particle size ≤50 mesh; the sludge is industrial sludge with a SiO2 content of 55.37%, an Al2O3 content of 13.34%, an organic matter content of 20.25%, a moisture content ≤5%, and a particle size ≤100 mesh; the biomass waste is corn cob with an inorganic matter content of 4.92%, a moisture content of 4.1%, and is crushed and ground to a size ≤5mm; the solid waste admixture is slag with a specific surface area of ​​400-500 m². 2 / kg.

[0063] The preparation method of adaptive nutrient slow-release aggregate in this embodiment includes the following steps:

[0064] 1) Place the sludge in a microwave reduction decomposition furnace and heat it to 450℃ for 3 hours, then let it cool naturally to room temperature to obtain pretreated sludge; mix biomass waste and water at a mass ratio of 1.5:1 and let it stand at room temperature (20-25℃) for 2 days to age it with water content to obtain pretreated biomass waste.

[0065] 2) Mix potassium magnesium phosphate cement, pretreated sludge, pretreated biomass waste, nutrients, solid waste admixture and water evenly to obtain a core mixture with a moisture content of 22%. After granulation, let it stand and solidify for 2 hours at a temperature of 22℃ and a humidity of 50% to obtain a core with a particle size of 10mm.

[0066] 3) Mix potassium magnesium phosphate cement, waste thermal shrinkable particles, solid waste admixture and water evenly to obtain an outer shell mixture with a moisture content of 22%. Coat the inner core surface with the mixture and cure it for 7 days at a temperature of 22℃ and a humidity of 50% to obtain adaptive nutrient slow-release aggregate.

[0067] Comparative Example 1

[0068] Comparative Example 1 is the same as Example 1 in other steps and parameters, except that no waste heat-shrinkable particulate matter is added.

[0069] Comparative Example 2

[0070] Comparative Example 2 is the same as Example 1 in other steps and parameters, except that no biomass waste is added.

[0071] Performance testing

[0072] 1)1d K + Dissolution concentration: The aggregates obtained from each example and comparative example were used as the matrix layer in green roofs. After 1 day of use, they were removed and placed in deionized water at a solid-liquid ratio of 1:10 at room temperature or 50°C. After standing for 1 day, the supernatant was taken and K was determined by ICP. + concentration.

[0073] 1) 1-day water retention rate: The aggregates obtained from each embodiment and each comparative example were used as the matrix layer for the green roof. After 1 day of use, they were taken out and immersed in deionized water at room temperature. After standing for 1 day, the difference between the water content of the aggregate and the initial water content of the aggregate was taken out and measured as the 1-day water retention rate.

[0074] 3) 28d K + Dissolution concentration: The aggregates obtained from each example and comparative example were used as the matrix layer in green roofs. After 28 days of use, they were removed, placed in deionized water at a solid-liquid ratio of 1:10, and at room temperature or 50°C. After standing for 1 day, the supernatant was taken and K was determined by ICP. + concentration.

[0075] 4) 28-day water retention rate: The aggregates obtained from each embodiment and each comparative example were used as the matrix layer for the green roof. After 28 days of use, they were taken out, immersed in deionized water at room temperature, and left to stand for 1 day. The difference between the water content of the aggregate and the initial water content of the aggregate was the 28-day water retention rate.

[0076] Table 1

[0077]

[0078]

[0079] The data above shows that the aggregate prepared in this embodiment of the invention has a K value at 50°C. + The significantly higher leaching temperature compared to room temperature indicates that the thermoconstrictible particles in its shell have the functional property of controlling the release of nutrients from the core, releasing more potassium at high temperatures. + At low temperatures, the release of K decreases. + It exhibits adaptive properties. The aggregate prepared in this embodiment of the invention can still release K after 28 days of use. + This indicates that it has slow-release properties. In addition, due to the addition of biomass waste, the water retention rate of the aggregate increases with the increase of usage time, which greatly improves the water storage performance of the product.

[0080] The above embodiments are merely examples for clear illustration and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations, and any obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. An adaptive nutrient slow-release aggregate, characterized in that, The aggregate has a core-shell structure, with the raw material mass ratio of the core to the shell being (4~6):1; the core comprises the following raw materials by mass percentage: 45~60% potassium magnesium phosphate cement, 20~30% sludge, 10~20% biomass waste, 2~5% nutrients, and 5~10% solid waste admixture; the shell comprises the following raw materials by mass percentage: 70~90% potassium magnesium phosphate cement, 5~20% waste heat-shrinkable particles, and 5~10% solid waste admixture. The sludge is pretreated before use. The pretreatment method is as follows: the sludge is placed in a microwave reduction decomposition furnace and heated and kept at a certain temperature, and then naturally cooled to room temperature. The biomass waste is pretreated before use. The pretreatment method is as follows: water is added to the biomass waste and mixed evenly, and then left to stand at room temperature for water aging. The waste heat-shrinkable particulate matter is trans-1,4-polyisoprene rubber, the solid waste admixture is at least one of slag and silica fume, and the nutrients are fertilizers required for plant growth.

2. The adaptive nutrient slow-release aggregate according to claim 1, characterized in that, The components of the potassium magnesium phosphate cement, by mass parts, are: 380-450 parts magnesium oxide, 280-320 parts potassium dihydrogen phosphate, 40-50 parts sodium borate, with a particle size ≤50 mesh.

3. The adaptive nutrient slow-release aggregate according to claim 1, characterized in that, The sludge is at least one of municipal sludge, river and lake silt, and industrial sludge; the sludge has a SiO2 content of 40-60%, an Al2O3 content of 5-20%, an organic matter content of ≥20%, a moisture content of ≤5%, and a particle size of ≤100 mesh.

4. The adaptive nutrient slow-release aggregate according to claim 1, characterized in that, The biomass waste is at least one of agricultural straw, reed stalks, and corn cobs; the inorganic content of the biomass waste is ≤10%, the moisture content is ≤5%, and it is crushed and ground to a fiber and particle size of ≤5mm.

5. The adaptive nutrient slow-release aggregate according to claim 1, characterized in that, The particle size of the waste thermo-shrinkable particulate matter is ≤50 mesh; the specific surface area of ​​the solid waste admixture is ≥400 m². 2 / kg; the nutrients are nitrogen, phosphorus and potassium ternary compound fertilizer, with a moisture content of ≤5% and a particle size of ≤50 mesh.

6. A method for preparing adaptive nutrient slow-release aggregate as described in any one of claims 1 to 5, characterized in that, Includes the following steps: 1) The sludge and biomass waste are pretreated separately to obtain pretreated sludge and pretreated biomass waste; 2) Mix potassium magnesium phosphate cement, pretreated sludge, pretreated biomass waste, nutrients, solid waste admixture and water evenly to obtain core mixture, granulate it and let it stand to solidify to obtain core. 3) Mix potassium magnesium phosphate cement, waste thermal shrinkable particles, solid waste admixtures and water evenly to obtain the outer shell mixture, coat it on the core surface, and after curing, obtain adaptive nutrient slow-release aggregate.

7. The method for preparing adaptive nutrient slow-release aggregate according to claim 6, characterized in that, The curing temperature is 20~25℃, the humidity is 30~60%, and the time is 1~2 hours; the curing temperature is 20~25℃, the humidity is 30~60%, and the product is put into use after curing for 3~7 days.

8. The application of an adaptive nutrient slow-release aggregate as described in any one of claims 1 to 5 in green roofs.

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