Preparation method of saline-alkali soil improvement slow-release fertilizer

Abstract

The application relates to the technical field of saline-alkali soil improvement, and particularly discloses a preparation method of a saline-alkali soil improvement slow-release fertilizer, which comprises the following steps: (1) uniformly mixing carbon powder, plant nutrient solution, molasses and seaweed acid powder, granulating the obtained mixture, mixing the obtained granules with carbon powder again to coat the granules, separating the granules, drying the granules, and obtaining a nutrient core; (2) uniformly mixing gypsum powder, carbon powder and water to form a coating slurry; coating the slurry on the surface of the nutrient core, and drying the nutrient core to obtain precursor granules; (3) uniformly mixing boric acid or lactic acid, carbon powder, gypsum powder and water to form a coating slurry; coating the slurry on the surface of the precursor granules, and drying the precursor granules to obtain the saline-alkali soil improvement slow-release fertilizer. The slow-release fertilizer prepared by the process can improve the exchange capacity of sodium ions in the soil, improve the soil nutrition degree and air permeability, and is beneficial to the growth of plants.

Description

Technical Field

[0001] This invention relates to the field of saline-alkali soil improvement technology, and in particular to a method for preparing a slow-release fertilizer for saline-alkali soil improvement. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Saline-alkali land improvement generally refers to the transformation and utilization of saline soil, alkaline soil, and saline-alkali land. After soil salinization, the excessive salt and alkaline substances make the soil unsuitable for plant growth, especially in arid and semi-arid regions with low rainfall and high evaporation. Salt migrates to the soil surface with water, and after evaporation, salt accumulates in the topsoil, forming saline-alkali soil. In addition, long-term irrigation with brackish water or industrial wastewater with high salt content, as well as improper irrigation methods, can also easily lead to soil salinization. The main reason for the alkalinity and high salt content of saline-alkali soil is the high content of carbonate and sodium ions. Carbonate ions hydrolyze to become alkaline, resulting in an alkaline soil.

[0004] Using gypsum to improve saline-alkali soil is a common method. The principle is to utilize the calcium released by the gypsum. 2+ Exchangeable Na in soil colloids + A displacement reaction occurs, causing the poorly soluble Na to... + The gypsum is converted into easily soluble sodium sulfate, which, after being leached away by water, can effectively reduce the soil's pH and alkalinity. However, the inventors have discovered a problem in this process: the calcium ions released by the gypsum are more easily captured by carbonate ions in the soil to form calcium carbonate, thus solidifying the calcium ions and affecting the Na+ in the soil colloids. + The replacement capacity is insufficient. Furthermore, gypsum is ineffective in addressing the problems of infertility, compaction, and poor aeration in saline-alkali soils. Therefore, the traditional method of using gypsum to improve saline-alkali soils still has many shortcomings. Summary of the Invention

[0005] This invention provides a method for preparing a slow-release fertilizer for improving saline-alkali soil. This fertilizer not only enhances the soil's ability to exchange sodium ions but also improves soil nutrient content and aeration, thus promoting better plant growth. Specifically, the technical solution of this invention is as follows.

[0006] A method for preparing a slow-release fertilizer for improving saline-alkali soil includes the following steps:

[0007] (1) Mix carbon powder, plant nutrient solution, molasses and alginic acid powder evenly, then granulate the mixture, mix the granules with carbon powder again for coating, then separate the granules and dry them to obtain the nutrient core for later use.

[0008] (2) Mix gypsum powder, carbon powder and water evenly to form a coating slurry. Then coat the surface of the nutrient core with the slurry and dry it to obtain precursor particles.

[0009] (3) Mix boric acid or lactic acid, carbon powder, gypsum powder and water evenly to form a coating slurry. Then coat the precursor particles with the slurry and dry them to obtain the slow-release fertilizer for improving alkaline soil.

[0010] Further, in step (1), the ratio of the carbon powder, plant nutrient solution, molasses, and alginic acid powder is 1g:0.2~0.3g:0.15~0.35g:0.1~0.18. Optionally, the carbon powder has a fineness of 50~80 mesh. The plant nutrient solution can be a commercially available product as needed.

[0011] Further, in step (1), the mass ratio of the particles to the toner is 1:0.5~0.7. Optionally, the fineness of the toner is 200~500 mesh; the size of the particles is 5~15mm, and other suitable particle sizes can also be prepared as needed.

[0012] Furthermore, in step (1), the drying temperature is 70~100℃ and the time is 20~40min.

[0013] Further, in step (2), the mass ratio of gypsum powder to carbon powder is 1:0.21~0.33. Optionally, the fineness of the carbon powder is 100~150 mesh.

[0014] Furthermore, in step (2), the solid content of the coating slurry is 50~65 wt.%.

[0015] Further, in step (2), the nutrient core and the coating slurry are mixed at a mass ratio of 1g:1.8~2.5.

[0016] Furthermore, in step (2), the drying temperature is 70~100℃ and the time is 20~40min.

[0017] Further, in step (3), the mass ratio of boric acid or lactic acid, carbon powder, and gypsum powder is 1~2:3~5.5:1~1.5. Optionally, the fineness of the carbon powder is 50~80 mesh.

[0018] Furthermore, in step (3), the solid content of the coating slurry is 52~65 wt.%.

[0019] Further, in step (3), the precursor particles and the coating slurry are mixed at a mass ratio of 1:1.3~1.6.

[0020] Furthermore, in step (3), the drying temperature is 80~95℃ and the time is 20~35min.

[0021] Compared with the prior art, the technical solution of the present invention has the following beneficial technical effects:

[0022] The slow-release fertilizer for improving saline-alkali soil of the present invention first uses carbon powder, plant nutrient solution, molasses, and alginic acid to form a nutrient core. Then, an inner coating layer formed by gypsum powder and carbon powder is coated on its surface, followed by an outer coating layer formed by boric acid or lactic acid, carbon powder, and gypsum powder. This outer coating layer is a structure formed by zeolite aggregates formed by the cementation of gypsum hydration products and the boric acid or lactic acid distributed within it. When this slow-release fertilizer is applied to saline-alkali soil, on the one hand, the outer coating layer releases boric acid or lactic acid under the action of water, consuming carbonate ions in the soil and converting them into carbon dioxide, which is easily discharged from the soil, reducing the carbonate ion content. Simultaneously, the gypsum in the outer coating layer can also release some calcium ions, further consuming the remaining carbonate ions in the soil, thereby reducing the capture of calcium ions released from the inner coating layer and improving the exchangeable Na+ in the soil colloids. + The outer coating layer undergoes a displacement process. As the boric acid or lactic acid and gypsum in the outer coating layer dissolve, the outer coating layer transforms into a porous structure, facilitating contact between the gypsum in the inner coating layer and moisture in the soil, thereby dissolving and releasing more Ca into the soil. 2+ Exchangeable Na in soil colloids + The process involves displacement, thereby reducing the soil's pH and alkalinity. After the aforementioned improvement steps, the inner coating layer also forms a slow-release shell due to the partial dissolution of gypsum, allowing nutrients in the nutrient core to be gradually released into the soil. Simultaneously, the released molasses provides carbon and nitrogen sources for soil microorganisms, improving their living environment and thus contributing to soil structure improvement. Furthermore, the alginate reacts with sodium ions in the soil under alkaline conditions to form sodium alginate, which cross-links under the action of calcium ions to form an insoluble gel, thereby solidifying the sodium ions and further reducing the soil's pH and alkalinity. Additionally, the gypsum component in this invention has undergone hydration during the coating layer formation process, preventing it from cementing soil particles after entering the soil, thus effectively avoiding the problem of exacerbating soil compaction. Attached Figure Description

[0023] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. Hereinafter, embodiments of the invention will be described in detail with reference to the accompanying drawings, wherein:

[0024] Figure 1 The image shows a sample of the slow-release fertilizer for improving saline-alkali soil prepared in Example 1 below. Detailed Implementation

[0025] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of skill in the art. All reagents and materials used in this invention are readily available through conventional means, and unless otherwise specified, they shall be used in accordance with conventional methods in the art or as per the product instructions.

[0027] Furthermore, any methods and materials similar to or equivalent to those described herein can be applied to the methods of this invention. The invention will now be further described in conjunction with the accompanying drawings and specific embodiments. The preferred embodiments and materials described herein are for illustrative purposes only.

[0028] Example 1

[0029] A method for preparing a slow-release fertilizer for improving saline-alkali soil includes the following steps:

[0030] (1) Mix carbon powder (80 mesh), plant nutrient solution, molasses, and alginic acid powder in a ratio of 1g:0.25g:0.3g:0.14g and stir evenly. Then granulate the mixture. Mix the resulting particles with carbon powder (300 mesh) in a ratio of 1g:0.55g and tumble the mixture to coat the particles with carbon powder again. Then remove the particles and dry them at 90℃ for 30 minutes to obtain the nutrient core for later use.

[0031] (2) Gypsum powder, carbon powder (120 mesh), and water are mixed evenly to form a coating slurry with a solid content of 60 wt.%, wherein the mass ratio of gypsum powder to carbon powder is 1:0.28. Then, the nutrient core is mixed with the coating slurry at a mass ratio of 1:2 and rolled to uniformly coat the surface of the nutrient core with the slurry. After completion, the resulting particles are dried at 75°C for 30 minutes to obtain precursor particles for later use.

[0032] (3) Lactic acid powder, 50-mesh carbon powder, gypsum powder, and water are mixed evenly to form a coating slurry with a solid content of 60 wt.%, wherein the mass ratio of lactic acid powder, carbon powder, and gypsum powder is 1.6:4.5:1.2. Then, the precursor particles are mixed with the coating slurry at a mass ratio of 1:1.5 and tumbled to uniformly coat the surface of the precursor particles with the slurry. After completion, the particles are removed and dried at 90℃ for 30 minutes to obtain the slow-release fertilizer for improving alkaline soil (e.g., Figure 1 (As shown).

[0033] Using a saline-alkali soil with a pH of 8.51 as the experimental subject, the slow-release fertilizer for improving alkaline soil prepared in this embodiment was added at a rate of 350 kg / mu. After mixing evenly, the soil was moistened with water and then left to stand for 30 days (moistening the soil every three days). The pH of the soil was then tested. 20 and salt content (CO3) 2- Na + Cl - ), calculate the desalination rate. The results are shown below: pH 20 =7.28, desalination rate = 64.36%.

[0034] Example 2

[0035] A method for preparing a slow-release fertilizer for improving saline-alkali soil includes the following steps:

[0036] (1) Mix carbon powder (60 mesh), plant nutrient solution, molasses, and alginic acid powder in a ratio of 1g:0.2g:0.35g:0.18g and stir evenly. Then granulate the mixture. Mix the resulting particles with carbon powder (200 mesh) in a ratio of 1g:0.7g and tumble the mixture to coat the particles with carbon powder again. Then remove the particles and dry them at 100℃ for 20 minutes to obtain the nutrient core for later use.

[0037] (2) Gypsum powder, carbon powder (150 mesh), and water are mixed evenly to form a coating slurry with a solid content of 50 wt.%, wherein the mass ratio of gypsum powder to carbon powder is 1:0.21. Then, the nutrient core is mixed with the coating slurry at a mass ratio of 1:1.8 and rolled to uniformly coat the surface of the nutrient core with the slurry. After completion, the granules are removed and dried at 70℃ for 40 min to obtain precursor granules for later use.

[0038] (3) Lactic acid powder, 80-mesh carbon powder, gypsum powder, and water are mixed evenly to form a coating slurry with a solid content of 65 wt.%, wherein the mass ratio of lactic acid powder, carbon powder, and gypsum powder is 1.0:3.0:1.0. Then, the precursor particles are mixed with the coating slurry at a mass ratio of 1:1.6 and tumbled to uniformly coat the surface of the precursor particles with the slurry. After completion, the particles are removed and dried at 95°C for 20 minutes to obtain the slow-release fertilizer for improving alkaline soil.

[0039] Using a saline-alkali soil with a pH of 8.51 as the experimental subject, the slow-release fertilizer for improving alkaline soil prepared in this embodiment was added at a rate of 350 kg / mu. After mixing evenly, the soil was moistened with water and then left to stand for 30 days (moistening the soil every three days). The pH of the soil was then tested. 20 and salt content (CO3) 2- Na + Cl - ), calculate the desalination rate. The results are shown below: pH 20 =7.42, desalination rate = 61.79%.

[0040] Example 3

[0041] A method for preparing a slow-release fertilizer for improving saline-alkali soil includes the following steps:

[0042] (1) Mix carbon powder (50 mesh), plant nutrient solution, molasses, and alginic acid powder in a ratio of 1g:0.3g:0.15g:0.1g and stir evenly. Then granulate the mixture. Mix the resulting particles with carbon powder (300 mesh) in a ratio of 1g:0.5g and tumble the mixture to coat the particles with carbon powder again. Then remove the particles and dry them at 70℃ for 40 minutes to obtain the nutrient core for later use.

[0043] (2) Gypsum powder, carbon powder (100 mesh), and water are mixed evenly to form a coating slurry with a solid content of 65 wt.%, wherein the mass ratio of gypsum powder to carbon powder is 1:0.27. Then, the nutrient core is mixed with the coating slurry at a mass ratio of 1:2.5 and rolled to uniformly coat the surface of the nutrient core with the slurry. After completion, the resulting particles are dried at 100℃ for 20 min to obtain precursor particles for later use.

[0044] (3) Boric acid powder, 60-mesh carbon powder, gypsum powder, and water are mixed evenly to form a coating slurry with a solid content of 52 wt.%, wherein the mass ratio of boric acid powder, carbon powder, and gypsum powder is 2.0:5.5:1.5. Then, the precursor particles are mixed with the coating slurry at a mass ratio of 1:1.3 and tumbled to uniformly coat the surface of the precursor particles with the slurry. After completion, the particles are removed and dried at 80℃ for 35 minutes to obtain the slow-release fertilizer for improving alkaline soil.

[0045] Using a saline-alkali soil with a pH of 8.51 as the experimental subject, the slow-release fertilizer for improving alkaline soil prepared in this embodiment was added at a rate of 350 kg / mu. After mixing evenly, the soil was moistened with water and then left to stand for 30 days (moistening the soil every three days). The pH of the soil was then tested. 20 and salt content (CO3) 2- Na + Cl - ), calculate the desalination rate. The results are shown below: pH 20 =7.16, desalination rate = 67.56%.

[0046] Example 4

[0047] A method for preparing a slow-release fertilizer for improving saline-alkali soil includes the following steps:

[0048] (1) Mix carbon powder (80 mesh), plant nutrient solution, molasses, and alginic acid powder in a ratio of 1g:0.25g:0.3g:0.14g and stir evenly. Then granulate the mixture. Mix the resulting particles with carbon powder (300 mesh) in a ratio of 1g:0.55g and tumble the mixture to coat the particles with carbon powder again. Then remove the particles and dry them at 90℃ for 30 minutes to obtain the nutrient core for later use.

[0049] (2) Gypsum powder, carbon powder (120 mesh), and water are mixed evenly to form a coating slurry with a solid content of 60 wt.%, wherein the mass ratio of gypsum powder to carbon powder is 1:0.28. Then, the nutrient core is mixed with the coating slurry at a mass ratio of 1:2 and rolled to evenly coat the surface of the nutrient core with the slurry. After completion, the granules are removed and dried at 75℃ for 30 minutes to obtain the slow-release fertilizer for improving alkaline soil.

[0050] Using a saline-alkali soil with a pH of 8.51 as the experimental subject, the slow-release fertilizer for improving alkaline soil prepared in this embodiment was added at a rate of 350 kg / mu. After mixing evenly, the soil was moistened with water and then left to stand for 30 days (moistening the soil every three days). The pH of the soil was then tested. 20 and salt content (CO3) 2- Na +Cl - ), calculate the desalination rate. The results are shown below: pH 20 =7.97, desalination rate = 52.07%.

[0051] Example 5

[0052] A method for preparing a slow-release fertilizer for improving saline-alkali soil includes the following steps:

[0053] (1) Mix carbon powder (60 mesh), plant nutrient solution, molasses, and alginic acid powder in a ratio of 1g:0.2g:0.35g:0.18g and stir evenly. Then granulate the mixture. Mix the resulting particles with carbon powder (200 mesh) in a ratio of 1g:0.7g and tumble the mixture to coat the particles with carbon powder again. Then remove the particles and dry them at 100℃ for 20 minutes to obtain the nutrient core for later use.

[0054] (2) Lactic acid powder, 80-mesh carbon powder, gypsum powder, and water are mixed evenly to form a coating slurry with a solid content of 65 wt.%, wherein the mass ratio of lactic acid powder, carbon powder, and gypsum powder is 1.0:3.0:1.0. Then, the nutrient core is mixed with the coating slurry at a mass ratio of 1:1.6 and rolled to evenly coat the surface of the nutrient core with the slurry. After completion, the granules are removed and dried at 95℃ for 20 minutes to obtain the slow-release fertilizer for improving alkaline soil.

[0055] Using a saline-alkali soil with a pH of 8.51 as the experimental subject, the slow-release fertilizer for improving alkaline soil prepared in this embodiment was added at a rate of 350 kg / mu. After mixing evenly, the soil was moistened with water and then left to stand for 30 days (moistening the soil every three days). The pH of the soil was then tested. 20 and salt content (CO3) 2- Na + Cl - ), calculate the desalination rate. The results are shown below: pH 20 =8.04, desalination rate = 30.48%.

[0056] Example 6

[0057] A method for preparing a slow-release fertilizer for improving saline-alkali soil includes the following steps:

[0058] (1) Mix carbon powder (50 mesh), plant nutrient solution, molasses, and alginic acid powder in a ratio of 1g:0.3g:0.15g:0.1g and stir evenly. Then granulate the mixture. Mix the resulting particles with carbon powder (300 mesh) in a ratio of 1g:0.5g and tumble the mixture to coat the particles with carbon powder again. Then remove the particles and dry them at 70℃ for 40 minutes to obtain the nutrient core for later use.

[0059] (2) Gypsum powder, carbon powder (100 mesh), and water are mixed evenly to form a coating slurry with a solid content of 65 wt.%, wherein the mass ratio of gypsum powder to carbon powder is 1:0.27. Then, the nutrient core is mixed with the coating slurry at a mass ratio of 1:2.5 and rolled to uniformly coat the surface of the nutrient core with the slurry. After completion, the resulting particles are dried at 100℃ for 20 min to obtain precursor particles for later use.

[0060] (3) Carbon powder (60 mesh), gypsum powder, and water are mixed evenly to form a coating slurry with a solid content of 52 wt.%, wherein the mass ratio of carbon powder to gypsum powder is 5.5:1.5. Then, the precursor particles are mixed with the coating slurry at a mass ratio of 1:1.3 and tumbled to uniformly coat the surface of the precursor particles with the slurry. After completion, the granules are removed and dried at 80℃ for 35 minutes to obtain the slow-release fertilizer for improving alkaline soil.

[0061] Using a saline-alkali soil with a pH of 8.51 as the experimental subject, the slow-release fertilizer for improving alkaline soil prepared in this embodiment was added at a rate of 350 kg / mu. After mixing evenly, the soil was moistened with water and then left to stand for 30 days (moistening the soil every three days). The pH of the soil was then tested. 20 and salt content (CO3) 2- Na + Cl - ), calculate the desalination rate. The results are shown below: pH 20 =7.85, desalination rate = 55.12%.

[0062] Example 7

[0063] A method for preparing a slow-release fertilizer for improving saline-alkali soil includes the following steps:

[0064] (1) Mix carbon powder (60 mesh), plant nutrient solution, and molasses in a ratio of 1g:0.2g:0.35g:0.18g and stir evenly. Then granulate the mixture. Mix the resulting particles with carbon powder (200 mesh) in a ratio of 1g:0.7g and tumble the mixture to coat the particles with carbon powder again. Then remove the particles and dry them at 100℃ for 20 minutes to obtain the nutrient core for later use.

[0065] (2) Gypsum powder, carbon powder (150 mesh), and water are mixed evenly to form a coating slurry with a solid content of 50 wt.%, wherein the mass ratio of gypsum powder to carbon powder is 1:0.21. Then, the nutrient core is mixed with the coating slurry at a mass ratio of 1:1.8 and rolled to uniformly coat the surface of the nutrient core with the slurry. After completion, the granules are removed and dried at 70℃ for 40 min to obtain precursor granules for later use.

[0066] (3) Lactic acid powder, 80-mesh carbon powder, gypsum powder, and water are mixed evenly to form a coating slurry with a solid content of 65 wt.%, wherein the mass ratio of lactic acid powder, carbon powder, and gypsum powder is 1.0:3.0:1.0. Then, the precursor particles are mixed with the coating slurry at a mass ratio of 1:1.6 and tumbled to uniformly coat the surface of the precursor particles with the slurry. After completion, the particles are removed and dried at 95°C for 20 minutes to obtain the slow-release fertilizer for improving alkaline soil.

[0067] Using a saline-alkali soil with a pH of 8.51 as the experimental subject, the slow-release fertilizer for improving alkaline soil prepared in this embodiment was added at a rate of 350 kg / mu. After mixing evenly, the soil was moistened with water and then left to stand for 30 days (moistening the soil every three days). The pH of the soil was then tested. 20 and salt content (CO3) 2- Na + Cl - ), calculate the desalination rate. The results are shown below: pH 20 =7.76, desalination rate = 58.23%.

[0068] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a slow-release fertilizer for improving saline-alkali soil, characterized in that, Includes the following steps: (1) Mix carbon powder, plant nutrient solution, molasses and alginic acid powder evenly, then granulate the mixture, mix the granules with carbon powder again for coating, then separate the granules and dry them to obtain the nutrient core for later use. (2) Mix gypsum powder, carbon powder and water evenly to form a coating slurry; then coat the surface of the nutrient core with the slurry and dry it to obtain precursor particles; (3) Mix boric acid powder or lactic acid powder, carbon powder, gypsum powder and water evenly to form a coating slurry; then coat the surface of the precursor particles with the slurry and dry it to obtain the slow-release fertilizer for improving alkaline soil. In step (1), the ratio of the carbon powder, plant nutrient solution, molasses, and alginic acid powder is 1g:0.2~0.3g:0.15~0.35g:0.1~0.18g; the fineness of the carbon powder is 50~80 mesh. In step (2), the mass ratio of gypsum powder to carbon powder is 1:0.21~0.33; In step (2), the fineness of the carbon powder is 100~150 mesh; In step (3), the mass ratio of boric acid powder or lactic acid powder, carbon powder, and gypsum powder is 1~2:3~5.5:1~1.5; the fineness of the carbon powder is 50~80 mesh.

2. The method for preparing slow-release fertilizer for saline-alkali soil improvement according to claim 1, characterized in that, In step (1), the mass ratio of the particles to the carbon powder is 1:0.5~0.7; In step (1), the fineness of the carbon powder is 200~500 mesh; In step (1), the size of the particles is 5~15mm.

3. The method for preparing slow-release fertilizer for saline-alkali soil improvement according to claim 1, characterized in that, In step (1), the drying temperature is 70~100℃ and the time is 20~40min.

4. The method for preparing slow-release fertilizer for saline-alkali soil improvement according to claim 1, characterized in that, In step (2), the solid content of the coating slurry is 50~65 wt.%.

5. The method for preparing slow-release fertilizer for saline-alkali soil improvement according to claim 1, characterized in that, In step (2), the nutrient core and the coating slurry are mixed at a mass ratio of 1:1.8~2.5; In step (2), the drying temperature is 70~100℃ and the time is 20~40min.

6. The method for preparing slow-release fertilizer for saline-alkali soil improvement according to claim 1, characterized in that, In step (3), the solid content of the coating slurry is 52~65 wt.%.

7. The method for preparing slow-release fertilizer for saline-alkali soil improvement according to any one of claims 1-6, characterized in that, In step (3), the precursor particles and the coating slurry are mixed at a mass ratio of 1:1.3~1.6; in step (3), the drying temperature is 80~95℃ and the time is 20~35min.

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