Composite repairing material, preparation method thereof and application of composite repairing material in farmland nitrogen and phosphorus pollution prevention and control

Abstract

The invention provides a composite repairing material, a preparation method thereof and application of the composite repairing material in farmland nitrogen and phosphorus pollution prevention and control, and belongs to the technical field of agricultural environment protection. The preparation method comprises the following steps: activating steel slag by adopting an acid solution, mixing the obtained modified steel slag with modified attapulgite, diatomite and a binder, granulating to obtain a precursor material, and carrying out low-temperature calcination and ferric salt impregnation to obtain the composite repair material. The composite repairing material which is good in stability and high in removal rate is obtained by cooperating with multi-source solid waste and based on the synergistic effect of chemical adsorption, physical adsorption and coordination adsorption, and the adsorption performance of the material on nitrogen and phosphorus elements in farmland is greatly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of agricultural environmental protection, and particularly relates to a composite repair material, a preparation method thereof, and an application in the prevention and control of nitrogen and phosphorus pollution in farmland. Background Art

[0002] Nitrogen and phosphorus elements are two essential macronutrients for crop growth. To increase grain yield, a large amount of nitrogen and phosphorus fertilizers are usually used. However, the use of a large amount of fertilizers will cause nitrogen and phosphorus pollution in farmland, which will not only deteriorate water bodies, but also cause the nitrate content in groundwater to exceed the standard, leading to water eutrophication and posing great harm to animals, plants and human health. At present, the prevention and control technologies for nitrogen and phosphorus pollution in farmland mainly rely on optimizing fertilization and ecological ditch interception, but it is difficult to effectively cope with the instantaneous pollution load brought by heavy rainfall weather. In recent years, the adsorption material repair technology has attracted much attention due to its simple operation and controllable cost. Chinese Patent CN104876410A provides an active porous ecological concrete covering material, which can achieve in-situ continuous repair of the sediment of nitrogen and phosphorus polluted water bodies. However, its active coarse aggregate is one or more of zeolite, volcanic stone or activated carbon, and cement is used as the gelling material, which has limitations such as insufficient adsorption performance and poor durability; although the rare earth composite filter disclosed in Chinese Patent CN111167403A can synchronously remove nitrogen and phosphorus, there are problems such as the high cost of rare earth components and the possible ecological risks brought by the release of rare earth elements; Chinese Patent CN113072123A lays an ecological bag with soil and plant seeds on the surface of a nylon woven mesh bag filled with filler. The filler in the nylon woven mesh bag is used as an adsorbent, and the adsorbed nitrogen and phosphorus provide nutrients for the growth of plant seeds. However, its filler preparation steps are many, and the natural biomass material chitosan used may degrade after long-term use, affecting the adsorption effect.

[0003] In view of the above problems, there is an urgent need to develop a composite repair material with high removal rate, stability and environmental friendliness, which can not only achieve the synergistic adsorption of nitrogen and phosphorus, but also deeply integrate with the farmland ecological system to promote the dual goals of pollution prevention and control and resource recovery. Summary of the Invention

[0004] The purpose of the present invention is to provide a composite repair material, a preparation method thereof, and an application in the prevention and control of nitrogen and phosphorus pollution in farmland to overcome the above problems.

[0005] To achieve the above invention purpose, the present invention provides the following technical solutions:

[0006] The present invention provides a preparation method of a composite repair material, comprising the following steps:

[0007] Mix steel slag with an acid solution and activate it to obtain modified steel slag;

[0008] Mix the modified steel slag, modified attapulgite, diatomite and binder, and granulate to obtain a precursor material;

[0009] Calcine the precursor material to obtain a matrix material;

[0010] Immerse the matrix material in an iron salt solution for modification, and obtain a composite repair material after drying.

[0011] Preferably, the CaO content in the steel slag is ≥40%, and the Fe2O3 content is ≥15%;

[0012] The acid solution includes hydrochloric acid solution, citric acid solution or oxalic acid solution, and the mass concentration of the acid solution is 2-10 wt%;

[0013] The mass ratio of the steel slag to the volume of the acid solution is 1 g: 40-60 mL.

[0014] Preferably, the activation temperature is 20-80 °C and the time is 0.5-2 h.

[0015] Preferably, the preparation method of the modified attapulgite is: mix attapulgite with dilute HCl, stir at 160 °C for 18 h, mix the obtained pretreated modified attapulgite with an Al(OH)3 solution with a concentration of 0.5 mol / L, and calcine at 550 °C for 2 h to obtain modified attapulgite;

[0016] The binder includes sodium silicate, polyvinyl alcohol or polyacrylamide.

[0017] Preferably, the mass ratio of the steel slag, modified attapulgite, diatomite and binder is 40-55: 25-35: 10-20: 5-10.

[0018] Preferably, the extrusion pressure during granulation is 8-12 MPa, and the particle size of the precursor material is 3-5 mm.

[0019] Preferably, the calcination temperature is 150-300 °C and the time is 0.5-1.5 h.

[0020] Preferably, the iron salt solution includes ferric chloride solution or ferric nitrate solution, the concentration of the iron salt solution is 0.05-1 mol / L, and the mass ratio of the matrix material to the volume of the iron salt solution is 1 g: 8-12 mL;

[0021] The modification temperature is 80-200 °C and the time is 8-12 h;

[0022] The drying temperature is 100-110 °C and the time is 2-4 h.

[0023] The present invention provides a composite repair material prepared by the above preparation method.

[0024] The present invention provides the application of the above composite repair material in the prevention and control of farmland nitrogen and phosphorus pollution.

[0025] Advantages of the present invention:

[0026] The present invention proposes a three-stage treatment process of acid modification, low-temperature calcination, and iron salt impregnation. First, the acid modification process is adopted to activate the calcium and iron active sites of steel slag, promote the phase transformation of γ-C2S in steel slag into β-C2S, improve the hydration activity of steel slag, and enhance its ability to precipitate with phosphorus, thereby improving the adsorption performance, which belongs to the chemical mechanism; on the basis of maintaining the original pore structure of modified attapulgite, low-temperature calcination forms a stable skeleton structure composed of diatomite and binder. The modified attapulgite has a small average pore diameter and a high specific surface area, providing a large number of adsorption sites, which can effectively adsorb nitrogen and phosphorus elements. Diatomite contains a lamellar structure and can capture NH4 + , improve the adsorption performance of the composite repair material, which belongs to the physical mechanism; finally, through iron salt impregnation, a nano-hydroxy iron oxide layer is constructed on the surface of the material. The atoms or ions of phosphorus elements and the iron atoms in the nano-hydroxy iron oxide layer are combined through coordination bonds to form Fe-O-P bonding, and the adsorption of phosphorus elements is realized through coordination adsorption, and the adsorption effect is lasting and stable. The present invention synergistically uses multi-source solid wastes and obtains a composite repair material with good stability and high removal rate based on the synergistic effect of chemical adsorption-physical adsorption-coordination adsorption, greatly improving the adsorption performance of the material for nitrogen and phosphorus elements in farmland. Detailed implementation manners

[0027] The present invention provides a preparation method of a composite repair material, comprising the following steps:

[0028] Mix steel slag with an acid solution and activate to obtain modified steel slag;

[0029] Mix the modified steel slag, modified attapulgite, diatomite and binder according to mass parts and granulate to obtain a precursor material;

[0030] Calcine the precursor material to obtain a matrix material;

[0031] Immerse the matrix material in an iron salt solution for modification, and obtain the composite repair material after drying.

[0032] In the present invention, unless otherwise specified, the required preparation raw materials are all commercially available products well-known to those skilled in the art.

[0033] The present invention preferably coarsely crushes steel slag with a jaw crusher, then wet-grinds it with a planetary ball mill, mixes the obtained crushed steel slag with an acid solution and activates to obtain modified steel slag.

[0034] In the present invention, the content of CaO in the steel slag is preferably ≥40%, and the content of Fe2O3 is preferably ≥15%; the steel slag contains Ca 2+ and Fe 3+ , which can adsorb phosphorus elements to form precipitates of CaHPO4 and FePO4.

[0035] In the present invention, the particle size of the pulverized steel slag is preferably 80 - 100 mesh.

[0036] In the present invention, the acid solution preferably includes hydrochloric acid solution, citric acid solution or oxalic acid solution, and more preferably citric acid solution; the mass concentration of the acid solution is preferably 2 - 10 wt%, and more preferably 5 - 10 wt%; acid etching can promote the transformation of γ-C2S phase (inert dicalcium silicate) in the steel slag into β-C2S (active phase), enhancing the subsequent ability to hydrolyze and release Ca 2 +; acid etching can also form honeycomb-like pores on the surface of the steel slag, providing conditions for subsequent loading.

[0037] In the present invention, the mass ratio of the steel slag to the volume of the acid solution is 1 g:40 - 60 mL, and more preferably 1 g:40 - 50 mL.

[0038] In the present invention, the activation temperature is preferably 20 - 80 °C, and more preferably 60 - 80 °C, the time is preferably 0.5 - 2 h, and more preferably 1 - 2 h. The activation is carried out under stirring, and the stirring speed is preferably 150 - 300 rpm, and more preferably 200 - 300 rpm.

[0039] In the present invention, after activation, suction filtration is preferably carried out. The filter residue is washed with deionized water until neutral, and then dried at 80 °C to obtain modified steel slag.

[0040] The present invention preferably adds the above-mentioned modified steel slag, modified attapulgite, diatomite and binder into a double-screw mixer for mixing, and then uses a twin-screw extruder to form and granulate under a set pressure to obtain a precursor material.

[0041] In the present invention, the preparation method of the modified attapulgite is preferably: after grinding and ultrasonic purification of attapulgite, it is treated with dilute HCl, stirred at 160 °C for 18 h, the obtained pretreated modified attapulgite is mixed with an Al(OH)3 solution with a concentration of 0.5 mol / L, the pH is adjusted to 7 with HCl with a concentration of 0.1 mol / L, and left to stand for 24 h. The obtained precipitate is washed, centrifuged, dried, sieved, and calcined at 550 °C for 2 h, and then cooled to obtain modified attapulgite; the modified attapulgite has a high mesoporous structure, small pore diameter and large specific surface area, and can intercept NH4 through pores and adsorb it by van der Waals force +and phosphorus element.

[0042] In the present invention, the binder preferably includes sodium silicate, polyvinyl alcohol or polyacrylamide, and more preferably includes polyacrylamide; the binder is used to improve the compressive strength of the composite repair material.

[0043] In the present invention, the mass ratio of the steel slag, modified attapulgite, diatomite to the binder is preferably 40-55:25-35:10-20:5-10, and more preferably 40-50:25-30:10-15:8-10.

[0044] In the present invention, the rotation speed of the mixing is preferably 30-50 rpm, more preferably 40-50 rpm, and the time is preferably 1-2 h.

[0045] In the present invention, the pressure during extrusion during granulation is preferably 8-12 MPa, and more preferably 8-10 MPa.

[0046] In the present invention, after the granulation is completed, it is preferably pre-dried at 50-60 °C for 1-2 h to obtain a precursor material.

[0047] In the present invention, the particle size of the precursor material is preferably 3-5 mm, and more preferably 4-5 mm.

[0048] In the present invention, the precursor material is preferably placed in a muffle furnace and calcined at a low temperature. After the calcination is completed, it is cooled to room temperature with the furnace to obtain a matrix material; the low-temperature calcination can avoid the collapse of the structure of the modified attapulgite and maintain its porous structure. At the same time, the calcination can also promote the phase transformation of γ-C2S (dicalcium silicate) in the steel slag into β-C2S, further activate the hydration activity of the steel slag, enhance its ability to precipitate with phosphorus, and improve the adsorption performance of the composite repair material.

[0049] In the present invention, the temperature of the calcination is preferably 150-300 °C, more preferably 150-250 °C, the time is preferably 0.5-1.5 h, more preferably 0.5-1 h, and the heating rate is preferably 2-5 °C / min, more preferably 3-5 °C / min.

[0050] In the present invention, the iron salt is preferably dissolved in deionized water to prepare an iron salt solution. The matrix material is vacuum-impregnated in the obtained iron salt solution for modification. After the modification is completed, it is centrifuged and dried to obtain a composite repair material.

[0051] In the present invention, the iron salt solution preferably includes a ferric chloride solution or a ferric nitrate solution, and more preferably includes a ferric chloride solution.

[0052] In the present invention, the concentration of the iron salt solution is preferably 0.05 - 1 mol / L, more preferably 0.5 - 0.8 mol / L.

[0053] In the present invention, the mass ratio of the matrix material to the volume of the ferric chloride solution is preferably 1 g: 8 - 12 mL, more preferably 1 g: 10 mL.

[0054] In the present invention, the modification temperature is preferably 80 - 200 °C, more preferably 80 - 100 °C, and the time is preferably 8 - 12 h, more preferably 8 - 10 h.

[0055] In the present invention, the drying temperature is preferably 100 - 110 °C, more preferably 105 - 110 °C, and the time is preferably 2 - 4 h, more preferably 3 - 4 h.

[0056] The present invention also provides a composite repair material prepared by the above preparation method.

[0057] The present invention also provides the application of the above composite repair material in the prevention and control of farmland nitrogen and phosphorus pollution.

[0058] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0059] In Examples 1 - 4 and Comparative Examples 1 - 2, the CaO content in the steel slag used is 40%, and the Fe2O3 content is 15%;

[0060] The preparation method of the modified attapulgite used is as follows: After the attapulgite is ground and ultrasonically purified, it is treated with dilute HCl, stirred at 160 °C for 18 h, the obtained pretreated modified attapulgite is mixed with an Al(OH)3 solution with a concentration of 0.5 mol / L, the pH is adjusted to 7 with HCl with a concentration of 0.1 mol / L, left standing for 24 h, the obtained precipitate is washed, centrifuged, dried, sieved, and calcined at 550 °C for 2 h, and cooled to obtain the modified attapulgite.

[0061] Example 1

[0062] In this example, the mass ratio of the steel slag, the modified attapulgite, the diatomite and the polyacrylamide is 40:35:15:10.

[0063] After the steel slag is coarsely crushed by a jaw crusher, it is wet-milled by a planetary ball mill. The crushed steel slag with a particle size of 100 mesh is stirred with a citric acid solution with a mass concentration of 5 wt% at 60 °C and 200 rpm for 2 h for activation. The mass ratio of the citric acid solution to the crushed steel slag is 5:1. After activation, suction filtration is carried out, and the filter residue is washed with deionized water until neutral, and then dried at 80 °C to obtain modified steel slag;

[0064] The modified steel slag, modified attapulgite, diatomite and binder are added to a double-screw mixer according to the mass ratio, the rotation speed is set to 40 rpm, and the time is 1 h for mixing. Then, it is formed by a twin-screw extruder at 10 MPa, granulated, and pre-dried at 60 °C for 1 h to obtain a precursor material with a particle size of 4 mm;

[0065] The precursor material is placed in a muffle furnace, the heating rate is 5 °C / min, and it is calcined at 200 °C for 1 h. After calcination, it is cooled to room temperature with the furnace to obtain a matrix material;

[0066] FeCl3·6H2O is dissolved in deionized water to prepare a ferric chloride solution with a mass concentration of 1 mol / L. The above matrix material is vacuum-impregnated in the obtained ferric chloride solution. The mass ratio of the matrix material to the volume of the ferric chloride solution is 1 g:10 mL. Modification is carried out at 80 °C for 10 h. After modification, centrifugal separation is carried out and dried at 105 °C for 3 h to obtain a composite repair material.

[0067] Example 2

[0068] The difference from Example 1 is only that:

[0069] In this example, the mass ratio of steel slag, modified attapulgite, diatomite and polyacrylamide is 40:30:15:10.

[0070] Example 3

[0071] The difference from Example 1 is only that:

[0072] In this example, the mass ratio of steel slag, modified attapulgite, diatomite and polyacrylamide is 50:35:10:5.

[0073] Example 4

[0074] The difference from Example 1 is only that:

[0075] In this example, the mass ratio of steel slag, modified attapulgite, diatomite and polyacrylamide is 55:25:10:10.

[0076] Comparative Example 1

[0077] The difference from Example 1 is only that:

[0078] Without calcining the precursor material, directly immerse the precursor material in the iron salt solution;

[0079] The obtained material is used as the composite repair material of Comparative Example 1.

[0080] Comparative Example 2

[0081] The difference from Example 1 is only that:

[0082] Do not impregnate the matrix material with iron salt;

[0083] The obtained material is used as the composite repair material of Comparative Example 2.

[0084] Performance test

[0085] 1. Add the composite repair materials prepared in Examples 1-4 and Comparative Examples 1-2 into the prepared nitrogen and phosphorus solution (TN = 50 mg / L, TP = 10 mg / L) at a dosage of 1 g / L at room temperature, oscillate and adsorb for 24 h, take the supernatant after centrifugation, measure the remaining TN and TP concentrations, and calculate the removal rate. The results are shown in Table 1.

[0086] Table 1 Removal rates of the composite repair materials in Examples 1-4 and Comparative Examples 1-2

[0087] Serial number TN removal rate / % TP removal rate / % Example 1 86.9 90.7 Example 2 89.7 91.2 Example 3 90.2 93.5 Example 4 88.9 91.6 Comparative example 1 60.8 66.7 Comparative example 2 61.7 68.2

[0088] As can be seen from Table 1, the TN and TP removal rates of the composite repair materials in Examples 1-4 are significantly higher than those in Comparative Examples 1-2, proving the enhancing effect of the low-temperature calcination and iron salt impregnation process on the adsorption performance of the composite repair material.

[0089] 2. Add the composite repair materials obtained in Example 1 and Comparative Examples 1-2 into the nitrogen and phosphorus solution (TN = 50 mg / L, TP = 10 mg / L) at a dosage of 1 g / L at room temperature, oscillate and adsorb for 24 h, and perform cyclic adsorption 5 times (after each adsorption for 24 h, centrifuge and recover the material, dry it and reuse it). Record the TN and TP removal rates of the material after each cycle. The results are shown in Table 2.

[0090] Table 2 TN and TP removal rates of the composite repair materials in Example 1 and Comparative Examples 1-2 after 5 cycles

[0091]

[0092] As can be seen from Table 2, the decline in the adsorption performance of Example 1 after repeated use is relatively small (the TN removal rate decreases by 8.2%, and the TP decreases by 8.7%), while those of Comparative Example 1 and Comparative Example 2 decrease by more than 50%, indicating that the low-temperature calcination and iron salt impregnation significantly improve the stability of the composite repair material.

[0093] As can be seen from Tables 1-2 in combination with Examples 1-4 and Comparative Examples 1-2, the composite repair materials of Examples 1-4 achieved the synergistic effect of chemical-physical-coordination adsorption through the three-stage modification process of acid modification, low-temperature calcination, and iron salt impregnation, significantly improving the nitrogen and phosphorus adsorption performance and cycle stability. Among them, the TN removal rate > 85%, TP > 90%, and the performance remained > 82% after 5 cycles of adsorption, which was better than that of Comparative Examples 1-2 (TN removal rate < 65%, TP < 70%, and the performance < 50% after 5 cycles of adsorption).

[0094] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of a composite repair material, characterized in that It includes the following steps: Mix steel slag with an acid solution and activate it to obtain modified steel slag; Mix the modified steel slag, modified attapulgite, diatomite and binder, and granulate to obtain a precursor material; Calcine the precursor material to obtain a matrix material; Immerse the matrix material in an iron salt solution for modification, and dry it to obtain a composite repair material.

2. The preparation method according to claim 1, characterized in that, The content of CaO in the steel slag is ≥40%, and the content of Fe2O3 is ≥15%; The acid solution includes hydrochloric acid solution, citric acid solution or oxalic acid solution, and the mass concentration of the acid solution is 2-10 wt%; The mass ratio of the steel slag to the volume of the acid solution is 1 g: 40-60 mL.

3. The preparation method according to claim 1 or 2, characterized in that The activation temperature is 20-80 °C, and the time is 0.5-2 h.

4. The preparation method according to claim 1, characterized in that, The preparation method of the modified attapulgite is as follows: Mix attapulgite with dilute HCl, stir at 160 °C for 18 h, mix the obtained pretreated modified attapulgite with an Al(OH)3 solution with a concentration of 0.5 mol / L, and calcine at 550 °C for 2 h to obtain modified attapulgite; The binder includes sodium silicate, polyvinyl alcohol or polyacrylamide.

5. The preparation method according to claim 4, characterized in that, The mass ratio of the steel slag, modified attapulgite, diatomite and binder is 40-55: 25-35: 10-20: 5-10.

6. The preparation method according to claim 5, wherein, The extrusion pressure during granulation is 8-12 MPa, and the particle size of the precursor material is 3-5 mm.

7. The preparation method according to claim 6, characterized in that, The calcination temperature is 150-300 °C, and the time is 0.5-1.5 h.

8. The preparation method according to claim 7, wherein The iron salt solution includes ferric chloride solution or ferric nitrate solution, the concentration of the iron salt solution is 0.05-1 mol / L, and the mass ratio of the matrix material to the volume of the iron salt solution is 1 g: 8-12 mL; The modification temperature is 80-200 °C, and the time is 8-12 h; The drying temperature is 100-110 °C, and the time is 2-4 h.

9. The composite repair material prepared by the preparation method according to any one of claims 1-8.

10. The application of the composite repair material according to claim 9 in the prevention and control of farmland nitrogen and phosphorus pollution.

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