Core-shell type slow-release water-retention nutritional aggregate as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of nutritional aggregates, and particularly relates to a core-shell type slow-release water-retention nutritional aggregate as well as a preparation method and application thereof. The method comprises the following steps: 1) mixing a nutrition base material and rice hull powder to obtain first coating layer powder; 2) adding ceramsite and a cementing material into a ball forming mill, and premixing to obtain ceramsite coated with the cementing material; (3) adding a binder and the first coating layer powder obtained in the step (1) into the ball forming mill, continuously premixing, and forming a second coating layer on the surface of the ceramsite coated with the cementing material to obtain a core-shell material; (4) curing the core-shell material; and 5) drying and screening the core-shell material to obtain the core-shell type slow-release water-retention nutritional aggregate. The comprehensive improvement of mechanical properties, water retention, slow release and environmental adaptability is realized.

Description

Technical Field

[0001] The invention belongs to the technical field of nutrient aggregates, and in particular relates to a core-shell type slow-release water-retaining nutrient aggregate, a preparation method and application thereof. Background Art

[0002] Existing ecological aggregates are mostly mixed with a single material, which has problems such as rapid nutrient release, poor water retention, and loose structure. In the existing technology, although ceramsite is widely used as a lightweight aggregate, its surface density leads to insufficient nutrient adsorption capacity and lacks a sustained-release mechanism. In addition, the conventional cementitious material wrapping process is prone to shell cracking and poor durability. For this reason, it is urgent to develop a core-shell structure aggregate that can achieve synergistic optimization of mechanical properties, water retention and nutrient sustained release through shell material innovation. Summary of the Invention

[0003] To address the shortcomings of the existing technology, the present invention provides a core-shell slow-release water-retaining nutrient aggregate, its preparation method, and application. The core-shell slow-release water-retaining nutrient aggregate provided by the present invention utilizes rice husk powder as a raw material and utilizes core-shell structural technology to address the issues of low strength, poor water retention, rapid release, and poor durability of existing ecological aggregates. It achieves comprehensive improvements in mechanical properties, water retention and slow release, and environmental adaptability. It can be applied to slope greening, slope restoration, soil improvement, or desertification control, with significant results.

[0004] The technical solutions provided by the present invention are as follows:

[0005] A method for preparing a core-shell type slow-release water-retaining nutrient aggregate comprises the following steps:

[0006] 1) mixing the nutrient base material and rice husk powder to obtain a first coating layer powder;

[0007] 2) adding ceramsite and gelling material into a pelletizing machine and premixing to obtain ceramsite coated with gelling material;

[0008] 3) adding a binder and the first coating layer powder obtained in step 1) into the pelletizer, continuing premixing, and forming a second coating layer on the surface of the ceramsite coated with the gelling material to obtain a core-shell material;

[0009] 4) curing the core-shell material;

[0010] 5) Drying and sieving the core-shell material to obtain the core-shell type slow-release water-retaining nutrient aggregate.

[0011] The above technical solution uses spherical expanded clay as the core material, cement, fly ash, admixtures and nutrient substrate to form the shell material, adopts a ball-forming process of coating and shelling, and produces a slow-release nutrient aggregate with a core-shell structure after curing.

[0012] The outer layer of the core-shell slow-release water-retaining nutrient aggregate is made of rice husks that absorb and retain water, while the nutrient matrix provides a slow-release function. The outer layer is solidified with a binder to provide a suitable hardness.

[0013] Specifically, in step 1), the nutrient substrate comprises garden soil, organic nutrient soil, ferrous sulfate, urea, and slow-release fertilizer in a mass ratio of (55-65):(25-35):(2-3):(1-3):(3-5). The ferrous sulfate is used to regulate acid-base balance.

[0014] Specifically, in step 1), the mass ratio of the nutrient substrate to the pretreated rice husk powder is (30-50):(5-15).

[0015] Specifically, in step 2), the particle size of the ceramsite is 10-15 mm.

[0016] Specifically, in step 2), the cementitious material includes cement and fly ash in a mass ratio of (1-3): (2-5).

[0017] Specifically, in step 2), the mass ratio of the ceramsite to the gelling material is (1:0.25)-(1:2).

[0018] Specifically, in step 2), the premixing speed is 30-60 r / min; and the premixing time is 30-90 seconds.

[0019] Specifically, in step 3), the amount of the binder is 1-2.5% of the mass of the total gelling material.

[0020] Specifically, the thickness of the formed second coating layer is 1-2 mm.

[0021] Specifically, in step 3), the binder is styrene-butadiene emulsion or mortar glue, preferably styrene-butadiene emulsion. Based on this, an outer layer with suitable hardness can be obtained, and the outer layer has good slow-release and water-retention functions.

[0022] Specifically, the premixing speed is 30-60 r / min; and the premixing time is 30-90 seconds.

[0023] Furthermore, in step 1), the rice husk powder is pretreated, and the pretreatment includes the following steps:

[0024] a. Soak rice husk powder in 1-5wt% NaOH solution for 12-24 hours, then wash with water until neutral;

[0025] b. Carbonize the soaked rice husk powder at 300-500°C for 1-2 hours.

[0026] Through the above technical solution, the rice husk powder can form more microporous structures and enhance the water retention capacity of the rice husk powder.

[0027] Specifically, the curing methods include steam curing, moisturizing curing (refer to the standard curing for cement-based composite materials, 20±3°C, relative humidity ≥90%), and natural curing, which can be used in combination of two or three. Alternatively, steam curing at a temperature of 40°C to 80°C followed by water curing at a temperature not lower than 10°C can be used in combination.

[0028] The present invention also provides a core-shell type slow-release water-retaining nutrient aggregate prepared by the above preparation method.

[0029] Specifically:

[0030] Its bulk density is 300-500kg / m 3 ;

[0031] Its 28d cylinder compressive strength ≥3.2MPa;

[0032] Its water retention rate is ≥80%;

[0033] Its pH value is 7.5-9.5; the cumulative nitrogen release rate in 30 days is ≤85%.

[0034] The present invention also provides an application of the core-shell type slow-release water-retaining nutrient aggregate for slope greening, slope repair, soil improvement or desertification control.

[0035] The present invention has the following beneficial effects:

[0036] 1) Cement fly ash is used as the cementitious material, which does not contain clay components and is conducive to protecting the non-renewable resources of the land;

[0037] 2) The coating technology is simple, with low investment, and is easy to carry out large-scale production and on-site application;

[0038] 3) The prepared aggregate is of high quality, with high specific strength, good particle shape, and good nutrient release function, which can be combined with functionality. At the same time, the production cost is low and the economy is good, achieving the unity of low cost and high performance;

[0039] 4) The smaller-sized aggregate produced can be used to produce vegetation concrete materials or as a plant growth matrix. The 7-day cylinder compressive strength is ≥2.5MPa, the 28-day water absorption rate is ≤35%, and the 30-day cumulative nitrogen release rate is controlled at 65-80%, solving the problems of poor water retention and uncontrollable release rate of traditional nutrient materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is an optical photograph of the core-shell type slow-release water-retaining nutrient aggregate provided by the present invention. DETAILED DESCRIPTION

[0041] The principles and features of the present invention are described below. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0042] Unless otherwise specified, the test methods used in the examples are conventional methods; the materials and reagents used are commercially available reagents and materials unless otherwise specified.

[0043] The nutrient substrate includes garden soil, organic nutrient soil, ferrous sulfate, urea and slow-release fertilizer in a mass ratio of 60:30:2:3:5.

[0044] The particle size of ceramsite is distributed in the range of 10-15 mm.

[0045] Example 1

[0046] A method for preparing a core-shell type slow-release water-retaining nutrient aggregate comprises the following steps:

[0047] 1) mixing the nutrient base material and rice husk powder to obtain a first coating layer powder;

[0048] 2) adding ceramsite and gelling material into a pelletizing machine and premixing to obtain ceramsite coated with gelling material;

[0049] 3) adding a binder and the first coating layer powder obtained in step 1) into the pelletizer, continuing premixing, and forming a second coating layer on the surface of the ceramsite coated with the gelling material to obtain a core-shell material;

[0050] 4) curing the core-shell material;

[0051] 5) Drying and sieving the core-shell material to obtain the core-shell type slow-release water-retaining nutrient aggregate, which can be referred to Figure 1 It can be seen that the nutrient substrate is evenly attached to the surface of the expanded clay core under the joint action of the cementitious material and the binder. The prepared aggregate is uniform in shape and size, and there is no shell breakage or falling off.

[0052] The values ​​of cement: fly ash: nutrient substrate: rice husk are shown in Group 1 in Table 1.

[0053] In step 2):

[0054] The mass ratio of the ceramsite to the gelling material is 1.2:1.35.

[0055] The premixing speed is 30 r / min; the premixing time is 60 seconds.

[0056] In step 3):

[0057] The amount of the binder is 1.1% of the total powder mass;

[0058] The thickness of the formed second coating layer was 1.5 mm.

[0059] The binder is styrene-butadiene emulsion;

[0060] The premixing speed is 30 r / min; the premixing time is 60 seconds.

[0061] In step 1), the rice husk powder is pretreated, and the pretreatment comprises the following steps:

[0062] a. Soak rice husk powder in 4wt% NaOH solution for 12 hours and then wash with water until neutral;

[0063] b. The soaked rice husk powder was carbonized at 300°C for 1 hour.

[0064] Example 2

[0065] A method for preparing a core-shell type slow-release water-retaining nutrient aggregate comprises the following steps:

[0066] 1) mixing the nutrient base material and rice husk powder to obtain a first coating layer powder;

[0067] 2) adding ceramsite and gelling material into a pelletizing machine and premixing to obtain ceramsite coated with gelling material;

[0068] 3) adding a binder and the first coating layer powder obtained in step 1) into the pelletizer, continuing premixing, and forming a second coating layer on the surface of the ceramsite coated with the gelling material to obtain a core-shell material;

[0069] 4) curing the core-shell material;

[0070] 5) Drying and sieving the core-shell material to obtain the core-shell type slow-release water-retaining nutrient aggregate.

[0071] The values ​​of cement: fly ash: nutrient substrate: rice husk are shown in Group 2 in Table 1.

[0072] In step 2):

[0073] The mass ratio of the ceramsite to the gelling material is 1:2.

[0074] The premixing speed is 30 r / min; the premixing time is 90 seconds.

[0075] In step 3):

[0076] The amount of the binder is 1.1% of the total powder mass;

[0077] The thickness of the formed second coating layer was 2.0 mm.

[0078] The binder is styrene-butadiene emulsion;

[0079] The premixing speed is 30 r / min; the premixing time is 90 seconds.

[0080] In step 1), the rice husk powder is pretreated, and the pretreatment comprises the following steps:

[0081] a. Soak rice husk powder in 4wt% NaOH solution for 12 hours and then wash with water until neutral;

[0082] b. The soaked rice husk powder was carbonized at 300°C for 1 hour.

[0083] Example 3

[0084] A method for preparing a core-shell type slow-release water-retaining nutrient aggregate comprises the following steps:

[0085] 1) mixing the nutrient base material and rice husk powder to obtain a first coating layer powder;

[0086] 2) adding ceramsite and gelling material into a pelletizing machine and premixing to obtain ceramsite coated with gelling material;

[0087] 3) adding a binder and the first coating layer powder obtained in step 1) into the pelletizer, continuing premixing, and forming a second coating layer on the surface of the ceramsite coated with the gelling material to obtain a core-shell material;

[0088] 4) curing the core-shell material;

[0089] 5) Drying and sieving the core-shell material to obtain the core-shell type slow-release water-retaining nutrient aggregate.

[0090] The values ​​of cement: fly ash: nutrient substrate: rice husk are shown in Group 3 in Table 1.

[0091] In step 2):

[0092] The mass ratio of the ceramsite to the gelling material is 1.2:1.89.

[0093] The premixing speed is 30 r / min; the premixing time is 90 seconds.

[0094] In step 3):

[0095] The amount of the binder is 1.1% of the total powder mass;

[0096] The thickness of the formed second coating layer was 1.7 mm.

[0097] The binder is styrene-butadiene emulsion;

[0098] The premixing speed is 30 r / min; the premixing time is 90 seconds.

[0099] In step 1), the rice husk powder is pretreated, and the pretreatment comprises the following steps:

[0100] a. Soak rice husk powder in 4wt% NaOH solution for 12 hours and then wash with water until neutral;

[0101] b. The soaked rice husk powder was carbonized at 300°C for 1 hour.

[0102] Table 1 shows the formula of shell material and the properties of core material

[0103] Table 1

[0104]

[0105] Comparative Example 1

[0106] With reference to Example 1, the difference is that without adding rice husk powder, the water absorption rate is significantly reduced to 26.4%, and the bulk density, cylinder pressure strength 7d (MPa) and cylinder pressure strength 28d (MPa) are also changed to 427kg / m 3 , 2.97MPa and 3.82MPa.

[0107] Comparative Example 2

[0108] With reference to Example 1, the difference is that the styrene-butadiene emulsion is replaced by mortar glue, the water absorption rate is significantly reduced to 26.1%, the bulk density, cylinder compressive strength 7d (MPa) and cylinder compressive strength 28d (MPa) are also changed to 311kg / m 3 , 2.47MPa and 3.26MPa.

[0109] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a core-shell type slow-release water-retaining nutrient aggregate, characterized in that: The following steps are involved: 1) mixing the nutrient base material and rice husk powder to obtain a first coating layer powder; 2) adding ceramsite and gelling material into a pelletizing machine and premixing to obtain ceramsite coated with gelling material; 3) adding a binder and the first coating layer powder obtained in step 1) into the pelletizer, continuing premixing, and forming a second coating layer on the surface of the ceramsite coated with the gelling material to obtain a core-shell material; 4) curing the core-shell material; 5) Drying and sieving the core-shell material to obtain the core-shell type slow-release water-retaining nutrient aggregate.

2. The method for preparing the core-shell type slow-release water-retaining nutrient aggregate according to claim 1, characterized in that: In step 1): The nutrient substrate comprises garden soil, organic nutrient soil, ferrous sulfate, urea and slow-release fertilizer in a mass ratio of (55-65):(25-35):(2-3):(1-3):(3-5); The mass ratio of the nutrient substrate to the rice husk powder is (30-50):(5-15).

3. The method for preparing the core-shell type slow-release water-retaining nutrient aggregate according to claim 1, characterized in that: In step 2): The particle size of the ceramsite is 10-15 mm; The cementitious material comprises cement and fly ash in a mass ratio of (1-3):(2-5); The mass ratio of the ceramsite to the gelling material is (1:0.25)-(1:2).

4. The method for preparing the core-shell type slow-release water-retaining nutrient aggregate according to claim 1, characterized in that: In step 2), the premixing speed is 30-60 r / min and the premixing time is 30-90 seconds.

5. The method for preparing the core-shell type slow-release water-retaining nutrient aggregate according to claim 1, characterized in that: In step 3): The amount of the binder is 1-2.5% of the mass of the gelling material; The thickness of the formed second coating layer is 1-2 mm.

6. The method for preparing the core-shell type slow-release water-retaining nutrient aggregate according to claim 1, characterized in that: In step 3): The binder is styrene-butadiene emulsion or mortar glue; The speed of continuing premixing is 30-60 r / min; the time of continuing premixing is 30-90 seconds.

7. The method for preparing the core-shell type slow-release water-retaining nutrient aggregate according to any one of claims 1 to 6, characterized in that: In step 1), the rice husk powder is pretreated, and the pretreatment comprises the following steps: a. Soak rice husk powder in 1-5wt% NaOH solution for 12-24 hours, then wash with water until neutral; b. Carbonize the soaked rice husk powder at 300-500°C for 1-2 hours.

8. A core-shell type slow-release water-retaining nutrient aggregate prepared according to the preparation method according to any one of claims 1 to 7.

9. The core-shell type slow-release water-retaining nutrient aggregate according to claim 8, characterized in that: Bulk density 300-500kg / m 3 ; 28d cylinder pressure strength ≥3.2MPa; Water retention rate ≥80%; pH value 7.5-9.5; cumulative nitrogen release rate 30 days ≤85%.

10. Use of the core-shell type slow-release water-retaining nutrient aggregate according to claim 8 or 9, characterized in that: Used for slope greening, slope repair, soil improvement or desertification control.

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